Questions tagged [linear-systems]

A linear system operates on inputs with only linear operators so the response to a complex input can be analysed as the sum of the response to a set of simpler inputs. This mathematical property makes the analysis of linear systems much simpler than non-linear systems where this summation or superposition does not hold. Linear systems are generally further classified as time invariant, meaning that there characteristics do not change over time.

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3
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6answers
536 views

Design a LTI system which returns DC value of the input signal

Suppose that $h(t)$ is the impulse response of LTI system. The input signal $x(t)$ is periodic with period $T$. Determine $h(t)$ so that the output signal $y(t)$ only be the DC component of $x(t)$. Is ...
0
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1answer
331 views

Initial rest condition for the linear constant-coefficient differential equations

Suppose that system has the input/output relation as follows $$\sum_{k=0}^{N}a_k \frac{d^ky(t)}{dt^k} = \sum_{k=0}^{M}b_k \frac{d^kx(t)}{dt^k}$$ Where $a_k, b_k \in \mathbb{R}$. Obviously we need ...
7
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2answers
439 views

Negative group delay and envelope advance

I am having a doubt reading about delays in signal processing. Let there be an input to a LTI system with frequency response $H(f)$, given signal $x(t) = a(t)\cos(2\pi f_ot)$, where $a(t)$ is a ...
-2
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1answer
31 views

LTI system impulse response [closed]

I am learning signal processing and need some help with this question $h[n]=-x[n]+2x[n-1]-3x[n-3]$ Given the following input signal $x[n]$ calculate y[n] the output of the system $x[0]=2, x[1]=0, x[...
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0answers
43 views

Is a LTI system with dead-time equivalent with a LTI system with no dead-time but delayed input signal?

I wonder if the system parameters would remain the same after all. According to the definitions, the gain is the change of the output induced by the change of the input if we assume that the gain is ...
0
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2answers
119 views

Determine the haar wavelet function is linear or nonlinear

I'm looking for analytical justification of linearity or non linearity of the wavelet transform with the real Haar mother wavelet function. I have googling already. But I can't find and understand ...
0
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2answers
101 views

Characterizing an unknown LTI system

What are the best approaches to characterize an unknown discrete time LTI system? I believe one of the approaches is to input a known input and measure the output to find a transfer function. What are ...
0
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0answers
65 views

Characterizing a non-LTI system

How should we characterize a non-LTI system? For example we have: $y[n]=x[3n]+x[2n]+x[n]$ which is clearly not LTI. Also, the impulse response will be $h[n]=3\delta[n]$ and if we take the DTFT of this ...
0
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0answers
31 views

Discretizing my continuous system in Matlab

I was hoping someone could help me with conducting my discretization in MATLAB. I have a linear system with known data: sampling interval $T$, system matrix $\mathbf{A}$, input matrix $\mathbf{B}$, ...
0
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1answer
75 views

On the use of Permutation matrix to perform iFFT

I have a question about using the permutation matrix for performing $iFFT$ for such matrix and then reshape it row-wise and column-wise way. Let's say that we have a random matrix $x$ whose size is (...
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3answers
86 views

System classification: unit-time delay

I'm reading a book on linear systems and I can't understand why the unit-time delay is a distributed system. This is the example given in the book: I understand that the initial state of the system ...
0
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1answer
587 views

Autocorrelation of LTI system output

I'm having trouble showing the following relation: The autocorrelation of a LTI system with impulse response $h[n]$, input $x[n]$ and output $y[n]=h[n]*x[n]$ is given as: $r_{yy} = r_{hh}*r_{xx}$ ...
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2answers
73 views

Filter response to sinusoidal input signal

This question is related to Does 46 dB gain of a filter for a frequency imply 200 times more amplitude? In the accepted answer it is mentioned that "For a sine wave input the amplitude of the steady ...
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1answer
24 views

DTFT of inverse of any function

In my book solution is given like this. But i am solving like this , am i doing wrong??
3
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3answers
175 views

Estimating the Signal by Deconvolution with a Prior on the Filter Coefficients and the Signal Samples

Assume I have signal $y[n]$ which is a result of convolution between channel $h[n]$ and signal $x[n]$. which means: $$y[n] = h[n] \ast x[n]$$ where $\ast$ is the convolution operation The signal $...
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3answers
315 views

Whether $y(t) = x(t/3)$ is a memoryless system?

