Backscatter Transponder Based on Frequency Selective Surface for FMCW Radar Applications

This paper describes an actively-controlled frequency selective surface (FSS) to implement a backscatter transponder. The FSS is composed by dipoles loaded with switching PIN diodes. The transponder exploits the change in the radar cross section (RCS) of the FSS with the bias of the diodes to modulate the backscattered response of the tag to the FMCW radar. The basic operation theory of the system is explained here. An experimental setup based on a commercial X-band FMCW radar working as a reader is proposed to measure the transponders. The transponder response can be distinguished from the interference of non-modulated clutter, modulating the transponder’s RCS. Some FSS with different number of dipoles are studied, as a proof of concept. Experimental results at several distances are provided

Frequency-modulated continuous-wave LiDAR compressive depth-mapping

We present an inexpensive architecture for converting a frequency-modulated continuous-wave LiDAR system into a compressive-sensing based depth-mapping camera. Instead of raster scanning to obtain depth-maps, compressive sensing is used to significantly reduce the number of measurements. Ideally, our approach requires two difference detectors. % but can operate with only one at the cost of doubling the number of measurments. Due to the large flux entering the detectors, the signal amplification from heterodyne detection, and the effects of background subtraction from compressive sensing, the system can obtain higher signal-to-noise ratios over detector-array based schemes while scanning a scene faster than is possible through raster-scanning. %Moreover, we show how a single total-variation minimization and two fast least-squares minimizations, instead of a single complex nonlinear minimization, can efficiently recover high-resolution depth-maps with minimal computational overhead. Moreover, by efficiently storing only $2m$ data points from $m<n$ measurements of an $n$ pixel scene, we can easily extract depths by solving only two linear equations with efficient convex-optimization methods

Investigation of Non-coherent Discrete Target Range Estimation Techniques for High-precision Location

Ranging is an essential and crucial task for radar systems. How to solve the range-detection problem effectively and precisely is massively important. Meanwhile, unambiguity and high resolution are the points of interest as well. Coherent and non-coherent techniques can be applied to achieve range estimation, and both of them have advantages and disadvantages. Coherent estimates offer higher precision but are more vulnerable to noise and clutter and phase wrap errors, particularly in a complex or harsh environment, while the non-coherent approaches are simpler but provide lower precision. With the purpose of mitigating inaccuracy and perturbation in range estimation, miscellaneous techniques are employed to achieve optimally precise detection. Numerous elegant processing solutions stemming from non-coherent estimate are now introduced into the coherent realm, and vice versa. This thesis describes two non-coherent ranging estimate techniques with novel algorithms to mitigate the instinct deficit of non-coherent ranging approaches. One technique is based on peak detection and realised by Kth-order Polynomial Interpolation, while another is based on Z-transform and realised by Most-likelihood Chirp Z-transform. A two-stage approach for the fine ranging estimate is applied to the Discrete Fourier transform domain of both algorithms. An N-point Discrete Fourier transform is implemented to attain a coarse estimation; an accurate process around the point of interest determined in the first stage is conducted. For KPI technique, it interpolates around the peak of Discrete Fourier transform profiles of the chirp signal to achieve accurate interpolation and optimum precision. For Most-likelihood Chirp Z-transform technique, the Chirp Z-transform accurately implements the periodogram where only a narrow band spectrum is processed. Furthermore, the concept of most-likelihood estimator is introduced to combine with Chirp Z-transform to acquire better ranging performance. Cramer-Rao lower bound is presented to evaluate the performance of these two techniques from the perspective of statistical signal processing. Mathematical derivation, simulation modelling, theoretical analysis and experimental validation are conducted to assess technique performance. Further research will be pushed forward to algorithm optimisation and system development of a location system using non-coherent techniques and make a comparison to a coherent approach

RF Front End for an Integrated Silhouette Capture and Boundary Detection Frequency Modulated Continuous Wave Ultra-Wideband Radar System for the Extension of Independent Living

