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Test: Matched Filter - Electronics and Communication Engineering (ECE) MCQ


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10 Questions MCQ Test Communication System - Test: Matched Filter

Test: Matched Filter for Electronics and Communication Engineering (ECE) 2024 is part of Communication System preparation. The Test: Matched Filter questions and answers have been prepared according to the Electronics and Communication Engineering (ECE) exam syllabus.The Test: Matched Filter MCQs are made for Electronics and Communication Engineering (ECE) 2024 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests for Test: Matched Filter below.
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Test: Matched Filter - Question 1

Which of the following statements about the matched filter in a communication receiver are correct ?
(A) It may produce phase error if synchronization is improper
(B) Its impulse response depends on the singal shape
(C) The characteristics of the matched filter is matched with the transmitted data
(D) It produces inter symbol interference
(E) It measures the correlation between incoming received message and its impulse response
Choose the correct answer from the options given below : 

Detailed Solution for Test: Matched Filter - Question 1

Matched Filter:

  • Matched Filter is used to produce an output in such a way that it maximizes the ratio of the output peak power to the mean noise power in its frequency response.
  • The frequency response of Magnitude and phase angle of the Matched Filter varies uniformly with frequency.
  •  The impulse response of the matched filter depends upon the signal shape. It is the mirror image of the received signal about a time instant.
  • The Characteristics of the matched filter are matched with the transmitted data.
  • The matched filter reduces INTERSYMBOL INTERFERENCE by attenuating the beginning and end of each symbol period.
  • Matched Filter measures the correlation between incoming received message and its impulse response.

Important Points:

  • A time delay is necessary for the specification of the filter for reasons of physical realizability since there can be no output from the filter until the signal is applied.
  • The frequency-response function of the matched filter is the conjugate of the spectrum of the received waveform except for the phase shift exp (- j2Πft).
  • This phase shift varies uniformly with frequency. Its effect is to cause a constant time delay.
Test: Matched Filter - Question 2

Consider the pulse shape s(t) as shown. The impulse response h(t) of the filter matched to this pulse is

Detailed Solution for Test: Matched Filter - Question 2

The shown bock diagram will be considered as the receiver in digital communication.

The impulse response of the filter is calculated by:

h(t) = s*(Tb - t)
Calculation:
In the given signal the duration is T. So, Tb = T
The shifted signal by T is given by:
s(t+T)

The time-reversed signal will be

Option 3 is correct.

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Test: Matched Filter - Question 3

The received signal in a binary communication system is given by r(t) = s(t) + n(t). Where n(t) is AWGN with PSD of N0/2 (W / Hz) and s(t) is shown in the figure below.

The maximum value of signal to noise ratio at the output of the matched filter is _________.

Detailed Solution for Test: Matched Filter - Question 3

A matched filter is used to increase the signal to noise ratio (S/N) at the receiver by correlating with the known input signal.

If h(t) = si(T – t), maximum signal to noise ratio will be there at the output receiver.
Signal strength (s) = Energy of s(t)

Test: Matched Filter - Question 4

If Eb, the energy per bit of a binary digital signal, is 10-5 Ws (Watt-Second) and the one-sided power spectral density of the white noise, N0 = 10-6 W/Hz, then the output SNR of the matched filter is

Detailed Solution for Test: Matched Filter - Question 4

The output SNR is given by:

In a matched filter the filter response is shaped according to the input signal waveform.
The peak amplitude of the output of the filter is proportional to the input signal energy, hence the probability of error depends on the signal energy.

Test: Matched Filter - Question 5

Let  and h(t) is a filter matched to y(t). If y(t) is applied as input to h(t) then the Fourier transform  of the output is:

Detailed Solution for Test: Matched Filter - Question 5

Test: Matched Filter - Question 6

Signal e-|t| is applied to matched filter. The amplitude spectrum of the output signal will be _______.

Detailed Solution for Test: Matched Filter - Question 6


y(t) = s(t) × h(t)
y(t) = s(t) × s(Tb – t)

Test: Matched Filter - Question 7

A binary baseband digital communication system employs the signal

for transmission of bits. The graphical representation of the matched filter output y(t) for this signal will be

Detailed Solution for Test: Matched Filter - Question 7

1. The matched filter impulse response h(t) for input x(t) is h(t) = x(T-t).
2. For matched Filter The output has a duration that is twice the duration of the input signal (due to convolution) and its peak value is the energy of the input signal
Application: Since p(t) is a uniform signal, Ts time long, the matched filter h(f) will also be Ts time long. So, the convolution of  p(t) and h(t) will be 2Ts time long signal.
Now, the energy of p(t) will be calculated as:

E = 1
So, the peak value of y(t) will be 1.
Note: It is the rule that is always followed by outputs of matched filters. The output has a duration that is twice the duration of the input signal (due to convolution) and its peak value is the energy of the input signal.

Test: Matched Filter - Question 8

A zero mean white Gaussian noise having power spectral density N0/2 is passed through an LTI filter whose impulse response h(t) is shown in the figure. The variance of the filtered noise at t = 4 is

Detailed Solution for Test: Matched Filter - Question 8

Convolution of a signal x(t) with unit impulse δ(t) is the signal itself. i.e. x(t) ⊕ δ(t) = x(t)
Fourier transform of auto-correlation function of a power signal x(t) is power spectral density Sx(f). i.e. 
And E(x2 (t)) = RX (0)
The variance of the signal x(t) is defined as:

Fourier transform of unit impulse is 1.

Let n(t) be the input white noise with zero mean and  N0/2 power spectral density.
Mean of the white noise = E(n(t)) = 0
Power spectral density is:

And the auto-correlation function is:

Let yn(t) is the output noise.

Mean of the output noise:

The variance of the output noise is:

Test: Matched Filter - Question 9

Determine the matched filter response h(t) for signal s(t) shown below:

Detailed Solution for Test: Matched Filter - Question 9

matched filter is used to increase the signal-to-noise ratio (S/N) at the receiver end by correlating the filter impulse response with the known input signal.
i.e. provided h(t) = Si*(T - t), where Signal Si(t) exists for 0 ≤ t ≤ T, the filter is said to be a matched filter.
i.e. h(t) = (SiR(T - t) + jSiImg (T - t))*
⇒ h(t) = (SiR(T - t) – jSiImg(T - t))
Where, SiR = Real part of Si(t)
And SiImg = Imaginary part of Si(t).
Calculation:
Given, Si(t) as shown;

So the real part of the filter impuse response must be –ve of the shifted part shown below,

And the imaginary part must be,

- [SiImg (T - t)] will be,

So, Option (4) is Correct.

Test: Matched Filter - Question 10

The matched filter response for a given signal, sampled at t = T is:

Detailed Solution for Test: Matched Filter - Question 10

A matched filter is used to increase the signal to noise ratio (S/N) at the receiver by correlating with the known input signal.

Provided h(t), which is the impulse response of the matched filter , where signal si(t) exists for 0 ≤ t ≤ T, the signal to noise ratio will be maximum at the receiver end.
For a real input signal,  
So, if h(t) = si(T – t), the maximum signal to noise ratio will be there at the output receiver.
Given,
Si(t) as shown:

So, Si(-t)

And Si(-t+T) will be;

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