1. Open Your Driving Vision BPAB: Binary Partition Assisted Emergency Broadcast Protocol for Vehicular Ad Hoc Networks March 11, 2013 國立中央大學資訊工程所 吳曉光 教授 國立政治大學資訊科學系演講 ABC News 2008: Social Networking for Cars Can Help You Avoid Traffic Jams ~ We are having cars talk to each other about traffic data.

2. Outline  Introduction  Multihop Broadcast Protocols in VANET  Binary Partition Assisted Broadcast  Performance Evaluation  Conclusion and Future work

3. Wireless & Multimedia Network Laboratory  New usage IP cars IP fridge IP everywhere

4. Wireless & Multimedia Network Laboratory  異質無線多網多媒體分享與推薦平台場景圖 電信國家型計畫建置案 metadata 1 metadata 2 metadata n 搜尋 推薦 傳送 Internet WiFi Bluetooth Alice …. WiMax 搜尋 推薦 傳送 人際網路 Bob

5. Wireless & Multimedia Network Laboratory  Scenario of VANET safety applications Multicasting warning messages Emergency Event !! Car accident happen !! About 100 meters from the me. Please prepare to change into the right lane. Car accident happen in the left lane. You can take exit to avoid traffic jam. Multicast the warning message

6. The Enabling Standard: DSRC / IEEE 802.11p Car-Car communications at 5.9Ghz Derived from 802.11a three types of channels: Vehicle-Vehicle service, a Vehicle-Roadside service and a control broadcast channel. Ad hoc mode; and infrastructure mode 802.11p: IEEE Task Group for Car-Car communications

7. Wireless & Multimedia Network Laboratory  CR (Cognitive Radio)  The CR idea was initially introduced by Joseph Mitola. On average, only 2% of allocated spectrum in the U.S. is actually in use

8. Introduction Traffic jam Road Accident

9. Car to Car communications for Safe Driving Vehicle type: Cadillac XLR Curb weight: 3,547 lbs Speed: 65 mph Acceleration: - 5m/sec^2 Coefficient of friction:.65 Driver Attention: Yes Etc. Vehicle type: Cadillac XLR Curb weight: 3,547 lbs Speed: 45 mph Acceleration: - 20m/sec^2 Coefficient of friction:.65 Driver Attention: No Etc. Vehicle type: Cadillac XLR Curb weight: 3,547 lbs Speed: 75 mph Acceleration: + 20m/sec^2 Coefficient of friction:.65 Driver Attention: Yes Etc. Vehicle type: Cadillac XLR Curb weight: 3,547 lbs Speed: 75 mph Acceleration: + 10m/sec^2 Coefficient of friction:.65 Driver Attention: Yes Etc. Alert Status: None Alert Status: Passing Vehicle on left Alert Status: Inattentive Driver on Right Alert Status: None Alert Status: Slowing vehicle ahead Alert Status: Passing vehicle on left

10. V2V Applications (cont) Efficient Navigation GPS Based Navigators Dash Express (just came to market):

11. ITS (Intelligent Transportation System) Applications  Electronic Toll Collection  Traffic Congestion Notification  Collision Avoidance Systems  Driver Assistance Systems  Freeway Management  Parking Lot Management

12. Benefits of ITS Cost Avoidance Time savings Enhanced Customer satisfactionReduced number of accidents and fatalities

13. ITS Communication Paradigm Vehicle-to-vehicle Communication Vehicle-to-Infrastructure Communication VANET (Vehicular Ad Hoc Networks) Ad Hoc Network  No Infrastructure  Self-organizing  High Mobility  Restricted movement patterns  Predictable speed,  Predictable movement.

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15. CarTorrent: Basic Idea Download a piece Internet Transferring Piece of File from Gateway Outside Range of Gateway

16. Co-operative Download: Car Torrent Vehicle-Vehicle Communication Internet Exchanging Pieces of File Later

17. Vehicular Sensor Network

18. Accident Scenario: storage and retrieval Public/Private Cars (eg, busses, taxicabs, police, commuters, etc): –Continuously collect images on the street (store data locally) –Process the data and detect an event –Classify the event as Meta-data (Type, Option, Loc, time,Vehicle ID) –Distribute Metadata to neighbors probabilistically (ie, “gossip”) Police retrieve data from public/private cars Meta-data : Img, -. (10,10), V10

19. VANET Projects Why VANET  No deployment cost.  Easy introduction of technology.  Availability of cost-effective GPS and other location services. Academia Government Automotive industries CAR TALK 2000 SeVeCom PreDRIVE C2X PReVENT Network on Wheels Fleetnet PATH DRIVE-IN

20. Safety Message in VANET  Vehicles exchange position, velocity with neighbors.  Single-hop broadcast  Dissemination of warning message to the following vehicles.  Multihop Broadcast  Periodic Message  Event-driven Message Drivers are aware of the potential danger (e.g. intersection collision, accidents ahead) before it occurs. Allow drivers to react in time Beacon Emergency Message Emergency Event Emergency Message Specific area-of- interest (Accident, unsafe road surface, obstacle, etc. )

