Comparative estimate of user capacity for FDMA and direct-sequence CDMA in mobile radio

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Abstract
A comparative estimate of the available channel capacity per user for frequencydivision multiple-access (FDMA) and direct-sequence code-division multiple-access (DS-CDMA) systems operating in a Rayleigh fading environment is presented in this paper. In a gaussian noise environment, channel capacity is estimated by the Shannon-Hartley theorem. In mobile radio, where signal fading is a considerable capacity degradation factor, channel capacity can be estimated in an average sense and used as a figure of merit for system operation. The presented analysis is based on the inherent diversity potential that each of these systems offers as a physical means for fading mitigation and leads to the estimation of physical and/or logical channel capacity per user under certain assumptions. It is shown that, in the case of a cooperative DS-CDMA model, the average capacity per user is higher than that of FDMA and a quantitative evaluation of that with respect to the environment type is provided in terms of a defined (average) capacity gain factor.

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