A FAST ANALYTICAL METHOD FOR OPTIMUM INTEGER BIT LOADING IN OFDM SYSTEMS

Abstract

In this paper the problem of minimizing the total transmitting power subject to a fixedtotal bit rate in OFDM systems is considered. Upper bounds on transmitting power and bit rate ofeach subcarrier can also be taken into account. In practice, the number of bits of each subcarriershould be integer and nonnegative. In this paper an analytical optimal solution is derived for thecase of assuming the bits to be integer. Then, the solution is extended for the case of nonnegativeinteger bits and the cases in which we have constraints on the maximum power and bit rate of eachsubcarrier. In an OFDM system with N subcarriers the complexity of computing the proposedanalytical solution is O(N) which is lower than the computational complexity of existingalgorithms. In addition to the mathematical proofs, computer simulations confirm that theproposed analytical solution is optimal and faster than the existing algorithms.