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The sixth generation (6G) of wireless networks are envisioned to support a plethora of human-centric applications and offer connectivity to a massive number of devices with diverse requirements, thus enabling massive Machine Type Communications. Nevertheless, with the rapid growth of the number of connected devices as well as the ever-increasing network traffic, network energy consumption has become a major challenge. Additionally, 6G is expected to catalyze the emergence of new applications that are characterized by their harsh environmental conditions, with ultra-small and low-cost wireless devices. Therefore, there is a pressing need for developing sustainable solutions that take into consideration all these requirements in order to realize the full potential of 6G networks. Within this context, zero-energy devices (ZEDs) have emerged as a prominent solution for the next generation green communication architecture. Such devices eliminate the need for recharging plugins and replacing batteries by integrating disruptive technologies, such as radio frequency energy harvesting, backscatter communications, low power computing, and ultra-low power receivers. Motivated by this, this article provides an in-depth review of the existing literature on the newly emerging ZEDs for future networks. We further identify different relevant use cases and provide an extensive overview on the key enabling technologies and their requirements for realizing ZED-empowered networks. Finally, we discuss potential future research directions and challenges that are envisioned to enhance the performance and efficiency of ZED-based networks.

Inter-cell interference (ICI) and inter-user interference (IUI) constitute a major issue towards achieving the optimum spectral efficiency (SE) and energy efficiency (EE) performance in multi-cell visible light communication (VLC) networks. Hence,advanced multiple access techniques need to be leveraged in order to improve the provided service to the users of such interfering networks. To this end,the present contribution proposes the integration of coordinated beamforming (CB) with rate-splitting multiple access (RSMA) in multi-cell VLC systems. Specifically,we consider the design of beamformers for the common and private streams in a coordinated manner between different attocells,which is shown to provide efficient mitigation of the incurred interference. Additionally,the formulated optimization problem aims to minimize the sum of the mean squared error across all attocells in order to jointly determine the optimum receive filters and coordinated transmit beamformers for RSMA streams. In this context,we illustrate through extensive computer simulations,which are carried out in a realistic setup that assumes noisy channel state information acquisition,the distinct flexibility and robustness of CB-based RSMA in mitigating the incurred interference. Finally,the offered results demonstrate the superiority of CB-based RSMA in terms of achievable SE and EE performance in multi-cell VLC networks compared to the conventional CB-based space division multiple access counterpart. publishedVersion

Visible light communication (VLC) has been recognized as a promising technology for handling the continuously increasing quality of service and connectivity requirements in modern wireless communications, particularly in indoor scenarios. In this context, the present work considers the integration of two distinct modulation schemes, namely spatial modulation (SM) with space time block codes (STBCs), aiming at improving the overall VLC system reliability. Based on this and in order to further enhance the achievable transmission data rate, we integrate quasi-orthogonal STBC (QOSTBC) with SM, since relaxing the orthogonality condition of OSTBC ultimately provides a higher coding rate. Then, we generalize the developed results to any number of active light-emitting diodes (LEDs) and any $M$-ary pulse amplitude modulation size. Furthermore, we derive a tight and tractable upper bound for the corresponding bit error rate (BER) by considering a simple two-step decoding procedure to detect the indices of the transmitting LEDs and then decode the signal domain symbols. Notably, the obtained results demonstrate that QOSTBC with SM enhances the achievable BER compared to SM with repetition coding (RC-SM). Finally, we compare STBC-SM with both multiple active SM (MASM) and RC-SM in terms of the achievable BER and overall data rate, which further justifies the usefulness of the proposed scheme.

Fifth-generation and beyond (5G and xG) wireless networks are envisioned to meet the requirements of vertical applications like high traffic throughput, ultra-massive connectivity, extremely low latency, and high quality of service. Disruptive technologies, such as massive multiple-input multiple-output, millimeter wave, and multiple access are being deployed to meet these requirements. However, their deployment poses several challenges, including a lack of network transparency, management decentralization, and reliability. Moreover, the heterogeneity of future networks raises security concerns, e.g., confidentiality, privacy, and trustworthiness. Indeed, due to the emergence of novel paradigms, e.g., quantum computing, traditional security approaches are no longer sufficient to protect over-the-air communications. Hence, 5G/xG networks must consider smart security techniques to operate seamlessly and efficiently. Within this context, physical layer security (PLS) and blockchain represent promising solutions to complement existing methods. By exploiting the characteristics of wireless links, PLS can enhance the security of communications, while blockchain may enable networks' decentralization, integrity, and trustworthiness. Motivated by these advancements, we provide an in-depth review of the existing PLS and blockchain literature. Then, for the first time in the literature, we present a framework to integrate PLS with blockchain in 5G/xG systems. We first provide a thorough discussion about the potential of PLS and blockchain for 5G/xG systems. Then, we present our vision of a cross-layer architecture that leverages PLS and blockchain. Through a case study, we demonstrate the high potential of cross-layer design to improve the security of vehicular networks. Finally, we identify related challenges and shed light on future research directions.

