Digital mobile radio
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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.
The DMR interface is defined by the following ETSI standards:
- TS 102 361-1: Air interface protocol
- TS 102 361-2: Voice and General services and facilities
- TS 102 361-3: Data protocol
- TS 102 361-4: Trunking protocol
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 modulation is 4-state FSK, which creates four possible symbols over the air at a rate of 4,800 symbols/s, corresponding to 9,600 bit/s. After overhead, forward error correction, and splitting into two channels, there is 2,450 bit/s left for a single voice channel using DMR, compared to 4,400 bit/s using P25 and 64,000 bit/s with traditional telephone circuits.
The standards are still (as of late 2015) under development with revisions being made regularly as more systems are deployed and discover improvements that can be made. 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.
DMR covers the RF range 30 MHz to 1 GHz.
There are DMR implementations, (as of early 2016), that operate as low as 66 MHz (within the European Union, in 'Lo-Band VHF' 66 - 88 MHz.)
The DMR Association and manufacturers often claim that DMR has superior coverage performance to analogue FM. Forward error correction can achieve a higher quality of voice when the receive signal is still relatively high. In practice, however, digital modulation protocols are much more susceptible to multipath interference and fail to provide service in areas where analogue FM would otherwise provide degraded but audible voice service. At a higher quality of voice, DMR outperforms analogue FM by about 11 dB. But at a lower quality of voice, analogue FM outperforms DMR by about 5 dB.
Where digital signal processing has been used to enhance the analogue FM audio quality then analogue FM generally outperforms DMR in all situations, with a typical 2-3 dB improvement for "high quality" voice and around 5 dB improvement for "lower quality" voice. Where digital signal processing is used to enhance analog FM audio, the overall "delivered audio quality" is also considerably better than DMR. However DSP processing of analog FM audio does not remove the 12.5 kHz requirement so DMR is still more spectrally efficient.
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.
Tier I products are specified for non-infrastructure use only without the use of repeaters. 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. ETSI DMR specifies two slot TDMA in 12.5 kHz channels for Tier II and III.
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.
- HQT DMR Series
- DMR Tier II:
- Digital Portable Radio: DH-9800
- Digital Mobile Radio: DM-9800
- Digital Repeater: DR-9200
- Dispatch System: DS-9200
- DMR Tier II:
- Samhoo DMR Series
- DMR Tier II :ST3,SC3
- DMR Tier III
- PORTABLE:SPH6040(UHF 400 - 470 MHz),SPH6035(UHF 350 - 400 MHz),SPH6015(VHF)
- MOBILE :SPM6040(UHF 400 - 470 MHz),SPM6035(UHF 350 - 400 MHz),SPM6015(VHF)
- module board:SPB6040(UHF 400 - 470 MHz),SPB6035(UHF 350 - 400 MHz),SPB6015(VHF)
- Aselsan Models Include: DMR4700 Series
- Avtec, Inc.
- Scout True IP Console
- Etherstack licensing: Mobile Protocol Stack (DMR Tier II/III), Base Protocol Stack (DMR Tier II/III), AIS
- Fylde Micro
- DMR trunking infrastructure (DMR Tier III)
- EXCERA (www.excera.com.cn)
- DMR TIER II & III: EP8100,EM8100
- Harris Momentum
- Hytera DMR series
- DMR Tier II: PD35X, PD36X, PD50X, PD56X, PD60X, MD65X, PD66X, PD68X, RD62X
- DMR Tier III (trunking): X1p, X1e, PD70X, PD78X, MD78X, PD79X, PD79X Ex, RD96X, RD98X, DS-6210, DS-6211, DS-6310
- Kenwood (JVCKENWOOD) DMR Series
- DMR Tier II: Hand-portables: TK-D200 and TK-D300 Series, TK-D240 and TK-D340 Series
- DMR Tier II: Mobiles: TK-D740 and TK-D840
- DMR Tier II: Repeaters: TKR-D710 and TKR-D810
- Motorola MOTOTRBO
- System Types: IP Site Connect, Capacity Plus, Linked Capacity Plus, Connect Plus, Capacity Max (full DMR Tier III when engineered in "interoperability mode")
- Repeaters: XPR8300, XPR8400, MTR3000, SLR5000 series, SLR8000 series
- Portable Subscribers: CP200d, XPR6300, XPR6550, XPR6580, XPR7350, XPR7380, XPR7550, XPR7580, SL7550, SL7580, SL300, XPR3000e series, XPR 7000e series, SL7000e series
- Mobile Subscribers: XPR4000 series, CM200d, CM300d, XPR2500, XPR5000 series, XPR5000e series
- Tait Communications
- Radio Activity Solutions
- RADIODATA GmbH
- RADIODATA DIPRA Radios Include: MS2217D (VHF Low), MS2221D (VHF), DM2217D (VHF Low, datamodem), DM2221D (VHF, datamodem)
- RADIODATA DIPRA DMR trunking infrastructure (DMR Tier III)
- SELEX Elsag
- Sepura DMR
- Sepura DMR Equipment Includes: SBP Series, SBM8000, SBR8000
- Simoco Group
- Digital Portable Radio SDP750 and SDP760
- Digital Mobile Radio SDM730
- DMR infrastructure (DMR Tier II and Tier III)
- TECHBOARD S.r.l. Communications Division EMC-TB
EMC-TB Models Include: LANDER DMR, DATALANDER DMR, ROMULUS DMR
- Tytera: MD-280, MD-380 (firmware editable), MD-390, MD-9600
- Vertex Standard EVX series
Vertex Standard Models Include: EVX-530 Series, EVX-5300/5400, EVX-R70
A full list of DMR Equipment Manufacturers is available from the DMR association. DMR products that have successfully passed interoperability testing are posted on the DMR Association website, along with their test certificates.
- ETSI. "DMR Standard Overview" (PDF). ETSI. Retrieved 22 March 2012.
- DMR association press release Oct 27 2015 stating revision to standard
- "ETSI TS 102 361-1, DMR Air Interface PRotocol" (PDF).
- "DMR Association".
- "MD380 Tools on GitHub".
- "DMR Equipment Manufacturers & Product Showcase".
- "DMR Interoperability Certificates".