Abstract:Aiming at the phase jitter caused by environmental factors such as temperature and vibration changes in the process of optical fiber time-frequency transmission, a high-precision phase stability stress technology based on Proportional-Integral-Derivative(PID) feedback control is proposed. Michelson interferometer is employed for real-time phase detection. The real-time compensation is carried out through piezoelectric ceramics. This method can effectively overcome the bottleneck in compensation accuracy and speed of traditional phase discrimination and delay line. After calculation of environmental factors and PID compensation simulation, the transmission delay measurement accuracy of this method in 800 m optical fiber transmission is 2.2 fs, the transmission delay stability is <8.8 fs, and the initial state time is within 0.088 s under the external axial tension less than 100 N.

Abstract:With the increasing demand of Low Earth Orbit(LEO) communication satellite services, LEO satellites need to use Ka band for communication. In order to solve the problem of co-frequency interference between LEO satellite and Geostationary Orbit(GEO) satellite when Ka band is utilized, the spatial separation method based on link separation angle is adopted to analyze the angle interval of interference avoidance. The influence of different interference scenarios and ground station distribution on the interference angle interval is studied, and the interference avoidance measures are put forward for LEO satellites within the angle interval.

Abstract:An E-band continuous wave Traveling Wave Tube Amplifier(TWTA) for communication is presented. The TWTA integrates the E-band folded waveguide traveling wave tube with the miniaturized high-voltage power supply. It can be powered by low voltage supply in the outer part. The main properties of TWTA include operating frequency 81~86 GHz, saturated output power >80 W, small signal gain >38 dB, total efficiency >22%, size of 38 cm×20 cm×6.3 cm and airborne environmental adaptability. The TWTA bears the advantages of high power, high efficiency, miniaturization, and high reliability.

Abstract:Millimeter wave transmission in particulate environment is a fundamental topic in the communication community. In order to make controllable measurement, a dual-reflector Gaussian beam transmission system is designed based on the quasi-optical theory. This system consists of a pair of multi-flare angle horns, and two ellipsoidal focusing reflectors. The multi-flare angle horns are employed to generate Gaussian beam with 96% Gaussianity, and the focusing reflectors transform the incident beam to be identical to the input beam. In addition, the measurement on the system loss is conducted in the range of 75~110 GHz by using a vector network analyzer and extenders. It is found that the system loss is in the range of 2~4 dB, showing a satisfactory transmission performance. The preliminary study on water-spraying paves the way for future controllable measurement.

Abstract:In the channel coding of the terahertz communication system, the CPU multi-core is employed to perform parallel computing to achieve acceleration of the compiling code program for Turbo code. The optimized acceleration of Turbo code including four aspects, namely reserved memory space, parallel cycle, the optimization of coding structure and the decoding formula, thereby realizing shortening of code runtime. After experimental verification, the calculation of the compiling code is performed on different code length data. It is found that the parallel calculation can be shortened by 56.6% when the input code length is 10 000 bit.

Abstract:Terahertz time-domain spectroscopy is utilized to detect the spectra of 3,4-dichloroaniline and 2,5-dichloroaniline isomers within the spectral range of 0.2 to 2 THz. There are absorption peaks at 1.00, 1.48 and 1.88 THz in the spectra of 3,4-dichloroaniline, comparing with absorption peaks at 0.83, 1.04 and 1.17 THz in the spectra of 2,5-dichloroaniline. The intensity of the absorption peaks for the two isomers are also obviously different. DFT(Density Functional Theory) is adopted to simulate the theoretical spectrum of two isomers, which indicates the theoretical spectra and experimental spectra are in good consistency. The results reveal that terahertz time-domain spectroscopy can be applied in the fingerprint detection of 3,4-dichloroaniline and 2,5-dichloroaniline isomers. It provides a rapid and accurate method for the detection of toxic compounds which have obvious absorption peaks in terahertz band.

