Advanced classification of OFDM and MIMO signals with enhanced second order cyclostationarity detection
Department of Electrical and Computer Engineering
Doctor of Philosophy
Giannakis, Georgios B.
With the emergence of cognitive radio and the introduction of new modulation techniques such as OFDM and MIMO, the problem of Modulation Classification (MC) becomes more challenging and complicated. In the first part of the thesis, we explore the automatic modulation classification to blindly distinguish OFDM from single carrier signals. We use the fourth order cumulants; an approach which in the past has been also applied to classify single carrier signals. A blind OFDM parameter estimation scheme was then followed, which includes the estimation of number of subcarriers, CP length, timing and frequency offset and the oversampling factor for the OFDM signal. For the second part of the thesis, we improve the statistical signal processing techniques that were used in the first part. Particularly, the second order cyclostationarity based methods have been examined and improved. Based on the fact that most of the cyclostationary communication signals has a real cyclostationary part and a complex non-cyclostaionary part, we suggest an approach that enhance the second order cyclostationarity and hence increase its probability of detection. Using such improved second-order cyclostationarity, we present an improved synchronization method based on second order cyclostationarity. With the proposed approach, it is shown that the timing estimator, is independent of the frequency offset estimator, and therefore performs better than the previously proposed class of blind synchronization methods. To negate the dependence of the blind synchronization scheme on the prior knowledge of the raised cosine pulse shaping filters, we proposed a blind roll-off factor estimator based on the second order cyclostationarity. Last, we address the MIMO classification problem, wherein we estimate the number of transmitting antennas. Here the second order cyclostationarity test has been applied in distinguishing STC from BLAST modulation.
njit-etd2010-039 (144 pages ~ 6,357 KB pdf)
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Created October 11, 2011