Abstract
Receiver in-phase/quadrature (IQ) imbalance caused by imperfect analog receiver front end can rapidly degrade system performance in Nyquist-subcarrier-modulation (Nyquist-SCM) direct detection scheme. These imbalances, including IQ skew, IQ gain and phase imbalance, become increasingly important when higher symbol rate, higher modulation order, and lower roll-off pulse shape are used. Here, an adaptive four real-valued widely linear equalizer in an inner two-by-two butterfly structure is used to compensate receiver IQ imbalance and channel linear distortion, which has the same computational complexity with the conventional complex-valued FIR filter. In addition, the effectiveness of adaptive equalizer is validated experimentally with offline processing through a 20-Gbps 16-QAM Nyquist-SCM signal over 40-km standard single mode fiber transmission.
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