Abstract
Short-packet transmission has attracted considerable attention due to its potential to achieve ultralow latency in automated driving, telesurgery, the Industrial Internet of Things (IIoT), and other applications emerging in the coming era of the Six-Generation (6G) wireless networks. In 6G systems, a paradigm-shifting infrastructure is anticipated to provide seamless coverage by integrating low-Earth orbit (LEO) satellite networks, which enable long-distance wireless relaying. However, how to efficiently transmit short packets over a sizeable spatial scale remains open. In this paper, we are interested in low-latency short-packet transmissions between two distant nodes, in which neither propagation delay, nor propagation loss can be ignored. Decode-and-forward (DF) relays can be deployed to regenerate packets reliably during their delivery over a long distance, thereby reducing the signal-to-noise ratio (SNR) loss. However, they also cause decoding delay in each hop, the sum of which may become large and cannot be ignored given the stringent latency constraints. This paper presents an optimal relay deployment to minimize the error probability while meeting both the latency and transmission power constraints. Based on an asymptotic analysis, a theoretical performance bound for distant short-packet transmission is also characterized by the optimal distance–latency–reliability tradeoff, which is expected to provide insights into designing integrated LEO satellite communications in 6G.
Highlights
With latency at a submillisecond level, short-packet transmissions are necessary [5]
In [19], we extended the decode-and-cancel protocol proposed in our previous work [20] to cancel inter-relay interference (IRI) in the scheme CAO-SIR
Applying Lemma 1, we present the approximation for the overall signal-to-noise ratio (SNR)
Summary
With latency at a submillisecond level, short-packet transmissions are necessary [5]. We should consider finite-blocklength channel coding to ensure reliability in URLLC. For the finite-blocklength (FBL) regime, the authors of [6] formulated the maximal coding rate of FBC over additive white Gaussian noise (AWGN) channels. Latency is due to the physical layer transmission discussed in the literature above, but is caused by the queuing of data packets in the network layer [11]. With a cross-layer design of variable-length coding for a single link, we have achieved extremely low-latency communications in [12]. The cross-layer design for URLLC was discussed in [13,14]. In [14], the violation probabilities of the maximal delay and peak-age of information were given for URLLC
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