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P25
Training Guide
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Codan Radio P25 Training Guide

P25 Radio Systems
TRAINING GUIDE
www.codanradio.com
P25 RADIO SYSTEMS | TRAINING GUIDE
P25 Radio
Systems
Training Guide
Page i
NOTE
DOCUMENT REVISION
DEFINITION
© 2013 Codan Limited. No part of this guide may be reproduced, transcribed, translated into any language or transmitted in any form whatsoever without the prior written consent of Codan Limited.
CODAN™, NGT™, Easitalk™, CIB™ and CALM™ are trademarks of Codan Limited. Other brand, product, and company names mentioned in this document are trademarks or registered trademarks of their respective holders.
IMBE™ and AMBE+2™ are trademarks of Digital Voice Systems, Inc. EDACS® is a registered trademark of M/A-COM, Inc. Aegis™ is a trademark of M/A-COM, Inc. iDEN™ is a trademark of Motorola, Inc. GSM™ is a trademark of GSM Association. ANSI® is a registered trademark of the American National Standards Institute
The English version takes precedence over any translated versions.
Documentation uses a three-level revision system. Each element of the revision number signifi es the scope of change as described in the diagram below.
1-0-0
Major Revisions:
The result of a major change to
product function, process or requirements.
The result of a minor change to
product, process or requirements.
The result of typing corrections or
changes in formatting, grammar or wording.
Three-level revision numbers start at 1-0-0 for the fi rst release. The appropriate element of the revision number is incremented by 1 for each subsequent revision, causing any digits to the right to be reset to 0.
For example: If the current revision = 2-1-1 Then the next major revision = 3-0-0 If the current revision = 4-3-1 Then the next minor revision = 4-4-0 If the current revision = 3-2-2 Then the next editorial revision = 3-2-3
Document revision history is provided at the back of the document.
Codan Radio Communications
43 Erie Street, Victoria, BC Canada V8V 1P8 www.codanradio.com LMRsales@codanradio.com
Toll Free Canada and USA: Phone: 1-800-664-4066 Fax: 1-877-750-0004
International: Phone: 250-382-8268 Fax: 250-382-6139
Minor Revisions:
Editorial Revisions:
PRINTED IN CANADA
Document Number:
Revision:
Revision Date:
TG-001 4-0-0 September 2013
Page ii
P25 RADIO SYSTEMS | TRAINING GUIDE
On August 7th, 2012 - Codan Limited (ASX: “CDA”) announced the acquisition of Daniels Electronics Limited, a leading designer, manufacturer and supplier of land mobile radio communications (LMR) solutions in North America. The acquisition of Daniels delivers on Codan’s stated strategy of growing market share and diversifying its radio communications product offering. Codan Limited designs, manufactures and markets a diversifi ed range of high value added electronic products, with three key business divisions; radio communications, metal detection and mining technology.
Codan Radio Communications is a leading international designer and manufacturer of premium communications equipment for High Frequency (HF) and Land Mobile Radio (LMR) applications. We’ve built our reputation for reliability and customer satisfaction over 50 years in radio communications, in some of the toughest conditions on the planet.
For over 50 years Codan has provided customers in North America and internationally with highly reliable Base Stations and Repeaters that are environmentally robust to operate in rugged and extreme temperature conditions where low current consumption (solar powered) is a key requirement.
Codan is a pioneering member of the P25 Digital standard, for radio system interoperability between emergency response governmental organizations, providing enhanced functionality and encryption. Our products operate between 29 - 960 MHz and are available in a variety of Base Station and Repeater confi gurations for two way voice and mobile data applications.
DANIELS ELECTRONICS IS NOW CODAN RADIO COMMUNICATIONS
ABOUT CODAN RADIO COMMUNICATIONS
Our self-servicing customers range from Forestry and National Park services through Police and Fire departments and on to Utility and Transportation groups. Our products have been deployed in every imaginable situation from the Antarctic to Hawaiian mountaintops to Alaska, enabling respondents to Forest Fires, Ground Zero rescue and routine patrols.
Codan is an industry leader in Analog and P25 radio systems design. We offer modular rack-mounted Base Stations and Repeaters capable of operating in Low Band VHF,VHF AM , VHF FM, UHF FM, 700 MHz, 800 MHz, 900 MHz
Pete Lunness is a member of the Applied Science Technologists & Technicians of British Columbia, has a Diploma in Electronics Engineering Technology from Camosun College and a Certifi cate in Adult and Continuing Education from the University of Victoria.
Pete has been at Daniels / Codan since 1996, working in engineering, sales and customer support, and has been instructing technical training courses since 1998.
Many people helped write, compile, research and check the information contained in this document including Steve Burfoot, Peter Chan and Dale Reitsma.
ABOUT THE AUTHOR
Page iii
REFERENCES
Many references were used in the creation of this document. Following is a list of references for P25 information:
Aerofl ex, Inc.
