Capacity comparison of single-tone and multitone CDMA systems

Performance of multitone-CDMA communications over multipath fading channels with coherent RAKE reception is studied. A random-delay, two-path, Rayleigh-fading channel model is considered. Bit error probability for maximal ratio combining is derived. Analytical results show that the multiple-access capacity of a multitone-CDMA system, under conditions of equal bandwidth and equal bit transmission rate, is identical to that of a single-tone direct-sequence spread-spectrum system. It indicates that using more subcarriers to increase the processing gain does not achieve a larger capacity.