Spectral efficiency for FDMA and DS-CDMA in cellular systems

The spectral efficiency achieved by FDMA and DS-CDMA schemes during cellular operation in an additive white Gaussian noise (AWGN) and a Rayleigh fading environment is evaluated in terms of the assigned downlink and uplink channel capacity (in the Shannon sense). In particular, in Rayleigh fading, channel capacity is estimated in an average sense considering the inherent diversity potential that each scheme provides as a physical means for fading mitigation. However, in contrast to cellular FDMA, multiple-access and co-channel interference that are present in cellular DS-CDMA cause substantial spectral efficiency reduction. Hence, it is analytically shown that, under normalized conditions, FDMA spectral efficiency is always higher than that of DS-CDMA regardless the fact that DS-CDMA systems reduce the channel capacity degradation that is caused by signal fading.