Tham khảo tài liệu 'quality of service and resource allocation in wimaxfig part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 166 Quality of Service and Resource Allocation in WiMAX Fig. 10. DL hybrid scheduling block UGS rtPS and ErtPS are managed by the WRR scheduler and queues corresponding to non real time flows nrtPS and BE are managed by the same WRR discipline. This stage guarantees a fixed bandwidth for UGS and ErtPS classes and a minimum bandwidth for rtPS while ensuring fairness between flows because the rtPS packets have variable size and this flow could monopolize the server if the traffic is composed by packets with larger size than those of Class 1 and 2. In the second stage output of the two WRR schedulers are enqueued in two queues F1 and F2 packets of these queues are managed by a priority PQ scheduler which gives higher priority to real time stream stored in F1 which are more constringent in term of throughput and delay than the non-real time traffic stored in F2 which are less time sensitive. Once scheduled the MPDUs are placed in a FIFO queue of infinite size. The next step is to choose the users and therefore MPDUs that must be served in this queue it is also necessary to determine how much MPDUs will be served and what are the slots allocated to them Step 3 The users selection We consider that for each source that transmitting a traffic class i a system have to allocate an s minimum required bandwidth to satisfy its QoS constraints. If we consider that this source has traffic with k service classes to send the BS has to allocate a minimum required bandwidth denoted by S for each user n to satisfy its QoS constraints. If we assume that this user carries traffic with the five service classes i Ễ U so this bandwidth Sn corresponds to 5 n E ấ 27 i 1 Where s is the required bandwidth to satisfy QoS constraints of class i. Note that these parameters varies periodical in time. Without loss of generality let s suppose that each user has only one type of traffic class to receive. So either it should be noted sn Si. let s consider that for every user n in the system we can
