Irregular and regular LDPC codes with high spectrum efficiency modulation in image transmission over fading channel

If the degree distribution is chosen carefully, the irregular low-density parity-check (LDPC) codes can outperform the regular ones. An image transmission system is proposed by combining regular and irregular LDPC codes with 16QAM/64QAM modulation to improve both efficiency and reliability. Simulaton results show that LDPC codes are good coding schemes over fading channel in image communication with lower system complexity. More over, irregular codes can obtain a code gain of about 0.7 dB compared with regular ones when BER is 10 -4. So the irregular LDPC codes are more suitable for image transmission than the regular codes.

High efficiency spreading spectrum modulation using double orthogonal complex sequences

This paper presents a novel scheme of high efficiency spreading spectrum modulation using double orthogonal complex sequences （DoCS）. In this scheme, input data bit-stream is split into many groups with length M. Each group is then mapped into a word of width M and then utihzed to select one sequence from 2u-2 DoCS sequences each with length L. After that, the selected sequence is modulated on carrier in quadrature phase shift keying （QPSK） mode. In addition, a new method named forward phase correction （FPC） is put forward for carrier recovery. Theoretical analysis and bit-error-ratio（BER） experiment results indicate that the proposed scheme has better performance than the conventional direct sequence spread spectrum（DSSS） scheme both in bandwidth efficiency and processing gain of the receiver.

High Coupling Efficiency of the Fiber-Coupled Module Based on Photonic-Band-Crystal Laser Diodes

The coupling efficiency of the beam combination and the fiber-coupled module is limited due to the large vertical divergent angle of conventional semiconductor laser diodes. We present a high coupling efficiency module using photonic-band-crystal （PBC） laser diodes with narrow vertical divergent angles. Three PBC single-emitter laser diodes are combined into a fiber with core diameter of 105μm and numerical aperture of 0.22. A high coupling efficiency of 94.4% is achieved and the brightness is calculated to be 1.T MW/（cm2.sr） with the injection current of 8A.

Enhancing Solar Photovoltaic Efficiency:A Computational Fluid Dynamics Analysis

The growing need for sustainable energy solutions,driven by rising energy shortages,environmental concerns,and the depletion of conventional energy sources,has led to a significant focus on renewable energy.Solar energy,among the various renewable sources,is particularly appealing due to its abundant availability.However,the efficiency of commercial solar photovoltaic(PV)modules is hindered by several factors,notably their conversion efficiency,which averages around 19%.This efficiency can further decline to 10%–16%due to temperature increases during peak sunlight hours.This study investigates the cooling of PV modules by applying water to their front surface through Computational fluid dynamics(CFD).The study aimed to determine the optimal conditions for cooling the PV module by analyzing the interplay between water film thickness,Reynolds number,and their effects on temperature reduction and heat transfer.The CFD analysis revealed that the most effective cooling condition occurred with a 5 mm thick water film and a Reynolds number of 10.These specific parameters were found to maximize the heat transfer and temperature reduction efficiency.This finding is crucial for the development of practical and efficient cooling systems for PV modules,potentially leading to improved performance and longevity of solar panels.Alternative cooling fluids or advanced cooling techniques that might offer even better efficiency or practical benefits.

Disease Recognition of Apple Leaf Using Lightweight Multi-Scale Network with ECANet

To solve the problem of difficulty in identifying apple diseases in the natural environment and the low application rate of deep learning recognition networks,a lightweight ResNet(LW-ResNet)model for apple disease recognition is proposed.Based on the deep residual network(ResNet18),the multi-scale feature extraction layer is constructed by group convolution to realize the compression model and improve the extraction ability of different sizes of lesion features.By improving the identity mapping structure to reduce information loss.By introducing the efficient channel attention module(ECANet)to suppress noise from a complex background.The experimental results show that the average precision,recall and F1-score of the LW-ResNet on the test set are 97.80%,97.92%and 97.85%,respectively.The parameter memory is 2.32 MB,which is 94%less than that of ResNet18.Compared with the classic lightweight networks SqueezeNet and MobileNetV2,LW-ResNet has obvious advantages in recognition performance,speed,parameter memory requirement and time complexity.The proposed model has the advantages of low computational cost,low storage cost,strong real-time performance,high identification accuracy,and strong practicability,which can meet the needs of real-time identification task of apple leaf disease on resource-constrained devices.

