Phase Tracking Scheme Research Articles

Hardware-Efficient, Ultra-Fast and Joint Polarization and Carrier Phase Tracking Scheme Based on Frequency Domain Pilot Tones for DSCM Systems

The coherent digital subcarrier multiplexing (DSCM) has recently been proposed as a cost saving solution to realize flexible and scalable point-to-multipoint (PTMP) networks. In this work, a hardware-efficient, ultra-fast and joint polarization and carrier phase tracking scheme for the DSCM systems based on frequency domain pilot tones (named as PTJ) is proposed and demonstrated via both simulations and experiments. By extracting the amplitude and phase of the pilot tones with a low-pass filter (LPF), the transmission matrix of random birefringence and carrier phase can be obtained prior to subcarrier demultiplexing and channel equalization. For the hardware-efficient implementation, a simplified LPF based on sliding window averaging (SWA) is proposed to filter out the pilot tones. Compared to previous scheme using pilot tones to track polarization and carrier phase in a cascaded manner (named as PTC), our proposed scheme shows better BER performance over wide polarization rotation rates and reduces more than 90% of computation resources by the SWA and joint tracking of polarization and carrier phase. The experimental results show that the proposed scheme can track polarization rotation rate up to 20 Mrad/s with the OSNR penalty of 0.2 dB at 7% FEC threshold. This indicates that an OSNR sensitivity gain of 2.8 dB is achieved compared with the PTC scheme. The proposed scheme provides a hardware-efficient and fast-tracking solution to recovery the polarization and carrier phase for digital subcarrier multiplexing (DSCM) and polarization division multiplexing (PDM) based optical fiber communication system.

Low-Overhead Low-Complexity Carrier Phase Recovery Technique for Coherent Multi-Band OFDM-Based Superchannel Systems Enabled by Optical Frequency Combs

Abstract In this paper, we have designed a low-overhead low-complexity carrier phase tracking scheme for OFDM-based superchannel transmission system enabled by optical frequency combs. In this scheme, taking advantage of the broadband phase coherence provided by optical frequency combs among the OFDM-bands, the carrier phase retrieved from pilot-subcarriers of the OFDM-band on the central wavelength channel is reused for the OFDM-bands on the other wavelength channels. In this case, the overall pilot-subcarrier overhead and DSP complexity is significantly reduced since the pilot-subcarriers occupy a small fraction of the overall OFDM bandwidth. The feasibility of this joint-carrier phase tracking scheme has been verified successfully via comprehensive simulation, where results show that the BER threshold for soft-decision FEC could be achieved for 50GHz-spaced 5-band 4-QAM, 8-QAM, 16-QAM and 32-QAM OFDM-based superchannel signals with zero guard-band and both laser and nonlinear phase noise effects after 7000km, 4000km, 3000km and 2000km SSMF transmission respectively. The simulation results show that there exist chromatic dispersion-induced differential phase offset among the OFDM-bands whose impact on joint-carrier phase tracking depends on the modulation format, channel count and fiber length. Finally, we demonstrate experimentally the feasibility performance of the designed master-slave carrier phase tracking technique for comb-based OFDM-based superchannels.

Modulation-transparent and Robust Frequency Offset and Phase Tracking Scheme Using Self-learning Kalman Filter for Intelligent Receiver

