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ECE Objective Questions { Digital Communication System }



78. Spectral density expresses
A. Average voltage
B. Average current
C. Average power in a waveform as a function of frequency
D. None of the above

79. For a Gaussian process, auto-correlation also implies
A. statistical dependence
B. statistical independence
C. ergodic process
D. none of the above

80. The auto-correlation function of a signal (t) at to = 0 is equal to
A. zero
B. infinite
C. average voltage of the signal
D. average power of the signal

81. The auto-correlation function is
A. an odd function in to
B. an even function in to
C. an exponential function in to
D. none of the above

82. The auto-correlation function of a function x(t) is defined as 1 f?T
A. R (to) =j 0 x (t) x (t +to) dt
B. R (to) =foT x (t) x (t to) dt
C. R (to) = -TI-, 01. x (t - to) x (t + to) dt
D. R (to) = -TI TT X (t ? to) X (t + to) dt

83. The auto-co-relation function of an ergodic random process is given by IT
A. Lt x (t) (t - t) dt T--*co T 0 1 cr
B. Lt x (t) (t - ?r) dt T 0 f T
C. Lt -x (t) (t ? dt T-400 21 oI
D. Lt -x (t) (t ? dt T--Ko 2T 0

84. If n is the positive-frequency power density, the power density spectrum white noise S(co) is equal to
A. 1/1
B.02-Jan
C.ri
D.21

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