Limitations of current eldercare monitoring systems leave a need for new solutions. A monitoring system based on a frequency modulated continuous wave ultra-wideband short-range radar is proposed for this application. The complete proposed monitoring system is comprised of four blocks: boundary detection, silhouette capture, human identification, and data transmission. This paper develops the RF front end hardware for the silhouette capture subsystem. System requirements are derived for the silhouette capture subsystem. An architecture for the RF front end is designed, and required individual component specifications are determined. Components are selected off the shelf or custom designed for each socket. Full transmitter and receiver level plans are calculated to ensure expected system performance meets system requirements. A component library and full system schematic is created, PCB layout is completed, and PCB files are generated and sent for fabrication. PCB traces and individual components are characterized over frequency, and methods that improve inadequate performance are documented and discussed

Millimeter-wave Communication and Radar Sensing — Opportunities, Challenges, and Solutions

With the development of communication and radar sensing technology, people are able to seek for a more convenient life and better experiences. The fifth generation (5G) mobile network provides high speed communication and internet services with a data rate up to several gigabit per second (Gbps). In addition, 5G offers great opportunities of emerging applications, for example, manufacture automation with the help of precise wireless sensing. For future communication and sensing systems, increasing capacity and accuracy is desired, which can be realized at millimeter-wave spectrum from 30 GHz to 300 GHz with several tens of GHz available bandwidth. Wavelength reduces at higher frequency, this implies more compact transceivers and antennas, and high sensing accuracy and imaging resolution. Challenges arise with these application opportunities when it comes to realizing prototype or demonstrators in practice. This thesis proposes some of the solutions addressing such challenges in a laboratory environment.High data rate millimeter-wave transmission experiments have been demonstrated with the help of advanced instrumentations. These demonstrations show the potential of transceiver chipsets. On the other hand, the real-time communication demonstrations are limited to either low modulation order signals or low symbol rate transmissions. The reason for that is the lack of commercially available high-speed analog-to-digital converters (ADCs); therefore, conventional digital synchronization methods are difficult to implement in real-time systems at very high data rates. In this thesis, two synchronous baseband receivers are proposed with carrier recovery subsystems which only require low-speed ADCs [A][B].Besides synchronization, high-frequency signal generation is also a challenge in millimeter-wave communications. The frequency divider is a critical component of a millimeter-wave frequency synthesizer. Having both wide locking range and high working frequencies is a challenge. In this thesis, a tunable delay gated ring oscillator topology is proposed for dual-mode operation and bandwidth extension [C]. Millimeter-wave radar offers advantages for high accuracy sensing. Traditional millimeter-wave radar with frequency-modulated continuous-wave (FMCW), or continuous-wave (CW), all have their disadvantages. Typically, the FMCW radar cannot share the spectrum with other FMCW radars.\ua0 With limited bandwidth, the number of FMCW radars that could coexist in the same area is limited. CW radars have a limited ambiguous distance of a wavelength. In this thesis, a phase-modulated radar with micrometer accuracy is presented [D]. It is applicable in a multi-radar scenario without occupying more bandwidth, and its ambiguous distance is also much larger than the CW radar. Orthogonal frequency-division multiplexing (OFDM) radar has similar properties. However, its traditional fast calculation method, fast Fourier transform (FFT), limits its measurement accuracy. In this thesis, an accuracy enhancement technique is introduced to increase the measurement accuracy up to the micrometer level [E]

