Abstract：With the construction of BDS III satellite nearing completion, Beidou service will transition smoothly to be provided mainly by BDS III system. The B2b signal interface document was announced on December 27, 2019. B2b signals are divided into two types: B2b signal that provides basic navigation services and PPP-B2b signal that provides precise point positioning services. Based on the B2b signal interface control file, this paper introduces the B2b signal information structure, message type, and analysis results of satellite signals in the sky, and gives the positioning accuracy results of B2b signals. The PPP-B2b information in the sky is also analyzed. This article also explores the Q branch signal of B2b.

Abstract：The existing Beidou signal receiver has a low-noise amplifier scheme in the S-band, and the noise figure is between 1.5 dB～1.7 dB under the condition of meeting the gain requirements and the noise performance can be further optimized. The scheme studies a low noise amplifier(LNA) based on a high-bandwidth millimeter wave tube. The tube is based on NPN broadband silicon germanium RF transistor process. Amplifier uses two-stage conjugate matching to achieve the best balance between circuit noise and gain，and uses LDO circuit linear regulated output to minimize power supply noise. ADS software simulation, Altium designer board and actual measurement of Agilent noise analyzer show that it′s single-stage amplifier has a minimum noise figure of 0.4 dB. At 2.492 GHz, the maximum gain of the solution is 32 dB, and the corresponding noise figure is 1.23 dB. The low-noise amplifier scheme is applied to the front end of Beidou user receiver, which can effectively improve the system noise performance and improve the signal receiving efficiency.

Abstract：Based on 0.18 μm RFCMOS technology, a high linearity low noise amplifier(LNA) for low voltage GPS receivers was designed. By using the trans-conductance derivative superposition technique with bulk bias control, the adjustment accuracy of auxiliary transistor was remarkably improved. An extra capacitance is added between gate and source nodes of input transistor in a parallel manner to reduce the effect of second-order harmonic on IMD3. In addition, folded cascade structure is adopted to make the circuit work under low voltage conditions. The simulation results shown that the LNA achieves a 6.63 dBm IIP3, a noise figure of 1.53 dB, a 13.16 dB power gain, the input and output return losses are -32.43 dB and -24.58 dB at 1.575 GHz with the core LNA consuming 8.78 mW at 0.9 V power supply.

Abstract：Because the designed frequency band of Geosynchronous synthetic aperture radar(GEO SAR) satellite signal possibly shares or overlaps with the frequency band of various Global Navigation Satellite System(GNSS) signals which have been put into use, the ground GNSS receiver may be subject to the pulse radio frequency interference generated by GEO SAR signal. In order to evaluate the influence of GEO SAR signal on the performance of GNSS ground receiver, a parametric theoretical model based on International Telecommunication Union(ITU) related standards is proposed in this paper. The model uses the "source-path-receiver" analysis method to extract parameters from the three aspects of GEO SAR signal, signal propagation path and receiver model for interference evaluation. Then, according to ITU standards, the influence of high-orbit SAR signal as additive pulse radio frequency interference on the performance of GNSS receiver is evaluated. Taking the representative B3I signal as an example, this paper evaluates the performance of different types of B3I receivers for GEO SAR signal under the condition of the assumed design parameters. The results show that the performance of the receiver decreases slightly in the presence of high-orbit SAR signal interference, but it can still work normally.

Abstract：Based on the characteristics of suddenness, complexity, dynamics and lack of information of navigation accidents, UAV technology has been organically integrated with China′s navigation accident emergency rescue system, becoming a research hotspot of maritime emergency communication. The user-centered UAV base station group network breaks the traditional base-centered architecture, and selects the set of potential service sites for each user to build a dynamic base station group, so that users can make full use of the diversified gain of potential service sites within the base station group and the cooperation gain between potential service sites. In this paper, a user-centered base station group networking scheme for UAV is proposed, and the user initial access scheme suitable for ship formation scenario is designed and its performance is simulated and evaluated.

