This paper has covered some security aspects to consider when deploying 6LoWPAN in wireless sensor networks. The issues mentioned in this paper revolve around encryption and authentication methods as well as key distribution mechanism. Security features at the link and network layer have been evaluated and the conclusion is that both do provide with good security but it is not always sufficient. For example, hop-by-hop security at the link layer could be really strong if you are in control of all links between source and destination, however, when transmitting data over the Internet this is rarely the case. As an alternative the network layer provide with an end-to-end solution with a compressed version of IPsec, but due to insufficient models for key distribution the keys are required to be distributed manually. This means that there is no support for asymmetric keys in a wireless sensor network at the time, but further research might solve these issues.

by Ng Ho Hing. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves 118-120). / Abstract also in Chinese. / Abstract --- p.2 / Acknowledgement --- p.3 / Content --- p.4 / Chapter Chapter 1: --- Introduction --- p.6 / Chapter Chapter 2: --- Background and Theories --- p.11 / Chapter 2.1 --- Background History --- p.11 / Chapter 2.2 --- Circuit Theories --- p.12 / Chapter 2.3 --- Electromagnetic Wave Theories --- p.14 / Chapter 2.3.1 --- Finite Difference Time Domain Method --- p.14 / Chapter 2.4 --- Active Antenna theory --- p.23 / Chapter 2.4.1 --- Active Component Finite Difference Time Domain --- p.23 / Chapter Chapter 3: --- Injection Locked Mixer --- p.32 / Chapter 3.1 --- Introduction --- p.32 / Chapter 3.2 --- Circuit Topology and Theory --- p.32 / Chapter 3.2.1 --- Mixer Fundamental --- p.32 / Chapter 3.2.2 --- Oscillator Fundamental --- p.33 / Chapter 3.2.3 --- Injection locking theory --- p.35 / Chapter 3.2.4 --- Regenerative mixer theory --- p.38 / Chapter 3.3 --- Design Methodology --- p.40 / Chapter 3.3.1 --- DC Bias point consideration --- p.40 / Chapter 3.3.2 --- AC signal path consideration --- p.42 / Chapter 3.3.3 --- Mixing and feedback at the base-emitter junction --- p.46 / Chapter 3.3.4 --- Final Circuit Configuration --- p.48 / Chapter 3.4 --- Circuit Characteristics --- p.49 / Chapter 3.4.1 --- Experiment parameters --- p.50 / Chapter 3.4.2 --- "Relationship between conversion gain, injection power and center frequency" --- p.50 / Chapter 3.4.2 --- Locking Bandwidth and phase shift --- p.56 / Chapter 3.4.3 --- "Regenerative Effect, Mode 1 injection mixing" --- p.58 / Chapter 3.4 --- Transient simulation --- p.63 / Chapter 3.4.1 --- DC Bias Simulation --- p.64 / Chapter 3.4.2 --- AC Simulation --- p.66 / Chapter 3.5 --- Summary --- p.78 / Chapter Chapter 4: --- Injection Locked Transceiver --- p.79 / Chapter 4.1 --- System Architecture --- p.79 / Chapter 4.2 --- Circuit Design --- p.81 / Chapter 4.2.1 --- Up-conversion Consideration --- p.81 / Chapter 4.2.2 --- Local Oscillator Consideration --- p.81 / Chapter 4.2.3 --- Bias Consideration --- p.82 / Chapter 4.2.4 --- Active Down-converting Mixer --- p.83 / Chapter 4.2.5 --- Mode 2 injection Mixing --- p.85 / Chapter 4.3 --- Antenna Design --- p.85 / Chapter 4.3.1 --- Antenna Choice --- p.85 / Chapter 4.3.1 --- FDTD Characterization --- p.85 / Chapter 4.4 --- Integration --- p.87 / Chapter 4.4.1 --- Matching Techniques --- p.87 / Chapter 4.5 --- INJECTION LOCKED OSCILLATOR (LO) OPTIMIZATION --- p.89 / Chapter 4.5.1 --- Active Mixer Optimization --- p.89 / Chapter 4.6 --- Simulation using Extended FTDT --- p.90 / Chapter 4.7 --- Discussion --- p.91 / Chapter 4.8 --- Summary --- p.91 / Chapter Chapter 5: --- Injection Locked System --- p.92 / Chapter 5.1 --- Introduction --- p.92 / Chapter 5.2 --- System Requirement --- p.93 / Chapter 5.3 --- System Architecture --- p.93 / Chapter 5.3.1 --- Sub-system Choices --- p.95 / Chapter 5.3.2 --- Frequency Synthesizer --- p.96 / Chapter 5.3.3 --- Active Transceiver --- p.96 / Chapter 5.3.4 --- IF System --- p.97 / Chapter 5.4 --- System Performance --- p.98 / Chapter 5.4.1 --- Stability --- p.98 / Chapter 5.4.2 --- Field pattern of the antenna --- p.100 / Chapter 5.4.3 --- Locking Bandwidth versus Injection Power --- p.101 / Chapter 5.4.4 --- Radiative Sensitivity and Image Selectivity --- p.102 / Chapter 5.4.5 --- Intermodulation --- p.103 / Chapter 5.4.6 --- Output Power vs Injection Frequency --- p.105 / Chapter 5.4.7 --- IF Output Vs Frequency --- p.106 / Chapter 5.4.8 --- IF Output vs DC Supply --- p.107 / Chapter 5.4.9 --- Output Power --- p.108 / Chapter 5.4.10 --- Type Approval Consideration --- p.108 / Chapter 5.4.11 --- Manufacturability consideration --- p.113 / Chapter Chapter 6: --- Summary and Conclusion --- p.114 / Chapter 6.1 --- Summary and Contribution --- p.114 / Chapter 6.2 --- Future Work --- p.115 / Bibliography --- p.118 / Publication List --- p.120

