A Survey on UAV-Aided Maritime Communications: Deployment Considerations, Applications, and Future Challenges

Maritime activities represent a major domain of economic growth with several emerging maritime Internet of Things use cases, such as smart ports, autonomous navigation, and ocean monitoring systems. The major enabler for this exciting ecosystem is the provision of broadband, low-delay, and reliable wireless coverage to the ever-increasing number of vessels, buoys, platforms, sensors, and actuators. Towards this end, the integration of unmanned aerial vehicles (UAVs) in maritime communications introduces an aerial dimension to wireless connectivity going above and beyond current deployments, which are mainly relying on shore-based base stations with limited coverage and satellite links with high latency. Considering the potential of UAV-aided wireless communications, this survey presents the state-of-the-art in UAV-aided maritime communications, which, in general, are based on both conventional optimization and machine-learning-aided approaches. More specifically, relevant UAV-based network architectures are discussed together with the role of their building blocks. Then, physical-layer, resource management, and cloud/edge computing and caching UAV-aided solutions in maritime environments are discussed and grouped based on their performance targets. Moreover, as UAVs are characterized by flexible deployment with high re-positioning capabilities, studies on UAV trajectory optimization for maritime applications are thoroughly discussed. In addition, aiming at shedding light on the current status of real-world deployments, experimental studies on UAV-aided maritime communications are presented and implementation details are given. Finally, several important open issues in the area of UAV-aided maritime communications are given, related to the integration of sixth generation (6G) advancements

Electrical Vehicles: Current State of the Art, Future Challenges, and Perspectives

The goal of the study presented in this article is to provide a general overview of the various aspects related to electric vehicles (EVs), along with all associated emerging challenges and perspectives. In this context, the basic types of EVs and the corresponding charging technologies are analyzed. Since EVs are expected to be a key component of future smart electrical grids (SEG), connection to the grid issues, along with advanced charging techniques (i.e., wireless power transfer), are analyzed as well. To this end, the main features, the requirements of vehicle to grid (V2G) communications, as well as future developments and scenarios of electrification, are also presented and analyzed. Moreover, integration issues with currently deployed fifth generation (5G) mobile wireless networks are also outlined, in order to ensure optimum transmission and reception quality in V2G communications and improved user experience. This integration is also expanded in autonomous vehicles (AVs) technology (self-driving objects), since optimized information processing from various diverse sources is required in order to ensure advanced traffic management aspects. Document type: Articl

A New Subcarrier Allocation Strategy for MIMO-OFDMA Multicellular Networks Based on Cooperative Interference Mitigation

The goal of the study presented in this paper is to investigate the performance of a new subcarrier allocation strategy for Orthogonal Frequency Division Multiple Access (OFDMA) multicellular networks which employ Multiple Input Multiple Output (MIMO) architecture. For this reason, a hybrid system-link level simulator has been developed executing independent Monte Carlo (MC) simulations in parallel. Up to two tiers of cells around the central cell are taken into consideration and increased loading per cell. The derived results indicate that this strategy can provide up to 12% capacity gain for 16-QAM modulation and two tiers of cells around the central cell in a symmetric 2×2 MIMO configuration. This gain is derived when comparing the proposed strategy to the traditional approach of allocating subcarriers that maximize only the desired user’s signal

An artificial intelligence-based collaboration approach in industrial IoT manufacturing : key concepts, architectural extensions and potential applications

The digitization of manufacturing industry has led to leaner and more efficient production, under the Industry 4.0 concept. Nowadays, datasets collected from shop floor assets and information technology (IT) systems are used in data-driven analytics efforts to support more informed business intelligence decisions. However, these results are currently only used in isolated and dispersed parts of the production process. At the same time, full integration of artificial intelligence (AI) in all parts of manufacturing systems is currently lacking. In this context, the goal of this manuscript is to present a more holistic integration of AI by promoting collaboration. To this end, collaboration is understood as a multi-dimensional conceptual term that covers all important enablers for AI adoption in manufacturing contexts and is promoted in terms of business intelligence optimization, human-in-the-loop and secure federation across manufacturing sites. To address these challenges, the proposed architectural approach builds on three technical pillars: (1) components that extend the functionality of the existing layers in the Reference Architectural Model for Industry 4.0; (2) definition of new layers for collaboration by means of human-in-the-loop and federation; (3) security concerns with AI-powered mechanisms. In addition, system implementation aspects are discussed and potential applications in industrial environments, as well as business impacts, are presented

