Modulation format identification enabled by the digital frequency-offset loading technique for hitless coherent transceiver

Conventional fast Fourier transform based frequency offset estimation (FFT-FOE) algorithm is suitable for QPSK and 8/16/64QAM signals. However, due to the nonrectangular distribution of constellation points, the conventional FFT-FOE is not suitable for 32-QAM signal. In this paper, we report a factor γ which can indicate whether the FFT-FOE algorithm can be used for frequency offset estimation for different modulation formats. The FFT-FOE algorithm is hard to apply for frequency offset estimation if the value of γ is low. Fortunately, the value of γ can be increased by digital amplification and phase rotation. Based on the digital amplification and phase rotation, a modified FFT-FOE algorithm is proposed and can realize the frequency offset estimation of 32-QAM signal with only 512 symbols. The bit error ratio (BER) of a 28 Gbaud 32-QAM signal is lower than the soft-decision forward-error correction (SD-FEC) limit with the optical signal-to-noise ratio (OSNR) of 22 dB. The proposed method has better robustness to phase noise. If BER at SD-FEC limit is considered for 28Gbaud 32-QAM signal, the required OSNR is relaxed by 2 dB when the laser linewidth is greater than 5 MHz. This will make sense when the wide-linewidth laser is used in short reach optical communication system. The experimental results from 10 Gbaud 32-QAM system with 300 km fiber transmission indicate that the proposed method can be applied when OSNR is greater than 14 dB. The results demonstrate that the proposed frequency offset estimation scheme is also suitable for QPSK and 8/16/64QAM signals. Thus, the proposed algorithm can perform blind frequency offset estimation for a coherent transceiver.

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“…In refs. [13], [15], conventional FFT-FOE can be used for frequency offset estimation for QPSK and 8/16/64QAM signals with 512 symbols. Fig.…”

Section: Simulation Resultsmentioning

confidence: 99%

“…In refs. [13], [15], the FFT size is chosen as 512 for QPSK and 8/16/64QAM signals using conventional FFT-FOE. However, due to the non-rectangular distribution of constellation points, the conventional FFT-FOE cannot be applied to the 32-QAM signal with 512 symbols unless there are huge number of symbols.…”

Section: Introductionmentioning

confidence: 99%

Blind Frequency Offset Estimation Based on Phase Rotation For Coherent Transceiver

et al. 2020

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“…1. chromatic dispersion (CD) equalization, timing recovery and constant modulus algorithm (CMA) are modulation format independent and we can use the fast Fourier transform (FFT) based frequency-offset estimation [16]- [19] to obtain frequency-offset for most commonly-used modulation formats. In ref.…”

Section: Principle Of Proposed Mfimentioning

confidence: 99%

“…In [15], a MFI method using nonlinear power transformation was reported. The digital frequency-offset loading technique at the transmitter side was reported in [16]. MFI is also performed based on iterative partition schemes and calculating the peak to average power ratio of the corresponding spectra [17].…”

Section: Introductionmentioning

confidence: 99%

Blind Modulation Format Identification Using the DC Component

2019

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We propose a blind modulation format identification (MFI) method based on direct-current (DC) component for coherent receivers. The DC value is affected by the distributions of received signal's modulated phase and amplitude. A monitoring factor R is defined as the ratio of DC value with and without phase rotation of a partial received signal. Simulation and experimental results for three commonly used modulation formats QPSK, 16-QAM, and 64-QAM demonstrate that the proposed MFI method can perform an identification with lower optical signal-to-noise ratio values than 7% forward error correction thresholds. The proposed MFI method needs no extensive training process and can tolerate the phase noise and fiber nonlinearity.

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“…However, it will sacrifice the spectral efficiency because of the inserted pilot sequence. 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.…”

Section: Introductionmentioning

confidence: 99%

Joint Modulation Format Identification and Frequency Offset Estimation Based on Superimposed LFM Signal and FrFT

Yang

Wang

et al. 2019

IEEE Photonics J.

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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.

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Modulation format identification enabled by the digital frequency-offset loading technique for hitless coherent transceiver

Cited by 38 publications

References 19 publications

Blind Frequency Offset Estimation Based on Phase Rotation For Coherent Transceiver

Blind Frequency Offset Estimation Based on Phase Rotation For Coherent Transceiver

Blind Modulation Format Identification Using the DC Component

Joint Modulation Format Identification and Frequency Offset Estimation Based on Superimposed LFM Signal and FrFT

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