—Spectrum sharing has become a promising approach to meet the rapid development of cognitive radio technologies and improving the spectrum utilization and mitigate the spectrum starvation problems. This paper discusses the achievable transmission capacity of secondary users in a cognitive radio network employing collaborative spectrum sensing and undergoes Nakagami-m fading channel. Efficient and spectrum detection of licensed user is crucial to a successful deployment of cognitive radio. However, spectrum detection in mobile fading channels is challenging and it affects the detection performance. The proposed system model consists of a primary or licensed network, secondary users' network and infrastructure collaborative spectrum sensor, each with independent and none identical propagation channel model that follow Nakagami-m fading statistics. We develop a new mathematical framework and derive new expressions for the transmission capacity of secondary users with all channels undergoing Nakagami-m fading with non-integer fading parameters. Among numerus combining methods, we consider the impact of soft and hard decision combining of the spectrum detector on the transmission capacity. Moreover, we derived exact and alternative expressions of the transmission capacity for integer-fading parameter cases. The pertinent numerical results are generated to evaluate our analytical solution for the transmission capacity under various scenarios such as primary network traffic, channel fading parameters and collaborative sensing methods. `

본 논문에서는 무선인지시스템에서 스펙트럼 센싱을 효율적으로 수행하기 위한 선택적 협력 스펙트럼 검출 기법을 제안한다. 제안된 알고리즘에서는 각 무선인지 사용자가 자신의 유도비(likelihood ratio)를 기반으로 자신의 센싱 신뢰도를 평가하고, 센싱 신뢰도에 따른 타이머를 활용하는 경쟁기반의 센싱 결과 보고 메커니즘을 활용한다. 이를 통해, 제안된 선택적 협력 스펙트럼 기법에서는 가장 높은 센싱 신뢰도를 갖는 무선인지 사용자만이 국부 스펙트럼 센싱값을 융합센터로 전송함으로써, 스펙트럼 센싱의 성능을 일정한 레벨로 유지하고, 협력 스펙트럼 센싱의 단점인 제어 트래픽 및 협력 센싱 시간을 줄이는 이점을 갖는다.

본 논문에서는 동적 스펙트럼 접근을 위한 유전자 알고리즘 기반 전송 매개변수 최적화 기법을 제안한다. 구체적으로는 전송 매개변수 최적화를 위해 다목적 적합도 함수를 단일 목적 적합도 함수들의 가중합으로 표현하고, 유전자 알고리즘을 이용하여 주어진 전송 시나리오에 최적화된 전송 매개변수 값을 얻는다. 모의실험을 통하여 제안한 다목적 적합도 함수를 이용하여 주어진 시나리오에 따라 전송 매개변수를 최적화한 결과를 보인다.

