Browsing by Subject "Wireless"
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Item A Packet Scheduling Mechanism for Wireless Peer-to-Peer Content Distribution(2013-11-26) Liu, YaoThis thesis studies the problem of content distribution in wireless peer-to-peer networks with selfish nodes. In this problem a group of wireless nodes need to exchange a set of files over a lossless broadcast channel. Each node aims to maximize its own download rate and minimize its upload rate. We propose a distributed protocol that provides incentives for selfish nodes to participate in the content exchange. Our protocol does not require any exchange of money and reputation and hence can be easily implemented without additional infrastructure. Then, we will analyze the performance of our protocol by focusing on the import\-ant case in which the system contains two files that need to be distributed. We derive a closed-form expression of Nash Equilibrium and characterize the corresponding system performance in discrete time. Furthermore, we propose a distributed mechanism where the strategy of each node is only based on the observed history of the system and not on the private information of other nodes. We also study the performance characteristics of the systems that employ network coding to facilitate data exchange. We show that, due to the free rider problem network coding does not necessary improve the performance of the system and, in some cases, may lead to worse system performance. We propose a novel approach to this problem based on random coding. The performance of the network coding algorithms is validated by performing extensive simulation study.Item Analyzing video compression for transporting over wireless fading channels(Texas A&M University, 2006-10-30) Kannan, KarthikWireless video communication is becoming increasingly popular these days with new applications such as TV on mobile and video phones. Commercial success of these applications requires superior video quality at the receiver. So it is imperative to analyze the effect of a wireless channel on a video transmission. The aim of this research is to analyze the video transmission over Rayleigh fading channels for various bit error rates (BER), signal to noise ratios (Eb/N0) and Doppler rates, and to suggest which source coding scheme is best at which BER, Eb/N0 and Doppler rates. Alternative schemes such as hybrid (digital/analog) schemes were considered and their performances were compared with pure digital communication. It is also shown that the combination of digital and analog video communication does not yield any better performance compared to pure digital video communication.Item Capacity of multi-antenna ad hoc networks via stochastic geometry(2012-12) Hunter, Andrew Marcus; Andrews, Jeffrey G.; de Veciana, Gustavo; Heath, Robert W.; Stone, Peter; Haenggi, MartinThis thesis takes as its objective quantifying, comparing, and optimizing multiple-antenna (MIMO) physical layer techniques in dense ad hoc wireless networks. A framework is developed from the spatial shot noise interference model for packet radio network analysis. The framework captures the behavior of a wide variety of signal and interference distributions, which permit inspection of a number of signal processing methods including representatives from most of the major MIMO techniques. Multi-antenna systems for point-to-point are becoming mature and being developed and deployed in many wireless communication systems due to their potential to combat fading, increase spectral efficiency, and overcome interference. The framework permits an algorithm or system designer to view the network from the perspective of a typical user, to optimize performance in the midst of a given environment, or to view the network as a whole, to determine behavior that maximizes network performance. In particular, it enables questions to be answered quantitatively, such as which MIMO techniques perform best in a given environment? Or what rate and power settings should be used across the available spatial modes? Or what is the maximum benefit of channel state information? Or what gain should an individual device, or the network as a whole expect to see given a particular physical layer strategy? The dissertation begins by developing the framework for a generic set of assumptions on network behavior and signal and interference distributions. It then presents a progression of applications to representative MIMO techniques. Broad and intuitive scaling laws are developed as well as detailed exact results for careful comparison. Capacity scaling with the number of antennas is given for systems employing beamforming, selection combining, space-time block coding, and spatial multiplexing. These applications are used as the basis for developing simple distributed algorithms for optimizing MIMO settings with QoS constraints and in heterogeneous networks. Lastly, the framework is expanded to permit comparison and optimization of MIMO performance under alternative medium access strategies. In general it is found that significant performance gains can be reaped with multi-antenna physical layers, provided the proper techniques are employed. It is also shown that the availability of multiple spatial channels impacts the inherent tradeoff between per-link throughput and spatial reuse.Item Comparative study of the end-to-end compliant TCP protocols for wireless networks(2005-12) Todorovic, Milan; Lopez-Benitez, Noe; Andersen, Per H.The inability of the traditional TCP protocols to recognize the non-congestion