Abstract:From the literature of the threshold type decision pulse position keying system, it is found that the theoretical formula given by the literature cannot describe the Bit Error Rate(BER) accurately. Especially under low signal to noise ratio, the BER calculated by the theoretical formula is bigger than 0.5, which is in inconformity with communication theory. The problems of the literature in deducing the formula are analyzed and a new theoretical formula is given for the BER of the threshold type decision pulse position keying system. Simulation results show that the new theoretical formula can describe the BER accurately, and the BER calculated by the theoretical formula is below 0.5 under low signal to noise ratio, which is in conformity with communication theory. Based on the new theoretical formula, the energy efficiency of the threshold type decision pulse position keying system is analyzed and compared with that of Binary Phase Shift Keying(BPSK) system. The results show that the threshold type decision pulse position keying system is energy efficient and even better than BPSK system in some situations.

Abstract:With the development of railway communication system and the rapid advancement of 5G technology, 5G-R (5G-Railway) is expected to become the next generation standard of railway communication system. As a potential frequency band of 5G-R, the propagation characteristics in classical railway scenarios of 2 100 MHz need to be studied urgently. In this paper, a 3D model conforming to the typical characteristics of the scenario is constructed, and the propagation characteristics of 2 100 MHz wireless channel in the semi-enclosed high-speed railway platform scene are studied based on ray tracing simulation method. Transmitters are deployed beside columns and escalators. Meanwhile, the parameters of propagation models are defined, and massive simulations are conducted on hand-held and vehicle-mounted mobile devices respectively. Finally, channel characteristics such as path loss, delay spread and angular spread are analyzed respectively, providing a reference for coverage power prediction, network planning and optimization of 5G-R deployment, which makes up for the shortage of research on railway application of this frequency band.

Abstract:Radio Frequency(RF) fingerprinting identification based on the physical layer of wireless devices is an effective way to ensure communication security. The conventional RF feature extraction methods are susceptible to interference from changes in the Signal-to-Noise Ratio(SNR) of the channel, which are not suitable to dynamic SNR communication situation. A RF fingerprint identification method based on Convolutional Neural Network(CNN) is proposed, which could fulfill RF fingerprinting identification under dynamic SNR condition and significantly improve the recognition rate under low SNR condition. In addition, the experiments are implemented to identify four different power amplifier devices. The experimental results show that the comprehensive recognition rate of the proposed method is 89.4% under dynamic SNR of 0.5~14.5 dB.

Abstract:Considering the motion parameter estimation problem for a high?speed maneuvering target with complex motions, a novel motion parameter estimation algorithm based on the Robust Cross-Correlation Function(RCCF) and Polynomial Chirplet Transform(PCT), i.e., RCCF-PCT, is proposed. Firstly, after range profile image enhancement using the power-law transformation, the cross-correlation and robust polynomial regression operations are adopted to measure the target's motion parameters, which are used for the preliminary correction of the Range Migration(RM). Then, it employs the PCT to obtain the parameterized Time?Frequency Representation(TFR) of the Doppler Frequency Migration(DFM) coarsely compensated signal, and estimates the residual motion parameters with the time?frequency ridge feature extracted from the TFR. Finally, several numerical experiments are presented to demonstrate the effectiveness.

Abstract:In order to eliminate the problems of the silhouette and crosstalk noise in the interference-based and multiple image cryptosystems, an asymmetric optical cryptography mechanism for multiple color images based on Gyrator transform and unequal modulus vector decomposition is designed. Firstly, all color images are decomposed into three primary color components of red, green and blue. Then, each color is classified and superimposed, and fused into a three-channel form. The random phase mask is generated by Logistic mapping to modulate the superimposed color components. Secondly, the modulated image components are rotated under the Gyrator transform domain to form three complex distribution functions. Thirdly, it is decomposed into two vectors with different amplitudes and phases, the first vector is a fixed shared, and the second vector is a different decrypted. Finally, the shared vector is further applied with inverse Gyrator transform to produce the final password image. The encryption process is characterized by no contour, no crossover and high sensitivity. Experimental data show that the proposed algorithm has stronger anti-cracking ability than the existing multi-target encryption technology, which can better solve the problem of crosstalk noise.

