ND SatCom SKYWAN IDU 7000, SKYWAN IDU 2570, SKYWAN IDU 2070, SKYWAN IDU 1070 User Manual

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SkyWAN® Indoor Unit

IDU 7000 Series

IDU 7000, Software Rel. 7.11 IDU 2570, Software Rel. 7.11 IDU 2070, Software Rel. 7.11

IDU 1070 Series

IDU 1070, Software Rel. 1.11

Network Design and Engineering Guide

Document Number OM2044E_9400711 Document Revision B Revision Date 2010-10-26

ND SatCom Product GmbH Graf-von-Soden-Strasse 88090 Immenstaad

Germany

Phone: +49 (0)7545 939 0 E-Mail: info@ndsatcom.com

This document is protected by copyright law. This document is the property of ND SatCom Product GmbH (hereafter referred to as ’ND SatCom’), which reserves all rights. This document or parts of it may not be reproduced, duplicated or distributed to third parties. Nor may their content be disclosed to third parties without the express written approval of ND SatCom Product GmbH. Misuse will be subject to legal action and fines. All rights to patents and utility models are reserved.

MANUAL CONVENTIONS

There are a few graphical symbols and formatting conventions used to show information clearly arranged and easy to find.

Symbol used for

Information Symbol is used to notify a user of special or useful information.

Action Item

 Prerequisite

Step (1) action step 1 Step (2) action step 2

Action objective after finishing action steps

string (word, number) in code formatting

<string_A> The <string_A> between the brackets is placeholder for

’string_B’ As quoted string ’string_B’ names and labels are pre-

Screenshots may not always contain valid data. Slight differences may occur in the graphical presentation shown (i.e. in the Graphical User Interface (GUI) of a program).

Action Items

are used to direct the user to execute the steps in the given order for a successful completion of the action.

 fulfilled precondition for successful action comple-

tion

Step (1) perform described action (1) Step (2) perform described action (2)

Action objective reached

Type this word, number or string as input, i.e. as command line or in a tool input field.

a variable. Fill in the contents of the placeholder without brackets.

sented: e.g. name of a variable, a window or field name, label of a button.

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Page intentionally left blank

2 Network Design and Engineering Guide 2010-10-26

Manual Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Table of Contents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

1.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

1.2 Manual Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

1.2.1 Who should read this document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

1.2.2 What do you need to know . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

1.3 SkyWAN

1.4 General Design and Engineering Process. . . . . . . . . . . . . . . . . . . . . . . . . . . 16

1.5 Related Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

1.5.1 SkyWAN

2 General Carrier Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19

2.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

2.2 Data and Voice Networking Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

2.3 Essential SkyWAN

2.3.1 SkyWAN

2.3.2 Master and Slave Functionality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Solutions and Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

IDU Manuals Suite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Voice connections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Voice Codecs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Satellite Link Layer Features. . . . . . . . . . . . . . . . . . . . . 23

Network Topologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Reception Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Control Communication: Reference and Request Bursts . . . . . . . . . . . 25

Active and Backup Master Role . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

2.3.3 SkyWAN

MF-TDMA functionality. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

TDMA Frame. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Transmit and Receive Carriers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Data Slot Time Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

TDMA Superframe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

2.3.4 Downlink and Uplink Populations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

2.3.5 SkyWAN

Reference Burst Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

MRB Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

MRB-DUB Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

NFB-DUB Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

2.3.6 Capacity Request and Allocation for User Data . . . . . . . . . . . . . . . . . . . . 33

Free Slot Assignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Ranging Subframe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Stream Slots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Dynamic Slots. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

2010-10-26 Network Design and Engineering Guide 3

2.3.7 Guaranteed Throughput . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36

Guaranteed Throughput Example Scenarios. . . . . . . . . . . . . . . . . . . . 36

Scenario 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Scenario 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Scenario 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Scenario 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

2.4 Network Traffic Estimation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41

Traffic Profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Traffic Estimation Example Scenario . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Summarize Example Traffic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

2.4.1 Capacity Calculation Tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44

Capacity Calculation Worksheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Erlang B Calculation Worksheet. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Voice Traffic Flow Worksheet. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Carrier Configuration Worksheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

2.4.2 Limitations of the Traffic Estimation Approach . . . . . . . . . . . . . . . . . . . . . .49

2.5 From User Traffic to Satellite Link Carriers . . . . . . . . . . . . . . . . . . . . . . . . . . .51

2.5.1 Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54

2.6 TDMA Carrier Design with ’TDMA Calculator’. . . . . . . . . . . . . . . . . . . . . . . . .55

2.6.1 Section ’General Data Input’. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57

2.6.1.1 Parameter Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .58

2.6.2 Section ’Data Input per Frequency Channel’ . . . . . . . . . . . . . . . . . . . . . . .59

2.6.2.1 Parameter Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60

2.6.3 Area ’General Data Output’. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62

2.6.3.1 Parameter Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62

2.6.4 Area ’Data output per frequency channel’. . . . . . . . . . . . . . . . . . . . . . . . . .63

2.6.4.1 Parameter Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65

2.6.5 Exporting and Importing TDMA Calculator Values . . . . . . . . . . . . . . . . . . .66

2.7 From Capacity Estimation to TDMA Structure. . . . . . . . . . . . . . . . . . . . . . . . .67

One Carrier Solution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

Adjustment and Optimization Considerations . . . . . . . . . . . . . . . . . . . 68

Optimized Three Carrier Solution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

Adjustment and Optimization Considerations . . . . . . . . . . . . . . . . . . . 69

3 Outdoor Unit and Satellite Link Design . . . . . . . . . . . . . . . . . . . . . .73

3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .73

Select Satellite Transponder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

Calculate Link Budget . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

Perform Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

3.2 Satellite Beam Footprints. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .74

Satellite Choice Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

3.3 Fundamentals of Link Budget Calculation. . . . . . . . . . . . . . . . . . . . . . . . . . . .76

Uplink and Downlink. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

Equivalent Isotropic Radiated Power (EIRP) and Antenna Gain . . . . . 76

4 Network Design and Engineering Guide 2010-10-26

Path Loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

Saturation Flux Density (SFD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

Noise, Figure of Merit G/T and Signal-to-Noise Ratio Eb/No . . . . . . . . 77

Satellite Link Quality Dependencies . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

Power Equivalent Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

Rain fade. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

Rain Margin and Uplink Power Control. . . . . . . . . . . . . . . . . . . . . . . . . 80

3.4 Considerations for SkyWAN

Link Budget Calculations . . . . . . . . . . . . . . . . 82

3.4.1 Network Topology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

3.4.2 Downlink Optimization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

3.4.3 Uplink Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

3.5 SkyWAN

Link Budget Calculation Tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

3.5.1 Satellite Data Worksheets (Ku- and C-Band) . . . . . . . . . . . . . . . . . . . . . . 86

3.5.2 Antenna Data Worksheets (Ku- and C-Band) . . . . . . . . . . . . . . . . . . . . . . 87

3.5.3 Stations Worksheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

Use pre-defined Network Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

Specify Network Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

Output Back-Off . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

Stations with 2 Demodulator Boards. . . . . . . . . . . . . . . . . . . . . . . . . . . 90

3.5.4 Tx Amplifier Worksheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

3.5.5 Summary Worksheet. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

Optional Link Filter for Complex Topologies. . . . . . . . . . . . . . . . . . . . . 95

3.5.6 Required Settings for MRB-DUB Networks. . . . . . . . . . . . . . . . . . . . . . . . 95

Transponder Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

Hub Stations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

UpLink Area 1 (ULA1). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

UpLink Area 2 (ULA2). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

Carrier Topology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

Link Calculations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

3.6 Link Budget Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

3.6.1 Scenario 1: Ku-Band 5 Stations Fully Meshed . . . . . . . . . . . . . . . . . . . . 100

Satellite Transponder Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

Antenna Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

Optimizations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

Link Budget Calculation Result Analysis. . . . . . . . . . . . . . . . . . . . . . . 103

Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

3.6.2 Scenario 2: Ku-Band 5 Stations Star Network with 2 Hubs. . . . . . . . . . . 103

Compare Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105

3.6.3 Scenario 3: Ku-Band 5 Stations Star Network with 3 Hubs. . . . . . . . . . . 106

4 Data Networking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .107

4.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

2010-10-26 Network Design and Engineering Guide 5

4.2 SkyWAN® Internet Protocol Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .107

4.2.1 SkyWAN SkyWAN

IP Router Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .107

IDU 7000 Series Interfaces. . . . . . . . . . . . . . . . . . . . . . . . 109

4.2.2 Basic IP Network Topologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .111

4.2.3 Static Routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .112

Static Routing in a Star Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

4.2.4 Dynamic Routing with OSPF. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .114

Redistribution of Static Routes via OSPF. . . . . . . . . . . . . . . . . . . . . . 114

4.2.5 Load Balancing for IP Unicast Traffic . . . . . . . . . . . . . . . . . . . . . . . . . . . .115

4.2.6 Equalizing Path Costs for OSPF Networks. . . . . . . . . . . . . . . . . . . . . . . .116

4.2.7 IP Multicast Forwarding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .117

IGMP Querier Role. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

Standard and FMCA Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

4.2.8 IP Service Differentiation (Quality of Service). . . . . . . . . . . . . . . . . . . . . .118

Gold-TCP-A, Gold, Silver, Bronze, Default . . . . . . . . . . . . . . . . . . . . 120

Titanium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120

Platinum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120

Platinum Dynamic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121

4.2.9 Robust Header Compression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .122

4.2.10 Transmission Control Protocol Acceleration (TCP-A). . . . . . . . . . . . . . . .123

4.3 SkyWAN

Frame Relay Networking Features. . . . . . . . . . . . . . . . . . . . . . . .125

4.3.1 Serial port properties. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .125

4.3.2 Basic Frame Relay Services. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .126

4.3.3 FR Communication Services and Quality of Service . . . . . . . . . . . . . . . .127

4.3.4 SkyWAN

FAD Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .128

FAD ’Class 7’ traffic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128

4.3.5 Traffic Shaping and Congestion Management . . . . . . . . . . . . . . . . . . . . .128

Realtime Service for Isochronous FRAD Ports . . . . . . . . . . . . . . . . . 129

Congestion Management of Non-Realtime FR Packets. . . . . . . . . . . 129

5 Summary and Design Implementation . . . . . . . . . . . . . . . . . . . . . .131

6 Appendix A - What’s new in this manual . . . . . . . . . . . . . . . . . . . .133

7 Appendix B - Abbreviations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .135

8 Appendix C - Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .141

9 Appendix D - Install TDMA Calculator Standalone Tool . . . . . . . .147

9.1 Hardware Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .147

9.2 Software Requirements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .147

9.3 Install TDMA Calculator Standalone Tool . . . . . . . . . . . . . . . . . . . . . . . . . . .148

9.4 Run TDMA Calculator Standalone Tool. . . . . . . . . . . . . . . . . . . . . . . . . . . . .148

9.5 Uninstall TDMA Calculator Standalone Tool . . . . . . . . . . . . . . . . . . . . . . . . .148

6 Network Design and Engineering Guide 2010-10-26

LIST OF TABLES

Table 1-1 SkyWAN® IDU 7000 / 1070 Series Manuals Suite . . . . . . . . . . . . . . . . . . 17

Table 2-1 IP Voice Call Data Rates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Table 2-2 Frame Relay Voice Call Data Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Table 2-3 Summary ’General Data Input’ Parameter. . . . . . . . . . . . . . . . . . . . . . . . . 59

Table 2-4 Summary ’Data Input Per Frequency Channel’ Parameter . . . . . . . . . . . . 62

Table 2-5 Summary ’General Data Output’ Parameter . . . . . . . . . . . . . . . . . . . . . . . 63

Table 2-6 Summary ’Data Output Per Frequency Channel’ Parameter. . . . . . . . . . . 65

Table 3-1 Eb/No Values for different FEC Coding and Modulations . . . . . . . . . . . . . 78

Table 3-2 Carrier Power and Bandwidth for TDMA structure example . . . . . . . . . . . 78

Table 3-3 Relation between Modulation, Coding and Carrier PEB . . . . . . . . . . . . . . 79

Table 3-4 Output Back-Off SSPA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

Table 3-5 Scenarion 1 - 2 Carrier Solution Requirements. . . . . . . . . . . . . . . . . . . . 101

Table 3-6 Scenario 1 - Carrier Coding and Bandwidth . . . . . . . . . . . . . . . . . . . . . . 102

Table 3-7 Scenario 1 - Summarized Power Requirements . . . . . . . . . . . . . . . . . . . 102

Table 3-8 Scenario 2 - Carrier Coding and Bandwidth . . . . . . . . . . . . . . . . . . . . . . 104

Table 3-9 Scenario 2 - Summarized Power Requirements . . . . . . . . . . . . . . . . . . . 104

Table 3-10 Scenario 2 - Optimized Carrier Coding and Bandwidth. . . . . . . . . . . . . . 105

Table 3-11 Scenario 2 - Optimized Power Requirements . . . . . . . . . . . . . . . . . . . . . 105

Table 4-1 IP Interface Usage of IDU 7000 series . . . . . . . . . . . . . . . . . . . . . . . . . . 109

Table 4-2 IP Interface Usage of IDU 1070. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110

Table 4-3 Threshold of Forwarding Behaviors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120

Table 4-4 Codecs supported for RoHC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

Table 4-5 UIM Board FR Serial Port Types. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125

Table 6-1 What’s new in the Engineering Manual . . . . . . . . . . . . . . . . . . . . . . . . . . 133

Table 6-2 What’s new in Rev. B. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133

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8 Network Design and Engineering Guide 2010-10-26

LIST OF FIGURES

Figure 1-1 Overview VSAT Station. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Figure 1-2 Overview Design and Engineering Process . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 2-1 Carrier Design Steps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Figure 2-2 SkyWAN Figure 2-3 Voice over SkyWAN

Figure 2-4 Network Topologies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Figure 2-5 Data Reception Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Figure 2-6 Master - Slave Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Figure 2-7 Active and Backup Master. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Figure 2-8 TDMA Frame Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Figure 2-9 Tx Frequency Hopping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Figure 2-10 Data Slot Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Figure 2-11 TDMA Superframes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Figure 2-12 Two Uplink Populations with Cross-Strapped Transponder . . . . . . . . . . . 31

Figure 2-13 MRB-DUB Frame of a 3 Carrier Network . . . . . . . . . . . . . . . . . . . . . . . . . 32

Figure 2-14 NFB-DUB Frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Networking at a Glance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Figure 2-15 Capacity Request . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Figure 2-16 Free Slot Assignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Figure 2-17 Slot Assignment with Ranging Subframe . . . . . . . . . . . . . . . . . . . . . . . . . 34

Figure 2-18 Slot Assignment Differences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Figure 2-19 TDMA Structure of Throughput Example. . . . . . . . . . . . . . . . . . . . . . . . . . 36

Figure 2-20 Throughput Scenario 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Figure 2-21 Throughput Scenario 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Figure 2-22 Throughput Scenario 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Figure 2-23 Throughput Scenario 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Figure 2-24 Traffic Estimation Scenario IP Traffic . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Figure 2-25 Traffic Estimation Scenario Fame RelayTraffic . . . . . . . . . . . . . . . . . . . . . 43

Figure 2-26 Traffic Calculation Example - Capacity Worksheet . . . . . . . . . . . . . . . . . . 44

Figure 2-27 Per Network Traffic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Figure 2-28 Traffic Calculation Example - Erlang B Worksheet . . . . . . . . . . . . . . . . . . 46

Figure 2-29 Traffic Calculation Example - Voice Traffic Flow Worksheet. . . . . . . . . . . 47

Figure 2-30 Traffic Calculation Example - Carrier Configuration Worksheet . . . . . . . . 48

Figure 2-31 Traffic Calculation Example - Carrier Config. with Network Traffic . . . . . . 49

Figure 2-32 SLL Encapsulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Figure 2-33 Gross Container Information Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Figure 2-34 Add Turbo-Phi Coding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Figure 2-35 Modulated Gross Container. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Figure 2-36 Signalling Time Slots. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

2010-10-26 Network Design and Engineering Guide 9

Figure 2-37 Signal Preparation - Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54

Figure 2-38 Start integrated SkyNMS TDMA Calculator . . . . . . . . . . . . . . . . . . . . . . . .55

Figure 2-39 TDMA Calculator GUI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56

Figure 2-40 TDMA Calculator - two Uplink Populations specified . . . . . . . . . . . . . . . . .57

Figure 2-41 TDAM Calculator - Define different traffic compositions . . . . . . . . . . . . . . .60

Figure 2-42 Results from Capacity Calculation Tool . . . . . . . . . . . . . . . . . . . . . . . . . . .67

Figure 2-43 TDMA Calculator with Optimized 1 Carrier Solution. . . . . . . . . . . . . . . . . .69

Figure 2-44 TDMA Calculator Output for Optimized 3 Carrier Solution . . . . . . . . . . . . .70

Figure 3-1 Steps for Outdoor Unit and Satellite Link Design . . . . . . . . . . . . . . . . . . . .73

Figure 3-2 SES World Skies NSS-7 Satellite Wide Beam Footprints. . . . . . . . . . . . . .74

Figure 3-3 SES World Skies NSS-7 Satellite Spot Beam Footprint . . . . . . . . . . . . . . .75

Figure 3-4 Up- and Downlink Link Budget . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76

Figure 3-5 ITU-T Rainzones Europe and North-Africa. . . . . . . . . . . . . . . . . . . . . . . . .80

Figure 3-6 Attenuation under maximum Rain Fade Condition. . . . . . . . . . . . . . . . . . .81

Figure 3-7 Power Conditions with constant Power Level. . . . . . . . . . . . . . . . . . . . . . .81

Figure 3-8 Power Conditions with Uplink Power Control . . . . . . . . . . . . . . . . . . . . . . .82

Figure 3-9 Downlink Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83

Figure 3-10 Uplink Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .84

Figure 3-11 Link Budget Tool - Satellite Data Worksheet(s) . . . . . . . . . . . . . . . . . . . . .86

Figure 3-12 Link Budget Tool - Antenna Data Worksheet(s) . . . . . . . . . . . . . . . . . . . . .87

Figure 3-13 Link Budget Tool - C-Band Antenna Data. . . . . . . . . . . . . . . . . . . . . . . . . .87

