The objective of this research is to investigate the power-control problem and analyze the network capacity in cognitive radio (CR) networks. For CR users or Secondary users (SUs), two spectrum-access schemes exist: namely, spectrum underlay and spectrum overlay. Spectrum overlay improves the spectrum utilization by granting SUs the authority to sense and explore the unused spectrum bands provided by PUs. in this scheme, designing effective spectrum-sensing techniques in PHY layer is the major concern. Spectrum underlay permits Sus to share the same spectrum bands with PUS at the same time and location. In this scheme, designing robust power control algorithms that guarantee the QoS of both primary and secondary transmissions is the main task. In this thesis, we first investigate the power-control problems in CR networks. Especially, we conduct two research works on power control for CDMA and OFDMA CR networks. Being aware of the competitive spectrum-access feature of SUs, the non-cooperative game theory, as a standard mathematics, is used to study the power-control problem. Note that game-theoretical approaches provide distributed solutions for CR networks,, which fits the needs of CR networks. However, it requires channel state information (CSI) exchange among all SUs, which will cause great overheads in the large network deployment. To gain better network scalability and design more robust power-control algorithm for any hostile radio-access environments, we propose a reinforcement-learning-based repeated power-control game that solve the problem for the first time. The left part of the dissertation is to study the throughput capacity scaling of the newly arising cognitive ad hoc networks (CRAHNs). Stimulated by the seminal work of Gupta and Kumar, the fundamental throughput scaling law for large-scale wireless ad hoc networks has become an active research topic. This research is of great theoretical value for wireless ad hoc networks. Our proposed research studies it in the scenario of CRAHNs under the impact of PU activity. It is a typical and important network scenario that has never been studied yet. We do believe this research has its unique value, it will have an impact to the research community.

Cognitive Radio Networks (CRNs) provide a solution for the spectrum scarcity problem facing the wireless communications community. However, due to the infancy of CRNs, further research is needed before we can truly benefit from CRNs. The basic concept of CRNs relies on utilizing the unused spectrum of a primary network, without interfering with the activity of primary users (PUs). In order to successfully achieve that, users in a CRN has to perform spectrum sensing, spectrum management, spectrum mobility, and spectrum sharing. The latter, which is the focus of our research, deals with how secondary users (SUs) share the unused spectrum. Furthermore, to be able to utilize CRNs in practical applications, a certain level of quality-of-service (QoS) should be guaranteed to SUs in such networks. QoS requirements vary according to the application. Interested in voice communications, we propose a packet scheduling scheme that orders the SUs' transmissions according to the packet dropping rate and the number of packets queued waiting for transmission. Two medium access control (MAC) layer protocols, based on the mentioned scheduling scheme, are proposed for a centralized CRN. In addition, the scheduling scheme is adapted for a distributed CRN, by introducing a feature that allows SUs to organize access to the available spectrum without the need for a central unit. Finally, extensive simulation based experiments are carried out to evaluate the proposed protocols and compare their performance with that of other MAC protocols designed for CRNs. These results reflect the effectiveness of our proposed protocols to guarantee the required QoS for voice packet transmission, while maintaining fairness among SUs in a CRN.

The wireless spectrum is currently regulated by government agencies and is assigned to license holders or services on a long-term basis over vast geographical regions. Recent research has shown that a large portion of the assigned spectrum is used sporadically, leading to underutilization and waste of valuable frequency resources. Consequently, dynamic spectrum access techniques are proposed to solve these current spectrum inefficiency problems. This new area of research foresees the development of cognitive radio (CR) networks to further improve spectrum efficiency. The basic idea of CR networks is that the unlicensed devices (also called CR users) share wireless channels with the licensed devices (also known as primary users) that are already using an assigned spectrum. CR networks, however, impose unique challenges resulting from high fluctuation in the available spectrum, as well as diverse quality-of-service (QoS) requirements. These challenges necessitate novel cross-layer techniques that simultaneously address a wide range of communication problems from radio frequency (RF) design to communication protocols, which can be realized through spectrum management functions as follows: (1) determine the portions of the spectrum currently available (spectrum sensing), (2) select the best available channel (spectrum decision), (3) coordinate access to this channel with other users (spectrum sharing), and (4) effectively vacate the channel when a primary user is detected (spectrum mobility). In this thesis, a spectrum management framework for CR networks is investigated that enables seamless integration of CR technology with existing networks. First, an optimal spectrum sensing framework is developed to achieve maximum spectrum opportunities while satisfying interference constraints, which can be extended to multi-spectrum/multi-user CR networks through the proposed sensing scheduling and adaptive cooperation methods. Second, a QoS-aware spectrum decision framework is proposed where spectrum bands are determined by considering the application requirements as well as the dynamic nature of the spectrum bands. Moreover, a dynamic admission control scheme is developed to decide on the spectrum bands adaptively dependent on the time-varying CR network capacity. Next, for spectrum sharing in infrastructure-based CR networks, a joint spectrum and power allocation scheme is proposed to achieve fair resource allocation as well as maximum capacity by opportunistically negotiating additional spectrum based on the licensed user activity (exclusive allocation) and having a share of reserved spectrum for each cell (common use sharing). Finally, we propose a novel CR cellular network architecture based on the spectrum-pooling concept, which mitigates the heterogeneous spectrum availability. Based on this architecture, a unified mobility management framework is devised to support both user and spectrum mobilities in CR networks.

