Study On Uplink Packet Scheduling Algorithm Of WiMAX

1,IntroductionIn the information age,IT technology has been developing so rapidly that communications industry is at a new turning point.A variety of new businesses came into being,the user pursuit the setting of audio,video,graphics,animation and other multimedia into one broadband service.WiMAX/IEEE802.16 wireless MAN standards came into being to meet the "last mile" of communication requirements.On october 19,2007,the International Telecommunication Union approved WiMAX as a mobile wireless standard.And gethered with WCDMA,CDMA2000,TD-SCDMA to become the world's fourth 3G standard.In the field of mobile communication technology,WiMAX is bound to become an important part of global communications architecture in the future.Radio resource management(RRM) can use limited wireless resources more reasonable and more effectively,it includes power control,handover,call admission control,congestion control,packet scheduling and so on.Packet scheduling algorithm is one of the core technology for achieving network QoS,its main function is allocate bandwidth and reuse mechanism at packet-level through the scheduling strategy,and ensure reserve bandwidth or delay of time.Call admission control and congestion control strategies are used depending on the specific scheduling rules.WiMAX/IEEE802.16 standard defined four different types of scheduling services,can provide users with a constant bit-rate service,periodic real-time business,cyclical service,as well as non-real-time non-guaranteed quality of services,meeting the needs of different users at different bandwidth and time relay request,but did not give the standard scheduling mechanism and the scheduling algorithm for implementation.In this paper,based on the existing scheduling architecture an improved scheduling algorithm ICBQ for uplink is proposed.At the same time,draw cross-layer scheduling and joint weighted parameter into scheduling architecture,propose JWC scheduling algorithm.The improved scheduling algorithms can improve the radio resource utilization,enhance the user fairness.2,Improved Packet Scheduling Algorithm of the UplinkWiMAX/IEEE802.16 standard defined four different types of scheduling services: Unsolicited Grant Service(UGS),Real-Time Polling Service(rtPS),non-real-time Polling Service(nrtPS) and the Best Effort(BE).Each type of service has different QoS needs.The proposed algorithm in this paper has two schedulers on logic,conventional scheduler and hierarchical scheduler.Using conventional scheduler to meet all services needs when the system does not at the state of congestion.Status meeting the formula(1) is considerd non-congestion state,for all four types services without distinction to meet their bandwidth needs.Otherwise the system enters the congestion status,scheduling with two dispatching.BS grants fixed-size bandwidth for UGS service,so there is no need for the first dispatching,scheduling at the second dispatching directly,do it with the First Come,First Served rule.At the first dispatching,rtPS service scheduling uses CEDF(Compention Eealist Deadline First) scheduling strategy under the minimum operational flow rate conditions;nrtPS service uses IWFQ scheduling strategy under the minimum operational flow rate conditions;for BE service,although system is in congestion status,we must also take into account user fairness between many of the BE flow,so dispatch with RR scheduling strategy to provide the same opportunity to stream packet transmission.At the second dispatching,schedule with static priority approach.3,Joint Weighted Cross-layer Scheduling AlgorithmFor more reasonable use of wireless resources,at the second dispatching,in this paper, the physical layer and MAC layer informations are carried out for cross-layer scheduling. Physical layer is modeled with Nakagami model which fit measures data well,combined with the BER requirements of business,getting relationship of the SNR and AMC.BS grants fixed-size bandwidth for UGS business,so there is no need for the first dispatching, scheduling at the second dispatching directly,do it with the FCFS rule.At the first dispatching,the other three businesses are dispatched similar to previous.At the second dispatching,hight SNR businesses have high priority.Taking the different of time delay,rate requirements of the three types of services into account,this article introduce a joint weighted parameters.P_i =W_R~* R_i +W_c~*C_i(2)e select the greatest priority packet at the second dispatching.4,The simulation and analysis of the improved Uplink Packet Scheduling AlgorithmsBased on the improved algorithm and traditional algorithm simulation comparison,it can be seen from the results that the improved uplink scheduling architecture of this paper effectively improves the nrtPS,BE scheduling opportunities under metting rtPS QoS requirements,improves the system bandwidth utilization rate and the fairness of the user.At the same time,Joint weighted cross-layer scheduling algorithm effectively improves the system throughput and user fairness.