Research On Resource Allocation Algorithms In NOMA Systems

As one of the key candidate technologies of the fifth generation(5G)mobile communication system,non-orthogonal multiple access(NOMA)has attracted extensive attention in both industrial and academic world.By applying superposition coding at the transmitter side and successive interference cancellation(SIC)at the receiver side,NOMA can significantly improve the system throughput and the average throughput of cell edge users.In recent years,with the rise of the concept of green communication,the system energy efficiency(EE),along with spectrum efficiency(SE),has become another important index to measure the performance of a communication system.Improving the EE of communication networks helps reduce greenhouse gas emissions and electromagnetic pollution,and is in line with the concept of green communication.This dissertation focus on the resource allocation algorithms in wireless communication systems using NOMA to improve the system EE and SE.The main innovations and contributions of this dissertation are summarized as follows:1.For downlink NOMA system,we optimize the system EE and SE jointly and give a low-complexity optimal power allocation algorithm.The maximum transmit power constraint at the base station and users' quality of service(QoS)requirements are both taken into account.It is proved that the system EE is a strictly quasi-concave function of transmit power.Based on this pseudoconvexity,we formulate the original optimization problem into a bilayer optimization problem and obtain an optimal transmit power allocation algorithm.Besides,we have investigated the relationship between the circuit power and the optimal transmit.It is proved that the optimal transmit power is non-decreasing with the ciucuit power.2.For downlink NOMA system,we propose energy-efficient energy-efficient resource allocation strategies.We study the resource allocation algorithms to maximize the system EE considering the maximum transmit power constraint at the BS,users' QoS requirements and complexity of receivers,and give an novel subchannel assignment algorithm and low-complexity subchannel power allocation algorithm.Besides,the optimal power allocation coefficients among subchannel multiplexed users are also determined.An novel user sub-channel matching algorithm based on the equivalent channel gain matrix is proposed.Compared with the existing algorithms,the proposed algorithm has good performance and low complexity.For power allocation,this dissertation first formulates the optimal power allocation coefficients among subchannel multiplexed users.Then,we formulated the power allocation problem between sub-channels and users as a sum of ratio problem(SoRP)and give a sub-optimal solution.3.For cooperative relaying systems using NOMA,we give an low-complexity optimal power allocation algorithm.We study the optimal power allocation algorithm to maximize the system GEE considering the maximum transmit power constraints at both the source node and relay node.It is proved that to maximize the optimal system GEE,the rate of any symbol in the first time slot should be equal to that in the second time slot.Based on this important conclusion,we propose an optimal transmit power allocation algorithm.The influence of the location relationship between the destination nodes and the relay node on the system GEE is also analyzed and the provided results can provide some reference for the design of cooperative relay system using NOMA in the future.