An Improved Overloading Scheme for Downlink CDMA
© Vanhaverbeke and Moeneclaey 2005
Received: 24 July 2003
Published: 20 April 2005
An improved overloading scheme is presented for single-user detection in the downlink of multiple-access systems based on OCDMA/OCDMA (O/O). By displacing in time the orthogonal signatures of the two user sets that make up the overloaded system, the cross-correlation between the users of the two sets is reduced. For random O/O with square-root cosine rolloff chip pulses, the multiuser interference can be decreased by up to 50% (depending on the chip pulse bandwidth) as compared to quasiorthogonal sequences (QOS) that are presently part of the downlink standard of Cdma2000. This reduction of the multiuser interference gives rise to an increase of the achievable signal-to-interference-plus-noise ratio for a particular channel load.