高速光纤通信系统中信号损伤缓解与补偿技术的研究
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摘要
光纤凭借其巨大的带宽、极低的损耗和低廉的造价,成为长距离、大容量通信的首选介质。在追求更高的通信速率和更远的通信距离的过程中,光纤链路中信号损伤的缓解与补偿成为光纤通信系统升级的关键。
在40G系统中,偏振模色散这一原先被忽略的现象逐渐成为限制系统升级的主要因素之一,对于较早铺设的PMD系数较大的光纤链路,必须对偏振模色散进行补偿。在直接检测系统中,电域补偿成本过高,因此在40G直接检测系统中,光域偏振模色散补偿成为克服偏振模色散对系统影响的首选方案。由于偏振模色散具有随机特性,光域偏振模色散补偿主要使用反馈控制结构。采用什么作为反馈控制信号,如何根据反馈信号操控补偿单元,如何尽量减少反馈控制环的时间消耗,这些都是研究者所面临的挑战。
进入100G时代,随着偏振复用、各种高级码型调制格式和相干接收的应用,链路中的色散、偏振串扰、偏振模色散、激光器的相位噪声以及光纤非线性成为系统性能恶化的主要原因。由于采用了相干接收技术,在电域补偿光纤链路中的信号损伤成为可能。如何设计高效的数字信号处理算法来补偿信号损伤成为研究者所面临的新的挑战。
本文围绕高速光纤通信系统中信号损伤缓解与补偿技术这一主题,对40G系统、100G系统和100G以上系统中信号损伤的缓解与补偿技术进行了深入的研究。主要工作包括：
(1)40G系统中采用高级码型调制技术与光域偏振模色散补偿技术相结合的技术方案的实验研究。作为项目核心成员,参与研制国内第一台自适应光域偏振模色散补偿原型机。经过硬件设计和控制算法两方面深度优化,跟踪能力达到45.4u s；在43Gb/s RZ-DQPSK系统中,实验证明该原型机引入的光信噪比代价小于0.8dB;1dB光信噪比代价下可使系统一阶偏振模色散容忍度由17ps提高至45ps；在差分群时延跳变、信号偏振态和偏振主态分别以85rad/s的速度快速变化时达到10小时工作无误码；在1200km传输实验中,达到12小时工作无误码。
(2)100G以上系统中采用高阶QAM码型调制与相干接收的技术方案的研究。提出一种仅使用2电平信号驱动I-Q调制器产生16-QAM的方案,避免了特殊调制器的使用和昂贵的4电平方案；提出针对16-QAM码型的低复杂度的数字信号处理算法,成功实现对色散、偏振串扰、偏振模色散、激光器相位噪声和频率偏差的补偿；仿真测试了上述方案在31种不同链路环境中的性能,实验产生224-Gb/s PM-16-QAM信号,采取相干接收和离线数字信号处理,证明上述方案的可行性。
(3) Hexagonal-16-QAM产生技术以及相应的相干接收机数字信号处理算法的研究。首次提出一种Hexagonal-16-QAM信号的简单可行的产生方案,其星座点在I-Q平面上达到二维密堆积,相比传统的Square-16-QAM,在不改变符号携带比特数目的情况下达到更高的能量利用率；提出针对Hexagonal-16-QAM信号的基于训练序列的相干接收数字信号处理算法；实验实现了100-Gb/s Hexagonal-16-QAM信号的产生和接收。
By virtue of its huge bandwidth, ultralow loss and low cost, fiber proved to be a preferred medium for long-haul and large-capacity communications. In pursuit of larger capacity and further reach, mitigation and compensation for signal impairment in the fiber link is the key to system upgrade.
In40G optical fiber transmission systems, PMD became one of the main factors limiting system upgrade, which was previously ignored. In the earlier laid fiber with large PMD, PMD compensation is required. In systems employing direct detection, to compensate signal impairment in electrical domain means higher cost. Optical PMD compensator should be a preferred solution to overcome PMD in a40G direct detection system. Duo to the random characteristics of PMD, feedback control structure was mainly applied for OPMDC. Researchers have to meet challenges including how to find out a batter feedback control signal, how to manipulate the compensation unit in accordance with the feedback signal and how to minimize the duration of the feedback control loop.