Simulation is a technique of growing importance and is becoming an indispensable tool applied in various academic industries, including packet networks. Simulation provides an alternative research approach to implementing a real environment, owing to its features of scalability, exibility and ease of setup. However, simulating large-scale networks can be very time and resource consuming. It can take several days to run one long simulation experiment, which may be expensive or even unaffordable. Therefore, planning simulation is important. This research proposes to plan simulation run length through predicting the required shortest run length that approximates steady-state, in the form of mathematical and logical expressions, i.e. building an analytical model. Previously related research always focused on classical models, such as the M/M/1 queue model, M/G/1 queue model, and so on. This research expands the research base to include a packet multiplexing model of homogenous sources which is widely accepted and used. This thesis investigates different traffic types (Markovian/Pareto) and different QoS parameter (delay/losses), as well as applying them to end-to-end networks. These scenarios are analysed and expressed, in terms of different desired precision level. Final results show that run length time is well predicted using the developed analytical model, which can be a guide for simulation planning in packet networks of the present and the future. This can be of great significance for performance evaluation studies.

Cooperation is seen as a means to improve the signal in OFDMA wireless networks by overcoming the inter-cell interference. Such co-operation can be deployed in both the physical layer and the MAC layer. In this thesis, a cross-layer cooperation strategy is considered. Firstly, in the physical layer, a cooperative coding scheme with private information sharing is proposed based on dirty paper coding; this is analyzed in a scenario with two transmitters and two receivers. To implement the cooperation, a rate limited link is deployed at the transmitters’ side in order to share the information. A new achievable rate region is established in both strong interference regime and weak interference regime. Secondly, in the MAC layer, a graph-based dynamic coordinated clustering scheme is proposed. An interference weighted graph is constructed to assist dynamic coordinated clustering for inter-cell interference mitigation and to improve the cell-edge user performance. Only 2 bits are allowed for the signalling exchange between transmitters and this reduces the overhead of the approach. The system throughput and cell-edge throughput with different user distributions are used to evaluate the performance. Thirdly, a transmit antenna selection algorithm is presented to optimize system performance with the constraint of fairness. A graph is generated by using the channel condition between the transmit antennas and Mobile Stations. Based on the graph, a heuristic algorithm is proposed to choose the transmit antenna for each user in order to improve the system performance and guarantee the user fairness. Finally, combining the cooperative coding scheme and cooperative clustering scheme, a cross-layer cooperation scheme is presented. In the physical layer, the cooperation coding scheme mitigates the interference and increases the transmission rate; in the MAC layer, the cooperative clustering scheme provides efficient cooperative transmission. Simulation results show that the proposed scheme can effectively increase both the system throughput and cell-edge throughput.

Mobile ad hoc networks are of growing interest because of their unique characteristics and advantages in many practical applications. QoS provision acts as a major challenge in the routing protocol design in the real-world mobile ad hoc networks, especially for the real-time services. OFDM is a new technology which has many advantages over the other modulation schemes. Because of its prominent features, many popular wireless standards have adopted it as physical layer modulation, such as IEEE 802.11 series, WiMAX, 3GPP LTE etc, and it is extended to multiuser environment known as OFDMA. So far none of the existing ad hoc routing protocols fully account for the OFDMA based mobile ad hoc networks. In this thesis, a QoS routing protocol is proposed for OFDMA based mobile ad hoc networks. A signal strength-based sub-channel allocation scheme is proposed in the routing protocol aiming to reduce the signalling overhead and cochannel interference. The performance of the proposed routing protocol is compared with other alternative proposals through simulations using OPNET simulator. Moreover, a partial time synchronization and a null subcarrier based frequency synchronization algorithms are also proposed for OFDMA based ad hoc network to further support and facilitate the proposed sub-channel allocation scheme and routing protocol.