M. Tech. Electrical Engineering. / Discusses the performance of CRs that can be hampered by the environment, modulation schemes and how they can be selected based on the current environment i.e link adaptation, bandwidth efficient schemes and those that are prone to noise, formulate a set of decisions and actions based on the knowledge about the current environment and its effects on propagation and how to use a game theoretic approach for fair use of the spectrum.

Cognitive Radio Networks (CRNs) provide a solution for the spectrum scarcity problem facing the wireless communications community. However, due to the infancy of CRNs, further research is needed before we can truly benefit from CRNs. The basic concept of CRNs relies on utilizing the unused spectrum of a primary network, without interfering with the activity of primary users (PUs). In order to successfully achieve that, users in a CRN has to perform spectrum sensing, spectrum management, spectrum mobility, and spectrum sharing. The latter, which is the focus of our research, deals with how secondary users (SUs) share the unused spectrum. Furthermore, to be able to utilize CRNs in practical applications, a certain level of quality-of-service (QoS) should be guaranteed to SUs in such networks. QoS requirements vary according to the application. Interested in voice communications, we propose a packet scheduling scheme that orders the SUs' transmissions according to the packet dropping rate and the number of packets queued waiting for transmission. Two medium access control (MAC) layer protocols, based on the mentioned scheduling scheme, are proposed for a centralized CRN. In addition, the scheduling scheme is adapted for a distributed CRN, by introducing a feature that allows SUs to organize access to the available spectrum without the need for a central unit. Finally, extensive simulation based experiments are carried out to evaluate the proposed protocols and compare their performance with that of other MAC protocols designed for CRNs. These results reflect the effectiveness of our proposed protocols to guarantee the required QoS for voice packet transmission, while maintaining fairness among SUs in a CRN.

The focus of this thesis is on cooperative spectrum sensing and related security issues in multi-channel cognitive radio networks (MCCRNs). We first study the channel assignment for cooperative spectrum sensing in MCCRNs to maximize the number of available channels. In centralized implementation, a heuristic scheme is proposed along with a greedy scheme to reduce the reported information from the cognitive radios (CRs). In distributed scenario, a novel scheme with multi-round operation is designed following the coalitional game theory. Next, we focus on the physical layer security issues for cooperative spectrum sensing in MCCRNs, caused by Byzantine attacks. New counterattacks are proposed to combat attacks comprising coalition head and CRs as Byzantine attackers, which target to reduce the number of available channels for sensing in distributed MCCRNs. First, a new secure coalition head selection is proposed, by using statistical properties of the exchanged SNRs in the coalitions. Then, an iterative algorithm is proposed to block out attackers, if they continue attacking the system. The important problem of key management is considered next, and an energy-efficient identity-based and a certificate-based distributed key management schemes are proposed. First, a new elliptic curve cryptography (ECC)-based distributed private key generation scheme is proposed to combat the single point of failure problem along with novel distributed private key generator (DPKG) selection schemes to preserve security and energy-efficiency. Because of its importance in the proposed identity-based key management scheme, we further propose a low-complexity DPKG assignment, based on multi-objective programming, which can capture DPKG fairness in addition to energy-efficiency. Finally, a more powerful and intelligent distributed cooperative Byzantine attack on the proposed multi-channel cooperative spectrum sensing is proposed, where attackers collude by applying coalitional game theory to maximize the number of invaded channels in a distributed manner. As a remedy, a hierarchical identity-based key management scheme is proposed, in which CRs can only play on a certain number of requested channels and channel access for sensing is limited to the honest CRs selected in the coalitional game. Simulation results show that the proposed schemes can significantly improve cooperative spectrum sensing and secure the system against Byzantine attacks.

