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

Document Type: Research Paper

Authors

Dept. of Communications and Electronics, School of Electrical and Computer Engineering, Shiraz University, Shiraz, I. R. of Iran

Abstract

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

Keywords