Narrow Bandwidth Signals Research Articles

Location Adaptive Motion Recognition Based on Wi-Fi Feature Enhancement

Action recognition is essential in security monitoring, home care, and behavior analysis. Traditional solutions usually leverage particular devices, such as smart watches, infrared/visible cameras, etc. These methods may narrow the application areas due to the risk of privacy leakage, high equipment cost, and over/under-exposure. Using wireless signals for motion recognition can effectively avoid the above problems. However, the motion recognition technology based on Wi-Fi signals currently has some defects, such as low resolution caused by narrow signal bandwidth, poor environmental adaptability caused by the multi-path effect, etc., which make it hard for commercial applications. To solve the above problems, we first propose and implement a position adaptive motion recognition method based on Wi-Fi feature enhancement, which is composed of an enhanced Wi-Fi features module and an enhanced convolution Transformer network. Meanwhile, we improve the generalization ability in the signal processing stage to avoid building an extremely complex model and reduce the demand for system hardware. To verify the generalization of the method, we implement real-world experiments using 9300 network cards and the PicoScenes software platform for data acquisition and processing. By contrast with the baseline method using original channel state information(CSI) data, the average accuracy of our algorithm is improved by 14% in different positions and over 16% in different orientations. Meanwhile, our method has best performance with an accuracy of 90.33% compared with the existing models on public datasets WiAR and WiDAR.

Joint Target and Ionosphere Parameter Estimation in Over-the-Horizon Radar

Target localization, especially the estimation of target altitude, is a challenging task in over-the-horizon radar (OTHR) because of the narrow signal bandwidth as well as the complexity and uncertainty involved in the ionosphere conditions. This task becomes further complicated when the height of the ionosphere layer varies over time. Therefore, it is important to jointly estimate the instantaneous height of the ionosphere and the target altitude as well as other motion parameters. In this article, we achieve these objectives by analyzing the Doppler frequencies of the target local-multipath signals and the clutter. We reveal that the change of the ionosphere height can either enhance or deteriorate the performance of target parameter estimation depending on its direction of motion relative to the target’s motion profile. In addition, it is found that the received target and clutter Doppler signatures follow the chirp signal profile at the OTHR receiver. Based on these observations, we develop a general framework that achieves joint target and ionosphere parameter estimation and accounts for the velocity and accelerations of both target and ionosphere layer. Unlike existing time-frequency-based strategies for target localization and tracking in OTHR, where the Doppler signatures only directly determine target vertical velocity and the target altitude is estimated indirectly, the proposed model enables direct estimation of target altitude and ionosphere parameters. The parameter estimation problem in the proposed strategy is analytically derived and the effectiveness is verified using extensive simulation results.

An Improved Imaging Algorithm for Multi-Receiver SAS System with Wide-Bandwidth Signal

When the multi-receiver synthetic aperture sonar (SAS) works with a wide-bandwidth signal, the performance of the range-Doppler (R-D) algorithm is seriously affected by two approximation errors, i.e., point target reference spectrum (PTRS) error and residual quadratic coupling error. The former is generated by approximating the PTRS with the second-order term in terms of the instantaneous frequency. The latter is caused by neglecting the cross-track variance of secondary range compression (SRC). In order to improve the imaging performance in the case of wide-bandwidth signals, an improved R-D algorithm is proposed in this paper. With our method, the multi-receiver SAS data is first preprocessed based on the phase center approximation (PCA) method, and the monostatic equivalent data are obtained. Then several sub-blocks are generated in the cross-track dimension. Within each sub-block, the PTRS error and residual quadratic coupling error based on the center range of each sub-block are compensated. After this operation, all sub-blocks are coerced into a new signal, which is free of both approximation errors. Consequently, this new data is used as the input of the traditional R-D algorithm. The processing results of simulated data and real data show that the traditional R-D algorithm is just suitable for an SAS system with a narrow-bandwidth signal. The imaging performance would be seriously distorted when it is applied to an SAS system with a wide-bandwidth signal. Based on the presented method, the SAS data in both cases can be well processed. The imaging performance of the presented method is nearly identical to that of the back-projection (BP) algorithm.

