Backscatter Modulation Research Articles

Toward Software-Defined Backscatter Modulation via Signal Emulation

Toward Software-Defined Backscatter Modulation via Signal Emulation

Antenna Array Measurements by a Scalable Backscatter Modulation Procedure

Antenna Array Measurements by a Scalable Backscatter Modulation Procedure

Optimal 4QAM backscatter modulation for passive UHF CRFID tags

With the development of the Internet of Things (IoT), the amount of transmitted data is getting huge. Traditional passive UHF CRFID Tag currently adopts 2ASK or 2PSK backscatter modulation, and each symbol conveys 1 bit of information. Still, this modulation has the problems of low throughput, poor real-time, and low energy utilization. This paper proposes an optimal 4 Quadrature Amplitude Modulation (4QAM) backscatter scheme at 920 MHz, which can increase the throughput and simultaneously improve energy utilization. In this optimal scheme, the reflection coefficient modulus |Γ| is closely related to the energy. The low power of the passive tag requires that the modulation circuit’s design consider how to choose |Γ|opt (optimal reflection coefficient modulus). Therefore, we build the energy model of CRFID to explore the |Γ|opt at different symbol rates and use the |Γ|opt to design a more reasonable constellation diagram for passive tags. Finally, this paper analyzes the decoding of multinary backscatter signals, and an improved Kmeans algorithm can solve the cluster offset problem at high symbol rates. After experiments, |Γ|opt is around 0.67, the maximum throughput of 4QAM backscatter modulation can reach 16 Mbit/s, and the power consumption is 4.38 mW. Compared with the traditional binary modulation, the tag in this paper can double the throughput at the same symbol rate.

Backscatter Modulation for Wearable RFID Tags: RFID Tag Optimization for Maximum Backscatter Energy

Backscatter Modulation for Wearable RFID Tags: RFID Tag Optimization for Maximum Backscatter Energy

A Robust Backscatter Modulation Scheme for Uninterrupted Ultrasonic Powering and Back-Communication of Deep Implants

A Robust Backscatter Modulation Scheme for Uninterrupted Ultrasonic Powering and Back-Communication of Deep Implants

On the Correlation Between the SAR Backscatter Modulation and Surface Waves Orbital Velocity

On the Correlation Between the SAR Backscatter Modulation and Surface Waves Orbital Velocity

Energy Efficient Enhancement in a 5.8 GHz Batteryless Node Suitable for Backscattering Communications

This work presents a compact batteryless node architecture suitable with the backscattering communication (BackCom) approach. The key functional blocks are demonstrated at 5.8 GHz, making use of commercially available components involving a DC/DC step-up converter, a 3.3 V data generator, and an ASK backscattering modulator based on a single GaAs HEMT in a cold-FET configuration. The node integrates a patch antenna exhibiting a non-50 Ω optimal port impedance; the value is defined by means of a source pull-based optimization technique aimed at maximizing the DC/DC input current supplied by the RF to DC converter. This approach maximizes the node compactness, as well as the wireless power conversion efficiency. A prototype was optimized for the −5 dBm power level at the input of the RF to DC converter. Under this measurement condition, the experimental results showed a 63% increase in the harvesting current, rising from 145 to 237 μA, compared to an identical configuration that used a microstrip matching network coupled with a typical 50-Ω patch antenna. In terms of harvested power, the achieved improvement was from −13.2 dBm to −10.9 dBm. The conversion efficiency in an operative condition improved from 15% to more than 25%. In this condition, the node is capable of charging a 100 μF to the operative voltage in about 27 s, and operating the backscattering for 360 ms with a backscattering modulation frequency of about 10 MHz.

On the Performance of Square, Rectangular, Star, and Hexagonal QAM for Backscatter Systems

Applications on wireless sensing and internet of things (IoT) require communication systems based on low power with high data rates. Thus, backscatter communication plays an important role in the new emerging IoT communications. In the literature, several works have been reported about backscatter modulators with high-order modulation formats. However, only the square quadrature amplitude modulation (S-QAM) scheme is considered, although it is not optimal in the sense of power efficiency. In this letter, the performance of two dimensional (2-D) signal constellations is evaluated, namely rectangular QAM, star QAM, and hexagonal QAM, in terms of the symbol error rate, in backscatter systems context. A power consumption analysis is presented for these modulation schemes. To provide the symbols of the aforementioned constellations, a practical high-order backscatter modulator, corroborated by measurement campaigns, is implemented. Several SER curves are also presented in this work.

