A study of the vehicular ad hoc network

1. A study of the vehicular ad hoc network Speaker: Chih-Sheng Chen

2. Outline • Overview • Applications Issues • Network Issues • ITS • Radiolocation • Dissemination of alarm messages • Routing scheme Issues • Conclusion • Reference

3. Outline • Overview • Applications Issues • Network Issues • ITS • Radiolocation • Dissemination of alarm messages • Routing scheme Issues • Conclusion • Reference

4. Overview( 1/6) Disproportionate increase in car ownership relative to population growth in China, India

5. Overview( 2/6) • Safety: 6 Million crashes, 41,000 fatalities in U.S. per year ($150 Billion) • Congestion: 3.5 B hours delay, 5.7 B gal. wasted fuel per year in U.S. ($65 Billion) • Pollution: > 50% hazardous air pollutants in U.S., up to 90% of the carbon monoxide in urban air Source: 2005 Annual Urban Mobility Report (http://mobility.tamu.edu) Texas Natural Resource Conservation Commission (http://www.tnrcc.state.tx.us/air)

6. Overview( 3/6)

7. Overview( 4/6) • Over the last decades passive safety systems have helped to reduce the number of fatalities. • The further reduction of severe accidents will be achieved by adding active safety systems to vehicle.

8. Overview( 5/6) • Vehicular Ad-hoc NETworks( VANET) are special cases of MANET. • Inter-vehicular communication( IVC) network. • Road-Vehicle Communications( RVC). • The difference between VANET and MANET: • VANET nodes are highly mobile, so network topology is changing very fast. • VANET nodes are vehicles, so there are less power and storage constraints. • VANET nodes move non-randomly along specific paths( roads).

9. Overview( 6/6) • New applications of wireless ad hoc networks with vehicular traffic • Infrastructure based systems are not sufficient • Infrastructure may not be present • Signs may not be visible • Mobility is constrained and directional • Links between peers will be dynamic and unstable • Manual systems too slow

10. Outline • Overview • Applications Issues • Network Issues • ITS • Radiolocation • Dissemination of alarm messages • Routing scheme Issues • Conclusion • Reference

11. Applications Issues( 1/8) • Many recent incidents • Fog • Vehicular road accident in a busy highway • Delays in emergency vehicle reaching the accident point • Unseen vehicles • Broadband connectivity to area hospitals to relay patient’s vital information

12. Applications Issues( 2/8) • Use peer ad hoc networks to send messages (both upstream and downstream) to reserve highway lanes for emergency vehicles • Law enforcement • ambulance • fire truck • Overtaking

13. Applications Issues( 3/8) • Internet access in cars( Cont.) • Information services • Traffic/road monitoring • Traveler & Tourist Assistance • Entertainment (distributed games) • Links with fixed and mobile • Internet Conversation • Control Internet device

14. Applications Issues( 4/8) • Internet access in cars

15. Applications Issues( 5/8) • Classifying Applications( Cont.) 1. Assistance for Safe Navigation( ASaN) 2. Traffic Regulation and Internet Connectivity( TRIC)

16. Applications Issues( 6/8) • Classifying Applications( Cont.)

17. Applications Issues( 7/8) • Classifying Applications( Cont.) • Assistance for Safe Navigation • Collision avoidance applications through accident, sudden braking, or road maintenance notifications, • Hazardous driving condition detection, • Emergency services call after an accident, and • Detection of a rogue driver going the wrong way.

18. Applications Issues( 8/8) • Classifying Applications • Traffic Regulation and Internet Connectivity • Advanced Navigation Assistance (ANA) such as passing assistance, car pool formation, real time congestion notification, expected weather driving conditions, etc., • Internet connection services for added travel comfort and improved productivity, • Vehicular Relay Chat (VRC) between users of the same highway, and • Custom Local Shopping Advertisement( CuLSA), which lets local businesses inform travelers of local shops, malls, etc. Local gas stations could also advertise their location to attract cars that may not see them from the highway.

