Iterative signal detection based soft interference cancellation for satellite-terrestrial downlink NOMA systems

To improve the bit error rate (BER) performance of multi-user signal detection in satellite-terrestrial downlink non-orthogonal multiple access (NOMA) systems, an iterative signal detection algorithm based on soft interference cancellation with optimal power allocation is proposed. Given that power allocation has a significant impact on BER performance, the optimal power allocation is obtained by minimizing the average BER of NOMA users. According to the allocated powers, successive interference cancellation (SIC) between NOMA users is performed in descending power order. For each user, an iterative soft interference cancellation is performed, and soft symbol probabilities are calculated for soft decision. To improve detection accuracy and without increasing the complexity, the aforementioned algorithm is optimized by adding minimum mean square error (MMSE) signal estimation before detection, and in each iteration soft symbol probabilities are utilized for soft-decision of the current user and also for the update of soft interference of the previous user. Simulation results illustrate that the optimized algorithm i.e. MMSE-IDBSIC significantly outperforms joint multi-user detection and SIC detection by 7.57dB and 8.03dB in terms of BER performance.