Optimal power control for multiple access channel with peak and average power constraints

In this paper, we study optimal power control for multiple access channel with peak and average power constraints. Perfect channel information is assumed to be available at both the transmitter and the receiver. We characterize the structures of the optimal power control policy and show that the optimal policy allows multiple users to transmit at peak power and at most one user to transmit at an intermediate power level. This is different from the optimal TDMA policy (at most one user is allowed to transmit at any given time) for the case of average power constraint only. We and closed-form expressions for computing the optimal power control policy and the maximal sum capacity. Numerical results indicate that under the peak power constraint, the optimal power control policy still achieves very close to the sum capacity of the multiple access channel with average power constraint only.