A joint and robust frequency offset (FO) and phase noise tracking scheme using self-learning Kalman filter is proposed and demonstrated experimentally. In our scheme, a self-learning Kalman filter based on kurtosis error is used to track FO and phase noise simultaneously in a constellation decision-free manner. Then, a mean-shift clustering-assisted maximum likelihood estimator is used for residual phase noise compensation. Simulation results indicate that the proposed scheme has advantages in FO estimation accuracy, OSNR sensitivity penalty, and FO jitter rate tolerance and nonlinearity tolerance, compared with the conventional FO and phase noise estimation scheme. With 7% FEC threshold, the proposed scheme can tolerate FO jitter rate up to 10 MHz for 16QAM, which is around 100 times and 20 times than that of VVPE1 +BPS and FFT+UCPE. With 1 dB OSNR penalty, the linewidth tolerance of the proposed scheme is 300 kHz for 64QAM, which is around 30 times and 5 times than that of FFT+UCPE+ML and FFT+ VVPE2. For 16QAM, the proposed scheme also shows excellent nonlinearity tolerance over wide launched power, and it provides around 0.4 dB and 0.2 dB Q-factor improvement over VVPE1+ VVPE2 VVPE1 +BPS for 16QAM, respectively. The 28GBaud PDM 16QAM experimental results also indicate that the proposed scheme outperforms the rest of the tested scheme under both back-to-back and fiber transmission cases. With optimal launched power, the proposed scheme can provide around 0.2 dB, 0.4 dB, and 0.7 dB Q-factor improvement over VVPE1 +BPS, FFT+UCPE, and VVPE1+ VVPE2 after 915 km fiber transmission, respectively. To the best of our knowledge, it is the first time that a joint and modulation transparent with robust nonlinearity and FO jitter rate tolerance is proposed and demonstrated for 64QAM.

Real-Time Phase Tracking Scheme With Mismatched-Basis Data for Phase-Coding Quantum Key Distribution

Phase drift is an inevitable problem in the practical implementation of phase-coding quantum key distribution (QKD) systems. Conventional active phase tracking and compensation solutions cannot be implemented during the key transmission process, resulting in reduced efficiency of the system. In this paper, we propose a single-photon level real-time phase tracking scheme using only the estimated quantum bit error rate (QBER) and mismatched-basis data to acquire the phase drift parameter instead of a phase scanning process or reference light pulses, without extra hardware or interrupting the transmission of quantum signals. This scheme is applied into a phase-coding QKD system with active phase disturbance and obtains an average QBER of $1.01\%$ with a standard derivation of $0.37\%$ over 50 h of continuous operation. Experimental results show that this scheme enables QKD systems to operate continuously with long-term stability and keep a low level of QBER even with rapid phase drift, suggesting its suitability for practical applications.

Low complexity, modulation-transparent and joint polarization and phase tracking scheme based on the nonlinear principal component analysis.

A low complexity, modulation-transparent and joint polarization and phase tracking scheme based on the nonlinear principal component analysis (NPCA) is proposed and demonstrated via both simulation and experiment. Based on high-order statistics, NPCA can achieve joint polarization and phase tracking successfully without any prior information of modulation format. Meanwhile, owing to fact that the estimated matrix is constrained to be a unitary matrix, NPCA can avoid the singularity problem. Compared with the format dependent scheme such as CMA/MMA + VVPE, NPCA shows comparable BER performance under the back-to-back case and shows fast-tracking capability over wide polarization rotation rates ranges. Moreover, for 16QAM signals, the proposed NPCA-based scheme has reduced around 30% computation resources compared with the format dependent scheme, which confirms the advantage of low implementation complexity.

An Adaptive Phase Tracking Scheme of OFDM Wireless Communication System

This paper proposes a new phase tracking algorithm for the 802.11a system. Since this system illuminates the basic structure of 802.11a system, and introduces the OFDM frame generation principle based the transmitter, phase error estimation and channel estimation. On the basis of this, this paper presents a phase tracking scheme based on adaptive Kalman filter, and then simulates the process based on 802.11a system. The result indicates that the BER has been improved because of this adaptive phase tracking scheme.

