• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 2735
  • 158
  • 144
  • 104
  • 101
  • 49
  • 13
  • 13
  • 13
  • 13
  • 13
  • 13
  • 13
  • 10
  • 9
  • Tagged with
  • 3919
  • 3919
  • 1958
  • 814
  • 793
  • 769
  • 619
  • 379
  • 377
  • 356
  • 344
  • 276
  • 268
  • 267
  • 266
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Channel adaptive techniques for wireless resources management in AD Hoc networks

Lin, Xiaohui, 林曉輝 January 2003 (has links)
published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

New beamforming and DOA estimation techniques in wireless communications

Wang, Nanyan. 10 April 2008 (has links)
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.

The use of point-to-point lasers for navy ships

Bonk, Scott S. 06 1900 (has links)
Approved for public release; distribution is unlimited / Currently the Navy uses microwave technology to wirelessly connect ships at sea. These systems provide approximately a 1.5Mb/s transfer rate and have some significant drawbacks. Microwave antennas provide a very large electromagnetic signature, require a large power source, and require a lot of support equipment and personnel to maintain connections. Laser technology can offer connection speeds 50 times greater than microwave, have no electromagnetic signature, use only a fraction of the space and power requirements, and require little to no personnel maintenance. Lasers offer many advantages to its microwave counterpart but it may also have some drawbacks. This paper addresses the effects inclement weather will have on range and bandwidth. Weather ranging from fog to heavy rain also is analyzed in relation to the current system. Aside from communications between ships, lasers offer other untouched tactical benefits including - enhanced communications between ships and remote controlled drones. Unmanned vehicles could provide full motion video, telemetry, atmospheric conditions, and provide an uplink for smaller water or land based terminals to the ship. / Ensign, United States Navy

Pricing communication networks: optimality and Incentives. / CUHK electronic theses & dissertations collection

