Samsung SLS 2C40680700 User Manual

Ver.

L TE eNB

System Description

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INTRODUCTION

Purpose

This manual describes the features, functions and configuration of LTE eNB.

Content and Organization

This manual consists of five Chapters and Abbreviations.

LTE eNB System Description

CHAPTER 1. Overview of Samsung LTE System

 Introduction to Samsung LTE System  Network Configurations of Samsung LTE Network  Functional Architecture of Samsung LTE

CHAPTER 2. Overview of LTE eNB

 Introduction to LTE eNB  Key Functions  Specifications  System-to-System Interfaces

CHAPTER 3. LTE eNB Architecture

 Hardware Architecture  Software Architecture

CHAPTER 4. Message Flows

 Call processing Message Flow  Data Message Flow  Network Synchronization Flow  Alarm Signal Flow  Loading Flow  Operation/Maintenance Message Flow

INTRODUCTION

CHAPTER 5. Supplementary Functions and Tools

 Web-EMT  About CLI

ABBREVIATIONS

Provides explanations of the abbreviations used throughout this manual.

Conventions

The following symbols are used in this manual. The following types of paragraphs contain special information that must be carefully read and thoroughly understood.

NOTE This provides references for additional information.

Revision History

EDITION DATE OF ISSUE REMARKS

1.0 06. 2011. First Edition

LTE eNB System Description

INTRODUCTION I

Purpose....................................................................................................................................... I

Content and Organization............................................................................................................ I

Conventions................................................................................................................................II

Revision History.......................................................................................................................... II

CHAPTER 1. Overview of Samsung LTE System 1-1

1.1 Introduction to Samsung LTE System................................................................................. 1-1

1.2 Samsung LTE Network Configuration.................................................................................. 1-2

1.3 LTE System Functional Architecture....................................................................................1-4

CHAPTER 2. Overview of LTE eNB 2-1

2.1 Introduction to LTE eNB........................................................................................................ 2-1

2.2 Key Functions........................................................................................................................ 2-7

2.2.1 Physical layer processing ........................................................................................... 2-7

2.2.2 Call Processing......................................................................................................... 2-10

2.2.3 IP Processing............................................................................................................ 2-12

2.2.4 SON.......................................................................................................................... 2-13

2.2.5 Convenient Operation and Maintenance .................................................................. 2-14

2.3 Specifications ...................................................................................................................... 2-16

2.4 System-to-System Interface................................................................................................ 2-18

2.4.1 Interface Architecture................................................................................................ 2-18

2.4.2 Protocol Stack........................................................................................................... 2-19

CHAPTER 3. LTE eNB Architecture 3-1

3.1 Hardware Architecture .......................................................................................................... 3-1

3.1.1 UADU ......................................................................................................................... 3-4

3.1.2 L8HU .......................................................................................................................... 3-6

3.1.3 Power supply .............................................................................................................. 3-8

3.1.4 Environmental Devices............................................................................................. 3-10

TABLE OF CONTENTS

3.1.5 External Interface ......................................................................................................3-13

3.2 Software Architecture ..........................................................................................................3-15

3.2.1 Basic Software Architecture.......................................................................................3-15

3.2.2 CPS Block................................................................................................................. 3-18

3.2.3 OAM Blocks...............................................................................................................3-21

CHAPTER 4. Message Flows 4-1

4.1 Call-Processing Message Flows...........................................................................................4-1

4.2 Data Message Flow ..............................................................................................................4-21

4.3 Network Synchronization Flow...........................................................................................4-22

4.4 Alarm Signal Flow................................................................................................................4-23

4.5 Loading Flow........................................................................................................................4-24

4.6 Operation and Maintenance Message Flow .......................................................................4-25

CHAPTER 5. Supplementary Functions and Tools 5-1

5.1 Web-EMT.................................................................................................................................5-1

5.2 CLI ...........................................................................................................................................5-2

ABBREVIATION I

A ~ C ..........................................................................................................................................I

D ~ G .........................................................................................................................................II

H ~ M ........................................................................................................................................III

N ~ Q ....................................................................................................................................... IV

R ~ T ........................................................................................................................................ V

U ~ W ....................................................................................................................................... VI

LTE eNB System Description/Ver.1.0

LIST OF FIGURES

Figure 1.1 Samsung LTE Network Configurations.................................................................. 1-2

Figure 1.2 Functions of E-UTRAN and EPC........................................................................... 1-4

Figure 2.1 Indoor eNB + L8HU Installation............................................................................. 2-2

Figure 2.2 Outdoor eNB + L8HU Installation.......................................................................... 2-3

Figure 2.3 LTE eNB System Interface Architecture .............................................................. 2-18

Figure 2.4 UE eNB Protocol Stack ....................................................................................... 2-19

Figure 2.5 eNB S-GW User Plane Protocol Stacks..........................................................2-20

Figure 2.6 eNB MME Control Plane Protocol Stacks....................................................... 2-20

Figure 2.7 eNB  eNB User Plane Protocol Stacks........................................................... 2-21

Figure 2.8 eNB eNB Control Plane Protocol Stacks ........................................................ 2-21

