Multipath Propagation in Indoor Environments

Mitigate multipath effects, inaccuracies in the building database and time-variant obstacles for the prediction of indoor wave propagation.

In indoor scenarios, there are many possible rays between a transmitter and a receiver, as shown in Figure 1. On the one hand, the computation of all of these rays is time-consuming, on the other hand, these rays are not time-invariant and depend on the accuracy of the database.

If, for example, a door is opened, the determined rays are no longer valid, and the predicted field strength is wrong. Also, people and furniture are time-variant obstacles and can not be included in the database of the building. The second problem is if the positions of the walls and edges are not known exactly (they may vary inside a specified area) some of the determined rays do not reach the receiver. In most databases, the positions of the walls are not known as precisely as they should be for a ray-tracing algorithm.

Therefore a new approach for the prediction of the field strength should not rely on the knowledge of all possible rays between a transmitter and a receiver. Only the representative paths should be determined, and they should be independent of the accuracy of the database and of the time-variant effects. While these effects influence the wave propagation, there are many rays passing the same rooms between the transmitter and the receiver with different reflection and diffraction points. Consequently, changes in these points of interaction do not influence the received power.

Figure 1. Multipath propagation in an indoor scenario and dominant paths.

It is only necessary to know which rooms are passed by the rays and which walls are penetrated. The wave guiding by multiple reflections must not be determined by the computation of all possible reflection and diffraction points. It should be determined independently of the different points of interaction. All these aspects are included in the approach with dominant paths which is described in the next section.