January 2012 (has links)
網絡定價是一個基于對網絡技術和微觀經濟學深刻理解而產生和發展的交叉學科。其目標在於通過合理分配稀缺的網絡資源以滿足不同用戶的服務質量,同時又兼顧考慮對網絡中各個不同實體的相應激勵,以而實現令人滿意的網絡性能。適宜的定價設計在通訊網絡的運營和管理中都是必不可缺的。在本論文中,我們將網絡定價分為四類:面向優化的靜態定價、面向優化的動態定價、利潤驅動的靜態定價,和利潤驅動的動態定價。第一類定價問題已經在文獻中深入討論,本論文將集中討論後三類定價問題。對于每一類定價問題,我們將通過一個網絡定價設計實例來闡明定價設計中的關鍵挑戰與深刻見解。 / 首先,我們研究了利潤驅動的靜態定價。我們考慮了一個壟斷型的網絡運營商的利潤最大化問題,討論其如何設計激勵相容的價格,主人而使得有限的網絡資源在不同類型用戶間合理地分配。我們通過完全信息和非完全信息下的雙層斯塔伯格博博弈模型來建模刻畫運營商和用戶之間的相互作用。在完全信息下,我們研究了三種定價策略:完全價格分化、部分價格分化,和無價格分化。我們分析了這些不同定價策略在系統性能和複雜度之間的權衡關係。在不完全信息下,我們展示了設計價格分化策略的可能性,並且給出這種激勵相容的定份策略能使運營商獲得完全信息下價格分化定價策略所獲得之相同收益的充分必要條件。 / 接著,我們研究了利潤驅動的動態定價。我們考慮了一個認知網絡虛擬移動網絡運營商的資源分配勻利潤最大化的一般問題。認知網絡的動態性包括動態的用戶需求、不穩定的檢測頻譜資源、動態的頻譜租用價格,以及時變的無線信道條件。另外,為使網絡模型更接近于現實,我們還考慮了多用戶差異性和有缺陷的頻譜檢測技術。我們設計和展了一套低複雜度的在線控制策略,能夠在不知動態網絡參數的統計特性的情況下,確定定價和資源分配。我們證明這套動態定價的算法在適當權衡網絡延時的條件下,可以無限趨近最大利潤。 / 最後,我們研究了面向優化的動態定價。我們考慮一個節點容量受限的拓撲時變的多播網絡。通過運用網絡編碼,我們設計了一套動態定價策略可以分佈式地實現無限趨近最優的網絡性能。另外,我們證明這套算法是激勵相容的. 即無論節點在網絡中充當任何角色,該算法都可以保證該節點獲得非負的收益。這個結果表明,該算法可以給網絡節點提供有效的激勵,使之加入網絡、停留在網絡中,並且即使在沒有自身感興趣內容時,也願意充當其他節點的中繼,這一結果在多用戶的節點容量受限網絡(如P2P 網絡)的構建中有著重要的現實意義。 / 以上本論文推導之結果都展示了網絡定價在通訊網絡中的重要意義。尤其顯示了網絡定價是實現最優網絡性能,同時對各網絡實體提供激勵的有效工具。本論文不僅幫助我們更好地理解網絡定價問題,同時也給出網絡定價設計中的深刻見解。 / Network pricing is a cross-disciplinary research area, which requires deep understanding of both networking technology and microeconomics. The goal of network pricing is to achieve satisfied network performances by allocating the scarce resource to satisfy different users’ qualities of services while keeping in mind the incentives of different network entities. Proper design of pricing schemes is indispensable to the operation and management of communication networks. In this thesis we divide network pricing into four categories: static optimization-oriented pricing, dynamic optimization-oriented pricing, static profit-driven pricing, and dynamic profit-driven pricing. The first one is well studied in the literature, and our focus will be on the latter three categories. For each category, we illustrate the key design challenges and insights through a concrete networking example. / First, we investigate the issue of static profit-driven pricing. We consider a revenue maximization problem for a monopolist service provider, and discuss how to set incentive-compatible prices to induce proper allocation of limited resources among different types of users. We capture the interaction between the service provider and users through a two-stage Stackelberg game with both complete and incomplete information. With complete information, we study three pricing schemes: complete price differentiation, partial price differentiation, and no price differentiation. We characterize the trade-offs between the performance and complexity of different schemes. With incomplete information, we show that it is still possible to realize price differentiation, and provide the sufficient and necessary condition under which an incentive compatible price differentiation scheme can achieve the same revenue as the best scheme with complete information. / Then we investigate the issue of dynamic profit-driven pricing. We consider a general resource allocation and profit maximization problem for a cognitive virtual mobile network operator. Dynamics of the cognitive radio network include dynamic user demands, unstable sensing spectrum resources, dynamic spectrum prices, and time-varying channel conditions. In addition, we also consider multiuser diversity and imperfect sensing technique so that the network model is more realistic. We develop a low-complexity on-line control policy that determines pricing and resource scheduling without knowing the statistics of dynamic network parameters. We show that the proposed algorithm with dynamic pricing can achieve arbitrarily close to the optimal profit with a proper trade-off with the queuing delay. / We later investigate the issue of dynamic optimization-oriented pricing. We consider a node-capacitated multicast network with time-varying topology. By utilizing network coding, we design a dynamic pricing scheme that can achieve arbitrarily close to maximum network utility in a distributed fashion, while maintaining network stability. Moreover, we show that this algorithm is incentivecompatible, i.e., no matter what role a node plays in the network, the algorithm guarantees that the node has a non-negative profit. This result has practical importance for constructions for node-capacitated networks with multiple individual users (e.g., P2P networks), since it provides the proper incentives for individual nodes to join, stay, and contribute as relays in the network even if they have no interested contents. / The results developed in this thesis highlight the importance of pricing in communication networks. Specifically, our results show that pricing can be used as an effective tool to achieve optimal network performances while providing proper incentives for all network entities. This not only helps us better understand network pricing, but also gives us insights on the design of network pricing schemes. / 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, Shuqin. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 155-168). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese. / Abstract --- p.i / Acknowledgement --- p.vi / Contents --- p.viii / List of Figures --- p.xii / List of Tables --- p.xv / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Pricing Schemes in Communication Networks --- p.3 / Chapter 1.2 --- Two Main Algorithm Design Techniques --- p.5 / Chapter 1.2.1 --- Network Utility Maximization --- p.5 / Chapter 1.2.2 --- Lyapunov Stochastic Optimization --- p.7 / Chapter 1.3 --- Thesis Outline --- p.10 / Chapter 2 --- Price Differentiation for Communication Networks --- p.13 / Chapter 2.1 --- Usage-based Pricing Schemes --- p.14 / Chapter 2.2 --- System Model --- p.17 / Chapter 2.3 --- Complete Price Differentiation under complete information --- p.20 / Chapter 2.3.1 --- User’s Surplus Maximization Problem in Stage 2 --- p.20 / Chapter 2.3.2 --- Service Provider’s Pricing and Admission Control Problem in Stage 1 --- p.20 / Chapter 2.3.3 --- Properties --- p.25 / Chapter 2.4 --- Single Pricing Scheme --- p.26 / Chapter 2.4.1 --- Problem Formulation and Solution --- p.27 / Chapter 2.4.2 --- Properties --- p.28 / Chapter 2.5 --- Partial Price Differentiation under Complete Information --- p.32 / Chapter 2.5.1 --- Three-level Decomposition --- p.33 / Chapter 2.5.2 --- Solving Level-2 and Level-3 --- p.36 / Chapter 2.5.3 --- Solving Level-1 --- p.39 / Chapter 2.6 --- Price Differentiation under Incomplete Information --- p.43 / Chapter 2.6.1 --- Extensions to Partial Price Differentiation under Incomplete Information --- p.48 / Chapter 2.7 --- Connections with the Classical Price Differentiation Taxonomy --- p.49 / Chapter 2.8 --- Numerical Results --- p.50 / Chapter 2.8.1 --- When is price differentiation most beneficial? --- p.50 / Chapter 2.8.2 --- What is the best tradeoff of Partial Price Differentiation? --- p.56 / Chapter 2.9 --- Summary --- p.58 / Chapter 2.10 --- Appendix of Chapter 2 --- p.59 / Chapter 2.10.1 --- Complete Price Differentiation under complete information with General Utility Functions --- p.59 / Chapter 2.10.2 --- Proof of Proposition 2.1 --- p.64 / Chapter 2.10.3 --- Proof of Lemma 2.2 --- p.65 / Chapter 2.10.4 --- Proof of Theorem 2.4 --- p.66 / Chapter 2.10.5 --- Proof of Theorem 2.6 --- p.72 / Chapter 3 --- Profit Maximization of Cognitive Mobile Virtual Network Operator in A DynamicWireless Network --- p.73 / Chapter 3.1 --- Dynamic Spectrum Access --- p.74 / Chapter 3.2 --- Related Work --- p.77 / Chapter 3.3 --- System Model --- p.79 / Chapter 3.3.1 --- Imperfect Spectrum Sensing --- p.81 / Chapter 3.3.2 --- Collision Constraint --- p.82 / Chapter 3.3.3 --- Spectrum Leasing with Dynamic Market Price --- p.82 / Chapter 3.3.4 --- Power Allocation --- p.83 / Chapter 3.3.5 --- Demand Model --- p.84 / Chapter 3.3.6 --- Queuing dynamics --- p.86 / Chapter 3.4 --- Problem Formulation --- p.87 / Chapter 3.5 --- Profit Maximization Control (PMC) Policy --- p.89 / Chapter 3.5.1 --- Lyapunov stochastic optimization --- p.89 / Chapter 3.5.2 --- Profit Maximization Control (PMC) policy --- p.93 / Chapter 3.5.3 --- Algorithms for Cost Minimization Problem --- p.96 / Chapter 3.5.4 --- Performance of the PMC Policy --- p.101 / Chapter 3.5.5 --- Extension: More General Model of Primary Users’ Activities --- p.102 / Chapter 3.6 --- Heterogeneous Users --- p.104 / Chapter 3.6.1 --- Multi-queue Profit Maximization Control (M-PMC) Policy --- p.106 / Chapter 3.6.2 --- Performance of the M-PMC Policy --- p.111 / Chapter 3.7 --- Simulation --- p.112 / Chapter 3.8 --- Summary --- p.116 / Chapter 3.9 --- Appendix of Chapter 3 --- p.118 / Chapter 3.9.1 --- (Waterfilling) Power Allocation Algorithm --- p.118 / Chapter 3.9.2 --- Threshold Searching Algorithm --- p.118 / Chapter 3.9.3 --- Proof for Theorem 3.2 (a) --- p.119 / Chapter 3.9.4 --- Proof for Theorem 3.2 (b) --- p.121 / Chapter 3.9.5 --- Impact of Queueing on Revenue Maximization --- p.123 / Chapter 4 --- Distributed Resource Allocation for Node-Capacitated Networks with Network Coding --- p.126 / Chapter 4.1 --- Node-Capacitated Networks --- p.126 / Chapter 4.2 --- Network Model --- p.132 / Chapter 4.2.1 --- Time-varying network topology and node upload capacities --- p.132 / Chapter 4.2.2 --- Multicast with intra-session network coding --- p.133 / Chapter 4.3 --- Stochastic Network Utility Maximization Problem --- p.135 / Chapter 4.4 --- Low Complexity Distributed Algorithm --- p.138 / Chapter 4.5 --- Performance Analysis --- p.141 / Chapter 4.5.1 --- Network Stability --- p.141 / Chapter 4.5.2 --- Network Utility Maximization --- p.143 / Chapter 4.5.3 --- The Incentives Issue --- p.146 / Chapter 4.6 --- Summary --- p.150 / Chapter 5 --- Conclusion --- p.151 / Chapter 5.1 --- Extensions on Static Profit-driven Pricing --- p.152 / Chapter 5.2 --- Extensions on Dynamic Profit-driven Pricing --- p.153 / Chapter 5.3 --- Extensions on Dynamic Optimization-oriented Pricing --- p.153 / Bibliography --- p.155