Aerofl ex Incorporated is a multi-faceted high-technology company that designs, develops, manufactures and markets a diverse range of microelectronic and test and measurement products. Aerofl ex is the manufacturer of the IFR 2975 P25 Radio Test Set.
www.P25.com www.aerofl ex.com
APCO International
The Association of Public-Safety Communications Offi cials - International, Inc. is the world’s oldest and largest not-for-profi t professional organization dedicated to the enhancement of public safety communications
www.apcointl.org
DVSI
Digital Voice Systems, Inc., using its proprietary voice compression technology, specializes in low-data-rate, high-quality speech compression products for wireless communications, digital storage, and other applications. DVSI is the manufacturer of the IMBE™ and AMBE+2™ vocoders.
www.dvsinc.com
PTIG
The Project 25 Technology Interest Group (PTIG) is a group composed of public safety professionals and equipment manufacturers with a direct stake in the further development of, and education on, the P25 standards. PTIG’s purpose is to further the design, manufacture, evolution, and effective use of technologies stemming from the P25 standardization process.
www.project25.org
TIA
The Telecommunications Industry Association is the leading U.S. non-profi t trade association serving the communications and information technology industry, with proven strengths in market development, trade shows, domestic and international advocacy, standards development and enabling e-business.
www.tiaonline.org
Page iv
Contents
P25 RADIO SYSTEMS | TRAINING GUIDE
Chapter 1: Introduction To P25 ..............................................1
What is Project 25? ....................................................................................1
P25 Phases ................................................................................................2
Conventional vs. Trunked ..........................................................................3
How does Phase 1 P25 work? ...................................................................4
P25 Radio System Architecture ................................................................. 5
Benefi ts of P25 ...........................................................................................8
Other Digital Standards ............................................................................ 12
Chapter 2: P25 Interface Standards .................................... 15
P25 Standards – General System Model ................................................. 15
RF Sub-System ........................................................................................ 17
Common Air Interface .............................................................................. 17
Inter Sub-System Interface ...................................................................... 18
Telephone Interconnect Interface ............................................................. 19
Network Management Interface ............................................................... 19
Data Host or Network Interface ................................................................ 19
Data Peripheral Interface ......................................................................... 20
Fixed Station Interface ............................................................................. 20
Console Sub-System Interface ................................................................ 21
Chapter 3: P25 Technical Information .................................. 23
Analog to P25 Transition .......................................................................... 23
P25 Frequency Bands ............................................................................. 23
Hexadecimal and Binary Numbering ....................................................... 23
P25 Digital Code Defi nitions ....................................................................24
P25 Voice Message Options .................................................................... 32
P25 Data Applications .............................................................................. 34
Conventional Control Messages .............................................................. 35
P25 Location Services ............................................................................. 36
P25 Encryption ......................................................................................... 40
Analog vs. P25 Digital Coverage ............................................................. 41
P25 Radio System Performance Testing ................................................. 44
P25 vs. Analog Delay Times .................................................................... 46
Page v
Chapter 4: Anatomy of the Common Air Interface ............... 49
Voice ........................................................................................................49
Data ......................................................................................................... 50
Frame Synchronization and Network Identifi er ........................................ 50
Status Symbols ........................................................................................ 51
Header Data Unit ..................................................................................... 51
Voice Code Words ...................................................................................52
Logical Link Data Unit 1 ........................................................................... 53
LInk Control Word .................................................................................... 54
Logical Link Data Unit 2 ........................................................................... 56
Terminator Data Unit ................................................................................ 57
Packet Data Unit ...................................................................................... 58
Data Header and Data Block Formats ..................................................... 59
Other Data Formats ................................................................................. 62
Chapter 5: Conventional Fixed Station Interface ................. 63
Introduction .............................................................................................. 63
Analog Fixed Station Interface ................................................................. 65
Digital Fixed Station Interface .................................................................. 68
Chapter 6: P25 Trunking ...................................................... 71
Introduction to P25 Trunking .................................................................... 71
Implicit / Explicit ....................................................................................... 72
Registration .............................................................................................. 73
Addressing ............................................................................................... 74
Control Channel Messages ...................................................................... 76
Inbound Signaling Packet Access via Slotted ALOHA ............................. 76
Trunking System Operation ..................................................................... 77
Traffi c Channel Ownership .......................................................................78
Encryption ................................................................................................ 79
Data Packet Structures for Single and Multi Block Messages ................. 79
Chapter 7: P25 Phase 2 ....................................................... 85
Introduction .............................................................................................. 85
TDMA vs FDMA Radio Access Technologies ........................................... 86
P25 Phase 2 Trunking System Operation ................................................ 88
Phase 2 TDMA Common Air Interface Layers ......................................... 91
Benefi ts of P25 Phase 2 ..........................................................................96
Chapter 8: IMBE™ and AMBE+2™ Vocoders ..................... 97
Chapter 9: P25 Glossary of Terms ....................................... 99
Page vi
P25 RADIO SYSTEMS | TRAINING GUIDE
CHAPTER 1: INTRODUCTION TO P25
This document is written with the intention of supplying the reader with a simple, concise and informative description of Project 25. The document assumes the reader is familiar with conventional Two-Way Radio Communications systems. The naming and numbering conventions used in this document are those used in the TIA documents. Some manufacturers use different naming and numbering conventions. Project 25 is a standards initiative, to be amended, revised, and added to as the users identify issues, and as experience is gained.
WHAT IS PROJECT 25?
