A cognitive radio (CR) network should have the ability to detect the presence of incumbent users and adjust its transmission in order to utilize unused licensed spectrum without causing interference to incumbent users. To effectively protect incumbent users, properly modeling expected interference from the CR system is therefore important.We model the accumulative interference generated from a cellular CR network and formulate interference constraints of digital television (DTV) system, e.g. coverage area loss, as a function of feasible network planning parameters, e.g. minimum isolation distance and maximum transmitted power. Then interference constraints of the DTV system can be translated to feasible network planning parameters. Furthermore, we investigate how network parameters affect sensing requirements of the CR system to meet DTV interference constraints.