Reduced-Overhead Channel Estimation for FTN Signaling via Pilot Superimposition and Spectral Interference Alignment

This paper proposes low-overhead and low-complexity channel estimation (CE) of frequency-domain equalization (FDE)-aided faster-than-Nyquist (FTN) signaling. In the proposed CE scheme, the concept of pilot superimposition is employed, where the FTN block is designed to superimpose pilot symbols with information symbols, thereby eliminating the need for dedicated time and frequency resources or guard bands. Furthermore, interference induced by the pilot superimposition is eliminated by invoking a novel scheme, referred to as spectral interference alignment, where a specially-designed data-dependent sequence is subtracted from the transmitted information symbols to achieve interference-free CE. The theoretical mean-square error (MSE) of the proposed CE is derived, confirming that the MSE is no longer affected by interference from the pilot superimposition. Our performance results demonstrate that the proposed CE achieves lower CE errors, better bit-error rates, higher achievable rate, and spectral efficiency with half of the overhead compared with the conventional benchmark.