R-3 Repository :: Browsing by Author "Knightly, Edward"

Browsing by Author "Knightly, Edward"

Now showing 1 - 18 of 18

AP-side WLAN Analytics
(2019-10-23) Nayak, Peshal; Knightly, Edward
Monitoring the network performance experienced by the end user is crucial for managers of wireless networks as it can enable them to remotely modify the network parameters to improve the end user experience. Unfortunately, for performance monitoring, managers are typically limited to the logs of the Access Points (APs) that they manage. This information does not directly capture factors that can hinder station (STA) side transmissions. While the AP-observable measurements do indeed help to characterize the PHY performance for downlink and uplink, managers today lack models and tools to translate them into user experience metrics (such as for instance TCP throughput). Consequently, state-of-the-art methods to measure such metrics primarily involve active measurements. For instance, typically to measure achievable download and upload TCP throughputs, users use internet speed tests which perform 10s of MB of TCP uploads and downloads. Unfortunately, such active measurements increase traffic load and if used regularly and for all the STAs can potentially disrupt user traffic, thereby worsening performance for other users in the network and draining the battery of mobile devices. This thesis enables a passive AP-side network analytics. Therefore, for performance monitoring, I consider that a monitoring framework will have access only to the logs of the AP that the manager controls. Further, I consider that there is no STA side co-operation and no access to STA side logs. As a result, the framework is constrained to make an estimate solely based on passive AP-side observables. In the first part of the thesis, I present virtual speed test, a measurement based framework that enables an AP to estimate speed test results for any of its associated clients solely based on AP-side observables. Virtual speed test employs a novel L2 edge TCP model to perform throughput estimation. We implemented virtual speed test using commodity hardware, deployed it in office and residential environments, and conducted measurements spanning multiple days having different network loads and channel conditions. Overall, virtual speed test has mean estimation error less than 10% compared to ground truth speed tests, yet with zero overhead, and outcomes available at the AP. Next, I present Uplink Latency Microscope (uScope), an AP-side framework for estimation of WLAN uplink latency for any of the associated STAs and decomposition into its constituent components. Similar to virtual speed test, uScope makes estimations solely based on passive AP-side observations. The key idea in uScope is to leverage the layer-4 handshake as a virtual probe to estimate and decompose layer-2 latency. We implement uScope on a commodity hardware platform and conduct extensive field trials on a university campus and in a residential apartment complex. In over 1 million tests, uScope demonstrates high estimation accuracy with mean estimation errors under 10% for all the estimated parameters.
Broadband Terahertz Signal Generation and Radiation Based on Direct Digital-to-Impulse Radiating Arrays in Silicon
(2018-04-16) Assefzadeh, Mahdi; Babakhani, Aydin; Knightly, Edward
Broadband terahertz (THz) signal generation and radiation has unique applications in 3-D hyper-spectral imaging, molecular sensing, and high-speed wireless communication. THz waves interact with the rotational and vibrational transitions of molecules with applications in material detection and biomedical sensing. They also penetrate through non-metallic and non-polar mediums that can be used to image concealed objects for security purposes. Conventional terahertz pulse generation techniques are based on the optical excitation of a III-V photoconductive antenna with a femtosecond optical laser pulse. This method of THz pulse generation and detection is widely used in THz time-domain spectroscopy systems. Although THz-TDS is a powerful technique, its dependence on bulky, expensive and power-hungry femtosecond lasers, optomechanical components, and costly photoconductive antennas compromises its speed, accessibility and scalability. In this dissertation, an on-chip laser-free direct digital-to-impulse (D2I) architecture is introduced that is capable of radiating a THz pulse by creating and exciting a broadband radiating resonator consisting of an on-chip antenna and a broadband matching network. This novel method converts a digital trigger edge to a radiated THz pulse with a high timing accuracy. A broadband matching network and an ON/OFF impulse-shaping technique are designed to maximize the amplitude of the pulse and minimize ringing. This method achieves a high DC-to-radiated efficiency by turning off the current switch shortly after turning it on. The deep nonlinear switching mechanism results in numerous harmonics from GHz to THz. Based on the high timing accuracy of the radiated THz pulses in D2I, a novel trigger-based beamforming architecture is introduced that enables broadband pulse beamforming in which all frequency content is steered