Figure 3-14 Link Budget Tool - Station Worksheet. . . . . . . . . . . . . . . . . . . . . . . . . . . . .88

Figure 3-15 Link Budget Tool - Define Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .89

Figure 3-16 Link Budget Tool - Station with 2 Demodulators. . . . . . . . . . . . . . . . . . . . .90

Figure 3-17 Link Budget Tool - TxAmp Worksheet . . . . . . . . . . . . . . . . . . . . . . . . . . . .91

Figure 3-18 Link Budget Tool - Summary Worksheet Input. . . . . . . . . . . . . . . . . . . . . .92

Figure 3-19 Link Budget Tool - Summary Worksheet Uplink . . . . . . . . . . . . . . . . . . . . .93

Figure 3-20 Link Budget Tool - Summary Worksheet Downlinks. . . . . . . . . . . . . . . . . .93

Figure 3-21 Link Budget Tool - Summary Worksheet Up- and Downlinks. . . . . . . . . . .94

Figure 3-22 Link Budget Tool - Summary Worksheet Complex Filter . . . . . . . . . . . . . .95

Figure 3-23 MRB-Dub Network Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .96

Figure 3-24 MRB-DUB Network - Satellite Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .96

Figure 3-25 MRB-DUB Network - Transponder in Stations Sheet. . . . . . . . . . . . . . . . .96

Figure 3-26 MRB DUB Network - Hub Stations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .97

Figure 3-27 MRB DUB Network - ULA1 Stations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .97

Figure 3-28 MRB DUB Network - ULA2 Stations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98

Figure 3-29 MRB DUB Network - Summary Topology. . . . . . . . . . . . . . . . . . . . . . . . . .98

Figure 3-30 MRB DUB Network - Link Calculations ULA1. . . . . . . . . . . . . . . . . . . . . . .99

Figure 3-31 MRB DUB Network - Link Calculations ULA2. . . . . . . . . . . . . . . . . . . . . . .99

Figure 3-32 Scenario 1 - Uplink Footprint. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .100

10 Network Design and Engineering Guide 2010-10-26

Figure 3-33 Scenario 1 - Downlink Footprint. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

Figure 3-34 Scenario 1 - Ku-Band Transponder Data . . . . . . . . . . . . . . . . . . . . . . . . 101

Figure 3-35 Scenario 1 - Ku-Band Antenna Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

Figure 3-36 Scenarion 1 - 2 Carrier Solution Stations . . . . . . . . . . . . . . . . . . . . . . . . 102

Figure 4-1 SkyWAN Figure 4-2 SkyWAN Figure 4-3 SkyWAN Figure 4-4 SkyWAN

IP Protocol Stack IDU 7000 series. . . . . . . . . . . . . . . . . . . . . 109

IP Protocol Stack IDU 1070 . . . . . . . . . . . . . . . . . . . . . . . . . . 110

Meshed IP Data and Management Network . . . . . . . . . . . . . 111

Hybrid IP Data and Management Network. . . . . . . . . . . . . . . 112

Figure 4-5 Static Routing in a Star Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

Figure 4-6 OSPF Cost Metric . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

Figure 4-7 Mapping of Forwarding Behaviours to Transmit Queues . . . . . . . . . . . . 119

Figure 4-8 RoHC Feature Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123

Figure 4-9 TCP-A Feature Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124

Figure 4-10 Mapping of FR Services to Transmit Queues . . . . . . . . . . . . . . . . . . . . . 127

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12 Network Design and Engineering Guide 2010-10-26

Introduction

Summary

1 INTRODUCTION

1.1 Summary

SkyWAN® is a flexible and versatile VSAT system to establish wide area corporate network in- frastructures via satellite for enterprises and governmental institutions, supporting a wide variety of end user business applications.

The SkyWAN media services (voice, video) and data transport sent with small antennas over transparent satellite transponder frequency channels. Beside the IDU, a SkyWAN equipment (ODU) like antenna, transceiver, amplifier, control units, redundancy control units, converters etc. as engineered for customer premisses.

Indoor Unit (IDU) is a satellite modem with advanced features. It offers multi-

network contains outdoor

Figure 1-1 Overview VSAT Station

1.2 Manual Content

This SkyWAN® Network Design and Engineering Guide provides information about how to design and engineer a SkyWAN Some typical network design scenarios will be discussed; starting from customer traffic requirements an optimized SkyWAN Satcom Design tools discussed.

This guide consists of the following main sections:

- General Carrier Design.

The SkyWAN

Satellite Link Layer implementation and functionality is described. A detailed description of the Time Division Multiple Access (TDMA) structure of SkyWAN riers is given. The procedure how to translate customer network traffic requirements into an optimized SkyWAN purpose are described.

2010-10-26 Network Design and Engineering Guide 13

Satellite Network based on the SkyWAN® IDU modem series.

Carrier and Outdoor Unit Design will be derived using the ND

car-

carrier structure is outlined. The ND Satcom Design Tools for this

Introduction Manual Content

- Satellite Link and Outdoor Unit Design To perform satellite communication over satellite links with sufficient quality the earth stations have to fulfill specific requirements concerning their transmission power and antenna gain. A proper network design is based on an estimation of the link properties, taking into account parameters of the satellite transponder and of the earth stations. The ND Satcom Link Budget Tool which can be used to calculate satellite link power requirements will be described in this section.The output will be an optimal selection of transmitter and antenna types for each earth station.

- SkyWAN A detailed description of the SkyWAN

Data Networking Features

support of Data Networking Protocols TCP/IP and Frame Relay will be given. Implication for typical applications and services will be discussed.

Information for installation, line-up, network commissioning and system overview is covered in

the SkyWAN

manuals suite; refer to chapter 1.5.

1.2.1 Who should read this document

This document is intended for engineers designing a SkyWAN® Satellite Network. Participation of a SkyWAN

engineering training is recommended.

1.2.2 What do you need to know

It is expected that the user has general understanding how to design and engineer a VSAT network. Before reading this document you should have a good understanding of the following:

- Understanding of satellite communication hardware and technology.

- Understanding of protocols e.g. IP, TCP, OSPF, SNMP, IGMP, PPP.

- Understanding of Frame Relay and Voice over IP (VoIP).

- Understanding of LAN and WAN architecture.

14 Network Design and Engineering Guide 2010-10-26

Introduction

SkyWAN

Solutions and Benefits

1.3 SkyWAN® Solutions and Benefits

SkyWAN® uses an MF-TDMA system supporting a variety of satellite network topolo gies (fully- meshed, hybrid, star). Main network features are:

- Wide hopping range (from burst to burst) over 800 MHz (transponder hopping)

- Data rates from 64 kbit/s up to 10 Mbit/s per channel, up to 8 channels are supported

- Highly dynamic assignment of transmission capacity

- Integration of real-time and non-real-time applications into a packet switching architecture

- Frame Relay switching, including Quality of Service (QoS) support

- IP routing, including QoS support

- Acceleration of transmission control protocol connections (TCP-A)

- Support of many applications like

- Traditional telephony systems (ISDN, analogue)

- Voice and Video over IP (V2oIP) with efficient header compression

- LAN interconnection via Frame Relay and/or IP

- GSM backhaul solutions

- SNMP based network management system

- L-Band transmit- and receive interface between indoor unit (IDU) and outdoor unit (ODU). SkyWAN

Technology offers the following advantages over competing satellite communication

technologies:

- Flexibility: By allowing meshed, star and hybrid topologies, SkyWAN

networks can be

ideally adapted to diverse customer requirements.

- Versatility: By supporting IP based and legacy network protocols any type of business communication may be supported.

- Scalability: From small networks consisting of few stations to large ones with hundreds of stations SkyWAN

networks can be tailored cost efficiently to customer demands.

- Availability: The built-in Master/Backupmaster functionality with automatic switchover establishes a network without single point of failure.

- Performance: Symbol rates ranging from 100 to 6000 ksps per carrier allow support of high bandwidth applications.

- Efficiency: By defining a common bandwidth pool for station groups, overall network bandwidth consumption is reduced by statistical multiplexing.

2010-10-26 Network Design and Engineering Guide 15

Introduction General Design and Engineering Process

1.4 General Design and Engineering Process

The general design process of a SkyWAN® network is an ongoing process starting with compiling the end user requirements. Result is a cost efficient network, fulfilling the service requirements defined. The process may be summarized by the following picture:

Figure 1-2 Overview Design and Engineering Process

Good requirement engineering is the basis of a well designed network and should not be neglected. With the customer input information you start to engineer the network including the aspects cost, feasibility and product characteristics. If the solution is satisfying, the network will be implemented. To prove the successfull realization of the requirements some tests have to be done. If a service does not meet the customer cond itio ns, a new design phase is required.

Customer Input which is required as a starting point for the design typically consists of the following information:

- Description of applications and utilisation scenarios.

- Descripton of the customer network environment.

- Satellite transponder data.

- Station locations.

- General SkyWAN

requirements.

- Specific requirements for IP based applications.

- Specific requirements for Frame Relay applications and the Frame Relay Access Device. To request these parameters from a customer, a standardized questionnaire form ’SkyWAN

Network Design and Engineering Requirements’ may be used.

The core SkyWAN

design process can be split into different phases, which are linked:

- The general carrier design, where all carrier specific data is defined.

- The outdoor units design, where all outdoor specific data, including the space segment is defined.

- The detailed indoor unit design, where all details about hardware and licenses are defined.

- The finalization of the design including costs optimization.

These steps are discussed in detail within the subsequent sections of this guide.

16 Network Design and Engineering Guide 2010-10-26

1.5 Related Documents

1.5.1 SkyWAN® IDU Manuals Suite

Your intention is Document Title Document Content

to understand features and

services of a SkyWAN IDU and its networking possibilities.

SkyWAN 1070 Series System Description

IDU 7000 /

Describes the technical concept

of a SkyWAN

Satellite Network and its features and applications. Explains the system components and provides a comprehensive technical specification.

Introduction

2 GENERAL CARRIER DESIGN

The general principle of the carrier design may be summarized by the following steps, refer to figure 2-1:

Figure 2-1 Carrier Design Steps

2.1 Introduction

Within this chapter we will

- introduce the SkyWAN

- introduce the essential SkyWAN

- discuss the traffic calculation procedure taking into account the relevant SkyWAN and voice networking features. The ND SatCom ’Capacity Calculator Tool’ has to be used.

- discuss how to derive an optimized carrier structure which fulfils the original customer requirements with the help of the ND SatCom ’TDMA Calculator’ tool.

Consider the resulting effects of the design approach to network efficiency, network behavior and future expansions.

The original plain requirements (refer to section A1 in figure 2-1) represent the customer input. In general such requirements have to be adapted in order to make them suitable as input for the satellite communication design.

The first task in section A1 Traffi c Calculation is to define suitable ’core design requirements’. Often it is necessary to convert the customer view to the specifics of a satellite network in contrast to terrestrial networks / fixed leased lines etc. Keep in mind the SkyWAN questioning the customer. Define the requirements down to a suitable level. This task cannot be supported completely by a certain tool. Our suggested tool will give you an idea and some guidance about what is necessary to document.

data and voice networking.

MF-TDMA satellite link layer features.

data

features, when

2010-10-26 Network Design and Engineering Guide 19

General Carrier Design Data and Voice Networking Overview

Within the task A2 Carrier Design the n etwork efficiency / TDMA overhead will be determined. The average TDMA overhead is 15%. But as the overhead range is between 5% and 30% it will be worth to elaborate and downsize such ’nasty peanuts’. With some experience you can start with a good guess about the carrier sizes and feed the ’SkyWAN

TDMA Calculation Tool’

to prove your guess.

2.2 Data and Voice Networking Overview

To send data and voice applications traffic over satellite the end user equipment is connected to an IP or Frame Relay input port of the SkyWAN

Figure 2-2 SkyWAN® Networking at a Glance

IDU.

The figure 2-2 represents a brief overview of the supported data networking protocols; depicted

is an IP connection. On the ethernet port (interface 1) SkyWAN

supports the Internet Protocol (IP) routing functionality. On the serial ports 2-5 (interfaces 2-5) the Frame Relay (FR) switching functionality is supported.

Both types of data packet protocols are transported over the satellite link layer interfaces (modulator port Tx Out and demodulator port(s) Rx In) using an efficient proprietary Satellite Link Layer (SLL) encapsulation.

During forwarding the ethernet packets will have their header stripped. The remaining IP packet will be encapsulated in an SLL frame which includes a 2 Byte SLL header and a 4 Byte CRC check sum. Frame Relay frames will be encapsulated in a similar SLL frame. The SLL frames will be put into a SkyWAN

TDMA container. If the frame sizes are larger than the remaining space in such a container, the SLL frames will be fragmented. A TDMA header will be added to the container. Finally the complete gross container will be encoded and modulated.

a. Note that to use the Frame Relay serial ports a run-time license is required on the IDU.

20 Network Design and Engineering Guide 2010-10-26

General Carrier Design

Data and Voice Networking Overview

On the receiving station the whole procedure is reversed:

- Demodulation and decoding,

- Reassembly of fragments into SLL frames,

- Replacing of SLL by Ethernet headers (for IP packets),

- Forwarding of Ethernet (or FR frames) over the Ethernet (or serial) port.

Voice connections

The requirement for data traffic is generally specified in terms of a required data rate. Fo r voice traffic usually the required number of (bidirectional) voice connections is specified. To translate that into a data rate requirement it is necessary to know the data rate per voice call. This rate depends on the codec rate of the used voice codec (typically in the range 6-64 kbps) and the additional overhead due to the applied network protocol. In SkyWAN network technologies are used:

- Voice over IP using IP/UDP/RTP encapsulation of the voice payload (VoIP).

- Voice over SkyWAN

FAD using the Frame Relay functionality (VoFR).

networks two different

The data networking overhead for both options is quite different, leading to a higher bandwidth consumption for VoIP calls compared to VoFR calls: The VoIP overhead (IP/UDP/RTP) summarizes to 40 Bytes whereas the VoFR overhead is 8 Bytes.

Since the typical voice payload per packet is in the range of 10-40 Byte, the VoIP overhead represents a large fraction of the required data rate. This may be reduced by the Robust Header Compression (ROHC) technique. A detailed description of this procedure will be given in a subsequent section of this Guide.

Figure 2-3 Voice over SkyWAN®

2010-10-26 Network Design and Engineering Guide 21

General Carrier Design Data and Voice Networking Overview

Voice Codecs

The following tables specify the required data rate per call and direction for both VoIP and VoFR calls using the most popular voice codecs. For the user tra ffic estimation use the tab les below:

- For VoIP connections: use columns ’IP Bit rate w/o ROHC’ or ’ROHC Bit rate’ of table 2-1.

- For VoFR connections: use columns ’IDU Input Data Rate’ of table 2-2. The columns labelled ’incl. SLL encapsulation’ provide an estimation for the data re quirements

including SLL encapsulation.

Codec Codec

Bit Rate [bps]

G.711 64,000 160 87,200 G.722 32,000 80 55,200 G.723 6,300 24 21,525 G.728 16,000 60 31,466 G.729 8,000 20 31,200

Table 2-1 IP Voice Call Data Rates

Codec IDU Input Data

ACELP CN 8kx1 12,440 18 20 15,120 ACELP CN 8kx2

Voice Payload

[byte}

Bit Rate Ethernet

[bps]

IP Bit Rate w/o RoHC

[bps]

80,000 83,200 65,600 68,800 48,000 51,200 33,600 36,800 16,773 18,885 7,269 9,381 26,714 28,826 17,210 19,322 24,000 27,200 9,600 12,800

Frame Rate [bps]

10,670 36 40 12,000

Time

[ms]

IP Bit Rate (incl. SLL encaps.) [bps]

Voice Payload [byte]

RoHC Bit Rate

[bps]

Data Rate (incl. encaps.) [bps]

RoHC Bit Rate (incl. SLL encaps.) [bps]

ACELP CN 8kx3 ACELP CN 6kx1 ACELP CN 6kx2 ACELP CN 6kx3

Table 2-2 Frame Relay Voice Call Data Rates

22 Network Design and Engineering Guide 2010-10-26

9,930 54 59 10,820 10,670 18 16 13,340 8,890 36 32 10,230 8,150 54 47 9,040

General Carrier Design

Essential SkyWAN

Satellite Link Layer Features

2.3 Essential SkyWAN® Satellite Link Layer Features

The following section discusses the essential properties of a satellite link in a SkyWAN® network. A proper understanding of the properties and features is essential for a successful network design.

2.3.1 SkyWAN® Network Topologies

Figure 2-4 Network Topologies

SkyWAN® networks support any kind of satellite network topology. The simple topologies pre- sented in the picture above have the following characteristics:

- Fully Meshed: Each station has a direct satellite link to each other station. These stations are commonly referred to as “peer stations”.

- Star: Star terminals have only a satellite link to a common hub station.

Besides these simple topologies, SkyWAN

networks can also have hybrid topologies. In a hybrid topology a part of the network may be fully meshed while some sta tions may only have star connectivity. Or a multi-star topology may be configured where the star terminals have connectivity to multiple hub stations.

The optimal choice of topologies depends on the required network connectivity. A network where data and voice connections can go from any to any station are optimally served by a meshed topology, where latency and bandwidth consumption on the satellite link is minimal.

Star topologies require double satellite hops between terminal stations. That means double delay and double bandwidth necessary for any of these connections. If, however, no or only a small amount of communication is necessary between terminal stations, operating them in a star mode might reduce the requirements on the outdoor units. Reducing e.g. transmit power and antenna size would lead to a reduction of station hardware costs. Even in this case, a multistar topology might have an advantage, especially if redundancy is required in a network.

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Figure 2-5 Data Reception Modes

Reception Modes

In principle a SkyWAN® station can operate in any kind of topology. However, to be able to communicate with more than two other stations in the network a ’Regular Data Reception’ (RDR) license is required. Hence the peer and hub stations represented in the figure would need an RDR license, whereas the star terminals could run with the default ’Limited Data Reception’ (LDR) license. The LDR license would still be sufficient if the star terminals have to communicate with two hub stations.

The restriction imposed by the LDR mode does not apply to node management via IP based protocols (SNMP, FTP, Telnet). It is therefore possible to manage the star terminals by a network management station which is not connected to the hub but to one of the peer stations.