Project 25 (P25) is a set of standards produced through the joint efforts of the Association of Public Safety Communications Offi cials International (APCO), the National Association of State Telecommunications Directors (NASTD), selected Federal Agencies and the National Communications System (NCS), and standardized under the Telecommunications Industry Association (TIA). P25 is an open architecture, user driven suite of system standards that defi ne digital radio communications system architectures capable of serving the needs of Public Safety and Government organizations. The P25 suite of standards involves digital Land Mobile Radio (LMR) services for local, state/provincial and national (federal) public safety organizations and agencies. P25 open system standards defi ne the interfaces, operation and capabilities of any P25 compliant radio system. A P25 radio is any radio that conforms to the P25 standard in the way it functions or operates. P25 compliant radios can communicate in analog mode with legacy radios and in either digital or analog mode with other P25 radios. The P25 standard exists in the public domain, allowing any manufacturer to produce a P25 compatible radio product.
Chapter 1: Introduction To P25 Page 1
P25 LMR equipment is authorized or licensed in the U.S., Canada and Australia.
in the U.S. under the National Telecommunications and Information Administration (NTIA) or Federal Communications Commission (FCC) rules and regulations.
in Canada under Industry Canada (IC) rules and regulations.
in Australia under the Australian Communications and Media Authority (ACMA) rules and regulations.
Although developed primarily for North American public safety services, P25 technology and products are not limited to public safety alone and have also been selected and deployed in other private system applications, worldwide. The Project 25 users’ process is governed by an eleven-member steering committee made up of nine U.S. federal, state and local government representatives and two co­directors. Project 25 has four main objectives:
• ensure competition in system life cycle procurements through Open Systems Architecture
• allow effective, effi cient and reliable intra-agency and inter-agency communications
• provide enhanced functionality and capabilities with a focus on public safety needs
• improve radio spectrum effi ciency
TIA (Telecommunications Industry Association) is a national trade organization of manufacturers and suppliers of telecommunications equipment and services. It has substantial experience in the technical aspects of radio communications and in the formulation of standards with reference thereto. TIA is accredited by the American National Standards Institute (ANSI®) as a Standards Developing Organization.
P25 PHASES
P25 compliant technology was deployed in two phases.
Phase 1
Phase 1 FDMA radio systems operate in 12.5 KHz analog, digital or mixed mode. Phase 1 radios use Continuous 4 level FM (C4FM) non-linear modulation for digital transmissions. Phase 1 P25 compliant systems are backward compatible and interoperable with legacy systems, across system boundaries, and regardless of system infrastructure. In addition, the P25 suite of standards provide an open interface to the RF Sub-System to facilitate interlinking of different vendors’ systems.
Chapter 1: Introduction To P25Page 2
P25 RADIO SYSTEMS | TRAINING GUIDE
Phase 2
The P25 Phase 2 Standards are based on a two-slot TDMA channel access method within 12.5 kHz channel bandwidth and is used for P25 trunking systems. P25 Phase 2 two-slot TDMA trunking is an addition to the P25 Standard and does not replace P25 Phase 1 FDMA. The P25 two-slot TDMA for Phase 2 doubles the spectrum effi ciency of Phase 1 (12.5 kHz).
The P25 Phase 2 TDMA CAI uses two different modulation schemes for over-the-air transmission of the 12 kbps data stream, Harmonized Continuous Phase Modulation (H-CPM), is a common constant­envelope non-linear modulation and is transmitted by the subscriber equipment. Harmonized Differential Quadrature Phase Shift Keyed modulation (H-DQPSK), is a non-coherent modulation scheme and is transmitted by the fi xed site equipment.
A P25 Phase 2 FDMA solution was fi nalized (CQPSK), but never widely used.
The majority of this guide primarily deals with P25 Phase 1. More detailed information about P25 Phase 2 can be found in Chapter 7.
CONVENTIONAL VS. TRUNKED
In general, radio systems can be separated into conventional and trunked systems. A conventional system is characterized by relatively simple geographically fi xed infrastructure (such as a repeater network) that serves to repeat radio calls from one frequency to another. A trunked system is characterized by a controller in the infrastructure which assigns calls to specifi c channels. P25 supports both trunked and conventional radio systems. While this document deals primarily with conventional radio systems, more detailed information about P25 trunking can be found in Chapter 6.
Chapter 1: Introduction To P25 Page 3
HOW DOES PHASE 1 P25 WORK?
Phase 1 P25 radios operate in a similar manner to conventional analog FM radios. P25 radios will operate in conventional analog mode, making them backwards compatible with existing analog radio systems. When the P25 radio operates in digital mode, the carrier is moved to four specifi c frequency offsets that represent four different two-bit combinations. This is a modifi ed 4 level FSK used in analog radio systems. In analog mode, the P25 radio will operate exactly the same as conventional analog systems, with the capability for CTCSS, DCS, pre-emphasis and de-emphasis, wideband or narrowband operation and other standard analog features.
In P25 digital mode, the P25 transmitter will convert all analog audio to packets of digital information by using an IMBE™ vocoder, then de-vocode the digital information back to analog audio in the receiver. Error correction coding is added to the digital voice information as well as other digital information. Analog CTCSS and DCS are replaced by digital NAC codes (as well as TGID, Source and Destination codes for selective calling). Encryption information can be added to protect the voice information, and other digital information can also be transmitted such as a user defi ned low speed data word or an emergency bit.
