<p>This thesis proposed and presented technical details of new probabilistic metrics of trust in the links wireless ad hoc networks for unobservable communications. In covert communication networks, only the end nodes are aware of the communication characteristics of the overall path. The most widely used protocols of ad hoc networks was overviewed. The routing protocols of ad hoc networks with trust considerations and select Destination Sequence Routing, a protocol that can be used in distributed ad hoc network settings for path discovery, was also reviewed. It establishes a path through which all packets sent by a source must pass to the destination. The end nodes are responsible for examining the statistics of the received packets and deriving inferences on path feature variations which are used for computing new trust metrics. When a path is judged not trustworthy based on the metrics, the Destination Sequence Routing is informed to undertake a new trusted path discovery between the end points. The thesis added a new feature based on the quality of service parameters of the path to create trust in the links in recognition of attacks.</p>

Several new multiuser detectors are developed for different direct-sequence codedivision multiple-access (DS-CDMA) application environments. The first detector is based on a semidefinite-programming (SDP) relaxation technique. In this detector, maximum likelihood (ML) detection is achieved by 'relaxing' the associated combinatorial problem into an SDP problem, which leads to a detector of polynomial complexity. It is shown that the SDP-relaxation (SDPR) based detector can be obtained by solving a dual SDP problem which leads to improved efficiency. Computer simulations demonstrate that the SDPR detector offers near-optimal performance with much reduced computational complexity compared with that of the ML detector proposed by Verdu for both synchronous and asynchronous DS-CDMA systems. The second detector is based on a recursive convex programming (RCP) approach. In this detector, ML detection is carried out in two steps: first, the combinatorial problem associated with ML detection is relaxed to a convex programming problem, and then a recursive approach is used to obtain an approximate solution for ML detection. Efficient unconstrained relaxation approach is proposed for the proposed detector to reduce the involved computational complexity. Computer simulations demonstrate that the proposed detectors offer near-optimal detection performance which is superior to that offered by many other suboptimal detectors including the SDPR detector. However, the computational complexity involved in the proposed detectors is much lower relative to that involved in Verdu's ML detector as well as our SDPR detector. The third detector entails a subspace estimation-based constrained optimization approach for channel estimation in DS-CDMA systems with multipath propagation channels. The proposed approach offers an improved approximation for the noise iii subspace compared with that offered by several existing algorithms. Computer simulations show that the performance of the proposed detector offers nearly the same performance as that of existing subspace detectors but leads to a significant reduction in the amount of computation. Relative to some existing constrained optimization methods, the proposed detector offers a significantly improved performance while requiring a comparable amount of computation. The fourth detector is proposed based on a vector constant-modulus (VCM) approach. This detector is designed for DS-CDMA systems with multipath propagation channels where the effective signatures observed at receiver are distorted by multipath propagation and aliasing concurrently. In this detector, detection is carried out by solving a linear constrained optimization problem whose objective function is formulated based on the VCM criterion. Two adaptation algorithms, namely, the constrained stochastic gradient algorithm and the recursive vector constant-modulus algorithm, are developed. Analysis are presented to investigate the performance of the proposed detector. Computer simulations show that the proposed detectors are able to suppress multiuser interference and inter-symbol interference effectively. More importantly, they offer robust detection performance against the effective signature distortion caused by aliasing at the receiver.

No description available.