Figure 2.9 eNB  LSM Interface Protocol Stacks............................................................... 2-22

Figure 3.1 Removable eNB’s Internal Configuration .............................................................. 3-2

Figure 3.2 Outdoor eNB Configuration ................................................................................... 3-3

Figure 3.3 Configuration......................................................................................................... 3-4

Figure 3.4 L8HU Configuration............................................................................................... 3-6

Figure 3.5 Power Supply........................................................................................................ 3-8

Figure 3.6 Power Diagram ..................................................................................................... 3-9

Figure 3.7 Outdoor eNB’s Heat Discharge ........................................................................... 3-10

Figure 3.8 UADU Heat-Discharge Mechani sm......................................................................3-11

Figure 3.9 Sensors............................................................................................................... 3-12

Figure 3.10 UADU External Interface................................................................................... 3-13

Figure 3.11 L8HU External Interface .................................................................................... 3-14

Figure 3.12 eNB Software Architecture ................................................................................ 3-15

Figure 3.13 CPS Architecture ...............................................................................................3-18

Figure 4.1 Attach Process...................................................................................................... 4-2

Figure 4.2 Service Request Process by UE ........................................................................... 4-4

Figure 4.3 Service Request Process by Networking .............................................................. 4-5

Figure 4.4 Detach Process by UE .......................................................................................... 4-6

Figure 4.5 Detach Process by MME....................................................................................... 4-8

Figure 4.6 X2-based Handover Process ................................................................................ 4-9

Figure 4.7 S1-based Handover Process ...............................................................................4-11

Figure 4.8 E-UTRAN-UTRAN PS Handover Process........................................................... 4-14

Figure 4.9 UTRAN-E-UTRAN PS Handover Process........................................................... 4-16

Figure 4.10 CS Fallback to UTRAN Process (UE in Active Mode, No PS HO Support)....... 4-18

Figure 4.11 CS Fallback to GERAN Process (UE in Active Mode, No PS HO Support)....... 4-19

TABLE OF CONTENTS

Figure 4.12 eNB System Control and Traffic Flow................................................................4-21

Figure 4.13 eNB Network Synchronization Flow...................................................................4-22

Figure 4.14 eNB System Alarm Flow....................................................................................4-23

Figure 4.15 Loading Signal Flow...........................................................................................4-24

Figure 4.16 Operation and Maintenance Signal Flow ...........................................................4-25

Figure 5.1 Web-EMT Interface ................................................................................................5-1

LTE eNB System Description

CHAPTER 1. Overview of Samsung

LTE System

1.1 Introduction to Samsung LTE System

The Samsung LTE system is a wireless network system supporting 3GPP Long Term Evolution (3GPP LTE; hereafter, LTE) based services. It improved the disadvantages of low transmission speed and the high cost of the data services provided by the existing 3GPP mobile communication system. The Samsung LTE system is a next generation wireless network system that can provide high-speed data services at a low cost regardless of time and location. The Samsung LTE system supports the downlink Orthogonal Frequency Division Multiple Access (OFDMA) transmission technology and the uplink Single Carrier (SC) FDMA transmission technology in Frequency Division Duplex (FDD) mode, and supports a scalable bandwidth for supporting various spectrum allocations to provide high-speed data services. In addition, system performance and capacity have increased as a result of highperformance hardware; the Samsung LTE system can easily accommodate a variety of functions and services.

The Samsung LTE system consists of the evolved UTRAN Node B (eNB), Evolved Packet Core (EPC), and LTE System Manager (LSM). The eNB is a system between the UE and EPC, and processes packet calls by connecting to the User Equipment (UE) wirelessly in accordance with the LTE Air standards. The EPC is between the eNB and the Packet Data Network (PDN), and performs various control functions. The EPC consists of the Mobility Management Entity (MME), the Serving Gateway (S-GW), and PDN Gateway (P-GW). The LSM also provides an interface with an operator, functions to manage software, configurations, performance, and failures as well as an ability to act as a Self-Organizing Network (SON) server.

Supported System Specifications The Samsung LTE system is based on the Rel-8 and Rel-9 standards of the LTE

3rd Generation Partnership Project (3GPP).

CHAPTER 1. Overview of Samsung LTE System

1.2 Samsung LTE Network Configuration

The Samsung LTE system consists of eNB, LSM, and EPC (MME, S-GW, P-GW), and its network configurations are shown below.

PDN

EPC

OCS

S10

MME S-GW

S1MME

X2-C

X2-U

PCRF

S6a

HSS

EMS

ESM

EMS

LSM

MSS

RMI

OFCS

TL1

SNMP/FTP/UDP

P-GW

S5/S8

S11

S1-U

eNB eNB

Figure 1.1 Samsung L TE Ne t work Conf igur ations

evolved UTRAN Node-B (eNB)

The eNB is located betwee

n the UE and EPC. It processes packet calls by connecting to the UE wirelessly according to the LTE Air standard. The eNB performs functionalities such as transmission and receipt of wireless signals, modulation and demodulation of packet traffic signals, packet scheduling for efficient utilization of wireless resources, Hybrid Automatic Repeat Request (HARQ)/ARQ processing, Packet Data Convergence Protocol (PDCP) for packet header compression, and wireless resources control. It also performs handovers interoperating with the EPC.

