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Questions tagged [coherence]

Coherence is a stastic to examine the relation between two signals.

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DFT Matrix Oversampled In Frequency?

Edit 2: I am trying to replicate results from this paper Compressed Sensing with Coherent and Redundant Dictionaries. On page 3 the "oversampled DFT" is mentioned as an example of an "...
coult099's user avatar
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Difference between Coherent and Non-Coherent in Fibre Optics?

I have been given the following equation to show the difference between coherence and non-coherence in optics and how the third term represents the interference between two optical pulses. Can someone ...
prof123's user avatar
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Is it possible to use np.fft.fft to pick out the Fourier coefficients from one timepoint, at a specific frequency?

I am trying to apply np.fft.fft on a 2D array of data of shape (98, 1024), where 98 is the number of trials and 1024 is the sampling rate in Hz. I am trying to find ...
Lisa Duan's user avatar
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Emergence - what constitutes a minimally coherent source that "just begins" to produce stationary interference patterns?

A superposition of two signals with different frequencies will never produce visible (i.e. stationary) interference patterns. Such waveforms will produce spatiotemporal beat patterns, but they rapidly ...
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Coherence between two signals at a particular frequency is less than one, yet the corresponding frequency components differ by a scalar multiple

I'm sampling from the functions $x(t)=\cos(2\pi f_0t)$ and $y(t)=\cos(2\pi f_0t^{1.005})$, for one second, where $f_0=300$ and my sampling rate is $f_s=1000$. ($N=1000$). A plot of the coherence ...
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Is the coherence between two signals defined at frequencies above the Nyquist frequency?

Suppose I sample from two continuous signals, $x$ and $y$, with sampling rate $f_s=1000$ Hz yielding $N$ samples. A plot using coherence from ...
fishbacp's user avatar
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What is the actual coherence value between two simple signals, one a cosine and the other a sine?

Suppose $f=300$ and I sample from $x=\cos(2\pi f t)$ and $y=\sin(2\pi f t)$ for a period of one second with sampling frequency $f_s=1000$. Then the number of samples is $N=1000$ and the DFT's for $x$ ...
fishbacp's user avatar
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Coherence between two signals: How to convey the underlying idea using spectral decomposition and orthogonal projections?

My question is somewhat similar to one I posted previously I understand how coherence is defined in terms of spectral densities, but I would be elated if I could explain the basic concept of coherence,...
fishbacp's user avatar
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Constructing spectral components of signals using the Fourier matrix and interpreting coherence using the results

I have an EEG signal of length 2 sec. sampled at a rate of 200 Hz. If $\vec{x}$ denotes my signal in $\mathbb{R}^{400}$, then I can obtain the DFT by computing $W\vec{x}$, where $W$ denotes the 400-by-...
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Is it possible to explicitly express a simple coherence calculation in terms of linear regression?

I'm a mathematician seeking to improve my conceptual understanding of what the coherence between two signals, $x$ and $y$, represents. I know it's analogous to a linear regression coefficient, in that ...
fishbacp's user avatar
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For two signals having a common frequency, w, and differing by a fixed phase shift, why is the coherence even defined at frequencies other than w?

This question is related to one posted a couple years ago at (Why the spectral coherence is unity for all frequencies between single-frequency time series and itself). Suppose two signals have common ...
fishbacp's user avatar
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For two sinusoidal waves, what does the magnitude of their coherence tell us, and why do the periodogram and csd commands yield incorrect results?

Suppose I have 2 seconds of data sampled at 1000 Hz., and two sinusoids differing only in amplitude and phase shift: ...
fishbacp's user avatar
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Why is there coherence below the cutoff frequency of two high-pass filtered signals?

I record surface EMG signals from two muscles at 1500 Hz. The following preprocessing steps are performed using basic MATLAB commands. First, I decimate both signals to 500 Hz (Lowpass filtering ...
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Coherent detection in fading channel

I want to design an optimum receiver for a fading AWGN channel for ML Detection. I know that in the case of non-coherent communication we have to use an energy detector(even when the fading channel is ...
indmath's user avatar
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1 answer
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Magnitude-squared coherence using pwelch function yields different results than mscohere

I am trying to reproduce mscohere function from Matlab. $$C_{xy}(f) = \frac{\left\lvert P_{xy}(f)\right\rvert^2}{P_{xx}(f)P_{yy}(f)}$$ This is inside Algorithm section in docs for mscohere: mscohere ...
Alamakanambra's user avatar
2 votes
3 answers
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Identify which of the three signals is closest to a sinusoidal curve

I have some acceleration values from a sensor. These values are reported as x, y and z components of the acceleration. As can be seen in the attached figure, it is clear that the z signal has a clear ...
ashorj's user avatar
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From Delay Spread to Coherence Bandwidth?

