# Sum of signal and its probability density

1. ### Chriszz

11
Dear,

I assume that a signal S is expressed as S = a*S1 + b*S2,
where a, b are weight constant, and S1, S2 are the different signals.

In addition, S1, S2 have similar distribution such as Gaussian or Laplacian distribution,
and theirs pdf is p_S1 and p_S2.

In the above assumption, what is the pdf of signal S ?
How can I derive or reference of this pdf p_S ???

Thanks.

2. ### jbunniii

3,377
In general, the answer depends upon the joint distribution of ##S_1## and ##S_2##. If they are statistically independent, then the answer is much simpler: the pdf of ##S## is the convolution of the pdfs of ##aS_1## and ##bS_2##. For a proof, see here for example: http://math.la.asu.edu/~jtaylor/teaching/Fall2010/STP421/lectures/lecture20.pdf

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