在都市環境中基於方向之車輛定位服務

車用行動通訊網路(VANET)是無線移動網路中一種新興的且極具挑戰性的新型態。VANET是由行動中的車輛所自行形成的分散式網路。為了能夠有效率地將訊息由來源車輛傳送到目的車輛,必須仰賴VANET追蹤記錄其網路節點位置的能力。由於車輛的高移動性,車輛位置服務一直是個極具挑戰性的議題。目前位置服務機制的研究可分為flooding-based與quorum-based兩大類,但是都不適用於VANET中。Flooding-based的方法,網路中的行動節點需要對其他所有節點送出位置更新或詢問的訊息,如此將造成網路上大量的負擔。Quorum-based的方法,一些行動節點被選為位置伺服器(亦即quorums),需要維護大量的資訊。當因為車輛移動而需要更換位置伺服器時,可能造成訊息來不及換手而產生遺失的狀況。本文提出一個針對都市環境中,基於方向(Direction-based)的車輛位置服務協定。利用在都市中高車輛密度與車輛高速移動的特性,位置資訊的更新透過車輛於交叉路口交會時互相交換。同時考量VANET中通訊,大部分都有區域化的特點,也就是車間通訊通常發生在地理位置相近的車輛間。並且每部車輛被查詢的頻率也有所差異 (例如,某部車輛有一些有趣的短片可供分享)。因此我們將依據與目的節點的距離,車輛被查詢的頻率與位置資訊的新舊等因素,計算出緩存區中位置資訊的重要性,並以資訊重要性來決定需要傳遞的範圍。在實驗中,我們能以較高的位置查詢成功率與縮短查詢的時間,並同時降低資訊更新與查詢的訊務量,減少網路的負擔。

關鍵字

車輛定位服務；車用行動通訊網路

並列摘要

The VANET’s ability to keep track of the location of its nodes (vehi- cles) is crucial for a node to efficiently route messages to destinations. Duo to the high mobility of vehicles, topology in VANETs changes rapidly. The existing location service employed in MANETs is not very suitable for VANETs. Therefore, location management in VANETs remains a major challenge. In this paper, we present a direction-based location service protocol (DLSP) in cities. Consider the movement of vehicles is constrained by streets and a moving vehicle usually does not change direction until it reaches the next intersection. The main goal of DLSP is that a query message can reach the destination by following the guidepost located at intersections. Vehicles exchange se- lected location update information only at intersections. Furthermore, due to DLSP is locality-aware, it achieves minimum control overhead. We compare the performance of our protocol with that of other promi- nent location service protocols by simulation. The results show that our protocol features lower control overhead and higher query suc- cess rate.

並列關鍵字

Direction-based ； Location Service ； VANET

參考文獻

[1] X. Bai, X. Ye, H. Jiang, and J. Li. ”A Novel Traffic Information System for VANET Based on Location Service”. In Proceeding of IEEE International Con- ference on Networks, pages 1–6, 2008.

[3] G.-Y. Chang, Y.-Y. Chen, and J.-P. Sheu. ”A Region-based Hierarchical Loca- tion Service with Road-adapted Grids for Vehicular Networks”. In Proceed- ing of International Conference on Parallel Processing Workshops, pages 554–561, 2010.

[4] Y.-J. Chang and S.-Y. Wu. ”Intersection Location Service for Vehicular Ad Hoc Networks with Cars in Manhattan Style Movement Patterns”. In Ubiq- uitous Intelligence and Computing, pages 284–296, 2008.

[5] S. M. Das, H. Pucha, and Y. C. Hu. ”Performance Comparison of Scalable Location Services for Geographic Ad Hoc Routing”. In Proceeding of IEEE Computer and Communications Societies, pages 1229–1339, 2005.

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國際替代計量

在都市環境中基於方向之車輛定位服務

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