Step into the100G era, polarization multiplexing, various of advanced modulation formats and coherent detection have been widely used. The degradation of system performance has been caused by the chromatic dispersion, polarization crosstalk, PMD, phase noise of laser and optical fiber nonlinearity in the optical link. It was possible for signal compensation in electrical domain due to the adoption of coherent receiver. How to design efficient DSP algorithms to compensate the signal impairment became the new challenge now.
This paper concentrates on the mitigation and compensation technologies of signal impairment in high-speed optical fiber communication system. It has carried on a thorough research on these technologies used in40G,100G and beyond100G systems. Highlighted work includes:
(1) An experiment was performed in a40G optical communication system, using a combination of advanced modulation formats and OPMDC. The first domestic prototype of adaptive OPMDC has been developed. The tracking speed was45.4μs; The experiment proved that in a43Gb/s RZ-DQPSK system, the OSNR introduced by the prototype was less than0.8dB; Given1dB OSNR margin, the tolerance of first-order PMD for the system increased from17ps to45ps; It could work through10hours error free at present of DGD change, as well as rapid SOP and PSP change at a speed of85rad/s; In an experiment of1200km transmission, it could work error free through12hours
(2) A study of the technologies of high-order QAM modulation and coherent detection was made in beyond100G optical communication systems. A scheme to generate16-QAM signals only using dual-drive I-Q modulator driven by2-level signals was proposed, which could avoid the use of special structured modulator or expensive four-level scheme; A low complexity DSP algorithm for16-QAM format was put forward to compensate CD, PMD, polarization crosstalk, laser phase noise and frequency offset; Simulations was done to test the performance of the proposed solution in31different testing cases, which proved the feasibility of the solution.
(3) Hexagonal-16-QAM generating technology and the corresponding DSP algorithms in coherent receiver. A new way to generate Hexagonal-16-QAM signal was proposed. Compared to conventional square16-QAM format, hexagonal16-QAM format which have the triangular lattice leads to hexagonal closest packing on plane allows for higher energy efficiency; Training-based DSP algorithm for hexagonal-16-QAM signal was proposed; Experimental realization of a100-Gb/s Hexagonal-16-QAM signal generation and reception.
在40G系统中,偏振模色散这一原先被忽略的现象逐渐成为限制系统升级的主要因素之一,对于较早铺设的PMD系数较大的光纤链路,必须对偏振模色散进行补偿。在直接检测系统中,电域补偿成本过高,因此在40G直接检测系统中,光域偏振模色散补偿成为克服偏振模色散对系统影响的首选方案。由于偏振模色散具有随机特性,光域偏振模色散补偿主要使用反馈控制结构。采用什么作为反馈控制信号,如何根据反馈信号操控补偿单元,如何尽量减少反馈控制环的时间消耗,这些都是研究者所面临的挑战。
进入100G时代,随着偏振复用、各种高级码型调制格式和相干接收的应用,链路中的色散、偏振串扰、偏振模色散、激光器的相位噪声以及光纤非线性成为系统性能恶化的主要原因。由于采用了相干接收技术,在电域补偿光纤链路中的信号损伤成为可能。如何设计高效的数字信号处理算法来补偿信号损伤成为研究者所面临的新的挑战。
本文围绕高速光纤通信系统中信号损伤缓解与补偿技术这一主题,对40G系统、100G系统和100G以上系统中信号损伤的缓解与补偿技术进行了深入的研究。主要工作包括：
(1)40G系统中采用高级码型调制技术与光域偏振模色散补偿技术相结合的技术方案的实验研究。作为项目核心成员,参与研制国内第一台自适应光域偏振模色散补偿原型机。经过硬件设计和控制算法两方面深度优化,跟踪能力达到45.4u s；在43Gb/s RZ-DQPSK系统中,实验证明该原型机引入的光信噪比代价小于0.8dB;1dB光信噪比代价下可使系统一阶偏振模色散容忍度由17ps提高至45ps；在差分群时延跳变、信号偏振态和偏振主态分别以85rad/s的速度快速变化时达到10小时工作无误码；在1200km传输实验中,达到12小时工作无误码。
(2)100G以上系统中采用高阶QAM码型调制与相干接收的技术方案的研究。提出一种仅使用2电平信号驱动I-Q调制器产生16-QAM的方案,避免了特殊调制器的使用和昂贵的4电平方案；提出针对16-QAM码型的低复杂度的数字信号处理算法,成功实现对色散、偏振串扰、偏振模色散、激光器相位噪声和频率偏差的补偿；仿真测试了上述方案在31种不同链路环境中的性能,实验产生224-Gb/s PM-16-QAM信号,采取相干接收和离线数字信号处理,证明上述方案的可行性。
(3) Hexagonal-16-QAM产生技术以及相应的相干接收机数字信号处理算法的研究。首次提出一种Hexagonal-16-QAM信号的简单可行的产生方案,其星座点在I-Q平面上达到二维密堆积,相比传统的Square-16-QAM,在不改变符号携带比特数目的情况下达到更高的能量利用率；提出针对Hexagonal-16-QAM信号的基于训练序列的相干接收数字信号处理算法；实验实现了100-Gb/s Hexagonal-16-QAM信号的产生和接收。
By virtue of its huge bandwidth, ultralow loss and low cost, fiber proved to be a preferred medium for long-haul and large-capacity communications. In pursuit of larger capacity and further reach, mitigation and compensation for signal impairment in the fiber link is the key to system upgrade.
