Resource allocation in future green wireless networks : applications and challenges

Over the past few years, green radio communication has been an emerging topic since the footprint from the Information and Communication Technologies (ICT) is predicted to increase 7.3% annually and then exceed 14% of the global footprint by 2040. Moreover, the explosive progress of ICT, e.g., the fifth generation (5G) networks, has resulted in expectations of achieving 10-fold longer device battery lifetime, and 1000-fold higher global mobile data traffic over the fourth generation (4G) networks. Therefore, the demands for increasing the data rate and the lifetime while reducing the footprint in the next-generation wireless networks call for more efficient utilization of energy and other resources. To overcome this challenge, the concepts of small-cell, energy harvesting, and wireless information and power transfer networks can be evaluated as promising solutions for re-greening the world. In this dissertation, the technical contributions in terms of saving economical cost, protecting the environment, and guaranteeing human health are provided. More specifically, novel communication scenarios are proposed to minimize energy consumption and hence save economic costs. Further, energy harvesting (EH) techniques are applied to exploit available green resources in order to reduce carbon footprint and then protect the environment. In locations where implemented user devices might not harvest energy directly from natural resources, base stations could harvest-and-store green energy and then use such energy to power the devices wirelessly. However, wireless power transfer (WPT) techniques should be used in a wise manner to avoid electromagnetic pollution and then guarantee human health. To achieve all these aspects simultaneously, this thesis proposes promising schemes to optimally manage and allocate resources in future networks. Given this direction, in the first part, Chapter 2 mainly studies a transmission power minimization scheme for a two-tier heterogeneous network (HetNet) over frequency selective fading channels. In addition, the HetNet backhaul connection is unable to support a sufficient throughput for signaling an information exchange between two tiers. A novel idea is introduced in which the time reversal (TR) beamforming technique is used at a femtocell while zero-forcing-based beamforming is deployed at a macrocell. Thus, a downlink power minimizationscheme is proposed, and optimal closed-form solutions are provided. In the second part, Chapters 3, 4, and 5 concentrate on EH and wireless information and power transfer (WIPT) using RF signals. More specifically, Chapter 3 presents an overview of the recent progress in green radio communications and discusses potential technologies for some emerging topics on the platforms of EH and WPT. Chapter 4 develops a new integrated information and energy receiver architecture based on the direct use of alternating current (AC) for computation. It is shown that the proposed approach enhances not only the computational ability but also the energy efficiency over the conventional one. Furthermore, Chapter 5 proposes a novel resource allocation scheme in simultaneous wireless information and power transfer (SWIPT) networks where three crucial issues: power-efficient improvement, user-fairness guarantee, and non-ideal channel reciprocity effect mitigation, are jointly addressed. Hence, novel methods to derive optimal and suboptimal solutions are provided. In the third part, Chapters 6, 7, and 8 focus on simultaneous lightwave information and power transfer (SLIPT) for indoor applications, as a complementary technology to RF SWIPT. In this research, Chapter 6 investigates a hybrid RF/visible light communication (VLC) ultrasmall cell network where optical transmitters deliver information and power using the visible light, whereas an RF access point works as a complementary power transfer system. Thus, a novel resource allocation scheme exploiting RF and visible light for power transfer is devised. Chapter 7 proposes the use of lightwave power transfer to enable future sustainable Federated Learning (FL)-based wireless networks. FL is a new data privacy protection technique for training shared machine learning models in a distributed approach. However, the involvement of energy-constrained mobile devices in the construction of the shared learning models may significantly reduce their lifetime. The proposed approach can support the FL-based wireless network to overcome the issue of limited energy at mobile devices. Chapter 8 introduces a novel framework for collaborative RF and lightwave power transfer for wireless communication networks. The constraints on the transmission power set by safety regulations result in significant challenges to enhance the power transfer performance. Thus, the study of technologies complementary to conventional RF SWIPT is essential. To cope with this isue, this chapter proposes a novel collaborative RF and lightwave power transfer technology for next-generation wireless networks

Υβριδικά συστήματα επικοινωνίας ορατού φωτός και ραδιοσυχνοτήτων (VLC – RF). Προκλήσεις και ζητήματα όπως προκύπτουν από τη διερεύνηση της διεθνούς βιβλιογραφίας.