P25 Radio
System
Digital
Mode
Conventional Trunked
Voice
Message
Secure
(Encrypted)
Routine
Group Call
Figure 1-1: P25 Radio System Operation
Clear
(Not Encrypted)
Emergency Group Call
Data
Packet
Confirmed Unconfirmed
Individual
(Unit to Unit)
Call
Unit to PSTN
(Trunked)
Narrowband
CTCSS DCS Carrier
TSBK
Call
Analog
Mode
Wideband
Announcement
Group Call
(Trunked)
Figure 1-1 shows the different operational modes of P25 Radio Systems in digital and analog modes.
P25 systems use the Common Air Interface (CAI). This interface standard specifi es the type and content of signals transmitted by P25 compliant radios. A P25 radio using the CAI should be able to communicate with any other P25 radio using the CAI, regardless of manufacturer.
Phase P25 1 radios are designed for 12.5 kHz channel bandwidths. Phase 1 P25 radios must also be able to operate in analog mode on 25 kHz or 12.5 kHz channels. This backward compatibility allows P25 users to gradually transition to digital while continuing to use analog equipment.
In Phase 2, P25 radios will use a 12.5 kHz channel bandwidth but will be divided into two time slots, effectively giving 6.25 kHz of bandwidth per voice channel. Phase 2 radios must also be able to operate in Phase 1 mode for backwards compatability with Phase 1 radio systems.
Chapter 1: Introduction To P25Page 4
P25 RADIO SYSTEMS | TRAINING GUIDE
P25 secure transmissions may be enabled by digital encryption. The P25 standards specify the use of the Advanced Encryption Standard (AES) algorithm, Data Encryption Standard (DES-OFB) algorithm, and other encryption algorithms. There are additional standards and specifi cations for over-the-air rekeying (OTAR) features. OTAR allows subscriber encryption key management through a radio network.
Phase 1 P25 channels that carry voice or data operate at 9600 bits per second (bps). These voice or data channels are protected by forward error correction, which compensates for poor RF conditions and improves useable range. Phase 1 P25 supports data transmission, either piggybacked with voice (low speed data), or in several other modes up to the full traffi c channel rate of 9600 bps.
P25 RADIO SYSTEM ARCHITECTURE
Micro­phone
A to D
Speech
Coder
IMBE™ Vocoder
Channel
Coder Modulator Tx Amplifier
IDs &
FEP
Baseband
filters
V.C.O.
Repeat Path
Speaker
D to A
IMBE™ Vocoder
Speech
Decoder
IDs &
EC
Channel Decoder
Filters &
Equalizer
Figure 1-2: P25 Radio System Architecture
Figure 1-2 represents a basic digital transceiver.
C4FM
C4FM
Demod-
ulator
Duplexer
-
Rx
Amplifier
Chapter 1: Introduction To P25 Page 5
The P25 Radio System Architecture can be broken down into three main areas.
A to D / D to A and Speech Coding / Decoding
An Analog to Digital conversion is performed on the audio before speech coding and a Digital to Analog conversion is performed to create audio after the speech decoding. P25 uses a specifi c method of digitized voice (speech coding) called Improved Multi-Band Excitation (IMBE™). The IMBE™ voice encoder-decoder (vocoder) listens to a sample of the audio input and only transmits certain characteristics that represent the sound. The receiver uses these basic characteristics to produce a synthetic equivalent of the input sound. IMBE™ is heavily optimized for human speech. Older IMBE™ vocoders didn’t always do well in reproducing other types of sounds, including dual-tone multifrequency (DTMF) tones and continuous test tones. Since 2009, the enhanced IMBE™ vocoder works signifi cantly better with DTMF and continuous tones.
The IMBE™ vocoder samples the microphone input producing 88 bits of encoded speech every 20 milliseconds. Therefore, the vocoder produces speech characteristics at a rate of 4400 bits per second.
Channel Coding / Decoding
Channel Coding is the method in which digital RF systems utilize forward error protection / error correction techniques to ensure that the data (voice or control) arrives and is recovered correctly. The forward error protection / error correction are designed to improve the system performance by overcoming channel impairments such as noise, fading and interference. Channel Coding can also include the addition of all overhead data that is included with the voice information, including NAC, TGID, SID, MFID, KID, ALGID and many others.
P25 error protection / correction channel codes include; interleaving and linear block codes such as Hamming codes, Golay codes, Reed-Solomon codes, Primitive BCH, and shortened cyclic codes.
Modulating / Demodulating and Filtering
In Phase 1, a 12.5 KHz channel is used to transmit C4FM modulated digital information. C4FM modulation is a type of differential Quadrature Phase Shift Keying (QPSK) where each symbol is shifted in phase by 45 degrees from the previous symbol. Although the phase (frequency) is modulated for C4FM, the amplitude of the carrier is constant, generating a constant envelope frequency modulated waveform.
Chapter 1: Introduction To P25Page 6
P25 RADIO SYSTEMS | TRAINING GUIDE
The modulation sends 4800 symbols/sec with each symbol conveying 2 bits of information. The mapping between symbols and bits is shown below:
Information Bits Symbol C4FM Deviation (Phase 1)
01 +3 +1.8kHz
00 +1 +0.6kHz
10 -1 -0.6kHz
11 -3 -1.8kHz
The C4FM modulator is comprised of a Nyquist Raised Cosine Filter, a shaping fi lter, and an FM modulator.
