Impulse Radio Ultra-wideband Research Articles

Antenna Delay Calibration of UWB Nodes

Impulse-radio ultra-wideband (IR-UWB) networks are gaining wide acceptance in short-to-medium range wireless sensing and positioning applications that require high accuracy. It is achieved generally via signal message exchange between ultra-wideband (UWB) transceiver nodes, where the signal propagating through their analog circuitry suffers transmitting and receiving antenna delays. Such delays, unless measured and properly corrected for, may induce an error in range estimation between UWB nodes and eventually affect the accuracy of real-time location systems (RTLSs) based on the IR-UWB. This paper presents a system to measure the antenna delays of UWB nodes. It provides comprehensive mathematical modeling, design, and implementation of the proposed antenna delay measurement system. Experimental evaluation in a line-of-sight (LOS) environment shows its effectiveness for maintaining the accuracy of the range measurement between UWB nodes by taking into consideration the antenna delays measured by the proposed system.

A differential IR-UWB transmitter using PAM modulation with adaptive PSD

The current state of the telecommunications market exhibits a high potential to absorb efficient innovations in wireless connectivity, especially those that can be applied to the Internet of Things and similar domains. Contributing in that direction, this paper describes the design and implementation of a fully differential impulse-radio ultra-wideband (IR-UWB) transmitter using pulse-amplitude modulation, with an adaptive power spectrum density (PSD). The architecture can produce up to eight differential monocycles per clock pulse at its output. The number of monocycles controls the bandwidth (thus the PSD) in the mask of IR-UWB technologies, allowing adaptation to multiple standards. The complete transmitter has four main blocks: (a) a pulse generator, comprising two pulse generating circuit groups, to modulate and create a rectangular waveform; (b) an active balun with two amplifiers, to generate differential signals; (c) a digital demultiplexer, to alternate data to the pulse generating circuit groups; (d) a binary-to-thermometer decoder, to control the amount of generated monocycles per pulse. Simulations demonstrate an output pulse amplitude of 120 mV for the high logic level and of 70 mV for the low logic level, both at a 100 MHz Pulse Repetition Frequency. This produces a mean pulse duration of 277 ps, a mean central frequency of 3.8 GHz, and a mean power consumption 6.7 mW. The transmitter takes the form of an intellectual property core in a 130 nm CMOS technology. The complete transmitter area is 0.067 mm $$^2$$ , without I/O pads. The outcomes suggest that the proposed circuit can narrow or widen the output signal bandwidth, providing adaptability to different emission requirements.

TOA and DOA Estimation for IR‐UWB Signals: An Efficient Algorithm by Improved Root‐MUSIC

The automatically paired time of arrival (TOA) and direction of arrival (DOA) can be jointly estimated via a high‐precision multidimensional spectral peak search‐ (SPS‐) based multiple signal classification (MUSIC) algorithm in the impulse radio ultrawideband (IR‐UWB) positioning system, while heavy computational burden is required. To tackle this issue, we propose an improved root‐MUSIC algorithm for joint TOA and DOA estimation. After modelling the frequency domain form of the received signal, the algorithm first uses the signal subspace to establish the relationship between the two antennas. Then, the MUSIC spatial spectrum function is reconstructed with this relation, which enables it to offer a spectrum function in regard to the one‐dimensional (1D) parameter of time delay. For further reducing the complexity, the TOA estimates of one antenna are obtained via 1D polynomial root finding instead of SPS, and the TOA estimates of the other antenna can be calculated by the established relationship. Finally, the DOA estimation can be achieved with the estimated TOAs. Due to the relationship between two antennas with signal subspace, the parameters estimated by the proposed algorithm are autopaired. Numerical simulations substantiate the superiority of the proposed algorithm.

Time-Domain Ultrawideband Chipless RFID Readers

This article evaluates time-domain techniques for the applications of ultrawideband (UWB) chipless radio frequency identification (RFID) readers. In UWB time-domain readers, the chipless RFID tag response to a UWB pulse excitation is simultaneously measured in time domain and then the frequency-domain signature of the tag is calculated by a time-to-frequency conversion method such as fast Fourier transform. A 32-bit UWB chipless RFID tag is designed and three time-domain readers based on impulse radio UWB, chirped-pulse Fourier transform microwave (CP-FTMW), and dual-comb techniques are analyzed and implemented by using microwave equipment including arbitrary waveform generator, network analyzer, and high-speed oscilloscope. It is demonstrated that CP-FTMW reader is a fast, accurate with high signal-to-noise ratio, and high-frequency resolution time-domain technique. Dual-comb reader is slower, however, it offers a viable solution for a low cost and potentially miniaturized and portable chipless RFID readers.

