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Title: Smart content caching for device-to-device data dissemination
Creator: Wang, Rui (Graduate of Michigan State University)
Date: 2020
Collection: Electronic Theses & Dissertations
Description: Wide popularity of wireless devices and their data-enabled applications have created an evolving marketplace for digital content ecosystems. A common operation in those ecosystems is to disseminate content in a cost-optimal manner. With the conventional download model, a user downloads content directly from a Content Provider's (CP) server via a Communication Service Provider's (CSP) network. Downloading content through CSP's network involves a cost, which must be paid either by End Consumers...
Show moreWide popularity of wireless devices and their data-enabled applications have created an evolving marketplace for digital content ecosystems. A common operation in those ecosystems is to disseminate content in a cost-optimal manner. With the conventional download model, a user downloads content directly from a Content Provider's (CP) server via a Communication Service Provider's (CSP) network. Downloading content through CSP's network involves a cost, which must be paid either by End Consumers (EC) or the CP. The main objective of the thesis is to provide caching mechanisms that minimizes the overall provisioning cost in different network topologies. This is implemented by caching right objects in data-enabled mobile devices such as smartphones, smart pads, vehicles and novel edge devices. In this thesis, several number of existing caching strategies are studied. Then, an incentive based cooperative content caching framework is developed for both fully-connected Social Wireless Networks (SWNETs) and mobile wireless networks in which content demands are hierarchically heterogeneous. Furthermore, a D2D cooperative caching framework is proposed for streaming video with heterogeneous quality demands in SWNETs. This caching framework contains two main components: a value-based caching strategy in which the value of caching a streaming video segment is defined for given pricing and video sharing models, and an Adaptive Quality (AQ) provisioning algorithm that minimizes the overall video content provisioning cost within an SWNET. Additionally, a vehicular content caching mechanism is developed for disseminating navigational maps while minimizing cellular network bandwidth usage. The key concept is to collaboratively cache the dynamic components of navigational maps in roadside units (RSUs) and vehicles such that the majority of dissemination can be accomplished using V2V and V2I communication links. Moreover, a novel caching mechanism is proposed which is based on Connectionless Edge Cache Servers in vehicular networks. The goal is to intelligently cache content within the vehicles and the edge servers so that majority of the vehicle-requested content can be obtained from those caches, thus minimizing the amount of cellular network usage needed for fetching content from a central server. A notable feature of the cache servers in this work is that they do not have backhaul connectivity. This makes the connectionless servers to be relatively less expensive compared to the usual Roadside Service Units (RSUs), and potentially moveable in response to specific events that are expected to generate content in large volumes. Finally, a list of future work on this topic is compiled that includes: 1) developing machine learning models for predicting content demand and spatiotemporal localities of node movements, 2) developing mechanisms for edge cache server placement for performance optimization, and 3) analyzing the impacts of selfishness on the performance of caching.
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Title: Reliable 5G system design and networking
Creator: Liang, Yuan (Graduate of Michigan State University)
Date: 2019
Collection: Electronic Theses & Dissertations
Description: The upcoming fifth generation (5G) system is expected to support a variety of different devices and applications, such as ultra-reliable and low latency communications, Internet of Things (IoT) and mobile cloud computing. Reliable and effective communications lie in the core of the 5G system design. This dissertation is focused on the design and evaluation of robust 5G systems under both benign and malicious environments, with considerations on both the physical layer and higher layers. For...
