What is noise?
The noise is the unwanted signals that tend to disturb the operation of a system and over which we have incomplete control.
Two broadly used categories of noise are given below –
External noises: The noise whose sources are external to the communication system is known as external noise. Example- atmospheric noises, extraterrestrial noises, man-made noises etc.
Internal noises: The noise which get generated within the communication system is known as internal noise. Example- shot noise, thermal noise, transit-time noise, miscellaneous internal noises etc.
What is Signal?
A signal is formally defined as a function of one or more variables that conveys information on the nature of a physical phenomenon.
Several types of signal’s are given below-
Continuous-time signal: A signal that is specified for every value of time is a continuous time signal. Example- telephone and video camera output.
Discrete-time signal: A signal that is specified for only discrete values of time, is a discrete-time signal. Example- monthly sales of a corporation.
Analog signal: A signal whose amplitude can take on any value in a continuous range is an analog signal.
Digital signal: A signal whose amplitude can take on only a finite number of values is known as digital signal.
Periodic signal and aperiodic signal:- A signal g(t) is said to be periodic if for some positive constant T0 ,
g(t) = g(t + T0 )
The smallest value of T0 is the period of g(t). A signal is aperiodic if it is not periodic.
Deterministic signal:- A signal whose physical description is known in either a mathematical form or a graphical form is a deterministic signal.
Random signal:-A signal which is known in terms of probabilistic description such as mean value, mean squared value and so on rather than its complete mathematical or graphical description is a random signal.
Energy signal:- A signal with finite energy is an energy signal. In other words, a signal g(t) is an energy signal if
Power signal:- A signal with finite power is a power signal. In other words, a signal g(t) is a power signal if
Causal signal:- A signal that does not start before t=0 is called a causal signal.
g(t) = 0 ; where t less than zero
