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Chen, ChanglongRobust and Secure Spectrum Sensing in Cognitive Radio Networks
Doctor of Philosophy in Engineering, University of Toledo, 2013, College of Engineering
With wireless devices and applications booming, the problem of inefficient utilization of the precious radio spectrum has arisen. Cognitive radio is a key technology to improve spectrum utilization. A major challenge in cognitive radio networks is spectrum sensing, which detects if a spectrum band is being used by a primary user. Spectrum sensing plays a critical role in cognitive radio networks. However, spectrum sensing is vulnerable to security attacks from malicious users. Detecting malicious users is a crucial problem for cognitive radio networks. First, the channel shadowing and fading result in spatial variability and uncertainty of the PU signal, and hence the sensing reports among geographically separated secondary users are usually distinct. This makes it easy for malicious users to hide the dishonest sensing reports under the natural variation of the sensing reports. Second, due to the open and easy reconfiguration nature of cognitive radio, the cognitive radios are more prone to be compromised and, once compromised, they are prone to more diverse misbehavior. This makes the malicious user detection more difficult than finding faulty or misconfigured users whose effects on the cognitive radio networks are more evident and easy to predict. We propose a decentralized scheme to detect malicious users in cooperative spectrum sensing. The scheme utilizes spatial correlation of received signal strengths among secondary users in close proximity. We also propose to use an alternative mean to make our scheme more robust in malicious user detection. Utilizing alternative mean can filter a portion of outliers (extreme sensing results), thus making the mean more close to the true value of sensing results from benign secondary users, and hence increasing detection accuracy. We have also proposed a neighborhood majority voting approach for the secondary users to decide if a specific user is malicious. Cooperative spectrum sensing is vulnerable to the spectrum sensing data falsification attack. Specifically, a malicious user can send a falsified sensing report to mislead other (benign) secondary users to make an incorrect decision on the PU activity. Therefore, detecting the spectrum sensing data falsification attack or identifying the malicious sensing reports is extremely important for robust cooperative spectrum sensing. This dissertation proposes a distributed density based detection scheme to countermeasure the spectrum sensing data falsification attack. Density based detection scheme can effectively exclude the malicious sensing reports from spectrum sensing data falsification attackers, so that a benign secondary user can effectively detect the PU activity in distributed cooperative spectrum sensing. Moreover, density based detection scheme can also exclude abnormal sensing reports from ill-functioned secondary users. Furthermore, we propose another advanced distributed conjugate prior based detection scheme to defend the spectrum sensing data falsification attack. Conjugate prior based detection can effectively exclude abnormal sensing reports from both spectrum sensing data falsification attackers and ill-functioned secondary users. With this scheme, a benign secondary user can effectively detect the PU activity in distributed cooperative spectrum sensing. On the other hand, denial of service attack is one of the most serious threats to cognitive radio networks. By launching denial of service attack over communication channels, the attacker can severely degrade the network performance. The channel jamming attack is one of denial of service attacks that are simple to launch, and difficult to be countermeasured. The jamming attack is a security threat where the attacker interferes a set of communication channels by injecting a continuous jamming signal or non-continuous short jamming pulses. As a result, the communication channels either cannot be accessed or the signal to noise ratio in these channels is heavily deteriorated. We model the jamming and anti-jamming process as a Markov decision process. With this approach, secondary users are able to avoid the jamming attack launched by external attackers and therefore maximize the payoff function. We first use a policy iteration method to solve the problem. However, this approach is computationally intensive. To decrease the computation complexity, Q-function is used as an alternate method. Furthermore, we propose an algorithm to solve the Q-function. In this dissertation, we propose a malicious user detection scheme, a density based SSDF detection scheme, a conjugate prior based SSDF detection scheme, and an anti-jamming algorithm to achieve robust and secure cooperative spectrum sensing in cognitive radio networks. Performance analysis and simulation results show that our proposed schemes can achieve very good performance in detecting malicious users, excluding abnormal sensing reports, and defending the jamming attack, thus improve spectrum sensing performance in cognitive radio networks.

