Two-Way Radio Goes Digital

Communications News, Sept, 1984

Ten years ago the big news in two-way radio was "digital". RCA introduced its Voice-PLUS Digital communications equipment line for two-way mobile systems combining normal voice transmissions with the ab ility to send up to 99 digital code messages instantly by push button, with automatic vehicle identification, a digital data master station, and a selective-calling sender. Motorola introduced its "MODAT" data system which allowed automatic transfer of information between vehicles and the dispatch center. Using the Modat control head, the vehicle operator pressed the desired function button and the message and vehicle ID were automatically sent. The mobile unit automatically sent its message only when the frequency was clear. It automatically retransmitted when the channel was clear until acknowledgement was received, or a maximum of four times. When the message had been sent, received and decoded at the base station, an "acknowledge" message was transmitted to the mobile unit, causing the "acknowledge" light to go out. A total of 24 digital messages could be incorporated into one equipped mobile unit.

Today, a decade later, the future of mobile digital communications looks bright . . . with organizations like Federal Express "going digital" in a big way.

While earlier mobile data terminals were not very user-friendly . . . and while the early radios lacked reliability and the early computers used in the systems lacked flexibility . . . today the technology, says Business Radio, is "enhanced, refined and field-proven" and mobile digital radio is again on the move. The systems available today are greatly improved.

Mobile Data International, a Canadian company that designs and manufactures exclusively mobile digital systems, is enjoying a surge in systems sales in North America and in offshore markets as well. Since 1978, MDI has installed systems for public safety organizations in North America, Europe, and the Far East. The Phoenix, Arizona Fire Department's communications system, considered the world's most advanced, includes MDI terminals. Police in Stockton, California and Vancouver, Canada use MDI terminals to run nationwide license checks in under ten seconds, and these forces will soon be joined by police in Calgary, New York, Toronto, and Oakland, California.

More recently, MDI's market has broadened from its public-safety base. A major Toronto power utility uses MDI terminals to improve safety and cost-efficiency. A Calgary taxi fleet operator uses MDTs to eliminate favoritism by dispatchers. Federal Express uses them to improve efficiency and morale. A major manufacturer of household chemical products has ordered an MDI system that will become an integral part of its warehousing and materials handling systems.

"All indications are," says Business Radio, "that mobile digital technology will become an important part of the business radio scene in the coming years."

An excellent article in the February, 1984 issue of Business Radio describes the MDI systems which feature compact, rugged, self-contained terminals that are microprocessor-based and user-friendly, saying: "A typical MDI system consists of a dispatch station with keyboard and video screen, a host computer, channel control equipment, a base station, and mobile terminals with screens and keyboards that replace mikes and speakers. Indicators on the MDT screen advise the operator of its operating status. Messages composed on a keyboard, or canned messages stored in the system's memory (status messages, for example) are transmitted with a touch of a key.

"One advantage of the system is speed. MDI'S SYSTEM TRANSMITS AT 4800 BPS . . . meaning that a complete message is normally transmitted, received, and made available to be read in less than three seconds. Because of this speed, and the nature of the coded message, eavesdropping is virtually impossible. Also, depending on the way the system is configured, the dispatcher can choose to send any message to a single unit, to a group of units, or to all units.

"Channel efficiency is another reason some fleet operators go to digital technology. MDI's system can put up to 300 mobile units on one full-duplex channel with its largest, most sophisticated MDT (315-character CRT display, six-screen memory). With the Model 7031 terminal (two-line liquid crystal display and 12-line memory) the system can handle up to 700 units on one channel. Given the difficulty of acquiring additional frequencies and the desirability of having all units on one channel, this is a powerful argument for digital communication.

"A third advantage the mobile data communications system has is that the system can guarantee that every message is received with perfect accuracy. MDI's system will not display a message that contains even a single-character error; its error correction software delivers the message intact. Conditions at the vehicle . . . noise or confusion . . . do not affect the driver's comprehension of the dispatch. If he is away from the vehicle, the message is stored until he returns. The terminal can store up to six messages, which, in the case of some terminals (like the MDI Model 9031 MDT) can include graphics like maps, for example, or diagrams.