simultaneously. This is in contrast with conventional phased-array architectures that have a limited bandwidth, where an RF signal is time-delayed. One of the main challenges of sampling a picosecond pulse in the time domain is ensuring that both the receiver and its antenna are broadband and have a linear phase response. Pyramidal horn antennas cannot be used to receive picosecond pulses, due to their limited bandwidth and nonlinear phase response. In addition, commercially available sampling oscilloscopes have a 3-dB bandwidth of less than 70 GHz, therefore cannot be used to sample a pulse with a FWHM of \textasciitilde 2 ps. To address this problem, we propose a direct time-domain measurement scheme based on femtosecond-laser-based THz sampling systems. Having a high-power, broadband frequency-comb source is critical in imaging and spectroscopy applications. By applying a periodic trigger signal, the D2I architecture radiates an impulse train in the time domain, which has a frequency-comb spectrum with a spacing of $1/T$. To perform spectroscopy, T can be controlled to sweep the whole spectrum. Further in this thesis, we will present our THz pulse radiating chips applied in imaging and spectroscopy experiments. This is the first time that a fully electronic chip is capable of generating and radiating harmonic tones at frequencies higher than 1 THz. Owing to the high scalability of the D2I architecture, combined with the broadband pulse beam-forming method, large arrays of D2I radiators can be built to radiate high-power, steerable narrow beams. In this thesis, ultra-short pulse radiating sources will be presented that were used to demonstrate laser-free broadband gas spectroscopy and THz imaging.
Distributed Low-Complexity Maximum-Throughput Scheduling for Wireless Backhaul Networks
(2007) Kabbani, Abdul; Salonidis, Theodoros; Knightly, Edward; Center for Multimedia Communications (http://cmc.rice.edu/)
We introduce a low-complexity distributed slotted MAC protocol that can support all feasible arrival rates in a wireless backhaul network (WBN). For arbitrary wireless networks, such a maximum throughput protocol has been notoriously hard to realize because (i) even if global topology information is available, the problem of computing the optimal link transmission set at each slot is NP-complete (ii) no bounds exist on the number of steps required for such a computation (per-slot overhead). For the logical tree structures induced by the WBN traffic matrices, we first introduce a centralized algorithm that solves the optimal scheduling problem in a number of steps at most linear in the number of nodes in the network. This is achieved by discovering and exploiting a novel set of graph-theoretical properties of the WBN contention graph. Guided by the centralized algorithm, we design a distributed protocol where, at the beginning of each slot, nodes coordinate and incrementally compute the optimal link transmission set. We then introduce an algorithm to compute the minimum number of steps to complete this computation, thus minimizing the per-slot overhead. Using both analysis and simulations, we show that in practice our protocol yields low overhead when implemented over existing wireless technologies and significantly outperforms existing suboptimal distributed slotted scheduling mechanisms.
Experimental Evaluation of AoA Estimation for UAV to Massive MIMO
(2023-04-19) Rice, Tarence; Knightly, Edward; Sabharwal, Ashutosh; Chi, Taiyun
Massive MIMO (multiple-input, multiple-output) base stations are widely used for wireless networks to deploy multiple antennas, increasing their quality, throughput, and radio link capacity. Unmanned aerial vehicles (UAV) are prevalent due to their low cost and ease of use. Unmanned aerial vehicles (UAV) are prevalent due to their low cost and ease of use, allowing for multiple use cases that provide telemetry information to civilian, commercial, and military applications. In particular, we implement a suite of Angle of Arrival (AoA) estimation algorithms exploring their performance for UAV communication networks. From the evaluation of the five AoA estimations, Beamscan offers a spatial, spectral response that enables us to analyze both secondary propagation paths and the most likely AoA, providing us with a complete picture of the environment. We discovered with convergence time that when under-sampled, the AoA estimator detects the multi-path with a higher normalized power, impacting the AoA estimate result. We estimated azimuth AoA via horizontal subarrays and its effects on the multi-path AoA estimates for hovering drones. We discovered the effects of Rice football stadium seats as we decreased the number of antennas. We find that when evaluating hovering drones' azimuth and elevation AoA estimation, elevation estimation yields a median error of 13.8\degree higher error than azimuth for the 5x5 antenna scenario. Evaluated was the performance of the 2-D Beamscan spatial spectrum estimator. It provides higher accuracy between the two different channels of azimuth and elevation. This work will inform system designers on specifications from AoA estimations when designing a Massive MIMO to drone network.
