Phase Noise Suppression Method Research Articles

Gaussian wavelet basis expansion based phase noise suppression method for coherent optical OFDM systems

In this paper, we developed a phase noise suppression method based on Gaussian wavelet basis expansion (GWBE) for coherent optical orthogonal frequency-division-multiplexing (CO-OFDM) systems. Compared with traditional phase noise suppression methods, the GWBE method significantly enhances the system’s robustness to laser phase noise, providing improved phase noise suppression, especially in scenarios with high linewidth. Additionally, the method demonstrates excellent performance in 32-QAM and 64-QAM. By employing the proposed GWBE method, the impact of laser phase noise on CO-OFDM can be effectively mitigated.

Phase drift and noise suppression method based on SEE-SGMD-PCC in a distributed acoustic sensor

The problems of laser source frequency drift (LSFD) and phase noise in distributed acoustic sensor (DAS) make it difficult to recover the true vibration phase curve, which limits its application scope in the field of seismic exploration. In order to suppress the influence of phase noise and phase drift on the phase signal and improve the signal-to-noise ratio (SNR) of the phase curve, this paper proposes a method based on symmetric extreme value expansion, symplectic geometry mode decomposition and Pearson correlation coefficient (SEE-SGMD-PCC). Firstly, the mathematical principles and processing flow of the SEE-SGMD-PCC algorithm were introduced, and the effectiveness of this method was verified through multiple sets of simulation experiments. Secondly, The DAS system implemented using digital heterodyne coherent detection technology was used as the experimental platform, and the phase drift and phase noise sources of the phase signal were analyzed in detail. Next, in single frequency and multi frequency vibration signal experiments, compared with other methods, the SNR of the phase signal is significantly improved, and the phase information is effectively restored. Finally, the feasibility of the proposed method was demonstrated through two on-site experiments. The proposal of this method further promotes the application process of DAS in complex seismic exploration environments.

Phase Noise Suppression for φ-OTDR With Optimized Minima Controlled Recursive Averaging Method

We propose a phase noise suppression method for phase-sensitive optical time-domain reflectometer ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varphi $ </tex-math></inline-formula> -OTDR) system. The signal-to-noise ratio (SNR) of the demodulated phase is improved by the optimized minima controlled recursive averaging (MCRA) method. First, the original phase waveform is divided into frames. Then, the minimum control is used to track the minimum power spectrum of phase noise with Gaussian distribution. The prior variance of noise is corrected by recursive averaging. The attenuation factor is determined by appropriate threshold parameters and the noise prior variance. Ultimately, the phase waveform is reconstructed in the time–frequency domain. In this way, the SNR of the reconstructed waveform is intensified remarkably. Experimental results show that the SNR of the demodulated phase is improved by 9.12–19.63 dB in the range of 20–1200 Hz. Furthermore, the enhancement of acoustic extracted from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varphi $ </tex-math></inline-formula> -OTDR could also be verified experimentally with the proposed approach.

Experimental demonstration of pseudo-pilots-aided Gaussian basis expansion-based phase noise suppression scheme for CO-OFDM

In this paper, we propose a novel phase noise suppression scheme called pseudo-pilots-aided Gaussian basis expansion (PS-GBE) for coherent optical orthogonal frequency division multiplexing (CO-OFDM) system. Integrating with the pseudo-pilots, the Gaussian basis can suppress and fit phase noise effectively with high spectral efficiency (SE). We experimentally demonstrate the proposed scheme in 200-Gb/s optical QPSK-OFDM superchannel and 400-Gb/s optical 16QAM-OFDM superchannel. According to the experimental results, the proposed PS-GBE has a phase noise suppression performance similar to the GBE scheme. However, different from the GBE scheme, fewer pilots are needed for phase noise estimation in PS-GBE. Hence, the proposed PS-GBE can achieve higher SE. Compared to the pseudo-pilots-aided orthogonal basis expansion-based (PS-OBE) phase noise suppression and traditional common phase noise compensation (CPEC) methods, the proposed PS-GBE can get a significant performance enhancement. In the QPSK-OFDM system, a Q-factor improvement of 1.1 dB is obtained compared to the PS-OBE method. In the 16QAM-OFDM system, the BER is enhanced from 1.00E-03 to 2.05E-04. Further simulation results indicate that our proposed PS-GBE scheme can effectively increase laser linewidth tolerance. The proposed scheme can be applied to CO-OFDM and extended to coherent optical filterbank multicarrier (CO-FBMC) and coherent optical single carrier frequency domain multiplexing (CO-SCFDM) transmission system.

