Performance of Low-Complexity Uniform Power Loading OFDM Systems With Reduced Feedback Over Rayleigh Fading Channels

In this paper, we consider a low-complexity uniform power loading scheme for orthogonal frequency division multiplexing (OFDM) systems with two reduced feedback mechanisms and analyze its performance over Rayleigh fading channels. In the first feedback mechanism, the receiver feeds back to the transmitter the channel gains and the indices of the best M subchannels; while for the second feedback mechanism, the receiver feeds back only the indices of the best M subchannels. The available power budget is equally distributed over the best M subchannels for both feedback mechanisms. We derive closed-form expressions for the achievable capacity and an upper bound on the outage capacity of the first and second mechanisms, respectively. A simple elimination algorithm is provided to find the optimal number of best subchannels M that maximizes the achievable capacity. Numerical results show the dependence of the optimal number of the best subchannels M on the system parameters. Additionally, the presented results interestingly show that the low-complexity uniform power loading scheme can achieve up to 98.72% of the channel capacity, obtained using the well-known waterfilling solution, when the optimal value of M is used. Moreover, the uniform power loading scheme can achieve up to 88.86% of the energy efficiency at reduced complexity.