Information-Theoretic Comparison of Channel Capacity for FDMA and DS-CDMA in a Rayleigh Fading Environment

In this paper, a comparative estimate of the channel capacity assigned to each user for frequencydivision multiple-access (FDMA) and direct-sequence code-division multiple-access (DS-CDMA) schemes operating in a Rayleigh fading channel is presented. Then, the achievable channel capacity per user (in the Shannon sense) is estimated in an average sense considering the inherent diversity potential that both schemes provide in a Rayleigh fading channel. The non-equal user rate for the DS-CDMA case is studied, considering the ratio of two neighboring user channel capacities. Hence, it is shown that, in contrast to the equal user rate, for non-equal user rate case in DS-CDMA and under normalized conditions, the average channel capacity per user, in FDMA, is higher than that of DS-CDMA and this result is quantitatively evaluated in terms of a defined average capacity gain factor. Key-Words:Channel capacity, code-division multiple-access, frequency-division multiple-access, Rayleigh fading.