related packet loss and the efficiency ramifications that might have on the quality of the communication in the wireless and mixed networks must not be ignored. The appropriate modifications have to be made to compensate for this shortcoming. The recently proposed solutions, Freeze-TCP, TCP-Probing, TCP Westwood/Westwood+, TCP Veno, TCP-Jersey, and JTCP, all present a considerable improvement over the traditional TCP protocols that treat all packet loss as a sign of congestion. But, to make sure which of these solutions is the best choice and worthy of possibly being adopted as a future standard, we must compare these solutions to each other. Such comparison has not been done, but would offer a significant insight into the effectiveness of different mechanisms in these solutions. The underlying idea is to test the proposed protocols in various network layouts under different circumstances with differing external interferences in an attempt to most accurately simulate the real-life scenarios. The ultimate goal is to isolate the most efficient solution to the non-congestion packet loss problem of the TCP protocol in wireless networks. If no solution, however, yields itself an absolute winner, it is the secondary goal of this research to identify the most efficient mechanisms from these solutions and, if possible, propose a hybrid solution that would include all the advantages of the protocols presented. The information about the performance of these protocols was obtained as the results of the ns-2 simulations. However, only TCP Westwood, TCP-Jersey, TCP Veno, and JTCP were tested as they are the only ones implemented in the ns-2 simulator by their designers. Simulations were designed to test the protocols in non-congested environments, UDP congested environments and the environments where all of the protocols are competing for the bandwidth. The performance of the protocols was measured based on three benchmark parameters: throughput, average congestion window, and time to complete a file transfer. According to the simulation results, a small group of protocols appeared on top of the leader board in all simulations. TCP Westwood and JTCP outperformed their competition under the random packet loss in both burst and long flow testing, with the realization that the performance of TCP Westwood was much better in LAN than in WAN topologies. JTCP displayed remarkable performance in all environments under both random and disconnection packet loss but showed a significant drop in throughput when competing with other TCP flows. Under disconnection loss we saw two protocols dominating: TCP SACK and once again JTCP. TCP Westwood posted average results in disconnection loss simulations. Based on the nature of the tested environments we concluded that the dynamic bandwidth estimation algorithm, a force behind TCP Westwood's congestion modification, proved to be the most efficient mechanism in networks facing random packets loss. During disconnection loss, when multiple successive packets within the same window are lost, the SACK option surfaced as the most adept mechanism. The jitter ratio based mechanism for distinguishing between the congestion and non-congestion packet loss was what allowed JTCP to perform well in the tests. According to these findings, a hybrid was proposed, TCP Westwood-JSACK, a protocol that uses TCP Westwood's congestion window modification algorithm, JTCP's mechanism for identifying the cause of a packet loss, and TCP SACK's efficient method for recovering from heavy continuous packet loss.Item Comparative study of the end-to-end compliant TCP protocols for wireless networks(Texas Tech University, 2005-12) Todorovic, Milan; Lopez-Benitez, Noe; Andersen, Per H.The inability of the traditional TCP protocols to recognize the non-congestion related packet loss and the efficiency ramifications that might have on the quality of the communication in the wireless and mixed networks must not be ignored. The appropriate modifications have to be made to compensate for this shortcoming. The recently proposed solutions, Freeze-TCP, TCP-Probing, TCP Westwood/Westwood+, TCP Veno, TCP-Jersey, and JTCP, all present a considerable improvement over the traditional TCP protocols that treat all packet loss as a sign of congestion. But, to make sure which of these solutions is the best choice and worthy of possibly being adopted as a future standard, we must compare these solutions to each other. Such comparison has not been done, but would offer a significant insight into the effectiveness of different mechanisms in these solutions. The underlying idea is to test the proposed protocols in various network layouts under different circumstances with differing external interferences in an attempt to most accurately simulate the real-life scenarios. The ultimate goal is to isolate the most efficient solution to the non-congestion packet loss problem of the TCP protocol in wireless networks. If no solution, however, yields itself an absolute winner, it is the secondary goal of this research to identify the most efficient mechanisms from these solutions and, if possible, propose a hybrid solution that would include all the advantages of the protocols presented. The information about the performance of these protocols was obtained as the results of the ns-2 simulations. However, only TCP Westwood, TCP-Jersey, TCP Veno, and JTCP were tested as they are the only ones implemented in the ns-2 simulator by their designers. Simulations were designed to test the protocols in non-congested environments, UDP congested