Sensor Fusion For Cooperative Driving

The aim of this project is to modify, adapt, correct and test two target tracking algorithms to check their feasibility for future implementation in Advanced Driving Assistance Systems (ADAS). These systems, which range from automatic brake action to direct intervention in vehicle steering, require constant real-time monitoring of the environment (other cars, pedestrians, wild animals, etc.) and, in this respect, tracking algorithms have a crucial role to play, as they allow the continuous estimation of a target's trajectory in an accurate and efficient way. This project is the continuation of a project initiated by the Wireless Communications Research Unit of the Institute of Telecommunications of the TU Wien. As a starting point, two algorithms designed and implemented by the researchers working on the original project have been used. The first of these algorithms is a Particle Filter (PF) implemented in Python, developed to track a single target, while the second consists of a complex algorithm combining a Multiple Hypothesis Tracking (MHT) algorithm coupled to a Particle Filter (PF), also implemented in Python, with the intention of performing multiple target tracking. The project has been developed as follows. First, a random trajectory of a target was simulated in Matlab, using a random walk. Then, a Frequency Modulated Continuous Wave (FMCW) radar simulator, implemented in Matlab, developed by researchers at TU Wien, was used to perform the corresponding measurements. For the measurement process, a system consisting of four FMCW radars, placed in a square arrangement, was simulated. Finally, all data coming from the four radars was introduced into the two algorithms and combined by means of sensor fusion techniques in order to improve the quality of the trajectory estimates.El objetivo de este proyecto es modificar, adaptar, corregir y probar dos algoritmos de seguimiento de objetivos para comprobar su viabilidad de cara a su futura implantación en sistemas avanzados de asistencia a la conducción (ADAS). Estos sistemas, que van desde la actuación automática de los frenos hasta la intervención directa en la dirección del vehículo, requieren una monitorización constante en tiempo real del entorno (otros coches, peatones, animales salvajes, etc.) y, en este sentido, los algoritmos de seguimiento tienen un papel crucial, ya que permiten la estimación continua de la trayectoria de un objetivo de forma precisa y eficiente. Este proyecto es la continuación de un proyecto iniciado por la Unidad de Investigación de Comunicaciones Inalámbricas del Instituto de Telecomunicaciones de la TU Wien. Como punto de partida, se han utilizado dos algoritmos diseñados e implementados por los investigadores que trabajan en el proyecto original. El primero de estos algoritmos es un Filtro de Partículas (PF) implementado en Python, desarrollado para el seguimiento de un único objetivo, mientras que el segundo consiste en un complejo algoritmo que combina un algoritmo de Seguimiento de Hipótesis Múltiples (MHT) acoplado a un Filtro de Partículas (PF), también implementado en Python, con la intención de realizar el seguimiento de múltiples objetivos. El proyecto se ha desarrollado de la siguiente manera. En primer lugar, se simuló una trayectoria aleatoria de un objetivo en Matlab, utilizando un randomwalk. A continuación, se utilizó un simulador de radar de Onda Continua Modulada en Frecuencia (FMCW), implementado en Matlab, desarrollado por investigadores de TU Wien, para realizar las mediciones correspondientes. Para el proceso de medición, se simuló un sistema formado por cuatro radares FMCW, colocados en una disposición cuadrada. Por último, todos los datos procedentes de los cuatro radares se introdujeron en los dos algoritmos y se combinaron mediante técnicas de fusión de sensores para mejorar la calidad de las estimaciones de la trayectoria.L'objectiu d'aquest projecte és modificar, adaptar, corregir i provar dos algorismes de seguiment d'objectius per comprovar-ne la viabilitat de cara a la implantació futura en sistemes avançats d'assistència a la conducció (ADAS). Aquests sistemes, que van des de l'actuació automàtica dels frens fins a la intervenció directa a la direcció del vehicle, requereixen una monitorització constant en temps real de l'entorn (altres cotxes, vianants, animals salvatges, etc.) i, en aquest sentit, els algorismes de seguiment tenen un paper crucial, ja que permeten l'estimació contínua de la trajectòria d'un objectiu de manera precisa i eficient. Aquest projecte és la continuació d'un projecte iniciat per la Unitat de Recerca de Comunicacions Sense Fils de l'Institut de Telecomunicacions de la TU Wien. Com a punt de partida, s'han utilitzat dos algorismes dissenyats i implementats pels investigadors que treballen al projecte original. El primer d'aquests algoritmes és un Filtre de Partícules (PF) implementat a Python, desenvolupat per al seguiment d'un únic objectiu, mentre que el segon consisteix en un complex algorisme que combina un algorisme de seguiment d'hipòtesis múltiples (MHT) acoblat a un Filtre de Partícules (PF), també implementat a Python, amb la intenció de fer el seguiment de múltiples objectius. El projecte s'ha desenvolupat de la manera següent. En primer lloc, es va simular una trajectòria aleatòria d'un objectiu a Matlab, fent servir un randomwalk. A continuació, es va utilitzar un simulador de radar d'Onda Contínua Modulada en Freqüència (FMCW), implementat a Matlab, desenvolupat per investigadors de TU Wien, per realitzar els mesuraments corresponents. Per al procés de mesura, es va simular un sistema format per quatre radars FMCW, col·locats en una disposició quadrada. Finalment, totes les dades procedents dels quatre radars es van introduir als dos algoritmes i es van combinar mitjançant tècniques de fusió de sensors per millorar la qualitat de les estimacions de la trajectòria

