Cooperative Wideband Spectrum Sensing Based on Joint Sparsity

COOPERATIVE WIDEBAND SPECTRUM SENSING BASED ON JOINT SPARSITY By Ghazaleh Jowkar, Master of Science A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science at Virginia Commonwealth University Virginia Commonwealth University 2017 Major Director: Dr. Ruixin Niu, Associate Professor of Department of Electrical and Computer Engineering In this thesis, the problem of wideband spectrum sensing in cognitive radio (CR) networks using sub-Nyquist sampling and sparse signal processing techniques is investigated. To mitigate multi-path fading, it is assumed that a group of spatially dispersed SUs collaborate for wideband spectrum sensing, to determine whether or not a channel is occupied by a primary user (PU). Due to the underutilization of the spectrum by the PUs, the spectrum matrix has only a small number of non-zero rows. In existing state-of-the-art approaches, the spectrum sensing problem was solved using the low-rank matrix completion technique involving matrix nuclear-norm minimization. Motivated by the fact that the spectrum matrix is not only low-rank, but also sparse, a spectrum sensing approach is proposed based on minimizing a mixed-norm of the spectrum matrix instead of low-rank matrix completion to promote the joint sparsity among the column vectors of the spectrum matrix. Simulation results are obtained, which demonstrate that the proposed mixed-norm minimization approach outperforms the low-rank matrix completion based approach, in terms of the PU detection performance. Further we used mixed-norm minimization model in multi time frame detection. Simulation results shows that increasing the number of time frames will increase the detection performance, however, by increasing the number of time frames after a number of times the performance decrease dramatically

Spectrum measurement, sensing, analysis and simulation in the context of cognitive radio

The radio frequency (RF) spectrum is a scarce natural resource, currently regulated locally by national agencies. Spectrum has been assigned to different services and it is very difficult for emerging wireless technologies to gain access due to rigid spectmm policy and heavy opportunity cost. Current spectrum management by licensing causes artificial spectrum scarcity. Spectrum monitoring shows that many frequencies and times are unused. Dynamic spectrum access (DSA) is a potential solution to low spectrum efficiency. In DSA, an unlicensed user opportunistically uses vacant licensed spectrum with the help of cognitive radio. Cognitive radio is a key enabling technology for DSA. In a cognitive radio system, an unlicensed Secondary User (SU) identifies vacant licensed spectrum allocated to a Primary User (PU) and uses it without harmful interference to the PU. Cognitive radio increases spectrum usage efficiency while protecting legacy-licensed systems. The purpose of this thesis is to bring together a group of CR concepts and explore how we can make the transition from conventional radio to cognitive radio. Specific goals of the thesis are firstly the measurement of the radio spectrum to understand the current spectrum usage in the Humber region, UK in the context of cognitive radio. Secondly, to characterise the performance of cyclostationary feature detectors through theoretical analysis, hardware implementation, and real-time performance measurements. Thirdly, to mitigate the effect of degradation due to multipath fading and shadowing, the use of -wideband cooperative sensing techniques using adaptive sensing technique and multi-bit soft decision is proposed, which it is believed will introduce more spectral opportunities over wider frequency ranges and achieve higher opportunistic aggregate throughput.Understanding spectrum usage is the first step toward the future deployment of cognitive radio systems. Several spectrum usage measurement campaigns have been performed, mainly in the USA and Europe. These studies show locality and time dependence. In the first part of this thesis a spectrum usage measurement campaign in the Humber region, is reported. Spectrum usage patterns are identified and noise is characterised. A significant amount of spectrum was shown to be underutilized and available for the secondary use. The second part addresses the question: how can you tell if a spectrum channel is being used? Two spectrum sensing techniques are evaluated: Energy Detection and Cyclostationary Feature Detection. The performance of these techniques is compared using the measurements performed in the second part of the thesis. Cyclostationary feature detection is shown to be more robust to noise. The final part of the thesis considers the identification of vacant channels by combining spectrum measurements from multiple locations, known as cooperative sensing. Wideband cooperative sensing is proposed using multi resolution spectrum sensing (MRSS) with a multi-bit decision technique. Next, a two-stage adaptive system with cooperative wideband sensing is proposed based on the combination of energy detection and cyclostationary feature detection. Simulations using the system above indicate that the two-stage adaptive sensing cooperative wideband outperforms single site detection in terms of detection success and mean detection time in the context of wideband cooperative sensing

