Optimum Power Control for Fading CDMA with Deterministic Sequences
Onur Kaya, Şennur Ulukuş · 2002
We characterize the optimum power allocation policy that maximizes the information theoretic sum capacity of a code division multiple access (CDMA) system where the users are assigned arbitrary signature sequences in a frequency flat fading environment. We provide an iterative waterfilling algorithm to obtain the powers of all users at all channel fade levels, and prove its convergence to the optimum solution. Under certain mild conditions on the signature sequences, the optimum power allocation dictates that more than one user transmit simultaneously in some non-zero probability region of the space of all channel states. We identify these conditions, and provide an upper bound on the maximum number of users that can transmit simultaneously at any given time. 1