Cognitive radios for dynamic spectrum access - polyphase multipath radio circuits for dynamic spectrum access

Twente Univ., Enschede
IEEE Communications Magazine (Impact Factor: 4.46). 06/2007; DOI: 10.1109/MCOM.2007.358856
Source: IEEE Xplore

ABSTRACT Dynamic access of unused spectrum via a cognitive radio asks for flexible radio circuits that can work at an arbitrary radio frequency. This article reviews techniques to realize radios without resorting to frequency selective dedicated filters. In particular, a recently proposed polyphase multipath technique canceling harmonics and sidebands is discussed. Using this technique, a wideband and flexible power upconverter with a clean output spectrum has been realized on a CMOS chip, aiming at flexible radio transmitter application. Prototype chips can transmit at an arbitrary frequency between DC and 2.4 GHz. Unwanted harmonics and sidebands are more than 40 dB lower than the desired signal up to the 17th harmonic of the transmit frequency

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    ABSTRACT: Currently, how to achieve a flexible RF front-end of cognitive radio becomes a research hotspot. Cognitive user receives the wideband signal which contains the unwanted signals, and suffers from the issue that LO harmonics will down-convert the unwanted signals to the baseband along with the desired baseband signal. In this paper, we propose a novel Adjustable Harmonic Rejection Mixer (AHRM) which utilizes the nonlinearity of mixer and changes the number of operation-paths to satisfy the variable harmonic rejection requirement of cognitive user. The simulation results show that the harmonic rejection ratio of the AHRM can reach about 300dB for the required harmonics, and the AHRM uses as few operation-paths as possible to save power consumption.
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    ABSTRACT: Dynamic spectrum access relying on spectrum sensing requires reliable detection of signals in negative signal-to-noise ratio (SNR) conditions to prevent harmful interference to licensed users. Energy detection (ED) is a quite general solution, which does not require any knowledge of the signals to be detected. Unfortunately, it suffers from noise uncertainty in the receiver, which results in an SNR-wall below which signals cannot be reliably detected. Furthermore, distortion components originating from nonlinearity in the sensing receiver cannot be distinguished from true input signals, and is thus another effect that may obscure weak signals and cause false alarms or missed detections. Cross-correlation was recently proposed to reduce the SNR-wall and, at the same time, allow the receiver to be designed for high linearity. This allows for high-fidelity spectrum sensing, both in the presence of strong interference as well as for signals with a negative SNR. In this work, an integrated complementary metal-oxide-semiconductor prototype exploiting cross correlation is presented and tested in practice. The prototype achieves a high linearity of +25 dBm IIP3 at a sensitivity of -184 dBm/Hz, 10 dB below the kT noise floor. The measured results agree well with theory, and, compared to the traditional ED-approach, show both a significant improvement in sensing time, as well as a reduction of 12 dB in the SNR-wall itself. Overall, cross-correlation makes ED faster, more sensitive, more resilient to strong interferers, and more energy-efficient.
    Emerging and Selected Topics in Circuits and Systems, IEEE Journal on. 12/2013; 3(4):566-575.
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