SIST EN 301 841-1 V1.2.1:2003

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Electromagnetic compatibility and Radio spectrum Matters (ERM); VHF air-ground Digital Link (VDL) Mode 2; Technical characteristics and methods of measurement for ground-based equipment; Part 1: Physical layer and MAC sub-layer35.100.10Physical layer33.100.01Elektromagnetna združljivost na splošnoElectromagnetic compatibility in general33.060.99Druga oprema za radijske komunikacijeOther equipment for radiocommunicationsICS:Ta slovenski standard je istoveten z:EN 301 841-1 Version 1.2.1SIST EN 301 841-1 V1.2.1:2003en01-december-2003SIST EN 301 841-1 V1.2.1:2003SLOVENSKI
STANDARD
ETSI ETSI EN 301 841-1 V1.2.1 (2003-08) 2
Reference REN/ERM-TG25-022-1 Keywords aeronautical, radio, testing ETSI 650 Route des Lucioles F-06921 Sophia Antipolis Cedex - FRANCE
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© European Telecommunications Standards Institute 2003. All rights reserved.
DECTTM, PLUGTESTSTM and UMTSTM are Trade Marks of ETSI registered for the benefit of its Members. TIPHONTM and the TIPHON logo are Trade Marks currently being registered by ETSI for the benefit of its Members. 3GPPTM is a Trade Mark of ETSI registered for the benefit of its Members and of the 3GPP Organizational Partners. SIST EN 301 841-1 V1.2.1:2003

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Contents Intellectual Property Rights.6 Foreword.6 Introduction.6 1 Scope.7 2 References.7 3 Definitions and abbreviations.8 3.1 Definitions.8 3.1.1 Basic reference model definitions.8 3.1.2 Service conventions definitions.8 3.1.3 General definitions.8 3.2 Abbreviations.9 4 General architecture of VDL Mode 2.11 5 Physical layer protocols and services functional specifications.12 5.1 Overview.12 5.1.1 Functions.12 5.1.2 Data reception by the receiver.13 5.1.3 Data transmission.13 5.2 Transmission procedure.14 5.3 Modulation scheme.15 5.4 Training sequence.15 5.4.1 RF power rise time definition.15 5.5 Physical layer Service Access Point.16 5.6 Tuning range and channel increments.16 6 VDL MODE 2 equipment requirements.16 6.1 Receiver requirements.16 6.1.1 Sensitivity.16 6.1.2 First Adjacent Channel Rejection.16 6.1.3 Rejection of signals within the VHF Aeronautical band.17 6.1.4 Rejection of signals outside the VHF Aeronautical band.17 6.1.5 Desired signal dynamic range.17 6.1.6 Symbol rate capture range.17 6.1.7 Frequency capture range.18 6.1.8 Co-channel interference.18 6.1.9 Conducted spurious emission.18 6.1.10 In-band Intermodulation.18 6.1.11 Cabinet radiation.18 6.2 Transmitter requirements.19 6.2.1 Protection of the transmitter.19 6.2.2 Manufacturer's declared output power.19 6.2.3 RF power rise time.19 6.2.4 RF power release time.19 6.2.5 Modulation rate.19 6.2.6 Symbol constellation error.20 6.2.7 Conducted Spurious emissions.20 6.2.8 Adjacent channel power.20 6.2.9 Wide-band noise.20 6.2.10 Frequency Tolerance.20 6.2.11 Cabinet radiation.20 6.2.12 Load VSWR capability.20 6.3 Transceiver timing requirements.21 6.3.1 Receiver to transmitter turn-around time.21 6.3.2 Transmitter to receiver turn-around time.21 SIST EN 301 841-1 V1.2.1:2003

