VADD: Vehicle-Assisted Data Delivery in Vehicular Ad Hoc Networks Jing Zhao, Guohong Cao The Pennsylvania State University IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, TVT 2007

Outline Introduction The VADD model Vehicle-Assisted Data Delivery Protocol Performance evaluation Conclusion

Introduction Vehicular ad hoc networks have been envisioned to be useful in road safety and many commercial applications. There are many researches in the VANETs such as medium access control (MAC) issues, and transportation safety issues. Most of the aforementioned works are limited to one hop or short range multihop communication. Multi-hop data delivery through VANETs is complicated by the fact that vehicular networks are highly mobile and sometimes sparse.

Introduction - Scenario 假設A車欲跟目的地-餐廳訂位，在不藉由其他固體建設的協助下，欲透過VANET將訂位訊息送至餐廳。 此時A車有兩種選擇的方式，1.透過B車

Introduction - Motivation Carry and forward A B C 假設A車欲跟目的地-餐廳訂位，在不藉由其他固體建設的協助下，欲透過VANET將訂位訊息送至餐廳。 此時A車有兩種選擇的方式，1.透過B車

Introduction - Goal Find a forwarding path with the smallest packet delivery delay A B C

The VADD model Assumption Packet modes Principles Delay model

The VADD model - Assumption Vehicles can communicate with each other through short range wireless channel (100m-250m). Every vehicle knows its location by GPS device. Vehicles enclose their physical location, velocity and direction information in their periodic beacon messages for their one-hop neighbors. Vehicles are equipped with pre-loaded digital maps. B A C

The VADD model - Packet modes Move into intersection radius StraightWay Mode Intersection Mode Move outside intersection radius Move into destination area Move into destination area Destination Mode

The VADD model - Principles Transmit through wireless channels as much as possible. If the packet has to be carried through certain roads, the road with higher speed should be chosen. Dynamic path selection should continuously be executed throughout the packet forwarding process.

The VADD model – Delay model R : the wireless transmission range. c : the average one hop packet transmission delay. Ij Ii A

The VADD model – Delay model Dmn : the expected packet delivery delay from Im to the destination through road rmn. Pmn : the probability that the packet is forwarded through road rmn at Im. N(j): the set of neighboring intersections of In.

The VADD model – Delay model

The VADD model – Add a boundary It is impossible to find the minimum forwarding delay between two arbitrary intersections. The radius is the distance between the packet and the destination plus 1000 meters.

The VADD model – Calculation of D n : the number of roads within the boundary. xij : the expected packet delivery delay through road rij. Pij : the probability that the packet is forwarded through road rij at Ii.

The VADD model – Calculation of P Ij Ii A

The VADD model – Calculation of P Tij : the contacting time for packet carriers which enter intersection Ii and move towards Ij. Rint : the radius of the intersection area. CPij : the probability for a packet to meet at least one contacts road rij. ij : the average rate of contacts leaving Ii and moving towards road rij.

The VADD model – Calculation of P Both contacts are available Ii Ia A B C Ib

The VADD model – Calculation of P Ii Ia Ib

The VADD model – Calculation of P Qic : the probability of a vehicle moving (going straight or turning) from current intersection Ii towards next intersection Ic. 此條件機率的表示式代表，在車子決定自己將packet 帶往前Rijc走的時候， packet 傳往Rijp的機率 1.

Vehicle-Assisted Data Delivery Protocol Location First Probe (L-VADD) Direction First Probe (D-VADD) Hybrid Probe (H-VADD)

Location First Probe (L-VADD) W S Optimal direction Priority =1 Priority =2 Priority =3 C A B

Location First Probe (L-VADD) W S Optimal direction Priority =1 Priority =2 Priority =3 A B

Location First Probe (L-VADD) routing loops N E W S Optimal direction Priority =1 Priority =2 Priority =3 A B Record all the previous hops

Direction First Probe (D-VADD) W S Optimal direction Priority =1 Priority =2 Priority =3 C A B D-VADD only probes vehicles moving towards the direction whose priority is higher than or equal to the moving direction of current packet carrier.

Direction First Probe (D-VADD) W S Optimal direction Priority =1 Priority =2 Priority =3 C A B D-VADD is free from routing loops at intersection areas.

Hybrid Probe (H-VADD) D-VADD L-VADD with loop detection An ideal VADD protocol should minimize the geographic forwarding distance and does not have routing loops. Loop occur L-VADD with loop detection D-VADD Loop free

Hybrid Probe (H-VADD) D Priority =1 Priority =2 Priority =3 N E W S E F A D C B

Performance evaluation

Performance evaluation

Performance evaluation

Performance evaluation

Performance evaluation

Performance evaluation

Performance evaluation

Performance evaluation

Conclusion They adopted the idea of carry and forward, where a moving vehicle carries the packet until a new vehicle moves into its vicinity and forwards the packet. They proposed several vehicle-assisted data delivery (VADD) protocols to find a forwarding path with the smallest packet delivery delay.

Thank you!