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VANET & Geographic Routing

VANET & Geographic Routing . 指導教授：柯開維教授 Speaker ： 張文諸 Date ： 2010/04/14. Outline. Part I VANET 簡介 VANET 網路 架構 Part II Geographic Routing in City Scenarios Part III Conclusions and Future work. Outline. Part I VANET 簡介 VANET 網路 架構 Part II Geographic Routing in City Scenarios

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VANET & Geographic Routing

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  1. VANET& Geographic Routing 指導教授：柯開維教授 Speaker：張文諸 Date：2010/04/14

  2. Outline • Part I • VANET 簡介 • VANET網路架構 • Part II • Geographic Routing in City Scenarios • Part III • Conclusions and Future work

  3. Outline • Part I • VANET 簡介 • VANET網路架構 • Part II • Geographic Routing in City Scenarios • Part III • Conclusions and Future work

  4. VANET 簡介 • 車載網路（Vehicular Ad Hoc Network，VANET） 車載網路是一種透過隨意網路提供車輛之間的通訊，藉由無線通訊與資料傳遞技術，串聯交通工具以及路邊交通設施，所形成的特殊的專用網路，屬於高度客制化的行動式隨意網路。主要功能在於讓所有的用路人可以即時取得與傳遞與交通相關的資訊，以便提高行車效率，增進用路安全與舒適性。

  5. VANET 簡介 • 目前VANET大多應用在IEEE 802.11b (Wi-Fi) 上，但也朝IEEE 802.11p 或 IEEE 802.16 (WiMax)方面推展。VANET的應用略分為幾類：安全性應用、交通管理與環境資訊。如安全性應用方面，VANET可以在前方有塞車或是撞車情形時即時的對駕駛提出警告，當前方的車子減速時，也可以提醒後方的車輛放慢速度避免碰撞的發生。

  6. VANET與MANET的比較 • VANET可說是MANET的一種延伸應用，基本的架構是相同的，具有無基礎設施、多點式跳越連接、動態拓樸的特性。但兩者之間仍多許多不同之處，下表列出VANET與MANET的特性之比較。

  7. VANET與MANET的比較

  8. Outline • Part I • VANET 簡介 • VANET網路架構 • Part II • Geographic Routing in City Scenarios • Part III • Conclusions and Future work

  9. VANET網路架構 • 在VANET 網路架構的分類裡，主要可以分為以下三大種類： VANET 示意圖

  10. VANET網路架構 • Roadside-to-Vehicle Communications（RVC）： 所有車輛都會透過路旁的AP或是base station來與server溝通，可取得所需的資訊。 Roadside-to-Vehicle Communications （RVC）

  11. Roadside-to-Vehicle Communications • 在此架構下主要的研究議題有： a. Mobility management： 由於在VANET的環境中每個node具有高移動性的特質，所以時常會離開目前使用中AP的服務範圍而進入另一AP的服務範圍，這就是所謂的換手(handover)問題。目標為如何維持原本的資訊傳輸而不造成封包遺失，讓使用者覺得連線是一直存在的，不需要有重新連線的動作。 b. Choosing Internet gateway: 一台車時常會在不只一個AP的服務範圍內，這類的問題主要在如何選擇一台AP以達到最高傳輸效益。考慮的因素包括路徑上可使用之頻寬大小或是需要經過的hop數目等等。

  12. VANET網路架構 • Inter-Vehicle Communications (IVC)： 在此架構下車輛可以透過其他車輛主動要求所需的資訊，或是當前方有緊急事件發生時，車輛彼此間也可以迅速交換訊息。由於此方式並無路旁的AP或是基地台可供使用，故當車輛間距離太遠，超出彼此能夠通訊的範圍時將會發生斷線的情況。 Inter-Vehicle Communications （IVC）

