Digital computer simulation of high rate convolutional coding systems

Often communications systems are too complicated to analyze completely by using only analytical techniques, or a complete analytical approach would be too costly in terms of personnel and time. In these cases, a digital computer simulation is used, as shown in this paper, to provide a practical approach to system design and analysis. This paper presents computer simulation to design convolutional systems of rate 1/2 and 3/4 with Viterbi decoding algorithm and QPSK modulator. The systems are differentially encoded and decoded and signal waveforms at each node of the rate 1/2 system are shown. Simulation curves of the performance of the two systems are also presented. These curves are plotted in the soft-decision case with eight level quantization and are repeated for unquantized soft-decision decoding over an AWGN channel. The simulation provides coding performance very near the theoretical limits for the optimal constraint length K=7 rate 1/2 and 3/4 Viterbi decoder algorithm