Energy-efficient joint UAV secure communication and 3D trajectory optimization assisted by reconfigurable intelligent surfaces in the presence of eavesdroppers

We consider a scenario where an unmanned aerial vehicle(UAV),a typical unmanned aerial system(UAS),transmits confidential data to a moving ground target in the presence of multiple eavesdroppers.Multiple friendly reconfigurable intelligent surfaces(RISs) help to secure the UAV-target communication and improve the energy efficiency of the UAV.We formulate an optimization problem to minimize the energy consumption of the UAV,subject to the mobility constraint of the UAV and that the achievable secrecy rate at the target is over a given threshold.We present an online planning method following the framework of model predictive control(MPC) to jointly optimize the motion of the UAV and the configurations of the RISs.The effectiveness of the proposed method is validated via computer simulations.

Experimental and Numerical Study on Vibration of the Full-Revolving Propulsion Ship Stern

In order to solve the severe vibration problems of an ocean engineering ship with a full-revolving propulsion system, the navigation tests, including forced vibration response test and modal test, are carded out in its stem. It is concluded from the comparison of the time-domain waveform and spectrum from different measurement points that three main factors lead to a high-level stern vibration. Firstly, the specific dynamic stiffness of a water tank is relatively small compared with its neighbor hold, which makes it act like a vibration isolator preventing vibrational energy transmitting to the main hold. Secondly, there exists high-density local modes in the working frequency range of the main engine and thus the local resonance occurs. Thirdly, the abnormal engagement of gears caused by the large deflection of the shaft bearing due to its low mounting rigidity leads to violent extra impulse excitations at high speeds. Then the modification against the dynamic defects is given by simply improving the specific stiffness of the water tanks. And the effect is validated by the FEM calculation. Some important experience is obtained with the problems being solved, which is useful in the design of ships with the same propulsion system. It is also believed that the dynamic consideration is as important as the static analysis for the ships, and that most of the vibration problems may be avoided with a proper acoustic design.

A Positioning System based on Communication Satellites and the Chinese Area Positioning System(CAPS)

The Chinese Area Positioning System （CAPS） is a positioning system based on satellite communication that is fundamentally different from the 3＂G＂ （GPS, GLONASS and GALILEO） systems. The latter use special-purpose navigation satellites to broadcast navigation information generated on-board to users, while the CAPS transfers ground-generated navigation information to users via the communication satellite. In order to achieve accurate Positioning, Velocity and Time （PVT）, the CAPS employs the following strategies to over- come the three main obstacles caused by using the communication satellite： （a） by real-time following-up frequency stabilization to achieve stable frequency; （b） by using a single carrier in the transponder with 36 MHz band-width to gain sufficient power; （c） by incorporating Decommissioned Geostationary Orbit communication satellite （DGEO）, barometric pressure and Inclined Geostationary Orbit communication satellite （IGSO） to achieve the 3-D posi- tioning. Furthermore, the abundant transponders available on DGEO can be used to realize the large capacity of communication as well as the integrated navigation and communication. With the communication functions incorporated, five new functions appear in the CAPS： （1） combination of navigation and communication; （2） combination of navigation and high accu- racy orbit measurement; （3） combination of navigation message and wide/local area differen- tial processing; （4） combination of the switching of satellites, frequencies and codes; and （5） combination of the navigation message and the barometric altimetry. The CAPS is thereby labelled a PVT5C system of high accuracy. In order to validate the working principle and the performance of the CAPS, a trial system was established in the course of two years at a cost of about 20 million dollars. The trial constellation consists of two GEO satellites located at E87.5° and E110.5°, two DGEOs located at E130° and E142°, as well as barometric altimetry as a virtual satellite. Static and dynamic performance tests were completed for the Eastern, the Western, the Northern, the Southern and the Middle regions of China. The evaluation results are as follows： （1） land static test, plane accuracy range： C/A code, 15-25 m; P code, 5-10 meters; altitude accuracy range, 1- m; （2） land dynamic test, plane accuracy range, C/A code, 15-25 m; P code, 8-10m; （3） velocity accuracy, C/A code, 0.13-0.3 m s-1, P code, 0.15-0.17 m s- 1; （4） timing accuracy, C/A code, 160 ns, P code, 13 ns; （5） timing compared accuracy of Two Way Satellite Time and Frequency Transfer （TWSTFT）, average accuracy, 0.068 ns; （6） random error of the satellite ranging, 10.7 mm; （7） orbit determination accuracy, better than 2 m. The above stated random error is 1σ error. At present, this system is used as a preliminary operational system and a complete system with 3 GEO, 3 DGEO and 3 IGSO is being established.