The phase difference of two sinusoids is given as: | TX --(r)--->RX <------- (Reflection)| d: whole path from sender to reflecting object $ \Delta \theta = 2 \pi \cdot \frac{(2d - r)-r}{c} f + \...
user674907's user avatar
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the amplitude-frequency spectrum and the phase-frequency spectrum of a coherent packet of radio pulse

Who can tell you how to draw the amplitude-frequency spectrum and the phase-frequency spectrum of a coherent packet of radio pulses?
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Coherence for order spectra

The scipy signal coherence function computes for two time series the coherence as a function of the frequency. For rotating systems however, it is sometimes meaningful to analyze the two recorded ...
AlexGuevara's user avatar
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Fast/Slow Fading: How are doppler shift and coherence time related?

In the literature I've read that fast fading happens if the bit duration is larger than the coherence time of the channel. The coherence time of a channel is proportional to $\frac{1}{f_{Doppler}}$. ...
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Changing Coherence function from float to fixed point

I want to calculate the coherence between two audio signals. After referring a few websites, I found that the coherence is calculated by using the equation $(1)$ which is as follows $$\rm Coherence = \...
rkc's user avatar
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1 answer
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Why coherence function calculation needs averaging of different segments of the signal?

I am trying to understand coherence function calculation. I am working with a non-linear system without any noise. Coherence function is defined as: I understand that coherence is 1 for N=1, but I ...
Swati Jain's user avatar
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Probability of similarity for two random white noises

I'm looking for the method to calculate theoretical similarity of two random noises $x$ and $y$ with mean $0$ and standard deviation $1$, I've got also $12500$ samples of signal, sampled $2.5$ Ga/s. ...
Malum Wolfram's user avatar
2 votes
3 answers
149 views

What is the physical meaning of coherence bandwidth in mmWave massive MIMO channel?

I am doing some research about millimeter wave massive MIMO channel now. We first take account about static MIMO channel, cause we only have SISO measurement system now. We use scanner to move our ...
Y.Y.Lin's user avatar
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5 answers
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Intuitive explanation of coherence

I am a biologist so apologies for the basic question. I am trying to get an intuitive understanding of what the coherence between 2 signals actually means. I have read a couple of introductory texts ...
Apollo23's user avatar
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2 answers
466 views

Coherent detection in radar and radio signals

Coherent demodulation\detection is usually done via matched filtering in RF signal processing. In radar signals, coherent integration can be done if the phases of the returns are known. In terms of ...
Cindy's user avatar
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Removing DC Offset (via removing mean) of input and output signals affects their coherence

I have input $x$ and output $y$ signals (fs=10 Hz, length N=10800). I have removed DC offset via the following equation: $x_{normalized} = 100 \frac{(x-\bar x)} {\bar x }$ where $\bar x$ is the mean ...
Jack's user avatar
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Coherent Radar -- How do we justify it?

How can we justify doing coherent radar when the phase of the return is unknown? For instance, after a reflection, assuming a stationary target, we should get something akin to: $$ x_{rx}(t) = |\...
the_src_dude's user avatar
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Time spans in coherence computation

Currently I'm writing my master thesis and I'm having troubles with coherence definition. My question is similar to https://stats.stackexchange.com/questions/92412/clear-steps-to-calculate-coherence-...
Jorge Mendoza Ruiz's user avatar
1 vote
1 answer
417 views

Why is the coherence function unity at all frequencies when only one reading is done?

Several papers on the internet states that the coherence function is unity for all frequencies if only one reading is done, and that the coherence function requires an average of two or more readings ...
hermanjakobsen's user avatar
3 votes
0 answers
299 views

How to compare imaginary coherence values?

High, I am currently writing my Master's thesis on susceptibility for hypnosis. I am comparing EGG signals of lowly and highly susceptible individuals. The imaginary coherence is given by: $$ \...
andyfilip's user avatar
1 vote
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244 views

Mscohere in Matlab-why would the coherence tends to 1 as nfft increases?

Does anyone have a clue as to why -using mscohere- the coherence becomes exactly one for all frequencies if nfft is set to about 190-200. I know it's standard practice to set it to a number that is a ...
Fede C's user avatar
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Coherence and non-linear interactions

Reportedly, coherence-based metrics are primarily influenced by linearity in phase. However, Klein et al report that coherence is also: ... very sensitive to fluctuations of linearity in ...
hH1sG0n3's user avatar
1 vote
2 answers
307 views

Why Coherence is not a valid metric when performing impact excitation?

INTRODUCTION I have understood that Coherence is a function that explains the linear relationship between an excitation signal and a response signal. I know how it is calculated and why it is bounded ...
sdiabr's user avatar
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1 answer
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Is it possible to zero-pad series when using MSCOHERE in matlab?

