In the preceding chapter we have considered the fundamental properties of an optical signal carrying definite information. Such an optical signal has been regarded as specified completely in space and time. In real systems the transmission and reception of information occurs against a background of random interference which causes the actual signal to deviate from the intended form. The signal which appears at the receiving end cannot be regarded as a determinate optical signal. In general, it must be regarded as a random signal, and only in some special cases is it a superposition of determinate and random signals.
KeywordsEnergy Spectrum Random Process Autocorrelation Function Average Power Random Noise
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