A novel construction algorithm of the LDPC code for high-speed long-haul optical transmission systems

According to the transmission characteristics of high-speed long-haul optical transmission system, the main construction method of Low-Density Parity-Check (LDPC) code for optical transmission system is presented and a novel construction algorithm of LDPC code is proposed, the theoretical analysis shows that the parity check matrix of the LDPC code constructed by the proposed construction algorithm has no four-girth phenomenon, this is also theoretically proved out. Both the novel LDPC(3969,3720) code with 6.69% redundancy and the novel LDPC(8281,7920) code with 4.56% redundancy for optical transmission systems are constructed by using the presented construction method and proposed construction algorithm. The simulation results show that the net coding gain (NCG) of the two novel LDPC codes at the eighteenth iteration for the BER of 10^?12 are respectively 1.63 dB and 1.49 dB more than that of the RS(255,239) code in ITU-T G.975. Moreover, the decoding of the LDPC code in the hardware can parallel be implemented, so the decoding speed of the two novel LDPC codes are very rapid, the complexities of implementing the two novel LDPC codes, compared with the concatenated codes in ITU-T G.975.1, are relatively lower, furthermore, the hardware overhead and storage space can relatively be saved and the computation complexity can be reduced in implementing the hardware in the future. As a result, the two novel LDPC codes can better be suitable for high-speed long-haul optical transmission systems.     

A novel super-FEC code based on concatenated code for high-speed long-haul optical communication systems

The structures of the novel super forward error correction (Super-FEC) code type based on the concatenated code for high-speed long-haul optical communication systems are studied in this paper. The Reed-Solomon (RS) (255, 239) + Bose-Chaudhuri-Hocguenghem (BCH) (1023, 963) concatenated code is presented after the characteristics of the concatenated code and the two Super-FEC code type presented in ITU-T G.975.1 have theoretically been analyzed, the simulation result shows that this novel code type, compared with the RS (255, 239) + convolutional-self-orthogonal-code (CSOC) (k₀/n₀ = 6/7, J = 8) code in ITU-T G.975.1, has a lower redundancy and better error-correction capabilities, and its net coding gain (NCG) at the third iteration is 0.57 dB more than that of RS (255, 239) + CSOC (k₀/n₀ = 6/7, J = 8) code in ITU-T G.975.1 at the third iteration for the bit error rate (BER) of 10⁻¹². Therefore, the novel code type can better be used in long-haul, larger capacity and higher bit-rate optical communication systems. Furthermore, the design and implementation of the novel concatenated code type are also discussed.     

基于低密度奇偶校验码的超强前向纠错码设计

光纤中的传输效应(如色散、偏振模色散(PMD)和非线性效应等)会严重影响传输速率和传输距离的进一步提高。因而有必要研究性能更好的新超强前向纠错(Super-FEC) 码型,使其在光通信系统中获得更高的编码增益和更好的纠错性能。简单介绍了低密度奇偶校验(LDPC)码, 然后提出光通信系统中一种基于LDPC码的超强前向纠错(Super-FEC)码型,构造了冗余度为6.68%的新颖LDPC(3969,3720)码, 并给出超强FEC码型的仿真结果。通过与RS(255,239)及BCH(3860,3824)+BCH(2040,1930)进行对比分析, 还分析与探讨了新LDPC码型的编译码电路的设计实现问题。通过理论分析与仿真结果表明这种超强 FEC 码型具有良好的性能, 可以节省硬件开销, 比较适用于光通信系统中, 可作为超强 FEC 码型的候选码。     

A New Simple Ultrahigh Speed Decoding Algorithm for BCH Code

In order to content with forward error correction (FEC) technology of the high-speed optical communication system, a new simple decoding algorithm for triple-error correcting Bose, Chaudhuri, and Hocquenghem (BCH) code is proposed. Without complicated matrix-operation or division-operation or intricate iterative algorithm, the algorithm is high efficient and high-speed because of its simplicity in structure. The result of hardware emulation confirms that the algorithm is feasible completely. Introduction of the parallel structure increases the speed of coding greatly. The algorithm can be used in the high-speed optical communication system and other fields.     

