Conventional bit and power allocation algorithms in multiuser OFDM systems have many problems

including high computational complexity

time consuming

and they did not consider the proportional fairness among users.In this paper

we investigate efficient and linear bit and power allocation algorithms in downlink OFDM transmission.This algorithm ensures the proportional fairness among users to minimize the total transmit power while satisfying the rate requirement and BER constraint of each user.Comparison with computer simulation indicates that our approach results in a more efficient assignment of transmit power and with proportional constraints the capacity is distributed more fairly and rationally（among） users.