Trunked radio system
Encyclopedia
Talkgroup
A Talkgroup is the term given to assigned groups on a trunked radio system. Unlike a conventional radio which assigns users a certain frequency, a trunk systems takes a number of frequencies allocated to the system. Then the control channel coordinates the system so talkgroups can share these...
s. 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
Government
Government refers to the legislators, administrators, and arbitrators in the administrative bureaucracy who control a state at a given time, and to the system of government by which they are organized...
to provide two-way communication for fire department
Fire department
A fire department or fire brigade is a public or private organization that provides fire protection for a certain jurisdiction, which typically is a municipality, county, or fire protection district...
s, police
Police
The police is a personification of the state designated to put in practice the enforced law, protect property and reduce civil disorder in civilian matters. Their powers include the legitimized use of force...
and other municipal services, who all share spectrum
Electromagnetic spectrum
The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object....
allocated to a city, county, or other entity.
In 1997, radio scanners compatible with trunked systems appeared on the market. One of the first companies to bring these devices to market, Uniden
Uniden
is a Japanese company in the wireless communication industry.-History:Uniden was established on February 7, 1966 by its founder Hideo Fujimoto...
, trademarked the term trunk tracking on December 5, 1997.
Control channels
In essence, a trunked radio system is a packet switchingPacket switching
Packet switching is a digital networking communications method that groups all transmitted data – regardless of content, type, or structure – into suitably sized blocks, called packets. Packet switching features delivery of variable-bit-rate data streams over a shared network...
computer network. Users' radios send data packets to a computer, operating on a dedicated frequency — called a Control Channel
Control channel
In radio communication, a control channel is a central channel that controls other constituent radios by handling data streams. It is most often used in the context of a trunked radio system, where the control channel sends data which coordinates users in talkgroups.In GSM networks, Control...
— 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.
This arrangement allows multiple groups of users to share a small set of actual radio frequencies without hearing each others' conversations. Trunked systems primarily conserve limited radio frequencies and also provide other advanced features to users.
Comparison with telephone trunking
The concept of trunking (resource sharing) is actually quite old, and is taken from telephone company technology and practice. Consider two telco central office exchanges, one in town "A" and the other in adjacent town "B". Each of these central offices has the theoretical capacity to handle ten thousand individual telephone numbers. (Central office "A", with prefix "123", has available 10,000 numbers from 123-0000 to 123-9999; central office "B", with prefix "124", the same.)How many telephone lines are required to interconnect towns A & B? If all 10,000 subscribers in "A" were to simultaneously call 10,000 subscribers in "B", then 10,000 lines, (in telco parlance "trunk lines", or simply "trunks") would be required between the two towns. However, the odds of that happening are remote. Telephone companies have well-proven formulas which predict the optimal number of trunk lines actually needed, under normal conditions, to interconnect two telephone exchanges, called the Erlang-B formula.
This concept has simply been applied to radio user groups, to determine the optimal number of channels needed, under normal conditions, to accommodate given number of users. In the event of a widespread emergency such as a major earthquake, many more users than normal will attempt to access both the telephone and radio systems. In both cases once the trunking capacity of the systems is fully used, all subsequent users will receive a busy signal.
In our example of police dispatch, different talk-groups are assigned different system priority levels, sometimes with "preempt" capability, attempting to ensure that communication between critical units is maintained.
Differences from conventional two-way radio
"Trunked" radio systems differ from "conventional" radio systems in that a conventional radio system uses a dedicated channel (frequency) for each individual group of users, while "trunking" radio systems use a pool of channels which are available for a great many different groups of users.For example, if police communications are configured in such a way that twelve conventional channels are required to permit citywide dispatch based upon geographical patrol areas, during periods of slow dispatch activity much of that channel capacity is idle. In a trunked system, the police units in a given geographical area are not assigned a dedicated channel, but instead are members of a talk-group entitled to draw upon the common resources of a smaller pool of channels.
Advantages of trunking
Trunked radio takes advantage of the probability that with any given number of user units, not everyone will need channel access at the same time, therefore fewer discrete radio channels are required. From another perspective, with a given number of radio channels, a much greater number of user groups can be accommodated. In the example of the police department, this additional capacity could then be used to assign individual talk groups to specialized investigative, traffic control, or special-events groups which might otherwise not have the benefit of individual private communications.To the user, a trunking radio looks just like an "ordinary" radio: there is a "channel switch" for the user to select the "channel" that they want to use. In reality though, the "Channel switch" is NOT switching frequencies as in a conventional radio but when changed, it refers to an internal software program which causes a talkgroup affiliation to be transmitted on the control channel. This identifies the specific radio to the system controller as a member of a specific talkgroup, and that radio will then be included in any conversations involving that talkgroup.
This also allows great flexibility in radio usage - the same radio model can be used for many different types of system users (i.e. Police, Public Works, Animal Control, etc.) simply by changing the software programming in the radio itself.
Trunked radio systems also provide a small level of extra privacy since the talkgroups are constantly transmitting on different frequencies. This makes it difficult for a scanner listener without a programmed trunk tracking scanner to keep up with the conversation.
Types of trunked radio systems
- Ericsson GE
- EDACS ProvoiceEDACS ProvoiceProVoice is Tyco Electronics' implementation of IMBE digital modulation for radio communications. It is not APCO-25 compliant, but does use the same IMBE vocoder developed by Digital Voice Systems, Inc....
- EDACSEDACSEDACS stands for The Enhanced Digital Access Communication System, a radio communications protocol and product family invented in the General Electric Corporation in the mid 1980s.- History :...
- GE Mark VGE Mark VGE Marc V is a historic U.S. format or protocol of trunked, two-way radio introduced by General Electric Mobile Radio in the early 1980s. This equipment was also sold in Australia. The product name looks and sounds similar to GE-Mark V, a turbine controller made by General Electric...
