Generation And Detection Of Multilevel Modulated OOFDM Signal

With the development of communication technology, the next optical network requests a wider bandwidth and larger capacity. Optical communication systems are moving toward in the direction of higher speed, higher transmission capacity and longer transmission distance. Introducing OFDM technology to the optical fiber communication system can make full use of OFDM advantages, such as high spectrum utilization and flexibility of subcarrier’s modulation. Using OFDM technology can greatly increase the transmission distance of optical fiber communication network and transmission capacity, also can enhance the dispersion and nonlinear resistance ability of optical fiber communication system.In this paper, we focus on the generation and detection technology of OOFDM system. On the basic principle and key technology of OFDM, we further study the generation and detection technology of multi-level modulation OOFDM system. Then we design a novel OOFDM system based on multi-level modulation, polarization multiplexing, subcarrier multiplexing technologies. Construct simulation system of multi-level modulation OOFDM system on OptiSystem simulation platform. Use the simulation software to study the key performance parameters, such as dispersion, number of subcarriers, modulation order.(1) Study the generation technology of multi-level modulation OOFDM signalOn the basic principle of optical modulation technology and generation technology of OOFDM, we proposed a novel OOFDM transmission scheme based on multi-level modulation, polarization multiplexing, subcarrier multiplexing technologies.(2) Study the detection technology of multi-level modulation OOFDM signalOn the basic principle of photoelectric detection theory and detection technology of OOFDM, we further study receiving scheme of multi-level modulation OOFDM system.(3) Simulate and research the multi-level modulation OOFDM systemBased on the generation and detection scheme, build the simulation platform of multi-level modulation OOFDM system. Study the key performance parameters, such as dispersion, number of subcarriers, modulation order. The simulation results show that:when the dispersion value increases, the received signal’s constellation point will be more divergent, but we can use equalization technique to correct the constellation diagram effectively. The greater the number of subcarriers is, the smaller the subcarrier frequency spacing is. This will extremely easy cause inter-carrier interference phenomenon. Conversely, when the number of subcarriers is too small, it will make the throughput of the system decreased, and reducing the utilization ratio of spectrum. When modulation order is low, the spectrum utilization rate will be lower, but the system bit error rate will be smaller. In the other hand, when modulation order is higher, the spectrum utilization of system will be improved at the same time, but the bit error rate will be increased.Therefore, each factor in OOFDM system should be synthetically considered to choose the optimal system parameters.(4) Study the channel estimation method of multi-level modulation OOFDMStudy channel estimation theory. Improve the performance of multi-level modulation OOFDM system by ISFA method.