Terrestrial wireless channel modeling

An increasing number of prediction tools is available to compute coverage areas for terrestrial wireless information systems using the VHF/UHF frequency band. Accurate digital terrain data files are more often required and easily available. However, for broadband applications, a comprehensive characterization of the transmission channel may be needed. The paper proposes a method based on a parabolic equation (PE) propagation algorithm to compute the complex impulse response of wireless channels. A full-wave method is used instead of asymptotic algorithms because the last are inappropriate for terrestrial UHF/VHF paths, where, in comparison with the wavelength, scatterers and diffracting obstacles are often close to each other and to the ground. The PE method is limited because horizontal scattering and diffraction, as well as depolarization, cannot be taken into account because of its 2D nature. We obtained our results in the following way. First, the propagation algorithm gives the complex signal (amplitude and phase) at the receiver in CW operation for several values of frequency (i.e. sampled values of the transfer function). The impulse response of the determinist channel is then obtained after FFT computing. This approach can be extended to stochastic channels as follows: the described steps are repeated for a number of possible implementations of the channel (Monte Carlo drawing); full statistical characterization is then obtained taking into account a possible additive noise. We show some comparisons between computed results and experimental data obtained with a vector-type Cox sounder for terrestrial VHF links located in rural or urban areas.