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相干接收原理及补偿算法

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相干接收原理及补偿算法. 演讲人:赵源 北京邮电大学 Open Internet Laboratory. Outline. 相干接收原理 DSP 结构 色散( CD )补偿 Phase offset recovery PMD compensation. Outline. 相干接收原理 DSP 结构 色散( CD )补偿 Phase offset recovery PMD compensation. 相干接收原理 -1. MZM 输出的光信号是单偏振的,容易进行偏振复用 E x , E y 是 x,y 偏振态上的光电场(光信号)

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slide1

相干接收原理及补偿算法

演讲人:赵源

北京邮电大学

Open Internet Laboratory

outline
Outline
  • 相干接收原理
  • DSP结构
  • 色散(CD)补偿
  • Phase offset recovery
  • PMD compensation
outline1
Outline
  • 相干接收原理
  • DSP结构
  • 色散(CD)补偿
  • Phase offset recovery
  • PMD compensation
slide4
相干接收原理-1
  • MZM输出的光信号是单偏振的,容易进行偏振复用
  • Ex , Ey是x,y偏振态上的光电场(光信号)
  • PDM-QPSK,在x,y两个偏振方向上分别对I,Q路进行调制,运用全部自由度
  • Ix = Re{Ex}, Qx = Im{Ex}, Iy = Re{Ey}, Qy = Im{Ey},
slide5
相干接收原理-2
  • 在传输过程中,信号受到CD,PMD,NL等因素影响,接收端PBS对不准信号偏振态,偏振态互相耦合,接收端Ex , Ey Ex’, Ey’
  • 相干接收,一般用零差接收机(homodyne receiver), fLO = fcarrier,
  • 两个90°混频器(optical hybrid)分别接收Ex’, Ey’两个偏振态上的信号, 得到Ix’ = Re{Ex’}, Qx’ = Im{Ex’}, Iy’ = Re{Ey’}, Qy’ = Im{Ey’}
  • Ix’ ,Qx’ ,Iy’ ,Qy’ 经过2sample/symbol的ADC抽样变成数字信号,经过DSP电路处理,希望得到Ix, Qx, Iy, Qy即发送的信息。
outline2
Outline
  • 相干接收原理
  • DSP结构
  • 色散(CD)补偿
  • Phase offset recovery
  • PMD compensation
dsp 1
DSP结构图-1
  • 一般情况:先补偿色散,再补偿PMD,然后carrier recovery
  • 判决结果可以反馈给蝶形滤波器和carrier recovery module来更新滤波器权值
dsp 2
DSP结构图-2
  • 图中,xin = Ex’ , yin = Ey’ , i1, i2, i3, i4 分别是Ix’ ,Qx’ ,Iy’ ,Qy’
  • 色散补偿模块,使用慢变的数字滤波器
  • 蝶形自适应滤波器,用于polarization recovery and de-multiplexing, polarization mode dispersion (PMD) compensation as well as residual CD compensation.
outline3
Outline
  • 相干接收原理
  • DSP结构
  • 色散(CD)补偿
  • Phase offset recovery
  • PMD compensation
slide10
色散补偿
  • CD是线性效应,光纤信道的传递函数为:
  • :色散参数,
  • L:光纤长度
  • 可以在频域色散均衡(frequency domain dispersion equalization, FDE)也可以在时域色散均衡(time domain dispersion equalization, FDE)
outline4
Outline
  • 相干接收原理
  • DSP结构
  • 色散(CD)补偿
  • Phase offset recovery
  • PMD compensation
phase offset recovery 1
Phase offset recovery-1
  • Phase offset后果:

没有phase offset时的星座点位置

有phase offset后星座点位置

phase offset.

Phase offset使得星座图旋转一个角度

pmd 1
PMD补偿-1
  • 蝶形自适应滤波器,用于polarization recovery and de-multiplexing, polarization mode dispersion (PMD) compensation as well as residual CD compensation. 权值的更新算法可以是CMA,DD-LMS
  • 优化FIR滤波器的权值:

hxx, hxy, hyx, hyy,

  • 我理解:自适应滤波是

一种最优化算法,

最小化某几个目标函数

pmd constant modulus algorithm cma 1
PMD补偿-Constant Modulus Algorithm (CMA)算法-1
  • 最小化:
  • 最小化时满足:
  • 用随机梯度算法,用如下方法改变权值
pmd constant modulus algorithm cma 2
PMD补偿-Constant Modulus Algorithm (CMA)算法-2
  • 当达到最小化时,
  • 星座图落在单位圆上
  • 之后用phase offset recovery可以把落在单位圆上的星座点移到正确的点上
  • 蝶形自适应滤波器,用于polarization recovery and de-multiplexing, polarization mode dispersion (PMD) compensation as well as residual CD compensation.
  • CMA的最主要作用是使解耦合,对准发射的Ex,Ey偏振态。
pmd dd lms
PMD补偿- DD-LMS算法
  • 一旦CMA算法收敛,眼图睁开,均衡器可以进入decision directed mode,用decision directed least mean squared (DD-LMS) 算法:
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