A Low-Cost Indoor Real-Time Locating System Based on TDOA Estimation of UWB Pulse Sequences

One of the most popular technologies adopted for indoor localization is ultrawideband impulse radio (IR-UWB). Due to its peculiar characteristics, it is able to overcome the multipath effect that severely reduces the capability of receivers (sensors) to estimate the position of transmitters (tags) in complex environments. In this article, we introduce a new low-cost real-time locating system (RTLS) that does not require time synchronization among sensors and uses a one-way communication scheme to reduce the cost and complexity of tags. The system is able to evaluate the position of a large number of tags by computing the time difference of arrival (TDOA) of UWB pulse sequences received by at least three sensors. In the presented system, the tags transmit sequences of 2-ns UWB pulses with a carrier frequency of 7.25 GHz. Each sensor processes the received sequences with a two-step correlation analysis performed first on a field-programmable gate array (FPGA) chip and successively on an on-board processor. The result of the analysis is the time of arrival (TOA) of the tag sequence at each sensor and the ID of the associated tag. The results are sent to a host PC implementing trilateration algorithm based on the TDOA computed among sensors. We will describe the characteristics of the custom hardware that has been designed for this project (tag and sensor) as well as the processing steps implemented that allowed us to achieve an optimum localization accuracy of 10 cm.

Feasibility of non-contact cardiorespiratory monitoring using impulse-radio ultra-wideband radar in the neonatal intensive care unit.

Current cardiorespiratory monitoring equipment can cause injuries and infections in neonates with fragile skin. Impulse-radio ultra-wideband (IR-UWB) radar was recently demonstrated to be an effective contactless vital sign monitor in adults. The purpose of this study was to assess heart rates (HRs) and respiratory rates (RRs) in the neonatal intensive care unit (NICU) using IR-UWB radar and to evaluate its accuracy and reliability compared to conventional electrocardiography (ECG)/impedance pneumography (IPG). The HR and RR were recorded in 34 neonates between 3 and 72 days of age during minimal movement (51 measurements in total) using IR-UWB radar (HRRd, RRRd) and ECG/IPG (HRECG, RRIPG) simultaneously. The radar signals were processed in real time using algorithms for neonates. Radar and ECG/IPG measurements were compared using concordance correlation coefficients (CCCs) and Bland-Altman plots. From the 34 neonates, 12,530 HR samples and 3,504 RR samples were measured. Both the HR and RR measured using the two methods were highly concordant when the neonates had minimal movements (CCC = 0.95 between the RRRd and RRIPG, CCC = 0.97 between the HRRd and HRECG). In the Bland-Altman plot, the mean biases were 0.17 breaths/min (95% limit of agreement [LOA] -7.0-7.3) between the RRRd and RRIPG and -0.23 bpm (95% LOA -5.3-4.8) between the HRRd and HRECG. Moreover, the agreement for the HR and RR measurements between the two modalities was consistently high regardless of neonate weight. A cardiorespiratory monitor using IR-UWB radar may provide accurate non-contact HR and RR estimates without wires and electrodes for neonates in the NICU.

A Tunable CMOS IR-UWB Pulse Generator Based on Feedback Controlled Oscillator Switching

This brief presents a tunable Impulse-Radio Ultra-Wideband (IR-UWB) pulse generator based on feedback oscillator switching. The circuit provides a wide range of pulse amplitude and width tuning, thus enabling the required pulse shaping for a desired pulse repetition rate and/or a wireless transmission range. Feedback controlled switching prevents the potential omission of the UWB pulse generation and provides low UWB pulse energy variations at low bias currents and a wide temperature range, ensuring system robustness with respect to temperature variations. The pulse amplitude is tunable within 0.27 Vpp to 2.05 Vpp, while the pulse width tuning range is 1-6.5 ns. The total energy consumption of the IR-UWB pulse generator at the 50 Mpps pulse repetition rate is equal to 25.4 pJ/pulse for the pulse amplitude equal to 0.27 Vpp, while for the pulse amplitude equal to 2.05 Vpp, it is increased up to 99.8 pJ/pulse. The circuit occupies a core area of 0.56 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in a 0.18 μm CMOS technology.

