1. 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

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

3. 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.

4. 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

5. 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

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

7. The VADD model
Assumption
Packet modes
Principles
Delay model

8. 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

9. 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

10. 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.

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

12. 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.

13. The VADD model – Delay model

14. 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.

15. 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.

16. The VADD model – Calculation of PIj Ii A

17. 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.

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

19. The VADD model – Calculation of PIi Ia Ib

20. 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.

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

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

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

24. 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

25. 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.

26. 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.

27. 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

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

29. Performance evaluation

30. Performance evaluation

31. Performance evaluation

32. Performance evaluation

33. Performance evaluation

34. Performance evaluation

35. Performance evaluation

36. Performance evaluation

37. 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.

38. Thank you!