tokens: We formulate the joint sub - channel allocation and structure optimization as a sum rate maximization of SUs in OFDM based heterogeneous CR networks by using RF energy harvesting , where interference limits are imposed to protect the PUs , rate requirements for both real - time and non - real - time SUs are considered to guarantee fairness for SUs in each CR network , and cooperative spectrum sensing is employed to provide more reliable results of channel sensing while considering imperfect spectrum sensing .