Design and performance of fading insensitive orthogonal frequency division multiplexing (OFDM) using polyphase filtering techniques

We describe a modification of orthogonal frequency division multiplexing (OFDM) which ameliorates system performance degradation due to fast fading multipath channels. This technique continues to employ the fast Fourier transform (FFT) for efficient modulation and demodulation of the contiguous subcarriers. It differs from conventional OFDM by the use of time domain shaping and duration extension to reduce the spectral sidelobes of the orthogonal signal set. The extended waveshape duration causes significant but known intersymbol interference (ISI) which is removed after the matched filtering process by a post-processing equalizer. The combined process of spectral shaping at the modulator and matched filtering and equalization at the receiver exhibits significant but known adjacent channel interference (ACI) which is removed by cross coupled canceling filters.