by Fu Kar Kit. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1998. / Includes bibliographical references (leaves 158-160). / Abstract also in Chinese. / Chapter Chapter 1: --- Introduction --- p.1 / Chapter Chapter 2: --- Background and Theories --- p.3 / Chapter 2.1 --- Background History --- p.3 / Chapter 2.2 --- Finite Difference Time Domain Method --- p.4 / Chapter 2.2.1 --- Basic Formulation --- p.4 / Chapter A ) --- Governing Equations --- p.4 / Chapter B ) --- Discretization of Differential Equations --- p.6 / Chapter C ) --- Numerical Stability --- p.7 / Chapter 2.2.2 --- Absorbing Boundary Condition ( PML - Bandlimited ) --- p.8 / Chapter A ) --- Berenger Perfectly Matched Layer --- p.8 / Chapter B ) --- "Theroy, Two-Dimensional TE Case" --- p.10 / Chapter B-1 ) --- Propagation of a Plane Wave in a PML Medium --- p.11 / Chapter B-2 ) --- Transmission of a Wave through PML-PML Interfaces --- p.15 / Chapter B-3 ) --- PML for the FD-TD technique in 2-D domain --- p.18 / Chapter C ) --- Extension to Three-Dimension Case --- p.22 / Chapter 2.2.3 --- Modeling of Source and Passive Lumped-Circuit --- p.25 / Chapter 2.2.4 --- Obtaining the frequency dependent parameters --- p.27 / Chapter 2.2.5 --- Time Domain Extrapolation --- p.29 / Chapter 2.2.6 --- Near-to-Far-Field Transformation --- p.33 / Chapter A ) --- FD-TD implementation of Near-to-Far-Field Transformation --- p.35 / Chapter B ) --- Numerical Techniques to compute the Antenna Directivity --- p.38 / Chapter 2.3 --- Transmission Line Circuit Theories --- p.40 / Chapter 2.3.1 --- Stripline --- p.43 / Chapter 2.3.2 --- Microstrip Line --- p.46 / Chapter 2.3.3 --- Quadrature 90° Hybrid --- p.50 / Chapter 2.3.4 --- Butler Matrices --- p.50 / Chapter A ) --- Types of hybrids --- p.54 / Chapter B ) --- Number of hybrids --- p.51 / Chapter C ) --- Number of fixed phase shifters --- p.51 / Chapter D ) --- Positions and magnitudes of fixed phase shifters --- p.51 / Chapter E ) --- Values of total phase shift at output ports and produced by input ports --- p.53 / Chapter 2.4 --- Antenna Theories --- p.54 / Chapter 2.4.1 --- Microstrip Patch Antenna --- p.54 / Chapter A ) --- Bandwidth Enhancement --- p.55 / Chapter B ) --- Antenna design methodology --- p.55 / Chapter B-1 ) --- Substrate selection --- p.55 / Chapter B-2 ) --- Rectangular element analysis and design --- p.56 / Chapter 1) --- Electromagnetically coupled patch --- p.57 / Chapter 2) --- Aperture coupled patch --- p.61 / Chapter 2.4.2 --- Array Antenna --- p.67 / Chapter Chapter 3: --- Butler Matrix Analysis and Design --- p.73 / Chapter 3.1 --- Circuit Topology --- p.73 / Chapter 3.1.1 --- Basic Operation of the 4x4 Butler Matrix --- p.74 / Chapter 3.2 --- Design Methodology and Circuit Characteristics --- p.75 / Chapter 3.2.1 --- 3 dB branch-line coupler --- p.76 / Chapter 3.2.2 --- 0 dB branch-line coupler --- p.79 / Chapter 3.2.3 --- 4x4 Butler matrix Beamforming network --- p.82 / Chapter Chapter 4: --- Multibeam Array Analysis and Design --- p.90 / Chapter 4.1 --- Antenna Architecture --- p.90 / Chapter 4.2 --- Antenna Design --- p.91 / Chapter 4.2.1 --- Antenna Choice --- p.91 / Chapter A ) --- Microstrip Dipole --- p.91 / Chapter B ) --- Rectangular Microstrip Patch --- p.91 / Chapter C ) --- Circular Patch --- p.92 / Chapter D ) --- Compact Patch --- p.93 / Chapter E ) --- Annular Resonators --- p.94 / Chapter F ) --- Antenna Choice of the 4x4 Butler Matrix Network --- p.94 / Chapter 4.2.2 --- Choice of Feeding and Matching Technique --- p.95 / Chapter 4.2.3 --- Basic Antenna Parameters and Measurement Technique --- p.95 / Chapter A ) --- Radiation Pattern --- p.95 / Chapter B ) --- Radiation Pattern Lobes --- p.96 / Chapter C ) --- Antenna Gain --- p.97 / Chapter D ) --- Input Impedance --- p.97 / Chapter E ) --- Bandwidth --- p.97 / Chapter 4.2.4 --- FDTD Characterization --- p.98 / Chapter 4.3 --- Multibeam Antenna Design and Optimization --- p.104 / Chapter 4.4 --- Stripline Fed - Multibeam Antenna --- p.107 / Chapter 4.4.1 --- Design Methodology of the Stripline 3 dB Hybrid --- p.109 / Chapter 4.4.2 --- Design Methodology of the Stripline 0 dB Hybrid --- p.111 / Chapter 4.4.3 --- Design Methodology of the Stripline 4x4 Butler Matrix Network --- p.113 / Chapter 4.4.4 --- Design Methodology of the Stripline Aperture Coupled Patch --- p.138 / Chapter 4.4.5 --- Design Methodology of the Stripline Multibeam Antenna --- p.142 / Chapter Chapter 5: --- Design Examples and Application of Multibeam Antenna --- p.150 / Chapter 5.1 --- Wireless Local Loop (WLL) System --- p.150 / Chapter Chapter 6: --- Conclusions and Recommendations for Future Work --- p.156 / Chapter 6.1 --- Conclusions --- p.156 / Chapter 6.2 --- Recommendations for Future Work --- p.157 / Bibliography --- p.158 / Publication List --- p.160

