Spectrally Precoded OFDM Without Guard Insertion

Orthogonal frequency-division multiplexing (OFDM) signaling format is commonly associated with guard subintervals in order to reject intersymbol interference (ISI) and enable simple one-tap frequency-domain equalization at the receiver when received over dispersive channels. Despite the advantage, the guard subintevals expand the width of spectrum main-lobe, which is proportional to the ratio of guard subinterval length to useful data subinterval length, and thus trade off the spectral efficiency significantly. In this paper, the nonguarded OFDM (NG-OFDM) signaling format which is exactly OFDM without inserting guard subintervals is considered in order to save mainlobe width, and combined with spectral precoding to further suppress spectrum sidelobes. In particular, spectral precoders are designed for NG-OFDM to provide extremely compact signal spectrum while maintaining low peak-to-average power ratio (PAPR) in the transmitted waveform. In order to reject ISI among different NG-OFDM blocks, guard subintervals are removed at the conventional OFDM receiver and this turns the resultant receiver to be nonorthogonal over subcarrier subchannels, thus resulting in artificial intercarrier interference (ICI). Based on our analysis, the capacity achieved by this NG-OFDM system can remain unchanged but with higher spectral efficiency when channel length is small enough. LMMSE-FDE and hybrid interference cancellation (HIC) with guard removal receiver architectures are also proposed for elminate the severe interference. Particularly, in heavy delay spread multipath fading channel, reduced-PAPR orthogonally coded NG-OFDM with guard removal and LMMSE-FDE can outperform nonprecoded CP-OFDM and nonprecoded NG-OFDM.