Low-cost high-precision positioning RTK system based on BDS + GPS dual-system carrier phase inter-satellite mixing difference algorithm

Abstract

The invention discloses a low-cost high-precision positioning RTK system based on a BDS + GPS dual-system carrier phase inter-satellite frequency mixing difference algorithm, and relates to the technical field of BDS Beidou satellites, GPS positioning systems and high-precision positioning measurement. The user receiver receives measurement data broadcasted to the satellite receiver by the BDS Beidou system and the GPS system, and the frequency carrier phase integer ambiguity of the BDS Beidou system and the carrier phase integer ambiguity of the GPS system are respectively determined through a carrier phase equation; recovering the integer characteristics of the phase inter-satellite difference ambiguity parameters of the carrier of the BDS Beidou system and the carrier of the GPS system; and determining the distance from the user BDS + GPS dual-mode receiver to the satellite. According to the method, the influence of different carrier phases of the BDS Beidou system frequency and the GPS system frequency can be avoided, and the integer characteristics of the phase ambiguity parameters of the BDS carrier and the GPS carrier of the mixed-frequency inter-satellite difference are recovered.

Description

Technical Field

[0001] The invention belongs to the field of satellite positioning system and positioning measurement technology, and particularly relates to RTK of a carrier phase mixing difference algorithm of B1I / B2I frequency of a BDS Beidou satellite system and L1 / L2 frequency of a GPS satellite system. Background Art

[0002] BeiDou Navigation Satellite System (BDS) is a satellite navigation and positioning system independently developed by my country with independent intellectual property rights. It is the third satellite navigation system that can be located internationally after the GPS of the United States and the GLONASS of Russia. At present, the BDS BeiDou Navigation Satellite System has begun to officially provide continuous passive positioning, navigation, timing and other services to the Asia-Pacific region. There are some shortcomings in single-constellation positioning, such as limited visible satellites and weak stability. Therefore, the research on multi-frequency and multi-system navigation and positioning has become a new hot spot in navigation and positioning. The use of multi-frequency and multi-system combined positioning will double the number of satellites, which is conducive to enhancing the strength of satellite geometry and improving positioning accuracy and stability. At the same time, the development of multi-frequency and multi-system has also challenged the compatibility and scalability of positioning models of different systems and frequencies. The present invention is based on a non-combined algorithm that is well compatible with the positioning solution of different satellite positioning systems of the BDS BeiDou satellite system B1 / B2 frequency and the GPS satellite system L1 / L2 frequency.

[0003] When positioning a dual-system receiver of the Beidou system and the GPS system, the commonly used technical means is to use the inter-satellite differential combination technology of the carrier phase to determine the carrier phase measurement value, and then obtain the distance value from the dual-system receiver to the satellite, and then use the distance from the receiver to the satellite to calculate the position of the dual-system receiver.

[0004] RTK is a technology that uses GPS carrier phase observations for real-time dynamic relative positioning. It can provide three-dimensional positioning results of the measuring station in a specified coordinate system in real time. It is a technology that uses BDS Beidou system GPS system frequency carrier phase observations for real-time dynamic relative positioning. When resolving the integer ambiguity of the BDS Beidou satellite system Bl frequency and GPS satellite system L1 frequency carrier phase measurement values, if you want to obtain the integer ambiguity of the BDS Beidou system Bl frequency and GPS system L1 frequency carrier phase, you must eliminate the errors in the measurement values. For the BDS Beidou satellite system and GPS satellite system dual system, the atmospheric delay, satellite orbit, satellite clock error and other errors in the BDS Beidou system B1 frequency and GPS system L1 frequency carrier phase measurement values ​​can be eliminated or weakened through an external reference station network to ensure that these errors do not affect the integer characteristics of the BDS Beidou system Bl frequency and GPS system L1 frequency carrier phase ambiguity. In addition, there is also the influence of the dual system receiver clock error, and the receiver clock error has a great influence, which is the main reason why the ambiguity of the BDS Beidou system Bl frequency and GPS system L1 frequency carrier phase measurement values ​​cannot restore the integer characteristics. An effective method to eliminate receiver clock errors is to perform intersatellite differentiation on the BDS Beidou system B1 / B2 frequency and GPS system L1 / L2 frequency carrier phase measurement values, eliminating the influence of receiver errors in the carrier phase measurement values ​​of different satellites Bl / B2 frequency and L1 / L2 frequency of the same dual-system receiver. However, the commonly used method currently requires intersatellite differentiation between the carrier phase measurement values ​​of the same system, B1 / B2 frequency or L1 / L2 frequency to eliminate the influence of receiver errors and restore the integer characteristics of the intersatellite differential ambiguity of the carrier phase observation values ​​of the same system and the same frequency. The reason why intersatellite differentiation can only be performed between single-frequency carrier phase measurement values ​​of a single system, BDS Beidou system B1 / B2 frequency or GPS system L1 / L2 frequency is that the wavelengths of carrier phases of different frequencies are different. Due to the different wavelengths of carrier phase measurement values, after the intersatellite differential combination of carrier phase measurement values ​​of different frequencies, the ambiguity of intersatellite differential carrier phase measurement values ​​does not have integer characteristics. The ambiguity of the inter-satellite differential carrier phase measurement value does not have an integer characteristic, which will result in the inability to quickly resolve the inter-satellite differential ambiguity in real time and achieve high-precision real-time rapid positioning.

