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# 相干接收原理及补偿算法 - PowerPoint PPT Presentation

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### 相干接收原理及补偿算法

Open Internet Laboratory

• 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

• DSP结构

• 色散（CD）补偿

• Phase offset recovery

• PMD compensation

• 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},

• 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。

• 相干接收原理

• DSP结构

• 色散（CD）补偿

• Phase offset recovery

• PMD compensation

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.

• 相干接收原理

• DSP结构

• 色散（CD）补偿

• Phase offset recovery

• PMD compensation

• 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)

• 相干接收原理

• DSP结构

• 色散（CD）补偿

• Phase offset recovery

• PMD compensation

• Phase offset后果：

phase offset.

Phase offset使得星座图旋转一个角度

Phase offset – 补偿方法：Mth power method

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：