Spectral efficiency and spectral shaping of faster-than-nyquist signals

Capacity calculations for Faster-than-Nyquist (FTN) signaling are presented. When using root raised cosine (RRC) pulses, the spectral efficiency decreases monotonically with the roll-off factor. When using FTN with RRC pulses, one can increase information rates through spectral shaping. The best spectral shaping under input and output power constraints at the transmit filter is derived. An FTN-OFDM system is developed that implements spectral shaping. Simulations demonstrate the advantages and limitations of the methods.