Show moreThe upcoming fifth generation (5G) system is expected to support a variety of different devices and applications, such as ultra-reliable and low latency communications, Internet of Things (IoT) and mobile cloud computing. Reliable and effective communications lie in the core of the 5G system design. This dissertation is focused on the design and evaluation of robust 5G systems under both benign and malicious environments, with considerations on both the physical layer and higher layers. For the physical layer, we study secure and efficient 5G transceiver under hostile jamming. We propose a securely precoded OFDM (SP-OFDM) system for efficient and reliable transmission under disguised jamming, a serious threat to 5G, where the jammer intentionally confuses the receiver by mimicking the characteristics of the authorized signal, and causes complete communication failure. We bring off a dynamic constellation by introducing secure randomness between the legitimate transmitter and receiver, and hence break the symmetricity between the authorized signal and the disguised jamming. It is shown that due to the secure randomness shared between the authorized transmitter and receiver, SP-OFDM can achieve a positive channel capacity under disguised jamming. The robustness of the proposed SP-OFDM scheme under disguised jamming is demonstrated through both theoretic and numerical analyses. We further address the problem of finding the worst jamming distribution in terms of channel capacity for the SP-OFDM system. We consider a practical communication scenario, where the transmitting symbols are uniformly distributed over a discrete and finite alphabet, and the jamming interference is subject to an average power constraint, but may or may not have a peak power constraint. Using tools in functional analysis and complex analysis, first, we prove the existence and uniqueness of the worst jamming distribution. Second, by analyzing the Kuhn-Tucker conditions for the worst jamming, we prove that the worst jamming distribution is discrete in amplitude with a finite number of mass points. For the higher layers, we start with the modeling of 5G high-density heterogeneous networks. We investigate the effect of relay randomness on the end-to-end throughput in multi-hop wireless networks using stochastic geometry. We model the nodes as Poisson Point Processes and calculate the spatial average of the throughput over all potential geometrical patterns of the nodes. More specifically, for problem tractability, we first consider the simple nearest neighbor (NN) routing protocol, and analyze the end-to-end throughput so as to obtain a performance benchmark. Next, note that the ideal equal-distance routing is generally not realizable due to the randomness in relay distribution, we propose a quasi-equal-distance (QED) routing protocol. We derive the range for the optimal hop distance, and analyze the end-to-end throughput both with and without intra-route resource reuse. It is shown that the proposed QED routing protocol achieves a significant performance gain over NN routing. Finally, we consider the malicious link detection in multi-hop wireless sensor networks (WSNs), which is an important application of 5G multi-hop wireless networks. Existing work on malicious link detection generally requires that the detection process being performed at the intermediate nodes, leading to considerable overhead in system design, as well as unstable detection accuracy due to limited resources and the uncertainty in the loyalty of the intermediate nodes themselves. We propose an efficient and robust malicious link detection scheme by exploiting the statistics of packet delivery rates only at the base stations. More specifically, first, we present a secure packet transmission protocol to ensure that except the base stations, any intermediate nodes on the route cannot access the contents and routing paths of the packets. Second, we design a malicious link detection algorithm that can effectively detect the irregular dropout at every hop (or link) along the routing path with guaranteed false alarm rate and low miss detection rate.
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Title: Large-signal RF simulation and characterization of electronic devices using Fermi kinetics transport
Creator: Miller, Nicholas Charles
Date: 2017
Collection: Electronic Theses & Dissertations
Description: Design of radio frequency (RF) power amplifiers (PAs) for wireless communications requires small- and large-signal data collected from the underlying transistors, including scattering parameters (S-Parameters) and load-pull (LP), to determine optimal impedance targets. High speed devices operating with fundamental frequencies above 35 GHz present extreme challenges for measuring the harmonic signals resulting from nonlinear effects. Predictive physics based simulations in conjunction with...
Show moreDesign of radio frequency (RF) power amplifiers (PAs) for wireless communications requires small- and large-signal data collected from the underlying transistors, including scattering parameters (S-Parameters) and load-pull (LP), to determine optimal impedance targets. High speed devices operating with fundamental frequencies above 35 GHz present extreme challenges for measuring the harmonic signals resulting from nonlinear effects. Predictive physics based simulations in conjunction with compact modeling capabilities are promising alternatives to expensive and time-consuming measurements. To date, tools either exist in the electron transport domain or in the behavioral modeling domain and a key goal is to treat these problems simultaneously because they are strongly coupled at millimeter wave frequencies. Accurate physics based simulations of high speed and high power transistors require proper treatment of hot-electron, self-heating, and full-wave effects. The Boltzmann solver called Fermi kinetics transport (FKT) has been shown to capture all of these important physical effects. FKT can approach the accuracy of Monte Carlo methods while maintaining the computational efficiency of deterministic solvers. The latter trait allows simulation of large electronic devices such as the output stages of PAs. Previous work on FKT provided proof of concept results which demonstrated its versatility and accuracy as an electronic device simulation framework.The purpose and contribution of this thesis is the use of FKT as a predictive TCAD tool to generate RF data required for PA design. This work begins with a thorough investigation of the underlying physical equations and their numerical solution for electronic device simulations. Included in this investigation is an analysis of the full-wave discretization technique called Delaunay-Voronoi surface integration (DVSI), a derivation of the FKT device equations and their discretization in energy- and real-space, and a detailed account on the numerical solution of the fully coupled nonlinear system of equations. The detail provided in this work is meant to provide future device engineers and researchers a thorough understanding of the numerical framework for their application and simulation needs. The FKT device simulator is then applied to real device geometries to generate useful data for RF circuit designers. Extensions of the FKT method required for large-signal LP simulations are presented with representative applications. Additionally, compact behavioral models are extracted directly from FKT device simulations, enabling a computationally efficient means for simulated LP data generation. The resulting TCAD tool is a promising simulation capability for high power RF transistor design and characterization. It is anticipated that PA design for 5G applications will be using techniques like these in the near future.
