The DMR standard continues to mature

The DMR standard continues to mature with the arrival of Tier III trunking systems from several vendors. While it is still early days yet, manufacturers are optimistic that the take up of DMR is accelerating and that it will offer a lower cost digital option to rival some of the other high end systems- reports James Atkinson

Amid the flurry of digital two-way radio standards that have emerged over the last decade in the wake of high-end public safety orientated systems such as TETRA, Tetrapol and P25, there seems little doubt that DMR (digital mobile radio) is the one making the most impact.

DMR has attracted the widest range of vendors and the largest market share since it was certified as an open ETSI standard based on two-slot TDMA in 12.5kHz channels in 2005.

There are three tiers to the standard: Tier I Unlicensed, which covers products for license-free use in the 446MHz band; Tier II Conventional DMR covers licensed conventional radio systems in the PMR bands 66MHz-960MHz; and Tier III Trunked, which operates in the same range as Tier II supporting voice, SMS and packet data services in various formats.

DMR was conceived largely as a lower cost (compared with TETRA etc) digital replacement for analogue systems. Tier II has been making good headway, but it is the arrival of Tier III trunking systems as a digital replacement for MPT1327 analogue trunking over the last two years that is the most exciting development.

Proprietary elements

Tim Clark, Mototrbo Product Director EMEA at Motorola Solutions, says: ‘Independent research shows that TETRA and DMR are the most popular choices at high end and mid-to lower end. We are not seeing the same takeoff with dPMR, although there are some sales on NXDN.

‘It’s no coincidence that DMR is the most widely adopted standard, as TDMA (time division multiple access) is a very successful technology. Given the advantages it brings for professional users, more and more manufacturers are starting to adopt the DMR standard.’

Most manufacturers have some proprietary elements in their DMR systems at the moment, largely due to the fact that products have been developed faster than the slow work of the standards bodies can keep up with. Motorola’s Mototrbo branded range of DMR Tier II products, for example, conform to the DMR standard to give a base level of interoperability with other DMR vendors, but then has a range of proprietary features on top.

The aim, however, for most other DMR vendors is to create an open and interoperable standard, so customers can buy new products with the confidence that they will work with any manufacturers’ equipment. The standard has not yet reached this goal for Tier III, but to be fair it is early days yet.

However, Tait Communications, Selex ES, Hytera and Harris have completed DMR Association IOP-certified interoperability testing and have products on the market. Simoco is due to launch its Tier III products in November this year.

Now DMR Tier III products are coming on to the market, is it likely that customers will see it as an alternative to the likes of TETRA? A paper entitled TETRA versus DMR, published by the TETRA + Critical Communications Association in October 2012, noted that DMR has an equivalent for most of TETRA’s key features with the exception of duplex voice, standard encryption, direct mode repeater and gateways and Bluetooth (no longer the case).

But in its view, the only unique selling points of DMR not offered by TETRA are simulcast networks and Tier II VHF repeater operations.

Spectrum advantages

Andy Grimmett, Chief Technologist at Simoco, comments: ‘The history of TETRA Group is that it was developed as a public safety standard from day one, while DMR was developed as a low cost digital system; that was the main driver, but as it has got more mature more things have been added, so we will see high end features such as duplex voice that you get with TETRA radios.

‘You won’t see public safety organisations with mature TETRA systems switching to DMR,’ he acknowledges, ‘but in other countries where there isn’t a national buying programme, the local sheriff may want full trunking, duplex voice, encryption and so on, but not want to operate outside their local county border, so DMR may well fit the bill.’

Hytera’s GS Kok, VP Public Security & Safety Dept, CTO, adds: ‘The DMR standard was only ratified in 2005, but now the digital technology is widely known. However, it is a bit too early to compare DMR Tier III and TETRA. TETRA has a very strong hold on the public safety market and DMR is new and slowly maturing and you can’t compete against a mature technology at this stage of the development cycle.’

Jamie Bishop, Marketing Manager, Tait EMEA, is a little more bullish, arguing: ‘DMR Tier III pretty much goes up to TETRA, but the advantage is you can get it in VHF and a lot of people have that. TETRA doesn’t as yet, although a standard is being worked on, and TETRA does add a degree of complexity for non-public safety users, which is not necessarily required.’

Grimmett agrees: ‘DMR works across the entire PMR range from 66MHz to 900MHz, but TETRA is confined to 400MHz and 800MHz spectrum and is only now coming around to VHF, but will it go down as far as 66MHz?’

