Digital Communication - Study Mode

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[#26] The received signal level for a particular digital system is -151 dBW and the effective noise temperature of the receiver system is 1500 K. The value of $$frac{{{{ ext{E}}_{ ext{b}}}}}{{{{ ext{N}}_0}}}$$xa0required for a link transmitting 2400 bps is:

(A) -12 dB

(B) -1.2 dB

(C) +1.2 dB

(D) +12 dB

Correct Answer

(D) +12 dB

[#27] PAM signals are constructed by using a low pass filter of pass band slightly greater than base band to avoid aliasing. This avoids distortion

(A) True for flat top pulses

(B) True if low pass filter has sharp cut-off

(C) Flat top-pulses introduce envelope delay

(D) Flat top pulses introduce amplitude distortional and delay

Correct Answer

(D) Flat top pulses introduce amplitude distortional and delay

[#28] The raised cosine pulse p(t) is used for zero ISI in digital communications. The expression for p(t) with unity roll-off factor is given by $$pleft( t
ight) = frac{{sin 4pi Wt}}{{4pi Wtleft( {1 - 16{W^2}{t^2}}
ight)}}.$$ xa0 xa0 xa0The value of p(t) at $$t = frac{1}{{4W}}$$ xa0is

(A) -0.5

(B) 0

(C) 0.5

(D) $$infty $$

Correct Answer

(C) 0.5

[#29] A binary symmetric channel (BSC) has a transition probability of $$frac{1}{8}.$$xa0 If the binary transmit symbol X is such that $$Pleft( {X = 0}
ight) = frac{9}{{10}},$$ xa0xa0 then the probability of error for an optimum receiver will be

(A) $$frac{7}{{80}}$$

(B) $$frac{{63}}{{80}}$$

(C) $$frac{9}{{10}}$$

(D) $$frac{1}{{10}}$$

Correct Answer

(A) $$frac{7}{{80}}$$

[#30] Choose the correct one from among the alternatives a, b, c, dafter matching an item from Group 1 with the most appropriate item in Group 2 . Group 1 Group 2 1. FM P. Slope overload 2. DM Q. H-law 3. PSK R. Envelope detector 4. PCM S. Capture effect T. Hilbert transform U. Matched filter

(A) 1-T, 2-P, 3-U, 4-S

(B) 1-S, 2-U, 3-P, 4-T

(C) 1-S, 2-P, 3-U, 4-Q

(D) 1-U, 2-R, 3-S, 4-Q

Correct Answer

(C) 1-S, 2-P, 3-U, 4-Q