[0005] When using the BDS Beidou system and GPS system dual system receiver for high-precision positioning, if the number of satellites in a single system is small (for example, in areas where satellite signals are severely blocked by many buildings and forests), in order to ensure that the BDS Beidou system B1 / B2 frequency and GPS system L1 / L2 frequency carrier phase measurement values ​​can be used to achieve high-precision positioning, it is necessary to perform inter-satellite differential combination of the BDS Beidou system B1 / B2 frequency and the GPS system L1 / L2 frequency carrier phase mixing, and be able to restore the integer characteristics of the inter-satellite differential ambiguity, so as to facilitate the integer ambiguity resolution. Due to the small number of single-system satellite observations, if the inter-satellite differential combination of the B1 frequency or L1 frequency carrier phase measurement values ​​is performed within the Beidou system and the GPS system, the utilization rate of the carrier phase observation data will be further reduced. When the number of dual-system satellites is small (for example, there are four satellites in the two systems), the number of inter-satellite differential observations is insufficient, and it is difficult to resolve the inter-satellite differential BDS Beidou system Bl / B2 frequency and GPS system L1 / L2 frequency carrier phase integer ambiguity through the geometric model, and high-precision positioning cannot be achieved. If the inter-satellite differential combination of the BDS Beidou system Bl / B2 frequency and GPS system L1 / L2 frequency carrier phase observation values ​​is not performed, and the ambiguity parameters of the Bl / B2 frequency and L1 / L2 frequency carrier phase observation values ​​of a single satellite are resolved, it is difficult to eliminate the receiver-related errors (mainly the receiver clock error) in the single satellite measurement value. In this way, not only are there more parameters to be estimated, but also due to the existence of errors related to the dual-system receiver, the ambiguity of the BDS Beidou system Bl / B2 frequency and GPS system L1 / L2 frequency carrier phase cannot be correctly calculated. The mixed-frequency inter-satellite difference of the BDS Beidou system B1 / B2 frequency and the GPS system L1 / L2 frequency carrier phase measurement values ​​can improve data utilization and achieve high-precision real-time rapid positioning when the number of BDS+GPS single system observation satellites is small. However, due to the different wavelengths of the BDS BeiDou system B1 / B2 frequency and the GPS system L1 / L2 frequency carrier phase observation values, after the mixed inter-satellite difference, the coefficients of the ambiguity of each single satellite are different, and the integer ambiguity parameters of the inter-satellite single difference cannot be formed, which will introduce too many non-difference integer ambiguity parameters of a single satellite, making it difficult to resolve the integer ambiguity parameters of a single satellite. If the B1 / B2 frequency and L1 / L2 frequency carrier phase ambiguity parameters of a single satellite of the BDS BeiDou system and the GPS system are combined into one ambiguity parameter after the inter-satellite single difference, due to the different wavelengths of the BDS BeiDou system B1 / B2 frequency and the GPS system L1 / L2 frequency carrier phase, the inter-satellite single difference ambiguity parameters will not have integer characteristics, and the real-time and fast resolution of the carrier phase integer ambiguity cannot be performed. Summary of the invention

[0006] The invention discloses a low-cost and high-precision positioning RTK system based on a BDS+GPS dual-system carrier phase inter-satellite mixing differential algorithm. The system is an embedded real-time RTK positioning system with a carrier phase mixing differential calculation function of a GNSS system developed on the basis of an integrated navigation development board. The embedded system first receives raw data broadcasted by satellites of the BDS+GPS dual systems to a satellite receiver for observation, and then confirms the BDS carrier phase integer ambiguity and the GPS carrier phase integer ambiguity respectively through a carrier phase observation equation, and performs RTK positioning using the carrier phase inter-satellite mixing differential algorithm; the obtained RTK positioning result is used to restore the integer characteristics of the ambiguity parameters of the carrier phase mixing inter-satellite differential in the updating process, thereby further improving the accuracy and reliability of the integrated navigation positioning result.

[0007] To achieve the above object, the technical solution of the present invention is as follows:

[0008] A low-cost, high-precision positioning RTK system based on the BDS+GPS dual-system carrier phase inter-satellite mixing differential algorithm. The hardware platform includes an embedded OPENSOURCE MCU network communication LTE Cat1 module, a satellite signal receiving module, and a power module. The satellite positioning receiving module is connected to an external GNSS spiral antenna. The GNSS spiral antenna is used to receive satellite signals. The BDS+GPS dual-system satellite raw data signal is used to determine the BDS carrier phase integer ambiguity and the GPS carrier phase integer ambiguity respectively through the carrier phase observation equation; the carrier phase inter-satellite mixing differential algorithm is used to restore the integer characteristics of the differential ambiguity parameters to improve the system positioning accuracy. The power module provides stable voltage for each functional module of the embedded platform. The serial communication module is used for the communication of data related to the embedded hardware platform and the local device, and the LTE CAT1 communication module is used to obtain base station data from the network in real time.

[0009] The embedded opensource MCU wireless communication LTE Cat1 module adopts the lowest-cost Hezhou Air724 and is compatible with China Mobile IoT's ML307.

[0010] The satellite signal processing module adopts the UM20 module of Unicore Starlink, which supports satellite signals such as BDS B1 / B2, GPS L1 / L2, GLONASS L1 / L2, Galileo E1 / E5b, and QZSS L1 / L2.

[0011] The voltage conversion circuit of the power module uses the DC / DC switching power conversion chip TPS5430, uses a 12V DC power supply as the input power supply of the TPS5430, and adds necessary resistors, capacitors, and diodes to the periphery of the TPS5430 chip to form two output voltages of 5V and 3.3V.

[0012] The RTOS embedded operating system is selected as the operating system of the device, and a low-cost high-precision positioning RTK system based on the embedded platform and based on the BDS+GPS dual-system carrier phase inter-satellite mixing differential algorithm is provided. The purpose of the present invention is to utilize the B1 / B2 frequency carrier phase measurement value of the BDS Beidou satellite system and the L1 / L2 frequency carrier phase measurement value of the GPS satellite system, perform a mixing inter-satellite RTK differential method on the BDS Beidou satellite system B1 / B2 frequency and the GPS satellite system L1 / L2 frequency carrier phase measurement value, and restore the integer characteristics of the mixing inter-satellite differential carrier phase ambiguity, so as to better realize the high-precision real-time rapid positioning of the BDS Beidou satellite system B1 / B2 frequency and the GPS satellite system L1 / L2 frequency carrier phase measurement value, and improve the dual-system positioning service capability, especially the positioning service capability when the satellite signal is severely blocked and the number of single-system satellites is insufficient.

