Due to its comb filter characteristics, Sampled optical Fiber Bragg Grating (SFBG) has attracted wide-spread attention and become a new focus in the research of optical fiber grating technology. The research work on designing optical filters with high channel numbers, flat tops, and narrow pass bands is of great importance in practical situation. Consequently, an Multi-Phase Shift Interpolated Sampling optical Fiber Grating (MPS-ISFBG) filter is proposed.

ISFBG has a large number of reflection channels and can introduce multiple flat top narrow transmission channels by inserting multi-phase shift. By optimizing the location of the two π phase-shift distributions of the inserted ISFBGs, an optical filters with 41 transmission channels was designed which covers the C-band with a channel interval of 100 GHz. Each channel has a flat-top response, a narrow 3 dB bandwidth (<1 GHz) and a small shape factor (<3.2). With structure parameters unchanged, three π phase shifts are inserted, which can further reduce the shape factor, thus improving the rectangular shape of the transmission channel. Finally, doubling the number of channels with half of the channel interval is achieved by introducing the MPS technique and inserting three π phase shifts into the ISFBG.

The filter with 81 channels flat-top narrow bandwidth covering the C-bands with 50 GHz channel spacing is demonstrated. The 3-dB bandwidths of the multiple channels are 900.5 MHz and the shape factors are close to 2.17. Meanwhile, the effect of the magnitude of the multiphase shift, the location and the equivalent length of the fiber on the actual fabrication is discussed.

The designed filter has a large number of channels. Each channel has a flat-top response and narrow bandwidth, in line with the design purpose. Such filters have potential applications in multi-wavelength lasers and multi-wave microwave signal processing systems.

In this paper, an ultra-low power consumption optical transmitter is developed to broaden the application of optical communication in short-reach interconnection such as board level and backplane level. The basic principle of the scheme is that the Vertical-Cavity Surface-Emitting Laser (VCSEL) laser generates an optical pulse signal after loading a bias current and a modulation signal through a Bias-T circuit.

In this work, the feasibility of the scheme is verified by means of simulation. It is also found that the main factors affecting the increase of the transmission rate are the parasitic parameters of the laser device and the impedance matching of the drive circuit. The two electrical transmission distances of 200 and 10 mm are studied by experiments. And the law of eye diagram quality and bit error rate as a function of driving voltage and bias current is studied through experiments under two electrical transmission distances.

The results show that a larger effective extinction ratio ranging from 0.84 to 6.69 dB can be obtained by shortening the electrical transmission distance to 10 mm with the minimum differential driving voltage of 200 mV, the minimum bias current of 15 mA, and the power consumption of 1.2 mW/Gbit/s. Compared with traditional optical modules, the power consumption of optical transmission is reduced by about 80%.

This optical transmitter solution can be applied to intra-data center. Combined with low-power optical receivers, the overall power consumption of the data center can be significantly reduced.

With the continuous advancements in satellite and communication technologies, the integration of space laser communication and ranging technology becomes more mature. As deep space exploration, satellite navigation, and other fields continue to develop, there is a growing demand for higher communication capacity and ranging accuracy between satellites. Thus, the need to achieve laser satellite high-speed communication while completing ranging and further improving ranging accuracy, under the premise of considering satellite payload and power consumption, has become an urgent issue.

This article designs and implements a coherent communication and ranging integrated system that supports both QPSK and BPSK, based on the principle of dual one way ranging. To further improve the ranging performance, the differential time sampling method is used to obtain the frequency difference and phase difference between the sending clock and the receiving clock through frequency and phase discrimination, thereby achieving higher clock accuracy and correcting the ranging value.

The system can operate stably in an environment where the received optical power is greater than-48 dBm. Different rates can be set for different application requirements, with a maximum rate of 5 Gbit/s in QPSK mode and rates of 2.5 Gbit/s, 1.25 Gbit/s, and 625 Mbit/s in BPSK mode. The theoretical ranging accuracy of the system can reach a minimum of 53 ps. In normal communication, using Matlab and Vivado to calculate and process ranging data, the ranging accuracy of the system is verified to be less than 0.1 ns. Furthermore, using the differential time sampling method under simulation conditions, the ranging accuracy can be improved to the order of 10^-3 of the symbol width, reaching±0.36 cm.

