Interference Rejection Capability Research Articles

A planar BPF for UWB communication systems with single/multiple interference rejection bands

Abstract The design and development of a microstrip-based planar ultra-wideband (UWB) bandpass filter (BPF) with single/multiple interference rejection capability is presented. The proposed BPF structure is developed based on the broadside coupled mechanism of microstrip/coplanar waveguide (CPW). The BPF has microstrips and short-circuited CPW capacitively coupled through the substrate. The basic frequency response generated from this geometry covers the necessary UWB spectrum (3.1–10.6 GHz) and possesses appreciable characteristics due to dual transmission zeros at either passband boundary. Multiple resonators are embedded in the basic BPF structure to develop passband notches to circumvent unnecessary interferences. A low-pass filter is later integrated into geometry to extend the upper stopband. The proposed structure is compact and covers an area of only 14 × 11.4 mm2.

Robust or nonrobust: On MC-DS-CDMA acquisition in LEO satellite communications

Low Earth Orbit (LEO) satellite communications can provide global coverage in the sixth generation communication (6G) networks. To combat the strong Partial Band Interferences (PBIs) and multipath fading in LEO satellite communication systems, the Multicarrier Direct Sequence Code Division Multiple Access (MC-DS-CDMA) technique is a promising alternative to the traditional Single-carrier Direct Sequence Code Division Multiple Access (SC-DS-CDMA) system for its advantages of high bandwidth efficiency, superior interference rejection capability, and low complexity of parallel signal processing. However, limited studies have been conducted on the performance analysis of MC-DS-CDMA acquisition systems in the presence of a large Doppler shift, a unique characteristic of LEO satellite communications. To bridge this gap, we investigate the performance of MC-DS-CDMA systems with two-dimensional acquisition and noncoherent equal gain combining over Rician fading channel in the presence of the Doppler shift and PBIs. The performance metrics are detection probability and Mean Square Error (MSE) of the Doppler factor and delay. Specifically, we derive the closed-form expressions for the MSE and the Probability Density Function (PDF) of the acquisition decision variable and obtain the detection probability. We conduct extensive numerical experiments to verify the theoretical analysis and performance gain of MC-DS-CDMA over the SC-DS-CDMA. The results show that MC-DS-CDMA with two-dimensional acquisition is more robust to multipath Rician fading than SC-DS-CDMA. Moreover, MC-DS-CDMA outperforms SC-DS-CDMA regarding the detection probability and MSE when combating the strong PBIs.

Double-Differential Amplifier for sEMG Measurement by Means of a Current-Mode Approach

This work proposes a Double Differential (DD) amplifier topology which exploits the advantages of the current-mode approach. DD amplifiers are useful as front-ends in standalone active electrodes for superficial electromyography (sEMG) wearable applications and electroneurography (ENG) measurement devices. Front-ends for these applications need to attain low noise, high common-mode rejection ratio, and high input impedance to measure biopotential signals and can further benefit from low power operation, a small size, and an easily adaptable output. Presently published DD amplifiers are either complex in terms of a high part count, leading to higher power consumption and size, or suffer from limited interference-rejection capabilities and require further analog processing for compatibility with single-ended systems. Therefore, in this work, second-generation current conveyors have been leveraged to obtain a simple topology combining a small active-part count, a high common-mode rejection ratio, and a flexible output stage. The current-mode DD amplifier is presented and analyzed in detail to estimate its parameters and model the effects of nonidealities in the circuit. In order to validate the proposed topology, a discrete-component implementation was realized as a proof-of-concept. The results experimentally demonstrated the properties of the proposed topology and its feasibility for measuring superficial sEMG DD signals.

