Signals and Noise in Communication Systems

1. Signals and Spectra 1

2. Properties of Signals and Noise • In communication systems, the received waveform is usually categorized into the desired part containing the information and the extraneous or undesired part. • The desired part is called the signal, and • the undesired part is called noise.

3. Physically Realizable Waveforms • The waveform has significant nonzero values over a composite time interval that is finite. • There is no known waveform that has existed forever. • The spectrum of the waveform has significant values over a composite frequency interval that is finite. • All practical systems have limited bandwidth which would no allow for infinite bandwidth.

4. Physically Realizable Waveforms • The waveform is a continuous function of time. • A discontinuity in the function would require infinite bandwidth. • The waveform has finite peak values. • Any physical device would be destroyed before producing an infinite peak value. • The waveform is a Real function. • Only real waveforms have been observed in the real world.

5. Physically Realizable Waveforms

37. Gibbs phenomenonhttp://en.wikipedia.org/wiki/File:Gibbs_phenomenon_10.svg

38. Gibbs phenomenonhttp://upload.wikimedia.org/wikipedia/commons/d/dc/Gibbs_phenomenon_250.svg