The development and performance evaluation of new techniques for direction of arrival (DOA) estimation, single-user beamforming (SUB), and multiuser beamforming (MUB) to be used in wireless communications are investigated. Two of the most commonly used beamformer configurations in direct-sequence code-division multiple access (DS-CDMA) systems, the chip-based (CB) and the symbol-based (SB) configurations for the base station (BS) receiver, are studied and their performance is evaluated. It is shown that using the CB configuration, different interfering components are rejected based on the spatial distribution of their power. In the SB configuration, spatial diversity is exploited after despreading and different interfering components are rejected based on their interfering strength which depends on both their power and code correlation with the signal of interest. For the SB configuration, more effort is applied to rejecting the interfering components with higher interfering strength and thus a more selective and efficient system is achieved. Detailed performance analysis and simulations show that in the presence of multipleaccess interference, the SB configuration can lead to a significant improvement in the signal-to-interference-plus-noise ratio relative to that achieved with the CB configuration for both asynchronous and synchronous DS-CDMA systems. A new technique for DOA estimation is proposed. The new technique, called subarray beamforming-based DOA (SBDOA) estimation, uses two virtual subarrays to form a signal whose phase relative to the reference signal is a function of the DOA. The DOA is then estimated based on the computation of the phase shift between the reference signal and the phaseshifted target signal. Since the phase-shifted target signal is obtained after interference rejection through beamforrning, the effect of co-channel interference on the estimation is significantly reduced. The proposed technique is computationally simple and the number of signal sources detectable is iii not bounded by the number of antenna elements used. Performance analysis and extensive simulations show that the proposed technique offers significantly improved estimation resolution, capacity, accuracy, and tracking capability relative to existing techniques. A new SUB algorithm is proposed for the downlink in wireless communication systems. The beam pattern at the BS is determined using a new optimality criterion which takes into consideration the fact that signals from the BS to different mobile stations (MSs) have different power and thus have different resistance to co-channel interference. In this way, the power of co-channel interference in the direction of an MS whose downlink signal has low resistance to co-channel interference can be significantly reduced. Simulation results show that the new algorithm leads to better performance than conventional algorithms in terms of system outage probability. A new MUB algorithm is proposed for joint beamforming and power control for the downlink in wireless communication systems. The optimization problem of optimal MUB is reformulated by modifying the constraints so that the weight vectors at the BS for different MSs are optimized in a feasible region which is a subset of the one of the original MUB problem. The downlink beamforming weight vectors of different MSs are then jointly optimized in a subspace instead of searching in the entire parameter space. Simulation results show that the modified optimization problem leads to solutions that satisfy the signal-to-noise-plus-interference ratio specification at each MS and, at the same time, the total power transmitted from the BS is very close to the optimal one. The solution of the modified optimization problem requires significantly less computation than that of the optimal MUB problem.

