Interferer-Robust Compressed Sensing Receiver Based on Mixer Harmonics

Abstract

The underlying assumption in much of the existing work on cognitive radios (CRs) has been the availability of a high-performance CR receiver. Designing an efficient wideband radio that can sense over a broad spectrum is challenging, especially since high-levels of integration and low power are essential for CR systems operating in battery-powered mobile systems. Recently, sensing strategies based on compressed sensing (CS) have been proposed to reduce the sensing time at minimal hardware overhead. Existing CS receivers, however, assume that the signal energy outside the frequency range of interest is negligible. In a real system, unfortunately, this is not an accurate assumption. Because of the difficulty of designing a wideband and high-order filter, the out-of-band interferers remain largely unattenuated, especially those near the edge of the frequency band of interest. The problem with existing CS receivers is that they are sensitive to these out-of-band interferers, which fold in-band and result in significant performance degradation. This paper presents a CS receiver that is more robust to out-of-band interferers, which are inevitably present in realistic operating scenarios. In the proposed receiver, a cascade of multi-phase clocks exploit the harmonics of modern hard-switching commutating mixers to fold the wideband signal to baseband. The proposed receiver is shown to be similar to existing multi-coset receiver but without the folding of the out-of-band interferers. A possible circuit realization of the mixer block is presented, and the effects of circuit non-idealities have been quantified. The proposed receiver outperforms existing CS receiver even in the absence of out-of-band interferers, because unlike existing receivers, it does not fold the out-of-band noise floor to in-band. In the presence of out-of-band interferers, existing CS receivers cease to function while the proposed receiver remains largely unaffected.