Study On Resource Allocation Algorithm In Downlink Multiuser OFDM System

OFDM(Orthogonal Frequency Division Multiplexing)is the pivotal technology of the fourth generation mobile communication system.OFDM has ability of combating channel fading and eliminating inter-symbol interference,which can achieve low time delay and high spectral efficiency.In the future,with the increase of mobile communication services and mobile devices,the communication system should achieve higher spectral efficiency and energy efficiency.In practical applications,we also need to consider the different business requirements of users,which can be expressed by proportional rate constraints.Proportional rate constraints reflect the fairness between users.Satisfying the proportional rate constraints strictly leads to low system performance.Lots of papers improve the system performance by relaxing proportional rate constraints,but the system fairness is not well quantified.In order to flexibly achieve the tradeoff between fairness and system performance,this paper introduces the concept of the fairness threshold.This paper tries to improve the performance of OFDM system when satisfying fairness threshold.Therefore,this paper studies the spectrum efficiency optimizing algorithm and energy efficiency optimizing algorithm based on fairness threshold.The main works are as follows: 1、Joint subcarrier and power allocation algorithm based on fairness thresholdIn this paper,we incorporate the water-filling power allocation algorithm and subcarrier exchange into the subcarrier allocation.On the one hand,this algorithm can make full use of water-filling power allocation algorithm to guide the subcarrier allocation.On the other hand,the system can improve the spectral efficiency and get a rough degree of fairness through exchanging subcarrier.Then we use particle swarm optimization algorithm to adjust power allocation,which makes the system satisfy the fairness threshold.The simulation results show that the proposed algorithm can effectively achieve the tradeoff between fairness and spectral efficiency.It can improve spectral efficiency of OFDM system when satisfying fairness threshold.2、Energy Efficient resource allocation with variable fairness threshold based on BBOWith the increasing demand for multimedia services and the interconnection of all things,the energy consumption of the communication system will increase explosively.Therefore energy efficiency becomes more and more important in the field of “green radio”.This paper uses two steps to allocate subcarriers and power.When the subcarriers are allocated,we use biogeography based optimization algorithm to optimize the water level of each user in order to improve the energy efficiency of OFDM system when satisfying the fairness threshold.The simulation results show that the higher fairness threshold constraint results in lower energy efficiency,and energy efficiency can be improved by relaxing the fairness threshold.The proposed algorithm which can adjust the fairness threshold and achieve the tradeoff between fairness and energy efficiency is a more flexible algorithm.