Planar Sectoral Antenna for IR-UWB Localization With Minimal Range Estimation Biasing

A planar sectoral antenna is presented, optimized for highly precise impulse-radio ultrawideband (IR-UWB) indoor localization with minimal range estimation biasing. By judiciously combining two planar inverted-F antenna elements into one footprint, a large half-power beamwidth (HPBW) is obtained in the [3.2448-4.7424] GHz band, thereby covering channels 1-4 of the IEEE 802.15.4a-2011 standard. Through system-level optimization, the system fidelity factor (SFF) is maximized for a minimal value of at least 90$\text{\%}$ within its entire HPBW, while minimizing the orientation-specific range estimation biasing down to 10 mm. To validate the antenna performance, measurements have been performed in both the frequency and time domain, showing a HPBW larger than 120$^\circ$ in the complete frequency band of operation and an SFF larger than 90$\text{\%}$ and range biasing lower than 4 mm within the antenna's HPBW.

Multi-Classification Algorithm for Human Motion Recognition Based on IR-UWB Radar

In this paper, a multi-classification algorithm for human motion recognition based on Impulse-Radio Ultra-wideband (IR-UWB) radar is presented. The algorithm includes three parts. First, the k-NearestNeighbor (KNN) algorithm is used to classify the radial features of pre-processed signal to determine the subject’s radial displacement direction. Then, the power spectrum feature extraction algorithm and Doppler shifts feature extraction algorithm are proposed to extract and visualize the characteristics from the different categories classified by the first part. Finally, the feature spectrograms obtained by the second part are sent into Convolutional Neural Networks (CNNs) for training and testing to realize the recognition of human motions. To verify the performance of proposed algorithm, dataset was created from 15 persons including 12 kinds of motions. The Five-Fold Cross Validation was conducted to calculate the recognition accuracy. As a result, the average accuracy of judging the radial displacement directions of subjects was up to 99%. Furthermore, the average accuracy of estimating the motions of subjects reached 98%. Experiments have proved that the proposed algorithm can achieve high recognition accuracy in daily human motions and is feasible in a variety of test environments.

IR-UWB Sensor Based Fall Detection Method Using CNN Algorithm.

Falls are the leading cause of fatal injuries in the elderly such as fractures, and secondary damage from falls can lead to death. As such, fall detection is a crucial topic. However, due to the trade-off relationship between privacy preservation, user convenience, and fall detection performance, it is generally difficult to develop a fall detection system that simultaneously satisfies all conditions. The main goal of this study is to build a practical fall detection framework that can effectively classify the various behavior types into “Fall” and “Activities of daily living (ADL)” while securing privacy preservation and user convenience. For this purpose, signal data containing the motion information of objects was collected using a non-contact, unobtrusive, and non-restraint impulse-radio ultra wideband (IR-UWB) radar. These data were then applied to a convolutional neural network (CNN) algorithm to create an object behavior type classifier that can classify the behavior types of objects into “Fall” and “ADL.” The data were collected by actually performing various activities of daily living, including falling. The performance of the classifier yielded satisfactory results. By combining an IR-UWB and CNN algorithm, this study demonstrates the feasibility of building a practical fall detection system that exceeds a certain level of detection accuracy while also ensuring privacy preservation and user convenience.

A TD-ADC for IR-UWB Radars With Equivalent Sampling Technology and 8-GS/s Effective Sampling Rate

A high-speed time domain analog-to-digital converter (ADC) customized for impulse radio ultra-wideband (IR-UWB) radars is proposed in this brief. It adopts a power efficient architecture combining time domain implementation and equivalent sampling technology. The equivalent sampling rate is high up to 8 GS/s. Compared to time interleaved (TI) ADC, the proposed time domain ADC (TD-ADC) not only has less power consumption and silicon area, but also is free from complicated digital calibration. The prototype ADC was fabricated in a 65nm CMOS technology. The achieve area is 320 μm × 300 μm. With the Nyquist middle frequency input of 1.376 GHz, the measured spurious free dynamic range (SFDR) and signal to noise and distortion ratio (SNDR) are over 57.6 dB and 43.0 dB, while the real time power consumption is only 8.2 mW. The figure of merit (FOM) is about 147 fJ/step.

Time-shift immunity for wireless sensor network based on discrete wavelet packets

Wavelet-based Ultra Wide Band communications rely on receiver collecting data simultaneously from many transmitters and without interference thanks to the orthogonality between primitive wavelet packets. Nevertheless, there is a particular case for which the communication fails. Indeed, the time-shift between primitive wavelet packets results in a loss of the orthogonality of these wavelet packets. This paper proposes an asynchronous Impulse Radio-Ultra Wide Band (IR-UWB) transmission suitable in Wireless Sensor networks without any distinction between the transmitters. The originality of the proposed solution is to ensure a time-shift immunity of IR-UWB receivers by finding the unique combination of shifted primitive packets. For this purpose, finding the one zero result of successive subtractions between received and primitive packets is performed. Considering a given wavelet, the proposed solution is able to decode the shifted-mixed primitive packets from multiple transmitters whatever the time-shift between each packets.

