Research On The Synchronization Algorithm Of Direct Detection Optical OFDM System

With the rapid development of broadband integrated services digital network, and the rapid popularization of the Internet, the social’s demand for the amount of information in almost every half year doubled, which is into explosive growth. Therefore, the construction of information superhighway has become a worldwide craze. Optical fiber communication technology which as the pillar and the core of the information superhighway becomes the priority among priorities of the information construction. From the optical fiber communication technology we can know that, optical orthogonal frequency division multiplexing (OOFDM) modulation technique, for easing the cause of polarization mode dispersion and chromatic dispersion symbol interference and improving the utilization of spectrum resources, is widely used in optical fiber communication.Synchronization plays a very important role in every communication system, it is no exception for OOFDM system. In this system, the synchronization of different types will cause the corresponding effect. If the carrier is not synchronous, the system will generate intercarrier interference; and if the timing is not synchronous, system will generate symbol interference; the asynchronous of sampling frequency in receiver will make symbol interference and carrier interference. The principle of synchronization and wireless communication are similar to that of OOFDM, so most of the current synchronization algorithms are proposed in the wireless communication system, but apparently, characteristics of fiber itself has the influence to synchronization which must be considered, therefore, research on Synchronization Algorithm for optical fiber communication system is of great significance.In OOFDM systems, According to the receiving mode of the receiver, the system can be divided into two kinds:direct detection system and coherent detection system. Directly detected belong to the intensity detector, with the respect to the coherent detection system, it is easy to implement and has low cost. And the direct detection system only receives the sequence of real numbers. Based on this basic point, the work of this paper is as follows:First, The detail analysis of the causes reason and the impact of the synchronization error in direct detection optical OFDM system from the theory. The paper introduces the principles, advantages and disadvantages of the three kinds of classical synchronization algorithms. Based on the direct detection optical OFDM transmission system, the application of three kinds of classical algorithm is simulated, some comparison analysising are done from the following aspects:the computational complexity of each algorithm, the timing measurement function curves under the fixed condition of algorithms, the constellation of each algorithm in different fiber length.Second, the thesis proposes an improved Golay aided timing synchronization algorithm, and build the optical direct detection OFDM experimental system, in order to verify the validity of the new algorithm. Compared with other three kinds of classic algorithms, analysis and comparison have been done under two kinds of circumstances:back-to-back and200km optical fiber transmission which include that the timing offset mean value, the mean square error value and the capture rate of the new algorithm and the classical algorithm.