Factors influencing outdoor to indoor radio wave propagation

An important requirement from mobile radio systems is the provision of reliable services to the increasing number of users across the outdoor to indoor interface. To achieve this, and at the same time reduce the possibility of interference, the radio network has to be carefully planned and optimised. For this reason, the radio propagation modeller has to appreciate the conditions which can influence the accuracy of modelling predictions or even the practical measurements which are carried out for planning purposes. The paper starts by briefly describing the different factors which have been reported and can influence outdoor to indoor propagation, highlighting some apparently contradictory observations obtained through measurements. Some researchers have suggested that building penetration loss decreases with frequency over a certain range, while specific losses through materials increase with frequency. We try to explain the reasons for those results. Findings have been obtained through simulation. These include the non-linear variation of material loss with material thickness or frequency and the average predicted penetration loss versus frequency for a windowed wall. Detailed explanations are given why these effects take place, providing a possible answer on the contradicting observations.