Interference Suppression in Massive MIMO VLC Systems

The focus of this dissertation is on the development and evaluation of methods and principles to mitigate interference in multiuser visible light communication (VLC) systems using several transmitters. All components of such a massive multiple-input multiple-output (MIMO) system are considered and transformed into a communication system model, while also paying particular attention to the hardware requirements of different modulation schemes. By analyzing all steps in the communication process, the inter-channel interference between users is identified as the most critical aspect. Several methods of suppressing this kind of interference, i.e. to split the MIMO channel into parallel single channels, are discussed, and a novel active LCD-based interference suppression principle at the receiver side is introduced as main aspect of this work. This technique enables a dynamic adaption of the physical channel: compared to solely software-based or static approaches, the LCD interference suppression filter achieves adaptive channel separation without altering the characteristics of the transmitter lights. This is especially advantageous in dual-use scenarios with illumination requirements. Additionally, external interferers, like natural light or transmitter light sources of neighboring cells in a multicell setting, can also be suppressed without requiring any control over them. Each user's LCD filter is placed in front of the corresponding photodetector and configured in such a way that only light from desired transmitters can reach the detector by setting only the appropriate pixels to transparent, while light from unwanted transmitters remains blocked. The effectiveness of this method is tested and benchmarked against zero-forcing (ZF) precoding in different scenarios and applications by numerical simulations and also verified experimentally in a large MIMO VLC testbed created specifically for this purpose

