Navigation positioning method based on broadcasting RTCM-104-2.X data

Abstract

The application discloses a navigation positioning method based on broadcasting RTCM-104-2.X data. The navigation positioning method receives and processes GPS satellite L1 frequency point signals to realize navigation positioning. Meanwhile, positioning position coordinates, pseudo-range correction numbers, change rates of the pseudo-range correction numbers, uncorrected carrier phase observations and uncorrected pseudo-range observations are encoded in the RTCM-104 2.X format to form a binary coded data stream, which is transmitted to a radio station with a transmitting function in the form of RS232 level through a serial port and is broadcasted. The application can be used as a differential GPS reference station. The RTCM-104 2.X format differential GPS correction numbers, pseudo-range observations and carrier phase observations can be received through a specific data link to be used for pseudo-range differential or carrier phase differential positioning. The application improves the positioning precision to the meter level or even the centimeter level.

Description

Technical Field

[0001] This invention relates to a navigation and positioning method based on broadcasting RTCM-104 2.X data, which is mainly applied to differential GPS reference stations that need to broadcast RTCM data and belongs to the field of satellite navigation and positioning. Background Technology

[0002] Beginning in the 1970s, the United States began developing a new generation of global satellite navigation and positioning system, GPS (Global Positioning System). Using corresponding equipment to receive signals transmitted by satellites, it can achieve global, all-weather, real-time navigation and positioning functions, providing users with real-time location information. However, to this day, the Precise Positioning Service (PPS) of the GPS system remains closed to the public. Ordinary users can only use the Standard Positioning Service (SPS) using the C / A code. Although the US government announced the cancellation of the Selective Availability (SA) policy at the end of the last century, the current single-point positioning accuracy of GPS receivers using the C / A code is approximately 25 meters (95% confidence level, two-dimensional horizontal error), which still cannot meet the requirements of some systems requiring high positioning accuracy. It is based on this practical need that the Differential GPS system emerged. In a Differential GPS system, a reference GPS receiver, called the Differential GPS reference station, is included. This reference station completes the calculation of all visible GPS satellite differential corrections, pseudorange, carrier phase, and other related data items and broadcasts them to users (mobile stations) within a certain range via a specific data link.

[0003] Because different users use GPS receivers from different manufacturers, the differential information published by differential GPS reference stations must conform to standard protocols to be applied to receivers from various manufacturers. Currently, the most widely used protocol adopted by receiver manufacturers is the RTCMSC-104 differential protocol developed by the International Maritime Radio Technical Committee (RTCM).

[0004] The RTCM-104 standard format is a data format standard for providing differential GPS services proposed by the International Maritime Radio Technical Committee in November 1983. Version 1.0 was published in November 1985. After five years of experimental research and the acquisition of abundant experimental data, the document was upgraded and revised, resulting in Version 2.0 published in January 1990. To meet the needs of carrier phase differential GPS, Version 2.1 was published in January 1994. This version retained the basic messages and added several new messages to support Real-time Dynamic Positioning (RTK). With the increasing sophistication of the GLONASS system and the emergence of GNSS-compatible receivers on the market, Version 2.2 was published in January 1998. This version, while retaining the basic messages of Version 2.1, added several new messages to support the GLONASS system.

[0005] With the development of GPS and wireless communication technologies, high-precision, real-time differential GPS positioning technology has been widely applied in many fields. The use of GPS receivers capable of transmitting RTCM SC-104 messages is also increasing. Currently, foreign companies developing and producing GPS receivers, such as NovAtel (Sweden), AshTech (France), Trimble (USA), and JAVAD, have all developed and produced GPS receivers capable of transmitting RTCM SC-104 messages. Domestically produced devices of this type generally utilize hardware systems composed of foreign GPS OEM boards and microprocessors. Therefore, it is essential to conduct relevant algorithm and data processing research, combining signal reception technology, navigation and positioning algorithms, and related differential information data processing technologies to produce GPS receivers with independent intellectual property rights capable of transmitting RTCM SC-104 messages. Summary of the Invention

[0006] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide a navigation and positioning method based on broadcasting RTCM-1042.X data. This method utilizes the received GPS satellite L1 frequency signal to realize navigation and positioning functions, and completes the calculation of all relevant data items such as differential corrections, pseudoranges, and carrier phases of visible GPS satellites. These data items are encoded in RTCM-1042.X format to form a binary encoded data stream, which is then transmitted to other external data devices via a serial port in RS232 level format.

