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Security Mechanisms for Mobile Ad Hoc and Wireless Sensor Networks
PhD, University of Cincinnati, 2008, Engineering : Computer Science and Engineering

Wireless Ad Hoc Networks have emerged as an advanced networking paradigm based on collaborative efforts among multiple self-organized wireless communication devices. Without the requirement of a fixed infrastructure support, wireless ad hoc networks can be quickly deployed anywhere at any time when needed. The decentralized nature, minimal configuration and quick deployment of wireless ad hoc networks make them suitable for various applications, from disaster rescue, target tracking to military conflicts. Wireless ad hoc networks can be further categorized into mobile ad hoc networks (MANETs), wireless sensor networks (WSNs), and wireless mesh networks (WMNs) depending on their applications.

Security is a big challenge in wireless ad hoc networks due to the lack of any infrastructure support, dynamic network topology, shared radio medium, and resource-constrained wireless users. Most existing security mechanisms applied for the Internet or traditional wireless networks are neither applicable nor suitable for wireless ad hoc network environments. In MANETs, routing security is an extremely important issue, as the majority of the standard routing protocols assume non-hostile environments. Once deployed in a hostile environment and working in an unattended mode, existing routing protocols are vulnerable to various attacks. To address these concerns, we propose an anonymous secure routing protocol for MANETs in this dissertation, which can be incorporated with existing routing protocols and achieve enhanced routing security with minimum additional overheads.

In WSNs, key distribution and management is the core issue of any security approaches. Due to extremely resource-constrained sensor nodes and lack of any infrastructure support, traditional public-key based key distribution and management mechanisms are commonly considered as too expensive to be employed in WSNs. In this dissertation, we propose two efficient pairwise key pre-distribution and management mechanisms for both distributed and hierarchical large-scale WSNs, which enable establishing secure links between any two sensor nodes located within their communication range. As we know, sensing and communication are two fundamental characteristics of WSNs, and they cannot be addressed separately. Existing work on sensing coverage mainly focus on how to use the minimum number of sensors to achieve a required coverage, while security constraints are not sufficiently addressed. We propose an effective key distribution approach for randomly deployed WSNs, based on random graph theory and a realistic random key pre-distribution mechanism, in order to achieve both robust sensing coverage and secure connectivity simultaneously in a hostile deployment environment.

#### Committee:

Dharma Agrawal (Committee Chair); Jerome Paul (Committee Member); Wen-Ben Jone (Committee Member); Chia-Yung Han (Committee Member); Ernest Hall (Committee Member)

#### Subjects:

Communication; Computer Science

#### Keywords:

Wireless Ad Hoc Network; Mobile Ad Hoc Network (MANET); Wireless Sensor Network (WSN); Routing; Security; Cryptography; Key Management; Distributed Wireless Network; Hierarchical Wireless Network; Sensing Coverage; Secured Connectivity

Integration of Radio Frequency Harvesting with Low Power Sensors
Doctor of Philosophy, The Ohio State University, 2018, Electrical and Computer Engineering
This dissertation gives guidelines for state-of-the-art power harvesters and for optimizing its components, e.g., rectifier, matching network, and antenna, in various applications. A single diode rectifier using a quarter-wave matching circuit with a measured efficiency of 73.7% is also presented. Several experimental demonstrations are included for powering a number of sensors and devices, such as a clock, computer mouse, calculator, thermometer, medical insulin pump, and super capacitor with power management circuitry. To increase the amount of RF harvested power, an array of rectifying antennas (rectennas) is presented and used in experiments up to 60 meters. Wireless power transfer demonstrations at near field distances are also presented. For the latter, we show a strong tolerance to misalignment while delivering high levels of power (1.2 mW over 42 cm). As an application, a medical pump is successfully powered over this distance. Further, bandwidth widening techniques are presented along with rectifier optimizations. To reduce the overall dimensions of the rectenna, miniaturization techniques are discussed. This leads to a rectenna size of 1.5 x 2.5 cm^2, making it ideal for medical or on-body applications. This rectenna was used to successfully activate a body-worn thermometer across 65 cm. In the case of implantable devices, a dielectric matching layer was found useful and validated using pig skin. A related SAR analysis ensured the safety of the proposed RF powering harvesting techniques.

#### Committee:

John Volakis (Advisor); Asimina Kiourti (Advisor); Liang Guo (Committee Member)

#### Subjects:

Electrical Engineering; Electromagnetics

#### Keywords:

power harvesting; wireless power; WPT; medical devices; wireless power transfer; wireless power transmission

FREQUENCY-SELECTIVE DESIGN OF WIRELESS POWER TRANSFER SYSTEMS FOR CONTROLLED ACCESS APPLICATIONS
Master of Science, Miami University, 2016, Computational Science and Engineering
Wireless power transfer (WPT) has become a common way to charge or power many types of devices, ranging from cell phones to electric toothbrushes. WPT became popular through the introduction of a transmission mode known as strongly coupled magnetic resonance (SCMR). This means of transmission is non-radiative and enables mid-range WPT. Shortly after the development of WPT via SCMR, a group of researchers introduced the concept of resonant repeaters, which allows power to hop from the source to the device. These repeaters are in resonance with the WPT system, which enables them to propagate the power wirelessly with minimal losses to the environment. Resonant repeaters have rekindled the dream of ubiquitous wireless power. Inherent risks come with the realization of such a dream. One of the most prominent risks, which we set out in this thesis to address, is that of accessibility to the WPT system. We propose the incorporation of a controlled access schema within a WPT system to prevent unwarranted use of wireless power. Our thesis discusses the history of electromagnetism, examines the inception of WPT via SCMR, evaluates recent developments in WPT, and further elaborates on the controlled access schema we wish to contribute to the field.

