Digital mobile radio (DMR) is an open digital mobile radio standard defined in the European Telecommunications Standards Institute (ETSI) Standard TS 102 361 parts 1–4 and used in commercial products around the world. DMR, along with P25 phase II and NXDN are the main competitor technologies in achieving 6.25 kHz equivalent bandwidth using the proprietary AMBE+2 vocoder. DMR and P25 II both use two-slot TDMA in a 12.5 kHz channel, while NXDN uses discrete 6.25 kHz channels using frequency division.
DMR was designed with three tiers. DMR tiers I and II (conventional) were first published in 2005, and DMR III (trunked) was published in 2012, with manufacturers producing products within a few years of each publication.
The primary goal of the standard is to specify a digital system with low complexity, low cost and interoperability across brands, so radio communications purchasers are not locked into a proprietary solution. In practice, many brands have not adhered to this open standard and have introduced proprietary features that make their product offerings non-interoperable.
DMR Tier I
DMR Tier I products are for licence-free use in the European 446 MHz band. In the US, the 446 MHz range is primary US Government with the amateur radio service a heavy secondary user. Some DMR radios that make it across the ocean have caused interference issues with licensed amateur operations. ETSI DMR specifies two slot TDMA in 12.5 kHz channels for Tier I, II and III.
This part of the standard provides for consumer applications and low-power commercial applications, using a maximum of 0.5 watt RF power.
DMR Tier II
DMR Tier II covers licensed conventional radio systems, mobiles and hand portables operating in PMR frequency bands from 66–960 MHz. The ETSI DMR Tier II standard is targeted at those users who need spectral efficiency, advanced voice features and integrated IP data services in licensed bands for high-power communications. A number of manufacturers have DMR Tier II compliant products on the market.
DMR Tier III
DMR Tier III covers trunking operation in frequency bands 66–960 MHz. Tier III supports voice and short messaging handling similar to TETRA with built-in 128 character status messaging and short messaging with up to 288 bits of data in a variety of formats. It also supports packet data service in a variety of formats, including support for IPv4 and IPv6. Tier III compliant products were launched in 2012.
In 2005, a Memorandum of Understanding (MOU) was formed with potential DMR suppliers including Tait Communications, Fylde Micro, Selex, Motorola, Hytera, Vertex Standard, Kenwood and Icom to establish common standards and interoperability. While the DMR standard does not specify the vocoder, MOU members agreed to use the half rate DVSI Advanced Multi-Band Excitation (AMBE) vocoder to ensure interoperability. In 2009, the MOU members set up the DMR Association to work on interoperability between vendors equipment and to provide information about the DMR standard. Formal interoperability testing has been taking place since 2010. Results are published on the DMR Association web site. There are approximately 40 members of the DMR Association.
The standard allows DMR manufacturers to implement additional features on top of the standards which has led to practical non-interoperability issues between brands, in contravention to the DMR MOU.
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