Pulse design for maximizing SIR in partially equalized OFDM/BFDM systems

Mobile wave propagation undergoes severe distortions caused by inter symbol interference (ISI) and inter carrier interference (ICI), which are due to multipath and high mobility. OFDM/BFDM techniques have a good ability to overcome ISI limiting quality effects whereas ICI can be increased for severe Doppler spreading. In this paper, we study the use of well localized time-frequency pulse shaping to reduce the effect of these interferences. The linear combination of several of the first most localized Hermite waveforms enables the design of an optimal transmit/receive pulse. By subtracting the interferences coming from some neighborhood symbols that will be treated by a partial equalization scheme, considerable gain in the signal to interference ratio (SIR) is achieved. With a reduced complexity OFDM system, partial equalization of the interference coming from 2-frequency neighbor symbols results in a gain of about 20 dB in the SIR, at high spectral efficiency and severe channel spreading. More gain in the desired ratio is achieved by optimizing the time-frequency spacing of the underlying lattice.

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