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Recent questions and answers in Communications
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1
GATE ECE 2020  Question: 8
The components in the circuit shown below are ideal. If the opamp is in positive feedback and the input voltage $V_{i}$ is a sine wave of amplitude $1$ $\text{V}$, the output voltage $V_{o}$ is a noninverted sine wave of $2$ $\text{V}$ amplitude. an inverted sine ... . a square wave of $5$ $\text{V}$ amplitude. a constant of either $+5$ $\text{V}$ or $5$ $\text{V}$.
asked
Feb 13, 2020
in
Communications
by
jothee
(
1.9k
points)

293
views
gate2020ec
communications
amplitude
0
votes
0
answers
2
GATE ECE 2020  Question: 12
A digital communication system transmits a block of $N$ bits. The probability of error in decoding a bit is $\alpha$. The error event of each bit is independent of the error events of the other bits. The received block is declared erroneous if at least one of its bits is decoded ... $\alpha ^{N}$ $1\alpha ^{N}$ $1\left ( 1\alpha \right )^{N}$
asked
Feb 13, 2020
in
Communications
by
jothee
(
1.9k
points)

166
views
gate2020ec
digitalcommunications
communications
0
votes
0
answers
3
GATE ECE 2020  Question: 22
A binary random variable $X$ takes the value $+2$ or $2$. The probability $P(X=+2)=\alpha $. The value of $\alpha$ (rounded off to one decimal place), for which the entropy of $X$ is maximum, is __________.
asked
Feb 13, 2020
in
Communications
by
jothee
(
1.9k
points)

62
views
gate2020ec
numericalanswers
entropy
communications
0
votes
0
answers
4
GATE ECE 2020  Question: 42
For the modulated signal $x\left ( t \right )=m\left ( t \right )\cos\left ( 2\pi f_{c}t \right )$, the message signal $m\left ( t \right )=4\cos\left ( 1000\pi t \right )$ and the carrier frequency $f_{c}$ is $1\: MHz$. The signal $x(t)$ is passed ... $\cos\left ( 920\pi t \right )$ $\cos\left ( 1000\pi t \right )$ $\cos\left ( 540\pi t \right )$
asked
Feb 13, 2020
in
Communications
by
jothee
(
1.9k
points)

71
views
gate2020ec
communications
demodulator
0
votes
0
answers
5
GATE ECE 2020  Question: 47
$S_{PM}(t)$ and $S_{FM}(t)$ as defined below, are the phase modulated and the frequency modlated waveforms, respectively, corresponding to the message signal $m(t)$ ... $S_{PM}(t)$ and $S_{FM}(t)$ are same, then the value of the ratio $\dfrac{K_{p}}{K_{f}}$ is ________ seconds.
asked
Feb 13, 2020
in
Communications
by
jothee
(
1.9k
points)

33
views
gate2020ec
numericalanswers
communications
frequencymodulation
0
votes
0
answers
6
GATE ECE 2020  Question: 48
In a digital communication system, a symbol $S$ randomly chosen from the set $\left \{ s_{1},s_{2},s_{3},s_{4} \right \}$ is transmitted. It is given that $s_{1}=3,s_{2}=1,s_{3}=+1$ and $s_{4}=+2$. The received ... decoding when the transmitted symbol $S=s_{i}$. The index $i$ for which the conditional symbol error probability $P_{i}$ is the highest is ___________.
asked
Feb 13, 2020
in
Communications
by
jothee
(
1.9k
points)

24
views
gate2020ec
numericalanswers
digitalcommunications
communications
0
votes
0
answers
7
GATE ECE 2019  Question: 7
A linear Hamming code is used to map $4bit$ message to $7bit$ codewords. The encoder mapping is linear. If the message $0001$ is mapped to the codeword $0000111$, and the message $0011$ is mapped to the codeword $1100110$, then the message $0010$ is mapped to $0010011$ $1100001$ $1111000$ $1111111$
asked
Feb 12, 2019
in
Communications
by
Arjun
(
4.5k
points)

364
views
gate2019ec
communications
hammingcodes
0
votes
0
answers
8
GATE ECE 2019  Question: 34
A single bit, equally likely to be $0$ and $1$, is to be sent across an additive white Gaussian noise (AWGN) channel with power spectral density $N_{0}/2.$ Binary signaling with $0 \mapsto p(t),$ and $1 \mapsto q(t),$ is used for the transmission, along with ... $E$ would we obtain the $\textbf{same}$ biterror probability $P_{b}$? $0$ $1$ $2$ $3$
asked
Feb 12, 2019
in
Communications
by
Arjun
(
4.5k
points)

