As a new type of military reconnaissance equipment with broad development prospects, the miniature reconnaissance robot can rapidly monitor battlefield movements and environmental conditions, as well as combat damage assessment in real time, which can improve the speed and accuracy of operations. An important development direction of the reconnaissance robot system is to form a network distributed structure, that is, each device in the monitoring center must simultaneously supervise multiple reconnaissance robots scattered in the remote place, improve the monitoring efficiency, and use the GPS positioning system to obtain the position of the robot in front Information is an indispensable link. The fusion of robot motion sensor information and GPS positioning information in reconnaissance robots, combined with electronic maps, centrally displays the robot's spatial location and attribute information on the screen of the monitoring center, provides decision support for monitoring and management, and greatly improves management efficiency. The second generation satellite navigation system. Because it can provide real-time high-precision three-dimensional position, three-dimensional speed and time information to any place on the global surface and near-Earth space, it has been widely used in various fields of military and civilian use. However, in practical applications, the GPS receiver I must undergo secondary development, combine the received data with the surrounding terrain data or building | object data, and correct and supplement the positioning data to overcome the various professionalisms provided by it. The inconvenience caused by the data to users, while overcoming GPS positioning accuracy errors caused by atmospheric refraction delays, satellite clock differences, and the use of selective SA measures by the US Department of Defense. 1 System composition and working principle The remote operation reconnaissance robot system we developed is a comprehensive application system that integrates the global satellite positioning system (GPS), wireless data transmission module, electronic map and information processing system. The system structure is shown as follows: The receiver has 12 parallel channels and outputs the original data such as carrier phase and pseudorange, and its ephemeris output is indispensable for reverse pseudorange differential work. As a differential workstation, the control center is realized by an ordinary microcomputer. Among them, COM1 is connected to the serial port 2 of GPS25LVS as a differential workstation, and COM2 is connected to the wireless data transmission module for front and rear data communication. The wireless digital transmission module ± attached to the front robot sends the differential GPS data in RTCM-SC104 format output from the serial port 2 of the GPS receiver to the rear control center. The wireless data transmission module uses the FC-TK404 / RS-232 data transmission component. Before the system works, it is necessary to pay attention to the initial setting of the hardware module used, and initialize the GPS25-LVS receiver to the automatic positioning mode. In order to facilitate the decision-making of the staff in the control center, it is necessary to visualize the position of the robot in front. Therefore, we combine the data processed by the reverse pseudorange difference processing with the electronic map to perform combined positioning to achieve the purpose of visual positioning. There are many methods for the development and management of electronic maps. The system adopts the method of storing and developing background maps in the form of BMP bitmaps under the VB6.0 environment. The electronic map can intuitively represent the background feature information. The electronic map in the system has a map editing function, which can easily modify, insert, and delete space targets and attributes. Due to the characteristics of the distributed structure of the reconnaissance robot network, taking into account the fact that the general area of ​​the reconnaissance robot is known, in order to simplify the management of the system, we adopt the method of dividing the surveillance area twice, so that each surveillance area is on the monitor Within, divide the large-scale electronic map into several small maps. For the first positioning, use high-scale positioning to give the monitors an overall grasp, and then enter the low-scale positioning, and transfer to the map that meets the requirements. By implementing operations such as zooming in, zooming out, panning, and roaming, the map can accurately locate the position of the robot and realize the graphic display function of the electronic map. At the same time, it also avoids the problem that the map targets due to the limitation of the scale will be piled up and crowded together during the zoom-out operation, resulting in the unrecognizable target. 