If a client device on the 5Ghz band has a 16dBm transmit power and a -2dB antenna gain, then it has an effective transmit power of 14dBm. The client device might work well with an AP set to 14dBm transmit power, but the AP antenna gain will also have to be taken into account as it will affect the cell size by a similar amount in both the transmit and receive directions.

The cell size will be designed to the expected client device behaviour. For example, if this is designed to Apple client guidelines Apple device then roaming boundaries will be designed with a -65dBm signal strength and a 12dB better (or 8db better if only using data) Signal to Noise Ratio boundary.

The minimum cell size will take into account of other effects such as polarisation or attenuation. The orientation of a device affects the signal polarisation and this can reduce the effective transmit/receive signal strength by about 6dB. Attenuation may occur if, for example, users obstruct the path between the client device and the AP.

Based on the power levels required to meet the required tolerances for these effects, the maximum cell size can be measured to determine how this this cell will interfere with the rest of the network. The correct AP antenna must be used, and tested in its installed orientation, because the antenna gain will also affect the cell size (in both the transmit and receive directions). Additional assumptions will also have to be made for how client devices at the edge of the cell will extend the cell. This is because client devices will extend the contention/interference of the cell's channel when they communicate with the AP when they are at the edge of the cell with their normal power settings.

The design can then be fine-tuned accordingly.

As we have demonstrated elsewhere, devices roam in unusual ways, so actual roaming behaviour will need to be checked to ensure it performs as expected.