Optimal Order of Time-Domain Adaptive Filter for Anti-Jamming Navigation Receiver

Adaptive filtering algorithms can be used on the time-domain processing of navigation receivers to suppress interference and maintain the navigation and positioning function. The filter length can affect the interference suppression performance and hardware utilization simultaneously. In practical engineering, the filter length is usually set to a large number to guarantee anti-jamming performance, which means a high-performance receiver requires a high-complexity anti-jamming filter. The study aims at solving the problem by presenting a design method for the optimal filter order in the time-domain anti-jamming receiver, with no need for detailed interference information. According to interference bandwidth and jam-to-signal ratio (JSR), the approach designed a band-stop filter by Kaiser window for calculating the optimal filter order to meet interference suppression requirements. The experimental results show that the time-domain filtering processing has achieved good interference suppression performance for engineering requirements with optimal filter order in satellite navigation receivers.

Influence of digital filtering parameters on the pulse waveform in reflectance photoplethysmography

Photoplethysmography (PPG) is an optical method for recording pulse wave (PW) propagating in the tissue microvasculature. As a rule, filters with infinite impulse response (Butterworth, Bessel, etc.) often used in PPG signal processing introduce distortions in the PW signal. At the same time, the filtering parameters for a more accurate reproduction of PW have not yet been substantiated. The aim of this work is to study the influence of digital filtering parameters, such as bandwidth and filter order, on the pulse waveform. In the study, a digital bandpass Butterworth filter was used. The lower cutoff frequency of the filter varied from 0.1 to 1 Hz, the upper cutoff frequency varied from 2 to 10 Hz and the filter order – from 2nd to 6th. It was found that an increase in the lower cutoff frequency of the bandpass filtering leads to a decrease in the amplitude of the reflected diastolic wave and distortion of the front of the direct systolic wave. A decrease in the upper cutoff frequency leads to damping of the dicrotic notch and a phase shift of the PW. Increasing the filter order decreases the reflected wave amplitude. The minimal distortions of the PPG signal were observed at the lower cutoff frequency of 0.1 Hz, the upper one at 10 Hz and the filter order equal to 2. Thus, these parameters of a bandpass filtering can be recommended for processing PPG signals for a more accurate morphological analysis of PW. The obtained results make it possible to create devices for PW analysis with substantiated medical and technical requirements for filtration parameters.

Design and Research Process of Microstrip Low-Pass Filters with High Slope Steepness

This paper presents the results of design process and scientific investigation of planar low pass filters with cut-off frequencies of 6 and 7 GHz. Main features of this design are high steep performance, high level of rejection out of band (in comparison to conventional topologies), high filter order and small occupied area. The analysis of high absorptive electromagnetic material influence on filter performance are shown as well

A novel time domain polarization filter based on a correlation matrix analysis

Polarization filters are widely used for denoising seismic data. These filters are applied in the field of seismology, microseismic monitoring, vertical seismic profiling and subsurface imaging. They are primarily useful to suppress ground-roll in seismic reflection data and enhance P and S wave arrivals. Traditional implementations of the polarization filters involved the analysis of the covariance matrix or the SVD decomposition of a three-component seismogram matrix. The linear polarization level, known as rectilinearity, is expressed as a function of the covariance matrix eigenvalues or by the data matrix singular values. Wavefield records that are linearly polarized are amplified while others are attenuated. Besides the described implementations, we introduced a new time domain polarization filter based on the analysis of the seismic data correlation matrix. The principal idea is to extend the notion of the correlation coefficient in 3D space. This new filter avoids the need for diagonalization of the covariance matrix or SVD decomposition of data matrix, which are often time consuming. The new implementation facilitates the choice of the rectilinearity threshold: we demonstrate that linear polarization in 3D can be represented as three classic 2D correlations. A good linear polarization is detected when a high linear correlation between the three seismogram components is mutually observed. The tuning parameters of the new filter are the length of the time window, the filter order, and the rectilinearity threshold. Tests using synthetic seismograms show that optimal results are reached with a filter order that spans between 2 and 4, a rectilinearity threshold between 0.3 and 0.7, and a window length that is equivalent to one to three times the period of the signal wavelet. Compared to covariance-based filters, the new filter can enhance the signal-to-noise ratio by 6 to 20 dB and reduces computational costs by 25%.

ASIC Implementation of Linear Equalizer Using Adaptive FIR Filter

Power consumption plays a crucial role in the design of portable wireless communication devices, as it has a direct influence on the battery weight and volume required for operation. This article presents a novel design for a linear LMS equalizer for the optimization of filter order. The article describes the use of a variable length algorithm for dynamically updating the tap-length of the LMS adaptive filter to optimize the performance and for reducing the power in the adaptive filter core. An algorithm is applied to reduce and adjust the order of the filter in linear equalizer according to the channel conditions. The proposed design is implemented in the synopsis TSMC 65nm technology. The results from using the algorithm uses 28% less power when compared with the conventional 64-tap fixed length adaptive filter design. It has also been shown that the low-complexity of the additional circuitry needed for the variable length adaptive filter presents minimal overhead for this architecture.

Techniques for the generation of multiple additional transmission zeros in H-plane waveguide filters

In this paper, different techniques for the generation of additional transmission zeros (TZs) in planar waveguide filters are investigated. In the classical theory, TZs are generated only by destructive interference of non-adjacent cavities, limiting the available number of TZs to the filter order itself. However, more approaches for the generation of TZs are known, including bypass-coupling in oversized cavities, frequency-dependent coupling apertures as well as dispersive/resonant TZs which can be realized by the direct source to load cross-coupling. The aim of this paper is to combine several of the strategies in one physical filter set-up to increase the maximal number of TZs beyond the filter order. Different Ku-band fourth-order filter set-ups are presented, showing in total between six and eight real as well as complex TZs. Three filters are manufactured as a proof of concept and compared with the simulation, showing very good agreement.