On carrier spacing in multicarrier CDMA systems

This paper considers multicarrier CDMA systems where each user´s data stream is serial to parallel converted to a number of lower rate streams. Each lower rate stream is then spread by a random spreading code with a suitable chip rate before modulating orthogonal carriers. It is shown that, for a fixed system bandwidth and a given number of carriers, them exists an optimal carrier spacing that minimizes the multiple access interference. Numerical examples also show that the multicarrier DS-CDMA system previously proposed by DaSilva and Sousa (1994) performs very close to the multicarrier CDMA system using the optimal carrier spacing.