Η μελέτη και σχεδίαση των σύγχρονων δικτύων ασύρματων επικοινωνιών επιβάλλει την υιοθέτηση αποτελεσματικών τεχνικών για την καταπολέμηση των παρεμβολών προκειμένου να εξασφαλίζεται η ταυτόχρονη πρόσβαση των χρηστών σε εφαρμογές που απαιτούν υψηλό ρυθμό μετάδοσης δεδομένων και μεγάλη αξιοπιστία σε πραγματικό χρόνο. Η παραπάνω ανάγκη γίνεται συνεχώς και πιο επιτακτική εξαιτίας της ολοένα αυξανόμενης πυκνότητας των χρηστών, αλλά και των περιορισμένων διαθέσιμων πόρων σε φάσμα που έχει οδηγήσει σταδιακά στη χρήση τεχνικών πολλαπλών φερόντων για επικοινωνία άνω και κάτω ζεύξης τόσο σ τα επίγεια όσο και σ τα δορυφορικά συσ τήματα νέας γενιάς. Η διδακτορική διατριβή οργανώνεται σε δύο μέρη. Το πρώτο μέρος είναι αφιερωμένο στα διαφορετικά είδη των παρεμβολών, τις επιπτώσεις τους και τους τρόπους αντιμετώπισης τους σε σύγχρονα και μελλοντικά συστήματα ασυρμάτων επικοινωνιών. Επιπλέον, εξετάζεται η επίδραση των ομοκαναλικών παρεμβολών σε ευφυή συστήματα ασύρματων επικοινωνιών, κατά την ανιχνευση φασματικών κενών, και παρουσιάζονται κατάλληλες εκφράσεις για την αξιολόγηση των επιδόσεων του ενεργειακού ανιχνευτή και τον ορισμό των παραμέτρων ανίχνευσης, οι οποίες λαμβάνουν υπόψιν τους τα επιπέδου των παρεμβολών. Το δεύτερο μέρος είναι αφιερωμένο στις επιπτώσεις των ατελειών του υλικού του αναλογικού τμήματος των πομποδεκτών σε σύγχρονα συστήματα ασυρμάτων επικοινωνιών. Πιο συγκεκριμένα, αφού παρουσιάστούν τα σημαντικότερα φαινόμενα που προκαλούνται εξαιτίας των ατελειών των πομποδεκτών, ήτοι ασυμφωνία συμφασικής και ορθογωνικής συνιστώσας, φασικός θόρυβος, και μη-γραμμικότητες ενισχυτών, γίνεται ανασκόπηση των επιδράσεων τους σε συστήματα ενός και πολλαπλών φερόντων. Παρατηρούμε ότι σε συστήματα ενός φέροντος προκαλούν παραμορφώσεις του σήματος, ενώ σε συστήματα πολλαπλών φερόντων προκαλούν επιπρόσθετα παρεμβολές από κατοπτρικά ή γειτονικά φέροντα (κανάλια). Στη συνέχεια, η διδακτορική διατριβή επικεντρώνεται στην ποσοτικοποίηση των επιδράσεων του φαινομένου της ασυμφωνίας συμφασικής και ορθογωνικής συνιστώσας σε ασύρματα συστήματα παρουσία κασκοδικών διαλειπτικών καναλιών. Ακολουθεί διερεύνηση των επιπτώσεων της ασυμφωνία συμφασικής και ορθογωνικής συνιστώσας, καθώς επίσης και του μερικού περιορισμού των εσω-παρεμβολών, στην ανίχνευση του φάσματος σε αμφίδρομα ευφυή συστήματα επικοινωνίας. Επίσης, μελετάται η επίδρασης των διαλείψεων και του συνδυασμού των ατελειών του υλικού στην ανίχνευση του φάσματος. Το επόμενο πρόβλημα που εξετάζεται αφορά την κατανομή ενέργειας από το σταθμό βάσης σε πολλούς χρήστες σε συστήματα ορθογωνικής πολλαπλής εισόδου στο πεδίο της συχνότητας, στα οποία ο κάθε εξοπλισμός χρήστη έχει διαφορετικά επίπεδα των ασυμφωνία συμφασικής και ορθογωνικής συνιστώσας. Στα πλαίσια του προβλήματος αυτού, παρουσιάζεται μία καινοτόμα χαμηλής-πολυπλοκότητας μέθοδος για την κατανομή της ενέργειας στους χρήστες, η οποία λαμβάνει υπόψιν τα επίπεδα της ασυμφωνία συμφασικής και ορθογωνικής συνιστώσας των προς εξυπηρέτηση χρηστών, και εγγυάται δικαιοσύνη από την άποψη του εφικτού ρυθμού δεδομένων των χρηστών. Τα αποτελέσματα δείχνουν ότι ο εφικτός ρυθμός δεδομένων των χρηστών μπορεί να αυξηθεί δραστικά, με τη χρήση της προτεινόμενής τεχνικής κατανομής ενέργειας. Τέλος, δίνεται ένα καινοτόμο σχήμα, χαμηλής πολυπλοκότητας, το οποίο στοχεύει στην βελτίωση των επιδόσεων τηλεπικοινωνιακών συστημάτων πολλαπλών φερόντων, όπου οι εμπλεκόμενες συσκευές διαθέτουν μία κεραία και ο δέκτης παρουσιάζει ασυμφωνία συμφασικής και ορθογωνικής συνιστώσας. Το προτεινόμενο σχήμα όχι μόνο καταπολεμά τις καταστροφικές επιπτώσεις της ασυμφωνίας συμφασικής και ορθογωνικής συνιστώσας, αλλά, μέσου κατάλληλης επεξεργασίας σήματος, επιτρέπει επίσης εκμετάλλευση των παρεμβολών, που δημιουργούνται εξαιτίας της ασυμφωνίας συμφασικής και ορθογωνικής συνιστώσας, ώστε να πετύχει διαφορισμό δεύτερης τάξης.

