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March and April between two suppliers, which we have not publicly announced yet. “T e Tier III tests are potentially slightly


more complicated. T ere’s a fairly short list of mandatory interoperability specifi cations, but there’s a long list of optional features that you can test, because the Tier III standard has got a lot more defi ned features than the Tier II part of the DMR standard.” At the same time, the DMR Association


has been working on encryption standards for various levels of security and a methodology has been agreed. On application development, work within


the association has concentrated on establish- ing a common way of doing voice applica- tions – but work would probably now swing towards an agreed common implementation for data applications.


Full functionality Jamie Bishop, representing Tait, said his com- pany’s release of Tier III products this coming September had been planned alongside long-


‘You’ll have full MPT 1327 functionality and full conventional functionality.... If people have used legacy interfaces, we will be able to carry them over’


term projects to migrate major customers with MPT 1327 or conventional PMR systems into DMR Tier III. “You will see things within that like legacy


interfaces but you will also see full legacy func- tionality”, he promised. “You’ll have full MPT 1327 functionality and full conventional func- tionality in there. So if people have used legacy interfaces, we will be able to carry them over and use them on the new system.” But he added: “We are also playing a leading


role in the common AIS (Application Inter- face Specifi cation). T ere’s quite a signifi cant amount of work which Tait did in the early days included in that, so we are very, very fa-


miliar with the specifi cation and will fully sup- port it. And that will extend to things like AVL as well as dispatch-type applications. “In terms of interoperability testing, we are


one of the DMR Association members who are working on Tier III interoperability.... We are in discussions with every vendor who has an- nounced DMR Tier III and we hope for inter- operability with at least one of those members to some degree when we release our portfolio.”


On-site, off-site An optimistic view of Tier III DMR came from Tim Sunderland, of the systems integra- tor Servicom. “We’ve got some considerable


feature that Arqiva customers are really interested in, John Mills said, is integrat- ing their PMR system with their telephone network. But he explained: “One of the major problems that there has always been with tele-radio connect of any sort is that the radio system is simplex. Even if it’s two- frequency, it’s still simplex. That’s no problem for people who use the radio every day, but the guy who picks up the telephone is not used to a press-to-talk system. So full-duplex [simultaneous two-way speech] is actually something that is quite important.


“What’s wanted is a direct connection to the PABX so that your terminals are actually extensions of the PABX, if you require it.”


Airtime charges


Tim Sunderland asked: “Given that that facility is already available on Tetra, do we know how much it’s used?”


“It’s used less on Airwave, basically because the end-users have prohibited it, because it’s too expensive”, John Mills answered. “To look at Airwave as a traffi c predictor for a general Tetra system is a bit unusual because of the way Airwave charges for its airtime. The police methodology of operation is all-informed, and it costs them a fortune – really costs a fortune! “With the ambulance service, they don’t have that money. In the Department of Health contract, the airtime is even more expensive than the PITO contract for the police. So in an


Sponsored by


Simplex, duplex: connecting with the wider world outside A


ambulance situation, you do not make talk- group calls. Every call is a point-to-point call with control room or with another user.” David Taylor added: “I think the police use duplex occasionally when they are talking on telephony. Some of the offi cers will have a telephone number, an MSISDN, as it’s called, so that members of the public can call them. That call is a full-duplex call because it’s for an untrained user. “I was involved in transportation systems


where, even though the Metro train was un- manned, you were actually using Tetra to talk to the panic button. And that, again, had to be full duplex. OK, Airwave doesn’t use it very much – but it’s obviously a lot easier to do on Tetra because of the four-slot TDMA than the two-slot TDMA with DMR. It’s a challenge – but challenges are usually there to be solved!” John Mills said: “I believe two manufac-


turers have said that they are going to do it, and one has actually got something that works, from what I can gather.” “It’s in the standard, at a high level”, con-


fi rmed Tom Mockridge. “And one [member] of the DMR Association has an activity to give a greater level of defi nition to what’s in the standard, which is quite light. As David point- ed out, because you’ve only got two slots to play with, there are technical problems.” “The one manufacturer I’ve spoken to has told me how they approached it and solved the technical problems”, said John


Mills. “The other manufacturer is one of the German ones and I don’t think they’ve got any equipment available at all yet.”


Refi ning the standard “One of the reasons why Tait is not saying that it will do duplex is because we’re not leading the standard in that area”, explained Jamie Bishop. “Until we know what the standard is going to be, we will only do DMR Tier III functionality within the standard, and that’s all we’re committing to at this point in time. We cannot say that we can do full du- plex yet. We need the standard to develop.” In Adrian Grilli’s industry, there was special


interest in full-duplex radio because many utility sites were areas of poor mobile phone coverage. “When you go to a power station, to the receptionist, she can never talk to the person”, he said. “But if they had full-duplex telephony, the receptionist would be quite happy to talk to them. Once you’ve got a full duplex system there, everyone in the power station can have DMR Tier III radio.” Summing up, Tom Mockridge stressed what


he described as one of his great selling points for DMR. “The structure and the use of the 12½ kHz bandwidth mean that you can get these things like duplex in the future – which you can’t, going down an FDMA road”, he emphasized. “These aren’t 20-year-out, pie- in-the-sky things: they are all things which people are genuinely looking at.”


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