The Downlink Resource Allocation Scheme Of SCMA Based On Capacity And User Fairness

In order to meet the requirements of the next generation wireless communication technology, such as user rate, coverage, time delay and so on, multi-access technology is facing great challenges. From the perspective of information theory, the traditional Orthogonal Multiple Access(OMA) is close to the Shannon limit, the Non-orthogonal Multiple Access(NOMA), Compared with OMA, can carry more users to achieve overload in different degree on the same resource of time domain, so as to get wide attention and become a research hotspot by increasing the system throughput. Among them, the Sparse Code Multiple Access(SCMA) is a strong candidate in the NOMA program. Inspired by Low Density Signature (LDS) sequence, the transmitter of SCMA will transform the traditional modulation of the spread spectrum process into a process that first conducts constellation modulation, and then spreads sparse spectrum. At the receiver, by using Message Passing Algorithm(MAP) in LDS to do multi-user detection, in order to achieve the requirements of performance and complexity .Firstly, this paper introduces the system model of SCMA, mentions the principle of SCMA in the process of encoding and decoding, and studies the similarities and differences of SCMA in the process of information processing in uplink and downlink. It mainly focuses on the key technologies of SCMA, namely, codebook design and multi-user detection algorithm.Building the SCMA link level simulation platform, and by comparing the codebook and LDS, we can find that the performance of SCMA is better than that of LDS .In view of the scarcity of wireless resources, this paper mainly studies the resource allocation of SCMA from two aspects between system capacity and fairness. Among them,the SCMA resources primarily include power and codebook.In order to maximize system capacity, we put forward a resource allocation scheme based on system capacity. The simulation results show that the proposed scheme has a significant improvement in system capacity compared with the average power allocation scheme.Based on the fairness of the system, a resource allocation scheme is proposed to maximize the fairness and efficiency of the system. It can be seen from the simulation that the fairness index of the proposed scheme is different under multiple fairness factors. At the same time, the system capacity and bit error rate performance under different fairness factors are studied to cover the consideration of requirements due to various fairness degrees. Then,we can adjust the proportion of fairness and energy efficiency to meet the various needs.