A comparison between different approaches for fading evaluation in wideband mobile communications

Existing systems, eg., UMTS and HIPERLAN, and others to appear in the future, are wideband ones; hence, the observed short-term fading depths are usually smaller than the ones obtained from the Rayleigh or Ricean distributions. Overestimating short-term fading margins, by considering those distributions, leads to shorter cells, or to higher transmitting powers, thus, higher interference. In this paper, one proposes a simple relationship between the physical and the geometrical environment properties, and the rms delay spread of the propagation channel, therefore, allowing one to use different model for evaluating the fading depth in a given environment. Using the proposed relationship, fading depth results from two different models are compared, and a good agreement is verified. Furthermore, since the presented models account for the influence of system bandwidth, hence, providing more accurate fading margins (e.g., the fading margins for UMTS are usually 2 to 10 dB below the ones obtained from Rayleigh or Ricean distributions), the proposed approach allows a better power budget evaluation, enabling the optimisation of existing networks, and better and less costly radio network planning of future ones.