#### Committee:

Dmitriy Garmatyuk, PhD (Advisor); Mark Scott, PhD (Committee Member); Herbert Jaeger, PhD (Committee Member)

#### Subjects:

Computer Engineering; Electrical Engineering; Electromagnetics; Electromagnetism; Engineering

#### Keywords:

wireless power transfer; WPT; resonance; magnetic resonance; electromagnetism; power security; power encryption; wireless power transfer security; wireless power transfer encryption; SCMR; strongly coupled magnetic resonance; power transfer;

INTEGRATED ARCHITECTURE AND ROUTING PROTOCOLS FOR HETEROGENEOUS WIRELESS NETWORKS
PhD, University of Cincinnati, 2006, Engineering : Computer Science and Engineering
One of the main challenges in next generation wireless networks is to integrate heterogeneous wireless technologies to provide seamless connectivity, with guaranteed Quality of Service (QoS), to mobile users “anytime, anywhere and with any device”. In this dissertation, we investigate the problem of integrating cellular networks and Wireless Local Area Networks (WLANs) with the multi-hop communication paradigm used in Mobile Ad hoc Networks (MANETs) to exploit all the connectivity alternatives available to different types of Mobile Stations (MSs). We propose an integrated architecture based on three basic functionalities, namely, topology discovery, gateway discovery, and link quality estimation. We combine these three functionalities into an integrated routing mechanism that exploits all connectivity alternatives available in a generic heterogeneous scenario. Then, we provide a simulation-based analysis of our architecture and integrated routing mechanism in different heterogeneous networking scenarios. Our results show improvements in network’s capacity and coverage achieved by our architecture as compared to isolated networks. The results also highlight the importance of the link quality estimation in providing QoS to users, as well as indicate that multi-hop links can be exploited in a controlled network configuration, but the QoS in multi-hop routes cannot be always guaranteed. Furthermore, we address the problem of selecting the best connectivity opportunity for a given service type based on the applications’ QoS requirements, as well as on the network condition and user mobility profile. We propose the Connectivity opportunity Selection Algorithm (CSA) that allows MSs to select the connectivity opportunity most appropriate for a given type of service and mobility profile. Furthermore, we describe how our proposed selection algorithm can be introduced into the IEEE 802.21 standard for Media Independent Handover services.

#### Committee:

Dr. Dharma Agrawal (Advisor)

Computer Science

#### Keywords:

Heterogeneous Wireless Networks.; Routing Protocols for Heterogeneous Wireless Networks; Multi-hop communications in integrated wireless networks; network selection; always best connectivity

A MODIFIED WIRELESS TOKEN RING PROTOCOL TO PREVENT DATA COLLISON IN WIRELESS TRAFFIC SENSORS
MS, University of Cincinnati, 2006, Engineering : Civil Engineering
Intelligent Transportation Systems, or ITS, is about using technology to solve transportation engineering problems. There is a major push by the Departments of Transportation to use wireless sensors all over the highways to provide accurate traffic information in real-time. Wireless Token Ring Protocol (WTRP), a wireless protocol based loosely on IEEE 802.4 [8] Token Bus Protocol, is an excellent Medium Access Control layer level protocol to prevent data collision in this wireless sensor network on the freeways. The distances between wireless sensors on the freeway were calculated, based on sensor frequency, sensitivity of the receiver and the transmitters, using the Free Space Path Loss Equation. Based on these calculations, it was found that Wireless Token Ring Protocol could fail, as the distances between the sensors was quite large and the data packets got lost, when being transmitted from the last sensor back to the first sensor. The Wireless Token Ring Protocol was modified such that instead of being uni-directional, transmitting data in one direction only; it became bi-directional, transmitting data in both directions. As such, during simulation, it was found that, the performance of the Modified Wireless Token Ring Protocol was better than that of Wireless Token Ring Protocol. The number of data packets that were lost in transmission or corrupted using Modified Wireless Token Ring Protocol was drastically less than that using Wireless Token Ring Protocol, over the same node positions. Hence, the Modified Wireless Token Ring Protocol is more effective than the Wireless Token Ring Protocol to prevent data collision and corruption on the field.

#### Committee:

Dr. Prahlad Pant (Advisor)

#### Subjects:

Engineering, Civil

#### Keywords:

Wireless Token Ring Protocol; Modified Wireless Token Ring Protocol; Wireless Sensors; ITS

Wireless Strain Gauge System in a Multipath Environment
Master of Science, The Ohio State University, 2008, Electrical and Computer Engineering

A wireless strain sensing system utilizing passive, wireless, physically small and light weight sensors is desirable for measuring strain in harsh environments such as jet engine compressor and turbine blades. A cluttered and time varying environment results in high loss, blockage, multipath and modulation of the electromagnetic wave. Also, temperature changes affect the sensitivity of the strain measurement. Isolating the information signal from the reverberations in the environment requires time delays in the order of 100s of ns for jet engine environment. Therefore, a wireless strain gauge system that utilizes surface acoustic wave (SAW) strain sensors was studied and tested.

SAW strain sensors are designed to operate at 2.45GHz. Electron beam lithography is used to achieve minimum required feature size at this frequency. The fabrication process is outlined and scanning electron microscope images of some results are given.

A transceiver circuit is designed and constructed. The circuit is tested in free space, in the presence of signal blockage and a time varying channel. Measurements are shown to be in good agreement with predicted data. Sources of errors in the setup are identified to be leakage from transceiver circuit switches and bounce waveforms from the transceiver antenna.

A General Electric J85 jet engine compressor section is analyzed for signal propagation characteristics. Minimum frequency that can propagate through the compressor section is determined to be 5.2GHz. Measurements are done to show that circumferential polarization propagates stronger than radial inside the compressor section. An analytical approximation for the compressor section is generated by modeling compressor section blades as rectangular waveguides. Good agreement on cutoff frequency is achieved for circumferential polarization with the analytical predictions and measurement.

SAW temperature and strain sensors are measured in comparison to traditional gauges. This concept can be generalized to measuring many different physical quantities wirelessly without disturbing the operation of the equipment.

#### Committee:

Roberto Rojas-Teran (Advisor); Eric Walton K. (Committee Member); Jonathan Young D. (Committee Member)

#### Subjects:

Electrical Engineering; Engineering; Experiments

#### Keywords:

wireless strain sensor; surface acoustic wave (SAW); jet engine; multipath; RFID; strain gauge; wireless strain measurement; SAW fabrication; Lithium Niobate

