Overhead-Free Channel Estimation using Implicit Training for Polarization-Multiplexed Coherent Optical Systems (original) (raw)
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IEEE Photonics Technology Letters, 2014
In this letter, we propose a nonlinearity-tolerant channel estimation technique for training-aided singlecarrier polarization-division-multiplexed (PDM) coherent optical systems. Simply by compensating the effects of fiber nonlinearity on the received training sequence, linear channel estimation and equalization can be improved; this approach is very efficient, which requires a negligible computational effort since training only occupies a very small portion of the total data. The concept is verified using simulations for both QPSK and 64-quadrature amplitude modulation (QAM) systems and experimental measurements for a 120-Gb/s PDM 64-QAM system with 800-km erbium-doped fiber amplifier (EDFA)-only transmission. The experimental results show that the system performance is improved by 0.4 dB at the optimal launched power and 1.6 dB in the highly nonlinear region, compared with conventional training-aided channel estimation approaches.
IEEE Photonics Technology Letters, 2012
Owing to its low transmitter complexity and low sensitivity to nonlinear impairments, phase noise, and frequency offset, the single carrier system with frequency domain equalization (SC-FDE) is of interest for high-bit-rate optical transmission. In this letter, we experimentally demonstrate a 8×40-Gb/s optical coherent polarization-multiplexed SC-FDE over 2080-km fiber transmission using novel training sequences. The sequences are designed based on Chu and Golay complementary sequences to have binary levels and are fully compatible with the commercial quadrature phase-shift keying (QPSK) systems. The use of these training sequences helps achieve accurate channel estimation and equalization in full-system demonstration.
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We propose an optical signal-to-noise ratio (OSNR) estimation technique using self-equalized complementary Golay sequences for both QPSK and 16-QAM coherent optical systems. The training sequences have complementary spectra, which enable accurate channel estimation and equalization, and have length-independent constellation for high-performance estimation. Estimation performances are verified through 100-and 40-Gb/s QPSK and 200-and 80-Gb/s 16-QAM coherent polarization-multiplexed optical systems, with an accuracy of 0.4 and 0.7 dB, in both simulations and experiments, respectively.
Optics Express, 2015
Polarization dependent loss (PDL) causes imbalanced optical signal to noise ratio (OSNR) of the two polarizations, thus remains one of the major bottlenecks for next-generation polarization-division-multiplexed (PDM) coherent optical transmission systems. In this paper, we investigate Pairwise Coding for adaptive PDL mitigation in PDM coherent optical systems. By pre-coding across two polarizations, the PDL-induced performance degradation can be largely mitigated without any coding overhead. We present details of the coding and decoding design, and also derive the analytical symbol/bit error rate of the Polarization Pairwise Coding scheme, which can be used to predict the performance gain as well as for optimal rotation angle calculation. Simulation results verify that Pairwise Coding achieves substantial system performance gains over a wide range of PDL values. Compared with other digital coding techniques, Polarization Pairwise Coding shows improved performance than Walsh-Hadamard transform since it maximizes the coordinate diversity; and also Pairwise Coding is computationally much simpler to decode compared with the Golden and Silver Codes, therefore is practical for current 100-Gb/s and future 400-Gb/s and 1-Tb/s digital coherent transceivers.
100Gb/s Direct-Detection OFDM Transmission on Independent Polarization Tributaries
IEEE Photonics Technology Letters, 2010
We propose a low-overhead method of polarization-multiplexed direct detection optical orthogonal frequency-division-multiplexing transmission that requires no digital multiple-input and multiple-output processing at the receiver. Optical filtering of carrier components allows a simple polarization separation. Using 16-quadrature amplitude modulation and only 31-GHz bandwidth, 100-Gb/s transmission over 80 km of standard single-mode fiber is successfully demonstrated. The crosstalk penalty was only 1.2 dB. We also investigated the laser frequency offset tolerance for the proposed 100-Gb/s transmission method.
Simplified backpropagation equalization in WDM coherent polarization multiplexed systems
ICTON 2009: 11th International Conference on Transparent Optical Networks, 2009
The digital equalization of fibre impairments in coherent optical communications allows for ultimate limits of spectral efficiency to be achieved, while reducing the cost and complexity compared to optical based solutions. Digital backpropagation (BP) was proposed recently as a reduced complexity approach for jointly compensating linear and non-linear impairments in single polarization coherent optical systems. Furthermore, polarization division multiplexed quadrature phase-shift keying (PDM-QPSK) has emerged as a promising format to increase spectral efficiency. Here we assess the performance of the simplified backpropagation equalization in both single channel and multiple channel transmission in combination with polarization multiplexing for different dispersion map configurations. It is shown that polarization multiplexing induces a degradation in performance due to cross-phase modulation polarization scattering, the backpropagation algorithm still overperforming linear equalization.
IEEE/OSA Journal of Lightwave Technology, 2008
To provide higher capacity networks, 40-Gb/s transmission systems are under active development and their cost is on the way to be competitive with the one of 4 10 Gb/s. However, their lower tolerance to linear and nonlinear fiber impairments remains a major drawback for field deployment. To address the issue of linear impairments, coherent detection of multilevel formats with polarization division multiplexing appears as a promising solution by reducing the symbol rate to 10 Gbaud. Indeed, such coherent based systems have already demonstrated an improved tolerance to optical noise and an interesting capability to compensate for large amount of chromatic dispersion. In this paper, the tolerances to narrow optical filtering, chromatic dispersion, and polarization mode dispersion are investigated with coherent detection of 10-Gbaud quadrature phase shift keying (QPSK) with and without polarization division multiplexing. Moreover, the efficient mitigation of these linear impairments by digital processing in a coherent receiver is demonstrated in an ultralong haul transmission (4080 km) of 40-Gb/s QPSK polarization multiplexed data.
Optics Express, 2013
We introduce and simulate a technique enabling to utilize the polarization dimension in direct-detection optical transmission, supporting polarization multiplexing (POL-MUX) over direct-detection (DD) methods previously demonstrated for a single polarization such as direct-detection OFDM. POL-MUX is currently precluded in self-coherent DD with remotely transmitted pilot, as signal x pilot components may randomly fade out. We propose POL-MUX transmission of advanced modulation formats, such as 16-QAM and higher, by means of a novel low-complexity photonic integrated optical front-end and adaptive 3x2 MIMO DSP. The principle of operation is as follows: an additional X x Y cross-polarizations signal is generated, providing three projections onto an over-complete frame of three dependent vectors. This enables to resiliently reconstruct the received state of polarization even when the remotely transmitted pilot fades along one of the received polarization axes.
Channel Parameter Estimation for Polarization Diverse Coherent Receivers
IEEE Photonics Technology Letters, 2008
A robust in-service estimation of fiber channel parameters from equalizer parameters of a polarization diverse coherent receiver is presented. The equations used for estimation are evolved from a theoretical fiber channel model. The theory is validated based on simulations and data from transmission experiments.