Digital Taking the third way
A unique digital radio format developed by a French company is claimed to offer some worthwhile advantages over today’s other PMR technologies
(Tetra) or two (DMR). But at the recent PMR- Expo in Cologne, the French radio company Detracom showed an innovative family of radio products based on a system with three time-slots. It calls this technology e-DMR. “Two slots can be used (for example) for
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voice communication and the third slot is al- ways available for the transmission of data”, ex- plains Jean-Claude Maruejouls, the company’s international marketing manager. “It can be GPS, it can be short data messages. It is also available for signalling – for example, the ex- changes between the base stations and the radio terminals. Also, it is used for the updating of the database to know which terminal has regis- tered with which base station.” Detracom, which has its own r&d team of
some 25 engineers and is a communications supplier to the French government, began de- veloping its three-slot format some years ago,
General manager Serge Huc demonstrates Detracom’s e-DMR analogue/digital handportable. The technology has many similarities to DMR, but the third time-slot adds extra capabilities by relieving a pinch-point
or businesses requiring a TDMA-based private mobile radio system, the main choice has been between four time-slots
before the two-slot ETSI DMR standard was fi- nalized. It says it did this to meet a demand from customers.Te technology is designed for use in single-site and multi-site PMR installations, a system which the company calls Detranet.
Choice and programming M. Maruejouls likens e-DMR’s third slot to the control channel in a trunked radio sys- tem. “Te advantage is that you always have two slots available to handle audio voice com- munication”, he says. “Or, if you like, you can dedicate the three slots for data transmission. It’s not only two voice plus one data – it could be also full data on three slots. It’s a question of choice and programming.” While acknowledging the benefits of the
DMR standard – and its backing by an associa- tion of manufacturers – he points out a limi- tation of DMR’s two-slot format. “When one slot is busy transmitting or receiving data, that means that only one slot is available for voice”, he argues. “So then we are back to analogue, and we wanted to avoid that. “We say, OK, we have to be as efficient as
possible in terms of spectrum because with tiny spectrum we have to use it to the most.” Te reserved data time-slot inevitably steals
some transmission capacity from the other two slots, but the company insists that this is not to the detriment of speech quality. With two slots always available for speech or
data, the Detranet system embodies capabilities such as simultaneous two-way speech (full-du- plex speech) – for making a distress call, for ex- ample. “It is sent full duplex so the other person will receive it in full duplex and you don’t have to PTT for the conversation”, M. Maruejouls says. “It’s automatic.” Tis feat is possible because a telephone in-
terconnect occupies just one slot on the uplink and one on the downlink – leaving the remain- ing pair of traffic slots free for a second tele- phone call, or just for ordinary radio commu- nications. Signalling for both is handled via the third slot. However, between two mobiles the channel can support only one full-duplex call. But since Detracom’s repeaters all have tele-
phone interconnect, any mobile or handport- able can make and receive phone calls from PABX or PSTN, in full duplex.
20 “We can establish two parallel, independ-
ent telephone communications in full duplex, while at the same time I can send you a text message”, M. Maruejouls continues. “So we believe it is much more efficient than DMR, and this is one of the advantages of e-DMR.” Besides setting up and managing calls, the
third slot can be used for short data messages, registering additional radio terminals on the network, alarms and GPS position reports. And it enables priority and pre-emptive calls to he handled.
Reviving VHF Detracom now offers a range of Detranet radio products based on e-DMR technology, includ- ing mobiles, handportables and base station repeaters. Models are available for three VHF bands – 30–50, 68–88 and 146–174MHz, for standard ETSI channel widths – and, for backward compatibility and easy migration, the radios can also operate in analogue mode. Teir manufacture is contracted out to another company. Last year Detracom won a local government
contract for a Detranet system in the Loiret département, the district surrounding Orléans. “Also the Ministry of Roads is using the sys- tem”, M. Maruejouls continues. “And we are currently building a network but for the time being I cannot tell you where. For the time be- ing we want to keep that a low profile. It’s new, it’s a big project, with a lot of repeater stations, a lot of mobiles and terminals.” In addition, he says, the system has been op-
erating in a digital/analogue installation on the Indian Ocean island of Réunion, a French over- seas territory. “It’s Electricité de France which has placed the order for that system, which is a network that covers the whole island. I would say from north to south it’s approximately 250 kilometres and from east to west more or less the same. It’s multi-site, so all in all I believe we have five cells and 11 or 12 repeater stations.” Tis network supports a full range of e-
DMR features, including selective or open- channel calling, static and dynamic group calls, full-duplex PSTN interconnects, emergency calls, short messages and GPS. “In La Réunion they have been using it for close to two years, without any problem”, says
LAND mobile January 2012
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