Ultra-Reliable Short-Packet Communications: Half-Duplex or Full-Duplex Relaying?

Abstract

Abstract-This letter analyzes and compares the performance of full-duplex relaying (FDR) and half-duplex relaying (HDR) for ultra-reliable short-packet communications. Specifically, we derive both approximate and asymptotic closed-form expressions of the block error rate (BLER) for FDR and HDR using short packets with finite blocklength codes. We define and attain a closed-form expression of a critical BLER, which can be used to efficiently determine the optimal duplex mode for ultra-reliable low latency communication scenarios. Our results unveil that FDR is more appealing to the system with relatively lower transmit power constraint, less stringent BLER requirement and stronger loop interference suppression.Index Terms-Ultra-reliable, low latency, short-packet communication, finite blocklength, full-duplex relay. I. INTRODUCTIONIn conventional wireless systems, extremely long packet has been used in coding and transmission. However, to support ultra-reliable low latency communications (URLLC) as a new service type of 5G cellular systems [1], short-packet transmissions are essential. In this case, errors cannot be reduced to arbitrarily low for a given coding rate due to the limited packet size. Motivated by this, [2] developed a new fundamental framework for short-packet communications and derived an error probability bound for a given blocklength and coding rate. It was shown that the block error rate (BLER) increases as the blocklength of the system decreases. This new theoretical framework opens a new research direction for the revisit of conventional communication networks, which were mainly designed based on the Shannon formula and thus cannot be directly applied to short-packet communications.References [3], [4] investigated a classical three node cooperative network under finite blocklenth regime with static and quasi-static channel conditions. It was shown that there exists a performance tradeoff between cooperative and noncooperative communications: On the one hand, a relay can boost the power gains of both hops and thus improve the system performance; on the other hand, it can degrade the system performance by halving the blocklength of each packet transmission. However, only half-duplex relaying (HDR) was considered in [3], [4]. To the best knowledge of the authors, the performance of full-duplex relaying (FDR) under the finite blocklength regime has not been studied so far in open literature. Compared to HDR, FDR has a great potential to improve the system performance since it has a longer blocklength for each packet transmission, which is twice longer as that of HDR. On the other side, FDR suffers from additional interference caused by receiving and transmitting information at the same time, degrading the system performance [5], [6].

On the Multiplexing of Data and Metadata for Ultra-Reliable Low-Latency Communications in 5G

“…The authors in [36] focus on mobile edge computing and user/server association to ensure low-latency communication. Finally, different cooperative protocols and resource allocation schemes for URLLC have been extensively considered in [37]- [41].…”

Short Packet Communications in Large-Scale Wireless Powered Networks

“…For the sake of tractability, the Q-function is evaluated using the following linear approximation [6]…”

“…[4]. As a result, many studies have appeared recently in the literature, focusing on short-packets in various contexts, such as relay networks [5], [6], full-duplex [6], non-orthogonal multiple access [7], as well as wireless powered communications [8]- [11].…”

Stability of a TDMA Network Subject to Finite Blocklength Constraints

“…Linear approximation, though not the tightest, is attractive since it provides simple expressions that can be physically interpreted. Recent works on topics related to finite blocklength analysis employ such approximations, for the finite blocklength analysis of the incremental redundancy Hybrid ARQ (HARQ) [12] and for full-duplex and half-duplex relaying for short packet communications [13]. Let, the linear approximation of the probability of successful transmission be denoted byP c (k, n), and the resulting approximations of the throughput and of the data packet size be denoted byû(k, n) andk, respectively.…”