The objective in any perforated completion is to maximize the productivity index in a cost effective manner, which is to increase the flow rate for a given driving force (draw down) or to minimize the draw down for a given rate that could be achieved through minimizing the total well skin effect. Underbalance perforation through Tubing Conveyed Perforating (TCP) system is one of the best practices to ensure less damage to the perforation tunnels (perforating skin) leading to increased well productivity. However, it is very challenging in cases of completions using Electrical Submersible Pump's (ESP) to maintain productivity with undamaged reservoir by preventing any contact between reservoir and completion fluid and achieve the above simultaneously with safe well control during ESP deployment. Otherwise, the alternative solution is to perforate over balance using casing guns or run TCP string in single run then kill the well after perforation in order to install the ESP completion meanwhile both alternative ways lead to damage in the perforated tunnels. As reducing operating costs is a must, maximizing well productivity, and minimizing wellbore clean-up time, an innovative solution was designed and successfully implemented for perforating artificially lifted wells in static underbalanced condition meanwhile installing ESP completion in single run without killing the well. It combines the use of TCP system containing special hydraulic firing head (delaying technique with orifice and chamber filled with oil) equipped with hydraulic packer with on-off tool. TCP gun string with the hydraulic packer has been run by tubing and set hydraulically against the required intervals, then the ESP has been separately installed and the guns has been activated through a hydraulic firing head for a shoot-and-stay operation. The static underbalance condition has been created by the ESP thanks to the delayed firing time. After this operation, the well has been directly lined up to production flow-line with minimal wellbore clean-up time. The combination of static underbalanced perforation with deep penetration charges which is able to bypass invasion zone with depth of penetration more than 65 inch, can create a clean perforation tunnel, and significantly reduce the post-perforating damage by killing fluid, and finally maximize the well productivity. Despite the challenging reservoir conditions (Depth= 10200 FT, Pressure=3850 Psi, Temperature= 28544 deg. F), the Productivity Index (PI) of the wells were three times compared to the offset wells. This job has been performed by Agiba Petroleum Company, one of the main operators in Western Desert of Egypt, employing this combined TCP-ESP technique which has resulted in significant savings in cost as well as rig time and increased operating efficiency. This paper summarizes the practical experiences gained during the development and deployment of this integrated technique, in addition to an evaluation of the impact compared to the conventional perforation techniques through ESP downhole sensor data and well modelling.

With the advancements of high-resolution cameras, highly sensitive photodetectors, and energy-efficient light-emittingdiodes, optical wireless communication (OWC) has emerged as keyenabling technology for 6G and beyond. Similarly, digital twin (DT) technology has been recently proposed to meet the diverse requirements of emerging applications and provide efficient optimization of the overall system resources by enabling self-sustaining and proactive online learning. In DT, various technology disciplines, including big data, artificial intelligence, machine learning, intelligent computing, communication, and security-aware technologies, are integrated to create a virtual replica that reflects the physical system. Motivated by this, the presented article discusses DT and its role in the reliable and ubiquitous implementation of OWC networks. We first provide an overview of this emerging research area by shedding light on the key enabling technologies and potential applications in the context of smart-autonomous OWC networks. Subsequently, we provide recent advancements and design aspects related to DT-assisted OWC systems. Finally, future research directions and the impact of different system and environmental factors on the overall network performance are discussed. To the best of the authors’ knowledge, this is the first in-depth review in the literature on the integration of DT with OWC networks.

The increased proliferation of connected devices requires a paradigm shift towards the development of innovative technologies for the next generation of wireless systems. One of the key challenges, however, is the spectrum scarcity, owing to the unprecedented broadband penetration rate in recent years. Visible light communications (VLC) has recently emerged as a possible solution to enable high-speed short-range communications. However, VLC systems suffer from several limitations, including the limited modulation bandwidth of light-emitting diodes. Consequently, several multiple access techniques (MA), e.g., space-division multiple access (SDMA) and non-orthogonal multiple access (NOMA), have been considered for VLC networks. Despite their promising multiplexing gains, their performance is somewhat limited. In this article, we first provide an overview of the key MA technologies used in VLC systems. Then, we introduce rate-splitting multiple access (RSMA), which was initially proposed for RF systems and discuss its potentials in VLC systems. Through system modeling and simulations of an RSMA-based two-use scenario, we illustrate the flexibility of RSMA in generalizing NOMA and SDMA, as well as its superiority in terms of weighted sum rate (WSR) in VLC. Finally, we discuss challenges, open issues, and research directions, which will enable the practical realization of RSMA in VLC., 19 pages, 14 figures. arXiv admin note: substantial text overlap with arXiv:2002.07583