environments and the environments where all of the protocols are competing for the bandwidth. The performance of the protocols was measured based on three benchmark parameters: throughput, average congestion window, and time to complete a file transfer. According to the simulation results, a small group of protocols appeared on top of the leader board in all simulations. TCP Westwood and JTCP outperformed their competition under the random packet loss in both burst and long flow testing, with the realization that the performance of TCP Westwood was much better in LAN than in WAN topologies. JTCP displayed remarkable performance in all environments under both random and disconnection packet loss but showed a significant drop in throughput when competing with other TCP flows. Under disconnection loss we saw two protocols dominating: TCP SACK and once again JTCP. TCP Westwood posted average results in disconnection loss simulations. Based on the nature of the tested environments we concluded that the dynamic bandwidth estimation algorithm, a force behind TCP Westwood's congestion modification, proved to be the most efficient mechanism in networks facing random packets loss. During disconnection loss, when multiple successive packets within the same window are lost, the SACK option surfaced as the most adept mechanism. The jitter ratio based mechanism for distinguishing between the congestion and non-congestion packet loss was what allowed JTCP to perform well in the tests. According to these findings, a hybrid was proposed, TCP Westwood-JSACK, a protocol that uses TCP Westwood's congestion window modification algorithm, JTCP's mechanism for identifying the cause of a packet loss, and TCP SACK's efficient method for recovering from heavy continuous packet loss.Item Design, Simulation, and Analysis of Substation Automation Networks(2012-07-16) Kembanur Natarajan, ElangovanSociety depends on computer networks for communication. The networks were built to support and facilitate several important applications such as email, web browsing and instant messaging. Recently, there is a significant interest in leveraging modern local and wide area communication networks for improving reliability and performance in critical infrastructures. Emerging critical infrastructure applications, such as smart grid, require a certain degree of reliability and Quality of Service (QoS). Supporting these applications requires network protocols that enable delay sensitive packet delivery and packet prioritization. However, most of the traditional networks are designed to provide best effort service without any support for QoS. The protocols used in these networks do not support packet prioritization, delay requirements and reliability. In this thesis, we focus on the design and analysis of communication protocols for supporting smart grid applications. In particular, we focus on the Substation Automation Systems (SAS). Substations are nodes in the smart grid infrastructure that help the in transportation of power by connecting the transmission and distribution lines. The SAS applications are con figured to operate with minimal human intervention. The SAS monitors the line loads continuously. If the load values are too high and can lead to damage, the SAS declares those conditions as faults. On fault detection, the SAS must take care of the communication with the relay to open the circuit to prevent any damage. These messages are of high priority and require reliable, delay sensitive delivery. There is a threshold for the delay of these messages, and a slight increase in the delay above the threshold might cause severe damages. Along with such high priority messages, the SAS has a lot of background traffic as well. In spite of the background traffic, the substation network must take care of delivering the priority messages on time. Hence, the network plays a vital role in the operation of the substation. Networks designed for such applications should be analyzed carefully to make sure that the requirements are met properly. We analyzed and compared the performance of the SAS under di erent network topologies. By observing the characteristics of the existing architectures, we came up with new architectures that perform better. We have suggested several modi cations to existing solutions that allow significant improvement in the performance of the existing solutions.Item EtherLux, a low power wireless display(2009-12) Hocker, Andrew Edward; Aziz, Adnan; McDermott, MarkReal time information is essential in many businesses and as a method to inform employees and consumers, so that they can make informed decisions. In offices, warehouse and stores it can be advantageous to have tens to hundreds of smaller displays to deliver a variety of information. This paper details the design, implementation and testing of a wireless low power solar powered display system as a solution to deliver real time information. The system uses an Organic LCD to maintain an image for years on no power and uses very little power to update and refresh the display. The system uses off- the-shelf components to achieve multiple updates per day and, with the right lighting conditions, can perform up to one refresh per minute. The system is entirely powered by incandescent light, has a built in radio, and utilizes capacitors to store charge and deliver power, removing the need for rechargeable batteries. The wireless signal works at 2.4GHz and uses the low power 802.15.4 protocol to send and receive data at a range of 75 feet. It has no observable issue operating in