Noncoherent trellis coded π/4-shift DQAM with diversity reception for future digital mobile/cellular communication systems

The authors derive the optimal sequential noncoherent diversity receiver for trellis coded π/4-shift differentially encoded quadrature amplitude modulated (π/4shift DQAM) signals received over l (1⩽l⩽Λ) independent channels. Each of these channels corrupts the transmitted signal by a mixture of additive white Gaussian noise (AWGN) and flat fading. To reduce the overall implementation complexity, the authors have proposed and evaluated suboptimal (e.g., having a small number of differential detectors and equal combining diversity structures) versions of the receivers. Some bit error rate (BER) performance evaluation results are presented for a π/4-shift 8-DQAM scheme, clearly indicating significant performance improvements, including substantial error floor reductions, as compared to a conventional differentially detected Π/4-shift differentially encoded quadrature phase shift keying (π/4-shift DQPSK) scheme