energy signal

can any body pl tell me why to calculate the energy or power of a signal.what is the need and why energy signals have zero average power and power signals have infinite energy.

Answer 1

[David Goodmanson]

Hi k.v.

For a given real signal y(n) of length N, n = 1 to N, the power at any point n is y(n)^2, the average power P is

Pave = (1/N)*sum(y.^2)

(the Matlab sum is autmatically from n = 1 to N),

and the total energy is

E = sum(y.^2)

So E = N*Pave, and for very large N then [1] if E is some nonzero (bounded) quantity then Pave is almost zero and [2] if Pave is some nonzero (bounded) quantity, E is almost infinite

[Paul]

Hi David,

I just want to point out that some (actually most in my experience, though admittedly not all) treatments of the concepts of energy and (average) power don't distinguish between finite and non-finite duration signals; there is only one definition that applies to a signal in general. Here is one link: EEE 5502 UFL. Under those definitions, the energy in a finite duration signal is finite, but the average power in a finite duration signal is zero.