High-performance wireless interface for implant-to-air communications

Nous élaborons une interface cerveau-machine (ICM) entièrement sans fil afin de fournir un système de liaison directe entre le cerveau et les périphériques externes, permettant l’enregistrement et la stimulation du cerveau pour une utilisation permanente. Au cours de cette thèse, nous explorons la modélisation de canal, les antennes implantées et portables en tant que propagateurs appropriés pour cette application, la conception du nouveau système d’un émetteur-récepteur UWB implantable, la conception niveau système du circuit et sa mise en oeuvre par un procédé CMOS TSMC 0.18 um. En plus, en collaboration avec Université McGill, nous avons conçu un réseau de seize antennes pour une détection du cancer du sein à l’aide d’hyperfréquences. Notre première contribution calcule la caractérisation de canal de liaison sans fil UWB d’implant à l’air, l’absorption spécifique moyennée (ASAR), et les lignes directrices de la FCC sur la densité spectrale de puissance UWB transmis. La connaissance du comportement du canal est nécessaire pour déterminer la puissance maximale permise à 1) respecter les lignes directrices ANSI pour éviter des dommages aux tissus et 2) respecter les lignes directrices de la FCC sur les transmissions non autorisées. Nous avons recours à un modèle réaliste du canal biologique afin de concevoir les antennes pour l’émetteur implanté et le récepteur externe. Le placement des antennes est examiné avec deux scénarios contrastés ayant des contraintés de puissance. La performance du système au sein des tissus biologiques est examinée par l’intermédiaire des simulations et des expériences. Notre deuxième contribution est dédiée à la conception des antennes simples et à double polarisation pour les systèmes d’enregistrement neural sans fil à bande ultra-large en utilisant un modèle multicouches inhomogène de la tête humaine. Les antennes fabriquées à partir de matériaux flexibles sont plus facilement adaptées à l’implantation ; nous étudions des matériaux à la fois flexibles et rigides et examinons des compromis de performance. Les antennes proposées sont conçues pour fonctionner dans une plage de fréquence de 2-11 GHz (ayant S11-dessous de -10 dB) couvrant à la fois la bande 2.45 GHz (ISM) et la bande UWB 3.1-10.6 GHz. Des mesures confirment les résultats de simulation et montrent que les antennes flexibles ont peu de dégradation des performances en raison des effets de flexion (en termes de correspondance d’impédance). Finalement, une comparaison est réalisée entre quatre antennes implantables, couvrant la gamme 2-11 GHz : 1) une rigide, à la polarisation simple, 2) une rigide, à double polarisation, 3) une flexible, à simple polarisation et 4) une flexible, à double polarisation. Dans tous les cas une antenne rigide est utilisée à l’extérieur du corps, avec une polarisation appropriée. Plusieurs avantages ont été confirmés pour les antennes à la polarisation double : 1) une taille plus petite, 2) la sensibilité plus faible aux désalignements angulaires, et 3) une plus grande fidélité. Notre troisième contribution fournit la conception niveau système de l’architecture de communication sans fil pour les systèmes implantés qui stimulent simultanément les neurones et enregistrent les réponses de neurones. Cette architecture prend en charge un grand nombre d’électrodes (> 500), fournissant 100 Mb/s pour des signaux de stimulation de liaison descendante, et Gb/s pour les enregistrements de neurones de liaison montante. Nous proposons une architecture d’émetteur-récepteur qui partage une antenne ultra large bande, un émetteur-récepteur simplifié, travaillant en duplex intégral sur les deux bandes, et un nouveau formeur d’impulsions pour la liaison montante du Gb/s soutenant plusieurs formats de modulation. Nous présentons une démonstration expérimentale d’ex vivo de l’architecture en utilisant des composants discrets pour la réalisation les taux Gb/s en liaison montante. Une bonne performance de taux d’erreur de bit sur un canal biologique à 0,5, 1 et 2 Gb/s des débits de données pour la télémétrie de liaison montante (UWB) et 100 Mb/s pour la télémétrie en liaison descendante (bande 2.45 GHz) est atteinte. Notre quatrième contribution présente la conception au niveau du circuit d’un dispositif d’émission en duplex total qui est présentée dans notre troisième contribution. Ce dispositif d’émission en duplex total soutient les applications d’interfaçage neural multimodal et en haute densité (les canaux de stimulant et d’enregistrement) avec des débits de données asymétriques. L’émetteur (TX) et le récepteur (RX) partagent une seule antenne pour réduire la taille de l’implant. Le TX utilise impulse radio ultra-wide band (IR-UWB) basé sur une approche alliant des bords, et le RX utilise un nouveau 2.4 GHz récepteur on-off keying (OOK).Une bonne isolation (> 20 dB) entre le trajet TX et RX est mis en oeuvre 1) par mise en forme des impulsions transmises pour tomber dans le spectre UWB non réglementé (3.1-7 GHz), et 2) par un filtrage espace-efficace du spectre de liaison descendante OOK dans un amplificateur à faible bruit RX. L’émetteur UWB 3.1-7 GHz peut utiliser soit OOK soit la modulation numérique binaire à déplacement de phase (BPSK). Le FDT proposé offre une double bande avec un taux de données de liaison montante de 500 Mbps TX et un taux de données de liaison descendante de 100 Mb/s RX, et il est entièrement en conformité avec les standards TSMC 0.18 um CMOS dans un volume total de 0,8 mm2. Ainsi, la mesure de consommation d’énergie totale en mode full duplex est de 10,4 mW (5 mW à 100 Mb/s pour RX, et de 5,4 mW à 500 Mb/s ou 10,8 PJ / bits pour TX). Notre cinquième contribution est une collaboration avec l’Université McGill dans laquelle nous concevons des antennes simples et à double polarisation pour les systèmes de détection du cancer du sein à l’aide d’hyperfréquences sans fil en utilisant un modèle multi-couche et inhomogène du sein humain. Les antennes fabriquées à partir de matériaux flexibles sont plus facilement adaptées à des applications portables. Les antennes flexibles miniaturisées monopôles et spirales sur un 50 um Kapton