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    题名: 使用品質掃描機制提升車載行動網路中的換手效率
    其它题名: Improving handoff efficiency over VANET by qualityscan
    作者: 詹弘麟;Chan, Hung-lin
    贡献者: 淡江大學電機工程學系碩士班
    吳庭育;Wu, Tin-yu
    关键词: 行動車載網路;智慧型運輸系統;存取點控制器;VANET;ITS;APC
    日期: 2010
    上传时间: 2010-09-23 17:52:21 (UTC+8)
    摘要: 車載行動網路是將無線通訊整合至車輛的新興智慧型運輸系統科技,智慧型運輸系統的應用包含著行車安全性、運輸效率、資訊及娛樂等應用。在車載的環境下主要的終端設備為汽車,與一般人攜行走動的終端設備來比較,其移動性較高,換手的行為將會經常發生,若換手造成的延遲過長時將會影響網路傳輸的品質,尤其對於一些即時性的網路服務將有重大的影響,故傳統的行動管理機制已經不能符合車載行動網路的需求,許多快速換手的機制相繼提出。然而一般選擇換手存取點的方式為選取最佳訊號強度的存取點當做換手的存取點,並沒有考慮到不同存取點的負載狀況,故不能使網路的頻寬有效的利用,當某些存取點過度忙碌時將會使服務的品質下降。
    在車載的環境中,存取點可事先建置完成,並依照不同路段的車流量可以調整區域內存取點的數量以達到網路流量分散提高服務品質的目的,例如在容易塞車的路段相對地網路使用量較高,若是只有一個存取點做服務,勢必造成網路壅塞的狀況。我們提出一適用於車載環境的快速換手機制,除了減少換手的延遲並考慮到區域存取點的負載平衡,透過建置好的存取點控制器可以定期收集各存取點忙碌的狀況,並預測下一時刻的網路流量,經由計算過後的參數透過廣播訊標訊框時廣播給鄰近的行動車輛節點,行動車輛節點可依據此參數選取對本身服務品質最佳的存取點。如此一來,可以達到區域存取點的負載平衡並提高服務的品質,提升車載行動網路中的換手效率。
    Vehicular ad hoc network (VANET) is an emerging intelligent transportation system (ITS) that integrates wireless communications with vehicles. ITS applications currently include driving safety, transportation efficiency, information and entertainment-related applications. Compared with handheld devices, the mobility of vehicles, the main terminals in VANETs, is obviously higher and the handoff procedure consequently occurs frequently. Too long handoff latency works upon the transmission quality, especially on some real-time network services. Since traditional mobility management mechanisms no longer meet the needs of VANETs, many fast handoff schemes were proposed. However, without considering the loading status of different APs, most handoff mechanisms choose the AP with the optimal signal strength as the handoff location. In such a manner, the network bandwidth cannot be utilized efficiently and the overload of some APs may degrade service quality.
    In VANETs, APs can be established in advance. According to different traffic flow, the number of APs can be adjusted in order to distribute network traffic and improve service quality. For example, the network traffic is undoubtedly high in a crowded road section. If only one AP provides service, the network traffic is bound to be congested. Therefore, we proposed QualityScan, a fast handoff scheme for VANETs to reduce the handoff latency and keep the APs load-balanced by deploying AP controller (APC) that periodically collect the status of the APs in the subnet and predict the network traffic at the next moment. Based on the result parameter broadcasted in beacon frames, the neighboring MNs can determine the best AP for the service. Thus, the APs in the area can be load-balanced, the service quality can be improved, and the handoff efficiency over VANETs can be further enhanced.
    显示于类别:[電機工程學系暨研究所] 學位論文

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