ABSTRACT
Currently, drivers must utilize a third-party, suchas a radio or broadband device, to learn aboutlocal traffic conditions. However, this informationis often out of date by the time it reaches adriver, and the area covered by such services isoften limited. The fastest and most efficient wayto transmit information about road conditions todrivers would be to create vehicle-to-vehiclewireless networks. This way, cars can freelyshare information with each other in real-time,allowing drivers to be more aware of the currentconditions.
This project demonstrates the capabilities andpotential impact of vehicle-to-vehicle networks. Ituses modified versions of existing WiFitechnology and the emerging Wireless Access inthe Vehicular Environment (W.A.V.E.) family ofprotocols, operating between 5.85GHz and5.925 GHz. W.A.V.E. is currently proposedthrough draft amendment IEEE 802.11p.
The system detects specific events from theexisting computer systems in a Toyota Prius andcommunicates this information wirelessly tonearby drivers. A GPS receiver is also used toprovide accurate location and timingsynchronization to within 20 μs. Informationreceived from other vehicles is selectivelydisplayed to the user, and in emergency settingsa tone is generated to ensure that the driver canreact quickly enough to avoid a dangeroussituation.
Location Division Multiple Access (LDMA) wasimplemented to allow for multiple vehicles totransmit without message collision. We wereable to successfully demonstrate the generation,retransmission, and reception of eventinformation, triggered from both simulated andreal events in the vehicle.
AUTHORS:
Andrew Avrin CTE ’09
Brandon Duick EE ’09
Daniel Lustig EE ‘09
ADVISOR:
Dr. Rahul Mangharam
DEMO TIMES:
Thursday, April 23rd, 2009
10:30 AM
1:30, 3:00, 3:30 PM
GROUP #17
Department of Electrical and SystemsEngineering
UNIVERSITY OF PENNSYLVANIA
Vehicle-to-Vehicle Communication Platform
IN-VEHICLE UNIT
The in-vehicle unit is composed of three subsystems: a networking element (the router), an interface to the vehicle’s existingcomputers and sensors (the controller), and a graphical display. The operational flow of the unit is seen below. To detect events theunit takes advantage of the controller-area network (CAN) bus which allows for communication among the various control units in aToyota Prius. This bus is accessible through the on-board diagnostics port found above the driver’s right knee. The controlleranalyzes the messages on the bus, and if it is determined that a safety related incident has occurred, it notifies the router so that analert can be broadcast to other drivers.
RESULTS
Hardware SetupOverview of PartsExample GUI
The value of the RSSI, or Received Signal StrengthIndicator, shows that even as the signal strengthdrops, the number of packets successfully receivedremains high.
NETWORKING SPECIFICATIONS
When an incident or an event is detected from within a particular vehicle, it is immediately transmitted to any other vehicles within range.Nearby vehicles then retransmit this information if it is determined to still be relevant. The scheme used to prevent transmissions fromcolliding is Location Division Multiple Access, or LDMA. The map is divided into a grid, and a vehicle may only retransmit a message itreceives within a particular time window, determined by its position within the grid. However, since it is important for the vehicles nearestto an incident to be informed as quickly as possible, this scheme is only employed for retransmissions.
The image on the left represents LDMA implemented only as a function of latitude. The image on the right represents LDMAimplemented in two dimensions. Each color represents a particular time window for transmission.
Two specific messages that are found on the bus are shown in the table below.As an example, the controller can check for a sudden halt by monitoring thelatest speed and the last known brake strength.
The router combines the vehicle-state information with GPS data to form a WiFipacket. This packet is transmitted at 5.9 GHz, according to the IEEE 802.11pW.A.V.E. standard. Other vehicles receive these packets, and determine basedon the message contents and the local GPS data whether or not to notify thedriver.
MESSAGE PROPAGATION
The above diagram shows how a message is propagatedand processed between three cars. When a car receivesa new message which is still relevant, it notifies the driverand retransmits that message to other cars in range.When it receives a duplicate message, it does not notifythe driver or retransmit it.
ID#
Description
Brakes
0x030
Byte 4: Strength: 0x00=out,
0x7F=full brake
Speed
0x3CA
Byte 2: Speed in km/h
Timing Synchronizationbetween Units
20μs
Time from EventOccurrence to Notificationof Driver in Area
~30ms