 |
 |
 |
 |
|
 |
 |
SAE J2735-Draft-Rev15 [issued: 01-30-07]
-
149 -
This is an SAE Motor Vehicle Council draft document of the DSRC committee, subject to change.
Left Turn Assistant
Stop Sign Movement Assistance
Lane Change Warning
The use of the specified message sets in the relevant vehicle safety application scenarios is described in this
annex in Sections A-1 through A-7. These sections of the annex present vehicle safety application scenarios and
are meant to illustrate the use of the messages specified in this Recommended Practice, rather than to specify or
prescribe these applications or to recommend the best way to deploy these applications. It is expected that these
same initial message sets will fully or partially enable additional vehicle safety applications to be developed. As
these additional applications are developed, those illustrations may be added in additional sections to this annex in
future versions of this Recommended Practice.
Other future vehicle safety applications that are expected to be developed may require additional message sets,
data frames and data elements that have not yet been specified in this Recommended Practice. 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 Recommended Practice 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 (ACID 20) and others are likely to be public safety applications (ACID 19).
The technical committee intends for this Recommended Practice 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 meet the requirements of vehicle safety systems implemented using this technology.
The frequency of transmission above the application requirements is also expected to generally compensate for the
inherently unreliable nature of radio frequency communications.
Although the bandwidth available within a DSRC channel at any given point is at least 3 Mbps, and the default
transmission rate is 6 Mbps, the net cumulative effect of many vehicles broadcasting within the same local area (in
particular during heavy traffic conditions) is likely to create potentially excessive channel loading. For this reason, it
has been the focus of the technical committee to use a concise selection of required information to include in
these common messages and to provide effective coding to minimize the size of the message payload for these
repetitive messages. The common message set that was developed by the committee to meet the requirements of
the initial vehicle safety application scenarios was therefore split into three parts:
MSG_BasicSafetyMessageFrame, Part I, which 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-changing
data. Part I is broadcast most frequently, providing an update rate that is consistent with the scan rates for on-
board vehicle safety system sensors.
MSG_BasicSafetyMessageFrame, Part II, which is added to Part I on a less-frequent basis in order to complement
abbreviated fields in Part I, such as time and position, in order to communicate the complete time or position. As
well, additional data that is important to vehicle safety applications, but is required less-frequently, is included in
Part II.
MSG_BasicSafetyMessageFrame, Part III, which contains additional data frames or data elements with open-
ended tags. Part III is added on an ‘as required’ basis to allow the communication of data that is not included in
Part I or Part II.
2.
Applicable documents
A detailed description of the identification and selection of the high-priority vehicle safety applications, as well as
the background descriptions of the application scenarios, are included in the “Vehicle Safety Communications
Project Task 3 Final Report: Identify Intelligent Vehicle Safety Applications Enabled by DSRC”, published by the