Magdy F. Iskander
A wide variety of radio propagation models for different wireless services that specifically address varying propagation environments and operating frequency bands are generally known (Pahlavan et al. 1995; Jakes 1974). A large number of propagation prediction models have been developed for various terrain irregularities, tunnels, urban streets and buildings, earth curvature, etc. (E. Vehicular Technology Society 1988; Lee 1989; Parsons et al. 1998). For propagation models addressing satellite communications systems, on the other hand, different types of issues including rain attenuation and atmospheric effects are routinely considered (Dissanayake et al. 1997). The level of sophistication in the development of these models also depends on the longevity of the related technology. For example, the importance of developing propagation models suitable for satellite communications, and in particular the development of reliable models for rain attenuation and other atmospheric impairments along earth-satellite paths, has long been recognized; and extensive research activities have been focused on addressing these effects (Capsoni et al. 1987; Stutzman 1995). With the development of new satellite services incorporating very small aperture terminals (VSAT) and ultra small aperture terminals (USAT) in the Ka-band (20-30 GHz) frequencies, more recent research efforts in this area have focused on refining available propagation models to account for and accurately predict the total propagation link margin that includes other propagation impairments such as cloud attenuation, gaseous absorption, and low-angle fading. European and U.S. agencies are compiling several databases that should enable the evaluation of propagation models that attempt to combine different propagation effects (Dissanayake 1997). These research activities and available results should also be useful in addressing the needs of new emerging high frequency and point to multi-point terrestrial wireless communication systems such as the local multi-point and point-to-point distribution systems (LMDS and PPDS, respectively) and wireless local area networks.
With the phenomenal growth in mobile and portable terrestrial wireless communication systems, and due to their potential utilization in a wide variety of high data rate and multimedia services, higher frequency bands need to be allocated and utilized for these services. New devices and components for high frequency and millimeter wave integrated front-end receivers are being developed, active and low cost phased array antennas are being designed, and advanced software issues in coding, modulation, switching, and networking are being researched and developed. In addition to these rather obvious advances that are needed to enable the next generation wireless technology, developing new and more computationally efficient propagation models is also essential. Development of reliable propagation models and the availability of the associated simulation software tools would be absolutely necessary for the successful implementation of the future terrestrial wireless systems and also for their integration with other technologies including the satellite, LMDS, and the wireline based services. Accurate propagation models will help in using the rather congested frequency spectrum more efficiently, in planning more effective radio networks, and in implementing cost effective solutions for a desirable and user specific communication coverage pattern.