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The influence of quantization and fixed point arithmetic upon the BER performance of turbo codes

The majority of the performance studies of turbo codes presented in the literature to date have assumed the use of floating point arithmetic. However, if fixed point arithmetic is employed, a corresponding degradation in the BER performance of the turbo decoding algorithm is expected. In this paper, the effects of quantization and fixed point arithmetic upon the log-MAP and APRI-SOVA decoding algorithms for a BPSK communication system are quantified via simulation. It is shown that, with proper scaling of the signal prior to quantization, no degradation of the BER performance is incurred with eight-bit quantization, and even four-bit quantization can provide acceptable BER performance.