Power control and spreading sequence allocation in a CDMA forward link

In this paper, we consider power control and sequence allocation to meet signal-to-interference ratio (SIR) targets for users in a code-division multiple-access (CDMA) forward link. Particular attention is given to the case when the number of users is larger than the spreading gain. Users in the system are classified into two classes, namely, overfaded users and nonoverfaded users, according to their effective noise densities and SIR targets. Overfaded users are allocated orthogonal channels, and nonoverfaded users share the remaining channels. The spreading sequences allocated belong to the class of sequences which minimize the extended total squared correlation (ETSC). Power efficiency of this allocation scheme is examined through comparison to Lagrangian-based searching results. The proposed allocation scheme is shown to be effective under most channel conditions. Two adaptive algorithms are presented to construct the spreading sequences iteratively. One assumes fixed power allocation and adapts the sequences only, and the other adapts both transmission powers and sequences simultaneously. Convergence of the two adaptive algorithms and the performance of joint transmitter-receiver adaptation with imperfect real-time channel parameters estimation are examined via computer simulations.