Various sectors are likely to carry a set of emerging applications while targeting a reliable communication with low latency transmission. To address this issue, upon a spectrally-efficient transmission, this paper investigates the performance of a 1 full-dulpex relay system and considers for that purpose, 2 basic relaying schemes, namely, the symbol-by-symbol transmission, i.e., amplifyand-forward and the block-by-block transmission, i.e., selective decode-andforward. The conducted analysis presents an exhaustive comparison, covering both schemes, over 2 different transmission modes, i.e., the noncombining mode where the best link, direct, or relay link is decoded and the signals combining mode, where direct and relay links are combined at the receiver side. While targeting latency purpose as a necessity, simulations show a refined results of performed comparisons and reveal that amplify-and-forward relaying scheme is more adapted to combining mode, whereas the selective decode-and-forward relaying scheme is more suitable for noncombining mode.KEYWORDS amplify-and-forward, full-duplex, low latency applications, outage probability, selective decode-andforward 1 | INTRODUCTION An immense amount of data is created every day from different sensors and peripherals, namely, GPS embedded in vehicles, attached to objects or worn by people, sensors monitoring the environment, real time video streams, radars on roads, social network feeds, etc. Such type of data belongs to real time's domain, where schedulability is one of the main characteristics of this domain, which means its propensity to respect the expected time constraints. In fact, a real time system implies a system ability to ensure that investigated processing produces consistent results, i.e., functionally correct, at the right time. Therefore, to ensure the radio communication for such applications, a low latency as well as extreme reliability are required. In this context, the use of cooperation concept provides spatial and temporal diversity and constitutes a good alternative to support advanced communications with increased channel capacity. 1,2 However, in regards to the end-to-end latency, this requirement has a significant impact on the system quality and the fluidity of communications, and it is influenced by different features upon the transmission, we mention in particular, the propagation delay as well as the relay delay processing. In fact, depending on the environment and on the application, we can get rid of some supplementary sources of delay, as example, for industrial environments such factories, the distance between 2 automated robots is not considerable. Hence, the delay propagation can be neglected, and the only generated delay in this case is that related to the relay processing, which depends mainly on the used relaying technique.
The Release 16 completion unlocks the road to an exciting phase pertain to the sixth generation (6G) era. Meanwhile, to sustain far-reaching applications with unprecedented challenges in terms of latency and reliability, much interest is already getting intensified toward physical layer specifications of 6G. In support of this vision, this work exhibits the forward-looking perception of full-duplex (FD) cooperative relaying in support of upcoming generations and adopts as a mean concern the critical contribution of hybrid automatic repeat request (HARQ) mechanism to ultra-reliable and low-latency communication (URLLC). Indeed, the HARQ roundtrip time (RTT) is known to include basic physical delays that may cause the HARQ abandonment for the 1 ms latency use case of URLLC. Taking up these challenges, this article proposes a hybrid FD amplify-and-forward (AF)-selective decode-and-forward (SDF) relay-based system for URLLC. Over this build system, two HARQ procedures within which the HARQ RTT is shortened, are suggested to face latency and reliability issues, namely, the proposed and the enhanced HARQ procedures. We develop then an analytical framework of this relay based HARQ system within its different procedures. Finally, using Monte-Carlo simulations, we confirm the theoretical results and compare the proposed relay-assisted HARQ procedures to the source-to-destination (S2D) HARQ-based system where no relay assists the communication between the source and the destination.
The advent of Reconfigurable Intelligent Surfaces (RISs) in wireless communication networks unlocks the way to support high frequency radio access (e.g. in millimeter wave) while overcoming their sensitivity to the presence of deep fading and blockages. In support of this vision, this work exhibits the forward-looking perception of using RIS to enhance the connectivity of the communication links in edge computing scenarios, to support computation offloading services. We consider a multi-user MIMO system, and we formulate a long-term optimization problem aiming to ensure a bounded end-to-end delay with the minimum users' average transmit power, by jointly selecting uplink user precoding, RIS reflectivity parameters, and computation resources at a mobile edge host. Thanks to the marriage of Lyapunov stochastic optimization, projected gradient techniques and convex optimization, the problem is efficiently solved in a per-slot basis, requiring only the observation of instantaneous realizations of time-varying radio channels and task arrivals, and that of communication and computing buffers. Numerical simulations show the effectiveness of our method and the benefits of the RIS, in striking the best trade-off between power consumption and delay for different blocking conditions, also when different levels of channel knowledge are assumed.
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