This paper considers a general approach for the computation of all functional characteristics of a probabilistic wireless channel model using a bidirectional parametric description. It is shown that under mild conditions the WSSUS property is valid for these models and explicit relations are derived for the computation of the time-frequency autocorrelation from which one can easily derive the Doppler and delay power spectra. As an illustrative example, we consider the single ring of scatterers channel model. We also briefly mention how all these concepts can be generalized to the MIMO case.

The orthogonal frequency division multiplexing (OFDM) transmission scheme is currently experiencing increased popularity due to advances in very large scale integration technology. It is used for a variety of broadband systems such as asymmetric digital subscriber lines, very-high-speed digital subscriber lines, digital video, and audio broadcasting, and wide local area network standards such as IEEE 802.11a, IEEE 802.11 g, and ETSI Hiperlan/2. However, propagation impairments can cause severe degradation in bit error rates (BER) for coherent detection. We derive a semi-analytical method to evaluate BER of a quadrature phase shift keying (QPSK)-OFDM system in Nakagami, m < 1 fading and additive noise where pilot-assisted linear channel estimation and channel equalization are used. This allows modeling of more severe fading environments than can be depicted by a Rayleigh distribution. Numerical simulations are used to validate the proposed methods. The techniques developed can be applied to other channel estimation techniques, modulation schemes and the performance evaluation of equalized single carrier narrowband systems.

Nakagami fading channels have been used as a very flexible, and fairly accurate approximation of realistic fading in wireless systems [1-3]. In particular, sub-Rayleigh fading, i.e. fading with severity parameter 0.5 ≤ m ≤ 1, describes situation where only a few major scatterers contribute to the signal in the antenna of the receiver, and there is no Line of Sight (LOS) present. Due to a finite spatial correlation of the incident electromagnetic field, and the movement of the vehicle, the fading process possesses certain correlation properties [13], which must be accurately represented when numerical simulation of wireless systems is considered. There are very few algorithms which allow such accurate modelling [3-5]. Most of these algorithm are either based on some numerical evaluation of the parameters of the model [4], or provide an approximation for the resulting correlation function with a fixed uncontrollable error [5]. As a result these models have limiting application in laborious Monte Carlo simulation of the wireless systems. In this paper we suggest a model which allows complete analytical description of the marginal probability density function (PDF) of the envelope and its correlation function. At the same time it provides for an accurate numerical simulation algorithm along with the possibility to derive probability density of any order. In contrast to [4], we provide analytically tractable algorithms which allows the model parameters to be found in closed form. At the same time we avoid the complications related to the representation of a correlation function as a product of two correlation functions [4]. As an example we consider application of the simulation technique suggested to a system with antenna diversity.