In this report. wave propagation inside a perfectly conducting room with two homogeneous dielectric walls has been studied. The thicknesses and losses of the dielectric walls are arbitrary. therefore it is possible to model wave phenomena inside various indoor environments. Green's function technique is used to calculate the electric fields excited by point sources and half wave dipole transmitters. In order to design an optimal receiver, the interaction between the electromagnetic fields and the receiving antenna must be modelled. The Lorentz reciprocity theorem is used to predict the received voltage, which depends on the location of the receiver inside the room. The fluctuations of the received voltages inside the room can be reduced by using diversity techniques. Switching diversity, selection diversity, equal gain combining and maximal ratio combining have been compared to each other. Finally, the signal-to-noise ratio and the bit error rate of a DECT receiver have been presented.