The Study Of Synchronization Technology For OFDM Communication System Based On Software Radio

The requirements of service quality and transmission rate in mobile communications are more and more urgent since all kinds of demands are increasing day by day. That needs better system performances in mobile communications. In the future, the communications service will transform from voice to multimedia such as data, image and vedio. Since the frequency bandwidth is limited in wide-band mobile communication, advanced technology must be adopted to make use of the precious frequency resources so as to obtain higher data rate and huge channel capacity. At the same time multi-path fading and multi-path inference over wireless channel have to be overcome in high data rate. OFDM and Software Radio are both charming technologies of mobile communications in the future. OFDM is one of multicarrier technologies, which basic theory is that high rate data flow are assigned to subcarrier in relative low transmission rate by serial-parallel conversion. So its resistibility against echo is strengthened by extending the period of transmission symbol. Then cyclic prefix is inserted into different OFDM symbols to eliminate the intersymbol inference because of multi-path transmission. However, one of its main disadvantages is that OFDM systems are sensitive to carrier frequency offset. So synchronization is one of main research issues in OFDM techniques. Software Radio is a new concept and system to realize wireless communications which is presented recently. Its key method is that A/D and D/A convertor should approach antenna as well as transmitter-receiver's function should be defined by software to the best of its ability. Software Radio uses hardware for the basic platform of wireless communications. It is universal, flexible and exoteric. So it is convenient for interconnection and update. It maybe become the third revolutionary following analog to digital communications and fixed communications to mobile communications. At the same time, in mobile communications new standards appear endlessly. So the new and old communication systems will coexist. It induces the difficulty in interconnection between different communication systems. So the traditional communications based on hardware will unfit itself for the development of communications. At the same time Software Radio is just the best solution. This paper mainly focuses on the combination of OFDM system with the Software Radio technology and presents OFDM transceiver scheme based on Software Radio platform. Symbol timing and carrier frequency offset are mainly researched in this paper. An improved OFDM symbol is presented after different synchronization algorithms are analyzed. Symmetrical data segments are added to the front of the OFDM symbol or at the tail of the OFDM symbol. So repeated maximum likelihood and symmetrical maximum likelihood algorithms can be combined to time symbol synchronization precisely. Ten training symbols are used to estimate frequency offset. The effectiveness and correctness are verified in the end. At last OFDM-CDMA system based on Software Radio platform is discussed primarily.