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Performance analysis of OFDM with Wiener phase noise and frequency selective fading channel
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Elektroniikan, tietoliikenteen ja automaation tiedekunta |
Master's thesis
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S-88
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en
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75
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Abstract
This thesis studies the effect of Wiener phase noise on the performance of orthogonal frequency division multiplexing (OFDM) systems. The main performance metrics used in the analysis are capacity and signal-to-interference-plus-noise ratio (SINR). OFDM is a multi-carrier modulation technique in which data is transmitted in parallel streams using closely spaced (in frequency) orthogonal carriers. Phase noise is the random fluctuation in the phase of the oscillator signal used in the frequency translation between baseband and radio frequency. These fluctuations occur because of the inherent imperfections in the components that make up the oscillator. With respect to OFDM, phase noise destroys the orthogonality between the carriers and this causes interference between the parallel streams of data which results in degradation of the capacity and SINR.
We derive closed-form analytical expressions of average capacity and average SINR and highlight the key parameters of the phase noise process and OFDM system that affect its behaviour. In comparison with previous works, a probability density function (PDF) based approach is used in arriving at these performance metrics. This approach necessitates the derivation of the PDF of a sum of gamma random variables. In earlier literature, this result is available for gamma variables that have a full-rank square-root normalized covariance matrix. We generalize the result for the rank-deficient case and apply this result to obtain the statistical expressions of capacity and SINR.