[0013] The technical solution of the present invention realizes: a method for RTK differential of dual frequency mixing carrier phase of BDS Beidou satellite system B1 / B2 frequency and GPS satellite system L1 / L2 frequency, comprising the following steps:

[0014] Step 1: The user dual-system receiver receives the raw measurement data broadcasted to the user receiver by the BDS Beidou satellite system and the GPS satellite system, including:

[0015] BDS BeiDou satellite system’s B1 / B2 frequency pseudo-range observation data and B1 / B2 frequency carrier phase observation raw data;

[0016] The pseudo-range observation data of the L1 / L2 frequency and the carrier phase observation raw data of the B1 / B2 frequency of the GPS satellite system;

[0017] Step 2: Determine the B1 / B2 frequency carrier phase integer ambiguity of the BDS Beidou satellite system and the L1 / L2 frequency carrier phase integer ambiguity of the GPS satellite system through the dual-frequency mixing carrier phase observation equation;

[0018] (1) For the BeiDou system: The carrier phase integer ambiguity of the B1 / B2 frequency of the BDS BeiDou satellite system is determined by formula (1), which is:

[0019] λ BDS ·Φ BDS =ρ BDS +C·(t REV -t BDS )-λ BDS ·N BDS +0 BDS -I BDS +T BDS +M BDS +Δ BDS(1)

[0020] In the formula, λ BDS is the wavelength of the BDS BeiDou satellite system Bl / B2 frequency carrier phase; Φ BDS is the BDS Beidou satellite system B1 / B2 frequency carrier phase measurement value, the subscript BDS represents the Beidou system; ρ BDS is the geometric distance from the BDS BeiDou satellite to the user dual-system receiver, which is calculated from the initial position coordinates of the measuring station and the BeiDou satellite coordinates. The initial position coordinates of the measuring station are obtained by single-system pseudo-range single-point positioning, and the satellite coordinates are provided by the navigation file recorded by the receiver; C is the speed of light in vacuum, t REV is the dual-system receiver clock difference, in seconds; t BDS is the clock error of the Beidou system satellite clock; N BDS is the integer ambiguity of the BeiDou system Β1 frequency carrier phase observation value, 0 BDS is the Beidou system satellite orbit error, that is, the error of the satellite position coordinates; I BDS is the ionospheric delay error of the carrier phase observation value of the BeiDou system Β1 / B2 frequency, T BDS is the tropospheric delay error of the BeiDou system; M BDS is the multipath effect error of the carrier phase observation value of the BeiDou system Β1 / B2 frequency; Δ BDS is the carrier phase observation noise and unmodeled error of the BeiDou system Bl / B2 frequency;

[0021] (2) For the GPS satellite system: The carrier phase integer ambiguity of the L1 / L2 frequency of the GPS system is determined by formula (2), which is:

[0022] λ GPS ·Φ GPS =ρ GPS +C·(t REV -t GPS )-λ GPS ·N GPS +0 GPS -I GPS +T GPS +M GPS +Δ GPS (2)

[0023] In the formula, λ GPS is the wavelength of the L1 / L2 frequency carrier phase of the GPS satellite system, Φ GPS is the GPS system L1 / L2 frequency carrier phase observation value; ρ GPSis the geometric distance from the GPS satellite to the receiver, which is calculated from the initial position coordinates of the measuring station and the GPS satellite coordinates. The initial position coordinates of the measuring station are obtained by pseudo-range single-point positioning of a single system, and the satellite coordinates are provided by the navigation file recorded by the receiver; GPS is the clock error of the GPS system satellite clock, N GPS is the integer ambiguity of the GPS system L1 / L2 frequency carrier phase observation value; 0 GPS is the GPS system satellite orbit error, that is, the error of the satellite position coordinates; I GPS is the ionospheric delay error of the carrier phase observation value of the GPS system L1 frequency; T GPS is the GPS system tropospheric delay error; M GPS is the multipath effect error of the carrier phase observation value of the GPS system L1 / L2 frequency; Δ GPS The carrier phase observation noise and unmodeled error of the GPS system L1 / L2 frequency;

[0024] Step 3: Using the carrier phase wavelength of the BDS Beidou satellite system B1 / B2 frequency as the coefficient of the B1 / B2 frequency and L1 / L2 frequency carrier phase inter-satellite differential ambiguity parameter, or using the carrier phase wavelength of the GPS satellite system L1 / L2 frequency as the coefficient of the B1 / B2 frequency and L1 / L2 frequency carrier phase inter-satellite differential ambiguity parameter, select one of the two to restore the integer characteristics of the BDS Beidou satellite system B1 / B2 and GPS satellite system L1 / L2 carrier phase inter-satellite differential ambiguity parameters;

[0025] Among them, using the carrier phase wavelength of the BDS Beidou satellite system B1 / B2 frequency as the coefficient of the BDS Beidou satellite system B1 / B2 frequency and the GPS satellite system L1 / L2 frequency carrier phase inter-satellite differential ambiguity parameter to restore the integer characteristics of the BDS Beidou satellite system B1 / B2 frequency and the GPS satellite system L1 / L2 frequency carrier phase inter-satellite differential ambiguity parameter includes the following steps:

[0026] 【1】: Using the undifferenced error correction number COR of the BDS BeiDou satellite system B1 / B2 frequency carrier phase provided by an external reference station BDS ,GPS satellite system L1 / L2 frequency carrier phase undifference error correction COR GPS , correct the formula (1) and formula (2) in step 2 to eliminate the tropospheric delay error, ionospheric delay error, satellite orbit error and satellite clock error. The specific formula is as follows:

[0027] For the BDS Beidou satellite system, the formula after error correction is:

[0028] λ BDS ·Φ BDS+COR BDS =ρ BDS +C·t REV -λ BDS ·N BDS +M BDS +Δ BDS (3)

[0029] In the formula, Δ BDS is the observation noise of B1 / B2 frequency carrier phase of BDS BeiDou satellite system;

[0030] For the GPS satellite system, the specific formula after error correction is:

[0031] λ GPS ·Φ GPS +COR GPS =ρ GPS +C·t REV -λ GPS ·N GPS +M GPS +Δ GPS (4)

[0032] In the formula, Δ GPS is the observation noise of the L1 / L2 frequency carrier phase of the GPS satellite system;

[0033] 【2】: Mixing inter-satellite difference is performed between the frequency carrier phase observation values ​​of the BDS Beidou satellite system B1 / B2 and the GPS satellite system L1 / L2 to eliminate the receiver clock error t in formula (3) and formula (4). The specific formula is:

[0034] λ BDS ·Φ BDS -λ GPS ·Φ GPS +COR BDS -COR GPS =ρ BDS -ρ GPS -(λ BDS ·N BDS -λ GPS ·N GPS ) (5)

[0035] The λ on the right side of formula (5) BDS ·N BDS -λ GPS ·N GPS The term represents the ambiguity of the frequency carrier phase between the BDS BeiDou satellite system B1 / B2 and the GPS satellite system L1 / L2;

[0036] The ambiguity of the carrier phase of the BDS Beidou satellite system B1 / B2 frequency and the GPS satellite system L1 / L2 frequency is expressed in the form of an ambiguity integer initial value and a smaller integer correction value, the formula is:

[0037] In the formula, is the initial integer solution of the BDS BeiDou satellite system B1 / B2 frequency carrier phase ambiguity, For GPS system L1 / L2.

