ACHIEVING HIGH SPECTRUM COMPACTNESS WITH SPECTRALLY PRECODED NONGUARDED OFDM: ANALYSIS OF CAPACITY AND DATA ESTIMATION

To prevent spectrum extension, spectral precoding is employed in conjunction with nonguarded OFDM (NG-OFDM) signaling formats to achieve high spectrum compactness. NG-OFDM, which is essentially OFDM without guard subintervals, is utilized. It is intended for spectral precoders, specifically for NG-OFDM to minimize spectral side lobes, resulting in a highly compact signal spectrum and a low peak-toaverage power ratio. However, the removal of guard subintervals from each received block introduces non-orthogonality across subcarrier subchannels, leading to intercarrier interference (ICI) caused by intersymbol interference (IBI) among received NG-OFDM blocks over dispersive channels. An analysis is conducted on the estimated LMMSE data and the associated channel capacity. The study demonstrates that the suggested spectrally precoded NG-OFDM (SP-NG-OFDM) system can provide channel capacity similar to both nonprecoded and spectrally precoded OFDM with cyclic prefix (CP-OFDM), particularly when the guard removal ratio is low. Moreover, SP-NG-OFDM offers significantly higher channel capacity per unit bandwidth compared to spectrally precoded CP-OFDM, given a comparable data rate, as long as a small out-of-band power proportion is achieved. The effectiveness of the SP-NG-OFDM receiver in combating ICI and leveraging frequency diversity across dispersive channels is established when a sufficiently modest precoding rate is employed. This is achieved through the utilization of guard removal and LMMSE-FDE (Linear Minimum Mean Square Error-Feedforward Equalization).