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Case Study – TETRA emergency services

The Challenge

In fact when driving at 60 mph the accepted measurement rate is in excess of 70 measurements per second per channel. For 200 channels this needs a scanning rate of 14,000 channels per second – an order of magnitude faster than the best available receivers of the day.

Given the distance involved the simple solution, to drive at 4 mph, was not a practical option. The other obvious solution, 14 receivers in each vehicle would have been prohibitively expensive and cumbersome.

When deploying the TETRA emergency services network Airwave Solutions needed a way to verify that coverage was available across the vast majority of the UK road network; a distance of approximately 1 million miles.

At the time the tools available to make such measurements were analogue scanning receivers capable of making 1000 measurements per second. Since Airwave had 200 channels to measure, these receivers could make five measurements on each channel per second, whereas to eliminate the effects of fading many more than this are required.

Our Approach

MAC Ltd’s solution was to apply digital signal processing to the problem. Whilst it wasn’t possible to use 14 physical receivers, by using state of the art analogue to digital conversion coupled with high-speed signal processing using the latest field-programmable gate arrays (FPGAs), it was possible to put 200 digital receivers in one box.

The result was a software-defined radio that could measure each of the 200 channels allocated to the Airwave network up to 125 times a second (an equivalent scanning rate of 25,000 channels per second). The result was the CatchAll Receiver.

The advantage of the digital approach taken by MAC Ltd went beyond the scanning rate.

With further processing the CatchAll could demodulate and decode the TETRA broadcast signals, to provide more detailed diagnostic data and could also measure signal quality to aid in the detection of co- or adjacent channel interference. Such features were not possible in analogue scanning receivers.

The Outcome

Airwave deployed a fleet of drive test vehicles each equipped with a single CatchAll receiver and over the period in which it deployed the UK network it did cover the 1 million miles of A, B and C roads.

Airwave still maintains its fleet of CatchAll receivers, further enhanced by the second generation CatchAll designed for pedestrian use when measuring in buildings.

MAC Ltd sells the CatchAll to operators and installers of TETRA networks across the globe.

Now in its third generation, the CatchAll remains the benchmark for TETRA network measurement equipment and with enhanced signal processing capability will soon support measurements of LTE and 5GNR networks.

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