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Title: Secure and efficient spectrum sharing and QoS analysis in OFDM-based heterogeneous wireless networks
Creator: Alahmadi, Ahmed S.
Date: 2016
Collection: Electronic Theses & Dissertations
Description: "The Internet of Things (IoT), which networks versatile devices for information exchange, remote sensing, monitoring and control, is finding promising applications in nearly every field. However, due to its high density and enormous spectrum requirement, the practical development of IoT technology seems to be not available until the release of the large millimeter wave (mmWave) band (30GHz-300GHz). Compared to existing lower band systems (such as 3G, 4G), mmWave band signals generally require...
Show more"The Internet of Things (IoT), which networks versatile devices for information exchange, remote sensing, monitoring and control, is finding promising applications in nearly every field. However, due to its high density and enormous spectrum requirement, the practical development of IoT technology seems to be not available until the release of the large millimeter wave (mmWave) band (30GHz-300GHz). Compared to existing lower band systems (such as 3G, 4G), mmWave band signals generally require line of sight (LOS) path and suffer from severe fading effects, leading to much smaller coverage area. For network design and management, this implies that: (i) MmWave band alone could not support the IoT networks, but has to be integrated with the existing lower band systems through secure and effective spectrum sharing, especially in the lower frequency bands; and (ii) The IoT networks will have very high density node distribution, which is a significant challenge in network design, especially with the scarce energy budget of IoT applications. Motivated by these observations, in this dissertation, we consider three problems: (1) How to achieve secure and effective spectrum sharing? (2) How to accommodate the energy limited IoT devices? (3) How to evaluate the Quality of Service (QoS) in the high density IoT networks? We aim to develop innovative techniques for the design, evaluation and management of future IoT networks under both benign and hostile environments. The main contributions of this dissertation are outlined as follows. First, we develop a secure and efficient spectrum sharing scheme in single-carrier wireless networks. Cognitive radio (CR) is a key enabling technology for spectrum sharing, where the unoccupied spectrum is identified for secondary users (SUs), without interfering with the primary user (PU). A serious security threat to the CR networks is referred to as primary user emulation attack (PUEA), in which a malicious user (MU) emulates the signal characteristics of the PU, thereby causing the SUs to erroneously identify the attacker as the PU. Here, we consider full-band PUEA detection and propose a reliable AES-assisted DTV scheme, where an AES-encrypted reference signal is generated at the DTV transmitter and used as the sync bits of the DTV data frames. For PU detection, we investigate the cross-correlation between the received sequence and reference sequence. The MU detection can be performed by investigating the auto-correlation of the received sequence. We further develop a secure and efficient spectrum sharing scheme in multi-carrier wireless networks. We consider sub-band malicious user detection and propose a secure AES-based DTV scheme, where the existing reference sequence used to generate the pilot symbols in the DVB-T2 frames is encrypted using the AES algorithm. The resulted sequence is exploited for accurate detection of the authorized PU and the MU. Second, we develop an energy efficient transmission scheme in CR networks using energy harvesting. We propose a transmitting scheme for the SUs such that each SU can perform information reception and energy harvesting simultaneously. We perform sum-rate optimization for the SUs under PUEA. It is observed that the sum-rate of the SU network can be improved significantly with the energy harvesting technique. Potentially, the proposed scheme can be applied directly to the energy-constrained IoT networks. Finally, we investigate QoS performance analysis methodologies, which can provide insightful feedbacks to IoT network design and planning. Taking the spatial randomness of the IoT network into consideration, we investigate coverage probability (CP) and blocking probability (BP) in relay-assisted OFDMA networks using stochastic geometry. More specifically, we model the inter-cell interference from the neighboring cells at each typical node, and derive the CP in the downlink transmissions. Based on their data rate requirements, we classify the incoming users into different classes, and calculate the BP using the multi-dimensional loss model."--Pages ii-iii.
