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Trunked radio system
A trunked radio system (TRS) is a two-way radio system that uses a control channel to automatically assign frequency channels to groups of user radios. In a traditional half-duplex land mobile radio system a group of users (a talkgroup) with mobile and 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 simultaneously. In a conventional (non-trunked) system, channel selection is done manually; before use, the group must decide which channel to use, and manually switch all the radios to that channel. This is an inefficient use of scarce radio channel resources because the user group must have exclusive use of their channel regardless of how much or how little they are transmitting. There is also nothing to prevent multiple groups in the same area from choosing the same channel, causing conflicts and 'cross-talk'. A trunked radio system is an advanced alternative in which the channel selection process is done automatically, so as to avoid channel conflicts and maintain frequency efficiency across multiple talkgroups. This process is handled by what is essentially a central radio traffic controller, a function automatically handled by a computer system.
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 communicate with another user in the talkgroup, an idle 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 that 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. A secondary benefit of a trunking radio system is the ease with which it can accommodate radio interoperability and with proper planning, add authorized user agencies to the system post-implementation.
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 talkgroup. The controller sends a 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.
This arrangement allows multiple groups of users to share a small set of actual radio frequencies without hearing each other's conversations. Trunked systems primarily conserve limited radio frequencies and also provide other advanced features to users.
A 'talkgroup' is an assigned logical group of users on a trunked radio system. Unlike a conventional radio which assigns users a certain frequency, a trunk system uses a number of frequencies allocated to the entire system. Then the control channel coordinates the system so talkgroups can share these frequencies seamlessly. The purpose is to dramatically increase system capacity with optimal use of frequencies. Many radios today treat talkgroups as if they were frequencies, since they behave like such. For example, on a radio scanner it is very common to be able to assign talkgroups into banks or lock them out, exactly like that of conventional frequencies.
Each system is built with a number of system talkgroups identified as required by the planned user agencies, to which new talkgroups can easily be added as the system matures and new agencies or new requirements are identified. For each user agency, talkgroups are assigned in an agency 'fleetmap'. The fleetmap lays out the various talkgroups that the agency requires to successfully undertake its business. For example, in an ambulance service fleetmap there will be a talkgroup created for each of the hospital ER's that the ambulances interact with; talkgroups for communications with dispatch(s), talkgroups for special events or disasters, a talkgroup for air medical transport, and a number of talkgroups that are shared (with appropriate controls) with other first response agencies such as police and fire services. Each talkgroup is assigned a unique digital ID on the system so that the controller can direct transmissions to the radios which are intended to receive them. Within the same shared system there can be a fleet of ambulances, a fleet of police users, and a fleet of firefighters. In most shared public safety/public service systems, whether city-wide, or state/province-wide, there are often additional users sharing the system at a pre-determined lower priority for service such as animal control, public works, highways maintenance, correctional services, natural resources, etc. The system may also include talkgroups for federal agencies operating within the jurisdiction and in some cases commercial users which provide assistance to general public safety. These fleetmaps are considered subfleets of the actual talkgroups. The subfleets are intuitively programmed into the users' radios so that the users can easily find a talkgroup when s/he is required to switch for a particular situation. Alternatively, a trunking system dispatch console operator can actually 'patch' two talkgroups together making a new 'virtual' talkgroup to allow users from different agencies to communicate without having to switch channels.
Generally in planning a multi-agency trunking radio system, each agency is assigned a 'block' of talkgroup ID numbers based on the number of talkgroups they anticipate requiring, plus some excess for future expansion. Thus a police service block of talkgroup ID's might begin with 102100 up to 102199, and a fire service block on the same system might begin with 102200 up to 102299. This identifies the system as 102XXX and provides one hundred talkgroup ID's for each agency. Agency-shared talkgroups (sometimes referred to as Mutual Aid or Inter-agency) may be assigned a block starting at 102500 up to 102520, allowing for twenty shared talkgroups that can be offered for use by any authorized agency. In many province-wide systems, it is mandatory for participation in the system for user agencies to include all of the authorized shared talkgroups and/or shared simplex frequencies.
