Study On Blind Equalization Alogrithm Based On High-order Spectrum Theory

Equalization technology is a effective method which can remove intersymbol interference (ISI) in digital communication. Blind equalization technology is a very popular research topic because it can adaptively equalize without training sequence. Blind equalization algorithm based on HOS (higher-order statistics) was presented and developed in 80's. HOS convey not only amplitude but also complete phase information, so system can be identified only using output signal and can obtain the global solution.This paper researches blind equalization ruler, analyses the knowledge of HOS and summarizes some algorithms based on the HOS. Odd-order (third-second order and fifth-second order) normalized cumulant algorithms are introduced and a new blind equalization ruler is proved and introduced after researching even-order normalized cumulant algorithms. Then the steepest descent method is used to derive the algorithm.Odd-order normalized cumulant isn't used to equalize directly because the odd-order cumulant of symmetrically distributed signal theoretically vanishes. In order to overcome this, this paper introduces a new symmetric-to-asymmetric transformation ( SAT ) method. At input end, symmetric-to-asymmetric transformation ( SAT ) is implemented before transmitting and transform symmetric signal into asymmetric signal. But additive symmetrical distributed noise is vanishes through odd-order cumulant. This new transformation method does not change with convergence rate and result of algorithm. This algorithm has great fault tolerant ability.The computer simulation results show that the odd-order normalized cumluant algorithms give lower-complexity, faster convergence rate, smaller steady state mean square error (MSB) and great fault tolerant ability in comparison with even-order normalized cumluant algorithms in the same situation. They have better performance than some other algorithms in current.