<p>We examine the robust downlink beamforming design from the point of outage probability constraint. We further reason that since the estimated downlink channel correlation (DCC) matrices form a manifold in the signal space, the estimation error should be measured in terms of Riemannian distance (RD) instead of the commonly used Euclidean distance (ED). Applying this concept of measure to our design constraint, we establish approximated outage probability constraints using multidimensional ball set and multidimensional cube set. We transform the design problem into a convex optimization problem which can be solved efficiently by standard methods. Our proposed methods apply to both Gaussian distribution assumption and uniform distribution assumption. Simulation results show that the performance of our design is superior to those of other robust beamformers recently developed.</p> / Master of Applied Science (MASc)

No / Beamforming is used to achieve diversity gain. It is a technique in diversity to remedy power penalty due to channel fading. The beam-weights for multi-antenna system are evaluated for two different approaches. These weights are then used to weight the signal beams of each transmit antenna branch. Results reveal that by exploiting the transmit channel substructures exposed by the singular vector decomposition algorithm, the capacity of a multi-antenna system can be enhanced.

Optimum filter-and-sum beamforming is useful for array systems that suffer from spatially correlated noise and interference over large bandwidth. The set of finite impulse response (FIR) filter coefficients used to implement the optimum filter-and-sum beamformer are selected to optimize signal-to-noise ratio (SNR) and reduce interference from the certain directions. However, these array systems may also be vulnerable to dispersion caused by physical components such as antennas and cables, especially when the dispersion is unequal between sensors. The unequal responses can be equalized by using FIR filters. Although the problems of optimum-SNR beamforming, interference mitigation, and per-sensor dispersion have previously been individually investigated, their combined effects and strategies for mitigating their combined effects do not seem to have been considered. In this dissertation, combination strategies for optimum filter-and-sum beamforming and sensor dispersion correction are investigated. Our objective is to simultaneously implement optimum filter-and-sum beamforming and per-sensor dispersion correction using a single FIR filter per sensor. A contribution is to reduce overall filter length, possibly also resulting in a significant reduction in implementation complexity, power consumption, and cost. Expressions for optimum filter-and-sum beamforming weights and per-sensor dedispersion filter coefficients are derived. One solution is found via minimax optimization. To assess feasibility, the cost is analyzed in terms of filter length. These designs are considered in the context of LWA1, the first ``station'' of the Long Wavelength Array (LWA) radio telescope, consisting of 512 bowtie-type antennas and operating at frequencies between 10 MHz and 88 MHz. However, this work is applicable to a variety of systems which suffer from non-white spatial noise and directional interference and are vulnerable to sensor dispersion; e.g., sonar arrays, HF/VHF-band riometers, radar arrays, and other radio telescopes. / Ph. D.

A new technique to de-Dopplerize microphone signals from moving sources of sound is derived. Currently available time domain de-Dopplerization techniques require oversampling and interpolation of the microphone time data. In contrast, the technique presented in this dissertation performs the de-Dopplerization entirely in the frequency domain eliminating the need for oversampling and interpolation of the microphone data. As a consequence, the new de-Dopplerization technique is computationally more efficient. The new de-Dopplerization technique is then implemented into a frequency domain beamforming algorithm to locate moving sources of sound. The mathematical formulation for the implementation of the new de-Dopplerization technique is presented for sources moving along a linear trajectory and for sources moving along a circular trajectory, i.e. rotating sources. The resulting frequency domain beamforming method to locate moving sound sources is then validated using numerical simulations for various source configurations (e.g. emission angle, emission frequency, and source velocity), and different processing parameters (e.g. time window length). Numerical datasets for sources with linear motion as well as for rotating sources were simulated. For comparison purposes, selected datasets were also processed using traditional time domain beamforming. The results from the numerical simulations show that the frequency domain beamforming method is at least 10 times faster than the traditional time domain beamforming method with the same performance. Furthermore, the results show that as the number of microphones and/or grid points increase, the processing time for the traditional time domain beamforming method increases at a rate 20 times larger than the rate of increase in processing time of the new frequency domain beamforming method. / Ph. D.

