Adaptive Downsampling in Oversampled Filter Banks in the Presence of Quantization Noise

FIR Oversampled Filter banks (OFB) with degree zero polyphase matrices can be used as block codes over the field of real numbers. Since they can be regarded as real-valued codes, one can also use their potential advantage of joint source-channel coding and graceful degradation over noisy channels. Due to the variable state of noisy channels, increase in bit error probability is unavoidable hence increasing the injected redundancy of the input signal or decreasing the code rate is necessary. To decrease the code rate, the downsampling rate should be decreased as well as filter lengths to maintain the degree zero of the polyphase matrix. However, decreasing the filter lengths will deteriorate the performance of the OFB both in compression rate of the input signal and the amount of injected redundancy. This paper proposes the idea of adaptively changing the downsampling rate to modify the code rate without changing the filter length. This could be considered as some form of puncturing. We show that adaptive downsampling results in just changing the way input is fed into the OFB. Simulation results for quantized DFT codes with erasures show the efficiency of this method specially when the number of erasures is not very large.