Artificial Pheromone System Using RFID for Navigation of Autonomous Robots

Navigation system based on the animal behavior has received a growing attention in the past few years. The navigation systems using artificial pheromone are still few so far. For this reason, this paper presents our research that aim to implement autonomous navigation with artificial pheromone system. By introducing artificial pheromone system composed of data carriers and autonomous robots, the robotic system creates a potential field to navigate their group. We have developed a pheromone density model to realize the function of pheromones with the help of data carders. We intend to show the effectiveness of the proposed system by performing simulations and realization using modified mobile robot. The pheromone potential field system can be used for navigation of autonomous robots.

LNA Design for Future S Band Satellite Navigation and 4G LTE Applications

A good design of LNA for S band satellite navigation receivers and 4G LTE wireless communication system has been implemented in this paper.Due to increased congestion in the present L band,the S Band frequency from 2483.5-2500 MHz has been allocated for the future satellite navigation systems.For this purpose ATF-34143 amplifier(pHEMT)having high electron mobility and fast switching response has been chosen due to its very low Noise Figure(NF).The amplifier has been designed having bandwidth of 0.8 GHz from 1.8-2.6 GHz.Because of the large bandwidth,the amplifier could serve many wireless communication applications including 4G LTE mobile communication at 2.1 GHz.The design was implemented using the micro strip technology offering extremely low noise figure of 0.312 dB and 0.377 dB for 2.1 GHz and 2.49 GHz respectively.The gain of the amplifier was low and found to be 10.281 dB and 9.175 dB.For the purpose of increasing the gain of an amplifier,the proposed LNA design was then optimized by using Wilkinson Power Divider(WPD).The Balanced LNA design using WPD offered very low noise figure of 0.422 dB and 0.532 dB respectively and the gain was considerably increased and was found to be 20.087 dB and 17.832 dB respectively against 2.1 GHz and 2.49 GHz.Simulations and measurements were taken in Agilent Advanced Design System(ADS)software.The suggested LNA can be used for a variety of wireless communications applications including the future S band satellite navigation systems.

Communication-based positioning systems:past,present and prospects

This paper reviews positioning systems in the context of communication systems. First, the basic positioning technique is described for location based ser- vice （LBS） in mobile communication systems. Then the high integrity global posi- tioning system （iGPS） is introduced in terms of aspects of what it is and how the low Earth orbit （LEO） Iridium telecommunication satellites enhance the global posi- tioning system （GPS）. Emphasis is on the Chinese Area Positioning System （CAPS） which is mainly based on commercial geostationary （GEO） communication satellites, including decommissioned GEO and inclined geosynchronous communication satel- lites. Characterized by its low cost, high flexibility, wide-area coverage and ample frequency resources, a distinctive feature of CAPS is that its navigation messages are generated on the ground, then uploaded to and forwarded by the communication satellites. Fundamental principles and key technologies applied in the construction of CAPS are presented in detail from the CAPS validation phase to its experimental system setup. A prospective view of CAPS has concluded it to be a seamless, high ac- curacy, large capacity navigation and communication system which can be achieved by expanding it world wide and enhancing it with LEO satellites and mobile base stations. Hence, this system is a potential candidate for the next generation of radio navigation after GPS.