The huge advancement in the textiles industry and the accurate control on the mechanization process coupled with cost-effective manufacturing offer an innovative environment for new electronic systems, namely electronic textiles. The abundance of fabrics in our regular life offers immense possibilities for electronic integration both in wearable and large-scale applications. Augmenting this technology with a set of precepts and a simulation environment creates a new software/hardware architecture with widely useful implementations in wearable and large-area computational systems. The software environment acts as a functional modeling and testing platform, providing estimates of design metrics such as power consumption. The construction of an electronic textile (e-textile) hardware prototype, a large-scale acoustic beamformer, provides a basis for the simulator and offers experience in building these systems. The contributions of this research focus on defining the electronic textile architecture, creating a simulation environment, defining a networking scheme, and implementing hardware prototypes. / Ph. D.

The Eight-meter-wavelength Transient Array (ETA) system is a unique implementation of an array-based radio telescope. The instrument is designed to further astronomy by detecting and characterizing dispersed pulses received between 29–47 MHz. To aid data processing of radio signals received through 24 antennas, the ETA system performs real-time stream processing as data is passed from antennas to hard disk storage. The processing includes digital sampling, downconversion, filtering, Fast Fourier Transforms, and beamforming operations and is performed by 28 commercial-off-the-shelf (COTS) FPGA boards. Sixteen of the FPGA boards constitute the reconfigurable computing cluster (RCC) which performs the FFT and beamforming operations and is the focus of this thesis. The FPGA-based architecture allows the RCC to provide the high computational and communication throughput required by the ETA system. In addition, the FPGA design allows for a custom processing data path, parallel processing, global synchronization, and rapid development at a low cost. / Master of Science

The proliferation of connected embedded devices has driven wireless communications into commercial, military, industrial, and personal systems. It is unreasonable to expect privacy and security to be inherent in these networks given the spatial density of these devices, limited spectral resources, and the broadcast nature of wireless communications systems. Communications for these systems must have sufficient information capacity and secrecy capacity while typically maintaining small size, light weight, and minimized power consumption. With increasing crowding of the electromagnetic spectrum, interference must be leveraged as an available resource. This work develops a new beamforming method for direction-dependent modulation that provides wireless communications devices with enhanced physical layer security and the ability to simultaneously communicate and harvest energy by exploiting co-channel interference. We propose a method that optimizes a set of time-varying array steering vectors to enable direction-dependent modulation, thus exploiting a new degree of freedom in the space-time-frequency paradigm. We formulate steering vector selection as a convex optimization problem for rapid computation given arbitrarily positioned array antenna elements. We show that this method allows us to spectrally separate co-channel interference from an information-bearing signal in the analog domain, enabling the energy from the interference to be diverted for harvesting during the digitization and decoding of the information-bearing signal. We also show that this method provides wireless communications devices with not only enhanced information capacity, but also enhanced secrecy capacity in a broadcast channel. By using the proposed method, we can increase the overall channel capacity in a broadcast system beyond the current state-of-the-art for wireless broadcast channels, which is based on static coding techniques. Further, we also increase the overall secrecy capacity of the system by enabling secrecy for each user in the system. In practical terms, this results in higher-rate, confidential messages delivered to multiple devices in a broadcast channel for a given power constraint. Finally, we corroborate these claims with simulation and experimental results for the proposed method. / PHD

