EFFECTS OF RADIO PROPAGATION PATH LOSS ON DS-CDMA CELLULAR FREQUENCY REUSE EFFICIENCY FOR THE REVERSE CHANNEL

Analysis techniques that quantitatively describe the impact of propagation path loss and user distributions on wireless direct-sequence code-division multiple-access (DS-CDMA) spread spectrum systems are presented. First, conventional terrestrial propagation models which assume a d4 path loss law are shown to poorly describe modern cellular and personal communication system channels. Then, using both a two-ray propagation model and path loss models derived from field measurements, we analyze the impact of path loss on the frequency reuse efficiency of DS-CDMA cellular radio systems. Analysis is carried out for the reverse (subscriber-to-base) channel using a simple geometric modeling technique for the spatial location of cells, and inherent to the geometry is the ability to easily incorporate nonuniform spatial distributions of users and multiple layers of surrounding cells throughout the system. Our analysis shows the frequency reuse efficiency (F) of the reverse channel with a single ring of adjacent cells can vary between a maximum of 71% in d4 channels with a favorable distribution of users, to a minimum of 33% in d2 channels with a worst case user distribution. For three rings of adjacent users, F drops to 58% for the best d4 case, and 16 % for the worst d2 case. Using the two-ray model, we show that F can vary over a wide range of values due to the fine structure of propagation path loss. The analysis techniques presented here can be extended to incorporate site-specific propagation data.