Digital Communications

1Signal Analysis

In the course of history, human beings communicated with each other using their ears and eyes, by transmitting their messages via voice, sound, light, smoke, signs, paintings, and so on.[1] The invention of writing made written communications also possible. Telecommunications refers to the transmission of messages in the form of voice, image or data by using electrical signals and/or electromagnetic waves. As these messages modulate the amplitude, the phase or the frequency of a sinusoidal carrier, electrical signals are characterized both in time and frequency domains. The behavior of these signals in time and frequency domains are closely related to each other. Therefore, the design of telecommunication systems takes into account both the time‐ and the frequency‐characteristics of the signals.

In the time‐domain, modulating the amplitude, the phase and/or the frequency at high rates may become challenging because of the limitations in the switching capability of electronic circuits, clocks, synchronization and receiver performance. On the other hand, the frequency‐domain behavior of signals is of critical importance from the viewpoint of the bandwidth they occupy and the interference they cause to signals in the adjacent frequency channels. Frequency‐domain analysis provides valuable insight for the system design and efficient usage of the available frequency spectrum, which is a scarce and valuable resource. Distribution of the energy or the power of a transmitted ...