The Investigation On Electrical DSP Algorithms In Optical Coherent Receivers At 100GB/S And 400GB/S

The rapid development of high-speed and high-quality data and video services in communication networks has been demanding a much higher bandwidth of backbone networks. The evolution of optical fiber transport network, from the current 40Gb/s system to forthcoming 100Gb/s and even future 400Gb/s per wavelength channel system, has become one of future mainstream development directions in the current international communication field.In the background of mature digital signal processing (DSP) technologies and the development of high-speed digital circuit, polarization-division multiplexing (PM) coherent optical transmission system based on DSP, which not only improves the spectral efficiency by using PM, OFDM and multilevel modulation formats but also compensate amplitude and phase impairments of coherent detected signal flexibly in digital domain, has gained widespread attention and become one of hot topics of the optical communication.With the support of National 863 Project "Research of the Key Technologies of 100Gb/s Optical Coherent Transmission Systems (2009AA01Z221)", this thesis mainly focuses on the research of the timing synchronization algorithm in the coherent receiver of 100Gb/s PM-QPSK system and the DSP algorithms of 400Gb/s PM-CO-OFDM coherent receiver. The main contents are as follows.1. The system structure and mathematical model of 100Gb/s PM-QPSK coherent optical transmission system are investigated in this thesis, and then the study focuses on the function and algorithms of the receiver DSP moduls. 2. The principle of VCO clock synchronization and key parameters on the synchronization performance in the coherent receiver of 100Gb/s PM-QPSK system are analysed in detail. In order to improve the dispersion tolerance of the original synchronization loop, a novel VCO clock synchronization loop combined with dispersion equalization is proposed, and the binary fixed-point notations of the key parameters and intermediate variables are designed to provide a reference for the hardware design of the proposed loop. What's more, the parallel structure of the proposed loop which can break the restriction of hardware speed is presented. The feasibilities of all the proposed schemes are verified by simulation.3. The scheme of 400Gb/s optical transmission system within 50GHz channel space is designed based on the analysis of the feasibility of 400Gb/s per wavelength channel system.4. The investigation of pricinple of 400Gb/s PM-CO-OFDM system is conducted, focusing on the function and algorithms of the receiver DSP part. By analysis of mutual interactions between DSP algorithms, an improved RF-Aided phase noise estimation algorithm with the new function of optical carrier frequency offset estimation is proposed, and a residule-frequency-offset estimation method using trainning symbols of the channel estimation algorithm is put forward so as to reduce the impact of residual frequency offset on channel estimation. The receiver DSP struture is designed with feasibility testified by simulation.