光纤通信第九讲-课件.ppt

1、 Analog Transmission SystemsCHAPTER9Digital system:telecommunication,e.g.voice,dataAnalog system:microwave multi-signals,video distribution,radar signal processingnThe general operational aspects and componentsnCarriertonoise ratio,quantum noise effectnSubcarrier modulation tech.,harmonic and interm

2、odulation(IM)distortionWe will discuss the followingNoise contributors in an analog link Overview of Analog LinksCHAPTER9.1Analog modulation tech.AM,FM,PMPhotodetector with good linearnity Carrier-to-Noise ratioCHAPTER9.1CNR=Carrier powerSource+photodiode+amp+intermodulation noiseP(t)=Pt1+ms(t)m=Ppe

3、ak/Pt Carrier-to-Noise ratioCHAPTER9.1=RIN(A0P)2BRIN=/P2L=2q(Ip+ID)M2F(M)BC 0.5(mA0MP)2 N RIN(A0P)2B+2q(Ip+ID)M2F(M)B+4KBTBFt/Req=4KBTBFt/Req=Examples of RIN effects Relative Intensity NoiseCHAPTER9.2.3RIN(IB/Ith-1)-3CNR versus optical power level Limiting ConditionsCHAPTER9.2.5C 0.5(mA0MP)2 N 4KBTB

4、Ft/Req)1=(C 0.5 m2 A0PN 2qF(M)B)2=(C 0.5(mM)2 N RINB)3=(Standard FDM technique Multichannel Transmission Tech.CHAPTER9.3For example.CATV networksfrequency range:50 88MHz,120550MHzTech:amplitude-modulation-vestigial-sideband(AM-VSB)Channel bandwidth:6MHzP PI I23123.paIaIaINonlinear DeviceCHAPTER9.3Pr

5、ovided a number M of simultaneously present sinusoids lying between ,the second-order terms at frequencies appear.1=(-)+(+2121111cos(2)cos(2)cos(2)cos(2)cos(2)MiiiMMijijijMMijijijijlet IIf tII If tf tI Ifftfftf and f()ijffIn general a1 a2 a3 =It seems the second-order terms are more harmful than the

6、 third terms.If we make will lie completely outside the band 2ff ijff(,)ff.ijije gffffff two-tone third-order terms(because there are only two distinct frequencies)triple-beat(CTB)Define:Composite second order(CSO)distortion Composite triple-beat(CTB)distortionIn general CTB distortion is larger tha

7、n CSO distortion.3111cos(2)cos(2)cos(2)cos 2(),MMMijkijkijkijkijkII I If tf tf tffftfff are calledcos 2(),ijkijkfff tfff arecalled composite(),ijkijpower of the intermoudlation of fffffcarrier power(),ijkijkpower of the intermoudlation of ffffffcarrier powerlIM products on the r-th carrier for 2fi-f

8、j D1,2=1/2N-2-1/21-(-1)N(-1)rlIM products on the r-th carrier for fi+fj-fkD1,1,1=r/2(N-r+1)+1/4(N-3)2-5-1/21-(-1)N(-1)N+rTwo-tone are spread through the passband,The triple-beat be concentrated in the middle of passbandrN1234567810200301041221524442646776476910111096891214151514129The number of thir

9、d-order triple-beat IMrN1234567810200310141111521212622222273232323833333333The number of third-order two-tone IMPredicted CSO for 60 CATV channels Predicted CTB for 60 CATV channelsMultichannel FMCHAPTER9.3For AM C/N40dB,very stringent requirements on laser and receiver linearityFor FMw)ff(fB23log1

10、0)NC()NS(2vppvinout3644dBThe reduce C/N will make FM less susceptible to laser and receiverthan AMRIN versus optical modulation index Effects Of NonlinearityIntermodulation(IM,two-tone test).t)2cos(A43t)2cos(A43tcosA)A49(tcosA)A49()t(y,AALetAA43:2AA43:2.tcos)AA23A43A(tcos)AA23A43A(:,)tcosAt(cos)tcosAt(cos)tcosAtcosA()t(y,tcosAtcosA)t(xAssume12332133223112312122131221232122123323211221331311213221322212221112211Fig.9-11:Power budget vs optical modulation index4.3.2 Optical Single sideband Modulation