Ofdm-based Spread Spectrum Communications Technology Research

From the early development of wireless communication to present, how to effectively improve the anti-jamming and anti-fading capability of wireless communication systems has always been the focus of the research. In the modern wireless communication technology, spread spectrum communication technology has an excellent ant-jamming performance, while Othogonal Frequency Division Multiplexing (OFDM) thechnology has a high data transmission rate and spectral efficiency, and can combat frequency selective fading effectively, so it is useful to resign communication systems with these two technologies tegother. And to study their combined technologies has become a hot filed of wireless communications.In the spread spectrum communication, direct sequence spread spectrum(DSSS) and frequency hopping(FH) are the two kinds of most widely used spread spectrum technologies. DSSS system combats the jamming by reducing the effective power of jamming, and FH system does through the frequency hopping to avoid jamming. As the muti-carrier property of OFDM, it's possible to combine the DSSS and FH technology with OFDM respectively. Research on OFDM-based DSSS and FH technologies and their associated anti-jamming and anti-fading techniques is the focus of this article.In the third chapter, we introduce a kind of OFDM-based DSSS technology - two-dimensional spread spectrum(2DSS) technology. When the 2DSS system can not combat strong narrow-band interference, through the use of interference suppression techniques, it can further enhance its anti-jamming capability. Among them, the frequency domain narrow-band interfence suppression technique is simple and popular. So we mainly investigate this technique, and a new interference suppression algorithm based on tap weight leakage algorithm is proposed. Finaly, the algorithm is simulated in the 2DSS system. The results show that it can effectively suppress interference, and the performance is better than tap weight leakage algorithm.In the fourth chapter, we mainly investigate OFDM-based FH technology -sub-carrier FH technology, and propose a non-coherent FH mapping method different from regular FH mapping method, and then present the simulation of this method. The results show that the regular FH mapping method has a stronger anti-jamming ability, and the non-coherent FH mapping method is more suitable for fading channel environment without channel equalization. At last, we design a kind of OFDM-based fast frequency hopping(FFH) system(FFH-OFDM), and represent the FFH-OFDM system implement schemes.In the traditional FFH system, the use of appropriate diversity combining(DC) algorithms can greatly improve the system anti-jamming and anti-fading capability. Therefore, the fifth chapter mainly studies the application of the DC algorithms in the FFH-OFDM system, and represents their concrete manifestation in the FFH system. In the end, the performance of FFH-OFDM system combined with different DC algorithms is simulated and analyzed.