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Joining forces for a combined ‘Air Ground Air’ frequency plan
The next generation police communications networks covering the UK are close to full deployment with emergency services personnel enjoying the benefits of ubiquitous secure voice and data communications. ATDI’s latest involvement with these networks, designing a pan-UK frequency plan for ground-to-air services, adds to an already extensive involvement with this project.
Since spectrum is limited, radio base stations, whether serving the terrestrial or ground-to-air networks, must share frequencies geographically. Interference that might result between co-channel sharers in the terrestrial case is reduced by building and tree clutter. However, for helicopters and fixed wing aircraft, the interference picture is very different.
The propagation over the long interfering paths from air platform to base station needs special consideration if the interference is to be reduced to a manageable level.
Recognising the need to reduce interference, PITO, Ofcom, O2 Airwave and other stakeholders joined forces to contract ATDI to create a combined frequency plan into which their individual TETRA "Air Ground Air (AGA)" networks would fit. Although the scenario was limited to the UK, the plan also needed to consider the future needs of the emergency services in the Republic of Ireland and France, as laid out in various international agreements.
ATDI worked in close partnership with all those interested, firstly defining rules and then coordinating timescales and deliverables.
Initially the project predicted coverage for the wanted service and then went on to determine unwanted interference using ATDI’s air-ground-air software modelling methods. Consideration was also given to the additional constraint to spectrum that had already been carved up with channels designated ‘preferred’ and ‘non-preferred’ for territory use. This then provided the basis for frequency assignment and collation into the plan.
The final stage of the project checked the interference levels complied with current coordination agreements (TETRA National and European MoUs).
An iterative project lifecycle was essential, allowing for adjustment of technical parameters at all sites to make the plan workable. An initial plan was developed automatically. Manual fine tuning reduced interference both intra and inter network.