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6.4 MAC sub-layer requirements.21 6.4.1 MAC services.21 6.4.1.1 Multiple Access.21 6.4.1.2 Channel Congestion.21 6.4.2 MAC System Parameters.21 6.4.2.1 Timer TM1 (inter-access delay timer).21 6.4.2.2 Timer TM2 (channel busy timer).21 6.4.2.3 Parameter p (persistence).21 6.4.2.4 Counter M1 (maximum access attempts).21 6.4.3 Description of MAC Layer Procedures.21 6.4.3.1 Channel Sensing.21 6.4.3.2 Access Attempt.21 6.4.3.3 Signal Quality Parameter.22 6.4.4 Services (Part of DLS).22 6.4.4.1 Error Detection.22 6.4.4.2 Station Identification.22 7 General requirements.22 7.1 General.22 7.2 Controls and indicators.22 7.3 Class of emission and modulation characteristics.22 7.4 Warm up.22 8 Test conditions, power sources and ambient temperatures.23 8.1 Test power source.23 8.2 Test channels.23 8.3 General conditions of measurement.23 8.3.1 Receiver test signal arrangement.23 8.3.2 Performance check.23 8.4 Normal and extreme test conditions.24 8.4.1 Normal test conditions.24 8.4.1.1 Normal temperature and humidity.24 8.4.1.2 Normal power sources.24 8.4.1.2.1 Mains voltage and frequency.24 8.4.1.2.2 Other power sources.24 8.4.2 Extreme test conditions.24 8.4.2.1 Extreme temperatures.24 8.4.2.2 Procedure for tests at extreme temperatures.24 8.4.2.2.1 General.24 8.4.2.2.2 High temperature.25 8.4.2.2.3 Low temperature.25 8.4.2.3 Extreme values of test power sources.25 8.4.2.4 Other power sources.25 8.4.2.5 Performance check.25 9 Detailed Test Procedures for the physical layer.25 9.1 Receiver.26 9.1.1 BER test.26 9.1.2 Sensitivity.27 9.1.3 First Adjacent Channel Rejection.28 9.1.4 Rejection of signals within the VHF Aeronautical band.28 9.1.5 Rejection of signals outside the VHF Aeronautical band.29 9.1.6 Desired Signal dynamic range.30 9.1.7 Symbol rate capture range.31 9.1.8 Frequency capture range.31 9.1.9 Co-channel interference.32 9.1.10 Conducted spurious emission.32 9.1.11 In-band Intermodulation.33 9.2 Transmitter.34 9.2.1 Manufacturer's declared output power.34 9.2.2 RF power rise time.34 9.2.3 RF power release time.36 9.2.4 Symbol Constellation Error.37 SIST EN 301 841-1 V1.2.1:2003

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9.2.5 Spurious emissions.37 9.2.6 Adjacent channel power.38 9.2.6.1 Method of measurement for the first adjacent channel.38 9.2.6.2 Method of measurement for the second adjacent channel.39 9.2.6.3 Method of measurement for the fourth adjacent channel.39 9.2.7 Wideband noise.41 9.2.8 Protection of the transmitter.42 9.2.8.1 Method of measurement.42 9.2.8.2 Requirement.42 9.2.9 Frequency Error.42 9.2.9.1 Definition.42 9.2.9.2 Method of measurement.42 9.2.9.3 Limits.42 9.2.10 Load VSWR capability.42 9.3 Physical layer, system parameters.43 9.3.1 Receiver to Transmitter turn-around time.43 9.3.2 Transmitter to Receiver turn-around time.44 9.4 MAC sub-layer.46 9.4.1 MAC services.46 9.4.1.1 Multiple Access.46 9.4.1.2 Channel Congestion.46 9.4.2 MAC System Parameters.47 9.4.2.1 Timer TM1 (inter-access delay timer).47 9.4.2.2 Timer TM2 (channel busy timer).47 9.4.2.3 Parameter p (persistence).48 9.4.2.4 Counter M1 (maximum access attempts).49 9.4.3 Description of MAC Layer Procedures.50 9.4.3.1 Channel Sensing.50 9.4.3.2 Access Attempt.50 9.4.3.3 Signal Quality Parameter.50 9.4.4 Services (Part of DLS).51 9.4.4.1 Error Detection.51 9.4.4.2 Station Identification.51 Annex A (informative): Bibliography.53 History.54
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Intellectual Property Rights IPRs essential or potentially essential to the present document may have been declared to ETSI. The information pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web server (http://webapp.etsi.org/IPR/home.asp). Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web server) which are, or may be, or may become, essential to the present document. Foreword This European Standard (Telecommunications series) has been produced by ETSI Technical Committee Electromagnetic compatibility and Radio spectrum Matters (ERM). The present document is part 1 of a multi-part deliverable covering VHF air-ground Digital Link (VDL) Mode 2; Technical characteristics and methods of measurement for ground-based equipment, as identified below: Part 1: "Physical layer and MAC sub-layer"; Part 2: "Upper layers".
National transposition dates Date of adoption of this EN: 15 August 2003 Date of latest announcement of this EN (doa): 30 November 2003 Date of latest publication of new National Standard or endorsement of this EN (dop/e):
31 May 2004 Date of withdrawal of any conflicting National Standard (dow): 31 May 2004
Introduction The present document states the technical specifications for ground-based equipment implementing Very High Frequency (VHF) Digital Link (VDL) Mode 2 air interface, operating in the VHF band (117,975 MHz - 137,000 MHz) with 25 kHz channel spacing. Manufacturers should note that in the future, all or part of the frequency band 108,000 MHz to 117,975 MHz may become available for aeronautical communications. The present document may be used to produce tests for the assessment of the performance of the equipment. The performance of the equipment submitted for type testing should be representative of the performance of the corresponding production model. The present document has been written on the assumption that: - the type test measurements will be performed only once, in an accredited test laboratory, and the measurements accepted by the various authorities in order to grant type approval; - if equipment available on the market is required to be checked it may be tested in accordance with the methods of measurement specified in the present document. SIST EN 301 841-1 V1.2.1:2003