[0038] Initial integer solution for frequency carrier phase ambiguity, N′ BDS N′ is the integer correction value of the B1 / B2 frequency carrier phase integer ambiguity of the BeiDou system. GPS is the integer correction of the L1 / L2 frequency carrier phase ambiguity of the GPS system. The size of the integer correction of each carrier phase ambiguity is related to the integer initial value of the ambiguity;

[0039] Formula (6) is further processed to obtain the integer correction N′ of the B1 / B2 frequency carrier phase ambiguity of a satellite in the BDS BeiDou satellite system: BDS , the integer correction N′ of the L1 / L2 frequency carrier phase ambiguity of a satellite in the GPS system GPS A carrier phase ambiguity parameter is formed through inter-satellite difference, and then converted into inter-satellite differential ambiguity using the BDS Beidou satellite system B1 frequency carrier phase ambiguity wavelength as the coefficient. The formula is as follows:

[0040]

[0041] 【3】: Recover the ambiguity parameters of the intersatellite differential combination of BeiDou system Bl / B2 and GPS system L1 / L2 carrier phase

[0042] The integer characteristics of , the specific process is:

[0043] The wavelength of the carrier phase of the BDS Beidou satellite system B1 / B2 frequency and the GPS system L1 / L2 frequency is different. The wavelength ratio is calculated using the formula:

[0044]

[0045] Where A represents the carrier phase wavelength ratio of GPS system L1 / L2 and BeiDou system B1 / B2, and A∈(0,1);

[0046] Then the inter-satellite differential ambiguity parameters of the BDS Beidou satellite system B1 / B2 frequency and the GPS system L1 / L2 frequency carrier phase in equation (7) are

[0047] Further replaced with:

[0048]

[0049] Where N′ BDS and N′ GPS are all unknown integer weeks, namely N′ BDS -N′ GPS is the ambiguity parameter after the inter-satellite difference between the BDS BeiDou satellite system B1 / B2 frequency carrier phase and the GPS system L1 / L2 frequency carrier phase, (1-A)·N′ GPS is the inter-satellite single-difference ambiguity parameter N′ BDS -N′ GPS The residual error term of , for formula (5) is:

[0050]

[0051] 【4】:Determine the integer initial value of the GPS system L1 / L2 frequency carrier phase ambiguity to eliminate the residual error term and restore the ambiguity N′ BDS -N′ GPS The integer properties of

[0052] For the current GPS system, the residual error term (1-A)·N′ GPS When the absolute value is less than 0.5: if the L1 / L2 carrier phase ambiguity is calculated using the pseudo-range observations of the L1 / L2 frequency of the GPS system, the deviation of the initial value of the L1 frequency ambiguity of the GPS system should be less than 55 weeks;

[0053] For the current GPS system, the residual error term (1-Α)·N′ GPS When the absolute value is less than 0.25, the deviation of the initial value of the GPS system L1 / L2 frequency ambiguity should be less than 27 weeks;

[0054] For the above cases with different residual error terms, the residual error terms are also eliminated within the accuracy range of the initial value of the L1 / L2 frequency carrier phase ambiguity, and formula (10) is simplified to:

[0055]

[0056] Where N′ BDS -N′ GPS is the integer ambiguity, and the integer ambiguity parameter N′ at this time BDS -N′ GPS The solution of is the same as the traditional baseline ambiguity resolution method;

[0057] The method uses the L1 / L2 frequency carrier phase wavelength of the GPS satellite system as the inter-satellite differential ambiguity parameter coefficient and restores the integer characteristics of the inter-satellite differential ambiguity parameter, including the following steps:

[0058] 【5】: Formula (6) is further processed to obtain the integer correction value N′ of the B1 / B2 frequency carrier phase ambiguity of a satellite in the BDS Beidou satellite system BDS , the integer correction N′ of the L1 / L2 frequency carrier phase ambiguity of a GPS satellite GPS , after inter-satellite difference, it is combined into an ambiguity, and the L1 / L2 frequency carrier phase ambiguity wavelength of the GPS system is used as the coefficient to form the inter-satellite differential ambiguity. The formula is as follows:

[0059]

[0060] In the formula, is the ambiguity parameter of the inter-satellite differential combination of the BDS BeiDou system B1 / B2 frequency and the GPS system L1 / L2 frequency carrier phase,

[0061] 【6】: Restore the BDS Beidou satellite system B1 / B2 frequency and GPS satellite system L1 / L2 frequency carrier phase inter-satellite differential ambiguity parameters

[0062] The integer characteristics of , the specific process is:

[0063] The wavelength of the carrier phase of the BDS Beidou satellite system B1 / B2 frequency and the GPS system L1 / L2 frequency is different. The wavelength ratio is calculated using the formula:

[0064]

[0065] Where, B represents the B1 / B2 frequency carrier phase wavelength ratio of the BDS BeiDou satellite system and the L1 / L2 frequency carrier phase wavelength ratio of the GPS satellite system, and B∈(1,2);

[0066] According to equation (13), the inter-satellite differential ambiguity of the Beidou system B1 / B2 and GPS system L1 / L2 carrier phase in equation (12) is Further written as:

[0067]

[0068] In the formula, (B-1)·N′ BDS Integer week number N′ BDS -N′ GPS The residual error term of , for formula (5) is:

[0069]

[0070] If we want to make the BDS Beidou system B1 / B2 frequency and GPS system L1 / L2 frequency carrier phase inter-satellite differential ambiguity parameter N′ BDS -N′ GPS To restore the integer characteristics and resolve the integer ambiguity, the residual error term (B-1)·N′ needs to be BDS The impact is reduced to no impact on N′ BDS -N′ GPS The whole week characteristics;

[0071] 【7】: Set the integer initial value of the BDS BeiDou system B1 / B2 frequency carrier phase ambiguity so that the residual error term is (B-1)·N′ BDS The integer nature of the ambiguity parameters is not affected;