FALCON: Fine-Time-Measurement to Approach, Localize, and Track RF Targets via Drone Networks
(2020-04-23) Shaikhanov, Zhambyl; Knightly, Edward
We present FALCON, a novel mobile sensing system to approach, localize, and track RF targets via drone networks. We leverage existing Wi-Fi technology and its recent Fine Time Measurement (FTM) protocol to realize the first FTM sensing drones that can dynamically range targets in a mission. FALCON is also the first robotic system realizing FTM for autonomous navigation. In addition, we propose a new flight planning strategy to simultaneously approach and localize a target to enable higher resolution sensory measurements and to realize approaching-critical tasks in a mission in addition to localization and tracking. For that, we propose to jointly exploit drones' diversity of observation and dynamics of approaching the target, and dynamically adjust the intensities of approaching and observation based on a mission requirement. Our implementation of the flight planning strategy on custom FTM-enabled drones shows that FALCON achieves up to 2x localization accuracy gain compared to a baseline Bio-inspired approach, and in total spends 30% less time in localizing the target.
Feasibility of Passive Eavesdropping in Massive MIMO: An Experimental Approach
(2018-04-18) Yeh, Chia-Yi; Knightly, Edward
Massive MIMO systems have the potential for preventing passive eavesdropping as the signal transmitted by a large antenna array becomes highly focused. Prior works showed that passive eavesdropping becomes negligible when the number of BS antennas approaches to infinity in independent Rayleigh channel from a secrecy rate perspective. However, in practical massive MIMO systems, the number of BS antennas is in the order of a hundred, not infinity. Also, channels in the real world are not ideally independent. Furthermore, secrecy rate does not directly indicate whether a transmission can be decoded by the eavesdropper in practical wireless transmission. In this work, our analysis is based on real channel measurements from a 96-antenna ArgosV2 BS in 2.4 GHz band indoor environment with a LOS component. Instead of the asymptotic behavior, we focus on how the increasing number of BS antennas affect passive eavesdropping. Also, we propose to use the SNR difference between the intended user Bob and the eavesdropper Eve as a metric to determine how resistant to passive eavesdropping a system is. From our analysis based on real channel measurements, we find that increasing the number of antennas at the BS improves the ability of preventing passive eavesdropping, and a 96-antenna BS has the potential to prevent passive eavesdropping in the indoor LOS environment with careful power control. However, compared to the independent Rayleigh channel, indoor LOS environment is less passive-eavesdropping resistant under the same number of BS antennas. Furthermore, the marginal benefit of increasing an antenna in the indoor LOS environment decreases much faster than in the independent Rayleigh channel scenario.
Full-duplex Wireless with Large Antenna Arrays
(2015-12-03) Everett, Evan Jackson; Sabharwal, Ashutosh; Aazhang, Behnaam; Cox, Steven; Knightly, Edward; Kennedy, Timothy
To meet the growing demand for wireless data, base stations with very large antenna arrays are being deployed in order to serve multiple users simultaneously. Concurrently, there is growing interest in full-duplex operation. The challenge to full-duplex is suppressing the high-powered self-interference caused by transmitting and receiving at the same time on the same frequency. Unfortunately, the state-of-the-art methods to suppress self-interference require extra analog circuitry that does not scale well to large antenna arrays. However, large antenna arrays open a new opportunity to use digital beamforming to reduce the self-interference. In this thesis we study the use of digital beamforming to enable full-duplex operation on conventional antenna arrays. Unlike most designs that rely on analog cancelers to suppress self-interference, we consider all-digital solutions that can be employed on existing radio hardware.
Indelible Physical Randomness for Security: Silicon, Bisignals, Biometrics
(2014-11-11) Rostami, Masoud; Koushanfar, Farinaz; Wallach, Dan S; Knightly, Edward; Juels, Ari
In this thesis, I investigate the nature and properties of several indelible physical randomness phenomena. I leverage these indelible statistical properties to design robust and efficient security systems. Three different phenomena are discussed in this thesis: randomness in biosignals, silicon chips, and biometrics. In the first part, I present a system to authenticate external medical device programmers to Implantable Medical Devices (IMDs).IMDs have now built-in radio communication to facilitate non-invasive reprogramming, but lack well-designed authentication mechanisms, exposing patients to the risks of over-the-air attacks and physical harm. Our protocol uses biosignals for authentication mechanism, ensuring access only by a medical instrument in physical contact with an IMD-bearing patient. Based on statistical analysis of real-world data, I propose and analyze new techniques for extracting time-varying randomness from biosignals and introduce a novel cryptographic device pairing protocol that uses this randomness to protect against attacks by active adversaries, while meeting the practical challenges of lightweight implementation and noise tolerance in biosignals readings. In the second part, unavoidable physical randomness of transistors is investigated, and novel robust and low-overhead authentication, bit-commitment, and key exchange protocols are proposed. It will be meticulously shown that these protocols can achieve resiliency against reverse-engineering and replay attacks without a costly secure channel. The attack analysis guides us in tuning the parameters of the protocols for an efficient and secure implementation. In the third part, the statistical properties of fingerprint minutiae points are analyzed and a distributed security protocol will be proposed to safeguard biometric fingerprint databases based on the developed statistical models of fingerprint biometric.
