Business Radio / Private Mobile Radio Basics
- summary, overview or tutorial about the basics of Business Radio, often referred to as Private, Professional, Public Access Mobile Radio, PMR or PAMR.
Radio systems used for business applications are referred to by a variety of names. These names include: PMR, Private Mobile Radio, Professional Mobile Radio or even Public Access Mobile Radio, PAMR.
Business radio, Private Mobile Radio, PMR, is widely used within the business community to provide communications outside the normal cellular or public switch telephone networks. These private mobile radio, PMR, systems provide essential communications for business where there is a need for mobile communications with a variety of users - the requirements are very different to those provided by the cellular network.
PMR mobile radio development
The first PMR mobile radio systems were initially set up to enable a set of mobile business users to maintain contact with a base using radio communications technology. Organisations such as taxi firms, utility workers and the like all used these systems as they enabled them to maintain contact with their office. Additionally the emergency services used their own systems.
Initially these radio communications systems consisted of a base station with a number of mobile radio stations. Communication used a single frequency, with "simplex" push to talk transmissions using a single channel for both transmitting and receiving. As pressure rose on the radio frequency allocations, often frequencies had to be shared. As the systems almost invariably used frequency modulation, squelch was employed so that the audio from the received was only switched on when a signal was present. Developments of this known as DTMF (dual tone multiple frequency) and CTCSS (continuous tone, coded squelch system) were used to enable only the required users to hear the call. Only when the appropriate DTF code of CTCSS frequencies were transmitted would the relevant receiver be activated
The main element of this was known as trunking, where These radio communications systems were only able to communicate over relatively short distances. They used a single central base station to communicate with all the mobile radio stations. This considerably reduced their coverage area. To overcome this a system known as trunking was devised whereby several transmitters could be used and the signal was "trunked" to the correct station.
With many forms of radio communications migrating to digital technology, there was a similar need to undertake the same migration for business radio / PMR. There were many reasons for the move to digital technology:
- Improved spectral efficiency: With the number of users of business radio / private mobile radio, PMR increasing, it was necessary to increase the usage of the available spectrum.
- Improved data transmission performance: With the growing requirement for improved flexibility within communications systems, a growing variety of data transmission capabilities were needed. Digital technology obviously provides for data transmission.
- Increased flexibility and improved features: Digital technology provides for a greater flexibility in the what can be achieved within a transmission system. Accordingly migrating to digital technology enables more effective use to be made of the available systems.
- Improved voice quality: Digital PMR or land mobile systems can provide better voice quality under many circumstances, although they often have what may be described as a "digitised" sound to them.
- Improved range: Systems using digital modulation can provide improved range because it is often possible to copy a digital signal at a lower signal strength than an analogue one. However there is a very sharp cut-off - when the signal strength falls off the system suddenly stops operating giving a sharp transition - there is no gradual fade between good copy, poor copy and uncopyable.
In view of the advantages of digital formats, there is a steady migration to digital private mobile radio or business radio technologies. However the change is not as fast as in many other areas because of the investment required by many small companies for whom the analogue systems work well.
Private mobile radio / business radio technologies
There are many different business radio or private mobile radio technologies that are currently in use around the globe. These different business radio or private mobile radio technologies vary from analogue to digital and also vary in complexity according to the requirements.
Some of the main technologies are listed below:
- Analogue Private Mobile Radio, PMR: Analogue radio systems are not normally specified in the same way as digital ones require to be. Typically the use FM and have 25 kHz bandwidth requirements.
- Trunked Private Mobile Radio: Trunking is a system whereby PMR systems are able to operate over a wide area. Signals are picked up from the remote station and "trunked to the local station.
- MPT 1327: MPT 1327 is the most widely used standard for analogue trunked radio. Originally developed in the UK by the then Ministry of Posts and Telecommunications (MPT) it has been widely adopted across the globe.
- TETRA: This was one of the first digital standards to be launched. Originally the letters stood for Trans European Trunked RAdio, but as the system is now being used beyond Europe the abbreviation now stands for TErrestrial Trunked Radio. TETRA is widely deployed, especially for the emergency services.
- DMR: Digital Mobile Radio, DMR is one of the growing digital PMR systems
- dPMR: This digital Private Mobile Radio. It is a different specification to that of the DMR and utilises different techniques and is therefore not compatible.
- NXDN : This standard originated within the USA but it is also available in Europe and other countries.
- P25: P25, Project 25 or APCO-25 is a standardised digital radio communications system that is generally used by federal, state/province and local public safety agencies. It is similar in approach to TETRA.
- ARIB DCR: This digital private mobile radio standard originated within Japan
There is a proliferation of standards, but they do offer the ability to tailor a system to the requirements of the user more exactly.
By Ian Poole