FTN signaling improves data rates differently across signal types
FTN Signaling: Spectral Efficiency from BPSK to 16-QAM
Information Theory
Summary
Sending digital signals closer together than usual can increase how much information fits in the same space, but it creates interference between signals. The authors studied this technique called Faster-than-Nyquist (FTN) signaling with different types of digital signals, from simple ones like BPSK to more complex like 16-QAM. They found simpler signals can be packed more tightly to boost data rates, while more complex signals work best when sent closer to normal spacing. This means the choice of signal type matters when trying to speed up data transmission using FTN methods.
What this means in practice
- •For wireless communications engineers: Optimize wireless link configurations by selecting proper signal constellations and time spacing to maximize data throughput under power constraints.
- •For satellite system designers: Improve spectral efficiency of satellite communication channels by tuning FTN parameters according to symbol constellation complexity to reduce bandwidth use.
Authors
Emre Cerci, Adem Cicek, Melda Yuksel, Gokhan M. Guvensen, Enver Cavus, Yaser Dalveren, Halim Yanikomeroglu
Abstract
Faster-than-Nyquist (FTN) signaling can improve spectral efficiency by transmitting symbols closer together than the Nyquist limit, at the cost of additional inter-symbol interference (ISI). In this letter, we study the finite-alphabet symbol-wise achievable information rate (AIR) of FTN signaling for BPSK, QPSK, and 16-QAM under a transmit-power constraint and a common minimum mean square error (MMSE) channel-shortening (CS) detection framework, cross-validated for BPSK against an independent reduced-state Ungerboeck Bahl-Cocke-Jelinek-Raviv (BCJR) benchmark. Our results show a clear trend. Lower-order constellations can benefit from more aggressive time acceleration, while higher-order constellations become less tolerant of acceleration and achieve their best spectral efficiency closer to the Nyquist limit. At a reference signal-to-noise ratio (SNR) of 6 dB the optimum acceleration factor shifts from $τ^\star\approx0.65$ for BPSK to 0.75 for QPSK and 0.90 for 16-QAM. We further show that this trend is preserved in coded systems and remains robust to the detector memory. The impact of FTN operation on the instantaneous-to-average power ratio (IAPR) is also examined. Overall, the results highlight how constellation order should be considered when selecting the operating point for FTN signaling.