Spectrally Efficient Backscatter Systems: A Hardware-Oriented Survey

The growing interest in backscatter communications as a low-powered solution in various fields necessitates pushing the envelope of current backscatter systems in multiple frontiers, among which is spectral efficiency. The increase in spectral efficiency can drive real-time applications such as augmented reality. In most of backscatter-system applications such as radio-frequency identification, backscatter modulation is implemented using binary schemes realized with square pulses, which are not spectral efficient. To address the spectral efficiency concern, this article reviews—with a scope limited to prototyped systems—some of the existing works in the literature that pertain to increasing the spectral efficiency of backscatter systems. The prototyped systems can be grouped—based on the implementation technique used—into three groups: High-order modulation, single-sideband modulation, and pulse shaping. Based on the current trends and studied literature, the article concludes with discussions on some future directions and open-ended research problems such as optimal pulse shaping, the use of artificial intelligence, multi-carrier modulation, and agile modulation; which are all aim for overcoming the spectral-efficiency limit of contemporary backscatter systems.

Directional amplitude backscatter modulation with suppressed Doppler based on rotating resonant loop

The directional amplitude backscatter modulation with suppressed Doppler is demonstrated based on the scattering from a symmetrically rotating resonant loop. The concept is studied theoretically and experimentally with perfectly compatible results. The symmetrical rotation of the scatterer and the effect of radial resonance, as the two crucial points to realize the idea, are highlighted through the comparison between the symmetric and non-symmetric cases, and the results obtained for scatterers with and without radial resonance. The presented backscattering modulation technique provides an amplitude modulating waveform which is uniquely linked to the directional reradiation pattern of the rotating loop scatterer in a definite resonant mode. With the pure directional amplitude modulation (DAM) induced on the backscattered wave, the envelope waveform can be accurately retrieved form the received signal using the In-phase and Quadrature (IQ) representation. The contribution of the background in a real environment can be detected and removed to obtain the exact modulating waveform. This property of the proposed backscattering modulation method can be applied for sensing, localization, and identification purposes with high sensitivity, read range, and robustness.

Backscatter Communication Assisted by Reconfigurable Intelligent Surfaces

In a backscatter communication system, the backscatter device (BD) transmits its messages to the backscatter receiver (BR) by reflecting the incident signal from an external radio frequency (RF) emitter, instead of using power-hungry active RF components themselves. Thus, backscatter communication has shown great potential for achieving low-power communication. The double-fading effect associated with the backscatter link, however, is a major limiting factor to achieve efficient backscatter communication. Reconfigurable intelligent surfaces (RISs), a recently developed technology, can be applied at the BD to enhance the backscatter link thanks to the fact that both RIS and backscatter communication share the same reflective principle. Such a design can also allow the backscatter communication system to capture the desired RF signal as a reflective carrier in a complex radio environment. In this article, a comprehensive overview of backscatter communication assisted by RIS is given. We first introduce the basics of backscatter communication, which covers the antenna scattering principle, backscatter modulation, and link budget calculation. Then, the details of RIS are discussed, which include antenna-based RIS and metamaterial-based RIS, followed by the discussion of the roles of RIS in backscatter communication. After that, we provide an overview of three types of backscatter communication systems assisted by RIS, including RIS-assisted unmodulated backscatter communication, RIS-assisted ambient backscatter communication, and RIS-assisted symbiotic radio. Emerging applications of these systems, technical challenges, and future opportunities in this emerging field are also presented.

Chipless labels detection by backscattering for identification and sensing applications

There is currently a growing interest in the development of communication systems that consume as little energy as possible, with the idea of eliminating the presence of batteries, which are a very polluting component. This is why the principles of communication based on backscatter modulation, or even more simply on backscattering by a device that takes the form of a label, like a barcode, are being studied more and more. In the latter case, the idea is to use the radar signature of this totally passive label, the geometry of the elements printed on it having been specially designed to perform the desired functions. These new systems cannot claim to do the same things as those working with a power supply or a chip, but they may be of interest for certain applications where the reading distances do not exceed one metre. Compared to barcodes, the main advantages are related to the use of RF waves to communicate, which makes it possible to read through certain objects that are opaque to light, or to significantly reduce the acquisition time of identifiers by being able to scan larger reading areas more easily.

