  We present a mixed analog-digital spectrum sensing method that is especially
suited to the typical wideband setting of cognitive radio (CR). The advantages
of our system with respect to current architectures are threefold. First, our
analog front-end is fixed and does not involve scanning hardware. Second, both
the analog-to-digital conversion (ADC) and the digital signal processing (DSP)
rates are substantially below Nyquist. Finally, the sensing resources are
shared with the reception path of the CR, so that the lowrate streaming samples
can be used for communication purposes of the device, besides the sensing
functionality they provide. Combining these advantages leads to a real time map
of the spectrum with minimal use of mobile resources. Our approach is based on
the modulated wideband converter (MWC) system, which samples sparse wideband
inputs at sub-Nyquist rates. We report on results of hardware experiments,
conducted on an MWC prototype circuit, which affirm fast and accurate spectrum
sensing in parallel to CR communication.
