Iterative Demodulation and Decoding of Coded Non-Square QAM

It is shown that a non-square ( N S ) 2'"+'-ary quadrature amplitude modulation (QAM) can be decomposed into a single-parity-check (SPC) block encoder and a memoryless modulator in such a way that the inherent block encoder has a recursive nature. When concatenated with a forward-error-correcting (FEC) code, iterative demodulation and decoding of the FEC code and the inherent SPC code of NS-2'"+'-QAh4 is then possble. The capacity and bidsymbolerror-rate (BEWSER) performance of coded and uncoded NS-2'"+l-QAM systems are given and compared to those of other 2'"+'-ary systems. Simulation results show that, with iterative demodulation and decoding, coded NS-8QAM performs 0.5 dB better than standard SQAM and 0.7 dB better than SPSK at BER= when the FEC code is the (15 , l l ) Hamming code concatenated with a rate-1 accumulator code, while coded NS-32QAM performs 0.25 dB better than standard 32QAM.