Game Theoretic Countermeasure Analysis for Multistatic Radars and Multiple Jammers

AbstractRadar and jammer can be considered as two players in the countermeasure game of electronic warfare (EW). A game framework for joint beamforming and power allocation is investigated for multistatic radars and multiple jammers in this paper. Under a certain target detection criterion, the major aim of every radar is to reduce its power consumption and suppress various jammings. Conversely, the multi‐agent jammers determine their transmitting power strategies to interfere with the multistatic radar network, which is based on the transmitting power of the radars. According to the countermeasure game, both existence and uniqueness are strictly confirmed about the Nash Equilibrium (NE) of the proposed game. Besides, the receive beamformer weight vector can be obtained by minimum variance distortionless response (MVDR). And the corresponding transmit beamformer weight vector is also obtained. An algorithm for joint beamforming and power allocation is proposed, which is iteratively convergent. Finally, the convergence and validity for the proposed algorithm and the interference rejection capability of the multistatic radars are supported by the numerical results.

Non-Redundant OFDM Receiver Windowing for 5G Frames and Beyond

Contemporary receiver windowed orthogonal frequency division multiplexing (RW-OFDM) algorithms have limited adjacent channel interference (ACI) rejection capability under high delay spread and small Fast Fourier Transform (FFT) sizes. Cyclic prefix (CP) is designed to be longer than the maximum excess delay (MED) of the channel to accommodate such algorithms in current standards. The robustness of these algorithms can only be improved against these conditions by adopting additional extensions in a new backward incompatible standard. Such extensions would deteriorate the performance of high mobility vehicular communication systems in particular. In this paper, we present a low-complexity Hann RW-OFDM scheme that provides resistance against ACI without requiring any intersymbol interference (ISI)-free redundancies. While this scheme is backward compatible with current and legacy standards and requires no changes to the conventionally transmitted signals, it also paves the way towards future spectrotemporally localized and efficient schemes suitable for higher mobility vehicular communications. A Hann window effectively rejects unstructured ACI at the expense of structured and limited intercarrier interference (ICI) across data carriers. A simple maximum ratio combining successive interference cancellation (MRC-SIC) receiver is therefore proposed to resolve this induced ICI and receive symbols transmitted by standard transmitters currently in use. The computational complexity of the proposed scheme is comparable to that of contemporary RW-OFDM algorithms, while ACI rejection and bit-error rate performance is superior in both long and short delay spreads. Channel estimation using Hann RW-OFDM symbols is also discussed.

Robust Adaptive Beamforming with Improved Interferences Suppression and a New Steering Vector Estimation Based on Spatial Power Spectrum

In this paper, a new robust adaptive beamforming algorithm is proposed with increased attenuation of interference signals. This is achieved by reconstructing the interference-plus-noise covariance matrix using the Capon spatial power estimator. In the latter the total sample covariance matrix is replaced by its square, which is shown to enhance the interference rejection capability of the minimum variance distortionless response beamformer. Also, a new method for estimating the desired signal’s steering vector is introduced based on reconstructing the desired signal’s covariance matrix and employing the discrete Fourier transform of the correlation sequence. The effectiveness of the proposed method is demonstrated by numerical results.

Demonstration of non-absorbing interference rejection using wavelength modulation spectroscopy in high-pressure shock tubes

We experimentally demonstrate the non-absorbing interference rejection capabilities of wavelength modulation spectroscopy (WMS) speciation in shock tube experiments by directly comparing WMS measurements against direct-absorption spectroscopy (DA) measurements. The improved capability is demonstrated by probing the P(20) transition of the CO fundamental band using a quantum cascade laser in shock-heated mixtures of CO and N $$_2$$ across a wide range of pressures between 3.5 and 18 atm. In the WMS measurements, the second harmonic (2f) served as the detection signal, while the first harmonic (1f) provided normalization to counteract intensity drift and fluctuations. These perturbations occur in shock tubes because of significant beam-steering noise and imperfect optical alignment when experiments are conducted at elevated pressures. The WMS detection system was evaluated at reflected shock pressures of 3.5 atm, 8.5 atm, and 18 atm, demonstrating improvement in signal-to-noise ratio over concurrent DA measurements. To the authors’ knowledge, this work represents the first direct experimental quantification of the intensity-fluctuation rejection capabilities of a WMS-based TDLAS sensor at high pressures.

