Light, as a medium for communication, has the unique ability to transmit volumes of data with minimal energy loss. This capability not only sparked the revolution of internet-based communication over fiber optic networks, but also holds the potential to expand computing beyond our current capabilities. At present, data is stored densely in computer chips, but is sent out of the chip through centimeter-long electrical wires in a slow and energy-intensive process, before finally interfacing with optical transmitters. To bypass this bottleneck, electrical channels can be condensed and converted into light over a compact area using integrated photonic chips. In particular, the silicon photonics technology platform offers the potential for extremely dense data communications due to its high confinement waveguides and compact micro-resonators. However, three major obstacles stand in the way of realizing a low-energy and bandwidth-dense implementation of this technology: the integration of photonics with electronics, optical coupling from the photonic chip to fiber, and scaling up link architectures to multiplex data streams onto many wavelengths. The work in this thesis aims to confront these three challenges and advance integrated photonics technology to unprecedented bandwidth densities and energy efficiencies, with a focus on the first challenge of photonic-electronic integration. It begins with an overview of the escalating demand for inter-chip bandwidths and the potential solution offered by integrated photonics. Next, this thesis builds a theoretical framework for the performance parameters and sources of energy consumption that are addressed in the subsequent sections. After this introductory context, the thesis describes the achievement of the highest density and largest scale photonic-electronic integration to date, using a dense, 25 um pitch 3D bonding process. An 80-channel array fabricated in this integration records the lowest data link energies to date, at 120 fJ/bit, and transfers data at 10 Gbit/s/channel for a record 5.3 Tbit/s/mm2 bandwidth density. The discussion then shifts to the issue of chip-to-fiber coupling efficiency, traditionally the greatest source of loss in photonic links. A substrate-removed edge coupler design reduces this loss to a mere 1.1 dB, and an inverse-designed edge coupler taper shows a fourfold length reduction compared to linear tapers. Lastly, the thesis presents designs for wavelength scaling that increase the number of energy efficient channels on a single fiber. Specifically, it demonstrates a multi-channel, polarization diverse micro-comb receiver and a 3D-integrated transceiver with wavelength interleaving to waveguide buses of cascaded resonators. This thesis builds on photonic device developments to introduce photonic systems with the lowest energy and densest data communications to date. Together, these results unlock the tremendous potential of light as a fast and energy-efficient communication medium between chips, paving a sustainable path towards scaling artificial intelligence and disaggregating computation and memory resources.

<p> We consider the design of the precoders for a multi-input multi-output (MIMO) communication system equipped with a decision feedback equalizer (DFE) receiver. For such design problems, perfect knowledge of the channel state information (CSI) at both the transmitter and the receiver is usually required. However, in the environment of wireless communications, it is often difficult to provide sufficiently timely and accurate feedback of CSI from the receiver to the transmitter for such designs to be practically viable.</p> <p> In this thesis, we consider the optimum precoder designs for a wireless communication link having M transmitter antennas and N receiver antennas (M < N), in which the channels are assumed to be flat fading and may be correlated. We assume that full knowledge of CSI is available at the receiver. At the transmitter, however, only the first- and second-order statistics of the channels are available. Our first goal is to come up with an efficient design of the optimal precoder for such a MIMO system by minimizing the average arithmetic mean-squared error (MSE) of zero-forcing (ZF) decision feedback detection subject to a constraint on the total transmission power. Applying some of the properties of the matrix parameters, this non-convex optimization problem can be transformed into a convex geometrical programming problem which can then be efficiently solved using an interior point method. The performance of the MIMO system equipped with this optimum precoder and a ZF-DFE has also been found to be comparable, and in some cases, superior to that of V-BLAST which necessitates optimally ordered successive interference cancellation based on the largest post-detection signal-to-noise ratio (SNR). In terms of trade-off between performance and implementation simplicity, the proposed system is certainly an attractive alternative.</p> <p> In addition, we also utilize these important properties of our system parameters to investigate an "inverse problem" of our first design. That is, we design another precoding matrix by minimizing the total transmission power of the MIMO communication system subject to a constraint on the average MSE. Also, a closed-form solution is derived when the channels are uncorrelated while simulation results for the minimum power precoder designs is given at the end of this thesis.</p> / Thesis / Master of Applied Science (MASc)

