Computationally Efficient Algorithm For Sub-carrier, Bit, and Power Allocation

Abstract

An adaptive subcarrier assignment and bit loading strategy for multiple users in an orthogonal-frequency division multiplexing-based wireless system is considered. Based on the channel condition for each user, the algorithm minimizes the system total transmit power while satisfying each user's transmission rate constraint under a given bit error rate requirement. The minimization is attained by an optimal weighting for each user during the compete for the subcarrier. The problem of joint allocation is divided into two steps. First subcarrier assignment based on channel condition is performed. After that, the modulation level on each subcarrier is determined. Both the carrier assignment and bit allocation are iteratively adjusted by properly adjusting the weighting factor for each user until all the transmit constraints for all the users are satisfied. The purpose of such iteration is to ensure that total system power is minimized. During the iterative search, efficient estimation of the weighting factor is proposed.