Does DMR (Digital Mobile Radio) have a role in business-critical digital radio
Business radio provides a valuable but often unseen function in society. Its wide variety of users (emergency services, utilities and transport organisations, building sites and hotels) usually pay for the radio terminals, infrastructure and licence (there are some business radio service providers) to maximise the benefit for their businesses. Where public safety might be at stake, such as on trains, business radio is mission critical, but for many users it can simply make their business more efficient whilst also protecting the workforce from a health and safety point of view.
Companies opt for business radio so that:
they have control of the network
there are no variable monthly call charges
they have the coverage and facilities where and when they need them.
A bus transport company cannot rely on busy commercial networks to protect its drivers in the event of an accident or attack. Similarly, a utility company has to have coverage everywhere that its staff need to work, possibly beyond the boundaries of commercial networks.
Many of these users would like to migrate to digital radio because the communications path is generally clearer, codecs can be optimised to work in high noise environments, and there are better facilities, in particular IP packet data and additional features such as duplex voice. However, the choice of digital radio has been limited to date, unless a proprietary solution was adopted. The availability of equipment using the ETSI standard DMR (Digital Mobile Radio) is therefore welcome.
DMR is intended to be a digital replacement for conventional analogue PMR radios, as well as shared repeater systems and MPT 1327 trunked radio systems. There are three levels of complexity, or ‘tiers’, defined by the standard, but Tier I (which is for the lowest-cost ‘digital PMR446’-like application) is not supported commercially. The focus is on Tier II, conventional peer-to-peer and repeater, and Tier III, trunking. The standard is designed so that DMR channels can directly replace existing 12.5kHz channels, and fit within the existing emission mask. This provides a powerful capability to migrate from 12.5 kHz analogue channels to DMR, with a two-fold improvement in channel efficiency within a user’s existing channel assignments.
DMR systems can operate on frequencies between 66MHz and 960MHz (although equipment is likely to be available in the main PMR bands), and provide voice services (individual, group and broadcast), as well as short data and IP packet data.
The DMR standard has been available for a few years now and some equipment is already available. However, with the formation of the DMR Association, interest in DMR has really taken off in the last twelve months, and it is now a viable alternative for business-critical radio users who are looking to upgrade. Several hundred thousand DMR terminals have been sold in the UK to date, including to a Boots distribution service centre, the Liverpool Arena and Conference Centre and a ShopWatch scheme at the Antoine Centre in Cumbernauld. These are all Tier II systems.
There are other ETSI standards for digital radio for professional users, including the well- established TETRA standard, and the FDMA cousin to DMR, dPMR. Figure 1 shows the market tiers addressed by these standards, and highlights the significant overlap between them. TETRA is still the technology of choice when it comes to mission-critical systems, but there is an alternative now for business-critical systems.
Figure 1: Market tiers showing the overlap between the standards (Source: Analysys Mason)
Whilst it is the large national TETRA networks that readers will be familiar with, there are also many small TETRA networks. There is now a wide range of suppliers of small, or compact, TETRA systems, and an increasing number of terminal suppliers (at least nine involved in the IOP process). Since TETRA is a 25kHz technology, with four-slot TDMA, a single carrier can provide a control channel, two traffic channels, and a packet data channel. TETRA is therefore a good solution where the number of subscribers justifies the use of 25kHz channels, and where frequencies are available Choice is not just on capacity alone, TETRA has arguably the richest feature set of digital mobile radio technologies, including DMO, sophisticated encryption, telephony, duplex calls, etc. The London Underground Connect project is a large private TETRA network, and there are also a number of small TETRA systems in the UK, including the South Bank, airport systems, Cardiff RadioNet and thecentre:mk (a shopping centre in Milton Keynes). In addition, TETRA is being deployed for use by LOCOG in the London 2012 Olympics.
The TETRA standard includes the ACELP codec, and interoperability between systems and terminals is well established. It also has a number of different air-interface, encryption algorithms for public safety and commercial use, authentication of terminals and infrastructure, as well as powerful functionality as described in the previous paragraph.
Initially dPMR was a subset of the DMR standard, intended for licence-exempt, peer-to-peer, low-power (less than 500 mW) portable equipment with integral antennas. This was planned as a replacement for the low-end PMR446 system. Licence-exempt dPMR446 (digital equipment for the PMR 446 band) terminals are available from Icom.
The dPMR standard is for equipment that is FDMA and 6.25kHz channel bandwidth. Its targets are so-called highly functional solutions using low-cost and low-complexity technology. Within the last two years, the dPMR standard has been extended to cover licensed channels at higher power, and includes three modes (similar to the DMR Tiers), which provide peer-to-peer licensed, as well as repeater (simple and complex) operation. Effectively, Mode 1 is equivalent to Tier II (peer to peer), Mode 2 is equivalent to Tier II (Low complexity repeater) and Mode 3 is equivalent to Tier III (High throughput repeater/trunked).
Features are the same as DMR, being voice services (individual, group and broadcast), as well as short data and IP packet data. The codec is not mandated, but is expected to be AMBE. Again, encryption is not a part of the ETSI standard.
At the time of writing there are no dPMR equipments commercially available for the licensed standard. However there is a dPMR MoU Group which is well supported, is addressing interoperability, and equipment should become available in time.