A new coding scheme of QC-LDPC codes for optical transmission systems

Based on Galois Field (GF(q)) multiplicative group, a new coding scheme for Quasi-Cyclic Low-Density Parity-Check (QC-LDPC) codes is proposed, and the new coding scheme has some advantages such as the simpler construction, the easier implementation encoding, the lower complexity of the encoding and decoding, the more flexible adjustment of the code length as well as the code rate and so forth. Under the condition of considering the characteristics of optical transmission systems, an irregular QC-LDPC (3843,3603) code to be suitable for optical transmission systems is constructed by applying the proposed new coding scheme. The simulation result shows that the net coding gain (NCG) of the irregular QC-LDPC (3843,3603) code is respectively improved 2.14 dB, 1.19 dB, 0.24 dB and 0.14 dB more than those of the classic RS (255,239) code in ITU-T G.975, the LDPC (32640,30592) code in ITU-T G.975.1, the regular SCG-LDPC (3969,3720) code constructed by the Systematically Constructed Gallager (SCG) coding scheme and the regular QC-LDPC (4221,3956) code at the bit error rate (BER) of 10-8. Furthermore, all the five codes have the same code rate of 93.7%. Therefore, the irregular QC-LDPC (3843,3603) code constructed by the proposed new coding scheme has the more excellent error-correction performance and can be better suitable for optical transmission systems.     

Highly strained InxGa(1−x)As−InyAl(1−y)As (x>0.8,y<0.3) layers for short wavelength QWIP and QCL structures grown by MBE

Highly strained quantum cascade laser (QCL) and quantum well infrared photodetector (QWIPs) structures based on In_xGa_(1−x)As−In_yAl_(1−y)As (x>0.8,y<0.3) layers have been grown by molecular beam epitaxy. Conditions of exact stoichiometric growth were used at a temperature of 420°C to produce structures that are suitable for both emission and detection in the 2–5 μm mid-infrared regime. High structural integrity, as assessed by double crystal X-ray diffraction, room temperature photoluminescence and electrical characteristics were observed. Strong room temperature intersubband absorption in highly tensile strained and strain-compensated In_0.84Ga_0.16As/AlAs/In_0.52Al_0.48As double barrier quantum wells grown on InP substrates is demonstrated. Γ–Γ intersubband transitions have been observed across a wide range of the mid-infrared spectrum (2–7 μm) in three structures of differing In_0.84Ga_0.16As well width (30, 45, and 80 Å). We demonstrate short-wavelength IR, intersubband operation in both detection and emission for application in QC and QWIP structures. By pushing the InGaAs–InAlAs system to its ultimate limit, we have obtained the highest band offsets that are theoretically possible in this system both for the Γ–Γ bands and the Γ–X bands, thereby opening up the way for both high power and high efficiency coupled with short-wavelength operation at room temperature. The versatility of this material system and technique in covering a wide range of the infrared spectrum is thus demonstrated.     

Optimization of facet coating for highly strained InGaAs quantum well lasers operating at 1200 nm

The optical output power of a laser diode can be enhanced by anti-reflection (AR) and high-reflection (HR) facet coatings, respectively, at the front and back facet. AR and HR coatings also serve the purpose of protection and passivation of laser diode facets. In this work, we have designed and optimized a single layer λ/4 thick Al₂O₃ film for the AR coating and a stack of λ/4 thick Al₂O₃/λ/4 thick Si bi-layers for the HR coating for highly strained InGaAs quantum-well edge emitting broad area (BA) laser diodes. Effect of the front and back facet reflectivities on output power of the laser diodes has been studied. The light output versus injected current (L–I characteristics) measurements were carried out on selected devices before and after the facet coatings. We have also carried out the numerical simulation and analysis of L–I characteristics for this particular diode structure. The experimental results have been compared and verified with the numerical simulation.     

BCH信道编码对降低快跳频OCDMA系统中色度色散的影响

提出BCH信道编码的方案来降低色度色散对降低快跳频OCDMA系统性能的影响.采用BCH信道编码后,单重合码的长度将变短,即可以用较少的波长数来构造码字,因此降低了色度色散的影响.分析结果表明,在相同的信息比特速率、脉元间隔、资用波长数的情况下,BCH信道编码能显著改善FFH-OCDMA系统的误码率性能.同时,由于单重合码的长度将变短,大大降低了光纤光栅的制作难度.由于BCH信道编码在电域中实现,其硬件技术已相当成熟,所以对整个BCH/FFH-OCDMA系统的代价影响不大.     

A Sensitive Fluorimetric Method for the Determination of Epinephrine

A sensitive fluorimetric method for the determination of epinephrine (E) is described in this paper. The experiments indicate that epinephrine can react with formaldehyde (HCHO) in an acid medium to form a condensation product, which can be oxidized by potassium hexacyanoferrate(III) (K₃[Fe(CN)₆]) in borax buffer (pH = 9.5). The reaction product can emit strong fluorescence. Ascorbic acid (AA) is used in order to consume excess potassium hexacyanoferrate and stabilize the fluorescent product. Under optimum conditions, a linear relationship has been obtained between the fluorescence intensity and the concentration of epinephrine in the range of 1.4×10^–9–2.1×10^–6 mol/l, and the detection limit is 2.4×10^–10 mol/l (4.3×10^–11 g/ml, S/N = 3). The method is applied for the determination of E in both actual sample and the synthetic sample with E and norepinephrine (NE) by using the coupling technique of synchronous fluorimetry and H-point standard addition method, and the results obtained are satisfactory.     

