Hardware Impairments Monitoring Technology Of Optical Communication System Transmitter

Facing the continuous growth of Internet traffic driven by Internet applications such as cloud computing,coherent optical communication systems use ultra-high baud rate and high-order modulation format signals to effectively improve spectrum efficiency,supporting the demand for massive information transmission.At the same time,the optical signal is more sensitive to transmitter hardware impairments,and it is urgent to carry out research on hardware impairments monitoring and analysis technology.This thesis focuses on major hardware impairments such as signal in-phase/quadrature(IQ)component imbalance and time skew in optical communication systems,and focuses on a joint wide-range estimation scheme.And the estimation performance of the proposed scheme is verified through simulations.The thesis first focuses on the hardware impairments.The mechanism and process of IQ amplitude,phase imbalance and time skew impairments in optical transmitters and optical receivers are described in detail,and establishes a system model under multiple impairments.The thesis then analyzed a multi-impairments joint estimation method based on the Decision Direct Least Mean Square(DDLMS)algorithm for the IQ amplitude,phase imbalance and IQ time skew of the transmitter,then the thesis validated and analysised the algorithm performance.The algorithm uses standard constellation points as the criterion to make a decision,which reduced the decision error.At the same time,the transmission matrix of the signal in the transmitter can be obtained from the tap coefficients of the finite-length impulse response filter in the algorithm.By calculating the transmission matrix,each impairment in the transmitter can be obtained analytically.The results show that when there are IQ amplitude,phase imbalance and IQ time skew in the transmitter at the same time,the estimation method based on DDLMS can achieve the joint estimation of the three impairments with a small error cost.Further results show that when the optical signal-to-noise ratio is low,the frequency offset damage is large,and the laser linewidth is large,they will not significantly affect the accuracy of the error estimation.For the problems of narrow estimation range of IQ imbalance in the transmitter side,failure analysis was performed for the polarization de-multiplexing algorithm and carrier phase recovery algorithm when the imbalance impairments is too large.Proposed a new DSP scheme,realized the joint wide-range transmitter side IQ imbalance and IQ time skew estimation.In this scheme,polarization multiplexing and carrier phase recovery are realized respectively by using the independent component analysis based on maximum likelihood algorithm and the cascade DDLMS algorithm,and the transmitter impairments is estimated analytically from the tap coefficient of the DDLMS algorithm.Thanks to IQ damage insensitive polarization de-multiplexing and carrier phase recovery algorithm,the scheme achieves a wide range of impairments monitoring.The simulation results show that compared with the conventional DSP scheme,the estimation range of amplitude and phase imbalance of the transmitter in the proposed scheme is improved by about 100% and 33%,respectivelyIn the end of this thesis,for the problems of impairment estimation of time skew between the polarizations,a new estimation method based on multi-input and multi-output filters is proposed and its algorithm performance is analyzed.At the same time,combined with the possible impairment in the transmission channel,a digital signal processing algorithm scheme is proposed.When there are Polarization Mode Dispersion(PMD)and Chromatic Dispersion(CD)in the system,the scheme still can accurately estimate the time skew between polarizations at the transmitter.The simulation results show that the proposed joint estimation scheme for time skew between polarization and IQ imbalance works well in optical communication systems which affected by first-order PMD and CD.The technical solutions and performance analysis results proposed in the thesis have good application value for studying the monitoring of IQ imbalance and time skew in optical communication systems.The proposed multi-impairment joint estimation method in the optical communication system expands the estimation range of the transmitter IQ imbalance by improving the polarization de-multiplexing and carrier phase recovery algorithm.In addition,a joint estimation scheme for time skew beteew polarizations and transmitter IQ imbalance which influenced by PMD and CD is also discussed.The discussion of the monitoring mechanism and estimation scheme which under the coexistence of multiple impairments has obvious application value for the performance monitoring of transmitter,and it supports ultra-high baud rate and high-order optical modulation format systems.