A Study of mm-Wave Communications With Noncontiguous Aperture

Current millimeter wave (mm-wave) communications research is focused on large scale antenna with contiguous aperture. On the contrary, in this paper, we present a study of mm-wave communications between transmit and receive antennas based on noncontiguous aperture. Our design aims to form shaped beams with high spatial isolation. We first study the beam shaping feasibility in mm-wave communications with reduced transmit antenna element spacing. We then introduce active scatters, a class of active devices that stimulates scattering effect, to sustain the interference rejection capability of shaped beams. The composition of active scatters forms a (virtual) noncontiguous aperture that is larger than transmit and receive antennas in size. To form multiple orthogonal beam (OB) radiation patterns that have peaks and nulls at designated locations, which enable frequency reuse, we consider slightly increased aperture size of transmit antenna and noncontiguous aperture that is comprised of active scatters. In addition to beamforming via noncontiguous aperture, we also simulated QPSK-modulated signal streams transmitted via OBs and justified the simulated system by inspecting the bit error rate performance at the receiver.

Robust Adaptive Algorithm for Smart Antenna System With <inline-formula> <tex-math notation="LaTeX">$\alpha$ </tex-math> </inline-formula>-Stable Noise

One of the main problems facing beamforming in smart antenna system is the $ {\alpha }$ -stable noise. To address this problem, a novel algorithm, named the recursive continuous logarithmic mixed ${p}$ -norm (RCLMP) algorithm, which employs a logarithmic cost, is proposed in this brief. The proposed algorithm combines the logarithmic ${p}$ -norms ${1}{\leq } p \leq 2$ which does not need the parameter selection and prior knowledge of ${\alpha }$ -stable noise, and exhibits good robustness against ${\alpha }$ -stable noise. Moreover, we show some ${H}^{{\infty }}$ norm bounds for the proposed algorithm. Simulation results show that the RCLMP algorithm outperforms the existing algorithms in terms of interference rejection capability and estimation accuracy.

An Improved Deadbeat Control for a Three-Phase Three-Line Active Power Filter With Current-Tracking Error Compensation

An active power filter (APF) plays an important role in compensating the harmonic component of a nonlinear load current. In this paper, deadbeat control (DBC), which has high control performance and fast dynamic response, is used as a current controller for an APF. An improved DBC (Imp_DBC) is introduced to suppress the adverse effect of the current sampling error and to enhance the interference rejection capability of the control system. The characteristics of the conventional DBC and Imp_DBC are analyzed using transfer functions in the discrete-time domain. The robustness of the system is improved with the inductance variation. Specifically, aiming at the dramatic change of the harmonic component of the nonlinear load current, a current-tracking error compensation method is proposed. The phenomena of the upper co-nvex and lower concave in grid current are eliminated. Finally, the experimental setup of three-phase three-line APF is built, and the effectiveness of this method is verified by experiments.

Space-Time Adaptive Cancellation in Passive Radar Systems

A critical issue in the realization of passive radar systems is the effective suppression of the zero Doppler interference (ZDI). The performance of the clutter cancellation relies much on the used algorithms. Several state-of-the-art approaches consist in the independent use of spatial and temporal algorithms for ZDI suppression. In this paper, a novel interference cancellation algorithm is proposed, which jointly exploits the available information from both space and time domains. We call this novel method Space-Time Adaptive Cancellation (STAC), and it differs from previous schemes included among the tools of Space-Time Adaptive Processing (STAP). The STAC algorithm is able to cancel out the high power direct and multipath signals on all the surveillance antenna channels prior to the beamforming and other space domain processing methods. The proposed preprocessing technique facilitates the detection of targets even in the direction of the illuminator or large static scatterers. Moreover, the interference rejection capability is also enhanced in the space domain. The performance of the presented algorithm is verified through simulations and field measurements. The experiments show improvement over the currently available filtering techniques.

An improved robust adaptive beamforming based on worst-case performance optimization

Generally, the adaptive beamformer has better spatial resolution and much better interference rejection capability than the conventional data-independent beamformer. But, in practice, the performance of the traditional adaptive beamformer will degrade greatly if some assumptions or information on the propagation model, array parameters, and signal model are imprecise. In this paper, a new approach to robust adaptive beamforming based on optimization of worst-case performance by parameter auto-adjust (PAWCO) is proposed, which can estimate the power of the signal using Newton-Raphson interactions. The method can confirm the upper bound of the mismatch vector neither overly nor under estimated. Theoretical analysis and simulation results are presented to show the proposed beamformer can estimate the power of signal precisely while achieving better spatial resolution. The robustness of the PAWCO algorithm to environment mismatch is also demonstrated by the acoustical experimental data.

