Mc/ds-cdma versus Sc/ds-cdma in Mobile Radio: Spectral Efficiency Approach

The spectral efficiency of a multicarrier direct-sequence code-division multiple-access (MC/DS-CDMA) cellular system operating in a mobile radio environment with Rayleigh fading, is investigated. In this work, spectral efficiency is evaluated in terms of channel capacity (in the Shannon sense) per user, estimated in an average sense. It is analytically shown that, under normalized conditions and assuming a static model of operation, MC/DS-CDMA spectral efficiency, on downlink, is higher than that of single-carrier direct-sequence code-division multiple-access (SC/DS-CDMA). This result is justified by the combination of path-diversity reception, achieved by a conventional coherent maximal-ratio combining (MRC) RAKE receiver, and physical frequency diversity potential provided, in a fading environment, by frequency-division multiplexing on a set of orthogonal carriers. It is shown that the increase of the carrier frequencies, in the MC/DS-CDMA cellular system, leads to a respective improvement of the spectral efficiency achieved. Key-Words:-Spectral efficiency, multicarrier modulation, code-division multiple access, cellular systems.