The transmission link of CAPS navigation and communication system

The Chinese Area Positioning System (CAPS) is based on communication satellites with integrated capability, which is different from the Global Positioning System (GPS), the International Maritime Satellite Organization (Inmarsat) and so on. CAPS works at C-band, and its navigation information is not directly generated from the satellite, but from the master control station on the ground and transmitted to users via the satellite. The slightly inclined geostationary-satellite orbit (SIGSO) satellites are adopted in CAPS. All of these increase the difficulty in the design of the system and terminals. In this paper, the authors study the CAPS configuration parameters of the navigation master control station, information transmission capability, and the selection of the antenna aperture of the communication center station, as well as the impact of satellite parameters on the whole communication system from the perspective of the transmission link budget. The conclusion of availability of the CAPS navigation system is achieved. The results show that the CAPS inbound communication system forms a new low-data-rate satellite communication system, which can accommodate mass communication terminals with the transmission rate of no more than 1 kbps for every terminal. The communication center station should be configured with a large-aperture antenna (about 10-15 m); spread spectrum com- munication technology should be used with the spreading gain as high as about 40 dB; reduction of the satellite transponder gain attenuation is beneficial to improving the signal-to-noise ratio of the system, with the attenuation value of 0 or 2 dB as the best choice. The fact that the CAPS navigation system has been checked and accepted by the experts and the operation is stable till now clarifies the rationality of the analysis results. The fact that a variety of experiments and applications of the satellite communication system designed according to the findings in this paper have been successfully carried out confirms the correctness of the study results.

In-flight performance analysis of the navigation augmentation payload on LEO communication satellite:a preliminary study on WT01 mission

With the development of the Low Earth Orbit(LEO)communication constellations,it has become a hot area of research to provide additional navigation augmentation services.Limited by volume,weight,power consumption,and running time,the in-flight performance of navigation augmentation payload remains to be investigated.In this paper,we analyze the data quality of on-board GNSS observation and evaluate the precision of short-arc dynamic Precise Orbit Determination(POD)performance based on the WangTong-01(WT01)mission.Furthermore,the downlink navigation measurement data of WT01 satellites are analyzed and compared with the GNSS observations.The results show that the average multipath errors of the WT01 on-board GPS L1,L2 and BeiDou Satellite Navigation System(BDS)B1,B2 code observation are 0.54,0.74,0.65,and 0.58 m,respectively.The short-arc dynamic POD three-dimensional(3D)overlapping accuracy is 7.1 cm.The average multipath errors of downlink navigation signal Z1 and Z2 are 0.81 and 0.80 m,respectively,which at the same order of magnitude as GNSS signals.The maximum Carrier-to-Noise Ratio(C/N0)value of WT01 downlink measurement data can reach 60 dB Hz,which is much stronger than GNSS and indicates the navigation signals of LEO satellites can meet the basic requirement of navigation augmentation.

Ship performance and navigation data compression and communication under autoencoder system architecture

Modern vessels are designed to collect,store and communicate large quantities of ship performance and navigation information through complex onboard data handling processes.That data should be transferred to shore based data centers for further analysis and storage.However,the associated transfer cost in large-scale data sets is a major challenge for the shipping industry,today.The same cost relates to the amount of data that are transferring through various communication networks(i.e.satellites and wireless networks),i.e.between vessels and shore based data centers.Hence,this study proposes to use an autoencoder system architecture(i.e.a deep learning approach)to compress ship performance and navigation parameters(i.e.reduce the number of parameters)and transfer through the respective communication networks as reduced data sets.The data compression is done under the linear version of an autoencoder that consists of principal component analysis(PCA),where the respective principal components(PCs)represent the structure of the data set.The compressed data set is expanded by the same data structure(i.e.an autoencoder system architecture)at the respective data center requiring further analyses and storage.A data set of ship performance and navigation parameters in a selected vessel is analyzed(i.e.data compression and expansion)through an autoencoder system architecture and the results are presented in this study.Furthermore,the respective input and output values of the autoencoder are also compared as statistical distributions and sample number series to evaluate its performance.

喷水推进两栖车辆水面航行特性试验与数值计算研究

兼具陆上机动、水面航行及水陆交界地带作业能力的特种水陆两栖车辆,是未来多域协同系统中重要组成部分。以喷水推进两栖车辆为研究对象,基于船模拖曳水池试验,获得了弱约束条件下喷水推进两栖车辆的航行特性,建立了喷水推进器与两栖车辆一体化操控的数值计算方法,对喷水推进两栖车辆水动力性能展开研究并充分验证了数值计算方法的准确性,对比分析了两栖车辆设计航速下拖曳与约束自航条件下的航行特性。相比于常规的“船-泵”一体化研究,从两栖车的角度丰富了喷水推进器和水面航行体相互影响的研究。结果表明,约束自航条件下车体阻力相比无喷水推进条件下阻力增加17.6%,喷水推进器运行导致的车辆姿态变化是造成增阻的主要因素。约束自航条件与拖曳条件相比,虚长度延伸长度从-0.864 X/L(X为距车辆重心长度,L为两栖车总长)增加至-1.513 X/L。与此同时,鸡尾流波高高度与发散波面积显著增加,从0.037 H/L(H为波面高度)增加至0.061 H/L,增加了尾流场附近能量损失。

