Trunked radio system

A trunked radio system is a digital two-way radio system that uses a digital control channel to automatically assign frequency channels to groups of users. In a half-duplex land mobile radio system a group of users with portable two-way radios communicate over a single shared radio channel, with one user at a time talking. These systems typically have access to multiple channels, up to 40 - 60, so multiple groups in the same area can communicate. In a conventional (nontrunked) system, channel selection is done manually; before use the group must decide on which channel to use, and manually switch all the radios to that channel. There is nothing to prevent multiple groups in the same area from choosing the same channel, causing conflicts. A trunked radio system is an advanced alternative in which the channel selection process is done automatically. A trunked radio system is a digital two-way radio system that uses a digital control channel to automatically assign frequency channels to groups of users. In a half-duplex land mobile radio system a group of users with portable two-way radios communicate over a single shared radio channel, with one user at a time talking. These systems typically have access to multiple channels, up to 40 - 60, so multiple groups in the same area can communicate. In a conventional (nontrunked) system, channel selection is done manually; before use the group must decide on which channel to use, and manually switch all the radios to that channel. There is nothing to prevent multiple groups in the same area from choosing the same channel, causing conflicts. A trunked radio system is an advanced alternative in which the channel selection process is done automatically. Trunking is a more automated and complex radio system, but provides the benefits of less user intervention to operate the radio and greater spectral efficiency with large numbers of users. Instead of assigning a radio channel to one particular user group at a time, users are instead assigned to a logical grouping, a 'talkgroup'. When any user in that group wishes to converse with another user in the talkgroup, a vacant radio channel is found automatically by the system and the conversation takes place on that channel. Many unrelated conversations can occur on a channel, making use of the otherwise idle time between conversations. Each radio transceiver contains a microprocessor which handles the channel selection process. A control channel coordinates all the activity of the radios in the system. The control channel computer sends packets of data to enable one talkgroup to talk together, regardless of frequency. The primary purpose of this type of system is efficiency; many people can carry many conversations over only a few distinct frequencies. Trunking is used by many government entities to provide two-way communication for fire departments, police and other municipal services, who all share spectrum allocated to a city, county, or other entity. In essence, a trunked radio system is a packet switching computer network. Users' radios send data packets to a computer, operating on a dedicated frequency — called a control channel — to request communication on a specific talk-group. The controller sends a digital signal to all radios monitoring that talkgroup, instructing the radios to automatically switch to the frequency indicated by the system to monitor the transmission. After the user is done speaking, the users' radios return to monitoring the control channel for additional transmissions.