40
views
gate2019ec
gaussiannoise
autocorrelationandpowerspectraldensity
communications
0
votes
0
answers
9
GATE ECE 2019  Question: 45
Let a random process $Y(t)$ be described as $Y(t)=h(t) \ast X(t)+Z(t),$ where $X(t)$ is a white noise process with power spectral density $S_{x}(f)=5$W/Hz. The filter $h(t)$ ... power spectral density as shown in the figure. The power in $Y(t),$ in watts, is equal to _________ $W$ (rounded off to two decimal places).
asked
Feb 12, 2019
in
Communications
by
Arjun
(
4.5k
points)

34
views
gate2019ec
numericalanswers
communications
autocorrelationandpowerspectraldensity
0
votes
0
answers
10
GATE ECE 2019  Question: 46
A voice signal $m(t)$ is in the frequency range $5\:kHz$ to $15\:kHz$. The signal is amplitudemodulated to generated an AM signal $f(t)=A\left(1+m(t)\right)\cos 2\pi f_{c}t,$ where $f_{c}=600\: kHz.$ ... for the encoding. The rate, in Megabits per second (rounded off to $2$ decimal places), of the resulting stream of coded bits is ________ Mbps.
asked
Feb 12, 2019
in
Communications
by
Arjun
(
4.5k
points)

71
views
gate2019ec
numericalanswers
communications
amplitudemodulation
0
votes
0
answers
11
GATE ECE 2019  Question: 55
In the circuit shown, $V_{1}=0$ and $V_{2}=V_{dd}.$ The other relevant parameters are mentioned in the figure. Ignoring the effect of channel length modulation and the body effect, the value of $I_{out}$ is _________ $mA$ (rounded off to $1$ decimal place).
asked
Feb 12, 2019
in
Communications
by
Arjun
(
4.5k
points)

24
views
gate2019ec
numericalanswers
communications
modulations
0
votes
0
answers
12
GATE ECE 2016 Set 3  Question: 23
A binary baseband digital communication system employs the signal $p(t) = \begin{cases}\large\frac{1}{\sqrt T_s},&0\leq t\leq T_s \\ \: 0, & \text{otherwise} \end{cases}$ for transmission of bits. The graphical representation of the matched filter output $y(t)$ for this signal will be
asked
Mar 28, 2018
in
Communications
by
Milicevic3306
(
15.8k
points)

39
views
gate2016ec3
digitalcommunications
communications
0
votes
0
answers
13
GATE ECE 2016 Set 2  Question: 22
A speech signal is sampled at $8$ $kHz$ and encoded into $PCM$ format using $8$ bits/sample. The $PCM$ data is transmitted through a baseband channel via $4$level $PAM$. The minimum bandwidth (in $kHz$) required for transmission is _________
asked
Mar 28, 2018
in
Communications
by
Milicevic3306
(
15.8k
points)

19
views
gate2016ec2
numericalanswers
digitalcommunications
pulsecodemodulationsystems
communications
0
votes
0
answers
14
GATE ECE 2016 Set 2  Question: 48
An information source generates a binary sequence $\left \{ \alpha _{n} \right \}$. $\alpha _{n}$ can take one of the two possible values $1$ and $+1$ with equal probability and are statistically independent and identically distributed. This sequence is precoded ... there is a null at $f=\frac{1}{3T}$ in the power spectral density of $X(t)$, then $k$ is ________
asked
Mar 28, 2018
in
Communications
by
Milicevic3306
(
15.8k
points)

545
views
gate2016ec2
numericalanswers
autocorrelationandpowerspectraldensity
communications
0
votes
0
answers
15
GATE ECE 2016 Set 2  Question: 49
An ideal bandpass channel $500 \: Hz –2000 \:Hz$ is deployed for communication. A modem is designed to transmit bits at the rate of $4800$ bits/s using $16QAM$. The rolloff factor of a pulse with a raised cosine spectrum that utilizes the entire frequency band is __________
asked
Mar 28, 2018
in
Communications
by
Milicevic3306
(
15.8k
points)

