基于FPGA的光纤通信系统偏振模色散自适应均衡器的设计
摘要
随着光纤通信系统的扩容,偏振模色散(PMD)成为超长距离光传输系统的重要障碍。PMD电域补偿技术成本低,能够有效地消除由PMD引起的码间干扰,还能减小光纤非线性造成的影响,降低对光发射机与接收机性能的要求。现代FPGA芯片大多集成了支持高速乘累加(MAC)运算的DSP模块且I/O接口较多,可快速实现并行DSP算法。特别是一些高端芯片集成了可接收高速以太网信号的吉比特I/O,因此,可用FPGA来实现PMD电域均衡器。
本文对LE、DFE和MLSE三种均衡器的性能进行了对比,选择MLSE均衡器来均衡10Gbit/s的IM/DD系统中的PMD信号。分析了MLSE均衡器的原理、结构及光纤信道特性,用直方图估计法作为信道估计方法,将估计结果转化为分支度量,然后用维特比译码器进行译码,译码结果作为均衡器的输出。
由于光纤通信系统速率较高,为适应FPGA处理速度的要求,本文将10Gbit/s的IM/DD系统中受PMD影响的信号进行80路并行处理,即将所需的FPGA最大频率降至125MHz。并利用流水线技术将传统的MLSE均衡器改进成并行输入、并行输出的结构,以其适应并行系统的要求。MLSE均衡器在Altera(?)StratixⅡGX系列EP2SGX130GF1508C3芯片上实现,利用Modelsim软件进行仿真。仿真结果表明,所设计的均衡器性能稳定,均衡后的眼图张开高度和Q因数明显好于均衡前。
With the development of optical fiber communication systems which are large-capacity ,the polarization mode dispersion(PMD)is a big limitation for long-distance optical fiber transmission systems.The compensation technology in electrical domain can eliminate the inter-sysmbol interference caused by PMD with low-cost,and reduce the effect of the fiber non-linear,it can compensate adaptively. Modern FPGA families provide more I/O port and DSP arithmetic support with fast-carry chains that are used to implement multiply-accumulates (MACs) at high speed.So the DSP arithmetic in Parallel processing systems can be implement fastly on FPGA.Especially,some advanced chip provide the gigabit I/O which is used to receive signal of ethernet at high speed,as a result,it can be used to implement PMD electrical equalizer.
In this article,MLSE equalizer is selected for PMD compentation in 10Gbit/s IM/DD system by the comparision among LE、DFE and MLSE. Histogram method is used as the channel estimate method by the analysis of optical fiber channel characteristics and the theory,the structure of MLSE equalizer.The branch metrics transforming from the channel estimating result is used as the input of viterbi decoder.And result of the decoder can be treated as the output of the equalizer.
For the high transmission rate of optical fiber communication systems and the low processing speed of FPGA, the signal with PMD in 10Gbit/s IM/DD system is divided to 80 channels for parrallel processing in order to reduce the maximum freqence to 125MHz.Traditional MLSE equalizer is improved to the structure with parallel input and parallel output by pipelining technology for the parallel processing system. The MLSE equalizer is implemented on the chip of EP2SGX130GF1508C3 in Altera(?)StratixⅡGX family.The simulation implement by modelsim.The result shows that the equalizer is in stable performance,and the eye diagram height is obviously better than that before equalizing,as well as the Q factor.
