Research On User Grouping And Power Allocation Scheme For Uplink NOMA Systems

The upswing in multimedia applications places higher requirements on future mobile communications system.Furthermore,the number of terminal accesses is also increasing rapidly and will soon exceed the current system capacity due to the expeditiously developing Internet of Things.Therefore,the new generation mobile communication system(5G)needs to further expand the system capacity to meet the emerging new services.Faced with increasingly tight spectrum resources,orthogonal multiple-access technologies have been unable to meet demand,and new types of multiple-access technologies need to be introduced urgently.Non-orthogonal multiple access(NOMA)technology is being considered as one of the key technologies of 5G because it can not only support large-scale user access,but also greatly improve spectrum efficiency.In addition,NOMA technology can be compatible with other existing technologies,and a scenario where relay and NOMA technology are combined can be considered to further improve system performance.This thesis mainly studies the user grouping and power allocation scheme of uplink NOMA system from the perspective of system capacity and energy efficiency.First,this thesis studies the resource allocation problem of NOMA system with the goal of maximizing system capacity.Due to the complexity of the original problem,this thesis will study user pairing and power allocation.In this scenario,the user pairing scheme in a single cell is studied.Two hybrid pairing schemes are studied to reduce interference between users by combining the advantages of the original far-near pairing scheme and the uniform channel gain difference(UCGD)pairing scheme.Then a sum-throughput maximization problem for uplink is formulated under the constraints of the minimum rate requirements of the users,the maximum transmission power of the user and the total transmission power within a NOMA group.A power allocation scheme within a NOMA group is derived using the Karush-Kuhn-Tucker(KKT)conditions.Simulation results show that the capacity of the NOMA system with the proposed scheme is much better than that of the OMA system.Secondly,this thesis studies the resource allocation problem of relay-based multi-carrier non-orthogonal multiple access(MC-NOMA)system.The power allocation problem of user groups and relay is proposed to optimize system energy efficiency.The optimization problem mainly involves the power allocation of superimposed users on subcarriers and the power allocation of relays between subcarriers.When the first sub-problem is solved,the second sub-problem is alsosolved.Considering the user fairness,the power allocation problem is formulated as a maximization problem of weighted energy efficiency,which is defined as a ratio of the weighted sum rate to the total power consumption.By utilizing Dinkelbach algorithm and Lagrange dual decomposition approach,an iterative power allocation algorithm is proposed.Simulation results show that the energy efficiency of the NOMA system with the proposed algorithm is superior to traditional water-filling scheme and the orthogonal multiple access system.