- EDACS Provoice
- Logic Trunked RadioLogic Trunked RadioLogic Trunked Radio is a system developed in the late 1970s by the E. F. Johnson Company.LTR is distinguished from some other common trunked radio systems in that it does not have a dedicated control channel. Each repeater has its own controller and all of these controllers are coordinated together...
- LTR StandardLTR StandardLTR Standard systems have no dedicated control channel. All control data is sent as subaudible data along with voice transmissions. Systems can have any number of channels from 1 through a maximum of 20. Each channel in the system is assigned a unique number and these need not be sequentially...
- LTR PassportLTR PassportPassPort is a type of LTR Trunked radio system designed by Trident Micro Systems, which consists of multiple radio repeater sites linked together to form a wide-area radio dispatch network.-Purpose:...
- LTR Standard and PassportLTR Standard and PassportLTR Standard and Passport systems are hybrid Trunked Radio Systems that have some LTR Standard talkgroups and some LTR Passport talkgroups....
- LTR MultiNetLTR MultiNetLTR MultiNet Systems are APCO-16 compliant LTR Trunked Radio Systems and thus are mostly found in use as public safety systems. LTR MultiNet systems usually have one or more "status channels" that act like a control channel in a Motorola or EDACS system, however these channels can also carry...
- LTR-NetLTR-NetLTR-Net is a type of LTR Trunked Radio System that is a backward compatible with LTR Standard. LTR Standard radios can be used on an LTR-Net system....
- LTR Standard
- MotorolaMotorola Trunked Radio-Types:* Type I* Type II* Type IIi Hybrid* Type II SmartZone* Type II SmartZone OmniLink* Type II VOCMotorola Type I and Type II systems achieve the same thing in a slightly different way. One important distinction between these systems is the amount of data transmitted by each radio when the...
- Type IMotorola Type IMotorola Type I Is the original type of Motorola's Trunked radio system; it is based on Fleets and Subfleets. Each system had a certain number of Fleets assigned, and then each Fleet had a certain number of Subfleets and radio IDs. The distribution of Fleets and Subfleets on a Type I system is...
- Type IIMotorola Type IIMotorola Type II refers to the second generation Motorola Trunked radio systems that replaced fleets and subfleets with the concept of talkgroups and individual radio IDs. There are no dependencies on fleetmaps, therefore there are no limitations on how many radio IDs can participate on a...
- Type IIi HybridMotorola Type IIi HybridA Motorola Type IIi Hybrid system is a type of Trunked radio system that mixes "blocks" of Type I Fleets/Subfleets with Type II talkgroups. In some cases, all radios support Type II, but in some cases, Type I radios might be used exclusively in subfleets while the Type IIs are used exclusively in...
- Type II SmartZoneMotorola Type II SmartZoneSmartZone systems are composed of Type II SmartNet systems that are networked together via microwave or land-line data circuits to provide multi-site wide-area communications. Many large public safety and state agencies use SmartZone systems for wide-area communications...
- Type II SmartZone OmniLinkMotorola Type II SmartZone OmniLinkType II SmartZone OmniLink is a type of Trunked radio system with multiple sites, providing a broad range of robust system features and utilizing a distributed call processing architecture linking up to four multi-site systems together into one seamless network, supporting up to 192 sites...
- iDENIdenFor other uses of the word, see Iden The Iden was an English automobile manufactured from 1904 until 1907. Designed by George Iden, formerly of Daimler, they were four-cylinder 10/17 hp and 25/35 hp shaft-driven cars; each came with "Idens's frictionless radial gearbox"....
(integrated Digital Enhanced Network) - Motorola Harmony (see iDENIdenFor other uses of the word, see Iden The Iden was an English automobile manufactured from 1904 until 1907. Designed by George Iden, formerly of Daimler, they were four-cylinder 10/17 hp and 25/35 hp shaft-driven cars; each came with "Idens's frictionless radial gearbox"....
)
- Type I
- MPT-1327MPT-1327MPT 1327 is an industry standard for trunked radio communications networks.First published in January 1988 by the British Radiocommunications Agency, and is primarily used in the United Kingdom, Europe, South Africa, New Zealand, Australia and even China...
- OpenSky SystemOpenSkyOpenSky is a registered trademark of Harris Corporation and is the trade name for a wireless communication system, invented by M/A-COM Inc., that is now a division of Harris RF Communications...
- APCO Project 16APCO-16Project 16 or APCO Project 16 was a standard development effort started in the 1970s by the Association of Public-Safety Communications Officials-International , a trade association of mostly police and fire service providers...
- APCO Project 25
- SmarTrunk
- TETRATetrathumb|right|250px|Pristella tetra — [[Pristella maxillaris]].thumb|right|250px|Golden Pristella tetra, a [[morph |morph]] of [[Pristella maxillaris]].thumb|right|250px|[[Silvertip tetra]] — Hasemania nana....
- TETRAPOLTETRAPOLTETRAPOL is a digital professional mobile radio standard, as defined by the Tetrapol Publicly Available Specification , in use by professional user groups, such as public safety, military, industry and transportation organizations throughout the world....
- Kenwood NEXEDGE Digital trunked radioNXDNNXDN is a Common Air Interface technical protocol for mobile communications. It was developed jointly by Icom Incorporated and Kenwood Corporation. was formed in order to promote the NXDN protocol in North and South America...
- Icom IDAS Digital trunked Land Mobile Radio
- NXDN protocolNXDNNXDN is a Common Air Interface technical protocol for mobile communications. It was developed jointly by Icom Incorporated and Kenwood Corporation. was formed in order to promote the NXDN protocol in North and South America...