An essential hallmark of software for simulations of systems in the field of development of new products is the degree of nearness to reality. In this work the simulation tool SPW by Alta Group has been supplemented with three components, which are necessary to allow the modeling of time-variant indoor radio channels. With the use of the new functions TIME-VARIANT CHANNEL CARRIER & TIMING RECOVERY and QPSK BER ESTIMATOR a plausible and more realistic modeling of the transmission between transmitter and moving receiver is achieved. By exchanging the measured time-variant radio channel which has been used in this paper for a channel model, also predictions of the BER based on the used propagation model are possible.