A Survey on Spectrum Management in Cognitive Radio Networks

Cognitive radio networks will provide high bandwidth to mobile users via heterogeneous wireless architectures and dynamic spectrum access techniques. However, CR networks impose challenges due to the fluctuating nature of the available spectrum, as well as the diverse QoS requirements of various applications. Spectrum management functions can address these challenges for the realization of this new network paradigm. To provide a better understanding of CR networks, this article presents recent developments and open research issues in spectrum management in CR networks. More specifically, the discussion is focused on the development of CR networks that require no modification of existing networks. First, a brief overview of cognitive radio and the CR network architecture is provided. Then four main challenges of spectrum management are discussed: spectrum sensing, spectrum decision, spectrum sharing, and spectrum mobility

Spectrum cartography techniques, challenges, opportunities, and applications: A survey

The spectrum cartography finds applications in several areas such as cognitive radios, spectrum aware communications, machine-type communications, Internet of Things, connected vehicles, wireless sensor networks, and radio frequency management systems, etc. This paper presents a survey on state-of-the-art of spectrum cartography techniques for the construction of various radio environment maps (REMs). Following a brief overview on spectrum cartography, various techniques considered to construct the REMs such as channel gain map, power spectral density map, power map, spectrum map, power propagation map, radio frequency map, and interference map are reviewed. In this paper, we compare the performance of the different spectrum cartography methods in terms of mean absolute error, mean square error, normalized mean square error, and root mean square error. The information presented in this paper aims to serve as a practical reference guide for various spectrum cartography methods for constructing different REMs. Finally, some of the open issues and challenges for future research and development are discussed.publishedVersio

Estimation and Coordination of Sequence Patterns for Frequency Hopping Dynamic Spectrum Access Networks

In 2010, the Shared Spectrum Company showed in a survey of Radio Frequency (RF) bands that underutilization of spectrum has resulted from current frequency management practices. Traditional frequency allocation allows large bands of licensed spectrum to remain vacant even under current high demands. Cognitive radio\u27s (CR) use of Dynamic Spectrum Access (DSA) enables better spectrum management by allowing usage in times of spectrum inactivity. This research presents the CR problem of rendezvous for fast Frequency Hopping Spread Spectrum (FHSS) networks, and examines protocols for disseminating RF environment information to coordinate spectrum usage. First, Gold\u27s algorithm is investigated as a rendezvous protocol for networks utilizing fast frequency hopping. A hardware implementation of Gold\u27s algorithm on a Virtex-5 Field Programmable Gate Array (FPGA) is constructed to determine the resource requirements and timing limitations for use in a CR. The resulting design proves functionality of the algorithm, and demonstrates a decrease in time-to-rendezvous over current methods. Once a CR network is formed, it must understand the changing environment in order to better utilize the available spectrum. This research addresses the costs a network incurs to coordinate such environment data. Three exchange protocols are introduced and evaluated via simulation to determine the best technique based on network size. The resulting comparison found that smaller networks function best with polled or timedivision based protocols where radios always share their environment information. Larger networks, on the other hand, function best when a dispute-based exchange protocol was utilized. These studies together conclude that the selection of a rendezvous algorithm or a protocol for the exchange of environment data in a CR network are determined by the characteristics of the network, and therefore their selection requires a cognitive decision

Spectrum sharing security and attacks in CRNs: a review

Cognitive Radio plays a major part in communication technology by resolving the shortage of the spectrum through usage of dynamic spectrum access and artificial intelligence characteristics. The element of spectrum sharing in cognitive radio is a fundament al approach in utilising free channels. Cooperatively communicating cognitive radio devices use the common control channel of the cognitive radio medium access control to achieve spectrum sharing. Thus, the common control channel and consequently spectrum sharing security are vital to ensuring security in the subsequent data communication among cognitive radio nodes. In addition to well known security problems in wireless networks, cognitive radio networks introduce new classes of security threats and challenges, such as licensed user emulation attacks in spectrum sensing and misbehaviours in the common control channel transactions, which degrade the overall network operation and performance. This review paper briefly presents the known threats and attacks in wireless networks before it looks into the concept of cognitive radio and its main functionality. The paper then mainly focuses on spectrum sharing security and its related challenges. Since spectrum sharing is enabled through usage of the common control channel, more attention is paid to the security of the common control channel by looking into its security threats as well as protection and detection mechanisms. Finally, the pros and cons as well as the comparisons of different CR - specific security mechanisms are presented with some open research issues and challenges