21. Outline  Introduction  Multihop Broadcast Protocols in VANET  Binary Partition Assisted Broadcast  Performance Evaluation  Conclusion and Future work

22. Requirements for Safety Message Dissemination  Low communication delay  High Message Dissemination Speed  Reliable Packet Delivery  Bandwidth Efficiency Challenges  Choosing the right forwarder  Allocate minimum waiting time  Hidden Terminal Problem Multihop Broadcast Protocols in VANET

23. 4m Source ………… Urban Multihop Broadcast (UMB) 40m S1S1 S9S9 S0S0 Black burst duration (time slots) 019 09 RTB/CTB handshake is used to avoid hidden terminal problem. Select the furthest node as the forwarder. RTB CTB RTB CTB DATA ACK Drawbacks  Relay node is assigned the longest waiting time.  Wastage of time in collision resolution phase.  Control Packet Overhead.

24. Source Nodes randomly select waiting time from a back off window allocated to their segment. ………… S 10 S1S1 S2S2 40m W 1 = {0,1,2,3,4}W 2 = {5,6,7,8,9} W 10 = {45,46,47,48,49} Smart Broadcast (SB) RTB/CTB handshake is used to avoid hidden terminal problem. RTB DATA CTB

25. Range of A A B Range of B CDE F Range of DRange of C Range of E Drawback  Longer waiting time at irregular topologies. Smart Broadcast Back off times increases towards the sender Source Relay Node

26. Outline  Introduction  Multihop Broadcast Protocols in VANET  Binary Partition Assisted Broadcast  Performance Evaluation  Conclusion and Future work

27. Binary Partition Assisted Broadcast  Binary partitions are applied iteratively.  A segment is divided into two equal sub segments.  Potential segment is selected by black-burst approach.  It becomes the input segment for next iteration.  N binary partitions yields a furthest segment.  The width of furthest segment is R/2 N.  Finally, back off time is chosen from {0,1,…cw-1}.  The parameter ‘cw’ is a small value. Objective Features  Reduce Broadcast latency.  Maximize message progress  Efficient usage of network bandwidth.

28. Binary Partition Assisted Broadcast Source ….... Transmission range RTB Iteration 2 3 N 1 Segment Width R/2 R/4 R/8 R/2 N CTB DATA Two nodes contend using back off window {0,1, 2..cw} Elected relay node

29. R/2 R/4 R/8 R: Transmission Range Forward Node selection procedure Black Burst Transmission Source Black Burst Detection Black Burst Transmission Black Burst Detection Exit Contention Black Burst Transmission Black Burst Detection Exit Contention Random Contention Contention Winner Exit Contention Iteration 1 : Time Slot 1 Iteration 2 : Time Slot 2 Iteration 3 : Time Slot 3 Black burst is transmitted for one time slot duration Time slots spent per hop= N + t 3 Slot chosen from {1,2,..5} cw=6

30. Reliability Measures Source might lose CTB packet due to varying wireless channel conditions. Source CTB RTB lost Relay node selection ends Solution Source waits a time period (slots) = N + cw, Where N + cw -1 = Maximum possible waiting time, before a CTB could be sent. One extra time slot to determine the start of CTB reception.

31. Reliability Measures Source CTBRTB Relay node selection ends DATA RTB Source overhears RTB, thus DATA delivery is guaranteed. Implicit Acknowledgement Source CTBRTB Relay node selection ends DATA Source CTBRTB Relay node selection ends DATA lost Solution Source waits for a certain time period and then retransmits RTB to select a potential relay node. RTB Case 1Case 2 PROBLEMS

32. Outline  Introduction  Multihop Broadcast Protocols in VANET  Binary Partition Assisted Broadcast  Performance Evaluation  Conclusion and Future work

33. Performance Evaluation Simulation Set up  Vehicle Density : 150-650  Vehicle Speed : 20m/s – 40m/s  Transmission Range : 400m  Packet Size :100 bytes  MAC Protocol : IEEE 802.11b  Protocols compared : SB and UMB  NS-2 simulator.

34. Modeled Scenario Straight Highway Regular Topology Irregular Topology Normal flow of traffic Occurs when nodes move in close proximity of each other due to fog or ongoing road work at some intervals.

35. Performance Metrics  MAC Layer slots  Total number of slots expended for the message dissemination.  One hop message progress  Additional coverage provided by the relay node.  Control Overhead  Total number of RTB/CTB handshakes required during the message dissemination.

36. Total number of MAC layer Slots Regular Topology

37. One Hop Message Progress Regular Topology

38. Control Overhead Regular Topology

39. Total number of MAC layer Slots Irregular Topology

40. One Hop Message Progress Irregular Topology

41. Control Overhead

42. Conclusion  Improves broadcast efficiency by reducing delay.  Exhibits constant behavior in varying node densities.  Minimizes bandwidth consumption by using few number of control messages.  Offers high message progress. Future Work  Inclusion of multiple emergency message sources.  Adaptation of existing scheme to more complex road scenarios such as City environments.  Analytical determination of optimal value of N.

43. Thanks a lot…