Abstract：Constructing regional non-public network based on public network is a research hotspot of emergency communication solutions. The existing non-public network architecture defined by the 3GPP standard still has many disadvantages, such as the complexity of the protocol, the difficulty of deployment and configuration, and the poor compatibility of equipment from different manufacturers. Based on demand analysis of regional emergency communication scenarios, this paper proposes a non-public network improvement scheme based on network slice technology. While avoiding the complex perception of the core network of public network and UE to non-public network, this scheme has the advantages of strong compatibility, low deployment cost and quick and simple.

Abstract：With the establishment of the national emergency management department, state attaches more importance to emergency communications support after disasters. In order to solve the problem of the destruction of ground communications equipment after the disaster and the inability to guarantee normal communications, the research of quick“Sky to Ground Integrated” network building based on drone base stations has entered the planning and construction period. In order to meet the requirements of large bandwidth, low latency and low cost in the development of tethered type unmanned aerial vehicle(UAV) emergency system, based the key techniques such as large-scale antenna, edge computer and network slicing based on 5G, an emergency communication solution of tethered UAV based on 5G is put forward in this paper. The implementation architecture and key technologies of the scheme are analyzed, and the corresponding conclusion is given.

Abstract：The ground 5G base station provides low-frequency control signals to complete the control of the initial beam access. The aerial unmanned aerial vehicle(UAV) base station provides data services for the ground users. The heterogeneous network(HetNet) formed by the ground 5G base station and high-altitude UAV becomes an important research direction of integrated communication between heaven and earth in the future. In this paper, based on beam scanning and downlink control pilot multiplexing technology, an initial beam association mechanism for heterogeneous network architecture of UAV is proposed. While the upper and lower bounds of system coverage are given, the deployment optimization parameters corresponding to higher beamforming gain are obtained through simulation evaluation.

Abstract：Millimeter wave technology can greatly improve the system capacity and transmission rate of cellular network, which is one of the key technologies in the next generation(5G) cellular system. With the rapid increase of network traffic requirements, the ultra-dense networking(UDN) of millimeter-wave cellular networks can effectively improve the system spectrum efficiency and wireless resource utilization. For the technical characteristics of the millimeter-wave cellular network, firstly the current research at home and abroad on millimeter-wave cellular network technology is summarized. Then，the technical feature of millimeter-wave cellular network is introduced in details and the difficulties is pointed out. Finally, this paper introduced the key technologies of millimeter-wave cellular network and gave the prospect of future developments.

Abstract：A new deep learning model based on Seq2Seq and Bi-LSTM is proposed for Chinese text automatic proofreading. Different from the traditional rule-based and probabilistic statistical methods, a Chinese text automatic proofreading model is implemented by adding Bi-LSTM unit and attention mechanism based on Seq2Seq infrastructure improvement. Comparative experiments of different models were carried out through the open data sets. Experimental results show that the new model can effectively deal with long-distance text errors and semantic errors. The addition of Bi-RNN and attention mechanism can improve the performance of Chinese text proofreading model.

Abstract：Artificial neural network(ANN) is used to extract scattering parameters and noise parameters of GaAs high electron mobility transistors with different frequency bands and gate widths. Based on the two neural networks, the two groups of scattering parameters and noise parameters are trained and studied respectively. The average relative error and mean square error are obtained by comparing different hidden layers and the number of neurons. It is found that 8-8-6 and 6-4 correspond to the optimal hidden layers and number of neurons of the neural networks with scattering parameters and noise parameters. The test results show that the average relative error of scattering parameters is 2.79%. Compared with the conventional single neural network structure, the average relative error is increased by 31.3%. This shows that the model in this paper has better accuracy and reliability, which shows that this model has higher accuracy and is very suitable for parameter extraction of RF transistors with wide band gap and strong nonlinearity.

Abstract：In view of the disadvantages of the time series signal board,which is realized by logic combination with multiple IC chips,such as complex time series signal synchronization circuit,low synchronization accuracy,unadjustable pulse period and pulse width,and difficult circuit modification.This paper presents a design idea and implementation method of time series signal board based on CPLD,which can generate time series signals of different periods,improve the synchronization accuracy of time series signals,adjust the pulse width, send or receive multiple differential time series signals.It has the characteristics of on-line updating logic,high synchronization accuracy,flexible program control,simple circuit and high reliability.

