Experimental Analysis of the Joint Statistical Properties of Azimuth Spread, Delay Spread, and Shadow Fading

It is well known from numerous studies that the performance of terrestrial cellular systems is highly dependent on the radio propagation conditions. To give a few examples, the temporal dispersion in the radio channel provides frequency diversity for wideband systems such as WCDMA (Wideband Code Division Multiple Access), since the degree of frequency selectivity is related to the delay spread compared to the inverse of the signal bandwidth. Similarly, azimuthal dispersion affects the performance of advanced antenna array systems, as it determines the correlation between spatially separated antennas, and consequently the ability to mitigate fast fading by means of antenna diversity techniques. The azimuthal dispersion also impacts the optimal beam width of advanced antenna array systems using the spatial filtering technique. Empirical results characterizing the joint statistical properties of the local azimuth spread, the local delay spread, and the shadow (slow) fading component have been investigated. Measurement data from typical urban, bad urban, and sub urban environments have been analysed. It is found that a Log-Normal distribution accurately fits the distribution function of all the investigated parameters. The spatial auto-correlation function of both azimuth spread, delay spread, and shadow fading can be modelled with an exponential decay function. However, for sub urban environments the spatial auto-correlation function is better characterized by a composite of two exponential decaying functions. A positive cross-correlation is found between the azimuth spread and the delay spread, while both parameters are negatively correlated with shadow fading. All essential parameters required for the implementation of a simulation model considering the joint statistical properties of the azimuth spread, the delay spread, and shadow fading have been provided [Algans, 2002]. The results of this study provide sufficient information to jointly model the random behaviour of the local AS, the local DS, and shadow-fading component. This can help improve the reliability of e.g. the output of Monte-Carlo network simulations of modern wideband mobile communication systems with BS's deploying advanced antenna array systems. Furthermore, it can serve as useful a priory knowledge for planning and dimensioning purposes. (Albert Algans, Preben E. Mogensen; Klaus I. Pedersen, Nokia)