In LDR mode user traffic between a peer station and a star terminal is however not possible.

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2.3.2 Master and Slave Functionality

General Carrier Design

Satellite Link Layer Features

In a traditional star network the hub station acts as both, a traffic hub and a network management station. In a fully meshed SkyWAN

network, the traffic hub functionality is not necessary

since all stations can reach their peers directly over the satellite link. The network management functionality however is always necessary and is normally provided

by the SkyWAN

master station. A master station must fulfil the following fundamental require-

ments:

- Indoor Unit requirement: The master station must be a SkyWAN

IDU 7000 equipped with

a frame plan generator (FPG) board.

- Satellite link requirement: The master station must be able to reach each other station in

the network over a satellite link with sufficient quality. In a star or hybrid network this means that only peer or hub stations may perform the master role.

RDR license is required for a master station.

Control Communication: Reference and Request Bursts

The following figure 2-6 presents an overview of the control tasks performed by the master station:

Figure 2-6 Master - Slave Communication

The control communicaton between master and slave stations is based on specific signal types:

- Reference Burst: from Master to Slaves.

- Ranging and Request Bursts: from Slaves to Master. The master station uses reference bursts to transmit the frame plan which specifies the trans-

mission times for every station in the network. Additional information is distributed with these bursts:

- Slave station authentication.

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Satellite Link Layer Features

- Time stamps to enable transmission time synchronisation.

- Feedback to slaves concerning their transmission power settings and frequency offsets. The slave stations use the ranging burst for station registration and initial round trip time (earth

station to satellite to earth station) measurement. Registered slave stations use request bursts

- for requesting transmission capacity on the satellite link,

- to give feedback to the master concerning the power level of the master’s reference bursts.

Active and Backup Master Role

Figure 2-7 Active and Backup Master

Although at one time there can be only one active master station in a SkyWAN® network it is possible and recommended to configure two stations to be poten tial master stations. Bot h stations have to fulfil the master station requirements mentioned before. The station which enter s the network first will become active master, the other station backup master. If the backup master detects an outage of the active master it will take over the master role within 2 seconds. This ensures a seamless transition which does not interrupt network services. Note that there is no automatic switchback of the master role even if the original active master comes up again. In this case the new active master will keep this role whereas the recovered former active master will now be the backup master.

To increase the resiliency of a SkyWAN

network, it makes sense to locate the two master stations in different geographical locations. This ensures continued ne twork operation even if one of the master sites is knocked out due to severe environmental conditions (e.g. hurricanes, earth quakes, flooding, sun outages).

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Essential SkyWAN

Satellite Link Layer Features

2.3.3 SkyWAN® MF-TDMA functionality

SkyWAN® networks are based on a time division technique on multiple carriers which is called ’Multi-Frequency Time Division Multiple Access’ (MF-TDMA). Up to eight carriers can be defined for one SkyWAN tions by assigning discrete time slots to each station. This assignment is not stat ic and may be changed according to the current traffic on each station. This allows a flexible bandwidth on demand allocation of the carrier bandwidth for an optimal utilization of precious satellite capacity. Since multiple stations receive the same carrier, multicast forwarding of data without packet duplication is possible.

network. The bandwidth of individual carriers is shared by multiple sta-

TDMA Frame

The following picture represents the TDMA structure of a single carrier (channel 1). The TDMA frame starts with a time slot (furthermore notated as ’slot’) which is allocated to the active master to transmit the reference burst. The following slot is assigned to slave stations for tra nsmission of their request bursts. The rest of the TDMA frame consists of time slots for user traffic data bursts which are allocated on demand to various stations (indicated by color) in the network.

The allocation of slots to stations is defined by the master and signalled to the slave stations via the frame plan, which is transmitted as part of the reference burst. Note that the duration of each time slot (’base slot’) within the TDMA frame is identical. Multiple request bursts may be defined in one base slot whereas the reference burst will use one or multiple base slots. The maximum number of base slots per frame is 256 (SkyWAN

The frame time is the time between two reference bursts. This frame time and the size of an individual time slot can be defined by network configuration. One major task of the SkyWAN carrier design is the optimal definition of these parameters.

IDU Software Release 7.10).

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Figure 2-8 TDMA Frame Structure

Please note: a ranging slot is allocated only when a station is entering the network.

Transmit and Receive Carriers

Satellite Link Layer Features

SkyWAN® stations receive data on one or two carriers (e.g. IDU7000 with two demodulator boards) . These carriers are defined by station configuration and are referred to as ’Home Channel One’ and ’Home Channel Two’.

Restriction for master stations: Home Channel One must be carrier 1. In Dual Uplink Beam (DUB) modes Home Channel Two must be carrier 2.

SkyWAN hopping). By configuration the possible transmit carriers can be allocated (restricted) for each station.

A TDMA frame plan for a SkyWAN example carrier 1 and 2 carry a reference burst, carrier 3-8 only data bursts.

stations can transmit data on any active carrier in the network (frequency or carrier

network with 8 carriers is displayed in figure 2-9. In this

Figure 2-9 Tx Frequency Hopping

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Essential SkyWAN

The following restrictions apply:

- Home Channel One of each station must be one of the carriers containing a reference burst. In figure 2-9 only channel 1 and channel 2 could be configured as Home Channel One.

- A station cannot transmit simultaneously on two different frequency channels. This is the reason why in a ’column’ of the frame plan there are no duplicated ’colors’.

- On the other hand, hopping between two carriers is perfectly possible between consecutive time slots.

In order to send data to another station in the network a SkyWAN

- Figure out on which home channel(s) the receiving station can be reached. This task is performed by automatic signalling procedures in the network.

- Request capacity on the home channel(s) of the receiving station if it is not already allocated.

- Use the allocated time slot to transfer the data to the destination.

Satellite Link Layer Features

IDU must do the following:

Data Slot Time Factors

Base time slot durations are identical for every carrier used in the network. Th at does not mean, however, that the payload data is identical because symbol rate, modulation and coding may be configured differently on each carrier. Time slots on a carrier with high symbol rate carry larger amounts of data compared to those with a low symbol rate.

Figure 2-10 Data Slot Length

Slot time factors greater than 1 increase the container size for this carrier. A data slot time factor 2 means that two ’base slots’ are combined to form a double sized time slot on this carrier. Other possible factors are 4 and 8. Refer to figure 2-10 which presents a TDMA frame with carriers using data slot time factors 2 and 4.

Reference bursts may occupy more than one base slot if the data content of one slot is not sufficient to carry the frame plan information.

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TDMA Superframe

Another TDMA frame option is the definition of a superframe size. By default (superframe size=1) every station has to transmit a request burst in every frame. In a network with many stations this could consume many base slots on the respective carrier leaving few slots left for data bursts. This effect can be reduced by the superframe mechanism. This mechanism allows to split and distribute the request bursts, normally transmitted in one frame, to several frames of one superframe (sizes from 1 to 16 are applicable).

- Advantage: The overhead caused by request bursts is significantly reduced.

- Disadvantage: In the event of a sudden burst of data traffic, the time for the next transmission of request bursts to the master station needs more time than without superframing.

Figure 2-11 TDMA Superframes

In figure 2-11 the frame structure for superframe sizes of 1 and 6 is presented. Choosing a superframe size of 6 in this example will provide 5 additional data slots. A larger super frame size would not make sense here because 1 base slot is always needed for the request bursts.

2.3.4 Downlink and Uplink Populations

SkyWAN® stations within a network can be grouped according to the carrier o n which t hey re- ceive the reference burst from the master and on the carrier on which they transmit request bursts to the master.

- ’Downlink Population <N>’: Set of all stations which receive the reference burst on carrier number <N>, i.e. all stations with Home Channel One configured to carrier <N>. The master station(s) must belong to Downlink Population 1. The maximum number of SkyWAN stations in one downlink population is 255.

- ’Uplink Population <N>’: Set of all stations which use carrier number <N> to transmit request bursts to the master. By default all stations are using carrier number 1 to transmit request bursts to the master, i.e. they all belong to Uplink Population 1. The maximum number of stations in one uplink population is 255.

In ’Dual Uplink Beam’ (DUB) mode there is an Uplink Population 2 which comprises all stations which cannot use carrier 1 because they have no access to the carriers on this (looped) satellite transponder. For these stations a carrier 2 on a different (cross-strapped) transponder will be allocated. This carrier will be received by a second demodulator on the master station(s). The master station(s) will always be members of Uplink Population 1. The maximum numbe r of stations in a SkyWAN

network using MRB-DUB mode is 510.

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Essential SkyWAN

Figure 2-12 Two Uplink Populations with Cross-Strapped Transponder

General Carrier Design

Satellite Link Layer Features

2.3.5 SkyWAN® Reference Burst Modes

SkyWAN® networks support three different reference burst modes:

- Standard Multiple Reference Burst mode (MRB),

- Multiple Reference Burst with Dual Uplink Beam (MRB-DUB),

- No Direct Feedback on Reference Burst with Dual Uplink Beam (NFB-DUB). The characteristics of these modes are outlined lelow.

MRB Mode

For a network with <N> downlink populations, the first <N> carriers carry a reference burst. Additional carriers without reference burst may be added for reception on the second demodulator. Maximum number of downlink populations is 8. Only one uplink population is possible, therefore all slave stations send ranging and request burst on carrier 1 only. Symbolrate, modulation and coding may be set differently on each carrier. A graphical representation of the frame structure has been given in the section ’MF-TDMA Functionality’, refer to figure 2-9.

MRB-DUB Mode

For a network with <N> downlink populations carrier 1 and 3,..,N+1 carry a reference burst. There is no reference burst on carrier 2! The number of downlink populations can range from 2 to 7. There are two uplink populations, slave stations belonging to uplink population 1 use carrier 1 for ranging and request bursts, the other stations use carrier 2. The following restrictions apply:

- Master stations must be equipped with two demodulator boards: Home Ch annel Two on master station(s) must be set to carrier 2.

- Symbolrate, modulation and coding on carrier 1 and 2 must be identical.

- Slave stations in uplink population 2 by default operate in star topology. The master stations serve as hub stations for these slaves. If meshing between stations in uplink population 2 is required every slave herein needs a second demodulator board.

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Satellite Link Layer Features

A graphical representation of a 3 carrier MRB-DUB network is given in figure 2-13. For both MRB modes, the master stations must be able to receive their own bursts on carrier 1.

Figure 2-13 MRB-DUB Frame of a 3 Carrier Network

NFB-DUB Mode

This is the only mode where the master station does not need to receive its own reference burst. There is only one downlink population for all slave stations. The single reference burst is transmitted on carrier 3. Two uplink populations are possible, uplink population 1 uses carrier 1 and uplink population 2 carrier 2 for ranging and request bursts. If only one uplink population exists in the network, carrier 2 will not be defined. The following restrictions apply:

- Only one master station is possible, no backup master functionality.

- Pure star topology with the master station serving as a hub. No satellite link between slave stations.

- If two uplink populations are used, carrier 1 and 2 must have the same symbol rate, modulation and coding.

A graphical representation of the frame structure of an NFB-DUB network with one uplink population is given in figure 2-14. Note that in c ontrast to the MRB modes there is no time slot boundary alignment between carrier 1 (or 2) and carrier 3. This is not required here, because channel 3 is only used by the single master station which does not need to coordinate its transmission times with any other station in the network.

Figure 2-14 NFB-DUB Frame

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Satellite Link Layer Features

Despite its numerous limitations NFB-DUB mode is a better choice than MRB-DUB mode if

- A single star topology is sufficient,

- Master and slave stations are located in different satellite beams interconnected via a cross-strapped transponder.

If there is no other station located in the same beam as the master, MRB-DUB mode would require an extra carrier having the same bandwidth as the ’inbound’ carrier (from slave to master) just for master synchronization.

2.3.6 Capacity Request and Allocation for User Data

Figure 2-15 Capacity Request

There are two types of capacity requests: stream requests and dynamic requests. Both are computed for each carrier channel and forwarded to the active master station by means of a ’Request Burst’.

The SkyWAN

IDU provides transmit queues. With these queues data to be send via satellite

is treated differently regarding priority measures.

1. Highest priority: Real Time (RT) user data.

2. Less priority: Control data (internal station messaging and network management data)

3. Lowest priority: Non Real Time (NRT) user data.

The queueing principle is shown in figure 2-15. The differentiation is more precise and will be shown in more detail later. Note, that for each carrier individual queues are used.

Free Slot Assignment

Free Slot Assignment can be enabled per station and per carrier. Every station which

- is declared to participate in the Free Slot Assignment for a specific carrier and

- is registered in the network

gets empty slots which are not requested by any other station on this carrier. These available slots are assigned in a round robin fashion among every registered station. If the station has nothing to transmit it will just transmit „dummy data“. If the station suddenly gets any data packets in to the transmit queue, then it can transmit them immediately within these slots without

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having to request the capacity first. This mechanism is only available for non real-time data!

Figure 2-16 Free Slot Assignment

Ranging Subframe

The ranging subframe is a number of consecutive slots allocated to slave stations which are not yet registered in the network. These slots are not permanently assigned for this purpose. If there are no unregistered stations in the network ranging slots can be allocated as dynamic data slots. The size of the ranging section depends on the timeslot duration, typ ically it is in the range of 1-5 base slots.

Figure 2-17 Slot Assignment with Ran gi ng Subframe

Stream Slots

Stream Slots are triggered from data stored in the ’Real Time Transmit Queues’:

- Usage: for a real time application a station needs a constant data rate with low jitter (variance of delay). For a telephone call, the destination station will require the same data rate for the way back.

- Examples: Speech, Video Conference, Video Streaming.

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Satellite Link Layer Features

To minimize jitter for real time applications the allocation of stream slots for a station will be done as presented in figure 2-18. Once the capacity is allocated the position of the assigned stream slots in the frame will be maintained.

Another feature of streaming capacity allocation is that the capacity will be assigned in a semipermanent way: As long as the real-time service (e.g. voice call, video session) is still up, the master will assign the stream slots continuously to the station until the station signals that service is terminated. This ensures the service quality of running real-time services irrespective of the congestion state of the network. If the stream slots on a carrier are already allocated to stations, new stream slot requests will be rejected by the master. This causes a blocking of the real-time service!

Not every data slot in a frame may be assigned as stream slot. Generally the amount of available stream slots per channel may be restricted by configuration. This makes sense if one wants to avoid the situation that high priority real time traffic is occupying 100% of the available slots on a carrier, thus disrupting non real time application for an indefinite time.

The system limitation for the number of stream slots is equal to the number of data slots minus one (because one time slot is needed for potential key exchange for link encryption) on carr iers without request bursts. For carriers with request bursts additionally the slots needed for the ranging subframe may not be allocated as streaming slots.

Dynamic Slots

Dynamic Slots are triggered from data stored in any other transmit queue type (Control o r Non

Real Time):

- Usage: a station needs resources to transmit data which are not time critical.

- If specified, stations may get access to free resources without even asking for it: the IDU ’Free Slot Assignment’ feature, see description above.

- Examples: File Transfer, Web Browsing.

In contrast to streaming slots, dynamic slots may be allocated in arbitrary positions of the frame. If there are more requests for dynamic slots than available, the master allocates the slots via a fair sharing procedure. In any case requests for streaming slots up to the configured maximum will be served with higher priority than dynamic slots.

Figure 2-18 Slot Assignment Differences

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2.3.7 Guaranteed Throughput

By default every station is treated identically concerning the allocation of capacity. Optionally it is possible to define a guaranteed throughput for specific stations on specific carriers. If requested for, the master must allocate these slots even, if it has to reject requests from other stations.

There are two modes of guaranteed throughput which can be selected individually for every station:

- Stream Mode ’Normal’: In this mode the guarantee only applies to dynamic slot assignment. Concerning stream slot assignment, the stations with guaranteed throughput will still be treated as every other station. Their requests will be served if there are still slots from the ’common’ stream pool (specified by the general parameter: ’maximum number of stream slots’) available on this carrier.

- Stream Mode ’Stream within Guaranteed Throughput’: In this mode the guarantee also applies to streaming slots. Stations with a guaranteed throughput will have their ’private’ pool of possible streaming slots: No other station may be allocated streaming slots of this pool, but the station will also not get any streaming slots from the common pool if its private pool is already exhausted.

Oversubscription with guaranteed throughput definitions is not allowed. That means, that for every carrier the sum of guaranteed slots for all stations and the common streaming slot pool must be smaller or equal to the number of data slots on this carrier. The master is free to allocate any unrequested data slot as dynamic slot to any station in the network. For the allocation of streaming slots however, the general restriction is:

- Stations with stream mode Normal may be served out of the common streaming slot

pool.

- Stations with stream mode Stream within Guaranteed Throughput may only be

served out of the private pool as specified by the guaranteed throughput parameter for this station. That means that a stream slot request may be denied to a station even if there are currently unused slots in the frame.

Guaranteed Throughput Example Scenarios

To highlight possible applications of the guaranteed throughput in this paragraph we consider 4 scenarios. As general assumption a network is assumed with one carrier having the following properties, refer to figure 2-19:

- 38 frame slots including 35 data slots.

- Capacity of one data slot: 26 kbps (sufficient for 2 unidirectional voice calls).

- Common stream pool: 12 slots.

- Guaranteed throughput for stations IDU1 and IDU2: 6 slots.

- No guaranteed throughput for all other stations.

Figure 2-19 TDMA Structure of Throughput Example

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Satellite Link Layer Features

Scenario 1

Both IDU1 and IDU2 are configured for stream mode Normal. The traffic mix (see figure 2-20) consists of:

-A non real-time IP b ased PC application with a bidirectional bandwidth requirement of 128 kbps between these two stations.

- Additionally 6 parallel voice calls served by SkyWAN tive between the stations.

FAD real-time service should be ac-

Figure 2-20 Throughput Scenario 1

Effect

Due to the defined guarantee for both stations, the 6 dynamic slots needed for the PC application will always be available, irrespective of the general congestion state of the network. For the voice calls each station would need 3 streaming slots.

As long as there are enough free slots available in the common streaming pool, these calls can be set up. However, there is no guarantee for the calls: if other stations have already used a part of the streaming pool, some of the voice calls may be blocked.

