Cannot perform the operation: {convex} .* {real affine}

cvx_begin 
variables Pb Pj
expressions b e u
b = log(1+ Pb * real(Hb * Hb')/sigma)/log(2);
e =  log(Pj1 * real(Gj * Gj') + Pb1 * real(Gb * Gb')+sigma)/log(2)...
     + (real(Gj * Gj')*inv_pos(((real(Gb * Gb') * Pb+Pj * real(Gj * Gj')+sigma) * log(2))))*(Pj - Pj1)...
     + (real(Gb * Gb')*(Pb - Pb1))/((real(Gb * Gb') * Pb+Pj * real(Gj * Gj')+sigma) * log(2));
u = log(Pj * real(Gj * Gj') + sigma)/log(2);
minimize b-e+u

subject to

I encountered this error while running cvx, how can I fix it?

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.