Improved GNSS-Based Bistatic SAR Using Multi-Satellites Fusion: Analysis and Experimental Demonstration.

The Global Navigation Satellite System (GNSS)-based Bistatic Synthetic Aperture Radar (SAR) is getting more and more attention in remote sensing for its all-weather and real-time global observation capability. Its low range resolution results from the narrow signal bandwidth limits in its development. The configuration difference caused by the illumination angle and movement direction of the different satellites makes it possible to improve resolution by multi-satellite fusion. However, this also introduces new problems with the resolution-enhancing efficiency and increased computation brought about by the fusion. In this paper, we aim at effectively improving the resolution of the multi-satellite fusion system. To this purpose, firstly, the Point Spread Function (PSF) of the multi-satellite fusion system is analyzed, and focusing on the relationship between the fusion resolution and the geometric configuration and the number of satellites. Numerical simulation results show that, compared with multi-satellite fusion, dual-satellite fusion is a combination with higher resolution enhancement efficiency. Secondly, a method for dual-satellite fusion imaging based on optimized satellite selection is proposed. With the greedy algorithm, the selection is divided into two steps: in the first step, according to geometry configuration, the single-satellite with the optimal 2-D resolution is selected as the reference satellite; in the second step, the angles between the azimuthal vector of the reference satellite and the azimuthal vector of the other satellites were calculated by the traversal method, the satellite corresponding to the intersection angle which is closest to 90° is selected as the auxiliary satellite. The fused image was obtained by non-coherent addition of the images generated by the reference satellite and the auxiliary satellite, respectively. Finally, the GPS L1 real orbit multi-target simulation and experimental validation were conducted, respectively. The simulation results show that the 2-D resolution of the images produced by our proposed method is globally optimal 15 times and suboptimal 8 times out of 24 data sets. The experimental results show that the 2-D resolution of our proposed method is optimal in the scene, and the area of the resolution unit is reduced by 70.1% compared to the single-satellite’s images. In the experiment, there are three navigation satellites for imaging, the time taken to the proposed method was 66.6% that of the traversal method. Simulations and experiments fully demonstrate the feasibility of the method.

Increasing power efficiency.

Narrow-bandwidth signals and relaxed neural-recording parameters can substantially reduce the power requirements of brain–machine interfaces without degrading their performance.

A Novel Methodology to Study Synchrony, Causality and Delay in EEG Data

Synchrony and causality analyses performed in EEG data have improved the understanding of complex interactions within the human brain. However, few attempts have been conducted for using the delay magnitude as a feature of synchrony events. A new methodology for studying synchrony in EEG data is presented here. It includes synchrony detection and a novel mechanism to estimate delay magnitude and sign - hence causality - between narrow bandwidth signals. Synchrony detection and delay estimation are separated in two steps: first, significant synchrony is detected using a measure based on phase differences, then, the delay is estimated by analyzing the dispersion of measure maxima in the space spanned by time, frequency and delays. Synthetic EEG data is used to validate the methodology using a synchrony spectral model with controlled bandwidth and multivariate autoregressive models (MVAR). The proposed methodology achieves a superior performance in causality estimation than state-of-the-art techniques in accuracy and robustness to noise. We also present an analysis of data from a psychophysiological experiment of figure categorization. This methodology provides a reliable method to estimate the delay magnitude of synchrony events and it is a better alternative for studying causality than the state-of-the-art techniques employed here.

