k as generated by the following algorithm note the

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Unformatted text preview: The interleaver is a fundamental component of the Turbo encoding and decoding process. The interleaver for Turbo codes is a fixed bit-by-bit permutation of the entire block of data. Unlike the symbol-by-symbol rectangular interleaver used with Reed-Solomon codes, the Turbo code permutation scrambles individual bits and resembles a randomly selected permutation in its lack of apparent orderliness. 1) k shall be expressed as k=k1k2; the parameters k1 and k2 for the specified block sizes shall be selected from table 6-3. CCSDS 131.0-B-2 Page 6-3 August 2011 CCSDS RECOMMENDED STANDARD FOR TM SYNCHRONIZATION AND CHANNEL CODING Table 6-3: Parameters k1 and k2 for Specified Information Block Lengths Information block length k1 k2 1784 8 223 3568 8 223 × 2 7136 8 223 × 4 8920 8 223 × 5 2) The following operations shall be performed for s=1 to s=k to obtain permutation numbers π(s): p1 = 31; p2 = 37; p3 = 43; p4 = 47; p5 = 53; p6 = 59; p7 = 61; p8 = 67 NOTE – In the equation below, ⎣x⎦ denotes the largest integer less than or equal to x, and pq denotes one of the following eight prime integers: m= (s – 1) mod 2 i= s–1 2 k2 j= s–1 2 t= q= c= π(s) = – i k2 k1 (19i + 1) mod 2 t mod 8 + 1 (pq j + 21m) mod k2 k1 2(t + c 2 + 1) – m The permutation numbers shall be interpreted such that the sth bit read out on line ‘in b’ in figure 6-2 is the π(s)th bit of the input information block, as shown in figure 6-1. CCSDS 131.0-B-2 Page 6-4 August 2011 CCSDS RECOMMENDED STANDARD FOR TM SYNCHRONIZATION AND CHANNEL CODING ... 1st π (k) th ... 2nd . . . π(s)th . . . bits on line ‘in a’ (input of encoder a) π (1) th . . . ... s th k th bits on line ‘in b’ (input of encoder b) Figure 6-1: Interpretation of Permutation out 0a in a G0 INFORMATION BLOCK BUFFER D D D D G2 G3 out 3a RATE 1/2 ENCODER b G0 in b D = Exclusive OR D D D + G1 out 1b G2 Not used G3 = Take every symbol RATE 1/4 out 1a out 2a RATE 1/6 G1 RATE 1/3 Input Information Block ENCODER a out 3b = Take every other symbol D = Single bit delay Figure 6-2: Turbo Encoder Block Diagram h) Backward and forward connection vectors (see figure 6-2) shall be as follows: 1) Backward connection vector for both component codes and all code rates shall be G0 = 10011. 2) Forward connection vector for both component codes and rates 1/2 and 1/...
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This document was uploaded on 03/06/2014.

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