Doppler radar-based non-contact health monitoring for obstructive sleep apnea diagnosis: A comprehensive review

Today’s rapid growth of elderly populations and aging problems coupled with the prevalence of obstructive sleep apnea (OSA) and other health related issues have affected many aspects of society. This has led to high demands for a more robust healthcare monitoring, diagnosing and treatments facilities. In particular to Sleep Medicine, sleep has a key role to play in both physical and mental health. The quality and duration of sleep have a direct and significant impact on people’s learning, memory, metabolism, weight, safety, mood, cardio-vascular health, diseases, and immune system function. The gold-standard for OSA diagnosis is the overnight sleep monitoring system using polysomnography (PSG). However, despite the quality and reliability of the PSG system, it is not well suited for long-term continuous usage due to limited mobility as well as causing possible irritation, distress, and discomfort to patients during the monitoring process. These limitations have led to stronger demands for non-contact sleep monitoring systems. The aim of this paper is to provide a comprehensive review of the current state of non-contact Doppler radar sleep monitoring technology and provide an outline of current challenges and make recommendations on future research directions to practically realize and commercialize the technology for everyday usage

Revisiting Lightweight Encryption for IoT Applications: Error Performance and Throughput in Wireless Fading Channels with and without Coding

© 2013 IEEE. Employing heavy conventional encryption algorithms in communications suffers from added overhead and processing time delay; and in wireless communications, in particular, suffers from severe performance deterioration (avalanche effect) due to fading. Consequently, a tremendous reduction in data throughput and increase in complexity and time delay may occur especially when information traverse resource-limited devices as in Internet-of-Things (IoT) applications. To overcome these drawbacks, efficient lightweight encryption algorithms have been recently proposed in literature. One of those, that is of particular interest, requires using conventional encryption only for the first block of data in a given frame being transmitted. All the information in the remaining blocks is transmitted securely without the need for using heavy conventional encryption. Unlike the conventional encryption algorithms, this particular algorithm achieves lower overhead/complexity and higher data throughput. Assuming the additive white Gaussian noise (AWGN) channel, the performance of the lightweight encryption algorithm under study had been evaluated in literature in terms of throughput under the assumption that the first block, that undergoes conventional encryption, is free of error, which is practically unfeasible. In this paper, we consider the AWGN channel with Rayleigh fading and assume that the signal experiences a certain channel bit error probability and investigate the performance of the lightweight encryption algorithm under study in terms of bit error probability and throughput. We derive analytical expressions for these performance metrics considering modulated signals with and without coding. In addition, we propose an extension to the lightweight encryption algorithm under study by further enhancing its security level without significantly affecting the overhead size and processing time. Via numerical results we show the superiority of the lightweight encryption algorithm under study over the conventional encryption algorithms (like the AES) and the lightweight encryption algorithms proposed in literature in terms of error and throughput performance

Doppler Radar-Based Non-Contact Health Monitoring for Obstructive Sleep Apnea Diagnosis: A Comprehensive Review

Today’s rapid growth of elderly populations and aging problems coupled with the prevalence of obstructive sleep apnea (OSA) and other health related issues have affected many aspects of society. This has led to high demands for a more robust healthcare monitoring, diagnosing and treatments facilities. In particular to Sleep Medicine, sleep has a key role to play in both physical and mental health. The quality and duration of sleep have a direct and significant impact on people’s learning, memory, metabolism, weight, safety, mood, cardio-vascular health, diseases, and immune system function. The gold-standard for OSA diagnosis is the overnight sleep monitoring system using polysomnography (PSG). However, despite the quality and reliability of the PSG system, it is not well suited for long-term continuous usage due to limited mobility as well as causing possible irritation, distress, and discomfort to patients during the monitoring process. These limitations have led to stronger demands for non-contact sleep monitoring systems. The aim of this paper is to provide a comprehensive review of the current state of non-contact Doppler radar sleep monitoring technology and provide an outline of current challenges and make recommendations on future research directions to practically realize and commercialize the technology for everyday usage.</jats:p