Implementation of spectrum sensing techniques for cognitive radio systems

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.This work presents a method for real-time detection of secondary users at the cognitive wireless technologies base stations. Cognitive radios may hide themselves in between the primary users to avoid being charged for spectrum usage. To deal with such scenarios, a cyclostationary Fast Fourier Transform accumulation method (FAM) has been used to develop a new strategy for recognising channel users under perfect and different noise environment conditions. Channel users are tracked according to the changes in their signal parameters, such as modulation techniques. MATLAB® Simulation tool was used to run various modulation signals on channels, and the obtained spectral correlation density function shows successful recognition between secondary and primary signals. We are unaware of previous efforts to use the FAM characteristics or other detection methods to make a distinction between channel users as presented in this thesis. A novel combination of both cognitive radio technology and ultra wideband technology is interdicted in this thesis, looking for an efficient and reliable spectrum sensing method to detect the presence of primary transmitters, and a number of spectrum-sensing techniques implemented in ultra wideband and cognitive radio component (UWB-CR) under different AWGN and fading settings environments. The sensing performance of different detectors is compared in conditions of probability of detection and miss detection curves. Simulation results show that the selection of detectors rely on the different fading scenarios, detector requirements and on a priori knowledge. Furthermore, result showed that the matched filter detection method is suitable for detecting signals through UWB-CR system under various fading channels. A general observation is that the matched filter detector outperforms the other detectors in all scenarios by an average of SNR=-20 dB in the level of probability of detection (Pd) , and the energy detector slightly outperforms the cyclostationary detector, in the level Pd at SNR=-20 dB. Furthermore, the thesis adapts novel detection models of cooperative and cluster cooperative wideband spectrum sensing in cognitive radio networks. In the proposed schemes, wavelet-based multi-resolution spectrum sensing and a proposed approach scheme are utilized for improving sensing performance of both models. On the other hand, cluster based cooperative spectrum sensing with soft combination Equal Gain Combination (EGC) scheme is proposed. The proposed detection models could achieve improvement of transmitter signal detection in terms of higher probability of detection and lower probability of false alarm. In the cooperative wideband spectrum sensing model, using traditional fusion rule, existing worst performance of false alarms by measurement is 78% of the sensing bands at an average SNR=5 dB; this compares with the proposed model, which is by measurement 19% false alarms of scanning spectrum at the same SNR for cluster cooperative wideband spectrum sensing. The proposed combining methods shows improvements of results with a high probability of detection (Pd) and low probability of false alarm (Pf) at an average SNR=-16 dB compared with other traditional fusion methods; this is illustrated through numerical results

Wideband cyclostationary spectrum sensing and characterization for cognitive radios

Motivated by the spectrum scarcity problem, Cognitive Radios (CRs) have been proposed as a solution to opportunistically communicate over unused spectrum licensed to Primary users (PUs). In this context, the unlicensed Secondary users (SUs) sense the spectrum to detect the presence or absence of PUs, and use the unoccupied bands without causing interference to PUs. CRs are equipped with capabilities such as, learning, adaptability, and recongurability, and are spectrum aware. Spectrum awareness comes from spectrum sensing, and it can be performed using different techniques

Spectrum handoff strategy for cognitive radio-based Mac in industrial wirless sensor and actuator networks