Multi-antenna systems with resource allocation based on transmit and receive precoding matrices have proven to enhance the spectral efficiency of cellular systems. In this thesis, we extend these concepts to a spectrum sharing system with primary users and secondary users. The spectrum sharing area is modeled as an array of transmit and receive antennas, with the transmit power constraint defined as a function of the interference threshold of the primary user. The area covered by a database enabled spectrum access system is represented as spatial bins, which are regions of predefined sizes. Each bin is assumed to have a single secondary user base station and all the resources of that bin (i.e., available frequencies, transmit power, etc.) are consumed by this secondary user in that bin. With these assumptions, the service area of the database can be represented by a grid of secondary users. Such a grid of secondary users forms a array of transmit antennas with secondary users in each bin. Furthermore, the set of bins with its secondary users at the edge of the exclusion zone of the primary user are assumed to create an array of receive antennas. These receive antennas act as sensors that will measure the interference power at the edge of the exclusion zone of the primary users. So the overall system of secondary user base station transmit and receive antennas can be modeled as a multi-element antenna array system. A regulatory interference threshold (I_th) is defined for protection of the primary user at the edge of exclusion zones. This interference threshold is used by the resource allocation algorithms in the spectrum access system to calculate the transmit and receive precoding matrices for the secondary user antenna array. Using multiple-input multiple-output theory, the receive antenna array will measure the interference from the transmit antenna array and a feedback mechanism will update the resource allocation to keep the power at the receive array below the interference threshold of the primary user. For each array, the transmit/receive matrix is a beamforming vector which consists of a set of weights, one for each antenna. Furthermore, a codebook-based strategy is used by the spectrum access system database to choose a transmit matrix from the codebook which minimizes the interference at the primary user. The overall spectrum sharing system can be represented by a model based on four design parameters, namely, Δ = (I_th, P, V, B), where P is the transmit power constraint, V are the transmit and receive beamforming matrices, and B is the matrix with active secondary user base stations of the antenna array or the quality of service level of the secondary users. The Δ parameter is called the system index of the spectrum sharing system. We apply the multi-antenna model to the challenging problem of spectrum sharing where the primary users operational parameters, such as transmit power levels, waveform types, and service modes, can change with time. Moreover, there are several types of primary users in different bands. Most of these users are federal government systems and their operational parameters are not available to the spectrum access system database. Our framework is useful in sharing spectrum with federal primary users, since only the interference threshold is needed for sharing their bands. Furthermore, we quantify the uncertainty in the availability of these bands for secondary users and the variations in achievable capacity with sharing spectrum in these bands. / Ph. D. / The goal of this thesis is to build a Protected Shared Access Model (PSAM) through database enabled Spectrum Access System (SAS). A model for the SAS is proposed, which is based on our vision for the SAS as a more dynamic and responsive architecture as a geolocation database than the current TVWS database. Major functions and capabilities of the model include, calculations of exclusion zone (EZ) of primary users with different operational parameters, use interference estimation techniques for predicting interference levels that will be generated by the new secondary users (SUs) and existing systems operating in the database service area, allocate location based transmit power levels and provide an algorithm for communications among the PUs, SUs, and the SAS to implement management and authorization framework of spectrum resources to different types of SUs. The selection of a propagation model is of utmost importance in spectrum sharing studies. Existing literature on EZs with simplified propagation models does not consider the effect of LOS interference between the PU to SU link and SU to PU link on peak points in the terrain area around the PU. The use of a terrain profile based model captures the essence of propagation over irregular terrain. Terrain regions that are far away from the PU may have a LOS between the PU and SU. So its not only the nearest area where the PU/SU can get interference, but interference is present from areas further away on high grounds having a direct LOS with the PU antenna. The exclusion zone computation with terrain profile based propagation model captures this effect, and it is the same effect that makes the shape of the exclusion zone irregular. So the propagation model used in spectrum sharing studies must be able to use the terrain for the specific geographical area for precise propagation calculations, and provide statistical reliability parameters for the computed propagation values for area of interest. For a multi-tier shared access model with incumbent access (IA) users, priority access (PA) users and general authorized access (GAA) users. The SU interference tolerance thresholds varies by the type of SU's i-e., PA users like public safety systems and mission critical users have low tolerance for interference and hence need to operate further from the PU. While GAA users like commercial broadband systems have higher interference tolerances and can operate closer to the PU. This multi-tier shared access model requires varying levels of interference protection from PU, that can be provided with multiple exclusion zones defined for different types of SU's. We propose the concept of differential spectrum access hierarchy, and define it in the context of a multi-tiered EZs that are based on quantiles of tolerable interference levels for different tiers of SUs. We also quantify and show the gain in SU capacity (or throughput) obtained by using multi-tiered EZs for different tiers of SUs. Using simulation results, we show that the size of EZs can be significantly reduced with the use of a terrain profile-based propagation model that takes into account terrain profile for signal attenuation between PUs and SUs in the P2P link. The exclusion zones involve the use of interference test points at the circumference of the protection contour of the PU. They are monitoring test points that the SAS uses with a propagation model and locations of SUs to calculate interference. Consider a model of Figure 5.1, the coexistence environment with PU, SU and the SAS with a database. As more SUs enter the system, their transmit powers creates interference for the PUs. In the event of SU interference exceeding a predefined threshold level at any of the test points, the SAS uses an interference based power control algorithm to turnoff the nearest dominant interferer's. Turning off the dominant interferers eliminates interference generated by that node at the PU. This nearest node interference cancellation significantly reduces the outage probability at the PU. Unlike existing metrics for spectrum utilization efficiency that considers separate metrics for PU interference protection and maximum use of the band for secondary use, we define a new metric for spectrum utilization efficiency. This metric uses utility functions and cost functions to measure the impact of secondary use of the spectrum on PUs as well as the degree of satisfaction SUs can achieve from reuse of such spectrum. The new spectrum utilization metric is used to evaluate tradeoffs between interference protection of PUs and SU spectrum utilization.

