Impact of Direct Sequence Spreading on the Channel Capacity of Binary Non-Gaussian CDMA

Multi-user interference (MUI) severely degrades performance in wireless CDMA transmission. Due to the central limit theorem, such interference is usually (near) Gaussian distributed (Vembu and Viterbi, 1996; and Verdu, 1998). Recently, it has been shown that for frequency/time hopping CDMA with single-user demodulation/decoding at the receiver, one can intentionally create appropriate non-Gaussian multi-user interference that allows increasing the capacity up to five times when compared to CDMA with Gaussian MUI (Garba and Bajcsy, 2006 and 2008). This paper considers the impact of direct sequence (DS) spreading on the capacity increases for CDMA with nonGaussian MUI. First, appropriate channel models are constructed for non-Gaussian DS CDMA when traditional single-user matched filter demodulator is used as well as when the optimal single-user CDMA receiver is used. The obtained numerical capacity results show that the nonGaussian CDMA capacity gains can be realized with appropriate CDMA receiver.