Positioning in a Multipath Channel Using OFDM Signals With Carrier Phase Tracking

In developing a high accuracy terrestrial radio navigation system, as a complement to a global navigation satellite system (GNSS), it is recognized that the performance of time delay estimation is proportional to, and thereby limited by, the signal bandwidth. Given a possibly narrow signal bandwidth, the central carrier phase can, alternatively, provide a better distance accuracy, though the central carrier phase cycle ambiguity should be resolved. In practice, the carrier phase may be perturbed by multipath. In this paper, considering an orthogonal frequency division multiplexing (OFDM) signal, we propose a two-step carrier phase estimation method to reduce the error introduced by multipath. First, the propagation delay of the LoS path is coarsely determined, then the carrier phase is estimated using the earlier determined coarse time delays. Furthermore, a positioning model only based on carrier phase estimates is presented in this paper. The proposed technique is evaluated by statistical analyses and a simulated OFDM-based terrestrial positioning system in different roadway multipath environments. The results show that the impact of multipath on carrier phase estimation can be largely mitigated, so that the carrier phase can be used for precise positioning. In addition, fixing the integer carrier phase cycle ambiguities can significantly reduce the time for the position solution to converge to high precision.

A Phase-Canceled Backing Layer for Ultrasound Linear Array Transducer: Modeling and Experimental Verification.

In this study, a phase-canceled backing layer for ultrasound linear array transducer is presented. The proposed backing layer is composed of multiple blocks operated by a phase inversion technique. Inside the proposed backing layer, the phase of the reflected signals can be canceled by adjusting acoustic impedance, piezoelectric layer contact area, and thickness of each block constituting the backing layer. Therefore, the total thickness of the backing layer can be significantly reduced while maintaining the performance. Using finite element analysis (FEA) simulation, its performance was verified based on an 8-MHz linear array transducer. Two types of bulk-type backing layers with different thicknesses were also simulated to compare the performance of the proposed method. In the case of a narrow bandwidth signal without the matching layers, the 10-mm-thick bulk-type backing layer yielded a -6-dB bandwidth of 37.2%. When its thickness was reduced to 2 mm, the -6-dB bandwidth was decreased to 17.3% due to the reflected back-wall signals. However, the -6-dB bandwidth of the proposed backing layer with 2-mm thickness was 39.5%, which is similar to the thick bulk-type backing layer. In the case of broad bandwidth signal with the matching layers, the proposed transducer also exhibits similar performance compared with the thick bulk-type backing layer. The narrow bandwidth signal was experimentally implemented by using a prototype array transducer with the proposed technique, and the performance was similar to the simulation. Thus, the proposed method can reduce the thickness of the backing layer of various array transducers.

Influence of signal bandwidth and phase delay on complex susceptibility based magnetic particle imaging

In this paper, the influences of signal bandwidth and phase delay on the spatial resolution of complex susceptibility based magnetic particle imaging (csMPI) are investigated by modeling the transfer function of the measurement circuit. Based on the simulation and experimental results, it is found that the signal bandwidth and the phase delay will significantly impact on the spatial resolution of csMPI. To avoid the influence of narrow signal bandwidth and phase delay of measurement circuit on csMPI, a resonance measurement circuit with −3 dB bandwidth of 2.3 kHz (much larger than the signal bandwidth of the desired csMPI signal) and resonance frequency of 12.8 kHz is adopted to measure the weak nonlinear magnetization of the magnetic nanoparticles; a phase compensation is used when calculating the real and the imaginary components of ac magnetic susceptibility.

A TDOA Estimation Method Through Phase Difference Square Sums (PDSS)

In order to improve the performance of TDOA estimation under multipath, non-line-of-sight and narrow signal bandwidth conditions, a time difference of arrival (TDOA) estimation method by Phase Difference Square Sum (PDSS) is introduced. Within the baseline time-lags of two separate receivers, PDSS between two received samples of the same signal are calculated for per lag; the TDOA is estimated by searching the minimum of PDSS. Under the condition of different signal-to-noise ratio (SNR) and Sample rates to Signal bandwidth ratio, the estimation error distribution of the PDSS are simulated, and are compared with the generalized cross correlation with phase transform (GCC-PHAT). In multipath propagation and non-line-of-sight environment of the metropolis, the estimation success rates are experimented to evaluate PDSS’s performance relative to GCC_PHAT.