In this thesis, a Cognitive Radio(CR)-based MAC for Industrial Wireless Sensor and Actuator Network (IWSAN) applications is proposed. IWSANs are typically used for closed-loop control applications, and they demand strict requirements in terms of time and robustness. Low latency and low error rates are required in order not to endanger persons or machinery. Moreover, these applications operate in industrial environments such as factories or transport scenarios (as aeronautics or railway) where multipath fading and shadowing are present due to metal surfaces. Furthermore, interference from other communication systems or industrial machinery is also common in these environments. The proposed MAC, based on the CR paradigm, is capable of ensuring time and robustness requirements in industrial channels. In the process of designing the CR-based MAC for IWSAN applications, a comparison between several non-CR-based MACs and CR-based MACs has been carried out. This comparison, which allows stating the benefits of CR for these applications, is presented in this thesis. The performance of every MAC is determined theoretically using Network Calculus, and it is validated through OPNET simulations. CR solutions, due to their adaptability characteristics, are capable of avoiding interference and ensuring robustness in industrial environments. However, none of the selected MACs are capable of ensuring robustness without comprising time requirements, since interference is avoided but not in a bounded time. On the other hand, the MAC proposed in this thesis is capable of avoiding interference ensuring time and robustness requirements at the same time. This MAC is therefore suitable for IWSAN applications. To ensure a deterministic behavior against interference, a novel handoff algorithm, which detects interference and hops to another channel, has been proposed. This algorithm has been designed to be used jointly with one of the evaluated MACs. The detection of the interference and the hop to another channel is done in a bounded time, because the proposed algorithm detects interference while the system is transmitting. The performance of this proposal is evaluated using Network Calculus and OPNET simulations, and the results are compared with the system without the proposed handoff algorithm. The comparison of the results shows how the evaluated MAC is only capable of ensuring both time and robustness requirements when the proposed handoff strategy is used. Moreover, the spectrum sensing algorithm used to obtain information about the environment is delved and its performance is measured through MATLAB simulations. An energy detector has been chosen due to its simplicity. Also, a cyclostationary Modulation Classifier is presented and a simplification has been carried out allowing its implementation on real hardware. The Modulation Classifier is capable of distinguishing between OFDM, QPSK and GFSK signals. The performance of the algorithm is presented in this thesis for different signals and for different receiver impairments such as frequency offset, DC offset and I/Q imbalance. Finally, a cognitive platform to validate the spectrum sensing algorithms is presented. This platform has been designed using a Xilinx Virtex 6 FPGA by a working group composed of researchers from IK4-Ikerlan and Mondragon Unibertsitatea. The platform, which uses both spectrum sensing algorithms, is an Ethernet-to-RF bridge. It has been designed to replace an Ethernet wired link by a wireless one for IWSAN applications. The proposed platform ensures a reliable communication link against interference. In the proposed implementation, the energy detector is used by the transmitter in order to find a free channel to transmit data, whereas the modulation classifier is used by the receiver in order to distinguish between the signal transmitted by the RF-Ethernet bridge and other signals. In this way the receiver can find the channel where the transmitter is carrying out the communication.En esta tesis se propone una MAC basada en el paradigma de la Radio Cognitiva (RC) para redes de sensores y actuadores inalámbricos industriales. Estas redes se suelen utilizar para aplicaciones de control en lazo cerrado, que exigen requisitos estrictos de tiempo y robustez. Para