Optimum power allocation and control for OFDM in multiple access channels

This paper considers optimal power allocation in a multiple access channel, where multiuser orthogonal frequency division multiplexing is employed. We propose a power allocation algorithm for minimizing the sum of transmitted powers, when each of users in a multiple access cell has a desired data rate. The optimal power allocation can be found very efficiently by an iterative algorithm. The minimum sum power and the convergence behavior turn out to be strongly dependent on the decoding order of the users. We describe the best ordering scheme that provides the global minimum of the sum power. To cope with channel variation in a slowly time-varying channel, we also propose a power control algorithm that modifies the allocated power. In short, the power allocation algorithm assigns optimal power to each user for the initial channel information, and the power control algorithm tracks the channel variation after the initial power allocation.