A LINEARIZATION METHOD FOR A UWB VCO-BASED CHIRP GENERATOR USING DUAL COMPENSATION

Ultra-Wideband (UWB) chirp generators are used on Frequency Modulated Continuous Wave (FMCW) radar systems for high-resolution and high-accuracy range measurements. At the Center for Remote Sensing of Ice Sheets (CReSIS), we have developed two UWB radar sensors for high resolution measurements of surface elevation and snow cover over Greenland and Antarctica. These radar systems are routinely operated from both surface and airborne platforms. Low cost implementations of UWB chirp generators are possible using an UWB Voltage Controlled Oscillator (VCO). VCOs possess several advantages over other competing technologies, but their frequency-voltage tuning characteristics are inherently non-linear. This nonlinear relationship between the tuning voltage and the output frequency should be corrected with a linearization system to implement a linear frequency modulated (LFM) waveform, also known as a chirp. If the waveform is not properly linearized, undesired additional frequency modulation is found in the waveform. This additional frequency modulation results in undesired sidebands at the frequency spectrum of the Intermediate Frequency (IF) stage of the FMCW radar. Since the spectrum of the filtered IF stage represents the measured range, the uncorrected nonlinear behavior of the VCO will cause a degradation of the range sensing performance of a FMCW radar. This issue is intensified as the chirp rate and nominal range of the target increase. A linearization method has been developed to linearize the output of a VCO-based chirp generator with 6 GHz of bandwidth. The linearization system is composed of a Phase Lock Loop (PLL) and an external compensation added to the loop. The nonlinear behavior of the VCO was treated as added disturbances to the loop, and a wide loop bandwidth PLL was designed for wideband compensation of these disturbances. Moreover, the PLL requires a loop filter able to attenuate the reference spurs. The PLL has been designed with a loop bandwidth as wide as possible while maintaining the reference spur level below 35 dBc. Several design considerations were made for the large loop bandwidth design. Furthermore, the large variations in the tuning sensitivity of the oscillator forced a design with a large phase margin at the average tuning sensitivity. This design constraint degraded the tracking performance of the PLL. A second compensation signal, externally generated, was added to the compensation signal of the PLL. By adding a compensation signal, which was not affected by the frequency response effects of the loop compensation, the loop tracking error is reduced. This technique enabled us to produce an output chirp signal that is a much closer replica of the scaled version of the reference signal. Furthermore, a type 1 PLL was chosen for improved transient response, compared to that of the type 2 PLL. This type of PLL requires an external compensation to obtain a finite steady state error when applying a frequency ramp to the input. The external compensation signal required to solve this issue was included in the second compensation signal mentioned above. Measurements for the PLL performance and the chirp generator performance were performed in the laboratory using a radar demonstrator. The experimental results show that the designed loop bandwidth was successfully achieved without significantly increasing the spurious signal level. The chirp generator measurements show a direct relationship between the bandwidth of the external compensation and the range resolution performance

High-resolution three-dimensional imaging radar

A three-dimensional imaging radar operating at high frequency e.g., 670 GHz, is disclosed. The active target illumination inherent in radar solves the problem of low signal power and narrow-band detection by using submillimeter heterodyne mixer receivers. A submillimeter imaging radar may use low phase-noise synthesizers and a fast chirper to generate a frequency-modulated continuous-wave (FMCW) waveform. Three-dimensional images are generated through range information derived for each pixel scanned over a target. A peak finding algorithm may be used in processing for each pixel to differentiate material layers of the target. Improved focusing is achieved through a compensation signal sampled from a point source calibration target and applied to received signals from active targets prior to FFT-based range compression to extract and display high-resolution target images. Such an imaging radar has particular application in detecting concealed weapons or contraband