Power control and transmit diversity in multipath CDMA systems

We integrate power control with transmit diversity in the down-link to increase the capacity of third-generation (3-G) CDMA systems. First, we investigate the system performance by using power control with the conventional receiver. Here our goal is to minimize the total transmitted power by the system subject to the signal-to-interference ratio (SIR) requirements of users. We select the antenna weights of a user in such a way that the received power of that user is maximized. It is observed that the conventional system fails quickly to meet the SIR requirements as the number of users grows. To handle this situation, we propose an interference suppression technique with power control in the down-link. Under the proposed scheme, a base station simply employs the same weights at all the antennas and a user requires to know only its spreading sequences. In both cases, the power control algorithms are iterative, distributed and asynchronous. Convergence of those iterative algorithms have been shown for a multi-cell CDMA system. An experimental study is performed to compare the performance of both power control algorithms.