The proposed communication and ranging integrated system can achieve high-precision ranging while achieving high-speed communication, which is of practical significance for future applications of laser satellites.

With the development of the space-ground integrated information network, the Low Earth Orbit (LEO) satellite communication system is ushering in a development boom. The Paired Carrier Multiple Access (PCMA) technology is gradually developing to the low-orbit satellite communication due to its advantages of saving bandwidth resources. However, traditional PCMA technology is mostly used in high-orbit satellites, and cannot adapt to the highly dynamic fading channel character-istics of low-orbit satellite channels, which greatly degrades the bit error performance of the PCMA receiver. The bottleneck lies in the channel estimation and equalization technologies for overlapping signals.

Aiming at the channel characteristics of LEO satellites, this paper proposes a channel estimation scheme that combines training sequence estimation and Autoregressive (AR) model prediction. Based on the idea of superimposed training sequence channel estimation, an iterative method suitable for PCMA mixed signal channel estimation is introduced to improve the accuracy of training sequence channel estimation through iteration. The AR model is used to predict the Channel State Information (CSI) of the data sequence in real time. The use of AR model can also reduce the frequency of channel estimation in training sequences, so as to adapt to the dynamics of LEO satellite channels.

The simulation results show that the idea of superimposed training sequence channel estimation can be applied to the PCMA signals, and accurate channel estimation can be obtained after iterations. The method proposed in this paper can effectively improve the accuracy of channel estimation. After signal separation and demodulation, the bit error rate can reach the order of 10^-3when the signal-to-noise ratio is greater than 9 dB.

A channel estimation method for PCMA signal is proposed in this paper. The simulation results show that the bit error rate loss is within an acceptable range, which can support the application of PCMA technology in low-orbit satellite communication. The proposed algorithm has the advantages of simple structure, low complexity, and high practical value.

With the continuous development of satellite technology, the application of satellites to low coverage areas of ground information networks for personnel search and rescue is becoming increasingly popular. As an effective means of indicating the location of personnel and facilities, satellite search and rescue positioning technology is widely used in maritime, aviation, and personal distress rescue operations. Therefore, in the continuous development and research of global satellite search and res-cue systems, achieving high-precision and rapid positioning of search and rescue sources is the main goal.

In view of the sudden characteristics of satellite search and rescue signals, dual-satellite Time Difference of Arrival (TDOA) and Frequency Difference of Arrival (FDOA) positioning are adopted as the satellite search and rescue positioning methods. The estimation of the required TDOA and FDOA parameters is the key to improve the positioning accuracy. In order to improve the parameter estimation performance and positioning accuracy of dual-satellite TDOA and FDOA positioning technology, this paper proposes a search and rescue positioning technology scheme based on time-frequency difference estimation of windowed Cross Ambiguity Function (CAF). The method of filtering redundant noise by adding windows in time domain is introduced, and the accuracy of time-frequency difference estimation is improved by adding windows in time domain and CAF. The estimated value is substituted into dual-satellite TDOA and FDOA positioning equations to calculate the location of the search and rescue signal source. It means that the purpose of improving the positioning accuracy is to efficiently and accurately find the search/rescue source by improving the estimation accuracy of TDOA/FDOA parameters.

The simulation results show that the method of estimating the TDOA/FDOA parameters of CAF with windows can be applied to search and rescue positioning, and the accurate time-frequency difference estimation value can be obtained through this method. The method proposed in this paper can effectively improve the accuracy of time-frequency difference parameter estimation, and add Fourier transform to reduce the time of parameter estimation, thus optimizing the positioning performance. When the TDOA error is controlled within 4 μs and the FDOA error is controlled within 0.2 Hz, the positioning accuracy can reach the kilometers.

The time-domain windowed time-frequency difference parameter estimation scheme proposed in this paper has improved the positioning performance after being incorporated into the satellite search and rescue positioning technology, which can support the application of the satellite search and rescue positioning technology in the satellite search and rescue system. The algorithm has the advantages of simple structure, low complexity and practical feasibility.

