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Noncoherent Detection of Misbehaving Relays in Space-Time Coded Cooperative NetworksWang, Zhao-Jie 24 August 2011 (has links)
Cooperative systems exploit spatial diversity to improve communication quality. But system performances could be severely degraded in the existance malicious relay nodes. In this thesis, we consider a two-relay decode-and-forward (DF) cooperative network. Relay nodes adopt Orthogonal Space Time Block Code (OSTBC) to achieve spatial diversity. Assume that relay nodes may misbehave with a certain probability. If a relay is malicious, it will garble transmission signals, resulting in severe damage to system performance. In the literature, detecting malicious relays requires perfect channel state information. However, misbehavior of the relay will first lead to inaccurate channel estimation. Therefore, we propose a novel detecting misbehavior scheme to deal with the dilemma. Since misbehavior of relays influences statistical properties of the estimated channel coefficients, destination can detect misbehaving by comparing the distribution of channel estimates. The most important of all is that we don¡¦t need channel state information to enhance detecting performance. Through simulation results, we verify proposed scheme can detect misbehavior effectively without channel state information. Compared with signal-to-noise ratio, the number of received tracing symbols has more significant impact on detecting misbehavior of the relay.
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On Channel Estimation in Time-Varying Cooperative Networks Using Kalman FilterHong, Rong-Ding 20 October 2011 (has links)
In this thesis, we study channel estimation in time-varying cooperative network. Since channels vary with time, we insert training blocks periodically to trace channel variation. In this work, we adopt Kalman filter to trace channel variation due to its low complexity. By storing previous channel estimate, Kalman filter simply requires to process next received vectors to update current channel estimate. We use all past observations to estimate current channel state to avoid wasting information. In content of cooperation, we directly estimate effective channel from source through relay to the destination. The reason is that, we separately estimate the source-relay and relay-destination links, relays need extra efforts to estimate the channel and feedback estimates to the destination. It will increase the computational loading on relays, and the feedback channel may suffer channel fading, resulting in more distortion of estimates. Therefore, the destination directly estimate effective channel, using Kalman filter to trace variation. Furthermore, we design pre-coding scheme on relays for forwarding training symbols in order to reduce channel estimation errors and obtain more accurate channel information. To detect data symbols, we need to channel state information over each data block as well. Therefore, estimates over previous training blocks are interpolated to estimate channel over data blocks based on LMMSE criterion. Since estimates over training blocks are obtained from Kalman filter, it consequently improves estimation quality of the channel over the data blocks. The main contributions of the thesis are optimal training design to reduce the estimation error, the estimation based on Kalman filter, and linearly combing the estimates to provide more accurate estimates of the channels over data blocks.
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The Interaction between Japanese Government and NPOs in the New Period:Legal Regulation and Institutional Changeskuo, Tzu-hsuan 15 February 2012 (has links)
After the 1990s, Japan has been deeply influenced by international trends as well as its own political and economic development. With the traditional Tenno system, Japan confronted the rapid rise and impact of the civilians' social consciousness. The change can be observed and traced back to the period after the Great Hanshin earthquake in 1995, when a volunteering civic engagement started automatically and later spread up the realization and implementation of the Non-Profit Organizations (NPO) Act.
Based on my observations regarding legal regulations and institutional changes , this dissertation constructs a society-centered theory to explore and to analyze the relationship between the Japanese government and NPOs during the new period. This dissertation also seeks to explain how civic social ideologies developed and promoted the NPO Act and the establishment of the new JICA. In order to be more precise on the topic, I examine the change and the development by dividing the progress into ¡§traditional period¡¨ and ¡§new period¡¨ with after the cold war in the 1990s. On reviewing the changes of patterns and features of the development, I study the new interactive modes between state and society.
The emphasis of this study is to show how Japan accelerated the NPO and ODA legal regulation and institutional changes. Furthermore, the study discusses how, the unique and new type of intermediate organizations, that support NPOs, developed after the execution of the NPO Act, and how those agencies provided local governments with NPOs cooperative partnership. In addition, this dissertation uses the platform of NPO Center of Chiba Prefecture as a case study, to analyze how to effectively combine members to spread the idea of ¡§NPO Prefecture,¡¨ and how to reorganize the system of new JICA in order to adopt outward environment and inward NPO participation. In other words, by demonstrating this new mode of cooperative partnership, the study expects to provide scholars with a reference of relative subjects and hopes to support the development of civil society in the developing countries.
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Power Allocation Based on Limited Feedback in DF Cooperative and Cognitive Radio NetworksLi, Jia-Chi 03 August 2012 (has links)
This thesis investigates cooperative communication under the framework of cognitive
radio network, which consists of primary and secondary users(PU & SU). The
cooperative and cognitive radio network (CCR) adopts overlay dynamic spectrum
access, That is, the SU simultaneously assists PU¡¦s transmission and transmits its own
message using spectrum shared by primary user. The secondary user adopts
decode-and-forward (DF) relaying to assist the primary user in transmitting message.
