88 CHAPTER 4 Spectrum sensing and identification Table 4.1 Sensing Requirements in the 802.22 Draft Standard Parameter Channel detection time Channel move time Detection threshold (required sensitivity) Probability of detection Probability of false alarm SNR Digital TV 2 sec 2 sec -116 dBM (over 6 MHz) 0.9 0.1 -21 db Wireless Microphone (Part 74) 2 sec 2 sec -107 dBm (over 200 KHz) 0.9 0.1 -12 dB 4.2.1 Energy Detector In many cases, the signaling scheme of the PU may be unknown to the SU; this may correspond to the case where an agile PU has considerable flexibility and