Αναδιάρθρωση Αναθέσεων Πόρων σε Δίκτυα Γνωσιακής Ραδιοεπικοινωνίας

241 σ.Το στατικό μοντέλο διαχείρισης του ραδιοφάσματος αδυνατεί να ικανοποιήσει τη συνεχώς αυξανόμενη ζήτηση πρόσβασης στον εν λόγω πόρο, αποτελώντας ουσιαστικά τροχοπέδη στην ανάπτυξη περαιτέρω καινοτόμων ασύρματων υπηρεσιών. Ως καταλληλότερη τεχνολογία για την αποκατάσταση της αποδοτικότητας στον τρόπο εκμετάλλευσης του ραδιοφάσματος θεωρείται σήμερα η Γνωσιακή Ραδιοεπικοινωνία. Η εν λόγω τεχνολογία παρέχει στις ασύρματες συσκευές την ευελιξία να εκμεταλλεύονται ευκαιριακά μη-χρησιμοποιούμενες μερίδες του ραδιοφάσματος, προδιαγράφοντας τρείς θεμελιώδεις διαδικασίες, ήτοι την "Παρακολούθηση Φάσματος", τον "Μερισμό Φάσματος" και την "Κινητικότητα Φάσματος". Η παρούσα διδακτορική διατριβή εντάσσεται στο ευρύτερο ερευνητικό πεδίο της Γνωσιακής Ραδιοεπικοινωνίας και πραγματεύεται ανοιχτά θέματα τα οποία άπτονται και των τριών ανωτέρω διαδικασιών. Συγκεκριμένα, στην παρούσα διατριβή προσεγγίζεται το δημοφιλές πρόβλημα της Συνδυασμένης Εκχώρησης Καναλιών και Δρομολόγησης (διαδικασία "Μερισμού Φάσματος") υπό το πρίσμα των Δικτύων Γνωσιακής Ραδιοεπικοινωνίας και, βάσει αυτού, προτείνεται ένας μηχανισμός ελαχιστοποίησης της επιβάρυνσης η οποία προκαλείται στα εν λόγω δίκτυα κατά τη συχνότερη αναδιάρθρωση των αναθέσεων πόρων τους (διαδικασία "Κινητικότητας Φάσματος"). Τόσο το ανωτέρω πρόβλημα μερισμού φάσματος, όσο και ο μηχανισμός αποδοτικής αναδιάρθρωσης αναθέσεων πόρων μοντελοποιούνται, αρχικά, ως προβλήματα βελτιστοποίησης, ενώ στη συνέχεια αναζητούνται κατάλληλες ευρετικές μέθοδοι με σκοπό την πλησιοβέλτιστη επίλυση των εν λόγω προβλημάτων και, κατ’ επέκταση, την αποκατάσταση της δυνατότητας εφαρμογής τους σε πρακτικά Δίκτυα Γνωσιακής Ραδιοεπικοινωνίας. Ειδικότερα, για τον προδιαγραφόμενο μηχανισμό βέλτιστης αναδιάρθρωσης αναθέσεων πόρων, προτείνεται μια εξαιρετικά αποδοτική, εξειδικευμένη στο συγκεκριμένο πρόβλημα ευρετική μέθοδος. Στα πλαίσια της παρούσας διατριβής πραγματοποιείται, επίσης, μια Επισκόπηση Κατάληψης Φάσματος στη μητροπολιτική περιοχή των Αθηνών, ώστε να αξιολογηθεί η δυνατότητα του πραγματικού περιβάλλοντος ραδιοσυχνοτήτων να υποστηρίξει την εφαρμογή της τεχνολογίας της Γνωσιακής Ραδιοεπικοινωνίας στην πράξη και, κατ’ επέκταση, να ενδυναμωθεί η πρακτικότητα της πραγματοποιούμενης έρευνας. Κατόπιν ενδελεχούς εξέτασης των συλλεγμένων δεδομένων μετρήσεων, τέλος, αναδεικνύεται η ύπαρξη συσχετίσεων στη μετρούμενη ενέργεια γειτονικών καναλιών και, εν συνεχεία, προτείνεται μια μεθοδολογία η οποία εκμεταλλεύεται την εν λόγω ιδιότητα, επιτρέποντας στις ασύρματες συσκευές να αυξάνουν την ενημερότητά τους επί του εξ ορισμού άγνωστου περιβάλλοντος ραδιοσυχνοτήτων τους επεξεργαζόμενες αποκλειστικά όσα δεδομένα συλλέγουν κατά την τυπικά εφαρμοζόμενη διαδικασία της "Παρακολούθησης Φάσματος". Η αποκτώμενη ενημερότητα, μάλιστα, δύναται να δράσει υποστηρικτικά επί του συνόλου των διαδικασιών τις οποίες ορίζει η τεχνολογία της Γνωσιακής