In the Low Earth Orbit (LEO) satellite Internet of Things (IoT) scenario, the time delay and power consumption requirements of Narrowband (NB) -IoT terminal in wide coverage area vary due to different business scenarios. However, the ground NB-IoT terminal with a single business scenario adopts a fixed working state timer parameter configuration method, which cannot meet the needs of time delay and power consumption for multi-scenario terminals in large geographical areas of LEO satellite IoT.

In response to the wide coverage characteristics of LEO satellite IoT, the problem of different delay and power consumption requirements for terminal multi-scenario application services in LEO satellite IoT scenarios, this article proposes a method based on a simplified interaction process and Markov chain model for terminal work state switching. The method uses system downlink delay and terminal power consumption as Non-dominated Sorting Genetic Algorithms-Ⅱobjective functions to obtain a set of Pareto optimal solutions for multiple scenario frontiers. Furthermore, it selects working state timer parameters from the Pareto frontier to configure terminals online that meet different scenario delay and power consumption requirements.

The simulation results show that the multi-objective optimization method proposed in this paper can globally optimize the timing parameters of the working state timer, and overcome the shortcomings of traditional methods such as exhaustive search falling into local optima. Additionally, it has been verified that simplifying the random access interaction process can effectively reduce terminal delay and power consumption.

The multi-objective optimization method proposed in this paper can obtain the working state timer parameters of the terminal in various scenarios of LEO satellite IoT.

In Space Division Multiplexing (SDM) system, in order to achieve mode demultiplexing, it is necessary to adopt Multiple Input Multiple Output (MIMO) equalization scheme at the receiving end. As the number of transmission modes or transmission capacity increases, the computational complexity of MIMO increases significantly, resulting in high power consumption. Therefore, it is necessary to reduce the computational complexity of MIMO equalization.

We propose a frequency-domain joint equalization technique based on Cyclic Prefix (CP) to reduce the complexity compared with a traditional frequency-domain independent equalization and a separate dispersion compensation module in few-mode fiber short-range transmission systems.

Based on the few-mode fiber model in VPI simulation platform, we build a 6×6 few-mode fiber transmission system to verify the advantage of computational complexity reduction of the proposed technology. The simulation results show that, the performance and computational complexity reduction of different CP ratios are also different. Under the same simulation conditions, when the proportion of CP is larger, the reduction of computational complexity is also larger, vice versa. With the same performance, the computational complexity of the frequency-domain equalization scheme with CP accounting for 11.11%is only 15.29%of that of the traditional frequency-domain equalization scheme based on block convolution.

Compared with the traditional frequency-domain equalization combined with a separate dispersion compensation module, the proposed frequency-domain equalization with CP has lower computational complexity.

In Free Space Optical (FSO) communication, atmospheric turbulence can cause a decrease in communication link performance.

In this paper, a polar coding channel coding scheme is proposed for this problem, and Monte Carlo algorithm is used to construct polar codes for Gamma-Gamma distribution atmospheric turbulence channels commonly used in FSO communication. By comparing the Block Error Rates (BER) of the proposed polar coding scheme, uncoded transmission, and Low Density Parity Check (LDPC) codes with similar code lengths under Gamma-Gamma distribution atmospheric turbulence channels.

The simulation results show that when the Signal-to-Noise Ratio (SNR) is greater than 6.7 dB in weak turbulence, 10.3 dB in moderate turbulence, and 11.5 dB in strong turbulence, the proposed polar coding scheme performs better than uncoded transmission. Compared with LDPC codes, under weak turbulence conditions, when the SNR is greater than 7.1 dB, the overall performance of the proposed polar coding scheme is better than that of LDPC codes. Under moderate turbulence conditions, when the SNR is greater than 10.6 dB, the overall performance of the proposed polar coding scheme is better than that of LDPC codes. Under strong turbulence conditions, when the SNR is greater than 12 dB, the overall performance of the proposed polar coding scheme is better than that of LDPC codes. In addition, it is found that when the code length is short, the code rate is low, and the decoding width is small, the proposed polar coding scheme has better performance.

