Researches On Simplified Scheme Of DSP Complexity In Space Laser Communication

With the rapid development of high-speed network services such as high-definition video and webcast,users'demand for traffic is increasing.The space laser communication system can effectively improve the information transmission capacity,and the confidentiality is higher,which satisfies the demand for large data volume and high-speed data transmission rate.But not only the effects of dispersion and dispersion slope should be considered among the fiber-optic communication system that based on polarization multiplexed,but also the effects of three-component dispersion in the PM system,therefore the polarization state of light is prone to degenerate in the fiber.What's more,the requirements of the polarization de-multiplexing algorithm and channel equalization algorithm in digital signal processing are relatively high.After preliminary research,we noticed that compared with the fiber channel,the changes of polarization state and the channel characteristics of the two polarization states are relatively slow in space optical communication channel.And the polarization states of the polarization multiplexed signal remain well after several kilometers of transmission in the atmosphere.Moreover,there have no serious polarization mode dispersion(PMD)effect in the space channel.So that low-speed polarization de-multiplexing and channel equalization can be used in the space laser communication system to meet the system requirements.For the characteristics of polarization multiplexed signals in space laser communication systems,we researched on the simplified scheme of the digital signal processing(DSP)in space laser communication system.Firstly,this paper analyzes and researches the polarization de-multiplexing algorithm and channel equalization algorithm.It's determined that the intensity cross-correlation(ICC)algorithm is used for polarization de-multiplexing,and the constant mode blind equalization algorithm(CMA)is used for channel equalization.Next,the paper analyzes and studies the traditional time-domain equalization scheme,and designs a simplified time-domain equalization scheme to reduce the cost of hardware resources under the condition of expanding transmission capacity.For the relative stability of polarization states in space laser communication systems,we propose to use the ICC algorithm for low-speed polarization de-multiplexing,and then use the CMA algorithm for low-speed linear channel equalization for each polarization channel.The advantage of this method is that the logic resource consumption in hardware implementation will be reduced by reuse of the low-speed logic cells during FPGA processing while the ICC algorithm and CMA algorithm are running.Finally,in order to verify the feasibility of the scheme,we set up a transmitter to send the Nyquist 20-GBd PM-QPSK signal.The sampling signal of the receiver is separately processed by CMA and ICC&CMA with MATLAB,and the experimental data is compared and analyzed.By comparing the constellation diagram and BER after the two kinds of processing,we know that this method simplify the DSP by increased the BER slightly.