We propose an enhanced spatial modulation(SM)-based scheme for indoor visible light communication systems. This scheme enhances the achievable throughput of conventional SM schemes by transmitting higher order complex modulation symbol, which is decomposed into three different parts. These parts carry the amplitude, phase, and quadrant components of the complex symbol, which are then represented by unipolar pulse amplitude modulation(PAM) symbols. Superposition coding is exploited to allocate a fraction of the total power to each part before they are all multiplexed and transmitted simultaneously, exploiting the entire available bandwidth. At the receiver, a two-step decoding process is proposed to decode the active light emitting diode index before the complex symbol is retrieved. It is shown that at higher spectral efficiency values, the proposed modulation scheme outperforms conventional SM schemes with PAM symbols in terms of average symbol error rate(ASER), and hence, enhancing the system throughput. Furthermore, since the performance of the proposed modulation scheme is sensitive to the power allocation factors, we formulated an ASER optimization problem and propose a sub-optimal solution using successive convex programming(SCP). Notably, the proposed algorithm converges after only few iterations, whilst the performance with the optimized power allocation coefficients outperforms both random and fixed power allocation. publishedVersion

Visible light communication is envisaged as a promising enabling technology for sixth generation (6G) and beyond networks. It was introduced as a key enabler for reliable massive-scale connectivity, mainly thanks to its simple and low-cost implementation which require minor variations to the existing indoor lighting systems. The key features of VLC allow offloading data traffic from the current congested radio frequency (RF) spectrum in order to achieve effective short-range, high speed, and green communications. However, several challenges prevent the realization of the full potentials of VLC, namely the limited modulation bandwidth of light emitting diodes, the interference resulted from ambient light, the effects of optical diffuse reflection, the non-linearity of devices, and the random receiver orientation. Meanwhile, centralized machine learning (ML) techniques have exhibited great potentials in handling different challenges in communication systems. Specifically, it has been recently shown that ML algorithms exhibit superior capabilities in handling complicated network tasks, such as channel equalization, estimation and modeling, resources allocation, opportunistic spectrum access control, non-linearity compensation, performance monitoring, detection, decoding/encoding, and network optimization. Nevertheless, concerns relating to privacy and communication overhead when sharing raw data of the involved clients with a server constitute major bottlenecks in large-scale implementation of centralized ML techniques. This has motivated the emergence of a new distributed ML paradigm, namely federated learning (FL). This method can reduce the cost associated with transferring the raw data, and preserve clients privacy by training ML model locally and collaboratively at the clients side. Thus, the integration of FL in VLC networks can provide ubiquitous and reliable implementation of VLC systems. Based on this, for the first time in the open literature, we provide an overview about VLC technology and FL. Then, we introduce FL and its integration in VLC networks and provide an overview on the main design aspects. Finally, we highlight some interesting future research directions of FL that are envisioned to boost the performance of VLC systems.

Visible light communication is envisaged as a promising enabling technology for sixth generation (6G) and beyond networks. It was introduced as a key enabler for reliable massive-scale connectivity, mainly thanks to its simple and low-cost implementation which require minor variations to the existing indoor lighting systems. The key features of VLC allow offloading data traffic from the current congested radio frequency (RF) spectrum in order to achieve effective short-range, high speed, and green communications. However, several challenges prevent the realization of the full potentials of VLC, namely the limited modulation bandwidth of light emitting diodes, the interference resulted from ambient light, the effects of optical diffuse reflection, the non-linearity of devices, and the random receiver orientation. Meanwhile, centralized machine learning (ML) techniques have exhibited great potentials in handling different challenges in communication systems. Specifically, it has been recently shown that ML algorithms exhibit superior capabilities in handling complicated network tasks, such as channel equalization, estimation and modeling, resources allocation, opportunistic spectrum access control, non-linearity compensation, performance monitoring, detection, decoding/encoding, and network optimization. Nevertheless, concerns relating to privacy and communication overhead when sharing raw data of the involved clients with a server constitute major bottlenecks in large-scale implementation of centralized ML techniques. This has motivated the emergence of a new distributed ML paradigm, namely federated learning (FL). This method can reduce the cost associated with transferring the raw data, and preserve clients privacy by training ML model locally and collaboratively at the clients side. Thus, the integration of FL in VLC networks can provide ubiquitous and reliable implementation of VLC systems. Based on this, for the first time in the open literature, we provide an overview about VLC technology and FL. Then, we introduce FL and its integration in VLC networks and provide an overview on the main design aspects. Finally, we highlight some interesting future research directions of FL that are envisioned to boost the performance of VLC systems.