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1 Scope The present document applies to VDL Mode 2 ground-air digital communications using Differential Eight Phase Shift Keying (D8PSK), intended for channel increments of 25 kHz. The VDL Mode 2 system provides data communication exchanges between aircraft and ground-based systems. The scope of the present document is limited to ground-based stations. The VDL Mode 2 system is designed to be a Ground/Air sub-system of the Aeronautical Telecommunication Network (ATN) using the AM(R)S band and it is organized according to the Open Systems Interconnection (OSI) model (defined by ISO). It shall provide reliable subnetwork services to the ATN system. The present document provides functional specifications for ground-based radio equipment intended to be used for ground-air data communications. The present document is derived from the following documents:
• VDL Mode 2 SARPs version 3.0. ICAO Annex 10 Volume III part I [1]. • ED 92a [2]: "MOPS for an Airborne VDL Mode-2 Transceiver Operating in the frequency range 118-136.975 MHz" (2003), which specifies the airborne transceiver. The present document consists of two parts: • the first part provides functional specifications and test procedures for physical layer and MAC sub-layer; • the second part provides functional specifications and test procedures for link and sub-network access layers. 2 References The following documents contain provisions which, through reference in this text, constitute provisions of the present document. • References are either specific (identified by date of publication and/or edition number or version number) or non-specific. • For a specific reference, subsequent revisions do not apply. • For a non-specific reference, the latest version applies. Referenced documents which are not found to be publicly available in the expected location might be found at http://docbox.etsi.org/Reference. [1] Annex 10 to the Convention on International Civil Aviation: "Aeronautical Telecommunications". [2] ED 92a (2003): "MOPS for an Airborne VDL Mode-2 Transceiver Operating in the frequency range 118-136.975 MHz". [3] ISO/IEC 3309: "Information technology - Telecommunications and information exchange between systems - High-level data link control (HDLC) procedures - Frame structure". [4] ISO/IEC 8208: "Information technology - Data communications - X.25 Packet Layer Protocol for Data Terminal Equipment". [5] ISO/IEC 7498-1 (1994): "Information technology - Open Systems Interconnection - Basic Reference Model: The Basic Model". [6] ISO/IEC 10731 (1994): "Information technology - Open Systems Interconnection - Basic Reference Model - Conventions for the definition of OSI services". [7] ETSI EN 300 113-1: "Electromagnetic compatibility and Radio spectrum Matters (ERM); Land mobile service; Radio equipment intended for the transmission of data (and/or speech) using constant or non-constant envelope modulation and having an antenna connector; Part 1: Technical characteristics and methods of measurement". SIST EN 301 841-1 V1.2.1:2003

