Improving harmonic rejection for spectrum sensing using crosscorrelation

Harmonic downmixing may cause a spectrum sensing device to erroneously flag parts of the spectrum as occupied. Receivers employing harmonic rejection (HR) rarely obtain more than 60 dB of HR, which may not be enough for spectrum sensing for dynamic spectrum access. We improve HR by employing two RF-receivers, integrated in a single 65nm CMOS IC, and using a small offset in their LO-frequencies. The offset is corrected in the digital baseband, after which the final receiver outputs are crosscorrelated. Our measurements show that the HR can be significantly improved without calibration or time penalty, even for high initial HR, but that the improvement is limited by crosstalk between the receivers.