Evolved Packet Core (EPC)

stem

The EPC is a sy

between the eNB and PDN, consisting of the MME, S-GW and P-GW. The MME processes control messages through the eNB and the NAS signaling protocol, and processes the control functions for the control plane, such as mobility management, tracking area list management, and bearer and session management for UEs. The S-GW carries out the anchor function in the user plane between the 2G/3G access system and the LTE system, and manages the packet transport layer for downlink/uplink data.

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LTE eNB System Description/Ver.1.0

The P-GW allocates an IP address to the UE. For mobility between the LTE system and the non-3GPP access system, the P-GW carries out the anchor function and manages the charging and transmission rate according to the service level.

LTE System Manager (LSM)

The LSM provides an interface to perform

ations and maintenance on the eNB by the

oper operator, functions to manage software, configurations, performance, and failures as well as an ability to act as a Self-Organizing Network (SON) server.

EPC System Manager (ESM)

The ESM provides the user interface for the operator to run and m

intain the MME, S-GW,

and P-GW as system management activities.

Master SON Server (MSS)

The MSS interoperates wit

the local SON server as its higher node, performing the

h optimized interoperation for the multi-LSM. The MSS can work with OSS (Operating Support System) of the service provider who can decide whether to link them.

Home Subscriber Server (HSS)

The HSS is a database

man

agement system that stores and manages the parameters and location information for all registered mobile subscribers. The HSS manages key data such as the mobile subscriber’s access capability, basic services and supplementary services, and provides a routing function to the subscribed receivers.

Policy and Charging Rule Function (PCRF)

The PCRF creates policy

ules to dynamically apply the QoS (Quality of Service) and accounting policies differentiated by service flow, or creates the policy rules that can be applied commonly to multiple service flows. The IP edge includes the PCEF (Policy and Charging Enforcement Function), which allows implementation of policy rules sent from the PCRF per service flow.

Online Charging System (OCS)

The OCS sen

ds/receives

charging information required for a subscriber’s online charging

during calls.

Offline Charging System (OFCS)

The OFCS stores of

fline char

ging data and provides subscriber charging information.

CHAPTER 1. Overview of Samsung LTE System

1.3 LTE System Functional Architecture

The eNB manages UEs, which are in connected mode, at the AS (Access Stratum) level. The MME manages UEs, which are in idle mode, at the NAS (Non-Access Stratum) level, and the P-GW manages user data at the NAS level as well as working with other networks. The functional architecture of E-UTRAN eNB, MME, S-GW, and P-GW according to the 3GPP standards is shown below. The eNB is structured in layers while the EPC is not.

eNB

Inter Cell RRM

RB Control

Connection Mobility Control

Radio Admission Control

MME

NAS Security

Idle State Mobility

Handling

EPS Bearer Control

S-GW

Mobility Anchoring

P-GW

UE IP address allocation

Packet Filtering

eNB Measurement

Configuration & Provision

Dynamic Resource

Allocation (Scheduler)

RRC

PDCP

RLC

MAC

PHY

E-UTRA

EPC

Figure 1.2 Functions of E-UTRAN and EPC

Internet

eNB

The eNB serves the E-UTR

AN (Evolved UTRAN), a wireless access network in the LTE system. The eNBs are connected through the X2 interface whereas the eNB and EPC are connected through S1 interface. The eNB’s wireless protocol layers are divided into Layer 2 and Layer 3. Layer 2 is subdivided into the MAC (Media Access Control) layer, RLC (Radio Link Control) layer, and PDCP layer, each operating independently. Layer3 has the RRC layer.

The MAC layer distributes wireless resources to each bearer according to its priority, and carries out the multiplexing function and the HARQ function for the data received from the multiple upper logical channels.

The RLC layer carries out the following functions.

 Reconstructs the data received from the PDCP layer in accordance with the size

specified by the MAC layer (segmentation and reassembly).

1-4

 When data transmission fails in the lower layer, requests retransmission to recover

them (ARQ).

 Reorders the data recovered by performing HARQ in the MAC layer.

LTE eNB System Description/Ver.1.0

The PDCP layer carries out the following functions.

 Compresses and decompresses headers  Encrypts and decrypts the user plane and control plane data  Protects and verifies data integrity of the control plane  Transmits data and manages serial numbers  Removes data based on a timer as well as removing duplicates

The RRC layer is responsible for managing mobility in the wireless access network, keeping and controlling the RB (Radio Bearer), managing RRC connections, and sending system information.

Mobility Management Entity (MME)

The MME works with the

E-UTRAN (eNB), handlin

g S1-AP (S1 Application Protocol)

signaling messages in the SCTP (Stream Control Transmission Protocol) base to control call connections between the MME and eNB as well as handling NAS signaling messages in the SCTP base to control mobility and call connections between the UE and EPC. The MME also works with the HSS to obtain, modify and authenticate subscriber information, and works with the S-GW to request assignment, release and modification of bearer paths for data routing and forwarding using the GTP-C protocol. The MME can work with the 2G and 3G systems, SGSN, and MSC to provide mobility, HO (Handover), CS (Circuit Service) fallback, and SMS (Short Message Service) services. The MME is also responsible for managing mobility between eNBs, idle-mode UE reachability, TA (Tracking Area) list as well as for P-GW/S-GW selection, authentication, and bearer management. MME supports the handover between MMEs and provides the mobility for the handover between the eNBs. It also supports the SGSN selection function upon handover to a 2G or 3G 3GPP network.

