# Power of a Discrete time signal

I was learning on power of signal and i went through different formula in internet .

I get different results when i go through internet .

But in other site average power is written as

I dont know if both are different formula for different condition .

The power of a discrete-time signal $x[n]$ is given by

$$P_x=\lim_{N\rightarrow\infty}\frac{1}{2N+1}\sum_{n=-N}^{N}|x[n]|^2$$

which is identical to the first formula in your question. The second formula is wrong and does not even make any sense due to the infinite limits of the sum.

I'd advise you to use text books or high-quality internet resources such as MIT OpenCourseWare.

Both formulas are the same .. It's just that one of them is divide by 2N (number of points from -N till N excluding 0) and the other by 2N+1 (number of points from -N till N including 0). But that doesn't matter when N goes to infinity given that x[0] is bounded.

• And what about the limits $\pm\infty$ in the second formula? – Matt L. Jun 18 '18 at 6:51

I believe the second expression for power is not strictly professional, though I know it is trying to do the same as the first one. Please stick to the first version which should appear in any good textbooks.

• Not sure what you mean by an expression being "professional". It can either be correct or wrong, and the second formula is simply wrong. – Matt L. Jun 18 '18 at 9:23
• @MattL. You are right. It is a wrong one. – ZHUANG Jun 19 '18 at 9:35