Near-Optimal Pulse Design for Pilot-Aided Timing Estimation in Faster-than-Nyquist Systems

Faster-than-Nyquist (FTN) signaling is a promising strategy to achieve high spectral efficiency at fixed constellation size, notably over power-constrained channels. However, various traditional synchronization techniques cannot be reused in presence of FTN-induced intersymbol-interference. In this paper, we focus on timing synchronization in a pilot-aided scenario, where both data and pilots are transmitted at an FTN rate. We propose a density-dependent and near-optimal pulse design with respect to the Cramér-Rao lower bound (CRB), under bandwidth and energy constraints. We show the benefits of an FTN-specific pulse design compared to conventional root-raised cosine filters; we also discuss the performance/complexity tradeoff of the proposed solutions. Our results may be of interest in high-throughput systems where timing accuracy is essential (e.g., satellite communications).