19. Outline • Overview • Applications Issues • Network Issues • ITS • Radiolocation • Dissemination of alarm messages • Routing scheme Issues • Conclusion • Reference

20. Network Issues( 1/16) • ITS( Cont.) • Intelligent Transportation Systems( ITS) is receiving increased emphasis due to its role in traffic safety and ensuring better quality travel. • The successful deployment of ITS relies heavily upon inter-vehicle communication for effective dissemination of information.

21. Network Issues( 2/16) • ITS( Cont.) • Five basic types of messages that are exchanged between vehicles are: • Basic safety messages( highest priority) • Warning messages( high priority) • Infotainment messages( normal priority) • Routing messages( low priority) • Inter-personal messages( lowest priority)

22. Network Issues ( 3/16) • ITS( Cont.) • Basic safety messages • Contains data describing the sender characteristics and driving conditions( e.g. sender position, speed , vehicle brake and steering conditions). • Warning messages • Contains critical warning on emergency situations that has occurred or could possibly occur within the traffic.

23. Network Issues ( 4/16) • ITS • Infotainment messages • Contains data about services and resources available and offered by other vehicles and information of general interest( e.g. traffic conditions or meteorological data). • Routing messages • Contains data used by routing protocols. • Inter-personal messages • Contains different profiles of the drivers and of the passengers situated in the vehicles. These data are used when employing interpersonal applications.

24. Network Issues ( 5/16) • Radiolocation( Cont.) • In the case of an accident, vehicles without GPS have to be informed in the right moment. • Radio location is useful to the VANET uses position-based routing( PBR) when some vehicles without GPS. • Most generally used ones are based on signal propagation duration.

25. Network Issues ( 6/16) • Radiolocation( Cont.) • The main three different measurement methods are used in cellular ad hoc networks today : • Received-Signal-Strength Indicator( RSSI) • Time-of-arrival( TOA) and Time-Difference-of-arrival( TDOA) • Angle-of-arrival( AOA)

26. Network Issues ( 7/16) • Radiolocation( Cont.) • Received-Signal-Strength Indicator( RSSI) • RSSI measures the power of the signal at the receiver. Based on the known transmit power, the effective propagation loss can be computed. • TOA or time-difference of arrival( TDOA) • The propagation time can be directly translated into distance, based on known signal propagation speed. • Angle-of-arrival( AOA) • AOA techniques estimate the desired target by measuring the angle at which signals from several BSs through the use of directive antennas of antenna arrays.

27. Network Issues ( 8/16) • Radiolocation( Cont.) • SPA( 1/2) • Self-positioning algorithm( SPA) has been proposed for positioning mobile nodes in wireless ad hoc networks without relying on GPS. • SPA uses the distance between the nodes to build a relative coordinate system in which the node positions are computed in two dimensions.

28. Network Issues ( 9/16) • Radiolocation( Cont.) • SPA( 2/2) • A node executing SPA algorithm fails in some situations to computes its coordinates since it is based on some conditions on its neighbors. • SPA is not well suited for inter vehicle communication. • Another method for Using SPA for GPS-free position in VANET.

29. Network Issues ( 10/16) • Radiolocation( Cont.) • Using radiolocation on broadcast( 1/2) • The way with which a node is designated as relay is based on distance defer time algorithm. • The node that receives an alarm message does not rebroadcast it immediately but has to wait some time to take a decision about rebroadcast. • When the defer time expires, if it does not receive the same alarm message from another node behind it, it deduces that there is no relay node behind it.

30. Network Issues ( 11/16) • Radiolocation • Using radiolocation on broadcast( 2/2)

31. Network Issues ( 12/16) • Dissemination of alarm messages( Cont.) • RBM( Role Based Multicast) • Based on neighbor detection • TRADE( Track Detection) • Based on neighbor maintenance • DDT( Distance Defer Time) • Inserts distance-based defer time slots • ODAM( Optimized Dissemination of Alarm Messages) • Based on geographical multicast

32. Network Issues ( 13/16) • Dissemination of alarm messages( Cont.) • RBM • Based on neighbor detection • Consumes more bandwidth • Presents longer delays • More packet loss • TRADE • Based on neighbor maintenance • Consumes more bandwidth • Presents longer delays • The scalability in dense networks is limited.

