Coded π/2 phase shift NS-QAM modulation and its iterative decoding

In this paper, a novel pi/2 phase shift non-square (NS) 2 ²ⁿ⁺¹ - ary (nges1) quadrature amplitude modulation (QAM) scheme is presented. The modulated signal of this scheme has lower peak-average power ratio (PAPR) than conventional QAM signal by removing all 180deg phase shift between adjacent constellation points, so it can mitigate the impact of channel-nonlinearity on the signal spectrum. In addition, such modulation scheme contains inherent memory, which can be treated as a type of inner coding. When concatenated with simple outer codes, iterative decoding schemes can be adopted for the system. Simulation results show that this modulation scheme has much lower spectrum regrowth when passing through nonlinear channel, while the coded systems which adopt recursive system code (RSC) as outer code can achieve better coding gains than some other coded QAM systems in both additive white Gaussian noise (AWGN) and nonlinear channels.