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Scenario 2

Both IDU1 and IDU2 are configured for stream mode Normal. The traffic mix (see figure 2-21) consists of:

-A real-time IP based PC application with a bidirectional bandwidth requirement of 128 kbps between these two stations.

- Additionally 2 parallel voice calls served by SkyWAN tive between the stations.

FAD real-time service should be ac-

Figure 2-21 Throughput Scenario 2

Effect

Due to the fact that a real-time service is used for the PC application, 10 out of 12 available stream slots are already consumed by this application. If there are in addition two parallel voice calls between IDU1 and IDU2, all available stream slots would be allocated. Now any additional stream request would be blocked even if there are still unrequested slots outside the common stream pool.

In this scenario the current traffic is not guaranteed for IDU1 and IDU2 because with stream mode ’Normal’ the guaranteed throughput does not apply to streaming slots. If the common streaming pool is already used by other stations the real-time PC application might be blocked due to insufficient streaming bandwidth. Only additional non real-time traffic on IDU1 or IDU2 would benefit from the guarantee.

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Scenario 3

Both IDU1 and IDU2 are configured for stream mode Stream within Guaranteed Throughput. The traffic mix (see figure 2-22) consists of:

-A non real-time IP based PC application with a bidirectional bandwidth requirement of 128 kbps between these two stations.

- Additionally 3 parallel voice calls served by SkyWAN tive between the stations.

FAD real-time service should be ac-

Figure 2-22 Throughput Scenario 3

Effect

First two parallel voice calls are set up between the stations. The necessary streaming slot for this service must be taken out of the respective private bandwidth pools. If now additionally a non real-time bidirectional PC application is set up, the bandwidth for this service is still guaranteed because the required 5 slots for each station are still available in th e private pool. If however an additional voice call is set up between the stations the additional streaming slot again must be taken out of the private pool, leaving only four slots for other services. Note, that realtime services have always priority over non real-time services.

As long as the network is not congested, the PC application may still be served with sufficient bandwidth by allocating an unrequested slot from the common bandwidth pool. However there is no guarantee for this additional slot and the allocation may be withdrawn at any time by the master in case of network congestion.

Strictly speaking the guarantee and the limit for IDU1 and IDU2 in this scenario is 6 streaming slots for each station. For dynamic slots there is no fixed guarantee (but also no specific limit), only at times when the stations are not using the full private bandwidth for real-time services, the remaining part of the private pool would be guaranteed for non real-time services.

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Scenario 4

Both IDU1 and IDU2 are configured for stream mode Stream within Guaranteed Throughput. The traffic mix (see figure 2-23) consists of:

-A real-time IP based PC application with a bidirectional bandwidth requirement of 128 kbps between these two stations.

- Additionally 2 parallel voice calls served by SkyWAN tive between the stations.

FAD real-time service should be ac-

Figure 2-23 Throughput Scenario 4

Effect

Beside the real-time services application, which consumes 5 streaming slots, for each station one additional slot is available for other real-time services. This would allow 2 parallel voice calls. After that the private bandwidth pools for both stations are exhausted. Any additional streaming slot request from these stations would be rejected by the master, even if there are still available slots in the common streaming pool. Other stations could use this capacity for real-time services but IDU1 and IDU2 are limited to their private pools concerning real-time bandwidth. Additional non real-time services however might still be possible for these stations if there are unrequested slots in the common streaming or dynamic bandwidth pools.

For the specified real-time applications (PC application + 2 voice calls) both stations will always have access to the required bandwidth. There is no risk for them to have their rea l-time services blocked due to insufficient available streaming slots.

Note, that a reduced flexibility concerning the allocation of stream slots is engineered:

- IDU1 and IDU2 can never allocate real-time bandwidth beyond their specified guaranteed throughput.

- All other stations can never allocate real-time bandwidth beyond the specified common streaming pool.

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Network Traffic Estimation

For all scenarios this reduced flexibility only applies to real-time bandwidth served by streaming slots. For non real-time services the master can allocate an y unused slot to any requesting station even if this slot is located within the private bandwidth pool of another station.

2.4 Network Traffic Estimation

The starting point for a satellite network configuration is an evaluation of customer requirements. The mayor points to be specified here are:

- The quantity of locations to serve,

- Network topology (e.g. meshed, hybrid or star),

- Traffic profiles and patterns,

- Traffic types and user application requirements. For larger networks it is typically not possible to perform an explicit estimation for each individ-

ual station. Generally it is sufficient to classify stations according to their typical traffic quantity and profile and define only a few station types (e.g. Headquarters, regional hubs, remote sites). The assumption here is that all stations belonging to a specific station type have the same traffic profile.

The following results should be derived from the traffic estimation:

- The required network topology and connectivity.

- The total user traffic capacity required in the network.

- For SkyWAN SkyWAN

networks with multiple carriers: The required user traffic capacity for each

carrier.

Traffic Profiles

The traffic profile of a station typically consists of the following traffic types:

- Non real-time (NRT) data traffic (IP or Frame Relay),

- Real-time (RT) data traffic (IP or Frame Relay),

- Voice traffic (served by analog or digital SkyWAN

For the purpose of traffic estimation it makes no difference if the traffic is based on the IP or Frame Relay functionality. Estimations for non real-time and real-time traffic however, have to be done in a different way.

FAD interfaces or VoIP systems).

Non real-time traffic, for example file downloads, are “flexible” concerning their bandwid th requirement. They work if the available bandwidth is low or high, just the download time will vary according to the available network capacity. For the traffic estimation only a minimum or “committed” data rate has to be specified for this type of applications. In reality in SkyWAN works more bandwidth might be available because of the flexible bandwidth allocation allowing to assign currently unused capacity in the network to any station.

Real-time data traffic, for example real-time audio and video streaming, are by nature applications which require a constant data rate. If this rate is not available, the service will suffer from severe quality degradation or might not work at all. Therefore, the traffic estimation is based on the data rate given by the specific application.

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Voice traffic has in principle the same nature as real-time data traffic. However it has a few characteristics requiring a different treatment concerning the traffic estimation:

- Individual voice calls consume a relative low bandwidth, but there are many simultaneous calls possible.

- The voice capacity (streaming capacity) is not constantly in use.

- A certain amount of blocked calls due to insufficient network capacity is acceptable.

Therefor the network capacity needed for voice calls is not calculated by the number of voice interfaces multiplied with the bandwidth per call, but the maximum number of simultaneous calls in the network is estimated. This might be done by ’educated guessing’ taking into account the customer’s experience with the voice network or by an explicit statistical calculation (“Erlang calculation”) based on average usage rates of telephones.

Traffic Estimation Example Scenario

The following pictures represent an example for the traffic estimation of a network consisting of 50 stations. Four different station groups (station types) are defined: head offices, big sites, medium sites and small sites.

In figure 2-24 the non real-time traffic flow between stations of specific types is sketched. Keep in mind that the numbers here do not represent maximum but committed data rates for individual flows. For example, a small site will typically be able to send more non real-time data than 1 kbps to the head office, because it is unlikely that all other stations would be active simultaneously. The type of non real-time raffic assumed in this example is LAN (i.e. IP) data, but the approach would be not different for non real-time Frame Relay data. In this case the numbers in the traffic pattern sketch could be used to define the Frame Relay station parameter ’Committed Information Rate’ for each Frame Relay Circuit.

Figure 2-24 Traffic Estimation Scenario IP Traffic

A graphical representation of the real-time data requirements is given in figure 2-25. There is a bidirectional videoconference planned between the head offices and voice calls based on Frame Relay (SkyWAN

FAD) functionality. For the voice calls the traffic pattern is also specified. The total number of simultaneous voice calls required in this network has to be estimated additionally.

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Figure 2-25 Traffic Estimation Scenario Fame RelayTraffic

General Carrier Design

Network Traffic Estimation

The traffic patterns show a network which basically constitutes a double-hub star network. Keep in mind that the real network topology might still be partially or fully meshed. For the traffic estimation in most cases it is enough to consider the most important traffic flows. If traffic flows between medium and small sites for example account for only a small fraction of the network traffic, they can be neglected in the estimation of the network traffic.

The next step is to summarize the traffic requirements to derive the user traffic capacity for each station of a specific type. To sum up the capacity needed by one station on its receive carrier (Home Channel) we consider all traffic flows to a specific station in receive direction.

Summarize Example Traffic

The non real-time user traffic (IP LAN traffic) requirement for one head office is 64 + 32 + 2*5 + 21*1 = 127 [kbps]. For one small station 20 kbps traffic is assumed. The total requirement for all head offices is 2*127 = 254 kbps. For all small sites it is 42*20 = 840 kbps.

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2.4.1 Capacity Calculation Tool

To calculate the traffic requirement for the whole network a spreadsheet like the ’ND SatCom Academy Capacity Calculator’ may be used which will be presented in the following pages. The capacity calculator is an Excel tool which consists of several worksheets:

- Capacity calculation

- Erlang calculation sheet

- Voice traffic sheet

- Carrier configuration

- TDMA calculator input.

Capacity Calculation Worksheet

The capacity calculation worksheet allows the input of the following parameters:

- Number of stations per type (up to 4 station types possible).

- Number of voice interfaces per station.

- Real-time traffic (either per station or for the whole network) in receive direction.

- IP and Frame Relay non real-time traffic per station in receive direction. Input fields in this spreadsheet are indicated by a grey background. The following picture

presents a work sheet filled with data from the example presented in this section:

Figure 2-26 Traffic Calculation Example - Capacity Worksheet

The main results in this worksheet are:

- Network traffic requirement per traffic type (voice, real-time, FR non real-time, IP non real-

time)

- Total network traffic requirement Voice traffic requirements will be calculated with the Erlang worksheet. The result of this calcu-

lation is indicated by the blue fields in the capacity calculation sheet. Whereas the definition of non real-time traffic per station is straightforward, high bandwidth

real-time traffic may be more difficult to specify. In the example considered so far, only one bidirectional video conference between the two sta-

tions of type 1 (head office) with a data rate of 256 kbps per direction is required. In this case it is correct to define a real-time traffic requirement of 256 kbps per station of type 1.

In another scenario the situation is not so clear anymore. Let’s assume that the customer re-

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quirement is as follows: Two bidirectional video conferences with 256 kbps per direction should be simultaneously possible in the network. Each conference should be set up between one head office (type 1 station) and one small site (type 4 station). The assignment o f 256 kbps for each station of type 1 is still correct. For the type 4 stations the situation is more complex: Assigning 256 kbps for each type 4 station would lead to a network real-time traffic requirement of 42*256 = 10752 kbps which is definitely too high. On the other hand, spreading the real-time capacity requirement for the type 4 stations of 512 kbps among all small sites by defining only 512/42 = 12.2 kbps for each station would lead to the correct network traffic requirement.

However, if not all stations of this type are members of the same downlink population, this still could lead to wrong results. Assuming, for example, that one downlink population consists of only five type 4 stations, the required real-time capacity for the carrier of this population would be estimated to be 61 kbps which is even for one video conference not sufficient. For this reason it is more reasonable to assign the real-time capacity for the type 4 stations not to individual stations but to the whole network as it is displayed in the following picture:

Figure 2-27 Per Network Traffic

Erlang B Calculation Worksheet

The second work sheet includes formulas for an estimation of required voice circuits using the Erlang B distribution. This statistical method allows the calculation of the blocking probability (i.e. rejected calls due to network congestion) for a network with a given number of users, an average and peak value for the user’s hold time and the available number of voice circuits. Note that Erlang calculations provide accurate results only for sufficiently large networks (more than 50 users). An example of such a calculation is presented in the following picture. The assumptions for this example are:

- Number of users (identical to the number of voice interfaces): 200

- Service hours: 10

- Average hold time: 12 min/hour

- Peak factor = 2, meaning that in the most busy hour the telephone is used twice as often than on average

- Maximum acceptable blocking probability: 1.5%

Whereas the first four items are input parameter in the Erlang B worksheet, the blocking probability is derived from these input parameters and the number of voice channels, which is another input parameter of the sheet.

To determine the required number of voice channels in the network, an initial estimate has to be done and the resulting blocking probability observed. If the resulting blocking probability is

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higher than the acceptable value, the number of voice channels has to be incremented un til the blocking probability fulfils the requirement. In the example figure 2-28, 51 voice channels are required to achieve a blocking probability below 1.5%.

Figure 2-28 Traffic Calculation Example - Erlang B Worksheet

Generally the number of users is derived from the number of voice interfaces in the network. If the column “voice interfaces per location” on the capacity calculation worksheet is left blank, the number of users can be specified in the input field “Alternative Input for # of Users” on the Erlang B worksheet.

The total traffic requirement for voice is calculated by multiplying the number of (full duplex) voice channels with 2 x voice channel data rate.

The voice channel data rate depends on the used technology and codec rate, which can be selected by the input field ’Used Codec’. The most important voice over SkyWAN VoIP Codecs (with or without header compression) are already predefined in the sheet. If another codec should be used, the data rate for a ’Custom Codec’ may be defined in the lookup table. Note that the data rate must include the network layer overhead up to the IP or Frame Relay level.

The estimation for the total network traffic would be sufficient for a single carrier SkyWAN work. If a multi-carrier network is designed, the traffic requirement must be broken down to the requirements for each individual carrier. The general idea is to calculate a type specific data rate per station. Then the network designer has to decide how many stations are assigned to

FAD and

net-

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Network Traffic Estimation

a specific carrier, i.e. how many stations have this carrier configured as their home channel. The traffic requirement for this carrier can be derived by adding up the station traffic requirements of all stations assigned to this carrier.

Voice Traffic Flow Worksheet

The Erlang B calculation estimates the voice traffic for the whole network. To break this down to individual stations, an assumption concerning the traffic flows in the network must be made. The worksheet “Voice Traffic” allows the specification what fraction of the voice traffic will be necessary between stations of a specific type. The following picture represents that sheet filled with data from our network example:

Figure 2-29 Traffic Calculation Example - Voic e Traffic Flow Worksheet

The input values in this sheet are the fractions of voice calls switched within or between stations of a specific type, the output values the amount of voice traffic for one station of a specific type. Note that these fractions have to add up to 100%.

Carrier Configuration Worksheet

The next worksheet ’Carrier Configuration’ supports the definition of multi-carrier SkyWAN networks. The single carrier option is already predefined: Here all stations are assigned to carrier 1. The sheet allows the definition of networks with 2-8 carriers by arbitrarily distributing stations among carriers. The following picture figure 2-30 displays a possible 2 and 3 carrier solution for our example network.

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Figure 2-30 Traffic Calculation Example - Carrier Configuration Worksheet

Note that a general restriction is that master stations must be assigned to carrier 1. In star topology networks the hub station must be assigned to a different carrier than the star terminals. In many cases the optimal station distribution for a multi carrier solution is generating carriers with almost equal data rate requirements. Since the power requirement for a station is determined by the largest carrier, such a solution minimizes the transmitter power class or antenna size of a station. However, other considerations like traffic flows, satellite footprint variations or restrictions on possible antenna sizes for some stations (e.g. mobile stations) might lead to a solution with different carrier sizes. The latter consideration could be the result of a link budget analysis, which will be discussed in a later section of this guide.

In the example presented in the screenshot the multi carrier solutions were designed under the following assumptions:

- For administrative reasons the master stations must be located at the head offices. Therefore both stations of type 1 must be assigned to carrier 1.

- To create a 2 carrier solution with almost equally sized carriers, only the head offices (one big and one medium size office) are assigned to carrier 1 and all other stations to carrier 2.

- For the 3 carrier solution the assignment for carrier 1 cannot be changed as these are the master stations. The other stations are distributed evenly among carrier 2 and 3 to make at least these carriers equally sized.

As mentioned before real-time traffic requirements may be defined per station or for the whole network. In the latter case, distributing stations on carriers will not automatically take into account the real-time bandwidth. Instead the real-time bandwidth has to be assigned manually to one or multiple carriers using the row ’per network RT data rate’ in the carrier configuration sheet.

In the example presented before, it was assumed that the 42 small sites should support 2 simultaneous video sessions each with 256 kbps. Since the sessions are not linked to individual small sites, the required real-time data rate of 512 kbps was assigned to the whole network. In a multicarrier network this data rate has to be assigned to individual carriers. An example is displayed in the following picture figure 2-31.

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Figure 2-31 Traffic Calculation Example - Carrier Config. with Network Traffic

For the two carrier solution the 512 kbps real-time bandwidth must be allocated to ca rrier 2 because the small sites (station type 4) are all assigned to this carrier. For the three carrie r solution the small sites are divided in two subgroups, one is using carrier 2 and the other carrier 3. For that reason the real-time bandwidth was also split, 256 kbps are now assigned to carrier 2 and 3.

Note that this choice reduces the flexibility of bandwidth assignment: Whereas in the single and two carrier solution any 2 small sites may support the video session, for the three carrier solution the situation is different: If one video session is already active in the first subgroup, the second video session can only be established to a station in the second subgroup. If this restriction is not acceptable, the data rate requirement for both carrier 2 and 3 would be increased by 256 kbps. In that situation it may be more optimal to leave all small sites on one common carrier even if this leads to larger differences in data rates.

The last worksheet “TDMA Calc Input” is used to simplify TDMA structure optimization with the “TDMA Calculator” tool and will therefore be discussed together with this tool in chapter 2.7.

2.4.2 Limitations of the Traffic Estimation Approach

The network traffic estimation procedure outlined in the previous section works well in most scenarios. However, there are some limitations which the network designer should be aware of to prevent wrong decisions specifically concerning the carrier design. These limitations will be important especially if the traffic flows are asymmetric like e.g. in the case of a pure star network.

The assumption our traffic estimation is based on is that each station has to share the available bandwidth in receive direction with other stations assigned to the same carrier. There is no specific limitation for the transmit direction because a station ha ving a small carrier as home channelone may still transmit on another carrier with much higher bandwidth. As for the whole network the amount of received and transmitted data must be identical there is no need to es-

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timate data requirements in transmit direction separately. This argument holds as long as the transmission of data is evenly distributed among the stations, which is typically the case for a meshed network. It may not be valid however, if the transmission is concentrated on few or only one station, like in the case of a single hub star network.

