Research On User Pairing For The Cooperative Non-orthogonal Multiple Access Systems

The development of the Mobile Internet(MI)and the Internet of Things(IoT)has brought about double growth in mobile data traffic and the number of terminal connections.The new multimedia not only requires a lot of data traffic to support,but also attracts more and more users to flood into the network.Therefore,it leads to rapid increase of traffic demand in overall network.However,the limited resources have become the bottleneck of further development and expansion for the wireless communication technologies.The traditional multi-user access technology adopts orthogonal resource,and the optimal utilization of resources cannot be achieved from the perspective of information theory.Hence,it is difficult to support the larger number of user.Under the above fact.Non-Orthogonal Multiple Access(NOMA)technology has attracted more and more attention from the experts and scholars,and it is regarded as the potential candidate of multiple access for the next generation mobile communication system.In the NOMA system,it is worth noting that the users with better channel conditions have prior information about the messages of other users by exploring the Successive Interference Cancellation(SIC)at the receiver.The feature of information decoding provides a natural opportunity for the combination of NOMA and cooperative communication.On the other hand,the decoding complexity of system increases as the number of users increases when cooperative users employ SIC.In order to obtain the tradeoff between system performance and complexity,user pairing in the cooperative NOMA is proposed.Moreover,the better cooperation of multi-user can be achieved by adopting transmission of non-orthogonal and orthogonal method.Thus,it is of great significance to study the user pairing strategy based on the cooperative NOMA systems.In terms of above elaboration,this thesis focuses on the research of the user pairing in different cooperative NOMA communication scenarios.Firstly,the paper briefly introduces NOMA and cooperative NOMA.Then,for the hybrid VLC(Visible Light Communication)-RF(Radio Frequency)NOMA systems,a bipartite matching based user pairing scheme is proposed.On the other hand,for the cooperative NOMA systems with Simultaneous Wireless Information Power Transfer(SWIPT),a Stackelberg game based user pairing scheme is proposed.The main contributions and innovations in this paper can be summarized as follows:1)A bipartite matching based user pairing for hybrid VLC-RF cooperative NOMA systems is proposed,which is able to minimize the outage probability of system.First of all,the paper proposes a hybrid VLC-RF cooperative NOMA system to extend the coverage of VLC.In addition,the proposed system can also meet the requirement of multi-user communications at the same time.Subsequently,in the proposed system,the thesis analyzes the outage probability of system.Aiming at minimizing the outage probability of system,the thesis studies the user pairing and proposes a bipartite matching based user pairing scheme.By the graph theory and the rule of logarithmic operations.the original problem can be converted into the one of finding the maximum weighted matching in a bipartite graph.Kuhn-Munkres(KM)algorithm is utilized to solve the problem.Simulation results demonstrate that the system performance is markedly improved with our proposed scheme.2)A Stackelberg game based user pairing for cooperative NOMA systems with SWIPT is proposed,and the utility function of each user is maximized in the proposed scheme.In the cooperative NOMA systems with SWIPT,the achievable rate of each user is firstly analyzed.Furthermore,the near user uses the energy harvested by SWIPT to forward information for paired far user,which can improve the reliability of far user.However,the cooperative communication systems with SWIPT have influence on the achievable rate of near user.Thus,the near user is reluctant to take participate in the cooperative communication without compensation.To promote the near user as relay.game theory can be introduced.Then,the thesis analyzes the utility functions of each far user and each near user,and constructs the optimization problems of maximum utility functions.The paper also models the competitive relationship between far users and near users as multi-leader multi-follower Stackelberg game.According to the utility functions.the user pairing by exploring the Gale-Shapley(G-S)is researched,and a Stackelberg game based user pairing scheme is proposed.The results show that the proposed algorithm can improve the utility function of each user.