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Trunked radio system
A trunked radio system (TRS) is a two-way radio system that uses a control channel to automatically assign frequency channels to groups of user radios. In a traditional half-duplex land mobile radio system a group of users (a talkgroup) with mobile and 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 simultaneously. In a conventional (non-trunked) system, channel selection is done manually; before use, the group must decide which channel to use, and manually switch all the radios to that channel. This is an inefficient use of scarce radio channel resources because the user group must have exclusive use of their channel regardless of how much or how little they are transmitting. There is also nothing to prevent multiple groups in the same area from choosing the same channel, causing conflicts and 'cross-talk'. A trunked radio system is an advanced alternative in which the channel selection process is done automatically, so as to avoid channel conflicts and maintain frequency efficiency across multiple talkgroups. This process is handled by what is essentially a central radio traffic controller, a function automatically handled by a computer system.
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 communicate with another user in the talkgroup, an idle 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 that 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. A secondary benefit of a trunking radio system is the ease with which it can accommodate radio interoperability and with proper planning, add authorized user agencies to the system post-implementation.
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 talkgroup. The controller sends a 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.
This arrangement allows multiple groups of users to share a small set of actual radio frequencies without hearing each other's conversations. Trunked systems primarily conserve limited radio frequencies and also provide other advanced features to users.
A 'talkgroup' is an assigned logical group of users on a trunked radio system. Unlike a conventional radio which assigns users a certain frequency, a trunk system uses a number of frequencies allocated to the entire system. Then the control channel coordinates the system so talkgroups can share these frequencies seamlessly. The purpose is to dramatically increase system capacity with optimal use of frequencies. Many radios today treat talkgroups as if they were frequencies, since they behave like such. For example, on a radio scanner it is very common to be able to assign talkgroups into banks or lock them out, exactly like that of conventional frequencies.
Each system is built with a number of system talkgroups identified as required by the planned user agencies, to which new talkgroups can easily be added as the system matures and new agencies or new requirements are identified. For each user agency, talkgroups are assigned in an agency 'fleetmap'. The fleetmap lays out the various talkgroups that the agency requires to successfully undertake its business. For example, in an ambulance service fleetmap there will be a talkgroup created for each of the hospital ER's that the ambulances interact with; talkgroups for communications with dispatch(s), talkgroups for special events or disasters, a talkgroup for air medical transport, and a number of talkgroups that are shared (with appropriate controls) with other first response agencies such as police and fire services. Each talkgroup is assigned a unique digital ID on the system so that the controller can direct transmissions to the radios which are intended to receive them. Within the same shared system there can be a fleet of ambulances, a fleet of police users, and a fleet of firefighters. In most shared public safety/public service systems, whether city-wide, or state/province-wide, there are often additional users sharing the system at a pre-determined lower priority for service such as animal control, public works, highways maintenance, correctional services, natural resources, etc. The system may also include talkgroups for federal agencies operating within the jurisdiction and in some cases commercial users which provide assistance to general public safety. These fleetmaps are considered subfleets of the actual talkgroups. The subfleets are intuitively programmed into the users' radios so that the users can easily find a talkgroup when s/he is required to switch for a particular situation. Alternatively, a trunking system dispatch console operator can actually 'patch' two talkgroups together making a new 'virtual' talkgroup to allow users from different agencies to communicate without having to switch channels.
Generally in planning a multi-agency trunking radio system, each agency is assigned a 'block' of talkgroup ID numbers based on the number of talkgroups they anticipate requiring, plus some excess for future expansion. Thus a police service block of talkgroup ID's might begin with 102100 up to 102199, and a fire service block on the same system might begin with 102200 up to 102299. This identifies the system as 102XXX and provides one hundred talkgroup ID's for each agency. Agency-shared talkgroups (sometimes referred to as Mutual Aid or Inter-agency) may be assigned a block starting at 102500 up to 102520, allowing for twenty shared talkgroups that can be offered for use by any authorized agency. In many province-wide systems, it is mandatory for participation in the system for user agencies to include all of the authorized shared talkgroups and/or shared simplex frequencies.