DMR TECHNOLOGY
DMR (Digital Mobile Radio) is a digital radio communication standard approved by ETSI in 2005, designed to provide common standards and interoperability for professional mobile radio users. The first official interoperability tests among members were conducted in 2010, and the results of these tests are published on the DMR website. The DMR Association currently has approximately 40 members.
Like DMR, P25 and NXDN technologies are competing technologies that achieve 6.25 kHz equivalent bandwidth using the AMBE voice encoder. Both DMR and P25 use two-slot TDMA on a 12.5 kHz channel, while NXDN employs frequency division multiple access (FDMA) on 6.25 kHz channels.
The DMR standard operates within the 12.5 kHz channel spacing used globally in terrestrial mobile frequency bands, but it achieves two voice channels through two-slot TDMA technology built around a 30 ms structure. The modulation is 4-level FSK (Frequency-shift keying), creating four possible symbols at a rate of 4,800 symbols/s, equivalent to 9,600 bits/s.
DMR covers an RF range from 30 MHz to 1 GHz. There are DMR applications that operate up to 66 MHz (in the European Union, ‘Lo-Band VHF’ operates in the 66–88 MHz range).
DMR is designed in three layers. The DMR Layer I and II (traditional) standards were first published in 2005, and the DMR III (Trunk version) standard was published in 2012, with manufacturers beginning to produce products based on these standards.
DMR is defined by the following ETSI standards:
- TS 102 361-1: Air Interface Protocol
- TS 102 361-2: Voice and General Services
- TS 102 361-3: Data Protocol
- TS 102 361-4: Trunk Protocol
DMR Tier I (Unlicensed Radios)
DMR Tier I products are intended for unlicensed use in the PMR446 band. Tier I products are designed solely for infrastructure-free use (operating without the need for infrastructure or licensing). Radios operating under this standard work with a maximum RF power of 0.5 watts.
DMR Tier II (Conventional Radios)
DMR Tier II encompasses conventional radio systems operating in licensed frequency bands between 66 and 960 MHz. The ETSI DMR Tier II standard targets users requiring spectrum efficiency, advanced audio features, and integrated IP data services for high-power communications in licensed bands. ETSI DMR specifies two-slot TDMA on 12.5 kHz channels for Tier II and III.
DMR Tier III (Trunk Radios)
DMR Tier III covers channel operation in the 66–960 MHz frequency bands. Tier III allows for voice and short messaging similar to TETRA (Terrestrial Trunked Radio) with built-in 128-character status messaging and short messaging of up to 288 bits in various formats. It also supports packet data services in various formats, including IPv4 and IPv6 support.
DMR technology systems, suitable for development and capacity enhancement, are designed to accommodate user demands and needs for voice and data communication.