In40G optical fiber transmission systems, PMD became one of the main factors limiting system upgrade, which was previously ignored. In the earlier laid fiber with large PMD, PMD compensation is required. In systems employing direct detection, to compensate signal impairment in electrical domain means higher cost. Optical PMD compensator should be a preferred solution to overcome PMD in a40G direct detection system. Duo to the random characteristics of PMD, feedback control structure was mainly applied for OPMDC. Researchers have to meet challenges including how to find out a batter feedback control signal, how to manipulate the compensation unit in accordance with the feedback signal and how to minimize the duration of the feedback control loop.
Step into the100G era, polarization multiplexing, various of advanced modulation formats and coherent detection have been widely used. The degradation of system performance has been caused by the chromatic dispersion, polarization crosstalk, PMD, phase noise of laser and optical fiber nonlinearity in the optical link. It was possible for signal compensation in electrical domain due to the adoption of coherent receiver. How to design efficient DSP algorithms to compensate the signal impairment became the new challenge now.
This paper concentrates on the mitigation and compensation technologies of signal impairment in high-speed optical fiber communication system. It has carried on a thorough research on these technologies used in40G,100G and beyond100G systems. Highlighted work includes:
(1) An experiment was performed in a40G optical communication system, using a combination of advanced modulation formats and OPMDC. The first domestic prototype of adaptive OPMDC has been developed. The tracking speed was45.4μs; The experiment proved that in a43Gb/s RZ-DQPSK system, the OSNR introduced by the prototype was less than0.8dB; Given1dB OSNR margin, the tolerance of first-order PMD for the system increased from17ps to45ps; It could work through10hours error free at present of DGD change, as well as rapid SOP and PSP change at a speed of85rad/s; In an experiment of1200km transmission, it could work error free through12hours
(2) A study of the technologies of high-order QAM modulation and coherent detection was made in beyond100G optical communication systems. A scheme to generate16-QAM signals only using dual-drive I-Q modulator driven by2-level signals was proposed, which could avoid the use of special structured modulator or expensive four-level scheme; A low complexity DSP algorithm for16-QAM format was put forward to compensate CD, PMD, polarization crosstalk, laser phase noise and frequency offset; Simulations was done to test the performance of the proposed solution in31different testing cases, which proved the feasibility of the solution.
(3) Hexagonal-16-QAM generating technology and the corresponding DSP algorithms in coherent receiver. A new way to generate Hexagonal-16-QAM signal was proposed. Compared to conventional square16-QAM format, hexagonal16-QAM format which have the triangular lattice leads to hexagonal closest packing on plane allows for higher energy efficiency; Training-based DSP algorithm for hexagonal-16-QAM signal was proposed; Experimental realization of a100-Gb/s Hexagonal-16-QAM signal generation and reception.
引文
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[14]Q. Di, W. Zhang, X. Weng, et. al., "A new approach of calibrating the polarimeter module based on vector projection algorithm," Acta Optica Sinica, vol.30, no. suppl., Dec.2010.
[1]Essiambre, R.; Kramer, G.; Winzer, P.J.; et.al., "Capacity Limits of Optical Fiber Networks," Journal of Lightwave Technology, vol.28, no.4, pp.662-701, 2010.
[2]Tandra, R.; Sahai, A, "SNR Walls for Signal Detection," IEEE Journal of Selected Topics in Signal Processing, vol.2, no.1, pp.4-17,2008.