With secondary user¡¦s assistance, the cooperative system can be treat as an equivalent
multiple input single output (MISO) system to attain the spatial diversity of the primary
user. The virtual MISO system can reduce the outage probability and enhance the
transmission reliability. Under the requirement on primary user's transmission quality,
secondary user transmits both user¡¦s signals simultaneously, so that the secondary
acquires authority to access spectrum. Based on limited feedback regarding SNR of link
between primary transmitter and receiver, secondary user allocates transmission power
of primary signal and secondary signal to increase throughput and spectrum efficiency
of SU subject to satisfying PU¡¦s outage constraint.
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Robust Design of Precoder and Decoder for Relay-Assisted Decorrelating CDMA Systems with Imperfect CSITsai, Yong-Chun 25 August 2012 (has links)
In this paper, we explore a cooperative code-division-multiple-access(CDMA) network. Users cooperate by forwarding each other¡¦s messages toward the destination. For simplicity, we assume that signal reception at the destination is well-synchronized. Due to practical design issues of CDMA systems, spreading waveforms allocated to users are not perfectly orthogonal in general. This results in multiple-access interference(MAI) at relays and destination. In CDMA uplink networks one common approach is to adopt decorrelating multi-user detection, but it will lead to noise amplification[16,17]. Therefore, we employ relay-assisted decorrelating multiuser detector(RAD-MUD) to mitigate MAI[1] by performing half of decorrelation at the relay and destination respectively. Based on the availability of CSI at relays, we can further adopt cooperative strategies to improve performance, e.g., transmit beamforming and selective relaying. The destination side will use minimum mean-square error(MMSE) detector to demodulate source symbols. In the existing literatures, channel state information(CSI) is assumed to be perfectly known at relay and destination. Actually, CSI is obtained from channel estimation, which usually contains estimation errors. In order to alleviate effects of channel estimation, one goal of this thesis is to design a robust system. Using estimated CSI and statistical property channel estimation errors, we design robust precoder and detector for the relay and destination. It shows that, even with distortion on channel estimations, the system still achieve excellent transmission efficiency. From the simulation results, it shows that the robust design is better than the system without consider channel estimation errors. Finally, we can see that the stable robust design can effectively mitigate effects of imperfect CSI.
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Lifetime Maximization of Secondary Cooperative Systems in Underlay Cognitive Radio NetworksYu, Hao-Ting 30 August 2012 (has links)
In this thesis, we consider cognitive radio networks (CRN) combined with cooperative transmission, and investigate relay selection and power allocation strategies to maximize network lifetime (NLT). Cognitive radio network enhances spectrum efficiency resource by exploiting capabilities of cognition, learning and coordination against insufficient spectrum resource. In underlay cognitive radio network, however, transmitted energy of secondary user is constrained by interference level observed at primary user (PU). Though cooperation among secondary users (SU), multiple relays from virtual antenna array to improve transmission rate and reliability by exploiting spatial diversity. Most existing works assume that cooperative secondary users are plugged and with infinite energy device. In this thesis, we consider secondary cooperative systems where relays are battery-powered and with finite energy. We will investigate relay-selection schemes to reduce energy consumption of secondary relays and prolong network lifetime under the premises that secondary user¡¦s transmission rate is guaranteed and interference constraint of primary user is met. Our major difference between this work and previous works is the definition of network lifetime, which is defined by the maximum duration that the probability of secondary user¡¦s achievable rate below the guaranteed value, i.e. outage probability, is lower than a predetermined threshold. We proposed four relay-selection methods which take channel state information (CSI) and residual energy information (REI) into considerations to prolong network lifetime. Since the selection metrics of the proposed strategies requires CSI and REI of each individual relay, so the relay-selection can be accomplished in distributed manner through opportunistic sensing. No additional overhead is demanded for information exchange.
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Decentralized, Cooperative Control of Multivehicle Systems: Design and Stability AnalysisWeitz, Lesley A. 16 January 2010 (has links)
This dissertation addresses the design and stability analysis of decentralized, cooperative
control laws for multivehicle systems. Advances in communication, navigation,
and surveillance systems have enabled greater autonomy in multivehicle systems, and
there is a shift toward decentralized, cooperative systems for computational efficiency
and robustness. In a decentralized control scheme, control inputs are determined
onboard each vehicle; therefore, decentralized controllers are more efficient for large
numbers of vehicles, and the system is more robust to communication failures and
reconfiguration.
The design of decentralized, cooperative control laws is explored for a nonlinear
vehicle model that can be represented in a double-integrator form. Cooperative controllers
are functions of spacing errors with respect to other vehicles in the system,
where the communication structure defines the information that is available to each
vehicle. Control inputs are selected to achieve internal stability, or zero steady-state
spacing errors, between vehicles in the system.