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Title: Efficient and secure system design in wireless communications
Creator: Song, Tianlong
Date: 2016
Collection: Electronic Theses & Dissertations
Description: Efficient and secure information transmission lies in the core part of wireless system design and networking. Comparing with its wired counterpart, in wireless communications, the total available spectrum has to be shared by different services. Moreover, wireless transmission is more vulnerable to unauthorized detection, eavesdropping and hostile jamming due to the lack of a protective physical boundary.Today, the two most representative highly efficient communication systems are CDMA (used...
Show moreEfficient and secure information transmission lies in the core part of wireless system design and networking. Comparing with its wired counterpart, in wireless communications, the total available spectrum has to be shared by different services. Moreover, wireless transmission is more vulnerable to unauthorized detection, eavesdropping and hostile jamming due to the lack of a protective physical boundary.Today, the two most representative highly efficient communication systems are CDMA (used in 3G) and OFDM (used in 4G), and OFDM is regarded as the most efficient system. This dissertation will focus on two topics: (1) Explore more spectrally efficient system design based on the 4G OFDM scheme; (2) Investigate robust wireless system design and conduct capacity analysis under different jamming scenarios. The main results are outlined as follows.First, we develop two spectrally efficient OFDM-based multi-carrier transmission schemes: one with message-driven idle subcarriers (MC-MDIS), and the other with message-driven strengthened subcarriers (MC-MDSS). The basic idea in MC-MDIS is to carry part of the information, named carrier bits, through idle subcarrier selection while transmitting the ordinary bits regularly on all the other subcarriers. When the number of subcarriers is much larger than the adopted constellation size, higher spectral and power efficiency can be achieved comparing with OFDM. In MC-MDSS, the idle subcarriers are replaced by strengthened ones, which, unlike idle ones, can carry both carrier bits and ordinary bits. Therefore, MC-MDSS achieves even higher spectral efficiency than MC-MDIS.Second, we consider jamming-resistant OFDM system design under full-band disguised jamming, where the jamming symbols are taken from the same constellation as the information symbols over each subcarrier. It is shown that due to the symmetricity between the authorized signal and jamming, the BER of the traditional OFDM system is lower bounded by a modulation specific constant. We develop an optimal precoding scheme, which minimizes the BER of OFDM systems under full-band disguised jamming. It is shown that the most efficient way to combat full-band disguised jamming is to concentrate the total available power and distribute it uniformly over a particular number of subcarriers instead of the entire spectrum. The precoding scheme is further randomized to reinforce the system jamming resistance.Third, we consider jamming mitigation for CDMA systems under disguised jamming, where the jammer generates a fake signal using the same spreading code, constellation and pulse shaping filter as that of the authorized signal. Again, due to the symmetricity between the authorized signal and jamming, the receiver cannot really distinguish the authorized signal from jamming, leading to complete communication failure. In this research, instead of using conventional scrambling codes, we apply advanced encryption standard (AES) to generate the security-enhanced scrambling codes. Theoretical analysis shows that: the capacity of conventional CDMA systems without secure scrambling under disguised jamming is actually zero, while the capacity can be significantly increased by secure scrambling.Finally, we consider a game between a power-limited authorized user and a power-limited jammer, who operate independently over the same spectrum consisting of multiple bands. The strategic decision-making is modeled as a two-party zero-sum game, where the payoff function is the capacity that can be achieved by the authorized user in presence of the jammer. We first investigate the game under AWGN channels. It is found that: either for the authorized user to maximize its capacity, or for the jammer to minimize the capacity of the authorized user, the best strategy is to distribute the power uniformly over all the available spectrum. Then, we consider fading channels. We characterize the dynamic relationship between the optimal signal power allocation and the optimal jamming power allocation, and propose an efficient two-step water pouring algorithm to calculate them.
