Study On The Sparse Multiple Code Access

In the future,the fifth generation(5G)mobile communication system requires massive connectivity,high quality of service,large throughputs and low latency.These problems cannot be solved by the orthogonal multiple access(OMA)technology.As one of the most core competitive non-orthogonal multiple access technologies(NOMA)for 5G,sparse code multiple access(SCMA)is brought up to face the challenges.SCMA utilizes the non-orthogonal superposition of user signals to support overload.Therefore,it can increase the number of user access as many as possible.The codebook of SCMA can provide high shaping gain.Moreover,the sparse factor graph enables the receiver to adopt high-efficient message passing algorithm(MPA).First,the optimization of dynamic resource allocation based on the channel state information is proposed.One exhaustive search-based algorithm and two greedy-based algorithms are proposed.The simulations show that the proposed dynamic factor graph matrix can effectively improve the performance of system compared to the fixed factor graph.Among the three algorithms,the exhaustive search has the best performance with the highest complexity,while the other two algorithms achieve a good tradeoff between BER performance and computational complexity.This paper also proposes two low-complexity detection algorithms for uplink sparse code multiple access(SCMA)systems.The first,called symbol flipping algorithm(SFA),is an analogy of the bit-flipping decoding algorithm in the low-density parity check code field.Specifically,the local hard-decision is first performed at each resource node,and the decided signal in the least reliable resource node is flipped.The reliability update and the symbol flipping operations are performed iteratively till the stopping condition is satisfied.The simulation results show that the proposed hard-decision SFA can achieve a numerous complexity reduction compared with message passing algorithm(MPA).The second is an improved partial marginalization(PM)-MPA.Based on the reliability definition introduced in SFA,the variable nodes to be marginalized are determined dynamically during the MPA iteration procedure,and the resulted detector is termed as dynamic PM-based MPA(DPM-MPA).The simulations show that the proposed dynamic PM-based MPA has better performance and lower complexity than PM-based MPA.