Ring-up-doped fiber for the generation of more than 600 W single-mode narrow-band output at 1018 nm.

We present the amplification of a narrow-bandwidth signal at a wavelength of 1018nm to a power exceeding 600W with a stable output polarization state. The beam showed an excellent, nearly diffraction-limited beam quality. The high-power output could be realized using an in-house designed and fabricated fiber with a core-cladding diameter ratio of 32/260, ultra-low NA of 0.041, and ring-up doping. A seed source with high amplified spontaneous emission (ASE) suppression was also required, which was realized by a double-pass pre-amplifier with 13W output power.

DATA ACQUISITION AND PROCESSING OF PARALLEL FREQUENCY SAR BASED ON COMPRESSIVE SENSING

Traditional synthetic aperture radar (SAR) utilizes Shannon-Nyquist theorem for high bandwidth signal sampling, which induces a complicated SAR system, and it is di-cult to transmit and process a huge amount of data caused by high A/D rate. Compressive sensing (CS) indicates that the compressible signal using a few measurements can be reconstructed by solving a convex optimization problem. A novel SAR based on CS theory, named as parallel frequencies SAR (PFSAR), is proposed in this paper. PFSAR transmits a set of narrow bandwidth signals which compose the large total bandwidth. Therefore, PFSAR only uses much less data to obtain a superiority image compared with a traditional SAR system. The data acquisition mode of PFSAR is developed and an algorithm of target scene reconstruction based on compressive sensing applied to PFSAR is proposed. The azimuth imaging of PFSAR is carried out based on the Doppler Efiect, and then, the range imaging is performed by using compressive sensing of parallel frequencies signal. Several simulations demonstrate the feasibility and superiority of PFSAR via compressive sensing.

Theoretical Study of Switching Characteristics of 40 and 100 Gbps Pulse Trains by Weighted Collinear Acoustooptic Switches

Optical switching of high-bit-rate pulse trains using collinear acoustooptic (AO) devices is theoretically discussed. Since the collinear AO devices have wavelength selectivity, the switched optical pulse trains suffer from distortion when the bandwidth of the pulse train is comparable to the pass bandwidth of the AO device. As the AO device, a sidelobe-suppressed device with a tapered surface-acoustic-wave (SAW) waveguide and a Butterworth-type filter device with a lossy SAW directional coupler are considered. Distortion of optical pulse trains at 40 to 100 Gbps is numerically analyzed. Although filtering characteristics of collinear AO devices for continuous wave or narrow-bandwidth signals have been reported so far, distortion of short pulse trains having wide bandwidth is clarified for the first time.

Theoretical Study of Switching Characteristics of 40 and 100 Gbps Pulse Trains by Weighted Collinear Acoustooptic Switches

Optical switching of high-bit-rate pulse trains using collinear acoustooptic (AO) devices is theoretically discussed. Since the collinear AO devices have wavelength selectivity, the switched optical pulse trains suffer from distortion when the bandwidth of the pulse train is comparable to the pass bandwidth of the AO device. As the AO device, a sidelobe-suppressed device with a tapered surface-acoustic-wave (SAW) waveguide and a Butterworth-type filter device with a lossy SAW directional coupler are considered. Distortion of optical pulse trains at 40 to 100 Gbps is numerically analyzed. Although filtering characteristics of collinear AO devices for continuous wave or narrow-bandwidth signals have been reported so far, distortion of short pulse trains having wide bandwidth is clarified for the first time.

Increased pump acceptance bandwidth in spontaneous parametric downconversion process using Bragg reflection waveguides

In this paper we show that by suitably tailoring the dispersion characteristics of a Bragg reflection waveguide (BRW) mode, it is possible to achieve efficient photon pair generation over a large pump bandwidth while maintaining narrow signal bandwidth. The structure proposed consists of a high index core BRW with a periodically poled GaN core and periodically stratified cladding made up of alternate layers of Al(0.02)Ga(0.98)N and Al(0.45)Ga(0.55)N. Such photon-pair generators should find applications in realizing compact and stable sources for quantum information processing.

