Digital mobile radio

It was created by the European Telecommunications Standards Institute (ETSI),[1] and is designed to be low-cost and easy to use.

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.

The DMR interface is defined by the following ETSI standards: The DMR standard operates within the existing 12.5 kHz channel spacing used in land mobile frequency bands globally, but achieves two voice channels through two-slot TDMA technology built around a 30 ms structure.

The standards are still (as of late 2015) under development with revisions being made regularly as more systems are deployed and improvements are discovered.

[3] It is very likely that further refinements will be made to the standard, which will necessitate firmware upgrades to terminals and infrastructure in the future to take advantage of these new improvements, with potential incompatibility issues arising if this is not done.

[6] 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 specifies two slot TDMA in 12.5 kHz channels for Tier II and III.

[7] DMR Tier III covers trunking operation in frequency bands 66–960 MHz.

In April 2013, Hytera participated in the completion of the DMR Tier III interoperability (IOP) test.

[8] In 2005, a memorandum of understanding (MOU) was formed with potential DMR suppliers including Tait Communications, Fylde Micro, Selex, Motorola, Hytera, Sanchar Communication, Vertex Standard, Kenwood and Icom to establish common standards and interoperability.

[11] The low-cost and increasing availability of internet-linked systems has led to a rise in DMR use on the amateur radio bands.

[13] DMR hotspots are often based on the open source Multimode Digital Voice Modem, or MMDVM, hardware with firmware developed by Jonathan Naylor.

[19] The Basic mode from other manufacturers offers 10-, 32-, or 64-character keys to produce a 882-bit fixed string of random characters that is combined via XOR with AMBE frames.

The entire superframe, rather than each individual AMBE frame, is XORed with this longer static key.

For the Enhanced (ARC4) or Advanced (AES) mode, each complete superframe is also encrypted with a 32-bit IV (initialization vector).

These 4 bits are therefore lost, degrading the voice quality, which is not the case with fixed ciphers in Basic mode.

According to cryptologist Eric Filiol, it is likely that all exported products with a key length of more than 56 bits have a backdoor, as this is a legal requirement due to the Wassenaar Arrangement.