| In order to solve the exit issues about non-line of sight transmission, signal blind spots, edge effects and so on in IEEE802.16, relevant working group has developed the 802.16j standard. It has added relay station to complete cooperative communication based on IEEE802.16e. Beacse of relay station’s cost is far less than base station, so 802.16j standard can improve system throughput while achieving high coverage under lower cost. It has pushed the WiMAX to a higher stage. In February 2009, the latest draft about 802.16j official standard was announced. The protocol has provided to support the operation about relay station but should not change subscriber station’s specification. So far, the development on the PHY and MAC layer has been matured basically.From the existing researches of IEEE802.16j, we have learned it not only need continue to improve and revise the procotol, but alos there are still some open issues need to solve by researchers. In currently, the issue about QoS is a resrarch hot of some broadband wireless access technologies. The QoS may include many aspects, our works are based on path selection; deploy relay station and bandwidth allocation.In IEEE802.16j network, we can not consider the cooperative transmission between ralay stations, the end subscriber stations need to select the best communication path to access. The working group of 802.16j has doing a lot of contributions in the relay station, but does not specify how to choose communication path and the best deployment location. In this paper, we have studied about several basic routing algorithms firstly. Then to be improved on the basis of algorithm based on channel capacity, and considered the direct service range of relay station and base station, to distinguish the regions about subscriber stations, with the maximum capacity of target to get the optimum deployment location of RS. And considering the shadow effect can more fully reflect the channel conditions. Channel capacity can be considered as the maximum transfer rate and it was seen an important indicator of QoS. Simulation results show that the improved algorithm can through achieve greater channel capacity than the original algorithm and direct network to improve QoS.The MAC layer of IEEE802.16j standard defines five QoS mechanisms services, and provides non-transparent relay station can decision bandwidth allocation of their subscriber stations by itself in the distributed scheduling mode. The subscriber stations which located in the service range of relay station need the cooperative communication by relay station. In this paper, during the bandwidth allocation process in relay link, we have quoted the existing utility function and considered the different Quality-of-Service (QoS) services, then proposed an improved algorithm. The algorithm first allocated the minimum guaranteed bandwidth to QoS services, and then let remaining bandwidth was sequentially allocated to the service which can obtain maximum effectiveness and most competitive, in order to achieve optimal user average utility. The bandwidth allocation process in access link, we have used different scheduling algorithms for different QoS services. Simulation results show that, the improved algorithm is not only can guarantee the QoS of different services, but also superior over PQ and WRR in throughput and average latency. |
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