Digital mobile radio (DMR) is an open digital radio standard for professional mobile radio (PMR) users specified in the European Telecommunications Standards Institute (ETSI) Standard TS 102 361 parts 1-4 and used in products sold in all regions of the world. The applicable ETSI emissions compliance standards are EN 300 113 and EN 300 390. The standard was first published in 2005 and has been widely adopted by radio manufacturers and users. Products built to the DMR standard also comply with the U.S. Federal Communications Commission (FCC) mandates in the United States for the use and certification of 12.5 kHz and 6.25 kHz narrowband technology for systems covered by Part 90 regulations. Designed as a low cost entry level radio system for commercial use, consequently DMR is not classed as a mission critical or critical communications platform. A situation further compounded by vendors introducing proprietary standards over and above the limited ETSI DMR standards list and nulling interoperability between different vendor offerings.
The DMR standard operates within the existing 12.5 kHz channel spacing used in land mobile frequency bands globally. Its primary goal 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 the brands have not adhered to this open standard and have introduced proprietary features that make their product offerings non-interoperable. DMR provides voice, data and other supplementary services. DMR is a two-slot, time division multiple access (TDMA) system offering voice, data and a range of other features and applications. The specification covers the RF frequency range 30 MHz to 1 GHz and uses 4 level FSK constant envelope modulation
DMR Tier 1
DMR Tier I products are for license-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 PMR radios that make it across the ocean have caused interference issues with licensed amateur operations.
This part of the standard provides for consumer applications and low-power commercial applications, using a maximum of 0.5 watt RF power. The first license-free DMR446 radio to market was Hytera PD505LF released in August 2014.
DMR Tier II 2
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. ETSI DMR Tier II specifies two slot TDMA in 12.5 kHz channels. 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. The Tier III standard specifies two slot TDMA in 12.5 kHz channels. Tier III supports voice and short messaging handling similar to TETRA and MPT-1327 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.