I am a newbie in signal and system, and feeling confused about the memoryless property, it says at the definition, if a system gives output only depends on present input, then its memoryless. So if at ...
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0answers
41 views

Trouble checking if a given difference equation corresponds to an LTI System

I'm having trouble on how to check if a given difference equation corresponds to an LTI system. For instance, Does the following difference equation correspond to a LTI DT system ? Explain. $$y[...
6
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3answers
445 views

Oscillations in a first-order discrete-time linear systems

According to my understanding, continuous first order systems do not exhibit oscillatory behavior because a first order system has only one energy storage element and thus oscillation is not possible. ...
4
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1answer
124 views

What are the properties of continuous-time improper systems?

I am trying to better understand the properties of improper systems $H(s) = \frac{b(s)}{a(s)}$, for which the order of the numerator $b(s)$ is greater than the order of the denominator $a(s)$ (in the ...
3
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1answer
201 views

Proving linearity and time-invariance

This question was asked in one of our quiz. Question is Determine if the system with the input-output relationship given by $$y(t) = \int_{t-10}^{t} \cos(\tau)x(\tau)d\tau$$ is linear and time ...
0
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1answer
127 views

Time invariance and linearity of recursive system

I am confused about the definition of linearity and time invariance of recursive system Given $$y[n] = y[n-1] - y[n-2] - x[n]$$ To test time invariance, we shift the input $x[n]$ for shifting and ...
0
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1answer
41 views

Difference equation with variable coefficients in MATLAB

Given the following difference equation $$y[n]-\left(\dfrac{n}{n+1}\right)y[n-1] = n\cdot x[n]$$ How can we use MATLAB to solve it? I know if the coefficients are constant we can simply use ...
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1answer
78 views

Determining if a system is Linear

Having $h[n]=u_0[n]+0.8u_0[n-1]+1.6u_0[n-2]$ and $x[n]=(u_1[n]-u_1[n-3])$ The goal is to determine if the system $y[n]=h[n]*x[n]$ is linear. I know that I would have to test it for Homogenity and ...
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2answers
134 views

If the frequency response of a system is time-independent, is this system LTI?

Intuitively, I feel like a time-variant system would necessarily have a time-dependent frequency response, and vice-versa. So, is the time-independence of the frequency response necessary and ...
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2answers
141 views

Cross-correlation of maximum length sequence with noise

Background I am using a maximum length sequence to find the impulse response of a linear system. I want to calculate the expected SNR. I know that my signal amplitude is scaled by the length of the ...
3
votes
2answers
146 views

Response of an ideal integrator to a cosine wave

It sounds like a very elementary question on system theory but I got quite confused about it, so hopefully you guys can enlighten me. I'm considering an ideal analog integrator, i.e., a system with ...
0
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1answer
15 views

Frequency response of each component of a system given its global response

Given the following block diagram, find the frequency responses $H1(f)$ and $H2(f)$. The frequency response of the whole system has to be $H(f)=(\alpha_0+\alpha_1e^{-j2\pi T_1f}+\alpha_2e^{-j2\pi T_2f}...
2
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1answer
228 views

Frequency response of a system given its block diagram

Given the following block diagram, I am asked to find the frequency response $H(f)$ of the system. This is what I have done: The output of the first block is $j2\pi fX(f)$, and after going through $...
1
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1answer
41 views

Impulse response of a system in z domain

The question 3-23 in the "Discrete-Time Signal Processing - Second Edition" is: and the solution is: I cannot understand the solution. In the second row of the answer when I multiply (-4) with ...
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2answers
42 views

Are there existing third system (linearity, non linear, !!!)?

I like to know your idea about is there any third system after linear, none linear classification. Could we consider more universe dimension than 4 dimensions (time, XYZ) like 11 dimensions of  ...
3
votes
1answer
141 views

LTI, causal, discrete time system output

Consider a discrete time LTI causal system $S: y = S(u)$, with its impulse response $h:{Z} \rightarrow R:h(n)=3^{n+1}{H(n)}$ with $H$ the Heaviside function. We know the values of input: $$u(0) = 2$$...
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1answer
137 views

is y[n] = x[n] + n time invariant?

My steps were as follows: $\ x_2[n] = x[n-k] $ $\ y[n-k] = x[n-k] + (n-k) $ and $\ y_2[n] = x_2[n] + n = x[n-k]+(n-k)$ Does this mean that it is indeed time invariant?
0
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1answer
47 views

Does constant Q transform have linearity property in the transformed domain?

