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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

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

• 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。
Outline
• 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.
Outline
• 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)
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后果：

phase offset.

Phase offset使得星座图旋转一个角度

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

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：