no poner en peligro la salud de las personas o la maquinaria es necesario que la red asegure una baja latencia y una tasa baja de errores. Además, al trabajar en ambientes industriales como fábricas o transportes (trenes, aviones, etc.), estas redes tienen que hacer frente a canales con mucho desvanecimiento por multitrayecto y efecto sombra debido a las superficies metálicas. También es común en estos entornos que haya interferencias de otros sistemas de comunicaciones o de la propia maquinaria industrial. La MAC propuesta en esta tesis es capaz de asegurar los requisitos temporales y de robustez demandados trabajando en este tipo de entornos. En el proceso de diseño de la MAC basada en RC para redes de sensores y actuadores inalámbricos industriales, se ha llevado a cabo una comparación de diferentes MACs diseñadas para estas redes. Se han evaluado tanto MACs basadas en RC como no basadas en ella, estableciendo las ventajas de la RC para estas aplicaciones. La evaluación se ha llevado a cabo haciendo un estudio teórico mediante Network Calculus, cuyos resultados se han validado mediante simulaciones en OPNET. Los resultados muestran como la RC es capaz de evitar interferencias y asegurar robustez en ambientes industriales. Sin embargo, ninguna de las MACs seleccionadas ha conseguido asegurar ambos requisitos, temporales y de robustez, al mismo tiempo; se puede evitar las interferencias pero no sin comprometer los requisitos temporales de la aplicación. Sin embargo, la MAC propuesta es capaz de evitar interferencias asegurando al mismo tiempo los requisitos temporales y de robustez. Por lo tanto, la MAC propuesta es apropiada para este tipo de redes. Para asegurar el comportamiento determinista del sistema, se ha propuesto un novedoso algoritmo de handoff que es capaz de detectar una interferencia y saltar a otro canal. Este algoritmo se ha diseñado para ser utilizado conjuntamente con una de las MACs previamente evaluadas. La detección de la interferencia y el salto a otro canal se hace en un tiempo determinado de tiempo, ya que es posible detectar interferencias mientras el sistema está transmitiendo. Su rendimiento se ha evaluado mediante Network Calculus y simulaciones en OPNET, y se ha comparado con los resultados obtenidos con la MAC cuando no se utiliza el esquema propuesto. De la comparación se deduce que el esquema de handoff añade a la MAC la capacidad de asegurar a la vez los requisitos temporales y de robustez. Además, en la tesis se explica el algoritmo de spectrum sensing que la MAC utiliza para obtener información del entorno, y su rendimiento se ha estudiado mediante simulaciones en MATLAB. Debido a su simplicidad, se ha optado por un detector de energía para este propósito. También se presenta un clasificador de modulaciones cicloestacionario. Este clasificador ha sido simplificado todo lo posible para posibilitar su implementación en hardware real. El clasificador de modulaciones es capaz de distinguir entre señales OFDM, QPSK y GFSK. Su rendimiento se detalla para diferentes señales y para diferentes deficiencias presentes en el receptor, como son offset de frecuencia, offset de continua o desequilibrios I/Q. Por último, se presenta una plataforma cognitiva que se ha utilizado para validar los algoritmos de spectrum sensing. Un grupo de trabajo compuesto por investigadores de IK4-Ikerlan y Mondragon Unibertsitatea ha diseñado esta plataforma sobre una FPGA Virtex 6 de Xilinx. La plataforma, que utiliza los dos algoritmos de spectrum sensing, es un puente Ethernet-RF. Su objetivo es reemplazar un enlace cableado de Ethernet por uno inalámbrico para aplicaciones de redes de sensores y actuadores industriales. Gracias a los algoritmos de spectrum sensing, la plataforma es capaz de asegurar un enlace robusto ante interferencias. El detector de energía se utiliza en el transmisor para encontrar los posibles canales libres donde transmitir la información. Mientras que el clasificador de modulaciones se utiliza en el receptor para distinguir entre la señal del transmisor y otras posibles señales. Esto permite al receptor saber en qué canal de todos los posibles está el transmisor.Tesi honetan proposatzen da Irrati Kognitiboaren (IK) paradigman oinarritutako MAC bat industriako haririk gabeko sentsore