High-Precision Doppler Frequency Estimation Based Positioning Using OTFS Modulations by Red and Blue Frequency Shift Discriminator

Orthogonal Time Frequency and Space(OTFS) modulation is expected to provide high-speed and ultra-reliable communications for emerging mobile applications, including low-orbit satellite communications. Using the Doppler frequency for positioning is a promising research direction on communication and navigation integration. To tackle the high Doppler frequency and low signal-to-noise ratio(SNR) in satellite communication, this paper proposes a Red and Blue Frequency Shift Discriminator(RBFSD) based on the pseudo-noise(PN) sequence.The paper derives that the cross-correlation function on the Doppler domain exhibits the characteristic of a Sinc function. Therefore, it applies modulation onto the Delay-Doppler domain using PN sequence and adjusts Doppler frequency estimation by red-shifting or blue-shifting. Simulation results show that the performance of Doppler frequency estimation is close to the Cramér-Rao Lower Bound when the SNR is greater than -15dB. The proposed algorithm is about 1/D times less complex than the existing PN pilot sequence algorithm, where D is the resolution of the fractional Doppler.

航行背压对超高速水下航体动力系统空化特性影响规律分析

为揭示水深变化带来的航行背压差异对水下航体动力系统空化特性的影响规律,建立了航体-喷水推进泵组成的全流域数值平台,并以核心的旋转叶轮区域为对象进行了数值方法校核,结合旋转坐标系下的相对涡量输运理论对不同巡航深度下的动力系统空化实施了分析研究。结果表明:随着航行背压的增加,相较于航行背压0.4pr,b,航体动力系统扬程、效率、耗功、推力在0.4pr,b~2.0p_(r,b)内分别下降5.6%,1.7%,4.5%,6.9%(pr,b为额定航行背压);基于涡量输运理论揭示叶轮流道内的空化特性与涡量分布呈强相关性,辐射项在动力系统全流场涡量变化中均有体现,拉伸项对叶片前缘空化的产生起主导作用,随后斜压项可有效捕捉空化边界,而扭转项可有效捕捉空化尾迹;动力系统内的瞬时压力脉动、叶轮轴向力和径向力与航行背压呈负相关,不同时刻下拉伸项和斜压项基本不发生变化,而辐射项和扭转项展现涡团在叶片区的聚集与脱落趋势。

冰区航行船舶推进系统设计的若干考虑

冰区航行船舶由于其特殊的工作环境与气候条件,其设计要求与传统的推进系统有着很大的不同。针对冰区航行条件下船舶推进系统所需要面临的问题,及这些问题所导致的冰区推进系统的特殊性进行了整理和分析,指出了推进系统设计过程中为应对冰区航行条件下的海冰、低温以及空泡噪声等问题所应采取的改进措施,为冰区航行船舶推进系统的设计提供了参考。

冰区航行船舶电力推进轴系机电耦合的扭振分析

通过螺旋桨桨叶与冰块的相互作用过程,建立单冰块对螺旋桨扭转振动的激励函数;同时建立机电耦合振动数学模型,推导得到机电耦联动力学方程,研究电机电磁激励力对扭转振动的影响。以3500吨科考船电力推进轴系为研究对象,基于冰载荷激励力和电磁激励力对轴系扭转振动进行分析,为复杂的船舶电力推进轴系在冰区航行时的振动研究奠定了基础。

小型航海保障工作船主推进及定位系统分析

为优化连云港港30万吨级航道配套新型航海保障工作船的主推进及定位系统方案,基于小型航海保障工作船的功能需求分析,通过对固定螺距螺旋桨、可调螺距螺旋桨、全回转舵桨、全回转可调螺距舵桨、电力推进、锚泊定位、动力定位等系统的分析阐述,结合该新型航海保障工作船的设计和设备选型分析,提出可以运用模块化设计思路,在保留标准化船型的基础上,派生出多用途、系列化船型,让单一船型形成更大的技术经济效益。

