Browsing by Author "Aziz, Mohsin"

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    Blind Compensation of Impairments in Wireless Transceivers
    (2018-07-24) Aziz, Mohsin; Ghannouchi, Fadhel M.; Helaoui, Mohamed; Fapojuwo, Abraham Olatunji; Potter, Michael E.; Sawan, Mohamad
    Modern wireless communication systems suffer from hardware imperfections that degrade the quality of transmission signals and make the detection of signal quite difficult at the receiver. This thesis focuses on the gain and phase imbalances caused by the modulators and demodulators and nonlinearity stemming from the transmitter power amplifier. Broadly, the contribution of this thesis is two folds: Blind solutions to mitigate the above mentioned hardware impairments of the wireless link through the proposal of a methodology based on the derivation of closed form expressions for the probability density functions (PDFs) of the signals in the presence of these impairments. In this regards, firstly, a PDF in the presence of modulator’s and demodulator’s in-phase and quadrature phase imbalances has been derived and validated. A maximum likelihood estimation of the imbalance parameters has been proposed to mitigate these imperfections. The proposed methodology has been evaluated using extensive simulations and measurements. To evaluate the static performance of the proposed methodology, 10 KHz modulated signal has been used. Measurement results show that an image rejection of greater than 30 dB can be achieved. For a larger bandwidth signal of 1 MHz, around 19 dB improvement in NMSE can be achieved using the proposed methodology, as compared to the uncompensated case. Secondly, a closed form PDF in the presence of gain and phase imbalances and the transmitter’s power amplifier nonlinearity has been derived and validated. A cumulative distribution function-based methodology has been adopted to mitigate the effects of power amplifier’s amplitude distortions. For the modulator’s impairments, a maximum likelihood estimation of the imbalance parameters has been used to estimate and compensate for the modulator’s imperfections. Using measurements, for a 3 MHz LTE signal, a normalized mean squared error and an error vector magnitude of -35 dB and 1.5% can be achieved, respectively.
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    Rational Function and Distributed Two Block Architecture based Models for the Mitigation of Various Imperfections in Direct Conversion Transmitters
    (2013-09-30) Aziz, Mohsin; Ghannouchi, Fadhel M.
    Nonlinearity in power amplifiers and in-phase and quadrature-phase (I/Q) imperfections in the transmitter are of enormous concern. Two models to alleviate these imperfections have been proposed. The first method employs a Rational Function based model for the joint mitigation of these impairments, while the second method is a Memory Polynomial based distributed two block model. The Rational Function model has an improvement of around 2 dB in NMSE and around 3 dB in ACEPR than the state of the art parallel Hammerstein based model. For the distributed two block model, we are able to reduce the complexity while maintaining reasonable performances. The number of coefficients and the number of floating point operations are reduced by around 17 percent, matrix conditioning is improved by 12-33 dB and the dispersion coefficient is reduced by 16-42 dB as compared to the previously proposed joint modulator and power amplifier nonlinearity compensation technique.