IR-UWB Pulse Generation Using FPGA Scheme for through Obstacle Human Detection.

This research proposes a scheme of field programmable gate array (FPGA) to generate an impulse-radio ultra-wideband (IR-UWB) pulse. The FPGA scheme consists of three parts: digital clock manager, four-delay-paths stratagem, and edge combiner. The IR-UWB radar system is designed to detect human subjects from their respiration underneath the rubble in the aftermath of an earthquake and to locate the human subjects based on range estimation. The proposed IR-UWB radar system is experimented with human subjects lying underneath layers of stacked clay bricks in supine and prone position. The results reveal that the IR-UWB radar system achieves a pulse duration of 540 ps with a bandwidth of 2.073 GHz (fractional bandwidth of 1.797). In addition, the IR-UWB technology can detect human subjects underneath the rubble from respiration and identify the location of human subjects by range estimation. The novelty of this research lies in the use of the FPGA scheme to achieve an IR-UWB pulse with a 2.073 GHz (117 MHz–2.19 GHz) bandwidth, thereby rendering the technology suitable for a wide range of applications, in addition to through-obstacle detection.

Application of impulse-radio ultra-wideband radar as a non-contact portable monitoring device for the diagnosis of obstructive sleep apnea

Objective:To compare the effect of impulse-radio ultrawideband（IR-UWB） radar technology and polysomnography（PSG） in sleep assessment. Method:A total of 79 OSA patients were randomly divided into two groups: 40 patients in group A received PSG and IR-UWB, and 39 patients in group B received micromovement sensitive mattress（MSM） and IR-UWB. Pearson correlation and ROC curve were used for statistics. Result:AHI PSG and AHI MSM were significantly correlated with AHI IR-UWB（r=0.91, P＝0.00; r=0.92, P＝0.00）. Bland-Altman analysis showed that AHI IR-UWB value was highly consistent with AHI PSG value（95.00%）, and AHI IR-UWB value（97.44%）. The sensitivity and specificity of AHI IR-UWB compared with PSG were 70.40% and 89.90%, respectively. The area under ROC curve was 0.915. Conclusion:IR-UWB has a high diagnostic value for adult OSA in terms of minimum blood oxygen saturation, average blood oxygen saturation, average number of central sleep apnea, average number of complex sleep apnea, average heart rate, sleep efficiency, REM sleep duration, average AHI, etc. It is an economic and practical sleep evaluation tool.

MMT-HEAR: Multiple Moving Targets Heartbeats Estimation and Recovery Using IR-UWB Radars.

Populations around the world are rapidly ageing. Age-friendly environments address the significance of continuous inhome vital sign monitoring. Impulse Radio Ultra-WideBand (IR-UWB) radar serves as a household healthcare assistance, providing non-contact vital sign monitoring without privacy issues and illumination limitation. However, the body movements bring difficulty in extracting heartbeat from radar signals, let alone obtaining complete information with body occlusions among multiple targets. This paper proposes a Multiple Moving Targets Heartbeat Estimation And Recovery (MMT-HEAR) approach to extract vital signs using IR-UWB radars. CLEAN and Joint Probability Data Association (JPDA) algorithms are firstly performed on each radar to estimate target-to-antenna distances of multiple targets. Considering signal obstruction and attenuation for targets occluded by others, the location-based distance optimization is proposed to refine these distances by combining information from all radars. Then the mapping from signal amplitudes to refined distances is introduced and combined with the Variational Nonlinear Chirp Mode Decomposition (VNCMD) to extract vital signs with body movements. To the best of our knowledge, this is the first attempt to monitor vital signs of multiple moving targets with radars. The averaging accuracy for two moving targets heartbeat monitoring during a 20-minutes observation is 85.93% with MMT-HEAR. Compared to two other conventional methods, the MMT-HEAR approach yields improvements of 16.11% and 10.16%, revealing the efficiency and robustness of this proposed approach.

Body Orientation and Vital Sign Measurement With IR-UWB Radar Network.