Line-of-sight and non-line-of-sight links for dispersive terahertz wireless networks
(AIP Publishing LLC, 2021) Ghasempour, Yasaman; Amarasinghe, Yasith; Yeh, Chia-Yi; Knightly, Edward; Mittleman, Daniel M.
Despite the rapidly growing interest in exploiting millimeter and terahertz waves for wireless data transfer, the role of reflected non-line-of-sight (NLOS) paths in wireless networking is one of the least explored questions. In this paper, we investigate the idea of harnessing these specular NLOS paths for communication in directional networks at frequencies above 100 GHz. We explore several illustrative transmitter architectures, namely, a conventional substrate-lens dipole antenna and a leaky-wave antenna. We investigate how these high-gain directional antennas offer both new challenges and new opportunities for exploiting NLOS paths. Our results demonstrate the sensitivity to antenna alignment, power spectrum variations, and the disparity in supported bandwidth of various line-of-sight (LOS) and reflected path configurations. We show that NLOS paths can, under certain circumstances, offer even higher data rates than the conventional LOS path. This result illustrates the unique opportunities that distinguish THz wireless systems from those that operate at lower frequencies.
Location information from a receiver in a wireless network
(2024-08-27) Mittleman, Daniel; Knightly, Edward; Rice University; Brown University; United States Patent and Trademark Office
A multi-frequency wireless access device including a first waveguide having a pair of parallel metal plates with open sides and a slot in one of the metal plates, the slot permitting radiation to leak out, the leaked radiation illuminating a range of angles depending on frequency.
Measurement Driven Deployment of a Two-Tier Urban Mesh Access Network
(ACM Press, 2006-06-01) Camp, Joseph; Robinson, Joshua; Steger, Christopher; Knightly, Edward; Center for Multimedia Communications (http://cmc.rice.edu/)
Multihop wireless mesh networks can provide Internet access over a wide area with minimal infrastructure expenditure. In this work, we present a measurement driven deployment strategy and a data-driven model to study the impact of design and topology decisions on network-wide performance and cost. We perform extensive measurements in a two-tier urban scenario to characterize the propagation environment and correlate received signal strength with application layer throughput. We find that well-known estimates for pathloss produce either heavily overprovisioned networks resulting in an order of magnitude increase in cost for high pathloss estimates or completely disconnected networks for low pathloss estimates. Modeling throughput with wireless interface manufacturer specifications similarly results in severely underprovisioned networks. Further, we measure competing, multihop flow traffic matrices to empirically define achievable throughputs of fully backlogged, rate limited, and web-emulated traffic. We find that while fully backlogged flows produce starving nodes, rate-controlling flows to a fixed value yields fairness and high aggregate throughput. Likewise, transmission gaps occurring in statistically multiplexed web traffic, even under high offered load, remove starvation and yield high performance. In comparison, we find that well-known noncompeting flow models for mesh networks over-estimate network-wide throughput by a factor of 2. Finally, our placement study shows that a regular grid topology achieves up to 50 percent greater throughput than random node placement.
