Low PAPR SCMA Systems Based on Carrier Techniques

Sparse Code Multiple Access (SCMA) is a nonorthogonal multiple access (NOMA) scheme with high spectrum efficiency and reliability. However, the peak-to-average power ratio (PAPR) of the existing multi-carrier SCMA (MC-SCMA) system based on orthogonal frequency division multiplexing (OFDM) is high. In this paper, a single carrier SCMA system (SC-SCMA) with frequency domain equalization (FDE) is firstly proposed to reduce PAPR. Since the performance of SC-SCMA is largely affected by the deep fading point in time domain, to tackle this problem, a hybrid carrier SCMA (HC-SCMA) system based on weighted-type fractional Fourier transform (WFRFT) is further proposed. Simulation results show that both of the proposed systems can obtain a lower PAPR. Moreover, HC-SCMA achieves the optimal bit error rate (BER) performance compared with SC-SCMA and MC-SCMA systems over the doubly selective fading channel.