Understanding on Motley–Keenan Model for WCDMA
Site-specific models of indoor propagation, as the name implies, take the specific characteristics of a particular building as their input. Often these models count the number of walls, floors or other obstacles between the transmitter and the receiver to produce a value of attenuation for propagation along that path. If we repeat this procedure for many hypothetical receiver (EU) positions, we can trace the contours of the received signal strength equivalent.
These propagation predictions are ideal for computer automation. At the time of this writing, several propagation forecasting tools covered in the market use variations of this technique. One of these models, often quoted, has come to be known as the Motley-Keenan model after the researchers who published the first time. This model takes the form of a free space propagation model with attenuation added for each wall, floor, or obstruction encountered along the route.
Mathematically, we can write the LO path loss as:
LO = PO + 20 log(d) + p × WAF + k × FAF
where:
Po= 20Log[4 πf/C]
d = distance between transmitter and receiver
p = number of walls between transmitter and receiver
WAF = Wall Attenuation Factor
k = number of floors between transmitter and receiver
FAF = Floor Attenuation Factor
The free space propagation model should be evident from the first two terms in the equation. The additional terms represent the loss through any obstacle. This site specific model is general enough to accommodate a wide range of frequencies with the appropriate choice of attenuation factors.
The literature is full of attenuation values measured for a variety of materials and at different frequencies, and more are published regularly. In general, the frequencies used for personal communication (800-2100 MHz), the inner walls of a modern office building have aWAF of about 3 dB.
Brick interior walls and structural supports have a WAF of about 10 dB. Floors vary depending on the building, but they usually have a FAF between 13 and 18 dB.