Metasurface-in-the-Middle Attacks: Wavefront Manipulation Threats and Countermeasures
(2024-04-18) Shaikhanov, Zhambyl; Knightly, Edward
Transcending the capabilities of traditional devices, metasurfaces offer nearly limitless control of the EM properties of wireless signals and have recently been shown to facilitate wireless communication with unique designs. However, in this thesis, I explore the security threats posed by malicious metasurfaces and demonstrate that, along with new opportunities, they bring forth unprecedented security challenges. In particular, I expose a new class of “MetaSurface-in-the-Middle” attacks, wherein malicious agent, Eve, can intercept pencil-beam directional links - conventionally believed to be immune from eavesdropping - with an almost imperceptible trace. By exploring the foundation of the attack in WLAN scenarios, I demonstrate that such malicious metasurfaces could be fabricated in under 5 minutes and at the cost of several cents. Furthermore, I study the attack with wireless backhaul links, which are crucial for many functions like low-latency financial trading on Wall Street. I show how Eve designs and employs MetaFly to covertly manipulate the EM wavefront on highly directional backhaul links, secretly inducing eavesdropping diffraction beams. I implement and demonstrate these attacks in both large indoor and outdoor rooftops in a metropolitan area, showcasing how Eve can intercept transmissions with nearly zero bit error rate while maintaining minimal impact on legitimate communication.
Multipath Multicarrier Misinformation to Adversaries
(2023-04-05) Liu, Zhecun; Knightly, Edward
Wireless channels are vulnerable to eavesdroppers due to their broadcast nature. One approach to thwart an eavesdropper (Eve) is to decrease her SNR, e.g., by reducing the signal in her direction. Unfortunately, such methods are vulnerable to (1) a highly directional Eve that can increase her received signal strength and (2) Eve that is close to the receiver, Bob, or close to the transmitter, Alice. In this paper, we design and experimentally evaluate Multipath Multicarrier Misinformation to Adversaries (M3A), a system for Alice to send data to Bob while simultaneously sending misinformation to Eve. Our approach does not require knowledge of Eve’s channel or location and, with multipath channels, randomly transforms Eve’s symbols even if Eve is located one wavelength-scale distance from Bob (approximately 10 cm) or if Eve is located between Alice and Bob in their direct path (Eve is approximately 1/3 closer to Alice). In particular, our approach is to move each of Eve’s received symbols (over time and across subcarriers), to an independently random transformation as compared to Bob, without Alice or Bob knowing Eve’s location or channel. We realize this by modulating Alice’s per-subcarrier beamforming weights with an i.i.d. random binary sequence, as if Alice had a separate antenna array for each subcarrier, and could randomly turn antennas in each array on and off. We implement M3A on a real-time Massive MIMO testbed, and show that M3A increases Eve’s bit error rate up to more than two hundredfold compared to beamforming, even if she is positioned approximately a wavelength away, whether above, below, or beside Bob. Finally, to ensure reliability at Bob, we show that with M3A, Bob’s bit error rate is approximately an order of magnitude lower than achieved with prior work.
Next-Generation Wireless Systems for Joint Communication and Sensing in Millimeter-Wave and Terahertz Spectrum
(2020-04-24) Ghasem Pour, Yasaman; Knightly, Edward
The use of mmWave and THz spectrum (30 GHz to 1 THz) for wireless communication is rapidly emerging as one the key paradigms for future (5G and beyond) wireless systems. mmWave/THz communication has the potential to realize an order of magnitude increase in data rates due to the availability of wide spectral bands. However, the increased propagation loss necessitate directional links which brings many challenges including user mobility, blockage, and scaling to dense user populations. This thesis presents design, implementation, and experimental evaluation of novel solutions for mobility adaptation and e cient multi-stream transmissions in mmWave and THz regime. The key idea is to exploit the wireless sensing capabilities of these higher frequencies to enhance directional communication. Namely, the mm-scale wavelength together with wide spectral band can potentially provide high-resolution sensing of user motion. Further, we can pack two order of magnitudes more antennas (i.e., potential \sensors") into the same form factor (compared to legacy 2.4 and 5 GHz bands) or exploit novel high-frequency steering devices that enhance sensing. In particular, in order to scale to dense user populations, I present the first efficient multi-stream beam training protocol for 60 GHz WLANs. I demonstrate how we can leverage channel sparsity, GHz-scale sampling rate, and the knowledge of mm-Wave RF codebook beam patterns to sense a set of beam pattern that can capture diverse or ideally orthogonal paths in order to obtain maximum stream separability. I then present the fi rst single-shot single-antenna motion sensing system in THz wireless networks that allows nodes to proactively adapt their highly directional beams under user mobility or blockage. Combined, these innovations address the key challenges of directional networking in mmWave and THz spectrum. This thesis builds the foundation for uni ed communication and sensing in future wireless technology.
