|Joint OSNR and frequency offset estimation using signal spectrum correlations
|Lu, Chao (EIE)
|Optical fiber communication
Network performance (Telecommunication)
Hong Kong Polytechnic University -- Dissertations
|Department of Electronic and Information Engineering
|60 pages : color illustrations
|With the development of Internet technology, the demand of human society for network capacity increases rapidly. As the main medium of information transmission, optical fiber communication system will develop towards high speed, large capacity and dynamic reconfigurable direction in order to meet the demand of ever-increasing information transmission capacity requirement. In order to ensure reliable information transmission in optical fiber communication system, optical performance monitoring is essential. Optical signal-noise ratio (OSNR) is one of the key optical performance monitoring parameters, which directly affects the bit error rate of the system. Significant amount of research has been carried out on OSNR monitoring techniques. Traditional OSNR monitoring adopts the out-of-band linear interpolation technique to estimate the level of in-band noise through the level of out-of-band noise. With the development of optical fiber communication system, there is a need to increase the efficiency of optical spectrum utilization, and the wavelength channel spacing is reduced as a result. This makes the linear interpolation technique ineffective, and new OSNR monitoring technique has to be developed towards in-band monitoring. With the advent of coherent receiver with digital signal processing, new OSNR monitoring techniques have been proposed, which greatly reduces the cost and error of OSNR monitoring. OSNR monitoring scheme based completely on digital signal processing (DSP) algorithm in coherent detection system has the disadvantages of modulation format dependence and high computation complexity. Moreover, noise generated by DSP algorithm may affect the accuracy of the monitoring results. At the same time, the emerging machine learning based schemes are very sensitive to system configuration and have high requirements on the quantity and quality of training sets, which are difficult to be used in practice.
We propose an efficient and modulation format transparent scheme to jointly estimate OSNR and frequency offset (FO) by using signal spectral correlation of coherent optical fiber communication systems. Based on spectrum correlation analysis, rough FO estimation (FOE) and corresponding compensation can be performed after dispersion compensation (CDC). Then, OSNR can be accurately monitored without performance degradation due to FO effects. Meanwhile, in the elaborate FOE phase, down-sampling processing could be used on signals to reduce the complexity of a fast Fourier transform-based FOE (FFT-FOE) without losing the FOE resolution. The simulation results show that when OSNR is in the range of 10 dB to 30 dB, the absolute OSNR estimation error of the scheme is less than 0.18 dB. Finally, we used 28 Gbaud dual polarization (DP) -4/16/32 quadrature amplitude modulation (QAM) format and absolute OSNR estimation error to show experimentally that the proposed scheme can achieve noise estimation error lower than 0.66 dB in the range of 15 dB to 30 dB for back to back (B2B) transmission link.
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