在信息傳輸過程中如何保證信息的安全性是通信中的重要問題之一。目前常用的保密傳輸方式是基於密鑰的加密技術，但是隨著現代無線通信網絡的發展和計算資源的不斷豐富，基於密鑰的技術在無線網絡中的應用正面臨着巨大挑戰。這些挑戰一方面來自於無線介質的開放性使得竊聽更為容易，另一方面由於動態無線網絡和自組織無線網絡的發展使得密鑰的發布和管理更為困難。因此，為解決密鑰技術所面臨的挑戰，基於物理層的保密傳輸技術研究在近些年受到了很大關注。該技術最早在七十年代由Wyner 提出，其核心思想是利用無線信道的隨機性和目標用戶與竊聽者間無線信道容量的差異，通過對發射信號進行編碼設計使得目標用戶能正確解碼信息但竊聽者卻不能。該技術的關鍵問題之一是如何對發射信號進行設計從而提高保密信息的傳輸速率（或保密容量）。本論文的主要工作即是以此出發，旨在研究不同通信場景下最優化發射信號的設計，具體而言，本論文主要研究了以下場景下的最優發射信號設計： / 本論文的第一部分考慮一個多天線的發射機傳輸保密信息給一個單天線的目標用戶，同時有多個多天線的偷聽者在偷聽的場景。我們的目標是設計最優化發射信號使得保密信息傳輸速率最大化。該優化問題的難點在於保密信息速率函數是發射信號的一個非凸函數，因而很難求解到全局最優解。我們通過運用凸鬆弛技術證明這個非凸優化問題的全局最優解可以由它的凸鬆弛問題得到，並且我們證明了最優化的發射信號方案是採用波束聚焦。以上結論在發射機完全知道和部分知道接收機的信道信息時均成立。 / 本論文的第二部分是在第一部分的基礎上考慮在發射信號中加入人為噪聲以輔助保密信息的傳輸。具體而言，發射機可以分配部分功率來發射人為噪聲以達到干擾竊聽者的接收的目的。儘管在現有很多研究中已經證明了這種人為噪聲輔助的發射方式可有效提高保密信息傳輸速率，但是如何對保密信號和人為噪聲進行聯合優化設計使得保密傳輸速率最大化的問題一直未能有效解決。在本論文中，我們給出了一種保密信號和人為噪聲聯合最優化的求解方案。該方案是基於優化理論中的半正定規劃算法來獲得全局最優解，並且該算法在發射機完全知道和部分知道接收機信道信息時均適用。 / 本論文的第三部分主要考慮的是發射機、目標用戶和偷聽者均是多天線情況下，最大化保密信息容量的發射信號設計問題。該優化問題可以看作是之前單天線目標用戶的一個推廣，但較之前的最優信號設計問題更加具有挑戰性。在目前已知的工作中，該優化問題還沒有一個有效的多項式時間算法能求解到全局最優解。這裡，我們提出了一種基於交替優化算法的發射信號設計方案來獲得（局部）最優發射信號設計。我們證明該交替優化算法可以通過迭代注水算法來實現，因而具有很低的複雜度，並且該算法可以保證收斂到原最優化問題的穩定點，因而可以在多數情況下獲得（局部）最優解。同時在該部分，我們也研究了在發射機部分知道信道信息狀態時魯棒性發射信號的設計問題，並給出了基於交替優化算法的魯棒發射信號設計。 / 除以上提到的主要結果，本論文還考慮了多播保密信息速率最優化發射信號設計，和具有中斷概率約束的保密信息速率最優化發射信號的設計。 / Security is one of the most important issues in communications. Conventional techniques for achieving confidentiality in communication networks are based on cryptographic encryption. However, for wireless networks, this technique is faced with more challenges due to the open nature of the wireless medium as well as the dynamic topology of mobile networks. In the 1970's, Wyner proposed a physical layer-based approach to achieve perfectly secure communication without using encryption. One of the key problems of Wyner's approach is how to optimally design the transmit signal such that a high secrecy rate (i.e., the data rate at which the confidential information can be securely transmitted) can be achieved. In our work, we aim to solve this transmit signal optimization problem under various scenarios using convex optimization techniques. Specifically, the thesis consists of the following three main parts: / In the first part, we consider a multi-input single-output (MISO) scenario, where a multi-antenna transmitter sends confidential information to a singleantenna legitimate receiver, in the presence of multiple multi-antenna eavesdroppers. Our goal is to maximize an achievable secrecy rate by appropriately designing the transmit signal. The challenge of this secrecy rate maximization (SRM) problem is that it is a nonconvex optimization problem by nature. We show, by convex relaxation, that this seemingly nonconvex SRM problem admits a convex equivalent under both perfect and imperfect channel state information (CSI) cases. Our result also indicates that transmit beamforming is an optimal transmit strategy, irrespective of the number of eavesdroppers and the number of antennas employed by each eavesdropper. This provides a useful design guideline for practical implementations. / In the second part, we consider a scenario where the transmitter is able to simultaneously generate artificial noise (AN) to interfere the eavesdroppers during the transmission of the confidential message. While the efficacy of AN in improving the system security has been demonstrated in many existing works, how to jointly optimize the AN and the transmit signal is still an unsolved problem. In this part, we solve this AN-aided SRM problem under the same scenario as the first part, and give an efficient, semidefinite program (SDP)- based line search approach to obtain an optimal transmit signal and AN design under both perfect and imperfect-CSI situations. / In the last part, we consider a secrecy capacity maximization (SCM) problem for a multi-input multi-output (MIMO) scenario, where the legitimate receiver and the eavesdropper are both equipped with multiple antennas. This MIMOSCM problem is