Overhead Constrained Joint Adaptation of MCS, Beamwidth and Antenna Sectors for 60 GHz WLANs with Mobile Clients
(2015-10-27) Haider, Muhammad Kumail; Knightly, Edward
The 60 GHz frequency band, with its 7 GHz wide unlicensed spectrum, opens up avenues to multi-Gigabit communication. However, the extremely short wavelength (on the order of a few millimeters) results in very high path loss and little diffraction or scattering. To extend range, directional antennas or electronically steerable beam-arrays are used to get directivity gain. This makes links in 60 GHz networks inherently directional and this directivity introduces new challenges in terms of communication link establishment and maintenance. First, the beamwidth of the directional antennas plays an important role in determining the maximum rate, unlike in omni-directional networks. Moreover, 60 GHz links are susceptible to breakage due to misalignment and blockage due to their highly directional nature. In this thesis, I have designed, implemented and evaluated a novel cross-layer protocol, BeamRAP, for adapting the beamwidth of directional antennas and the data rate at the physical layer jointly in 60 GHz directional networks. This joint adaptation is necessary since beamwidth and alignment of directional antennas, are the key determinants of link strength and thereby the data rates. Moreover, misalignment of directional antennas due to nodal mobility or link blockage due to environmental mobility cannot be addressed by existing rate adaptation protocols. Therefore, in BeamRAP, I have implemented a new algorithm for beamwidth adaptation in response to the frequency of blockage and misalignment events, to maximize link throughput. I have also introduced new mechanisms for link breakage detection, and fast recovery to restore links without exhaustive search over all antenna sectors. I have also developed a 60 GHz programmable node and testbed using VubIQ 60 GHz transceivers with WARP baseband, and have conducted an extensive measurement study to collect signal strength traces over-the-air for various LOS, reflection and antenna-misalignment scenario. My experiments under multiple environmental and nodal mobility scenario show that BeamRAP achieves up to 2x gains in throughput as compared to a baseline 802.11ad scheme, which does not implement beamwidth adaptation.
Scaling 60 GHz WLANs: Creating and Identifying Opportunities for Multi-User Transmission
(2016-10-17) Ghasem Pour, Yasaman; Knightly, Edward
The millimeter scale carrier wavelength of the 60 GHz spectrum makes it feasible to pack two order of magnitudes more antennas into the same form factor compared to legacy bands (i.e. 2.4 and 5 GHz band). Prior works in 60 GHz have exploited this large antenna arrays to enhance the link budget of a single user transmission, which suffers from high path loss in 60 GHz. We are proposing a scalable multi-user scheme in 60 GHz WLANs in order to serve multiple clients with multi-Gbps data rate simultaneously in the same environment using the same frequency channel. To this end, we first propose a scalable beam training protocol, which tracks the users for directional transmissions. Then we have designed and evaluated incremental policies that add clients to a transmission sequentially until the AP's resources are exhausted or client link budgets, including interference, are exceeded. We further target polarization diversity and non-uniform antenna partitioning as mechanisms to dramatically reduce inter-stream interference enabling vastly improved aggregate rate. At lower bands, multi-user aggregation is typically achieved by zero-forcing inter-user interference via sender-side digital pre-coding using channel state information at the source. Unfortunately, such techniques do not scale to 60 GHz since (i) 60 GHz transmission is highly directional and lacks the rich scattering propagation environment assumed for most prior work; (ii) even efficient mechanisms for CSIT collection do not scale to large antenna arrays; (iii) prior techniques employ a large number of radio frequency chains (up to one per antenna) which are not feasible in our scenario. Our experiments through over-the-air testbed built over WARP platform and trace-driven simulations show that our methodology can achieve performance near to that of exhaustive search of all possible client combinations, yet with substantially less overhead.