The function fft allows one to zero-pad, and mscohere, after all works with auto and cross spectra, which, presumably, have all been calculated with fft. I haven't found any mention on zero-padding in ...
Fede C's user avatar
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2 votes
1 answer
172 views

Cross power spectral matrix from PSDs and coherence using matrix notation

I have a vector containing all the PSD of a series of signals $\underline{s} = \left[ |S_{x_1x_1}| |S_{x_2x_2}| |S_{x_3x_3}| ...\right]^T$ I also have a matrix $\gamma^2$ containing all the ...
Luca's user avatar
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1 vote
0 answers
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Simulating two signals with a desired coherence

I'm trying to simulate two frequency-domain signals with a desired coherence, and I'd like to check if my idea is right. To simulate two time-domain signals with a desired correlation, we can use the ...
Anon's user avatar
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1 vote
2 answers
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Why does the addition of noise improve coherence between two signals?

Taking a simple example of the coherence between two signals, each composed of two sinusoids of frequency 100 and 200 Hz, I expect the coherence to show two peaks in the spectrum located at precisely ...
Dipole's user avatar
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1 answer
1k views

Should scipy.signal.coherence be 1 for single input and output signals?

I am trying to calculate the coherence between input and output signals. I thought I could work with a single input and a single output time series and calculate the coherence $\gamma^2$ between them. ...
Bax Menker's user avatar
2 votes
2 answers
362 views

Optimal segment length for coherence estimation

I have a question about the computation of coherence between two signals with Welch's method. The two signals are relatively short (e.g. 256 samples) and I would like as correct an estimate of shared ...
FirstSecondThird's user avatar
1 vote
1 answer
385 views

Averaging magnitude squared coherence across multiple time series

In a previous post, A. Donda had suggested that, in order to calculate the average magnitude squared coherence of more than one pair of time series (e.g. y1 and x1, and y2 and x2), one ought to follow ...
Matt Vowels's user avatar
3 votes
1 answer
1k views

Deciding for the correct way to calculate coherence time

I have to calculate the coherence time of an indoor environment. The signal I am sending is modulated with GFSK, the carrier frequency is about 2.4 GHz and my symbol time is 1 microsecond. During my ...
Furkan Küçük's user avatar
1 vote
1 answer
391 views

confidence interval estimate for coherence

Is there any solution for estimating Confidence interval of coherence derived by Welch method with overlapping segments? Moreover, the window length is not same for all the observations, only the ...
Akanksha 's user avatar
2 votes
1 answer
227 views

Multi-taper Coherence, With Tapers=1

I had a question regarding multi-taper estimated coherence. It appears when the number of tapers is set to 1, all coherency values, per frequency, are always 1. It's obvious solving for autospectra $...
BobBarker's user avatar
0 votes
1 answer
3k views

Compute phase coherence between two eeg signals

I have two EEG signals/channels and I would like to compute phase coherence in MATLAB. I have this paper: https://www.nature.com/npp/journal/v39/n5/full/npp2013330a.html but it does not say what Sij ...
Ali Gul's user avatar
1 vote
1 answer
175 views

Is Spectral Coherence (MSC) dependent to the initial amplitude of the comparing signals?

Given the signals \begin{align} x(t) &= A_1\sin(\omega t)\\ y(t) &= A_2\sin(\omega t) \end{align} Do $A_1$ and $A_2$ play a role in the $C_{xy}$ coherence estimator? MATLAB's ...
IDKreally's user avatar
2 votes
3 answers
3k views

What is meant by "correlation" when referring to spectral coherence

I've been reading that coherence measures the correlation between two waves as a function of frequency. I also read that difference in phase does not mean less coherence at a given frequency, and that ...
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1 vote
1 answer
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Calculating spectral coherence coefficient (scc) - implementation help

I am trying to calculate the SCC of a cyclostationary signal. I have estimated the Spectral Correlation Function (scf) of the signal using FFT Accumulation Method (FAM). I implemented the following ...
Pacu's user avatar
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-1 votes
1 answer
358 views

How to implement Cross Spectral Density [duplicate]

I am writing a program to compute the cross spectral density of an image, and a template image, which is the image I am trying to find in other image. Reading wiki1,wiki2,wiki3 from wikipedia, and ...
DebareDaDauntless's user avatar
1 vote
1 answer
268 views

Calculating incoherency in compressive sensing

CS is based on a choice of a sensing basis $\Phi$ relative to a representation basis $\Psi$. There are many well known pair matrices for $\Phi$ and $\Psi$ like random Gaussian and FFT, and also they ...
Haybert Markarian's user avatar