Research And Simulation Of Downlink Resource Scheduling Algorithm In LTE System Based On Network Simulator 3

In the LTE system,downlink resource scheduling should not only guarantee system throughput and fairness,but also satisfy the QoS requirements of the users.So downlink resource scheduling has become one of the important research directions of the LTE.Firstly,this paper introduces the protocol stack and the frame structure in the LTE system.Next the downlink resource scheduling,reporting policy of the Channel Quality Indication,the Adaptive Modulation and Coding technology,the type of the radio bearer and the performance of measuring the scheduling algorithm are expounded.Based on 3 GPP LTE standard of R9 and the network simulator 3,this paper designs the downlink scheduling signaling and the scheduling process of the downlingk scheduler.Then,this paper analyzes four traditional scheduling algorithms detailedly,namely the Maximum C/I(Max C/I),Round Robin(RR),Proportional Fair(PF)and MLWDF(Modified Largest Weighted Delay First).Max C/I,RR and PF can't guarantee the delay of the users while MLWDF can guarantee the delay of the users.However the MLWDF has two main shortcomings.One is that it can not sufficiently reduce the queue delay of the delay-sensitive bearer.The another is that it can't guarantee the data rate of the users.In view of the first shortcoming of MLWDF algorithm,this paper designs the modified algorithm MLWDF-D.By changing the delay factor of the scheduling priority,MLWDF-D can dramaticlly improve the scheduling priority of the delay-sensitive bearer so that the delay-sensitive bearer can obtain the priority scheduling,thus the communication quality of the users can be guaranteed.Then,the utility of C++ language realizes MLWDF and MLWDF-D algorithms respectively in the NS-3.These algorithms select the scheduling users and confirm the transport block size and location.Then the typical single cell simulation scenario is set up.All users are uniformly distributed in the cell.Fifty percent of the users transfer another bearer whose maximum queue delay is 100 milliseconds,and the others transfer the bearer whose maximum queue delay is 300 milliseconds.It can be shown from the simulation results that MLWDF-D can reduce the packet loss rate of the whole system compared with MLWDF.It also can reduce the queue delay of the delay-sensitive bearer and reduce by 11.007%on average.It means that MLWDF-D can better schedule the delay-sensitive bearer within timing constraint.However,MLWDF-D may increase the queue delay of the other bearers and sacrifices the fairness among the users.In view of the second shortcoming of MLWDF algorithm,based on MLWDF and MLWDF-D,this paper designs the modified MLWDF-T algorithm.By introducing a guarantee bit rate parameters,MLWDF-T can rapidly improve the scheduling priority of the bearer whose guarantee bit rate can't be met and make the bearer receive priority scheduling.Then,the utility of C++ language realizes MLWDF-T algorithm in the NS-3.It adds the guarantee bit rates from different bearers.And the typical single cell simulation scenario is set up.It can be shown from the simulation results that MLWDF-T can improve the throughput of bearer whose guarantee bit rate can't be met and improve 14.053%on average compared with MLWDF.It also can reduce the delay of the bearer.However,it can reduce the throughputs of the other bearers and loses the fairness among the users.