# COST-Multi-Wall Model (MW)

The multi-wall model gives the path loss as the free space loss including losses introduced by the walls and floors in the direct path between transmitter and receiver.

The multi-wall model gives the path loss as the free space loss including losses introduced by the walls and floors in the direct path between transmitter and receiver (see Figure 1). It has been observed that the total floor loss is a function of the number of penetrated floors. This characteristic is taken into account by introducing an additional empirical correction factor.

The individual penetration losses for the walls (depending on their material parameters) are considered for the prediction of the path loss. Therefore the multi-wall model can be expressed as follows:

where

${l}_{FS}$ = free space loss between transmitter and receiver,

${l}_{c}$ = constant loss,

${k}_{\mathrm{wi}}$ = number of penetrated walls of type i,

${k}_{f}$ = number of penetrated floors,

${l}_{\mathrm{wi}}$ = loss of wall type i,

${l}_{f}$ = loss between adjacent floors,

${N}_{}$ = number of different wall types.

It is important to note that the loss factors in the formula are not physical wall losses but model coefficients which are optimized with the measured path loss data. Consequently, the loss factors implicitly include the effect of furniture. This model has a low dependency on the database accuracy and because of this simple approach a very short computation time. However, wave guiding effects are not considered with this model leading to a moderate accuracy level.

No preprocessing of the building data is needed for the computation of the prediction, and no settings have to be changed for this prediction model.