Committee:

Min Song (Advisor); Mansoor Alam (Committee Member); Vijay Devabhaktuni (Committee Member); Mohammed Niamat (Committee Member); Hong Wang (Committee Member)

Subjects:

Computer Science

Keywords:

Cognitive radio networks; spectrum sensing; security

Alizadeh, ArdalanCognitive Communications for Emerging Wireless Systems
Doctor of Philosophy, University of Akron, 2016, Electrical Engineering
The current explosion of information and demand for high speed data communication call for novel solutions to utilize the radio resources more efficiently. The cognitive communication paradigm aims to mitigate this spectrum crunch by exploiting unused resources that are allocated to the primary communications systems. The aim of this research is to employ the concept of cognition in wireless devices and combine it with three recently introduced wireless communication techniques namely, K-user multi-input multi-output (MIMO) interference networks, spatial modulation scheme and molecular communications. Firstly, the feasibility of cognitive radio (CR) is studied in the presence of a K-user MIMO interference channel as the primary network. Assuming that the primary interference network has unused spatial degrees of freedom, the sufficient condition on the number of antennas is investigated at the secondary transmitter under which the secondary system can communicate and then the secondary precoding and decoding matrices are derived to have zero interference leakage into the primary network. A fast sensing method based on the eigenvalue analysis of the received signal covariance matrix is proposed to determine the availability of spatial holes. Also, a fine sensing method is provided based on the generalized likelihood ratio test to decide the absence of individual primary streams. The second part of this research is relevant to the application of spatial modulation (SM) in overlay CR networks, in which the primary and secondary networks work concurrently over the same spectrum band. The CR transmitter assists the primary network as a relay to amplify-and-forward (AF) the transmitted symbols of the primary. The secondary transmitter retransmits the primary symbols in amplitude-phase modulation domain, while its own information is transmitted by the index of transmitting antenna. The performance of the optimal detectors in terms of the average symbol error rate (ASER) and the asymptotic behavior of the ASER at both the primary and secondary at high signal-to-noise ratios (SNRs) are then provided. In the last part, a novel nanonetwork with cognitive capabilities is proposed, which is able to intelligently sense a primary molecular channel and use the channel opportunistically for its own transmission. In the proposed method, the secondary nanonetwork measures the concentration of molecules as a criterion to decide the presence or absence of the primary communication using a molecular energy detection scheme. When the molecular channel is available, the secondary transmitter sends its information using the same carrier molecules. Depending on the availability of timing information at the sensing nanodevice, two synchronous and asynchronous sensing mechanisms are provided based on the likelihood ratio test as the optimal detection method.

Committee:

Hamid Reza Bahrami, PhD (Advisor); Nathan Ida, PhD (Committee Member); Nghi Tran, PhD (Committee Member); Ping Yi, PhD (Committee Member); Malena Ines Espanol, PhD (Committee Member)

Subjects:

Electrical Engineering; Nanoscience

Keywords:

Cognitive radio networks; K-user MIMO interference channel; spatial sensing; spatial hole; spatial modulation; amplify-and-forward overlay CR networks; molecular communications; nano-networks, molecular channel sensing

