Suppression of multipath and other interferers using electronically variable time delay elements

Wide-band interference (WBI) is a critical issue for synthetic aperture radar (SAR), which may severely affect the imaging quality of SAR systems. To suppress WBI effectively, a novel interference suppression algorithm based on robust principal component analysis (RPCA) in time-frequency-pulse (TF-P) domain is proposed. For SAR echoes in TF-P domain, there are two useful properties: 1) The TF characteristic of useful signal in adjacent pulse are similar, indicating that useful signal has low-rank property; 2) Due to its variation of position and sparsely distrusted in TF-P domain, WBI has sparse characteristic. According to these properties, RPCA method is applied to decompose the TF-P matrix into a low-rank matrix (i.e. useful signal) and a sparse matrix (i.e. WBI). Finally, the WBIs can be reconstructed and subtracted from the echoes to realize the interference suppression. The experimental results of simulated data demonstrate that the proposed algorithm not only can suppress interference effectively, but also preserve the useful information as much as possible.

The paper is understood as a continuation of a series of papers on surface metrology for application in quality control of printed matter. A stereoscopic device for extremely rugged applications, especially in quality control in printing industry, is presented. The device developed is based on variable tilted delay elements, which allow the use of a single imaging sensor and robust definition of parallax shift. Variable orthogonal delay elements were already used for variation of plane of focus in surface inspection, as described in previous papers. The method can be applied for macroscopical as well as for microscopic imaging. Beside mechanical design issues, the theoretical description, geometrical-optical approaches, and the treatment of the dispersion problem are discussed. Experimental results are included.

Sensor arrays have been proven to be an effective mechanism for attenuating directional interferences when they are statistically uncorrelated with the desired signal. In this case, signal processing techniques that rely on adjusting the sensor weights can be adapted so as to minimize the output power while maintaining a unity response to the desired signal. If, on the other hand, the interferences are correlated with the desired signal, these techniques can also lead to strong cancellation of the desired signal components. Therefore, in order to successfully pass the desired signal, the array response in the directions of arrival of the interferences must be properly shaped. Techniques for optimizing the shape of the array response, so that wideband interferences which are correlated with a desired signal can be attenuated, are discussed. Examples showing the effectiveness of these techniques are also presented.KeywordsSensor ArrayInterference CancellationSignal BandwidthArray ResponseRejection ResponseThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Teleoperation system performance suffers from the delays in communication lines. These delays are usually variable time delays. The customary wave variable technique used for constant time delays cannot provide satisfactory results to stabilize the system under variable delays. Another problem is observed in the position tracking performance of the limited-workspace teleoperation systems. Although wave variable technique is proven to track position demands successfully under constant time delays given that there is no communication failure, position tracking performance also degrades under variable delays. In this paper, a new controller is proposed to stabilize the system and enhance position tracking performance under variable time delays. This proposed controller is then applied to an identical master-slave teleoperation configuration which qualifies as a limited-workspace teleoperation system.

A circuit for on-chip measurement of duty cycle for unknown clock is demonstrated. The circuit consists of variable delay, counter and AND gate, and can be implemented on FPGA that has variable delay element without any external supporting circuit and occupies a very small portion of the FPGA. The major benefit over the previous measurement technology is that statistical analysis of the duty cycle of a large number of continuous clock cycles is possible through a single measurement.

This paper presents the design and FPGA implementation of interpolated continuously variable fractional delay structure based filter (ICVFD filter) with fine control over the cutoff frequency. In the ICVFD filter, each unit delay of the prototype lowpass filter is replaced by a continuously variable fractional delay (CVFD) element proposed in this paper. The CVFD element requires the same number of multiplications as that of the second-order fractional delay structure used in the existing fractional delay structure based variable filter (FDS based filter), however it provides fractional delays corresponding to the higher-order fractional delay structures. Hence, the proposed ICVFD filter provides wider cutoff frequency range compared to the FDS based filter. The ICVFD filter is also capable of providing variable bandpass and highpass responses. We use two-stage approach for the FPGA implementation of the ICVFD filter. First, we use pipelining stages to shorten the critical path and improve the operating frequency. Then, we make use of specific hardware resource, i.e. RAM-based Shift Register (SRL) to further improve the operating frequency and resource usage.

