ECE · all questions

Digital Communication
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Q61

In binary frequency shift keying (FSK), the given signal waveforms are
u₀(t) = 5cos(20000πt); 0 ≤ t ≤ 7 and u₁(t) = 5cos(22000πt); 0 ≤ t ≤ T,
where T is the bit-duration interval and t is in seconds. Both u₀(t) and u₁(t) are zero outside the interval 0 ≤ t ≤ T. With a matched filter (correlator) based receiver, the smallest positive value of T (in milliseconds) required to have u₀(t) and u₁(t) uncorrelated is

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Q62

BPSK stands for

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Q63

Companding is used in PCM to

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Q64

For atmost distortionless reception of signal in pulse modulation it is required that the speed should be:

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Q65

Which of the following statements about the matched filter in a communication receiver are correct?
1. Its impulse response depends on the signal shape
2. It maximizes the SNR at the detection instant
3. It produces ISI
4. It may produce phase error if synchronization is improper
Select the correct answer from the options given below:

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Q66

Which one of the following statements is not correct regarding the features of CDMA?

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Q67

A 1.0 kHz signal is flat top sampled at the rate of 1800 samples/sec and the samples are applied to an ideal rectangular LPF with cut-off frequency of 1100 Hz, then the output of the filter contains

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Q68

The outputs of 18 numbers of 20 Hz low pass filters are sampled, multiplexed and A/D converted. If the sampling is at the Nyquist rate of 40 samples/s, corresponding to signal of 20 Hz band-width and if we use 3 bits/sample to represent each voltage sample, the bit rate is

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Q69

The modulation techniques used to convert analog signal into digital signal are

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Q70

During transmission over a communication channel, bit errors occur independently with probability p. If a block of n bits is transmitted, the probability of at most one bit error is equal to

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Q71

Consider a binary digital communication system with equally likely 0's and 1's. When binary 0 is transmitted the detector input can lie between the levels -0.25 V and +0.25 V with equal probability: when binary 1 is transmitted, the voltage at the detector can have any value between 0 and 1 V with equal probability. If the detector has a threshold of 0.2 V (i.e., if the received signal is greater than 0.2 V, the bit is taken as 1), the average bit error bit error probability is

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Q72

Which of the following is worst affected by Noise?

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Q73

Which type of encoding is used in USB?

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Q74

Which of the following pulse modulation are digital?
1. PCM
2. Differential PCM
3. PWM
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Q75

The Nyquist sampling rate for the signal

s (t) = \frac{sin ( 500 π t )}{π t} \times \frac{sin ( 700 π t )}{π t}

is given by

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Q76

The granular noise can be reduced by

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Q77

Match List-I with List-II and select the correct answer as per the options:

List-I	List-II
a. RF band is divided into small frequency bands	1. TDMA
b. Store and forward system	2. FDMA
c. Spread spectrum multiple access	3. Navigation technique
d. Dead reckoning	4. CDMA

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Q78

In a band limited channel higher bit rate can be transmitted with

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Q79

A message signal with its amplitude uniformly distributed between -2 V and +2 V is transmitted by a 8-bit binary PCM system. The (SNR)_q would be

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Q80

The bit error probability for GMSK is given by

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