Wireless, Implantable Microsystem for Chronic Bladder Pressure Monitoring
Doctor of Philosophy, Case Western Reserve University, 2014, EECS - Electrical Engineering
This work describes the design and testing of a wireless implantable bladder pressure sensor suitable for chronic implantation in humans. The sensor was designed to fulfill the unmet need for a chronic bladder pressure sensing device in urological fields such as urodynamics for diagnosis and neuromodulation for bladder control. Neuromodulation would particularly benefit from a wireless bladder pressure sensor providing real-time pressure feedback to an implanted stimulator, resulting in greater bladder capacity while using less power. The pressure sensing system consists of an implantable microsystem, an external RF receiver, and a wireless battery charger. The implant is small enough to be cystoscopically implanted within the bladder wall, where it is securely held and shielded from the urine stream, protecting both the device and the patient. The implantable microsystem consists of a custom application-specific integrated circuit (ASIC), pressure transducer, rechargeable battery, and wireless telemetry and recharging antennas. Because the battery capacity is extremely limited, the ASIC was designed using an ultra-low-power methodology in which power is dynamically allocated to instrumentation and telemetry circuits by a power management unit. A low-power regulator and clock oscillator set the minimum current draw at 7.5 µA and instrumentation circuitry is operated at low duty cycles to transmit 100-Hz pressure samples while consuming 74 µA. An adaptive transmission activity detector determines the minimum telemetry rate to limit broadcast of unimportant samples. Measured results indicated that the power management circuits produced an average system current of 16 µA while reducing the number of transmitted samples by more than 95% with typical bladder pressure signals. The wireless telemetry range of the system was measured to be 35 cm with a bit-error-rate of 10-3, and the battery was wirelessly recharged at distances up to 20 cm. A novel biocompatible packaging method consisting of a silicone-nylon mesh membrane and a compliant silicone gel was developed to protect the sensor from water ingress while only reducing the sensor sensitivity by 5%. Dynamic offset removal circuitry extended the system dynamic range to 2,900 cm H2O but limited the sensor AC accuracy to 3.7 cm H2O over a frequency range of 0.002 – 50 Hz. The DC accuracy of the sensor was measured to be approximately 2.6 cm H2O (0.9% full-scale). Functionality of wired prototypes was confirmed in feline and canine animal models, and wireless prototypes were implanted in a female calf large-animal model. Measured in vivo pressure recordings of bladder contractions correlated well with reference catheters (r =0.893–0.994).

#### Committee:

Steven Garverick (Advisor); Swarup Bhunia (Committee Co-Chair); Margot Damaser (Committee Member); Pedram Mohseni (Committee Member); Christian Zorman (Committee Member)

#### Subjects:

Biomedical Engineering; Electrical Engineering

#### Keywords:

Implantable electronics; bladder pressure sensor; low-power; integrated circuit; wireless; chronic implantation; bladder implant; pressure sensor; power management; adaptive transmission rate; wireless battery recharge

Reliable and secure data transport in large scale wireless networks of embedded devices
Doctor of Philosophy, The Ohio State University, 2006, Computer and Information Science
Recent advances in semiconductor technology have resulted in techniques that can build miniaturized radios and sensor-actuators, which can be deployed in the physical world in a large scale. These inexpensive devices can be used to provide coordinated dense sensing, processing, and communicating. Combining these capabilities with robust system software will empower physical sciences with real-time data of high fidelity. To realize this opportunity, computer scientists must address new challenges posed for development of robust system software for the large scale resource constrained wireless networks of embedded devices (sensors). These devices have limited resources in terms of processing, memory, radio bandwidth, and energy. Further, once deployed these devices will necessarily remain untouched and expect to work for an extended period of time. All though Internet is a large scale network, all of the above mentioned constrained do not apply to the nodes in the Internet. Therefore, network services must be designed specifically for the large scale wireless sensor networks. The network services for large scale sensor network must have low time complexity and memory complexity. We provide low complexity reliable and secure data transport for large scale wireless networks of embedded devices. We focus on bulk data transport for two of the most commonly used services, viz. data dissemination and data collection. Our services are better than the state-of-the-art. We address the problem of key maintenance for providing secured communication in the presence of key compromise and denial-of-service attacks. We also investigate the use of testbed to facilitate experimentations for large scale wireless networks.

#### Committee:

Anish Arora (Advisor)

Computer Science

#### Keywords:

Network protocols; Real-time systems and embedded systems; Wireless; Wireless sensor networks; Computer security

Analytical Model for Energy Management in Wireless Sensor Networks
PhD, University of Cincinnati, 2013, Engineering and Applied Science: Computer Science and Engineering
Wireless sensor networks (WSNs) are one type of ad hoc networks with data-collecting function. Because of the low-power, low-cost features, WSN attracts much attention from both academia and industry. However, since WSN is driven by batteries and the multi-hop transmission pattern introduces energy hole problem, energy management of WSN became one of fundamental issues. In this dissertation, we study the energy management strategies for WSNs. Firstly, we propose a packets propagation scheme for both deterministic and random deployment of WSNs so to prolong their lifetime. The essence of packets propagation scheme is to control transmission power so as to balance the energy consumption for the entire WSN. Secondly, a characteristic correlation based data aggregation approach is presented. Redundant information during data collection can be effectively mitigated so as to reduce the packets transmission in the WSN. Lifetime of WSN is increased with limited overhead. Thirdly, we also provide a two-tier lifetime optimization strategy for wireless visual sensor network (VSN). By deploying redundant cheaper relay nodes into existing VSN, the lifetime of VSN is maximized with minimal cost. Fourthly, our two-tier visual sensor network deployment is further extended considering multiple base stations and image compression technique. Last but not the least, description of UC AirNet WSN project is presented. At the end, we also consider future research topics on energy management schemes for WSN.

#### Committee:

Dharma Agrawal, D.Sc. (Committee Chair); Kenneth Berman, Ph.D. (Committee Member); Yizong Cheng, Ph.D. (Committee Member); Chia Han, Ph.D. (Committee Member); Wen Ben Jone, Ph.D. (Committee Member)

#### Subjects:

Computer Engineering

#### Keywords:

Wireless Sensor Networks;Wireless Visual Sensor Network;Energy Management;Data Aggregation;Gaussian Random Distribution;Lifetime Optimization;

Reliability of Data Collection and Transmission in Wireless Sensor Networks
Master of Science in Engineering, Youngstown State University, 2013, Department of Electrical and Computer Engineering
A network of wireless sensor nodes that are connected to a centralized base station is presented to conduct a study on reliability of data collection and transmission in wireless sensor networks (WSNs) with focus on data loss and data duplication. Software applications for specific sensor nodes called Sun SPOTs are presented, and programming techniques, for example packet transmitting time delay and data checking for loss and duplication, are implemented in these software applications to improve the functionality of the network. Acceleration data on a vibration plate are collected at sampling frequency of 100 Hz to validate the operation of the network. Additionally, the wireless sensor network is optimized to enhance the synchronization of data collection from different nodes. The result of this research shows that the reliability of the network is related to data sampling frequency, synchronization of the wireless data traffic, wireless sensor node signal strength, and wireless data routing protocols. The indoor tests on signal strength show the limitation of -70 dBm and higher for optimum data collection without data or packet loss.

