 |
 |
 |
 |
|
 |
 |
SAE J2735-Draft-Rev15 [issued: 01-30-07]
-
150 -
This is an SAE Motor Vehicle Council draft document of the DSRC committee, subject to change.
National Highway Traffic Safety Administration in March 2005 and publicly available from National Technical
Information Service, Springfield, Virginia 22161 (or online at www.nrd.nhtsa.dot.gov/pdf/nrd-
3.
Application message sequences
The repetitive broadcast of vehicle safety messages is expected to increase the range of vehicle environmental
awareness beyond the range of any on-board sensors. Each vehicle will broadcast its relevant information
frequently via the MSG_BasicSafetyMessageFrame, Part I and MSG_BasicSafetyMessageFrame, Part II
messages and receive the equivalent messages from all DSRC-equipped vehicles in the immediate vicinity.
Messages from other vehicles can then be analyzed by on-board processors to identify impending situations that
would warrant warning the driver or initiating other actions, for example, pre-tensioning of seat belts.
4.
Application use with DSRC
The messages in the vehicle safety application area denoted by ACID 20 [the “vehicle-safety” service as defined by
IEEE 1609.4 or its successors] are transmitted using the Wave Short Message Protocol (WSMP) stack in a
periodic broadcast mode on the Control Channel (CCH) to other devices (typically other mobile OBUs) which have
determined to receive this type of message (based on ACID value and running a suitable application). Therefore,
this is a provider application that does not employ a Wave Basic Service Set (WBSS) as per IEEE 1609.4 Clause
5.3, and there is no confirm and join operation. It is recommended for channel bandwidth preservation, that these
common messages are sent with {ACM=0} as to permit any vehicle safety or public safety application to determine
its relevance, and avoid rebroadcast of the same information under multiple ACMs within a ACID.
Receivers of these messages are expected to process all such messages. Upon reception of such messages,
they are examined for message content and relevance at the application layer of the protocol stack. Based on the
data exchanged in this application area, devices may determine the need to initiate other services or applications
using other ACID values.
The expected repetition rate for the MSG_BasicSafetyMessageFrame, Part I messages broadcast in this
application is expected to be consistent with the scan rates for on-board sensors used for vehicle safety systems.
Based on this expectation, the repetition rate is nominally considered to be one new message every 100
milliseconds. However, to help prevent the possibility of vehicle broadcast messages overloading the control
channel bandwidth, the frequency of transmissions may need to be adjusted in dense traffic environments and may
be adjusted based on speed, number of vehicles in close proximity or other parameters in dense traffic
environments where many vehicles are stopped or close to being stopped (e.g., a toll plaza).
The nominal expectation for the inclusion of a MSG_BasicSafetyMessageFrame, Part II broadcast message along
with Part I is every 10th Part I transmission, or whenever requested by another vehicle or roadside unit.
In all seven of the following application scenarios, a GPS unit and a connection to the vehicle data bus, in addition
to a DSRC radio unit, are necessary to send out the correct information to, and receive the necessary information
from, other vehicles.
ANNEX A-1 INTERSECTION COLLISION WARNING
Application Description
This application warns drivers when a side-impact or straight crossing path collision at an intersection is probable.
DSRC communications can be used to allow a vehicle approaching an intersection to detect all nearby vehicles,
their position, velocity, acceleration, and turning status. The in-vehicle unit analyzes these parameters for the
other vehicles as contained in their MSG_BasicSafetyMessageFrame, Part I and
MSG_BasicSafetyMessageFrame, Part II messages and projects expected future vectors for these vehicles. If this
analysis determines that a collision is likely, an appropriate warning is issued to the driver.
Flow of Events