[3]Fludger, C.R.S.; Duthel, T.; van den Borne, Dirk; et.al., "Coherent Equalization and POLMUX-RZ-DQPSK for Robust 100-GE Transmission," Journal of Lightwave Technology, vol.26, no.1, pp.64-72,2008.
[4]Jansen, S.L.; Morita, I.; Schenk, T.C.W.; et.al., "Coherent Optical 25.8-Gb/s OFDM Transmission Over 4160-km SSMF," Journal of Lightwave Technology, vol.26, no.1, pp.6-15,2008.
[5]Pfau, T.; Hoffmann, S.; Noe, R., "Hardware-Efficient Coherent Digital Receiver Concept With Feedforward Carrier Recovery for M-QAM Constellations," Journal of Lightwave Technology, vol.27, no.8, pp.9898-999,2009.
[6]Winzer, P.J.; Gnauck, A.H.; Doerr, C.R.; et.al., "Spectrally Efficient Long-Haul Optical Networking Using 112-Gb/s Polarization-Multiplexed 16-QAM," Journal of Lightwave Technology, vol.28, no.4, pp.547-556,2010.
[7]oberts, K.; O'Sullivan, M.; Kuang-Tsan Wu; et.al., "Performance of Dual-Polarization QPSK for Optical Transport Systems,"Journal of Lightwave Technology, vol.27, no.16, pp.3546-3559,2009.
[8]Kuschnerov, Maxim; Hauske, F.N.; Piyawanno, K.; et.al., "DSP for Coherent Single-Carrier Receivers," Journal of Lightwave Technology, vol.27, no.16, pp. 3614-3622,2009.
[9]Jin-Jun Xiao; Shuguang Cui; Zhi-Quan Luo; et.al., "Linear Coherent Decentralized Estimation," IEEE Transactions on Signal Processing, vol.56, no. 2, pp.757-770,2008.
[10]Renaudier, J.; Charlet, Gabriel; Salsi, Massimiliano; et.al., "Linear Fiber Impairments Mitigation of 40-Gbit/s Polarization-Multiplexed QPSK by Digital Processing in a Coherent Receiver," Journal of Lightwave Technology, vol.26, no. 1, pp.36-42,2008.
[11]Sano, Akihide; Yamada, E.; Masuda, Hiroji; et.al., "No-Guard-Interval Coherent Optical OFDM for 100-Gb/s Long-Haul WDM Transmission," Journal of Lightwave Technology, vol.27, no.16, pp.3705-3713,2009.
[12]Bosco, G.; Carena, A.; Curri, V.; et.al., "Performance Limits of Nyquist-WDM and CO-OFDM in High-Speed PM-QPSK Systems," Photonics Technology Letters, vol.22, no.15, pp.1129-1131,2010.
[13]Fatadin, I.; Ives, D.; Savory, S.J., "Blind Equalization and Carrier Phase Recovery in a 16-QAM Optical Coherent System," Journal of Lightwave Technology, vol.27, no.15, pp.3042-3049,2009.
[14]Agrell, E.; Karlsson, M., "Power-Efficient Modulation Formats in Coherent Transmission Systems," Journal of Lightwave Technology, vol.27, no.22, pp. 5115-5126,2009.
[15]Savory, S.J., "Digital Coherent Optical Receivers:Algorithms and Subsystems," IEEE Journal of Selected Topics in Quantum Electronics, vol.16, no.5, pp.1164-1179,2010.
[16]Fatadin, I.; Savory, S.J.; Ives, D., "Compensation of Quadrature Imbalance in an Optical QPSK Coherent Receiver," Photonics Technology Letters, vol.20, no. 20, pp.1733-1735,2008.
[17]Ip, E.M.; Kahn, J.M., "Fiber Impairment Compensation Using Coherent Detection and Digital Signal Processing," Journal of Lightwave Technology, vol. 28, no.4, pp.502-519,2010.
[18]Taylor, M.G., "Phase Estimation Methods for Optical Coherent Detection Using Digital Signal Processing," Journal of Lightwave Technology, vol.27, no.7, pp. 901-914,2009.
[19]Charlet, Gabriel; Renaudier, J.; Mardoyan, H., "Transmission of 16.4-bit/s Capacity Over 2550 km Using PDM QPSK Modulation Format and Coherent Receiver," Journal of Lightwave Technology, vol.27, no.3, pp.153-157,2009.