Approved for public release; distribution is unlimited / Wireless networks can be broadly classified into two types - infrastructure based networks and ad hoc networks. The former uses fixed base stations (infrastructure) which are responsible for coordinating communication between the mobile hosts (nodes). These base stations are interconnected by wired back bones, where as mobile nodes communicate with the base station through the wireless media. The latter one consists of mobile nodes which communicate with each other through wireless medium without any fixed infrastructure. Hence there is no centralized infrastructure that takes care of the routing of information among the participants in the network. There has been a growing interest in ad hoc network in recent years as mobile devices have become more powerful and are capable of processing data like their desktop counterparts. When such a capability is available these devices should be able to share information among them without reliance on existing network infrastructure. Mobile devices are self configurable into either infrastructure or ad hoc mode. Protocols and software have been developed to enable mobile devices to connect to an infrastructure node, where as the same is not the case in the ad hoc environment. Host mobility causes frequent and unpredictable topological changes in a wireless environment. Finding and maintaining routes in ad hoc networks is a non trivial task. This thesis will develop software components that will enable communication in an ad hoc network. These components could be used to build collaborative services in such and ad hoc (802.11) wireless environment. / Major, Indian Air Force

In this dissertation, direct-sequence code-division multiple access (DS-CDMA) systems with multiuser detectors used at receiver are investigated and two kinds of multiuser detectors are developed for DS-CDMA systems. In the investigation of DS-CDMA systems using multiuser detectors at receiver, a study on the performance of the system is presented, where heterogeneous traffic with different transmission rates and quality of service (QoS) requirements is supported. The effects of some realistic factors, such as imperfect power control and the existence of multiple cells, on the system performance are studied. In addition, algorithms are proposed to deal with the forward link power allocation problem based on the measurements of random characteristics of the received signals. This power allocation problem is formulated as a constrained optimization problem. To make the problem easy to solve, an additional appropriate constraint is proposed. Two methods are developed to identify the feasible region of this constrained optimization problem. The first proposed multiuser detector is an adaptive minimum mean-squared-error (MMSE) detector. Particularly, it is desirable for the cases where communication channels have severe near-far problem, and thus the convergence rates of adaptive MMSE detectors for users with different power are quite different. To improve the convergence rates of adaptive MMSE detectors for weak power users, the interference effects of the strong power user signals are subtracted from the received signal successively. The method to estimate the parameters required in the proposed detector is also developed. It is shown that the proposed detector achieves fast convergence rates in various near-far scenarios. Other studies conducted include the transient mean-squared-error (MSE) analysis to explain the different convergence rates of adaptive MMSE detectors for users with different power, and the bit-error-rate (BER) performance analysis for the proposed detector. The second proposed multiuser detector is a set of semi-blind linear parallel interference cancellation (PIC) detectors for the reverse link of multiple-cell systems, where only information about intra-cell users is available. To decrease the interference from inter-cell users whose information is unavailable to the receiver, the inter-cell user signal subspace is identified first by making use of the available information about intra-cell users. The eigenvectors and eigenvalues of this signal subspace are then used in the traditional linear PIC structure, in place of the unknown inter-cell users’ signature codes and signal amplitudes. Based on this idea, three detection schemes are proposed. In addition, an efficient adaptation implementation method is developed, and the performance of the proposed detectors is studied. The proposed detectors are shown to be suitable for practical implementations and have satisfactory performance. / Graduate