a generalization of the previous MISO-SRM problems. So far there is no known efficient algorithm to solve this problem in a global optimal manner. Herein, we propose an alternating optimization algorithm to tackle the SCM problem. The proposed algorithm has a nice iterative water-filling interpretation and is guaranteed to converge to a stationary solution of the MIMO-SCM problem. Extensions to robust SCM are also investigated in this part. / Besides the above three main results, this thesis also developed some approximate solutions to the multicast SRM of multiple MISO legitimate channels overheard by multiple MIMO eavesdroppers, and to the outage-constrained SRM of an MISO legitimate channel overheard by multiple MISO eavesdroppers. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Li, Qiang. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Contributions of This Thesis --- p.3 / Chapter 1.2 --- Organization of This Thesis --- p.5 / Chapter 2 --- Fundamentals of Physical-Layer Secrecy --- p.6 / Chapter 2.1 --- Elements of Information Theoretic Security --- p.6 / Chapter 2.2 --- Transmit Design for Physical-layer Secrecy: State-of-the-Art --- p.14 / Chapter 2.2.1 --- MISO Secrecy Capacity Maximization --- p.14 / Chapter 2.2.2 --- MIMO Secrecy Capacity Maximization --- p.17 / Chapter 2.2.3 --- AN-aided Secrecy Rate Maximization --- p.21 / Chapter 2.2.4 --- Secrecy Rate Maximization with Additional Covariance Constraints --- p.24 / Chapter 2.2.5 --- Robust Transmit Design for Physical-Layer Secrecy under Imperfect CSI --- p.28 / Chapter 2.3 --- Summary --- p.36 / Chapter 2.4 --- Appendix: GSVD --- p.37 / Chapter 3 --- MISOMEs Secrecy Rate Maximization --- p.38 / Chapter 3.1 --- System Model and Problem Statement --- p.39 / Chapter 3.1.1 --- System Model --- p.39 / Chapter 3.1.2 --- Problem Statement --- p.40 / Chapter 3.2 --- An SDP Approach to SRM Problem (3.4) --- p.43 / Chapter 3.2.1 --- The Secrecy-Rate Constrained Problem --- p.44 / Chapter 3.2.2 --- The Secrecy-Rate Maximization Problem --- p.46 / Chapter 3.3 --- Secrecy-Rate Optimization with Imperfect CSI --- p.49 / Chapter 3.3.1 --- Robust Secrecy-Rate Problem Formulations --- p.49 / Chapter 3.3.2 --- The Robust Secrecy-Rate Constrained Problem --- p.50 / Chapter 3.3.3 --- The Robust Secrecy-Rate Maximization Problem --- p.53 / Chapter 3.4 --- Simulation Results --- p.55 / Chapter 3.4.1 --- The Perfect CSI Case --- p.56 / Chapter 3.4.2 --- The Imperfect CSI Case --- p.58 / Chapter 3.5 --- Summary --- p.59 / Chapter 3.6 --- Appendix --- p.61 / Chapter 3.6.1 --- Proof of Proposition 3.1 --- p.61 / Chapter 3.6.2 --- Verifying Slater's Constraint Qualification for Problem (3.10) --- p.63 / Chapter 3.6.3 --- Proof of Theorem 3.1 --- p.63 / Chapter 3.6.4 --- Relationship between Super-Eve Design and the Optimal SDP Design --- p.65 / Chapter 3.6.5 --- Proof of Proposition 3.4 --- p.67 / Chapter 3.6.6 --- Proof of Proposition 3.5 --- p.70 / Chapter 3.6.7 --- Worst-case Secrecy Rate Calculation --- p.71 / Chapter 4 --- Multicast Secrecy Rate Maximization --- p.73 / Chapter 4.1 --- System Model and Problem Statement --- p.74 / Chapter 4.2 --- An SDP Approximation to Problem (4.2) --- p.75 / Chapter 4.3 --- Simulation Results --- p.78 / Chapter 4.4 --- Summary --- p.79 / Chapter 4.5 --- Appendix --- p.81 / Chapter 4.5.1 --- Proof of Proposition 4.1 --- p.81 / Chapter 4.5.2 --- Proof of Theorem 4.1 --- p.82 / Chapter 5 --- AN-aided MISOMEs Secrecy Rate Maximization --- p.85 / Chapter 5.1 --- System Model and Problem Statement --- p.86 / Chapter 5.1.1 --- System Model --- p.86 / Chapter 5.1.2 --- Problem Statement --- p.87 / Chapter 5.2 --- An SDP-based Approach to the SRM Problem --- p.89 / Chapter 5.2.1 --- A Tight Relaxation of the SRM Problem (5.4) --- p.90 / Chapter 5.2.2 --- An SDP-based Line Search Method for the Relaxed SRM Problem (5.9) --- p.92 / Chapter 5.3 --- Robust Transmit Design for Worst-Case SRM --- p.94 / Chapter 5.3.1 --- Worst-Case Robust SRM Problem Formulation --- p.95 / Chapter 5.3.2 --- A Tight Relaxation of the WCR-SRM Problem (5.17) --- p.96 / Chapter 5.3.3 --- An SDP-based Line Search Method for the RelaxedWCRSRM Problem (5.23) --- p.98 / Chapter 5.4 --- Robust Transmit Design for Outage SRM --- p.100 / Chapter 5.4.1 --- A Sphere-bounding Safe Approximation to OCR-SRM Problem (5.29) --- p.101 / Chapter 5.5 --- Simulation Results --- p.103 / Chapter 5.5.1 --- The Perfect-CSI Case --- p.104 / Chapter 5.5.2 --- The Imperfect-CSI: Bounded Spherical Uncertainty --- p.105 / Chapter 5.5.3 --- The Imperfect-CSI: Gaussian Random Uncertainty --- p.108 / Chapter 5.6 --- Summary --- p.111 / Chapter 5.7 --- Appendix --- p.112 / Chapter 5.7.1 --- Proof of Proposition 5.1 --- p.112 / Chapter 5.7.2 --- Proof of Theorem 5.1 --- p.114 / Chapter 5.7.3 --- Proof of Theorem 5.2 --- p.117 / Chapter 6 --- Outage Secrecy Rate Maximization for MISOSEs --- p.120 / Chapter 6.1 --- System Model and Problem Statement --- p.121 / Chapter 6.2 --- A Bernstein-type Inequality-Based Safe Approximation to Problem (6.2) --- p.122 / Chapter 6.3 --- Simulation Results --- p.127 / Chapter 6.4 --- Summary --- p.128 / Chapter 6.5 --- Appendix --- p.129 / Chapter 6.5.1 --- Proof of Lemma 6.1 --- p.129 / Chapter 6.5.2 --- Proof of Proposition 6.1 --- p.130 / Chapter 7 --- MIMOME Secrecy Rate Maximization --- p.134 / Chapter 7.1 --- An Alternating Optimization Approach to the MIMO-SCM Problem (7.1) --- p.135 / Chapter 7.2 --- An Alternating Optimization Approach to theWorst-case MIMOSCM Problem --- p.140 / Chapter 7.3 --- An Alternating Optimization Approach to the Outageconstrained SCM --- p.142 / Chapter 7.4 --- Simulation Results --- p.145 / Chapter 7.4.1 --- The Perfect CSI Case --- p.146 / Chapter 7.4.2 --- The Imperfect CSI case --- p.149 / Chapter 7.5 --- Summary --- p.150 / Chapter 7.6 --- Appendix --- p.153 / Chapter 7.6.1 --- Proof of Proposition 7.1 --- p.153 / Chapter 7.6.2 --- Proof of the monotonicity of Tr(W? ) w.r.t. --- p.154 / Chapter 7.6.3 --- Proof of Proposition 7.2 --- p.155 / Chapter 8 --- Conclusion --- p.157 / Chapter 8.1 --- Summary --- p.157 / Chapter 8.2 --- Future Directions --- p.158 / Bibliography --- p.161

As the demand for wireless communication systems grows, the need for spectrum grows accordingly. However, a large portion of the usable spectrum has already been exclusively licensed to various entities. This exclusive allocation method encourages spectrum to be left unused if the licensee has no need for that spectrum. In order to better utilize spectrum and formulate new approaches for greater spectrum use efficiency, it is imperative to possess a thorough understanding about how wireless spectrum behaves over time, frequency, and space. In this thesis, a practical, scalable, and low-cost wideband distributed spectrum sensing system is designed, implemented, and tested. The proposed system is made up of a collection of nodes that use general purpose, off-the-shelf computer hardware as well as a collection of inexpensive software-defined radio (SDR) equipment in order to collect and analyze spectrum data that varies across time, frequency, and space. The spectrum data the proposed system collects is the power present at a given frequency. The tools needed to analyze the gathered data are also created, including a periodogram and spectrogram function, which visualize average spectrum use over a period of time and as spectrum use varies with time, respectively. The proposed system also facilitates the testing of a spatio-spectrum characterization method using real data. This method has only been simulated up to this point. The characterization technique allows for spatially varying spectrum measurements to be visualized using heat maps.

The recent research interest in wireless sensor networks has caused the development of many new applications and subsequently, these emerging applications have ever increasing requirements. One such requirement is that of mobility, which has inspired an entirely new array of applications in the form of mobile wireless sensor networks (MWSNs). In terms of communications, MWSNs present a challenging environment due to the high rate at which the topology may be changing. As such, the motivation of this work is to investigate potential communications solutions, in order to satisfy the performance demands of new and future MWSN applications. As such this work begins by characterising and evaluating the requirement of a large variety of these emerging applications. This thesis focuses on the area of routing, which is concerned with the reliable and timely delivery of data from multiple, mobile sensor nodes to a data sink. For this purpose the technique of gradient routing was identified as a suitable solution, since data can quickly be passed down a known gradient that