Abstract: A low-complexity orthogonal modulation scheme with non-coherent detection is presented, which is suitable to the low-rate region. Information bits are first encoded by a Zigzag encoder and then the coded bits satisfying a single parity check constraint are mapped into a PPM symbol. According to the equivalence between soft-out demodulation and decoding of orthogonal Hadamard codes, demodulation and decoding can be considered as a whole at the receiver side, so not only can the iterative operations between decoding and demodulation be avoided, but also the fast Hadamard transform(FHT) and the so-called a posteriori probability fast Hadamard transform(APP-FHT) algorithm can be adopted to further decrease decoding complexity. Furthermore, linear interleavers with a joint design are used to improve the error floor problem in our scheme. Simulation results show that our scheme can lead to performance comparable to that of other non-coherent orthogonal modulation schemes.

Key words: low-density parity-check codes, orthogonal modulation, non-coherent detection, iterative decoding