Research On Key Techiques For OFDM System

One of the most important characteristics of wireless communication is multipath transmission.Multipath transmission results in signals overlapping each other,and brings to Inter Symbol Interference (ISI).The Orthogonal Frequency Division Multiplexing (OFDM) technique divides the frequency spectrum available into many independent sub-carriers.The sub-carriers keep orthogonal to one another and the spectrum overlap. It increases the spectral usage efficiency, and at the same time, it can reduce ISI greatly. The OFDM technique is applicable to high-speed data transfer in environment of multipath and frequency selectivity channel.Because of these merits of OFDM technique it catches people's extensive attention. People think that OFDM technique not only is the developmental current in the field of Wireless Broadband Access, but also will be the key technique of mobile communication system in the future. The work of this thesis is designing an OFDM simulation system and implementing simulation algorithm for basic modules on the platform of Matlab6.0. It will be a platform for continuous studying OFDM key techniques. Based on these,the work also includes study OFDM key techniques.The work of this thesis is mainly summarized as follows:①In this thesis, an OFDM simulation system on the platform of Matlab6.0 was designed as a platform for continuous studying OFDM key techniques.The simulation system includes the establishment of the wireless signal channel model,the realization of OFDM transmitter and the realization of OFDM receiver.②The thesis introduces the principle of OFDM and The key techniques of OFDM ( the synchronism technology, the estimation of the signal channel , PAPR technology and the signal channel coding).The definition of PAPR,its statistical description are presented.Some PAPR reduction techniques found in literature are introduced,simulated and discussed.③The thesis also introduces a new method based on the analysis of the traditional idea of compressing and expanding to reduce the PAPR of OFDM system. Sequentially, a modified version basing on the method are put forward and is simulated.The simulation results show that the method can reduce the PAPR of OFDM system effectively with moderate function ,simple method and strong practicality.④The thesis analyses and studies the channel estimation based on pilot frequency in the wireless communication OFDM system.Channel estimation based on pilot frequency in the wireless communication OFDM system mainly includes two methods-blind estimation and estimation based on pilot frequency.The latter can achieve better function. Subsequently,the author analyses and compares some main channel estimation principles and techniques for OFDM systems.