Closed-loop equations of motion for the cooperative system can be written in a
structural form, where damping and stiffness matrices contain control gains acting on
the velocity and positions of the vehicles, respectively. The form of the stiffness matrix
is determined by the communication structure, where different communication structures yield different control forms. Communication structures are compared using
two structural analysis tools: modal cost and frequency-response functions, which
evaluate the response of the multivehicle systems to disturbances. The frequency-response
information is shown to reveal the string stability of different cooperative
control forms.
The effects of time delays in the feedback states of the cooperative control laws
on system stability are also investigated. Closed-loop equations of motion are modeled
as delay differential equations, and two stability notions are presented: delay-independent
and delay-dependent stability.
Lastly, two additional cooperative control forms are investigated. The first control
form spaces vehicles along an arbitrary path, where distances between vehicles
are constant for a given spacing parameter. This control form shows advantages over
spacing vehicles using control laws designed in an inertial frame. The second control
form employs a time-based spacing scheme, which spaces vehicles at constant-time
intervals at a desired endpoint. The stability of these control forms is presented.
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Pursuit and evasion games: semi-direct and cooperative control methodsParish III, Allen S. 15 May 2009 (has links)
Pursuit and evasion games have garnered much research attention since the
class of problems was first posed over a half century ago. With wide applicability to
both civilian and military problems, the study of pursuit and evasion games showed
much early promise. Early work generally focused on analytical solutions to games
involving a single pursuer and a single evader. These solutions generally assumed simple system dynamics to facilitate convergence to a solution. More recently, numerical
techniques have been utilized to solve more difficult problems. While many sophisticated numerical tools exist for standard optimization and optimal control problems,
developing a more complete set of numerical tools for pursuit and evasion games is
still a developing topic of research.
This thesis extends the current body of numeric solution tools in two ways.
First, an existing approach that modifies sophisticated optimization tools to solve
two player pursuer and evasion games is extended to incorporate a class of state
inequality constraints. Several classical problems are solved to illustrate the e±cacy
of the new approach. Second, a new cooperation metric is introduced into the system
objective function for multi-player pursuit and evasion games. This new cooperation
metric encourages multiple pursuers to surround and then proceed to capture an
evader. Several examples are provided to demonstrate this new cooperation metric.
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Characteristics of cooperative spontaneous radiation with applications to atom microscopy and coherent XUV radiation generationChang, Juntao 15 May 2009 (has links)
Cooperative effect in the radiation process has been studied in for more than half a
century. It is important in the sense of both basic physics and applied science.
In this work, we study the dynamics of the cooperative spontaneous emission
from an ensemble of N atoms which is uniformly excited by absorbing a single photon.
We reveal that there are two different regimes in which the system exhibits
totally different behaviors. One of them is the superradiance type of behavior: the
system decays much quicker than single atom decay, with a decay rate proportional
to N(λ/R)2, where N is the atom numbers, R is the size of the atom cloud, and λ
is the wavelength. We call it Markovian regime because the sytem does not persist
memory effect. The other regime is called non-Markovian regime and the system oscillates
with effective Rabi oscillation frequency
while slowly decaying with a rate
proportional to the photon escaping rate. The effective Rabi oscillation is a new type
of dynamics which analogs well known Cavity QED behavior.
Particularly in the Markovian regime, we study the system dynamics as a manybody
eigenfunction and eigenvalue problem. For a dense cloud, we find analytical solutions for the eigenstates and corresponding eigenvalues, which can help to generally
describe the system dynamics for any initial conditions in this regime.
One of the applications is in atom microscopy. We propose a scheme to measure
the distance between two atoms/molecules beyond diffraction limit. It covers the
whole range from half the wavelength to sub-nanometers, utilizing both the atom
localization technique and the collective frequency shift effect due to the cooperative
effect in the radiation of the two atoms.
Another application that we propose is to generate Coherent XUV radiation using
Raman-type superradaince. We prove that intense short pulses of XUV radiation can
be produced by Raman type superradiance from an ensemble of atoms/ions driven
by visible or IR laser pulses.
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Cooperative Modeling and Design History Tracking Using Design Tracking MatrixKim, Jonghyun 2009 August 1900 (has links)
This thesis suggests a new framework for cooperative modeling which supports
concurrency design protocol with a design history tracking function. The proposed
framework allows designers to work together while eliminating design conflicts and
redundancies, and preventing infeasible designs. This framework provides methods to
track optimal design path and redundant design history in the overall design process.
This cooperative modeling architecture consists of a modeling server and voxel-based
multi-client design tool. Design change among server and multiple clients are executed
using the proposed concurrency design protocol. The design steps are tracked and
analyzed using Design Tracking Graph and Design Tracking Matrix (DTM), which
provide a design data exchange algorithm allowing seamless integration of design
modifications between participating designers. This framework can be used for effective
cooperative modeling, and helps identify and eliminate conflicts and minimize delay.
The proposed algorithm supports effective cooperative design functions. First, it
provides a method to obtain the optimal design path which can be stored in a design
library and utilized in the future design. Second, it helps capture modeling pattern which can be used for analyzing designer's performance. Finally, obtained redundancies can be
used to evaluate designer?s design efficiency.
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