Research On Modulation Classification And Parameter Estimation Of Ofdm Signals In Wireless Fading Channels

Orthogonal Frequency Division Multiplexing(OFDM) is winning an increasingly widespread application in wireless communication area as an multi-carrier modulation technique with high bandwidth efficiency, anti-interference ability, and it is suitable for high speed data transmission. Communication signal modulation classification and parameters estimation are important components in signal analysis area. At present, the modulation identification technique of single-carrier digital modulation signal in AWGN channel is studied deeply home and aboard, and a favorable effect has been achieved. But in the OFDM signal classification area, related studies are in phase of theory discussion. The OFDM signal recognition and parameters estimation is discussed in depth in Gauss and Rayleigh fading channel models.Firstly, the principle of OFDM is analyzed, and the characteristics and classifications are studied in order to provide theory foundation for the coming problems.Secondly, traditional classification methods based on high-order statistics are analyzed, and the statistics of OFDM signal in Gauss and Rayleigh channel are studied, on which the classification characteristic parameters and classifier are based in Gauss and Rayleigh channel. Main problems are pointed out, and an improved classification method base on Normalized six-order cumulant is proposed. Simulation results indicate the, the algorithm can have high recognition rate when observing samples are long enough.Thirdly, the cyclostationary properties of over sample digital modulated signal is analyzed and then the High-order cyclic cumulants expressions of single-carrier signal and OFDM signal are deduced. According to that there exists peak when time delay is OFDM symbol effective length, an identification method based on second-order cycle cumulant is proposed. The performance of the method is analyzed in Gauss and Rayleigh channel, and the simulation results verify the effectiveness of the algorithm.Finally, key parameter estimation of OFDM signal is studied. Two methods are proposes for time-domain parameters estimation: one is time-domain correlation method taking advantage of the characteristics of cyclic prefix, another is second-order cyclic cumulant method making use of the characteristics of cyclostationary. Simulation results verify the feasibility and satisfying estimation performance of the algorithms.