33 research outputs found
Retroreflector and Multibeam Antenna for a Millimeter Wave Collision Avoidance System
RĂSUMĂ La section efficace du radar (SER) pour des cibles automobiles a une rĂ©ponse angulaire Ă©troite. Une variation de plusieurs dĂ©cibels par mĂštre carrĂ© (dBsm) peut Ă©galement ĂȘtre observĂ©e avec un lĂ©ger changement de lâorientation de la cible. La localisation de telles cibles est difficile pour un radar automobile. En outre, un matĂ©riel complexe est gĂ©nĂ©ralement nĂ©cessaire pour mettre en oeuvre un radar efficace, ce qui se traduit par des systĂšmes coĂ»teux
qui ne sont abordables que dans les vĂ©hicules haut de gamme. Cela dĂ©fie lâobjet dâun systĂšme de sĂ©curitĂ© pour Ă©viter les accidents de la route Ă grande Ă©chelle. Cette thĂšse prĂ©sente une nouvelle balise dâamĂ©lioration de SER et une antenne multifaisceaux pour des applications de
radar automobile. Ces composants peuvent Ă©ventuellement amĂ©liorer les performances dâun algorithme de super-rĂ©solution, et permettre le dĂ©veloppement dâun radar dâĂ©vitement de collision automobile simple et peu coĂ»teux. Une architecture de systĂšme simple et rentable
est particuliĂšrement importante dans la gamme de frĂ©quences dâondes millimĂ©triques, allouĂ©e pour cette application, oĂč les attĂ©nuations du signal et les coĂ»ts de dispositif sont significativement Ă©levĂ©s. Les structures proposĂ©es dans cette thĂšse peuvent Ă©galement trouver des applications dans dâautres applications en ondes millimĂ©triques.
Un systĂšme radar est analysĂ© en Ă©tudiant les propriĂ©tĂ©s de lâalgorithme de super-rĂ©solution bien connu ESPRIT. Sur la base dâune simulation numĂ©rique MATLAB de cet algorithme, il
est Ă©tabli quâune SER stable est importante pour lâutilisation de cet algorithme dans des applications
automobiles. Ceci peut ĂȘtre rĂ©alisĂ© en Ă©quipant la cible dâun marqueur dâamĂ©lioration de la SER. DeuxiĂšmement, dans cet algorithme, la taille du rĂ©seau de rĂ©cepteurs dĂ©termine
le nombre de cibles dĂ©tectables. En sectorisant le CdV du radar en utilisant une antenne multifaisceaux, lâerreur de localisation angulaire peut ĂȘtre rĂ©duite pour un plus grand nombre de cibles. La balise proposĂ©e est conçue Ă 77 GHz, fonctionnant dans la bande attribuĂ©e au radar automobile
(76 GHz Ă 81 GHz). Les caractĂ©ristiques des radars automobiles dans la littĂ©rature suggĂšrent un CdV en forme de faisceau en Ă©ventail pour la balise avec un CdV plus large dans le plan azimutal. De CdV de 120o et 9o dans les plans dâazimut et dâĂ©lĂ©vation sont respectivement choisis comme critĂšres de conception pour la balise proposĂ©e. La propriĂ©tĂ© de rĂ©trorĂ©flexion dans le plan dâazimut aide Ă amĂ©liorer la SER de la balise. La balise proposĂ©e
reflÚte le signal incident avec une rotation de polarisation linéaire de 90o. Cette modulation de
polarisation permet dâamĂ©liorer la visibilitĂ© de la cible par rapport au bruit de fond. De plus, une modulation dâamplitude est Ă©galement implĂ©mentĂ©e dans la balise.----------Rear radar cross section (RCS) of automotive targets has a narrow angular response. A
variation of several decibel per square meter (dBsm) can also be observed with slight change in the target orientation. Localization of such targets is challenging for an automotive radar. Furthermore, complex hardware is typically required to implement an effective radar resulting
in high-cost systems that are affordable only in high-end vehicles. This defies the object of a safety system to avoid roadside accidents at large scale. This dissertation présents novel RCS enhancing tag and multibeam antenna for automotive radar applications. These components can possibly improve the performance of a super-resolution algorithm, and enable the development of a simple, low-cost automotive collision avoidance radar. Simple and costeffective system architecture is particularly important in millimeter wave frequency range, allocated for this application, where the material losses and device costs are significantly high. The proposed structures in this thesis can also find applications in other millimeter
wave applications. A radar system is analyzed by studying the properties of Estimation of Signal Parameters via
Rotational Invariance Technique (ESPRIT), a well know super-resolution algorithm. Based on a MATLAB numerical simulation of this algorithm, it is established that a stable target RCS is important for employing this algorithm in automotive applications. This can be achieved by equipping the target with a RCS enhancing tag. Secondly, in this algorithm, the size of the receiver array determines the number of detectable targets. By sectoring the