Let us consider the following example: A single hub star network consisting of the hub station and 10 remote terminals. For the sake of simplicity we assume that only non real-time traffic should be supported with a committed data rate (in receive direction) of 500 kbps for the hub station and 100 kbps for each remote terminal. Putting the hub station on carrier 1 and the terminals on carrier 2 we have the following data rate requirements for the carriers:

Carrier 1: 500 kbps Carrier 2: 1000 kbps Let’s now assume that the network should be extended by another 10 remote terminals. As-

suming the same data rate requirements for the additional terminals, the new summary requirement for the second carrier would be:

Carrier 2: 2000 kbps If the hub station could not support the additional bandwidth due to power limitations, one might

be tempted to increase the network capacity by adding an additional ca rrier instead, i.e. having a carrier configuration like:

Carrier 2: 1000 kbps Carrier 3: 1000 kbps

If the additional 10 stations are assigned to the new carrier 3, such a solution would formally fulfill the capacity requirements of the enlarged network according to the carrier configuration worksheet of the capacity calculation tool. This could only lead to problems if all stations have to be served with a datarate of 100 kbps at the same time. In reality however the throughput from the hub to all remote terminal stations would still be limited to 1000 kbps only. The reason is that the hub station cannot simultaneously transmit on both carrier 2 and 3. To increase the throughput from hub to remote terminals there are only two possible solutions:

- Increase the maximum power level on the hub station to allow larger bandwidths.

- Migrate to a double-hub star network: In this case one hub station may transmit on carrier 2 when simultaneously the second hub transmits on carrier 3. This allows the full utilization of the available bandwidth of both carriers. Additional benefit would be an improved redundancy in the network: If one hub fails traffic to the remotes could still be forwarded via the second hub.

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From User Traffic to Satellite Link Carriers

2.5 From User Traffic to Satellite Link Carriers

After the estimation of the required user data rate per carrier, the calculation of the respective bandwidth on the satellite link must consider the following (refer to the steps in procedure description below):

- Step 1 and 2: Encapsulation of IP and Frame Relay packets on the satellite link layer .

- Step 3: Added redundancy bits for Forward Error Correction (FEC) functionality.

- Step 4: Added synchronization symbols to ensure demodulator synchronization even at low Signal-to-Noise levels.

- Step 5: Transmission gaps between time slots to avoid signal collisions due to transmission time inaccuracies of the stations.

- Step 6: Added time slots for signaling data like reference or request slots.

- Step 7: Minimal frequency spacing between adjacent carriers.

Taking these steps into account, it is possible to derive the required carrier bandwidth from the user data rate on the IP or Frame Relay network level. This calculation is no trivial task, but is supported by the “ND Satcom TDMA Calculator Tool” which will be discussed in the next section.

To illustrate the individual procedures we discuss the example of forwarding a LAN packet over satellite.

1. On reception of an Ethernet packet on the LAN port, the SkyWAN

Ethernet header. The SkyWAN mation will not be transported over the satellite link. After inspection of the IP destination address the IDU will perform the routing procedure to decide if the packet has to be forwarded over one of the available satellite link carriers. If that is the case it will enqueue the packet in the corresponding transmit queue taking into account also potential quality of service (QoS) definitions . During this process, the IP packet is encapsulated in a Satellite Link Layer (SLL) frame which adds a 2 Byte header and a 4 Byte CRC checksum to the packet, refer to figure 2-32.

Figure 2-32 SLL Encapsulation

2. If a timeslot on the satellite carrier is available the payload of the timeslot’s gross container is filled up with enqueued SLL frames. If such a frame does not fit into the remaining part of the container, it may be fragmented and the remaining fragment will be put in the next container. This procedure adds a 2 Byte descriptor to each fragment, additionally each gross container includes a 9 Byte TDMA header; refer to upper part of figure 2-33. If there are not enough user data to fill up a container the remaining p art is filled with dummy bits.

IDU operates as an IP router, therefore Ethernet infor-

IDU will first strip the

The size of the gross container can be configured in a SkyWAN® network. Possible gross container size range: 100-3000 Byte.

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Figure 2-33 Gross Contai ner Information Content

3. So far we have determined the information content of a gross container. This information is protected by adding redundancy bits which allow the receiver to detect and correct a certain ratio of bit errors generated during the transmission over the satellite link. This pro-

cedure is called “Forward Error Correction” (FEC). The technology applied in SkyWAN networks is called Turbo-Phi representing the most advanced method for forward error correction of TDMA burst signals. The FEC rates are selectable per carrier with possible rates of 1/3, 2/5, 4/9, 1/2, 2/3, 3/4, 4/5, 5/6, 6/7 for QPSK modulation and 2/3, 3/4, 4/5, 5/6, 6/7 for 8PSK modulation.

The lower the FEC rate the lower the requirement on Signal-to-Noise ratio on the satellite link for an error-free transmission. A lower FEC rate reduces power requirements on both , the earth station and the satellite transponder. On the other hand the redundancy bits increase the data rate and thus increase the bandwidth requirement for the carrier.

Figure 2-34 Add Turbo-Phi Co ding

4. The result of step 3 is a coded gross container which includes the error correction bits. This information is transported over the satellite link by modulating the carrier using phase

shift keying. SkyWAN

IDU 7000 supports quadrature (QPSK) and 8 (8PSK) phase shift keying. Generally the number of PSK symbols relates to the number of coded bits by: Symbols = coded Bits/modulation factor, where the modulation factor is given by the number of bits represented by one symbol: QPSK = 2, 8PSK = 3. To ensure proper synchronization of the demodulator the symbols derived from the information bits are interspersed with additional synchronization symbols started by a preamble followed by midambles and finally finishing the burst with a postamble. Four different preamble patterns are used for reference, request, ranging, and data bursts, respectively, to exclude reception of unexpected bursts. Preamble length is 64 symbols, midambles and postamble lengths are 16 symbols each.

5. Finally the modulated burst has to be put into a time slot of the carrier. Since an absolute precise synchronization between transmission times of all stations is not feasible, there are transmission gaps at the start and the end of each time slot allowing a transmission time inaccuracy of some microseconds:

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Figure 2-35 Modulated Gross Container

6. Not all timeslots carry bursts which have been constructed from user data. Depending on

the reference burst mode (see chapter 2.3.3 “SkyWAN

MF-TDMA”) some carriers include reference or request bursts. These signaling time slots do require a p art of the carriers bandwidth but do not contribute to the user traf fic ca pa city of the carrier. In the example of a TDMA carrier presented in figure 2-36, out of 15 time slots in the frame only the 12 slots (indicated by a grey color) are used to transport user traffic. One slot is used for a reference burst and two slots for request bursts. That means that for this carrier 20% of the bandwidth is consumed for signaling traffic. Note that ranging slots are not considered here, as they are needed only if there are unregistered stations in the network. This is generally only the case for a brief period after a network restart, once all stations are registered again at the active master, these slots may be allocated as user traffic slots.

Figure 2-36 Signalling Time Slots

7. At this point we have constructed a TDMA carrier which has enough capacity to carry the required user traffic data rate as well as the necessary signaling information. The bandwidth of the carrier is specified by its symbol rate (symbols per second sps). The frequency bandwidth which has to be leased on the satellite transponder is however larger. It must be ensured that outside the leased frequency band the carrier signal does not interfere with adjacent carriers. Usually the satellite operator requires that outside the leased band the spectral power density of the carrier is at least 17 dB lower than the power den-

sity in the center of the band. SkyWAN

IDU 7000 applies a root-raised-cosine Nyquist filter technique to limit the required frequency bandwidth. The filter bandwidth which is specified by the roll-off factor may be configured. Possible values are 0.2, 0.3 and 0.4. With that filter the required frequency bandwidth is given by:

frequency bandwidth = symbol rate x (1 + roll-off factor)

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Generally a selection of 0.2 for the roll-off factor will save bandwidth on the satellite transpo nder. Smaller roll-off factors mean increased signal power ripples in the time domain which might pose a problem if transmitters on the earth stations or the satellite are operated close to the saturation power level. In these cases a higher roll-off factor may be necessary.

2.5.1 Summary

The following picture is a graphical summary of the signal preparation steps as discussed before. For each step the additional overhead is specified explicitly. Note the two different definitions of data rates:

- User data rate: The data rate of user traffic received on the terrestrial interf aces (LAN, serial ports). Note that the LAN data does not include the Ethernet header and CRC checksum as this will be stripped before forwarding to the satellite link.

- Modem data rate: The data rate of all information bits which will be encoded by the forward error correction procedure. Besides the user data rate itself it also includes all necessary headers for SLL framing and gross container encapsulation. Additionally the signaling bits transported in reference and request bursts are included. Note th at the error correction bits are not included in the modem data rate.

Figure 2-37 Signal Preparation - Summary

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TDMA Carrier Design with ’TDMA Calculator’

2.6 TDMA Carrier Design with ’TDMA Calculator’

As outlined in the previous section, the calculation of the required frequency bandwidth o f Sky-

WAN

- the contributions of the satellite link layer,

- the modulation scheme,

- the modem overhead. The ’ND SatCom Products GmbH TDMA Calculator’ is a java based tool, which ca lculates for

each carrier the user data rate and frequency bandwidth, based on the given modem data rate from the network capacity calculation. Two versions of the tool are available: a stand-alone version and a tool, which is invoked from the ’SkyNMS Network Configurator’. Both versions have the same GUI and functionality; therefore only specifics and differences are pointed out explicitely.

- stand-alone ’ND SatCom Products GmbH TDMA Calculator’: open application by double-

- ’TDMA Calculator’ as tool integrated in the ’SkyNMS Network Configurator’ application. In

carriers for an estimated user data rate must take into account

click on desktop icon or via ’Start -> Programs -> ND SatCom Products GmbH -> TDMA Calculator -> ND SatComs Products GmbH TDMA Calculator’. The calculated output parameter can be exported and copied into the relevant configuration profile parameter. A menu bar is available for exiting the application, export and import to/from a file and to show via ? and About entry the toolrelease version. A status line is provided, where ou tput messages are displayed. The stand-alone version is a software application that does not need a login.

SkyNMS the tool is invoked in the following way: in SkyNMS menu ’Network Configuration’ select the entry ’SkyNMS Network Configurator’. Browse in the configuration tree to the appropriate network group and profile. In the mouse context menu select entry ’Open TDMA Calculator’. The integrated tool version allows for transfering the calculated output data into the corresponding profile parameter with a mouse click. In the SkyNMS integrated TDMA Calculator (error) messages are displayed in the ’Output’ window and the statusline of the ’SkyNMS Network Configurator’. Arrange the windows in such a way, that the ’SkyNMS Network Configurator’ messages (in the background) are visible for you. Running the ’TDMA Calculator’ from the Network Configurator is only possible with the user right ’Full Access’. In other cases, the execution is not permitted.

Figure 2-38 Start integrated SkyNMS TDMA Calculator

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The GUI is providing one main screen for general parameter (left hand) and channel specific parameter (right hand), each with an input and an output are. The input parameter section specifies the values to use; in the output parameter section the results are shown after a calculation is performed.

Figure 2-39 TDMA Calculator GUI

Input sections marked red.

screenshot displays integrated SkyNMS TDMA Calculator.

The necessary input is the TDMA frame structure and the user traffic mix which is estimated for each carrier. The figure 2-39 gives an overview of the input fields in the ’TDMA Calculator’ tool. On the lefthand side the section ’General Data Input’ and on the right the section ’Data Input per Frequency Channel’. Detailed descriptions for the particular fields are given in chapter 2.6.1 and chapter 2.6.2. For each channel input data can be specified separately. When starting the SkyNMS integrated ’TDMA Calculator’, input fields are pre-defined either with values requested from SkyNMS for the corresponding configuration profile or with default values.

Below the ’General Data Input’ section and righthand from the ’Data Input per Frequency Channel’ the output fields can be found. Detailed descriptions for the particular fields are given in chapter 2.6.3.

The TDMA Calculator opens with data either specified in the invoking IDU profile or pre-defined as default input values. If the user finished a calculation, the results can be exported into the profile by clicking button ’Apply to Configuration Profile’. The lastly stored input values of the Configuration Profile will be preset when the TDMA Calculator is opened again.

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TDMA Carrier Design with ’TDMA Calculator’

2.6.1 Section ’General Data Input’

The parameters in the fields of the ’General Data Input’ section have the following meaning: ’Minimum TDMA frame time’: Fill in the target value for the TDMA frame time, i.e. the time in-

terval between two reference bursts. The SkyWAN

system will automatically select the number of time slots such that the actual TDMA frame time (see also chapter 2.6.3 “General Data Output”) will be larger but as close as possible to the target frame time. The range for this value is 40-400 ms. Small frame times reduce the burst delay jitter for real time traffic (streaming) but will also reduce the user data rate due to a higher TDMA overhead. Large values increase the user data rate but also the burst delay jitter. A good compromise between jitter and efficiency is a TDMA frame time of 110 ms if both real-time and non real-time services should be supported. If some of the real-time services are very sensitive to network delay, smaller values for TDMA frames may be chosen. A network with pure non real-time services may use larger frame times to increase efficiency, but values larger than 200 ms are not recommended.

’Number of uplink populations’ and ’Size of uplink populations’: If ’Number of uplink populations’ is selected to ’1’, MRB mode will be used. If it is selected to ’2’, a DUB mode is specified. In this case, additional input fields will appear, refer to figure 2-40. The input field ’Size of UL population 1’ defines the number of stations in the network.

Figure 2-40 TDMA Calculator - two Uplink Populations specified

If ’Number of uplink populations’ is specified to ’2’, the following input fields will appear additionally:

- In the select box ’Masterstation with self reception’ the reference burst run mode is speci-

fied:

- select entry ’Yes’ to choose the MRB-DUB;

- select entry ’No’ to choose the NFB-DUB mode (without self reception).

- Use the input fields ’Size of uplink population 1’ and ’Size of uplink population 2’ to define

the number of stations in uplink population 1 and 2.

’Number of frequency channels’: The number of SkyWAN

carriers used in this network. This

number includes both carriers with and without reference bursts. ’Number of downlink populations’: The number of downlink populations in the network, which

is identical to the number of carriers with a reference burst. ’Size superframe (max.) [TDMA frames]’: The number of TDMA frames between transmissions

of a request burst from a station. A value range of 1-16 is supported, however superframe sizes larger than 5 should only be used, if the applications support a long latency between capacity requirement and assignment. If services with a real-time characteristic are supported using dynamic slot assignment, superframe size should be set to 1. This parameter allows for increasing the user data rate on carrier 1 (and carrier 2 for DUB modes) by reducing the number of base slots used for the request slots.

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frequency bandwidth = symbol rate * (1 + roll-off factor).

TDMA Carrier Design with ’TDMA Calculator’

’Roll-off factor’: Minimum distance between two SkyWAN® carriers. This value is used to calculate the frequency bandwidth of a carrier:

2.6.1.1 Parameter Summary

Parameter Name Definition

Minimum TDMA frame time [ms]

Number of uplink populations

Masterstation with self reception

Size of uplink population 1 [stations]

In a SkyWAN network the master sends control communication ( e.g. capacity allocation) to slave stations within the reference burst. The time between two reference burst TDMA slots is called TDMA frame time.

Slave stations transmit their request burst on a defined transmit (Tx) carrier to the master. All stations using the same 'request burst carrier' belong to the same 'Uplink Population' (ULP).

- Select 1 to define one ULP using carrier 1.

- Select 2 if a cross-strapped satellite transponder is used (Dual Uplink Mode - DUB) a second ULP has to be defined using carrier 2.

MRB and MRB-DUB mode both require a master able to receive its own reference burst. If this self-reception is not possible, NFB-DUB mode has to be configured.

- ’YES’: MRB-DUB mode: 2 Uplink Populations, 2 to 7 Downlink Populations.

- ’No’: NFB_DUB mode. max. 2 Uplink Populations, 1 Downlink Population; Star topology only.

Quantity of stations belonging to Uplink Population 1.

- MRB, MRB-DUB mode: Max. network size 510 stations (ULP 1 + ULP 2).

- NFB-DUB mode: max. 255 stations.

Size of uplink population 2 [stations]

Quantity of stations belonging to Uplink Population 2.

- MRB, MRB-DUB mode: Max. network size 510 stations (ULP 1 + ULP 2).

- NFB-DUB mode: max. 255 stations.

Number of frequency channels

Quantity of frequency channels to use.

- MRB mode: 1 - 8

- MRB-DUB mode: 2 - 8

- NFB-DUB mode: 2 or 3

58 Network Design and Engineering Guide 2010-10-26

Parameter Name Definition

General Carrier Design

TDMA Carrier Design with ’TDMA Calculator’

Number of downlink populations

Master stations transmits TDMA and network information in the reference burst to all stations on a defined carrier. All stations receiving the reference burst on the same carrier belong to the same 'Downlink Population (DPL)'.

Max. quantity of stations configured in one DL is 255.

- MRB mode: max quantity of DLP is 8 (dependent on the quantity of frequency channnels configured).

- MRB-DUB mode: 7

- NFB-DUB mode: 1

Size superframe (max) [TDMA frames]

Roll-off factor The roll-off factor basically gives the distance between two carriers

Superframing allows to split and distribute the slaves request b ursts to several TDMA frames, thus saving capacity for data.

Value range of 1 to 16.

needed for sufficient interference suppression. Select

-0.2

-0.3

-0.4

Table 2-3 Summary ’General Data Input’ Parameter

2.6.2 Section ’Data Input per Frequency Channel’

The parameters have to be specified for each SkyWAN® carrier. Please find the parameter descriptions below:

’Modem data rate [kbit/s]’: The channel’s information rate excluding error correction bits and synchronization patterns. For a detailed discussion of this quantity refer to the preceeding chapter 2.5.

’Modem data rate’, ’Modulation Scheme’, ’Code rate’ and ’BER’: define the channel coding, modulation and the maximum acceptable bit error rate of this carrier. With these parameters the tool will calculate the required symbol rate and frequency bandwidth. Note, that the calculated results for Eb/No and Es/No values have to be proved against a link budget calculation, which will be discussed in the chapter 3.5.

User traffic composition fields: For each carrier the composition of the user traffic can be specified. There are 6 different traffic types possible:

- ’1- FR Voice’: Frame Relay Voice (Voice over SkyWAN Codec or protocol used.