Capacity Scaling Limits and New Advancements in Optical Transmission Systems

Optical transmission technologies have gone through several generations of development.Spectral efficiency has significant ly improved,and industry has begun to search for an answer to a basic question：What are the fundamental linear and nonlin ear signal channel limitations of the Shannon theory when there is no compensation in an optical fiber transmission system？Next-generation technologies should exceed the 100G transmis sion capability of coherent systems in order to approach the Shannon limit.Spectral efficiency first needs to be improved be fore overall transmission capability can be improved.The means to improve spectral efficiency include more complex modulation formats and channel encoding/decoding algorithms,prefiltering with multisymbol detection,optical OFDM and Ny quist WDM multicarrier technologies,and nonlinearity compen sation.With further optimization,these technologies will most likely be incorporated into beyond-100G optical transport sys tems to meet bandwidth demand.

Fabrication of a novel lumped electro-absorption modulator with a lower RC-time constant

A novel lumped electro-absorption modulator with a charge layer and an undercut ridge waveguide （DU-EAM） was fabricated and measured.Also,two other kinds of EAM with straight ridge waveguides,one with a charge layer（D-EAM） and another with no charge layer（N-EAM）,were fabricated and tested to ensure that the design of the DU-EAM would reduce the RC-time constant.The measured capacitance of the D-EAM and the DU-EAM is lower than that of the N-EAM under reverse bias voltage from -1 to -8 V due to the inserted charge layer.The capacitances of the N-EAM,the D-EAM and the DU-EAM are 0.375,0.225 and 0.325 pF,respectively, at -3 V.In addition,the DU-EAM had a larger extinction ratio（25 dB at -3 V） and higher modulation efficiency （13 dB/V between -1 and -2 V） than two other straight-ridge-waveguide ones（the D-EAM performed 22 dB and 10 dB/V,the N-EAM performed 20 dB and 10 dB/V） due to the 5.2μm wider active region.

Design and preliminary test results of Daya Bay RPC modules

Resistive Plate Chamber （RPC） modules will be used as one part of the cosmic muon veto system in the Daya Bay reactor neutrino experiment. A total of 189 RPC modules will cover the three water pools in the experiment. To achieve track reconstruction and high efficiency, each module consists of 4 layers, each of which contains two sizes of bare chambers. The placement of bare chambers is reversed in different layers to reduce the overlapping dead areas. The module efficiency and patch emciency were studied both in simulation and test of the data analysis. 143 modules have been constructed and tested. The preliminary study shows that the module and patch 3 out of 4 layers efficiency reaches about 98%.

Feasibility of Solar Tracking System for PV Panel in Sunbelt Region

In the study of the feasibility of solar tracking systems for crystalline silicon photovoltaic(PV)panels in hot and cold regions,it is argued recently that a tracking system is not necessary for sunbelt countries owing to the overheating that results from excessive exposure to solar irradiance.This conclusion has been formulated based on a mathematical model,which in turn is based on the assumption that the PV module temperature can be calculated using an empirical relation of this temperature to ambient temperature,available solar irradiance,and nominal operation cell temperature(NOCT).To support this conclusion,it is claimed that the mathematical model is validated experimentally.However,this assumption is vague and widely used in the literature.The objective of the present work is to reevaluate the above-mentioned assumption and to discuss the results deriving from it.It is shown experimentally in the present work that the above-mentioned assumption overestimates the PV module temperature.At a solar irradiance of 900 W/m2,ambient temperature of 25℃,and wind speed of 5 m/s,the measured PV module temperature is lower than the value calculated based on the mentioned assumption by 29.26%.