On Discrete-Time Modeling of Time-Varying WSSUS Fading Channels

The general property of noncommutativity of linear time-varying (LTV) systems has to be considered when a digital transmission system composed of LTV channel and transmit/receive filtering shall be represented in the equivalent discrete-time domain. In this correspondence, we analyze the implications of serially concatenated LTV systems with respect to the discrete-time representation of wide-sense stationary uncorrelated scattering (WSSUS) fading channels. We provide a detailed discussion of the largest tolerable channel Doppler spread (in relation to the system bandwidth) for which the concatenation is commutative in good approximation. In this case, the discrete-time description facilitates an efficient simulation model. The approximation accuracy is quantified by a detailed error analysis and further verified by numerical simulation adopting Universal Mobile Telecommunications System (UMTS) parameters.