environments with 2.4GHz wireless signals, such as 802.11g. The whole system can be built for under $75.00, and takes up an area of 6" x 8" including the photovoltaic cells.Item High performance RF and baseband building blocks for wireless receivers(Texas A&M University, 2007-09-17) Bahmani, FaramarzBecause of the unique architecture of wireless receivers, a designer must understand both the high frequency aspects as well as the low-frequency analog considerations for different building blocks of the receiver. The primary goal of this research work is to explore techniques for implementing high performance RF and baseband building blocks for wireless applications. Several novel techniques to improve the performance of analog building blocks are presented. An enhanced technique to couple two LC resonators is presented which does not degrade the loaded quality factor of the resonators which results in an increased dynamic range. A novel technique to automatically tune the quality factor of LC resonators is presented. The proposed scheme is stable and fast and allows programming both the quality factor and amplitude response of the LC filter. To keep the oscillation amplitude of LC VCOs constant and thus achieving a minimum phase noise and a reliable startup, a stable amplitude control loop is presented. The proposed scheme has been also used in a master-slave quality factor tuning of LC filters. An efficient and low-cost architecture for a 3.1GHz-10.6GHz ultra-wide band frequency synthesizer is presented. The proposed scheme is capable of generating 14A novel pseudo-differential transconductance amplifier is presented. The proposed scheme takes advantage of the second-order harmonic available at the output current of pseudo-differential structure to cancel the third-order harmonic distortion. A novel nonlinear function is proposed which inherently removes the third and the fifth order harmonics at its output signal. The proposed nonlinear block is used in a bandpass-based oscillator to generate a highly linear sinusoidal output. Finally, a linearized BiCMOS transconductance amplifier is presented. This transconductance is used to build a third-order linear phase low pass filter with a cut-off frequency of 264MHz for an ultra-wide band receiver. carrier frequencies.Item Interference alignment from theory to practice(2013-05) El Ayach, Omar; Heath, Robert W., Ph. D.Wireless systems in which multiple users simultaneously access the propagation medium suffer from co-channel interference. Untreated interference limits the total amount of data that can be communicated reliably across the wireless links. If interfering users allocate a portion of the system's resources for information exchange and coordination, the effect of interference can be mitigated. Interference alignment (IA) is an example of a cooperative signaling strategy that alleviates the problem of co-channel interference and promises large gains in spectral efficiency. To enable alignment in practical wireless systems, channel state information (CSI) must be shared both efficiently and accurately. In this dissertation, I develop low-overhead CSI feedback strategies that help networks realize the information-theoretic performance of IA and facilitate its adoption in practical systems. The developed strategies leverage the concepts of analog, digital, and differential feedback to provide IA networks with significantly more accurate and affordable CSI when compared to existing solutions. In my first contribution, I develop an analog feedback strategy to enable IA in multiple antenna systems; multiple antennas are one of IA's key enabling technologies and perhaps the most promising IA use case. In my second contribution, I leverage temporal correlation to improve CSI quantization in limited feedback single-antenna systems. The Grassmannian differential strategy developed provides several orders of magnitude in CSI compression and ensures almost-perfect IA performance in various fading scenarios. In my final contribution, I complete my practical treatment of IA by revisiting its performance when CSI acquisition overhead is explicitly accounted for. This last contribution settles the viability of IA, from a CSI acquisition perspective, and demonstrates the utility of the proposed feedback strategies in transitioning interference alignment from theory to practice.Item LDPC code-based bandwidth efficient coding schemes for wireless communications(2009-06-02) Sankar, HariThis dissertation deals with the design of bandwidth-efficient coding schemes with Low-Density Parity-Check (LDPC) for reliable wireless communications. Code design for wireless channels roughly falls into three categories: (1) when channel state information (CSI) is known only to the receiver (2) more practical case of partial CSI at the receiver when the channel has to be estimated (3) when CSI is known to the receiver as well as the transmitter. We consider coding schemes for all the above categories. For the first scenario, we describe a bandwidth efficient scheme which uses highorder constellations such as QAM over both AWGN as well as fading channels. We propose a simple design with LDPC codes which combines the good properties of Multi-level Coding (MLC) and bit-interleaved coded-modulation (BICM) schemes. Through simulations, we show that the proposed scheme performs better than MLC for short-medium lengths on AWGN and block-fading channels. For the first case, we also characterize the rate-diversity tradeoff of MIMO-OFDM and SISO-OFDM systems. We design optimal coding