2 Selection of GPS positioning methods Currently, there are three methods for obtaining GPS positioning information: GPS single-point positioning, forward differential GPS positioning and reverse differential GPS positioning. Due to the limitation of GPS technology in the United States, if GPS single-point positioning is used, the positioning data output by the attached GPS receiver will be transmitted to the monitoring center by wireless data transmission radio stations without any processing. This positioning method has simple equipment but low positioning accuracy (about 100m), which cannot meet the positioning accuracy requirements of the reconnaissance robot system. Namely position difference, pseudorange difference, phase smoothing pseudorange difference and phase difference. The working principles of these four types of differential methods are the same, that is, GPS observation is performed on the reference station, the correction value of the reference station to the satellite is calculated using the known precise coordinates of the reference station, and the correction value is sent out in real time. While receiving GPS observations, the user receiver also receives the correction value of the reference station and corrects its observations. Afterwards, the corrected result is used to perform positioning calculation to solve the position of the accurate user receiver. Because this kind of correction can cancel common errors, such as satellite clock deviation, ephemeris error, ionosphere error, troposphere error, etc., thereby improving the positioning accuracy, real-time positioning accuracy from 100m to 5 ~ 3m, the monitoring center can obtain Precise positioning information. However, since each mobile station should receive the differential correction value sent by the GPS reference station, the differential reference station needs a high-power transmitter to broadcast the correction information to a relatively large area, and the mobile station needs to receive and send two links to report accurate positioning Information, the system is complex, the time overhead is large, and the channel bandwidth requirements are high, so it is not suitable for this system. The reverse differential GPS algorithm is basically the same as the general forward differential GPS algorithm, both of which are differential ideas. Therefore, it is possible to obtain accuracy comparable to ordinary forward differential GPS, but all calculations are performed by the base station. The mobile station GPS transmits all the observed original distance information to the reference station through the data link. The reference station GPS simultaneously collects distance information and ephemeris data, calculates the satellite position from the ephemeris, and uses the satellite position and the known position of the reference station to obtain The true distance R is calculated to calculate the correction value, and then the calculated correction value is used to correct the distance information sent by the mobile station. This greatly improves the distance accuracy, and finally uses the corrected data for positioning and calculation to obtain the real-time position of the mobile station. Therefore, the reverse differential GPS has the following characteristics: the data communication chain is transmitted by the mobile station to the reference station, which is reverse, and the transmitted content is the original data information of the mobile station; the mobile station does not perform any calculation, and the reference station completes all Differential correction and positioning solution; the mobile station does not know its position, but the reference station can know the position of the mobile station in real time; due to the reverse of the data link and the solution of the mobile station by the reference station, a reference station can only Limited mobile stations work together. Based on the above characteristics, the inverse differential GPS method is particularly suitable for moving targets with antenna repeaters and targets requiring very simple mobile stations. Pseudorange differential is currently the most widely used technology by users. Almost all commercial differential GPS receivers use this technology. The RTCMSC-104 recommended by the International Maritime Radio Commission also uses this technology. Considering the miniaturization of the micro reconnaissance robot system we designed and the asymmetry of the GPS positioning information required by the reference station and mobile station, for this purpose, the software of the reverse pseudorange difference GPS 3 reverse difference algorithm is used to achieve the reverse difference The software implementation of the algorithm is briefly described as follows: After the program starts, the position of the reference station is first obtained. The accurate determination of the geocentric coordinates of the reference station is the key to the differential GPS positioning center. There are two methods for the geocentric coordinates of general reference stations: single point multiple measurement method and joint measurement method. Since China has established manual ranging stations around the country, the use of GPS combined surveying based on this can make the accuracy of the differential reference stations we use reach the required magnitude. The geocentric coordinates of the reference station are 6. For differential stations, pseudorange, carrier phase information and ephemeris information are required to calculate and correct the information, while the mobile station only requires pseudorange and carrier phase information. These settings only need to send a series of control commands to the receiver through the serial port. At the same time, initialization processing such as setting the baud rate must be performed on the