ccsds 131.0-b-2

CCSDS RECOMMENDED STANDARD FOR TM SYNCHRONIZATION AND CHANNEL CODING3.2.4 QUANTIZATIONSoft bit decisions with at least three-bit quantization should be used whenever constraints(such as complexity of decoder) permit.3.3 BASIC CONVOLUTIONAL CODE SPECIFICATION3.3.1 The basic convolutional code shall be the non-systematic code with the followingcharacteristics:(1) Nomenclature: Convolutional code with maximum-likelihooddecoding.(2) Code rate (r): 1/2 bit per symbol.(3) Constraint length (K): 7 bits.(4) Connection vectors: G1 = 1111001 (171 octal); G2= 1011011(133 octal).(5) Symbol inversion: On output path of G2.NOTE – An encoder block diagram is shown in figure 3-1. When a single encoder isused, G2 inversion provides no benefit to data randomization when even-ordermodulations higher than BPSK are used. G2 inversion does provide value whencoding is done after channel splitting and with separate encoders on eachchannel.3.3.2 The output symbol sequence shall be: C 1 (1),3.3.3 When suppressed-carrier modulation systems are used:____ ____C 2 (1), C 1 (2), C 2 (2). . . .a) Non-Return-to-Zero-Mark (NRZ-M) or Non-Return-to-Zero-Level (NRZ-L) may beused as a modulating waveform.b) If the user contemplates differential encoding, i.e., conversion of his modulatingwaveform from NRZ-L to NRZ-M, such conversion should be performed at the inputto the convolutional encoder.NOTES1 Since the convolutional codes are transparent, differential encoding can be usedbefore the convolutional encoder to help phase ambiguity resolution and,correspondingly, the conversion at the receiving end from NRZ-M to NRZ-L shouldbe performed at the output of the convolutional decoder. Differential encoding afterthe convolutional encoder is not advised because it introduces considerable loss ofperformance. It also would require differential detection, which is more complex withsoft symbols.CCSDS 131.0-B-2 Page 3-2 August 2011