schemes which achieve this tradeoff when transmission is from a constrained constellation. Through simulations, we show that with a sub-optimal iterative decoder, the performance of this coding scheme is very close to the optimal limit for MIMO (flat quasi-static fading), MIMO-OFDM and SISO OFDM systems. For the second case, we design non-systematic Irregular Repeat Accumulate (IRA) codes, which are a special class of LDPC codes, for Inter-Symbol Interference (ISI) fading channels when CSI is estimated at the receiver. We use Orthogonal Frequency Division Multiplexing (OFDM) to convert the ISI fading channel into parallel flat fading subchannels. We use a simple receiver structure that performs iterative channel estimation and decoding and use non-systematic IRA codes that are optimized for this receiver. This combination is shown to perform very close to a receiver with perfect CSI and is also shown to be robust to change in the number of channel taps and Doppler. For the third case, we look at bandwidth efficient schemes for fading channels that perform close to capacity when the channel state information is known at the transmitter as well as the receiver. Schemes that achieve capacity with a Gaussian codebook for the above system are already known but not for constrained constellations. We derive the near-optimum scheme to achieve capacity with constrained constellations and then propose coding schemes which perform close to capacity. Through linear transformations, a MIMO system can be converted into non-interfering parallel subchannels and we further extend the proposed coding schemes to the MIMO case too.Item Low-Power Wireless Medical Systems and Circuits for Invasive and Non-Invasive Applications(2014-04-23) Gaxiola-Sosa, Jesus EfrainApproximately 75% of the health care yearly budget of public health systems around the world is spent on the treatment of patients with chronic diseases. This, along with advances on the medical and technological fields has given rise to the use of preventive medicine, resulting on a high demand of wireless medical systems (WMS) for patient monitoring and drug safety research. In this dissertation, the main design challenges and solutions for designing a WMS are addressed from system-level, using off-the-shell components, to circuit implementation. Two low-power oriented WMS aiming to monitor blood pressure of small laboratory animals (implantable) and cardiac-activity (12-lead electrocardiogram) of patients with chronic diseases (wearable) are presented. A power consumption vs. lifetime analysis to estimate the monitoring unit lifetime for each application is included. For the invasive/non-invasive WMS, in-vitro test benches are used to verify their functionality showing successful communication up to 2.1 m/35 m with the monitoring unit consuming 0.572 mA/33 mA from a 3 V/4.5 V power supply, allowing a two-year/ 88-hour lifetime in periodic/continuous operation. This results in an improvement of more than 50% compared with the lifetime commercial products. Additionally, this dissertation proposes transistor-level implementations of an ultra-low-noise/low-power biopotential amplifier and the baseband section of a wireless receiver, consisting of a channel selection filter (CSF) and a variable gain amplifier (VGA). The proposed biopotential amplifier is intended for electrocardiogram (ECG)/ electroencephalogram (EEG)/ electromyogram (EMG) monitoring applications and its architecture was designed focused on improving its noise/power efficiency. It was implemented using the ON-SEMI 0.5 ?m standard process with an effective area of 360 ?m2. Experimental results show a pass-band gain of 40.2 dB (240 mHz - 170 Hz), input referred noise of 0.47 Vrms, minimum CMRR of 84.3 dBm, NEF of 1.88 and a power dissipation of 3.5 ?W. The CSF was implemented using an active-RC 4th order inverse-chebyshev topology. The VGA provides 30 gain steps and includes a DC-cancellation loop to avoid saturation on the sub-sequent analog-to-digital converter block. Measurement results show a power consumption of 18.75 mW, IIP3 of 27.1 dBm, channel rejection better than 50 dB, gain variation of 0-60dB, cut-off frequency tuning of 1.1-2.29 MHz and noise figure of 33.25 dB. The circuit was implemented in the standard IBM 0.18 ?m CMOS process with a total area of 1.45 x 1.4 mm^(2). The presented WMS can integrate the proposed biopotential amplifier and baseband section with small modifications depending on the target signal while using the low-power-oriented algorithm to obtain further power optimization.Item Mobileflow: Applying SDN to Mobility in Wireless Networks(2014-08-10) Al-Shaikhli, RaghdahWireless technology has become an increasingly popular way for network access. Wireless networks provide efficient, reliable service; supporting a broad range of emerging applications including multimedia streaming and video conferencing. Currently, there are two dominant technologies for providing wireless network access: cellular broadband networks and wireless local area networks (Wi-Fi). Cellular networks offer ubiquitous coverage, high reliability, and support mobility; yet such networks require expensive specialized equipment and expensive spectrum bands. In contrast, Wi-Fi networks utilize unlicensed frequency bands; relying on commodity equipment. As a result, Wi-Fi infrastructure operational costs are lower than cellular network costs. Wi-Fi networks however, have limited coverage, do not support mobility, and are less reliable than cellular networks. Recently, software-defined-networking