Gaussian basis expansion phase noise suppression method for CO-OFDM systems

In this paper, we propose a novel phase noise suppression method based on Gaussian basis expansion (GBE) for CO-OFDM systems. We analyze the basic phase noise suppression principle of GBE and then demonstrate it in optical OFDM transmission systems. Compared with common phase compensation (CPE), orthogonal basis expansion (OBE) and eigenvector basis expansion (EBE) schemes, the proposed GBE scheme has better phase noise fitting ability with similar computation complexity. Futhermore, no additional back to back (BTB) pre-training is needed for the GBE scheme. Performance improvements by the GBE is experimental validated in the QPSK/16-QAM OFDM system with different transmission scenarios (different number of pilots and input power). In the QPSK-OFDM system, after 160 km SSMF transmission, a Q-factor improvement of 1.7 dB and 0.5 dB are achieved compared with the CPE and OBE schemes at the optimum input power of -4 dBm, respectively. In the 16-QAM-OFDM system, the measured BER improved from 8.21×10-4 to 2.36×10-4 with the GBE scheme. To further verify the effectiveness of the GBE scheme, we change the laser linewidth and measure the long transmission distance performance by simulation, the results show that the GBE scheme can effectively increase the laser linewidth tolerance and extend transmission distance. When the linewidth is 2-MHz, the proposed GBE scheme can extend the transmission distance from 1120 km to 1540 km at the BER of 10-4. Experimental and simulation results show that the proposed GBE scheme is a promising alternative phase noise suppression for CO-OFDM system.

A novel transmitter IQ imbalance and phase noise suppression method utilizing pilots in PDM CO-OFDM system

In this paper, we develop a novel pilot structure to suppress transmitter in-phase and quadrature (Tx IQ) imbalance, phase noise and channel distortion for polarization division multiplexed (PDM) coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. Compared with the conventional approach, our method not only significantly improves the system tolerance of IQ imbalance as well as phase noise, but also provides higher transmission speed. Numerical simulations of PDM CO-OFDM system is used to validate the theoretical analysis under the simulation conditions: the amplitude mismatch 3 dB, the phase mismatch 15°, the transmission bit rate 100 Gb/s and 560 km standard signal-mode fiber transmission. Moreover, the proposed method is 63% less complex than the compared method.

Eigenvector Basis Expansion-Based Phase Noise Suppression Method for CO-OFDM Systems

Coherent optical orthogonal frequency division multiplexing (CO-OFDM) system is known vulnerable to the laser phase noise. In this letter, we propose a novel phase noise suppression method based on eigenvector basis expansion (EBE) for CO-OFDM systems. With the help of the proposed method, the induced phase noise effects can be mitigated efficiently. Numerical results show that compared with the orthogonal basis expansion-based phase noise suppression method, by performing an EBE to the phase noise, a more accurate description of the phase noise can be achieved, and hence leads to a better system performance. Besides, the additional computational complexity is limited, since the eigenvector basis only depends on the laser linewidth.

Phase Noise Estimation and Suppression for PDM CO-OFDM/OQAM Systems

Phase noise induced common phase error and inter-carrier-interference are serious impairments for coherent optical orthogonal frequency-division multiplexing (CO-OFDM) systems. As have been discussed in previous publications, extra signal-to-noise-ratio (SNR) penalty is required to maintain the system performance under the interference of laser phase noise. The SNR penalty is proportional to the laser linewidth, the time duration of an OFDM symbol, and the system SNR. Therefore, the phase noise induced interference remains the bottleneck for CO-OFDM systems, especially for those systems employing high-order modulation formats, or with long fast Fourier transform window. Thanks to the usage of specially designed filter banks, CO-OFDM/offset quadrature amplitude modulation (CO-OFDM/OQAM) systems demonstrate lower out-of-band leakage and higher spectral efficiency compared with conventional CO-OFDM systems. Recently, both theoretical studies and experimental demonstrations for CO-OFDM/OQAM systems have been widely reported. With the relaxation of orthogonal condition from the complex field to the real field, phase noised induced interference in CO-OFDM/OQAM systems is more complicated than that in conventional CO-OFDM systems. To our best knowledge, there have been no studies on the phase noise estimation and suppression methods for CO-OFDM/OQAM systems. In this paper, we systematically study and analyze phase noise induced interference for CO-OFDM/OQAM systems. Based on the theoretical analysis and the concept of orthogonal basis expansion, we develop a time-domain phase noise estimation and suppression method for polarization-division-multiplexed CO-OFDM/OQAM systems. As shown in numerical Montel Carlo simulations, the proposed method can improve the system robustness against phase noise effectively.

