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高频谱利用率Nyquist-SCM信号的光纤传输及DSP算法研究
Research on Optical Fiber Transmission of the High Spectrum Efficiency Nyquist-SCM Signal and DSP Algorithms
【作者】 李丹宇；
【导师】 陈林；
【作者基本信息】 湖南大学 ， 信息与通信工程， 2015， 硕士
【摘要】 随着移动通信、数字多媒体业务飞速发展,人们对传输速率及带宽的要求越来越高,寻找超高速、超大容量的光纤通信技术势在必行。有研究显示,无论是相干光通信系统,还是强度调制/直接检测（Intensity Modulation/Direct Detection,IM/DD）系统,采用新的调制格式以及先进的数字信号处理技术都可以提高信号频带利用率,实现信号高速传输。本文围绕高频谱利用率的奈奎斯特副载波调制（Nyquist Subcarrier Modulation,Nyquist-SCM）通信系统开展研究,采用先进的数字信号处理技术来提升信号在光纤信道中的传输性能。具体创新性工作如下:第一,提出了一种适用于IM/DD短距离光纤通信系统的Nuquist-SCM调制格式,该格式具有很高的频谱利用率,并且采用盲均衡技术增加其传输距离。Nuquist-SCM调制技术结合副载波调制与Nyquist脉冲整形技术,使副载波频率为符号速率的一半,提高了频谱效率。同时采用盲均衡中的常模算法（Constant Modulus Algorit hm,CMA）进行信道估计、偏振解复用及信道均衡,提高了接收符号的准确度,降低了误码率。实验搭建了16QAM（Quadrature Amplitude Modulat ion,QAM）Nyquist-SCM IM/DD光纤通信系统,研究非偏振复用及偏振复用的16QAM副载波调制信号在不同传输距离下的传输性能。实验结果表明,48Gbit/s 16QAM的副载波调制信号在标准单模光纤中传输83km后,信号的接收光功率是-10.3dBm,对应的误码率小于7%的前向纠错（Forward Error Correction,FEC）门限值。因此,采用Nuquist-SCM调制格式能够提高频谱利用率,同时结合相应的数字信号处理技术,可以提高传输距离及传输性能。第二,在上述研究基础上,提出了基于数据辅助的信道估计及重叠的频域均衡（Overlap Frequency Domain Equalization,OFDE）算法,进一步提高Nyquist-SCM系统的频谱利用率及传输效率。实验实现了采用预均衡、基于数据辅助的信道估计及OFDE算法的64QAM Nyquist-SCM系统。与16QAM Nyquist-SCM系统相比较,64QAM Nyquist-SCM系统的频谱利用率提高了1.5倍。此外,将盲均衡算法与基于数据辅助的算法进行比较。实验结果表明,在标准单模光纤中传输43km后,当达到FEC门限值3.8?10-3时,36Gbit/s 64QAM偏振复用信号的接收光功率为-9dBm;当达到FEC门限值2.4?10-2时,偏振复用信号的接收光功率为-13dBm。实验结果验证了基于数据辅助的信道估计及OFDE算法对提高Nyquist-SCM系统的频谱利用率及传输效率具有可行性。
【Abstract】 With the rapid deve lopment of mobile communicat ion and digital multimedia services,it’s imperat ive to seek for ultra-high speed and large-capacity optical fiber communication technolo gies to satis fy the ever-increasing require ments for higher transmission rate and network bandwidt h.Studies have shown that new modulat ion for mats and advanced digitals igna l processing technolo gy can improve the signa l bandwidth effic ienc y as well as achie ve high-speed trans miss ion both in the coherent optica l communicat ion syste m and in the inte ns ity modulat ion/d irect detection（IM/DD）syste m.In this thesis,research has been done on Nyquist subcarrier modulat ion（Nyquist-SCM）communicatio n syste ms with high spectrum effic ie ncy.In these syste ms,advanced digita l signal processing techniq ues are used to improve transmiss io n performa nce.The specific innovat ive results are as fo llows:First,Nuquist-SCM wit h high spectrum e ffic iency is proposed for IM/DD short distance optica l fiber communicat ion syste m.The blind equa lizat io n techno logy is used for this system to extend the trans miss ion distance.Nuquist-SCM techno logy comb ining t he subcarrier modulat io n with Nyquist pu lse-shaping technique makes the frequenc y of subcarrier equal to ha lf of symbo l rate,and then spectrum e ffic iency is improved.At the same time,the constant modulus a lgor it hm is used for channe l estimat ion,polar izat ion demult ip lexing and channel equa lizat io n.Therefore,the accuracy of t he received symbols is increased and the bit error rate is reduced.16QAM Nyquist-SCM IM/DD optical fiber communicat ion s ystem is exper imenta lly demo nstrated in order to study the tra ns missio n perfor mance of non-polar izat ion mult ip lexing a nd po larizat ion mult ip lexing 16QAM subcarrier modulat ion s igna ls under different distances.The experimenta l results show that when 48Gbit/s 16QAM subcarrier signal has trans mitted over 83km standard single mode fiber,the received optical power is-10.3dBm and the correspond ing b it error rate is less than 7%FEC thresho ld.Therefore,spectrum effic ienc y and transmiss io n performa nce can be improved by comb ining Nuquist-SCM wit h t he correspond ing digita l s igna l process ing techno logy.Second,on the basis of the above studies,data-aided channe l estimat io n and overlap frequency doma in equa lizat io n（OFDE）are proposed to further improve the spectrum effic iency and transmiss ion effic ie ncy of Nyquist-SCM syste m.64QAM Nyquist-SCM syste m is experime ntally demonstrated using pre-equalizat ion,data-aided channe l estimat ion and OFDE algor it hm.The spectrum ut ilizat ion has been increased by 1.5 t imes compar ing to 16QAM Nyquist-SCM syste m.Meanwhile,the blind equalizat ion and data-aided algor it hm are compared.The experimenta l results show that after 43km standard single mode fiber trans miss ion,the received optica l power of 36Gb it/s 64QAM polar izatio n mult ip lexed signa l is-9dBm when FEC thresho ld is3.8′10-3,and the received optica l power is-13dBm whe n the thresho ld is2.4′10-2.The proposed data-aided channe l est imat ion and OFDE algorithm are feasib le to improve t he spectrum effic ie ncy and trans miss ion e ffic ienc y of Nyquist-SCM syste m by the experiment.