Study On The Scheduling Of Uplink RtPS Service In WiMAX

The technology of WiMAX, which is based on IEEE802.16standards, has becomea research hotspot in the field of communication for its high transmission rate, servicesof heterogeneous classes of traffic and effective network mode. WiMAX has aguarantee of the different QoS parameters for different business, and bandwidthscheduling in the MAC layer is the key to guarantee the QoS parameters. However,IEEE802.16standards don’t do the hard and fast rules on how to achieve the resourcebandwidth allocation. Scheduling algorithm applicable to different business are not thesame, so it is necessary to research efficient scheduling algorithm combining differentbusiness characteristics to improve system performance and achieve satisfying qualityof service.The QoS parameters of real-time service (rtPS) often need strict requirements, soits bandwidth scheduling algorithm requires targeted design, in order to ensure asatisfactory service. The paper selected two typical variable-rate rtPS businesses, MPEGvideo and VoIP voice. With a combination of business features analysis, research uplinkscheduling algorithm in the MAC layer for these two types of rtPS business.According to the problems of low resource utilization and large access delay whenertPS algorithm serving business such as MPEG whose transmission length changescontinuously or gradually, considering the characteristics of MPEG video an improvedalgorithm is proposed on the basis of the ertPS’s workflow. By optimizing transmissionconditions of bandwidth request in the bandwidth polling slot at user station and takingthe urgency of connections into account, the improved algorithm can minimizes thenumber of bandwidth requests. The simulation results show that the proposed algorithmobviously decreases UL delay by15%and slightly enhances throughput compared withertPS.VoIP, another type of rtPS business, has an important characteristic of voicecommunication, that is only about40%that contains voice and other times are mute orbackground noise. It would cause a lot of waste of resources during the silence periodwhen ertPS algorithm serves this kind of business like VoIP. Considering thecharacteristics of VoIP CODEC with VAD/DTX/CNG and the different user variants ofthe silence duration, an uplink scheduling algorithm is proposed for ITU-T G.729B VoIPCODEC with VAD/DTX/CNG. The improved algorithm uses ertPS scheduling algorithm during the active peroid, but during the silence period it adopts two types ofauthorization mechanism instead according to the variants of SID frames for uplinkresource allocation. Actually the improved algorithm saves uplink resources at the costof increasing access delay. The simulation results show that the average uplink delay ofthe improved algorithm is still within what the QoS parameters require, while systemcapacity has a17%increase.