Serving Gateway (S-GW)

The S-GW

carries out the m

obility anchor function upon inter-eNB handover and inter3GPP handover, and processes routing and forwarding of packet data. The S-GW allows the operator to set a different charging policy by UE, PDN or QCI, and manages the packet transport layer for uplink/downlink data. The S-GW also works with the MME, P-GW, and SGSN to support the GTP (GPRS Tunneling Protocol) and PMIP (Proxy Mobile IP).

PDN Gateway (P-GW)

The P-GW

works with PCRF to carry

out charging and bearer policies, and manage the charging and transmission rate based on the service level. It also provides packet filtering per subscriber, assigns IP addresses to UEs, and manages the packet transmission layer of the downlink data.

CHAPTER 1. Overview of Samsung LTE System

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1-6

LTE eNB System Description

CHAPTER 2. Overview of LTE eNB

2.1 Introduction to LTE eNB

The LTE eNB system is located between the UE and EPC, and interfaces via a wireless connection according to the LTE Air Interface, providing subscribers with wireless communication services. The eNB engages in sending and receiving radio signals with the UE, and handling traffic modulation/demodulation signals. The LTE eNB is also responsible for packet scheduling and wireless bandwidth allocation as well as for handovers by interfacing with the EPC.

It consists of a DU (Digital Unit), i.e., UADU (Universal platform type A Digital Unit) and a RU (Radio Unit), i.e., L8HU (LTE eNB remote radio Head Unit). The UADU is a 19 inch shelf-type digital unit and can be mounted on a 19 inch rack in an indoor/ outdoor environment.

The L8HU is an RF integration module consisting of a transceiver, power amplifier, and filter. It sends and receives traffic, clock information, and alarm/control messages to and from the L9CA. The L8HU has a 2Tx/4Rx structure with optic CPRI support, and can be installed on a wall or pole in an outdoor environment.

CHAPTER 2. Overview of LTE eNB

The LTE eNB can be installed as shown below:

Indoor eNB + L8HU

The L9CA from

the UADU mounted on an indoor 19 inch rack is connected to the L8HU.

The L8HU can be installed on a wall or pole.

Figure 2.1 Indoor eNB + L8HU Instal lation

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LTE eNB System Description/Ver.1.0

Outdoor eNB + L8HU

The L9CA from the UADU mounted on an outdoor rack is connected to the L8HU. The L8HU can be installed on a wall or pole.

Figure 2.2 Outdoor eNB + L8HU Installation

CHAPTER 2. Overview of LTE eNB

The LTE eNB system has the following key features:

High Compatibility and Interoperability

Sams

ung LTE system adheres to specifications released in accordance with the 3GPP

standards, providing excellent compatibility and interoperability.

High-Performance Modular Structure

The L

TE eNB sy

stem uses a high-performance processor and has a modular structure that

allows an easy hardware and software upgrade.

Support for Advanced RF and Antenna Solutions

The L

TE eNB sy

stem adopted a power amplifier to support bandwidth for broadband

operation, and also supports MIMO (Multiple Input Multiple Output).

Maintenance with Enhanced Security

The L

TE eNB sy

stem provides security functions (SNMPv2c, SSH, FTP/SFTP, and HTTPs) for all channels for operation and maintenance. It authenticates operators accessing the system, grants them permissions, and stores their system execution histories as logs.

6Rx Multi Antenna Support

pared to generic eNBs with 2Rx antennas that receive 2Rx in one sector, Samsung LTE eNB has enhanced reception, receiving antenna signals up to 6Rx from its own sector as well as from the repeater mode.

OFDMA/SC-FDMA Scheme

The L

TE eNB perform

s the downlink OFDMA/uplink SC-FDMA (Single Carrier

Frequency Division Multiple Access) channel processing that supports the standard LTE physical layer. The downlink OFDMA allows the system to transmit data to multiple users simultaneously using the subcarrier allocated to each user. Depending on the channel status and the transmission rate requested by the user, the downlink OFDM can allocate one or more subcarriers to a specific subscriber to transmit data. Moreover, when all subcarriers are divided for multiple users, the FDMA can select and assign to each subscriber a subcarrier with the most appropriate features, distributing resources efficiently and increasing data throughput.

The uplink SC-FDMA, which is similar to the modulation/demodulation method of the OFDMA, minimizes the PAPR (Peak-to-Average Power Ratio) of the transmitter by computing, for each user, DFT (Discrete Fourier Transform) during modulation at the transmitting end, and IDFT (Inverse Discrete Fourier Transform) during demodulation at the receiving end, and continuously assigns frequency resources to users. As a result, it saves the UE’s power.

