Spectral Precoding for OFDM without Guard Interval Insertion

In this paper, the orthogonal frequency-division multiplexing signal without inserting guard subintervals (NG-OFDM) is considered and combined with spectral precoding to achieve high spectrum compactness. In order to reject interblock interference among received NG-OFDM blocks over dispersive channels, a guard subinterval in each received block is removed at the receiver and this turns the resultant receiver to be nonorthogonal over subcarrier subchannels and thus subject to artificial intercarrier interference. It is shown that the proposed spectrally precoded NG-OFDM system can provide channel capacity very close to nonprecoded and spectrally precoded OFDM using cyclic prefix (CP-OFDM) when the removal guard ratio is small, and much higher channel capacity per unit bandwidth than spectrally precoded CP- OFDM conveying the same data rate provided that a small out-of-band power proportion is required.