The inadequacy of conventional CDMA receivers in a multiple access interference-limited mobile radio environment has spurred research on advanced receiver technologies. This research investigates the use of adaptive receivers for single user demodulation to overcome some of the deficiencies of a conventional receiver and, hence, enhance the system capacity. Several new adaptive techniques are proposed. The new techniques and some existing schemes are analyzed. The limitation of existing blind algorithms in multipath channels is analyzed and a new blind algorithm is proposed that overcomes this limitation. The optimal receiver structure for multi-rate spread spectrum systems is derived and the performance of this receiver in various propagation channels is investigated. The application of coherent and differentially coherent implementations of the adaptive receiver in the presence of carrier frequency offsets is analyzed. The performance of several new adaptive receiver structures for frequency offset compensation is also studied in this research. Analysis of the minimum mean-squared error receiver is carried out to provide a better understanding of the dependence of its performance on channel parameters and to explain the near-far resilience of the receiver. Complex differentially coherent versions of the sign algorithm and the signed regressor algorithm, algorithms that have a much lower computational complexity than the least-means square algorithm, are proposed and applied for CDMA interference rejection. / Ph. D.

Parallel interference cancellation for DS-CDMA has been shown to suffer from biased amplitude estimates if a matched-filter estimator is used. The bias magnitude is proportional to the number of interfering users. For heavy system loads, the bias has been shown to adversely effect the accuracy of the interference cancellation process, thereby impairing BER after cancellation. Empirical simulation work has demonstrated that weighting down interference estimates can improve BER performance. This thesis substantiates these BER improvements by modelling and analyzing a soft interference cancellation technique which mitigates the effects of the bias by minimizing BER after cancellation in a bit-synchronous parallel interference cancellation CDMA receiver. We analyze system decision metrics with down-scaled interference estimates and determine both the mean and variance of the biased decision statistics. From these two metric moments, system BER is evaluated, and the optimal interference scaling function which minimizes BER is derived. We demonstrate BER performance enhancements by simulating this soft interference cancellation technique in systems under perfect power control and in the near-far situation. We further discuss the applicability of the results to asynchronous systems. / Master of Science

Portable communication systems require, in part, high-efficiency radio frequency power amplifiers (RF PA) if battery lifetime is to be conserved. Conventional amplifier classifications and definitions are presented in a unified and concise format. The Bipolar Junction Transistor (BJT) and Metal-Semiconductor Field Effect Transistor (MESFET) are evaluated as active devices in high-efficiency RF PA designs. Two amplifier classes (class CE and class F) meet the system requirements of an 850 MHz operating frequency, a power output of 3 W, a battery supply voltage of 9 Vdc, and a sinusoidal-type signal to be amplified. Both classes are evaluated through recent research literature and simulated using the PSpice® computer simulation program. Class CE and class F are found to provide efficiencies exceeding 80 percent under the given system constraints.</p. / Master of Science

This research aims at solving an engineering design problem encountered in the field of wireless communication systems using mathematical programming techniques. The problem addressed is an indispensable part of micro-cellular radio system design. It involves an optimal location of radio transmitters, given a distribution of receivers and desired signal characteristics. The study has been conducted with the intent of making this problem an integral part of a CAD system for designing radio communication systems. The tool that has been developed for locating a transmitter in such a context is sensitive to different needs of coverage at different locations in the design space. The physical nature of this problem enables it to be conceptualized as a traditional facility location problem. The transmitter is a service facility responsible for serving all the receivers in the design space. A cost is incurred in terms of path-loss, delay spread, and other separation-based measures, whenever service is extended to a receiver. The objective is to place this transmitter in such a way that it optimally serves all the receivers, as measured according to some merit function. However, the nature of the latter merit or objective function, and the nature of the acceptable region for transmitter placement, imparts a special structure to the problem that distinguishes it from traditional facility location problems. The aim of this research effort is to construct a suitable representative mathematical model for this problem, and to design and compare various solution methodologies that are computationally competitive, numerically stable, and accurate. / Master of Science

