PCM/TDMA satellite communication systems with error correcting and error detecting codes

Effects of digital errors are analyzed for both uncoded and coded nonlinear PCM systems. Simple formulas for the digital noise are derived which are applicable to both block codes and convolutional codes. The variation of digital-error effects with input signal level is investigated for natural binary and binary folded PCM. Effects of digital errors in PCM systems modulated with differentially encoded four-phase modulation are investigated. Both differentially coherent and coherent demodulators are considered. Error detecting codes can be used to improve the performance of PCM systems. When an error is detected in a PCM word, an estimate based on the previous samples is used instead. For speech signals with high correlation between the samples, this gives errors much smaller than the digital errors. Combined error correction and detection is also possible. These methods are analyzed, and results for some codes are given. The implementation of error correcting and detecting codes in planned satellite communication systems is briefly discussed.