architectures are gaining interest. The Software-Defined Networking (SDN) approach separates control (forwarding decisions) and data plane (packet processing). This approach provides an abstraction of a network switch and an interface for manipulating this abstraction with clear semantics. The SDN approach enables applications to control underlying network services without knowing the low-level details of specific network equipment. Thus, this approach allows network programming by modifying the behavior of the routers and switches to meet network application requirements. This thesis introduces a reference architecture that supports user mobility through integration of the SDN technology into Wi-Fi networks. This project then implements a mobility manager application on top of an SDN controller to handle clients? handoff between access points. It proposes an algorithm for mobility prediction, allowing the network operator to minimize packet loss and delays during handoffs. Algorithm validation uses real data traces from the Texas A&M University network. Trace analysis was conducted to extract mobility patterns to build a prediction model which was implemented as an application in the SDN controller. The approach was tested by measuring packet loss that was decreased by approximately nine times. Collected mobility traces were used to analyze our prediction model performance, whose accuracy reached 65% and 95% when selecting five users with Last-in-First-out scheme with a high- and low-load access point, respectively. This research lays out groundwork for enhancing the functionality of WiFi networks, including mobility support, while maintaining their advantages in terms of lower cost, flexibility, and user of off-the-shelf components.Item Realtime Streaming with Guaranteed QOS over Wireless D2D Networks(2014-05-22) Paul, SumanThe increase in the processing power of mobile devices has led to an explosion of available services and applications. However, the cost of mobile data is a hindrance to the adoption of data intensive applications. We consider a group of co-located wireless peer devices that desire to synchronously receive a live content stream. Devices desire to minimize the usage of their B2D interfaces (3G/4G) to reduce cost, while maintaining synchronous reception and playout of content. While it might be possible for a cellular base station to broadcast or multicast live events to multiple handsets, such content would be restricted to a few selected channels, and only available to subscribers of a single provider. Utilizing both B2D and D2D (WiFi) interfaces enables users to pick any event of interest, and "stitch together" their B2D capacities regardless of provider support. Our objective is to enable users to listen or watch real time streams while incurring only a fraction of the original costs. Our system setup is as follows. The real-time stream is divided into blocks, which must be played out soon after their initial creation. If a block is not received within a specific time after its creation, it is rendered useless and dropped. The blocks in turn are divided into random linear coded chunks to facilitate sharing across the devices. We transform the problem into the two questions of (i) deciding which peer should broadcast a chunk on the D2D channel at each time, and (ii) how long B2D transmissions should take place for each block. The thesis studies the performance of a provably-minimum-cost algorithm that can ensure that QoS targets can be met for each device. We use a Lyapunov stability argument to show that a stable delivery ratio can be achieved using our mechanism. We show that the optimal D2D scheduling algorithm has a simple and intuitive form under reliable broadcast, which allows for easy implementation and development of good heuristics. We study this via simulations, and present an overview of the implementation on Android phones using the algorithm as a basis. Additionally, we design an incentive framework that promotes cooperation among devices. We show that under this incentive framework, each device benefits by truthfully reporting the number of chunks that it received via B2D and its deficit in each frame, so that a system-wide optimal allocation policy can be employed. The incentive framework developed is lightweight and compatible with minimal amounts of history retention. The Android testbed used in the experiments consisted of multiple Google Nexus 4 phones. A modified version of Android Jelly Bean (v 4.3) was built in order to conduct the experiments which removes the limitation wherein the phone switches off its 3G data connection (B2D) whenever a known WiFi network (D2D) becomes available. Since the Nexus 4 devices are incapable of operating in ad-hoc mode, we used a WiFi network (without Internet connectivity) to emulate the D2D part. Hence, devices must use their 3G interfaces to receive chunks for the server (via the Internet). We present experimental results, and show that it would be possible to follow popular streams on hand held devices incurring only a fraction of the costs while achieving a high QoS.Item Robust Framework for System Architecture and Hand-offs in Wireless and Cellular Communication Systems(2010-01-14) Varma, Vishal V.Robustness of a system has been defined in various ways and a lot of work has been done to model the robustness of a system, but quantifying or measuring robustness has always been very difficult. In this research, we develop a framework for robust system architecture. We consider a system of a linear estimator (multiple tap