Resource Allocation For User Fairness In MC-NOMA Systems

In fifth Generation(5G)wireless communication systems,non-orthogonal multiple access(NOMA)greatly improves network capacity and reduces communication latency by providing services to multiple users simultaneously on a same resource block.In addition,the communication requirements of users in large-scale connection scenarios are effectively guaranteed.NOMA is able to serve much more users than orthogonal multiple access(OMA).In NOMA system,multiple signals are integrated into a same resource block by superposition coding,the receiver decodes and separates the signal by using the serial interference cancellation technology.However,even though service experience and system throughput have been improved,NOMA system still has a series of problems that urgently need to be solved.Among those problems,ensuring the fairness of user rate is an inherent trouble in NOMA system optimization.That is due to the premise of SIC in NOMA system is divide users on a same resource block into strong or weak user according to user's channel gains.However,serial interference cancellation can't eliminate the interference from strong users to weak users,which leads to a huge difference in the rates of strong and weak users on the same resource block,thus the communication demands of weak users cannot be guaranteed.Undoubtedly,it is urgent and necessary to study resource allocation to ensure user fairness in NOMA system.In a single carrier NOMA system,resource allocation is mainly a power allocation problem on a single resource block.In contrast,the resource allocation of multi-carrier nonorthogonal access(MC-NOMA)system needs to consider the joint allocation of carrier and power,which is more complex.Based on the above considerations,this paper investigating the resource allocation problem on the background of MC-NOMA system with user fairness.Through joint optimization of subcarrier allocation and power allocation,the performance of MC-NOMA system can be improved and the rate fairness of each user can be guaranteed.The contents are as follows:1.Joint subcarrier and power allocation based on proportional fairness.This part considers the joint optimization problem by treating the logarithmic sum of MC-NOMA user rate as the optimization objective.By using variable substitution,this chapter turning the original problem into a convex optimization problem,and the optimal power and subcarrier allocation solutions are obtained.Based on this,an iterative algorithm is proposed to realize the joint optimization of subcarrier and power while maximizing the utility function of MC-NOMA system.Simulation results show that the proposed resource allocation algorithm has obvious advantages over traditional OMA systems in whether utility,rate or fairness.2.Proportional rate constrained MC-NOMA system resource allocation.This part of the paper explores subcarrier and power optimization under proportional rate constraint.Essentially,the proportional rate constraint can be thought of as a general form of user rate proportional fairness.Non-affine equality constraints are transformed into affine constraints by introducing auxiliary variables.Thus,the convex optimization theory is used to find the optimal solutions for the allocation of subcarrier and power.Based on that,a resource allocation algorithm focused on optimal subcarrier allocation solution is proposed,and offers a subcarrier allocation algorithm with proportional rate constraint as a benchmark comparison algorithm.Simulation results show that the proposed algorithm achieves higher user sum rate compared with existing algorithms,while the user fairness can be well guaranteed.