Abstract

Linear system is a physical device that produce an output signal y(t) in response to an input signal x(t), such as filters or communication channels operating in their linear region. The filter is a frequency selective device that is used to limit the spectrum of a signal to some band of frequencies while the communication channel is a transmission medium that connects the transmitter to the receiver through a certain band of frequencies. The linear system refers to superposition principle, where the response of a linear system to a number of different inputs applied simultaneously, equals the sum of the responses of the system when each input is applied individually. While, time invariant system refers to the principle of, if the input signal is delayed by certain delay, the output signal will be delayed by the same amount of delay.