(Z N×) n−1 generalization of the chiral Potts model

We show that theR-matrix which intertwines twon-by-N ^n–1 state cyclicL-operators related with a generalization ofU _q(sl(n)) algebra can be considered as a Boltzmann weight of four-spin box for a lattice model with two-spin interaction just as theR-matrix of the checkerboard chiral Potts model. The rapidity variables lie on the algebraic curve of the genusg=N ^{2(n–1)((n–1)N-n)+1} defined by 2n–3 independent moduli. This curve is a natural generalization of the curve which appeared in the chiral Potts model. Factorization properties of theL-operator and its connection to the SOS models are also discussed.     

The double-phase transition of ErFe4Ge2. An XRPD study

High-quality powder XRD data of the compound ErFe₄Ge₂ collected in the ESRF beam line BM16, are presented for the entire magnetically ordered regime (T_N=44 K). The data analysis reveals the occurrence of a double symmetry breaking at the magnetic transition. This experiment has allowed us to distinguish between structural and magnetic satellites, both present in the neutron patterns, and to demonstrate the interdependence of structural and magnetic transitions. The high-temperature (HT) phase disproportionates by a first-order transition into two distinct phases: P4₂/mnm (T_c, T_N=44 K)→Cmmm (majority LT phase)+Pnnm (minority IT Phase) which coexist in proportions varying with temperature down to 4 K. The phase diagram comprises three temperature regions: (a) the HT range with T>T_N for the tetragonal P4₂/mnm phase; (b) the IT (intermediate temperature) range, 20 K<T<T_N, where the two phases coexist in strongly variable proportions and the Pnnm phase reaches its highest concentration (≈31%) around 30 K and (c) the LT (low temperature) range, 1.5–20 K, where the Cmmm phase is dominating (up to 95%). We suggests that this phenomenon is the result of competing magneto-elastic mechanisms involving the Er crystal field anisotropy, the Er–Er, Er–Fe and the Fe–Fe exchange interactions and their coupling with the lattice strains.     

A simple model for optimization design of high performance In1−x−y Ga y Al x As strained MQW DFB lasers

It is well known that complex rate equations and the couple wave equation have to be solved by the method of iteration in the simulation of multi-quantum well (MQW) distributed feedback Bragg (DFB) lasers, and a long CPU time is needed. In this paper, from the oscillation condition of lasers, we propose a simple and fast model for optimization of In_1–x–y Ga _y Al _x As strained MQW DFB lasers. The well number and the cavity length of 1.55 m wavelength In_1–x–y Ga _y Al _x As MQW DFB lasers are optimized using the model. As a result, the simple model gives almost the same results as the complex one, but 90% CPU time can be saved. In addition, a low threshold, high maximum operating temperature of 550–560 K, and high relaxation oscillation frequency of over 30 GHz MQW DFB laser is presented.     

Optical properties of red, green and blue emitting rare earth benzenetricarboxylate compounds

Red, blue and green emitting rare earth compounds (RE³⁺=Eu³⁺, Gd³⁺ and Tb³⁺) containing the benzenetricarboxylate ligands (BTC) [hemimellitic (EMA), trimellitic (TLA) and trimesic (TMA)] were synthesized and characterized by elemental analysis, complexometric titration, X-ray diffraction patterns, thermogravimetric analysis and infrared spectroscopy. The complexes presented the following formula: [RE(EMA)(H₂O)₂], [RE(TLA)(H₂O)₄] and [RE(TMA)(H₂O)₆], except for Tb-TMA compound, which was obtained only as anhydrous. Phosphorescence data of Gd³⁺-(BTC) complexes showed that the triplet states (T) of the BTC³⁻ anions have energy higher than the main emitting states of the Eu³⁺ (⁵D₀) and Tb³⁺ (⁵D₄), indicating that BTC ligands can act as intramolecular energy donors for these metal ions. The high values of experimental intensity parameters (Ω₂) of Eu³⁺-(BTC) complexes indicate that the europium ion is in a highly polarizable chemical environment. Based on the luminescence spectra, the energy transfer from the T state of BTC ligands to the excited ⁵D₀ and ⁵D₄ levels of the Eu³⁺ and Tb³⁺ ions is discussed. The emission quantum efficiencies (η) of the ⁵D₀ emitting level of the Eu³⁺ ion have been also determined. In the case of the Tb³⁺ ion, the photoluminescence data show the high emission intensity of the characteristic transitions ⁵D₄→⁷F_J (J=0-6), indicating that the BTC ligands are good sensitizers. The RE³⁺-(BTC) complexes act as efficient light conversion molecular devices (LCMDs) and can be used as tricolor luminescent materials.     