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Title: Flexible spectrum use in channel bonding wireless networks
Creator: Yang, Xi (Software engineer)
Date: 2014
Collection: Electronic Theses & Dissertations
Description: Channel bonding, which assembles multiple narrow channels into one logical channel, can speed up data transmission and achieve better bandwidth utilization in wireless networks. Since introduced in 802.11n, channel bonding has been extended continually to support wider channels, making low-lag high-speed wireless communication possible. However, different radio technologies have different requirements on channel width. Devices that use different channel widths coexist in a contention domain...
Show moreChannel bonding, which assembles multiple narrow channels into one logical channel, can speed up data transmission and achieve better bandwidth utilization in wireless networks. Since introduced in 802.11n, channel bonding has been extended continually to support wider channels, making low-lag high-speed wireless communication possible. However, different radio technologies have different requirements on channel width. Devices that use different channel widths coexist in a contention domain may cause inefficiency and unfairness issues. For example, narrowband devices are easier to obtain medium access opportunities because they do not need to wait for the entire wide band to be idle. Therefore, although wideband devices can provide higher transmission speed, they are at an unfavorable position in contentions with narrowband devices.To this end, we propose a flexible spectrum use channel bonding (FSUB) protocol in which a node is allowed to start a transmission whenever there are some idle narrow channels and gradually increases the channel width during transmission. Because a node dynamically adjusts the channel width in a communication, we use a convolution method to achieve fast spectrum agreement between the transmitter and the receiver. To address contentions between devices in a wide band of spectrum, we introduce a compound preamble to make the collisions detectable in the frequency domain and use a parallel bitwise arbitration mechanism to quickly determine the winner. We implement and evaluate the proposed protocol through both the GNU Radio/USRP platform and ns-2 simulations. The results show that the proposed protocol well addresses the inefficiency and unfairness issues caused by heterogeneous radio coexistence. Channel bonding devices usingFSUB have more medium access opportunities and can aggregate wider channels than using other channel bonding protocols in presence of narrowband interference. The FSUB enables a device to always benefit from channel bonding without concerns about narrowband interference level.
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Title: Measurement and modeling of large scale networks
Creator: Shafiq, Muhammad Zubair
Date: 2014
Collection: Electronic Theses & Dissertations
Description: The goal of this thesis is to identify measurement, modeling, and optimization opportunities for large scale networks -- with specific focus on cellular networks and online social networks. These networks are facing unprecedented operational challenges due to their very large scale.Cellular networks are experiencing an explosive increase in the volume of traffic for the last few years. This unprecedented increase in the volume of mobile traffic is attributed to the increase in the subscriber...
Show moreThe goal of this thesis is to identify measurement, modeling, and optimization opportunities for large scale networks -- with specific focus on cellular networks and online social networks. These networks are facing unprecedented operational challenges due to their very large scale.Cellular networks are experiencing an explosive increase in the volume of traffic for the last few years. This unprecedented increase in the volume of mobile traffic is attributed to the increase in the subscriber base, improving network connection speeds, and improving hardware and software capabilities of modern smartphones. In contrast to the traditional fixed IP networks, mobile network operators are faced with the constraint of limited radio frequency spectrum at their disposal. As the communication technologies evolve beyond 3G to Long Term Evolution (LTE), the competition for the limited radio frequency spectrum is becoming even more intense. Therefore, mobile network operators increasingly focus on optimizing different aspects of the network by customized design and management to improve key performance indicators (KPIs).Online social networks are increasing at a very rapid pace, while trying to provide more content-rich and interactive services to their users. For instance, Facebook currently has more than 1.2 billion monthly active users and offers news feed, graph search, groups, photo sharing, and messaging services. The information for such a large user base cannot be efficiently and securely managed by traditional database systems. Social network service providers are deploying novel large scale infrastructure to cope with these scaling challenges.In this thesis, I present novel approaches to tackle these challenges by revisiting the current practices for the design, deployment, and management of large scale network systems using a combination of theoretical and empirical methods. I take a data-driven approach in which the theoretical and empirical analyses are intertwined. First, I measure and analyze the trends in data and then model the identified trends using suitable parametric models. Finally, I rigorously evaluate the developed models and the resulting system design prototypes using extensive simulations, realistic testbed environments, or real-world deployment. This methodology is to used to address several problems related to cellular networks and online social networks.
