How to implement log linear fractional function in CVX?

How can I implement the following in cvx: f(x)=log(1+a.*x./(b+c.*x)) subject to: sum(x)=N, x>=0. Where x is an optimization variable while a, b, c, are known positive constants vector.

And I can prove that f(x) is a concave function when x>=0, a, b, c are positive.

Thank you!

It cannot be done, unfortunately. A similar question was asked here), and there you can find some more detailed discussion.