[0072] The BDS BeiDou system B1 / B2 frequency pseudorange observations are used to calculate the integer initial value of the BeiDou system B1 / B2 frequency carrier phase ambiguity. The minimum requirement that the initial value should meet is:

[0073] For the current BeiDou system, the residual error term (B-1)·N′ BDS When the absolute value is less than 0.5: if the BDS Beidou satellite system B1 / B2 frequency pseudo-range observation value is used to calculate the B1 / B2 frequency carrier phase ambiguity integer initial value, the deviation of the Beidou system B1 / B2 frequency carrier phase ambiguity initial value should be less than 54 weeks;

[0074] For the current BeiDou system, the residual error term (B-1)·N′ BDS When the absolute value is less than 0.25, the deviation of the initial value of the BDS Beidou system B1 / B2 frequency carrier phase ambiguity should be less than 27 weeks;

[0075] For the above cases with different residual error terms, the residual error term is also eliminated within the accuracy range of the initial value of the carrier phase ambiguity of the B1 / B2 frequency, and then formula (15) is:

[0076]

[0077] Where N BDS -N′ GPS This is the integer ambiguity parameter of the observation equation (16). The integer ambiguity N′ at this time is BDS -N′ GPS The solution of is the same as the traditional baseline ambiguity resolution method;

[0078] Step 4: Inter-satellite mixing difference integer ambiguity N′ of carrier phase observations of BDS BeiDou system B1 / B2 frequency and GPS system L1 / L2 frequency BDS -N′ GPSAfter the determination, the station location parameters are calculated using formula (11) or formula (16), and then the initial integer solutions of the BDS Beidou system B1 / B2 frequency carrier phase ambiguity and the GPS system L1 / L2 frequency carrier phase ambiguity are calculated using the station location parameters. That is, the determined integer ambiguity is used to iteratively calculate the initial integer solution of the ambiguity to determine the final integer ambiguity, and then the BDS Beidou satellite system B1 / B2 and GPS system L1 / L2 carrier phase observation values ​​and ambiguities are used to determine the distance from the user's BDS Beidou / GPS dual system receiver to the satellite.

[0079] The invention provides a low-cost high-precision positioning RTK system based on the BDS+GPS dual-system carrier phase inter-satellite mixing differential algorithm with beneficial effects: The invention provides a BDS Beidou satellite system B1 / B2 frequency and GPS system L1 / L2 frequency carrier phase mixing inter-satellite RTK method. After the BDS Beidou satellite system B1 / B2 frequency and GPS system L1 / L2 frequency dual-frequency carrier phase measurement values ​​are mixed and combined inter-satellitely, the method calculates the initial values ​​of the B1 / B2 frequency and L1 / L2 frequency carrier phase ambiguities of the BDS Beidou satellite system and the GPS system single satellite, transforms the inter-satellite observation equation of the BDS Beidou satellite system B1 / B2 frequency carrier phase and the GPS system L1 / L2 frequency carrier phase, and uses the correction amount of the initial values ​​of the BDS Beidou satellite system B1 / B2 frequency and GPS system L1 / L2 frequency carrier phase ambiguities as the carrier phase ambiguity parameter. The invention can avoid the influence of the different frequencies of the B1 / B2 frequency carrier phase of the BDS Beidou satellite system and the L1 / L2 frequency carrier phase of the GPS system, so that the B1 / B2 frequency and L1 / L2 frequency carrier phase ambiguity parameters of the mixed-frequency inter-satellite difference can be restored to integer characteristics. When the number of satellites observed and measured by the BDS Beidou satellite system and the GPS system is small, the inter-satellite RTK method can not only eliminate the receiver error in the BDS Beidou satellite system B1 / B2 frequency carrier phase measurement value and the GPS satellite system L1 / L2 frequency carrier phase measurement value, but also provide the prerequisite for the real-time and rapid resolution of the inter-satellite single difference ambiguity, that is, the inter-satellite single ambiguity parameter has an integer characteristic. The present invention performs inter-satellite differentiation on the BDS Beidou satellite system B1 / B2 frequency and the GPS system L1 / L2 frequency carrier phase, maintains the integer characteristics of the dual-system inter-satellite differential ambiguity parameters, and can solve the problem of how to achieve high-precision dynamic positioning when the number of satellites observed and measured by the BDS Beidou satellite system and the GPS system is insufficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] Figure 1 This is a framework diagram of a low-cost, high-precision positioning RTK system based on the BDS+GPS dual-system carrier phase inter-satellite mixing differential algorithm;

[0081] Figure 2This is a flow chart of the BDS+GPS dual-system carrier phase inter-satellite mixing difference algorithm in an embodiment of the present invention; DETAILED DESCRIPTION

[0082] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are only

[0083] It is used to illustrate the present invention but not to limit the scope of the present invention.

[0084] Example 1: A low-cost high-precision positioning RTK system based on the BDS+GPS dual-system carrier phase inter-satellite mixing differential algorithm. The framework diagram of the low-cost high-precision positioning RTK system based on the BDS+GPS dual-system carrier phase inter-satellite mixing differential algorithm can be found in Figure 1 The system hardware platform includes an embedded OPENSOURCE MCU network communication LTE Cat1 module, a satellite signal receiving module, a power module, and a satellite positioning receiving module with an external GNSS spiral antenna. The GNSS spiral antenna is used to receive satellite signals. The BDS+GPS dual-system satellite raw data signal is used to determine the BDS carrier phase integer ambiguity and the GPS carrier phase integer ambiguity respectively through the carrier phase observation equation; the carrier phase inter-satellite mixing difference algorithm is used to restore the integer characteristics of the differential ambiguity parameters to improve the system positioning accuracy. The power module provides stable voltage for each functional module of the embedded platform. The serial communication module is used for the communication of data related to the embedded hardware platform and the local device, and the LTE CAT1 communication module is used to obtain base station data from the network in real time.

[0085] The embedded opensource MCU wireless communication LTE Cat1 module adopts the lowest-cost Hezhou Air724 and is compatible with China Mobile IoT's ML307.

[0086] The satellite signal processing module adopts the UM20 module of Unicore Starlink, which supports satellite signals such as BDS B1I / B2I, GPS L1 / L2, GLONASS L1 / L2, Galileo E1 / E5b, and QZSS L1 / L2.

