Ever since the first radiomatic garage-door opener was developed in 1926, wireless technology has been used to make car-related activities easier, more enjoyable, and convenient. Throughout the history of vehicular-communications or telematics systems, however, one rule has always held true: Everyone has his or her own idea about how to do things. OnStar has its system. Tele Aid has its technology. Wingcast does its own thing. Shell Stations use one type of fob for gasoline payment, while Exxon Mobil uses another. Each accomplishes similar goals, but uses different equipment and protocols.

As a result, the variety of RF tags and active transponders used for things like electronic toll-collection systems and parking garages outnumbers the amount of models that car manufacturers currently build. This situation is of no help to third parties wanting to build applications supported by a variety of automotive equipment. It is even more frustrating for public agencies and private companies wanting to take advantage of different vehicles' built-in systems. The myriad of proprietary technologies limits the development and adoption of telematics applications.

In 1999, the FCC realized this problem and allocated 75 MHz of spectrum—from 5.850 to 5.925 GHz—for use by Dedicated Short Range Communications (DSRC)systems in the service of Intelligent Transportation Systems (ITSs). The allocation held that services within the band would use non-voice radio techniques to transfer data over short distances, such as between roadside and mobile radio units, between mobile radio units, and between portable and mobile units. Services in this band would include operations related to the improvement of traffic flow, traffic safety, and other ITS applications in a variety of public and commercial environments. This allocation of transportation-specific spectrum is comparable in size to the 83.5 MHz of spectrum available for all unlicensed services in the 2.4-GHz band. Because it's part of the 5-GHz band, however, the higher-performance technology designed for this upper band can be used in the new spectrum. This technology was known provisionally as 802.11a R/A (road access), and is now the ASTM E2213-02 telecommunications standard. It is a derivative of the IEEE 802.11a standard used for wireless networks from 5.150 to 5.850 GHz. Because it's based on an existing open standard, it has the advantage of being technically proven. It also benefits from existing research and development efforts.

One key variation necessary for the E2213-02 spec is the definition and channelization of the protocol for the 5.9-GHz spectrum. Under the FCC Part 15 rules for unlicensed wireless operations, the core IEEE 802.11a spec defines 20-MHz channels in the spectrum from 5.150 to 5.825 GHz. 802.11a R/A instead defines 10-MHz channels in the spectrum from 5.850 to 5.925 GHz under the Part 90 rules for operation.

Seven independent, 10-MHz-wide channels are available in the United States from 5.850 to 5.925 GHz(see figure). Because of the availability of 5.825 to 5.850 GHz, three independent channels also are available in Canada. These channels are short range (less than 100 m typical). They support data rates of up to 27 Mbps, and may be used simultaneously by many vehicles and applications.

802.11a R/A is a component of licensed services operating in the DSRC band. As a result, it has less restrictive emission-mask and guard-band rules than IEEE 802.11a products operating in the Unlicensed National Information Infrastructure (U-NII) and Industrial, Scientific, and Medical (ISM) bands. Less overall spectrum is available (75 to 100 MHz) in the DSRC band than in the U-NII and ISM bands (350 MHz), however. This prompted the decision to halve the clock of the protocol, but run the channels to the edge of the band as permitted by the Part 90 emission-mask rules. Thanks to this change, each E2213-02 channel consumes only half as much spectrum as IEEE 802.11a channels at the expense of delivering half the maximum data rate (27 Mbps instead of 54 Mbps).

Fundamentally, the protocol remains IEEE 802.11a. It just does so at a half-clock rate while operating in the DSRC spectrum. To accommodate the needs of the vehicular environment, it also has undergone slight modifications to parameters like RSSI sensitivity and adjacent-channel rejection. The keeper of this standard for telematics applications is the American Society for Testing and Materials (ASTM) subgroup E17.51.

To target the vehicular environment, RF designers also must adjust timing, calibration, and other parameters in their 802.11a systems (see table). According to field trials and simulation testing, these modifications allow for applications at a relative speed of up to 120 mph. They also permit up to 255 simultaneous users on a single channel.

E2213-02 is not a universal telematics technology. It is optimized for short-range or local communications. It complements technologies like GPS, automated emergency communications systems, and cellular phones. Other technologies offer different methods for delivering information/ services from a remote location. Yet, E2213-02 provides a universal method for exchanging information in a vehicle's local area.