One Slope Model (Modified Free Space Model)

The one slope or modified-free-space model analyzes the building structure only regarding LOS / NLOS situation in the vertical plane between transmitter and each receiver point.

Different path loss exponents and offsets are considered for LOS / NLOS. The attenuations of the walls are not considered during the computation. Therefore, this model computes the path loss similar to the free space loss with adaptable exponent and offset for line-of sight (LOS) and non-line-of-sight (NLOS) areas. Herewith it assumes that the path loss depends only on the distance d with a specific attenuation coefficient n and the offset lc.

(1) l M F =   n 10 log 4 π d λ + l c

According to this simple approach the prediction results are fairly inaccurate and only suited for a rough estimation.

Click Project > Edit Project Parameter and click the Computation tab.

Figure 1. Propagation result in the 3D view.

To calibrate this model with measurement data the exponents and the offsets to be used for this model can be specified by using the Settings button. For LOS situations the values for n are in the range between 2.0 and 2.8, in NLOS scenarios values up to 4.0 are possible. The offsets are applied to field strength / power / neg. path loss results (larger offsets mean more optimistic results).

Figure 2. The Parameter: One Slope Model dialog.