[0087] The voltage conversion circuit of the power module uses the DC / DC switching power conversion chip TPS5430, uses a 12V DC power supply as the input power supply of the TPS5430, and adds necessary resistors, capacitors, and diodes to the periphery of the TPS5430 chip to form two output voltages of 5V and 3.3V.

[0088] The RTOS embedded operating system is selected as the operating system of the device. A low-cost and high-precision positioning RTK system based on this embedded platform is developed based on the BDS+GPS dual-system carrier phase inter-satellite mixing differential algorithm.

[0089] The BDS+GPS dual-system carrier phase inter-satellite mixing differential algorithm implemented by the present invention has the following process: Figure 2 As shown, the following steps are included;

[0090] Step 1: The user's BDS+GPS receiver receives the raw measurement data broadcasted to the user's receiver by the satellites of the BDS Beidou system and the GPS system, including:

[0091] B1 frequency pseudorange measurement data and B1 frequency carrier phase measurement data of the BDS BeiDou system. The B1 frequency pseudorange measurement value is used to calculate the initial integer solution of the B1 frequency carrier phase ambiguity of the BDS BeiDou system. The frequency of the B1 frequency carrier phase observation value is 1561.098MHz, and the wavelength of the corresponding B1 / B2 carrier phase observation value is 0.19203 meters;

[0092] The GPS system's L1 frequency pseudorange measurement data and L1 frequency carrier phase measurement data. The L1 frequency pseudorange measurement value is used to calculate the initial integer solution of the GPS system's L1 frequency carrier phase ambiguity and the calculation of the user's receiver's initial position. The frequency of the L1 frequency carrier phase measurement value is 1575.42MHz, and the corresponding wavelength of the L1 frequency carrier phase observation value is 0.19029 meters;

[0093] Step 2: Determine the carrier phase integer ambiguity of the BDS BeiDou satellite system B1 frequency and the carrier phase integer ambiguity of the GPS system L1 frequency;

[0094] (1) For the BDS BeiDou satellite system: The BDS BeiDou system B1 frequency carrier phase observation equation is used to determine the B1 frequency carrier phase integer ambiguity of the BeiDou system. The formula of the BDS BeiDou system B1 frequency carrier phase observation equation is:

[0095] λ BDS ·Φ BDS =ρ BDS +C·(t REV -t BDS )-λ BDS ·N BDS +0 BDS -I BDS +T BDS +M BDS +Δ BDS (1)

[0096] In the formula, λ BDS is the wavelength of the BDS BeiDou system B1 frequency carrier phase; Φ BDS is the BDS BeiDou system B1 frequency carrier phase observation value, the subscript BDS represents the BeiDou system; ρ BDSis the geometric distance from the BeiDou satellite to the receiver, which is calculated from the initial position coordinates of the station and the BeiDou satellite coordinates. The initial position coordinates of the phase center of the station receiver antenna are obtained through the pseudo-range single-point positioning of the GPS system. The satellite coordinates are determined by the broadcast ephemeris in the BeiDou system navigation file recorded by the receiver through the Kepler six parameters and orbit extrapolation. The speed of light in vacuum is the receiver clock error, that is, the difference between the time when the receiver clock records the observation data and the BeiDou system time, in seconds; t BDS is the clock error of the BeiDou system satellite clock, which is the difference between the BeiDou satellite clock and the BeiDou system time; N BDS is the integer ambiguity of the BDS BeiDou system B1 frequency carrier phase observation value; 0 BDS is the Beidou system satellite orbit error, that is, the difference between the Beidou system satellite position coordinates calculated by broadcast ephemeris and the actual satellite position coordinates; I BDS is the ionospheric delay error of the carrier phase observation value of the BDS BeiDou system Bl frequency; is the tropospheric delay error of the BeiDou system; BDS is the multipath effect error of the carrier phase observation value of the BDS BeiDou system Β1 frequency; Δ BDS is the carrier phase observation noise and unmodeled error of the BeiDou system B1 frequency;

[0097] (2) For the GPS system: The GPS system L1 frequency carrier phase observation equation is used to determine the GPS system L1 frequency carrier phase integer ambiguity. The formula of the GPS system L1 frequency carrier phase observation equation is:

[0098] λ GPS ·Φ GPS =ρ GPS +C·(t REV -t GPS )-λ GPS ·N GPS +0 GPS -I GPS +T GPS +M GPS +Δ GPS (2) In the formula, λ GPS for

[0099] The wavelength of the GPS system L1 frequency carrier phase, Φ GPS is the L1 frequency carrier phase observation value of the GPS system, the subscript GPS represents the GPS system; ρ GPSis the geometric distance from the GPS satellite to the receiver, which is calculated from the initial position coordinates of the station and the GPS satellite coordinates. The initial position coordinates of the station are obtained by the pseudo-range single-point positioning of the GPS system. The satellite coordinates are determined by the broadcast ephemeris in the GPS system navigation file recorded by the receiver and the orbit extrapolation of the Kepler six parameters to obtain the receiver clock error. Here, it is the difference between the time recorded by the receiver clock and the Beidou system time, in seconds; t GPS is the clock error of the GPS system satellite clock, which is the difference between the GPS satellite clock and the GPS system time. When the GPS system observation data is acquired, the GPS system time is used as the standard. In this implementation mode, after the observation data of the GPS system L1 frequency is acquired, the GPS system time is unified with the Beidou system time and converted to the Beidou system time as the reference; N GPS is the integer ambiguity of the carrier phase observation value of the GPS system L1 frequency; 0 GPS is the GPS system satellite orbit error, that is, the difference between the GPS system satellite position coordinates calculated by broadcast ephemeris and the satellite's actual position coordinates; I GPS is the ionospheric delay error of the GPS system L1 frequency carrier phase observation value; T GPS is the tropospheric delay error of the GPS system satellite; M GPS is the multipath effect error of the GPS system L1 frequency carrier phase observation value; Δ GPS The GPS system L1 frequency carrier phase observation noise and unmodeled error;