Adaptive algorithm for increasing image rejection ratio in low-IF receivers

An adaptive method for compensating mismatch effect on an I/Q demodulation is presented. It is based on the correlation between the desired and image band that appears when there is a mismatch in any branch. The proposed algorithm is specially intended for narrowband low-IF receivers. No calibration source is neccesary. Up to 91 dB of image rejection ratio is achieved with narrow-bandwidth signals (up to 6.25% of the sampling frequency).

Methods and systems for generating phase-derivative sound

Methods and systems for digitally generating sound from phase and amplitude information of a narrow bandwidth signal, such as a narrow bandwidth locator signal. Phase-derivative information is determined from the phase information. The bandwidth of the phase-derivative information is spread out, or stretched, over a wider bandwidth, so that the frequency variations will be more perceptible to users. The result is combined with an audio band carrier frequency, the result of which controls an oscillator. The oscillator output is combined with the amplitude information to generate an analog audio signal that is modulated with the amplitude information and the phase-derivative information. The amplitude information wider bandwidth phase-derivative information are used to modulate an audio carrier in both frequency and amplitude. The overall process can be thought of as a translation of the frequency and amplitude information from the narrow bandwidth around the locate frequency to a wider bandwidth on a chosen carrier frequency in the audio band. The received amplitude and phase information is received at an input sample rate. Where the input sample rate is relatively low, the amplitude and phase information are up-sampled to an output sample rate that is higher than a desired audio frequency. The higher output sample rate insures that there are sufficient samples of the signal during each cycle or period of the audio frequency. The higher sample rate is typically also the sample rate of a digital to analog converter that outputs an analog signal to a speaker. The amplitude information and/or phase derivative information are optionally scaled to system gain. The sound heard by the operator can optionally be adjusted with an optional selectivity filter.

High Sensitivity 900-MHz ISM Band Transceiver

Integrated 900-MHz ISM band transceiver LSI for analog cordless telephone has been realized by cost-effective process technology with sufficient performance. This LSI consisted of fully integrated transceiver, from RF-LNA to audio amplifier for RX chain, from microphone's amplifier to RF-PA for TX chain, and integrated RX- and TX-LO consisting of PLLs and VCOs. In view of narrow signal bandwidth with analog modulation, extremely low phase noise at low offset frequency from carrier was required for integrated VCO. Also, in view of fully duplex operations, signal isolation between TX and RX was required. Despite such a high integration and high performance, chip cost had to be minimized for low-cost applications. The 12-dB SINAD RX sensitivity was -111.2 dBm, the output power of TX was +3 dBm, and the phase noise of integrated VCO was -77 dBc/Hz at 3 kHz offset away from carrier. The current consumption at fully duplex operation was 76 mA at 3.6 V power supply. The chip was realized by 0.8 μm standard silicon BiCMOS process.

VLBI observation of narrow bandwidth signals from the spacecraft

We carried out a series of VLBI observations of Nozomi by using a dedicated narrow bandwidth VLBI system. The three carrier waves with frequency interval of 515 kHz were recorded in 3 channels of the system and correlated by a software method. As a result of the correlation, the residual fringe phases of the main carrier wave are obtained for every 1.3 seconds. We can also continuously track them for 100 minutes. The variation of the residual fringe phase is +/− 150 degrees. Moreover, we can derive succesively the group delay for every 100 seconds by using these three carrier waves. The RMS of the group delays is 13 nsec and its average is well accorded with the delay determined by the range and Doppler measurements within an error of 2 nsec. Consequently, we confirmed the validity of the narrow bandwidth VLBI system, and it could be expected that this system, in addition to range and Doppler measurements, can be applied to three-dimensional tracking of a spacecraft and the precise gravity measurement of the Moon and the planets.

Correction to "Higher order pmd distortion mitigation based in optical narrow bandwidth signal filtering"

Correction to "Higher order pmd distortion mitigation based in optical narrow bandwidth signal filtering"