Modeling and characterization of multipath fading channels in cellular mobile communication systems

Khan, Noor Muhammad, Electrical Engineering & Telecommunications, Faculty of Engineering, UNSW January 2006 (has links)
Due to the enormous capacity and performance gains associated with the use of antenna arrays in wireless multi-input multi-output (MIMO) communication links, it is inevitable that these technologies will become an integral part of future systems. In order to assess the potential of such beam-oriented technologies, direct representation of the dispersion of multipath fading channel in angular and temporal domains is required. This representation can only be achieved with the use of spatial channel models. This thesis thus focuses on the issue of spatial channel modeling for cellular systems and on its use in the characteri- zation of multipath fading channels. The results of this thesis are presented mainly in five parts: a) modeling of scattering mechanisms, b) derivation of the closed-form expressions for the spatio-temporal characteristics, c) generalization of the quantitative measure of angular spread, d) investigation of the effect of mobile motion on the spatio-temporal characteris- tics, and e) characterization of fast fading channel and its use in the signature sequence adaptation for direct sequence code division multiple access (DS-CDMA) system. The thesis begins with an overview of the fundamentals of spatial channel modeling with regards to the specifics of cellular environments. Previous modeling approaches are dis- cussed intensively and a generalized spatial channel model, the 'Eccentro-Scattering Model' is proposed. Using this model, closed-form mathematical expressions for the distributions of angle and time of multipath arrival are derived. These theoretical results for the picocell, microcell and macrocell environments, when compared with previous models and available measurements, are found to be realistic and generic. In macrocell environment, the model incorporates the effect of distant scattering structures in addition to the local ones. Since the angular spread is a key factor of the second order statistics of fading processes in wireless communications, the thesis proposes a novel generalized method of quantifying the angular spread of the multipath power distribution. The proposed method provides almost all parameters about the angular spread, which can be further used for calculating more accurate spatial correlations and other statistics of multipath fading channels. The degree of accuracy in such correlation calculations can lead to the computation of exact separation distances among array elements required for maximizing capacity in MIMO systems or diversity antennas. The proposed method is also helpful in finding the exact standard deviation of the truncated angular distributions and angular data acquired in measurement campaigns. This thesis also indicates the significance of the effects of angular distribution truncation on the angular spread. Due to the importance of angular spread in the fading statistics, it is proposed as the goodness-of-fit measure in measurement campaigns. In this regard, comparisons of some notable azimuthal models with the measurement results are shown. The effect of mobile motion on the spatial and temporal characteristics of the channel is also discussed. Three mobile motion scenarios are presented, which can be considered to be responsible for the variations of the spatio-temporal statistical parameters of the multipath signals. Two different cases are also identified, when the terrain and clutter of the mobile surroundings have an additional effect on the temporal spread of the channel during mobile motion. The effect of increasing mobile-base separation on the angular and temporal spreads is elaborated in detail. The proposed theoretical results in spatial characteristics can be extended to characterizing and tracking transient behavior of Doppler spread in time-varying fast fading channels; likewise the proposed theoretical results in temporal characteristics can be utilized in designing efficient equalizers for combating inter-symbol interference (ISI) in time-varying frequency-selective fading channels. In the last part of the thesis, a linear state-space model is developed for signature sequence adaptation over time-varying fast fading channels in DS-CDMA systems. A decision directed adaptive algorithm, based on the proposed state-space model and Kalman filter, is presented. The algorithm outperforms the gradient-based algorithms in tracking the received distorted signature sequence over time-varying fast fading channels. Simulation results are presented which show that the performance of a linear adaptive receiver can be improved significantly with signature tracking on high Doppler spreads in DS-CDMA systems.

An investigation of the impact of routing protocols on MANETs using simulation modelling a dissertation submitted to Auckland University of Technology in partial fufilment of the requirements for the degree of Master of Computer and Information Sciences, 2008 /

Lol, Wilford Gibson. January 2008 (has links)
Thesis (MCIS - Computer and Information Sciences) -- AUT University, 2008. / Includes bibliographical references. Also held in print ( xi, 105 leaves : ill. ; 30 cm.) in the Archive at the City Campus (T 621.382 LOL)

Downlink beamforming for mobile communications

Arredondo, Alberto. January 2001 (has links)
Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI/Dissertation Abstracts International.

Multiresolution joint source and channel coding for wireless communications /

Wang, Xufang. January 2001 (has links)
Thesis (M. Phil.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 83-90).

Bandwidth allocation and call admission control in multi-services mobile wireless cellular networks /

Li, Bin. January 2003 (has links)
Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references (leaves 139-144). Also available in electronic version. Access restricted to campus users.

Downlink beamforming for mobile communications

Arredondo, Alberto 15 March 2011 (has links)
Not available / text

Page generated in 0.1817 seconds