© 2020 John Wiley & Sons, Ltd.. This is the accepted version of the following article: Simpson, O, Sun, Y. Efficient evidence‐based decision fusion scheme for cooperative spectrum sensing in cognitive radio networks. Trans Emerging Tel Tech. 2020;e3901., which has been published in final form at https://doi.org/10.1002/ett.3901.

xvi Chapter

where • Ai is the amplitude of the i th useful signal; • τi is the code phase delay introduced by the transmission channel; • ci(t − τi) is the spreading sequence which is given by the product of several terms and it is assumed to take value in the set {−1, 1}; • di(t − τi) is the navigation message, Binary Phase Shift Keying (BPSK) modulated, containing satellite data, each binary unit is called bit;

radio system provide us a solution for spectrum congestion problem, but the effectiveness of the system is only depends on the technique used for spectrum sensing, that how effectively the detection is performing at very low SNR. In this research paper we proposed a technique of spectrum sensing based on CAF and third order cumulant. And the proposed algorithm effectively able to detect the presence of primary user at very LOW SNR, as compared to existing technologies present in literature.

pectrum sensing is an essential function for the operation of cognitive radios. This paper, considers the application of periodogram-based energy detection for spectrum sensing and presents a generalized mathematical model which includes the case of a complex non-zero mean primary signal. The model is then used to obtain accurate performance analysis of this technique. By defining and exploiting the noncentral quadratic form of the periodogram, the cumulative distribution function (CDF) is obtained directly through numerical inversion. The presented model is simplified through manipulating the characteristics of the hermitian matrix of the quadratic form along with the covariance matrix of the received signal. Using this, the non-zero eigenvalue of the corresponding product is obtained and the probabilities of false alarm and missed detection are derived. Furthermore, the performance of detecting multiple frequencies simultaneously is considered by investigating the independence requirements of the corresponding quadratic forms. The presented results are validated with the aid of Monti-Carlo simulations.

ii Abstract (in Finnish) iiiin Finnish) iii

espanolEl rapido crecimiento de la tecnologia inalambrica demanda emplear eficientemente el espectro disponible. En este trabajo se disena un detector de energia para ser usado en un escenario de Radio Cognitivo utilizando una plataforma de Radio Definido por Software. El diseno de este detector es desarrollado empleando los softwares: Simulink y Xilinx System Generator de MATLAB para ser implementado en un dispositivo de tipo Arreglo de Compuertas Programables por Campo (FPGA). Para sensar el espectro, la deteccion de energia es el metodo de sensado mas utilizado debido a su baja complejidad computacional. Ademas, el detector de energia ofrece la capacidad de identificar espacios disponibles en el espectro sin requerir un conocimiento previo de las caracteristicas de transmision de los usuarios primarios. Sin embargo, establecer un umbral para la deteccion de energia requiere el conocimiento de la potencia de ruido del canal, que puede ser establecida por metodos de estimacion apropiados. En este sentido, un nuevo metodo es propuesto e implementado en FPGA para establecer el umbral y detectar correctamente la presencia de senales en el espectro. Los resultados obtenidos revelan el satisfactorio desempeno del detector propuesto dado por Pd>0.9 y Pfa=0.1 para relaciones senal a ruido bajas en el rango [-8, 15] dB. Por otro lado, en el caso de la television digital en Cuba se requiere un metodo robusto y eficiente de deteccion automatico de senales que permita identificar los espacios en blanco de las bandas de television. Los usuarios cognitivos pueden utilizar estos espacios en blanco para aumentar y mejorar la conectividad en aplicaciones de comunicaciones inalambricas. Con este fin, este trabajo tiene como objetivo detectar los espacios en blanco en el espectro de Television Digital usando la tecnica de deteccion de energia. Los resultados de simulacion demuestran que el detector propuesto posee un correcto comportamiento para este escenario EnglishThe rapid growth of wireless technology demands to employ the available spectrum efficiently. In this work, an Energy Detector is designed to be used in a Cognitive Radio scenario using a platform based on Software Defined Radio principles. The design of this detector is developed by using Simulink and Xilinx System Generator MATLAB software to be implemented on a Field Programmable Gate Array (FPGA) device. To sense the spectrum, the energy detector (ED) is the most used approach due to its low computational complexity. Furthermore, ED offers the ability to identify spectrum holes without prior knowledge regarding transmission characteristics of primary users. However, setting a threshold for energy detection requires to estimate noise power, which can be established by appropriate estimation methods. In this regard, a new method is proposed and implemented on FPGA to establish a threshold and detect properly the available spectrum. Results obtained reveal a proper performance of the proposed detector given by Pd>0.9 and Pfa=0.1, respectively, in the SNR range [-8, 15] dB. On the other hand, Digital Television in Cuba requires a robust and efficient automatic signal detection method to identify Television white spaces. Cognitive radio users would use these spectral holes to increase bandwidth and improve connectivity for wireless communications applications. To this end, this work is aimed to detect white spaces of the Digital Television spectrum using energy detector method. Simulation results show that the detector performs correctly on this scenario

