How does RF propagation affect Location?
Figure 1 – (a) Power law propagation (b) shadowing, for example, by two walls (c) multipath fading A. The signal strength between a client and an AP varies at different distance scales, as shown in the Figure. The large scale helps with location accuracy, the medium scale can help or hinder, but the small scale is nothing but a nuisance: • Large—As a rule of physics, signal strength varies inversely with the square of distance in free space. As a rule of thumb, signal strength varies inversely with (about) the cube of distance indoors. This power law propagation is the main indicator of range between AP and client. The signal drops most steeply near an AP, and so this yields the best distance information. • Medium—Environmental clutter such as bookcases, filing cabinets, cube walls, and whiteboards can screen the client from the AP. Conversely, lack of clutter such as hallways gives a better link. In both cases these are major errors from the power law propagation. This is called shado
