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SMR is a land-based radio service that provides one-to-many and many-to-one communications. SMR has also been called trunked radio or public access mobile radio. In terms of application, SMR systems are designed to help roaming field personnel stay in touch with the home office and are often called "dispatch services."

SMR services were established in the late 1970s in the United States when the FCC allocated spectrum for land-based commercial mobile communications. In other words, some commercial operator sets up the system and provides services to subscribers for a fee.

An SMR system consists of base station transmitters and end-user radio equipment. The system uses trunking, which means that several radio channels are pooled so that users within an area have access to any free channel within the pool.

SMR end users may operate in either an "interconnected" mode or a "dispatch" mode. In interconnected mode, the SMR unit can act as a mobile telephone because it is connected through the base station to the public-switched telephone network. In dispatch mode, over- the-air communications can take place between two or more mobile units, or between mobile units and fixed units (and end user's office and a truck).

Companies using the service include construction companies, delivery services, and transportation services that have dispatch operations in a central office. More recently, SMR systems have been expanded to support fax services and data services. The service has traditionally been analog, but the bandwidth is now being used for more-efficient digital operations. Digital services include two-way acknowledgment paging and inventory tracking, credit card authorization, automatic vehicle location, fleet management, inventory tracking, remote database access, and voice mail.

SMR operates in the 800 MHz and 900 MHz frequency ranges with a total spectrum of approximately 19 MHz (14 MHz in the 800-MHz band and 5 MHz in the 900-MHz band). The 800-MHz SMR systems operate on two 25-kHz channel pairs, while the 900-MHz systems operate on two 12.5-kHz channel pairs. Additional information about SMR and its frequency spectrum allocations may be found at the FCC Web site listed on the related entries page. In September 2000, the FCC auctioned 700-MHz "guard band" frequencies consisting of 2-MHz and 4-MHz bands that can be used for the services described here, but not for cellular or PCS services due to possible interference.

Nextel Communications (http://www.Nextel.com) and Southern Communications (http://www.southernco.com) are major holders of SMR spectrum.

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