[1] In this paper, we consider a wideband cognitive radio system that operates over multiple idle subchannels. A joint optimization of sensing threshold and transmission power is proposed, which maximizes the total throughput subject to the constraints on the total interference, the total power, and the probabilities of false alarm and detection of each subchannel. An alternative joint optimization is proposed, which minimizes the total interference under the constraint of the total throughput. The bilevel optimization method is used to solve the proposed optimization problems with a minimized iteration complexity. The mixed-variable optimization problem is divided into two single-variable convex optimization subproblems: the upper level for threshold optimization and the lower level for power optimization. Weighed cooperative sensing is proposed to maximize the detection probability by choosing the optimal weighed factors. The simulations show that the proposed joint optimization algorithm can achieve desirable improvement on the throughput of cognitive radio at the same interference level to primary user, or vice versa within the limits on the probabilities of false alarm and miss detection, and the weighed cooperative sensing can considerably improve sensing performance compared with the unweighed cooperative sensing and single-user sensing.

Without an efficient way to achieve the reliability of the decision, the implementation of weighted data fusion is limited in the hard decision combination for cooperative spectrum sensing. To address this problem, a new cooperative spectrum sensing scheme based on the location information of the primary user (PU) and cognitive radio (CR) is proposed. In the new scheme, depending on the location information, the channel condition between the PU and each CR is obtained at the fusion center (FC), with which the local sensing reliability is first achieved. Then we calculate the transmission reliability between the CR and FC. Based on both the local sensing reliability and the transmission reliability, the combining weighting factor is determined for optimal data fusion. On the basis of this proposed scheme, we study the global sensing false alarm and detection probabilities, derive the expressions to obtain the optimal local sensing threshold, and perform an error analysis that demonstrates the impact of imperfect channel knowledge. Using both analytical and simulation methods, we find that the proposed scheme achieves better performance compared with the conventional logical fusion rules in the hard decision combination for cooperative spectrum sensing.

Within the sequential sensing and transmission paradigm (SSTP), spectrum sensing over the whole primary user (PU) band always suspends secondary user (SU) data transmission in the sensing interval. Delay incurred by this kind of suspension may be intolerable to delay sensitive SU services. To alleviate this problem, we adopt a parallel sensing and transmission paradigm (PSTP), within which the SU transmits and senses simultaneously. In this paper, we investigate the relationship between the achievable SU throughput and bandwidth allocated for spectrum sensing within the PSTP, under the constraint that the PU is sufficiently protected. We also study the delay improvements of the PSTP over that of the SSTP. Both theoretical analyses and simulation results that there exists an optimal sensing bandwidth that maximizes the achievable SU throughput within the PSTP. Furthermore, compared to the SSTP, the SU delay is reduced by using the PSTP.