Abstract:The feature point-based matching methods suffer from unsatisfactory matching effect when employed in complex texture scenes. Therefore, a block based image matching method, which combines Speeded Up Robust Features(SURF) algorithm and Coherency-Sensitive Hashing(CSH) is proposed. This method is divided into three stages: firstly, using the SURF algorithm to extract feature points from the image; secondly, determining the feature areas with the SURF feature points as the center; thirdly, the feature areas are matched by CSH. In order to further speed up the method, SURF algorithm is modified to remove the calculation of the direction of feature points when extracting feature points. Experimental results show that the new method is better than the general image matching methods based on feature point in complex texture image matching. The efficiency of the proposed method has been increased by 10% to 15% compared with that of the CSH algorithm.

Abstract:Cluster routing is an effective strategy to save energy of Wireless Sensor Networks (WSNs).The selection of cluster head is the key of cluster routing. However, the traditional cluster routing is to update the cluster-head in a fixed period without considering the residual energy of the cluster-head. Therefore, the Stable Election Protocol(SEP) is improved to propose a cluster-head update strategy based on multi-level energy threshold, denoted as I-SEP. The I-SEP route considers three types of nodes with different initial energies. According to the energy and proportion of the three types of nodes, the probability and threshold of them becoming cluster heads are calculated. At the same time, the energy of the cluster head is calculated in each round. Only when the energy of the cluster head is less than the energy threshold, the cluster head is updated; otherwise, the original cluster head remains, thus reducing the energy consumption caused by the replacement of the cluster head. Simulation results show that compared with SEP, the proposed I-SEP route effectively reduces the energy consumption and prolongs the network life.

Abstract:The recovery of random numbers is one of the key issues for the simulation system to realize the time traceability. The simulation system usually contains a large number of random numbers. In order to restore the system state at any time before, it is necessary to track and record the state evolution of the random number. This kind of tracking and recording work requires a great time and space cost. In order to solve the problem of random number recovery in the simulation system, based on the idea of reversible computation, a reversible linear congruential random number generator is proposed, and the random number generator is realized through the inverse function, general term formula, and inverse distribution function, respectively. It can not only generate random numbers in the forward direction, but also recover the previous random numbers in the reverse direction. The experimental results show that the reversible random number generator is superior to the current general checkpointing implementation in terms of overall space-time performance.

Abstract:Urban area is a very typical non-uniform area with complex surface type and fast temperature change. It is a very challenging task to study the thermal anomaly detection and extraction of urban buildings on-orbit. A thermal anomaly detection and extraction method of urban buildings on-orbit using LANDSAT images is presented. Firstly, urban buildings are automatically extracted based on the multi-exponential feature and geometric feature, then the single-channel algorithm is utilized to retrieve the temperature of the buildings, and finally the on-orbit thermal anomaly detection and extraction of urban buildings is completed according to the temperature inversion results. The feasibility and effectiveness of the method are verified in Wuhan city referenced to ASTER officially surface temperature products. Experiment results show that the proposed method can accurately extract the urban buildings, and the root-mean-square error of target temperature inversion is less than 3 K, indicating that this method is an effective method for detecting and extracting thermal anomalies of urban buildings on-orbit.

Abstract:Due to the need for external power supply, the conventional matter wave guide on chip with the ring structure cannot form a perfectly closed ring. The defects naturally exist in the generated ring magnetic trap, which hinds the effective manipulation of cold atom. Using Through-Silicon Via(TSV) technology could insert wires perpendicular to the surface of the atom chip, potentially reducing the impact of the inserted wires on the ring magnetic trap. Here a ring atomic matter wave guide based on TSV technology is modeled via finite element method. The magnetic fields produced by the wires with various loading current are analyzed. The effects of the cross-sectional shape, the depth, and the gap of the TSV on the magnetic trap produced by the ring wire are systematically studied. Finally, combined with the simulation results, a ring waveguide atomic chip based on TSV structure that is feasible in processing technology is designed.