1. Vehicular Communication Technology
Vehicular Communication Technology

2. Vehicular Communication Technology
Motivation
Safety and transport efficiency
In Europe around 40,000 people die and more than 1.5 millions are injured every year on the roads
Traffic jams generate a tremendous waste of time and of fuel
Most of these problems can be solved by providing appropriate information to the driver or to the vehicle
Vehicular Communication Technology

3. Vehicle Communication (VC)
VC promises safer roads,
… more efficient driving,
Vehicular Communication Technology

4. Vehicle Communication (VC)
… more fun,
… and easier maintenance.
Vehicular Communication Technology

5. Vehicular Communication Technology
Smart Vehicle
Vehicular Communication Technology

6. Approaches to vehicular communication
Communication using Communication using
dedicated infrastructures cellular systems
Direct Communication
Vehicular Communication Technology

7. Vehicular Ad Hoc Network (VANET)
A network with minimal or no infrastructure
Self-organizing
Each node can act as the source of data, the destination for data and a network router
Vehicular Ad Hoc network (VANET)
Uses equipped vehicles as the network nodes
Nodes move at will relative to each other but within the constraints of the road infrastructure
Vehicular Communication Technology

8. Differences VANETs from MANETs
Rapid Topology Changes
High relative speed of vehicles => short link life
Frequent Fragmentation
Chunks of the net are unable to reach nodes in nearby regions
Small Effective Network Diameter
A path may cease to exist almost as quickly as it was discovered (reactive routing)
Limited Redundancy
The redundancy in MANETs is critical to providing additional bandwidth
In VANETs the redundancy is limited both in time and in function
Vehicular Communication Technology

9. Vehicular Ad Hoc Network (VANET)
Message propagates to destination using a number of intermediate links
Vehicular Communication Technology

10. Vehicular Ad Hoc Network (VANET)
If vehicle mobility causes links to break, message rerouted using a different path
Vehicular Communication Technology

11. Vehicular Communication Technology
Why use VANETS?
Easier deployment
Decreased dependency on fixed infrastructure
Sparse network of roadside beacons
Permit gradual introduction of technology
Location-oriented services can be provided with little or no running costs to the users
Vehicular Communication Technology

12. Lot of Involved Parties
Vehicular Communication Technology

13. Major problems in this area
Communication / Networking
Localization
Vehicular Communication Technology

14. Requirements on vehicular communication
Mobility
Delay bounded (real-time)
Scalability
Bandwidth efficiency
Cost
Fairness
Any time, any place, any hosts (GPS unequipped vehicles, standardization between cars’ manufactures)
Vehicular Communication Technology

15. Addressing the challenges
Physical Layer
limited bandwidth
Link Layer
congestion control, latency, throughput, fairness and scalability
Network (Routing) Layer
rapid topology changes and network fragmentation
Vehicular Communication Technology

16. Dedicated Short Range Communications (DSRC)
DSRC operates at 5.9 GHz
Vehicular Communication Technology

17. DSRC – Operating Characteristics
IEEE p protocol (802.11a modification for VC)
Maximum range: 1000 m
Vehicle speeds up to 100 mph
Low latency: 50 ms
Application priority: 8 levels
Channel 172: vehicle safety only
Vehicular Communication Technology

18. Vehicular Communication Technology
How does DSRC work?
Road-Side Unit (RSU)
Announces to OBUs 10 times per second applications it supports on which channel
On-Board Unit (OBU)
Listens on Channel 172
Executes safety applications first
Then switches channels
Executes non-safety applications
Returns to Channel 172 and listens
Vehicular Communication Technology

19. Channel allocation (MAC)
Existing MAC protocols (CSMA/CA, MACA, MACA-BI) are contention-based => not delay bounded
Proposed MCS/CDMA
Each vehicle senses all the spreading codes, finds a code that is not used by nearby vehicles, and transmits data using the selected code
Search for free code, contention for free code (if vehicles > codes) => large delays
Vehicular Communication Technology

20. Channel allocation (MAC)
Location-based Channel Access (LCA)
The geographical area is divided into a cellular structure
Each cell has a unique channel associated with it
Multiple access scheme, such as CSMA/CA and MCS/CDMA, can be used within each cell
Main design parameters: cell size and channel reuse distance
Advantages: no central station for channel assignment, no wait before transmit, no contention for free channels, reuse of channels => delay bounded, fairness, bandwidth efficiency, scalability and mobility
Vehicular Communication Technology

21. Vehicular Communication Technology
Routing Schemes
Proactive (table-driven)
Each node attempts to maintain a current representation of the network topology
Advantage: lower message latency (routes are immediately available)
Disadvantage: bandwidth overhead (to maintain routes), restricted scalability
Reactive (source-driven, on-demand)
Routes are requested by source nodes only when needed
Advantage: bandwidth economy (no control messages for non-active routes)
Disadvantage: latency (establishing a route)
Hybrid
ZRP – proactive within zone, reactive outside zone
Vehicular Communication Technology

22. Major problems in this area
Communication / Networking
Localization
Vehicular Communication Technology

23. Vehicular Communication Technology
GPS
Vehicular Communication Technology

24. Vehicular Communication Technology
Space Segment
Vehicular Communication Technology

25. Vehicular Communication Technology
How does GPS work?
Vehicular Communication Technology

26. How do we compute Position?
GPS is a Distance (Range) Measuring System
Stable Frequency Standards in the Satellites and Receivers
Able to compute a Clock Offset
Velocity of Radiowave is known
Thus Distance = V x T
Since the coordinates of the Satellites are known at any point of time, with 4 ranges the position of the GPS Antenna can be computed
3-D Trilateration: Distance, Distance, Distance and Distance Intersection
Vehicular Communication Technology

27. Vehicular Communication Technology
DGPS
Differential GPS can improve accuracy from several meters to a few centimeters
Vehicular Communication Technology

28. Vehicular Communication Technology
However…
Vehicles may be unequipped with GPS or sometimes cannot obtain line-of-sight access to satellites (in tunnels)
In order to discover their position (or at least driving direction), GPS-U vehicles can use communication with GPS-E vehicles
GPS-U periodically broadcasts PREQ message to its one-hop neighbors
When GPS-E receives PREQ, it sends back PREP message including its current position
The knowledge of the exact position depends on the number of neighbors sending PREP messages
GPS-U can compute its exact position if it receives at least three PREP from three different vehicles (by triangulation)
Vehicular Communication Technology

29. Vehicular Communication Technology
Thank You!
Vehicular Communication Technology