Research On IQ Imbalance Monitoring And Compensation Technology Based On Digital Signal Processing Of Coherent Receiver

With the continuous emergence of new network services and the rapid increase in the number of terminal users,the demand for network traffic is increasing day by day.As the main carrier of Internet traffic,the optical fiber backbone network has been faced the challenges of huge traffic demand and will surely promote the future optical fiber backbone network to ultra-large capacity,ultra-high speed and ultra-long distance.Coherent detection technology can greatly improve the receiving performance of the system,due to its advantages such as high-sensitivity reception and long repeaterless transmission distance.It has received widely attention from researchers in optical communications.However,various signal damages in the transmission process will seriously affect the system performance,making it need to take algorithms to estimate and recover the damaged signals on receiver digital signal processing(DSP)module before demodulating and judging the received signals.Aiming at the problem of in-phase quadrature(IQ)imbalance damages in single-carrier digital coherent optical communication systems,this dissertation studies the monitoring and compensation performance of commonly-used gram-schmidt orthogonalization procedure(GSOP)algorithm and constant module algorithm(CMA)-based adaptive channel equalization algorithm on the three types of IQ imbalances(IQ gain mismatched,IQ phase imbalance and IQ skew)between transmitter and coherent receiver.The research results include:(1)Based on a back-to-back PDM-QPSK coherent communication transmission system,the separation effect of different frequency offsets is verified.The simulation shows the frequency offset of 5 MHz can be employed to separately monitor and compensate the IQ imbalances from transceiver.(2)The effectiveness of GSOP algorithm and CMA-based adaptive channel equalization algorithm in monitoring and compensating for three types of IQ imbalances at the transceiver side respectively is compared.Compared with the receiver,the monitoring accuracy of IQ gain mismatched at the transmitter is reduced by about 0.5 dB,the monitoring accuracy of phase imbalance is reduced by about 0.3° and the monitoring accuracy of skew is reduced by about 0.2 ps.The overall system signal-to-noise ratio recovery can reach more than 17 dB.(3)The effect on the monitoring effectiveness of the above algorithms are compared when three types of IQ imbalances exist on the same side at the same time.The skew interference at the receiver side causes the phase imbalance monitoring accuracy to decrease by nearly 0.2°,the same phase imbalance interference causes the skew monitoring accuracy to decrease by nearly 0.2 ps.The gain mismatched and phase imbalance at the transmitter side affect each other,the overall accuracy of gain mismatched monitoring decreases by about 0.1 dB.The overall accuracy of phase imbalance monitoring decreases by about 0.5°.The impact on the monitoring effectiveness of the above algorithms are compared when three IQ imbalances exist simultaneously on different sides.The overall skew monitoring accuracy at the receiver side degrades by about 0.5 ps under the phase and skew impairment interference at the transmitter side.The impairment interferences are negligible in all other cases.