The use of the proposed polar coding scheme effectively improves the atmospheric turbulence effect in FSO communication systems. Moreover, in the harsh atmospheric turbulence channel environment of moderate and high turbulence intensities, the proposed polar coding scheme exhibits more obvious advantages than LDPC codes. This indicates that polar codes have good development prospects in FSO communication.

When analyzing the nonlinear mutation frequency interference problem in all optical communication networks, interference detection mainly relies on estimating channel covariance directly, without expanding network communication signal transformation processing, resulting in low F1-score values of the detection results. Therefore, a nonlinear abrupt frequency interference detection algorithm based on finite difference time domain is proposed for all-optical communication networks.

We collect all optical communication network traffic data by combining packet capturing and mirroring methods, followed by cleaning, conversion, and protocol processing. Relying on the working principle of finite difference time-domain method, we first describe the time width and bandwidth of the signal in time-domain and frequency-domain space. Then we apply derivative and Fourier transform algorithm to transform the real-time collected network communication signal. Next, we use the transformed signal to analyze the nonlinear abrupt frequency interference. Finally the transformed signal is detected and analyzed. With the aid of the time-frequency joint feature analysis method, the time-domain and frequency-domain features of the interference signal are extracted. Relying on the back propagation algorithm and the minimization of the loss function, the detection process of nonlinear abrupt frequency interference is simplified. The characteristic distance function is used to replace the network loss function, and it is input into the interference recognition model based on the twin network to obtain the detection results of nonlinear abrupt frequency interference.

The experimental results show that under different noise conditions, the F1-score value of the proposed algorithm's nonlinear mutation frequency interference detection results remains above 0.95. The detection time is less than 40 ms.

The new detection method using the finite difference time-domain method can more accurately reflect the interference situation of the current communication network. It ensures the normal operation of the communication network, and meets the interference detection requirements of all-optical communication network.

Undersea optical cable plays a leading role in international communication. In the planning of undersea optical cable communication system, several groups of possible schemes are often determined according to experience. The scheme with relatively better transmission performance and investment cost is then selected. However, with the development of communication equipment and communication technology, the number of optional modulation formats and optical fibers keeps are increasing. The number of alternative schemes is too large to quickly determine the optimal scheme. Therefore, it is necessary to establish a cost optimization model of undersea optical cable communication system to solve the cost optimal scheme.

Aiming at the problem of system planning and configuration in the undersea optical cable communication system, a cost optimization model considering the parameters of transmission performance, transmission capacity and supply voltage is established by taking the span length, optical fiber type, number of optical fiber pairs, repeater output power, modulation format and number of practical channels as the variables. The cascaded-lexicographic method is used to solve the cost optimization model.

The results show that the difference between the planning results of the proposed optimization algorithm and full traversal algorithm are no more than 0.34%. However, the number of operations of the optimization algorithm proposed in this paper is far less than that of the full traversal algorithm, with only 1/100 of that of the full traversal algorithm. Secondly, the number of operations of the cascade genelexicography method is less affected by the range of variables than that of the total traversal method. Finally, by comparing the optimal cost of the undersea cable communication system under different span length, it is found that the planning results have no regularity.

The variables always influence each other. The optimal cost design of the system cannot be obtained according to experience, so it needs to establish a model. The algorithm used in this paper is not only accurate, but also uses fewer operation times.

Aiming at the problems of low spectral efficiency and limited system throughput in Optical Quadrature Spatial Modulation (OQSM), a Signed Optical Quadrature Spatial Modulation (SOQSM) scheme is proposed in Free Space Optical Communication (FSOC) in this paper. In addition, in view of the fact that the channel used in the performance analysis of OQSM is not suitable for all turbulence, this paper also adopts the Málaga channel, which is suitable for all turbulence intensities to analyze the bit error performance of the system.

First, the scheme divides the input binary bit stream into five parts at the sending end. The first part is used for constellation symbol mapping, and the last four parts are used for laser mapping. Then, the constellation symbol mapping is used to transmit the real and imaginary parts of the constellation symbol and its inverse symbol. The laser mapping is divided into two parts, the in-phase phase and the quadrature phase, which are used to activate the laser sequence mapping. Finally, after transmitting through the channel, the signal received and processed at the receiving end.