The instantaneous performance of a site diversity system is analyzed. This analysis is performed using instantaneous diversity gain (a new parameter for describing diversity performance) and the correlation coefficient. Also, a relationship between the correlation coefficient and instantaneous diversity gain was established. In addition, a review of statistical diversity gain and existing models of statistical diversity gain were also presented. Measured statistical diversity gain data from the VPI&SU site diversity experiment were also presented and compared with instantaneous diversity gain. The relationship between the correlation coefficient and instantaneous diversity gain was used to present a crude model of diversity gain. This model was compared with the model of Hodge. Margin calculations were performed to display the usefulness of instantaneous diversity gain. These were performed using the VPI&SU site diversity experiment data. / Master of Science

Proliferation of new wireless technologies has rekindled the interest on the design, analysis and implementation of suboptimal receiver structures that provide good error probability performance with reduced power consumption and complexity particularly when the order of diversity is large. This thesis presents a unified analytical framework to perform a trade-off study for a class of hybrid generalized selection combining technique for ultra-wideband, spread-spectrum and millimeter-wave communication receiver designs. The thesis also develops an exact mathematical framework to analyze the performance of a dual-diversity equal gain combining (EGC) receiver in correlated Nakagami-m channels, which had defied a simple solution in the past. The framework facilitates efficient evaluation of the mean and variance of coherent EGC output signal-to-noise ratio, outage probability and average symbol error probability for a broad range of digital modulation schemes. A comprehensive study of various dual-diversity techniques with non-independent and non-identical fading statistics is also presented. Finally, the thesis develops some closed-form solutions for a few integrals involving the generalized Marcum Q-function. Integrals of these types often arise in the analysis of multichannel diversity reception of differentially coherent and noncoherent digital communications over Nakagami-m channels. Several other applications are also discussed. / Master of Science

Receiver sensitivity is an important parameter in the design of optical communication systems. Prior results on receiver sensitivity for on-off keying modulated direct detection systems with an optical preamplifier are generalized for the cases of frequency-shift keying and subcarrier modulation. Our results, obtained by using the Gaussian approximation, are compared to those obtained by an 'exact' analysis. The results are also generalized for N-ary modulation schemes and systems having optical amplifiers as linear repeaters. Simple analytic formulae are derived for the maximum system gain of optical amplifiers systems for the following two cases: 1) Constant signal power at each amplifier. 2) Equal amplifier spacing, which ensures constant total power at each amplifier. The functional dependence of system gain on various system parameters, and the effects of optical filtering at the receiver as well as at the intermediate amplifiers, is studied. The analysis is extended to include the effects of random power variations at the output of each amplifier. / Master of Science

The rapidly developing wireless market has spawned a multitude of different standards for cellular, PCS, and wireless data. To allow users the ability to access services conforming to disparate standards, multimode handsets capable of software reconfiguration are needed. These "software radios" are distinguished from their traditional counterparts by their strong reliance on digital channel filtering and demodulation which may be reprogrammed to receive different standards. In these radios, higher dynamic range is required from the analog portion, most notably, the analog-to-digital converter (ADC). This research examines through analysis and simulation the performance requirements of analog-to-digital converters for use in radios which are conformant to the AMPS, IS-54, GSM, and IS-95 cellular standards. Simulations reveal the degradation in performance under conditions of off-channel interference, fading, and converter nonlinearities. Included in this analysis is the design of automatic gain control (AGC) for narrowband and IS-95 spread spectrum systems to optimize quantization noise and distortion due to A/D overload. Lastly, methods for improving the dynamic range of the analog-to-digital interface such as nonuniform quantization, companding, and dither are presented. The development of a novel A/D using a direct-sequence pseudo-noise (DSPN) technique in conjunction with an asymmetrical quantizer is presented and compared with standard dither techniques. Advantages of this technique compared to ordinary ADC's include an almost one bit improvement in resolution, quantization noise whitening, elimination of A/D offsets, and the ability to simultaneously digitize multiple analog signals with a single quantizer. The technique requires no synchronization and is easily implemented. / Master of Science