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AN EFFICIENT BROADCAST TECHNIQUE FOR VEHICULAR NETWORKS 報告學生：翁偉傑 1 Journal of Information Processing Systems, Vol.7, No.2, June 2011 Ai Hua Ho*, Yao H. Ho**, Kien A. Hua*,Roy Villafane***, and Han-Chieh Chao OUTLINE INTRODUCTION CELL BROADCAST FOR STREET ENVIRONMENTS (CB-S) SIMULATION RESULTS ANALYSIS OF CB-S CONCLUSION 2 INTRODUCTION (1/2) A vehicular network is a form of mobile ad hoc network. Reducing control overhead Broadcast storm 在狹窄的都市街道，很難傳送訊息到不同的街道。 The network topology among nodes changes very Large buildings limit the coverage of a broadcast 因為多數節點將都轉送、廣播 3 INTRODUCTION (2/2) 在十字路口的節點有更好的機會達到其他節點。 本文提出的協議是Cell Broadcast for Street Environment (CB-S) 提高傳輸率 減少hop次數 減少成本 4 CELL BROADCAST FOR STREET ENVIRONMENTS (CB-S) (1/10) 車輛都配備了GPS和MAP。 A street divided into intersections and street segments. 5 CELL BROADCAST FOR STREET ENVIRONMENTS (CB-S) (2/10) Cell A and Cell C are called intersection cells. Cell B is called a segment cell Cell A can communicate with any node in Cells B and C. 6 CELL BROADCAST FOR STREET ENVIRONMENTS (CB-S) (3/10) 街道大於無線電廣播範圍，為了防止多餘的廣播， 所以化分為cell。 7 CELL BROADCAST FOR STREET ENVIRONMENTS (CB-S) (4/10) To broadcast a packet for a destination, a source node includes the following information in the packet: Source Node ID Destination Node ID Packet ID Current Node Position Incident Location Dissemination Radius 8 CELL BROADCAST FOR STREET ENVIRONMENTS (CB-S) (5/10) 當節點N收到封包從節點M，決定是否需要轉送封包： Algorithm I: 1. If n is outside the dissemination area, it drops the packet. 2. If n has broadcast the packet before, it drops the packet. 3. If n is not on a downstream cell of m’s cell, it drops the packet. 4. If n has heard the same packet broadcast from another node in its cell, it drops the packet. 9 CELL BROADCAST FOR STREET ENVIRONMENTS (CB-S) (6/10) 5. If n has heard the same packet broadcast from its overtaking neighboring cells, it drops the packet. 6. If all previous conditions fail, n sets the delay. 7. If at the end of the delay, one of the previous conditions satisfies, n drops the packet. 8. Otherwise, n rebroadcasts the packet. 10 CELL BROADCAST FOR STREET ENVIRONMENTS (CB-S) (7/10) In Steps 5 and 6 of the above algorithm, n determines its overtaking neighboring cells and delay based on whether m’s radio range can reach the next intersection cell. Algorithm II: 11 CELL BROADCAST FOR STREET ENVIRONMENTS (CB-S) (8/10) Algorithm II: The significance of Algorithm II is that nodes in intersections rebroadcast first and thus eliminate the need for rebroadcasts from the segment cells between the intersection cells. 12 CELL BROADCAST FOR STREET ENVIRONMENTS (CB-S) (9/10) m’s radio range is too small to reach the next intersection due to a long road segment 13 CELL BROADCAST FOR STREET ENVIRONMENTS (CB-S) (10/10) Algorithm III: 14 SIMULATION RESULTS GloMoSim 1,640 mobile nodes The field is 1000m × 1000m space Street width of 10 meters Street block size of 100m × 100m There are 81 street blocks in total (1/5) 15 SIMULATION RESULTS (2/5) Each simulation emulates 15 minutes of time. Before the simulation begins, 10% of the nodes are randomly picked to be the set of nodes . Each node has a radio range of about 120 meters. The nodes then move in the directions permitted in the streets. Upon arriving at an intersection, a node probabilistically changes its direction of movement. 16 SIMULATION RESULTS (3/5) Effect of Speed 17 SIMULATION RESULTS (4/5) Effect of Building Obstruction 18 SIMULATION RESULTS (5/5) Effect of Message Dissemination Radius 19 ANALYSIS OF CB-S (1/3) 20 ANALYSIS OF CB-S (2/3) Induction Hypothesis: hop(k) = k for 1≤ k ≤ n and n ≥1. 21 ANALYSIS OF CB-S (3/3) 22 CONCLUSION 在本文中，我們提出了街道環境的CB-S的廣播技術。 並證明了這種模式可以達到每個節點用最小的成本、 hop次數。 我們模擬結果顯示：與其他四個技術。結果表明， CB-S的傳輸率，開銷和延遲比其他方法好。 23