Compared with OQSM, SOQSM carries an additional2log₂N_t bits of information in the space domain within a transmission period. The upper bound of the average bit error rate is then calculated in the symbol domain and the space domain respectively. Finally, the upper bound of the average bit error rate of the SOQSM scheme is obtained, and the method of calculating the upper bound of the average bit error rate has good convergence. This solution greatly improves the spectral efficiency and transmission rate of the system, and has good bit error rate performance.

The Monte Carlo simulation results show that compared with Optical Spatial Modulation (OSM) and OQSM, the bit error performance of the SOQSM scheme is better when the spectral efficiency is the same. The bit error rate can reach 10^-6 when the signal-to-noise ratio is 16dB. When the modulation order is the same, the bit error performance of SOQSM is better, especially when the signal-to-noise ratio is high. It is also shown that the simulation and theory fit well. In the Málaga channel, the bit error rate performance of the weak turbulence is better. In addition, different turbulence intensities have little influence on the trend of the bit error rate performance of the SOQSM scheme. However, with the increase of the signal-to-noise ratio, the influence will gradually increase. Therefore, SOQSM has better bit error rate performance than OQSM and OSM.

With the development of the sixth generation mobile communication technology, the inter-carrier interference in the traditional Orthogonal Frequency Division Multiplexing (OFDM) system makes the channel estimation performance insufficient to provide highly reliable communication, and Orthogonal Time-Frequency Space (OTFS) system can effectively solve the problem of communication system reliability degradation caused by fast time variability and Doppler effect, which has received wide attention in recent years.

In order to effectively meet the channel estimation performance requirements of OTFS systems, this paper uses an Optimized Generalized Complex Exponential (OGCE) Basis Expansion Model (BEM) to calculate the channel impulse response as a time-invariant basis function with basis function coefficients, which can effectively fit fast time-varying channels in high-speed mobile communication scenarios. The OGCE-BEM improves the spectral leakage by more intensive sampling and reduces the error of the high-frequency basis model by adding correction coefficients to reduce the error of the HF-based model.

The simulation results show that the proposed algorithm is suitable for high-speed mobile communication scenarios with more reasonable design of the basis function. The estimation method has lower mean square error than the fixed forgetting factor, and the channel estimation results are more accurate. Compared with Least Square (LS), BEM-LS and BEM-Linear Minimum Mean Square Error (LMMSE) channel estimation methods, the performance of mean square error is significantly improved.

It can be seen that the channel estimation algorithm based on OGCE-BEM can effectively reduce the number of unknown parameters to be estimated and improve the accuracy of channel estimation.

The non-linear characteristics of Light Emitting Diodes (LEDs) contribute to the degradation of Bit Error Rate (BER) performance in Visible Light Communication (VLC) systems, particularly in Optical Orthogonal Frequency Division Multiplexing (O-OFDM) systems with high Peak-to-Average Power Ratio (PAPR). A single-stage equalizer based on the Volterra series can handle the high-order non-linear distortions of LEDs with low latency. However, solving the traditional Volterra series necessitates multiple integration operations, resulting in the high implementation complexity of the Volterra-based equalizer. Additionally, the single-stage equalizer accumulates errors with limited performance improvements.

Firstly, to address the issue of high computational complexity in the traditional calculations of the Volterra series, a proposition is made to retain only the high-order power series terms of the various nonlinear terms and kernel coefficients within the Volterra series. This approach, known as the Memory Polynomial-based Volterra Series (MPVS), not only reduces the computational complexity compared to the traditional Volterra series but also enhances the accuracy of nonlinear system modeling by considering all input signals at the current moment. Subsequently, the design of channel equalizer considers the Memory Polynomial-based Volterra (MPV) equalizer and the Memory Polynomial-based Volterra Decision Feedback Equalizer (MPV-DFE). For a single-stage MPV-DFE, if an error occurs in the decision part leading to an incorrect symbol decoding, this error tends to manifest as a consecutive series of errors, thereby impacting the entire symbol sequence. To mitigate this, a proposal is made to cascade the two non-linear equalizers, MPV and MPV-DFE, forming a hybrid equalizer called MPV+MPV-DFE. The MPV equalizer performs a primary equalization on the LED's nonlinear distortion signal, effectively suppressing a portion of the non-linear distortions and thereby reducing symbol decoding errors in the MPV-DFE. Subsequently, a secondary equalization is carried out by the MPV-DFE, leading to improved suppression of residual nonlinear distortions.

