Most people are familiar with DMR and TETRA digital solutions, but they are less likely to have heard of e-DMR. Extended-DMR is the brainchild of French digital equipment manufacturer Detracom and is largely aimed at PMR customers using wide area VHF networks.
Detracom is a young company established in 2002. In 2006, it started to develop a digital system, which is now available. The Detranet range consists of base, mobile and hand-portable stations designed to be easily integrated into existing networks or for the deployment of new single or multi-site digital networks.
The equipment conforms to ETSI standards (PMR) ETS 300 086 and ETS 300 113 with 12.5KHz channel spacing. It operates in all PMR frequency bands including 30-50MHz, 68-88MHz, 146-174MHz and 410-470MHz.
Jean-Claude Maruejouls, marketing and international marketing and sales at Detracom, explains: ‘We are in the position of supplying full networks in VHF frequencies, including very low frequencies, but we don’t plan to go into the UHF spectrum, because that is where TETRA is. We see ourselves as complementary to TETRA and besides, we are targeting different customers.’
The customers Detracom is targeting are users of wide area networks (WAN) or even national networks already operating in VHF frequencies. Maruejouls points out that many of these networks are reaching obsolescence and their users are now contemplating moving to digital.
‘We are suffering an economic crisis, so they need to look at cost-effective solutions,’ says Maruejouls. ‘It makes economic and operational sense for them to keep the same frequencies, which they have already been allocated. To change to another frequency, such as UHF, means they would have to redesign their networks.’
In addition, points out Maruejouls, these customers often have wide area networks with a high number of repeaters, but a low density of mobile and hand-portable terminals, which makes a TETRA-style solution not only very expensive, but in most cases unnecessary.
‘They have a number of existing sites with shelters, masts and antennas, so they would then have to add new sites to compensate for the propagation weakness of UHF. It is a very important point,’
argues Maruejouls. ‘They have a large number of base stations and terminals that are analogue, so from a budgetary point of view they want to go step by step in a phased migration towards digital.’
The Detranet system is designed to provide full compatibility between analogue equipment with CTCSS and 5 tone signalling and digital equipment. The Detracom radio terminals are designed to operate in either analogue or digital mode through a manual selector. It is an important provision, as it allows customers to gradually change over to a digital system in a smooth way and over a timescale they can afford by spreading the financial burden over months or years.
Detracom is delivering its first low band digital system to French utilities giant EDF Distribution, which has its own spectrum and an existing analogue wide area network in France. ‘Our pilot network is proving very satisfactory,’ assures Maruejouls. ‘We supplied the complete network infrastructure, terminals and portables.’
Third slot with e-DMR
But back to e-DMR: the ‘enhanced’ part of Detracom’s clever solution is the addition of a third slot to DMR’s traditional two-slot technology.
‘It can be compared with a dedicated “control channel” in analogue trunked technologies,’ says Maruejouls, ‘where it is used for the establishment and clearing down of calls, the handling of signalling exchange and data updating between different base stations and radio terminals.’
This innovation provides a 50% higher spectral efficiency than DMR, but within the 12.5KHz channel spacing.
The existence of the third slot allows Detracom to offer customers additional services. The real advantage is that the customer can keep two voice communication slots open and use the third slot for short data transmissions such as GPS, SMS, signalling, network registration and the like. It can also be used to send an alarm message to or from a lone worker. The alarm will have priority and reach the dispatcher or controller in charge of receiving alarms.
‘This kind of technology allows simultaneous transmission of voice and data without either one disturbing the other; they are fully independent,’ says Detracom’s general manager Serge Huc.
‘In PMR most communication is semi-duplex,’ continues Huc. ‘The higher spectral efficiency developed by Detracom means that with the third slot we can send two simultaneous voice communications and one data communication. We can also establish full duplex incoming and outgoing PSTN/PABX calls, plus a data communication.’
This offers maximum listening comfort to both talking parties and avoids the use of GSM for telephone calls to fixed subscribers, which keeps telephone operational costs down.
Network architecture and IP connectivity
As Detracom’s system is targeted at WAN users who cover a region or even a country, it uses a cell architecture design similar to GSM.
‘You can have an unlimited number of cells and each cell can have up to seven different base stations, which can be connected within the cell by some kind of connection: microwave, fibre optic, telephone interface, etc,’ says Huc.
In each cell a standard base station plays the role of a master station and is used to communicate with the other cells through IP wherever possible. Provided radio coverage is available, there is no interruption of communications when a mobile radio terminal travels from one base station to another within a cell, as it automatically registers with the visited base station offering the best signal to noise ratio.
Detracom’s technology is based on the digital signalling processing through DSP. The terminals are 100% controlled by the software inside. The hardware is compatible with DMR technology, but Detracom is not using the same protocol. However, Huc says it could implement DMR protocol into its existing hardware if necessary.
Besides working in dual mode for analogue and digital, the hand-portables also have an option for a GSM or GSMR module. For example, when PMR radio coverage is not sufficient, instead of using a separate GSM handset, the customer can use his DMR radio to call after setting it to GSM mode and use a mobile carrier’s network. So, just one radio can cover analogue, DMR and GSM, although the latter is a requested option.
The radios also have GPS, Bluetooth, a man-down function and different signalling modes, along with a direct mode communication. A camera can also be fitted to the back of the terminal. The charger has an IP connection so it can download software upgrades.
The company has also developed a remote microphone so users can receive a call outside their vehicle. Two versions are available: one with a 100m range and the other up to 400m.
Detracom has also designed mobile repeater stations that can be transported with fire trucks in forest areas, for example. If the fire trucks are in a valley beyond the coverage of a fixed base station, they can use the mobile one.
For the time being, Detracom is concentrating on France and its near neighbours, although it is eyeing up opportunities in the Middle East, where a pilot is due to start shortly.
‘If it goes well, then we will build 500 base stations and provide thousands of terminals,’ says Huc.
‘We are very ambitious,’ adds Huc. ‘We are a young company at the moment, but we want to become a significant player with a higher profile. However, for the time being we have to prove that our technology is OK.’
Huc adds that one of the company’s strengths is its ability to study what a customer needs and then supply bespoke solutions very quickly. ‘And if the customer really needs something new that we can add, we will do it. Be close to the customer is our philosophy,’ he says.