Using 220MHz digital radio networks in advisory systems:
Vehicle polling, tracking and driver emergency signals are provided by a 220MHz RF link in a system that also incorporates receivers for an FM subcarrier and for Global Positioning System (GPS) radiolocation signals.
While millions of tourists and residents wended their way through metropolitan Atlanta last summer during the Olympics, 200 of the vehicles moving among them were being used to develop technology to make navigating the roadways more efficient for fleet and consumer vehicles.
The vehicles were part of a field operational test of the Atlanta Driver Advisory System (ADAS), a real-time, in-vehicle system combining a 220MHz RF link, a 72.2kHz FM subcarrier and Global Positioning System (GPS) location signals, as shown in Figure 1 on page 38.
Funded by a $7.2 million grant from the Federal Highway Administration (FHWA), the test, which ran from April to December, is part of FHWA’s national effort to develop intelligent transportation system (ITS) technologies and national standards for those systems. The next phase, model deployment systems, is being carried out in the New York area, Phoenix, San Antonio and Seattle.
Partners in the Atlanta project included the FHWA, the Georgia Department of Transportation, Oak Ridge National Laboratory, Federal Express, TRW Transportation and Systems, Georgia Tech Research Institute, Georgia Institute of Technology, Clark Atlanta University, Concord Associates and Scientific Atlanta. Contributions from the partners in the project brought funding for the cooperative agreement to a total of $9.1 million. Scientific Atlanta coordinated the project and created a new 220MHz digital radio system for the Atlanta test. Motorola’s Position and Navigation Systems Business provided the GPS receivers.
Of the 200 test vehicles, 100 were delivery vehicles operating for Federal Express, making the test results applicable to fleet management as well as private vehicle operation.
“The 220MHz two-way radio system, we designed from scratch,” said Will Blakeley, ADAS project manager for Scientific Atlanta. “That was based on the desires of the FHWA to try out that frequency band for their own use.”
As part of the refarming process (see Refarming: The Telecom ‘Agribusiness’ of the Next Decade,” page 18), the FCC has allocated 10 channel pairs of 220MHz spectrum nationwide to the FHWA, which opens the opportunity for a national driver advisory network.
The other major radio component of the ADAS system is an FM subcarrier, or subcarrier traffic information channel (STIC). The STIC design was created by the non-profit Mitre Corporation on a commission from FHWA.
The National Radio Standards Committee (a joint industry effort of the National Association of Broadcasters [NAB] and the Electronics Industries Association [EIA]) has completed an independent study of different FM subcarrier systems, and the STIC product developed for the ADAS (which is also being used in the model deployment cities) was highly rated.
“We expected the FM subcarrier to perform very well in a mobile environment, Blakeley said. “The waveform is designed very robustly, almost like a Department of Defense secure communications link. It’s got all the various types of forward-error correction to combat multipath fading that you see in a mobile environment. I guess we were pleasantly surprised at just how well it did perform. We got excellent coverage all over the city, and in this study that the NRSC performed, there was just no comparison between STIC and competitors.”
“They [Mitre] designed the waveform, forward-error correction and all the different aspects of the digital wireless data link,” Blakeley said. “That was done in the interests of the FHWA to create an open, non-proprietary standard. We [Scientific Atlanta] then took that design, and we implemented it_we built actual hardware, and that’s what we’re offering now in San Antonio, Phoenix, Boston and elsewhere.” The model deployment systems in Phoenix and San Antonio are only using the FM subcarrier, not the 220MHz two-way link. A final evaluation of the ADAS test, including 220MHz, is scheduled to be released at the end of April by evaluators at Georgia Tech.
Finding a home for 220MHz “As part of these national architecture study teams, there are all kinds of competing technologies, and as you might imagine, on something the scale to cover the United States nationally, there are some very strong forces vying for having their technology deemed as the standard,” Blakeley said. Advocates can be found for 220MHz cellular, CDPD, satellite, 800MHz and 900MHz systems.
“There just hasn’t been yet, in the national architecture, a slot set aside that says okay, 220MHz is going to be used for this function,” Blakeley said.
Scientific Atlanta has proposed the 220MHz radio system it designed for the FHWA as a North American standard for ITS two-way communications use, using the allocated channels, as well as commercial channels. The system created for the ADAS includes short-range, roadside-to-vehicle transceivers, as well as long-range transceivers, as shown in Figure 2 on page 40. The short-range (local area) transceivers deliver in-vehicle signing, roadway conditions and traveler services information. The long-range (wide-area) system poll tests vehicles and provides a two-way “mayday” notification for vehicle distress. Polling information is used to estimate congestion levels along major roadways.
The 90W base station transmits at 220.0025MHz-220.9975MHz; the mobile at 221.0025MHz-221.9975MHz. Channel spacing of 5kHz is used, with modulation to meet FCC Part 90 requirements for 5kHz narrowband channels. Narrowband data rates were designed at 5,200bps uncoded and 2,880bps user data rate using standard error-correction coding. The full-duplex base station supports multiple transmit and receive channels. The half-duplex, 20W mobile unit locks to the base station signal for frequency stability and has the optional capability to receive two signals simultaneously. Receiver sensitivity of the mobile is 2110dBm for 0.01 bit-error rate (BER), uncoded, in a static environment and 295dBm for 0.01 BER in a mobile fading environment.
Blakeley said both performance and access are points supporting the proposed standard. “The real savings to the state DOTs or the federal government is that if this is going to be a function provided by a federal or state agency, they don’t have to buy any license fees; there are no usage fees; there are no message transaction fees, because they own that spectrum-that’s a huge advantage.”
The FHWA is trying to get some compatibility among the cities that were selected for the model deployment. Standardization is needed so that a radio receiver in San Antonio would work just as well as in Phoenix. Accordingly, the systems developers are using non-proprietary, open architectures. For any successful nationwide, or North American, deployment of ITS, standardization will be essential to provide vehicles with a ubiquitous system.
“We’re working very closely with the National Architecture Committee for ITS, that’s headed by FHWA and major contractors,” Blakeley said. “The one we’ve been speaking with most is Rockwell. They’re trying to establish a national architecture, so this could become ubiquitous in the future. If someone doesn’t establish standards like that, I don’t see that happening.”
In addition to fleet vehicles, applications for automobiles are gaining the attention of automotive electronics original equipment manufacturers (OEMs) such as Rockwell, Alpine, Siemens, Zexel and Philips. In-vehicle navigation systems are being tested in Hertz and Avis rental vehicles to give destination directions. Radio links will add the advantages of combining the GPS map data base with current traffic and detour information to compute a route based both on shortest distance and shortest time.