2-4

LTE eNB System Description/Ver.1.0

Support for Multiple System Configurations

The LTE eNB supports multiple system and network configurations with a digital unit (UADU) and radio unit (RRH: Remote Radio Head). The digital I/Q and C & M (Control & Maintenance) interface based on the CPRI (Common Public Radio Interface) standard is used between the DU and RU to send and receive data traffic signals and OAM information, and uses optic cable physically. The UADU and L8HU each have a power supply of DC -48 V.

 Multiple Configurations for Network Operation

The LTE eNB supports multiple configurations including RRH (L8HU). The RRH is highly flexible in its installation, and helps with setting up a network in a variety of configurations depending on the location and operation method.

 Easy Installation

The optic interface component that interfaces with the UADU and the RF signal processing component is integrated into the RRH, which becomes a very small and very light single unit. The L8HU can be installed on a wall or pole. Moreover, as the distance between the RRH and antenna is minimized, the loss of RF signals due to the antenna feeder line can be reduced so that the line can provide more enhanced RF receiving performance than the existing rack-type eNB.

 Natural Cooling

Because the RRH is installed outdoors and has an efficient design, it can radiate heat efficiently without any additional cooling system. No additional maintenance cost is needed for cooling the RRH.

 Loopback T e st

The LTE eNB provides the loopback test function to check whether communication is normal on the Digital I/Q and C & M interface line between the DU and RU.

 Remote Firmware Downloading

Operators can upgrade the L8HU and its service by replacing its firmware. They can download firmware to the L8HU remotely using a simple command from the LSM without visiting field stations. As a result, the number of visits is minimized, leading to reduced maintenance costs and system operation with ease.

 Monitoring Port

Operators can monitor the information for an L8HU using its debug port.

MIMO Support

The LTE eNB supports 2Tx/2Rx or

4Tx/4Rx MIMO by default using multiple antennas.

MIMO has the following techniques.

 SFBC (Space Frequency Block Coding)-Downlink

 Reliability for the links is increased. (Note that the peak data rate is not increased.)  This technology implements Space Time Block Coding (STBC) not on time but on

frequency.

 For 2 Tx: The method similar to STBC (Alamouti codes) is used.  For 4 Tx: Both the SFBC and Frequency Switched Transmit Diversity (FSTD) are

used simultaneously.

CHAPTER 2. Overview of LTE eNB

 SM (Spatial Multiplexing)-Downlink

 This technology can increase the peak data rate by dividing and sending other data

via multiple antenna paths. (Each path uses the same time/frequency resource.)

 SU (Single User)-MIMO: SM between the eNB and single UE, it increases the

UE’s peak data rate.

 MU (Multi-User)-MIMO: SM between the eNB and multiple UEs; it increases cell

throughput instead of the UE peak data rate.

 Open-loop SM: Runs without the UE’s PMI (Precoding Matrix Indicator) feedback

when the channel changes quickly or is unknown due to the UE’s fast mobility.

 Closed-loop SM: Runs with the UE’s PMI feedback received from the eNB when

there is channel information due to the UE’s slow mobility.

 UL (Uplink) Transmit Antenna Selection-Uplink

 The UE uses one RF chain and 2Tx antennas. The eNB informs the UE which Tx

antenna to use.

 Closed-loop selection of Tx antenna

 MU (Multi-User) MIMO or Collaborative MIMO-Uplink

 SM in which two UEs use the same time/frequency resources in the UL

simultaneously to transmit different data.

 Each UE uses a single Tx antenna.  The eNB selects two orthogonal UEs.  There is an increase in overall cell throughput, but not in each UE’s peak data rate.

2-6

LTE eNB System Description/Ver.1.0

2.2 Key Functions

Samsung LTE eNB has the following key features.

 Physical layer processing  Call processing  IP processing  SON  Convenient operation and maintenance

2.2.1 Physical layer processing

The LTE eNB sends/receives data via wireless channels between the eNB and UE. The eNB handles the following:

 Downlink reference signal generation/transmission  Downlink synchronization signal generation/transmission  Channel encoding/decoding  Modulation/demodulation  Resource allocation and scheduling  Link adaptation  HARQ  Power control  ICIC  MIMO

Downlink reference signal generation/transmission

The reference signal is used to demodulate downlink

signals in the UE, and to measure the characteristics of the channel for scheduling, link adaptation, and handover. Cell-specific and UE-specific reference signals are used when transmitting non-MBSFN. The cell-specific reference signal is used to measure the quality of the channel, calculate the MIMO rank, perform MIMO precoding matrix selection, and measure the strength of the signals for handover. To operate MIMO, a different reference signal is sent for each antenna path.

Downlink Synchronization Signal Generation/Transmission

The sy

onization signal is used to perform the initial synchronization when the UE

nchr starts to communicate with the base station. It can be PSS (Primary Synchronization Signal) or SSS (Secondary Synchronization Signal). The UE obtains cell identify through the synchronization signal, and other cell information through the broadcast channel. Transmission in the synchronization signal and broadcast channel occurs at 1.08 MHz of the cell’s channel bandwidth as the UE can identify cell ID and other basic information regardless of the eNB’s transmission bandwidth.