Cognitive radio (CR) technology allows devices to share the wireless spectrum with other users that have a license for operation in these spectrum bands. This area of research promises to solve the problem of spectrum scarcity in the unlicensed bands, and improve the inefficient spectrum utilization in the bands reserved for the licensed users. However, the opportunistic use of the available spectrum by the CR users must not affect the licensed users. This raises several concerns regarding spectrum sensing, sharing and reliable end-to-end communication in CR networks. This thesis is concerned with the design and implementation of communication protocols for the multi-hop infrastructure-less CR ad-hoc networks (CRAHNs). In addition, it also addresses the critical issue of interference-free spectrum usage in specific ad-hoc architectures, such as, resource-constrained wireless sensor networks and wireless mesh networks that have high traffic volumes. The problems of spectrum management that are unique to CR networks are first identified in this thesis. These issues are then addressed at each layer of the network protocol stack while considering the distributed operation in CRAHNs. At the physical layer an algorithmic suite is proposed that allows the CR devices to detect and adapt to the presence of wireless LANs and commercial microwave ovens. A common control channel is designed that allows sharing of the spectrum information between the CR users, even when the available spectrum varies dynamically. A spectrum sharing scheme for mesh networks is proposed at the link layer that allows cooperative detection of the licensed users and fair utilization of the available spectrum among the mesh devices. The spectrum availability and route formation are then considered jointly at the network layer, so that the licensed users are protected as well as the CRAHN performance is maximized. Finally, we extend the classical TCP at the transport layer to ensure end-to-end reliability in a multi-hop CR environment.

Thesis (M.E.-Res)--University of Wollongong, 2008. / Typescript. Includes bibliographical references: leaf 69-75.

Thesis (M.S.)--Auburn University, 2008. / Abstract. Vita. Includes bibliographical references (p. 42-44).

With the traditional static spectrum management, a significant portion of the licensed spectrum is underutilized in most of time while the unlicensed spectrum is over-crowded due to the growing demand for wireless radio spectrum from exponential growth of various wireless devices. Dynamic Spectrum Access utilizes the wireless spectrum in a more intelligent and flexible way. Cognitive radios are a promising enabler for Dynamic Spectrum Access because they can sense and access the idle channels. With cognitive radios, the unlicensed users (SUs) can opportunistically identify and access the vacant portions of the spectrum of the licensed users (PUs). In cognitive radio networks (CRNs), multiple idle channels may be available to SUs. If two or more SUs want to communicate with each other, they must select a channel which is available to all of them. The process of two or more SUs to meet and establish a link on a commonly-available channel is known as rendezvous. 1) Multiple Radios for Fast Rendezvous in CRNs: The existing works on rendezvous implicitly assume that each cognitive user is equipped with one radio (i.e., one wireless transceiver). As the cost of wireless transceivers is dropping, this feature can be exploited to significantly improve the rendezvous performance at low cost. We investigate the rendezvous problem in CRNs where cognitive users are equipped with multiple radios and different users may have different numbers of radios. We first study how the existing rendezvous algorithms can be generalized to use multiple radios for faster rendezvous. We then propose a new rendezvous algorithm, called role-based parallel sequence (RPS), which specifically exploits multiple radios for more efficient rendezvous. Our basic idea is to let the cognitive users stay in a specific channel in one dedicated radio and hop on the available channels with parallel sequences in the remaining general radios. We prove that RPS provides guaranteed rendezvous (i.e., rendezvous can be completed within a finite time) and derive the upper bounds on the maximum time-to-rendezvous (TTR) and the expected TTR. The simulation results show that i) multiple radios can cost-effectively improve the rendezvous performance, and ii) the proposed RPS algorithm performs better than the ones generalized from the existing algorithms. 2) Efficient Channel-Hopping Rendezvous Algorithm Based on Available Channel Set: All the existing rendezvous algorithms that provide guaranteed rendezvous (i.e., rendezvous can be achieved within finite time) generate channel-hopping (CH) sequences based on the whole channel set. However, some channels may be unavailable (e.g., being used by the licensed users) and these existing algorithms would randomly replace the unavailable channels by the available ones in the CH sequence. This random replacement is not effective, especially when the number of unavailable channels is large. We design a new rendezvous algorithm, called Interleaved Sequences based on Available Channel set (ISAC), that attempts rendezvous on the available channels only for faster rendezvous. ISAC constructs an odd subsequence and an even subsequence and interleaves these two subsequences to compose a CH sequence. We prove that ISAC provides guaranteed rendezvous. We derive the upper bounds on the maximum time-to-rendezvous to be O(