SM and QSM Oriented Codebook Design for Downlink Doubly-irregular SCMA

Sparse Code Multiple Access (SCMA) is a multiple access that has the potential to address the needs of future networks. However, the commonly researched SCMA has a traditional design known as regular SCMA, may have drawbacks in serving massive connection networks and supporting various user services. It has been hypothesized that Doubly-irregular SCMA (DI-SCMA) ameliorates the shortcomings of regular SCMA. In this study, we present codebook designs oriented to Spatial Modulation (SM-oriented) and Quadrature Spatial Modulation (QSM-oriented) with Multiuser Detection (MUD) Q=3 to enhance the spectrum efficiency of downlink DI-SCMA with an overloading factor of 225%. The SM-oriented and QSM-oriented codebook design permits downlink DI-SCMA to transmit more bits from multiple users concurrently. The simulation is performed in a Rayleigh fading channel, demonstrating that our proposed codebook designs are suitable for downlink DI-SCMA.