Doubly irregular sparse code multiple access with EXIT analysis

Abstract

Sparse Code Multiple Access (SCMA) is one of the potential candidates of multiple access technique to support future networks. This paper proposes doubly irregular SCMA (DI-SCMA) to increase the user capacity of massive wireless networks. The idea is coming from the fact that successive interference cancellation (SIC) works better when the degree distributions of the both user and resource nodes are irregular. Since iterative decoding is involved, we use extrinsic information transfer (EXIT) chart to predict the performances. With careful design of the degree distribution, we conduct computer simulations to observe the benefit of irregularity of the system. Our results confirmed that the proposed DI-SCMA can increase the user capacity with overloading factor of 300%. The efficiency of the proposed DI-SCMA is expected to be high as indicated by the small gap between area of capacity and coding rate in EXIT chart.