Finally, the effectiveness of the system design was validated using Monte Carlo simulation to analyze the BER. The results demonstrate that compared to the single-stage MPV equalizer and the linear-cascade nonlinear hybrid equalizer (LMS+MPV-DFE), the proposed hybrid equalizer achieves approximately 7 dB and 2 dB Signal-to-Noise Ratio (SNR) gains, respectively, in a 4 Quadrature Amplitude Modulation (QAM) -modulated Asymmetrically Clipped Optical OFDM (ACO-OFDM) system at a BER of 10^-4.

In conclusion, the implementation of the MPV equalizer is straightforward, and the cascaded design of the two-stage nonlinear equalizers as a hybrid equalizer enables better mitigation of the LED’s nonlinearity.

This paper discusses full lifecycle energy efficiency of optical communication systems in the purpose of energy conservation and carbon reduction. It aims to establish a universal model for description of energy efficiency, which covers all stages of system lifecycle, and it is not limited to specific technologies or network structures. It also analyzes the key influencing factors for improvement of energy efficiency of optical communication systems.

This paper explores the useful work and energy consumption of optical communication systems, to establish a universal model for energy efficiency. In the expression of useful work, in addition to the commonly used factor data rate, distance factor is introduced as an important factor. The paper recommends that the value generated by data transmissions which meet specific quality requirements and maintaining network connectivity in specific scenario applications should be considered in the description of the useful efficacy. The description method is named as comprehensive useful efficacy. In the discussion of energy consumption, the system lifecycle is decomposed into four stages: manufacturing, installation and construction, operation and maintenance, and waste recycling. Main influencing factors of energy efficiency improvement are discussed based on the established model.

Main results of the research include: (1) Distance factor can be one of the main factors for evaluating the useful work of a system, and distance factors affect energy consumption at various stages of the system's lifecycle; (2) For new scenarios and applications, setting weights for data transmissions which meet specific quality requirements and assigning values for maintaining connectivities status in description of the system useful work could reflect the value brought by the energy cost of the system to meet the needs of scenario applications; (3) Energy consumption factors of each stage of the life cycle should be considered in evaluation of energy consumption of the full lifecycle, and the energy consumption of each stage should be converted into unit time based on the system operating life for accumulation; (4) Optimized network topology and routing design, reduction of line losses, as well as evolution of optical transmission technology and equipment/facility energy saving technologies, are important means to reduce energy consumptions throughout the entire lifecycle of the system and improve the energy efficiency.

This paper discusses the comprehensive useful work and full life cycle energy consumption of optical communication systems, and establishes a universal model to describe the full life cycle energy efficiency of the system. This model takes distance as an important influencing factor in the expression of the useful efficiency and also energy consumption of the system, which corresponds the value of the optical communication system based on communication distance with the energy consumption in the life-cycle caused by distances. It also suggests considering the value generated by data transmissions which meet specific quality requirements and maintaining network connectivity in the evaluation of the useful efficiency. This model could comprehensively evaluate the energy efficiency of optical communication systems, for improvements of system energy efficiency, and could adapt and promote applications of optical communication systems in new scenarios.

The objective of this study is to investigate the resource allocation problem in Optical Wireless Communication (OWC) systems using Rate Splitting Multiple Access (RSMA) technique. We propose a joint precoding matrix and rate allocation algorithm based on linear approximation to enhance the system reliability and performance.

We employ variable transformation and linear approximation techniques to convert the non-convex fractional functions into convex ones. By using the joint precoding matrix and rate allocation algorithm, system resources can be effectively allocated to improve system performance. The optimization problem is solved using a continuous iterative algorithm to obtain the optimal solution.

Simulation results demonstrate that the proposed joint optimization scheme significantly reduces the system outage probability and exhibits a fast convergence rate. This indicates that the proposed method can provide more reliable and efficient communication performance in the RSMA-OWC system, which is based on rate splitting access.