[0007] The technical solution of this invention is:

[0008] A navigation and positioning method based on broadcasting RTCM-104-2.X data includes the following steps:

[0009] (1) Receive and process GPS satellite L1 frequency signals, and use the least squares method to achieve GPS satellite navigation and positioning;

[0010] (2) Encode the relevant information of GPS navigation and positioning in RTCM2X format to form a binary encoded data stream; the relevant information includes positioning coordinates, pseudorange correction, rate of change of pseudorange correction, uncorrected carrier phase observation and uncorrected pseudorange observation.

[0011] The steps for encoding in RTCM-104 2.X format are as follows:

[0012] (a) Pack the relevant information, continuously acquire 24 bits of RTCM-104 2.X telegram data at the current time and divide them into 4 groups, each containing 6 bits;

[0013] (b) Based on the current time message in step (a) and the last two digits of the previous time message. * 29 and d * 30 Find the parity bit of the telegraph message;

[0014] (c) Determine if the 30th bit of the telegram at the previous moment is 1. If it is 1, proceed to step (d); otherwise, proceed to step (e).

[0015] (d) Invert the d1 to d24 data of the telegram at the current time;

[0016] (e) Roll the 24-bit data obtained in step (d);

[0017] (f) Calculate the 29th and 30th bits of the current telegram for verification in the next time step, defined as d. * 29 and d * 30 ;

[0018] (g) Combine the 30-bit telegraphs processed in steps (a) to (f) into a single byte containing 8 bits that meets the conditions;

[0019] (3) Transmit the binary data stream formed in step (2) to other external data devices through the serial port in RS232 level form.

[0020] In step (2), "rolling" refers to swapping the four groups of 6-bit data in reverse order.

[0021] The specific steps for composing an 8-bit byte of data that meets the conditions in step (2) are as follows:

[0022] (1) If a 30-bit data message is composed of 5 bytes, then byte 1 contains the first six bits of the 30-bit data, D1 to D6, and byte 2 contains D7 to D6. 12 Byte 3 contains D 13 ~D 18 Byte 4 contains D 19 ~D 24 Byte 5 contains D 25 ~D 30 ;

[0023] (2) Each byte in step (1) is then ORed with 0X40 to obtain an 8-bit data byte.

[0024] The advantages of this invention compared to the prior art are:

[0025] (1) The method of the present invention directly encodes the differential information and other related data items in the RTCM-104 2.X format inside the receiver. The computational load required by the method is processed in the back-end navigation and interface part, without involving the front-end signal processing part. It has strong real-time performance and does not require additional hardware costs or auxiliary instruments. Therefore, it can reduce costs and save hardware resources compared with the traditional differential GPS base station method with RTCM encoding function designed by using OEM board and other circuits.

[0026] (2) The method of the present invention has independent intellectual property rights. Compared with the expensive GPS base stations imported from abroad, which cost tens of thousands or even hundreds of thousands of yuan, it is cheaper and more flexible in use.