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Title: Exploiting cross-technology interference for efficient network services in wireless systems
Creator: Zhou, Ruogu
Date: 2014
Collection: Electronic Theses & Dissertations
Description: In the last decade, we have witnessed the wide adoption of a variety of wireless technologies like WiFi, Cellular, Bluetooth, ZigBee, and Near-field Communication(NFC). However, the fast growth of wireless networks generates significant cross-technology interference, which leads to network performance degradation and potential security breach. In this dissertation, we propose two novel physical layer techniques to deal with the interference, and improve the performance and security of sensor...
Show moreIn the last decade, we have witnessed the wide adoption of a variety of wireless technologies like WiFi, Cellular, Bluetooth, ZigBee, and Near-field Communication(NFC). However, the fast growth of wireless networks generates significant cross-technology interference, which leads to network performance degradation and potential security breach. In this dissertation, we propose two novel physical layer techniques to deal with the interference, and improve the performance and security of sensor networks and mobile systems, respectively. First, we exploit the WiFi interference as a ``blessing" in the design of sensor networks and develop novel WiFi interference detection techniques for ZigBee sensors. Second, utilizing these techniques, we design three efficient network services: WiFi discovery which detects the existence of nearby WiFi networks using ZigBee sensors, WiFi performance monitoring which measures and tracks performance of WiFi networks using a ZigBee sensor network, and time synchronization which provides synchronized clocks for sensor networks based on WiFi signals. Third, we design a novel, noninvasive NFC security system called {\em nShield} to reduce the transmission power of NFC radios, which protects NFC against passive eavesdropping. nShield implements a novel adaptive RF attenuation scheme, in which the extra RF energy of NFC transmissions is determined and absorbed by nShield. At the same time, nShield scavenges the extra RF energy to sustain the perpetual operation. Together with the extremely lo-power design, it enables nShield to provide the host uninterrupted protection against malicious eavesdropping. The above systems are implemented and extensively evaluated on a testbed of sensor networks and smartphones.
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Title: Cooperative content caching for capacity and cost management in mobile ecosystems
Creator: Taghi Zadeh Mehrjardi, Mahmoud
Date: 2012
Collection: Electronic Theses & Dissertations
Description: The objective of this thesis is to develop an architectural framework of social community based cooperative caching for minimizing electronic content provisioning cost in Mobile Social Wireless Networks (MSWNET). MSWNETs are formed by wireless mobile devices sharing common interests in electronic content, and physically gathering in public settings such as University campuses, work places, malls, and airports. Cooperative caching in such MSWNETs are shown to be able to reduce content...
Show moreThe objective of this thesis is to develop an architectural framework of social community based cooperative caching for minimizing electronic content provisioning cost in Mobile Social Wireless Networks (MSWNET). MSWNETs are formed by wireless mobile devices sharing common interests in electronic content, and physically gathering in public settings such as University campuses, work places, malls, and airports. Cooperative caching in such MSWNETs are shown to be able to reduce content provisioning cost which heavily depends on service and pricing dependencies among various stakeholders including content providers, network service providers, and end consumers. This thesis develops practical network, service, and economic pricing models which are then used for creating an optimal cooperative caching strategy based on social community abstraction in wireless networks. The developed framework includes optimal caching algorithms, analytical models, simulation, and prototype experiments for evaluating performance of the proposed strategy. The main contributions are: 1) formulation of economic cost-reward flow models among the MSWNET stakeholders, 2) developing optimal distributed cooperative caching algorithms, 3) characterizing the impacts of network, user and object dynamics, 4) investigating the impacts of user non-cooperation, and finally 5) developing a prototype Social Wireless Network for evaluating the impacts of cooperative caching in a Mobile Social Wireless Networks.
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Title: Coding over resource-constrained wireless networks
Creator: Halloush, Rami D.