  13. IVCRouting • Unicast Routing • Cluster-Based Routing • Geocast Routing • Broadcast Routing

  14. Unicast Routing • 近年來提出的車對車routing protocol 如以下樹狀圖所示，主要的分類有： IVCrouting protocol

  15. Unicast routing • Topology-based routing protocols 使用目前網路中所有連線的資訊找出一條最佳路徑來決定怎麼傳封包，又可分為兩大類： • Proactive 每台車都會維護並且儲存一個table，紀錄與其他車輛間的連線狀況。所以每隔一段時間每台車都要廣播自己table的資訊給其他車輛，彼此交換訊息然後各自更新自己的table。 • Reactive 只有在需要的時候才開啟和某個台車之間的連線，並且只維護正在使用中的連線。

  16. Unicast routing • Geographic routing 每台車擁有的資訊只有目前附近車輛的狀況。主要根據下面兩個條件來決定封包怎麼傳送。 • 封包的目的地位置，這個位置會儲存在每個封包的 header中，而且在這邊會假設傳送端都會知道接收端的位置在哪裡(如GPS取得)。 • 根據目前one-hop neighbors的位置，one-hop neighbors就是那些可以直接重送到的車輛，也就是在一台車的傳送範圍內的車輛都是one-hop neighbors。

  17. Geographic routing • Geographic routing又可分為以下三類： • None-DTN (Non-Delay tolerant network) • DTN (delay tolerant network) • Hybrid

  18. None-DTN • 此類protocol不考慮連線有可能會斷斷續續的狀況，故主要用於車輛密度較高的VANET環境中。主要的觀念是Greedy forwarding，但Greedy forwarding會造成local maximum。所以這一類的routing protocol就是用各種方式來應付這種到達local maximum的狀況。常見的方法有GPSR, CAR, A-STAR, STBR等。

  19. Greedy forwarding • An intermediate nodes forward a packet to the direct neighbor which is closest to the geographic position of destination

  20. Local maximum

  21. Greedy Perimeter Stateless Routing (GPSR) Perimeter Forwarding

  22. DTN • 相反地，由於車輛通常有很高的移動性，所以DTN是考慮連線時常會中斷的環境。當傳送端準備要送出封包時若附近沒有其他車輛或是連線相當不穩定，就會先把封包存著，直到移動到附近有別的車輛再傳送出去(carry-and-forward)。常見的方法有VADD, GeOpps等。

  23. Hybrid • 綜合none-DTN和DTN兩種模式，有none-DTN的greedy mode和DTN的carry-and-forward。主要會使用none-DTN模式，但會根據下面幾種網路連線情況由none-DTN模式切換到DTN模式：目前封包已經經過了多少hop,附近車輛的傳送品質, 還有附近車輛相對於目的地的位置等等。

  24. IVCRouting • Unicast Routing • Cluster-Based Routing • Geocast Routing • Broadcast Routing

  25. Cluster-Based Routing • 每一個群組有一個群組的群首，它可以用來控制內部的網路運行 • 群體內的各節點可直接聯繫 • 每個群體通信通過群組的標頭

  26. Geocast Routing • The multicast of a message, using geographic routing, to nodes satisfying a geographical criterion is called geocast.

  27. Broadcast Routing • Broadcast是VANET常用的一種路由，像共享交通訊息、天氣、緊急訊息。 • 一種簡單的廣播服務是flooding，每個節點重新廣播收到的訊息。Flooding可以保證每個節點都收到訊息。Flooding在節點是數量少的時侯效能很好，當每個節點收到訊息並且要廣播訊息時，會造成封包的碰撞，會消耗大的頻寬

  28. VANET網路架構 • Hybrid Vehicular Communication Systems (HVC) 綜合上述的IVC和RVC，如果車輛不在路旁AP或基地台的服務範圍內，可以先用IVC透過一台或多台其他車輛連接到server，如同把其他車輛當做router一般。如此不但可以擴大路邊AP的服務範圍，甚至可以減少這些設施的數量。 結合RVC以及IVC之網路架構

