Propagation considerations of low power cellular boosters and case histories

Booster site selection often has tighter constraints placed upon it than cell site selection. Low-power 800-MHz cellular boosters usually provide a 250 mW ERP (effective radiated power) and are located several miles from the donor cell site. Two propagation problems must be analyzed, the donor-to-booster path loss and the booster coverage contour. In either case, the typical propagation model (e.g., free-space or Carey curves) may not provide enough accuracy. Free-space path loss assumes at least first Fresnel zone clearance, which often cannot be achieved. This can result in path losses 10 to 15 dB higher than expected and therefore possibly 10 to 15 dB less output from the booster, which could be devastating to its coverage. The path to the mobile is also important, and commonly used cellular propagation models, such as the Carey curves are not always accurate enough. A detailed terrain model, such as Longley-Rice, which can take topography into account, is essential. When this is added to a system engineer´s experience, a realistic coverage contour can be predicted. Several case histories are presented to show how the analysis was performed and how the prediction matched actual measurements