DMR’s ability to operate in the VHF band is good news for the standard though, says Hytera’s GS Kok. ‘Having a standard in VHF is a good opportunity for DMR. VHF is available in many countries and industries like forestry need long wavelengths. It is a real plus that DMR is able to operate across the PMR spectrum bands though.’

TETRA has the advantage of being an open standard with a high level of interoperability between vendors and a fully developed set of features. TDMA gives 6.25kHz channel efficiency with four timeslots in 25kHz compared with two timeslots in DMR’s 12.5kHz, and it has a high level of standardised encryption.

But all this comes at a cost. TETRA requires clean blocks of spectrum, partly to avoid interference with analogue channels, and because the standard requires that the transmit and receive frequencies of a channel are 10MHz apart. In parts of the world, especially Europe, TETRA frequencies are hard to come by.

TETRA is not easily backwards compatible with legacy analogue networks and coverage is significantly less than other PMR/LMR standards, so more radio sites are needed (a rough guide is two to three times as many sites as DMR) which is an important consideration in low density population areas and it may mean more licenses are required. In addition, TETRA bases stations/repeaters must be linear, which adds to the cost (although work has been done to mitigate this disadvantage now).

Grimmett notes: ‘The great strength of DMR Tier II and III systems is the reuse of existing analogue spectrum. The analogue radio market is by far the most dominant with around 80% of the installed base. The majority of that analogue base is 12.5kHz spectrum with some 25kHz thrown in, especially in Australia and the USA. What it means is you are not presented with the headache of getting new radio licenses and regulators don’t have to reallocate spectrum in different size chunks, which creates a messy spectrum landscape.’

Bishop says: ‘An analogue to digital migration is difficult with TETRA, so it is often a full rip and replace job. But it is easy on DMR, as it is available in the same frequency bands as analogue and

you can reuse the existing combiners and antennas. Also, TETRA uses 25kHz channel and four time slots and some customers won’t want four timeslots, so that can be wasteful.’

Another advantage of DMR is that users can make the migration to digital slowly, mixing analogue and digital equipment, as the main vendors have all made their DMR equipment backwards compatible.

Tait’s Bishop says: ‘We have multi-mode terminals so you get all the same functionality as you get on your MPT infrastructure and you move to DMR when you are ready or have a mix of the two, changing one site at a time. You get automatic roaming between MPT and DMR. Another alternative is to upgrade not site by site, but channel-by-channel, so old terminals can roam over the whole system.’

He adds: ‘Where TETRA has the advantage is that you have just four levels of priority on DMR, while TETRA has more, 15 or16, so you can assign different levels of priority for access. TETRA gives you more granularity. But we aren’t really chasing the customers that need that level of granularity and prioritisation.’

Very few vendors have opted to develop a dual-mode analogue and TETRA handset, the notable exception being Selex ES’s ElettraSuite Puma T3 Plus terminal.

TETRA is usually seen as the solution if you want a full mission critical TETRA system rolled out nationally. But most DMR vendors have ways to scale up from single sites to national networks of 1,000 sites and these can then be linked to other networks to create even bigger networks. Mototrbo offers Linked Capacity Plus, which in effect upgrades its Tier II conventional system to a trunked one, although not to Tier III standards.

Encryption

Turning to two of the key features identified by the TCCA paper as lacking in DMR, both Grimmett and GS Kok report that there is now agreement on standard encryption for DMR.

Grimmett says: ‘Encryption on DMR has now been standardised quite recently this year. We are all agreed on this standard with various levels right up to 256 bit encryption and it supports lower levels too. Yes, there are several proprietary encryptions from different vendors at the moment, but the market will drive a standard adoption.

GS Kok adds: ‘Everybody in the DMR Association is happy to go down a standard encryption route. We’ve worked on this for 12 months and it is not one company that had this vision, it is the whole DMR group.’

Standardisation of this feature is important, because as Grimmett points out, if a utility is buying several thousand radios they will want to have vendor choice and will want standard encryption, as they don’t want to be locked into one vendor.

Duplex voice

As for duplex voice, there are mixed messages. GS Kok says: ‘We have already deployed a duplex voice model since the end of last year for one customer and we are happy to propose it as a DMR standard, so it is on the table for others to look at.’

Tait’s Bishop adds: ‘Duplex voice is possible, but there are implications for the network on which it is deployed. From a spectral efficiency perspective you are using two slots simultaneously and that takes away some of the efficiency of a TDMA standard. You need more channels therefore and it becomes a trade off: what is the most valuable thing to you?