port. The control center sends a command to obtain the ephemeris to judge whether there is an external interruption. If there is any processing first, if not, extract the serial port pseudorange information, and then select the visible star: ①Read a frame of data at time t from the pseudorange random file , Can be seen asterisk 1,2 ..., 32) high angle (elevation angle) "(), select a valid satellite with a signal-to-noise ratio greater than 33 and a ()> 5 *, let the satellite j (j = 1, 2 , ..., 32) P (, t) ② Read a frame at time tk in the main pseudorange random file) Visible asterisk k (k = 4 repeat ①. ③ Select the largest a (gi) from the satellite g The satellite is the apex. ④ Read the ephemeris random file and calculate the coordinates (x, yz) of the g satellite at time t. Here, the position of the satellite at time t in the WGS-84 coordinate system is calculated according to the broadcast ephemeris. The accuracy of the broadcast ephemeris is not high, so here is a simplified method for calculating the satellite position. First, calculate the orbit parameters according to the "two-body problem" formula; then, according to the orbit perturbation parameters given by the navigation message, perform perturbation correction, calculate the corrected Orbital parameters; then calculate the coordinates of the satellite in the orbital coordinate system; Then, only considering the influence of the earth's rotation, the orbit coordinate system is converted into the WGS-84 coordinate system. That is, the geocentric coordinates k of each satellite in the WGS-84 coordinate system are calculated according to formula (1), where ik is the perturbation correction After the orbital inclination, Lk is the longitude of the ascending intersection at time t. In the GPS positioning system, the geometric accuracy factor GDOP is still used to represent the correlation factor of the positioning accuracy with the position of the satellite collection. In simple terms, GDOP is the positioning error coefficient. Among all the visible satellites, select a group from all possible combinations of four satellites to make GDOP the smallest. At this time, this group of satellites will provide the highest positioning accuracy. There are many methods for selecting constellations. Commonly used sagittal four sides The volumetric calculation method is very large, so we need to find a simple and practical method. Considering that the volume of the tetrahedron is proportional to its height and base area, so when choosing the constellation, it is not necessary to directly find the volume of the vector tetrahedron, but to find Its high and bottom areas simplify the method of selecting constellations. First, from the visible satellites, select the star with the highest high angle as the top star, and then among the remaining visible stars , With the height greater than 5 degrees as the constraint, select three satellites to calculate the area of ​​the sagittal triangle, and take the maximum area as the base star. Next, calculate the straight-line distance between the time difference workstation and the selected four stars: where the subscript represents the i-th satellite (i = correct pseudorange: when observing four satellites, ignore the observation random error, according to the observation equation = R * + C * dT + v () to solve the user coordinates (x, yz) D. Then coordinate conversion, position calculation. Where dT is the clock difference, v is the receiver noise, and Ru is the linear distance between the user and each satellite at time t. The software flow chart of the inverse difference algorithm is shown as follows: In the VB6.0 environment, the software implementation of the inverse pseudorange GPS difference algorithm) was carried out and the GPS information was independently developed by using the background map in the form of BMP bitmap storage The application of the processing system realizes the visualization of the specific positioning of the target ahead. 4: Sum is the curve of the collected base station and mobile station, and is the result curve of the differential processing. In the diagram in ~ 5, the "reference value" is the value of the reference point we measured. At the base coordinate, when the dropout changes by * 0.01 ', the absolute coordinate change of the geocentric is about Ax = ± 5.5m, = ± 10.8m, 4 = * 14.3m; when the longitude changes by * 0.01', the absolute coordinate of the geocentric The change is about Ax = * 0m. In the B-1 coordinate system and the L-1 coordinate system, the reference is B0, L0, and the upper and lower two lines are the deviation * 0. 03 'line. In the H-1 coordinate system, the reference is H0, the interval between every two lines is 20m, and the interval between the two lines is 40m. From the measured curve, the positioning results before the difference are constantly verified by the reverse pseudorange difference algorithm to improve GPS The receiver positioning accuracy is feasible, and the method is relatively simple and easy to implement. The experimental results show that the average maximum error of the absolute coordinates does not exceed * 5m. The inverse pseudorange difference algorithm is particularly suitable for situations within 100km. There must be at least four publicly visible satellites to achieve three-dimensional positioning. 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