[0027] (3) The present invention has a wide range of applications. The RTCM 104 protocol is a DGPS message formulated by the Maritime Radio Technical Committee. This message group has been widely recognized and applied internationally and is constantly being updated. The RTCM message broadcast by the present invention can meet the user's needs to realize the functions of position differential, pseudorange differential and carrier phase differential position. Attached Figure Description

[0028] Figure 1 This is a flowchart of the method of the present invention;

[0029] Figure 2 This is a schematic diagram of the RTCM 2X universal message format of the present invention. Detailed Implementation

[0030] The present invention will now be described in further detail with reference to the accompanying drawings and the specific features described herein:

[0031] This invention provides a navigation and positioning method based on a satellite navigation system, utilizing GPS satellite L1 frequency signals for navigation and positioning, and broadcasting differential information in RTCM 2.X message data format. It primarily employs the least squares method for navigation and positioning using the C / A code pseudorange of the GPS satellite L1 frequency, and encodes the calculated GPS satellite pseudorange corrections and other differential information data items according to the RTCM 2.X message data format. For example... Figure 1 As shown, the present invention includes the following specific steps:

[0032] (1) Receive and process GPS satellite L1 frequency signals and use the least squares method to achieve GPS navigation and positioning.

[0033] First, the user's location is determined using the principle of radio ranging. This principle requires measuring the time it takes for a radio signal to travel from a known satellite to the user. Multiplying this time by the speed of radio signal propagation (the speed of light) yields the distance between the satellite and the receiver, i.e., pseudorange. By measuring the pseudoranges between multiple satellites and the user, the user's location can be determined.

[0034] ρ=R+c×Δt svi +c×Δt Ai +c×α (1)

[0035] In the formula: ρ—pseudo-distance;

[0036] R—the geometric distance from the satellite to the receiver;

[0037] c — speed of light;

[0038] α — Receiver clock bias;

[0039] Δt svi —The deviation between the clock of the i-th satellite and the system clock;

[0040] Δt Ai —The propagation delay of the signal from the i-th satellite through the atmosphere, including the ionospheric and tropospheric delays;

[0041] In the above formula, the deviation between the satellite clock and the system clock, as well as the signal propagation delay, can be obtained by demodulation from the message information provided by the satellite. Furthermore, for the user, the receiver clock itself has frequency drift and cannot be synchronized with the satellite system clock. Therefore, due to the error introduced by the receiver clock bias, the distance between the measured point and the satellite observed by the receiver is not the actual distance; this is called pseudorange.

[0042] Let the spatial coordinates of the receiver (target) be (x, y, z), and the spatial coordinates of the i-th satellite be (x, y, z). i y i , z iSubtract the distance c×Δt caused by the deviation of the i-th satellite's clock from the system time from the left and right sides of equation (1) above. svi And the distance c×Δt caused by the propagation delay after passing through the atmosphere. Ai And let the pseudodistance ρ′ be:

[0043]

[0044] Substituting equations (2) and (3) into equation (1), we get:

[0045] ρ′=ρ-c×Δt svi -c×Δt Ai (4)

[0046] In equations (2) and (3), the satellite's spatial position coordinates (x i y i , z i The pseudorange can be obtained from the satellite's message. It is calculated by measuring the time delay between the pseudo-random sequence received by the receiver from the satellite and the matching pseudo-random sequence generated by the receiver, multiplied by the signal propagation speed (speed of light). Due to receiver clock bias, four equations are required to determine the receiver's three-dimensional coordinates; that is, at least four satellites are needed to determine the receiver's spatial position coordinates.

[0047] In the above formula, let Let be the estimated values ​​(known quantities) of x, y, z, and α; Δx, Δy, Δz, and Δα be the deviations (unknown quantities) between the estimated values ​​and the true values; and Δρ be the pseudorange, representing the true measured value ρ and the pseudorange estimate ρ′. u If the deviation is between them, then equation (2) can be written as:

[0048]

[0049] Expanding the above equation using a Taylor series and ignoring error terms of second order or higher, after observing four or more satellites, the equation can be written as:

[0050] A·ΔX=Δρ (6)

[0051] ΔX=(Δx, Δy, Δz, Δα) T (7)

[0052] Δρ=(Δρ1, Δρ2, Δρ3, Δρ4) T (8)

[0053]

[0054] Where A is the direction remainder matrix between the satellites and the receiver involved in the navigation calculation, and n represents the number of satellites; e ijIt is the direction cosine of the i-th satellite to the receiver in the ECEF coordinate system (Geocentric Earth-Fixed Coordinate System), where n = 4; when the receiver observes more than 4 satellites, equation (6) is transformed into the following equation using the least squares method:

[0055] A T ·A·ΔX=A T ·Δρ (10)

[0056] ΔX=[A T ·A] -1 ·A T ·Δρ (11)

[0057] In this case, n is greater than 4 in equation (9), which means the number of satellites participating in the positioning.

