Electronics and Communication Engineering
GATE ECE Digital communications PYQs
Build your understanding with focused practice from past exam papers.
How to practice Digital communications
Attempt a question, record the concept and assumptions, then check the available answer. Rework mistakes after revising the relevant concepts. Topic tags can overlap; review the question context.
Questions 1–10 of 26. Imported answers require independent review unless marked reviewed.
Question 22
Open questionECMCQ1 markNeeds review
Consider a discrete memoryless source with an alphabet of four source symbols.
is a multi-level (-1, 0, +1, +2) signal representing a long sequence of random symbols from the above source which is generating
symbols per second.Which of the following options is the correct value of equivalent Nyquist bandwidth of
?Your answerChoose one option.
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You can attempt this question now. Sign in to view the answer key, explanations and discussion.Log in to check answerQuestion 32
Open questionECNAT1 markNeeds review
A wireless digital transmission scheme is using 16-QAM over an additive white Gaussian noise channel and a maximum-likelihood receiver. Consider the information bit rate from source to be 4 × 10⁶ bits per second. The minimum transmission bandwidth (in MHz) of the modulated signal necessary for optimum recovery of information at the receiver is __. (rounded off to two decimal places)
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You can attempt this question now. Sign in to view the answer key, explanations and discussion.Log in to check answerQuestion 44
Open questionECMCQ2 marksNeeds review
A QPSK modulated signal from an additive white Gaussian noise (AWGN) channel is received with an
dB at the input of a coherent QPSK demodulator. A maximum-likelihood reception method is used in the demodulator.Assume the complementary error function
Which is the nearest bit error rate (BER) at the output of the demodulator?
Your answerChoose one option.
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You can attempt this question now. Sign in to view the answer key, explanations and discussion.Log in to check answerQuestion 63
Open questionECNAT2 marksNeeds review
The average bit error rate at the input of a (7, 4, 1) Hamming decoder is 0.10. The probability that the decoder will fail to decode a received word correctly is ___. (rounded off to two decimal places)
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You can attempt this question now. Sign in to view the answer key, explanations and discussion.Log in to check answerQuestion 33
Open questionECNAT1 markNeeds review
The generator matrix of a
binary linear block code is given below.
The minimum Hamming distance
between codewords equals _____ (answer in integer).Log in to check the answer
You can attempt this question now. Sign in to view the answer key, explanations and discussion.Log in to check answerQuestion 41
Open questionECMCQ2 marksNeeds review
A source transmits symbol
that takes values uniformly at random from the set
. The receiver obtains
, where
is a zero-mean Gaussian random variable independent of
. The receiver uses the maximum likelihood decoder to estimate the transmitted symbol
.Suppose the probability of symbol estimation error
is expressed as follows:
where
denotes the probability that
exceeds 1.What is the value of
?Your answerChoose one option.
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You can attempt this question now. Sign in to view the answer key, explanations and discussion.Log in to check answerQuestion 14
Open questionECMCQ1 markNeeds review
A digital communication system transmits through a noiseless bandlimited channel [
]. The received signal
at the output of the receiving filter is given by
where
are the symbols and
is the overall system response to a single symbol. The received signal is sampled at
. The Fourier transform of
is
. The Nyquist condition that
must satisfy for zero intersymbol interference at the receiver is ______.Your answerChoose one option.
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You can attempt this question now. Sign in to view the answer key, explanations and discussion.Log in to check answerQuestion 45
Open questionECMCQ2 marksNeeds review
A source transmits a symbol
, taken from
with equal probability, over an additive white Gaussian noise channel. The received noise symbol
is given by
, where the noise
is zero mean with variance 4 and is independent of
. Using
, the optimum symbol error probability is ______.Your answerChoose one option.
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You can attempt this question now. Sign in to view the answer key, explanations and discussion.Log in to check answerQuestion 35
Open questionECNAT1 markNeeds review
A symbol stream contains alternate QPSK and 16-QAM symbols. If symbols from this stream are transmitted at the rate of 1 mega-symbols per second, the raw (uncoded) data rate is ______ mega-bits per second (rounded off to one decimal place).
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You can attempt this question now. Sign in to view the answer key, explanations and discussion.Log in to check answerQuestion 63
Open questionECNAT2 marksNeeds review
Consider a channel over which either symbol
or symbol
is transmitted. Let the output of the channel
be the input to a maximum likelihood (ML) detector at the receiver. The conditional probability density functions for
given
and
are:
where
is the standard unit step function. The probability of symbol error for this system is ________ (rounded off to two decimal places).Log in to check the answer
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