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[8] International Civil Aviation Organization (ICAO), Doc 9776: "Manual on VHF Digital Link (VDL) Mode 2". 3 Definitions and abbreviations 3.1 Definitions 3.1.1 Basic reference model definitions The present document is based on the concepts developed in the open systems interconnect basic reference model and makes use of the following terms defined in ISO/IEC 7498-1 [5]: • layer • sublayer • entity • service • service access point • service data unit • physical layer • data link layer 3.1.2 Service conventions definitions For the purposes of the present document, the terms and definitions given in ISO/IEC 10731 [6] apply: • service provider • service user • service primitive • request • indication • confirm 3.1.3 General definitions For the purposes of the present document, the following terms and definitions apply: adjacent channel power: amount of the modulated RF signal power transmitted outside of the assigned channel NOTE: Adjacent channel power includes discrete spurious, signal sidebands, and noise density (including phase noise) at the transmitter output. adjacent channel rejection: receiver's ability to demodulate the desired signal and meet the uncorrected BER requirement in the presence of an interfering signal in an adjacent channel NOTE: The ratio (in dB) between the adjacent interfering signal level and the desired signal level necessary to achieve the specified minimum uncorrected BER, is the adjacent channel rejection (ACR) ratio. SIST EN 301 841-1 V1.2.1:2003

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aeronautical mobile service: mobile service between aeronautical stations and aircraft stations, or between aircraft stations, in which survival craft stations may participate average transmitter output power: average power supplied to the antenna transmission line by a transmitter during an interval of time sufficiently long, compared with the lowest frequency encountered in the modulation, taken under normal operating conditions Bit Error Rate (BER): ratio between the number of erroneous bits received and the total number of bits received NOTE: The uncorrected BER represents the BER without the benefit of Forward Error Correction (FEC). Co-Channel Interference (CCI): capability of a receiver to demodulate the desired signal and achieve the minimum specified BER performance in the presence of an unwanted signal at the same assigned channel NOTE: The ratio (in dB) between the wanted signal level and the unwanted signal level is the co-channel interference ratio. conducted measurements: measurements which are made using a direct rf connection to the equipment under test data rate: VDL Mode 2 symbol rate shall be 10 500 symbols/s, with a nominal data rate of 31 500 bits/s ground base station: aeronautical station equipment, in the aeronautical mobile service, for use with an external antenna and intended for use at a fixed location interleaver: creates the AVPL_TIRS sequence made from the block segmentation of the AVLC frame and the RS encoding NOTE: To this end one assumes the TIRS matrix made from the RS encoding of the AVLC block segmentation. The TIRS matrix is a matrix of octets made of 255 columns and c rows. spurious emissions: conducted rf emissions on a frequency or frequencies which are outside the necessary bandwidth and the level of which may be reduced without affecting the corresponding transmission of information NOTE: Spurious emissions include parasitic emissions, intermodulation products and frequency conversion products. X 25: ITU-T standard for the protocols and message formats that define the interface between a terminal and a packet switching network 3.2 Abbreviations For the purposes of the present document, the following abbreviations apply: ABM Asynchronous Balanced Mode ACK ACKnowledge(ment) ACR Adjacent Channel Rejection ADM Asynchronous Disconnected Mode AGC
Automatic Gain Control AM(R)S Aeronautical Mobile (Route) Service AMCP Aeronautical Mobile Communications Panel ATN Aeronautical Telecommunication Network AVLC Aviation VHF Link Control AVLC_LI Aviation VHF Link Control Length Indicator AVPL Aviation VHF Physical Layer
AVPL-Header AVPL Header and training sequence AVPL-RBS AVPL Received Bit de-Scrambled sequence AVPL-RHeader AVPL Reception Header AVPL-RIRS AVPL Received Interleaved and RS encoded sequence AVPL-RSS AVPL Received Symbol de-Segmented sequence AVPL-TBS AVPL Transmitted Bit Scrambled sequence AVPL-THeader AVPL Transmission Header sequence AVPL-THI AVPL Transmitted Header appended and Interleaved sequence AVPL-TIRS AVPL Transmitted Interleaved RS encoded sequence AVPL-TTS AVPL Transmitted Ternary Symbol sequence SIST EN 301 841-1 V1.2.1:2003

