Digital Mobile Radio (DMR)
Changes to the professional environment have meant that the operational requirements placed on communication equipment have evolved, and the traditional analogue service is no longer able to meet the users' needs completely. A demand for more sophisticated services has raised a need for a technology enhancement and inevitably this has led to a redefinition of PMR based on digital technology.
Analogue Private Mobile Radio (PMR)
Analogue Private Mobile Radio (PMR) has enjoyed great success in Europe for many years, and serves a very broad community of users. Available for both licensed and unlicensed spectrum use, PMR applications extend from low-cost walkie-talkies aimed at the consumer market through to public safety and mission-critical systems. A comparable technology known as Specialized Mobile Radio (SMR) exists in the United States.
Private Mobile Radio (PMR) - sometimes called Professional Mobile Radio - was developed for business users who need to keep in contact over relatively short distances with a central base station / dispatcher - a typical example is a taxi company. PMR is also widely used by emergency services. PMR networks consist of one or more base stations and a number of mobile terminals. Such a system serves a closed user group and that is normally owned and operated by the same organization as its users.
From their early designs, PMR systems have developed into 'trunked' systems, the most notable of which is TETRA, Terrestrial Trunked Radio. Trunking is a technique where the resources of the communications network are shared, thus providing both flexibility and economy in the allocation of network resources. Typically, a communication channel is allocated for the duration of a call and then automatically released to allow it to be used for another call, perhaps between different users on the same system. The technique also enables multiple base stations to be connected and to provide coverage across a wider area than with a single base station.
PMR systems generally provide facilities for closed user groups, group call and push-to-talk, and have call set-up times which are generally short compared with cellular systems. Many PMR systems allow Direct Mode Operation in which terminals can communicate with one another directly when they are out of the coverage area of a network.
PMR systems may also be developed to allow public access (by subscription), and they are then known as Public Access Mobile Radio (PAMR). The users of PAMR systems are usually not the same as the system's owner and operator. Traditionally, PMR systems have usually been based on European standards for the equipment, but operated under licence and subject to National frequency management plans. An exception is PMR 446, a consumer 'walkie-talkie' which has six analogue channels allocated in most European countries for use without a licence.
Our Role & Activities
DMR, a direct replacement for analogue PMR
Digital Mobile Radio (DMR) is a European standard, produced by ETSI, defining a direct digital replacement for analogue PMR. The PMR/DMR markets can be roughly divided into three broad categories. DMR has the capability to serve them all:
- Consumer and short-range industrial
- Professional / Business-Critical applications
- Public Safety / Mission-Critical applications.
DMR is a scaleable system that can be used in unlicensed mode (in a 446.1 to 446.2 MHz band), and in licensed mode, subject to national frequency planning. It is developed in three 'tiers':
- Tier 1 is the low-cost, licence-exempt 'digital PMR446'
- Tier 2 is for the professional market offering peer-to-peer mode and repeater mode (licensed)
- Tier 3 is for trunked operation (licensed).
The technology promises improved range, higher data rates, more efficient use of spectrum, and improved battery. Significantly, DMR has been designed to fit into existing licensed PMR bands, meaning that there is no need for rebanding or relicensing, thus aiding the transition from analogue to digital. The new standard imposes no fundamental changes in the architecture of either conventional or trunked systems - the focus is on a change in the over-the-air protocol that will facilitate the use of applications that are beyond the capability of analogue schemes.
Features supported include fast call set-up, calls to groups and individuals, short data and packet data calls. The communications modes include individual calls, group calls, broadcast calls and, of course, a direct communication mode among the mobiles. Other important DMR functions such as emergency calls, priority calls, full duplex communications, short data messages and IP-packet data transmissions are supported.
An alternative to TETRA
For business users, DMR may be seen as a commercially attractive alternative to TETRA, particularly for those users who do not need (or cannot afford) the complexity of this highly-successful digital technology. Many existing digital radio protocols suffer reduced radio coverage so a swap-out from analogue FM to digital is not possible. DMR has been specifically designed to offer at least the same range as 12.5kHz channel analogue FM so a direct replacement or upgrade from analogue to DMR is a practical proposition.
DMR tier 1 equipment on the market is often combined with analogue PMR 446, to provide 16 digital and 8 analogue physical channels at 446 MHz and, with privacy coding, even more logical channels. A new harmonized 446.1 - 446.2 MHz licence-exempt band is being opened up by several European countries over the next few years.
In order to help maximize the capacity of that allocation, ETSI has defined a narrow-band digital radio protocol for this band: 'digital PMR' which utilizes 6.25 kHz channel FDMA (Frequency Division Multiple Access). This protocol provides for consumer and low-power commercial applications using a maximum of 500mW e.r.p (effective radiated power).
ETSI Technical Report TR 102 398 provides a useful introduction to DMR. Technical Specification TS 102 362 parts 1 to 3 covers DMR protocol conformance testing and test suites, and Technical Specification TS 102 490 defines the narrow-band or 'digital PMR' protocol.
Work on PMR
TETRA, Terrestrial Trunked Radio, is a PMR/PAMR system developed by ETSI to respond to the requirements of commercial services and emergency services, and to give the possibility for cross-border networks in Europe.
Electromagnetic Compatibility (EMC) requirements for PMR/PAMR are covered by EN 301 489 part 1 and part 5.
Spectrum requirements for PMR/PAMR - ETSI works with the relevant European organizations to ensure that appropriate spectrum is available for ETSI radio standards. We have produced a series of System Reference Documents that define the spectrum requirements for various PMR implementations, and a range of Harmonised Standards that may be used to demonstrate compliance of equipment and components with the European Commission's Radio Equipment Directive.
A full list of related standards in the public domain is accessible via the ETSI standards search.