The Low Complexity Multi-user Detection Algorithms for Uplink SCMA System

5G research gradually focus on non-orthogonal multiple access technology, owing to huge traffic, more mobile terminals, and explosive growth of throughput capacity in recent years. Sparse code multiple access (SCMA) is a multi-dimensional codebook-based non-orthogonal multiplexing technique proposed to address the above requirements. This paper investigates the Message Passing Algorithm (MPA) in the receiver of SCMA and proposes two multi-user detection algorithms with low computational complexity in uplink. Improved Variable Message Passing Algorithm (IVMPA) reduces computational complexity compared to Variable Message Passing Algorithm (VMPA) by changing the users iteration order. Incomplete Iterative Message Passing Algorithm (IIMPA) is proposed to reduce the number of iteration for users with high signal-to-noise ratio (SNR) and reduces computational complexity compared to MPA.