Bandwidth-Based Wake-Up Radio solution through IEEE 802.11 technology

IEEE 802.11 consists of one of the most used wireless access technologies, which can be found in almost all consumer electronics devices available. Recently, Wake-up Radio (WuR) systems have emerged as a solution for energy-efficient communications. WuR mechanisms rely on using a secondary low-power radio interface that is always in the active operation mode and is in charge of switching the primary interface, used for main data exchange, from the power-saving state to the active mode. In this paper, we present a WuR solution based on IEEE 802.11 technology employing transmissions of legacy frames by an IEEE 802.11 standard-compliant transmitter during a Transmission Opportunity (TXOP) period. Unlike other proposals available in the literature, the WuR system presented in this paper exploits the PHY characteristics of modern IEEE 802.11 radios, where different signal bandwidths can be used on a per-packet basis. The proposal is validated through the Matlab software tool, and extensive simulation results are presented in a wide variety of scenario configurations. Moreover, insights are provided on the feasibility of the WuR proposal for its implementation in real hardware. Our approach allows the transmission of complex Wake-up Radio signals (i.e., including address field and other binary data) from legacy Wi-Fi devices (from IEEE 802.11n-2009 on), avoiding hardware or even firmware modifications intended to alter standard MAC/PHY behavior, and achieving a bit rate of up to 33 kbps.Postprint (published version

Scalable Surfaces for Electromagnetic Energy Harvesting and Wireless Power Transfer

The idea of collecting electromagnetic (EM) energy and converting it into various forms of useful power dates back to the early 20th century. Nikola Tesla's wireless power transfer experiments demonstrated the concept first, which was followed by researchers in Japan and the USA in subsequent decades. In terms of a working prototype, the first rectenna for efficient reception and rectification of microwave power was developed in the early 1960s. Later, the introduction of semiconductor diodes and the invention of Schottky diodes were significant developments towards the realization of practical rectennas. Since then, owing to the numerous applications in different technology domains (i.e. consumer electronics, renewable energy, transportation, internet of things, artificial intelligence, telecommunications, defense & space, biomedical engineering), wireless power transfer and EM energy harvesting have attracted significant interest. Harvesting the ambient EM energy has emerged more recently as a promising application with potential for commercial success and contribution to a sustainable future with renewable energy. Many studies have reported the available ambient power densities measured in several parts of the world demonstrating the potentials and limitations of the concept. Traditional single rectenna structures have found very little use due to their inherent limitations at low power densities. Large rectenna arrays or periodic structures covering larger surface areas have become particularly important in order to efficiently harvest and convert the energy. A rectenna consists of two main functional building blocks: the rectifier and the EM collector. The work in this thesis first focuses on improving these functional blocks individually. Regarding the rectifier function; a balanced full-wave rectifier is proposed where the circuit is differentially fed by two separate antennas. This configuration allows the received power to be rectified and transferred into a load between two antennas, making it convenient to channel the harvested power in rectenna arrays. The proposed concept is demonstrated using an array of T-matched dipole antennas at 2.45 GHz. It is also compared with half-wave rectennas that occupy the same footprint with an identical array layout. Measurement results show that, under the same circumstances, the proposed full-wave rectification performs better than the traditional half-wave rectification and it is indeed suitable for energy harvesting rectenna arrays. Regarding the EM collector; a novel Frequency Selective Surface (FSS) is developed as an absorber surface that accepts 98.5% of the available power and collects 97% of it exclusively on its resistive load (only 1.5% is dissipated as dielectric and metallic losses). To demonstrate its performance, a proof of concept FSS absorber is fabricated and its resistive load is replaced with a matched full-wave rectifier. Measurement results show that the overall Radiation-to-dc conversion efficiency of the complete rectenna system reaches 61%, which is considerably higher than the previously reported FSS based rectennas. Subsequent sections in this thesis expand the energy harvesting surface by adding dual-band and dual-polarization capabilities. Design details and simulation results are provided together with measurement results. Fabricated prototypes are tested and their overall performance is evaluated based on the rectified DC power at the system load as percentage of the available EM power on the physical surface area of the rectenna (i.e. radiation-to-dc conversion efficiency). A key contribution of this thesis is the introduction of the scalability concept for energy harvesting. The periodic absorber surfaces presented in this thesis have built-in channelling features that allow multi-cell configurations to feed a single rectifier. This is demonstrated to be an efficient means to increase the EM collector area per rectifier by effortlessly scaling the surface area while efficiently channelling the collected power. As a result, the number of diodes and diode losses are minimized in the system, leading to higher overall rectenna efficiencies. Real life ambient power densities can be on the order of nW/cm2 and the work in this thesis show that larger EM collectors can significantly mitigate the limitations posed by such low power levels. As an example; when integrated with a multi-cell configuration, an ordinary rectifier made with Schottky diodes was efficiently used at a power density that is less than 1/12th of that would be required if the same rectifier were to be used with a traditional single unit cell approach