本文对LE、DFE和MLSE三种均衡器的性能进行了对比,选择MLSE均衡器来均衡10Gbit/s的IM/DD系统中的PMD信号。分析了MLSE均衡器的原理、结构及光纤信道特性,用直方图估计法作为信道估计方法,将估计结果转化为分支度量,然后用维特比译码器进行译码,译码结果作为均衡器的输出。
由于光纤通信系统速率较高,为适应FPGA处理速度的要求,本文将10Gbit/s的IM/DD系统中受PMD影响的信号进行80路并行处理,即将所需的FPGA最大频率降至125MHz。并利用流水线技术将传统的MLSE均衡器改进成并行输入、并行输出的结构,以其适应并行系统的要求。MLSE均衡器在Altera(?)StratixⅡGX系列EP2SGX130GF1508C3芯片上实现,利用Modelsim软件进行仿真。仿真结果表明,所设计的均衡器性能稳定,均衡后的眼图张开高度和Q因数明显好于均衡前。
With the development of optical fiber communication systems which are large-capacity ,the polarization mode dispersion(PMD)is a big limitation for long-distance optical fiber transmission systems.The compensation technology in electrical domain can eliminate the inter-sysmbol interference caused by PMD with low-cost,and reduce the effect of the fiber non-linear,it can compensate adaptively. Modern FPGA families provide more I/O port and DSP arithmetic support with fast-carry chains that are used to implement multiply-accumulates (MACs) at high speed.So the DSP arithmetic in Parallel processing systems can be implement fastly on FPGA.Especially,some advanced chip provide the gigabit I/O which is used to receive signal of ethernet at high speed,as a result,it can be used to implement PMD electrical equalizer.
In this article,MLSE equalizer is selected for PMD compentation in 10Gbit/s IM/DD system by the comparision among LE、DFE and MLSE. Histogram method is used as the channel estimate method by the analysis of optical fiber channel characteristics and the theory,the structure of MLSE equalizer.The branch metrics transforming from the channel estimating result is used as the input of viterbi decoder.And result of the decoder can be treated as the output of the equalizer.
For the high transmission rate of optical fiber communication systems and the low processing speed of FPGA, the signal with PMD in 10Gbit/s IM/DD system is divided to 80 channels for parrallel processing in order to reduce the maximum freqence to 125MHz.Traditional MLSE equalizer is improved to the structure with parallel input and parallel output by pipelining technology for the parallel processing system. The MLSE equalizer is implemented on the chip of EP2SGX130GF1508C3 in Altera(?)StratixⅡGX family.The simulation implement by modelsim.The result shows that the equalizer is in stable performance,and the eye diagram height is obviously better than that before equalizing,as well as the Q factor.
引文
[1]F.P.KaPron,D.B.Keek and R.D.Maurer.Radiation losses in glass optical waveguides[J].APPI.Phys.lett., 1970,17:423- 425.
[2] I.Hayashi,M.B.panish,P.W.Foy and S.Sumski.Junction lasers which operate continuously at room temperature[J].PI.Phys.Lett., 1970,17:109-111.
[3] S.C.Rashleigh and R.Ulrich polarization mode dispersion in single mode fibers[J]. Opt.lett.,1978,3:60-62.
[4] C.J.Nielsen.Infuence of polarization mode coupling on the transmission bandwidth of single-mode fibers[J].Opt.Soc.Am.,1982,72:1142-1146.
[5] S.B.Poole,D.N.Payne,R.J.Mearsetal.Fabrication and characterization of low-1055 Optical.bers containing rareearth ions[J].Lightwave Technol.,1986,4:870-876.
[6]刘剑飞。高速光纤通信系统中的偏振模色散及其补偿技术的研究[D]。博士论文.天津大学。2002,12:12-13.
[7]朱连仓。偏振模色散相关技术[D]。硕士论文。郑州大学。2003,5:6-7.
[8] C.D.Poole , R.E.Wagner.Phenomenological approach to polarization dispersion in long single fiber[J].Electron.Lett.,1986,2219:1029-1030.
[9] S.C .Rashleigh,R .Ulrieh.Polarization mode dispersion in singl- mode fibers[J].Optics Letters,1978,vol.3,p60- 62.
[10] N.GiSin and the COST 241 Group.Definition of Porarization mode dispersion and first results of the COST 241 round- round measurements[J].Pure APPI.Optics,1995,vol.3,p511.
[11]N.Gisin,B.Hunter.Combined effects of Polarization mode dispersion and Polarization dependent losses in optical fibers[J].Optics Communieations,1997,vol.142,p119- 125.
[12] C. D. Poole,N.S.Bergano,R.E.Wagner,and H.J.Schulte.Polarization dispersion and Principal states in a 147km undersea lightwave eable[J].Journal of 1ightwave technology,1988,vol.6,No.7,p1185-1190.
