Quasi-cyclic low-density parity-check (QC-LDPC) codes with low-complexity hardware implementation and excellent performance have become a hot research topic in many optical communication systems. To meet the different requirements of code lengths in optical communication systems, lifting methods which remove all the short cycles equally are usually used to construct long QC-LDPC codes of larger lengths by lifting short QC-LDPC codes. A lifting method is proposed, which considers both length and connectivity of short cycles. The proposed lifting method reduces the complexity of calculating the approximated cycle extrinsic message degree -related metrics and improves connectivity of the Tanner graph. The numerical results prove that, by employing our proposed lifting method, the lifted long QC-LDPC codes have better bit error rate performance compared with the lifted codes employing the traditional lifting method.
Higher capacity and larger scales have always been the top targets for the evolution of optical access networks, driven by the ever-increasing demand from the end users. One thing that started to attract wide attention not long ago, but with at least equal importance as capacity and scale, is energy efficiency, a metric essential nowadays as human beings are confronted with severe environmental issues like global warming, air pollution, and so on. Here, different from the conventional energy consumption analysis of tree-topology networks, we propose an effective energy consumption calculation method to compare the energy efficiency of the tree-topology 10 gigabit ethernet passive optical network (10G-EPON) and ring-topology time- and wavelength-division-multiplexed passive optical network (TWDM-PON), two experimental networks deployed in China. Numerical results show that the ring-topology TWDM-PON networks with 2, 4, 8, and 16 wavelengths are more energy efficient than the tree-topology 10G-EPON, although 10G-EPON consumes less energy. Also, TWDM-PON with four wavelengths is the most energy-efficient network candidate and saves 58.7% more energy than 10G-EPON when fully loaded.
We present a new fusion structure of finite impulse response (FIR) filter and adaptive Kalman filter to suppress the angle random walk (ARW) of the fiber optic gyroscopes (FOGs). In our proposed fusion filter, a low-pass FIR filter first decomposes the discrete-time rotation rate into an approximation part and a detailed part. The detailed part is then put into an adaptive Kalman filter, which generates an increment part to compensate the high-frequency components of the rotation rate suppressed by the FIR filter. Different from the existing adaptive mechanism that modifies the covariance matrix of the error in the predicted estimate to cover model error, our proposal adaptively modifies the state equation of the Kalman filter to give a more accurate model. Therefore, it has the ability to distinguish the high-frequency components of the rotate rate from the high-frequency ARW noise. The new fusion structure integrates the advantages of these two filters. Experiments showed that with this new proposal, the ARW of a specific FOG had been reduced from 0.03741 deg/h√ to 0.00976 deg/h√ when the tap order M reached 1000, and the tracking error in dynamic cases was smaller than the digital resolution of the FOG.
An optical 90° hybrids based on silicon-on-insulator (SOI) 4×4 MMI couplers have been fabricated in 340nm top
silicon using E-Beam technology. Below 2.2° phase deviation of the hybrids for the across C-band of TE mode have
been simulated, which is well satisfied with the typical systems requirements. The measured optical transmission powers
from port to port show that the devices function well as a 6dB power divider with excess loss around 1dB at wavelength
λ=1550nm for TE mode. The measured transmission spectra of the 4×4 MMI coupler are seriously affected by the FP
resonance noise, which bring in error in phase deviation testing.
In order to further improve the laser phase noise tolerance of coherent optical orthogonal frequency division multiplexing
(CO-OFDM) systems, an iterative phase noise suppression algorithm is proposed in this paper, which is powerful in
mitigating the laser phase noise induced intercarrier interference (ICI) even when laser linewidth achieves 2 MHz.
Compared with the existing ICI suppression method, the performance gain brought by the proposal is significant when
the laser linewidth is larger than 1.5 MHz. The BER floor which can not be avoided by using the existing phase noise
suppression methods can be reduced effectively by employing the new iterative algorithm.
An all-passive dual polarization optical 90°-hybrid in silicon-on-insulator waveguides is proposed and designed. It
consists of two 2x2 MMI-MZI structures, working as polarization beam splitters, and two 4x4 MMI couplers,
working as 90°-hybrids. The fabrication process includes only one step of inductively coupled plasma (ICP) etching. It is
particularly suitable for silicon-based integration of DP-QPSK receiver.
As a very effective scheme to realize channel acquisition, clustering-based channel estimation algorithms have been proposed for optical fiber communication systems with a maximum-likelihood sequence estimation receiver. These algorithms can estimate the key channel parameters needed by the Viterbi processor accurately without assuming that the channel memory length is known a priori to the receiver. In this work, a corresponding adaptive channel tracking algorithm is proposed, which is proved to be very powerful in tracking the variation of the communication channel. Cooperation of the clustering-based channel acquisition and channel tracking is realized.
