Fast Optimal Bit and Power Allocation Based on the Lagrangian Method for OFDM Systems

This paper examines the bit and power allocation problem for orthogonal frequency division multiplexing systems in which the overall transmission power is minimized by constraining the fixed data rate and bit error rate. To provide the optimal allocation with less computational complexity, we propose new bit and power allocation schemes based on the Lagrangian method. Firstly, we propose an initial search range of the bisection search method to find the optimal Lagrangian multiplier efficiently. The simulation results verify that the proposed initial search range guarantees the optimal solution with less computational complexity. Secondly, a new iterative search method for the optimal Lagrangian multiplier is proposed using Newton’s search method. The simulation results demonstrate that the proposed scheme has significant computational advantages over the conventional algorithms while providing optimal performance. key words: multi-carrier, OFDM, bit and power allocation, adaptive modulation