[13] G. J. Foschini,C.D.Poole.Statisties theory of Polarization dispersion in single mode fibers[J].Journal of lightwave technology.1991,vol.9,No.11,p1439-1456.
[14]F.Curti,B.Daino,G.D.Macrhis,et al.Statistical treatment of the evolution of the principal states of Polarization single-mode fibers[J].Lighwtave Technol., 1990,8(8):1162-1166.
[15]Y.Namihira. J.Maeda.Comparison of various polar1zation mode dispersion measurement methods in optical fibers[J].Elecrton.Lett.,1992,28(25):2265-2266.
[16] A.Galtarossa.L.Pamlieri.Reflectometric measurements of polarization Properties in optical- fiber links[J]. IEEE transactions on instrumentation and measurement,2004,53(l):86-94
[17]N.Zou,M.Yoshida,Y.Namihira,et al.PMD measurement based on delayed self-heterodyne OFDR and experimental comparison with ITU-T round robin measurements[J].Electron.Lett.,2002,38(3):115-1166.
[18]P.Oberson , K.Julliard , N.Gisin.Interferometric polarization mode dispersion measurements with femtosecend sensitivity[J].J.Lightwave Technol.,1997.15(10):1852-1857.
[19]T.Ono,S.Yamazaki,H.Shimizu,K.Emura.Polarization Control Method for Suppressing Polarization Mode Dispersion Influence in Optical Transmission Systems[J].Journal of Lightwave Technology,1994, 12(5):891-898.
[20] T.Ono,S.Ymaazkai,H.Shimiuz,et al.Polarization control method of surpperssing polarization mode dispersion influence in optical transmission systems[J].Lighwtvae,Technol.,1994,12(5):891- 898
[21] J.H.winiesr , Z.Haas , M.A.Snatoro , et al.Optical equalization of polarization dispersion [J].Proc,SPIE,1997,1787:346-357.
[22] T.Takahashi,T.Imai,M.Aiki.Automatic compensation technique for timewise fluctuating polarization mode dispersion in in-line amplifier systems[J].Electronics Letters,1994,30(4):348-349.
[23] R.Noe,D.Sandel,M.Y.Dierolf, et al.Polarization mode dispersion compensation at 20Gbit/ s with fiber based distributed equalizer[J].Electron.Lett.,1998,34:2421-2422.
[24] S.Lee,R.Khosravani,J.Peng,V.Grubsky,et al.Adjustable Compensation of Polarization Mode Dispersion Using a High-Birefringence Nonlinearly Chirped Fiber Bragg Grating[J].IEEE Photonics Technology Letters,1999,11(10):1277~1279.
[25] M.Shtaif,A.Mecozzi,M.tur et al.A compensation for the effect of high- order polarization mode dispersion in optical fiber[J]. IEEE Photon.Technol.Lett.,2000,12:434-436.
[26] D.Schlump,B.Wedding,H.Bülow.Electronic Equalisation of PMD and Chromatic Dispersion Induced Distortion After 100 km Standard Fiber at 10 Gbit/s[J]Proc.ECOC,Madrid,Spain,1998,vol.I:535~536.
[27] A.Farbert,S.Langenbach,N.Stojanovic et.all.Performance of a 10.7Gb/s Receiver with Digital Equalizer using Maximum Likelihood Sequence Estimation[J].ECOC’2004,Proceedings PD-Th4.1.5 2004.
[28] B.W.Hakki.Polarization Mode Dispersion Compensation by Phase Diversity Detection[J].IEEE Photonics Technology Letters,1997,9(1):121~123.
[29]高育选,萧越,李循.偏振模色散对单模光纤的影响[J].半导体光电,2000,21(1):1~5.
[30] A.Eyal,Y.Li,W.K.Marshall et al.Statistical determination of the length dependence of high order polarization mode dispersion[J].Opt.Lett.,2000,25(12):875~877.
[31] Corning incorporated,LEAF? Optical Fiber Product Information Sheet[P].2003.