polyimide sont conçus, en utilisant high frequency structure simulator (HFSS), à être en contact avec des tissus biologiques du sein. Les antennes proposées sont conçues pour fonctionner dans une gamme de fréquences de 2 à 4 GHz. Les mesures montrent que les antennes flexibles ont une bonne adaptation d’impédance dans les différentes positions sur le sein. De Plus, deux antennes à bande ultralarge flexibles 4 × 4 (simple et à double polarisation), dans un format similaire à celui d’un soutien-gorge, ont été développés pour un système de détection du cancer du sein basé sur le radar.We are working on a fully wireless brain-machine-interface to provide a communication link between the brain and external devices, enabling recording and stimulating the brain for permanent usage. In this thesis we explore channel modeling, implanted and wearable antennas as suitable propagators for this application, system level design of an implantable UWB transceiver, and circuit level design and implementing it by TSMC 0.18 um CMOS process. Also, in a collaboration project with McGill University, we designed a flexible sixteen antenna array for microwave breast cancer detection. Our first contribution calculates channel characteristics of implant-to-air UWB wireless link, average specific absorption rate (ASAR), and FCC guidelines on transmitted UWB power spectral density. Knowledge of channel behavior is required to determine the maximum allowable power to 1) respect ANSI guidelines for avoiding tissue damage and 2) respect FCC guidelines on unlicensed transmissions. We utilize a realistic model of the biological channel to inform the design of antennas for the implanted transmitter and the external receiver. Antennas placement is examined under two scenarios having contrasting power constraints. Performance of the system within the biological tissues is examined via simulations and experiments. Our second contribution deals with designing single and dual-polarization antennas for wireless ultra-wideband neural recording systems using an inhomogeneous multi-layer model of the human head. Antennas made from flexible materials are more easily adapted to implantation; we investigate both flexible and rigid materials and examine performance trade-offs. The proposed antennas are designed to operate in a frequency range of 2–11 GHz (having S11 below -10 dB) covering both the 2.45 GHz (ISM) band and the 3.1–10.6 GHz UWB band. Measurements confirm simulation results showing flexible antennas have little performance degradation due to bending effects (in terms of impedance matching). Finally, a comparison is made of four implantable antennas covering the 2-11 GHz range: 1) rigid, single polarization, 2) rigid, dual polarization, 3) flexible, single polarization and 4) flexible, dual polarization. In all cases a rigid antenna is used outside the body, with an appropriate polarization. Several advantages were confirmed for dual polarization antennas: 1) smaller size, 2) lower sensitivity to angular misalignments, and 3) higher fidelity. Our third contribution provides system level design of wireless communication architecture for implanted systems that simultaneously stimulate neurons and record neural responses. This architecture supports large numbers of electrodes (> 500), providing 100 Mb/s for the downlink of stimulation signals, and Gb/s for the uplink neural recordings. We propose a transceiver architecture that shares one ultra-wideband antenna, a streamlined transceiver working at full-duplex on both bands, and a novel pulse shaper for the Gb/s uplink supporting several modulation formats. We present an ex-vivo experimental demonstration of the architecture using discrete components achieving Gb/s uplink rates. Good bit error rate performance over a biological channel at 0.5, 1, and 2 Gbps data rates for uplink telemetry (UWB) and 100 Mbps for downlink telemetry (2.45 GHz band) is achieved. Our fourth contribution presents circuit level design of the novel full-duplex transceiver (FDT) which is presented in our third contribution. This full-duplex transceiver supports high-density and multimodal neural interfacing applications (high-channel count stimulating and recording) with asymmetric data rates. The transmitter (TX) and receiver (RX) share a single antenna to reduce implant size. The TX uses impulse radio ultra-wide band (IR-UWB) based on an edge combining approach, and the RX uses a novel 2.4-GHz on-off keying (OOK) receiver. Proper isolation (> 20 dB) between the TX and RX path is implemented 1) by shaping the transmitted pulses to fall within the unregulated UWB spectrum (3.1-7 GHz), and 2) by spaceefficient filtering (avoiding a circulator or diplexer) of the downlink OOK spectrum in the RX low-noise amplifier. The UWB 3.1-7 GHz transmitter can use either OOK or binary phase shift keying (BPSK) modulation schemes. The proposed FDT provides dual band 500-Mbps TX uplink data rate and 100 Mbps RX downlink data rate, and it is fully integrated into standard TSMC 0.18 um CMOS within a total size of 0.8 mm2. The total measured power consumption is 10.4 mW in full duplex mode (5 mW at 100 Mbps for RX, and 5.4 mW at 500 Mbps or 10.8 pJ/bit for TX). Our fifth contribution is a collaboration project with McGill University which we design single and dual-polarization antennas for wireless ultra-wideband breast cancer detection systems using an inhomogeneous multi-layer model of the human breast. Antennas made from flexible materials are more easily adapted to wearable applications. Miniaturized flexible monopole and spiral antennas on a 50 um Kapton polyimide are designed, using a high frequency structure simulator (HFSS), to be in contact with biological breast tissues. The proposed antennas are designed to operate in a frequency range of 2–4 GHz (with reflection coefficient (S11) below -10 dB). Measurements show that the flexible antennas have good impedance matching while in different positions with different curvature around the breast. Furthermore, two flexible conformal 4×4 ultra-wideband antenna arrays (single and dual polarization), in a format similar to that of a bra, were developed for a radar-based breast cancer detection system

