Capacity region of power controlled fading CDMA: transmit strategies and convexity issues

In this paper a symbol synchronous CDMA system with processing gain where all the users transmit to a single receiver is considered. The receiver and the transmitter have perfect knowledge of the channel states. The set of long term achievable rates, i.e., the capacity region, for a power controlled scalar multiaccess channel is characterized for fading CDMA. The capacity region of a fading CDMA channel under additive white Gaussian noise, where users have perfect CSI and the powers are allocated as function of the CSI. The capacity region may contain a flat region but it is not strictly convex. The simultaneous transmission region with nonorthogonal signatures implies the sum-capacity, and therefore, a flat region on the capacity boundary exists