An equivalent refractive mathematic model is presented according to the geometrical structure of twin-hole poling optical fibers. The characteristics of losses and polarizations of the fibers are theoretically analyzed. The theoretical analysis and experimental results indicate that when the metal electrode is close to the fiber core, the loss of y-polarization mode is far lower than that of x-polarization mode, and the electrode-manufacturing method of inserting metal wires has better loss performance than that of injecting melting alloys. (The former is less than 0.04 dB/cm, and the latter is 2.5 dB/cm.) The experimental measurements agree well with the theoretical predictions.
We demonstrate a 10.7Gb/s-line-rate L-band WDM loop transmission over 1890km standard single-mode fiber (SSMF) with 100km amplifier spacing as well as non-return-to-zero (NRZ) format. For the first time, dispersion compensating fiber (DCF) plus chirped fiber Bragg grating (CFBG) is employed for hybrid inline dispersion compensation. The power penalty of each channel is less than 3dB after three loop transmission. The experimental results show that high-performance-CFBGs can be successfully used in ultra-long haul (>1000km) WDM systems. We also point out that all-CFBG compensation scheme is not suitable for re-circulating loop transmissions.
We describe how to use Markov chain Monte Carlo simulation (MCMC) to accurately estimate the outage probability of the optical communication system compensated by higher-order optical polarization mode dispersion (PMD) compensators. Markov chain fiber channel samples can drastically reduce the number of simulations required to estimate the outage probability of the compensated systems to 10–6 or less. Using MCMC, the efficiency of our proposed higher-order optical PMD compensator is proved further, and the accuracy of MCMC is affirmed.
We propose a new optical compensator for both first-order and higher-order polarization mode dispersion (PMD) effects in an optical fiber channel. The compensation scheme needs just one more polarization controller and one more variable differential group delay (DGD) element than first-order optical compensators with adjustable DGD elements. And the control algorithm for this compensator is easier and more stable than that for the typical higher-order optical polarization mode dispersion compensators. By an advised control method, the proposed compensator can always have better performance than first-order optical compensators. Numerical results are given to prove the efficiency of the proposed compensation scheme.
In this paper we compare differential quadrature phase-shift-keying (DQPSK) and quaternary differential phase amplitude-shift-keying (QDPASK) transmissions in 80Gb/s optical communication systems with highly nonlinear fiber (HNLF) channel and evaluate their tolerance against channel nonlinearity and receiver interferometer phase error (IPE). The results show that QDPASK signal has better receiver IPE tolerance while DQPSK signal has better channel nonlinearity tolerance. The performance of DQPSK system is better than QDPASK system only when IPE is not serious.
We demonstrate transmission of 36×10-Gbit/s WDM signals over 4134 km of standard single-mode fiber using all-Raman amplification and NRZ format. Wide-band fiber delay loop depolarizers are used in the Raman pump unit to reduce the depolarization dependent Raman gain.
Geometric and radiometric correction, image processing, information extraction and the integration of remote sensing, GIS and GPS in the specific approach for dynamic monitoring of land resources in mountainous areas are discussed. A synthesized method combining the image difference approach with comparison post classification is employed and a monitoring system based on remote sensing, GIS and GPS are set up. Different illumination conditions are key factors influencing the spectral features in mountainous areas, thus the comprehensive analysis of DEM and NDVI are employed to restrain the influence of terrain. Errors also commonly generate in the registration of different temporal images and much change information is usually lost when the mean-value smoothing template is employed in the image processing in mountainous areas. To reduce the information lost, a regional auto-adaptive smoothing template is employed. As a case study, according to the specific characteristics of mountainous areas, the TM images acquired from both 1994 and 1996 are processed for land change detection in Renhe District, Sichuan. Field experiments for radiometric correction are conducted in the areas of 25 Km2 in this district. The changed areas are precisely surveyed and validated after the fieldwork in which the database of detailed land survey is acquired. Combined with Geological Information System (GIS) technology and Global Position System (GPS), a 3S-based dynamic monitoring system of land resources change information in Renhe District is established, which helps the data renewal and daily management. Finally, the key factors influencing the accuracy of information extracting in mountainous areas are discussed.
In the paper, experiments and analysis of three pixel-based fusion methods had been discussed. The fusion methods include IHS, PCA and Brovey transform method. The fusion experiments were carried out in two circs, that is, between Landsat TM multi-spectral data and SPOT-4 Pan data, Landsat TM multi-spectral data and IRS-C Pan data. From the fusion results, the definition of all fusion images were improved greatly compared to the Landsat TM image. Especially the linear ground objects are much clear, such as the roads, the residents, the bridges, etc. According to the fusion between Landsat TM data and SPOT-4 Pan data, the Brovey fusion method was the best one. The PCA fusion method was better than the IHS fusion method. According to the fusion between Landsat TM data and IRS-C Pan data, the Brovey fusion method was also the best one. But the IHS fusion method was better than the PCA fusion method. Maximum likelihood method of classification was carried out on the fusion result, and classification accuracy of the classification results were evaluated. From the evaluation result, it can be concluded that classification accuracy of the Brovey fusion result is the highest between Landsat TM data and IRS-C Pan data. Classification accuracy of the IHS fusion result is the highest between Landsat TM data and SPOT-4 Pan data.
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