According to the statistics of the “Organization for International Economic Cooperation and Developmentâ€, in the industrialized countries, due to the lack of traffic information caused by the driver’s lack of navigation information, the average annual loss is several billion US dollars. Experts predict that by the end of the year, if no control measures such as navigation technology have been adopted, such losses will increase by a factor of four. The coordination of navigation technology with other information processing systems can effectively improve this situation. At the same time, it can also provide drivers with information other than traffic information, such as the function of querying resources. Specifically, the driver can not only know his location from the electronic map, and the best driving route determined and downloaded by the information processing center of the intelligent transportation system according to the current traffic conditions, but also can be accessed from the information processing center via the wireless network. Query all the information needed in the database. It can be seen that navigation technology has extremely important significance for the intelligentization of automobiles.
The status quo of car navigation technology Currently, car navigation technology is mainly divided into autonomous navigation, fleet management, and resource types. Navigation and fleet management are the most widely used applications. An inquiry-type self-autonomous so-called autonomous navigation means that the driver can intuitively understand the current position and speed of the vehicle through the navigation system and display system installed in the vehicle, and determine the best driving route according to the electronic map. This technology not only requires the installation of a navigation system but also the support of an electronic map system. Therefore, its application has certain difficulties and limitations, but this is the mainstream of the development of the entire car navigation technology. At present, autonomous navigation technology is mainly provided by automobile manufacturers as optional equipment for limousines. For fleet management, its implementation is relatively simple. It only needs to install a navigation system on the user's car and upload its position and speed information to the command center through the data station chain so that the command center can be assisted in real time with the help of the electronic map. Understand the user's location and speed information, while the command center can also download the command and scheduling information to the user. If the alarm signal is added to the upload information, safety monitoring is realized.
At present, fleet-managed car navigation systems have been applied in many parts of China. At present, the technologies used in car navigation systems include Ling, dead reckoning, map matching, land radio frequency and beacons. Among them, the above-mentioned adoption and dead reckoning techniques are used in the world-wide automotive navigation systems. The technical system component is an abbreviation of 1, the main function of this system is to use the navigation satellite to measure time and distance. It was constructed by the U.S. Department of Defense in phases beginning in the year and has now been completed and put into use. The system is divided into parts, that is, the space part. The ground support system is composed of unsynchronized navigation satellites evenly distributed in space orbits. The ground control stations, monitoring stations and monitoring stations make up the user receiver. There are two types of code receivers, of which the high-precision code receiver can only be used by licensed users of the U.S. military and its allies. Positioning principle positioning technology mainly uses code measurement pseudorange positioning principle.
The signals transmitted at the satellite include carriers with two frequencies and ranging codes and data codes modulated on the carrier. The ranging code pseudo code includes a code coarse ranging code and a code precision ranging code data code, ie, a broadcast message, which includes parameters such as satellite ephemeris, satellite orbit, position parameters, and clock correction. The receiver uses related technologies to track and lock satellite signals. When the pseudo-code of the satellite signal is aligned with the local pseudo-code of the receiver, the tracking and locking of the code is completed, in which the time delay Δ between the transmission and locking of the satellite signal is recorded, and then the satellite and the receiver are recorded. The distance pseudorange can be determined by the following equation. Delta, the distance between the satellite and the receiver, because it contains measurement errors, it is called pseudorange. The speed of light, Δ, is the time delay from launch to locking of the satellite signal.
Then, the position of the receiver can be determined by the following equation. In the formula, the coordinates of the geodetic coordinate system of the receiver antenna are unknown parameters ',,,' are the coordinates of the satellite in the geodetic coordinate system. These parameters are contained in the satellite ephemeris and are known parameters for the receiver. The error between the clock and the system clock is an unknown parameter. It can be seen that there is an unknown number in the formula. Therefore, as long as the satellites are observed at the same time, an equation similar to the equation can be obtained. The unknown equations can be solved by solving the equations together, thus realizing the positioning. In the initial stage of the positioning accuracy, the horizontal positioning accuracy of the code user, that is, the standard positioning service user, is the horizontal positioning accuracy of the code receiver user, that is, the precision positioning service user. Such high positioning accuracy makes the U.S. military unpredictable. Since the code is public, this accuracy will directly affect the immediate interests of the United States. Therefore, the US military has introduced measures to artificially reduce the positioning accuracy.
Therefore, the current user's horizontal positioning accuracy is, and the user's horizontal positioning accuracy is. At present, all users who use car navigation technology are users. Differential technology is considered as an ideal navigation and positioning system because it can provide location, speed, and time information on a global, all-weather, real-time basis, and even can provide attitude information. In addition, the device has a low price. However, for most users, the positioning accuracy is not satisfactory or even of practical value. Differential techniques have been created in this case. Differential technology, that is, it consists of differential stations, data links, and user receivers. The principle is to first measure the position of the differential table with other precision geodetic techniques as the true location of the point.
