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SAE J2735-Draft-Rev29 [issued: 12-11-08]
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238 -
This is an SAE Motor Vehicle Council draft document of the DSRC committee, subject to change.
Annex C Operation with the Vehicle Basic Safety Message
1.
Application Background
The Basic Safety Message [JBK3][JBK4]in this Standard was developed based on analysis of communications
requirements for seven high-priority vehicle-to-vehicle application scenarios with significant anticipated
safety benefits. These application scenarios are:
C.1
Intersection Collision Warning
C.2
Emergency Electronic Brake Lights
C.3
Pre-Crash Sensing
C.4
Cooperative Forward Collision Warning
C.5
Left Turn Assistant
C.6
Stop Sign Movement Assistance
C.7
Lane Change Warning
The use of the Basic Safety Message in the relevant vehicle safety application scenarios is described in this
annex in Sections C-1 through C-7. These sections of the annex present vehicle safety application scenarios
and are meant to illustrate the use of the Basic Safety Message specified in this Standard, rather than to
specify or prescribe these applications or to recommend the best way to deploy these applications. It is
expected that the message sets [JBK5]in this standard will fully or partially enable the development of
additional vehicle safety applications. Illustrations of such applications may be added to this annex in
future versions of this Standard.
Future vehicle safety applications may require additional message sets, data frames and data elements that
have not yet been specified in this Standard. The intention of the DSRC Technical Committee is for these
additional elements to be identified by the Technical Committee, analyzed, specified and added to future
versions of this Standard in order to support interoperability for an increasingly diverse range of vehicle
safety applications. These additions are likely to be especially noticeable in the area of future vehicle-
to/from-infrastructure safety applications that are envisioned. Some of these will likely be vehicle safety
applications and others are likely to be public safety applications. The technical committee intends for this
Standard to support the interoperability of all these safety applications between and among vehicles from
different manufacturers and roadside infrastructure operators/manufacturers throughout the entire region of
expected vehicle travel.
The basic premise of the initial vehicle safety applications is the use of frequent broadcasts of basic
information about each individual vehicle to enhance the awareness of vehicles that are in the vicinity. The
frequency of these broadcasts is expected to at least meet the requirements of vehicle safety systems
implemented using this technology, and if possible to exceed these requirements in order to compensate for
the inherently unreliable nature of radio frequency communications.
Due to the potential cumulative effect of many vehicles broadcasting within the same local area (in
particular during heavy traffic conditions), the DSRC communication channel is likely to encounter
excessive channel loading on occasion. For this reason, it has been the focus of the technical committee to
limit the required information in these common messages to a concise set, and to provide effective coding
to minimize the size of the message payload. The common message set that was developed by the
committee to meet the requirements of the initial vehicle safety application scenarios is the
MSG_BasicSafetyMessage, which has a mandatory section (Part I) and an optional section (Part II):
Part I of the MSG_BasicSafetyMessage contains a fixed data structure comprising the information that
must be updated most frequently or which must be known to determine the meaning of the frequently-