[32] A.Schuppen,H.Dietrich,U.Seilier,H.V.D.Ropp,U.Erben.A SiGe RF technology for mobile communication systems[J].Microw.Eng.Europe,1998:39-46.
[33] M.Nakarmura,H.Nosaka,M.Ida,K.Kurishima,M.Tokumistu.Electrical PMD equalizer ICs for a 40Gb/s transmission[J],In Techn.Dig.OFC’04,Los Angeles,Feb.22-27,TuG4,2004.
[34]B.Widrow,J.McCool,M.larimore,C.Johnson.Stationary and non-stationary learning characteristics of the LMS adaptive filter[J].Proc,IEEE,1976,64(8):1151-1162.
[35]R.W.Luck.Automatic equalization for digital communication[J].Bell Syst.Tech..J.,1965,44(4):547-558.
[36]刘娟。基于自适应算法的偏振模色散的电域补偿[D].硕士论文。河北工业大学2007.12:19-21.
[37]陈志阳。高速移动无线信道自适应MLSE均衡算法的研究与仿真[D]。硕士论文。北京交通大学,2008,6:33-34.
[38] O.E.Agazzi.Maximum-likelyhood Sequence Estimation in Dispersive Optical Channels[J].LightwaveTechonology,2005,23(2):749-763.
[39]顾畹仪。WDM超长距离光传输技术[M]。北京邮电大学出版社,2002:292-293.
[40] D. Marcuse,“Calculation of bit-error probability for a lightwave system with optical amplifiers and post-detection Gaussian noise[J]. Lightw. Technol., vol. 9, pp. 505–513, Apr. 1991.
[41] P. A. Humblet and M. Azizoglu,“On the bit error rate of lightwave systems with optical amplifiers[J]. Lightw. Technol., vol. 9, pp. 1576–1582, Nov. 1991.
[42] R. A.Kennedy, B.D.O. Anderson, and R. R. Bitmead,“Blind adaptation of decision feedback equalizers: Gross convergence properties[J]. Adapt Control Signal Process., vol. 7, pp. 497–523, 1993.
[43] E. A. Lee and D. G. Messerschmitt, Digital Communication[C], 2ded. Norwell, MA: Kluwer, 1994, p. 713.
[44] J. G. Proakis, Digital Communications[C], 3rd ed. New York: McGraw-Hill, 1995, p. 594.
[45]盛骤,谢式干,潘承毅。概率论与数理统计[M].2008,6:149-156.
[46]W.H.Tranter,K.S.Shanmugan,T.S.Rappaport,K.L.Kosbar.Principles of Communication Systems Simulation with Wireless Applications[M].Pearson Education,Inc.,2004:119-201.
[47] Uwe Meyer-Baerse.Digital Signal Processingwith Field Programmable Gate Arrays[M].NewYork:Springer-Verlag Barlin Heidaburg.2002:220-223.
[48]B.Dipert:”EDN’s First Annual PLD Directory[OL].”EDN pp.54-84(2000).Http://www.ednmag.com/ednmag/reg/2000/08172000/17cs.htm.
[49]陈新。高速光纤通信系统中色散和非线性补偿研究[D].博士论文,清华大学,2008,5:37-40.
[2] I.Hayashi,M.B.panish,P.W.Foy and S.Sumski.Junction lasers which operate continuously at room temperature[J].PI.Phys.Lett., 1970,17:109-111.
[3] S.C.Rashleigh and R.Ulrich polarization mode dispersion in single mode fibers[J]. Opt.lett.,1978,3:60-62.
[4] C.J.Nielsen.Infuence of polarization mode coupling on the transmission bandwidth of single-mode fibers[J].Opt.Soc.Am.,1982,72:1142-1146.
[5] S.B.Poole,D.N.Payne,R.J.Mearsetal.Fabrication and characterization of low-1055 Optical.bers containing rareearth ions[J].Lightwave Technol.,1986,4:870-876.
[6]刘剑飞。高速光纤通信系统中的偏振模色散及其补偿技术的研究[D]。博士论文.天津大学。2002,12:12-13.
[7]朱连仓。偏振模色散相关技术[D]。硕士论文。郑州大学。2003,5:6-7.
