The Research On Symbol Synchronization Technology In OFDMA-PON System

With the development of modern communication network technology, the information of access network is growing rapidly. Under this background, the passive optical network(PON) technology has becoming a primary research hotspot currently. At present, the Ethernet technology has been mature, the broadband services demand a higher transmission rate. The PON technology not only well realizes high broadband access network system, but also meets the diverse business needs of user. The requirement of the next generation PON system guarantees a low cost of access to achieve dynamic and flexible resource scheduling at the same time.Orthogonal Frequency Division Multiple Access(OFDMA) based on OFDM is a multi-user access technology. Inheriting the advantages of OFDM technology, it has broad application prospects as it guarantees higher spectrum efficiency and has a good performance in the aspect of optical fiber dispersion resistance. But OFDMA signal is extremely sensitive to synchronization error, once the orthogonality between carriers in the OFDMA system is destroyed, it will result in inter-carrier interference(ICI), inter-symbol interference(ISI), and the introduction of multi-access interference(MAI), degrading the performance of the system. Synchronization in the OFDMA system includes: symbol timing synchronization, sampling clock synchronization and carrier frequency synchronization.This thesis mainly studies symbol synchronization technology of OFDMA-PON. Firstly, this thesis proposes a subcarrier allocation scheme using short training sequence for OFDMA-PON downlink system. Experimental results demonstrate the improvement for reducing interference of the tailing of short training sequence for the receiver data symbols effectively. Secondly, a symbol synchronization scheme based on Gold code sequence for uplink transmission in OFDMA-PON system is proposed in this thesis. The correlation characteristics of Gold code sequence are used to identify and separate different users’ data. Meanwhile, this scheme supports asynchronous clock reception. Experimental results show that the proposed scheme is feasible.