Radio transmissions in real network environments are affected by various types of disturbance. On the way from sender to receiver, the signal is delayed by up to 100 microseconds due to its finite propagation speed. Radio waves that reflect at obstacles reach the receiver via paths of different delay, blurring the incoming data bits (delay spread) and causing rapidly varying power fluctuations when the receiver or transmitter is moving (multipath fading).

Motion furthermore causes Doppler shift and - in the pre-sence of reflections - Doppler spread of the carrier frequency, offsetting the sender and receiver bands and dispersing the power outside the band. Finally, due to the low power levels at the receiver, the signal is sensitive to thermal noise and interference by other transmitters.

Reliable and repeatable radio performance tests require a controlled radio environment that can only be achieved in a laboratory setup. 3GPP [1] and WiMax Forum [2] have specified a set of channel models - corresponding models are being specified by 3GPP2 [3] as well - primarily dealing with multi-path fading. Investigating the impact of multipath is particularly important for antenna diversity systems (MIMO, SIMO) that are designed to counter just this effect.