Performance evaluation of WCDMA networks with use of multiple antennas at the base station and user terminal

The object of present thesis is the analysis and performance evaluation of multicellular WCDMA networks, where each mobile user can be equipped with an antenna array. In the frame of this thesis, a semi-static simulator has been developed, where it was used for the calculation of capacity of WCDMA networks under different traffic scenarios as well as network deployments (networks with conventional sectors/fixed grid of beams per sector/adaptive beams). Results are presented for the capacity of WCDMA networks with up to four tiers of cells around the central cell, while a new adaptive beamforming strategy is proposed and evaluated for networks with non-uniform traffic. This strategy, apart from increased throughput per beam gain compared to a network with fixed grid of beams, provides more efficient radio resource management. The decreased number of beams formed by this strategy in order to cover capacity demands compared to the fixed grid of beams network, minimizes inter-beam handovers, reduces signalling requirements and leads to more available power in downlink. The semi-static simulator has also been used for the calculation of bit error rate for different transmission techniques in networks with multiple antennas at both sides. These techniques aim at either minimizing the overall bit rate through coherent combining (diversity combining), or the maximization of the bit rate per mobile user (spatial multiplexing). A new transmission strategy is proposed based on proper antenna selection which maximizes per user bit rate, while at the same time minimizes network resources, as in each user a minimum number of codes is assigned in order to achieve the desired capacity.Το αντικείμενο της παρούσας διδακτορικής διατριβής είναι η ανάλυση και επίδοση πολυκυψελωτών δικτύων WCDMA, όπου ο κάθε κινητός χρήστης μπορεί να είναι εφοδιασμένος με συστοιχία κεραιών. Στα πλαίσια της διατριβής, υλοποιήθηκε ημιστατικός προσομοιωτής όπου χρησιμοποιήθηκε για τον υπολογισμό της χωρητικότητας δικτύων WCDMA υπό διαφορετικά σενάρια κίνησης καθώς και υλοποίησης δικτύων (δίκτυα με συμβατικούς τομείς/σταθερό πλέγμα λοβών ανά τομέα/προσαρμοστικό πλέγμα). Παρουσιάζονται αποτελέσματα για την χωρητικότητα δικτύων με έως και τέσσερις σειρές κυψελών γύρω από την κεντρική κυψέλη, ενώ προτείνεται και αξιολογείται ένας προσαρμοστικός αλγόριθμος διαμόρφωσης δυναμικών λοβών για δίκτυα με ανομοιόμορφη κατανομή κίνησης. Ο αλγόριθμος αυτός, εκτός από σημαντικό κέρδος χωρητικότητας ανά λοβό σε σχέση με ένα δίκτυο σταθερών λοβών, προσφέρει περισσότερο αποδοτική διαχείριση των ασύρματων πόρων. Ο μειωμένος αριθμός λοβών που δημιουργεί για να καλύψει την ζήτηση σε σχέση με το σταθερό πλέγμα λοβών, οδηγεί σε ελαχιστοποίηση των διαπομπών, μείωση του φορτίου σηματοδοσίας, καθώς και σε περισσότερη διαθέσιμη ισχύς κάτω ζεύξης. Ο ημιστατικός προσομοιωτής, χρησιμοποιήθηκε και για τον υπολογισμό της πιθανότητας σφάλματος για διαφορετικές τεχνικές μετάδοσης δεδομένων σε συστήματα πολλαπλών κεραιών. Οι τεχνικές αυτές μετάδοσης επιδιώκουν είτε μέσω σύμφωνης άθροισης των σημάτων στην πλευρά του δέκτη την ελαχιστοποίηση του συνολικού ρυθμού σφαλμάτων (μεγιστοποίηση διαφορισιμότητας), είτε την μεγιστοποίηση του ρυθμού μετάδοσης ανά κινητό χρήστη (χωρική πολυπλεξία). Προτείνεται μια τεχνική μετάδοσης χωρικής πολυπλεξίας με κατάλληλη επιλογή κεραιών, η οποία μεγιστοποιεί τον ρυθμό μετάδοσης ανά χρήστη, με παράλληλη ελαχιστοποίηση των πόρων του συστήματος μιας και σε κάθε χρήστη ανατίθενται ελάχιστος αριθμός κωδικών προκειμένου να επιτευχθεί η επιθυμητή χωρητικότητα