[8] C.D.Poole , R.E.Wagner.Phenomenological approach to polarization dispersion in long single fiber[J].Electron.Lett.,1986,2219:1029-1030.
[9] S.C .Rashleigh,R .Ulrieh.Polarization mode dispersion in singl- mode fibers[J].Optics Letters,1978,vol.3,p60- 62.
[10] N.GiSin and the COST 241 Group.Definition of Porarization mode dispersion and first results of the COST 241 round- round measurements[J].Pure APPI.Optics,1995,vol.3,p511.
[11]N.Gisin,B.Hunter.Combined effects of Polarization mode dispersion and Polarization dependent losses in optical fibers[J].Optics Communieations,1997,vol.142,p119- 125.
[12] C. D. Poole,N.S.Bergano,R.E.Wagner,and H.J.Schulte.Polarization dispersion and Principal states in a 147km undersea lightwave eable[J].Journal of 1ightwave technology,1988,vol.6,No.7,p1185-1190.
[13] G. J. Foschini,C.D.Poole.Statisties theory of Polarization dispersion in single mode fibers[J].Journal of lightwave technology.1991,vol.9,No.11,p1439-1456.
[14]F.Curti,B.Daino,G.D.Macrhis,et al.Statistical treatment of the evolution of the principal states of Polarization single-mode fibers[J].Lighwtave Technol., 1990,8(8):1162-1166.
[15]Y.Namihira. J.Maeda.Comparison of various polar1zation mode dispersion measurement methods in optical fibers[J].Elecrton.Lett.,1992,28(25):2265-2266.
[16] A.Galtarossa.L.Pamlieri.Reflectometric measurements of polarization Properties in optical- fiber links[J]. IEEE transactions on instrumentation and measurement,2004,53(l):86-94
[17]N.Zou,M.Yoshida,Y.Namihira,et al.PMD measurement based on delayed self-heterodyne OFDR and experimental comparison with ITU-T round robin measurements[J].Electron.Lett.,2002,38(3):115-1166.
[18]P.Oberson , K.Julliard , N.Gisin.Interferometric polarization mode dispersion measurements with femtosecend sensitivity[J].J.Lightwave Technol.,1997.15(10):1852-1857.
[19]T.Ono,S.Yamazaki,H.Shimizu,K.Emura.Polarization Control Method for Suppressing Polarization Mode Dispersion Influence in Optical Transmission Systems[J].Journal of Lightwave Technology,1994, 12(5):891-898.
[20] T.Ono,S.Ymaazkai,H.Shimiuz,et al.Polarization control method of surpperssing polarization mode dispersion influence in optical transmission systems[J].Lighwtvae,Technol.,1994,12(5):891- 898
[21] J.H.winiesr , Z.Haas , M.A.Snatoro , et al.Optical equalization of polarization dispersion [J].Proc,SPIE,1997,1787:346-357.
[22] T.Takahashi,T.Imai,M.Aiki.Automatic compensation technique for timewise fluctuating polarization mode dispersion in in-line amplifier systems[J].Electronics Letters,1994,30(4):348-349.
[23] R.Noe,D.Sandel,M.Y.Dierolf, et al.Polarization mode dispersion compensation at 20Gbit/ s with fiber based distributed equalizer[J].Electron.Lett.,1998,34:2421-2422.
[24] S.Lee,R.Khosravani,J.Peng,V.Grubsky,et al.Adjustable Compensation of Polarization Mode Dispersion Using a High-Birefringence Nonlinearly Chirped Fiber Bragg Grating[J].IEEE Photonics Technology Letters,1999,11(10):1277~1279.
[25] M.Shtaif,A.Mecozzi,M.tur et al.A compensation for the effect of high- order polarization mode dispersion in optical fiber[J]. IEEE Photon.Technol.Lett.,2000,12:434-436.
[26] D.Schlump,B.Wedding,H.Bülow.Electronic Equalisation of PMD and Chromatic Dispersion Induced Distortion After 100 km Standard Fiber at 10 Gbit/s[J]Proc.ECOC,Madrid,Spain,1998,vol.I:535~536.
