Abstract: A data communication system is provided for use with a cellular system containing an array of cells and a cellular transmitter/receiver located within each cell of the array. Each cellular transmitter/receiver is adapted for transmitting and receiving voice and/or data communication over predetermined channelized frequencies associated with the particular cell in which the cellular transmitter/receiver is located. In accordance with the invention a base data transmission station is located in each cell and is adapted for transmitting a single data stream across a plurality of channels, each of which channels is adapted to carry a single stream of information. Each base data transmitting station does not transmit on the predetermined channels that are assigned to the particular cell in which the base data transmitting station is located (i.e., those channels are "notched").

Abstract: A data communications system is overlaid on a voice-based trunked radio system. Digital data packets are transmitted over available radio channels, thereby enabling data communication between a host dispatch system and mobiles and a base station in the trunked radio system. Radio channels associated with trunked channel groups are accessed when available by a communications controller. The communications controller is configured to communicate with various mobile units of the trunked radio system over available radio channels through multiple radio communication links. Radio channels are monitored to detect when the radio channels are presently unused for voice transmission and thereby accessible for data overlay. In particular, when the data overlay system detects that the transmission of analog voice information ceases over a particular radio channel, the trunked channel group association of that particular radio channel is caused to be switched from a voice group to a data group.