  29. Summary VANET RVC HVC IVC Mobility management Choosing Internet gateway Unicast Routing Cluster-Based Routing Geocast Routing Broadcast Routing

  30. Outline • Part I • VANET 簡介 • VANET網路架構 • Part II • Geographic Routing in City Scenarios • Part III • Conclusions and Future work

  31. Geographic Routing in City Scenarios Christian Lochert, Martin Mauve, HolgerFuBler, Hannes Hartenstein ACM SIGMOBILE Mobile Computing and Communications Review, 2005

  32. Introduction • It is related to the idea of position-based source routing as proposed for terminode routing. • The static street map is need due to its algorithm. • This paper provide a method without assumption that • Nodes have access to a static street map and • Without using source routing

  33. Position-based Routing • Greedy forwarding • An intermediate nodes forward a packet to the direct neighbor which is closest to the geographic position of destination • For this task, nodes has to be aware of • Its own position • The position of its direct neighbors • The position of the final destination

  34. Local maximum Problem

  35. Greedy Perimeter Coordinator Routing • Without using any global information such as static map. • GPCR consists of two parts: • A restricted greedy forward • A repair strategy based on the topology of real-world streets and junctions • Therefore, it doesn’t require a graph planarization algorithm.

  36. Restricted Greedy Routing • Junctions are only places where actual decision are taken • Packets should always be forwarded to a node on a junction rather than across a junction • If the forwarding nodes are all not located on a junction, chose the node that • Approximates an extension of the line between forwarding node’s predecessor and itself.

  37. Restricted Greedy Routing (cont.) Source : U Destination : D Greedy Routing vs. Restricted Greedy Routing in the area of a junction.

  38. Restricted Greedy Routing (cont.)

  39. Repair Strategy • As a consequence the repair strategy of GPCR consists of two parts: • (1) On each junction it has to be decided which street the packet should follow next. • (2) In between junctions greedy routing to the next junction, as described above, can be used.

  40. Example • A packet with destination D reaches a local maximumat node S. • The forwarding of the packet is then switched to the repair strategy and it is routed along the street until it hits the first coordinator node.

  41. Detecting junctions • By observing the beacon messages a node has the following information for each neighbor: its position and the position and presence of the neighbor’s neighbors. y x z

  42. Detecting junctions • We define xi and yi as the x-coordinate and y-coordinate of a nodei. • The variables x and y subsume the population of all these positions xi and yi respectively. • The mean of a population x is marked by x

  43. Cont. • A correlation coefficient close to 1 indicates a linear coherence as it is found when the node is located in the middle of a street • A correlation coefficient close to 0 shows that there is no linear relationship between the positions of the neighbors. Consequentially we conclude that the node is located on a junction

  44. Simulation Results • For the simulations we used a real city topology which is a part of Berlin,Germany. • The scenario consists of 955 cars (nodes)on 33 streets in an area of 6.25 km *3.45 km • IEEE 802.11 was used as MAC with a transmission rate of 2 Mbps. The transmission range was set to 500 m.

  45. GPCR vs. GPSR. – Delivery rate

  46. GPCR vs. GPSR. – Delivery rate

  47. Conclusions and Future work • Our approach does not require external information such as a static street map to avoid the problems that existing position-based approaches face in this type of environment • Future improvement • Currently the next street to be taken is determined without considering whether there is a sufficient number of nodes on the street to allow packet forwarding to the next junction.

  48. Outline • Part I • VANET 簡介 • VANET網路架構 • Part II • Geographic Routing in City Scenarios • Part III • Conclusions and Future work

  49. Conclusion • 以目前的技術來說，要將VANET實際應用在行車上可能還有很大的距離要走，像車對車之間的Geographic Routing，必須要先找到目的端的位置，將這個位置記錄在Packet中，但這位置可能因時間點的不同而有所移動，導致訊息無法送到等或找不到目的端，這都需要更適當的方法去解決。

  50. Future work • 對其他VANET Routing 深入探討與比較 • 真實的模擬運作

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