Spectrum Sensing: Analog (or Partially Analog) CMOS Real-Time Spectrum Sensing Techniques

Congestion of the radio spectrum, caused by licensed primary users and an increasing demand for new devices, has created a need for alternative methods of radio spectrum use in the future. Licensed primary users can be inactive for a specified time, leaving their allocated frequency band unoccupied so that secondary users can then use it. The U.S. Federal Communications Commission (FCC) has allowed unlicensed users to operate under specified circumstances for specific frequency bands. Secondary users cannot interfere with primary users at any time, whether by detecting the presence of primary signals and avoiding the occupied bands or by having a very small transmission power density compared to primary users. Hence, they appear as noise in primary receivers.