radar field of view (FoV) using a multibeam antenna, the localization error can be reduced for higher number of targets. The proposed tag is designed at 77 GHz, operating in the band allocated for automotive radar (76 GHz to 81 GHz). Automotive radar characteristics in the literature suggest a fan-beam shaped FoV for the tag with wider FoV in azimuth plane. Azimuth and elevation plane FoV
of 120o and 9o are selected as design criteria for the proposed tag. Retroreflection property
in the azimuth plane helps to improve the tag RCS. The proposed tag reflects the incident signal with 90o linear polarization rotation. This polarization modulation can enhance the target visibility against the background clutter. Additionally, an amplitude modulation is also
implemented in the tag. This modulation can help to communicate additional information. It can also facilitate the target detection by improving the signal to noise ratio of the processed received signal
Assistant Vehicle Localization Based on Three Collaborative Base Stations via SBL-Based Robust DOA Estimation
As a promising research area in Internet of Things (IoT), Internet of Vehicles (IoV) has attracted much attention in wireless communication and network. In general, vehicle localization can be achieved by the global positioning systems (GPSs). However, in some special scenarios, such as cloud cover, tunnels or some places where the GPS signals are weak, GPS cannot perform well. The continuous and accurate localization services cannot be guaranteed. In order to improve the accuracy of vehicle localization, an assistant vehicle localization method based on direction-of-arrival (DOA) estimation is proposed in this paper. The assistant vehicle localization system is composed of three base stations (BSs) equipped with a multiple input multiple output (MIMO) array. The locations of vehicles can be estimated if the positions of the three BSs and the DOAs of vehicles estimated by the BSs are known. However, the DOA estimated accuracy maybe degrade dramatically when the electromagnetic environment is complex. In the proposed method, a sparse Bayesian learning (SBL)-based robust DOA estimation approach is first proposed to achieve the off-grid DOA estimation of the target vehicles under the condition of nonuniform noise, where the covariance matrix of nonuniform noise is estimated by a least squares (LSs) procedure, and a grid refinement procedure implemented by finding the roots of a polynomial is performed to refine the grid points to reduce the off-grid error. Then, according to the DOA estimation results, the target vehicle is cross-located once by each two BSs in the localization system. Finally, robust localization can be realized based on the results of three-time cross-location. Plenty of simulation results demonstrate the effectiveness and superiority of the proposed method
Antenna array design for retrodirective wireless power transmission and radar
This thesis presents antenna array design and the integration of microwave circuit
systems for retrodirective wireless power transmission and radar. Wireless power
transmission (WPT) and automotive radar are emerging topics which have attracted
a lot of interest in the past few years. The development of these systems usually
brings high associated costs if competitive performance is required. The ïŹrst part
of the thesis is concerned with the development of a new retrodirective antenna
array (RDA) system for WPT which uses sub-arrays in transmit to save costs,
however, losing tracking in one plane. Nevertheless, depending on the application,
the proposed system might be an alternative solution to existing approaches as
similar performances are achieved, but at generally a lower cost for the proposed
RDA design as compared to the conventional solution. The proposed system has
been designed to work in the ISM band (2.5 GHz for receiving and 2.4 GHz for transmitting)
which exhibits an 80⊠3-dB half-power beamwidth for the monostatic
pattern. Additionally, it has been demonstrated that the system is able to work in
the near-ïŹeld region, being able to achieve wireless charging of a handeld electronic
device at a 50 cm distance. The power for the beacon signal sent by the device to
be charged by the system (for tracking purposes) is 6.6 dBm, whereas the received
RF power from the RDA is in excess of 27 dBm, which means that the device is
receiving a hundred times the power sent for battery charging.
