SCMA CODEBOOK DESIGN BASE ON CIRCULAR-QAM

Spare code multiple access (SCMA) is a promising multiple access scheme with massive connectivity for 5G cellular system. This paper proposes a new method to create multidimensional mother constellations of SCMA codebook by using circular quadrature amplitude modulation (circular - QAM) method. This proposed method can reduce the complexity of message passing algorithm (MPA) due to the sparsity of SCMA codewords. The complexity of MPA commensurates with the number of projection point. The less number of projection point is, the less complex MPA will be. Furthermore, the new codebook and low projections have been simulated with MIMO-SCMA performed in Rayleigh fading channels. Due to the efficiency of this new codebook, when its complexity is minimized, the simulation results show bit error rate (BER) performance gain of the existing low complexity structured codebooks and the codebooks that their complexity is not minimized.