Within the last years a discrepancy between the spectrum licenses and the actual usage of spectrum has been observed. While the vast majority of frequency bands attractive for wireless communication are licensed, measurement campaigns have shown that large portions of the spectrum are temporarily unused in many locations. Sensing-based opportunistic spectrum re-usage has been identified as an attractive approach to overcome this discrepancy. In this approach Cognitive Radio (CR) based Secondary Users (SUs) sense the licensed frequency bands owned by Primary Users (PUs) for available spectrum and use the temporarily available spectrum on an opportunistic basis with the constraint to vacate the spectrum as soon as the license holder returns. An apparent challenge for such secondary spectrum usage is the reliable detection of the PU communication. The SUs have to ensure that the licensed spectrum is always vacated in a timely manner and that no harmful interference is created to the PUs. However, not only the protection of the PU communication is a challenging task for such CR networks but also the maintenance of a proper Quality of Service (QoS) for the secondary communication. Due to the strict access priority of the PUs, the secondary communication potentially has to be often relocated to new, temporarily available frequency bands. In this thesis we present and evaluate a CR system design, which is able to cope with these two challenges. We show that the proposed system design can achieve both reliable PU protection and secondary QoS support even for small secondary networks consisting of simple, low complexity CRs using energy detection-based spectrum sensing for the PU protection. Using a proper amount of spectral overhead for spectrum sensing and for secondary QoS support, reliable PU protection and secondary QoS support can also be maintained in environments with very high variability of temporarily available spectrum. We evaluate the tradeoff between both overheads and show that there exists an optimal joint spectral overhead which maximizes the spectral efficiency. We further show that, while the spectral efficiency of initially small network deployments based on the proposed system design might be low, it is still significantly greater than zero. Furthermore, the spectral efficiency is improved, as the network size increases. This makes the proposed CR design an ideal approach for initial deployments of very small and cheap CR networks, which are perfectly scalable: with an increase of network size (which usually goes hand in hand with an increase in spectrum demand), also the spectral efficiency is increased.

With the recent growth in wireless technology, a lot of research has been done on the optimal power management of wireless devices. One approach is to exploit radio waves existing in the ambient environment for battery charging, called RF energy harvesting. In this paper, in order to improve the RF energy harvesting performance, we utilize spectrum sensing to allow the wireless devices to select the frequency band with maximum power that exceeds a predefined threshold to charge the device (this power threshold can be determined according to battery type and its required charging power) and the device can use this power for battery charging. Also, a novel voltage multiplier circuit is proposed. By means of simulations, it can be seen that after detection of our desired 1 mW RF signal, system output power is about 532 μW. In practice, the output power of our fabricated system is about 450 μW.

With the recent growth in wireless technology, a lot of research has been done on the optimal power management of wireless devices. One approach is to exploit radio waves existing in the ambient environment for battery charging, called RF energy harvesting. In this paper, in order to improve the RF energy harvesting performance, we utilize spectrum sensing to allow the wireless devices to select the frequency band with maximum power that exceeds a predefined threshold to charge the device (this power threshold can be determined according to battery type and its required charging power) and the device can use this power for battery charging. Also, a novel voltage multiplier circuit is proposed. By means of simulations, it can be seen that after detection of our desired 1 mW RF signal, system output power is about 532 μW. In practice, the output power of our fabricated system is about 450 μW.

With the recent advances in wireless technologies, high frequency radio has become the primary medium for long-distance communication. Among various types of modulation in signal transmission, morse code stands out due to its simplicity and efficiency in information transmission while costing small bandwidth. In practice, however, it is extremely laborious to locate morse signals in wideband communication. It’s a needle in a haystack, if morse code is sent in random carrier waves at random period. To avoid this, automatic morse signal detection has become a challenging task in wireless morse communications, and new solutions could be derived from the latest machine learning techniques. In this paper, we propose a deep learning framework, namely DeepMorse, to blindly detect morse signals in wideband spectrum data. In particular, we first develop a multi-signal sensing module to retrieve signal candidates from wideband spectrum without prior knowledge. Then, we construct a CNN-based module to extract informative features from the located candidates, in order to distinguish the morse signal from other types of modulation. To evaluate the proposed DeepMorse model, we set up a testbed utilizing commercialized long-distance wireless communication devices. The experimental results demonstrate that DeepMorse is able to effectively detect morse signals and outperform the state-of-the-art methods on four real-world datasets.