未来20年无人船舶展望

通过分析未来2 0年科学技术和世界贸易的发展,以及人力资源的变化,提出无人船舶的概念,并从导航、动力和通信等几个方面展开讨论。

基于电火箭推进的地-月轨道转移自主导航研究

以电推进力作为奔月航天器在进入月球影响球之后的螺旋式减速转移过程的主推进力和姿态控制力,建立限制性三体力学模型。采用星光导航方式,结合UKF非线性滤波方法进行自主导航研究。推力的引入方式能有效抑制由于航天器姿态与导航误差耦合而导致的推力矢量方向误差。通过大量的计算机仿真,详细研究和分析了电推进条件下自主导航的发散问题,有针对性地给出了抑止发散的方法,为工程实现提供了有利的参考依据。

船舶轮缘推进装置驱动电机及控制方法研究进展

轮缘推进装置(RDT)是一种先进的电力直驱式船舶推进器,具有高功率密度、高机动性能、减振降噪和节能环保等显著优点。与应用在陆地上的电机系统相比,浸泡在水中工作的RDT驱动电机面临电机气隙大、性能受流场制约、难以安装位置传感器、电机控制与航行控制关系复杂等难题。该文分析了RDT电机的工作特点,在此基础上详细阐述了RDT驱动电机类型、驱动电机的无位置传感器控制方法、RDT全回转控制方法以及多RDT的协同控制方法等方面的研究现状,指出尚待解决的问题和今后的研究方向。

基于地平/恒星的GEO航天器自主导航仿真分析

研究航天器自主导航的优化测试问题,针对我国的GEO轨道及施加小推力后的航天器自主导航的研究却很少。对GEO轨道航天器来说,若其不在我国测站测控范围内,则难以实现轨道测控。针对上述问题,提出采用地平仪和星敏感器的自主导航方案。同时,考虑众多的GEO轨道航天器采用高比冲电推进技术用于位置保持以及寿命末期离轨,还研究了在沿轨道速度方向连续小推力作用期间的自主导航问题。通过仿真,结果表明采用地平仪和星敏感器以及推广卡尔曼滤波的自主导航方法可以适用于GEO轨道航天器。

The principle of the positioning system based on communication satellites

It is a long dream to realize the communication and navigation functionality in a satellite system in the world. This paper introduces how to establish the system, a positioning system based on communication satellites called Chinese Area Positioning System (CAPS). Instead of the typical navigation satellites, the communication satellites are configured firstly to transfer navigation signals from ground stations, and can be used to obtain service of the positioning, velocity and time, and to achieve the function of navigation and positioning. Some key technique issues should be first solved; they include the accuracy position determination and orbit prediction of the communication satellites, the measur- ing and calculation of transfer time of the signals, the carrier frequency drift in communication satellite signal transfer, how to improve the geometrical configuration of the constellation in the system, and the integration of navigation & communication. Several innovative methods are developed to make the new system have full functions of navigation and communication. Based on the development of crucial techniques and methods, the CAPS demonstration system has been designed and developed. Four communication satellites in the geosynchronous orbit (GEO) located at 87.5°E, 110.5°E, 134°E, 142°E and barometric altimetry are used in the CAPS system. The GEO satellites located at 134°E and 142°E are decommissioned GEO (DGEO) satellites. C-band is used as the navigation band. Dual frequency at C1=4143.15 MHz and C2=3826.02 MHz as well as dual codes with standard code (CA code and precision code (P code)) are adopted. The ground segment consists of five ground stations; the master station is in Lintong, Xi’an. The ground stations take a lot of responsibilities, including monitor and management of the operation of all system components, determination of the satellite position and prediction of the satellite orbit, accomplishment of the virtual atomic clock measurement, transmission and receiving navigation signals to and from each satellite. In the north, the south, the east, the west and the center of Chinese main land, the function of CAPS demonstration system is checked and measured. In cars and on board the system is also checked and measured. The results are as follow: CA-code, horizontal positioning accuracy, 15-25 m (1σ), vertical, 1-3 m; P-code, horizontal positioning accuracy, 8-10 m (1σ), vertical, 1-3 m; velocity accuracy, CA-code, 0.13-0.30 m/s, P-code, 0.15-0.17 m/s; time accuracy, CA-code, 160 ns, P-code, 13 ns; determination accuracy of orbit ≤2 m. About 20 million US $ and two years are spent for the development of demonstration. A complete CAPS system is now being established.