CHAPTER 2. Overview of LTE eNB

Channel encoding/decoding

The LTE eNB encodes/decodes the channel to correct channel errors over the wireless channel. To do this, the LTE eNB uses turbo coding and 1/3 tail-biting convolutional coding. Turbo coding is used primarily to transmit large downlink/uplink data packets, and 1/3 tail-biting convolutional coding to transmit downlink/uplink control information and for the broadcast channel.

Modulation/Demodulation

When receiving downlink

data fro

m the upper layer, the LTE eNB processes it through the baseband procedure of the physical layer and then transmits it via a wireless channel. At this time, to send the baseband signals as far as they can go via the wireless channel, the LTE eNB modulates them and sends them on a specific high frequency bandwidth. For the uplink, the eNB demodulates the data transmitted over the wireless channel from the UE to a baseband signal, which is then decoded.

Resource Allocation and Scheduling

For mu

ltiple access, the LTE uses the OFDMA for downlink and the SC-FDMA for uplink. Both schemes allocate 2-dimensional time/frequency resources to multiple UEs in a cell, allowing a single eNB to communicate with the multiple UEs simultaneously. When in MU-MIMO mode, several UEs can use the same resources at the same time as an exceptional case. Allocating cell resources to multiple UEs is called ‘scheduling’ and each cell has an independent scheduler. The scheduler is designed to consider the channel environment, the requested data transmission rate and other various QoS factors of each UE, and perform an optimal resource allocation to provide maximum total cell throughput. It also can share information with other cell schedulers via the X2 interface to reduce interferences with the other cells.

2-8

Link Adaptation

The transm

ission rate and channel environment in the

wireless channel change according to circumstances. Link adaptation is a feature to increase transmission speed or maximize overall cell throughput using channel circumstances when they are known. MCS (Modulation Coding Scheme) is a link adaptation method that sets the modulation type and channel coding rate depending on the channel circumstances. If the channel circumstances are good, the MCS increases the number of transmission bits per symbol using high-order modulation, such as 64 QAM. If the circumstances are bad, it uses loworder modulation, such as QPSK, and a low coding rate to minimize channel errors. The MCS can run in MIMO mode if the channel environment allows MIMO, increasing the user’s peak data rate or cell throughput. If channel information turns out to be different from the actual case, or if the order given to the modulation or coding rate for the channel circumstances is higher than necessary, an error can occur, but be recovered by HARQ.

LTE eNB System Description/Ver.1.0

HARQ

HARQ is a technique for physical layer retransmission using the stop-and-wait protocol. The LTE eNB runs the HARQ, retransmitting or combining frames in the physical layer in order to increase throughput so that the impact from changes of the wireless channel environment or interference signal level can be minimal. The LTE uses the IR (Incremental Redundancy)-based HARQ. The CC (Chase Combining) method is treated as a special case of the IR scheme. It uses the asynchronous IR for downlink, and the synchronous IR for uplink.

Power Control

Power control refers to adjusting the tra

smission power level required to transmit a

specific data rate. Too much power causes interferences. Too little power increases the error rate, causing a retransmission or delay. Power control is less important in the LTE than in the CDMA, but a proper power control can enhance the LTE’s system performance. The LTE uses the SC-FDMA scheme for uplink and eliminates the near-far problem from the CDMA, but the UEs should transmit with optimal power to avoid interference with neighbor cells as the high level of interference with the neighbor cells can worsen the uplink performance. The LTE uplink can lower the inter-cell interference level by adjusting the UE power. The downlink can lower the inter-cell interference level by transmitting with optimal power according to the UE location and MCS, increasing overall cell throughput.

Inter-Cell Interference Coordination (ICIC)

Unlike the CDMA, the L

TE does not

have intra-cell interference. This is because UEs in a cell use orthogonal resources and thus there is no interference between them. However, in the event that the adjacent cells are considered, unavoidable interference occurs when other UEs use the same resource. Since this symptom is severe between the UEs located on a cell edge, performance on the cell edge may be degraded. Inter-cell interference is not severe for the UEs located close to the eNB because they receive much less interference from the adjacent eNBs than the UEs located on the cell edge. A technique used to address the intercell interference problem on the cell edge is ICIC. ICIC allows interference signals to be transmitted to other cells in the cell edge area in as small an amount as possible by allocating a basically different resource to each UE that belongs to a different cell and by carrying out power control according to the UE’s location in the cell. To prevent interference due to resource conflict on the cell edge, ICIC transmits scheduling information between base stations via the X2 interface. When the neighbor cell’s interference signal strength is too strong, ICIC notifies other base stations to control the interference, improving overall cell performance.

MIMO

The L

TE eNB supports 2Tx/2Rx or

4Tx/4Rx MIMO by default using multiple antennas. To achieve this, there must be in the eNB channel card the RF part that can separately process the baseband part and each path for MIMO processing. The LTE eNB provides high-performance data services by supporting several types of MIMO.

CHAPTER 2. Overview of LTE eNB

2.2.2 Call Processing

Cell Information Transmission

The LTE eNB periodically transmits, within the cell range being served, system information, i.e., the MIB (Master Information Block) and SIBs (System Information Blocks), which are then received by UEs to process calls appropriately.