#### Committee:

Li Frank, Ph.D. (Advisor); Munro Philip, Ph.D. (Committee Member); Mossayebi Faramarz, Ph.D. (Committee Member)

#### Subjects:

Computer Engineering; Electrical Engineering; Engineering; Information Technology

#### Keywords:

Wireless sensor networks; WSN; data collection; data transmission; reliability of wireless sensor networks

Secured Communication in Wireless Sensor Network (WSN) and Authentic Associations in Wireless Mesh Networks
MS, University of Cincinnati, 2010, Engineering and Applied Science: Computer Science
Wireless sensors are low power devices with small transmission range, restricted computation power, limited amount of memory and with portable power supply. Wireless Sensor Network (WSN) is a collection of such sensors where the number of sensors can vary from few hundreds to thousands. Performing secure pair-wise communication between sensors is a really difficult task due to inherent characteristics such as lack of any fixed infrastructure. As memory and power consumption are most stringent requirements for these devices, use of conventional techniques for secured communication are totally out of question. This thesis introduces scheme that enables a complete pair-wise secure connectivity between any two adjacent sensor nodes in spite of using small key ring (KR) for sensors. The Proposed Scheme (ELKPD) doesn't require any additional hardware while providing keys to the sensors irrespective of their location. Also, proposed scheme is easily scalable which allows enables addition of sensor nodes without any computational or hardware overheads. Due to the varying degree of mobility of Mesh Clients has provided much more flexibility in Wireless Mesh Networks. And establishing an Authentic Association among entities is a non -trivial problem. In this thesis, we introduce a Polynomial Based scheme which not only provides high pair-wise connectivity, low communication and storage overhead and high scalability but also makes on the fly Authentic Association feasible. The proposed scheme is also observed to be resilient against both the traffic analysis and the node capture attacks.

#### Committee:

Dharma Agrawal, DSc (Committee Chair); Raj Bhatnagar, PhD (Committee Member); Carla Purdy, C, PhD (Committee Member)

Computer Science

#### Keywords:

security;wireless sensor networks;key-predistribution;wireless mesh networks;bi-variate polynomials

TCP Performance With Multipath Routing in Wireless Ad Hoc Networks
MS, University of Cincinnati, 2003, Engineering : Computer Science
Majority of applications on the Internet today use TCP for reliable communication. TCP has been designed for and fine tuned to wired environments, but recent studies have shown that its performance suffers in wireless network environments, particularly in ad hoc networks because of the presence of multiple wireless hops. Routing has been the most focused area of research in recent years in wireless ad hoc networking area. Many on-demand routing protocols have been proposed to improve robustness in the face of link and route failures and facilitate packet transmission. Using multiple paths to route packets is one of them. We examine the performance of the TCP protocol with multiple paths in mobile ad hoc networks (MANETs). We set up multiple routes between the TCP source and destination either manually or using an on-demand multipath routing protocol, and forward packets on both paths to reduce the load on one single path. Ordinarily one would expect the multiple paths to reduce conflict between TCP data and acknowledgement packets thus giving better overall performance. Our results do incidate that TCP performance with multipath routing shows some improvement for long routes; however, shorter routes may experience slight degradation in performance as compared to single path routing. This observation remains true even when contention-based scheduling is used to schedule packets on different paths, or the multiple routes are chosen such that they have a minimum radio interference among themselves. We conclude that the TCP could gain only limited benefits with multipath routing.

#### Committee:

Dr. Samir R. Das (Advisor)

#### Keywords:

TCP over wireless; TCP over AD HOC Networks; multipath routing; TCP performance with multipath; multipath in wireless network

Development and Characterization of a Tunable Resonant Shielded Loop Wireless Non-Radiative Power Transfer System
Master of Science (M.S.), University of Dayton, 2011, Electrical Engineering
In this thesis, the theory of coupled resonators for non-adiative wireless power transfer are explored from a lumped element circuit perspective. A basic circuit model is developed and standard circuit parameters are defined. A directly fed resonant shielded loop for wireless power transfer is presented. Basic lumped component values and circuit parameters are experimentally extracted for two resonant shielded loops. Optimal efficiency conditions are derived and used to design optimal matching networks. Matching networks are constructed and the system is tested for power transfer efficiency. Two means of producing a tunable system are explored: frequency tuned sources and dynamic matching networks. It is shown that frequency tuned systems cannot achieve maximum efficiencies. A tunable system is constructed and tested. Experimental results show excellent agreement with theory, and the ability to achieve maximum achievable efficiencies.

#### Committee:

Robert Penno, PhD (Committee Chair); Anthony Grbic, PhD (Advisor); Monish Chatterjee, PhD (Committee Member); Augustine Urbas, PhD (Committee Member); John Weber, PhD (Other); Tony Saliba, PhD (Other)

#### Subjects:

Electrical Engineering; Electromagnetics; Electromagnetism; Energy; Engineering; Solid State Physics

#### Keywords:

Wireless; Power; Transfer; WNPT; resonant; shielded loop; non-radiative; wireless power transfer; WPT

Modeling and Performance Evaluation of Wireless Body Area Networks for Healthcare Applications
PhD, University of Cincinnati, 2015, Engineering and Applied Science: Computer Science and Engineering
Wireless Body Area Network (WBAN) is a low-power Personal Area Network involving sensor nodes (SNs) that sense and relay physiological data to a central station. WBANs are new and still evolving. We try to address three open research areas involving WBANs. The limited energy budget in WBANs necessitates energy conservation to prolong the network lifetime. The first challenge we try to address is related to improvement of the lifetime of a WBAN, given the small sizes of body sensor nodes (SNs) and the limited battery power that they run on. We proposed a dual-prediction framework for improvement of network lifetime. The framework allows for minimizing data transmission involving four important body parameters by reconstructing their information by time series prediction at reception. A sample elimination algorithm further optimizes the framework performance. We enhanced the framework by reducing the sampling frequency and implementing the algorithm on top, increasing the network lifetime further. The missing samples were reconstructed by interpolation at the receiver. We probed the effects of adaptive sampling and evaluated the increase in battery lifetime in WBANs. We then tried to test the behavior of a WBAN in the presence of other WBANs around it and check the issues faced by WBANs. Wireless systems can face severe interference problems if they use the same communication channels at a time. There are issues related to data routing because the critical nature of WBAN data requires assured communication of body data. For optimum network utilization, efficient scheduling of transmissions in multiple co-existing WBANs is important in order to avoid intra and inter-WBAN interference and for a graceful coexistence. We propose that inter-WBAN interference can be avoided by a QoS based MAC scheduling approach and that intra-WBANs interference can be circumvented by fuzzy scheduling of intra-WBAN transmissions. We also propose to use interference to the benefit of WBANs through a framework in which neighboring WBANs communicate for cooperative packet routing. This lets the WBANs use some spare transmission iii slots from their neighbor WBANs when required. This can happen when a WBAN with more or sudden, emergency data is strapped for transmission slots while its neighbor has some to spare. A routing tree is created using a weighted two-pass algorithm involving an assisting WBAN that can accommodate routing requests from its neighbor WBAN. We further evaluated the possibility of relaying data from a mobile WBAN through small scale networks for voice communication. The scheme uses dynamic virtual cells that grow and shrink in order to provide uninterrupted service, while reducing handovers. Although wireless systems are reliable in conveying sensor data but their use for control applications is still nascent. We tried to probe if WSNs in general or WBANs in particular could be used for wireless control. We have evaluated the performance of ON-OFF control involving a wireless sensor network for musical entertainment applications. We further extended our work and tested the feasibility of control in WSNs and in more critical real life applications in WBANs.