The differential station is also a receiver. It uses the difference between the difference station receiver and the true position as a common error correction amount, and then downloads the correction amount to the internal user machine through the data link. The user machine uses the correction amount to the The machine position output is corrected, and finally the meter-level positioning accuracy can be obtained. In practical applications, it is usually to perform networking and establish a wide-area differential system to expand the range of differential stations. At present, only a small number of foreign car navigation systems use technology. Although the system has many advantages, it is directly visible to the satellite because of its requirements. In addition, there are certain requirements on the number and geometric configuration of visible satellites. Especially in urban operating environments, buildings, overpasses, and even wet leaves will make visible satellites Blocking, causing the so-called receiver "lost lock", interrupt output. In addition, various types of radio interference in the city will further reduce the positioning accuracy, so relying solely on navigation is not enough. At this time, it is necessary to combine the integrated navigation technology with other navigation technologies to obtain highly accurate and highly reliable navigation data. At present, in the actual car navigation system, there are nearly map matching technologies used and combined, and decision-making techniques are used to achieve more accurate positioning. In addition, there are systems that use inertial navigation technology for dead reckoning and combining.
An automotive technology inertial navigation technology Inertial navigation technology is a navigation technology based on inertial sensors, ie, acceleration sensors, angular rate sensors and cybernetics. The basic principle is to use the accelerometer to sense the motion acceleration of the carrier and obtain the motion rate after one integration. Then, once again, an integral is obtained to obtain a movement distance and an angular rate sensor is used to sense the angular velocity of the carrier. After one integration, the movement angle is obtained. The inertial navigation system is a precision instrument system that uses inertial technology and control technology. It can accurately and accurately output the position, motion speed, heading and attitude information of the carrier. Due to its high degree of autonomy, it is widely used in military applications. And aerospace industry. One of the key technologies of inertial navigation technology is inertial sensor technology, among which the angular rate sensor is the most important. The early-use angular rate sensor was a gyroscope that sensed the angular rate using the gyroscope's fixed-axis, precession, and torque characteristics. The accuracy of the gyroscope will determine the accuracy of the entire inertial navigation system. High-precision gyroscopes, such as liquid-floating and electrostatic, must be mounted on a platform with a complex structure and the platform-based inertial navigation system is expensive, and the application is affected. limit. Therefore, there have been solid-state angular rate sensors, including laser gyros, fiber optic gyros, and micro-machined gyroscopes. Although these sensors are relatively low-precision, they are small in size and can be directly mounted on a carrier, which constitutes a strap-down inertial navigation system. Strapdown inertial navigation systems are low in price, simple in structure, small in size, and widely used in applications. They are currently the development direction of inertial navigation technology and mining. For the dead reckoning system used in car navigation, the speed information obtained by the car's own speed sensor can be used as the basis for position estimation. However, only the speed is not enough to calculate the car's position, and it must also have heading information. Therefore, an angular rate sensor is also needed. Commonly used are solid-state inertial sensors, such as fiber optic gyroscopes and micromachined gyroscopes, because of their lower price and accuracy that can meet the needs of car navigation. The simple technology of integrated navigation technology cannot meet the needs of car navigation. Therefore, other technologies and combinations must be used. Information fusion technology is used to process navigation information and obtain navigation information with high precision and high reliability. The simplest combination is to weight-average the output with the output of other navigation sensors and obtain the combined data directly.
For example, when it is unable to work normally, it can continue to work to ensure that the entire system works normally. The best combination mode is shown in the figure. Under normal circumstances, the filtered output is the system output, and the output at this time is the optimal estimate. The accuracy is statistically higher than that of the two navigation sensors, and when loss of lock occurs, the system will automatically switch to the mode until the signal is recaptured and the system switches back to the combined output. Prospects for car navigation technology At present, car navigation technology is mainly used as a positioning function for other navigation technologies. Due to technical and cost issues, navigation technology has not been used for precise measurement of speed and attitude. Since the advent of technology, car navigation technology has really started to develop. However, because of its low accuracy and its own shortcomings, navigation accuracy cannot be truly improved. However, with the continuous reduction in the cost of inertial measurement devices, it is believed that the future car navigation technology will effectively use inertial technology to accurately measure the attitude of a car, thus providing a data foundation for effective control of the body roll and fore and aft pitch, along with inertial technology. The application of car navigation accuracy will also have a qualitative improvement, so that car navigation technology plays a huge role in human social life.
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