[27] A.Farbert,S.Langenbach,N.Stojanovic et.all.Performance of a 10.7Gb/s Receiver with Digital Equalizer using Maximum Likelihood Sequence Estimation[J].ECOC’2004,Proceedings PD-Th4.1.5 2004.
[28] B.W.Hakki.Polarization Mode Dispersion Compensation by Phase Diversity Detection[J].IEEE Photonics Technology Letters,1997,9(1):121~123.
[29]高育选,萧越,李循.偏振模色散对单模光纤的影响[J].半导体光电,2000,21(1):1~5.
[30] A.Eyal,Y.Li,W.K.Marshall et al.Statistical determination of the length dependence of high order polarization mode dispersion[J].Opt.Lett.,2000,25(12):875~877.
[31] Corning incorporated,LEAF? Optical Fiber Product Information Sheet[P].2003.
[32] A.Schuppen,H.Dietrich,U.Seilier,H.V.D.Ropp,U.Erben.A SiGe RF technology for mobile communication systems[J].Microw.Eng.Europe,1998:39-46.
[33] M.Nakarmura,H.Nosaka,M.Ida,K.Kurishima,M.Tokumistu.Electrical PMD equalizer ICs for a 40Gb/s transmission[J],In Techn.Dig.OFC’04,Los Angeles,Feb.22-27,TuG4,2004.
[34]B.Widrow,J.McCool,M.larimore,C.Johnson.Stationary and non-stationary learning characteristics of the LMS adaptive filter[J].Proc,IEEE,1976,64(8):1151-1162.
[35]R.W.Luck.Automatic equalization for digital communication[J].Bell Syst.Tech..J.,1965,44(4):547-558.
[36]刘娟。基于自适应算法的偏振模色散的电域补偿[D].硕士论文。河北工业大学2007.12:19-21.
[37]陈志阳。高速移动无线信道自适应MLSE均衡算法的研究与仿真[D]。硕士论文。北京交通大学,2008,6:33-34.
[38] O.E.Agazzi.Maximum-likelyhood Sequence Estimation in Dispersive Optical Channels[J].LightwaveTechonology,2005,23(2):749-763.
[39]顾畹仪。WDM超长距离光传输技术[M]。北京邮电大学出版社,2002:292-293.
[40] D. Marcuse,“Calculation of bit-error probability for a lightwave system with optical amplifiers and post-detection Gaussian noise[J]. Lightw. Technol., vol. 9, pp. 505–513, Apr. 1991.
[41] P. A. Humblet and M. Azizoglu,“On the bit error rate of lightwave systems with optical amplifiers[J]. Lightw. Technol., vol. 9, pp. 1576–1582, Nov. 1991.
[42] R. A.Kennedy, B.D.O. Anderson, and R. R. Bitmead,“Blind adaptation of decision feedback equalizers: Gross convergence properties[J]. Adapt Control Signal Process., vol. 7, pp. 497–523, 1993.
[43] E. A. Lee and D. G. Messerschmitt, Digital Communication[C], 2ded. Norwell, MA: Kluwer, 1994, p. 713.
[44] J. G. Proakis, Digital Communications[C], 3rd ed. New York: McGraw-Hill, 1995, p. 594.
[45]盛骤,谢式干,潘承毅。概率论与数理统计[M].2008,6:149-156.
[46]W.H.Tranter,K.S.Shanmugan,T.S.Rappaport,K.L.Kosbar.Principles of Communication Systems Simulation with Wireless Applications[M].Pearson Education,Inc.,2004:119-201.
[47] Uwe Meyer-Baerse.Digital Signal Processingwith Field Programmable Gate Arrays[M].NewYork:Springer-Verlag Barlin Heidaburg.2002:220-223.
[48]B.Dipert:”EDN’s First Annual PLD Directory[OL].”EDN pp.54-84(2000).Http://www.ednmag.com/ednmag/reg/2000/08172000/17cs.htm.
[49]陈新。高速光纤通信系统中色散和非线性补偿研究[D].博士论文,清华大学,2008,5:37-40.