2.8 SUMMARY
We have considered time domain and frequency domain models for signals and systems. Since signal location in the frequency domain and signal bandwidth are important parameters of communication systems, frequency domain models were emphasized. The type of model used to represent a signal in the frequency domain depends on whether the signal is a periodic power signal, an aperiodic energy signal, or an aperiodic power signal. Regardless of the model used, a signal can be described in the frequency domain in terms of its spectral content. A summary of the important aspects of various signal models is given in table 2.1