In this paper coexistence and spectrum sharing between radar and communication systems are considered. In particular, the problem of target parameter estimation in a cooperative scenario is addressed. A time delay estimation method for multicarrier radar stemming from ML approach is proposed. The radar exploits the communication signal in a passive manner. It is demonstrated that the estimation performance improves when the radar and the communication systems cooperate. The performance of the proposed method is studied analytically by establishing the Cramer-Rao Bound (CRB) for the cooperative scenario as well as in simulations. Both the analytical results and simulations demonstrate that the CRB and RMS error are lower for the cooperative case than for the radar only case.