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Electronics Engineering Objective Questions { Digital Communication System }

246. I x I << 1, coth (x) can be a proximated as
A. x
B.b) x11
C. ?x 12
D. x10
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247. inn is sin(0 / 2) q-4.0 0
D. not defined
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248. If R(T) is the autocorrelation function of a real, wide-sense stationary random process, then which of the following is NOT true? x(t) ? 5 (sin 2n 1000t )3 + 7 ( nt sin In 1000t )3 nt would be (a) 2 x 103 (c) 6 x 103 A(t) Same Y2(t)
A. R(T) = R(-T) YU) m(t)y(t)
B. I R(T) I5 11(0) 2__.
C. R(T) = - R(-T) -130 +B f
D. The mean square value of the process is R(0)
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249. The 3-dB bandwidth of the low-pass signal e-t u(t), where u(t) is unit step function, is given by
A. ?2n Hz
B. ?2n 1/2--1z
C. co
D. 1 Hz
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250. The raised cosine pulse p(t) is used for zero ISI in digital communications. The expression for p(t) with unit roll-off factor is given by sin4nWt p(t) =47rWt(1 - 16W 2 t 2 ) (biBt) Y(f) 0 +B +2B
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251. In the following scheme, if the spectrum M(f) of m(t) is as shown, then the spectrum Y(/) of y(t) will be-aL The ratio of the average energy of Constellation 1 to the average energy of Constellation 2 is
A. 4a2
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252. If these constellations are used for digital communications over an AWGN channel, then which of the following statements is true?
A. Probability of symbol error for Constellation 1 is lower
B. Probability of symbol error for Constellation 1 is higher
C. Probability of symbol error is equal for both the constellations
D. The value of No will determine which of the two constellations has a lower probability of symbol error
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