Dilkap research institute of Engineering & Management studies DCOM Sem5 Sample MCQs

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Program: BE Electronics & Telecommunication Engineering
Curriculum Scheme: CBCS Revised 2016
Examination: Third Year Semester V
Subject Code: ECC502 and Subject Name: Digital Communication

Which of the statement is true

P(A/B) = (P(AB))/(P(B))

P(A/B) = (P(A))/(P(AB))

P(A/B) = (P(A))/(P(B))

P(A/B) = (P(AB))/(P(A))

Clear selection

Complementary error function is written as erfc(u) is defined as

2/√π ∫_u^∞▒e^(〖-x〗^2 ) dx

1/√π ∫_u^∞▒e^(〖-x〗^2 ) dx

2/√π ∫_(-∞)^u▒e^(〖-x〗^2 ) dx

1/√π ∫_0^u▒e^(〖-x〗^2 ) dx

Clear selection

Covariance µ of two random variables X and Y is defined as

E{(XY - m_x m_y)}

E{(X + m_x)(Y + m_y)}

E{(X - m_x)(Y - m_y)}

E{(XY + m_x m_y)}

Clear selection

Let X and Y are two random variables with means of both ‘0’ , variance σx and σy respectively and if X and Y are statistically independent then the variance of the random variable Z = X+Y is given by

σ_x^2 + σ_y^2

σx + σy

σ_x^2 - σ_y^2

σx / σy

Clear selection

The probability density function of a uniformly distributed random variable is given by f(x) = 1/(a+b)between ‘–a’ and ‘b’, and 0 elsewhere. Also ‘b’>’-a’. Then the mean of this random variable is ________.

1/(b-a)

b – a

(b-a)/2

(b+a)/2

Clear selection

If a band limited analog signal(0-4KHz) is sampled at Nyquist rate and each sample is encoded with 8 bit binary word. What is the data rate at the A/D converter output

64 Kb/s

32 Kb/s

16 Kb/s

252 Kb/s

Clear selection

The entropy of binary source with equal probability is given by in bits/symbol

Infinity

Clear selection

Which of the statement is wrong

H(X) = ∑_(k=0)^(K-1)▒〖p_k 〖log〗_2 (1/p_k )〗 ; H(X) is the average self information of K symbols and p_k is the probability of each symbol.

0 ≤ H(X) ≤ 〖log〗_2 K ; where K is the possible outcomes

I(x_1) ≥ 0 ; where I(x_1) is the self information of the event X = x_1

I(x_1,x_2) < I(x_1) + I(x_2) ; where x_1&x_2 are the symbols of a discrete memory less source

Clear selection

Let X be the ensemble of letters from a DMS with finite entropy H(X). Blocks of J symbols from the source are encoded into code words of length N from a binary alphabet. For any ‘ℇ’ >0 , the probability of error ‘P_e’ of a block coding failure can be made arbitrarily small if

N/J≤H(X)+ ℇ

N/J=H(X)+ ℇ

N/J≥H(X)+ ℇ

N/J≤H(X)- ℇ

Clear selection

In a systematic (6,4) block code with generator matrix G = [■(1 0 0 0 1 0 1@0 1 0 0 1 1 1@0 0 1 0 1 1 0@0 0 0 1 0 1 1)] . The code word for x_m = [■(1 0 1 0]) will be

[1 0 1 0 1 0 1]

[1 0 1 0 0 1 1]

[1 0 0 1 0 1 1]

[1 0 1 0 1 0 0]

Clear selection

In repetition code , how many conformation bits are present in addition to (n-1) parity bits

One

Two

Three

Four

Clear selection

For any integer ‘m’ ,The Binary Hamming code(n,k) will satisfy the relationship

(2^m, 2^m-m )

(2^(m-1), 2^(m-1)-m )

(2^(m-) 1, 2^m-m-1 )

(2^(m-1), 2^(m-2) )

Clear selection

In a linear code, the minimum Hamming distance between any two code words is _________ minimum weight of any non zero code word.

Less than

Greater than

Equal to

Greater than or equal to

Clear selection

The minimum distance of a linear block code(d_min) is equal to the minimum number of columns of H whose binary ________ is equal to zero vector.

Addition

Difference

Product

Division

Clear selection

For a (7,4) cyclic code if the generator polynomial is given by g(p) = p^3+p^2+1, the parity polynomial is

p^5+p^2+1

p^3+p^2+1

p^4+p^3+p^2+1

p^3+p+1

Clear selection

The probability of error of DPSK is _________ that of BPSK.

Less than

Higher than

Same as

Not predictable as

Clear selection

ASK modulated signal has the band width

Same as the bandwidth of the base band signal

Half the bandwidth of the base band signal

Double the bandwidth of the base band signal

1.5 times the bandwidth of base band signal

Clear selection

Overhead bits are

Framing and synchronizing bits

Data due to noise

Encoding bits

Data bits

Clear selection

In a BPSK if the band width requirement is ‘f_b’ then QPSK require a bandwidth of _________

f_b

f_b/2

2f_b

4f_b

Clear selection

ISI may be removed by using

Differential coding

Manchester coding

Polar NRZ

Polar RZ

Clear selection

The transmission bandwidth of the raised cosine spectrum is given by

2w(1+2α)

3w(1+α)

(1+α)w

2w(2+α)

Clear selection

Which type is used and preferred in digital logic circuits

NRZ-M

NRZ-S

NRZ-L

Clear selection

The signal to noise ratio SNR of a matched filter is given by

2E/N_o

2E/(2N_o )

E/N_o

2E/(N_o^2 )

Clear selection

When the noise is white Gaussian noise the optimum filter is known as

Low pan filter

Bare band filter

Matched filter

Bessel filter

Clear selection

Which are called as hard decision

Estimates of message symbol with error correcting codes

Estimates of message symbol without error correcting codes

Airrevocable decision is made about each individual message bit at the receiver

Estimation of message symbols at transmitting end

Clear selection

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