Resource Allocation And System Design For Sparse Code Multiple Access

Sparse Code Multiple Access(SCMA)is non-orthogonal multiple access technology based on pre-defined codebooks.In SCMA,bits mapping to symbols and spreading are combined into one process.Information bits are mapped directly to multidimensional codewords of pre-defined codebooks.The shaping gain of multidimensional constellation points is the major advantage of SCMA performance improvement,compared to the simple repetition of QAM symbols in low density signatures(LDS).Similar to LDS,SCMA can adopt a receiver based on message passing algorithm(MPA)with low complexity and near-optimal performance.This paper is divided into two parts,the first part is joint codebook and power allocation based on Gaussian input.Considering the design of a specific codebook structure,the system capacity is deduced,and the codebook allocation algorithm is proposed to complete the joint distribution of codebook and power.In this paper,the uplink SCMA capacity is derived and a specific codebook design method is proposed,which can cancel the effect of the dependency between the non-zero entries of codewords.The problem of maximizing the system and the rate can be transformed into two sub-problems,codebook allocation and power assignment.I propose a searching algorithm to solve the problem of codebook assignment.Then,in the case of known codebook,the problem of power allocation maximizing throughput can be proved as convex problem,and the optimal solution can be obtained by convex optimization.The second part is the design and implementation of low complexity SCMA system on FPGA.In the developing board DE5-NET,modules like encoding,channel,iterative decoding are designed to achieve the signal transmitting process in the SCMA system.Through the resulting bit error rate and computing time,SCMA decoding performance and the complexity can be analyzed.