Coding gains and error rates from the Big Viterbi Decoder
Abstract
A prototype hardware Big Viterbi Decoder (BVD) was completed for an experiment with the Galileo Spacecraft. Searches for new convolutional codes, studies of Viterbi decoder hardware designs and architectures, mathematical formulations, and decompositions of the deBruijn graph into identical and hierarchical subgraphs, and very large scale integration (VLSI) chip design are just a few examples of tasks completed for this project. The BVD bit error rates (BER), measured from hardware and software simulations, are plotted as a function of bit signal to noise ratio E sub b/N sub 0 on the additive white Gaussian noise channel. Using the constraint length 15, rate 1/4, experimental convolutional code for the Galileo mission, the BVD gains 1.5 dB over the NASA standard (7,1/2) Maximum Likelihood Convolution Decoder (MCD) at a BER of 0.005. At this BER, the same gain results when the (255,233) NASA standard ReedSolomon decoder is used, which yields a word error rate of 2.1 x 10(exp 8) and a BER of 1.4 x 10(exp 9). The (15, 1/6) code to be used by the Cometary Rendezvous Asteroid Flyby (CRAF)/Cassini Missions yields 1.7 dB of coding gain. These gains are measured with respect to symbols input to the BVD and increase with decreasing BER. Also, 8bit input symbol quantization makes the BVD resistant to demodulated signallevel variations which may cause higher bandwidth than the NASA (7,1/2) code, these gains are offset by about 0.1 dB of expected additional receiver losses. Coding gains of several decibels are possible by compressing all spacecraft data.
 Publication:

The Telecommunications and Data Acquisition Report
 Pub Date:
 August 1991
 Bibcode:
 1991tdar.nasa..170O
 Keywords:

 Bit Error Rate;
 Error Correcting Codes;
 Random Noise;
 Signal Encoding;
 Signal Processing;
 Signal To Noise Ratios;
 Viterbi Decoders;
 White Noise;
 Cassini Mission;
 Comet Rendezvous Asteroid Flyby Mission;
 Computer Programs;
 Computerized Simulation;
 Decomposition;
 Demodulation;
 Galileo Project;
 Maximum Likelihood Estimates;
 Very Large Scale Integration;
 Communications and Radar