Research On Theories And Algorithms For Resource Allocation In Device-to-Device Communications Underlaying Wireless Cellular Networks

With the rapid development of Internet applications as well as the growing popularity of smart phones and tablets,the huge demands for ubiquitous high data rate wireless communications not only bring heavy traffic load to base station(BS),but also cause shortage of spectrum resource and a sharp increase in energy consumption and greenhouse gas emission.Therefore,it is critical that how to effectively offload the traffic of BS,reduce the energy consumption of system,and improve the spectrum utilization efficiency.Device-to-device(D2D)communication has been recognized as one of the key technologies of 5G to alleviate the pressure of BS,improve the spectrum usage efficiency,increase the system capacity,and save the energy of mobile devices,and thus have attracted much attention recently.The thesis investigates the resource allocation problems from the view of inband and outband D2D communications scenarios and explores the problem how D2D communications can effectively improve the performance of system.In particular,we establish the optimization models,respectively,according to the characteristics of optimization problems.Then the resource allocation algorithms are designed to solve the proposed optimization problems.Simulation results demonstrate the effectiveness of the proposed resource allocation schemes.Specifically,the main contributions are as follows.(1)For inband D2D communications scenario,to further improve the spectral efficiency and system capacity,a joint subcarrier assignment and power allocation scheme is proposed to maximize the sum data rate of D2D users.Specifically,considering the "many-to-many" scenario that a D2D pair can be allowed to use multiple subcarriers and a subcarrier can be allocated to multiple D2D pairs,we build up a mathematical model to maximize the sum data rate of D2D user.To solve the mixed integer non-linear programming(MINLP)problem,this thesis divides it into subcarrier assignment and power allocation sub-problems,and then the subcarrier assignment algorithm and power allocation algorithm are designed to solve subcarrier assignment and power allocation subproblems,respectively.Simulation results show that the proposed scheme can significantly improve the achievable sum data rates of D2D pairs without deteriorating the quality of service(QoS)of cellular user equipments(CUEs)in the meantime.(2)For inband D2D communications scenario,to reduce the energy consumption in cellular D2D network and realize the green communication,the joint optimization of uplink subcarrier assignment and power allocation to minimize total power consumption problem is investigated,meanwhile guaranteeing the required data rate of all users,under the "many-to-many" scenario.Such an optimization problem is in general a MINLP problem that is NP-hard.To solve this problem,this thesis decomposes it into the subcarrier assignment and power allocation problems.For subcarrier assignment subproblem,we devise a heuristic algorithm to assign subcarrier.After that,we exploit the successive convex approximation(SCA)to transform the nonconvex power allocation subproblem into a sequence of convex problems,and then an effective power allocation algorithm is proposed to solve power allocation problem.Simulation results demonstrate the remarkable improvement in terms of power consumption by using proposed algorithms.(3)For relay-assisted access network(outband D2D communications scenario),a joint relay user selection and resource allocation scheme is proposed.Particularly,the problem formulation is to maximize the system utility.To reduce the complexity of the problem,it is divided into relay user selection and spectrum resource allocation problems.Considering the diversity of channel conditions,the matching between terminal users and relay users is modeled as the maximum weighted bipartite matching problem,and the Hungarian algorithm is adopted to solve it.After that,a two-stage Stackelberg game model is designed to solve the spectrum resource allocation problem.Simulation results show that the proposed scheme can effectively improve the downloading rates of terminal users and achieve a "win-win" strategy between the terminal users and relay users.