eta eragingailuen sareetarako. Sare horiek begizta itxiko kontrol aplikazioetarako erabili ohi dira, denbora eta sendotasunaren aldetik baldintza ugari eskatzen dute eta. Pertsonen osasuna eta makinak arriskuan ez jartzeko, beharrezkoa da sareak latentzia eta hutsegite tasa txikiak bermatzea. Gainera, industri giroetan lan egiteko direnez, esaterako, lantegietan edo garraioetan (trenak, hegazkinak, etab.), sare horiek gai izan behar dira gainazal metalikoek eragiten dituzten ibilbide aniztunaren eta itzal efektuaren ondorioz asko barreiatzen diren kanalei aurre egiteko. Ingurune horien ohiko ezaugarria da, baita ere, beste komunikazio sistema batzuen edo industriako makinen beraien interferentziak egotea. Tesi honetan proposatzen den MACa gai da honelako inguruetan lan egiteko denborari eta sendotasunari dagokienez eskatzen dituen baldintzak ziurtatzeko. IKan oinarrituta haririk gabeko sentsore eta eragingailu industrialen sareetarako MACa diseinatzeko prozesuan, horrelako sareetarako aurkeztu diren hainbat MAC alderatu dira. IKan oinarritutako MACak zein bestelakoak ebaluatu dira, eta IKak aplikazio hauetarako dituen abantailak ezarri dira. Ebaluaziorako Network Calculus erabili da, zeinaren bidez azterketa teoriko bat egin baita, eta azterketaren emaitzak OPNETen simulazioak eginda baliozkotu dira. Emaitzek erakusten dutenez, IKa gai da industriako inguruneetan interferentziak ekidin eta sendotasuna ziurtatzeko. Halere, aukeratu diren MACetatik batek ere ez du lortu baldintza biak, denborari buruzkoa zein sendotasunari buruzkoa, aldi berean ziurtatzea; interferentziak ekidin daitezke, baina ez aplikazioaren denborari buruzko baldintzak arriskuan jarri gabe. Dena dela, proposatu den MACak portaera determinista bat ziurtatzen du interferentziekiko, eta aldi berean denborari eta sendotasunari buruzko baldintzak ere ziurtatzen ditu. Hortaz, MAC hau egokia da sare mota honetarako. Sistemaren portaera determinista ziurtatzeko, handoff algoritmo berritzailea proposatu da, zeina interferentzia bat antzeman eta beste kanal bat igarotzeko gai den. Algoritmo hori aurretik ebaluatutakoa MACetako batekin batera erabiltzeko diseinatu da. Interferentzia antzeman eta beste kanal batera salto egitea denbora jakin batean egiten da, izan ere, sistema transmititzen ari dela antzeman baitaitezke interferentziak. Network Calculusen bitartez eta OPNETeko simulazioen bitartez ebaluatu da sistemaren errendimendua, eta proposatutako eskema erabiltzen ez denean MACak ematen dituen emaitzekin alderatu da. Alderaketa horretatik ondorioztatzen denez, handoff eskemak denborari eta sendotasunari buruzko baldintzak batera ziurtatzeko ahalmena ematen dio MACari. Gainera, tesiak azaltzen du inguruneari buruzko informazioa eskuratzeko MACak erabiltzen duen spectrum sensing algoritmoa, eta bere errendimendua MATLABen simulazioak eginez aztertu da. Bere sinpletasuna dela eta, energia detektore bat aukeratu da asmo honetarako. Modulazio sailkatzaile zikloegonkor bat ere aurkezten da. Sailkapen hori ahalik eta gehien sinplifikatu da benetako hardwarean inplementatu ahal izateko. Modulazioen sailkatzaileak OFDM, QPSK eta GFSK seinaleak bereizi ditzake. Bere errendimendua hargailuan dauden seinale eta akats desberdinetarako zehazten da, esaterako maiztasunaren offset-a,zuzenaren offset-a edo I/Q desorekak. Bukatzeko, spectrum sensing-eko algoritmoak baliozkotzeko erabili den plataforma kognitibo bat aurkezten da. IK4-Ikerlaneko eta Mondragon Unibertsitateko ikertzailez osatutako lantalde batek diseinatu du plataforma hori Xilinxen Virtex 6 FPGA baten oinarrutz. Plataformak spectrum sensing-eko bi algoritmo erabiltzen ditu eta Ethernet-RF zubi bat da. Bere helburua da Etherneteko kable bidezko lotura bat haririk gabeko batekin ordeztea industriako sentsore eta eragingailuen sareetan aplikatzeko. Spectrum sensing-eko algoritmoei esker, plataformak lotura sendoa bermatu dezake interferentziak gertatzen direnean. Energia detektorea transmisorean erabiltzen da informazioa transmititzeko erabilgarri egon daitezkeen kanalak aurkitzeko. Modulazioen sailkatzailea, berriz, hargailuan erabiltzen da transmisorearen seinalea eta egon daitezkeen beste seinale batzuk bereizteko. Horri esker, hargailuak badaki posible diren kanal guztietatik non dagoen transmisorea