This study provides an effective resource allocation method for RSMA technology in OWC systems, enhancing system reliability and performance. Further research should focus on the challenge of system outage probability in RSMA-OWC systems, as well as resource allocation, precoding design, and application scalability. This study offers valuable insights to promote the application and development of RSMA technology in the field of OWC.

Traditional Free Space Optical (FSO) communication requires both ends of the communication to be installed at the same time, including the laser transmitting system, laser receiving system and acquisition, tracking and aiming system. It results in the problems of weight, volume, power consumption, and equipment complexity, thus limiting the development of FSO communication. Using the passive modulation technology constructed by asymmetric space laser communication link, the design of small volume, light weight and low power consumption of the communication terminal is successfully realized, which provides convenience for the application of small and medium-sized space laser communication technology.

In this paper, the research status of passive modulation at home and abroad is reviewed, which is mainly summarized abroad. In addition, the composition of the reverse modulation system and the working principle of the reverse modulator are described. Common Modulated Retro-Reflector (MRR) such as angle reflector reverse modulator and cat’s eye reverse modulator are analyzed. The selection of wavelength and the size of optical receiver aperture are discussed.

This paper summarizes the different implementation types and characteristics of passive modulation, summarizes the application of passive modulation in FSO communication, and looks forward to the future development direction and prospect of this technology.

In the future, passive modulation can be developed along the direction of high speed, focal plane pixelation, two-way communication, coherent detection, and there is a lot of room for development. This paper can provide a reference direction for the research of passive modulation and a new idea for the research of FSO communication.

Replenishing the power supply system of an underwater communication system is usually very expensive and impractical. The underwater Simultaneous Light-wave Information and Power Transmission (SLIPT) communication systems based on solar cells are powerful solutions. However, the communication bandwidth of the silicon solar cell receiver is very limited, and it is easy to have the phenomenon of deep fading of the Signal-to-Noise Ratio (SNR) due to the underwater light attenuation effect.

For these problems, this manuscript employs a negative-biased solar cell light receiver scheme that increases the-3 dB bandwidth of silicon solar cells from 420 kHz to 768 kHz. Aiming at the deep fading of SNR caused by various degradation effects in the water environment, a Discrete Fourier Transfor (DFT) extended Orthogonal Frequency Division Multiplexing (OFDM) modulation scheme with a low peak-average power ratio is adopted to offset the deep fading phenomenon in the system.

The performance of DFT Spread OFDM (DFT-S-OFDM) and OFDM modulation systems in water environments with different turbidity (absorption and scattering characteristics) is compared. It is shown that the DFT-S-OFDM modulation and demodulation system is more robust.

Finally, experiments have shown that the total battery power efficiency of the energy harvesting system can be increased by 1.87 times under continuous illumination of white LEDs for 3 h, realizing synchronized energy harvesting in the communication process.

It is always difficult to timely locate the location of the network attack and achieve rapid deployment of defense strategies when the smart grid is attacked by the network.

In order to solve this problem, this article proposes a Convolutional Neural Network (CNN) model that integrates Convolutional Block Attention Modules (CBAM) (CNN-CBAM) to detect False Data Injection Attack (FDIA) positions. The attack identification problem of FDIA is modeled as a multi label classification problem, where CNN is used to extract spatial features of the data. The CBAM module can be directly integrated into the convolution operation of the CNN module, which not only focuses on important parameter information from the perspective of spatial domain, but also considers feature relationships in the channel domain, and allocates attention to the input data from two dimensions to improve the performance of the model.

The performance of the proposed CNN-CBAM network FDIA position detection model is verified on Institute of Electrical and Electronics Engineers (IEEE) 14 and IEEE118 node systems. The experimental results show that the FDIA position detection rates of CNN-CBAM on IEEE14 and IEEE118 node systems are 98.25%and 96.72%, respectively.

Compared with other methods, the CNN-CBAM network model proposed in this paper can effectively extract the spatiotemporal characteristics between data, with improved existence of FDIA. It also im-proves the accuracy of attack location identification with better robustness.