[0100] Step 3: Using the BDS BeiDou system B1 frequency carrier phase wavelength or the GPS system L1 frequency carrier phase wavelength as the coefficient of the B1 and L1 dual-frequency carrier phase inter-satellite differential ambiguity parameters, construct the carrier phase observation equation of the BDS BeiDou system B1 frequency and the GPS system L1 frequency inter-satellite mixing differential ambiguity parameters, and restore the integer characteristics of the BDS BeiDou system B1 and GPS system L1 carrier phase inter-satellite mixing differential ambiguity parameters, so that the BDS BeiDou system B1 and GPS system L1 carrier phase inter-satellite mixing differential integer cycle ambiguity resolution can be achieved. Using one of the BDS BeiDou system B1 frequency carrier phase wavelength and the GPS system L1 frequency carrier phase wavelength as a coefficient, restore the integer characteristics of the BDS BeiDou system B1 and GPS system L1 carrier phase inter-satellite differential ambiguity parameters;

[0101] Among them, taking the BeiDou system B1 frequency carrier phase wavelength as the coefficient of the BeiDou system B1 and GPS system L1 carrier phase inter-satellite differential ambiguity parameter to restore the integer characteristics of the BeiDou system B1 and GPS system L1 carrier phase inter-satellite differential ambiguity parameters includes the following steps:

[0102] 【1】: Using the undifferenced correction number COR of the BeiDou system B1 frequency carrier phase provided by an external reference stationBDS 、GPS system L1 frequency carrier phase non-difference error correction number COR GPS , perform error correction on formula (1) and formula (2) in step 2. If an external reference station is used, the error correction information required by the user station is obtained based on the measurement data of the reference station. If multiple external reference stations are used, the error correction information required by the user station is obtained by using the error interpolation fitting method based on the positions of the multiple reference stations relative to the user station and the error correction information of each reference station. By using the error correction information provided by the external reference station, the influence of the tropospheric delay error, ionospheric delay error, satellite orbit error and satellite clock error on formula (1) and formula (2) in step 2 is eliminated. The specific formula is as follows:

[0103] For the BeiDou system, the B1 frequency carrier phase observation equation after error correction is:

[0104] λ BDS ·Φ BDS +COR BDS =ρ BDS +C·t REV -λ BDS ·N BDS +M BDS +Δ BDS (3)

[0105] In the formula, Δ BDS is the observation noise of BDS BeiDou system B1 frequency carrier phase;

[0106] For the GPS system, the carrier phase observation equation of the L1 frequency is corrected by the error as follows:

[0107] λ GPS ·Φ GPS +COR GPS =ρ GPS +C·t REV -λ GPS ·N GPS +M GPS +Δ GPS (4)

[0108] In the formula, Δ GPS is the observation noise of the LI frequency carrier phase of the GPS system.

[0109] After the correction of the non-difference error correction number, the carrier phase observation equations (3) and (4) have eliminated the influence of tropospheric delay error, ionospheric delay error, satellite orbit error, GPS satellite clock error and Beidou satellite clock error. However, the influence of receiver clock error and observation noise is still included. The observation noise of B1 frequency and L1 frequency carrier phase is very small, and its influence on B1 and L1 carrier phase ambiguity can be ignored. Then, the receiver clock error in formulas (3) and (4) is eliminated by mixing inter-satellite difference between Beidou system B1 carrier phase and GPS system L1 carrier phase.

[0110] 【2】: The BDS BeiDou satellite system B1 frequency carrier phase observation equation and the GPS system L1 frequency carrier phase observation equation are mixed and inter-satellite differentiated to eliminate the receiver clock error t in formula (3) and formula (4). The specific formula is:

[0111] λ BDS ·Φ BDS -λ GPS ·Φ GPS +COR BDS -COR GPS =ρ BDS -ρ GPS -(λ BDS ·N BDS -λ GPS ·N GPS ) (5)

[0112] The λ on the right side of the equal sign in formula (5) BDS ·N BDS -λ GPS ·N GPS The term represents the ambiguity of the inter-satellite difference of the carrier phase mixing of the BDS BeiDou system B1 frequency and the GPS system L1 frequency. Formula (5) is the observation equation of the inter-satellite difference of the carrier phase mixing of the BDS BeiDou system B1 frequency and the GPS system L1 frequency;

[0113] The inter-satellite differential ambiguity λ between the BDS BeiDou system B1 and the GPS system L1 frequency carrier phase BDS ·N BDS -λ GPS ·N GPS Use model

[0114] The fuzziness is expressed in the form of integer initial value and integer correction. The formula is:

[0115]

[0116] In the formula, is the initial integer solution of the B1 frequency carrier phase ambiguity of the BeiDou system, is the initial integer solution of the GPS system L1 frequency carrier phase ambiguity; N′ BDS N′ is the integer correction of the initial integer solution of the BDS BeiDou system B1 frequency carrier phase ambiguity, GPS is the integer correction of the initial integer solution of the L1 frequency carrier phase ambiguity of the GPS system. The size of the integer correction of the L1 frequency carrier phase ambiguity is related to the integer initial value of the L1 frequency carrier phase ambiguity, that is, the integer correction N′ BDS , N′ GPS is the initial value of the fuzzy integer This embodiment controls the integer correction value N' BDS ,N′ GPS The value of N′ is used to restore the integer characteristics of the carrier phase mixing inter-satellite differential ambiguity between the BDS Beidou system B1 frequency and the GPS system L1 frequency. BDS , N′ GPS The value of must be as small as possible. The correction amount of the initial integer value of the B1 and L1 dual-frequency carrier phase ambiguity calculated by pseudorange observations is generally a few weeks to dozens of weeks.