Ραδιοεπικοινωνίας και – σε συνδυασμό με τον προτεινόμενο μηχανισμό βέλτιστης αναδιάρθρωσης αναθέσεων πόρων – να βελτιώσει σημαντικά την αποδοτικότητα των αντίστοιχων δικτύων.The current statically established model of spectrum management is unable to satisfy the constantly growing demand of users and networks for spectrum access, essentially obstructing the deployment of new and innovative wireless services in practice. Cognitive Radio is considered a promising technology for restoring efficiency in spectrum utilization, by providing the wireless devices with the flexibility to opportunistically exploit unused spectrum portions that potentially exist in their wireless environment. Cognitive Radio technology specifies in practice three fundamental processes, namely the "Spectrum Monitoring", the "Spectrum Sharing" and the "Spectrum Mobility", and this thesis focuses on the study of open issues related to all these three layers of conception. More specifically, the popular problem of Joint Channel Assignment and Routing ("Spectrum Sharing" process) is considered from the perspective of Cognitive Radio Networks and, based on that, a novel mechanism is proposed with the ulterior view to minimize the overhead that is induced on such networks during their frequent resource allocation reconfigurations ("Spectrum Mobility" process). Both the Joint Channel Assignment and Routing problem, as well as the proposed reconfiguration mechanism are first modeled as optimization problems. Then, proper heuristic methods are investigated for quickly providing near-optimal solutions to the above problems and, thus, making it viable to be applied to realistic Cognitive Radio Networks scaling in commercial sizes. Especially for the proposed reconfiguration mechanism, a novel and efficient heuristic method is designed, which exploits the unique nature of the respective optimization problem. Furthermore, within the framework of this dissertation, a Spectrum Occupancy Survey is carried out in the metropolitan area of Athens, aiming at evaluating the ability of the real spectrum environment to support the application of the Cognitive Radio technology in practice and, thus, empower the practicality of the conducted research. Finally, by further processing the collected measurement data, the existence of correlation properties in the sensed power of measured neighboring channels is advocated and, based on them, a new methodology is proposed for enabling the wireless devices to raise their awareness on their otherwise unknown operating spectrum environment by simply leveraging data that are collected during the typically applied "Spectrum Monitoring" process. Notably, the acquired awareness can be well exploited for improving all the above processes defined by the Cognitive Radio technology and – in combination with the proposed reconfiguration mechanism – to further increase the efficiency of such networks.Σταμάτιος Γ. Αρκουλή