#### Committee:

Dharma Agrawal, D.Sc. (Committee Chair); Raj Bhatnagar, Ph.D. (Committee Member); Prabir Bhattacharya, Ph.D. (Committee Member); Chia Han, Ph.D. (Committee Member); Marepalli Rao, Ph.D. (Committee Member)

Computer Science

#### Keywords:

Wireless Body Area Networks;Wireless Body Sensor Networks;Energy Efficiency;QoS based MAC;Interference in WBANs

REAL-TIME MONITORING OF LANDSLIDE USING WIRELESS SENSOR NETWORK
Doctor of Philosophy, The Ohio State University, 2009, Civil Engineering
Damage caused by landslides exceeds $3 billion annually in the U.S and more than$ 10 billion each year worldwide, making losses attributed to landslides greater than any other natural disaster except hurricanes. Along with massive property loss, thousands people are killed and injured every year as the result of landslides. Potentially, much of this property damage and many of the injuries and deaths can be avoided with an operational landslide warning system. The goal of this research is to develop a wireless sensor network to predict the onset of landslides. The system will work by recording orientation changes from tiltmeters deployed on the surface of landslide prone slopes. Basic wired detection systems have been installed but, due to the high costs, monitoring systems can only cover a limited portion of a slope and requiring pre-existing knowledge of the most likely slide locations. Wireless landslide detection systems today have many problems limiting their practicality. Current limitations include subsurface sensor installation costs, high energy consumption and actual validation at the network level. In this research software having the capacity to interpret signals and generate failure alerts is being developed. To validate the above system, measured displacement data using wired extensometers from select sites are converted to tilt values and for the same sites, failure modes showing vector plots are generated using a numerical analysis program. These failure modes will be compared with various non critical movements. These comparisons related to surface movement patterns will provide essential characteristics for the stable landslide warning algorithm. For demonstration of this system, a slope with forty nodes consisting of eight columns and five rows is considered to be representative a typical hill slope. This demonstration shows how to implement the proposed algorithm based on a simple on and off sensor which will perform similarly to a tiltmeter. Only one time streaming of an (on) signal is needed when tilt reaches pre-set level, so battery power is only needed to send this information without waking and sending data periodically. Demonstrations show that the proposed algorithm can be implemented and successfully detect landslides using current sensor network technology.

#### Committee:

William Wolfe, PhD (Advisor); Fabian Tan, PhD (Committee Member); Tarunjit Butalia, PhD (Committee Member)

#### Subjects:

Civil Engineering

#### Keywords:

Landslide; Wireless Sensor Network; Real-Time monitoring; Surface movement patterns; Wireless data acquisition

Scheduling in Wireless Networks with Limited and Imperfect Channel Knowledge
Doctor of Philosophy, The Ohio State University, 2014, Electrical and Computer Engineering
In a wireless network, the efficiency of scheduling algorithms over time-varying channels depends heavily on the accuracy of the Channel State Information (CSI), which is usually quite “costly” in terms of consuming network resources. In the meanwhile, communication channels in wireless systems typically fluctuate in a temporally-correlated manner. We hence consider scheduling in wireless networks with limited and imperfect channel state knowledge, where the scheduler can exploit the temporal-correlation inherent in channels with memory for better channel state knowledge. We consider the channel state acquisition mechanism with ARQ-styled feedback, whereby the channel states are revealed at the end of only scheduled users' transmissions. In the presence of temporally-correlated channel evolution, the desired scheduler must optimally balance the `exploitation-exploration trade-off’, whereby it schedules transmissions both to exploit those channels with up-to-date CSI and to explore the current state of those with outdated CSI. We model the scheduling problems as Partially Observable Markov Decision Processes (POMDPs). POMDPs are known to be difficult to solve. We are able to analyze the problems in the framework of Restless Multi-armed Bandit Processes and utilize the Whittle’s indexability analysis. Based on our analysis, we propose low-complexity scheduling algorithms that have optimality performance in different wireless networks. Our work reveals that, under limited and imperfect channel state information, exploiting channel memory and ARQ-styled feedback for scheduling can result in significant system-level performance gains and that the proposed polynomial-complexity algorithms have provably optimal performances in various settings.

#### Committee:

Ness Shroff (Advisor); Atilla Eryilmaz (Advisor); Hesham El Gamal (Committee Member)

#### Subjects:

Computer Science; Electrical Engineering; Engineering; Operations Research

#### Keywords:

wireless networks, scheduling, network control algorithm, time-correlated wireless channel, channel memory, imperfect channel state information, queueing networks, ARQ feedback, Partially Observable Markov Decision Process

