The Investigation Of Core Algorithm In O-OFDM System

In high capacity optical fiber communication systems, the demands for higher data transmission rate is increasing with the increasingly growth of people’s needs. When the transmission rate of the data is increasing, we also want the character of the system remain stable. Under these circumstances,O-OFDM technique was proposed and widely investigated. At the very beginning, OFDM is one of technologies studied in wireless communication field. Because of its many domain characters such as high frequency spectrum utilization, it can reduce the effect which caused by multipath scattering to the minimum. When applied in optical fiber communication field, the character of OFDM technique was still play an important role, which made OFDM technique suitable in high capacity optical fiber communication systems. Even in PON systems, which need short distance of optical fiber link, the dynamic subcarriers allocation of OFDM technique can still play an important role. In O-OFDM system, the amplitude and phase information of the OFDM signal can be affected by chromatic dispersion of the fiber or the linewidth of the laser, and subsequently make the performance of the system unstable. Aimed to reduce the damage of OFDM signal, the usual way is to design different algorithm which used at the receiver to reduce the damage caused by different kinds of optical effects. This kind of method can reduce the cost of the system and increase the system flexibility, compare to accomplish the compensation in optical fiber links. After all, the investigation in O-OFDM systems is of great important.With the support of National 863 Project "Research of the Key Technologies of 100Gb/s Optical Coherent Transmission Systems(2009AA01Z221)" and National Natural Science Foundation Project(61072053), this paper investigate the algorithm related to linewidth phase noise compensation as well as chromatic dispersion phase noise compensation in CO-OFDM system. Furthermore, the scheme of FFT hardware implementation in 40 Gbps PM-QPSK-CO-OFDM system was designed.1. The principle of CO-OFDM technique has been discussed, and a CO-OFDM simulation system has been built using simulation tools VPI and MATLAB. The way of setting important parameters of the systems has been found throughout simulation and analyze.2. For the compensation of phase noise caused by linewidth of the laser, an algorithm called pilot-aided phase noise compensation method was added to the system. The feasibility of this algorithm was proved throughout the simulation, and the setting of main parameters has been discussed.3. For the compensation of phase noise compensation caused by chromatic dispersion of the fiber, we have proposed two schemes to accomplish CD phase noise compensation. One is called pilot-aided CD phase noise compensation scheme which use a pilot to accomplish phase noise compensation. The other is called differential pre-coding CD compensation scheme, which using symmetrical pre-coding to the differential encoding symbols mapped from original bits to ensure that every two adjacent symbols get the same CD phase noise. The feasibility of two algorithms has been proved throughout simulation, and the advantages as well as disadvantages have been discussed.4. The computing principle of FFT has been discussed, and focus on 40Gbps PM-QPSK-CO-OFDM system, the scheme of FFT hardware implementation was designed.