A Ka-Band Wind Geophysical Model Function Using Doppler Scatterometer Measurements from the Air-Sea Interaction Tower Experiment

Physical understanding and modeling of Ka-band ocean surface backscatter is challenging due to a lack of measurements. In the framework of the NASA Earth Ventures Suborbital-3 Submesoscale Ocean Dynamics Experiment (S-MODE) mission, a Ka-Band Ocean continuous wave Doppler Scatterometer (KaBODS) built by the University of Massachusetts, Amherst (UMass) was installed on the Woods Hole Oceanographic Institution (WHOI) Air-Sea Interaction Tower. Together with ASIT anemometers, a new data set of Ka-band ocean surface backscatter measurements along with surface wind/wave and weather parameters was collected. In this work, we present the KaBODS instrument and an empirical Ka-band wind Geophysical Model Function (GMF), the so-called ASIT GMF, based on the KaBODS data collected over a period of three months, from October 2019 to January 2020, for incidence angles ranging between 40° and 68°. The ASIT GMF results are compared with an existing Ka-band wind GMF developed from data collected during a tower experiment conducted over the Black Sea. The two GMFs show differences in terms of wind speed and wind direction sensitivity. However, they are consistent in the values of the standard deviation of the model residuals. This suggests an intrinsic geophysical variability characterizing the Ka-band surface backscatter. The observed variability does not significantly change when filtering out swell-dominated data, indicating that the long-wave induced backscatter modulation is not the primary source of the KaBODS backscatter variability. We observe evidence of wave breaking events, which increase the skewness of the backscatter distribution in linear space, consistent with previous studies. Interestingly, a better agreement is seen between the GMFs and the actual data at an incidence angle of 60° for both GMFs, and the statistical analysis of the model residuals shows a reduced backscatter variability at this incidence angle. This study shows that the ASIT data set is a valuable reference for studies of Ka-band backscatter. Further investigations are on-going to fully characterize the observed variability and its implication in the wind GMF development.

SAR Altimetry Data as a New Source for Swell Monitoring

AbstractThis article shows the first spectral analysis of fully‐focused Synthetic Aperture Radar (FFSAR) altimetry data with the objective of studying backscatter modulations caused by swells. Swell waves distort the backscatter in altimetry radargrams by means of velocity and range bunching. These swell signatures are visible in the tail of the waveform. By locally normalizing the backscatter and projecting the waveforms on an along‐/cross‐track grid, satellite altimetry can be exploited to retrieve swell information. The analysis of FFSAR spectra is supported by buoy‐derived swell‐wave spectra of the National Oceanic and Atmospheric Administration network. Using cases with varying wave characteristics, we discuss the altimetry‐derived spectra and relate them to what is known from side‐looking SAR imaging systems. Besides having a vast amount of additional data for swell‐wave analysis, altimeter data can also help us to better understand the side‐looking SAR spectra.

A Passive Computational UHF RFID Platform Using Vector Backscatter Modulation

This article presents the design and implementation of a passive, computational ultra high frequency (UHF) radio frequency identification (RFID) platform using vector backscatter modulation on the uplink (tag-to-reader). The proposed RFID system consists of a software defined radio (SDR) reader and the corresponding passive, computational tag. The communication protocol is firmware-implemented, thus offering high flexibility in configuring its functionalities. A dual-gate MOSFET is used to implement the vector backscatter modulator. Experimental results prove the platform’s feasibility and show the benefits of using vector backscatter communication compared to using the standard binary phase-shift keying (BPSK). For the investigated 128-bit tag-to-reader message based on the EPC Class 1 Generation 2 communication protocol, the sequence length was shortened by a factor of 1.91.

Spoofing Attacks on FMCW Radars with Low-Cost Backscatter Tags.

This work studies the feasibility of using backscatter-modulated tags to introduce false information into a signal received by a frequency-modulated continuous-wave (FMCW) radar. A proof-of-concept spoofing device was designed in the 24 GHz ISM band. The spoofing device was based on an amplifier connected between two antennas, and modulation was carried out by switching the amplifier bias. The use of an amplifier allowed us to increase the level of spoofing signal compared with other modulated backscattering methods. The simulated and experimental results show that our method has the ability to generate a pair of false targets at different ranges and velocities depending on the modulation frequency of the chosen tag, since sidebands appear due to this modulation. Countermeasures to detect the spoofing attack based on changes in the slope of the frequency sweep between frames are also proposed.