[20]Curri, V.; Poggiolini, P.; Carena, A.; et.al., "Dispersion Compensation and Mitigation of Nonlinear Effects in 111-Gb/s WDM Coherent PM-QPSK Systems," Photonics Technology Letters, vol.20, no.17, pp.1473-1475,2008.
[21]Bosco, G.; Curri, V.; Carena, A.; et.al., "On the Performance of Nyquist-WDM Terabit Superchannels Based on PM-BPSK, PM-QPSK, PM-8QAM or PM-16QAM Subcarriers," Journal of Lightwave Technology, vol.29, no.1, pp.53-61, 2011.
[22]Xiang Zhou; Jianjun Yu, "Multi-Level, Multi-Dimensional Coding for High-Speed and High-Spectral-Efficiency Optical Transmission," Journal of Lightwave Technology, vol.27, no.16, pp.3641-3653,2009.
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[1]P.J. Winzer, A.H. Gnauck, C.R. Doerr, et. al., "Spectrally Efficient Long-Haul Optical Networking Using 112-Gb/s Polarization-Multiplexed 16-QAM," Journal of Lightwave Technology, vol.28, no.4, pp.547-556,2010
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[1]Essiambre, R.; Kramer, G.; Winzer, P.J.; et.al., "Capacity Limits of Optical Fiber Networks," Journal of Lightwave Technology, vol.28, no.4, pp.662-701, 2010.
[2]Tandra, R.; Sahai, A, "SNR Walls for Signal Detection," IEEE Journal of Selected Topics in Signal Processing, vol.2, no.1, pp.4-17,2008.
[3]Fludger, C.R.S.; Duthel, T.; van den Borne, Dirk; et.al., "Coherent Equalization and POLMUX-RZ-DQPSK for Robust 100-GE Transmission," Journal of Lightwave Technology, vol.26, no.1, pp.64-72,2008.
[4]Jansen, S.L.; Morita, I.; Schenk, T.C.W.; et.al., "Coherent Optical 25.8-Gb/s OFDM Transmission Over 4160-km SSMF," Journal of Lightwave Technology, vol.26, no.1, pp.6-15,2008.
[5]Pfau, T.; Hoffmann, S.; Noe, R., "Hardware-Efficient Coherent Digital Receiver Concept With Feedforward Carrier Recovery for M-QAM Constellations," Journal of Lightwave Technology, vol.27, no.8, pp.9898-999,2009.
[6]Winzer, P.J.; Gnauck, A.H.; Doerr, C.R.; et.al., "Spectrally Efficient Long-Haul Optical Networking Using 112-Gb/s Polarization-Multiplexed 16-QAM," Journal of Lightwave Technology, vol.28, no.4, pp.547-556,2010.
[7]oberts, K.; O'Sullivan, M.; Kuang-Tsan Wu; et.al., "Performance of Dual-Polarization QPSK for Optical Transport Systems,"Journal of Lightwave Technology, vol.27, no.16, pp.3546-3559,2009.
[8]Kuschnerov, Maxim; Hauske, F.N.; Piyawanno, K.; et.al., "DSP for Coherent Single-Carrier Receivers," Journal of Lightwave Technology, vol.27, no.16, pp. 3614-3622,2009.
[9]Jin-Jun Xiao; Shuguang Cui; Zhi-Quan Luo; et.al., "Linear Coherent Decentralized Estimation," IEEE Transactions on Signal Processing, vol.56, no. 2, pp.757-770,2008.
[10]Renaudier, J.; Charlet, Gabriel; Salsi, Massimiliano; et.al., "Linear Fiber Impairments Mitigation of 40-Gbit/s Polarization-Multiplexed QPSK by Digital Processing in a Coherent Receiver," Journal of Lightwave Technology, vol.26, no. 1, pp.36-42,2008.
[11]Sano, Akihide; Yamada, E.; Masuda, Hiroji; et.al., "No-Guard-Interval Coherent Optical OFDM for 100-Gb/s Long-Haul WDM Transmission," Journal of Lightwave Technology, vol.27, no.16, pp.3705-3713,2009.
[12]Bosco, G.; Carena, A.; Curri, V.; et.al., "Performance Limits of Nyquist-WDM and CO-OFDM in High-Speed PM-QPSK Systems," Photonics Technology Letters, vol.22, no.15, pp.1129-1131,2010.
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