25,543 research outputs found
Digital Filters for Instantaneous Frequency Estimation
This technical note is on digital filters for the high-fidelity estimation of
a sinusoidal signal's frequency in the presence of additive noise. The complex
noise is assumed to be white (i.e. uncorrelated) however it need not be
Gaussian. The complex signal is assumed to be of (approximately) constant
magnitude and (approximately) polynomial phase such as the chirps emitted by
bats, whale songs, pulse-compression radars, and frequency-modulated (FM)
radios, over sufficiently short timescales. Such digital signals may be found
at the end of a sequence of analogue heterodyning (i.e. mixing and low-pass
filtering), down to a bandwidth that is matched to an analogue-to-digital
converter (ADC), followed by digital heterodyning and sample rate reduction
(optional) to match the clock frequency of the processor. The spacing of the
discrete frequency bins (in cycles per sample) produced by the Fast Fourier
Transform (FFT) is equal to the reciprocal of the window length (in samples).
However, a long FFT (for fine frequency resolution) has a high complexity and a
long latency, which may be prohibitive in embedded closed-loop systems, and
unnecessary when the channel only contains a single sinusoid. In such cases,
and for signals of constant frequency, the conventional approach involves the
(weighted) average of instantaneous phase differences. General, naive, optimal,
and pragmatic (recursive), filtering solutions are discussed and analysed here
using Monte-Carlo (MC) simulations.Comment: Added arXiv ID to header and fixed a few typo
Efficient Fast-Convolution-Based Waveform Processing for 5G Physical Layer
This paper investigates the application of fast-convolution (FC) filtering
schemes for flexible and effective waveform generation and processing in the
fifth generation (5G) systems. FC-based filtering is presented as a generic
multimode waveform processing engine while, following the progress of 5G new
radio standardization in the Third-Generation Partnership Project, the main
focus is on efficient generation and processing of subband-filtered cyclic
prefix orthogonal frequency-division multiplexing (CP-OFDM) signals. First, a
matrix model for analyzing FC filter processing responses is presented and used
for designing optimized multiplexing of filtered groups of CP-OFDM physical
resource blocks (PRBs) in a spectrally well-localized manner, i.e., with narrow
guardbands. Subband filtering is able to suppress interference leakage between
adjacent subbands, thus supporting independent waveform parametrization and
different numerologies for different groups of PRBs, as well as asynchronous
multiuser operation in uplink. These are central ingredients in the 5G waveform
developments, particularly at sub-6-GHz bands. The FC filter optimization
criterion is passband error vector magnitude minimization subject to a given
subband band-limitation constraint. Optimized designs with different guardband
widths, PRB group sizes, and essential design parameters are compared in terms
of interference levels and implementation complexity. Finally, extensive coded
5G radio link simulation results are presented to compare the proposed approach
with other subband-filtered CP-OFDM schemes and time-domain windowing methods,
considering cases with different numerologies or asynchronous transmissions in
adjacent subbands. Also the feasibility of using independent transmitter and
receiver processing for CP-OFDM spectrum control is demonstrated
Automated Fourier space region-recognition filtering for off-axis digital holographic microscopy
Automated label-free quantitative imaging of biological samples can greatly
benefit high throughput diseases diagnosis. Digital holographic microscopy
(DHM) is a powerful quantitative label-free imaging tool that retrieves
structural details of cellular samples non-invasively. In off-axis DHM, a
proper spatial filtering window in Fourier space is crucial to the quality of
reconstructed phase image. Here we describe a region-recognition approach that
combines shape recognition with an iterative thresholding to extracts the
optimal shape of frequency components. The region recognition technique offers
fully automated adaptive filtering that can operate with a variety of samples
and imaging conditions. When imaging through optically scattering biological
hydrogel matrix, the technique surpasses previous histogram thresholding
techniques without requiring any manual intervention. Finally, we automate the
extraction of the statistical difference of optical height between malaria
parasite infected and uninfected red blood cells. The method described here
pave way to greater autonomy in automated DHM imaging for imaging live cell in
thick cell cultures
A kepstrum approach to filtering, smoothing and prediction
The kepstrum (or complex cepstrum) method is revisited and applied to the problem of spectral factorization
where the spectrum is directly estimated from observations. The solution to this problem in turn leads to a new
approach to optimal filtering, smoothing and prediction using the Wiener theory. Unlike previous approaches to
adaptive and self-tuning filtering, the technique, when implemented, does not require a priori information on the
type or order of the signal generating model. And unlike other approaches - with the exception of spectral
subtraction - no state-space or polynomial model is necessary. In this first paper results are restricted to
stationary signal and additive white noise
Efficient SAR Raw Data Compression in Frequency Domain
SAR raw data compression is necessary to reduce huge amounts of SAR data for a memory on board a satellite, space shuttle or aircraft and for later downlink to a ground station. In view of interferometric and polarimetric applications for SAR data, it becomes more and more important to pay attention to phase errors caused by data compression. Herein, a detailed comparison of block adaptive quantization in time domain (BAQ) and in frequency domain (FFT-BAQ) is given. Inclusion of raw data compression in the processing chain allows an efficient use of the FFT-BAQ and makes implementation for on-board data compression feasible. The FFT-BAQ outperforms the BAQ in terms of signal-to-quantization noise ratio and phase error and allows a direct decimation of the oversampled data equivalent to FIR-filtering in time domain. Impacts on interferometric phase and coherency are also given
An Efficient Polyphase Filter Based Resampling Method for Unifying the PRFs in SAR Data
Variable and higher pulse repetition frequencies (PRFs) are increasingly
being used to meet the stricter requirements and complexities of current
airborne and spaceborne synthetic aperture radar (SAR) systems associated with
higher resolution and wider area products. POLYPHASE, the proposed resampling
scheme, downsamples and unifies variable PRFs within a single look complex
(SLC) SAR acquisition and across a repeat pass sequence of acquisitions down to
an effective lower PRF. A sparsity condition of the received SAR data ensures
that the uniformly resampled data approximates the spectral properties of a
decimated densely sampled version of the received SAR data. While experiments
conducted with both synthetically generated and real airborne SAR data show
that POLYPHASE retains comparable performance to the state-of-the-art BLUI
scheme in image quality, a polyphase filter-based implementation of POLYPHASE
offers significant computational savings for arbitrary (not necessarily
periodic) input PRF variations, thus allowing fully on-board, in-place, and
real-time implementation
The FFX Correlator
We established a new algorithm for correlation process in radio astronomy.
This scheme consists of the 1st-stage Fourier Transform as a filter and the
2nd-stage Fourier Transform for spectroscopy. The "FFX" correlator stands for
Filter and FX architecture, since the 1st-stage Fourier Transform is performed
as a digital filter, and the 2nd-stage Fourier Transform is performed as a
conventional FX scheme. We developed the FFX correlator hardware not only for
the verification of the FFX scheme algorithm but also for the application to
the Atacama Submillimeter Telescope Experiment (ASTE) telescope toward
high-dispersion and wideband radio observation at submillimeter wavelengths. In
this paper, we present the principle of the FFX correlator and its properties,
as well as the evaluation results with the production version.Comment: 20 figure
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