The problem of extracting the desired signal from the recording of an array of sensors corrupted by multiple coherent interference and random noise is considered. The desired signal and interferences are assumed to have different arbitrary waveforms, and no a priori knowledge of such waveforms is assumed. The relative delay times of the interferences with respect to the desired signal are assumed to be known or can be accurately estimated. A vector of array filters is derived for the multichannel offline processing of the array recording with the objective of extracting the desired signal. These array filters achieve an all-pass condition for the desired signal, a strong suppression of the coherent interferences, and some degree of attenuation of the random noise. The tradeoff between suppressing the coherent interferences and attenuating the random noise is examined. An implementation of these array filters using the QR decomposition technique for rank determination is outlined. The ringing effect-sometimes observed in the output-is carefully analyzed as it relates to the residual coherent interferences. Two illustrative examples confirming the theoretical findings are presented. The third example is a preliminary investigation of the sensitivity of the results to estimation errors in the parameters of the coherent interferences.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Narrow-band interference (NBI) and Wide-band interference (WBI) are critical issues for synthetic aperture radar (SAR), which degrades the imaging quality severely. Since some complex signals can be modeled as linear frequency modulated (LFM) signals within a short time, LFM-WBI and NBI are mainly discussed in this paper. Due to its excellent energy concentration and useful properties (i.e., auto-terms pass through the origin of Delay-Doppler plane while cross-terms are away from it), a novel nonparametric interference suppression method using Delay-Doppler iterative decomposition algorithm is proposed. This algorithm consists of three stages. First, we present signal synthesis method (SSM) from ambiguity function (AF) and cross ambiguity function (CAF) based on the matrix rearrangement and eigenvalue decomposition. Compared with traditional SSM from Wigner distribution (WD), the proposed SSM can synthesize a signal faster and more accurately. Then, based on unique properties in Delay-Doppler domain, a mask algorithm is applied for interference identification and extraction using Radon and its inverse transformation. Finally, a signal iterative decomposition algorithm (IDA) is utilized to subtract the largest interference from the received signal one by one. After that, a well-focused SAR imagery is obtained by conventional imaging methods. The simulation and measured data results demonstrate that the proposed algorithm not only suppresses interference efficiently but also preserves the useful information as much as possible.

Nowadays, in the electromagnetism environment, the complex interferences, including the narrowband interferences (NBIs) and wideband interferences (WBIs), may severely affect the imaging quality of synthetic aperture radar (SAR) systems. Most traditional methods can only tackle with one kind of isolated interferences, NBIs or WBIs, which are widely distributed in the 1-D range frequency domain or 2-D range time-frequency domain. In this paper, we propose a complex tensor robust principal component analysis (CT-RPCA) method based on a novel 3-D range-azimuth-space tensor model to mitigate continuously distributed NBIs and WBIs simultaneously. The main contributions of this paper are summarized in three aspects. First, we strictly prove the low-rank property of the isolated NBIs and WBIs in the range-azimuth domain. Second, we use multiple views of the signal to construct a novel 3-D range-azimuth-space tensor model, where both the NBI tensor and the WBI tensor have spatial low-rank property due to the approximately stable frequency bands along the spatial dimension. Third, the CT-RPCA method is employed to efficiently suppress NBIs and WBIs simultaneously by solving the tensor RPCA problem. Finally, the real SAR data with simulated complex interferences are employed to demonstrate the effectiveness of the proposed method.

In this paper, the problem of stability and tracking performance of FRVF (Forbidden Region Virtual Fixture) for bilateral nonlinear teleoperation systems is studied in presence of varying time delay. It is proved that PD-like controllers can stabilize the teleoperation systems with FRVF in slave side and variable time delay in communication channels. It is also proved by proposed Lyapunov-Krasovskii's function that the mentioned problem of stability and tracking performance of FRVF is satisfied. Finally, the proficiency of this approach is demonstrated by simulating the method on a pair of 6-DOF (Degree of Freedom) PHANToM Omni robots with nonlinear dynamics. Keywords— Virtual fixture; variable delay; delayed teleoperation system; nonlinear teleoperation.

Signal correlator with programmable variable time delay based on optical coherent transients

On-chip high-bandwidth sampling circuits supplement traditional test and debug techniques by non-invasively probing analog voltages for off-chip measurement. Existing circuits rely on sub-sampling techniques and thus require a synchronous clock. We extend these ideas to asynchronous circuits by combining an analog sampling head with a variable delay element and activating this circuit with an asynchronously triggered event. Repeated triggering events with different delays emulate sub-sampling. Simulations in a 180 nm technology of SRAM timing margins and GasP control failure modes show this technique can probe asynchronous signals with high fidelity.

The interference suppression performance of the traditional adaptive beamforming method is affected by the collected interference samples. In this work, we proposed a method for interference cancellation in array radar. The problem of interference suppression is transformed into finding a weight vector to minimize the mean square error between the array output signal and the desired signal. According to the time-delay relationship between the target reflection echo and the radar transmitted signal, an auxiliary vector with constant modulus constraint is introduced to construct the desired signal expression. The alternative projection method is used to solve the non-convex optimization problem and obtain the optimal weight. The introduction of prior information on transmitted waveform avoids the interference sample selection and improves cancellation performance. Numerical results demonstrate the effectiveness of the proposed method.

A trigonometric approximation scheme for optimal periodic control problems with state and control dependent delays is considered. The formulation of approximate problems is here adapted to a specific form of state equation with variable time delays. Sufficient conditions for the sequence of nearly optimal solutions of approximate problems to be a generalized minimizing sequence for the basic problem are given. The application of the method proposed to a periodic control of chemical reactors with recycles and controlled piping is pointed out.

Improved stabilization criteria for Takagi–Sugeno fuzzy systems with variable delays