QoS Aware HARQ Mechanism in IEEE 802.16j MMR Network

IEEE 802.16標準中有所謂Mobile Multi-hop Relay（MMR）的概念，然而基地台覆蓋範圍不足及遮蔽效應等問題尚待解決，因此在IEEE 802.16j標準中提出Relay Station（RS）以提升網路傳輸量並增進無線通訊品質。在MMR中由於多了中繼傳輸站來傳遞資料，因此需要有較多的連線頻道，此外也不能保證所有頻道都處於良好狀態，所以會有很高的機率造成資料傳送失敗。混和自動重傳要求（Hybrid Automatic Repeat reQuest, HARQ）的提出便是用來保證資料傳遞成功的機制。HARQ在IEEE 802.16-2004就已被提出，然而我們發現該HARQ機制在802.16j中是不具效率的，而且也並無法確保QoS（Quality of Service）的要求。在本論文中我們改善Chen[4]所提出的Dynamic Pre-allocation HARQ（DP-HARQ）機制，藉由考慮slot分配不足及封包發生非連續錯誤時造成延遲時間增加等問題，並加入具服務品質感知（QoS aware）的機制，以降低整體延遲時間（delay）並能有效提高吞吐量（throughput）。最後，我們以具二個hop以上的模擬環境，證明我們所提出的方法優於802.16j的HARQ機制及Chen[4]的方法。Mobile Multihop Relay (MMR) had already been defined in IEEE 802.16 network. The major purpose of MMR is to efficiently extend the coverage of a base station and to solve the shadow fading problem. The Relay Station (RS) defined in IEEE 802.16j is thus proposed to fulfill these goals. Because of the MMR Relay Station, we need more channels to transmit packets. However we cannot guarantee that all chaneels are in good condtion, there might be a high probability of failure transmission. The Hybrid Automatically Repeat reQuest (HARQ) mechanism is therefor proposed to ensure the successful transmission. The HARQ proposed in IEEE 802.16-2004 is not sufficient in 802.16j. Besides it can not help to meet QoS (Quality of Service) requirements. In this reserch we improve Chen’s [4] Dynamic Pre-allocation HARQ (DP-HARQ) mechanism by considering some problems like lack of slot allocation and packet transmission failure with non-continuous error, etc. We add the QoS aware mechanism to reduce the overall delay time and improve the throughput effectively. Finally, we simulate three hops environment and show that our method outperforms both the standard IEEE 802.16j the HARQ mechanism and Chen’s [4] method