- ’2 - FR Realtime’: Frame Relay Real-time

- ’3 - FR Non-Realtime’: Frame Relay Non Real-time

- ’4 - VoIP’: Voice over IP

- ’5 - IP Realtime’: IP Real-time

- ’6 - IP Non-Realtime’: IP Non Real-time

FAD). Select the appropiate

For each traffic type the ’Average packet length [byte]’ and the fraction of the total user traffic

2010-10-26 Network Design and Engineering Guide 59

General Carrier Design

TDMA Carrier Design with ’TDMA Calculator’

’% of User Data Rate’ must be defined. In the case of ’1- FR voice’, select the FAD voice codec to get the packet length automatically. The same is due for the ’4-VoIP’ field: select the VoIP codec and get the predefined packet length automatically. Additionally it is possible to select entry 'Custom', if a user defined average packet length for VoIP shall be used. The information about user traffic composition and data packet lengths is used by the TDMA calculator to derive the satellite link layer encapsulation overhead which is necessary to calculate the carrier’s user data rate. By default traffic composition is assumed to be identical on all channels. If it is necessary to define different values for the traffic composition or packet lengths on indi-vidual carriers, in combo box ’Channel load enabled’ entry ’Yes’ has to be selected. Not copied from the channel 1 data are the first 4 fields - they have to be selected manually for each frequency channel.

Figure 2-41 TDAM Calculator - Define different traffic compositions

Time slot size optimization: The TDMA calculator has a built-in functionality which allows the

optimization of the time slot sizes. In combo box ’Time slot sizing: - ruled by’ choose

- ’1’ for slot size optimization depending on Frame Relay Voice (traffic type 1 FR Voice): If this option is selected, the TDMA calculator defines the base gross container size and slot time factor in such a way, that the resulting data rate per slot assignment will support the transport of one or multiple Frame Relay voice calls per slot. The data rate required for one FR voice call is defined by the selected FR voice codec.

- ’5’ or ’6’ for slot size optimization depending on traffic type ’5 IP RealTime’ or traffic type ’6 IP Non-RealTime’: If 5 or 6 is selected for slot size optimiza tion, the TDMA calculator defines the base gross container size and slot time factor so that the resulting time slot container can transport one or multiple packets of the selected traffic type including the satellite link layer framing. The packet size is assumed to be identical to the average packet length specified in the corresponding traffic type definition.

- The traffic type optimization is not supported for the traffic type 4 Voice over IP (VoIP).

- In networks with multiple carriers of different data rates a simultaneous ideal optimization for all carriers is generally not possible. The ’TDMA Calculator’ tool is then selecting values of the base gross container size and channel slot time factors so that the result will be the best possible match for the selected optimization criterion.

2.6.2.1 Parameter Summary

60 Network Design and Engineering Guide 2010-10-26

General Carrier Design

TDMA Carrier Design with ’TDMA Calculator’

Parameter Name Definition

Modem data rate [kbit/s] Type in the information rate, excluding er ror corr ection bits and syn-

chronization patterns for the given chan nel.

Type in for each channel. Modulation scheme Select the modulation scheme for each channel: QPSK, 8PSK. Code rate Select the Forward Error Correction code rat e for eac h ch an ne l BER Select the maximum acceptable bit error rate (BER) for this channel. Channel load enabled By default all parameters defined for channel 1 are copied to all ad-

ditional channels.

If in this box ’Yes’ is selected, the specified data from channel 1 is

used. (1 FR Voice)

Codec x samples per packet (1 FR Voice)

% of user data rate 2 (FR Realtime)

Average packet length [byte] (2 FR Realtime)

% of user data rate (3 FR Non Realtime)

Average packet length [byte] (3 FR Non Realtime)

% of user data rate (4 VoIP)

Voice over IP Codec (4 VoIP)

Average packet length [byte] (4 VoIP)

% of user data rate (5 IP Realtime)

Average packet length [byte]

Select the appropriate codec used for voice over SkyWAN FAD. Fac-

tor x1, x2, x3 specifies the quantity of voice packets per frame.

Type in the fraction of the user data traffic in p ercent used for Frame

Relay voice traffic.

Type in the average packet size in byte of Real-time Frame Relay

traffic.

Type in the fraction of the user data traffic used for Frame Relay

Real-time traffic.

Type in the average packet size in byte of Non Real-time Fr ame Re-

lay traffic

Type in the fraction of the user data traffic used for Frame Relay Non

Real-time traffic.

Select the appropriate codec used for voice over IP.

If no codec is select ed in the fiel d above, type in the average IP pack-

et length for the VoIP data.

Type in the fraction of the user data traffic used for VoIP traffic.

Type in the average packet size in byte of IP Realtime traffic (exclud-

ing Voice over IP) (5 IP Realtime)

% of user data rate (6 IP Non-Realtime)

Type in the fraction of the user data traffic used for IP Realtime traffic

(excluding Voice over IP).

Type in the average packet size in byte of IP Non-Realtime traffic Average packet length [byte]

(6 IP Non-Realtime) % of user data rate

2010-10-26 Network Design and Engineering Guide 61

Type in the fraction of the user data traffic used for IP

Non-Realtime traffic.

General Carrier Design TDMA Carrier Design with ’TDMA Calculator’

Parameter Name Definition

(Time slot sizing) ruled by

(Time slot sizing) per slot [call]

Table 2-4 Summary ’Data Input Per Frequency Channe l’ Parameter

Select '1' The base gross container size and slot time factor is defined in that

way that the resulting data rate per slot assignment will support the transport of one or multiple Frame Relay voice calls per slot.

Select '2', ’3', '5' or '6': The base gross container size and slot time factor is defined in that

way that the resulting time slot container will transport one or multiple packets of the selected traffic type including the satellite link layer framing and fragment descriptor. The packet size is assumed to be identical to the average packet length specified in the corresponding traffic type definition.

Type in how many packets shall be inserted in one data container.

2.6.3 Area ’General Data Output’

The general data output section of the TDMA calculator contains parameters which are not carrier specific. The following output parameters are displayed:

- TDMA structure parameter: ’Reference burst mode’, ’Number of reference channels’, ’TDMA Frame time’, ’Size superframe (act.) [TDMA frames]’, ’Length base gross container’, ’Time base slot’, ’Number request slots per base slot’.

- The summarized user data rate available on all SkyWAN [kbit/s]’.

- The summarized space segment usage including minimal carrier spacing: ’Total frequency bandwidth [kHz]’

- Spectral efficiency values: ’Total efficiency [bit/symbol]’ and ’Total efficiency [bit/s/Hz]’ .

carriers ’Total user data rate

2.6.3.1 Parameter Summary

Parameter Name Definition

Reference burst mode Displays the reference burst mode selected. Networks support three

different reference burst modes:

- Standard multiple reference burst mode (MRB),

- Multiple reference burst with dual uplink beam (MRB-DUB),

- No direct feedback on reference burst with dual uplink b eam (NFBDUB).

Number of reference channels

TDMA Frame time Displays the calculated value of TDMA frame time in microseconds. Size superframe (act)

[TDMA frames]

62 Network Design and Engineering Guide 2010-10-26

Displays the calculated amount of reference channels.

Displays the optimized actual superframe size.

Parameter Name Definition

General Carrier Design

TDMA Carrier Design with ’TDMA Calculator’

Length base gross container [byte]

Time base slot Displays optimized TDMA base slot time of the network in microsec-

Number request slots per base slot

Total user data rate [kbit/s] Displays calculated available data rate for the user applications for all

Total frequency bandwidth [kHz]

Total efficiency [bit/symbol] Displays the average efficiency of all channels :

Total efficiency [bit/s/Hz] Displays the average efficiency of all channel:

Table 2-5 Summary ’General Data Output’ Parameter

Displays the size of the base gross container of channel 1 with data slot length = 1, optimized for the specif ied traffic.

Traffic is sent over satellite in coded gross container packages. A base gross container holds the traffic data plus some overhead (e.g . TDMA header, SLL header, signalling bursts ) before adding the Forward Error Correction (FEC) bits.

onds. Displays quantity of request slots that could be placed in one base

data slot.

channels. User data rate per channel is derived as input from the traffic capacity calculation.

Displays total space segment size. Summary of all symbol rates x spacing factor of all channels

Efficiency = user data rate / symbol rate.

Efficiency = user data rate / frequency bandwidth.

2.6.4 Area ’Data output per frequency channel’

The following carrier specific parameters are displayed in this section:

- User data rate ’User data rate [kbit/s]’, symbol rate ’Symbol rate [kBaud]’ and frequency bandwidth per carrier ’Frequency bandwidth [kHz]’. This is the main result of the calculation, as it determines how much data rate is available on this channel for IP and Frame Relay based applications and as result how much space segment must be leased on the satellite transponder.

- Calculated minimal signal to noise ratio ’Eb/No [dB]’ and ’Es/No [dB]’ for the given modulation and coding.

Channel TDMA structure parameter: ’Data slot length [base slot s]’, length of the request subframe ’Length rqst. frame [time slots]’, length of the reference burst subframe ’Length ref. sl ot [time slots]’, channel gros s container size ’Length gross co ntainer [byte]’, data slots ’Data slots per TDMA frame’ and total time slots per TDMA frame ’Data rate per slot ass.[bit/s]’ .

Current SkyWAN® software supports up to 256 time slots per TDMA frame. If this number is exceeded on any carrier, the solution is invalid and no output results are given. An error message is displayed either in the stand-alone ’TDMA Calculator’ status line or in the ’SkyNMS Network Configurator’ Output window.

If the request burst length is larger than one, additional user capacity may be generated by increasing the superframe size.

- The spectral efficiency values per carrier ’Efficiency [bit/symbol]’ and ’Efficiency [bit/s/Hz]’.

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General Carrier Design TDMA Carrier Design with ’TDMA Calculator’

For the definition of the user data refer to chapter 2.5. The spectral efficiency is represented by two definitions:

- Efficiency per symbol = user data rate / symbol rate.

- Efficiency per Hz = user data rate / frequency bandwidth. The difference between these definitions is given by the carrier spacing factor.

64 Network Design and Engineering Guide 2010-10-26

General Carrier Design

TDMA Carrier Design with ’TDMA Calculator’

2.6.4.1 Parameter Summary

Parameter Name Definition

User data rate [kbit/s] Displays the user data rate for each channel. Symbol rate [kBaud] Displays the symbol rate for each channel. Eb/N0 [dB] Displays required Eb/N0 for the selected modulation scheme, FEC

code rate and gross container size for the given channel. Eb/N0 is defined as the ratio of Energy per Bit (Eb) to the Spectral Noise Density (N0).

Es/N0 [dB] Displays required Es/N0 for the selected modulation scheme, FEC

code rate and gross container size for the given channel. Es/N0 is defined as the ratio of Energy per Symbol (Es) to the Spectral Noise Density (N0).

Frequency bandwidth [kHz] Displays the calculated frequency bandwidth required on this chan-

nel. Frequency bandwidth = (1+ roll-off-factor) x symbol rate.

Data slot length [base slots] Displays how many ba se slots are conta ined in one da ta slot for this

channel.

Time slots per TDMA frame Displays how many time slots are conta ined in one T DMA fram e fo r

this channel. Attention: If the given number exceeds the allowed maximum (see

note above) the solution is invalid.

Length ref. slot [time slots] Displays how many data slots are configured as reference slot for

this channel.

Length rqst. frame [time slots] Displays how many data slots are configured for all req uest bursts for

this channel.

Data slots per TDMA frame Displays how many data slots are available within one TDMA frame

for this channel.

Data rate per slot ass. [bit/s]

Displays the datarate per slot (including SLL framing and fragment

descriptors) for each assigned data slot in this channel. Length gross container [byte] Displays the length of the gross container of this channel. Efficiency [bit/symbol] Displays the efficiency of this channel :

Efficiency = user data rate / symbol rate Efficiency [bit/s/Hz] Displays the efficiency of this channel:

Efficiency = user data rate / frequency bandwidth Maximum number of stream

slots

Table 2-6 Summary ’Data Output Per Frequency Channel’ Parameter

2010-10-26 Network Design and Engineering Guide 65

Displays the maximum quantity of data slots which can be allocated

as stream slots for this channel.

General Carrier Design TDMA Carrier Design with ’TDMA Calculator’

2.6.5 Exporting and Importing TDMA Calculator Values

Depending on the tool version, there are two differerent ways for exporting/importing the TDMA calculation values:

- ’TDMA Calculator’ standalone tool: Select from the main menu ’File’ the entry ’Export’ to create an XML file which contains all input and output parameter. This file can be printed or sent to the network commissioner who applies the values manually. Saved customer sheets can be imported in the TDMA Calculator using the ’Import’ function of the menu.

- SkyNMS integrated ’TDMA Calculator’: after calculation click the button ’Apply to Configuration Profile’ at the bottom of the window. The calculated parameters are imported in the ’SkyNMS Network Configurator’ (for the corresponding configuration profile) and stored in the SkyNMS database. The following configuration parameter are applied via mouseclick to the invoking IDU profile:

- Length base gross container

- Minimum TDMA frame time

- Number of reference channels

- Reference burst mode

- Size superframe

- Roll off factor

- Data slot length

- Code rate

-Symbol rate

- Modulation scheme

- Data slots per TDMA frame

66 Network Design and Engineering Guide 2010-10-26

General Carrier Design

From Capacity Estimation to TDMA Structure

2.7 From Capacity Estimation to TDMA Structure

In chapter 2.4 the procedures to estimate the user traffic for a SkyWAN® network and for indi-

vidual SkyWAN

carriers were discussed. The TDMA Calculator tool allows the calculation of a TDMA frame structure which fulfils the estimated requirements and which is optimized for the applications used on the network.

Starting point for the ’TDMA Calculator’ Input is the work sheet TDMA Calc Input of the Capacity Calculation tool described in chapter 2.4. For the example discussed there, this work sheet provides the following results for the 3 carrier solution:

Figure 2-42 Results from Capacity Calculation Tool

The following results are important for the TDMA calculation:

- The composition of the user traffic according to the different traffic types. These numbers

are used to define the corresponding channel input parameters in the TDMA Calculator.

- The user data rate per carrier for the single and multiple carrier solutions. The user data

rates calculated by the TDMA Calculator (shown in area ’Data output per frequency channel’) have to fulfill these requirements, i.e. they must be equal or larger than the estimated user data rates.

The channel data rate input parameters in the TDMA Calculator are the modem rates. As a starting point for these values, the Capacity Calculator proposes modem rates which are derived from the user data rate by adding an estimated TDMA overhead. A value of 15% for this overhead is for most scenarios a reasonable approximation.

Using the values from the Capacity Calculation tool the TDMA calculation can now be performed.

2010-10-26 Network Design and Engineering Guide 67

General Carrier Design

From Capacity Estimation to TDMA Structure

One Carrier Solution

Besides the values provided by the Capacity Calculation tool we make the following additional assumptions:

- Reference burst mode: MRB.

- Frame time min: 109 ms (should lead to an actual frame time close to the target value of 110 ms).

- Available Eb/No = 5 dB, max. BER 10-7.

- Packet length for IP Real-time: 1500 Byte, IP Non Real-time: 200 Byte.

- Slot size optimization is performed on the FR Voice service, option “1” is selected.

With these assumptions the initial input values of the “TDMA Calculator” are inserted. After clicking the button ’calculate’ an error message is displayed that the maximum number of

timeslots is exceeded. Perform the adjustments as described below to get an optimized 1 carrier solution; refer to .

Adjustment and Optimization Considerations

1. Evaluating the channel data output one notices that the number of time slots per TDMA

frame larger than the maximum supported by SkyWAN optimization rule to 3 calls per slot reduces this number to an allowed value (107).

If the number of time slots is exceeded, an error message is displayed in the output window but a further calculated value in field ’Time slots per TDMA frame’ is still visible (but no longer valid).

2. A further optimization can be achieved by reducing the number of data slots required forrequest bursts. St arting from the default sup erframe size of 1, 5 slots are n eeded. Increasingthe superframe size value to 5 reduces the number of request slots (parameter ’Length req. frame [time slots] ) to the minimum of one slot only.

3. With these settings the available user data rate is exceeding the estimated user traffic on carrier 1. In order to minimize the required space segment, it is now possible to reduce the modem rate until the user requirement is just fulfilled.

networks. Adjusting the time slot

68 Network Design and Engineering Guide 2010-10-26

General Carrier Design

From Capacity Estimation to TDMA Structure

Figure 2-43 TDMA Calculator with Optimized 1 Carrier Solution

Optimized Three Carrier Solution

A similar procedure can be used to optimize TDMA frames for multiple carrier solutions. We present here an optimized solution for the 3 carrier network for which the user data rates have also be estimated by the Capacity Calculation presented at the beginning of this section. All the assumptions made so far are still valid, however we must now find a solution which provides sufficient user data rates for all 3 carriers. The proposed optimized solution is presented in the following screenshots.

Adjustment and Optimization Considerations

1. For the 3 carrier solution we have selected smaller time slots which carry only 2 voice calls per slot instead of the 3 calls we used for the 1 carrier solution.

2. As the individual carriers are smaller in this case, the number of time slots is still within the

2010-10-26 Network Design and Engineering Guide 69

General Carrier Design From Capacity Estimation to TDMA Structure

supported range of maximal allowed slots on SkyWAN®. Although this smaller slot size will result in a smaller numerical efficiency due to an increased TDMA overhead, the overall network efficiency is typically higher. The reason for this is that stations, which require e.g. on a specific carrier just the capacity of 1 voice call must always request one full time slot, which will be much more than actually needed in the case of big time slots. If this extra capacity cannot be used for additional traffic on this carrier, it will be wasted.

3. Since the same optimization criterion 2 voice calls per slot has been selected for all channels, the ’TDMA Calculator’ uses a data slot length factor of 2 for the small carriers to create slots which can also carry 2 voice calls for these carriers. If we want an even finer capacity allocation granularity on these carriers, we could have specified 1 call p er slot on channel 2 and 3, leading to a solution which uses a data slot length of 1 a lso on t hese carriers.

The optimized 3 carrier solution is presented in figure 2-44:

Figure 2-44 TDMA Calculator Outp ut for Optimized 3 Carrier Solution

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General Carrier Design

From Capacity Estimation to TDMA Structure

The resulting user data rates for every carrier match the requirements which we have calculated with the capacity calculation sheet before.