On the Performance Evaluation of a MIMO–WCDMA Transmission Architecture for Building Management Systems

The goal of this study was to investigate the performance of a realistic wireless sensor nodes deployment in order to support modern building management systems (BMSs). A three-floor building orientation is taken into account, where each node is equipped with a multi-antenna system while a central base station (BS) collects and processes all received information. The BS is also equipped with multiple antennas; hence, a multiple input–multiple output (MIMO) system is formulated. Due to the multiple reflections during transmission in the inner of the building, a wideband code division multiple access (WCDMA) physical layer protocol has been considered, which has already been adopted for third-generation (3G) mobile networks. Results are presented for various MIMO orientations, where the mean transmission power per node is considered as an output metric for a specific signal-to-noise ratio (SNR) requirement and number of resolvable multipath components. In the first set of presented results, the effects of multiple access interference on overall transmission power are highlighted. As the number of mobile nodes per floor or the requested transmission rate increases, MIMO systems of a higher order should be deployed in order to maintain transmission power at adequate levels. In the second set of results, a comparison is performed among transmission in diversity combining and spatial multiplexing mode, which clearly indicate that the first case is the most appropriate solution for indoor communications

Reduced Complexity BER Calculations in Large Scale Spatial Multiplexing Multi-User MIMO Orientations in Frequency Selective Fading Environments

In this article, a computationally-efficient approach is presented for Bit Error Rate (BER) calculations in multi-user Multiple Input Multiple Output (MIMO) frequency selective fading environments, operating in spatial multiplexing transmission mode. To this end, theoretical expressions for the equivalent Signal to Interference plus Noise Ratio (SINR) per active user and transmission mode, as well as mean BER, are derived. The key idea is that all parameters related to BER calculations can be expressed as sums of identically distributed random variables (RVs). Hence, computational burden can be reduced, since summation formulas take into account the parameters of a standalone RV along with the correlation of an arbitrary pair of RVs. As results indicate, the proposed approach can accurately estimate mean BER in multiuser MIMO orientations with increased reception diversity order, for arbitrary number of transmit/receive antennas, a modulation scheme, and a number of resolvable multi-path components

A Comprehensive Study on Simulation Techniques for 5G Networks: State of the Art Results, Analysis, and Future Challenges

Ιn this review article, a comprehensive study is provided regarding the latest achievements in simulation techniques and platforms for fifth generation (5G) wireless cellular networks. In this context, the calculation of a set of diverse performance metrics, such as achievable throughput in uplink and downlink, the mean Bit Error Rate, the number of active users, outage probability, the handover rate, delay, latency, etc., can be a computationally demanding task due to the various parameters that should be incorporated in system and link level simulations. For example, potential solutions for 5G interfaces include, among others, millimeter Wave (mmWave) transmission, massive multiple input multiple output (MIMO) architectures and non-orthogonal multiple access (NOMA). Therefore, a more accurate and realistic representation of channel coefficients and overall interference is required compared to other cellular interfaces. In addition, the increased number of highly directional beams will unavoidably lead to increased signaling burden and handovers. Moreover, until a full transition to 5G networks takes place, coexistence with currently deployed fourth generation (4G) networks will be a challenging issue for radio network planning. Finally, the potential exploitation of 5G infrastructures in future electrical smart grids in order to support high bandwidth and zero latency applications (e.g., semi or full autonomous driving) dictates the need for the development of simulation environments able to incorporate the various and diverse aspects of 5G wireless cellular networks

Non-Orthogonal Multiple Access in Multiuser MIMO Configurations via Code Reuse and Principal Component Analysis

The goal of the study presented in this paper is to evaluate the performance of a proposed transmission scheme in multiuser multiple-input multiple-output (MIMO) configurations, via code reuse. Hence, non-orthogonal multiple access (NOMA) is performed. To this end, a correlation matrix of the received data is constructed at the transmitter, with feedback as only the primary eigenvector of the equivalent channel matrix, which is derived after principal component analysis (PCA) at the receiver. Afterwards, users experiencing improved channel quality (i.e., diagonal terms of the correlation matrix) along with reduced multiple access interference (i.e., the inner product of transmission vectors) are the potential candidates for their assigned code to be reused. As the results indicate, considering various MIMO configurations, the proposed approach can achieve almost 33% code assignment gain (CAG), when successive interference cancellation (SIC) is employed in mobile receivers. However, even in the absence of SIC, CAG is still maintained with a tolerable average bit error rate (BER) degradation