is anchored at the sink. However, in a mobile network, keeping the gradient up-to-date is a key issue. This work proposes the novel use of a global time division multiple access (GTDMA) MAC as a solution to this problem, which mitigates the need for regularly flooding the network. Additionally, the concept of blind forwarding is utilised for its low overhead and high reliability through its inherent route diversity. The key contribution of this thesis is in three novel routing protocols, which use the aforementioned principles. The first protocol, PHASeR, uses a hop-count metric and encapsulates data from multiple nodes in its packets. The hop-count metric was chosen because it is simple and requires no additional hardware. The inclusion of encapsulation is intended to enable the protocol to cope with network congestion. The second protocol, LASeR, utilises location awareness to maintain a gradient and performs no encapsulation. Since many applications require location awareness, the communications systems may also take advantage of this readily available information and it can be used as a gradient metric. This protocol uses no encapsulation in order to reduce delay times. The third protocol, RASeR, uses the hop-count metric as a gradient and also does not perform encapsulation. The reduced delay time and the relaxed requirement for any existing method of location awareness makes this the most widely applicable of the three protocols. In addition to analytical expressions being derived, all three protocols are thoroughly tested through simulation. Results show the protocols to improve on the state-of-the-art and yield excellent performance over varying speeds, node numbers and data generation rates. LASeR shows the lowest overhead and delay, which comes from the advantage of having available location information. Alternatively, at the expense of increased overhead, RASeR gives comparatively high performance metrics without the need for location information. Overall, RASeR can be suitably deployed in the widest range of applications, which is taken further by including four additional modes of operation. These include a supersede mode for applications in which the timely delivery of the most recent data is prioritised. A reverse flooding mechanism, to enable the sink to broadcast control messages to the sensor nodes. An energy saving mode, which uses sleep cycles to reduce the networks power consumption, and finally a pseudo acknowledgement scheme to increase the reliability of the protocol. These additions enable RASeR to satisfy the needs of some of the most demanding MWSN applications. In order to assess the practicality of implementation, RASeR was also evaluated using a small testbed of mobile nodes. The successful results display the protocols feasibility to be implemented on commercially available hardware and its potential to be deployed in the real world. Furthermore, a key issue in the real world deployment of networks, is security and for this reason a fourth routing protocol was designed called RASeR-S. RASeR-S is based on RASeR, but introduces the use of encryption and suggests a security framework that should be followed in order to significantly reduce the possibility of a security threat. Whilst the main focus of this work is routing, alternative MAC layers are assessed for LASeR. Unlike the other two protocols, LASeR uses available location information to determine its gradient and as such, it is not reliant on the GTDMA MAC. For this reason several MAC layers are tested and the novel idea of dedicated sensing slots is introduced, as well as a network division multiple access scheme. The selected and proposed MACs are simulated and the GTDMA and two proposed protocols are shown to give the best results in certain scenarios. This work demonstrates the high levels of performance that can be achieved using gradient orientated routing in a mobile network. It has also shown that the use of a GTDMA MAC is an efficient solution to the gradient maintenance problem. The high impact of this work comes from the versatility and reliability of the presented routing protocols, which means they are able to meet the requirements of a large number of MWSN applications. Additionally, given the importance of security, RASeR-S has been designed to provide a secure and adaptable routing solution for vulnerable or sensitive applications.

