This thesis proposes and analyzes data fusion algorithms that operate on the physical layer of a wireless sensor network, in the context of three applications of cognitive radios: 1. Cooperative spectrum sensing via binary consensus; 2. Multiple transmitter localization and communication footprint identification; 3.Target self-localization using beacon nodes. For the first application, a co-phasing based data combining scheme is studied under imperfect channel knowledge. The evolution of network consensus state is modeled as a Markov chain, and the average transition probability matrix is derived. Using this, the average hitting time and average consensus duration are obtained, which are used to determine and optimize the performance of the consensus procedure. Second, using the fact that a typical communication footprint map admits a sparse representation, two novel compressed sensing based schemes are proposed to construct the map using 1-bit decisions from sensors deployed in a geographical area. The number of transmitters is determined using the K-means algorithm and a circular fitting technique, and a design procedure is proposed to determine the power thresholds for signal detection at sensors. Third, an algorithm is proposed for self-localization of a target node using power measurements from beacon nodes transmitting from known locations. The geographical area is overlaid with a virtual grid, and the problem is treated as one of testing overlapping subsets of grid cells for the presence of the target node. The column matching algorithm from group testing literature is considered for devising the target localization algorithm. The average probability of localizing the target within a grid cell is derived using the tools from Poisson point processes and order statistics. This quantity is used to determine the minimum required node density to localize the target within a grid cell with high probability. The performance of all the proposed algorithms is illustrated through Monte Carlo simulations.

<p dir="ltr">Rapid evolution in wireless technology and the increasing demand for high bandwidth communication for 5G/6G and the Internet of Things (IoT) have necessitated a growing number of components in radio front-end modules in an increasingly overcrowded radio frequency (RF) spectrum. Low-cost ad-hoc radios have drawn consumer interest, enabling new devices like microelectromechanical (MEMS) resonators for on-chip clocking, frequency-selective filters, RF signal processing, and spectral sensing for their small footprint and low power consumption. Gallium nitride (GaN) is an attractive electromechanical material due to its high coupling coefficient, acoustic velocity, and low viscoelastic losses. These benefits enable high-Q MEMS resonators in GaN monolithic microwave integrated circuits (MMICs) with scaling capability up to mm-wave frequencies, making this technology platform a contender for high-performance programmable radios in RF/mm-wave, sensors for harsh environments, and information processing in quantum systems.</p><p dir="ltr">The bias-dependent control mechanism of the 2D electron gas (2DEG) in GaN heterostructures can be exploited to design different switchable and tunable devices for reconfigurable MEMS components. This work presents, for the first time, a comprehensive study of the electromechanical performances of different transduction mechanisms in switchable GaN MEMS resonators. A unique OFF-state shunt design, where the 2DEG in an AlN/GaN heterostructure is utilized to control electromechanical transduction in Lamb mode resonators, is also experimentally demonstrated in this work. To make a valid comparison among switchable transducers, equivalent circuit models are developed to extract key parameters from the measurements by fitting them in both ON and OFF states. The switchable transducer with Ohmic interdigitated transducers (IDTs) and Schottky control gate shows superior performance among the designs under consideration with complete suppression of the mechanical mode in the OFF state and a maximum frequency-quality factor product of 5x10¹²s^-1 and a figure-of-merit of 5.18 at 1GHz in the ON state.</p><p dir="ltr">Over the past few years, there have been numerous efforts to scale the frequencies of MEMS devices in the GaN platform towards mm-wave frequencies. However, challenges remain due to the multi-layer thick buffer, typical in the growth of GaN epilayer on a substrate. This work presents the investigation of SweGaN QuanFINEbuffer-free and ultrathin GaN-on-SiC for the performance of surface acoustic wave (SAW) devices beyond 10GHz. Finite element analysis (FEA) is performed to find the range of frequencies for the Sezawa mode in the structure. Transmission lines and resonators are designed, fabricated, and characterized. Modified Mason circuit models are developed for each class of devices to extract critical performance metrics and benchmark with the state-of-the-art and theoretical limits for GaN. Sezawa modes are observed at frequencies up to 14.3GHz, achieving a record high in GaN MEMS to the best of our knowledge. A maximum piezoelectric coupling of 0.61% and frequency-quality factor product of 6x10¹²s^-1 are achieved for Sezawa resonators at 11GHz, with a minimum propagation loss of 0.26dB/λ for the two-port devices. The devices also exhibit high linearity with input third-order intercept points (IIP3) of 65dBm at 9GHz.</p><p dir="ltr">This work also investigates tunable acoustoelectric (AE) devices in the QuanFINE platform, leveraging its inherent 2DEG in the AlGaN/GaN heterostructure. Using 9.7GHz Sezawa mode acoustic delay lines, we report the highest frequency of AE in GaN to date. Active and passive AE devices are designed for voltage-dependent non-reciprocity and propagation loss without modification to the standard process for the High Electron Mobility Transistors (HEMTs) in MMICs. Drain/source Ohmic contacts control the drift velocity of the 2DEG, and the Schottky gate modulates 2DEG carrier concentration, resulting in a 30dB/cm separation between forward and reverse acoustic waves for a 2.56kV/cm lateral DC electric field and a maximum change in propagation loss of 50dB/cm for -5V DC at the control gate, respectively. The QuanFINEtechnology with AlGaN/GaN heterostructure enables a platform for switchable MEMS resonators and tunable acoustoelectric devices in MMICs for reconfigurable front end approaching mm-wave frequencies.</p>

