“Either antennas or radiating cable can be used in tunnels, although signal level fluctuations are usually higher when antennas are used and signal propagation from a tunnel antenna can be affected by large vehicles blocking the signals and causing interference. Tunnel coverage systems using radiating cables have a more predictable signal distribution.

“The active equipment in a tunnel system must have emergency power, usually consisting of large batteries. Tunnel coverage systems using base stations connected to a large number of repeaters via optical fibres have been installed in tunnels up to 20 km in length. Theoretically, a tunnel 40 km in length could be covered by fibre-fed repeaters connected to one or two TETRA base stations.

“A similar concept and system design can also be deployed to support TETRA coverage in-building”, Samuelsson continued, “but in this scenario the use of antennas is more common.

“Distributed antenna systems (DAS), which use one or several repeaters, are most common for indoor solutions. The repeaters are connected via an outdoor antenna to the nearest base station (a so called off-air repeater) and one or several antennas inside the building provide coverage for any TETRA terminals used inside. The use of DAS provides better coverage with less signal variation throughout the building – although if the structure is large, and a large number of TETRA users are expected inside, then a dedicated base station may be used for the indoor system. If this is the case, then the system will resemble the type that would be deployed to support TETRA coverage in a tunnel.”



ENHANCING TETRA COVERAGE FOR A NEW FORMULA 1 CIRCUIT

At the Yas Marina motor racing circuit, in Abu Dhabi, opened in 2009, as many as four TETRA networks may be in use for a Formula One event. One network is used by circuit officials and staff – including security personnel, first aid workers, parking attendants and catering. Others are used during the race are used by the teams and drivers, the police and the FIA, the sport’s governing body.

A single TETRA base station was installed to serve the whole site – but at the opening F1 Abu Dhabi Grand Prix, the organizers discovered many undesirable gaps in its coverage. Parts of the race circuit and several of the stands and buildings were not adequately served, and in some places the signal was blocked by a large hotel complex located in the middle of the circuit.

To improve the coverage to the required level, the Finnish radio coverage specialist Creowave and its local partner, Waves Middle East, were chosen to supply a series of TETRA coverage enhancement systems for the circuit. They completed the project in February.

Repeater systems now extend the TETRA service into two underground tunnels, four buildings used by race team staff and their drivers for preparations and meetings during the races, and some of the stands used by spectators. The stands also include VIP areas as well as first-aid centres. In one stand, repeaters were installed at both ends of the stand using uplink and downlink antennas to carry the TETRA signal all the way through the stand.

In addition, coverage systems were provided for other service buildings used for administration and as storage by race teams during tests.