‘There are instances where duplex voice may be sensible, such as PBX access, for example. If you are making a call between a radio and a mobile phone or landline then theoretically it could be better to have duplex voice. But you have to think about the system design and the implications of that for spectrum efficiency. I’m not sure it is the right answer for many users,’ says Bishop.

Lower cost solutions

Analogue radios can be very reasonably priced and DMR vendors have been working to reduce the cost of equipment to encourage smaller sized analogue users to make the move to digital.

Tait decided to move straight to DMR Tier III as it has a large number of big MPT1327 users (such as London Bus) looking for a cost effective digital trunked solution. However, it is making the move to provide smaller, lower priced trunked systems for smaller users too in the shape of its Access and Express offerings. Tait’s Access system takes its Tier III core network with 2 x 12.5kHz channels and embeds it in a base station box just four units high, which fits in a standard 19-inch stack. It is aimed at construction sites, quarries and shopping centres.

‘You can scale up by using two base stations giving you 8 x 6.25kHz channels. It is like a small-scale trunked system, so if you don’t need DMR Tier III or don’t have the budget for it, you can get this instead,’ says Bishop. The Express product is a 6-site, 38 channel system, which opens up Tier III to larger airports, councils and other customer who need more of a wide area network.

Motorola’s Clark says the company launched a range of second generation Mototrbo products to market in 2012, including the DM4000 series with colour displays, built in GPS and Bluetooth, DM4000 ATEX products and the smaller SL4000 radios, aimed at opening up markets where traditional two-way radios are not attractive, such as front of house, hotels and managerial.

Applications

A key sales driver in the latter arena is adding ‘killer’ apps, such as work flow management and work ticketing, to increase business process efficiency. Hytera has also attacked this market with its small, compact X1e and X1p (with display screen and full keypad) DMR hand portables, where it too is finding success.

‘We concentrated a lot on the professional market in the past, but we have also spent a lot of time and effort focusing on the commercial arena and now we have the smaller radios for them,’ says GS Kok.

Mototrbo’s Clark adds: ‘Last year we also made the first steps towards bringing Mototrbo down to a lower price point than the DP4000 range, by introducing the mid-tier DP2000 Series. In the second half of this year, we’ll have other lower tier products, such as a compact radio with the DP4000 feature set, but in a smaller housing. This will give us a complete top to bottom portfolio.’

Tait’s Jaime Bishop concludes: ‘We have released a lot of our DMR Tier III equipment now, so where next? We are now getting to the applications and fun bits on top. The priority from digital perspective has been P25 opportunities in the US and Australia, but now we have DMR with its range of frequencies, we are starting to promote it more heavily into Western Europe. We are looking at how to increase our presence beyond our long-standing customers.’

Motorola’s position, according to Clark, is: ‘Going forward, for those that need WANs with more capacity nationwide, we will offer TETRA, so for us there is no need to go to DMR III yet. We have small TETRA systems with our Dimetra range and we don’t think the gap between DMR Tier II and TETRA justifies another standard. The DMR Tier III standard is very immature and still needs time and work. We can offer DMR Tier II with trunked enhancements with Connect Plus and Linked Capacity Plus on Mototrbo.’

Simoco’s Andy Grimmett thinks that DMR Tier III can grab a good share of the market. ‘When you look at what customers are not getting with DMR you ask, why wouldn’t they go for it? There is very little in the TETRA standard that is missing now encryption and duplex voice are being worked on. I can see TETRA in cities and DMR or an equivalent in less populated rural areas, as gateway technologies and systems integrators will have ways to do this.

Market interest

‘We are getting a huge amount of interest in both tiers. The take up of Tier III will come, but a lot of the systems we are talking to customers about are large networks, so the gestation period is six months to several years because of the need for technical evaluation, budget cycles, testing and due diligence. A lot of these big networks suitable for DMR Tier III systems won’t be ready yet, but there will be significant wins announced from about six months’ time onwards,’ he predicts.

Hytera’s GS Kok says: ‘There is a lot of standardisation now in DMR and a lot of protocols are being given interoperability tests, but in real deployments there are limitations still. So, as a key player when we say something is interoperable, we really want it to be interoperable. That way when customers migrate to DMR Tier III they will genuinely be using interoperable equipment.’

He reports that a lot of customers are after a mature DMR Tier III system. ‘Right now the protocol is very new and it will take some time to mature, but all these things are just features we can add. We can do it eventually and standardise it and we will do it if the demand is there. It is a very exciting for everybody.’

Origional article by Wireless.