| Summary: | 碩士 === 國立臺灣科技大學 === 電子工程系 === 106 === IEEE 802.16 is a standard for Wireless Metropolitan Area Network (WMAN). It can provide longer distance communication. To ensure the Quality of Service (QoS) for different multimedia applications, the service flows are classified into five classes. Nevertheless, IEEE802.16 does not provide standard for bandwidth scheduling of this network. Therefore, it is a good issue for exploring to design a scheduling algorithm to meet the QoS requirement of all classes. Polling is a mechanism which the base station (BS) polls subscribe stations (SS) in turn, and then subscribe station can only send bandwidth request in the event of being polled by the base station.
In “Polling according to the piggyback capable bandwidth request for WiMAX network”(PAPCBR)[1], base station changes polling interval of extended real-time Polling Service (ertPS) and real-time Polling Service (rtPS) according to bandwidth request from subscribe stations. If ertPS has bandwidth request, polling interval will be decreased to 10ms directly; if not, polling interval will be increased by 10ms until it is 40ms. And if rtPS has bandwidth request, polling interval will be decreased 10ms until it is 40ms; if not, polling interval will be increased 10ms until it is 150ms. Moreover, rtPS can piggyback its bandwidth request on the request of ertPS. In other words, once polling interval of ertPS arrives, ertPS and rtPS can send bandwidth request simultaneously. Therefore, rtPS can also get opportunity to transmit data in uplink.
In this dissertation, we propose “Polling According to Loss-rate Dependent Piggyback Bandwidth Request for WiMAX Networks”(PALDPBR) based on PAPCBR. Our goal is to improve the packet loss-rate of rtPS. When the traffic load is heavy and packet loss-rate is large, bandwidth can not be allocated to rtPS due to priority problem. Therefore, in this algorithm, rtPS can not only piggyback on the request of ertPS, it can also piggyback on the request of non-real-time Polling Service (nrtPS) and Best-Effort (BE) according to packet loss-rate. In this thesis, we set 10% as the threshold of packet loss-rate for rtPS. As soon as the packet loss-rate of real-time Polling Service is greater than 10%, rtPS can piggyback its bandwidth request on the request of nrtPS and BE. Therefore, rtPS has more opportunities than that in PAPCBR algorithm to get the bandwidth allocation. The simulation shows the result is better than that in PAPCBR algorithm.
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