Successive MAP Detection with Soft Interference Cancellation for Iterative Receivers in Hierarchical M-ary QAM Systems

This paper proposes a successive MAP(maximum a posteriori probability) detection scheme to reduce the receiver complexity of hierarchical M-ary QAM system. In order to detect a specific symbol in a hierarchical M-ary QAM symbol, modulation symbols generated from other data streams are treated as an Gaussian noise or eliminated as an soft interference according to their priorities. Then, the MAP detector calculates the log-likelihood ratio of the a posteriori probability of each bit successively with an adjusted noise variance in order to take the elimination and Gaussian assumption effect into account. By separating the detection process into the successive steps, the detection complexity is reduced to increase linearly with the number of bits per hierarchical M-ary QAM symbol. Simulation results show that the proposed detection scheme provides a slightly performance degradation compared to the optimal MAP detection scheme.