C4FM Modulator
Digital
Input
Figure 1-3: C4FM Modulator
Nyquist Raised
Cosine Filter
Shaping
Filter
FM
Modulator
C4FM
Output
Chapter 1: Introduction To P25 Page 7
CONSTANT ENVELOPE
C4FM DEMODULATOR
SPECTRUM
12.5 kHz Channel
TIME
C4FM
Figure 1-4: C4FM Demodulator
Receiver
Front
End
Digital IF
DSP
The C4FM demodulator receives a signal from the P25 C4FM modulator or analog FM modulator. The frequency modulation detector in the fi rst stage of the demodulator allows a single, Phase 1 demodulator to receive C4FM or analog FM. The benefi t of this is that when migrating to a P25 Phase 1 system, the receiver is capable of detecting and receiving both analog and P25 digital signals.
BENEFITS OF P25
P25 has many various benefi ts in performance, effi ciency, capabilities and quality. Key P25 technology benefi ts include:
Interoperability
Radio equipment that is compatible with P25 standards will allow users from different agencies or areas to communicate directly with each other. This will allow agencies on the federal state/provincial or local level (or any other agency) to communicate more effectively with each other when required (emergencies, law enforcement, etc.)
The APCO Project 25 Interface Committee (APIC) has formed the Compliance Assessment Process and Procedures Task Group (CAPPTG) to ensure that P25 equipment and systems comply with P25 standards for interoperability, conformance, and performance regardless of the manufacturer and in accordance with the User Needs Statement of Requirements.
Chapter 1: Introduction To P25Page 8
P25 RADIO SYSTEMS | TRAINING GUIDE
A
Multiple Vendors
The P25 open standard will allow competing products from multiple vendors to be interoperable. This will allow customers of the P25 product to benefi t from multiple manufacturing sources (decreased costs, open bidding, non-proprietary systems).
Backwards Compatibility
A basic requirement for Phase 1 P25 digital radio equipment is backward compatibility with standard analog FM radios. This supports an orderly migration into mixed analog and digital systems, enabling users to gradually trade out radios and infrastructure equipment. By selecting products and systems that comply with P25 standards, agencies are assured that their investment in the latest technology has a clear migration path for the future.
Analog Mode
nalog Portable
Figure 1-5: P25 Backwards Compatibility
P25 Portable P25 Mobile
Analog or Digital
Mode
Analog or Digital
Mode
P25 Repeater
Analog Mode
Analog Base
P25 radios operate in analog mode to older analog only radios, and either analog or digital mode to other P25 radios.
Phase 2 P25 radio systems are backwards compatible with Phase 1 P25 equipment.
Encryption Capability
The P25 standard includes a requirement for protecting digital communications (voice and data) with encryption capability. The encryption used in P25 is optional, allowing the user to select either clear (un-encrypted) or secure (encrypted) digital communication methods. The encryption keys also have the option of being re-keyed by digital data over a radio network. This is referred to as Over The Air Re­keying (OTAR). This capability allows the radio systems manager to remotely change encryption keys.
Chapter 1: Introduction To P25 Page 9
Spectrum Effi ciency
P25 maximizes spectrum effi ciency by narrowing bandwidths.
FM C4FM
H-CPM and
H-DQPSK
Analog Systems
25 KHz
P25 Phase 1
12.5 KHz
P25 Phase 2 (TDMA)
12.5 KHz (2 time slots)
6.25 KHz (effective bandwidth)
Figure 1-6: P25 Spectrum Effi ciency
The RF spectrum is a fi nite resource used by every country in the world. Spectrum effi ciency frees up more channels for radio system use.
Chapter 1: Introduction To P25Page 10
P25 RADIO SYSTEMS | TRAINING GUIDE
Improved Audio Quality
With 2800 bits per second of the total 9600 bits per second channel capacity allocated to error correction, Phase 1 P25 digital signals have improved voice quality over standard analog signals, especially at low or noisy RF carrier levels. The IMBE™ voice coder converts voice information into digital data and then the data is protected using error correction codes. The error correction is able to correct for small errors in the received signal. Since the audio is digitally encoded, the background noise typically present in analog systems is also removed.
2800 bits/s error
Voice
correction
2400 bits/s
signaling
4400 bits/s voice
20 ms of speech =
88 bits of
information to be transmitted over the radio link
Total 9600 bits/s
Signaling
1 25 kHz Channel 2 x 12.5 kHz Channels
Figure 1-7: Analog to P25 Channel Comparison
Enhanced Functionality
Phase 1 P25 radio systems use 2400 bits per second for signaling and control functions. The signaling capabilities include selective calling (Source and Destination ID), talk groups (TGID), network (repeater) access codes (NAC) and emergency fl ags all as standard P25 digital features.
Other P25 signaling includes; Manufacturers identifi cation codes (MFID) which uniquely identifi es different manufacturers to customize radio capabilities, Low Speed Data for user applications, encryption keys and algorithms for secure transmission and many other standard signaling formats.
