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.

翻译：我们探讨了超奈奎斯特（FTN）信令在有限块长（FBL）体制中的潜在优势。FTN信令的独特之处在于，它能在相同时间-频率资源内封装更多数据符号，从而获得比奈奎斯特速率信令严格更高的独立信令维数，进而增加块长。利用有限块长信息论，我们给出了任意有限时间带宽积下FTN信令最大信道编码速率（MCCR）的紧致界。其优势分为两个工作区域：当FTN的时间加速因子$\tau$高于或低于某一阈值$\tau_{0}$时。当$\tau > \tau_{0}$时，若采用非sinc脉冲形状，FTN的信道容量和MCCR均高于奈奎斯特速率信令。由于理想sinc脉冲相关问题在短数据包场景中更为突出，FTN的优势在FBL体制下更为显著。另一方面，当$\tau < \tau_{0}$时，信道容量保持不变，但FTN的MCCR可持续提升至一定程度，从而缩小信道容量与MCCR之间的差距。该优势与所用脉冲形状（包括理想sinc脉冲）无关，且为FBL体制所独有。除在固定块错误率下提升MCCR外，FTN也可在固定信道编码速率下降低块错误率。这些结果表明，FTN能降低短块长下有限信道编码的惩罚，并提升短数据包通信的性能与可靠性。