Research On Scma Technology In 5G Mobile Communication System

The fifth-generation mobile communication technology(5G)is expected to support better quality of service,which usually consists of higher throughput,lower latency,lower energy consumption and signaling overhead.Massive connectivity with a large number of devices is an important requirement for 5G networks.Current LTE system is not able to efficiently support those new features,especially on the uplink.In order to meet new characteristics of the next generation wireless network,the recently proposed SCMA which is based on the non-orthogonal multiple access technology and a new kind of SCMA codebook design which is based on a regular hexagonal constellation is studied in this paper.Firstly,this paper conduct the necessary research on the SCMA technology proposed by Huawei and the MPA decoding algorithm of SCMA.This paper focuses on the MPA algorithm,which is a iterative message passing algorithm.It is found that the MPA algorithm can get a stable probability distribution as a judgement through the iterative exchange of external information between the variable node(VN)and factor node(FN),which also is used for local decoding operations.At the same time,the results show that,the MPA algorithm which is maintaining the reasonable complexity,can make full use of the sparse characteristics of the SCMA codewords and obtain excellent performance which is close to the maximum likelihood detector by using posterior log-likelyhood ratio(LLR).Secondly,Based on UFMC and OFDM technology,this paper further studied the performance of the SCMA.In single-antenna and multi-antenna cases,by comparing the performance of SCMA and OFDMA system under ITU-R channel,it is found that SCMA can achieve a significant gain in data throughput at the expense of BER performance.On this basis,the research combine SCMA with UFMC into SCMA-UFMC.The simulation results show that the performance of SCMA-UFMC is identical with the performance of SCMA-OFDM.Their performance of BER worsen than OFDMA with 6dB while their performance of throughput capacity is increased by 50%.Finally,we propose a kind of SCMA codebook design which is based on a regular hexagonal constella-tion.This design can be applicable to SCMA system with 4 carriers 6 users.The design mainly includes the following steps.Firstly,According to the number of transmission layers,the number of resource blocks,and the system's overload rate requirements,draw on the design of the LDPC check matrix to generate a mapping matrix.Then,Distribute 12 points on two nested regular hexagonal to form the total constellation.After-wards,Generate sub-constellation by using the method of subset segmentation of trellis coded modulation and constellation rotation which is aimed at enlarging Euclidean distance of constellation points.In the end,Generate the codebook of each user by normalizing with the code provided by huawei.Compared to Huawei's codebook with 4 carrier 6-user,the complexity of the newly designed SCMA codebook is reduced by 1/4.At the same time,since the phase angles of all constellation points in the new design codebook can be represented by 30~?*n,the hardware of the SCMA codebook is further optimized.The simulation results show that the newly designed codebook has better system performance of BER in both AWGN and multipath channels at high SNR.Therefore,the performance of the SCMA-UFMC technology studied in this paper and the newly proposed SCMA codebook design scheme provide powerful data references for the use of next-generation wireless communication candidate technologies.