Research On Spatial Modulation-SCMA Joint Systerm Based On Polar Code

With the progress of society and the development of the economy,the demand for mobile communication for diversified,high-dynamic,and high-capacity services in the future is also constantly improving.As one of the current hot scenarios,the applications of the fifth-generation mobile communication in massive machine type of communication scenarios are becoming increasingly diverse.Services such as intelligent driving and smart cities will be widely applied soon.5G will face the challenge of multiple access,high gain,and highly reliable transmission in a complex environment,and the technology of multi-access using error control coding has become one of the important research directions.The traditional orthogonal multi-access technology is limited by the number of spectrum resources and cannot meet the need for simultaneous access to multiple user scenarios.At the same time,the demand for system transmission rate and spectral efficiency is also gradually increased in practical applications.People traditionally use multiple-input-multiple-output(MIMO)to solve this problem,however,the performance impact caused by the interference between channels needs to be solved by high reception complexity.This paper aims to improve the reliability of the multi-user access multi-antenna communication system and reduce the complexity of the receiving algorithm.Sparse code multiple access(SCMA)technology is a kind of non-orthogonal multiple access(NOMA)technology in the code domain.It provides relatively larger diversity gain and coding gain as well as increasing the number of access terminals.What's more,the detection technology with low complexity keeps close to optimal performance.Polar code is an excellent error control channel coding technology that can approximate Shannon channel tolerance theoretically.The SCMA system based on polar code realizes service quality through polar code.At the receiving end,the joint detection and decoding technology using soft information transfer not only reduces the complexity of the system but also improves the reliability of the system.In practical applications,SCMA and MIMO are often used together to realize a multi-antenna transmission system with high spectral efficiency with multi-user access.In order to solve the performance degradation caused by antenna interference in the MIMO-SCMA system,spatial modulation(SM)is used to replace the MIMO transmission to ensure system reliability.At the same time,we propose a joint detection algorithm with low complexity for the receiving end,and the improvement of system reliability is proved through simulation comparison.Through analysis,it is observed that the SM-SCMA system achieves lower complexity and better reliability as well.In this paper,differential spatial modulation(DSM)is applied to optimize the system to solve the effect of channel estimation error on performance in practical applications.Compared with the traditional spatial modulation,DSM further adopts the operation of differential modulation and demodulation in the time dimension.The modulation result extends from the form of a vector to the space-time element in the form of a matrix.The receiving ends adopt the differential detection and do not depend on channel estimation.On this basis,DSM and SCMA are combined to extend the system to multiple users.Finally,the simulation analysis concluded that DSM's spectral efficiency and bit error rate performance had a smaller loss in practice and reduced processing delay.For the joint DSM-SCMA system,the performance is better than that of the joint MIMO-SCMA system with multiple antennas,and it also provides a relatively low receiving complexity.