34
views
gate2016ec2
numericalanswers
communications
0
votes
0
answers
16
GATE ECE 2016 Set 2  Question: 50
Consider a random process $X\left ( t \right )=3V(t)8,$ where $V(t)$ is a zero mean stationary random process with autocorrelation $R_{v}\left ( \tau \right )=4e^{5\mid \tau \mid}.$ The power in $X(t)$ is _________
asked
Mar 28, 2018
in
Communications
by
Milicevic3306
(
15.8k
points)

35
views
gate2016ec2
numericalanswers
communications
autocorrelationandpowerspectraldensity
0
votes
0
answers
17
GATE ECE 2016 Set 2  Question: 51
A binary communication system makes use of the symbols zero and one . There are channel errors. Consider the following events: ... in bits that you obtain when you learn which symbol has been received (while you know that a zero has been transmitted) is _________
asked
Mar 28, 2018
in
Communications
by
Milicevic3306
(
15.8k
points)

27
views
gate2016ec2
numericalanswers
communications
0
votes
0
answers
18
GATE ECE 2016 Set 1  Question: 21
Consider binary data transmission at a rate of $56$ kbps using baseband binary pulse amplitude modulation (PAM) that is designed to have a raisedcosine spectrum. The transmission bandwidth (in kHz) required for a rolloff factor of $0.25$ is ________
asked
Mar 28, 2018
in
Communications
by
Milicevic3306
(
15.8k
points)

41
views
gate2016ec1
numericalanswers
communications
modulation
0
votes
0
answers
19
GATE ECE 2016 Set 1  Question: 24
Concentric spherical shells of radii $2$m, $4$m, and $8$ m carry uniform surface charge densities of $20 \: nC/m^2$, $ – 4 \: nC/m^2$ and $\rho_s$ respectively. The value of $\rho_s$ ($nC/m^2$) required to ensure that the electric flux density $\overrightarrow D$ = $\overrightarrow 0$ at radius $10$ m is ________
asked
Mar 28, 2018
in
Communications
by
Milicevic3306
(
15.8k
points)

27
views
gate2016ec1
numericalanswers
tobetagged
communications
0
votes
0
answers
20
GATE ECE 2016 Set 1  Question: 49
A digital communication system uses a repetition code for channel encoding/decoding. During transmission, each bit is repeated three times ($0$ is transmitted as $000$, and $1$ is transmitted as $111$). It is assumed that the source puts ... a $1$. Assuming a binary symmetric channel with crossover probability $p=0.1$, the average probability of error is _________
asked
Mar 28, 2018
in
Communications
by
Milicevic3306
(
15.8k
points)

294
views
gate2016ec1
numericalanswers
digitalcommunications
communications
0
votes
0
answers
21
GATE ECE 2015 Set 3  Question: 22
The modulation scheme commonly used for transmission from GSM mobile terminals is $4$QAM $16$PSK WalshHadamard orthogonal codes Gaussian Minimum Shift Keying (GMSK)
asked
Mar 28, 2018
in
Communications
by
Milicevic3306
(
15.8k
points)

35
views
gate2015ec3
communications
gaussianminimumshiftkeying
0
votes
0
answers
22
GATE ECE 2015 Set 3  Question: 36
A three bit pseudo random number generator is shown. Initially the value of output $Y\equiv Y_{2} Y_{1} Y_{0}$ is set to $111.$ The value of output $Y$ after three clock cycles is $000$ $001$ $010$ $100$
asked
Mar 28, 2018
in
Communications
by
Milicevic3306
(
15.8k
points)

38
views
gate2015ec3
communications
pseudorandomnumber
0
votes
0
answers
23
GATE ECE 2015 Set 2  Question: 51
Consider a binary, digital communication system which uses pulses $g(t)$ and $g(t)$ for transmitting bits over an AWGN channel. If the receiver uses a matched filter, which one of the following pulses will give the minimum probability of bit error?
asked
Mar 28, 2018
in
Communications
by
Milicevic3306
(
15.8k
points)

35
views
gate2015ec2
digitalcommunications
communications
0
votes
0
answers
24
GATE ECE 2015 Set 1  Question: 50
The transmitted signal in a GSM system is of $200$ kHz bandwidth and $8$ users share a common bandwidth using TDMA. If at a given time $12$ users are talking in a cell, the total bandwidth of the signal received by the base station of the cell will be at least (in kHz) ___________.
asked
Mar 28, 2018
in
Communications
by
Milicevic3306
(
15.8k
points)

