Tier III: a standard for digital trunking

DMR, the ETSI digital radio standard which provides two time-slots for voice or data in a standard 12·5 kHz business radio channel, has quickly become established as a technology upgrade for traditional PMR systems. Tier II DMR - a digital replacement for conventional, non-trunked, analogue PMR - offers clear, noise-free speech together with reliable radio coverage, opportunities for integration with IT systems, and it doubles the communication capability of existing channels.

But with the arrival of the third tier of DMR, the benefits of this open technology will be extended to operators of all but the most complex radio systems. It now offers an attractive upgrade path for trunked and networked installations - today’s MPT 1327 trunked analogue networks, for example.

However, opening Land Mobile’s round-table discussion on the coming Tier III world, Adrian Grilli cautioned against discussing Tier III in isolation. “We recognize that, in the world in which we operate, there are other technologies around”, he said. “One of the problems I always envisaged in the early days of Tetra was that people used to stick their heads in the sand quite a lot and not recognize the reality of the world out there. So Tier III DMR has got to survive in the real world.”

The morning opened with views on Tier III from the experts around the table, beginning with Tim Cull, who supplied a perspective from the FCS, the telecoms industry’s trade body. “Tier III DMR is a long-awaited enhancement of the DMR basic standard which has already proved extremely successful”, he said, “and there is absolutely no reason to believe that Tier III won’t also be strong in those markets needing that kind of system. There are tensions between other systems and other technologies - but that’s probably engineer-speak as much as anything else, because, from the customer’s perspective, they have a certain set of requirements which they’re meeting. And the requirements are not just about the modulation scheme or the organization of the spectrum channels - they are about what actually works.”

Options for updating

Taking as an example a “decent-sized” radio user who currently obtains good value from his existing analogue radio system, Mr Cull considered some of the options for replacing it. “The public communications operators, the LTE fraternity, of course, will be strong contenders because there are certain commercial efficiencies that can be achieved associated with that and like strategies”, he said. “However, that might be as far as it goes, because these commercial networks of course are commercial networks and they tend to run extremely close to the maximum capacity for profit margin reasons. If you have an extremely peaky traffic usage profile, you need to be aware of that.

“So the migration from where you are today on your old system to a public network may not be a simple question at all. And even if it is low-cost (and you have to argue whether it is or not), there is a public liability issue in the event that something goes wrong and you are held liable, that there are better systems working. So you have a due diligence issue whereby you appear to have taken one course, where due diligence should have driven you down another course.”

On the other hand, he went on, much of the value in a complex professional radio system is not in communications alone but in the applications, the features and facilities added to it. For a large proportion of these apps, migrating them into a Tier III environment would not be particularly hard.

“I should explain I was a software manager for many years but I am recovering slowly”, Tim Cull admitted - adding: “I rather suspect that a lot of these apps will actually be directly transportable, given a bit of heaving and straining, at a relatively low investment in development charges.

“And that is a really big issue for the migration strategy, because it really does mean that people do have the opportunity to get into a Tier III environment where previously they might not have thought it that easy.

“There are a few things you have to understand - latency, transit times, the basic IP-ness of it all - but even that is usually handled peripheral to the app. So if you can get rid of all of those issues, then with somebody’s sophisticated fleet control mechanism that connects directly into their logistical controls, stocks, record-keeping, all the other things the modern businesses have to do - suddenly it becomes very easy to think of the new technology like Tier III, or whatever, as being a viable way forward for that customer.”

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