Beamforming Techniques for Frequency-Selective and Millimeter-Wave Indoor Broadcast Channels
Doctor of Philosophy, The Ohio State University, 2018, Electrical and Computer Engineering
Wireless communication networks have become ubiquitous in recent years. Current wireless applications are possible thanks to small WiFi cells that provide high-speed indoor coverage and outdoor macro-cells that support user mobility. Next generation wireless networks will use similar architectures to enable new applications such as augmented and virtual reality, the internet of things, ultra-high definition video streaming, and massive data transmission and storage. However, these applications require unprecedented high-speed data transfer capabilities enabled by large frequency bandwidths. Motivated by spectrum scarcity in bands below 6 GHz, previously unused millimeter-wave (mmWave) bands, where large bandwidths are available, are now considered for future wireless networks. The necessity for efficient communication techniques for such large bandwidths and mmWave frequencies is the main motivation for this dissertation, with a focus on the complex radiowave propagation conditions found in indoor environments. Propagation mechanisms such as multiple reflections, diffractions, and transmissions through walls are commonly found in indoor wireless communications, which cause variations in the received signal along its bandwidth (wideband or frequency-selective channels). Traditionally, antenna arrays have been used together with beamforming (linear processing) techniques to improve the system's performance. However, those techniques were designed for narrowband systems (e.g., zero-forcing or matched filtering) and their application to wideband systems requires additional processing that increases system's complexity. In the first part of this dissertation, we tackle the problem of beamforming in frequency-selective channels with two approaches: \emph{i}) we use the electromagnetic time-reversal (TR) effect to directly design novel wideband beamformers, and \emph{ii}) we generalize the block-diagonalization (BD) procedure used in narrowband channels to the frequency-selective case. For both approaches, we derive theoretical performance bounds under different propagation conditions and provide numerical simulations for various operation parameters. We found that these frequency-selective beamforming solutions require low-complexity receivers and can efficiently address problems such as inter-symbol interference and inter-user interference. In the second part of this dissertation, we focus on the design of beamforming procedures for wideband mmWave systems considering their specific hardware constraints and propagation characteristics. In this case, antenna arrays with tens of elements are commonly used to compensate for large propagation losses. Hybrid analog/digital beamforming, that combines phase-shifters in the RF domain with digital baseband processing, has been proposed to reduce hardware complexity. Thus, we introduce a novel hybrid beamforming algorithm for multiuser wideband mmWave systems. The algorithm accounts for hardware constraints and realistic antenna array effects such as beam squint, antenna coupling, and individual element radiation patterns. We provide numerical evaluations of the algorithm with both statistical and ray-tracing channel models. Results show that the algorithm enables multi-Gbps connectivity to multiple users in real-life scenarios with only a 3 dB performance loss with respect to ideal fully-digital beamforming with much simpler hardware.

#### Committee:

Fernando Teixeira (Advisor)

#### Subjects:

Electrical Engineering

#### Keywords:

Beamforming, antenna arrays, millimeter-wave communications, wireless local area networks, wireless communications

DYNAMIC CHANNEL ALLOCATION AND BROADCAST DISK ORGANIZATION FOR WIRELESS INFORMATION DISSEMINATION
MS, University of Cincinnati, 2001, Engineering : Computer Science
Mobile computing has gained increasing attention recently as a variety of mobile terminals and convenient wireless connection becomes available. One of the major applications of mobile computing is information dissemination. The three fundamental methods of providing information on wireless communication channels are push, pull and hybrid push-pull. In a hybrid push-pull environment, the data of most interest is broadcast in the form of a broadcast disk, and the rest of the data is pulled from the server via explicit client requests. To achieve efficient data dissemination, the mobile server dynamically collects users’ query access patterns and allocates data in broadcast disks. However, few studies have been conducted in the area of channel allocation and broadcast disk organization that considerate dynamic access pattern collection and utilization. In this study, we use a bit vector technique to represent mobile users’ access patterns. We introduce a timestamp and a modification indicator to increase the accuracy of using bit vector technology. Algorithms for collecting access patterns are proposed and studied here. Algorithms for determining the optimal channel allocation and broadcast disk organization given a set of access patterns are proposed. The optimal allocation algorithm searches exhaustively for the optimal solution while the heuristic algorithm searches for a solution by finding the optimal number of broadcast channels first and then organizing the data pages on those channels. We also propose and investigate an algorithm for incremental broadcast disk reorganization. Performance studies are conducted using average access probe-wait time as a criterion. Performance studies indicate that the proposed algorithms always outperform the existing flat approach in channel allocation and broadcast disk organization. When the heuristic approach is compared with the optimal approach, experimental results demonstrate that no significant performance differences are observed between the two methods. We also study the performance of the proposed algorithms by varying different system parameter settings such as request rate, data page size, number of channels and the size of database. Experimental results show that in both approaches, the optimal allocation algorithm and heuristic algorithm, the channel allocation adapts to the request rate changes in order to maintain the best performance. That is, when the mobile users’ request rate is high enough, the dynamic channel allocation methods wisely adjusts its allocation method to be close to pure push methods so that the average access probe-wait time remains constant and the best performance is maintained. Increases in either data page size or database size results in longer access waiting times. The effectiveness of algorithm for incremental broadcast disk reorganization is studied as well. The resulting channel allocation and data page organizations are very close to those obtained by applying either the optimal allocation algorithm or the heuristic algorithm to create a new generation of broadcast disks.

#### Committee:

Dr. Karen C. Davis (Advisor)

Computer Science

#### Keywords:

CHANNEL ALLOCATION; DISK ORGANIZATION; WIRELESS INFORMATION DISSEMINATION; DYNAMIC DATA ORGANIZATION; WIRELESS BROADCAST

Wireless Technology in Higher Education: The Perceptions of Faculty and Students Concerning the use of Wireless Laptops
Doctor of Philosophy (PhD), Ohio University, 2005, Computer Education and Technology (Education)

This study was based on the hypothesis that gender differences and past experiences with computers and the Internet influence individuals’ perceptions of wireless laptops. The perception of wireless laptops was evaluated according to Rogers’ five attributes of innovations: relative advantages, compatibility, complexity, trialability, and observability. An online questionnaire was utilized in the study, and the total number of participants was 248. Analyses of the data were conducted using multiple regression analysis and one-way analysis of variance. The results of the data indicated that the overall perception of participants on the use of wireless laptops was positive. A statistically significant difference in the perceptions of wireless laptops was found in the groups of graduate students and faculty members. Faculty members showed lowest interest in trying wireless laptops, worried about security problems, and were concerned about the distraction that wireless laptops may bring to learning. The relationship between the perceptions of wireless laptops to five predictors (gender, wireless laptop ownership, wireless laptop experience, attitude toward computers, and attitude toward the Internet) was significant. In evaluating the contribution of each predictor, the attitude toward the Internet was found to be the most important factor in predicting the perceptions of wireless laptops, and was followed by gender, the computer attitude scale, wireless laptop ownership, and experience with wireless laptops. The findings of this study support prior research that an individual’s past experience with computers and the Internet have positive impacts on the perceptions toward technological innovations in terms of wireless laptops in this study. The gender perception about men holding a more positive attitude toward the technological innovation does not exist. This study suggests that in order to take the best advantage of wireless laptops, the utilization and skills of computers and the Internet need to be enhanced; the issues concerning file transmission security and the distraction of using wireless laptops in class should be addressed.

#### Committee:

Teresa Franklin (Advisor)

#### Subjects:

Education, Technology

#### Keywords:

Wireless Technology; Wireless Laptops; Perceptions; Higher Education; Faculty and Students; Ohio University

Performance Evaluation Of Hybrid Wireless Sensor Network Simulation At Scale
MS, Kent State University, 2011, College of Arts and Sciences / Department of Computer Science
Networks of wireless sensors are notoriously difficult to experiment with. Testbeds became the experimenter's tool of choice. However, some of potential sensor network applications require the scales that are difficult to achieve on a testbed. Simulation may be a possible substitute. Yet, the radio propagation patterns of low-power radios used by wireless sensors are difficult to model with high fidelity. The errors that the simulation introduces compound at large scale rendering the results suspect. We propose to a combined approach where radio communication between wireless sensor nodes on a testbed is used in real-time to boost the fidelity of large scale simulation. In this thesis we present a series of experiments that demonstrate the viability and evaluate the efficiency of this approach.