Ngai Cheuk Han. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (leaves 110-117). / Abstracts in English and Chinese. / Abstract --- p.i / Acknowledgement --- p.iv / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Background Study --- p.5 / Chapter 2.1 --- Mobile Ad Hoc Networks --- p.5 / Chapter 2.1.1 --- Definition --- p.5 / Chapter 2.1.2 --- Characteristics --- p.5 / Chapter 2.1.3 --- Applications --- p.6 / Chapter 2.1.4 --- Standards --- p.7 / Chapter 2.1.5 --- Routing Protocols --- p.8 / Chapter 2.2 --- Security in Mobile Ad Hoc Networks --- p.11 / Chapter 2.2.1 --- Vulnerabilities --- p.11 / Chapter 2.2.2 --- Motivation for the Attacks --- p.12 / Chapter 2.2.3 --- Types of Attacks --- p.13 / Chapter 2.3 --- Cryptography --- p.13 / Chapter 2.3.1 --- Cryptographic goals --- p.13 / Chapter 2.3.2 --- Symmetric-key encryption --- p.14 / Chapter 2.3.3 --- Asymmetric-key encryption --- p.14 / Chapter 2.3.4 --- Digital Signatures --- p.15 / Chapter 2.3.5 --- Digital Certificates --- p.15 / Chapter 2.3.6 --- Certificate Authority --- p.16 / Chapter 2.4 --- Literature Review --- p.17 / Chapter 3 --- Related Work --- p.23 / Chapter 4 --- Architecture and Models --- p.26 / Chapter 4.1 --- Architecture of the Authentication Service --- p.26 / Chapter 4.2 --- The Network Model --- p.28 / Chapter 4.2.1 --- Clustering-Based Structure --- p.31 / Chapter 4.2.2 --- Clusterhead Selection Criteria and Role --- p.33 / Chapter 4.3 --- The Trust Model --- p.37 / Chapter 4.3.1 --- Direct TVust --- p.40 / Chapter 4.3.2 --- Recommendation Trust --- p.41 / Chapter 4.3.3 --- Deriving Direct Trust --- p.41 / Chapter 5 --- Trust- and Clustering-Based Authentication Service --- p.43 / Chapter 5.1 --- Clustering Structure Formation and Maintenance --- p.43 / Chapter 5.1.1 --- Clustering Structure Formation --- p.43 / Chapter 5.1.2 --- Network Maintenance --- p.45 / Chapter 5.2 --- Security Operations --- p.50 / Chapter 5.2.1 --- Public Key Certification --- p.51 / Chapter 5.2.2 --- Identification of Malicious Nodes --- p.55 / Chapter 5.2.3 --- Trust Value Update --- p.58 / Chapter 5.3 --- Special Scenarios --- p.60 / Chapter 5.3.1 --- Join the network --- p.60 / Chapter 5.3.2 --- Move to another cluster --- p.61 / Chapter 5.3.3 --- Not Enough Introducer --- p.62 / Chapter 6 --- Simulations and Results --- p.65 / Chapter 6.1 --- Authentication Service Based on Trust and Network Mod- els --- p.65 / Chapter 6.1.1 --- Experiments Set-Up --- p.65 / Chapter 6.1.2 --- Simulation Results --- p.67 / Chapter 6.2 --- Clusters Formation and Maintenance --- p.85 / Chapter 6.2.1 --- Experiments Set-Up --- p.85 / Chapter 6.2.2 --- Simulation Results --- p.86 / Chapter 6.3 --- Authentication Service Based on Trust and Network Mod- els with Clusters Formation and Maintenance --- p.91 / Chapter 6.3.1 --- Experiments Set-Up --- p.91 / Chapter 6.3.2 --- Simulation Results --- p.94 / Chapter 7 --- Conclusion --- p.108 / Bibliography --- p.117