ETSI ETSI EN 301 841-1 V1.2.1 (2003-08) 10 AWG Arbitrary Waveform Generator BCD Binary Coded Decimal BER Bit Error Rate C/R Command/Response (bit) CCI Co Channel Interference CMD CoMmanD (frame) CRC Cyclic Redundancy Check CSC Common Signalling Channel CSMA Carrier Sense Multiple Access CW Continuous Wave D8PSK Differentially encoded 8 Phase Shift Keying dBc Decibels relative to the carrier dBi Decibels relative to isotropic radiator D-bit ISO/IEC 8208 delivery bit dBm Decibels relative to 1 milliwatt DCE Data Circuit-terminating Equipment DISC DISConnect (frame) DLE Data Link Entity DLS Data Link Service DM Disconnected Mode (frame) DTE Data Terminal Equipment DXE Denotes either: Data terminal Equipment or Data circuit-terminating Equipment EVM Error Vector Magnitude FCS Frame Check Sequence FEC Forward Error Correction FM Frequency Modulation FRM Frame Reject Mode FRMR Frame Reject (frame) GF Galois Field GSIF Ground Station Information Frame HDLC High-level Data Link Control Hex Hexadecimal HO Hand-Off HTC Highest Two-way Channel ICAO International Civil Aviation Organization ID IDentification (identifier) INFO INFOrmation (frame) IS Intermediate System ISH Intermediate System Hello (packet) ISO International Organization for Standardization ITU-R International Telecommunication Union - Radiocommunication Sector LCI Logical Channel Identifier LCR Link Connection Refused LME Link Management Entity Lsb Least significant bit LTC Lowest Two-way Channel M/I Maintained/Initialized status bit
MAC Media Access Control Msb Most significant bit NET Network Entity Title nmi Nautical miles OSI Open Systems Interconnection P/F Poll/Final (bit) PDU Protocol Data Unit PN Pseudo Noise ppm parts per million Q-bit ISO/IEC 8208 Qualifier bit RF/rf Radio Frequency RIRS matrix Reception de-Interleaver and RS-decoding matrix RMS Root Mean Square RNR Receive Not Ready (frame) RR Receive Ready (frame) SIST EN 301 841-1 V1.2.1:2003

ETSI ETSI EN 301 841-1 V1.2.1 (2003-08) 11 RS Reed-Solomon RSP ReSPonse (frame) SAP Service Access Point SARPS Standards And Recommended PracticeS (ICAO) SDL Specification and Description Language SDU Service Data Unit SINAD (Signal + Noise + Distortion) / (Noise + Distortion) SME System Management Entity SN SubNetwork SNAcP SubNetwork Access Protocol SNDCF SubNetwork Dependent Convergence Function SNPA SubNetwork Point of Attachment SNR Signal to Noise Ratio SNSAP SubNetwork Service Access Point SQP Signal Quality Parameter SREJ Selective REJect (frame) SRM Sent selective Reject Mode SVC Switched Virtual Circuit TIRS matrix Transmission Interleaver and RS encoding matrix UA Unnumbered Acknowledgment (frame) UI Unnumbered Information (frame) VDL VHF Digital Link VHF Very High Frequency VME VDL Management Entity VSA Vector Signal Analyser VSWR Voltage Standing Wave Radio XID Exchange ID (frame) XOR Exclusive OR 4 General architecture of VDL Mode 2 The general architecture of the VHF radio equipment operating in VDL Mode 2 is depicted in figure 1. This figure presents the different functional parts of the VDL Mode 2 equipment.
The VDL system is related to the three lower layers of the OSI model providing services described as follows: Layer 1 (Physical layer): provides transceiver frequency control, bit exchanges over the radio media, and notification functions. These functions are often known as radio and modulation functions. The physical layer handles information exchanges at the lowest level and manipulates bits. The physical layer handles modulation, data encoding and includes a forward error correction mechanism based on interleaving and Reed Solomon coding.
Layer 2 (Link Layer): is split into two sublayers and a link management entity: • The MAC sublayer provides access to the Physical layer by a CSMA algorithm in charge of channel access. The MAC layer controls channel access and sharing.
• The DLS sublayer is composed of the AVLC derived from the HDLC protocol (ISO/IEC 3309 [3]) whose main functions are frame exchanges, frame processing, and error detection.
• The LME controls the link establishment and maintenance between DLS sublayers. Layer 3: Only the lowest network sublayer of layer 3 (SNAcP) will be described in EN 301 841-2 (see bibliography). It is compliant with the subnetwork sublayer requirements defined in the ATN SARPs and conforms with the ISO/IEC 8208 [4] (or network layer of X.25). It provides packet exchanges over a virtual circuit, error recovery, connection flow control, packet fragmentation, and subnetwork connection management functions. The DLS and LME part of the Layer 2 and Layer 3 are specified in EN 301 841-2 (see bibliography). SIST EN 301 841-1 V1.2.1:2003

