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    Title: 一個提升車載網路上網速度的K-Hop資料轉送機制
    K-Hop Data Forwarding to Speed-Up Internet Access in Vehicular Networks
    Authors: 邱柏昇
    Contributors: 曾秀松
    Show-Shiow Tzeng
    Keywords: K-Hop;地理機會路由;車載網路
    K-Hop;Geographical Opportunistic Routing;Vehicular Networks
    Date: 2012-07-19
    Issue Date: 2012-11-27 16:30:18 (UTC+8)
    Abstract: 車載網路是無線網路的一種,它的組成包含了兩個群組,第一個群組為裝載了無線通訊裝置(例如:WiFi)的車子們,車子之間可以透過無線通訊裝置互相溝通,第二個群組為可連接網際網路的資訊站,資訊站通常設置在路邊,提供車輛以低成本就能與網際網路連線。由於無線通訊裝置的傳輸範圍是有限的,但車輛與資訊站的距離卻有可能十分遙遠,所以一輛車輛想要傳送封包給資訊站時,中間有可能必須經過一輛或多輛車輛來幫忙轉發封包,在這種情況下,要將封包送達目的資訊站,有可能會造成過多的時間延遲以及掉包的現象,我們需要盡可能的縮短傳輸時間以及封包的遺失率,提供使用者更好的服務。

    在過去的地理機會路由中,攜帶封包的車輛會嘗試在他的傳輸範圍內,去搜尋一個可以使封包在更短的時間內抵達目的地的車輛,並將封包轉發給他。如果找不到符合此條件的車輛,車輛就會自己持續攜帶著封包;然而,由於隱私的問題,或者某些車輛缺乏導航系統裝置以及在車輛密度較稀疏的區域時,車輛不是每次都能在一跳內找到一輛合格的車輛來傳遞封包。在此論文中,我們提出利用k-hop來找尋合格的車輛,它主要的想法是擴大搜尋的範圍。在k-hop搜尋中,較困難的地方是必須考慮到車輛會在傳輸時間中移動,而導致中繼的跳躍點找不到預定的下一跳來轉發,使得掉包的機率增加,並且會造成抵達目的地的時間被拉長。我們進行事件驅動的模擬,模擬的結果說明我們提出的k-hop搜索在封包的抵達延遲上明顯的低於one-hop搜索。
    Vehicular networks, which consist of (i) vehicles equipped with communication devices e.g. WiFi interface and (ii) infostations which are access points connecting Internet and usually are placed around the road side, provide vehicles with Internet services in a cheap and scalable manner. Due to the short transmission range of WiFi and possible long distance between a vehicle and an infostation, a vehicle sending a message to an infostation may require one or more vehicles to forward the message. It is critical to route the message such that the total time to arrive the destined infostation is short with low message loss.

    In previous geographical opportunistic routing, within the transmission range of a vehicle currently carrying a message, the vehicle attempts to find an eligible vehicle through which the message is delivered to the destination in a shorter time. If there is no eligible next vehicle, the vehicle continues carrying the message; however, due to privacy, lack of navigation equipment installation or sparse density of vehicles, a vehicle may not frequently find an eligible vehicle within one hop range to forward the message. In this paper, we propose a k-hop search to find an eligible vehicle, which core idea is to enlarge the search range. The difficulty of the k-hop search is that the intermediate hop must be selected carefully; otherwise, the message will be incorrectly forward to a wrong vehicle which prolongs delivery time and increases message loss. Simulation results show that the proposed k-hop search produces significantly lower packet delay than the one-hop search.
    Appears in Collections:[Optoelectronics communication engineering department] theses
    [Department of Optoelectronics Communication Engineering] Show-Shiow Tzeng

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