Chapter 1: Introduction To P25 Page 11
OTHER DIGITAL STANDARDS
Although P25 is the focus of this document, it is important to understand that there are many different digital radio standards in use around the world. P25 has primarily been adopted for use in North America, while another leading digital standard, TETRA (Terrestrial Trunked Radio) has primarily been adopted for use in Europe.
While P25 and TETRA appear to be the two leading digital Land Mobile Radio standards in the world today, there are other digital, spectrally-effi cient radio systems that have been submitted to the International Telecommunication Union’s Radiocommunication Sector’s (ITU-R) Study Group 8 and its Working Party 8A.
ITU-R is charged with determining the technical characteristics and operational procedures for a growing range of wireless services. The Radiocommunication Sector also plays a vital role in the management of the radio-frequency spectrum. Study Group 8 and its Working Party 8A is responsible for studies related to the land mobile service, excluding cellular, and to the amateur and amateur-satellite services.
Digital radio systems can operate using different channel access methods such as FDMA (Frequency Division Multiple Access), TDMA (Time Division Multiple Access), or other methods (FHMA - Frequency Hopping Multiple Access).
Project 25, Tetrapol, and EDACS® (Enhanced Digital Access Communications System) Aegis™ are three different FDMA systems. TETRA, DIMRS (Digital Integrated Mobile Radio System), and IDRA (Integrated Digital Radio) are three different TDMA systems.
Tetrapol
France submitted Tetrapol to ITU-R Working Party 8A. It uses a constant-envelope modulation technique that fi ts within a 10 kHz channel mask. Systems are in use in a number of countries in Europe and around the world. EADS is the principal manufacturer of this equipment.
EDACS® Aegis™
L.M. Ericsson AB (with support from the Swedish Administration) submitted EDACS® Aegis™ to ITU-R Working Party 8A. It uses a constant-envelope modulation technique and has four different selectable levels of deviation and fi ltering that can result in the signal fi tting within 25 kHz and 12.5 kHz channel masks. Systems are in use in a number of countries around the world. M/A-COM, Inc. is the principal manufacturer of this equipment.
Chapter 1: Introduction To P25Page 12
P25 RADIO SYSTEMS | TRAINING GUIDE
TETRA
A number of European countries submitted TETRA to ITU-R Working Party 8A on behalf of ETSI (the European Telecommunication Standards Institute). TETRA’s primary mode uses /4DQPSK modulation that requires a linear or linearized amplifi er and fi ts four-slot TDMA within a 25 kHz channel mask.
DIMRS
Canada submitted DIMRS to ITU-R Working Party 8A. It is a six-slot TDMA system using 16QAM modulation that fi ts within a 25 kHz channel mask. It is designed primarily for public systems and is in use in a number of countries around the world. Motorola Inc. is the principal manufacturer of this equipment, under the name IDEN™.
IDRA
Japan submitted IDRA to ITU-R Working Party 8A. It also is a six-slot TDMA system using 16QAM (16 point Quadrature Amplitude Modulation) that fi t within a 25 kHz channel mask. A major difference from DIMRS is the use of a different vocoder.
FHMA
Israel submitted FHMA to ITU-R Working Party 8A. The system primarily makes use of frequency hopping and sectorized base station antennas to gain spectrum effi ciency. The signals are error protected and when a radio is at a sector boundary, due to different frequency hop patterns between sectors, interference to and from nearby radios in the other sector is minimized.
Although the other digital standards seem to work well for their original intentions, APCO felt that these standards would not meet all of the requirements for a public safety agency within North America. P25 standards were designed primarily for the public safety user, with range and performance given very high priority. Also, unique fl exibility has been designed into the standards to enhance interoperability, privacy, gradual phase-in of new technologies, and the reliable transmission of voice and data.
Chapter 1: Introduction To P25 Page 13
This Page Intentionally Left Blank
Chapter 1: Introduction To P25Page 14
P25 RADIO SYSTEMS | TRAINING GUIDE
CHAPTER 2: P25 INTERFACE STANDARDS
P25 STANDARDS – GENERAL SYSTEM MODEL
This section will introduce the reader to the P25 General System Model and the P25 interface standards that are integral to the P25 radio systems.
There are currently more than forty technical documents in the set of P25 standards. The Telecommunications Industry Association (TIA) developed these standards through well defi ned user input. The P25 users continue to enlarge a Statement of Requirements while the industry develops the standards for those requirements and the Project 25 Steering Committee verifi es their adherence to the users’ needs. The P25 documents have also been approved by the American National Standards Institute (ANSI®) as ANSI® standards. This is the ultimate recognition in the United States of the utility and support of a technology as a standard.
The individual documents describe component interfaces needed to build systems. Depending upon the type of system the user needs, individual documents are available that detail how standardized elements can make up a standardized system. These systems can be trunked or conventional, they can be voice only, data only or voice and data, and they can be clear or encrypted.
The P25 standards are contained in the TIA-102 suite of documents. Copies of the standards documents may be purchased through Global Engineering Documents by commercial entities. Public agency users can get a copy of all of the documents on a CD-ROM from the National Communications System (NCS). NCS is the standards arm of the U.S. Department of Defense. Copies may also be obtained from the Department of Justice, National Institute of Justice (NIJ) Standards and Technology Group. NIJ is a primary advocate and supporter of the Project 25 process.