Partially-coherent receivers architectures for QAM communications in the presence of non-constant phase estimation error

In this paper, we present a new partially coherent receiver architecture motivated by optimum detection of quadrature amplitude modulation (QAM) signals in the presence of time-varying Tikhonov-distributed residual phase estimation error due to phase-locked loop (PLL)-aided phase tracking scheme. Performance is established in terms of bit error rate (BER). In this paper, an approximate performance measure motivated by union bound is presented for the proposed receiver architecture for 8- and 16-QAM constellations. The performance measures are assessed via simulation and analytical means for additive white Gaussian noise (AWGN) as well as for Rayleigh and Rician fading channels. The performance measures are shown to follow those of the optimum receiver over a wide range of signal-to-noise ratio (SNR), while outperforming a standard coherent receiver operating in the presence of residual phase error by as much as 2 dB.

Improvement of CCI and Residual Frequency Offset Compensation Using Feedback Phase Tracking in MIMO-OFDM Systems

In multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) systems, phase tracking schemes suffer from co-channel interference (CCI) and inter-carrier interference (ICI) caused by residual frequency offset. In this paper, we propose a residual frequency offset compensation scheme using feedback phase tracking to eliminate the effect of both ICI and CCI for MIMO-OFDM systems. The proposed phase tracking scheme estimates the amount of residual frequency offset in the frequency domain, and compensates for it in the time domain, periodically. Thus, the effect of ICI can be reduced. Furthermore, we consider two methods of channel estimation that enable the system to estimate the channel response several times within a packet to eliminate the effect of CCI. This is because the channel is generally estimated at the beginning of a packet, and this estimation is affected by residual frequency offset. First is the method that employs midambles. Second is the one that reuses the preamble. When the channel is estimated several times within a packet, the effect of CCI can be reduced. Simulation results show the proposed scheme can compensate for residual frequency offset and CCI more accurately than the conventional scheme, and improve the packet error rate (PER) performance.

A Phase Tracking Scheme Using Iterative Estimation of Residual Frequency Offset in OFDM Systems

OFDM (orthogonal frequency division multiplexing) systems are very sensitive to carrier frequency offset. Although frequency offset is generally compensated for by an automatic frequency control (AFC), residual frequency offset remains after the AFC. Moreover, OFDM signals are also affected by phase noise. Thus, a kind of phase tracking is needed to compensate for these effects. In an OFDM system such as IEEE 802.11a, a phase tracking scheme that uses pilot subcarriers to detect the phase rotation caused by residual frequency offset and phase noise is employed. However, the spectrum of the AFC output signal is shifted by residual frequency offset. That is, the detected phase is the composite phase of the pilot subcarrier and the adjacent subcarrier because of inter-carrier interference (ICI). The compensation based on the composite phase sometimes overcorrects or undercorrects the phase rotation. In this paper, we propose a phase tracking scheme using iterative estimation of residual frequency offset in OFDM systems. The proposed phase tracking scheme estimates residual frequency offset in the frequency domain, and compensates for it in the time domain. The compensation in the time domain mitigates the spectrum shift of the AFC output. Therefore, the proposed scheme can reduce ICI, and track phases more accurately than the conventional phase tracking scheme.

Recursive carrier phase tracking for synchronous multilevel 4QAM receivers

Four-quadrature amplitude modulation (4QAM) allows high spectral efficiency in coherent optical data transmission by exploiting the two phases and the two polarizations of the propagating wave. In this paper the performance of 4QAM is analyzed in the presence of laser phase noise and photodetection noise. A decision feedback phase tracking scheme based on the Kalman filter and leading to a novel hybrid PLL structure is employed and its accuracy evaluated. The computational complexity of the proposed phase estimator is also discussed. The performance of the resulting 4QAM system is evaluated in terms of bit error probability versus the signal-to-noise ratio E/sub b//N/sub 0/, for different ratios of the symbol rate R/sub s/ over the laser linewidth B/sub L/.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A prototype digital phase tracker for the fibre interferometer

A differential heterodyne Mach-Zehnder interferometer using a digital phase tracking scheme is described. The tracking device is a prototype for the new fibre optic hydrophone and is capable of maintaining the interferometer at a maximum sensitivity in the presence of large random drifts up to 200 pi rad s-1.