Studying For Techniques Of Synchronization In OFDM Systems

With the development of Internet, consumptive electronics and Multimedia, the demand is gradually increasing for broadband wireless data communications. To apply wireless communication network in the future to these broadband services, new techniques based on BWS (broadband wireless system) should be developed.Due to the delay spread caused by multi-path fading propagations in wireless environment, high-rate information leads to serious ISI (inter-symbol interference). This results in very high requirements for the equalizers in single-carrier systems and higher complexity of algorithms in the equalizers. Although, CDMA is an effective technique which will overcome the effect of multi-path fading, there is a contradiction between the spread-frequency gain and the rate of data. On condition that the bandwidth is invariable, the higher data rate each user requests, the lower spread-frequency gain the CDMA system can supply. Therefore, new technologies should be developed to provide the services based on BWS.For BWS, OFDM is a good-performance technique in physical layer. It provides an approach which enables data to be transferred in great delay channel at a high speed. In OFDM systems, the high rate data stream is divided into many sub-data streams with low rate, which have parallel transmission in relevant orthogonal sub-channels. Thus, the effect of ISI should be easily eliminated, because the symbol's duration on each sub-carrier is longer than the maximum of delays generated when sub-data streams are transferred through sub-channels.The dissertation introduces OFDM technology's advantages in broadband wireless communications, and analyses the basic principles, the guard intervals and the cyclic prefixes of OFDM, as well as the conceptual architecture and key techniques of OFDM modulators and demodulators. The dissertation is focused on synchronization of OFDM systems. The influences on OFDM system's performance, which are caused by the distortions of carrier frequency, carrier phase, samples frequency, samples phase and symbol timing, will be discussed respectively. A variety of algorithms for synchronization is discussed on details as well.Furthermore, the dissertation will go deep into study for short training sequences in IEEE802.11a, in which the symmetric particularity is discovered. An improved delay correlation algorithm for symbol timing should be deployed in terms of between this...