Hybrid RFID Based Batteryless Seat Sensor With Discontinuous RF Transmission

In this paper, a hybrid RFID tag and reader system is proposed for wireless and batteryless automotive sensors. The hybrid RFID tag operates in dual mode, which includes conventional RFID operation, and tag active transmission. The reader provides the carrier in conventional RFID communication, using which the tag performs backscatter modulation. In tag active transmit mode, the reader does not provide any carrier, and the tag synthesizes its own carrier for communication. The hybrid tag can communicate with the reader for a range of 21 in. A commercial seat belt sensor was integrated with the tag and a working prototype of the complete system was demonstrated. Time response is a critical parameter for the whole system to work coherently and hence the operational states were modeled for time estimation and address the key parameters. Individual subsystems within the tag and reader circuits are presented in detail to capture the complete system. The proposed system can reduce the effective on-time of the reader significantly and the analysis shows that the reader transmit time can be reduced as much as 90% compared to the conventional RFID reader. The system was validated by designing, fabricating, and testing of the tag and reader circuits within a lab environment.

A Design of Peak to Average Power Ratio Based SWIPT System in 180 nm CMOS Process for IoT Sensor Applications

In this paper, we propose a peak-to-average-ratio (PAPR) based simultaneous wireless information and power transfer (SWIPT) system for Internet-of-Things (IoT) sensor applications. Conventional SWIPT system is based on power-hungry transmitter and receiver modules. The presence of such blocks directly impact the power consumption in IoT devices. This problem can be solved by proposing an ultra-low-power communication mechanism. Recently SWIPT with multi-tone is under consideration because of its increased power conversion efficiency (PCE). We proposed a PAPR based SWIPT receiver that utilizes the multi-tone waveform for information decoding in SWIPT system. An adaptive power splitter (APS) smartly regulates the distribution of received radio frequency (RF) signals between the energy harvesting (EH) path and the information decoding (ID) path. A digital controller was designed to control the demodulation of the PAPR based modulated signal and retrieves the digital information. Back-scattering modulation has been opted for up-link data transfer. For the EH path we design an RF-DC converter with an adaptive matching to increase the dynamic range of input power. The propose SWIPT system based on the PAPR demodulator is implemented on the 180 nm CMOS process. The digital clock frequency at the SWIPT receiver is 64 kHz, which can provide a data rate of 8 kbps with power consumption of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$7.3~\mu \text{W}$ </tex-math></inline-formula> with area utilization of 0.4 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Advances in Wirelessly Powered Backscatter Communications: From Antenna/RF Circuitry Design to Printed Flexible Electronics

Backscatter communication is an emerging paradigm for pervasive connectivity of low-power communication devices. Wirelessly powered backscattering wireless sensor networks (WSNs) become particularly important to meet the upcoming era of the Internet of Things (IoT), which requires the massive deployment of self-sustainable and maintenance-free low-cost sensing and communication devices. This article will introduce the state-of-the-art antenna design and radio frequency (RF) system integration for wirelessly powered backscatter communications, covering both the node and the base unit. We capture the latest development in ultralow-power RF front ends and coding schemes for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{W}$ </tex-math></inline-formula> -level backscatter modulators, as well as the latest progress in wireless power transfer (WPT) and energy harvesting (EH) techniques. Newly emerged rectenna system, waveform design, and channel optimization are reviewed in light of the opportunities for adaptively optimizing the WPT/EH efficiency for low-power signals with varying conditions. In addition, advanced device packaging and integration technologies in, e.g., additively manufactured RF components and modules for microwave and millimeter-wave ubiquitous sensing and backscattering energy-autonomous RF structures are reported. Inkjet printing for the sustainable and ultralow-cost fabrication of flexible RF devices and sensors will be reviewed to provide a prospective insight into the future packaging of backscatter communications from the chip-level design to complete system integration. Finally, this article will also address the challenges in fully wireless powered backscatter radio networks and discuss the future directions of backscatter communication in terms of “Green IoT” and “Low Carbon” smart home, smart city, smart skin, and machine-to-machine (M2M) applications.

Simultaneous User Localization and Identification Using Leaky-Wave Antennas and Backscattering Communications

High-speed detection and identification of mobile terminals located in the vicinity of highly directive base stations is essential for future mm-wave communication systems. We propose a novel optoelectronic frequency modulated continuous wave (FMCW) radar system for detection, localization and identification of multiple mobile terminals. The simultaneous localization and identification of multiple mobile terminals is achieved by using frequency scanning mm-wave leaky-wave antennas (LWAs) and backscattering communications. LWAs provide RF-based beam steering for estimating the direction of arrival of the echoes using a FMCW radar signal. Additionally, the implementation of backscattering technology in the mobile terminals allows the identification of users. Hence, simultaneous user localization and identification without the use of any complicated radar signal post-processing algorithms is possible. Finally, the introduced modulated backscattering reflection shifts the signals of the targets at higher frequencies, which exhibit lower noise floor and thus have higher signal to noise ratio (SNR).