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This mock test of Digital Communications - MCQ Test 1 for Electronics and Communication Engineering (ECE) helps you for every Electronics and Communication Engineering (ECE) entrance exam.
This contains 15 Multiple Choice Questions for Electronics and Communication Engineering (ECE) Digital Communications - MCQ Test 1 (mcq) to study with solutions a complete question bank.
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QUESTION: 1

**has P.S.D. S _{xx} f then y has P.S.D**

Solution:

QUESTION: 2

**Consider Y= ax+b, a>0. If the density and distribution functions of x are F. (x) and f**_{x}** (x), then F**_{y} (y) is equal to

Solution:

QUESTION: 3

**Consider a random process x(t). Which of the following can represent R**_{x}**. (r)?**

Solution:

*Answer can only contain numeric values

QUESTION: 4

**It is required to transmit at 100 Kbit/s and a bandwidth of 2 MHz is used. The**

**minimum S/N ratio is ___________________ **

Solution:

⇒

*Answer can only contain numeric values

QUESTION: 5

**SNR when the system is uncoded is 4 dB, when it is coded is 2 dB then the coding gain is ________________ (dB)**

Solution:

Coding gain = SNR _{encoded }- SNR. _{coded }= 4.dB-2dB = 2dB

QUESTION: 6

**In the set up shown below, determine the number of bits required to encode each sample of x (t) such that bandwidth of signal y(t) is greater than 5 MHz.**

Solution:

Nyquist sampler is a sampler that samples a given signal at a rate twice the highest frequencies

f_{s} = 2 f_{m}, f_{5} = 2 x 350 kHz = 0.7MHz

Band width of output of PCM =

QUESTION: 7

A sinusoidal signal whose peak-peak amplitude is 6 V is modulated using deltamodulator. At what rate should be sinusoidal signal sampled such that slope over load distortion is prevented with step size of 0.942 V?

Solution:

2A = 6V ⇒ A = 3V

In order to overcome slope over load distortion in delta modulator

QUESTION: 8

The probability of the five possible outcomes of an experiment are given as

Determine the informationrate, if there are 8 outcomes per second.

Solution:

= 1.875 bits / sec; r=8 outcomes/sec

Information rate R=r.

=15bits / sec

QUESTION: 9

Probability of picking 3 symbols are **P _{0}, **P

Solution:

P_{O} =P_{1} =P_{2} =P; P_{O} + P_{1} + P_{2} ^{= 1;}^{ }3P=1^{ ⇒} P= 1/3

QUESTION: 10

Hartley's law can be defined as r = 2 Blog_{2} M . When compared to Shannon Hartley theorem, C, M are

Solution:

Comparing C=B log ; r = C;

QUESTION: 11

The probability of a bit decoded correctly at receiver is `p'. If n bits are sent, what is the probability that one bit is decoded correctly?

Solution:

correct : p; error: 1-p

out of n bits, only one bit is decoded correctly=

QUESTION: 12

A stationary random process x(t) has the following correlation function is constant) . Find the psd of random signal x(t).

Solution:

PSD of input is expressed as

QUESTION: 13

If random variable 'x' has Gaussian pdf with mean M, then y=2x has PDF andmean respectively

Solution:

so y has pdf N(2m,40^{2}) which is Gaussian

QUESTION: 14

If x has P.S.D S_{xx} (f), then y has P.S.D of ( Assume H(f) is the Fourier Transform

Solution:

QUESTION: 15

** **A Gaussian random variable 'x' has mean 1 and variance√2. If y = x^{2}, then the mean of y is

Solution:

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