ETSI ETSI EN 301 841-1 V1.2.1 (2003-08) 12 D8PSK (31,5 kbits/s)DLS (AVLC)MAC (CSMA)LMEINTERNETWORKSUBLAYERTRANSPORT LAYERSESSION LAYERPRESENTATIONLAYERAPPLICATIONLAYERVDL MODE 2 SARPs: ATN SARPsLayer 1Layer 2Layer 3Layer 4Layer 5Layer 6Layer 7SNAcP (ISO 8208) Figure 1: VDL SARPS in the ATN/OSI Organization 5 Physical layer protocols and services functional specifications 5.1 Overview The ground stations shall access the physical layer operating in simplex mode. 5.1.1 Functions The tasks of the physical layer include the following: • to modulate and demodulate radio carriers with a bit stream of a defined instantaneous rate to create an rf link; • to acquire and maintain bit and burst synchronization between Transmitters and Receivers; • to transmit or receive a defined number of bits at a requested time (packet mode) and on a particular carrier frequency; • to add and remove a training sequence; • to encode and decode the Forward Error Correction scheme; • to measure received signal strength; • to decide whether a channel is idle or busy, for the purposes of managing channel access attempts; • to offer a notification service about the quality of link. SIST EN 301 841-1 V1.2.1:2003

ETSI ETSI EN 301 841-1 V1.2.1 (2003-08) 13 5.1.2 Data reception by the receiver The receiver shall decode input signals and forward them to the higher layers for processing. 5.1.3 Data transmission The VDL physical layer shall appropriately encode the data received from the data link layer and transmit it over the rf channel. SIST EN 301 841-1 V1.2.1:2003

ETSI ETSI EN 301 841-1 V1.2.1 (2003-08) 14 5.2 Transmission procedure To transmit a sequence of frames, a station shall insert the bit numbers and, compute the FEC, interleave, insert the training sequence, carry out bit scrambling, and finally encode and modulate the rf signal. See figure 2. segment into RS blocksRS encoderinterleaverPreparetraining sequenceAVPL_THeadersymbol segmentationsymbol data burst to modulator(s)AVLC_LIbit scramblerTIRS_matrix(i,j)AVPL_TIRS sequenceAVPL_THI sequenceAVPL_TBS sequenceAVPL_TTS sequenceAVLC_LIAVLC_LIAVLC frame of length AVLC_LI to be transmitted Figure 2: Data burst formatting procedure SIST EN 301 841-1 V1.2.1:2003

ETSI ETSI EN 301 841-1 V1.2.1 (2003-08) 15 5.3 Modulation scheme Mode 2 shall use D8PSK, using a raised cosine filter with α = 0,6 (nominal value). The information to be transmitted shall be differentially encoded with 3 bits per symbol transmitted as changes in phase rather than absolute phase. The data stream to be transmitted shall be divided into groups of 3 consecutive data bits, with the least significant bit first. Zeros shall be padded to the end of the transmissions if needed for the final channel symbol. 5.4 Training sequence Data transmission shall begin with a demodulator training sequence consisting of five segments: • Transmitter ramp up and power stabilization (5 symbols); • synchronization and ambiguity resolution (16 symbols - the "unique word"); • reserved symbol (1 symbol); • transmission length (a single 17 bit word); • header FEC (5 bits). NOTE: Immediately after these segments there is an AVLC frame.
transmitter power synchronization and reserved transmission length header stabilization sequence ambiguity sequence (AVLC_LI) symbol FEC
Figure 3: AVPL-header training sequence structure 5.4.1 RF power rise time definition The purpose of the first segment of the training sequence, called the ramp-up, is to provide for transmitter power stabilization and receiver AGC settling and it shall immediately precede the first symbol of the unique word. The first segment also provides AGC settling time for the intended receiver. The time reference point (T), for the following specification is the centre of the first unique word symbol, a point that occurs 1/2 a symbol period after the end
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