Modified Free Space Model (MF)

The modified-free-space model analyzes the building concerning distances between walls and penetration losses of the walls, but the individual positions of the walls and their material properties are not considered.

This model computes the path loss similar to the free space loss with an adjustable exponent and offset. Herewith it assumes that the excess path loss (in dB) is linearly dependent on the distance with a specific attenuation coefficient n:

l MF =n( 20log 4πd λ )+ l c

The modified-free-space model does not consider the walls of the building, thus no database is required. With constant values for n and lc the prediction leads to field strength values decreasing in concentric circles around the transmitter. According to this the prediction results are fairly inaccurate and only suited for a rough estimation.

Figure 1. Principle of the modified free space model.

To calibrate this model with measurement data the exponent and the offset to be used for this model can be specified by using the Settings button. For line-of-sight to the transmitter, the values for n are in the range between 1.0 and 1.4, in non-line-of-sight scenarios values up to 2.0 are possible.