Abstract：With the development of high speed communication system and the improvement of the transmission speed, Phase Lock Loop(PLL) to be the core circuit of providing precision clock has been put forward higher request, not only required to produce low jitter and low noise clock, but also demanded wide frequency range and multi-protocol supportment. As the core module of PLL, the performance of the phase noise and frequency range of voltage control oscillation(VCO) directly influence the quality of transmission clock. To reach the different transmission frequency requirement of multi-protocol, a 6.5-to-11 GHz LCVCO with wide-frequency-range and low-phase-noise is designed. Using 6-bits frequency –band-selected signal to control tuning capacitor array for relalizing the division and adjustment of the output frequency, and design optimal Kvco within each band to cover all frequency points with low phase noise. This chip is fabricated in 40 nm CMOS process, the simulation results shown that the output frequency is from 6.5 GHz to 11 GHz and the phase noise is below 107.1 dBc@1 MHz.

Abstract：The paper firstly analyzes the formation mechanism of signal reflection in signal integrity, lists several typical waveforms of signal reflection ,and then puts forward the main measures to eliminate signal reflection. It focuses on the analysis of termination matching and the effective measures to be taken under different topologies, and gives the simulation verification of signal integrity combined with engineering cases.

Abstract：Aiming at the demand for intelligent detection and control of alcoholic gas concentration in the fields of the national economy, people′s productions and lives and so on, a wireless intelligent alcohol concentration detector is designed and developed in this paper. The instrument adopts the STC90C52RC microcomputer to control the 10-bit A/D converter TLC1549 to acquire the output voltage signal of the alcohol concentration sensor TGS2620. The alcohol concentration value is obtained by data processing. This value is displayed in real time by the LCD module DM-162, broadcasted by the speech recording and playback circuit ISD2560, and sent to the upper computer by the wireless transceiver chip nRF24L01 respectively. The user interface of the upper computer is developed by employing the general object-based programming language Microsoft Visual Basic 6.0 to display and save the alcohol concentration data. In the software, the anti-pulse interference average filtering algorithm is used to suppress the pulsating interference in the sampled data. The piecewise linear interpolation method is used for scaling transformation so as to improve the real-time performance of the system. And the linear fitting technique based on least square method is used to correct the system error. The actual testing results show that the measurement accuracy of the instrument is less than ±2% and the communication distance is less than 100 m, which verifies the correctness and effectiveness of the design.

Abstract：In view of the problem that numerous branch lines in medium and low voltage feeder lines limit the application of multiterminal line current differential protection, a new area protection device for middle and low voltage feeder line is proposed. And the structure, hardware circuit and protection criterion of the regional protection device are designed. Experimental simulation results show that the proposed regional protection device with adaptive ability can effectively identify the phase faults in the protection area and effectively isolate the faults in feeder branches.

Abstract：Radio spectrum occupancy prediction is a key technology in cognitive radio research. In the traditional method, only single step size prediction can be performed, and the effect of multi-step size prediction is significantly reduced. Referring to the idea of searching frequent item sets in Apriori algorithm，a multi-step spectrum occupation prediction method based on association rule mining is proposed. In terms of data acquisition, the electromagnetic spectrum detection system developed by the unit is used to monitor the frequency spectrum of FM broadcasting service(88~108 MHz) for 48 hours continuously, and some data whose occupancy meets the demand of spectrum occupancy prediction are selected for prediction and analysis. The experimental results show that the proposed method is effective in FM broadcasting frequency band, and the prediction accuracy of multi-step length is more than 70%. This paper also briefly analyzes the important parameters of the algorithm and points out the influence of the parameters on the accuracy of the output results.

Abstract：Aiming at the problem of uneven distribution of traditional wireless sensor networks, the optimization process of the cuckoo algorithm was improved based on Adam optimization algorithm, and the elimination probability of the cuckoo algorithm was improved by the learning rate attenuation method. With network coverage as the optimization goal, the mathematical coverage of the network coverage is used to describe the node coverage optimization problem of the water quality sensor network. Finally, the original cuckoo algorithm is compared with three other improved algorithms to prove that the improved cuckoo algorithm can be used. Fewer iterations allow better coverage of the water quality sensor network.

