Study on Key Technologies of OFDM Passive Optical Network
|School||Huazhong University of Science and Technology|
|Keywords||Orthogonal Frequency Division Multiple (OFDM) Passive Optical Network (PON) Wavelength-division-multiplexed (WDM) Direct detection Coherent detection|
Orthogonal frequency division multiplexing can convert the high-speed data streams into sub-parallel low-speed data streams, and can effectively reduce the ICI and the ISI, has become the core technology of next generation access network. Compared with the traditional TDM-PON or WDM-PON, the most important feature of OFDM-PON is it can deal with the original signal in electronics instead of in the optical field. Then it can deal with the dynamic bandwidth allocation, transmission loss compensation and multi-service access in electronic field. As DSP processing is used in the system, optical devices of mature, stable and low rate can be used in the OFDM-PON, which can reduce the complexity and device cost of the optical communication system. The research in this dissertation was supported by the national "Eleventh Five-Year" "863" Program Project, launched an in-depth analysis and technical innovation of OFDM-PON. The main contents of this thesis are as the followings:(1) The architecture and the key technologies of the next-generation PON are comprehensive analyzed and compared, and the trends of PON technology are pointed out. The research status in domestic and international and the development trend of optical OFDM technique is introduced.(2) The theoretical basis of OFDM technology is described, and several key issues of the optical OFDM system are summarized and analyzed. The signal processing technology of optical OFDM system is described in details, the FEC of OFDM system is studied, the principle of LDPC codes is analyzed, which has laid a theoretical foundation for the study of OFDM-PON.(3) The modulation formats of the optical OFDM systems are sudied in theoretical, and DQPSK and QAM are discussed in details by simulation. Several commonly used optical modulators in OFDM-PON are studied, including MZM, SOA-based optical modulator and electro-absorption modulator.(4) Based on the analysis and comparison of the existing architecture and light source of WDM-PON, a OFDM-WDM-PON structure of 10 Gb/s downstream and 2.5 Gb/s upstream is proposed and analyzed with different parameters. An OFDM-based long-distance WDM-PON network architecture is proposed. A simulaion system at 2.5 Gb/s is setup to help us to analyze the performance after the long reach transmission. Simulation results show that the OFDM signal is very suitable for long distance transmission of WDM-PON. Three kinds of colorless ONU (EAM/RSOA/FP-LD) are simulated and analyzed, in which the RSOA and the FP-LD can erase the downsream OFDM signal better.(5) The basic principle and channel model of the coherent optical OFDM system are studied, some key issues of transmitter design are in-depth analyzed. The bias point of optical transmitter in OFDM-PON is simulated and analyzed. The results show that the optimal MZM bias is the null point, in which the OFDM transmitter can get the least Q penalty and minimum additional insertion loss of modulation. By introducing the carrier frequency offset and phase noise compensation algorithm of the wireless OFDM to the CO-OFDM system, the simulation results demonstrate that the frequency offset and phase noise introduced by the laser can be effectively compensated, thus greatly improving system performance.