Research Of New Modulation Formats And Corresponding Dsp Algorithms In Coherent Optical Systems

With the proposal of the mobile internet, internet of things and big data, the data flow has increased in thousand times, which brings forward higher call for coherent optical system which is the main road of transmission. The combination of high modulation format and coherent detection based on the digital signal processing is one of the key technologies for achieving the goals of super large capacity and long distance. Among the fiber-induced impairments, nonlinear phase noise (NLPN) is a primary obstacle and severely limits the transmission distance as well as the capacity. So in order to improve the tolerance of NLPN, we focus on the design of modulation formats in the transmitter and study the corresponding compensation algorithms in the receiver.Firstly, the paper introduces the numerical simulation model for coherent optical communication systems as the basis of study. Then the paper focuses on the new modulation format, that is, the amplitude and phase shift keying (APSK). The main innovations are as followed:(1) the new optimization algorithm based on Gaussian probability detector is proposed for constellation diagram design in the transmitter. By phase pre-compensation, the probability distribution function (PDF) of the received signals can be approximately analyzed using Gaussian distribution function, which overcome the weakness of traditional algorithm by witch it has high complexity.(2) Support vector machine is applied as a detection scheme to mitigate the NLPN for coherent optical fiber APSK systems. Based on the received symbols rather than the probability density function (PDF) in theory, the SVM can generate optimum decision hyperplanes which classify the data more precisely. Compared with the traditional algorithms of APSK modulation format, the SVM conducts detection without the need to know the information of transmission link, which has certain actual meaning. And the detections in amplitude and phase direction are separated and irrelevant, which decreases the bit error rate. What’s more, the detection with S VM is suitable for any transmission link.To study the performance of algorithms in coherent APSK systems, we specify the16-points APSK constellations with three different modulation formats, that is,(4444)-APSK,(484)-APSK,(88)-APSK, and consider three transmission link based on the coherent optical systems model based on the above innovation. Various results indicate that compared to16-QAM modulation, the nonlinear tolerance of16-APSK constructed by GAP-D optimization algorithm can be improved by1.8dB. Besides, using the detection scheme with SVMs can gain a significant improvement of nonlinear tolerance over the traditional detector whether considering the dispersion or not.