Date: 2012
Collection: Electronic Theses & Dissertations
Description: In practice, wireless networks operate under multiple, mostly severe, constraints (bandwidth, energy resources, etc). Consequently, efficient techniques have to be employed in communicating data with sufficiently high data rates (depending on the application) while complying with the imposed constraints. Distributed Video Coding (DVC) and Network Coding (NC) are amongst the most dominant techniques employed in constrained data networks. In this dissertation, we address these two techniques...
Show moreIn practice, wireless networks operate under multiple, mostly severe, constraints (bandwidth, energy resources, etc). Consequently, efficient techniques have to be employed in communicating data with sufficiently high data rates (depending on the application) while complying with the imposed constraints. Distributed Video Coding (DVC) and Network Coding (NC) are amongst the most dominant techniques employed in constrained data networks. In this dissertation, we address these two techniques with the objective of realizing practical and efficient data networking solutions that fit in resource constrained wireless networks. In one part of the dissertation we address DVC over Visual Sensor Networks (VSNs) from a practical point of view, i.e., unlike a large body of research work related to this topic where the focus is on theoretical analysis and simulation, we study the practical aspects that arise when deploying DVC over real visual sensors. To that end, we develop a Resource-constrained DVC (RDVC) codec, deploy it over some of the widely used visual sensors, and conduct precise energy measurements that are used throughout our study.One RDVC-related challenge that we address in this dissertation is source rate estimation, i.e., trying to efficiently identify the source rate to be used in encoding a frame. This question is crucial since sending more bits than necessary will lead to inefficiency in compression while sending fewer bits will lead to failure in decoding. We propose a practical solution that completely eliminates the need for the costly feedback messages.Another challenge we address is the global choice between a DVC encoding option that involves intensive computations and leads to less transmission versus another choice with minimal computations that implies higher transmission-energy overhead. We carry out an operational energy-distortion analysis for a variety of options available to RDVC on visual sensors.Polar codes are the first codes proven to achieve capacity while having low encoding and decoding complexity. This motivates us to employ polar codes in our DVC platform. We compare the performance of polar codes with the more established and more investigated Low Density Parity Check Accumulate (LDPCA) codes in the context of DVC. Our results show that polar codes offer a clear advantage when coding smaller size image blocks. Consequently, polar codes could represent a viable solution for distributed sensor networks that capture low-resolution video signals. In the final part of the dissertation, we survey state-of-the-art NC solutions designed to achieve high throughput transmission in multicasting over wireless mesh networks while maintaining 100% packet delivery ratio. We propose HopCaster; a scheme that employs the cache-and-forward transport strategy. We show that HopCaster achieves significant performance gains compared to schemes that employ the end-to-end transport strategy.
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Title: Tackling the challenges of wireless interference and coexistence
Creator: Huang, Jun
Date: 2012
Collection: Electronic Theses & Dissertations
Description: Recent years have witnessed the phenomenal penetration rate of wireless networks in our daily lives, ranging from 802.11-based wireless LANs that provide ubiquitous Internet access, to 802.15.4-based wireless sensor networks that carry out various mission-critical tasks such as security surveillance and patient monitoring. However, despite the advances in the field of wireless networking, how to design high-performance wireless networks remains an open problem because of the fundamental...
Show moreRecent years have witnessed the phenomenal penetration rate of wireless networks in our daily lives, ranging from 802.11-based wireless LANs that provide ubiquitous Internet access, to 802.15.4-based wireless sensor networks that carry out various mission-critical tasks such as security surveillance and patient monitoring. However, despite the advances in the field of wireless networking, how to design high-performance wireless networks remains an open problem because of the fundamental challenges of wireless interference and coexistence.Interference is the fundamental factor that limits the link concurrency of wireless networks. Due to the broadcast nature of wireless channel, concurrent transmissions on the same frequency interfere with each other over the air, resulting in lower throughput and higher delivery delay. Handling interference in wireless networks is difficult because of the hidden terminal problem and the exposed terminal problem. Although the former is well studied in existing literature, the later is not, especially in networks where multiple bit rates are available.Another challenge is that interference significantly hinders the coexistence of different wireless technologies. In particular, recent studies show that wireless coexistence is becoming a growing issue due to the unprecedented proliferation of wireless devices in the unlicensed 2.4GHz band. When devices of heterogeneous physical layer operating on the same frequency, interference is more difficult to resolve as devices cannot decode the signals of each other. Moreover, co-existing devices commonly transmit at different powers, which leads to unfair channel usage. The issue is particularly critical to lower power wireless devices. This thesis tackles the fundamental challenges of wireless interference and coexistence to the link layer design of wireless networks. In particular, we identify two problems in the design of existing link layer protocols, and advance the state-of-the-art by offering practical solutions: (1) the rate-adaptive exposed terminal problem where link concurrency cannot be fully exploited by conventional link layers because of they are oblivious to the bit rate diversity; and (2) the blind terminal problem where existing link layer protocols fail to work in co-existing environments due to the heterogeneous physical layer and power asymmetry of co-existing devices. We motivate this research by showing that existing link layer protocols are surprisingly ineffective in handling these problems. Our experiments pinpoint the fundamental reasons of such ineffectiveness and reveal their implications on the design of link layer protocols. We then develop practical solutions to tackle the identified problems. Extensive testbed-based experiments validate the design of proposed solutions, and demonstrate their significant performance gains over existing link layer protocols.