The available Eb/No for a carrier is actually a quantity which can only be determined by a link budget calculation procedure, which will be explained in the following section of this guide. Only after that calculation the proper value for Eb/No can be inserted for each channel, leading to a new selection of modulation and error correction factors. This change will hardly affect the user data rate but will have a profound influence on the symbol rate and the required frequency bandwidth.

The input and output values of the TDMA Calculator include many of the SkyWAN

IDU’s TDMA master and network system parameters. Therefore the generated customer sheet is an important input source for the network commissioner.

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72 Network Design and Engineering Guide 2010-10-26

Outdoor Unit and Satellite Link Design

Introduction

3 OUTDOOR UNIT AND SATELLITE LINK

DESIGN

In the previous chapter ’General Carrier Design’ we discussed how to derive optimized Sky-

WAN link budget calculation for SkyWAN to optimize links and the outdoor equipment of earth stations.

The next steps in the engineering process are

- the choice of a suitable satellite rsp. satellite transponder(s) and

- an optimized outdoor unit design.

3.1 Introduction

The general principle of the satellite link and outdoor unit design may be summarized by the following steps as shown in figure 3-1.

TDMA carriers from user traffic requirements. In this chapter we discuss how t o perform

networks using the ND Satcom Link Budget tool and how

Figure 3-1 Steps for Outdoor Unit and Satellite Link Design

Select Satellite Transponder

Start with selecting a suitable satellite transponder (task B1 in figure 3-1). The necessary input for this task are

- the geographical location of the earth stations

- information about footprint disadvantages like rain fade or the coverage of the satellite

transponder beam.

2010-10-26 Network Design and Engineering Guide 73

Outdoor Unit and Satellite Link Design Satellite Beam Footprints

Calculate Link Budget

The satellite transponder parameters together with the results of the TDMA calculation (TDMA carrier modem rates, modulation and channel codings ) allow the calculation of t he satellite link budget. The result of this calculation determines the required ODU equipment: Antenna sizes and amplifier power classes.

Perform Optimization

It is possible that the result of the link budget calculation requires very large antenna sizes or high power classes for the amplifiers. In this case it might be necessary to go back to the carrier design and to reduce power requirements by e.g. splitting the necessary bandwidth to more carriers or changing the channel coding.

3.2 Satellite Beam Footprints

The first selection criteria for a satellite transponder is that its beam covers the area where the earth stations are located. Typically two types of beams are available:

- Wide beams (“global” or “hemispherical”) which cover a wide geographical area potentially including multiple continents.

- Spot beams which cover a restricted geographical area with a diameter of typically ~ 20003000 km.

Wide beams are typically available in the C-Band frequency band (uplink frequency ~ 5 GHz). The advantage of this type of beam is that it supports networks with earth stations spread over large geographical areas. The disadvantage is that the beam intensity is relatively low, as the limited signal power available for a transponder on the satellite is dispersed over a large area.

Spot beams which are mainly available in the Ku-Band (uplink frequency ~ 14 GHz) offer a higher beam intensity as their signal power is focused to a smaller area. The higher intensity of the satellite signal allows a more compact design of the earth stations (smaller antenna sizes and lower power level of the amplifiers) which reduces the earth station’s hardware cost.

Figure 3-2 SES World Skies NSS-7 Satellite Wide Beam Footprints

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Outdoor Unit and Satellite Link Design

Satellite Beam Footprints

The white contour lines represent areas with a specific signal intensity expressed in terms of Equivalent Isotropic Radiated Power [dBW]. The yellow contour lines specify the earth station elevation angle [°].

Figure 3-3 SES World Skies NSS-7 Satellite Spot Beam Footprint

Satellite Choice Considerations

Let’s assume that we have to design a network with stations in South America and Africa. The NSS-7 global beam would cover the entire area. If the stations would be located in Europe and Africa, the east hemisphere beam would be more suitable, because the beam intensity is typically 5 dB higher compared to the global beam.

Finally let’s consider a network with stations in Brazil and Angola. Both areas are served by a high power Ku-Band spot beam. If cross-strapping between these beams is supported on the satellite, a single SkyWAN spot beams. Compared to a network running on the global beam the power advantage would be typically 14 dB, allowing a substantial reduction of the earth station’s ODU equipment.

network operating in MRB-DUB or NFB-DUB mode may use this

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Outdoor Unit and Satellite Link Design

EIRP[dBW] = P

amp

[dBW] + G

ant

[dBi] – L

Ins

[dB]

Fundamentals of Link Budget Calculation

3.3 Fundamentals of Link Budget Calculation

This section is not supposed to be an extensive description of the techniques of link budget calculations. For that purpose we refer to the available text book literature covering this subject. The reader should however have a qualitative understanding how earth station and sa tellite parameters affect the quality of a satellite link. For that purpose we present here some fundamental considerations concerning the principles of link budget calculations.

The following picture presents a satellite link including the most important link parameters which are subsequently explained:

Figure 3-4 Up- and Downlink Link Budget

Uplink and Downlink

The uplink part of a satellite connection represents the signal propagation from the transmitting earth station to the satellite whereas the downlink part represents the signal path from the satellite to the receiving earth station.

Equivalent Isotropic Radiated Power (EIRP) and Antenna Gain

The signal intensity (signal power per area) of the earth station or satellite signal in the main beam direction of the antenna is determined by the output power of the amplifier P focusing effect of the parabolic antenna which is represented by the antenna gain G combination of both quantities is called the Equivalent Isotropic Radiated Power (EIRP) of the station. In logarithmic quantities this is given by:

In this formula L

is the signal loss which occurs in the feed system of the antenna after the

Ins

amplifier’s wave guide flange. The antenna gain is proportional to the square of the antenna’s diameter and the carrier frequency. Typical transmit antenna gains for a 2.4m parabolic antenna are 42 dBi for C-Band and 49 dBi for Ku-Band.

amp

and the

. The

ant

76 Network Design and Engineering Guide 2010-10-26

Outdoor Unit and Satellite Link Design

N = kB x T x B

Fundamentals of Link Budget Calculation

Path Loss

Due to the very long distance earth station – satellite (> 36000 km) only a small fraction of the radiated power will be picked up by the receive antenna of the earth station or the satellite. This signal attenuation is called the free space path loss a

and depends on both the distance

Path

and the radiation frequency. In addition to this constant loss at ’clear sky’ conditions, ad ditional atmospheric loss happens temporarily under rain conditions (rain fade). This will be discussed in more detail in a later section.

Saturation Flux Density (SFD)

The satellite transponder’s saturation flux density defines the power density which is needed to generate a signal on the downlink with the maximum downlink EIRP

. A lower SFD means

Sat

a higher satellite transponder gain.

Noise, Figure of Merit G/T and Signal-to-Noise Ratio Eb/No

Besides signal power losses and gains there is also an accumulation of noise along a satellite link. The most important noise sources are thermal noise picked up by the receiving antennas and noise produced by the Low Noise Amplifiers (LNA) in the earth station and satellite reception systems. The noise power N is typically represented by an effective noise temperature which is defined by the formula

where k

is Boltzmann’s constant and B the signal bandwidth. The noise production by both

the satellite and the earth station is usually combined with the antenna gain to the system’s figure of merit G/T.

The resulting signal received at the earth station’s demodulator will have both a signal carrier power C and a noise power N. The signal quality will be determined by the signal-to-noise ratio C/N. Instead of using the bandwidth dependent quantities C and N, the signal-to-noise ratio is expressed by Eb/No. Here No is the spectral noise power per 1 Hz bandwidth and Eb the energy per information bit which represents the carrier power divided by the carrier’s modem data rate. For the definition of modem data rate please refer to chapter 2.6.

Satellite Link Quality Dependencies

The quality of a satellite link is defined by the average ratio of bit errors which is generated on the link. Typical requirements for a satellite link quality is that the bit error rate must be lower than 10 error correction of the carrier. Lower FEC rates i.e. higher information redundancy on the carrier reduces the required Eb/No, 8PSK modulation increases the required Eb/No compared to QPSK. There is also a slight dependency on the TDMA container size: For gross container sizes smaller than 200 byte a higher Eb/No is needed due to a lower performance of the Turbo-Phi coding for short code words.

-8

…10-7. The required Eb/No level for that link quality depends on the modulation and

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Outdoor Unit and Satellite Link Design Fundamentals of Link Budget Calculation

The required SkyWAN® IDU 7000 Eb/No levels for different carrier modulation and coding val-

ues are both contained in the TDMA calculation tool and the SkyWAN

link budget tool. For a

brief discussion we have a look at 3 different values for a satellite link with a bit error rate

-7

< 10

, gross container size > 200 Byte:

Modulation FEC Rate Eb/No

QPSK 1/3 2.4 dB QPSK 6/7 5.6 dB 8PSK 6/7 8.8 dB

Table 3-1 Eb/No Values for different FEC Coding and Modu la tio ns

Let’s assume the result of the traffic estimation and TDMA calculation showed that a carrier with a modem data rate = 1000 kbps is required. For a TDMA structure with a frame time of 100 ms, a container size of 417 Byte and a carrier spacing factor of 1.2 t he resulting bandwidth and power requirements to achieve the above stated Es/No levels are shown in table 3-2

Modulation - FEC Rate Carrier Bandwidth [kHz] Relative Carrier Power

QPSK - 1/3 1904 100 % QPSK - 6/7 758 208 % 8PSK - 6/7 428 416 %

Table 3-2 Carrier Power and Bandwidth for TDMA structure example

Going from QPSK - 1/3 to 8PSK - 6/7 for a satellite carrier

- the bandwidth needed on the satellite transponder is reduced by 78%.

- the required power on both the satellite and the transmitting earth station is increased by

316%.

One important result of a link budget calculation is the determination of the optimal channel modulation and coding. The goal is to use the highest possible value for modulation and FEC to save bandwidth costs without exceeding the maximum power available on both the satellite transponder and the earth stations.

Power Equivalent Bandwidth

As already mentioned, the available power on a satellite transponder is limited. The available power is determined by the transponder’s saturation EIRP reduced by the necessary output back-off. This back-off is needed to prevent carrier interference which would occur if the amplifier on the satellite is operated at saturation level. If a carrier uses not the full transponder bandwidth but only a fraction, then the available power for this carrier is the same fraction of the transponder power. Hence the carrier power may also be expressed as a bandwidth: This is the definition of the “Power Equivalent Bandwidth” (PEB).

If the carrier PEB is higher than the carrier bandwidth, the PEB must be leased on the transponder. Since this increases the space segment cost without increasing the user bandwidth that situation should be avoided by selecting an optimized carrier coding and modulation.

Note that within a network using multiple carriers, it is possible that for some carriers PEB is larger than the carrier bandwidth whereas for other carriers PEB is smaller than the carrier

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bandwidth. As long as the summary PEB for all carriers is still smaller than the summary bandwidth of all carriers, no extra space segment has to be leased for the carriers with high power requirement.

Example: Available transponder EIRP: 50 dBW

Transponder bandwidth: 36 MHz Required carrier EIRP: 40 dBW

-> Carrier PEB: 3.6 MHz For an example we assume the values given above. Now we make a calculation for a Sky-

WAN

carrier with a modem rate of 1000 kbps, QPSK modulation and 1/3 coding. We find a carrier bandwidth of 1904 kHz (cf. previous example) and a power requirement for the satellite of 30 dBW. Using the results from the previous example, we can now derive the required bandwidth and PEB for other modulation and coding selections.

Modulation

- Coding

Carrier EIRP on Satellite

PEB [kHz] Carrier Band-

width [kHz]

Space Segment to lease on Transponder [kHz]

[dBW]

QPSK - 1/3 30.0 360 1904 1904 QPSK - 6/7 33.2 758 758 758 8PSK - 6/7 36.4 1571 428 1571

Table 3-3 Relation between Modulation, Coding and Carrier PEB

In this example, with QPSK 1/3 coding the carrier uses a much smaller fraction of the transponder’s power than the transponder’s bandwidth. Increasing the coding will increase the power requirement and decrease the carrier bandwidth. Indeed, at QPSK - 6/7 the satellite link power and bandwidth is optimally equilibrated as the carrier bandwidth and PEB are identical. Any further increase in modulation and coding will increase again the space segment cost, as the PEB increases even though the carrier bandwidth would still decrease. So the optimal modulation and coding for this downlink would be QPSK - 6/7.

Rain fade

In Ku-Band strong rain falls can attenuate the signal substantially resulting in a temporary drop of the Eb/No levels below the minimum requirement for a good quality satellite link. This may lead to a temporary outage of services. To prevent this the link budget has to include a rain margin for the satellite link power requirement. The amount of this margin depends on:

- The probability of intense rain at the geographical position of the earth station.

- The required availability for the satellite link.

- The carrier frequency. As the rain fade increases with the carrier frequency, it is basically negligible for C-Band but

has to be taken into account for Ku-Band or higher carrier frequencies. The probability of intense rain can be derived from the ITU-T rain zones which represent the maximum rain intensity at a specific location which is not exceeded in 99.9% of a typical year. Rain zones A (polar and desert regions) to Q (tropical Africa) are defined by the ITU-T. Finally, a required satellite

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link availability of 99.9% will result in a higher rain margin compared to an availability of only 98%. The following picture presents an overview of ITU-T rain zones in Europe and Northern Africa:

Figure 3-5 ITU-T Rainzones Europe and North-Africa

Rain Margin and Uplink Power Control

The inclusion of rain fade in the link budget calculation increases the power requirements on the earth stations and on the satellite transponder.

As an example we assume a situation where according to the required availability and the rain zones of the earth stations a necessary rain margin of 5 dB for the uplink and 4 dB for the downlink is determined. The difference between up- and downlink could result from different rain zone locations of the earth stations and the higher frequency of the uplink compared to the downlink. The power requirements for the earth station and the satellite transponder at maximum rain fade is shown in figure 3-6.

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Figure 3-6 Attenuation under maximum Rain Fade Condition

and XS represent the required EIRP for the transmitting earth station and the satellite transponder without

rain fade.

is the minimum Eb/No level for the given carrier modulation and coding.

If we are operating the earth stations with constant power level, the transmitting earth station would still use the same power even after the rain fade has disappeared, refer to figure 3-7.

Figure 3-7 Power Conditions with constant Power Level

At clear sky condition the satellite transponder would operate at a power level which is 5 dB higher than under maximum rain fade and actually 9 dB higher than necessary for clear sky conditions.

That leads to an unnecessary high power requirement for the satellite transponder which may even exceed the available power for that transponder. A more optimal approach is to dynamically adjust the transmission power on the uplink, so that the power requirement for the satellite remains constant, irrespective of the rain condition on the uplink. At clear sky condition this will result in the power levels as described in figure 3-8.

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Figure 3-8 Power Conditions with Uplink Power Control

Link Budget Calculations

Note that a further reduction to the minimum power requirement for clear sky conditions XT is possible but unnecessary.

This functionality is generally called “Uplink Power Control (UPC)” and is implemented in Sky-

WAN

networks as the built-in automatic Transmission Power Control (TPC). Generally the

power requirement for the satellite transponder including rain margin is given by: With UPC: EIRP Without UPC: EIRP

= EIRP

S,clear Sky S,clear Sky

+ Downlink rain fade + Downlink rain fade + Uplink rain fade

Note that the power requirement for the transmitting earth station is not affected by UPC, but is always given by:

EIRP

= EIRP

T,clear Sky

+ Downlink rain fade + Uplink rain fade

3.4 Considerations for SkyWAN® Link Budget Calculations

3.4.1 Network Topology

So far we have considered satellite links which include a transmitting and a receiving earth station using a specific satellite transponder. Most widely used link budget tools actually are designed for such point-to-point links, where each station uses a dedicated carrier to reach another station. In SkyWAN specific points:

-A SkyWAN

station in a meshed network communicates not only with one remote station

but with up to 509 remote stations.

-A SkyWAN

carrier is typically not only used by a single station but by a whole group of

stations.

-A SkyWAN

station may use not only one carrier but different carriers which may be locat-

ed on different transponders on a satellite.

To calculate the power requirement for a SkyWAN

networks however, we have to take into account the following

earth station, the individual power require-

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ment must be calculated to transmit signals with sufficient quality to all reachable remote stations on their respective home channels. For a master and backup master station this must include all stations in the network because the reference burst has to be sent to every station in the network. For slave stations at least master and backup master station must be reachable for the transmission of request and ranging burst. In a fully meshed SkyWAN course all stations in the network must be reachable by any SkyWAN

station. The required

network of

EIRP for each station is then determined by the highest power requirement of all these satellite links.

The power requirement and PEB for the satellite transponder must be calculated individually

for each SkyWAN the satellite all SkyWAN

carrier. Here the power must be calculated which is needed to reach from

stations which are members of the carrier’s downlink population. The maximum power requirement of these downlinks determines the required power and PEB for this carrier. Finally more than one set of transponder parameters is required to calculate Sky-

WAN

satellite links, specifically if MRB-DUB mode is used.

3.4.2 Downlink Optimization

Figure 3-9 Downlink Considerations

The performance of the satellite downlink is given by the maximum available EIRP of the satellite, the earth stations figure of merit and their location within the satellite beam footprint. The maximum EIRP is only available in the center of the beam, stations located at the beam edge will receive a weaker signal. The difference is called the “footprint disadvantage”. Note that the maximum EIRP is not identical to the saturation EIRP which is specified in the footprint diagrams. The difference is due to the required output backoff of the transponder.

Assuming that the satellite is transmitting with maximum EIRP, the earth stations will receive the signal with a quality Eb/No

which will determine the maximum possible modulation and

max

coding of the downlink carrier (cf. discussion Power Equivalent Bandwidth in previous section). Note that Eb/No EIRP

always refers to the full bandwidth of the satellite tr ansponder. Therefore, decreasing

max

does not depend on the downlink carrier bandwidth since the satellite

max

the bandwidth of individual carriers by splitting up capacity into multiple carriers will not increase Eb/No Eb/No

can only be increased by increasing the earth station’s G/T. As the noise part of

max

and the possible modulation and coding. For a given satellite beam,

max

G/T is mainly fixed by the LNA type, the only possibility to increase the figure of merit is to increase the antenna gain by using larger antennas.

