Abstract
In this study, we propose a non-data-aided algorithm of the cycle slip self-correcting carrier phase estimation (CSSC-CPE) which mitigates the cycle slips caused by blind CPE in the coherent wireless optical communication (WOC) system. The CSSC-CPE uses the output of CPE for cumulative averaging and selects the difference $\delta $ between two cumulative average segments as the discriminant parameter. The location and direction of cycle slips are determined by identifying the position and sign of the peak value of $\delta $ . The optimal thresholds for cycle slip detection could be derived from the probability density function (PDF) of $\delta $ obtained by calculation and deduction. Finally, numerical simulations and indoor experiments are carried out. The results show that CSSC-CPE can effectively eliminate cycle slips under weak turbulence condition. Compared with relative non-data-aided cycle slip correction algorithms, the CSSC-CPE achieves a better performance in suppressing the phase noise generated by atmospheric turbulence and laser linewidth, which enhances the accuracy of the cycle slip identification and lowers the SNR requirement when the cycle slip is not allowed.
Highlights
The coherent wireless optical communication (WOC) system has been extensively studied due to its superiority to the conventional direct detection system in sensitivity and spectral efficiency [1], [2]
Phase noise is attributed to the wavefront distortion caused by atmospheric turbulence, laser linewidth, additive white Gaussian noise generated by the receivers and residual carrier frequency offset (CFO)
A 1550 nm precise tunable laser source is used at the transmitter, the wavelength tuning accuracy is 10 pm and the linewidth is less than 10 kHz
Summary
The coherent WOC system has been extensively studied due to its superiority to the conventional direct detection system in sensitivity and spectral efficiency [1], [2]. Motivated by the third method, we propose a new algorithm CSSC-CPE which can correct cycle slips without the need of either data assistance or differential encoding/decoding in this paper. It is worth noting that the short-time subtraction can reduce the slowly varying laser linewidth noise to a certain extent, and the phase noise caused by atmospheric turbulence can be better suppressed by two times average of the CPE stage and the cycle slip correction stage. THE STRUCTURE OF CSSC-CPE ALGORITHM The kth input symbol of the CSSC-CPE can be represented as r [k] = exp {i [θS [k] + θN [k]]}, where the phase noise θN [k] considers the combined influences of the laser linewidth, atmospheric turbulence and receivers. The corrected phase information rcorr [k] can be obtained by conjugate multiplication of the corrected estimate xcorr [k] and r [k]
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