Call Control and Air Resource Assignment

The L

TE eN

B allows the UE to be connected to or released from the network. When the UE is connected to or released from the network, the LTE eNB sends and receives the signaling messages required for call processing to and from the UE via the Uu interface, and to and from the EPC via the S1 interface. When the UE connects to the network, the eNB carries out call control and resource allocation required for service. When the UE is released from the network, the eNB collects and releases the allocated resources.

Handover Processing

The L

TE eNB supports intra-frequency or inter

-frequency handover between intra-eNB cells, X2 handover between eNBs, and S1 handover between eNBs, and carries out the signaling and bearer processing functions required for handover. At intra-eNB handover, handover-related messages are transmitted via internal eNB interfaces; at X2 handover, via the X2 interface; at S1 handover, via the S1 interface. The eNB carries out the data forwarding function to minimize user traffic disconnections at X2 and S1 handovers. The source eNB provides two forwarding methods to the target eNB, direct forwarding via the X2 interface and indirect forwarding via the S1 interface. The eNB allows the UE to receive traffic without loss through the data forwarding method at handover.

Handover Procedure For more on the handover procedure, refer to Chapter 4. Message Flow.

Admission Control (AC)

The LTE eN

B provides capacity-based and QoS-based admission control for bearer setup requests from the EPC to avoid system overload. Capacity-based admission control and QoS-based admission control operate as follows respectively.

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 Capacity-based admission control

There is a threshold for the maximum number of connected UEs (new calls/handover calls) and a threshold for the maximum number of connected bearers that can be allowed in the eNB. When a call setup is requested, the permission is determined depending on whether the connected UEs and bearers exceed the thresholds.

LTE eNB System Description/Ver.1.0

 QoS-based admission control

The eNB provides the function for determining whether to permit a call depending on the estimated PRB usage of the newly requested bearer, the PRB usage status of the bearers in service, and the maximum acceptance limit of the PRB (per bearer type, QCI, and UL/DL).

RLC ARQ

The eNB carries out the

ARQ function f

or the RLC Acknowledged Mode (AM) only. The RLC can increase reliability of data communications by dividing the Service Data Unit (SDU) into the Protocol Data Unit (PDU) prior to transmission, and retransmitting the packets according to ARQ feedback from the receiver.

QoS Support

The eNB re

ives the QoS Class Identifier (QCI) in which the QoS characteristics of the bearer are defined, and the Guaranteed Bit Rate (GBR), the Maximum Bit Rate (MBR), and the Aggregated Maximum Bit Rate (AMBR) from the EPC. It provides the QoS for the wireless section between the UE and the eNB and the backhaul section between the eNB and the S-GW. In the wireless section, it carries out retransmission to satisfy the rate control due to the GBR/MBR/AMBR value, priority of bearer defined in the QCI, and scheduling considering packet delay budget, and Packet Loss Error Rate (PLER). In the backhaul section, the eNB carries out QCI-based packet classification, QCI to DSCP mapping, and marking for the QoS. The eNB provides queuing based on mapping results, and each queue transmits packets to the EPC according to strict priority, etc. In the EMS (Element Management System), besides the QCI predefined in the specifications, an operator specific QCI and a QCI-to-DSCP mapping can be set.

CHAPTER 2. Overview of LTE eNB

2.2.3 IP Processing

IP QoS

The LTE eNB can provide the backhaul QoS when communicating with the EPC by supporting the Differentiated Services (DiffServ). The LTE eNB supports eight backhaul QoS classes as well as mapping between the user traffic service class and the backhaul QoS class. It also supports mapping between the Differentiated Services Code Points (DSCP) and the 802.3 Ethernet MAC service classes.

IP Routing

The L

TE eN

B provides several Ethernet interfaces and stores in the routing table information on which Ethernet interface IP packets will be routed. The LTE eNB’s routing table is configured by the operator. The table configuration and its setting are similar to standard router settings. The LTE eNB supports static routing settings, but doesn’t support dynamic routing protocols such as OSPF (Open Shortest Path First) or BGP (Border Gateway Protocol).

Ethernet/VLAN Interfacing

The LTE eNB provides Et

hernet interfaces, and supports static link grouping, VLAN Virtual Local Area Network(VLAN), and Ethernet Class of Service(CoS) functions that comply with IEEE 802.3ad for Ethernet interfaces. A MAC bridge defined in IEEE 802.1D is excluded. The LTE eNB allows multiple VLAN IDs for an Ethernet interface. To support the Ethernet CoS, it maps the DSCP value of the IP header to the CoS value of the Ethernet header for Tx packets.

2-12

LTE eNB System Description/Ver.1.0

2.2.4 SON

System Self-Configuration and Self-Establishment

The self-configuration and the self-establishment automatically configure and establish radio parameters between the power-on stage and the service stage to minimize efforts in installing a base station. The detailed functions are as follows.

