UC San Diego

Cognitive radio (CR) can effectively increase the spectral efficiency. However, there is an inevitable interference problem between the primary licensed users and the unlicensed CR devices. A detection technique utilizing the local oscillator (LO) leakage signal coming from a nearby mobile terminal is proposed and evaluated for short-range wireless communication systems, such as an ultra-wide band (UWB) system. Due to the low-level LO leakage, the detection sensitivity is a great concern. Local oscillator phase noise of the detector can degrade the detection sensitivity. Spectrum broadening of the LO phase noise interaction with an adjacent channel signal through a multiplier is analyzed and the degradation in detection performance is evaluated. Spectrum broadening is applied to the cognitive radio (CR) device operation in UHF bands. A strong TV signal transmitted by a nearby TV station can interact with LO phase noise of a CR receiver, and induce serious in-band interference which possible degrades the receiver performance. In order to suppress strong TV signals, a wide dynamic range low-power CMOS-based RF tunable filter with image cancellation is presented using a balanced passive complex mixer and frequency dependent loads. The tunable RF notch filter with 17 dB attenuation and 1.6 dB insertion loss is achieved using parallel LC tank loads. A tunable RF bandpass filter is implemented with capacitive termination, and achieves 18 dB maximum attenuation and 1.8 dB insertion loss