Novel Training Symbol Structure for Transmitter IQ Mismatch Estimation for PDM Coherent Optical OFDM System

In this paper, two novel training symbol structures are proposed to mitigate transmitter IQ mismatch and channel distortion for polarization division multiplexed (PDM) coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. Accordingly, two corresponding estimation methods are proposed. Compared with the conventional estimation approach, the advantage of the first method is that IQ mismatch and channel distortion are estimated independently, and the benefit of the second method is that the overhead of training symbols is reduced. The theoretical analysis is validated by numerical Monte Carlo simulations of PDM CO-OFDM system. Under the simulation conditions: the phase mismatch 15°, the amplitude mismatch 3 dB, the transmission bit rate 100 Gb/s, the standard signal-mode fiber link 480 km, and bit error rate 1e-3, 24 dB optical signal-to-noise ratio (OSNR) is necessary for the first method, and 28 dB OSNR for the second one.