#### Committee:

Mikhail Nesterenko (Advisor)

#### Subjects:

Computer Engineering; Computer Science

#### Keywords:

wireless sensors;hybrid simulator;scale;MULE;mica2;mote;sensors;wireless;testbed;

Efficient Quality of Service Provision Techniques in Next Generation Wireless Networks
PhD, University of Cincinnati, 2014, Engineering and Applied Science: Computer Science and Engineering
Recent evolution of communication networks comprises of different segments and technologies, where each segment maybe implemented using different QoS. Further, the proposed all-IP core infrastructure of the future networks will offer varying QoS level multimedia services to the users. However, IP being a best effort service, seamless provision of end-to-end QoS guarantees is extremely important. In today's world, devices with multiple networking capabilities is quite common. The traditional approach in networking includes grouping identical traffic and allocating them to the network that has the maximum available data rate. This creates unbalanced traffic load in the network, leading to poor utilization of the associated resources. This problem can be greatly alleviated if the traffic can be allocated intelligently to the networks. For fair traffic distribution, we modeled the AP of each network as a single queuing server. Then, suitable equations and algorithms are designed to divide the incoming traffic flow into multiple subflows and allocated to the APs based on their available data rates. Network Selection in a Heterogeneous Cognitive Radio Wireless Network is a challenging task, since the users need to select the appropriate channels of the network in addition to the network itself. The varying levels of interference experienced by the secondary user (SUs) is due to the presence of primary user (PU)s in the adjacent channels. Hence, SUs transmitting highly sensitive data must find a channel that is interference free. In this dissertation, we develop a novel network and channel selection scheme that categorizes both the user applications and the network channels depending on their sensitivity level for interference and select them using a bipartite graph matching algorithm. The effectiveness of Cognitive Radios is based on opportunistic access of the licensed channels by SUs while protecting the PU transmission. But channel sensing incurs cost in terms of time overhead and energy consumption. However, infrequent sensing also results in loss of transmission opportunity for the SUs. Hence, an interesting and challenging question arise: when should the SU sense the channel, sleep or transmit, to minimize the total cost? In this dissertation, we developed a novel scheme for deriving the optimal inter-sensing duration in a Cognitive Radio network, on the requirement of protecting the PUs' communications while minimizing the cost for the SUs. The scheme has been presented for both non-erroneous and erroneous channel sensing conditions. Handling the "mobile data tsunami" in the future and providing indoor coverage is a significant challenge for the operators. The answer is LTE femtocells. However, limited spectrum availability in the cellular networks causes severe interference in the neighboring femtocell users that are transmitting in the same radio band. In densely deployed environments, interference problems in co-channel femtocells causes significant degradation in performance. In this dissertation, we proposed a CASFR scheme, that assigns distinct set of PRBs to each interfering femtocells in the downlink. In the uplink we proposed a PSE algorithm to further reduce any interference that may remain after performing CASFR. Finally, the topics for future work have been clearly identified.

#### Committee:

Dharma Agrawal, D.Sc. (Committee Chair); Raj Bhatnagar, Ph.D. (Committee Member); Yizong Cheng, Ph.D. (Committee Member); Chia Han, Ph.D. (Committee Member); Yiming Hu, Ph.D. (Committee Member)

Computer Science

#### Keywords:

Heterogeneous Wireless Networks;Next Generation Wireless Networks;Cognitive Radio;Inter-cellular Interference;Femtocells;4G

Attacks and Counterattacks on Physical Layer Primitives
Doctor of Philosophy, The Ohio State University, 2017, Computer Science and Engineering
It has long been believed that physical layer primitives extracted from wireless channel are not breakable given certain physical constraints. This belief is built upon the old faith in wireless channel’s uncontrollability and unpredictability, and it is a cornerstone of physical layer security. Through our study, however, we find that the trust on an unauthenticated wireless channel’s integrity is not valid. Here we propose various attacks and counterattacks on physical layer primitives including physical features about the environment and secret keys, and provide strong evidence that physical layer security solutions which purely rely on extracting these features from wireless channel need to be redesigned. In the thesis, we start with our finding that an in-band full-duplex forwarder can change wireless channel in fine granularity. We propose PhyCloak, which is a fine-grained channel controller. It works against a popular set of applications that relies on physical primitive extracted from the channel called communication based sensing. This work is the first to counter the threat of unwanted or even malicious communication based sensing: it proposes a blackbox sensor obfuscation technique which distorts only the physical information in the communication signal that leaks privacy. Moreover, the design allows coupling the PhyCloak module with legitimate sensors, so that their sensing is preserved, while that of illegitimate sensors is obfuscated. In the second part of the thesis, we focus on another popular set of applications that rely on physical primitives: channel based secret sharing. First, we introduce a channel based secret key extraction approach called Puzzle. In this part, we show how physical primitives can be extracted from the wireless channel, and be exploited to build a security solution. In addition, we will see more clearly what are the difficulties to break such channel based secret key extraction approaches. Next, in an effort to preserve channel reciprocity, we propose a channel controller called Channel Spoofer to force the two communicating ends to produce highly predictable secrets. This work is the first to demonstrate breaking of all extant channel based secret key extraction protocols, with no unrealistic assumptions on the environment. In the end, we propose a scheme to overcome the vulnerability of unauthenticated wireless channel by combining both physical layer solutions and traditional cryptographic solutions. We present a generic hop-to-hop secure communication protocol atop a physical layer that adapts various physical layer parameters. We believe that given the vulnerability revealed by the proposed channel controllers, systems which purely rely on secret primitives extracted from physical layer are not secure anymore, and therefore, combining traditional cryptographic primitives and physical primitive together is more sound.

