在車載網路中基於交通資訊之路邊網路單元佈署

Roadside Unit Deployment based on Traffic Information in VANETs

蔡至勇(Jr-yung Tsai)

指導教授 ： 江季翰

國立虎尾科技大學/電機資訊學院/資訊工程研究所/碩士(2011年)

摘要

在車載網路中，封包的傳送須依靠與車子之間利用無線網路相互通訊，或者利用車輛自行攜帶封包前進的方式來傳遞。這兩種最大的差別，就是所產生的封包延遲時間，無線網路使用無線電波是屬於光速，而車輛行駛的速度平均僅是數十公里/小時。除了通訊方式的不同之外，在車載網路的各條道路中，車流量與平均車速不盡相同。依照道路上的平均車速與車流量的關係，有的道路因車間距離短，適合使用無線網路的方式不斷傳遞封包。而有的道路而因為車間的距離長，非常仰賴由車輛自行攜帶的方式來傳遞封包。而主宰封包要進入何種類型的道路，關鍵在於十字路口，封包遞送到路口時，就決定著將進入什麼類型的道路，而傳送封包的延遲時間，也因所進入的道路類型不同而產生快慢變化。本篇論文的目的，即在使封包盡量前往無線網路傳遞多的道路，使得封包傳遞延遲時間縮短。
本論文提供一套計算方式，將道路分為傾向使用無線網路傳遞封包類型與傾向使用車輛攜帶封包前進類型。根據十字路口所連接的道路類型，將路口進行分類，研究發現當一個路口同時兼具這兩種類型的道路，代表該路口也決定著封包傳送時，會進入傳送速度極快或者傳送速度極慢的道路。因此本論文在具有此種特性的路口，架設路邊網路單元(Roadside Unit)。以Vehicle-Assisted Data Delivery(VADD)為路由協定下，本路邊網路單元的功能，在是當攜帶封包的車輛進入具有路邊網路單元的路口時，若無法將封包送往最佳方向的道路，或其他傾向使用無線網路傳遞封包的道路時，則將封包暫存於路邊網路單元中，等待良機再將封包送出，以增加無線網路的使用機會，減少車輛自行攜帶封包的情況出現。另外依據封包的持有者為車輛或路邊網路單元，封包持有者處於直路模式或路口模式，提供不同的搜尋方式，使的封包在車間或車輛與路邊網路單元間快速的傳遞，達到封包傳遞延遲時間縮短的目的。經過模擬，本文之方法，在路邊網路單元的輔助下封包到達率與封包傳遞延遲時間均有顯著的改善。

關鍵字

車載網路 ； 路邊網路設施 ； 路由協定 ； 車輛輔助封包遞送

並列摘要

In vehicular ad hoc networks (VANETs), packets are delivered by wireless transmission or carry and forwarding. The difference is the delay time, transmitted by carry and forwarding is very slowly then wireless transmission. In addition, there are different traffic flows and average vehicle velocities on each road. Some roads are suitable for wireless communication, but others are suitable to carry and forwarding. The key point is the intersection, the packets are delivered to the next road by crossed the intersection.
In this paper, there are two kinds of the roads, one is tend to be transmitted by wireless and the other one is tend to be transmitted by carry and forwarding. Based on what kinds of roads are connected to the intersection. But when an intersection is connected by the two kinds of roads at the same time, this intersection decides the packet will transmit to which kind of roads, fast or slowly. For this reason, we add roadside unit (RSU) at those intersections, based on the Vehicle-Assisted Data Delivery (VADD) routing protocol, when the packet reaches intersection, but there are no vehicles on the best direction, RSU will store the packet for a while, and waiting for an opportunity. The RSU increases the chance to use wireless communication, decreases the chance to use carry and forwarding. In addition, based on vehicle or RSU, straight or intersection, we provide the algorithms for each condition, the packet delivery delay is decreased. In accordance with our simulation results, the packet delivery ratio and delivery delay our method has a much better performance.

並列關鍵字

VANETs ； Roadside Unit ； Routing Protocol ； Carry-and-Forward

參考文獻

[1] Perkins, Charles E. and Bhagwat, Pravin,” Highly Dynamic Destination-Sequenced Distance-Vector Routing (DSDV) for Mobile Computers”, ACM SIGCOMM’94, 1994.

[2] DB Johnson, DA Maltz, “Dynamic source routing in ad hoc wireless networks”, In Mobile Computing, 1996.

[3] D. Goodman, J. Borras, N. Mandayam, and R. Yates, “INFOSTATIONS: A New System Model for Data and Messaging Services,” in IEEE VTC97, Vol. 2, 1997.

[4] C. E. Perkins and E. M. Royer, “Ad Hoc On-Demand Distance Vector Routing Protocol,” Proceedings of the 2nd IEEE Workshop on Mobile Computing Systems and Applications (WMCSA), 1999.

[5] L. Briesemeister and G. Hommel, “Role-Based Multicast in Highly Mobile but Sparsely Connected Ad Hoc Networks,” Workshop on Mobile Ad Hoc Networking and Computing, 2000.