A Very Simple Algorithm of Sequential IQ Imbalance and Carrier Frequency Offset Compensation in Coherent Optical OFDM

In this work, a hardware efficient algorithm for sequential in-phase (I) and quadrature (Q) imbalance (IQ imbalance) and carrier frequency offset (CFO) compensation under chromatic dispersion (CD) and phase noise (PN) environment is proposed. Two identical orthogonal frequency division multiplexing (OFDM) symbols, which are namely training sequences (TSs), are used to acquire CFO and IQ imbalance coefficients. The CFO is obtained by calculating phase differences between the two TSs. To achieve the image frequency interference factors which are caused by an IQ imbalance effect, each symbol of the TS is modulated on only a half of all the subcarriers while the remaining subcarriers are modulated with zeros. By doing this, the IQ imbalance coefficients are directly estimated without recursive calculation requirements. This brings a low complexity to implementation in hardware. The performances of the modeling system are evaluated by a numerical simulation method where the error vector magnitude (EVM), the bit error ratio (BER), and the mean square error (MSE) quantities are used as performance indicators. The numerical simulation results are showed that the performance of the modeling system is enormously improved even when highly dispersive channels and phase noise are considered.