Clarke's classical model of mobile radio reception assumes isotropic rich scattering around the mobile receiver antenna. The assumption of isotropic scattering is valid only in limited circumstances. In this contribution we develop a generalized Clarke model, which is applicable to mobile radio reception in general scattering environments. We give expressions for the autocorrelation and power spectral density (PSD) of the channel fading process and demonstrate the generality of the model by applying it to different non-isotropic scattering scenarios. Using the generalized model, we analyze the effect of mobile direction of travel and the non-isotropicity on the statistics of the channel fading process. We also show that if the mobile direction of travel is equiprobable in all directions, a non-isotropic scattering environment on average is as good as an isotropic scattering environment.

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Scattering encountered in many wireless communications scenarios is non-isotropic. Assumption of uniform distribution of Power Azimuth Spectrum (PAS) in a non-isotropic scattering environment introduces significant errors on the second order channel statistics which are the basis for the estimation of some important receiver parameters. Moreover, there are certain applications in communications that rely solely on the statistics of the channel. In this contribution, we use the wellknown Jacobi-Anger expansion of the plane wave to develop a discrete-time generalized Rayleigh fading channel model that models the statistics of the channel in closed form in general, nonisotropic and isotropic, scattering environments. We compare the statistics of the channel for different commonly used non-isotropic scattering distributions, first, on the basis of autocorrelation, and, then, using a function (mutual information) of the correlational properties of the channel. In the latter case, through simulations, we observe the effect of varying different parameters like the angular spread, the block length of transmission and the mobile velocity which gives some interesting insights.

Abstract-The classical Clarke model of mobile radio reception assumes a constant mobile velocity. We, in this paper, relax the assumption of constant mobile velocity to allow the mobile to have constant acceleration and derive expression for the non-stationary autocorrelation function of the channel process in general 2-dimensional (2D) scattering environments. Under suitable assumptions, an expression for Wigner-Ville spectrum is obtained in isotropic scattering environment which suggests that the Wigner-Ville spectrum is a natural generalization of the Clarke's model to constant mobile acceleration scenario.

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