filter) and then attempt to model the system performance and robustness in a graphical manner, which admits an analysis using the differential geometric concepts. We compare two different perturbation models, namely the gradient with biased perturbations (sub-optimal model) of a surface and the gradient with unbiased perturbations (optimal model), and observe the values to see which of them can alternately be used in the process of understanding or measuring robustness. In this process we have worked on different examples and conducted many simulations to find if there is any consistency in the two models. We propose the study of robustness measures for estimation/prediction in stationary and non-stationary environment using differential geometric tools in conjunction with probability density analysis. Our approach shows that the gradient can be viewed as a random variable and therefore used to generate probability densities, allowing one to draw conclusions regarding the robust- ness. As an example, one can apply the geometric methodology to the prediction of time varying deterministic data in imperfectly known non-stationary distribution. We also compare stationary to non-stationary distribution and prove that robustness is reduced by admitting residual non-stationarity. We then research and develop a robust iterative handoff algorithm, relating generally to methods, devices and systems for reselecting and then handing over a mobile communications device from a first cell to a second cell in a cellular wireless communications system (GPRS, W-CDMA or OFDMA). This algorithm results in significant decrease in amount of power and/or result is a decrease of break in communications during an established voice call or other connection, in the field, thereby outperforming prior art.Item Wireless data acquisition system for multi-phase electric power equipment(2009-05-15) Goodsell, Douglas AndreasIndustrial facilities that plan the shutdown of equipment for service have large financial savings compared to those managing unplanned shutdowns. To this end, a variety of algorithms have been developed and published in the literature that can monitor a machine's health and indicate when the machine starts to develop a fault. In order for such algorithms to be effective, they require raw data collected from machines. Often this involves the placement of accelerometers and other sensory devices for measurements of mechanical behavior. It is possible to extract much of the required information from the electrical signals of the equipment. This is normally a less expensive installation since one only needs access to the lines supplying electric power to the equipment. If these data acqusistion modules are accessible wirelessly, then one can monitor all the interfaced equipment from a central location. To successfully monitor such electrical equipment, a data acquisition unit is required that can sample on five or six channels simultaneously, depending on the switch gear configuration. This thesis details the development of an "endpoint" device that samples the required number of channels to monitor the electrical signals of industrial equipment, and interfaces to a wireless network. The hardware and software design of the "endpoint" is discussed in detail. Also, the software design of the server that receives the data from the "endpoint" is presented. The designed "endpoint" samples up to six channels simultaneously, at a rate of at least 8 kHz per channel, and a data resolution of 16 bits. The data are then transmitted wirelessly to a central server for processing. The system has been tested both in a laboratory environment and at an industrial environment. The desired specifications of the "endpoint" have been verified in both environments. Several "endpoints" have been assembled to form a network and have been tested in a laboratory setting. This work has resulted in the demonstration that an "endpoint" can be constructed using of the shelf components that is suitable for the continuous health monitoring of multi-phase electric machines through a wireless network.Item X-by-wireless: a novel approach to vehicle control(2009-05-15) Hoelscher, David LouisAs the cost of wireless devices approaches zero, it becomes more feasible to replace wires with wireless communication. Vehicle wiring harnesses are traditionally wired to communicate both power and information simultaneously, resulting in separate circuits for each vehicle device. X-By-Wireless seeks to supplant this configuration in favor of a shared power bus and wireless inter-component communication. In doing so, we can recognize a number of benefits such as reduced weight and increased reliability, flexibility, and upgradeability. However, this introduces new problems such as longer transmission delays, interference and encryption issues, fusing difficulties, and public perception regarding safety. The purpose of this thesis is to define the X-By-Wireless concept and to investigate the benefits and drawbacks in implementing X-By-Wireless. Furthermore, we do a theoretical and case study analysis to expand upon the weight reduction benefit so as to quantify the expected improvements. We also address each of the challenges presented by X-By-Wireless and integrate them into a proposed circuit that is capable of performing all the necessary functions of wireless control, wireless sensing, and fusing. We find that the proposed device can be mass-produced as an effective solution that meets the speed and security constraints necessary for most vehicle components.