Stochastic Geometry Based Transmission Performance Research Of Sparse Code Division Multiple Access

Driven by the development of mobile Internet,new services such as vehicular communications,smart home and smart cities are emerging.These services require capability of high spectral efficiency and massive connections,while the existing Orthogonal Frequency Division Multiple(OFDM)access technology is difficult to meet that performance requirements.Sparse Code division Multiple Access(SCMA)is a code domain non-orthogonal multiple access technology with high spectral efficiency,which can meet the need of massive connection communication effectively.Therefore,it is a promising multiple access method.In order to enhance system capacity,the deployment of The Fifth Generation(5G)mobile communication systems will tend to be dense,low-power nodes will exhibit the characteristics of small-radius and intensive coverage as well.However,this deployment trend will complicate the network topology,resulting in the worse interference environment.Therefore,for the sake of applying the sparse code division multiple access technology to the 5G mobile communication system properly,this thesis will research the transmission performance of the SCMA under characteristics of the above transmission scenarios,point process of the Stochastic Geometry theory is used to model the low-power small base stations and users,and the interference environment in that scenarios is modeled.Meanwhile,outage and capacity performance of the uplink and downlink transmission links are determined respectively,influencing factors of the performance indicators are sought and the specific impact mode is pointed out.Finally,orthogonal multiple access(OMA)mode is compared with the SCMA to seek a reasonable application interval and application mode,which provides a theoretical reference for the actual deployment of the SCMA technology in 5G systems.The main content and contributions of this thesis are as follows:Firstly,uplink transmission is modeled to research the transmission performance of the SCMA,influencing factors and influence modes of performance indicators are sought and applicable interval of the SCMA is determined.The uplink transmission is modeled based on point process model of the Stochastic Geometry theory,and the signal to interference and noise ratio expression is established according to the interference source received by the small base station.Meanwhile,outage performance and average sum rate performance are derived,and benchmark performance expression is obtained,accuracy of the above process is verified by the Monte Carlo simulation as well.Finally,main factors affecting the performance indicators are analyzed according to the expression,and the specific impact mode is determined.Compared with the OMA transmission mode,it is proved that under certain conditions,the SCMA transmission performance can achieve better performance by adjusting the number of users carried by the subcarriers,which provides better theoretical guidance for the deployment of SCMA uplink transmission.Secondly,downlink transmission is model to research the transmission performance of the SCMA,influencing factors and influence modes of performance indicators are sought and appropriate configuration mode of the SCMA is determined.The downlink transmission is modeled based on point process model of the Stochastic Geometry theory,and the signal to interference and noise ratio expression is established according to the interference source of the target user.Meanwhile,outage performance and ergodic capacity performance are derived,and closed-form expression of outage probability as well as benchmark performance expression of ergodic capacity are obtained,accuracy of the above process is verified by Monte Carlo simulation as well.Finally,main factors affecting the performance indicators are analyzed according to the expression,the specific impact mode is determined,and performance balance between SCMA outage performance and spectral efficiency is researched under fixed bandwidth allocation to seek the existence of boundary conditions.It is proved that the SCMA with specific configuration strategy such as a certain number of access users has superior overhead performance than the OMA under certain conditions,which provides better theoretical guidance for the deployment SCMA downlink transmission.