The usage of Unmanned Aerial Systems (UASs), such as quadcopters and hexacopters, has steadily increased over the past few years in both recreational and commercial use. This increased availability to purchase such systems has also given rise to many safety and security concerns. A common concern is that the misuse of a UAS can cause damage to airplanes and helicopters in and around airports. Another growing concern is the use of UASs for terrorist intentions such as using the UAS as a remote controlled bomb. There is clearly a need to be able to detect the presence of unwanted UASs in restricted areas. This thesis work presents the beginning work towards a method to detect the presence of these UASs using the blade pass frequency (BPF) of the motors and rotors of a home made quadcopter. A low cost uniform linear microphone array is first used to perform a simple delay-and-sum beamformer to spatially filter out noise sources. The beamformer output is then divided into sub-bands using three bandpass filters centered on the expected location of the fundamental BPF and its 2nd and 3rd harmonics. For each sub-band, an adaptive filter called an adaptive line enhancer is used to extract and enhance the narrowband signals. The response of the adaptive filters are then used to detect the quadcopter by looking for the presence of the 2nd and 3rd harmonics of the fundamental BPF. Static tests of the quadcopter out in a field showed promising results for this method with the ability to detect up to the 3rd harmonic 90ft away and the 2nd harmonic 130 ft away. / Master of Science / The usage of Unmanned Aerial Systems (UASs), such as quadcopters and hexacopters, has steadily increased over the past few years in both recreational and commercial use. This increased availability to purchase such systems has also given rise to many safety and security concerns. A common concern is that the misuse of a UAS can cause damage to airplanes and helicopters in and around airports. Another growing concern is the use of UASs for terrorist intentions such as using the UAS as a remote controlled bomb. There is clearly a need to be able to detect the presence of unwanted UASs in restricted areas. This thesis work presents the beginning work towards a method to detect the presence of a home made quadcopter based on the sound it produces. A series of microphone are first used to remove surrounding sounds that could interfere with the quadcopter’s sound. The output of this processes is then divided into smaller sections using three filters centered on the expected location of the most important and information rich parts of the quadcopter’s sound. For each section, a final filter is used to extract and enhance the signals of interest produced by the quadcopter. The response of these filters are then used to detect whether the quadcopter is present or not. Static tests of the quadcopter out in a field showed promising results for this method with the ability to detect the quadcopter 90 to 130 ft away.

The blind source separation problem has received a great deal of attention in previous years. The aim of this problem is to estimate a set of original source signals from a set of linearly mixed signals through any number of signal processing techniques. While many methods exist that attempt to solve the blind source separation problem, a new technique is being used that uniquely separates audio sources as they are received from a microphone array. In this thesis a new algorithm is proposed that that utilizes the ICA algorithm in conjunction with a filtering technique that separates source signals and then removes sources of interference so that a signal of interest can be accurately tracked. Experimental results will compare a common blind source separation technique to the new algorithm and show that the new algorithm can detect a signal of interest and accurately track it as it moves through an anechoic environment. / Master of Science