Low-latency communication plays an increasingly important role in delay-sensitive applications by ensuring the real-time exchange of information. However, due to the constraints on the maximum instantaneous power, bounded latency is hard to be guaranteed. In this paper, we investigate the reliability-latency-rate tradeoff in low-latency communications with finite-blocklength coding (FBC). More specifically, we are interested in the fundamental tradeoff between error probability, delay-violation probability (DVP), and service rate. Based on the effective capacity (EC), we present the gain-conservation equations to characterize the reliability-latency-rate tradeoffs in low-latency systems. In particular, we investigate the low-latency transmissions over an additive white Gaussian noise (AWGN) channel and a Nakagami-$m$ fading channel. By defining the service rate gain, reliability gain, and real-time gain respectively, we further adopt the asymptotic analysis approach to reveal the fundamental reliability-latency-rate tradeoff of ultra-reliable and low-latency communications in the high signal-to-noise-ratio (SNR) regime. To analytically evaluate the quality-of-service-constrained throughput of low-latency communications with FBC, an EC-approximation method is further conceived to derive the closed-form expression of quality-of-service-constrained throughput. Our results may provide some insights into the efficient scheduling of low-latency wireless communications in which statistical latency and reliability metrics are adopted.

翻译：低时延通信通过确保信息的实时交换，在时延敏感应用中发挥着日益重要的作用。然而，由于最大瞬时功率的限制，有界时延难以得到保证。本文研究了有限分组长度编码下低时延通信中的可靠性-时延-速率权衡。具体而言，我们关注错误概率、时延违反概率与服务速率之间的基本权衡关系。基于有效容量理论，我们提出增益守恒方程以表征低时延系统中可靠性-时延-速率间的权衡。特别地，我们分别研究了加性高斯白噪声信道和Nakagami-$m$衰落信道上的低时延传输。通过分别定义服务速率增益、可靠性增益和实时增益，我们进一步采用渐近分析方法揭示了高信噪比区间内超可靠低时延通信的基本可靠性-时延-速率权衡。为解析评估有限分组长度编码下低时延通信的服务质量约束吞吐量，我们进一步提出了一种有效容量近似方法，推导出服务质量约束吞吐量的闭式表达式。我们的研究结果可为采用统计时延和可靠性度量的低时延无线通信的高效调度提供理论参考。