Murawski, RobertPractical Interference Avoidance Protocols for Cognitive Radio Networks
Doctor of Philosophy, The Ohio State University, 2011, Electrical and Computer Engineering
Cognitive radios are devices which have the ability to adjust their communication parameters based on observations of the surrounding environment. Cognitive Radio Networks (CRNs) are envisioned for use in licensed communication channels, operating on ‘borrowed’ spectrum in a non-interference manner. This technology has the potential to revolutionize wireless communication and alleviate the overuse of certain unlicensed communication bands. Research in this area is relatively new, and significant effort must be placed into researching how cognitive radio devices can operate with a reasonably low effect on the licensed spectrum users. In this dissertation, three areas are researched, focusing on practical mechanisms which can provide service to CRNs while minimizing the impact on licensed users. First, a cross-layer routing selection algorithm is proposed which utilizes fuzzy-logic modeling to gracefully map network quality of service (QoS) requirements and CRN-aware requirements to a route cost function. The second method looks into utilizing cooperation between licensed users and cognitive radios to facilitate CRN communication while improving the throughput of licensed users. Finally, the use of directional transmissions is researched. Directional transmissions have the potential to significantly reduce the impact of cognitive radios on licensed users, however, directional transmissions introduce many complexities to the realm of wireless communication. Some of these complexities will be explored, along with practical and implementable solutions.

Committee:

Eylem Ekici, PhD (Advisor); Ümit Çatalyürek, PhD (Committee Member); Jin Wang, PhD (Committee Member)

Subjects:

Communication; Electrical Engineering; Engineering

Keywords:

Cognitive Radio Networks; Wireless Communication; Networking

Yoon, Suk-UnDynamic Radio Resource Allocation in Wireless Sensor and Cognitive Radio Networks
Master of Science, The Ohio State University, 2009, Electrical and Computer Engineering

In wireless networks, it is required to change an operating frequency as part of the radio resource management due to strong interference or system requirements of accessing radio resources. In this thesis, we propose two radio resource management schemes in wireless sensor networks and cognitive radio networks. In the proposed schemes, sensor networks switch to a new channel when they detect strong interference and a secondary user in cognitive radio networks moves to a new spectrum when it detects or predicts the presence of a primary user.

In the first part of the thesis, we propose a channel hopping scheme which can be used for interfered wireless networks. With the additive functionality of a channel hopping mechanism on the sensor network stack, we aim to avoid the interference from other sensor nodes and wireless technologies on ISM band as well as avoid narrow-band jamming. For simple and reliable channel hopping, we introduce an Adaptive Channel Hopping scheme, a spectrum environment aware channel hopping scheme, for interference robust wireless sensor networks. When the channel status becomes suboptimal to communicate, the adaptive channel hopping lets the sensors switch to a new clean channel. To generate channel selection/scanning orders which minimize channel hopping latency, we use two parameters which are link quality indicator (LQI) and channel weighting. The proposed adaptive channel hopping scheme is evaluated through simulations. Simulation results indicate that the proposed scheme significantly reduces the channel hopping latency and selects the best quality channel.

In the second part of the thesis, we propose a novel approach to spectrum management in cognitive radio networks. To support flexible use of spectrum, cognitive radio networks employ spectrum mobility management schemes, including spectrum handoff, which refers to the switching of the operating spectrum due to changes in licensed (primary) user activity. Spectrum handoff inevitably results in temporary disruption of communication for the unlicensed (secondary) user operating in a licensed band opportunistically. Minimization of secondary user service disruption is an important objective of spectrum handoff schemes. In this thesis, we introduce a new type of spectrum handoff called Voluntary Spectrum Handoff assisted by a primary user spectrum usage estimation scheme. The two mechanisms proposed under voluntary spectrum handoff method estimate opportune times to initiate unforced spectrum handoff events to facilitate setup and signaling of alternative channels without having communication disruption, which occurs when a secondary user is forced out of an operating spectrum due to primary user activity. To estimate primary user spectrum usage, channel usage information is continuously updated with a fixed spectrum sensing window and a variable history window. Proposed voluntary spectrum handoff and primary usage estimation schemes are evaluated through extensive simulations. Simulation results indicate that the proposed schemes significantly reduce the communication disruption duration due to handoffs.

Committee:

Eylem Ekici (Advisor); Bradley Clymer, D. (Committee Member)

Subjects:

Engineering

Keywords:

Channel Hopping; Wireless Sensor Networks; Spectrum Handoff; Cognitive Radio Networks