21
views
gate2015ec1
numericalanswers
communications
timedivisonmultipleaccessamplifiers
0
votes
0
answers
25
GATE ECE 2014 Set 4  Question: 23
In a double sideband (DSB) full carrier AM transmission system, if the modulation index is doubled, then the ratio of total sideband power to the carrier power increases by a factor of __________.
asked
Mar 26, 2018
in
Communications
by
Milicevic3306
(
15.8k
points)

20
views
gate2014ec4
numericalanswers
communications
amplitudemodulation
0
votes
0
answers
26
GATE ECE 2014 Set 4  Question: 51
An Mlevel PSK modulation scheme is used to transmit independent binary digits over a bandpass channel with bandwidth $100$ kHz. The bit rate is $200$ kbps and the system characteristic is a raisedcosine spectrum with $100 \%$ excess bandwidth. The minimum value of M is __________
asked
Mar 26, 2018
in
Communications
by
Milicevic3306
(
15.8k
points)

39
views
gate2014ec4
numericalanswers
communications
phaseshiftkeying
0
votes
0
answers
27
GATE ECE 2014 Set 3  Question: 19
A modulated signal is $y(t)= m(t)\cos(40000\pi t)$, where the baseband signal $m(t)$ has frequency components less than $5$ KHz only. The minimum required rate (in KHz) at which $y(t)$ should be sampled to recover $m(t)$ is _______.
asked
Mar 26, 2018
in
Communications
by
Milicevic3306
(
15.8k
points)

26
views
gate2014ec3
numericalanswers
digitalcommunications
communications
0
votes
0
answers
28
GATE ECE 2014 Set 3  Question: 23
Consider an $FM$ signal $f(t)= \cos\left [ 2\pi f_{c} t+\beta _{1}\sin2\pi f_{1}t+\beta _{2}\sin2\pi f_{2}t\right ].$ The maximum deviation of the instantaneous frequency from the carrier frequency $f_{c}$ is $\beta _{1}f_{1}+\beta _{2}f_{2}$ $\beta _{1}f_{2}+\beta _{2}f_{1}$ $\beta _{1}+\beta _{2}$ $f _{1}+f _{2}$
asked
Mar 26, 2018
in
Communications
by
Milicevic3306
(
15.8k
points)

42
views
gate2014ec3
digitalcommunications
frequencymodulation
communications
0
votes
0
answers
29
GATE ECE 2014 Set 3  Question: 49
Let $X(t)$ be a wide sense stationary $(WSS)$ random process with power spectral density $S_{X}(f).$ If $Y(t)$ is the process defined as $Y(t)= X(2t1)$, the power spectral density $S_{Y}( f )$ ... $S_{Y}( f )= \frac{1}{2}S_{X}\left ( \frac{f}{2} \right )e^{j2\pi f }$
asked
Mar 26, 2018
in
Communications
by
Milicevic3306
(
15.8k
points)

31
views
gate2014ec3
communications
autocorrelationandpowerspectraldensity
0
votes
0
answers
30
GATE ECE 2014 Set 3  Question: 50
A real bandlimited random process $X(t)$ ... pass filter of unity gain with centre frequency of $8$ $kHz$ and bandwidth of $2$ kHz. The output power (in Watts) is ___________.
asked
Mar 26, 2018
in
Communications
by
Milicevic3306
(
15.8k
points)

39
views
gate2014ec3
numericalanswers
autocorrelationandpowerspectraldensity
communications
0
votes
0
answers
31
GATE ECE 2014 Set 3  Question: 51
In a $PCM$ system, the signal $m(t)=\left \{\sin(100\pi t)+\cos(100\pi t) \right \}V$ is sampled at the Nyquist rate. The samples are processed by a uniform quantizer with step size $0.75$ $V$. The minimum data rate of the $PCM$ system in bits per second is ______.
asked
Mar 26, 2018
in
Communications
by
Milicevic3306
(
15.8k
points)

41
views
gate2014ec3
numericalanswers
digitalcommunications
pulsecodemodulationsystems
communications
0
votes
0
answers
32
GATE ECE 2014 Set 2  Question: 23
Consider sinusoidal modulation in an AM system. Assuming no overmodulation, the modulation index ($\mu$) when the maximum and minimum values of the envelope, respectively, are $3$ V and $1$ V, is ___________.
asked
Mar 26, 2018
in
Communications
by
Milicevic3306
(
15.8k
points)

