Many of us have experienced riding in a taxi. One of the more memorable aspects of a taxi ride-aside from the almost predictable stunt driver nature of the ride itself-is the squawk coming from the taxi's radio. This seemingly crude form of communication is an example of a private land mobile radio system. Other examples of private systems include those used for public safety, utilities and other applications.
Operating primarily in the 806-824 MHz and 851-869 MHz frequency bands, these private systems are usually conventional non-trunked9.10 systems. The channels are 25 KHz in bandwidth.
Specialized mobile radio or SMR 9.11 systems are regional trunked radio systems, which means that a number of users (radios) share a common channel, typically provided via a single base station.9.12 SMR systems have traditionally been used in small cities for local services such as fleet dispatch and public safety. Only scratchy-sounding voice has been supported by these analog systems, typically via 12.5 kHz channels, located in the 800 and 900 MHz bands.
Despite limited bandwidth, SMR systems are widely used. According to a 1995 survey of SMR operators and manufacturers, there were more than two million SMR subscribers at year-end 1995, a growth of some thirteen percent over the previous year.9.13 This net subscriber growth was actually lower than previous years, largely because of increased congestion of these 800 MHz networks.
This congestion has prompted a recent FCC proposal to auction additional SMR spectrum above 860 MHz in 1997. The proposed auction would allow large SMR service providers, such as Nextel and Pittencrieff Communications, to acquire the contiguous spectrum necessary to compete with other wireless services. A similar auction of SMR frequencies in the 900 MHz bands was held in the winter of 1995-96, largely in support of other SMR participants such as GeoTek.
Contiguousness of frequencies is important for any nationwide wireless service provider. In the late 1980's, Nextel and others began an effort to acquire SMR service providers with the objective of patching together a nationwide coverage. Unfortunately, many of the existing regional SMR services have operated in non-contiguous bands, hampering such a nationwide combination. The spectrum auctions will help this situation.
In the late 1980s, Motorola developed a digital or enhanced SMR (ESMR9.14 ) system called Motorola Integrated Radio System (MIRS).9.15 These systems support two-way data and paging as well as 7200 bps voice. 4800 bps circuit-switched data services via the PSTN are also available in the ESMR systems. New technologies and standards such as Enhanced Digital Access Communications Systems (EDACS) are encouraging additional vendors to participate in this industry.
So, where are we today? In 1996, Nextel continues its efforts to provide a nationwide ESMR service. With Craig McCaw's 1995 investment in a controlling interest came focus-toward remote and mobile office connectivity rather than the previous horizontal cellular-type services. Today's circuit-switched services are scheduled to be augmented with packet-switched data services in 1997.
Other SMR operators such as GeoTek Communications will also offer integrated voice and data services aimed at dispatch, one-way and two-way messaging, remote point-of-sale, auto vehicle location and other markets. Until the larger players in ESMR deploy nationwide services, these systems will continue to be regional or even local in nature. Mobility will remain constrained, much as it is with metropolitan networks such as Metricom.