Optimization of the OFDM prototype waveform for highly time and frequency dispersive channels through a maximization of the SIR

Recently, OFDM has been adopted in many communication and broadcasting systems. For these OFDM systems, the prototype waveform must guarantee orthogonality with its time and frequency shifted versions. In practice, the time-frequency dispersion of the radio mobile channel destroys this orthogonality, causing inter-symbol and inter-channel interference. In order to alleviate these interferences, a good localization of the prototype waveform is required. Unfortunately, this requirement cannot be guaranteed by conventional OFDM systems, which use rectangular waveforms with a bad frequency localization. In this paper, we carry an optimization of the OFDM system waveform for highly time and frequency dispersive channels. The optimized waveform is searched as a linear combination of several of the most localized Hermite functions. The optimization is done by maximizing the signal-to-interference ratio.