Specialized Mobile Radio (SMR) is used to provide two-way radio dispatch service for the public safety, construction, and transportation industries. In 1979, the FCC established SMR service in the 800-MHz band and, in 1986, established SMR service in the 900-MHz band. Although SMR is used primarily for voice communications, such systems also support data and facsimile services.
Generally, SMR systems provide dispatch services for companies with multiple vehicles using the “push to talk” method of communication. Atraditional SMR system consists of one or more base station transmitters, one or more antennas, and mobile radio units obtained from the SMR operator for a fee or purchased from a retail source.
SMR has limited roaming capabilities, but its range may be extended through interconnection with the Public Switched Telephone Network (PSTN), as if the user were a cellular subscriber. Both types of services operate over different assigned frequencies within the range of 800 to 900 MHz. Cellular services are assigned to bands between 824 and 849 MHz and 869 and 894 MHz.
SMR networks traditionally used one large transmitter to cover a wide geographic area. This limited the number of subscribers because only one subscriber could talk on one frequency at any given moment. The number of frequencies allocated to SMR is smaller than for cellular, and there have been several operators in each market. Because dispatch messages are short, SMR services were able to work reasonably well.
The 800-MHz SMR systems operate on two 25-kHz channels paired, while the 900-MHz systems operate on two 12.5-kHz channels paired. Because of the different sizes of the channel bandwidths allocated for 800- and 900-MHz systems, the radio equipment used for 800-MHz SMR is not compatible with the equipment used for 900-MHz SMR systems. SMR systems consist of two distinct types: conventional and trunked systems.
A conventional system allows an end user the use of only one channel. If someone else is already using that end user’s assigned channel, that user must wait until the channel is available. In contrast, a trunked system combines channels and contains processing capabilities that automatically search for an open channel. This search capability allows more users to be served at any one time. Amajority of the current SMR systems are trunked systems.
In 1993, Congress reclassified most SMR licensees as Commercial Radio Service (CMRS) providers and established the authority to use competitive bidding to issue new licenses. With the development of digital systems, the SMR marketplace now offers new services such as acknowledgment paging and inventory tracking, credit card authorization, automatic vehicle location, fleet management, inventory tracking, remote database access, and voice mail.