Frequency-Shift Filtering for OFDM Systems and Its Performance Analysis

Orthogonal frequency division multiplexing (OFDM) technique has been widely used in high data rate wireless applications, but it suffers performance degradation at low signal-to-noise (SNR) regions due to the impairments caused by noise-induced channel estimation errors. In this article, we propose to use frequency-shift (FRESH) filtering technique to exploit temporal and spectral correlation of the OFDM signals for noise reduction purpose. A closed form time-varying minimum mean squared error (MMSE) expression has been derived to analyze the performance of FRESH filtering under additive white Gaussian noise (AWGN) and Rayleigh fading channels. The MMSE analysis carried out here can be a reference for the design of practical OFDM systems. In addition, theoretical SNR is analyzed in this article to show the performance gain achieved by FRESH filtering. The numerical results verify that the maximum SNR improvements offered by FRESH filtering are over 0.6 dB and 1.6 dB under AWGN and Rayleigh fading channels, respectively.