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DSRC General FAQs

What is DSRC?

Dedicated Short Range Communications (DSRC) is a general purpose rf communications link between the vehicle and the roadside.

More specifically, it is a short to medium range communications service that supports both Public Safety and Private operations in roadside to vehicle and vehicle to vehicle communication environments. DSRC is meant to be a complement to cellular communications by providing very high data transfer rates in circumstances where minimizing latency in the communication link and isolating relatively small communication zones are important.

How is DSRC different from other radio communications?

(this is first cut for this chart, mostly as a placeholder. Final version to be completed soon)

How does the current 5.9 GHz program differ from existing DSRC?

The only system in use today in North America are proprietary designs operating in the 915 MHz band. There was a set of 915 MHz DSRC standards completed several years ago but no compliant products were ever developed. A "sandwich" specification was prepared for use by federally funded commercial vehicle operations (CVO) that consisted of the Physical and Application Layers from those standards combined with the proprietary Data Link Layer already used in most CVO applications. This sandwich spec design has been developed but not yet fielded.

There will be no commonality between any of these original 915 MHz designs nor standards and the new 5.9 GHz standards, though the applications themselves may not change as they migrate from one to the other.

There is a significant difference in capability between the 915 MHz systems and 5.9 GHz. The following table summarizes these differences:

When will standard compliant products be available?

The standards are scheduled to be completed by late 2002 or very early 2003. Perhaps another six months to a year may be spent in testing and verifying that they all meet the requirements without any issues or problems. Because the compliant products will be based on the existing IEEE 802.11a chip sets, the time to have such products in production will not be as long as it would be for a totally new design. We cannot speak for the manufacturers, but are hoping that compliant products will be in production and available for widespread use in late 2003 or early 2004.

How difficult will it be to migrate from an existing DSRC system to one based on the new standards?

We are being very sensitive to this issue and doing everything we can to minimize the trouble and expense of migrating from existing products to the new standard compliant DSRC products.

Because of the frequency difference (915 MHz versus 5.9 GHz) there should be no concern about rf incompatibilities or interference. This allows both old and new communications to overlap even if they are using totally different communication protocols, lane coverage, or even back office processing concepts. The new system can be installed on top of the old and vehicles equipped with the old transponders will interact with the old system and vehicles with the new transponders will operate with the new system. Of course, the system design must include provisions to prevent a vehicle containing both old and new transponders from being billed twice.

Because the basic protocol is using IEEE 802.11, all of the back office software systems can be developed at any time to be compliant with this and Internet- based applications. Thus all of the software and interface with the overall roadside and center-to-center operations can be fully implemented and tested with presently available hardware. If the existing system does not already utilize this type of design, then it is possible to implement or upgrade the software at any time, even before the 5.9 GHz hardware in put in place. The software system can be treated as any other software upgrade to the system and fully tested and proven without implementing the 5.9 GHz hardware.

System testing can occur with the presently available 802.11a hardware and then when the standard compliant 5.9 GHz hardware does become available, it is a relatively minor change to implement it in lieu of the base 802.11a hardware.

Since there is no radio interference between the existing 915 MHz systems and the 5.9 GHz systems, both can coexist on the same roadway during the period of transitioning all of the vehicles to the new standard. Thus a toll agency does not have to have any lanes dedicated to one or the other technology. Lanes that are already performing electronic toll collection can continue but with both types of transponders being recognized in each lane. The existing transponders can then be slowly phased out using whatever schedule is convenient to the agency.

Who is developing the standards?

The standards are being developed primarily be ASTM and IEEE committees, with additional elements being developed by SAE, AASHTO, and ISO. ITS America is providing the primary interface with the FCC. The following companies are participating at this time:

For further information, contact:

Lee Armstrong Armstrong Consulting, Inc. 454 Walnut Street Newton, MA 02460

(P) 617-244-9203 (F) 617-244-9204 LRA@tiac.net