Spectral Efficiency Comparison of TDMA and DS-CDMA in Cellular Mobile Radio Systems

A comparison of spectral efficiency achieved by time-division multiple-access (TDMA) and directsequence code-division multiple-access (DS-CDMA) systems, during cellular operation in a Rayleigh fading environment, is presented in this paper. Spectral efficiency, is evaluated in terms of the theoretically assigned downlink channel capacity per user (in the Shannon sense). In particular, in Rayleigh fading, channel capacity is estimated in an average sense considering the inherently offered diversity potential as a physical means for fading mitigation. In addition, both systems are assumed to allocate a fixed number of simultaneously transmitting users so that the total capacity of each system to be equally shared among its users. Hence, it is analytically shown that, under normalised conditions, the spectral efficiency of DS-CDMA is higher than that of TDMA regardless the fact that, in contrast to cellular TDMA, in cellular operation of DS-CDMA spectral efficiency is limited by multiple-access interference (MAI). Key-Words: Spectral efficiency, TDMA, DS-CDMA, Rayleigh fading.