33. Network Issues ( 14/16) • Dissemination of alarm messages( Cont.) • DDT • GPS-unequipped vehicles Computing defer time fails in some situations. • The lack of supporting fragmented ad hoc networks makes DDT unsuitable for light-crowded highways.

34. Network Issues ( 15/16) • Dissemination of alarm messages( Cont.) • ODAM • Using SPA for GPS-free position to Support localization of GPS-unequipped vehicles in VANET.

35. Network Issues ( 16/16) • Dissemination of alarm messages • ODAM • Based on geographical multicast, which consists in determining the multicast group according to the driving direction and the positioning of the vehicles

36. Outline • Overview • Applications Issues • Network Issues • ITS • Radiolocation • Dissemination of alarm messages • Routing scheme Issues • Conclusion • Reference

37. Routing scheme Issues( 1/27) • Routing challenges for VANET • The network can frequently form partitions preventing end-to-end communication strategies. • Resource discovery and naming are problematic as the vehicles are in general unreliable and frequent arrivals and departures occur.

38. Routing scheme Issues( 2/27) • Existing routing protocols designed for MANET are not suitable for VANET. • The VANET uses position-based routing( PBR), because it outperforms topology-based routing in highly dynamic vehicular environments.

39. Routing scheme Issues( 3/27) • PBR • PBR requires that each node determine its own position through the use of Global Positioning System( GPS). • PBR thus does not require the establishment or maintenance of routes but routing decisions at each node is based on the destination’s position contained in the packet header. • With PBR, each node selects for each packet the next reachable forwarder that is geographically closest to the destination.

40. Routing scheme Issues( 4/27) • Partitioned network( Cont.) • Mobility can also create temporary network partitions that interrupt end-to-end connectivity and cause packet loss. • In order to reduce the number of network partitions, oncoming traffic is included when determining next hops.

41. Routing scheme Issues( 5/27) • Partitioned network( Cont.) • Forward mode • Message forwarding within a partition • Catch-up mode • Vehicle movement allows message propagation between partitions

42. Routing scheme Issues( 6/27) • Partitioned network • In order to bridge gaps in IVC networks and improve multi-hop routing performance, an alternative would be to forward data packets to its destination via roadside infrastructures.

43. Routing scheme Issues( 7/27) • DDP( Cont.) • Directional Propagation Protocol( DPP) utilize the directionality of data and vehicles for information propagation. • DDP is comprised of three components: • Custody Transfer Protocol( CTP) • Inter-Cluster Routing Protocol • Intra-Cluster Routing Protocol

44. Routing scheme Issues( 8/27) • DDP( Cont.) • Each cluster has a header and a trailer, located at the front and rear of each cluster, entrusted with the task of communicating with other clusters.

45. Routing scheme Issues( 9/27) • DDP( Cont.) • Inter-Cluster Routing & Intra-Cluster Routing • Immediately routed to header or trailer depending upon the direction in which in which information needs to propagate. • Any duplicate messages received at any of the nodes are dropped.

46. Routing scheme Issues( 10/27) • DDP( Cont.) • Custody Transfer Protocol( CTP) • The custody is implicitly transferred to another cluster that is in front along the direction of propagation and is logically the next hop in terms of the message path. • The traffic in opposing direction acts as a bridge but is never given custody of the message. • The custody of the message may be accepted or denied by a cluster by virtue of it being unable to satisfy the requirements of the message.

47. Routing scheme Issues( 11/27) • DDP • algorithm

48. Routing scheme Issues( 12/27) • MOPR( Cont.) • Movement Prediction based Routing( MOPR) algorithm predicts future positions of vehicles involved in each routing path based on their positions, speeds, and directions. • So MOPR is able to estimate links lifetime. • MOPR predicts if an intermediate routing node is likely to cause a rupture link during the transmission time or not.

49. Routing scheme Issues( 13/27) • MOPR( Cont.) • MOPR dynamically selects the most stable route among the routes provided by classical multi-path routing algorithms. • What is a stable route? • It is the one composed by( more) stable nodes. • What is a stable node? • It should have a direction and a speed similar to the ones of the destination node( and the source node). • Note that intermediate nodes can be moving or static.

50. Routing scheme Issues( 14/27) • MOPR( Cont.)