I am trying to obtain PDF of $\gamma$ but not getting it correctly.
$\gamma = |\sum_{r=1}^R\mu_r|^2$----(1)
where R is some number and $\mu_r$ is a independent and identically distributed random variable with PDF given by
$f_{|\mu_r|}(x) = \sum_{k=0}^\infty\frac{x^{2k+1}}{\sigma^{2k+1}_1}W_{-k-0.5,0}(2\delta)\times\frac{2}{\sqrt{\alpha^2\sigma^2_2\sigma^2_3}}e^{\delta-\frac{x^2}{\sigma^2_1}}$
where $W_{a,b}(\cdot)$ is Whittaker function and all other elements are constants.
My query is how to obtain PDF of $\gamma$.
Any help in this regard will be highly appreciated.