A Study On Blind Equalization For OFDM In Non-cooperative Communication

Military electronic reconnaissance and military confrontation are the foundation of the future information warfare. However, factors like multipath fading, signal interference etc. in wireless channels lead to severe inter-symbol interference. Aiming at the non-cooperative communication system in particular environment, researchers have attempted to reduce the inter-symbol interference and resist the influence of the channel using signal detection technology, modulation recognition technology, and blind equalization technology in order to detect and restore the useful signal, and have achieved great breakthrough. Blind equalization is a new kind of adaptive equalization technique, which can well adapted to the non-cooperative communication and only statistics of receiving sequence itself is required for equilibrium of channel characteristic. Orthogonal frequency division multiplexing (OFDM) technology can efficiently improve bandwidth availability ratio of communication systems and resist the interference brought by multipath propagation as a kind of multicarrier modulation method. Based on OFDM multicarrier system model, blind equalization technology of OFDM in non-cooperative communication under the condition of multipath fading channel has been studied. Furthermore, data reuse and iteration of variable step have been used to deal with the short data of non-cooperative communication. Algorithm performance after improvement has been analyzed. The main contents are as follows:1. Blind equalization model with Bussgang property based on OFDM multi-carrier modulation has been established. Balanced expressions of MCMA algorithm, MMMA algorithm and DD algorithm have been given. Thus, switch rule and algorithm block diagram of MMMA_DD multimode equalization algorithm have been achieved. Constellation diagrams, symbol error rate curves, error of mean square, and residual inter-symbol interference of MMMA_DD and MCMA algorithms after equalization have been compared. According to comparison, performance of MMMA_DD algorithm is more excellent than MCMA algorithm. MMMA_DD algorithm has great equalization performance for different signal to noise ratio and under different multipath channel conditions.2. In non-cooperative communication system, staged data reuse technology has been chosen aiming at difficult to convergence of short data; improved iteration of variable step technology has been proposed for further increase of the convergence speed and equalization performance. The improvement of multiplex technique to equalization performance of MMMA_DD algorithm under short data input condition has been verified. Under variable step condition, convergence performance of MMMA_DD algorithm has been investigated. Experiment result indicates that great equalization performance of MMMA_DD algorithm can be realized using multiplex technique and variable step technique.This work may be used as theoretical reference for equalization of multi-carrier modulation in non-cooperative communication systems.