Research On Symbol Synchronization And Key DSP Algorithms In400G CO-OFDM Transmission System

Recently, with the rapid growth of the network band-width requirement, the transmission speed between the nodes in backbone transmission network and metropolitan area network are growing up to beyond100Gbps and100Gbps, respectively. Single frequency band PM-OFDM (Polarization Multiplexing Orthogonal Frequency Division Multiplexing) optical transmission system has been one of the alternative evolution schemes for the optical transmission beyond100Gbps. Besides, the throughput capacity will be improved greatly if coherent reception and DSP (Digital Signal Processing) impairment compensation technology with100Gbps PM-QPSK (Polarization Multiplexing Quadrature Phase Shift Keying) modulation format are applied in optical burst transport ring network (OBTRN).This paper mainly researches on the synchronization and parallel processing mechanism and the key DSP algorithms in optical burst coherent reception system with100Gbps PM-QPSK modulation format, and gains a several innovative research achievements. The main work and innovative contributions are listed as follows.1. The impairment characters of sampling clock offset, symbol synchronization offset, carrier frequency and phase offset, and dispersion of the fiber are deeply researched in PM-CO-OFDM optical transmission system. To eliminate the interaction effect of different synchronization offset, a joint synchronization scheme for sampling clock, symbol and carrier synchronization is proposed. In the joint scheme, sampling clock and residual carrier frequency offset are estimated simultaneously, and the sampling clock timing offset and symbol synchronization offset are compensated for by means of channel equalization in frequency domain. The performance of the joint scheme is simulated in480Gbps PM-CO-OFDM optical transmission system, and the simulation results show that the processing range of the sampling clock and carrier frequency offset can reach up to [-2000,2000] parts per million and [-3.5,3.5]GHz, respectively.2. To reduce the requirement of the DSP chip processing speed in optical transmission system beyond100Gbps, the requirement of parallel DSP processing is fully researched in480Gbps PM-CO-OFDM system. Then, a parallel processing scheme is proposed for the480Gbps PM-CO-OFDM system, whose DSP algorithms are designed for parallel processing. The performance of the parallel processing scheme is simulated in480Gbps PM-CO-OFDM optical transmission system. The simulation results show that the performances of the parallel and serial systems are almost the same, but the requirement for the DSP chip rate of the parallel system is reduced by three orders of magnitude compared to the serial system.3. To solve the laser transient effect caused by tunable laser wavelength switching in optical burst reception system, a burst-mode reception scheme with PM-DQPSK modulation format is proposed which is based on training sequences. In the scheme, the transient laser carrier frequency offset and power impairment are estimated by interpolation and fitting method, besides, the adaptive equalization, de-multiplexing based on LMS algorithm and phase offset estimation are jointly processed. The performance of the key DSP algorithms and entire scheme are fully simulated in112Gbps PM-DQPSK optical system. The simulation results show that the scheme can correctly track the carrier frequency and laser power transient effects, and the useful data can be transmitted during the tunable laser transient period which will reduce the overheads of the burst-mode packets down to3%.