Visible light communication (VLC) has been emerged as a technology that can increase the channel capacity in the next generations of wireless technologies by exploiting the largely unutilized, licence-free and huge visible light portion of the electromagnetic spectrum. In order to enable high-speed short-range wireless communications, VLC utilizes the installed high-switching rate light emitting diodes (LEDs) in the ceilings of indoor environments, which are primarily used for illumination, to modulate the signals into visible light intensity. However, VLC suffers from several limitations, such as the limited modulation bandwidth and the coverage area of LEDs that degrade the overall system spectral efficiency (SE). In this respect, the present contribution proposes rate splitting multiple access (RSMA) for multi-cell indoor VLC systems as a mean to enhance the overall system SE and energy efficiency (EE) as well as to provide ubiquitous indoor coverage and to address user mobility issues. Moreover, we utilize coordinated beamforming to design the precoders of the common and the private streams in each cell aiming to enhance the performance of cell-edge users. Finally, the formulated sum of the mean squared error optimization problem is solved sub-optimally using an alternating optimization approach. Extensive computer simulations demonstrate that RSMA improves the overall system performance in terms of the SE and EE compared to the recently used multiple access techniques, such as space division multiple access with coordinated beamforming which constitutes a special case of it. acceptedVersion

Visible light communication (VLC) is a promising solution to the current congestion in radio frequency (RF) spectrum. It achieves that by exploiting the huge unregulated visible light portion of the electromagnetic spectrum in order to enable high-speed short range wireless communications, as well as, providing an sufficient lighting. This new solution is envisioned to provide a considerably wider bandwidth that can accommodate ubiquitous broadband connectivity to indoor users and further offload data traffic from overloaded cellular networks. However, VLC suffers from several limitations, such as the limited modulation bandwidth of light-emitting diodes (LEDs) that degrades the overall system spectral efficiency. In this respect, several interesting solutions have been proposed in the recent literature to overcome this limitation, such as the implementation of efficient optical modulation and multipleinput-multiple-output (MIMO) schemes. In this paper, we investigate the performance of multiple active spatial modulation (MASM) integrated with orthogonal space time block codes (STBC) for indoor VLC systems. Additionally, in ordered to reduce the receiver complexity, a simplified version of the joint maximum likelihood (ML) detector is proposed which has a linear complexity with respect to the number of transmit LEDs and the constellation size. Extensive computer simulations demonstrate that STBC-MASM improves the overall system performance compared to MASM with a considerably simplified detection. acceptedVersion

Visible light communication (VLC) is considered a breakthrough wireless communication technology that has been proven capable of achieving very high data rates. This is a key advantage in indoor communication scenarios, since the vast majority of wireless traffic is witnessed in indoor communications. In every wireless system, the trade-off between achievable throughput, transmit signal power and corresponding error rate performance is largely dependent upon the considered modulation format. This is also the case in VLC systems, which are typically characterized by stringent performance requirements. Motivated by this, in the present contribution we introduce the space shift keying (SSK) modulation scheme in the context of non-orthogonal-multiple-access (NOMA) communications, which have been shown to be a performance enhancer of indoor based VLC systems. Based on this, all network users in the considered set up receive the same superimposed signal of all NOMA users, which is transmitted from the activated transmitters corresponding to the multiplexed SSK users information. Based on this and assuming a unique maximum likelihood detection, we quantity the system performance in terms of the corresponding bit error rate (BER) performance at each receiver. This analysis leads to the development of useful insights of theoretical and practical interest, which are expected to be useful in the effective design, implementation and deployment of SSK in NOMA based VLC systems. acceptedVersion

Recently, interest on the utilization of unmanned aerial vehicles (UAVs) has aroused. Specifically, UAVs can be used in cellular networks as aerial users for delivery, surveillance, rescue search, or as an aerial base station (aBS) for communication with ground users in remote uncovered areas or in dense environments requiring prompt high capacity. Aiming to satisfy the high requirements of wireless aerial networks, several multiple access techniques have been investigated. In particular, space-division multiple access(SDMA) and power-domain non-orthogonal multiple access (NOMA) present promising multiplexing gains for aerial downlink and uplink. Nevertheless, these gains are limited as they depend on the conditions of the environment. Hence, a generalized scheme has been recently proposed, called rate-splitting multiple access (RSMA), which is capable of achieving better spectral efficiency gains compared to SDMA and NOMA. In this paper, we present a comprehensive survey of key multiple access technologies adopted for aerial networks, where aBSs are deployed to serve ground users. Since there have been only sporadic results reported on the use of RSMA in aerial systems, we aim to extend the discussion on this topic by modelling and analyzing the weighted sum-rate performance of a two-user downlink network served by an RSMA-based aBS. Finally, related open issues and future research directions are exposed., 20 pages, 6 figures, Accepted (IEEE Open Journal on Vehicular Technology)