exponential trigonometric integration related to Rayleigh modeling: wireless channels

[mtcyp004]

I am trying to solve the following problem that arises in correlated Rayleigh modeling of wireless channels. Any help is appreciated!!

\(\displaystyle \large{ \displaystyle \int_0^{2\pi}\, \int_0^{2\pi}\, \int_0^{2\pi}\, e^{\,a\, \cos\left(\phi_1\, - \phi_2\right)\, +\, b\, \cos\left(\phi_1\, -\, \phi_3\right)\, +\, c\, \cos\left(\phi_2\, -\, \phi_3\right)}\, d\phi_1\, d\phi_2\, d\phi_3 }\)

http://math.stackexchange.com/quest...phi-1-phi-2b-cos-phi-1-phi-3c-cos-phi-2-phi-3

Thanks..