Performance Evaluation of Cognitive Radio Spectrum Sensing Techniques through a Rayleigh Fading Channel

In recent years, there has been a steep rise in the demand for bandwidth due to a sharp increase in the number of devices connected to the wireless network. Coupled with the expected commercialization of 5G services and massive adoption of IoT, the upsurge in the number of devices connected to the wireless network will continue to grow exponentially into billions of devices. To accommodate the associated demand for wireless spectrum as we step into this new era of wireless connectivity, traditional methods of spectrum utilization based on fixed and static allocation are no longer adequate. New innovative forms that support dynamic assignment of spectrum space on as-per-need basis are now paramount. Cognitive radio has emerged as one of the most promising techniques that allow flexible usage of the scarce spectrum resource. Cognitive radio allows unlicensed users to opportunistically access spectrum bands assigned to primary users when these spectrum bands are idle. As such, cognitive radio reduces the gap between spectrum scarcity and spectrum underutilization. The most critical function of cognitive radio is spectrum sensing, which establishes the occupation status of a spectrum band, paving the way for a cognitive radio to initiate transmission if the band is idle. The most common and widely used methods for spectrum sensing are energy detection, matched filter detection, cyclostationary feature detection and cooperative based spectrum sensing. This dissertation investigates the performance of these spectrum-sensing techniques through a Rayleigh fading channel. In a wireless environment, a Rayleigh fading channel models the propagation of a wireless signal where there is no dominant line of sight between the transmitter and receiver. Understanding the performance of spectrum sensing techniques in a real world simulation environment is important for both industry and academia, as this allows for the optimal design of cognitive radio systems capable of efficiently executing their function. MATLAB software provides an experimental platform for the fusion of various Rayleigh fading channel parameters that mimic real world wireless channel characteristics. In this project, a MATLAB environment test bed is used to simulate the performance for each spectrum sensing technique across a range of signal-to-noise values, through a Rayleigh fading channel with a given set of parameters for channel delay, channel gain and Doppler shift. Simulation results are presented as plots for probability of detection versus signal-tonoise ratio, receiver operating characteristics (ROC) curves and complementary ROC curves. A detailed performance analysis for each spectrum sensing technique then follows, with comparisons done to determine the technique that offers the best relative performance

Multiband Spectrum Access: Great Promises for Future Cognitive Radio Networks

Cognitive radio has been widely considered as one of the prominent solutions to tackle the spectrum scarcity. While the majority of existing research has focused on single-band cognitive radio, multiband cognitive radio represents great promises towards implementing efficient cognitive networks compared to single-based networks. Multiband cognitive radio networks (MB-CRNs) are expected to significantly enhance the network's throughput and provide better channel maintenance by reducing handoff frequency. Nevertheless, the wideband front-end and the multiband spectrum access impose a number of challenges yet to overcome. This paper provides an in-depth analysis on the recent advancements in multiband spectrum sensing techniques, their limitations, and possible future directions to improve them. We study cooperative communications for MB-CRNs to tackle a fundamental limit on diversity and sampling. We also investigate several limits and tradeoffs of various design parameters for MB-CRNs. In addition, we explore the key MB-CRNs performance metrics that differ from the conventional metrics used for single-band based networks.Comment: 22 pages, 13 figures; published in the Proceedings of the IEEE Journal, Special Issue on Future Radio Spectrum Access, March 201