Block-coded 16TAPSK and 16QAM for generalized differential encoding

In this paper, we consider noncoherent block-coded QAM (quadrature-amplitude modulation) and TAPSK (twisted amplitude and phase shift keying) for generalized differential encoding. For noncoherent block-coded MPSK over continuous channels, rotating signal points of an entire codeword, such that the first symbol is the same as the last symbol of previously transmitted codeword and thus can be omitted, increase bandwidth efficiency. This method is called generalized differential encoding. Since noncoherent block-coded QAM/TAPSK proposed before cannot be applied to generalized differential encoding, in this paper, we modify the definition of noncoherent block-coded QAM/TAPSK and the bit labeling of signal points. Simulations of various examples of noncoherent block-coded QAM/TAPSK with generalized differential encoding are made and discussed as well. We find that if the block length is very small than 8, NBC-16TAPSK performs better than NBC-16QAM due to its large minimum noncoherent distance. However, if the block is longer than 8, NBC-16QAM has better error performance because the codewords with small noncoherent distances are rare.