  We identify potential merits of faster-than-Nyquist (FTN) signaling in the
finite blocklength (FBL) regime. A unique aspect of FTN signaling is that it
can increase the blocklength by packing more data symbols within the same time
and frequency to yield strictly higher number of independent signaling
dimensions than that of Nyquist rate signaling. Using the finite-blocklength
information theory, we provide tight bounds on the maximum channel coding rate
(MCCR) of FTN signaling for any finite time-bandwidth product. The merits are
categorized into two operating regions of FTN, i.e., when the time-acceleration
factor of FTN, $\tau$, is above or below a certain threshold $\tau_{0}$. When
$\tau > \tau_{0}$, FTN has both higher channel capacity and MCCR than that of
Nyquist rate signaling, when the utilized pulse shape is non-sinc. Since the
issues associated with the ideal sinc pulse only get exacerbated when packets
are short, the benefit of FTN becomes more significant in the FBL regime. On
the other hand, when $\tau < \tau_{0}$, the channel capacity is fixed but MCCR
of FTN can continue to increase to a certain degree, thereby reducing the gap
between the capacity and MCCR. This benefit is present regardless of the
utilized pulse shape, including the ideal sinc-pulse, and is unique to the FBL
regime. Instead of increasing MCCR for fixed block error rates, FTN can
alternatively lower the block error rates for fixed channel coding rates. These
results imply that FTN can lower the penalty from limited channel coding over
short blocklength and can improve the performance and reliability of short
packet communications.
