This produced the error message
inv_pos(((real(Gb * Gb') * Pb+Pj * real(Gj * Gj')+sigma) * log(2))))*(Pj - Pj1)
That is basically a fractional linear form, which by itself is neither concave (as you want it) nor convex; and is not allowed in CVX. Have you proven the overall problem is convex? From the portion of the problem you showed, that looks rather dubious, and I will presume it is not, unless you show otherwise.