49
views
gate2014ec2
numericalanswers
communications
amplitudemodulation
0
votes
0
answers
33
GATE ECE 2014 Set 2  Question: 40
In the circuit shown, choose the correct timing diagram of the output (y) from the given waveforms $W1$, $W2$, $W3$ and $W4$. $W1$ $W2$ $W3$ $W4$
asked
Mar 26, 2018
in
Communications
by
Milicevic3306
(
15.8k
points)

48
views
gate2014ec2
communications
timingdiagram
0
votes
0
answers
34
GATE ECE 2014 Set 2  Question: 44
The inputoutput relationship of a causal stable LTI system is given as $y[n] = \alpha \: y[n1] + \beta \: x[n]$. If the impulse response $h[n]$ of this system satisfies the condition $\sum_{n=0}^{\infty}h[n]= 2$, the relationship between $\alpha$ and $\beta$ is $\alpha = 1\beta /2$ $\alpha = 1+\beta /2$ $\alpha = 2\beta$ $\alpha = 2\beta$
asked
Mar 26, 2018
in
Communications
by
Milicevic3306
(
15.8k
points)

24
views
gate2014ec2
communications
lineartimeinvariantsystems
0
votes
0
answers
35
GATE ECE 2014 Set 2  Question: 50
Coherent orthogonal binary FSK modulation is used to transmit two equiprobable symbol waveforms $s_{1}( t )= \alpha \cos 2\pi f_1 t$, and $s_2(t) = \alpha \cos 2 \pi f_2 t$ where $\alpha = 4$ ... error probability for a data rate of $500$ kbps is $Q(2)$ $Q(2\sqrt{2})$ $Q(4)$ $Q(4\sqrt{2})$
asked
Mar 26, 2018
in
Communications
by
Milicevic3306
(
15.8k
points)

41
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gate2014ec2
communications
frequencyshiftkeying
0
votes
0
answers
36
GATE ECE 2014 Set 2  Question: 51
The power spectral density of a real stationary random process $X(t)$ is given by $ S_X (f) = \begin{cases} \frac{1}{W}, & \mid f \mid \leq W \\ 0, & \mid f \mid > W \end{cases}$ The value of the expectation $E \left [ \pi X(t)X\left ( t\frac{1}{4W} \right ) \right ]$ is __________.
asked
Mar 26, 2018
in
Communications
by
Milicevic3306
(
15.8k
points)

30
views
gate2014ec2
numericalanswers
communications
autocorrelationandpowerspectraldensity
0
votes
0
answers
37
GATE ECE 2014 Set 1  Question: 22
In a codedivision multiple access $(\text{CDMA})$ system with $N = 8$ chips, the maximum number of users who can be assigned mutually orthogonal signature sequences is ________.
asked
Mar 26, 2018
in
Communications
by
Milicevic3306
(
15.8k
points)

35
views
gate2014ec1
numericalanswers
codedivisionmultipleaccess
communications
0
votes
0
answers
38
GATE ECE 2014 Set 1  Question: 51
Let $Q(\sqrt{\gamma})$ be the BER of a BPSK system over an AWGN channel with twosided noise power spectral density $N_{0}/2.$ The parameter $\gamma$ is a function of bit energy and noise power spectral density. A system with two independent and identical ... both the channels. If the BER of this system is $Q( b \sqrt{\gamma})$ then the value of $b$ is _____.
asked
Mar 26, 2018
in
Communications
by
Milicevic3306
(
15.8k
points)

32
views
gate2014ec1
numericalanswers
communications
digitalmodulation
basicelectricalrhythm
0
votes
0
answers
39
GATE ECE 2014 Set 1  Question: 52
A fair coin is tossed repeatedly until a ‘Head’ appears for the first time. Let $L$ be the number of tosses to get this first ‘Head’. The entropy $H(L)$ in bits is _____.
asked
Mar 26, 2018
in
Communications
by
Milicevic3306
(
15.8k
points)

24
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gate2014ec1
numericalanswers
entropy
communications
0
votes
0
answers
40
GATE ECE 2013  Question: 49
Bits $1$ and $0$ are transmitted with equal probability. At the receiver, the pdf of the respective received signals for both bits are as shown below. The optimum threshold to achieve minimum bit error rate $(BER)$ is $\frac{1}{2} \\$ $\frac{4}{5} \\$ $1\\$ $\frac{3}{2} $
asked
Mar 26, 2018
in
Communications
by
Milicevic3306
(
15.8k
points)

49
views
gate2013ec
communications
digitalmodulation
basicelectricalrhythm
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