Heterogeneous integration of optical wireless communications within next generation networks

Unprecedented traffic growth is expected in future wireless networks and new technologies will be needed to satisfy demand. Optical wireless (OW) communication offers vast unused spectrum and high area spectral efficiency. In this work, optical cells are envisioned as supplementary access points within heterogeneous RF/OW networks. These networks opportunistically offload traffic to optical cells while utilizing the RF cell for highly mobile devices and devices that lack a reliable OW connection. Visible light communication (VLC) is considered as a potential OW technology due to the increasing adoption of solid state lighting for indoor illumination. Results of this work focus on a full system view of RF/OW HetNets with three primary areas of analysis. First, the need for network densication beyond current RF small cell implementations is evaluated. A media independent model is developed and results are presented that provide motivation for the adoption of hyper dense small cells as complementary components within multi-tier networks. Next, the relationships between RF and OW constraints and link characterization parameters are evaluated in order to define methods for fair comparison when user-centric channel selection criteria are used. RF and OW noise and interference characterization techniques are compared and common OW characterization models are demonstrated to show errors in excess of 100x when dominant interferers are present. Finally, dynamic characteristics of hyper dense OW networks are investigated in order to optimize traffic distribution from a network-centric perspective. A Kalman Filter model is presented to predict device motion for improved channel selection and a novel OW range expansion technique is presented that dynamically alters coverage regions of OW cells by 50%. In addition to analytical results, the dissertation describes two tools that have been created for evaluation of RF/OW HetNets. A communication and lighting simulation toolkit has been developed for modeling and evaluation of environments with VLC-enabled luminaires. The toolkit enhances an iterative site based impulse response simulator model to utilize GPU acceleration and achieves 10x speedup over the previous model. A software defined testbed for OW has also been proposed and applied. The testbed implements a VLC link and a heterogeneous RF/VLC connection that demonstrates the RF/OW HetNet concept as proof of concept

Time and frequency offsets in all optical OFDM systems

Ultra-high-speed data transmission (terabit-per-second per channel) is urgently required in optical communication systems to fulfill the emerging demands of 3D multimedia applications, cloud computing, and bandwidth-hungry applications. In one way by using singlecarrier optical communication systems for the data transmission rates 1 Tb/s, we need the high baud rate and/or the high-order modulation formats (i.e. 512-QAM, 1024-QAM). Another way is to group the data carrying subcarriers without a guard bands (tightly spaced) to form a superchannel which gives increase in channel capacity. In a superchannel, the requirements of high-order modulation formats and high baud rates are relaxed. In an alloptical orthogonal frequency division multiplexing (AO-OFDM) system, the subcarriers are orthogonal and closely packed which gives more suitability to form superchannel. This thesis focuses on the time and frequency offsets in AO-OFDM systems. A theoretical model to investigate the performance of on-off-keying (OOK) modulated AO-OFDM system is developed for analytical simulation. The analytical (statistical) model considers the random characteristics of time and frequency offsets in adjacent subcarriers as well as the common noise sources such as shot and thermal noises to calculate the interference variances for evaluating the BER performance. The effects of time and frequency offsets on the BER performance of AO-OFDM system is evaluated with the number of optical subcarriers (NSC), receiver bandwidth (BWRX), and cyclic prefix (CP) We further develop an analytical model to evaluate the performance of AO-OFDM system with advanced modulation format (M-QAM) in the presence of time and frequency offsets, and the performance is compared with numerical simulations of other emulation setups (oddand- even subcarriers and decorrelated systems). The performance is investigated with NSC, BWRX, and CP in AO-OFDM system. A delay-line interferometer based all-optical method to reduce the effects of time and frequency offsets is proposed and evaluated. Finally, performance of demultiplexed subcarriers from an optical discrete Fourier transform (O-DFT) in AO-OFDM system in the presence of chromatic dispersion and limited modulation bandwidth is evaluated. The fiber Bragg grating (FBG) based passive device is proposed to reduce the interference and the results are compared with existing method using sampling gates. The proposed method using FBG for interference reduction provides a cost-effective design of AO-OFDM system