With FFT, I sometimes take advantage of the fact that I can pre-calculate a signals Fourier Transform, and then you can add the noise in the spectral domain: $$ \mathscr{F} (x[n] + h[n]) = \mathscr{F}...
2
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2answers
596 views

LTI system output given input and frequency response

The question I'm trying to understand is as follows: A linear time-invariant continuous-time system has the frequency response function $$H(\omega)=\frac{1}{j\omega+1} $$ Compute the output response $...
1
vote
1answer
94 views

System memory, causality, stability

im new into systems and im supposed to solve if the system has memory, us causal, linear, stationery, BIBO stable...The problem is i have never had experience with this type of system where the actual ...
0
votes
1answer
258 views

Parallel LTI system

Imagine I know that a system comprises two LTI subsystems $H_a$ and $H_b$ connected in parallel. Also, suppose that I can measure the impulse response of the whole system, $H_a \| H_b$, and the ...
0
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0answers
58 views

Phase response of an LTI-system

I've got an LTI-system such as follows: $$y'(t)+{2} y(t)={5} x(t-{3}), t>0, \\ \\ y(0)=0 \ \text{ ja } x(t)=0, \ t<0.$$ From this i've already figured out the transfer function: $$H(f)=\frac{5\...
0
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1answer
302 views

Is $y(t) = \cos(t) + x(t)$ a time-invariant system?

Is $y(t) = \cos(t) + x(t)$ a time-invariant system? $y(t-k) = \cos(t-k) + x(t-k)$ But it isn't equal to $\cos(t) + x(t-k)$ So, would it be time-invariant?
7
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4answers
3k views

Are all LTI systems invertible? If not, what is a good counterexample?

I have been trying to figure this out for a while now. Everywhere I have looked I could easily find examples of invertible LTI systems, but I could not find any counterexamples. Can anybody shed some ...
3
votes
3answers
387 views

I somehow “proved” that given any LTI system, its transfer function has to be constant. What am I missing?

A transfer function is defined as the Laplace transform of the ratio of output to input. Also, every LTI system has an eigenfunction. Given such eigenfunction as an input, the ratio of the output to ...
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1answer
143 views

Steady-State Output from Transfer Function

The progress I have made is as follows: $\sin(t)$ is our signal therefore $\omega = 1 = 2\pi f$ and $f$ = $\frac{1}{2 \pi}$ Also, $f_s$ = 10Hz therefore T = $\frac{1}{f_s}$ = 0.1s $H(z) = \frac{z}{...
2
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1answer
38 views

Show That a 2D Linear Transform $ T \left( \cdot \right) $ Is Homogeneous

By my understanding, a transform T is homogeneous if T[0] = 0. Then to prove that a linear transformation is homogeneous we say that: T[ax(n1, n2) + bx(n1, n2)] = aT[x(n1, n2)] + bT[x(n1, n2)] What ...
3
votes
2answers
694 views

The spectrum of the sum of two periodic signals

Considering the continue, periodic signals $s_1(t)$ and $s_2(t)$, with the period $P_1$ and $P_2$ respectively. Consider now a new signal $s$ the sum of the two pervious signals. I come to know ...
0
votes
3answers
629 views

impulse response VS zero-input response

I am new in the field of systems and signals, and I have a rather basic for the majority of the group, question: Can we find the impulse response function of homogeneous ODE, instead of its zero-...
5
votes
4answers
908 views

Can every type of linear filter be modelled by a convolution?

I have an input time series going through a filter that creates another time series as output. If I assume in first approximation that my filter is linear, does it necessarily mean that I can model ...
3
votes
2answers
866 views

Convolution of Signal with a Gaussian Filter / Kernel

Following up on Analytical Solution for the Convolution of Signal with a Box Filter, I am now trying to convolve a Gaussian filter with the sine signal by hand. My method is to use the definition of ...
2
votes
3answers
1k views

Initial Rest Condition for LCCDE causal LTI systems

I am self studying Alan Opennheim's course Signals and Systems. I am a math major and have no background in EE. I understand that for a linear constant-coefficient difference equation (LCCDE) system ...
7
votes
2answers
313 views

Why can adaptive IIR filters result in unstable solutions?

For adaptive filtering, both finite and infinite impulse response (FIR/IIR) filters can be utilized. As an advantage of FIR filters in this context, guaranteed stability is often mentioned, while IIR ...
3
votes
1answer
244 views

transient and steady-state response of first order system

Considering this general 1st order transfer function $$ H(z) = \frac{b_0 + b_1z^{-1}}{1-az^{-1}} $$ How to find (analytically) the transient and steady-state responses? With steady-state response I ...
2
votes
2answers
159 views

Are Chebyshev Type 1 filters very unstable at very high orders?

I am currently experimenting with a digital implementation of a Chebyshev Type 1 filter of mine, for audio purposes. I have written the code myself so I was wondering if the behavior I've noticed is ...

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