Research On Optical Fiber Transmission Of The High Spectrum Efficiency Nyquist-SCM Signal And DSP Algorithms

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.