130x1g2 - CCSDS

TM SYNCHRONIZATION AND CHANNEL CODING—SUMMARY OF CONCEPT AND RATIONALEFigure 6-5: Performance of Concatenated Coding Systems with Ideal Interleaving,E=16 and E=8, Punctured CodesEffects of Finite Interleaving — When the interleaving depth I is not large enough, theerrors at the output of the Viterbi decoder cannot be considered as independent since thisdecoder tends to produce errors in bursts. The performance under finite interleaving musttherefore take into account the statistics of these bursts either by devising a plausible modelor by simulation. A possible model for burst lengths and arrival times was developedin reference [27] and is called the geometric model. This model provides an approximateestimate of the performance under finite interleaving, but ignores the actual structure of theerror patterns within the bursts. On the other hand, simulation is also problematic since verylarge amounts of Viterbi decoded data is necessary to provide reasonable confidence in theestimates of performance. A detailed description of methods to obtain performance estimatesis given in reference [28].BER and WER results for finite interleaving are shown in figures 6-6 and 6-7, respectivelyfor the recommended concatenated system consisting of the non-shortened (255,223) RScode with E=16 and the non-punctured (7, 1/2) convolutional code, with differentinterleaving depths ranging from I = 1 to I = 16.CCSDS 130.1-G-2 Page 6-7 November 2012