Security of Angularly Dispersive Terahertz Links
(2022-01-07) Yeh, Chia-Yi; Knightly, Edward
Angularly dispersive links are characterized by frequency-dependent radiation direction. In practice, this property manifests from wide bandwidths, as are expected in the terahertz (THz) regime, and from antenna structures such as the leaky-wave antenna (LWA). To date, angular dispersion has been shown to enable beam steering and path discovery, both are critical for establishing directional THz links. While angular dispersion provides new opportunities for THz communications, it also introduces new security threats. Namely, with angular dispersion, to send a wider band transmission from the transmitter Alice to the receiver Bob necessarily expands the spatial footprint of the transmission, potentially aiding an eavesdropper Eve. This thesis presents the first security study of THz angularly dispersive links using LWAs via a mix of analytical models and over-the-air experiments. In the first part of the thesis, I consider the threat of a same-distance Eve in the line-of-sight (LoS) scenario and study the unique security properties of angularly dispersive links. I show via both models and experiments that the LWA’s angle-frequency coupling leads to non-uniform secrecy capacity across sub-channels yielding advantages to an eavesdropper at edge frequencies. Yet, because different frequencies emit energy at different angles, the eavesdropper is thwarted from easily intercepting an entire wideband transmission. The experiments diverge from the analytical model in that the model underpredicts the eavesdropper’s advantage at angles smaller than the target user and subsequent asymmetric performance across angles. Nonetheless, both the model and measurements show that increasingly wide bandwidth and correspondingly wide beams have only a modest marginal security penalty. Next, I study secure coding strategies for angularly dispersive links via two representative secure coding strategies, termed I-SCADL (Independent Secure Coding for Angular Dispersive Links) and J-SCADL (Joint SCADL), with the former must code each frequency channel independently while the latter allows joint coding across frequency channels. I show that, due to angular dispersion, the independently-coded strategy, I-SCADL, results in a notable insecure region expansion both angularly and radially as the transmission band widens, whereas the joint coding strategy, J-SCADL, can effectively alleviate the secrecy degradation with increasing bandwidth as it exploits the a priori known non-uniformity across the frequency channels. The experimental results further demonstrate the advantage of J-SCADL over I-SCADL under beam asymmetry and irregularities as J-SCADL can preserve secrecy when Eve receives strong side lobes only in a subset of frequency channels. Nonetheless, for angularly dispersive links, even with J-SCADL, we find the insecure area expands with bandwidth due to the associated emission angle difference. Yet, we also find that the insecure area growth due to increasing bandwidth is significantly smaller compared to other factors including a wider single-tone beamwidth or a higher secrecy coding rate, suggesting that the security concern for angularly dispersive links under larger bandwidth is minor as long as proper secure coding strategy, such as J-SCADL, is employed.
Wirelessly Powered Sensor Design with On-Chip Antenna in CMOS Technology
(2019-09-23) Sun, Yuxiang; Babakhani, Aydin; Knightly, Edward
In recent years, we have experienced a significant growth of the Internet of Things (IoT), wireless sensor network (WSN) and bio-implantable devices. There are 7 billion of IoT devices in use in 2018, which starts to surpass the number of the mobile devices. To extend the next level of connectivity from smart phone or tablet to each of the everyday objects, a battery-less small-footprint low-cost IoT circuit with sensing, computation and communication capability is critical for the advancement of the applications. In this thesis, to eliminate the need of battery and miniaturize the system size to millimeter scale, wireless power harvesting front-end with on-chip antenna is utilized to extend the operating distance. The operating frequency of the wireless power link is optimized for mm-sized on-chip antenna to minimize the device size and to achieve a higher received rectified power. Moreover, for wirelessly-powered transmitter design, a frequency-division scheme is adopted to solve the self-interference issue in conventional Radio-Frequency Identification (RFID) system. A duty cycle operation of the circuit is also proposed by utilizing power management unit, which reduces the minimum required harvested power for more power-hungry applications. Based on these methodologies, several wireless-powered CMOS circuits are implemented and tested for different applications. The first chip is a wirelessly-powered dielectric sensor with the size of 3.9 by 0.7mm2. It can detect the dielectric constant of different materials such as oil and epoxy shown on top of the chip. The second chip is targeted for absorption spectroscopy application by using a wirelessly-powered injection-locked oscillator to achieve wide tuning range from 4 to 5 GHz. The third chip is a millimeter sized wirelessly-powered pH sensor together with customized IrOx sensing electrode. The pH sensor transmits a pH-sensitive frequency signal that is converted from the sensed electrode reduction potential. In addition to sensor applications, a wirelessly-powered transmitter with on-chip antenna in 180 nm CMOS is designed, which achieves a data-rate up to 50 Mbps with on-off key modulation scheme. Moreover, a wirelessly-powered miniaturized pacemaker chip in 180 nm CMOS process is also implemented. The total size of the pacemaker chip with PCB package is 16 by 3.8mm2. The in-vivo experiment is demonstrated successfully on a live pig heart, that the heart rate can be tuned from 100 bpm to 172 bpm by the changing the stimulation from the chip.

Browsing by Author "Knightly, Edward"

Results Per Page

Sort Options