University of Macau / Faculty of Science and Technology. / Department of Electrical and Computer Engineering

無線通訊現已成為我們生活中不可或缺的一部份。除了較傳統的無線技術應用如電視廣播及衛星通訊外，日漸普及的平版電腦與智能手機對無線技術也有殷切的需求。然而，有限的無線電頻譜是無線通訊的其中一個限制。在有限的資源下，如何在壅塞的網絡環境有效地分配無線電頻譜成為一個重要的議題。在這篇論文中，我們會利用博奕論來分析壅塞網絡內用戶的行為和一些嶄新的頻譜共用機制。 / 在論文的首部份，我們會利用壅塞賽局來模擬認知無線電網絡中未授權無線電頻段的使用者(次級用戶)的互動在四個不同的賽局下，我們會評估納殊均衡與社會最優的效能比。此外，我們會鑑別導致嚴重失效能的最壞情況。有見及此，我們提議一個能夠改善壅塞網絡系統吞吐量與資源方配公平性的半合作方案。透過具體指定合作用戶的資源分配，我們論證次級用戶具有真誠合作的動機。除此之外，我們也計算出半合作方案跟完全合作方案在系統吞吐量上比較的下限。從數值結果的觀察中，可見次級用戶的半合作模式已比沒有任何合作的方案更有效地改善系統的吞吐量。另外，在壅塞的網絡環境下，半合作方案的系統效能不僅與最理想的情況相近，而且能夠減低溝通的開銷及演算法的複雜性。 / 在論文的第二部份，我們會考慮流動網絡的壅塞情況。透過使用斯塔克爾伯格模型去模擬網絡供應商和消費者的互動，我們會集中研究兩種不同的收費方法。通過考慮網絡壅塞的負面影響，兩個收費方法在不同的地區會有不同的定價。在特定的網絡資源及消費者功利下，我們證實特定地區收費比無地區區分收費更為可取。特定地區收費不但能增加網絡供應商的收益，也能改善消費者的社會福利。 / Wireless technology has become an inseparable part of our daily lives. In addition to the traditional wireless applications, such as TV broadcast or satellite communication, the demand of wireless access from tablets and smartphones has increased tremendously. One big challenge of wireless communications is that spectrum resource is limited. When the resource is scarce, resource allocation in congested networks is of particular importance. In this thesis, we are interested to investigate the user behavior and new spectrum sharing mechanisms in congested networks using the tool of game theory. / In the first part of the thesis, we model the interaction of secondary users (SUs) in cognitive radio networks as congestion games. We evaluate the inefficiency of the Nash equilibria with the social optimal in four families of games. Most importantly, we identify the worst case scenario which leads to a severe performance loss. In order to tackle the problem, we propose a partial cooperation scheme which provides an alternative to improve the system throughput and fairness of the congested network. By specifying the allocation for cooperating users, we show that SUs have incentive to cooperate truthfully. Moreover, we give the performance bound of system throughput compared with full cooperation scheme. We also observe from the numerical results that the partial cooperation of SUs can greatly improve the system throughput comparing with no cooperation of SUs. In addition, the performance of the partial cooperation scheme is close to optimal in congested networks with a reduced overhead and complexity of the algorithm. / In the second part, we consider the congestion of current mobile networks. By modeling the interaction between a network service provider and the mobile subscribers with the Stackelberg game, we study two pricing schemes which suggested how prices should be set in different regions with the consideration of negative effects of congestion. Under given conditions of resource allocation and utility of subscribers, we show that region- specific pricing is more preferable than region-agnostic pricing which can improve both the revenue of the network service provider and the social welfare of the subscribers. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Law, Lok Man. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 153-164). / Abstracts also in Chinese. / Abstract --- p.i / Acknowledgement --- p.v / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Motivation --- p.1 / Chapter 1.2 --- Thesis Outline --- p.3 / Chapter 2 --- Congestion Games in Cognitive Radio Networks --- p.6 / Chapter 2.1 --- Introduction --- p.6 / Chapter 2.1.1 --- Overview --- p.6 / Chapter 2.1.2 --- Related Work --- p.10 / Chapter 2.2 --- Game Model --- p.12 / Chapter 2.2.1 --- A Congestion Game Framework --- p.13 / Chapter 2.2.2 --- Price of Anarchy (PoA) --- p.16 / Chapter 2.3 --- PoA Analysis --- p.19 / Chapter 2.3.1 --- Identical Games --- p.20 / Chapter 2.3.2 --- Player-specific Symmetric Games --- p.24 / Chapter 2.3.3 --- Resource-specific Symmetric Games --- p.27 / Chapter 2.3.4 --- Asymmetric Games --- p.32 / Chapter 2.4 --- Applications --- p.41 / Chapter 2.4.1 --- Uniform MAC --- p.41 / Chapter 2.4.2 --- Slotted Aloha --- p.45 / Chapter 2.4.3 --- Insights for System Design --- p.48 / Chapter 2.5 --- Summary --- p.49 / Chapter 2.6 --- Appendix --- p.51 / Chapter 2.7 --- Notations --- p.53 / Chapter 3 --- Partial Cooperation in Cognitive Radio Networks --- p.54 / Chapter 3.1 --- Introduction --- p.54 / Chapter 3.1.1 --- Overview --- p.54 / Chapter 3.1.2 --- Related Work --- p.58 / Chapter 3.2 --- System Model --- p.61 / Chapter 3.3 --- Different Medium Access Control Schemes --- p.63 / Chapter 3.3.1 --- Benchmark MAC Schemes --- p.63 / Chapter 3.3.2 --- Priority-based Partial Cooperation Scheme (PPCS) --- p.66 / Chapter 3.4 --- PPCS with Identical Data Rates --- p.70 / Chapter 3.4.1 --- Random Priority PPCS (PPCS-RP) --- p.71 / Chapter 3.4.2 --- Fixed Priority PPCS (PPCS-FP) --- p.77 / Chapter 3.4.3 --- Numerical Results --- p.80 / Chapter 3.5 --- PPCS with Heterogeneous Data Rates --- p.85 / Chapter 3.5.1 --- Sparsely Populated PUs --- p.87 / Chapter 3.5.2 --- Densely Populated PUs --- p.95 / Chapter 3.6 --- PPCS with incomplete information --- p.98 / Chapter 3.6.1 --- The Allocation Rule --- p.98 / Chapter 3.6.2 --- Incentive for Group Formation --- p.100 / Chapter 3.6.3 --- Truth Revelation --- p.103 / Chapter 3.6.4 --- Numerical Results --- p.105 / Chapter 3.7 --- Summary --- p.111 / Chapter 3.8 --- Notations --- p.114 / Chapter 4 --- Regional Pricing in Mobile Networks --- p.115 / Chapter 4.1 --- Introduction --- p.115 / Chapter 4.1.1 --- Overview --- p.115 / Chapter 4.1.2 --- Related Work --- p.117 / Chapter 4.2 --- System Model --- p.119 / Chapter 4.2.1 --- Stackelberg Game --- p.121 / Chapter 4.2.2 --- Our Model --- p.123 / Chapter 4.3 --- The Two Pricing Schemes --- p.127 / Chapter 4.3.1 --- Region-specific Pricing --- p.127 / Chapter 4.3.2 --- Region-agnostic Pricing --- p.128 / Chapter 4.3.3 --- Extension to Multiple Regions --- p.130 / Chapter 4.4 --- Comparison of Schemes --- p.131 / Chapter 4.4.1 --- Overview of Two-region Case --- p.131 / Chapter 4.4.2 --- Revenue Ratio --- p.135 / Chapter 4.4.3 --- Utilization Ratio --- p.142 / Chapter 4.5 --- Summary --- p.144 / Chapter 4.6 --- Notations --- p.146 / Chapter 5 --- Conclusions and Future Work --- p.147 / Chapter 5.1 --- Conclusion --- p.147 / Chapter 5.2 --- Future Work --- p.148 / Chapter 5.2.1 --- Congestion Games in Cognitive Radio Networks --- p.148 / Chapter 5.2.2 --- Partial Cooperation in Cognitive Radio Networks --- p.149 / Chapter 5.2.3 --- Regional Pricing in Mobile Networks --- p.151 / Bibliography --- p.153

因為今天四通八達的無線通信網絡對高速高質量通信的要求,加之無線通信資源的稀缺,使得資源分配在無線通信領域的地位越發的重要.多種多樣的無線通信資源和不同的設計要永使得資源分配問題變得很複雜,我們也很難找到一個通用的方法去解決所有的資源分配問題.在本文中, 我們研究一些典型的資源分配問題,通過最優化設計,給出恰當的高效的算法予以解決.本文中將會涉及集中化算法和分佈式算法。 / 在本文中, 我們首先研究協作通信中的功率分配和中繼選擇問題。這個問題因為其問題的組合性而變得很複雜。為了保證系統的性能並且同時避免過量的冗餘信息, 我們提出了一個新的概念"中繼選擇自由度"。更重要的是, 為了使我們的方法能夠適用於集中信息很難的大型通信系統, 我們提出了分佈式的解決方案。該方法在實際中可以比較簡單的實現。 / 我們接著研究多用戶接入網絡的"軟"服務質量控制問題。我們這裡考慮的情形是:用戶們有各自的服務質量要求, 比如有一個目標速率。因為系統的資源總是有限的, 如果有過多用戶, 那麼同時滿足所有用戶的服務質量要求有時候是不可能的。我們的目標是在這種情況發生的時候,優化整個系統的資源分配。我們提出了分佈式算法來解決這一個問題。 / 最後, 我們研究下行鏈中的波束成形問題。這裡我們出於實際情況考慮,系統中存在兩種用戶:優先用戶和非優先用戶。我們想要盡可能最大化的提升非優先用戶的性能,同時必須首先滿足優先用戶的服務質量用要求。我們這裡用不同的波束成形向量來完成這個任務。這個問題是NP問題,我們做了必要的一些放鬆處理來得到有效的較優的解。 / Due to the limited resources and high performance requirements in today’s wireless networks, optimization methods in resource allocation play a significant role in reaping the benefits from wireless communications. Various available resources and different design goals make the resource allocation problem complex and we are unlikely to find a generic approach for all problems. Thus in this thesis, we investigate several resource allocation problems and propose the proper optimization methods and algorithms that can efficiently give us desired solutions. Also, both centralized and distributed methods will be shown in this thesis. / We first study the joint power allocation and relay selection