Visible Light Communication (VLC)

Visible light communication (VLC) using light-emitting diodes (LEDs) or laser diodes (LDs) has been envisioned as one of the key enabling technologies for 6G and Internet of Things (IoT) systems, owing to its appealing advantages, including abundant and unregulated spectrum resources, no electromagnetic interference (EMI) radiation and high security. However, despite its many advantages, VLC faces several technical challenges, such as the limited bandwidth and severe nonlinearity of opto-electronic devices, link blockage and user mobility. Therefore, significant efforts are needed from the global VLC community to develop VLC technology further. This Special Issue, “Visible Light Communication (VLC)”, provides an opportunity for global researchers to share their new ideas and cutting-edge techniques to address the above-mentioned challenges. The 16 papers published in this Special Issue represent the fascinating progress of VLC in various contexts, including general indoor and underwater scenarios, and the emerging application of machine learning/artificial intelligence (ML/AI) techniques in VLC

A Survey of Positioning Systems Using Visible LED Lights

© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.As Global Positioning System (GPS) cannot provide satisfying performance in indoor environments, indoor positioning technology, which utilizes indoor wireless signals instead of GPS signals, has grown rapidly in recent years. Meanwhile, visible light communication (VLC) using light devices such as light emitting diodes (LEDs) has been deemed to be a promising candidate in the heterogeneous wireless networks that may collaborate with radio frequencies (RF) wireless networks. In particular, light-fidelity has a great potential for deployment in future indoor environments because of its high throughput and security advantages. This paper provides a comprehensive study of a novel positioning technology based on visible white LED lights, which has attracted much attention from both academia and industry. The essential characteristics and principles of this system are deeply discussed, and relevant positioning algorithms and designs are classified and elaborated. This paper undertakes a thorough investigation into current LED-based indoor positioning systems and compares their performance through many aspects, such as test environment, accuracy, and cost. It presents indoor hybrid positioning systems among VLC and other systems (e.g., inertial sensors and RF systems). We also review and classify outdoor VLC positioning applications for the first time. Finally, this paper surveys major advances as well as open issues, challenges, and future research directions in VLC positioning systems.Peer reviewe

CMOS Data Converters for Closed-Loop mmWave Transmitters

With the increased amount of data consumed in mobile communication systems, new solutions for the infrastructure are needed. Massive multiple input multiple output (MIMO) is seen as a key enabler for providing this increased capacity. With the use of a large number of transmitters, the cost of each transmitter must be low. Closed-loop transmitters, featuring high-speed data converters is a promising option for achieving this reduced unit cost.In this thesis, both digital-to-analog (D/A) and analog-to-digital (A/D) converters suitable for wideband operation in millimeter wave (mmWave) massive MIMO transmitters are demonstrated. A 2 76 bit radio frequency digital-to-analog converter (RF-DAC)-based in-phase quadrature (IQ) modulator is demonstrated as a compact building block, that to a large extent realizes the transmit path in a closed-loop mmWave transmitter. The evaluation of an successive-approximation register (SAR) analog-to-digital converter (ADC) is also presented in this thesis. Methods for connecting simulated and measured performance has been studied in order to achieve a better understanding about the alternating comparator topology.These contributions show great potential for enabling closed-loop mmWave transmitters for massive MIMO transmitter realizations