Chapter 2: P25 Interface Standards Page 15
P25 defi nes six interfaces to an RF Sub-System (RFSS), one peripheral interface, and one over-the air interface. These are shown in Figure 2-1 the P25 General System Model. Within the RFSS, all equipment is unique to a single manufacturer. An example of a closed interface within the RFSS is the interface between a trunking controller and its base station. Each of the open interfaces shown in Figure 2-1 is defi ned in a TIA document.
The Inter Sub-System Interface (ISSI), Network Management Interface, Fixed Station Interface, and Console Interface are being developed. It is TIA’s intention to standardize these equipment sub-system interfaces whenever practical. The ISSI, console, and fi xed station interfaces are based on the use of Internet Protocol (IP).
The general system model of a P25 compliant digital radio system defi nes the system elements plus intra-system and inter-system interfaces and naming conventions of these elements and interfaces.
REPEATER
U
m
SUBSCRIBER
RADIO
P25 GENERAL
SYSTEM MODEL
DATA
PERIPHERAL
DATA
PERIPHERAL
DATA
PERIPHERAL
U
CAI =
m
U
m
U
m
U
m
U
m2
CONVENTIONAL
FIXED STATION
Fixed Station
Interface
CONVENTIONAL
OR TRUNKED
FIXED STATION
TRUNKED
FIXED STATION
FSI =
U
m
A
A
A
SUBSCRIBER
RADIO
U
m
Common Air
Interface
SUBSCRIBER
RADIO
U
m
SUBSCRIBER
RADIO
Um = Phase 1 FDMA CAI
m2
= Phase 2 TDMA CAI
U
CONVENTIONAL
SUB-SYSTEM
E
f
E
f
SUB-SYSTEM
(RFSS)
TRUNKED CONSOLE
SUB-SYSTEM
CONSOLE
E
c
CSSI = Console Sub-System Interface
E
t
PSTN
RF
G
Sub-System
Interface
G
ISSI =
Inter
E
n
E
d
OR NETWORK
NETWORK
MANAGEMENT
DATA HOST
OTHER
RF
SUB-SYSTEMS
Figure 2-1: P25 General System Model
Chapter 2: P25 Interface StandardsPage 16
P25 RADIO SYSTEMS | TRAINING GUIDE
The P25 Interface Standards as shown on the General System Model are as follows:
RF Sub-System (RFSS) Core Infrastructure Common Air Interface (Um) Radio to radio protocol Inter Sub-System Interface (ISSIg) RFSS to all other system interconnections (In progress) Telephone Interconnect Interface (Et) PSTN to RFSS defi nition Network Management Interface (En) Network to RFSS defi nition (In progress) Data Host or Network Interface (Ed) Computer aided dispatch to RFSS defi nition Data Peripheral Interface (A) Radio to Data Peripheral defi nition Fixed Station Interface (Ef) Base station to RFSS / Console Sub-System defi nition (in progress) Console Sub-System Interface (Ec) Console to RFSS defi nition (In progress)
RF SUB-SYSTEM
The P25 interfaces bound the RF Sub-System (RFSS) infrastructure. The RF Sub-System can be made from any collection of site equipment (single station/site or multiple station/site), whose only requirement is that the equipment supports the Common Air Interface, and contains all necessary control logic to support the open intersystem interfaces and call processing. The RF Sub-Systems are the building blocks for wide-area system construction and will connect with any other confi guration of equipment or RF Sub-Systems.
COMMON AIR INTERFACE
The Common Air Interface (Um) or CAI defi nes a standard (or reference point) at which communications between P25 radios can take place. The CAI is the core element of the P25 standard that assures the ability of one company’s P25 digital radio to communicate with another company’s P25 digital radio. Communications between P25 radios are done at a gross bit rate of 9.6 kbps and with FDMA channel access. Several processes take place to convert information for transmission. The Common Air Interface uses an IMBE™ voice coder (vocoder) to convert (compress) speech to a digital format for communication. This voice information is then protected with error correction coding to provide protection over the channel. The voice information and error correction is then transmitted with additional encryption information, unit identifi cation, and low speed data to fully utilize the 9.6 kbps of channel capacity in the Common Air Interface.
A breakdown of the information contained in the Common Air Interface can be found in Chapter 4: Anatomy of the Common Air Interface. Chapter 8 contains some detailed information on the operation and theory of the IMBE™ Vocoder.
Chapter 2: P25 Interface Standards Page 17
INTER SUB-SYSTEM INTERFACE
The Inter Sub-System Interface (G) is under development.
The Inter Sub-System Interface (G) or ISSI permits multiple RF Sub-Systems to be interconnected together into wide-area networks. The ISSI defi nes a multi-channel digital interface supporting standard protocols to enable interoperability utilizing mobility management and wide-area service support functionality. The interface is designed to give system designers the fl exibility to combine any number of RF Sub-Systems of any size. The Inter Sub-System Interface also provides a common meeting place for RF Sub-Systems of different technologies (TDMA, FDMA, micro-cell) and different RF bands. This interface is optional, and need only be supported when intercommunication amongst and across RFSS’s of Land Mobile Radio systems is desired.
