Tait Connection

The method

If random signal quality samples are taken, you can estimate the percentage of locations that meet or exceed the coverage design threshold. The associated degree of confidence will then depend on the number of samples you take.

For example: A radio network has specified area reliability of 90%, and coverage design threshold is -100dBm signal strength. You require a confidence level – the likelihood of the testing being accurate – of 99%.

The number of samples will depend on the reliability specification and predicted reliability – the smaller the gap between them, the more samples are required. Let’s look at some possible outcomes, based on different numbers of samples.

Looking at the table on the right, the first two examples fall well short in terms of confidence, due to their very small sample numbers. The third example exceeds both reliability and confidence, suggesting that the system may in fact have more radio sites than necessary to meet the specified criteria.

SAMPLES ≥ -100dBm < -100dBm Measured reliability Confidence* Acceptable

10 9 1 90% 50% No 20 19 1 95% 77% No 200 191 9 96% 99.5% Yes 900 831 69 92.3% 99.0% Yes

*using estimate of proportions technique The final example – with 900 samples and measured reliability around 92% - meets the confidence criteria, and best represents a realistic, well-executed Coverage Verification Test.

What happens if we increase the confidence figure further?

Diminishing returns set in quite quickly: 99.9% confidence requires 2150 samples. That is a significantly greater sampling overhead, so the sampling cost can get out of hand quite quickly.

So to sum up, the theoretical nature of coverage prediction can provide only part of the story. Physical, location signal measurements from a well-designed and executed coverage verification test can verify it in a robust, repeatable and affordable way.

“ … the theoretical nature of coverage prediction can provide only part of the story. Physical, location signal measurements from a well-designed and executed coverage verification test can verify it …”