4 connection vectors g1 1111001 171 octal g2

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Unformatted text preview: r 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 is used, G2 inversion provides no benefit to data randomization when even-order modulations higher than BPSK are used. G2 inversion does provide value when coding is done after channel splitting and with separate encoders on each channel. 3.3.2 ____ ____ The output symbol sequence shall be: C1(1), C2(1), C1(2), C2(2). . . . 3.3.3 When suppressed-carrier modulation systems are used: a) Non-Return-to-Zero-Mark (NRZ-M) or Non-Return-to-Zero-Level (NRZ-L) may be used as a modulating waveform. b) If the user contemplates differential encoding, i.e., conversion of his modulating waveform from NRZ-L to NRZ-M, such conversion should be performed at the input to the convolutional encoder. NOTES 1 Since the convolutional codes are transparent, differential encoding can be used before the convolutional encoder to help phase ambiguity resolution and, correspondingly, the conversion at the receiving end from NRZ-M to NRZ-L should be performed at the output of the convolutional decoder. Differential encoding after the convolutional encoder is not advised because it introduces considerable loss of performance. It also would require differential detection, which is more complex with soft symbols. CCSDS 131.0-B-2 Page 3-2 August 2011 CCSDS RECOMMENDED STANDARD FOR TM SYNCHRONIZATION AND CHANNEL CODING 2 When a fixed pattern (the fixed part of the convolutionally encoded Attached Sync Marker) in the symbol stream is used to provide node synchronization for the convolutional decoder, any modification of the pattern resulting from the modulating waveform conversion needs to be accounted for. G1 C1 1 INPUT D D D D D D S1 OUTPUT 2 C2 G2 NOTES: 1. D = SINGLE BIT DELAY. 2. FOR EVERY INPUT BIT, TWO SYMBOLS ARE GENERATED BY COMPLETION OF A CYCLE FOR S1: POSITION...
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This document was uploaded on 03/06/2014.

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