Eigenanalysis-based adaptive interference suppression for underwater target estimation

It is generally difficult for a passive sonar system to localize a weak source due to the complexity and variability of the ocean environment, especially in the presence of strong interferences. In this paper, an eigenanalysis-based adaptive interference suppression method (EAAIS) is presented for estimating the weak source bearing. Assuming the target of interest (TOI) is in a known bearing sector, we first define a contribution ratio for each eigenvector of the cross-spectral density matrix (CSDM). The eigenvectors not dominated by the TOI are adaptively identified and removed for interference suppression. The remaining eigenvectors are then used to reconstruct the CSDM for TOI bearing estimation with adaptive beamforming methods. In comparison with the basic ECA method, the proposed method has better interference rejection capability and wider fields of application. Simulation and experimental results also show that the proposed method can achieve accurate localization estimates even in the presence of strong interferences.

Iterative robust adaptive beamforming

The minimum power distortionless response beamformer has a good interference rejection capability, but the desired signal will be suppressed if signal steering vector or data covariance matrix is not precise. The worst-case performance optimization-based robust adaptive beamformer (WCB) has been developed to solve this problem. However, the solution of WCB cannot be expressed in a closed form, and its performance is affected by a prior parameter, which is the steering vector error norm bound of the desired signal. In this paper, we derive an approximate diagonal loading expression of WCB. This expression reveals a feedback loop relationship between steering vector and weight vector. Then, a novel robust adaptive beamformer is developed based on the iterative implementation of this feedback loop. Theoretical analysis indicates that as the iterative step increases, the performance of the proposed beamformer gets better and the iteration converges. Furthermore, the proposed beamformer does not subject to the steering vector error norm bound constraint. Simulation examples show that the proposed beamformer has better performance than some classical and similar beamformers.

Deadbeat Control Based on Current Predictive Calibration for Grid-Connected Converter Under Unbalanced Grid Voltage

Deadbeat control (DBC) is developed based on the system model, which is commonly used to achieve good control performance for a three-phase grid connected converter (GCC). Unbalanced grid voltage is a common phenomenon in power systems. In this study, an improved DBC based on current predictive correction (CPC_DBC) is used to control GCC under an unbalanced grid voltage. The main purposes of CPC_DBC are to reduce the adverse effects due to random sampling error to improve current control performance, and to enhance the interference rejection capability of the control system. Then, the characteristics of CPC_DBC and the conventional DBC (Con_DBC) are analyzed by transfer functions in the discrete time domain. Several common control objectives under an unbalanced grid voltage are used to demonstrate the superiority of CPC_DBC. Finally, the experimental results indicate that CPC_DBC can effectively reduce the adverse effects of random sampling error; the robustness of system due to the uncertain value of the filter inductance is improved as well.

Resistance‐to‐digital converter designed for high power‐line interference rejection capability

A novel resistance-to-digital converter (RDC), based on the integrating type analogue-to-digital converter principle, is presented in this study. The conversion time of the proposed scheme is not a function of the current value of the parameter being measured. Thus, by suitably setting this parameter, the converter can be made to reject the effects of interference at a particular frequency, such as, that due to power-line at 50/60 Hz. Error analysis was conducted to ascertain the effects of non-idealities of various components of the circuit, on its output. Simulation studies were carried out in LTSPICE to verify the linearity and the interference rejection capability of the converter. Further, a prototype RDC was developed in the laboratory and tested to confirm the results of the simulation.

