Current Issue : October-December Volume : 2021 Issue Number : 4 Articles : 5 Articles
In the Global Navigation Satellite System (GNSS), the multipath error affected by many aspects is the main error source that affects satellite navigation, and it is difficult to establish a much more accurate model to analyze it. Based on the ground multipath reflection model, it firstly deeply studies the influence of GNSS satellite orbit parameters on multipath fading frequency and establishes a multipath signal model related to satellite orbit parameters. Secondly, the influence of carrier phase cycle slip, receiver clock adjustment, and GNSS satellite orbit on multiparameter- (MP-) combined observations is analyzed in detail based on the measured data. Finally, aiming at the common phenomenon of code-carrier divergence in the Beidou system, the elevation-based pseudorange correction model and a sidereal filtering are built to correct the MP errors; experiments with measured data show that there is a fluctuation range reduction of 35.7% after sidereal filtering when the receiver reaches a steady state....
New information and communication technologies have led to the emergence of new techniques in our daily lives. Indeed, in topography, a lightning development of new techniques and new devices has been noticed. This development has given rise to a multitude of choices of devices and various classes of precision. This implies that the decision-makers have to study the adequate equipment and the appropriate technique according to the topographic task to be realized. The objective is not to compare GNSS and topographic techniques, but to point out the contribution of the Global Navigation Satelite System (GNSS) techniques of topographic work. Thus, a theoretical study with a critical eye on the scientific principle of calculating the third topographic dimension followed by a leveling campaign, Real Time Kinematic (RTK) surveys will be used in order to be able to compare and interpret the result from these campaigns. The study of the difference resulting from the practical campaigns will allow us to identify the contribution of GNSS technology....
When the bank of a reservoir slope slides along a weak structural plane at a high speed, “landslide slamming” will occur in the nearby water. +e formation of landslide-induced waves is a serious threat to the safety of wharfs, shore marks, buildings in the water, and vessels navigating in reservoir areas. To ensure the safety of navigating ships, this study proposes a landslide-induced wave water ship navigation safety risk response technology. +e propagation characteristics of landslide-induced waves are analysed based on a physical model experiment, and the characteristics of a ship’s motion response and mooring cable tensions are studied under conditions of bow and stern mooring and multipoint mooring. +e influences of the landslide-induced wave direction and ship navigation position on the ship rolling motion characteristics are discussed. +e results of this study can further improve the navigation safety of ships in landslide-induced wave waters....
Unmanned surface vehicles (USVs) have been widely used in research and exploration, patrol, and defense. Autonomous navigation and obstacle avoidance, as the essential technology of USVs, are the key conditions for successful mission execution. However, fine modeling of conventional algorithms cannot meet the real-time precise behavior control strategy of USVs in complex environments, which poses a great challenge to autonomous control policy. In this paper, a deep reinforcement learningbased UANOA (USVs autonomous navigation and obstacle avoidance) method is proposed. )e UANOA achieves the autonomous navigation task of USVs by real-time sensing of partially complex ocean information around and real-time output of rudder angle control commands of USVs. In our work, we employ a double Q-network to achieve end-to-end control from raw sensor input to output of discrete rudder action, and design a set of reward functions that can be adapted to USV navigation and obstacle avoidance. To alleviate the decision bias caused by partial observable of USVs, we use the long short-term memory (LSTM) networks to enhance the ability to remember the ocean environment of USVs. Experiments demonstrate that UANOA ensures a USV arrives at the target points with optimal path planning in complex ocean environments without any collisions occurring, and UANOA outperforms deep Q-network (DQN) and random control policy in convergence speed, sailing distance, rudder angle steering consumption, and other performance measurements....
Ubiquitous signal coverage is a basic demand of Internet of Things (IoT) communications, which meets the feature of satellite communications. Infinite user number is a basic demand of IoT location-based services, which meets the feature of Global Navigation Satellite System (GNSS). Both of these demands make Satellite Navigation and Communication Integration (SNCI) an important supporting technology for IoT. Inherited from the satellite communications system, GNSS itself has a certain data transmission capacity. Thus, enhancing the communication function of the GNSS is a promising means of achieving SNCI. Considering that a unified signal system cannot currently realize high-precision positioning and high-speed data transmission simultaneously in SNCI, this project proposes a Correlation Domain Indefinite Pulse Position Modulation (CDIPPM). A pilot channel and a data channel are introduced in this technology, which are distinguished by Code Division Multiplexing (CDMA). The synchronization function is provided by the pilot channel, thereby freeing the data channel of this function. The phase of the pseudorandom code can then be used as the carrier of information. In order to transmit more information, the transmitter of the proposed technology superimposes on the data channel multiple sets of spread spectrum sequence, which are generated from one set of spread spectrum sequence by different cyclic shifting operations. The receiver will identify the number and location of the correlation function peaks by a detection algorithm and recover the message. It can be seen by theoretical analysis and simulation verification. The technology can significantly improve satellite data transmission rates and maintain the original positioning function while minimizing change in the original GNSS signal. Therefore, the SNCI system based on this technology has the following advantages: a unified signal system, high positioning accuracy, high data transmission rate, and a backward navigation function, and it is easy to promote....
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