networks
rather than staying on the cell closest to it geographically, the radio signal may well end up getting ‘lost’ on the network. So, how neighbour lists are configured is very important.”
Voice and data When it comes to optimizing network performance for both voice and data, Mr Taylor said that engineers look mainly at bit error rate for voice using tools which have synthetic audio and can make a voice call whose quality is measured with a Mean Opinion Score (MOS) from 1-5. Test tools will send a voice sample over the radio and analyse its audio quality. As voice is the critical element, with data second, if good bit error rate and, hence, MOS, is achieved for voice, then quality is assumed as fine for data also. Mr Koski added that network performance for voice and data is very much dependent on the expected use of the network. He commented: “If a huge amount of data is expected to
be carried over the TETRA network, you can have separate control channels handling only the data traffic. But as with many other things, this is a requirement which needs to be addressed prior to the design of the network. Inside your TETRA system, even without TEDS [TETRA Enhanced Data Services], you can have dedicated time slots for voice only and dedicated time slots for data only. On top of that, some of the slots may be used for both, depending on the need at a given time.”
Importance of infrastructure Infrastructure optimization can also have an impact on network performance and having the right type of infrastructure equipment and the correct configuration is, according to Motorola’s Williams, essential if the required performance is to be achieved. Tis is particularly important in terms of coverage and capacity planning. Mr Taylor believes there are various things operators can do in relation to infrastructure hardware to improve optimization. “For a capacity increase you can sectorise the TETRA site by putting
in sectored antennas, usually three sites on the same location, and increase your capacity that way, adjusting transmit power accordingly.” He added that most TETRA sites tend to be low-altitude
sites, using towers that are only 30, 40, or 50 metres high, where down-tilt antennas can help use spectrum more efficiently. Equipment and components are available to adjust network design, including different kinds of antennas, electrical down-tilt, sectorisation, indoor coverage amplifiers, and multiple receive antennas, with three receivers and one transmitter, which will help to improve reception. On infrastructure, Creowave’s Koski added a note of
caution saying that although the use of repeaters – including for indoor coverage – can make an enormous difference, problems with some units on the market can create issues on the network. “In my opinion, units should be equipped to handle misuse and take account of poor coverage design, because, unfortunately, not all coverage designs are done by experts. Now, if you combine a poor design for coverage, with a unit that has no way of control, the end result can be that once the network is needed, it will be blocked by the users themselves. Te two things working together will destroy the signal, and the BTS [base transceiver station] will not be able to make any sense of the transmissions coming from the handsets.” He added that specifically for confined areas, operators
should ensure experts are involved in defining the rules of how and who should make coverage designs for their networks. “Tey should establish test routines, where the performance of such things as repeaters is tested beyond the parameters set by ETSI, particularly since variances occur between different vendor equipment once the unit is tested in extremes, such as when strong interference signals enter the system from an unknown source. In a worst-case scenario, equipment might be blocked if the design is poor; interference could be something as simple as a fire truck next to the antenna delivering signals into a building.”
The spinning turbines of wind farms could pose problems for RF design, as the spin can create a reflector effect and must be taken into account; water also creates interference problems as RF behaves strangely over water, but there are optimization tools to handle this challenge
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