Hybrid Overlay/Underlay Cognitive Radio Network With MC-CDMA

Cognitive radio allows secondary users (SUs) to exploit the underutilized radio spectrum of the primary networks. To fully utilize the primary spectrum and maximize spectral efficiency, overlay and underlay transmissions, which exploit the white and gray spaces, respectively, should be used together. However, for underlay, the SUs need to transmit at low power to avoid causing harmful interference to the primary users (PUs), whereas the PUs will cause high interference to the SUs. Thus, interference mitigation is a major issue in underlay spectrum utilization. In this paper, a hybrid transmission system that exploits both overlay and underlay is proposed using multicarrier code-division multiple access due to its interference rejection and diversity exploitation capabilities. Unlike existing approaches, which separate the use of overlay and underlay spectrum, the proposed schemes utilize the entire spectrum for underlay transmission to minimize the PU interference while using the spectrum holes for overlay transmission to maximize the data rate. Two techniques that operate at full-load and overload scenarios are proposed. The overload system is then extended to the multiuser underlay case to further improve spectrum utilization.

The Design of the Simple Structure-Specified Controller of Magnetic Bearings for the High-Speed SRM

Magnetic bearing system controllers using H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> algorithms provide excellent interference rejection capability and robustness. However, in the conventional H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> control design, the order of the controller is much higher than that of the plant, making implementation in practical engineering applications difficult. To solve the problem, based on the requirements of the theory of mixed sensitivity design method, this paper designs a simple structure-specified controller of magnetic bearings for the highspeed magnetic levitated switched reluctance motor (SRM) using backpropagation neural network function approximation characteristics. The proposed controller is of lower order than the traditional H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> controller, and meets performance of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> controller, which is more suitable for practical implementation. By contrast with the traditional mixed sensitivity controller, results of simulations verify that the controller is reasonable. The controller is applied on the high-speed magnetic levitated SRM platform, and experimental results verify that the controller can achieve control of magnetic bearing systems with good disturbance rejection and robustness.

Sine-wave parameter estimation by interpolated DFT method based on new cosine windows with high interference rejection capability

The parameters of a sine-wave are often estimated by means of the classical Interpolated Discrete Fourier Transform (IpDFTc) method based on cosine windows since this method provides high accuracy while requiring low computational effort. When the number of acquired sine-wave cycles is small, estimation accuracy is heavily affected by the interference due to spectral leakage from both the sine-wave image component and other disturbance tones such as signal harmonics. To reduce both these detrimental effects new cosine windows are proposed in this paper. Their spectra exhibit a deep null close to the image component interfering frequency and the highest allowed sidelobe decay rate, so assuring minimization of long range spectral leakage. These windows are called Maximum Image interference Rejection windows with Rapid Sidelobe Decay rate (RSD) or simply, MIR-RSD windows. The analytical expressions of the sine-wave parameter estimators provided by the IpDFTc method based on the H-term MIR-RSD window (H≥2) are also derived. To assess the effectiveness of the MIR-RSD windows in rejecting the spectral interference when analyzing noisy or harmonically distorted sine-waves, the accuracy of the proposed frequency estimator is compared with those provided by other IpDFT frequency estimators through simulation and experimental results.

Frequency estimation of a sinusoidal signal via a three-point interpolated DFT method with high image component interference rejection capability

This paper proposes a three-point Interpolated Discrete Fourier Transform (IpDFT) method for frequency estimation of a discrete-time sinusoidal signal. It is based on the maximum sidelobe decay (MSD) windows and is highly effective in rejecting the detrimental effect on the estimation accuracy due to the image component of the signal spectrum. This remarkable feature is achieved by using an analytical expression based on a suitable weighting of the three largest DFT spectrum samples. The proposed method provides good results when the effect of the spectral interference due to the image component dominates other estimation error sources. The accuracy of the proposed method and of other state-of-the-art methods such as the multi-point IpDFT methods and the four-parameter sine-fitting (4PSF) algorithm are compared through both computer simulations and experimental results in the case of ideal, noisy, and harmonically distorted sinusoids. A small number of acquired cycles is assumed in order to analyze situations in which the contribution from the image component interference is significant. The performed comparison shows that the proposed method outperforms the considered multi-point IpDFT methods when the Signal-to-Noise Ratio (SNR) is higher than 30 dB and the number of acquired cycles is enough small. The proposed method outperforms also the 4PSF algorithm when the frequency estimation error is dominated by harmonics rather than wideband noise.