Trigonometric functions are neither convex nor concave,. They can only be “convexified” by means of an approximation, such as a suitable Taylor series. The one term Taylor series approximation for sin(x) is x, and the two term Taylor series approximation is x - x^3/6, which is neither convex nor concave. A higher order Taylor series approximation for sin(x) will be neither convex nor concave.
Edit: Now I see you have an absolute value around the sin term. Only the one term Taylor series approximation could be used.
I recommend you use a non-convex nonlinear solver, which you can not do via CVX. You can consider using YALMIP. Why isn't CVX accepting my model? READ THIS FIRST!