Capacity limitations due to adjacent cell dissimilar technologies

A direct sequence spread spectrum code division multiple access (CDMA) communication system for cellular or PCN applications should be designed to use the entire bandwidth allocated. In this way the peak power spectral density is minimized. However, some CDMA systems have been designed to have a bandwidth which is much less than the allocated bandwidth. Such narrowband CDMA (N-CDMA) systems lack the LPI characteristics of spread spectrum. The authors address the mutual interference caused by the coexistence of N-CDMA and existing narrowband cellular telephone technologies (AMPS FDMA or TDMA). It is shown that when adjacent service areas are using AMPS or TDMA a dead zone of up to two cells is required before N-CDMA can be deployed. The resulting capacity of the N-CDMA service area is lessened to an extent dependent upon the service area geometry. The dead zone can be extensive enough where the N-CDMA would yield only marginal capacity improvement over AMPS and TDMA. Furthermore, significantly higher N-CDMA mobile transmit power would be required than would be true without adjacent cell interference