Although a P25 subscriber radio may only operate freely among systems with the standard P25 common air interface, the P25 ISSI has the potential to connect between different radio or telecommunications networks as long as they also support the ISSI interface.
The ISSI messaging defi nes the basic structures to be shared among all equipped RFSS’s. The ISSI can be supported on any possible networking confi guration, from a simple star confi guration to a full mesh, to an intelligent network. This can consist of private links and network support, or may be public links and network support confi gured as a private network. Any intervening network supporting the information of an ISSI link needs to preserve the ISSI messaging packet, but may intermediately represent the ISSI packet in whatever convenient form (e.g. ATM cell) is available.
The ISSI will support:
• mobility and data management,
• wide area service control,
• service transport,
• end to end protection of signaling information,
• trunking.
• other network interconnection.
Chapter 2: P25 Interface StandardsPage 18
P25 RADIO SYSTEMS | TRAINING GUIDE
TELEPHONE INTERCONNECT INTERFACE
P25 requires an open interface to telephone networks. The Telephone Interconnect Interface (Et) supports both analog and ISDN telephone interfaces, providing for selective use of proven standard telephone interfaces currently in use.
The Telephone Interconnect Interface defi nes a 2-wire loop start and a 2-wire ground start connection between the RF Sub-System and the PSTN or a PABX. In addition, other optional interfaces may be provided. The Telephone Interface deals only with voice service because it has been assumed that circuit connected data services would access a telephone network via a modem and connect to a data port on the radio system.
NETWORK MANAGEMENT INTERFACE
The Network Management Interface (En) is under development.
The Network Management Interface defi nes a network management interface to all RF Sub- Systems. According to a single selected network management scheme within any RF Sub-System, all fi ve classical elements of network management must be supported. It is expected that a network management scheme will be selected that will bring with it the ability to manage RF Sub-Systems with available network management system equipment. In addition, an existing network management system, including computer and telecommunications equipment, may well be able to encompass P25 radio systems.
DATA HOST OR NETWORK INTERFACE
The Data Host or Network Interface (Ed) defi nes four different types of data connectivity. These include a native open interface for connecting host computers, as well as the requirement to support three different types of existing computer network interfacing (TCP/IP, SNA and X.25).
Chapter 2: P25 Interface Standards Page 19
DATA PERIPHERAL INTERFACE
The Data Peripheral Interface (A) defi nes protocols by which mobile and portable subscriber units will support a port through which laptops, terminals, or subscriber unit peripherals may be connected. It is required that the supported open interface protocols are passed transparently into X.25, SNA, or TCP/ IP computer networks at another open interface on the fi xed equipment side. Transparency is listed as a requirement, and it is expected that application layer standards emerge for the connection of various peripheral devices.
FIXED STATION INTERFACE
The Fixed Station Interface provides for communication between a Fixed Station (FS) and either an RF Sub-System (RFSS) or a Console Sub-System.
The Fixed Station Interface defi nes a set of mandatory messages, supporting analog voice, digital voice (clear or encrypted), and data (under development). These messages will be of a standard format passed over the interface. Manufacturers can enhance this functionality using manufacturer specifi c messages.
The Conventional Fixed Station Interface (CFSI), which is a specialization of the Fixed Station Interface, has been defi ned. A breakdown of the information contained in the CFSI can be found in Chapter 5: Conventional Fixed Station Interface.
The CFSI defi nes both an Analog Fixed Station Interface (AFSI) and a Digital Fixed Station Interface (DFSI). Either one of these interfaces can be used to connect to a fi xed station operating in analog, digital or mixed mode.
The AFSI confi guration is 2 or 4-wire audio with E&M or Tone Remote Control.
The DFSI confi guration is an IP based interface. The physical interface is an Ethernet 100 Base-T with an RJ45 connector. The DFSI utilizes UDP for control information and RTP on UDP for voice information. Digital voice information is IMBE™ and analog voice information is PCM audio.
Chapter 2: P25 Interface StandardsPage 20
P25 RADIO SYSTEMS | TRAINING GUIDE
CONSOLE SUB-SYSTEM INTERFACE
The Console Sub-System Interface (Ec) is under development.
The Console Sub-System Interface (CSSI) defi nes a multi-channel digital interface. This interface is capable of supporting standard protocols to enable interoperable support functionality. The CSSI defi nes basic messaging structures to interface a console sub-system to an RFSS.
The CSSI can be supported using a variety of networking technologies and topologies, from a simple star confi guration to an intelligent backbone network. The networks may be private, or public networks confi gured as private networks.
The physical interface is an Ethernet 100 Base-T with an RJ45 connector. The CSSI will support Ethernet 10 Base-T and 1000 Base-T as an optional physical interface. The CSSI will optionally support auto-sensing. Other interfaces may be installed as a manufacturer’s option.
As a note, a console sub-system can connect directly to a fi xed station and support one or more Fixed Station Interfaces. Manufacturers may also optionally support a subset of the Data Host or Network Interface in the Console.
The Console Sub-System Interface is a sub-set of the fi xed station interface. Any device connected at these points will arbitrate to determine the type of connection.
Chapter 2: P25 Interface Standards Page 21
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Chapter 2: P25 Interface StandardsPage 22
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