Abstract：Aiming at the problem of poor image contrast and loss of visual information on electrowetting electronic paper display， this paper proposes an image hierarchical mapping technique based on human visual system. Firstly, the image is decomposed into the base layer and the detail layer, and the brightness of the base layer is enhanced. Then, the enhanced image is partitioned by Weber-Fechner law to realize the partition logarithmic mapping, and weighted and merged with the detail layer as the output image. At the same time, in order to achieve precise modulation of the electrowetting display, the brightness is local linearly stretched. The experimental results show that compared with traditional mapping methods, the entropy value of the algorithm in this paper is closer to the original map, the PSNR,SSIM and UIQI values of image evaluation index are respectively improved by 0.2~0.6，0.07~0.4 and 0.1~0.6. The method makes the relationship between the corrected voltage and brightness more linear, increases the image details on the electrowetting electronic paper, improves the contrast, and the overall visual effect is better.

Abstract：The use of automatic recording and broadcasting system enables teaching resources to break through the limitations of time and space, and make excellent teaching resources more popular with the public. But the traditional operation mode of recording and broadcasting requires artificial operation of multiple camera sources, which is not only complicated but also general in effect. Applying image recognition technology to the recording and broadcasting system can not only restore the authentic classroom, but also give full play to the auxiliary role of technology in teaching and provide more efficient recording and broadcasting services for teaching activities.

Abstract：Aiming at the requirement of nuclear radiation spectrum and positron annihilation coincidence Doppler broadening spectrum measurement, an all digital dual channel coincidence Doppler broadening system based on FPGA is designed. In this system, the analog signal collected by the high purity germanium detector is converted into digital signal by the front-end of 16 bit analog-to-digital conversion chip AD9269-80. The digital signal enters the FPGA chip at the back-end of the system for digital processing. FPGA realizes the processing of nuclear pulse signal through moving average window, ping-pong operation, custom IP core, etc., including waveform noise reduction, trapezoid filtering, baseline recovery, stack recognition, threshold judgment, data cache, etc., so as to obtain the amplitude information and time information of nuclear pulse. Then, the communication between the network port module and the upper computer is carried out, and the amplitude and time information are transmitted by UDP protocol to obtain the energy spectrum of the nuclear signal. The system uses two channels to measure the broadening spectrum of positron coincidence Doppler and obtains two-dimensional coincidence spectrum.

Abstract：A novel drive power supply is proposed for full bridge module of IGBT，traditional drive power supply adopts flyback topology or single primary side and multiple second side of transformer.The flyback topology only transmits energy to the secondary side when the switch is off which leads to poor transient performance.For transformer,the spatial distribution of 6 groups of driving power sources is too dense, and the electrical clearance and creepage path are difficult to meet the requirements. A driving power based on infineon FS400R07A3E3 full bridge module was designed in this paper. Firstly, the working principle and parameter calculation of each module was analyzed. Then the rationality of design on the simulation software was verified. Finally, prototype testing shows that the power supply has good adjustment rate and output accuracy which can drive IGBT stably.

Abstract：For DC off-grid photovoltaic power generation system, when the power demand of DC bus is large, Maximum Power Point Tracing(MPPT)is needed to keep the solar panels in the state of maximum power output for the output voltage and power are affected by temperature and illumination evidently. When the power demand is small, all converters working at the same time will lead to low efficiency of light load. The most simple and direct way to improve is to reduce the number of working modules, so as to ensure that the power system can achieve energy conversion efficiently within the full range. In order to solve the above problems, this paper proposes a control strategy for power generation system. This strategy makes full use of the solar array and adjusts the number of working modules dynamically according to the load demand. It provides a rationale for improving the operation efficiency of DC off-grid photovoltaic power generation system within the full load range. Finally, the effectiveness of the scheme is verified by simulations.