Abstract
We propose a novel technique for joint modulation format identification and frequency offset (FO) estimation. The linear frequency modulation signal which is obtained by a direct current signal and Fractional Fourier Transform (FrFT) is superimposed on the data symbols to mark and identify the modulation formats. Simulation results demonstrate our method can identify the DPBPSK, DPQPSK, DP8PSK, DP16QAM, DP32QAM and DP64QAM modulation formats correctly before chromatic dispersion compensation even the optical signal to noise ratio is extremely low. Additionally, due to the excellent time and frequency analysis properties of FrFT, the FO estimation range is greatly extended compared with the traditional Viterbi-Viterbi method.
Highlights
The emergence of novel data services such as 5G and internet of things brings great challenge to the current optical network
The optical signal is amplified by an erbium-doped fiber amplifier (EDFA) and transmitted over a fiber recirculating loop comprising of a 100 km span of standard single-mode fiber (SSMF) and an inline EDFA which is used to compensate the loss of SSMF
The time offset (TO) is set in the Delay module by changing the value of delay time and the frequency offset (FO) is set by changing the central frequency of the laser in coherent receiver
Summary
The emergence of novel data services such as 5G and internet of things brings great challenge to the current optical network. MFI can be achieved in Stokes space [5]–[9], which can monitor the modulation formats accurately in both quadrature amplitude modulation (QAM) systems and PSK systems This technique may be a little bit complex and it is vulnerable to the amplified spontaneous emission (ASE) noise. The MFI method based on the sub-carrier pilot was proposed in [13] It is valid even for the more complex modulation formats such as time hybrid QAM and multi-dimensional formats. Another MFI method enabled by digital frequency offset (FO) loading technique was demonstrated in [14] It can support more complex modulation formats without spectral efficiency reduction. All these MFI methods mentioned above must be conducted after the chromatic dispersion (CD) compensation or constant modulus algorithm (CMA) equalization. The FO estimation range is approximately extended to [−R s/2, +R s/2] (R s means the symbol rate) in theory and the absolute value of estimation error is less than 2 MHz when the FO is in the range of [−5 GHz, 5 GHz]
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