Novel Training Symbol Structure for Transmitter IQ Mismatch Compensation for Coherent Optical OFDM

The conventional compensation methods exist estimation error because of the sequential estimation process using pilot or training symbols for transmitter in-phase and quadrature (Tx IQ) mismatch in a coherent optical orthogonal frequency division multiplexing system. In this letter, a novel training symbol structure is proposed to overcome the performance degradation in conventional methods. The proposed scheme is composed of two adjacent training symbols. Each training symbol has three subsets: 1) the zero-value subset; 2) its mirror image position subset; and 3) other nonzero-value subset. Then, two estimation processes about channel distortion and Tx IQ mismatch factor are independent. The advantages of the proposed structure are displayed via channel mean square error (MSE) simulation and IQ mismatch factor MSE simulation, and the improvement of bit error rate is shown in simulations simultaneously.