On the other hand, the second part of the thesis relates to the development of two
important elements within a frequency-modulated-continuous-wave (FMCW) auto
motive radar working at 24 GHz: a substrate integrated waveguide (SIW) butler
matrix antenna array as the transmitter and a new post-processing technique called
Pwr+. These two in combination bring some interesting advantages in terms of angular resolution improvements when compared to conventional single-input-multiple
output (SIMO) radars. For example, the proposed system is able to distinguish two
targets which are 2 degrees apart as well as a higher ïŹeld-of-view (FOV) thanks to
the beamforming network that generates 4 individual beams covering a wide FOV.
The newly developed radar system is also comparable to multiple-input-multiple
output (MIMO) radars but with the added value of having a shorter processing time,
which for automotive radar applications is a crucial characteristic to be minimized,
and could, therefore, avoid potential road accidents.
It should also be mentioned that this thesis was supported by the Samsung Advanced Institute of Technology
Polarimetric Radar for Automotive Applications
Current automotive radar sensors prove to be a weather robust and low-cost solution, but are suffering from low resolution and are not capable of classifying detected targets. However, for future applications like autonomous driving, such features are becoming ever increasingly important. On the basis of successful state-of-the-art applications, this work presents the first in-depth analysis and ground-breaking, novel results of polarimetric millimeter wave radars for automotive applications
MIMO OFDM Radar-Communication System with Mutual Interference Cancellation
This work describes the OFDM-based MIMO Radar-Communication System, intended for operation in a multiple-user network, especially the automotive sector in the vehicle-to vehicle/infrastructure network. The OFDM signals however are weak towards frequency offsets causing subcarrier misalignment and corrupts the radar estimation and the demodulation of the communication signal. A simple yet effective interference cancellation algorithm is detailed here with real time measurement verification
NON-CONTACT TECHNIQUES FOR HUMAN VITAL SIGN DETECTION AND GAIT ANALYSIS
Human vital signs including respiratory rate, heart rate, oxygen saturation, blood pressure, and body temperature are important physiological parameters that are used to track and monitor human health condition. Another important biological parameter of human health is human gait. Human vital sign detection and gait investigations have been attracted many scientists and practitioners in various fields such as sport medicine, geriatric medicine, bio-mechanic and bio-medical engineering and has many biological and medical applications such as diagnosis of health issues and abnormalities, elderly care and health monitoring, athlete performance analysis, and treatment of joint problems. Thoroughly tracking and understanding the normal motion of human limb joints can help to accurately monitor human subjects or patients over time to provide early flags of possible complications in order to aid in a proper diagnosis and development of future comprehensive treatment plans.
With the spread of COVID-19 around the world, it has been getting more important than ever to employ technology that enables us to detect human vital signs in a non-contact way and helps protect both patients and healthcare providers from potentially life-threatening viruses, and have the potential to also provide a convenient way to monitor people health condition, remotely. A popular technique to extract biological parameters from a distance is to use cameras. Radar systems are another attractive solution for non-contact human vital signs monitoring and gait investigation that track and monitor these biological parameters without invading people privacy.
The goal of this research is to develop non-contact methods that is capable of extracting human vital sign parameters and gait features accurately.
To do that, in this work, optical systems including cameras and proper filters have been developed to extract human respiratory rate, heart rate, and oxygen saturation. Feasibility of blood pressure extraction using the developed optical technique has been investigated, too. Moreover, a wideband and low-cost radar system has been implemented to detect single or multiple human subjectâs respiration and heart rate in dark or from behind the wall. The performance of the implemented radar system has been enhanced and it has been utilized for non-contact human gait analysis. Along with the hardware, advanced signal processing schemes have been enhanced and applied to the data collected using the aforementioned radar system. The data processing algorithms have been extended for multi-subject scenarios with high accuracy for both human vital sign detection and gait analysis. In addition, different configurations of this and high-performance radar system including mono-static and MIMO have been designed and implemented with great success. Many sets of exhaustive experiments have been conducted using different human subjects and various situations and accurate reference sensors have been used to validate the performance of the developed systems and algorithms
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DISTRIBUTED PHASED ARRAY ANTENNAS IN WIDE AREA RFID
Ultra High Frequency (UHF) Radio Frequency Identification (RFID) has gained importance over the past two decades in many applications such as stock management, asset
tracking and access control. For wide area applications, Distributed Antenna Systems
(DAS) have been used to obtain good coverage with few antennas by making use of
multiple spatially distributed antennas and phase dithering. This implements a far-field
beamforming that maximises the instantaneous power at a tag. Separately, phased array
antennas have also been used to increase the read range by increasing the effective field
of view of an antenna and overcoming multipath fading through beam steering. This
dissertation explores a combination of both approaches to improve RFID read ranges in
wide interrogation zones.
