Real-time Implementation Of Carrier Phase Recovery Algorithm In Coherent Optical Communication

In recent years,the demand for high-speed and large-capacity transmission systems is increasing,and the research of coherent communication technology has become the mainstream in the field of optical communication.At the same time,with the rapid development of coherent detection technologies and digital signal processing technologies such as high-speed analog-to-digital converter(ADC),people pay more and more attention to the research of coherent optical communication system based on field programmable gate array(FPGA).At present,high-speed real-time parallel algorithms based on digital signal processing(DSP)have become the focus of research and expansion.In coherent optical communication system,this paper mainly completes the real-time implementation of carrier phase recovery(CPR)algorithms(including frequency offset estimation(FOE)algorithm and carrier phase estimation(CPE)algorithm),and comprehensively researches the performances and resources of various CPR algorithms.The main research contents of this paper include:(1)In this paper,the composition of QPSK coherent receiving system is introduced in detail,and the current situation of CPR algorithms at home and abroad is investigated and analyzed.CPR algorithms are divided into two types,one is based on complex operation,and the other is based on angle operation.The representative Viterbi-Viterbi phase estimation(VVPE)algorithm and Barycenter phase estimation(BCPE)algorithm are selected for principle analysis and comparative study.(2)The VVPE algorithm in complex domain and BCPE algorithm in angle domain are researched comprehensively for the first time,and the simulation performances under 10GBaud QPSK system are studied.It is found that under the same system environment,for FOE algorithm,the algorithms in complex domain and angle domain have a similar recovery performance and frequency compensation range.For CPE algorithm,the anti-noise capablitity of VVPE algorithm is stronger than BCPE algorithm.For VVPE algorithm,the probability of occuring cycle slip is lower than that of BCPE algorithm.The performances of two algorithms are similar when there is no cycle slip.The received power of VVPE algorithm is about 1dB lower than that of BCPE algorithm when cycle slip occurs.For BCPE algorithm,in order to achieve the similar recovery performance as VVPE algorithm,the length of average filter is about two times that of VVPE algorithm.(3)The recovery performance of various CPR algorithms has been verified in the off-line QPSK experimental system of 2.5GBaud and 10GBaud.For 2.5GBaud QPSK system,the receivd sensitivity of the two algorithms is-52dBm@1×10-3 after optimizing the length of average filter.The received power of VVPE algorithm and BCPE algorithm when cycle slip occurs is-54dBm and-53dBm.For 10GBaud QPSK system,the received sensitivity of the two algorithms is-47dBm@1×10-3 after optimizing the length of average filter.The received power of BCPE algorithm when cycle slip occurs is-52dBm.(4)Verilog programming of CPE algorithm in complex domain and angle domain is completed,the number of parallel channels and input bits of the algorithm is optimized,and the amount of hardware resources is researched.The experimental results show that for 10GBaud QPSK system with 64 parallel channels,the received sensitivity is-51 dBm@2×10-2 when VVPE algorithm has 8 bits of input signal and BCPE algorithm has 16 bits of input signal.Compared with VVPE algorithm,the look-up table hardware resource of the BCPE algorithm is reduced by about 6%.(5)Based on Virtex Ultrascale+FPGA of Xilinx company,the real-time CPR algorithms in complex domain and angle domain of 10GBaud QPSK system have been completed,and online experiments have been conducted.The results show that the real-time received sensitivity of the two CPR algorithms is-44.5dBm@1×10-3.The received power of BCPE algorithm when cycle slip occurs is-46dBm.