1. Ad hoc Data Dissemination in Vehicular Networks
Prof. Victor C. M. Leung
TELUS Mobility Research Chair in Advanced Telecom. Eng.
Department of Electrical and Computer Engineering
The University of British Columbia
Vancouver, BC, Canada
NSERC DIVA Workshop
Ottawa, Canada 9 September, © 2011

2. Outline Introduction Challenges of vehicular networking
Advanced heterogeneous vehicular communications platform
System evaluation methodology
Robust ad hoc data dissemination
Connectivity-aware minimum delay geographical routing
Vertical handoff decision for delay tolerant data
Conclusion

3. Introduction Wireless access technologies have matured in recent years
It is of interest to leverage anywhere anytime connectivity of wireless networks to improve well-being of society
Wireless vehicular networking can improve transportation safety, smooth traffic flow, reduce road congestion, lower trip time, reduce CO2 emission, keep drivers informed, entertain passengers
Transportation engineering has also evolved from a “brick and mortar” discipline to embrace information and communication technologies
Intelligent Transport Systems (ITS)
Wireless vehicular networking enables ITS 2.0

4. Challenges of Vehicular Networking
Vehicular ad hoc networks are not the same as general mobile ad hoc networks as vehicles are confined to roads and usually follow the rules of traffic
Ad hoc routing of packets between vehicles
Might fail if the road traffic is too sparce
Might lead to network congestion if the road is also congestion
Might have difficult traversing street corners
Routing mechanisms should be tailored to the supported application
Heterogeneous networking in vehicular environment has been largely unexplored

5. Advanced Heterogeneous Vehicular Communications Platform
Applications
Communications Model
Wireless technologies
Safety
WiMAX
Cellular
Wi-Fi
Traffic
management
Transmission strategies
Direct
transmission
Multihop
transmission
Cluster-based
transmission
Travel
information
Vehicle-to-Roadside
Medium access control
Control
Channels
Roadside
Entertainment
base stations
Centralized
Single
Single
Others
Distributed
Multiple
Multiple
Vehicle-to-Vehicle

6. Advanced Heterogeneous Vehicular Communications (AHVC) Platform
Heterogeneity
Various wireless access networks employing different wireless access technologies available at different geographic areas
Multiple radios available to vehicular users
Opportunities
Such a rich set of connectivity alternatives can be used to improve the performance of vehicular networks
Other benefits
Extended coverage of service availability
Simultaneous access to various types of vehicular infotainment applications by vehicular users

7. System Evaluation Methodology
Computer simulations most commonly used for system performance evaluations
Wireless networks commonly evaluated using simulators such as ns2
Vehicular networking in ITS characterized by movements that follow rules of traffic and confined to streets and highways
Need proper vehicular traffic simulator

8. Robust Ad Hoc Data Dissemination for Safety Applications
Challenge: overcoming ad hoc delivery failure around intersections

9. Enhanced Intersection-mode Data Dissemination (EIDD)
-Our proposed mechanism is to add 3 bits to the header of the emergency message as it enters a junction.
-Any of the 3 bits corresponds to message dissemination towards one of the possible out-going streets. (The corresponding bit is set to 1)
-The message is kept at the junction until all the 3 bits are 1.
-As all vehicles know the street structure via their digital maps, the number of bits can be adjusted according to the number of out-going streets.
Add some bits to the header of an emergency message as it enters a junction, each bit corresponding to one outgoing direction at the junction
A bit is set to one when the message is propagated to the corresponding outgoing direction at the junction
The message is kept at the junction until all the header bits are 1
Application-specific Data Delivery

10. Simulation Results
Define Delivery Ratio as the percentage of the vehicles that get notified in the simulation time
Comparison with Ad-hoc Multi-hop Broadcast (AMB)
Delivery Ratio of EIDD is close to 100% for almost all vehicle densities
EIDD shows the highest improvement in lower vehicle densities
-Ad-hoc Multi-hop Broadcast (AMB) is the most successful available mechanism.
-In AMB the message forwarding responsibility if delegated to the vehicle closest to the centre of the junction.
-Enhanced Intersection mode Data Dissemination (EIDD) is the name of our proposed protocol.
Application-specific Data Delivery

11. Connectivity-aware Minimum-delay Geographic Routing (CMGR)
Vehicular ad hoc networks (VANETs) are specialized mobile ad hoc networks (MANETs)
Highly variable vehicle densities and potential high speeds
Vehicles follow traffic rules and confined to roads
Proposed CMGR adapt to changing vehicular densities by
Favouring routes with higher connectivity to maximize the chance of reception when traffic is sparse
Avoiding congested routes when traffic is dense
Enhanced by a vehicular tracking mechanism to deal with the situation where the source vehicle has turned a corner
Keep velocity vector in intersection until route reply comes back
Performance comparisons with:
Anchor-based street and traffic aware routing (A-STAR)
Vehicle-assisted data delivery (VADD)

12. Packet Delivery Ratio

13. Packet Delivery Delay

14. Vertical Handoff Decisions in Heterogeneous Vehicular Networks
Which network to select for data delivery?
Objective: minimize total cost by considering the signaling costs of vertical handoffs
Distributed VHO decision algorithms for 3 scenarios
Cellular network only
Cellular + WLAN
Cellular + WLAN + ad hoc

15. Simulation Results

16. Ongoing Work – Routing in Vehicular Heterogeneous Networks

17. Conclusion
Wireless communications put vehicles in the loop in next generation intelligent transportation systems to enable many new applications beneficial to society at large
Vehicular networking architectures and protocols are highly dependent on applications
Proposed
Enhanced intersection-mode data dissemination
Connectivity-aware minimum delay geographical routing
Vertical handoff cost optimization for delay tolerant data
Future vehicular networks will likely support heterogeneous access technologies and lead to many interesting research problems

18. Thank you!