Digital Mobile Radio (DMR) products have many advantages over other digital public or land mobile radio technologies (PMR/LMR) targeted at the business critical and commercial sectors. As well as being able to match or better the existing features of analogue radios, the use of a two slot TDMA (Time Division Multiple Access) protocolresults in DMR giving simple and effective scalability, energy efficiency, cost efficiency and a rich new set of features. DMR also brings the range and audio clarity benefits of digital radio communication.
DMR is particularly well suited to the addition of new voice or data services because it doubles capacity in existing licenced channels. In particular, when new business-enhancing dataapplications are introduced, with DMR there is no impact on existing voice quality of service – a well known issue due to the “chatty” spectrum-hungry nature of many data applications. More over, DMR systems add this extra capacity at no cost to the user. Other commercial digital systems bring benefits but not the full range of advantages of DMR. Moreover DMR is an open European Telecommunications StandardsInstitute (ETSI) standard backed by many leading radio manufacturers, component suppliers and others. As a result, buyers can have confidence in long term supply and the benefits of competition-driven feature development, supplier responsiveness and market pricing.
DMR is the smart long-term choice for radio professionals.
Table of Contents
Executive Summary Introduction History and Designof DMR 1. Predictable doubling of capacity in existing channels 2. Backwards spectrum compatibility with legacy analogue systems 3. Efficient use of infrastructure equipment 4. Longer battery life and greater power efficiency 5. Ease of use and creation of data applications 6. System flexibility through simultaneous voice and data calls 7. Advanced control features 8. Superior audio performance9. Security of supply through a fully open, well established, widely backed standard Conclusion 2 3 3 4 7 8 9 10 10 11 11 12 13
The introduction of digital PMR products is bringing great benefits to the users of professional radio. It is however, bringing a degree of complexity in that there are many different types of digital radio protocols now on offer – DMR, dPMR, NXDN,TETRA, P25 – some standardised some proprietary. None of these protocols are compatible with each other and all bring different attributes to the table. All however, are more efficient in terms of spectrum use and also improve voice quality at the edges of a coverage area, when compared to analogue systems due to the efficiencies of digital processing.
It is important that the user understandssome basic differences in systems technology in order to make the right choice. Some differences in specific products are the result of the way different vendors have implemented features. Other differences are due to fundamental variations in the underlying technology used by the protocol. These underlying differences impact system scalability, power efficiency, feature possibilities and bothaccess to and use of spectrum.
Broadly speaking there are two underlying technologies to the various protocols; TDMA - used by DMR, TETRA and P25 Phase II - and 6.25 kHz FDMA (Frequency Division Multiple Access) - used by NXDN and dPMR. TDMA divides up spectrum using timeslots; user A gets a few milliseconds of access to the bandwidth, then its user B’s turn. FDMA, in contrast divides spectrum intodiscreet channels; user A has 100% use of a small slice of spectrum and user B has 100% use of another small slice of spectrum. There are a number of consequences of these two approaches.
DMR uses TDMA and many of its advantages come from this choice. The advantages of DMR are discussed in more detail in this paper.
History and Design of DMR
Compared to other radio technologies such as...