Research On Algorithm Of Chromatic Dispersion Estimation In Digital Coherent Optical Receiver

In the high speed coherent optical communication system, the optical pulses transmit through optical fiber link, the accumulated CD in the channel makes the neighboring symbols with severe intersymbol interference(ISI), as a result of its influence, the transmission capacity and distance of the fiber is limited. Therefore, it is necessary to estimate and compensate the CD at the receiving end of the DSP module, offset ISI introduced by CD. The main function of the digital coherent optical receiver is to obtain amplitude and phase information from the received sampling signals, and use the information by means of linear digital filter to search and compensate the CD in the channel. Generally speaking, we regard the stand or fall of the CD compensation as the crucial first step to the receiver, because accurate CD compensation is vital in order to relax the conditions for the subsequent equalization of polarization effects and to guarantee reliable frequency offset estimation and compensation. In this paper, we take advantage of the 112Gb/s PDM-QPSK coherent optical transmission system to further study the commonly used CD search and compensation algorithm.Only by use of small search step size and accurate ADC sampling phase from conventional CD searching algorithm, the purpose is to guarantee obtaining correct searching value so that restore original optical fiber channel model, in order to solve these problems, it needs more groups of frequency domain CD compensation functions to implement the search for the CD scope in the process of realization, as a consequence of this, it is a waste of resources on the hardware implementation. This paper provides a CD searching method based on training sequence with modified shift parameters and waveforms. The modified CD searching method not only allows a much larger search step size but also can achieve fast CD estimation with low computational cost. The performance of the modified CD searching method is also insensitive to ADC sampling phase. Based on simulation results, a very low search error probability is confirmed with only few signal blocks. Together with an adaptive TDE for residual dispersion compensation, the digital coherent receivers with the modified dispersion search method can achieve fast initialization and good performance for optical burst coherent receivers in elastic optical networks with sub-wavelength granularity in optical bursts.Modulation mode identification is a significant part in the field of the communication signal analysis, and has been widely implemented in the study of electronic countermeasures and electronic reconnaissance. The subtractive clustering, related calculation and maximum frequency domain identification algorithms are in common use to identify the chosen QAM signals, however, while there are a large number of CD accumulation in the channel link, modulation mode identification algorithms mentioned above will lose the role of identification because of the influence of the CD effect. Therefore, the modified CD searching algorithm has the ability to compensate most of the CD, at the same time, alleviate the impact of the CD on the modulation mode identification, ruling out the correct modulation mode and matching the subsequent DSP in the coherent receiver.