TABLE OF CONTENTS As might be expected from the discussions in preceding chapters, the propagation-path loss for hilly areas is greater than that for nonhilly areas. It therefore follows that the methods used to predict the signal strength of received transmissions are more difficult in hilly areas than in nonhilly areas [1]. The various shapes encountered in the contour of hilly terrain are unpredictably irregular. Often, the direct line-of-sight path is obstructed by the tops of intervening hills. To properly analyze the path loss in hilly areas, it is necessary to classify hilly terrain into either one of two classic types that are described in terms of the physical characteristics of the propagation path [1]. Type 1 is the line-of-sight path over hilly terrain where surface irregularities do not obstruct the direct signal path. Type 2 is the out-of-sight path over hilly terrain where surface irregularities project into, and therefore obstruct, the direct signal path. In type 2, diffraction loss due to the obstruction of hilltops (the out-of-sight case) must be considered. A formula for approximating the diffraction-loss prediction, and other special considerations for predicting the path loss over hilly terrain, are discussed in subsequent paragraphs.
Figure 4.1 illustrates a simple model for predicting propagation-path loss over flat, unobstructed terrain. As was shown in Eq. (3.46), a base-station antenna-height gain factor of 6 dB per octave can be predicted for this model situation. Measured data recorded in flat suburban and urban areas support predictions based on...