[0058] Through the above calculations, we can obtain the deviations Δx, Δy, and Δz between the estimated and true values, and thus obtain the true spatial coordinates of the receiver.

[0059]

[0060] (2) Encode the relevant information of GPS navigation and positioning in RTCM 2X format to form a binary encoded data stream; the relevant information includes positioning coordinates, pseudorange correction, rate of change of pseudorange correction, uncorrected carrier phase observation and uncorrected pseudorange observation.

[0061] The RTCM message differential protocol used in this invention defines a total of 63 message types, among which the message types used to implement differential positioning are mainly type 1, type 3, type 18 and type 19.

[0062] The RTCM message format retains the word length, word format, parity check rules, and other characteristics of GPS messages. The main difference between the two formats is that the length of each subframe in the GPS message format is fixed, while the differential GPS message format uses a variable-length format. The RTCM message format consists of two parts: a general message format and a part that varies depending on the message type. Each frame of an RTCM message is N+2 words long, where N is the data frame length, and 2 is a two-word general message applicable to all message types. This two-word general message serves as the header for each message type, with the same format and content, such as... Figure 2 As shown.

[0063] The RTCM message content is as follows:

[0064] Each word of an RTCM message is decomposed into five 6-bit bytes. The first four bytes contain data information, and byte five is a parity check code used to verify the correctness of the received RTCM data. RTCM messages use 8-bit bytes (bits 1 to 6 are the message content, bit 1 represents the LSB (least significant bit), and the last two bits are 0x40) for data transmission. Before encoding, it is necessary to determine whether to invert the current four bytes based on whether the last bit of the previous word is 1. Since the message is sent with the least significant bit first, a "rolling" process is required before transmission.

[0065] The relevant information is encoded in RTCM 2X format through the following steps:

[0066] (a) Pack the relevant information, continuously acquire 24 bits of RTCM 2X telegram data at the current time and divide them into 4 groups, each containing 6 bits;

[0067] The 24 bits of data acquired consecutively are represented as d1, d2, d3, ..., d24 and divided into 4 groups, each containing 6 consecutive bits of data. The complete RTCM frame message consists of N+2 30-bit words. Each word is decomposed into 5 6-bit bytes. Of the 5 6-bit bytes, 4 are valid data and 1 is parity check.

[0068] (b) Based on the current time message in step (a) and the last two digits of the previous time message. * 29 and d * 30 Find the parity bit of the message; similar to GPS navigation messages, the RTCM-104 format message uses a (32, 26) Hamming code for parity checking. The formula for finding the parity bit in the navigation message is as follows:

[0069]

[0070] The symbols in the above formula This indicates that an XOR operation is performed.

[0071] (c) Determine the d of the telegram from the previous moment. * 30 If the bit is 1, proceed to step (d); otherwise proceed to step (e).

[0072] (d) Based on the 30th position of the previous character, i.e., d * 30 Determine the character d1, d2, d3, ..., d 24 Whether to negate; that is, if d * 30 If the sum is 1, then set d1, d2, d3, ..., d24 Perform a bitwise NOT operation, changing 0 to 1 and 1 to 0; if d * 30 If the value is 0, then set d1, d2, d3, ..., d 24 No bitwise NOT operation is performed; the result remains unchanged. Execute. This will complete the function described in this step, where i = 1 to 24.