Noncontact Vital Signs Detection

Human health condition can be accessed by measurement of vital signs, i.e., respiratory rate (RR), heart rate (HR), blood oxygen level, temperature and blood pressure. Due to drawbacks of contact sensors in measurement, non-contact sensors such as imaging photoplethysmogram (IPPG) and Doppler radar system have been proposed for cardiorespiratory rates detection by researchers.The UWB pulse Doppler radars provide high resolution range-time-frequency information. It is bestowed with advantages of low transmitted power, through-wall capabilities, and high resolution in localization. However, the poor signal to noise ratio (SNR) makes it challenging for UWB radar systems to accurately detect the heartbeat of a subject. To solve the problem, phased-methods have been proposed to extract the phase variations in the reflected pulses modulated by human tiny thorax motions. Advance signal processing method, i.e., state space method, can not only be used to enhance SNR of human vital signs detection, but also enable the micro-Doppler trajectories extraction of walking subject from UWB radar data.Stepped Frequency Continuous Wave (SFCW) radar is an alternative technique useful to remotely monitor human subject activities. Compared with UWB pulse radar, it relieves the stress on requirement of high sampling rate analog-to-digital converter (ADC) and possesses higher signal-to-noise-ratio (SNR) in vital signs detection. However, conventional SFCW radar suffers from long data acquisition time to step over many frequencies. To solve this problem, multi-channel SFCW radar has been proposed to step through different frequency bandwidths simultaneously. Compressed sensing (CS) can further reduce the data acquisition time by randomly stepping through 20% of the original frequency steps.In this work, SFCW system is implemented with low cost, off-the-shelf surface mount components to make the radar sensors portable. Experimental results collected from both pulse and SFCW radar systems have been validated with commercial contact sensors and satisfactory results are shown

Repeat-Accumulate構造に基づく直列連接信号符号

電気通信大学201

Annual Report, 2013-2014

Beginning in 2004/2005- issued in online format onl

High resolution, process and temperature compensated phase shifter design using a self generated look up table

Phase resolution is one of the most important parameters in phased array RADAR determining the precision of antenna beam direction and side-lobe level. Especially, in tracking applications the antenna directivity should be high and side-lobe levels must be low in order to abstain from the signals of Jammers. Phase shifters (PS) set phase resolution and directivity; therefore, they are the key components for phased arrays. Among the PS topologies, vector sum type comes forward due to its significant advantage over the other design techniques, in terms of insertion loss, phase error, area and operation bandwidth. However, in design of vector sum type PS, phase and amplitude errors in vectors, and phase insertion of variable gain amplifiers degrades the phase resolution performance of the PS. In order to overcome these issues and improve bit resolution (reduced phase step size and lower phase error while covering 360° phase range), and improve the tolerance on process - temperature variations, the proposed solution in this thesis is the design of a calibration circuit consisting of Power detector (PD), Analog to Digital Converter (ADC) and a Digital Processing Unit (DPU). The main objective of the calibration loop is the generation of a Look up Table (LUT) for target frequency band and at operating temperature. With this technique, the first 7-bit Phase shifter is designed in SiGe- BiCMOS technology, which also has highest fractional bandwidth in literature