A practical implementation of the modulated wideband converter compressive sensing receiver architecture [electronic resource]

Cognitive radio systems promise to alleviate the shortage of wireless bandwidth by sensing the entire spectrum and operating in the underutilized whitespace. Prototypes based on the Modulated Wideband Converter (MWC) compressive sensing architecture have demonstrated both fast spectrum sensing and receiver flexibility. In this thesis, we demonstrate a MWC receiver capable of sensing four 1.4 MHz channels between 0 and 900 MHz that is robust to interference and meets the LTE specifications for both sensitivity and maximum allowable input power. The MWC quickly determines the spectral content of the entire input band by multiplying it with a spectrally diverse mixing signal which guarantees that every input channel is represented in measurements taken at baseband. While these spectrally diverse mixing signals are necessary for detection, they provide no blocker rejection, provide a very large effective noise bandwidth, and thus represent the worst-case mixing signal once the input spectrum is characterized. Therefore, in this thesis we introduce a separation between the detection and reception modes of the MWC. Once the detection mode establishes the signal and blocker band locations, we reconfigure the receiver to directly target the desired signals while actively nulling a single strong blocker. In order to null a blocker band, we introduce two independent techniques. In the first sequence-based technique, we develop an algorithm to modify targeted digital mixing sequences so that they additionally null an undesired harmonic. In the second delay-based technique we generalize a technique for harmonic cancellation commonly applied in power inverters. By finely controlling the relative delay between two parallel mixing paths, we are able cancel any single mixer harmonic in their sum, thus preventing a strong blocker in the corresponding band from interfering with the baseband measurements. We design, build, and test an integrated mixer prototype that demonstrates these two rejection techniques and allows us to compare the MWC receiver architecture against recently published alternatives. Our prototype achieves 50.2 dB of sequence-based rejection, 59.3 dB of delay-based rejection, and 62.8 dB of rejection when both techniques are applied to the same blocker. Likewise, the mixer demonstrates a 64.8 dBm IIP2, a 14.3 dBm IIP3, and a 31.5 dB noise figure while consuming 26.6 mW of signal-path power per branch. These performance parameters are in line with recently published harmonic rejection mixers. Additionally, when coupled to a hypothetical LNA that provides 25 dB of gain, 2.5 dB of noise figure, and a -10 dBm IIP3, we calculate a receiver sensitivity of -96.1 dBm and 10 dB of SNDR for up to -25 dBm of input power for the MWC receiver. We thus demonstrate that the MWC is competitive with traditional wideband receivers, while its additional flexibility makes it particularly attractive for cognitive radio systems.

Keywords: Electrical Engineering.
Advisor: Murmann Boris primary advisor. Thesis advisor
Arbabian Amin advisor. Thesis advisor
Lee Thomas