Application Of Frame Theory In Non-Orthogonal Multiple Access Systems

Non-orthogonal Multiple Access(NOMA)technology is now regard as one of the most promising technology of Fifth Generation wireless communication because it can significantly improve the spectral efficiency of the system.Unlike the traditional Orthogonal Multiple Access technologies,each time-frequency resource on NOMA hosts non-orthogonal multiple user signals,which can be accumulated on the same time-frequency resource to improve the system's spectral efficiency.However,the problem of NOMA technology is that in order to connect more users per resource,the user's overload rate of a single resource will be too high.In this case,high SE cannot be obtained,which will seriously reduce the system performance.In this paper,NOMA system is analyzed comprehensively,changes the spread spectrum codebook of NOMA system under the condition where has high overload factor,and studies the new NOMA scheme.A frame in a finite space is a set of vectors,which is usually redundant and has cross correlation.Therefore,a typical frame has more frame vectors than higher dimension frame,and the frame can be represented by each vector in the space in much ways.The maximum correlation between any elements in the framework should be as small as possible in order to be closer to the construction of orthogonal basis.Equiangular Tight Frame(ETF)has attracted the attention of many scholars because all Frame vectors in ETF have the same correlation with each other and are the smallest compared with other frames in the same dimension.However,the existing ETF construction methods are deficient and have various restrictions,and the dimensions of ETF construction are relatively low and difficult,so it cannot be widely used.In this paper,the structure characteristics and common construction methods of ETF are introduced,and the existing ETF construction methods are improved.Based on the Steiner system,the method can effectively construct a high dimensional multivariate ETF by using projective plane.Due to the low spectral efficiency of NOMA system under high overload condition,the performance of spread spectrum sequence at the transmitter of NOMA system is not superior.In this paper,the spread spectrum sequence of NOMA system is optimized according to the relevant characteristics of the ETF.Compared with the existing MUSA and OFDMA systems,the system can improve the signal-to-noise ratio gain.In addition,the multi-user detection method is improved,and the performance is improved compared with the original detection algorithm.This thesis mainly includes three parts.Firstly,the basic concept and performance of NOMA system are introduced,and the spread spectrum communication technology and multi-user detection technology involved in the spread spectrum based NOMA scheme are described.Then,presents some related content of the frame,and lists several familiar frame,equiangular tight frame properties and its existence conditions are introduced in detail,analyses the three common ETF constructor and its operation principle,and improves one of the existing method on this basis,construct a 19 dimension multivariate ETF.Finally introduces the typical spreading-based NOMA scheme—MUSA,and analyses the Welch boundary,get the relationship between ETF sequence,WBE and MWBE.Then the ETF sequence is used as the spread spectrum sequence of NOMA system and improve the performance of the existing NOMA scheme.In the meanwhile improves the original use of multi-user detection algorithm,and this improved algorithm has higher overload and lower delay.