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iSens: Detecting hidden busy channels in WM systems with interactive sensing for CRN

Cognitive radio (CR) implements dynamic spectrum access (DSA) mainly through performing spectrum sensing. In some circumstances, spectrum sensing is regarded as not sufficient for CR systems without generating unacceptable impact on primary users. For example, for wireless microphone (WM) systems when the transmitters either are turned off or stay idle while receivers are actively listening, CR systems decide to transmit message over the idle channel after spectrum sensing. At this moment, active WM receivers still can detect narrow-band BPSK/QPSK signals transmitted by customer premise equipments (CPEs) leading to unexpected audio signals. In this paper, we first address and study such a hidden busy channel (HBC) situation. The degree of audio interferences generated by narrow-band BPSK/QPSK signals on HBCs is evaluated through field testing. To detect HBCs, we propose a novel technique named iSens. Experiments show that detection the rate of iSens is higher than 90% while the false alarm rate is lower than 10%.