With the rapid proliferation of new wireless communication devices and services, the demand for the radio spectrum is increasing at a rapid rate, which leads to making the spectrum more and more crowded. The limited available spectrum and the inefficiency in the spectrum usage have led to the emergence of cognitive radio (CR) and dynamic spectrum access (DSA) technologies, which enable future wireless communication systems to exploit the empty spectrum in an opportunistic manner. To do so, future wireless devices should be aware of their surrounding radio environment in order to adapt their operating parameters according to the real-time conditions of the radio environment. From this viewpoint, spectrum sensing is becoming increasingly important to new and future wireless communication systems, which is designed to monitor the usage of the radio spectrum and reliably identify the unused bands to enable wireless devices to switch from one vacant band to another, thereby achieving flexible, reliable, and efficient spectrum utilisation. This thesis focuses on issues related to local and cooperative spectrum sensing for CR networks, which need to be resolved. These include the problems of noise uncertainty and detection in low signal to noise ratio (SNR) environments in individual spectrum sensing. In addition to issues of energy consumption, sensing delay and reporting error in cooperative spectrum sensing. In this thesis, we investigate how to improve spectrum sensing algorithms to increase their detection performance and achieving energy efficiency. To this end, first, we propose a new spectrum sensing algorithm based on energy detection that increases the reliability of individual spectrum sensing. In spite of the fact that the energy detection is still the most common detection mechanism for spectrum sensing due to its simplicity. Energy detection does not require any prior knowledge of primary signals, but has the drawbacks of threshold selection, and poor performance due to noise uncertainty especially at low SNR. Therefore, a new adaptive optimal energy detection algorithm (AOED) is presented in this thesis. In comparison with the existing energy detection schemes the detection performance achieved through AOED algorithm is higher. Secondly, as cooperative spectrum sensing (CSS) can give further improvement in the detection reliability, the AOED algorithm is extended to cooperative sensing; in which multiple cognitive users collaborate to detect the primary transmission. The new combined approach (AOED and CSS) is shown to be more reliable detection than the individual detection scheme, where the hidden terminal problem can be mitigated. Furthermore, an optimal fusion strategy for hard-fusion based cognitive radio networks is presented, which optimises sensing performance. Thirdly, the need for denser deployment of base stations to satisfy the estimated high traffic demand in future wireless networks leads to a significant increase in energy consumption. Moreover, in large-scale cognitive radio networks some of cooperative devices may be located far away from the fusion centre, which causes an increase in the error rate of reporting channel, and thus deteriorating the performance of cooperative spectrum sensing. To overcome these problems, a new multi-hop cluster based cooperative spectrum sensing (MHCCSS) scheme is proposed, where only cluster heads are allowed to send their cluster results to the fusion centre via successive cluster heads, based on higher SNR of communication channel between cluster heads. Furthermore, in decentralised CSS as in cognitive radio Ad Hoc networks (CRAHNs), where there is no fusion centre, each cognitive user performs the local spectrum sensing and shares the sensing information with its neighbours and then makes its decision on the spectrum availability based on its own sensing information and the neighbours’ information. However, cooperation between cognitive users consumes significant energy due to heavy communications. In addition to this, each CR user has asynchronous sensing and transmission schedules which add new challenges in implementing CSS in CRAHNs. In this thesis, a new multi-hop cluster based CSS scheme has been proposed for CRAHNs, which can enhance the cooperative sensing performance and reduce the energy consumption compared with other conventional decentralised cooperative spectrum sensing modes.

With the rapid growth of wireless communication networks, we are facing the challenge of integration of diverse wireless networks such as WLAN and WWAN. Therefore, it becomes important to think at vertical handoff solution where the user can move seamlessly among various type of networks, to provide the best QoS to the higher layers applications. In this paper, we propose a method to estimate the channel occupancy rate metric of an IEEE 802.11 network from the physical layer. This method can be applied for any network that use the CSMA/CA protocol. Our theorical results are validated using experimental measurements captured by RAMMUS RF Plateform.