 Self-configuration

 Initial PCI (Physical Cell Identity) self-configuration  Initial neighbor information self-configuration  Initial PRACH (Physical Random Access Channel) self-configuration

 Self-establishment

 Automatic IP address acquisition  Automatic OAM connectivity  S/W and Configuration data loading  Automatic S1/X2 setup  Self-test

Self-Optimization

 PCI auto-configuration

The SON server of the LSM provides the function for allocating the initial PCI in the self-establishment procedure of a new eNB, and the function for detecting a problem automatically and selecting, changing, and setting a proper PCI when a PCI collision/confusion occurs with the adjacent cells during operation.

 Automatic Neighbor Relation (ANR) optimization

ANR optimization minimizes the network operator’s effort to maintain the optimal NRT by dynamically managing the Neighbor Relation Table (NRT) according to the addition/removal of neighbor cells. It needs to automatically configure each eNB’s initial NRT, and recognize environment changes, such as cell addition/removal or new eNB installations during operation to maintain the optimal NRT. In other words, the ANR function updates the NRT for each eNB by automatically recognizing the topology change such as new adjacent cell or eNB installation/removal and adding or removing the Neighbor Relation (NR) to or from a new adjacent cell.

 Mobility robustness optimization

The mobility robustness optimization function is the function for improving handover performance in the eNB by recognizing the problem that handover is triggered at the incorrect time (e.g., too early or too late) before, after, or during handover depending on UE mobility, or handover is triggered to the incorrect target cell (handover to the wrong cell) and then by optimizing the handover parameters according to the reasons for the problem.

 Energy Saving Management (ESM)

The energy saving feature helps reduce the LTE eNB’s power consumption. The ESM adjusts power consumption automatically according to the specified schedule or through traffic quantity analysis. The basic principle is that power consumption is reduced by limiting the number of used Resource Blocks (RBs) and adjusting the PA bias voltage.

CHAPTER 2. Overview of LTE eNB

 Random Access Channel (RACH) optimization

RACH optimization (RO) can minimize access delay and interference by dynamically managing parameters related to random access. The RO function is divided into the initial RACH setting operation and the operation for optimizing parameters related to the RACH. The initial RACH setting operation is for setting the preamble signatures and the initial time resource considering the neighbor cells. The operation for optimizing parameters related to the RACH is for estimating the RACH resources, such as time resource and subscriber transmission power required for random access, that change depending on time, and for optimizing the related parameters.

2.2.5 Convenient Operation and Maintenance

The LTE eNB works with management systems (LSM, Web-EMT, CLI) to operate maintenance activities, such as resetting/restarting a system as well as managing system configurations, failure/status/diagnosis of system resources and services, statistics on system resources and various performance data, and security for system access and operation.

Graphics and Text Based Console Interfaces

The LSM ma

s the entire eNB system using the Database Management System (DBMS).

nage The eNB also works with a console terminal to allow the operator to connect directly to the Network Element (NE), not through the LSM, for operation and maintenance activities. The operator can choose between the graphic-based console interface (Web-EMT, Webbased Element Maintenance Terminal) or the text-based Command Line Interface(CLI) to suit operational convenience and purpose. The operator can access the console interfaces without separate software. For the Web-EMT, the operator can log in to the system using Internet Explorer. For the CLI, the operator can log in to the system using the telnet or Secure Shell (SSH) in the command window. Tasks such as managing configurations and operational information, failures and statuses, and monitoring statistics can be done through the terminal. However, increasing/decreasing resources or configuring neighbor lists in which multiple NEs are related can only be performed using the LSM.

Operator Authentication

The eNB c

n authenticate system operators and manage their privileges. An operator accesses the eNB using the operator’s account and password through the CLI. The eNB grants an operational privilege in accordance with the operator’s level. The eNB logs successes/failures of access to the CLI, activities during the login, etc.

2-14

Maintenance with Enhanced Security

The eNB supports the SNMP

(Sim

ple Network Management Protocol) and SFTP (SSH File Transfer Protocol) for security during communications with the LSM, and the HTTPs (Hyper Text Transfer Protocol over SSL) and SSH (Secure Shell) during communications with the console terminal.

LTE eNB System Description/Ver.1.0

Online Software Upgrade

When a software package is upgraded, the EPC can upgrade the existing package while it is still running. A package upgrade is performed in the following steps: download new package (Add) and change to the new package (Change). When upgrading the package, the service stops temporarily during the ‘change to the new package’ step to exit the existing process and start the new process. But the operating system does not restart, so it can provide the service within several minutes. After upgrading the software, the eNB updates the package stored in the internal nonvolatile storage.

Call Trace

When tracing calls for a specific UE usi

ng the MME, the eNB tran

smits to the LSM a

signaling message for the call in the UE.

OAM Traffic Throttling

The eNB provides the ope

rator with the function f

or suppressing the OAM-related traffic that can occur in the system using an operator command. At this time, the target OAMrelated traffic includes the fault trap messages for alarm reporting and the statistics files generated periodically. For the fault trap messages, the operator can suppress generation of alarms for the whole system or some fault traps using the alarm inhibition command, consequently allowing the operator to control the amount of alarm traffic that is generated. For the statistics files, the operator can control the amount of statistics files by disabling the statistics collection function for each statistics group using the statistics collection configuration command.

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