A MIMO-NOMA Framework With Complex-valued Power Coefficients

With the rapid development of mobile communication,spectrum resources are increasingly scarce.Non-orthogonal multiple access has become a promising candidate for future wireless networks because of its high spectrum efficiency.In this paper,we investigate multiple input multiple output(MIMO)technology and Non-orthogonal multiple access(NOMA)technology,as well as the combination of them.Aiming at the problem that the intra-cluster interference cannot be directly eliminated in the MIMO-NOMA system,a MIMO-NOMA downlink scheme based on complex-valued power allocation coefficients is proposed.And widely linear processing(WLP)is used to eliminate / suppress inter-cluster interference and intra-cluster interference to further improve system performance.In this paper,we give the system model,and do some work such as parameter optimization,system outage performance analysis,and capacity analysis.The main work and contributions of this paper are summarized as follows:Firstly,complex-valued power allocation coefficients are introduced to stagger the users' signals in phase,which is different from the traditional method to introduce the real power allocation coefficients.And expand the observation data dimension through widely linear processing to expand the "observation space".The phase of complexvalued power allocation coefficient is optimized,and the optimal power phase distribution strategy is obtained.It is verified that in the case of user pairing,widely linear processing can skip the steps of successive interference cancellation,directly eliminate intra-cluster interference,and greatly reduce the complexity of the system.Secondly,we first consider the system model of WL-MIMO-NOMA for user pairing,besides,the outage performance analysis and system sum capacity analysis are given.The closed expression of outage probability and the numerical expression of outage capacity experienced by each user are derived.On this basis,the model is extended to the general case of K-user cluster.Thirdly,we first consider the real-valued signal transmission of WL-MIMO-NOMA,based on zero forcing detection,at least half of the intra-cluster interference can be removed,especially in the case of user pairing,the intra-cluster interference can be completely eliminated.Finally,the proposed WL-MIMO-NOMA framework is extended to the general mixed case,i.e.the users with poor channel use real signals,and those with good channel adopt complex circular signals,which is quite common in adaptive modulation.In this paper,a lot of simulation work has been carried out.The simulation results show the numerical results agree well with the analytical analysis.And show that WLMIMO-NOMA has superior outage performance to MIMO-NOMA both in real-signal case and mixed-signal case.