Οι ασύρματες επικοινωνίες γίνονται με μεταδόσεις δεδομένων σε μη καθοδηγούμενα μέσα διάδοσης μέσω της χρήσης ασύρματων φορέων όπως τα κύματα ραδιοσυχνοτήτων και του ορατού φωτός. Η αυξανόμενη ζήτηση για υψηλούς ρυθμούς δεδομένων, αυξημένη χωρητικότητα, ασφάλεια δεδομένων, ειδικά σε σενάρια εσωτερικού χώρου, δίνει μεγαλύτερη βαρύτητα στις συμβατικές τεχνολογίες ραδιοσυχνοτήτων. Για αυτό το λόγο, τεχνολογίες όπως οι mmWave και οι γνωστικές ραδιοεπαφές έχουν υιοθετηθεί ως πιθανές λύσεις για τη λύση στο πρόβλημα έλλειψης φάσματος και άλλων περιορισμών των συμβατικών συστημάτων ραδιοσυχνοτήτων. Παράλληλα, ως εναλλακτική λύση έχει προταθεί η επικοινωνία ορατού φωτός (VLC), όπου χρησιμοποιείται η πηγή φωτός τόσο για φωτισμό όσο και για μετάδοση δεδομένων. Σε σύγκριση με τις ζεύξεις RF, οι ζεύξεις VLC παρουσιάζουν πολύ υψηλό εύρος ζώνης που επιτρέπει πολύ υψηλότερους ρυθμούς δεδομένων. Το VLC δεν επηρεάζεται από παρεμβολές από ηλεκτρομαγνητικές πηγές, έχει μη αδειοδοτημένα κανάλια επικοινωνίας, είναι σύστημα πολύ χαμηλής κατανάλωσης ενέργειας και δεν έχει κανέναν κίνδυνο για την υγεία. Το VLC αποτελεί πόλο έλξης για μελέτη, καθώς έχει ένα ευρύ φάσμα εφαρμογών, συμπεριλαμβανομένων των αξιόπιστων επικοινωνιών με χαμηλές καθυστερήσεις, όπως η επικοινωνία στην ασφάλεια του οχήματος. Παρά τα σημαντικά πλεονεκτήματα της τεχνολογίας VLC και την ποικιλία των εφαρμογών της, η χρήση της έχει εμπόδια λόγω των μειονεκτημάτων της, όπως η εξάρτησή της από την οπτική επαφή της σύνδεσης. Πρόσφατα, προτάθηκαν τα υβριδικά συστήματα τεχνολογίας RF / VLC για να επωφεληθούν από την υψηλή χωρητικότητα των ζεύξεων VLC και την καλύτερη συνδεσιμότητα των ζεύξεων RF. Έτσι, τα υβριδικά συστήματα τεχνολογίας RF / VLC αποτελούν βασικό εργαλείο για τη βελτίωση των ρυθμών και της κινητικότητας των χρηστών αφενός και για τη βελτιστοποίηση της χωρητικότητας, των παρεμβολών και της κατανάλωσης ενέργειας του συνολικού δικτύου, αφετέρου. Αυτή η εργασία επιδιώκει να παρέχει μια λεπτομερή επισκόπηση των υβριδικών συστημάτων τεχνολογίας RF / VLC. Μελετώνται βασικά χαρακτηριστικά και τοπολογίες, εφαρμογές και επιδόσεις τέτοιων δικτύων, αλλά και οι περιορισμοί που αντιμετωπίζουν, με βάση τη διεθνή βιβλιογραφία.Wireless communications are implemented by transmitting data to unguided propagation media through the use of wireless carriers such as radio frequency waves and visible light. The growing demand for high data rates, increased capacity, data security, especially in indoor scenarios, attaches more importance to conventional radio frequency technologies. For this reason, technologies such as mmWave and cognitive radio communications have been adopted as possible solutions to the problem of lack of spectrum and other limitations of conventional radio frequency systems. At the same time, visible light communication (VLC) has been proposed as an alternative, where the light source is used for both lighting and data transmission. Compared to RF links, VLC links have a very high bandwidth that allows much higher data rates. VLC is not affected by interference from electromagnetic sources, has unlicensed communication channels, is a very low power system and doesn’t affect human’s health. VLC is an attraction for study, as it has a wide range of applications, including reliable communications with low latency, such as vehicle safety communication. Despite the significant advantages of VLC technology and the variety of its applications, its use has drawbacks due to its disadvantages, such as its dependence on line of sight of the connection. Recently, hybrid RF / VLC technology systems have been proposed to take advantage of high VLC link capacity and better RF link connectivity. Thus, hybrid RF / VLC technology systems are a key tool for improving the rate and mobility of users on the one hand and for optimizing the capacity, interference and power consumption of the overall network on the other. This work seeks to provide a detailed overview of hybrid RF / VLC technology systems. Key features and topologies, applications and performance of such networks are studied, as well as the limitations they face, based on the international literature