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In a SkyWAN® network the maximum possible modulation and coding of a carrier will be determined by the weakest station within a downlink population, i.e. the station with the lowest Eb/No. This weak station may considerably decrease the possible coding efficiency for a carrier which leads to an increased bandwidth requirement for the network. To prevent this it might make sense to

- increase G/T for weak stations by using larger antennas for these stations.

- put the weak stations on a separate home channel. The latter option allows to use a high modulation and co ding for the strong stations and the low-

er coding efficiency only for a separate carrier for the weak stations. Th is increases the overall network coding efficiency. Remember that for SkyWAN

networks, modulation and coding may

be selected independently for each carrier.

3.4.3 Uplink Optimization

Figure 3-10 Uplink Considerations

In the downlink optimization discussion it was assumed that the satellite transmits with the ma ximum available EIRP to the earth stations. This is however only true, if the signal intensity received from the earth stations reaches the maximum Input Power Flux Density (IPFD). The IPFD is given by the transponder Saturation Flux Density (SFD) reduced by th e Input Back-Off (IBO), which is necessary to prevent excessive carrier intermodulation. To reach this flux density at the satellite, the earth station’s EIRP

must be large enough to compensate the path

max

loss and potential additional rain fade. If the station cannot reach the required EIRP it may be increased by using larger antennas or

higher power classes for the station amplifier. Another option would be to reduce the bandwidth of an individual carrier by splitting the required capacity into mu ltiple carriers. Splitting however only makes sense if the traffic flow topology allows the simultaneous use of all carriers by different SkyWAN

IDUs (cf. discussion in chapter 2.4.2). Note that a SkyWAN® unit may transmit on multiple carriers sequentially (by frequency channel hopping) but not simultaneously. Therefore the transmit power requirement of a station is determined by the largest carrier.

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If it is not feasible to equip every station using a specific carrier for transmission with an outdoor unit which produces a sufficient large EIRP to reach the maximum IPFD on the satellite, the satellite transponder will also transmit this carrier with an EIRP which is lower than the satellite EIRP

. In this case the reachable Eb/No will also be smaller and therefore the modulation

max

and coding of that carrier has to be adjusted accordingly.

3.5 SkyWAN® Link Budget Calculation Tool

To simplify link budget calculations for SkyWAN® networks, ND Satcom provides a spreadsheet which contains the necessary formulas to calculate power requirements for earth stations in SkyWAN

networks.

The ND Satcom SkyWAN

Link Budget Tool offers the following functionalities:

- Support of C-Band and Ku-Band satellite links.

- Data for up to 23 networks may be entered.

- Data of up to 20 earth stations may be defined per network.

- Support of meshed, star and hybrid network topologies.

- Up to 4 satellite transponder data sets may be used for each network. Result: Power requirement for every SkyWAN

The link budget tool is a Microsoft

Excel spreadsheet which consists of the following work

earth station in the network.

sheets:

- Summary: Input: Carrier parameters for up to 8 SkyWAN

carriers, required bit error rate level and rain availability. Output: Earth station power requirements, power equivalent bandwidth.

- Stations: Earth station data, link to satellite transponder used for the network.

- Link Data: Intermediary results for link budget calculations like e.g. path loss, rain fade etc.

- Local_Ku_Antdata: Antenna data for antennas used in Ku-Band.

- Local_C_Antdata: Antenna data for antennas used in C-Band.

- Ku_Satellites: Satellite transponder data for Ku-Band transponders.

- C_Satellite: Satellite transponder data for C-Band transponders.

- TxAmp: Available amplifier power classes for Ku and C-Band. In the following pages the various input and output fields of the link budget tool are explained. Note that the input cells are indicated by a dark grey background. Cells with a different back-

ground color are output fields which should NEVER be overwritten by user input to avoid any damage to the workbook’s built-in formulas. If an input field requires a numerical input, only the value but not the unit should be entered. Example: Saturation EIRP for the satellite transponder: Enter “37” not “37 dBW”.

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3.5.1 Satellite Data Worksheets (Ku- and C-Band)

The tool contains a satellite data sheets for defining C-Band and Ku-Band transponder.

Figure 3-11 Link Budget Tool - Satellite Data Worksheet(s)

For C-Band transponders the link polarization (circular/linear/unknown) must be specified, whereas the for Ku-Band linear polarization is assumed. The intermo dulation parameters I0 up/ down allow to specify signal degradation due to intermodulation on the up- and downlink. The default settings -300/-200 dBW/Hz describe a situation without intermodulation effects. If no detailed information about transponder intermodulation is available a typical way to estimate this effect is:

- Increase I0 up until the power requirement for the earth stations is increased by 20%.

- Increase I0 down until the power requirement for the earth stations is increased by additional 5%.

From the transponder data saturation, G/T, SFD, Input Back-Off and Output Back-Off the satellite gain is calculated. Note that these values refer to the center of the satellite beam. The transponder bandwidth is needed to calculate the PEB.

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3.5.2 Antenna Data Worksheets (Ku- and C-Band)

The tool contains antenna data sheets for antennas in C-Band and Ku-Band.

Figure 3-12 Link Budget Tool - An tenna Data Worksheet(s)

For both antenna types, antenna parameters like Tx/Rx gain, Tx insertion loss, Noise temperature for LNA and antenna at elevation angles 0-90° have to be inserted , refer to figure 3-12. The antenna name for each data set has to be unique. This name is used to link earth station properties to the antenna data.

In the case of C-Band antenna, data sets for linear and circular polarization may be specified. Here the link from earth stations to antennas is done via a common antenna name for both polarization types which is specified at the top of the antenna sheet, refer tofigure 3-13.

Figure 3-13 Link Budget Tool - C-Band Antenna Data

Depending on the transponder parameter ’polarization’ the antenna data for linear, circular or unknown polarization will be used.

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A) B) C)Calculation Name)

SkyWAN

Link Budget Calculation Tool

3.5.3 Stations Worksheet

Figure 3-14 Link Budget Tool - Station Worksheet

The station worksheet allows the storage of up to 23 network data.

Use pre-defined Network Data

To use pre-defined network data for the actual link budget calculation select the appropiate name by the pull-down menu ’Select Calculation here’. The data of the selected network are then displayed in the ’Active Calculation’ box (blue background).

Specify Network Data

Step (1) Specify each network by a ’Calculation Name’: Goto lower section ’Stored Calcu-

lations’ and enter network identifier heading field with grey background in column B.

Step (2) For each individual network 3 network parameters have to be defined using the

pull-down menu at the top of each Stored Calculations box. Please d efine these parameters before inserting the individual station data.

- A): Selected transponder for Uplink Area 1 (ULA1). For MRB-DUB and NFB-DUB modes additional transponders may be specified.

- B): Frequency band: C-Band or Ku-Band.

- C): Reference burst mode: MRB, MRB-DUB or NFB-DUB.

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Step (3) For each network up to 20 earth station parameter sets may be defined:

- “Location”: Each earth station is identified by a unique location name. The first column is reserved for one master station, because the home channel of th is station is fixed to carrier 1. For star networks, the first two columns represent the network’s hub stations, the remaining stations are considered the remote terminals of the network.

Figure 3-15 Link Budget Tool - Define Network

- ITU-T ’Rain Zone’.

- ’Longitude’ and’“Lattitude’: Geographical coordinates (positive values means northern/eastern hemisphere).

- ’Uplink/Downlink Pattern disadvantage’: To be taken from the satellite fo otprint diagram. Stations in the beam center have a disadvantage of 0 dB, for other stations the difference between maximum and actual G/T or EIRP has to be entered.

- ’Antenna’: type according to the defined frequency band of the network the pulldown menu allows the selection of any antenna type defined in the Ku- or C-Band antenna sheet before.

- ’Output Backoff’: The difference between saturation power and maximum usable output power of the station’s amplifier.

- ’Number of IDUs at location’: the number of IDUs which are connected to the station’s ODU.

- ’Altitude’ of geographical station position.

-’SkyWAN

Receive Home Channel’: The carrier used for reception on the prima-

ry demodulator.

Output Back-Off

The output back-off is needed to prevent intermodulation created by operating the amp lifier too close to the saturation level. The necessary back-off is higher when more than one carrier is transmitted at the same time. In the case of SkyWAN IDUs are connected to the same amplifier. In this case recommended values for output back-

stations this is only possible if multiple

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off of solid state power amplifiers (SSPAs) are given by the table table 3-4. Note that if the amplifier’s power class is not defined by the saturation level but the 1 dB com-

pression point (like for ND Satcom RFT 5000 series), no output back-off is required for single carrier operation.

Number of IDUs connect-

Output back-off

ed to one SSPA

11.0 23

34.5 4 and more 6

Table 3-4 Output Back-Off SSPA

If TWTA based high power amplifiers are used instead of SSPAs an additional back-off has to be added which is defined on the summary work sheet; refer to figure 3-18. If more than one IDU is connected to the same ODU, besides an additional back-off the power requirement for the amplifier is multiplied by the number of IDUs.

Stations with 2 Demodulator Boards

If a station is equipped with a second demodulator board, a second entry with the same station parameter set but a different home channel setting has to be entered. In figure 3-16 station “Casablanca” has two demodulators, one receiving on carrier 1, the other on carrier 2:

Figure 3-16 Link Budget Tool - Station with 2 Demodulators

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3.5.4 Tx Amplifier Worksheet

In the TxAmp sheet the available amplifier power classes for Ku- and C-Band can be defined. Note that power classes have to be defined in ascending order.

Besides defining the power classes it is also possible to specify the maximum power class available for SSPA amplifier types for Ku- and C-Band (input field markde in figure 3-18).

If the power requirement is higher than the available SSPA power class, the additional TWTA back-off is added to the station’s power requirement. Add the TWTA b ack-off value in the Summary sheet in the marked field shown in figure 3-18.

The tool will propose after the link calculation a station amplifier type wh ich has sufficient power for all calculated links including the station’s output back-off.

Figure 3-17 Link Budget Tool - TxAmp Wor ksheet

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3.5.5 Summary Worksheet

Input

Figure 3-18 Link Budget Tool - Summary Worksheet Input

The input section of the summary sheet allows the definition of the carrier parameters for all SkyWAN

carriers used in the network.

Step (1) Define the following carrier parameters:

- ’Carrier Modulation’

- ’FEC Rate’

- ’Modem Data Rate’ (as calculated by the SkyWAN

- ’Gross Container Size’ (as calculated by the SkyWAN

TDMA Calculator)

From the carrier input parameters the tool derives an estimated carrier symbol rate which is displayed at the bottom of the carrier parameter box. Note that this is only an estimated value; the precise values for the symbol rate have to be taken from the TDMA Calculator. Additionally the following link quality parameters must be defined:

- ’Maximum Bit Error Rate’

- ’Two Way Rain Availability’

Step (2) For each carrier the network topology may be selected from a pull-down menu:

’Mesh’ (mandatory for carrier 1) or ’Star’.

- ’Star’ topology: for all stations which use a ’Star Carrier’ as their home channel only links to the hub stations (the first two columns in the station sheet) are calculated.

- ’Mesh’ topology: For stations on a meshed carrier links to all other stations in the network are calculated.

Step (3) The carrier parameters may be copied to the Stations sheet using a copy button

located on this sheet. Another copy button on the Stations sheet allows the loading of stored carrier parameters for a specific network into the Summary sheet. The carrier parameters here will be used to calculate the links.

Step (4) Optionally define an additional back-off for TWTA amplifiers in the marked field of

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figure 3-18.

Step (5) The link calculation is triggered by pressing Ctrl-e or using the button on the upper

left corner of the Summary sheet.

Output

The main output section consists of 2 parts:

Figure 3-19 Link Budget Tool - Summary Worksheet Uplink

The first part calculates power requirements for all stations to a specific downlink which can be defined by the ’Selected Downlink Location’ input box. No input means that the power requirement for a station loop is calculated. The last line states the required amplifier p ower inclu ding the station output back-off.

Figure 3-20 Link Budget Tool - Summary Worksheet Downlinks

The second part represents the power requirement considering all downlinks to reachable stations. For fully meshed stations this includes all stations in the network; for remote terminals in star networks only the downlinks to the two hub stations are considered. Here the ’Power all links and channels’ output represents the required amplifier power including output back-off. The ’ODU all links’ output field proposes the amplifier power class according to the definitions

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in the TxAmp sheet. At the end of the general output field the ’Commercial Aspects for SkyWAN’ output represents the power requirement on the satellite transponder caused by the downlink to a specific station. Results for operation with and without UPC are stated in terms of a power equivalent bandwidth and are compared to the carrier bandwidth of the station’s home channel. If the PEB with UPC is higher than the carrier bandwidth, an indication “Power Limited” will appear in the output field.

For informational purposes the results for the individual links are also displayed on the Summary sheet. This can be used to identify links with a disproportionate power requirement and helps with ODU and link optimization.

Figure 3-21 Link Budget Tool - Summary Worksheet Up- and Downlinks

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Optional Link Filter for Complex Topologies

Normally the link budget tool calculates either meshed networks or star networks with up to two hub stations. More complex topologies like hybrid or multi-hub star networks may be defined by the link filter matrix at the bottom of the summary sheet.

Figure 3-22 Link Budget Tool - Summary Worksheet Complex Filter

By default every cell in this link filter matrix has the value 1. If a specific link should not be calculated for the link budget, the cell value must be set to 0. In the example presented in the figure, for station 4 and 5 only links to stations 1-3 are calculated, station loop links and links to station 4 and 5 are not considered. This would be an example for a star network with 3 hub stations (1-3) and two remote terminals (4-5) as described in chapter 3.6.3.

3.5.6 Required Settings for MRB-DUB Networks

A SkyWAN® network configured for MRB-DUB mode can be considered to consist of two subnetworks:

- Stations belonging to Uplink Population 1 are located in Uplink Area 1 (ULA1).

- Stations belonging to Uplink Population 2 are located in Uplink Area 2 (ULA2). To serve satellite links between stations located in these areas, carriers on up to four different

transponders may be required:

- Carrier 1 must be located on a looped transponder for ULA1. This carrier is used by the master and backup master station to send reference bursts and to receive request bursts from stations located in ULA1 and for the master synchronization which requires self-reception of the master stations. It is also used for data communication between all stations in ULA1.

- Carrier 2 is located on a cross-strapped transponder linking ULA2 to ULA1 for transmitting request bursts from stations in ULA2 to the master station. Also data b ursts from ULA2 stations to the master or potentially other stations in ULA1 use this carrier.

- Carrier 3 is located on a cross-strapped transponder linking ULA1 to ULA2 for transmitting reference and data bursts from the master stations to stations in ULA2. Potentially other station in ULA1 could also use this carrier to send data bursts to ULA2 stations.

- The optional carrier 4 is located on a looped transponder for ULA2. This carrier is used by stations in ULA2 to directly communicate with other stations in that area. Note that for such stations a second demodulator is needed, because the primary demodulator for these stations must be used to receive carrier 3. If meshing within ULA2 is not required, this carrier is not necessary.

Additional carriers may be defined if needed on looped transponders in ULA1 or ULA2.

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Figure 3-23 MRB-Dub Network Overview

As an example a link budget calculation for a network with stations located in Europe and Africa (ULA1) and America (ULA2) is presented. The transponders used for this network are served by the hemispherical beams on the SES World Skies Satellite NSS-7 (cf. chapter 3.2 for footprint diagrams of that satellite).

Transponder Data

For each beam of a cross strapped transponders additional entries in the satellite sheet are necessary.

Figure 3-24 MRB-DUB Network - Satellite Data

Figure 3-25 MRB-DUB Network - Transponder in Stations Sheet

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Specifications and Main Features

Frequently Asked Questions

User Manual

MANUAL CONVENTIONS

TABLE OF CONTENTS

LIST OF TABLES

LIST OF FIGURES

1 INTRODUCTION

1.1 Summary

1.2 Manual Content

1.2.1 Who should read this document

1.2.2 What do you need to know

1.3 SkyWAN® Solutions and Benefits

1.4 General Design and Engineering Process

1.5 Related Documents

1.5.1 SkyWAN® IDU Manuals Suite

2 GENERAL CARRIER DESIGN

2.1 Introduction

2.2 Data and Voice Networking Overview

Voice connections

Voice Codecs

2.3 Essential SkyWAN® Satellite Link Layer Features

2.3.1 SkyWAN® Network Topologies

Reception Modes

2.3.2 Master and Slave Functionality

Control Communication: Reference and Request Bursts

Active and Backup Master Role

2.3.3 SkyWAN® MF-TDMA functionality

TDMA Frame

Transmit and Receive Carriers

Data Slot Time Factors

TDMA Superframe

2.3.4 Downlink and Uplink Populations

2.3.5 SkyWAN® Reference Burst Modes

MRB Mode

MRB-DUB Mode

NFB-DUB Mode

2.3.6 Capacity Request and Allocation for User Data

Free Slot Assignment

Ranging Subframe

Stream Slots

Dynamic Slots

2.3.7 Guaranteed Throughput

Guaranteed Throughput Example Scenarios

Scenario 1

Scenario 2

Scenario 3

Scenario 4

2.4 Network Traffic Estimation

Traffic Profiles

Traffic Estimation Example Scenario

Summarize Example Traffic

2.4.1 Capacity Calculation Tool

Capacity Calculation Worksheet

Erlang B Calculation Worksheet

Voice Traffic Flow Worksheet

Carrier Configuration Worksheet

2.4.2 Limitations of the Traffic Estimation Approach

2.5 From User Traffic to Satellite Link Carriers

2.5.1 Summary

2.6 TDMA Carrier Design with ’TDMA Calculator’

2.6.1 Section ’General Data Input’

2.6.1.1 Parameter Summary

2.6.2 Section ’Data Input per Frequency Channel’

2.6.2.1 Parameter Summary

2.6.3 Area ’General Data Output’

2.6.3.1 Parameter Summary

2.6.4 Area ’Data output per frequency channel’

2.6.4.1 Parameter Summary

2.6.5 Exporting and Importing TDMA Calculator Values

2.7 From Capacity Estimation to TDMA Structure

One Carrier Solution

Adjustment and Optimization Considerations

Optimized Three Carrier Solution

Adjustment and Optimization Considerations

Outdoor Unit and Satellite Link Design

3.1 Introduction

Select Satellite Transponder

Calculate Link Budget