[0073] (e) Roll the 24-bit data obtained in step (d); due to the characteristics of data communication, the least significant bit (LSB) is sent first when data is sent. Therefore, during encoding, the 24-bit number must be rolled first. Rolling means swapping the four groups of 6-bit data in reverse order. For example, the number arranged as "bit1bit2bit3bit4bit5bit6" is arranged as "bit6bit5bit4bit3bi2bit1", and the number arranged as "bit7bit8bit9bit10bit11bit12" is arranged as "bit12bit11bit10bit9bi8bit7".

[0074] (f) Calculate the 29th and 30th bits of the current telegram for verification purposes at the next time, defined as d. * 29 and d * 30 ;d1, d2, d3, ..., d 24 After executing steps a, b, c, and d above, 24 consecutive bits of data have generated a 30-bit RTCM message, denoted as D30, D29, D28, ..., D2D1. Bits D30 and D29 at the current time are used for the message check calculation at the next time step, defined as d. * 29 and d * 30 , that is, d ＊ 29 =D 29 and d ＊ 30 =D 30 .

[0075] (g) Combine the 30-bit message processed in steps (a) to (f) into bytes containing 8 bits of data that meet the conditions. For example, combine the 30-bit RTCM message "D30, D29, D28, ..., D2D1" into 5 bytes. Byte 1 contains D1 to D6, and Byte 2 contains D7 to D8. 12 Byte 3 contains D 13 ~D 18 Byte 4 contains D 19 ~D 24Byte 5 contains D 25 ~D 30 Each byte is then ORed with 0x40 to obtain a byte containing 8 bits of data. The other words in the RTCM message are then encoded, thus forming a binary data stream that can be transmitted via the serial port in RS232 level format.

[0076] (3) Transmit the data stream formed in step (2) to other external data devices through the serial port in RS232 level form.

[0077] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A navigation and positioning method based on broadcasting RTCM-104-2.X data, characterized in that... The steps are as follows: (1) Receive and process GPS satellite L1 frequency signals, and use the least squares method to achieve GPS satellite navigation and positioning; (2) Encode the relevant information of GPS navigation and positioning in RTCM-104-2.X format to form a binary encoded data stream; the relevant information includes positioning coordinates, pseudorange correction, rate of change of pseudorange correction, uncorrected carrier phase observation and uncorrected pseudorange observation. The steps for encoding in RTCM-104-2.X format are as follows: (a) Package the relevant information, continuously acquire 24 bits of RTCM-104-2.X telegram data at the current time and divide them into 4 groups, each containing 6 bits; (b) Based on the current time message from step (a) and the last two digits (d*) of the previous time message. 29 and d* 30 Find the parity bit of the telegraph message; (c) Determine if the 30th bit of the telegram at the previous moment is 1. If it is 1, proceed to step (d); otherwise, proceed to step (e). (d) Invert the d1 to d24 data of the telegram at the current time; (e) Roll the 24-bit data obtained in step (d); (f) Find the 29th and 30th bits of the current telegram for verification in the next time step, and define them as D29 and D30; (g) Combine the 30-bit telegraphs processed in steps (a) to (f) into a single byte containing 8 bits that meets the conditions; The specific steps to assemble a byte of data that meets the requirements are as follows: (21) If a 30-bit data message is composed of 5 bytes, then byte 1 contains the first six bits of the 30-bit data, D1 to D6, and byte 2 contains D7 to D6. 12 Byte 3 contains D 13 ~D 18 Byte 4 contains D 19 ~D 24 Byte 5 contains D 25 ~D 30 ; (22) Each byte in step (1) is then ORed with 0X40 to obtain an 8-bit data byte; (3) Transmit the binary data stream formed in step (2) to other external data devices through the serial port in RS232 level form.

2. The navigation and positioning method based on broadcasting RTCM-104-2.X data according to claim 1, characterized in that: In step (2), "rolling" refers to swapping the four groups of 6-bit data in reverse order.

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