#### Committee:

Anish Arora (Advisor); Kannan Srinivasan (Advisor); Chunyi Peng (Committee Member); Ness Shroff (Committee Member); Yinqian Zhang (Committee Member)

Computer Science

#### Keywords:

wireless system; physical layer security; wireless channel

High-Performance Wireless Microsystem for MEMS Capacitive Strain Sensors
Doctor of Philosophy, Case Western Reserve University, 2011, EECS - Electrical Engineering
High-performance wireless microsystems consisting of MEMS sensors and low-power integrated circuits are crucial for applications such as the monitoring of biomedical signals, environmental monitoring, and advanced automotive and industrial sensing applications. These applications demand batteryless operation due to size and operation lifetime constraints. High-performance industrial sensing applications further impose design challenges due to the large signal bandwidth and dynamic range demanded for these applications. This work presents a complete stand-alone wireless microsystem for industrial strain sensing applications, such as point-stress and torque sensing for ball-bearings and rotating shafts and blades. The proposed microsystem consists of a MEMS capacitive strain sensor and integrated capacitive interface electronics with wireless powering and data telemetry capability. A prototype wireless strain sensing microsystem has been fabricated and tested. A capacitive differential MEMS strain sensor employs mechanical amplification through bent beam suspensions to achieve a sensitivity of 283 aF/microstrain. The sensor is wire-bonded to an IC consisting of a low-noise continuous-time synchronous-detection capacitance-to-voltage (C/V) converter and 2nd-order sigma-delta analog-to-digital converter (ADC) to digitize the strain information for reliable wireless data transmission. An on-chip temperature sensor and 1st-order sigma-delta ADC is included for system calibration. The microsystem is powered by a 51.2 MHz RF signal through an on-chip RF-DC converter and can simultaneously transmit two channels of digitized strain and temperature data over the RF powering link by passive phase shift-keying (PSK) and amplitude shift-keying (ASK) modulations, respectively, and a comparator generates the system timing clock from the incoming RF signal. The strain sensing microsystem exhibits a maximum DC input strain range of ±1000 microstrain, with an overall sensitivity of 816 mV/microstrain and 5.2% nonlinearity full-scale. Based on system noise characterization, the prototype design exhibits a strain resolution of 0.05 microstrain over a 10 kHz bandwidth. The temperature sensor exhibits a sensitivity of 3.8 mV/C from 25 °C to 150 °C with a resolution 0.01 °C due to electronic noise. The strain and temperature information are simultaneously telemetered to an external receiver at 2.56 Mbps and 128 kbps, respectively. The PSK and ASK channels are tested with a bit error rate of less than 10-7 The overall system consumes 2 mA from a 3V supply and occupies an area of 3 mm x 7 mm.

#### Committee:

Darrin Young (Advisor); Wen Ko (Committee Member); Francis Merat (Committee Member); Dominique Durand (Committee Member)

#### Subjects:

Electrical Engineering

#### Keywords:

MEMS; capacitive interface circuits; strain sensor; wireless microsystem; wireless sensor

A Novel Security Scheme during Vertical Handoff in Integrated Heterogeneous Wireless Networks
MS, University of Cincinnati, 2009, Engineering : Computer Science
In an integrated heterogeneous wireless network (IHWN), a user can connect itself to different types of networks on anytime, anywhere basis. Any of the following networks: cellular networks, WLANs, and ad hoc and sensor networks can constitute an IHWN network. The user is free to roam within networks seamlessly based on his needs and network availability. However, the security concerns associated with the IHWN count for some of the challenges involved in its implementation. These concerns combined with the different security requirements of various constituent wireless networks may have made security a serious issue. Seamless transfer of user’s credentials is a major requirement when considering security during vertical handoff between two different types of networks. A security scheme that can fit all types of networks is difficult to propose. However, a reasonable architecture that keeps both security and user convenience into consideration can be designed. The existing security schemes fail to address mobility and scalability requirements. Considering the importance of these aspects in securing a global network, we propose a novel security scheme that uses two different security algorithms depending on the number of vertical handoffs made by the mobile node after the first authentication in the home network. It makes use of existing network elements, such as RADIUS and Diameter protocols and supports scalability, mobility, and secure key exchange. We also introduce a time factor which is pre-set between the home network and foreign network. It delegates the task of authorizing subsequent requests from mobile node to connect to a different foreign network. Finally, we evaluate the efficiency and scalability of the scheme and prove its superiority over the existing schemes. The simulation results show a significant improvement over messages exchanged during key distribution at the time of vertical handoff. They also show how the scheme provides an excellent solution for delegated authentication. For a fair comparison, we also analyze the existing key distribution schemes and discuss their limitations in supporting the user security needs in current wireless networks.

#### Committee:

Raj Bhatnagar, PhD (Committee Chair); George Purdy, PhD (Committee Member); Ali Minai, PhD (Committee Member); Qing An Zeng, PhD (Committee Member)

Computer Science

#### Keywords:

Integrated Heterogeneous Wireless Network; Wireless Security; EAP-SKE

Investigation of Power Reduction Methods for Multi-User MIMO WLAN Applications
Master of Science in Engineering, University of Akron, 2014, Electrical Engineering
The communications industry has recently begun focusing on energy efficiency of networking devices, one of which is wireless local area network (WLAN) access points. Access points are continuously improving performance, but many aspects of the access point hardware and software consume more power as performance increases, namely power amplifiers (PAs), microprocessors, and security features. Multi-user multiple-input multiple-output (MU-MIMO) communication, transmitting disparate data to multiple receiving devices at the same time in the same frequency spectrum, has been researched for some time, but has just been standardized and is now starting to be implemented in WLAN access points. The benefits of this system performance enhancement do not come without cost, one of which is system power consumption. Investigations have begun on methods of reducing this additional power consumption and the impact those power reductions have on system performance. Some, like coding schemes that reduce power consumption can also increase system complexity and may not be practical without knowledge of the coding scheme at both ends of the link. Power reduction techniques such as optimizing user scheduling for energy efficiency, improving the energy efficiency of channel sounding, or turning off particular transmit chains have the potential to limit the effective capacity in the overall access network. Peak-to-average power ratio reduction often comes at the cost of system complexity, bit error rate increases, and even bandwidth limitations. Still, experimentation in this study shows that it is possible to decrease power consumption without sacrificing signal integrity by reducing peak-to-average power ratios and changing the bias point of select power amplifiers currently available and suitable for use in multi-user MIMO systems. Unfortunately, most available amplifiers do not facilitate external bias control to reap savings of lower peak-to-average power ratio signals. Despite all the challenges, pursuing energy efficiency improvements in wireless networking is a worthwhile endeavor and, through all the challenges, steps are continually being taken to move toward more energy efficient networks.

#### Committee:

Nathan Ida, Dr. (Advisor); Hamid Bahrami, Dr. (Committee Member); Nghi Tran, Dr. (Committee Member)

#### Subjects:

Electrical Engineering

#### Keywords:

MU-MIMO; wireless communication; power amplifier; energy efficiency; wireless networking; access point; peak-to-average power ratio; PAPR