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Title: Mobility and communication in wireless robot and sensor networks
Creator: Pei, Yuanteng
Date: 2011
Collection: Electronic Theses & Dissertations
Description: Mobility is a primary goal of many wireless communication systems. In recent years, mobile multi-hop wireless networks, such as mobile wireless sensor networks and wireless robot networks, have attracted increased attention and have been extensively studied. However, most current research does not consider the interdependence of communication and mobility and much assume an obstacle-free environment in their problem modeling and solving process.In this dissertation, we discuss several...
Show moreMobility is a primary goal of many wireless communication systems. In recent years, mobile multi-hop wireless networks, such as mobile wireless sensor networks and wireless robot networks, have attracted increased attention and have been extensively studied. However, most current research does not consider the interdependence of communication and mobility and much assume an obstacle-free environment in their problem modeling and solving process.In this dissertation, we discuss several research topics relevant to the above two issues of communication and mobility in wireless robot and sensor networks. First, we present multi-robot real-time exploration, which calls for the joint consideration of mobility and communication: it requires video and audio streams of a newly explored area be transmitted to the base station in a timely fashion as robots explore the area. Simulations show that our mobility model has achieved both improved communication quality and enhanced exploration efficiency.Second, we further investigate the above problem with two critical and real-world network conditions: (1) heterogeneous transmission ranges and link capacities, and (2) the impact of interference. The conditions increase the model complexity but significantly influence the actual available bandwidth and the required node size in placement. We jointly consider the relay placement and routing with these two critical conditions.Third, we introduce an online relay deployment paradigm to support remote sensing and control when mobile nodes migrate farther from the base station in a cost-effective system of mobile robots, static sensors and relays. A novel multi-robot real-time search method called STAtic Relay aided Search (STARS) is presented to allow robots to search in a known environment. Its solution is based on our near-optimal solution to a new variation of the multi-traveling salesman problem: precedence constrained two traveling salesman (PC2TSP).Fourth, we propose a heterogenous multi-robot exploration strategy with online relay deployment for an unknown environment called Bandwidth aware Exploration with a Steiner Traveler (BEST). In BEST, a relay-deployment node (RDN) tracks the FNs movement and places relays when necessary to support the video/audio streams aggregation to the base station. This problem inherits characteristics of both the Steiner minimum tree and traveling salesman problems. Extensive simulations show that BEST further enhances the exploration efficiency.While the first four topics deal with communication and mobility issues in powerful but expensive robotic systems, the fifth topic focuses on a special type of low cost, limited capability mobile sensors called hopping sensors, whose unique method of movement makes them suitable for rugged terrains. We present (1) a distributed message forwarding model called Binary Splitting Message Forwarding (BSMF) and (2) a grid based movement model unique to these hopping sensors. Simulation shows that our scheme significantly reduces the communication overhead and achieves relatively constant total energy consumption with varying amount of obstructions.Finally, we discuss the future work directions of this research work. We believe that a heterogeneous mobile platform to support real-time stream transmission by mobile robots, static sensor and communication devices, have great potential in various civilian and military applications, where the communication quality of service is critically important, as well as the mobility efficiency.
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