Cognitive Radios are emerging communication systems which efficiently utilize the unused licensed radio spectrum called spectral holes. They run Spectrum sensing algorithms to identify these spectral holes. These holes need to be identified at very low SNR (<=-20 dB) under multipath fading, unknown channel gains and noise power. Cooperative spectrum sensing which exploits spatial diversity has been found to be particularly effective in this rather daunting endeavor. However despite many recent studies, several open issues need to be addressed for such algorithms. In this thesis we provide some novel cooperative distributed algorithms and study their performance. We develop an energy efficient detector with low detection delay using decentralized sequential hypothesis testing. Our algorithm at the Cognitive Radios employ an asynchronous transmission scheme which takes into account the noise at the fusion center. We have developed a distributed algorithm, DualSPRT, in which Cognitive Radios (secondary users) sequentially collect the observations, make local decisions and send them to the fusion center. The fusion center sequentially processes these received local decisions corrupted by Gaussian noise to arrive at a final decision. Asymptotically, this algorithm is shown to achieve the performance of the optimal centralized test, which does not consider fusion center noise. We also theoretically analyze its probability of error and average detection delay. Even though DualSPRT performs asymptotically well, a modification at the fusion node provides more control over the design of the algorithm parameters which then performs better at the usual operating probabilities of error in Cognitive Radio systems. We also analyze the modified algorithm theoretically. DualSPRT requires full knowledge of channel gains. Thus we extend the algorithm to take care the imperfections in channel gain estimates. We also consider the case when the knowledge about the noise power and channel gain statistic is not available at the Cognitive Radios. This problem is framed as a universal sequential hypothesis testing problem. We use easily implementable universal lossless source codes to propose simple algorithms for such a setup. Asymptotic performance of the algorithm is presented. A cooperative algorithm is also designed for such a scenario. Finally, decentralized multihypothesis sequential tests, which are relevant when the interest is to detect not only the presence of primary users but also their identity among multiple primary users, are also considered. Using the insight gained from binary hypothesis case, two new algorithms are proposed.

Motivated by the increasing demand for higher data rates, coverage, and spectral efficiency, current and next generation wireless systems adapt transmission parameters and even who is being transmitted to, based on the instantaneous channel states. For example, frequency-domain scheduling(FDS) is an instance of adaptation in orthogonal frequency division multiple access(OFDMA) systems in which the base station opportunistically assigns different subcarriers to their most appropriate user. Likewise ,transmit antenna selection(AS) is another form of adaptation in which the transmitter adapts which subset of antennas it transmits with. Cognitive radio(CR), which is a next generation technology, itself is a form of adaptation in which secondary users(SUs) adapt their transmissions to avoid interfering with the licensed primary users(PUs), who own the spectrum. However, adaptation requires channel state information(CSI), which might not be available apriori at the node or nodes that are adapting. Further, the CSI might not be perfect due to noise or feedback delays. This can result in suboptimal adaptation in OFDMA systems or excessive interference at the PUs due to transmissions by the SUs in CR. In this thesis, we focus on adaptation techniques in current and next generation wireless systems and evaluate the impact of CSI –both perfect and imperfect –on it. We first develop a novel model and analysis for characterizing the performance of AS in frequency-selective OFDMA systems. Our model is unique and comprehensive in that it incorporates key LTE features such as imperfect channel estimation based on dense, narrow band demodulation reference signal and coarse, broad band sounding reference signal. It incorporates the frequency-domain scheduler, the hardware constraint that the same antenna must be used to transmit over all the subcarriers that are allocated to a user, and the scheduling constraint that the allocated subcarriers must all be contiguous. Our results show the effectiveness of combined AS and FDS in frequency-selective OFDMA systems even at lower sounding reference signal powers. We then investigate power adaptation in underlay CR, in which the SU can transmit even when the primary is on but under stringent interference constraints. The nature of the interference constraint fundamentally decides how the SU adapts its transmit power. To this end, assuming perfect CSI, we propose optimal transmit power adaptation policies that minimize the symbol error probability of an SU when they are subject to different interference and transmit power constraints. We then study the robustness of these optimal policies to imperfections in CSI. An interesting observation that comes out of our study is that imperfect CSI can not only increase the interference at the PU but can also decrease it, and this depends on the choice of the system parameters, interference, and transmit power constraints. The regimes in which these occur are characterized.

This dissertation is a historical evaluation of the movement of the English courts from the doctrine of pith and marrow to the Catnic test in the determination of non-textual infringement of patents. It considers how and why the doctrine was replaced with the Catnic test. It concludes that this movement occurred as a result of the adoption by a group of judges of literalism in the construction of patents while another group dissented and maintained the correct application of the doctrine. Although the Court of Appeal and the House of Lords initially approved the literalist approach, they, after realising its untennability, adopted the dissenters’ approach, but, ultimately, adopted the Catnic test in which features of the dissenters’ approach were included. The dissertation concludes that the doctrine of pith and marrow, correctly applied, should have been retained as the Catnic test creates uncertainty and confusion. / Mercantile Law / LL.M.

This dissertation is a historical evaluation of the movement of the English courts from the doctrine of pith and marrow to the Catnic test in the determination of non-textual infringement of patents. It considers how and why the doctrine was replaced with the Catnic test. It concludes that this movement occurred as a result of the adoption by a group of judges of literalism in the construction of patents while another group dissented and maintained the correct application of the doctrine. Although the Court of Appeal and the House of Lords initially approved the literalist approach, they, after realising its untennability, adopted the dissenters’ approach, but, ultimately, adopted the Catnic test in which features of the dissenters’ approach were included. The dissertation concludes that the doctrine of pith and marrow, correctly applied, should have been retained as the Catnic test creates uncertainty and confusion. / Mercantile Law / LL. M.