problem in cooperative communication. This problem is complex due to its combinatorial nature. In order to avoid high information overhead and system complexity while at the same time maintain system performance, we introduce a new concept called “relay selection degree bound“. Moreover, since in large scale cooperative communication network, collecting information and centralized control would be very difficult, we resort to distributed algorithms that can be easily implemented in practice. / We further consider the soft QoS control problem in multiple access network. Here we consider the situation where the users have quality of service(QoS) requirements, i.e., each user has a target rate for its application. Since the resources in the system are limited, these requirements will result in the infeasibility of the whole system if there are too many users. We aim at optimizing the performance of the whole system while this kind of infeasibility happens. We will see how distributed algorithms can work for this problem and give us desired results. / We finally consider the downlink beamforming problem where there are two kind of users in the system: priority users and non-priority users. We maximize the non-priority users performance while at the same time satisfying the priority users’ QoS requirements first. Here we adopt heterogeneous beamforming scheme to complete the task. Since the problem is NP hard, relaxation is done for efficient solutions. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Fang, Haoran. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 76-81). / Abstracts also in Chinese. / Abstract --- p.i / Acknowledgement --- p.iv / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Motivation --- p.1 / Chapter 1.2 --- Background --- p.3 / Chapter 1.2.1 --- Wireless Communication Schemes --- p.3 / Chapter 1.2.2 --- Mathematical Preliminaries --- p.9 / Chapter 1.3 --- Outline of the Thesis --- p.11 / Chapter 2 --- Resource Allocation for Cooperative Communication Networks --- p.13 / Chapter 2.1 --- Chapter Introduction --- p.13 / Chapter 2.2 --- system model and problem formulation --- p.16 / Chapter 2.3 --- optimal power allocation scheme for arbitrary configuration --- p.20 / Chapter 2.4 --- Relay selection in the MAC layer --- p.24 / Chapter 2.4.1 --- Algorithm Design --- p.24 / Chapter 2.4.2 --- Distributed Implementation of The Relay Selection Algorithm --- p.29 / Chapter 2.5 --- Numerical Results --- p.33 / Chapter 2.5.1 --- The Convergence of Distributed Power Allocation Algorithm --- p.33 / Chapter 2.5.2 --- Performance of The Overall Cross Layer Solution --- p.34 / Chapter 2.5.3 --- Improvements of Heuristic Markov algorithm --- p.36 / Chapter 2.6 --- Chapter Conclusions --- p.38 / Chapter 3 --- Soft QoS Control in Multiple Access Network --- p.39 / Chapter 3.1 --- Introduction --- p.39 / Chapter 3.2 --- system model --- p.41 / Chapter 3.3 --- Feasibility check and soft QoS control --- p.43 / Chapter 3.3.1 --- Feasibility Check --- p.43 / Chapter 3.3.2 --- Soft QoS Control --- p.45 / Chapter 3.3.3 --- Distributed Soft QoS Control --- p.47 / Chapter 3.3.4 --- Numerical Results --- p.53 / Chapter 3.4 --- Chapter Conclusion --- p.57 / Chapter 4 --- Heterogeneous resource allocation via downlink beamforming --- p.58 / Chapter 4.1 --- Introduction --- p.58 / Chapter 4.2 --- system model --- p.60 / Chapter 4.3 --- heterogeneous resource allocation via beamforming --- p.62 / Chapter 4.3.1 --- Relaxation and problem analysis --- p.62 / Chapter 4.3.2 --- Randomization for final solutions --- p.66 / Chapter 4.4 --- Numerical Results --- p.69 / Chapter 4.5 --- Conclusion --- p.70 / Chapter 5 --- Conclusions and Future Work --- p.73 / Chapter 5.1 --- Conclusions --- p.73 / Chapter 5.2 --- Future Work --- p.74 / Bibliography --- p.76

Shen, Siduo. / Thesis Ph.D. Chinese University of Hong Kong 2014. / Includes bibliographical references (leaves 147-161). / Abstracts also in Chinese. / Title from PDF title page (viewed on 15 September, 2016). / Shen, Siduo = Duo dian xie zuo : gan rao jian qing yu gan rao li yong / Shen, Siduo.