Capacity Enhancement of DS-CDMA Downlink through Multicarrier with Frequency Overlapping

Abstract

We present a technique based on the frequency diversity inherent in direct sequence spread spectrum (DS-SS) signals that allows to extend the capacity of CDMA systems based on DS-SS. The proposal makes use of several sets of DS-SS signals modulated by carriers separated by a fraction of the chip rate, so that there is frequency overlap between adjacent sets. The frequency diversity of DS-SS signals allows the use of correlated frequency bands to cancel the inter-set interference. For the case of a frequency separation between the interfering and cancelling components equal to the chip rate, the process is code independent and can therefore be applied in the downlink. Numerical results show that non-negligible bandwidth savings can be achieved at the expense of a small noise penalty.