GATE ECE Digital communications PYQs & Answers — Page 3

Questions 21–26 of 26. Imported answers require independent review unless marked reviewed.

A random variable

takes values

and

with probabilities 0.2 and 0.8, respectively. It is transmitted across a channel which adds noise

, so that the random variable at the channel output is

. The noise

is independent of

, and is uniformly distributed over the interval

. The receiver makes a decision

where the threshold

is chosen so as to minimize the probability of error

. The minimum probability of error, rounded off to 1 decimal place, is ______.

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A binary source generates symbols

which are transmitted over a noisy channel. The probability of transmitting

is 0.5. Input to the threshold detector is

. The probability density function

of the noise

is shown below.

Diagram for Electronics and Communication Engineering question 17

If the detection threshold is zero, then the probability of error (correct to two decimal places) is __________.

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Which one of the following statements about differential pulse code modulation (DPCM) is true?

Your answerChoose one option.

The sum of message signal sample with its prediction is quantized

The message signal sample is directly quantized, and its prediction is not used

The difference of message signal sample and a random signal is quantized

The difference of message signal sample with its prediction is quantized

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In a digital communication system, the overall pulse shape

at the receiver before the sampler has the Fourier transform

. If the symbols are transmitted at the rate of 2000 symbols per second, for which of the following cases is the inter symbol interference zero?

Your answerChoose one option.

Diagram for Electronics and Communication Engineering question 23

Diagram for Electronics and Communication Engineering question 23 (figure 2)

Diagram for Electronics and Communication Engineering question 23 (figure 3)

Diagram for Electronics and Communication Engineering question 23 (figure 4)

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A sinusoidal message signal is converted to a PCM signal using a uniform quantizer. The required signal-to-quantization noise ratio (SQN) at the output of the quantizer is 40 dB. The minimum number of bits per sample needed to achieve the desired SQN is __________

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In binary frequency shift keying (FSK), the given signal waveforms are

, and

, where

is the bit-duration interval and

is in seconds. Both

and

are zero outside the interval

. With a matched filter (correlator) based receiver, the smallest positive value of

(in milliseconds) required to have

and

uncorrelated is

Your answerChoose one option.

0.25 ms

0.5 ms

0.75 ms

1.0 ms

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GATE ECE Digital communications PYQs

Question 47

Question 17

Question 22

Question 23

Question 23

Question 50