Preparation of α-Fe2O3 nanoparticles by high-energy ball milling

α-Fe₂O₃ nanoparticles were prepared by high-energy ball milling using α-FeOOH as raw materials. The prepared samples were characterized by transmission electron microscopy (TEM), Mössbauer spectroscopy, X-ray diffraction (XRD) and differential thermal analysis–thermogravimetric analysis (DTA–TGA). The results showed that after 90 h milling α-Fe₂O₃ nanoparticles were obtained, and the particle size is about 20 nm. The mechanism of reaction during milling is supposed that the initial α-FeOOH powder turned smaller and smaller by the high-speed collision during ball milling, later these particles turned to be superparamagnetic, at last these superparamagnetic α-FeOOH particles were dehydrated and transformed into α-Fe₂O₃.     

Nanoparticulate cathode thin films with high electrochemical activity for low temperature SOFC applications

Nanocrystalline La_0.6Sr_0.4Co_0.2Fe_0.8O_3 − δ (LSCF) and La_0.25Ba_0.25Sr_0.5Co_0.2Fe_0.8O_3 − δ (LBSCF) with a high specific surface area (~ 40 m²/g) were synthesized by spray pyrolysis. The as prepared powder was characterized by X-ray diffraction, nitrogen adsorption, and high-resolution electron microscopy. Water-based dispersions of pure LSCF, LBSCF and mixtures containing gadolinium doped ceria (GDC) with agglomerate sizes of approx. 50 nm were prepared by application of ultrasonic energy. Spin coating was employed to prepare porous thin films. The thickness of the films (≤1 μm) was more than 10–20 times lower than conventional cathode layers. The interfacial polarization resistances of LBSCF cathodes are 19, 38, and 101 mΩ cm² at 650, 600, and 550 °C, respectively. The high performance is attributed to the nanometer-sized grain dimensions, the nanoporosity, and the large specific surface area within the cathode layer. The novel approach of preparing nanoparticulate thin film cathodes suggests strong benefit for Micro Solid Oxide Fuel Cells operating below 500 °C.     

Some properties of simple recursive differential equations

A few simple examples for a class of recursive differential equations of the form _t x(t)=F{x(t),x(t–x(t))} are studied. Some exact solutions, some rigorous bounds and an iteration procedure are given.     

Electromagnetic interference shielding characteristics of fabric complexes coated with conductive polypyrrole and thermally evaporated Ag

Through the chemical coating of polypyrrole (PPy) doped with naphthalene sulfonic acid (NSA) on electrically insulating poly (ethylene terephthalate) (PET) woven fabric, PPy–NSA/PET complexes were synthesized. By using the electrochemical coating of PPy doped anthraquinone-2-sulfonic acid (AQSA) on PPy–NSA/PET complexes, PPy–AQSA/PPy–NSA/PET complexes were synthesized. The silver (Ag) was thermally vacuum evaporated on the surface of PPy–AQSA/PPy–NSA/PET complexes (Ag|PPy–AQSA/PPy–NSA/PET). Electromagnetic interference (EMI) shielding efficiency (SE) and dc conductivity (σ_dc) of fabric complexes were measured for EMI shielding characteristics and theoretical simulation. The measurement of EMI SE in the frequency range from 50 MHz to 1.5 GHz was performed by using ASTM D4935-99 method. The EMI shielding characteristics such as transmittance, reflectance and absorbance were obtained from the S (scattering)-parameter analysis. We control the contribution of the absorbance or the reflectance to total EMI SE through the coating of conductive PPy and the evaporation Ag.     

Long- and Short-Range Correlations in Genome Organization

We study the size distribution of coding and non-coding regions in DNA sequences. For most organisms we observe that the size distribution P _c(S) of the coding regions of size S shows short range distribution, whereas the size distribution of the non-coding regions follows a power-law decay P _nc(S) S ^{–1 –} , with power exponents indicating clear long-range behavior. We argue, using the Generalized Central Limit Theorem, that the long-range distributions observed in the non-coding are related to the lower level clustering of purines and pyrimidines (1d islands) which follow similar long-range laws. We also address the question of clustering of coding segments in the two complementary strands of DNA. We observe a short-range clustering of coding regions in both strands, expressed by an exponential decay in the clustering size distribution. The decay exponent expresses the degree of short-range correlations and the deviation from random clustering.     

A New Simple Ultrahigh Speed Decoding Algorithm for BCH Code

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