Utilizing Impulse Radio Ultra-WideBand (IR-UWB) radar for vital sign monitoring has attracted growing interest due to the noncontact measurement without privacy concerns. Most of existing researches assume that the subject's chest is directed to the radar antenna, to ensure the strength of backscattered signals from chest movement. However, a large angle between the antenna and the subject's chest caused by the body orientation badly affects the monitoring accuracy. Multiple observations of the same cardiopulmonary activity from different orientations provide more available measurements. This paper addresses the challenge by using an IR-UWB radar network instead of a single radar. Three IR-UWB radars are placed as endpoints of an equilateral triangle to collect vital sign information of a subject sitting at the center. A Conditional Generative Adversarial Network (CGAN) method is proposed to fuse multisensory data. First, the body orientation is classified by combining signal features and a random forest classifier. Then the impact of different angles on vital sign monitoring results is discussed and validated in each orientation. The data fusion process is modelled as an extended generative network with orientation based condition to produce the enhanced vital signal. This signal is optimized with the discriminator network to a fitted sinusoidal wave with heartbeat and respiratory information. Experimental results on measuring Heartbeat Rate (HR) in different orientations reveal the effectiveness and stability of the proposed method.

A Hybrid Radar-Camera Respiratory Monitoring System Based on an Impulse-Radio Ultrawideband Radar.

This paper reports a pilot study of a hybrid radar-camera system that simultaneously monitors the respiration of two subjects. A prototype system was built involving a low-cost impulse-radio ultra-wideband (IR-UWB) radar module and an optical and depth-sensing camera module. The system detects subjects using the camera and utilizes the distance information acquired to guide the signal processing of the radar. This structure simplifies subject identification and tracking for the radar system, provides further context to the radar, and facilitates the extraction of respiration information. Experiments under different scenarios were conducted to evaluate the performance of the system at different distances and angles from subjects. The localization procedure has an average accuracy of 0.1 m. The respiration rates extracted from the radar are comparable with the values from the reference wearable sensor, reporting an average error of 0.79 respirations per minute (RPM) with a standard deviation of 0.71 RPM. The results suggest that the respiration signals from subjects could be accurately monitored with the presented framework. It is also feasible to monitor two subjects at the same time in most scenarios. The proposed framework shows promising potential to work as a ubiquitous monitoring system for multiple subjects.

Improvement of the Angle of Arrival Measurement Accuracy for Indoor UWB Localization

This paper shows that the accuracy of azimuth angle measurement for an interferometric localization system used to locate tags in its Line-of-Sight (LoS) can be improved by exploiting Impulse Radio-Ultra WideBand (IR-UWB) signals and without increasing the frequency bandwidth. This solution uses a Phase Correlation (PC) method, initially applied for Continuous Wave (CW) signals, adapted for Ultra WideBand (UWB) pulse signals. The obtained results are compared to those computed by a classical Energy Detection (ED) method where it becomes impossible to estimate azimuth angles for tag positions close to the orthogonal centered axis of the localization system baseline.

Circuit analysis and optimisation of the high‐voltage high‐efficiency IR‐UWB pulse generator for ranging and radar application

An in-depth circuital analysis of an energy-efficient high peak power impulse radio ultra-wideband (IR-UWB) pulse generator monolithic microwave integrated circuit (MMIC) design is presented. The proposed IR-UWB pulse generation process is explained in detail. A trade-off between the peak output power level and the frequency of operation is discussed. The proposed circuit is optimised for the highest possible peak output power in the 3–5 GHz UWB band for ranging and radar application. The presented IR-UWB pulse former makes use of the cascode heterojunction bipolar transistor (HBT) configuration for signal scaling operation instead of the common emitter configuration. The proposed cascode pair configuration results in higher output voltage swing as well as reduced power consumption. The effect of coupling capacitors on amplification factor of the pulse former stages as well as impedance profile of the distributed transmission line is discussed in great detail. The temperature-dependent parasitic component in the proposed circuit is studied. Its effect on the transient behaviour of the proposed IR-UWB pulse generator is analysed, which is important for IR-UWB beamforming applications. The required mathematical model for the parasitic effect is derived and explained.

A new method for vital sign monitoring using IR-UWB radar

Quadrature Demodulation IR-UWB radar is a new form of impulse-radio Ultrawide Band (IR-UWB) radar and it can improve the resolution of distance measurement. This paper focuses on a new method for vital sign – specifically breathing rate and heart rate – from the phase of recorded I/Q signals, using Quadrature Demodulation IR-UWB radar. The results of the experiment show that a better estimation of heart rate can be got from such a new method based on the phase difference.