Research On The Resource Allocation Algorithm For The Downlink Of Multi-user OFDM System

With the rapid development of wireless communication industry,the demand for wireless spectrum resource is increasing,the energy consumption and the load of wireless communication devices are both growing.So,how to allocate the existing wireless resource rationally to improve the spectrum utilization and energy efficiency has became one of the hotpots of wireless communication.Since the orthogonal frequency division multiplexing(OFDM)technology has unparalleled advantages than other multiplexing,it has been widely applied to the wireless communication system.It can effectively resist the multipath interference and fading,and has high bandwidth efficiency,high data transmission rate,good adaptive characteristics.And it is easy to combine with other technologies.Based on the good adaptive features of OFDM technology,how to allocate and optimize the resource reasonably will cause significant impacts on the performance according to the instantaneous channel state resources of users in multi-user OFDM system.This thesis studies how to allocate the resources such as the sub-carriers,power and bits reasonably in the downlink of the multi-user OFDM system based on the principle of fairness among the user's data rate to obtain a higher total system data rate.Specific contents of this paper are as follows:1.Firstly,we introduced the development of wireless mobile communication technology,the basic principles of OFDM technology and its practical application in the field,and analyzed the working principle of the multi-user OFDM system and made an detailed introduction on adaptive resource allocation principles of the system.Then we summarized and classified the existing resource allocation algorithms and further illustrated the research status and significance of resource allocation algorithm in the multi-user OFDM system etc.2.A single-user power allocation algorithm using the method of water-filling and greedy power allocation is proposed.The algorithm is as following:Allocating the power to every sub-carrier of the user using water-filling algorithm and finding the number of bits loaded on each sub-carrier at first.Then updating the power and bits of each sub-carrier using the method of greedy power allocation to make full use of the extra power and to improve the power utilization and user's data rate.And a fairness first resource allocation algorithm is proposed based on the single-user power allocation algorithm.Fairness of users' data rates is treated as the primary consideration in the allocation of sub-carriers.where the best free sub-carrier is first allocated the user with the greatest demand for data rate.After the sub-carriers are all allocated,updating the power of sub-carriers and bits of each user to obtain the final result using the method of greedy power allocation.The simulation results show that the proportion of users' data rates can be very close to the requirement one of the system in the algorithm and the performance of fairness is very good.Also,the total data rate of the system is greatly improved.3.Improve the greedy power allocation algorithm and propose a new resource allocation algorithm with optimized fairness based on that.The algorithm has the two factor with avoiding the worst sub-carrier and optimized fairness in the sub-carrier allocation.Sort all the users in ascending order according to their worst channel gain of all the sub-carriers and then assign each user a best sub-carrier successively.The remaining sub-carriers are allocated with the constraint on proportional fairness.Then update the power and bits for each sub-carrier of all the users using the improved greedy power allocation algorithm.Simulation results show that the algorithm improves the capacity of the system while ensuring the performance of fairness better.