The application of cost-effective lasers in coherent UDWDM-OFDM-PON aided by effective phase noise suppression methods

Digital coherent passive optical network (PON), especially the coherent orthogonal frequency division multiplexing PON (OFDM-PON), is a strong candidate for the 2nd-stage-next-generation PON (NG-PON2). As is known, OFDM is very sensitive to the laser phase noise which severely limits the application of the cost-effective distributed feedback (DFB) lasers and more energy-efficient vertical cavity surface emitting lasers (VCSEL) in the coherent OFDM-PON. The current long-reach coherent OFDM-PON experiments always choose the expensive external cavity laser (ECL) as the optical source for its narrow linewidth (usually<100 KHz). To solve this problem, we introduce the orthogonal basis expansion based (OBE) phase noise suppression method to the coherent OFDM-PON and study the possibility of the application of the DFB lasers and VCSEL in coherent OFDM-PON. A typical long-reach coherent ultra dense wavelength division multiplexing (UDWDM) OFDM-PON has been set up. The numerical results prove that the OBE method can stand severe phase noise of the lasers in this architecture and the DFB lasers as well as VCSEL can be used in coherent OFDM-PON. In this paper, we have also analyzed the performance of the RF-pilot-aided (RFP) phase noise suppression method in coherent OFDM-PON.

Orthogonal Basis Expansion-Based Phase Noise Suppression for PDM CO-OFDM System

In this letter, we develop an orthogonal basis expansion (OBE)-based phase noise suppression method for polarization-division-multiplexed (PDM) coherent optical orthogonal frequency-division-multiplexing (CO-OFDM) systems. Compared with the conventional phase noise suppression approach, the OBE method not only significantly promotes the system tolerance of laser phase noise, but also improves the system robustness against nonlinear phase noise. The theoretical analysis is validated by numerical simulations of PDM CO-OFDM systems with 16-quadrature-amplitude-modulation format.

Non-Data-Aided Phase Noise Suppression Scheme for CO-OFDM Systems

We propose a non-data-aided phase noise compensation technique that overcomes the limitation of the zero-overhead decision-directed (DD) phase noise suppression method in high-order constellations for coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. The proposed technique consists of two equalization stages. First, a blind adaptive phase offset recovery scheme based on high-order statics, called the dispersion minimization de-rotator, is applied to subcarrier symbols to achieve rough correction of the common phase error because of phase noise. Second, the conventional DD phase noise correction scheme is used to remove the residual common phase error. The proposed method effectively compensates phase noise without the help of pilot signals, especially for high-order constellation CO-OFDM systems, as confirmed by our simulation results.

PHASE NOISE SUPPRESSION IN GPS-DISCIPLINED FREQUENCY SYNCHRONIZATION SYSTEMS

Global positioning system (GPS)-disciplined quartz oscillator can provide a precise time and frequency standard. However, possible phase errors and biases caused by oscillator phase noise must be suppressed or compensated for some applications, e.g., distributed radar systems, in which a rigorous phase or frequency synchronization precision is required. Moreover, the quartz oscillator is necessary to provide a holdover of time or frequency when the GPS signals are lost. This letter presents a signal processing and hardware design strategy for suppressing phase noise in GPS-disciplined frequency synchronization systems. Firstly, the quartz oscillator frequency is disciplined by the GPS pulse-per-second (PPS) signals. Next, a recursive algorithm is applied to suppress the possible jitters when the GPS PPS signals are lost. Finally, a direct digital synthesizer (DDS)-based multiple frequency tuning synthesizer is presented to generate the whole system frequencies. Although the use of GPS signal to discipline oscillator for frequency transfer is not a new concept, the originality of this letter lies in the proposed phase noise suppression methods, along with the hardware design strategies.

A novel phase noise suppression method for coherent detection by utilizing two adjacent longitudinal modes generated from a supercontinuum multi-wavelength source

A novel phase noise suppression method for coherent detection is proposed. It uses two adjacent longitudinal modes of a multi-wavelength source, as signal light and coherent light respectively, which are both launched into the optical fiber. And heterodyne synchronous demodulation structure is used in the receiver. The performance of a back-to-back system with 100 Gbit/s NRZ-QPSK utilizing this novel method is investigated by VPI. The simulation results show that phase noise in this coherent detection scheme is suppressed significantly, which is resulted from the correlating phase and fixed frequency spacing of adjacent longitudinal modes.