This paper studies various sub-optimal versions of BCJR demodulator to examine the possibility of computational reduction. BCJR demodulator is used to deal with intentional intersymbol interference in bandwidth efficient systems. The complexity of BCJR demodulator can be reduced by using the approximation in the logarithm domain and by considering less number of trellis states instead of full states. To estimate the performance of different types of BCJR demodulator, we proposed the partial response signalling system with finite shaping pulse providing 10% gain of bandwidth efficiency. The simulation results of this study show that in the case without error correction coding the complexity of BCJR demodulator can be significantly decreased without energy losses. When low-density parity-check coding is used, it is possible to use these sub-optimal versions of BCJR demodulator, but the system may suffer additional energy losses.
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