Distributed antenna arrays are explored in the context of delivering high tag detection
probabilities in a multi-cell RFID system, while maximising inter-antenna separations.
A Distributed Antenna Array System (DAAS) is designed and shown to be capable of
providing comparable performance to a fixed DAS system with fewer antennas. The properties of the system are further studied and its upper performance limit is explored by
modelling a hypothetical perfectly steerable antenna array. The concept of using perfectly
steerable arrays is further explored to propose a cell-less RFID system, in which cell allocation in wide area RFID is replaced with a tag location-based interrogation requiring the
global reader antenna population to be used for interrogation of all tags, leading to significant potential increases in inter-antenna separation, and consequently good coverage
with fewer antennas. It is also argued that this system leads to the avoidance of complex
reader anti-collision policies, since only a single central reader is now required. Finally,
the design of a wide-scan-angle antenna array is presented as a compromise solution for
perfectly steerable antennas, whist still keeping the desired property of being flat panel.
A 3D RFID multi-antenna model is presented and used for simulating and analysing the
various described systems and for system planning
A Localization System for Optimizing the Deployment of Small Cells in 2-Tier Heterogeneous Wireless Networks
Due to the ever growing population of mobile device users and expansion on the number of devices and applications requiring data usage, there is an increasing demand for improved capacity in wireless cellular networks. Cell densification and 2-tier heterogeneous networks (HetNets) are two solutions which will assist 5G systems in meeting these growing capacity demands. Small-cell deployment over existing heterogeneous networks have been considered
by researchers. Different strategies for deploying these small-cells within the existing network among which are random, cell-edge and high user concentration (HUC) have also been explored. Small cells deployed on locations of HUC offloads traffic from existing network infrastructure, ensure good Quality of Service (QoS) and balanced load in the network but there is a challenge of identifying HUC locations.
There has been considerable research performed into techniques for determining user location and cell deployment. Currently localization can be achieved using time dependent methods such as Time of Arrival (ToA), Time Difference of Arrival (TDoA), or Global Positioning Systems (GPS). GPS based solutions provide high accuracy user positioning but suffer from concerns over user privacy, and other time dependent approaches require
regular synchronization which can be difficult to achieve in practice. Alternatively, Received Signal Strength (RSS) based solutions can provide simple anonymous user data, requiring no extra hardware within the mobile handset but often rely on triangulation from adjacent Base Stations (BS). In mobile cellular networks such solutions are therefore often only applicable near the cell edge, as installing additional BS would increase the complexity and cost of a network deployment.
The work presented in this thesis overcomes these limitations by providing an observer system for wireless networks that can be used to periodically monitor the cell coverage area and identify regions of high concentrations of users for possible small cell deployment in 2-tier heterogeneous networks. The observer system comprises of two collinear antennas separated by λ/2. The relative phase of each antenna was varied using a phase shifter so that the combined output of the two antennas were used to create sum and difference radiation
patterns, and to steer the antenna radiation pattern creating different azimuth positions for AoA estimation. Statistical regression analysis was used to develop range estimation models based on four different environment empirical pathloss models for user range estimation. Users were located into clusters by classifying them into azimuth-range classes and counting the number of users in each class. Locations for small cell deployment were identified based on class population. BPEM, ADEM, BUEM, EARM and NLOS models were developed for more accurate range estimation. A prototype system was implemented and
tested both outdoor and indoor using a network of WiFi nodes. Experimental results show close relationship with simulation and an average PER in range estimation error of 80% by applying developed error models. Based on both simulation and experiment, system showed good performance.
By deploying micro-, pico-, or femto-cells in areas of higher user concentration, high data rates and good quality of service in the network can be maintained. The observer system provides the network manager with relative angle of arrival (AoA), distance estimation and
relative location of user clusters within the cell. The observer system divides the cell into a series of azimuthal and range sectors, and determines which sector the users are located in. Simulation and a prototype design of the system is presented and results have shown system robustness and high accuracy for its purpose