[0117] When the integer initial value of the carrier phase ambiguity of the B1 frequency of the Beidou system and the integer initial value of the carrier phase ambiguity of the L1 frequency of the GPS system are calculated, the integer initial value of the carrier phase ambiguity is taken as a known value, and the integer correction value N′ in formula (6) is BDS , N′ GPS The two carrier phase integer ambiguity parameters in formula (5) are used to correct the integer correction N′ of the B1 frequency carrier phase ambiguity of a satellite in the BDS BeiDou system. BDS , the integer correction N′ of the L1 frequency carrier phase ambiguity of a satellite in the GPS system GPS An ambiguity parameter is formed through inter-satellite difference, and the BDS Beidou system B1 frequency carrier phase wavelength is used as the coefficient. The formula is:

[0118]

[0119] Then for formula (5), we have:

[0120]

[0121] 【3】: Recover the mixed inter-satellite difference between the BDS Beidou system B1 frequency carrier phase and the GPS system L1 frequency carrier phase

[0122] The inter-satellite differential ambiguity parameter in the observation equation (8) is The integer characteristics of , the specific process is:

[0123] The BDS BeiDou system B1 frequency and the GPS system L1 frequency carrier phase wavelength are different. The BDS BeiDou system B1 frequency carrier phase wavelength λ BDS = 0.19203 m, GPS system L1 frequency carrier phase wavelength λ GPS = 0.19029 m. Calculate the L1 carrier phase ambiguity parameter N′ in equation (8): GPS The coefficient of That is, the wavelength ratio of the carrier phase of the Beidou system B1 frequency and the GPS system L1 frequency is:

[0124]

[0125] Then for equation (7), the carrier phase inter-satellite differential ambiguity parameter is Further replaced by:

[0126]

[0127] In the formula, the initial integer value of the carrier phase ambiguity is The integer correction N′ BDS and N′ GPS are all unknown integers, that is, N′ BDS -N′ GPS is the ambiguity parameter after the intersatellite difference of the BeiDou system B1 and GPS system L1 carrier phase, 0.00907·N′ GPS is the inter-satellite differential ambiguity parameter N′ BDS -N′ GPS The residual error term of , for formula (8) is:

[0128]

[0129] 【4】: Determine the initial integer value of the GPS system L1 frequency carrier phase ambiguity so that the residual error term is 0.00907·N′ GPS It does not affect the resolution of the B1 and L1 dual-frequency carrier phase inter-satellite differential ambiguity parameters in equation (11), that is, the residual error term is 0.00907·N′ GPS The size of can restore and maintain the ambiguity parameter N′ BDS -N′ GPS The integer properties of

[0130] Residual error term 0.00907·N′ GPS When the absolute value is less than 0.5, the residual error term is 0.00907·N′ GPS It does not affect the resolution of the inter-satellite differential ambiguity parameters of the Beidou system B1 and the GPS system L1 carrier phase, and can restore the integer characteristics of the ambiguity parameters:

[0131] For the current GPS system, this implementation uses the GPS pseudo-range measurement value of the L1 frequency to calculate the integer initial value of the L1 frequency carrier phase ambiguity. The formula of the observation equation of the GPS system L1 frequency pseudo-range observation value after the external reference station non-difference error correction is:

[0132] P GPS +COR GPS =ρ GPS +C·t REV +M GPS +Δ GPS (12)

[0133] Where P GPS is the pseudorange observation value of GPS system L1 frequency; COR GPS is the undifferenced error correction of the pseudorange observation, provided by the external reference station, and has the same source as the undifferenced error correction of the user dual system receiver in [1]; ρ GPS is the geometric distance from the GPS satellite to the receiver, t REV is the receiver clock error, in seconds, and their meanings are the same as in formula (2); M GPS is the multipath effect error of the GPS system L1 frequency pseudorange observation value; Δ GPS is the pseudorange observation noise and unmodeled error of the GPS system L1 frequency.

[0134] The integer initial value of the carrier phase ambiguity of the L1 frequency is calculated by using the GPS pseudorange observation value of the L1 frequency after being corrected by the undifference error correction number of the external reference station. According to formula (4) and formula (12), ignoring the multipath effect, observation noise and non-modeled error, the formula for calculating the integer initial value of the carrier phase ambiguity of the L1 frequency is:

[0135]

[0136] In the formula, INT is the integer symbol, that is, the value in the bracket on the right side of the equation is taken to the nearest integer. The accuracy of the initial value of the L1 carrier phase ambiguity integer calculated using formula (13) mainly depends on the pseudorange observation value P of the L1 frequency of the GPS system. GPS accuracy.

[0137] For the current GPS system, the residual error term is 0.00907·N′ GPS When the absolute value of the value is less than 0.5; if the absolute value of the integer correction of the initial value of the carrier phase ambiguity of the GPS system L1 frequency calculated by formula (13) should be less than 55 weeks, that is, the integer correction N′ GPS The absolute value of is less than 55, formula (13) L1 frequency pseudorange observation value P GPSThe equivalent distance accuracy is 10.46 meters, then -0.5<0.00907·N′ GPS <0.5, that is, the inter-satellite differential ambiguity parameter N′ between the BDS Beidou system B1 frequency and the GPS system L1 frequency carrier phase mixing BDS -N′ GPS The residual error term of is less than 0.5 cycles and does not affect the inter-satellite differential ambiguity parameter N′. BDS -N′ GPS The integer characteristics of and the resolution of integer ambiguities;

[0138] For the current GPS system, when the absolute value of the residual error term is less than 0.25:

[0139] The integer correction N′ of the initial value of the carrier phase ambiguity of the GPS system L1 frequency calculated using equation (13) is GPS The absolute value of should be less than 27 weeks. The pseudo-range observation value P in formula (13) GPS The equivalent distance accuracy is 5.14 meters, that is, -0.25<0.00907·N′ GPS <0.25, does not affect the blurriness N′ BDS -N′ GPS Integer characteristics; Generally speaking, for the current GPS system, the accuracy of the pseudo-range observation value of the GPS system L1 frequency in formula (13) can meet this accuracy requirement;

[0140] Two methods are used to calculate the integer initial value of the L1 frequency carrier phase ambiguity using the pseudo-range observation value of the L1 frequency of the GPS system. One is to use the pseudo-range observation value of one epoch to calculate the integer initial value of the L1 frequency carrier phase ambiguity, which is mainly affected by the observation noise of the pseudo-range observation value of the L1 frequency, but for the GPS system, the accuracy of the above L1 frequency carrier phase ambiguity initial value is fully satisfactory. This method uses the L1 frequency pseudorange observation value of one epoch to calculate the integer initial value of the L1 frequency carrier phase ambiguity through formula (13); the second method is to improve the accuracy of the L1 frequency pseudorange observation value to calculate the integer initial value of the L1 frequency carrier phase ambiguity, use the L1 frequency pseudorange observation values ​​of multiple epochs before the current epoch to calculate the integer initial value of the L1 frequency carrier phase ambiguity, and then take the average of multiple identical L1 frequency carrier phase ambiguity integer initial values ​​to improve the accuracy of the L1 frequency carrier phase ambiguity integer initial value, that is, use the L1 frequency pseudorange observation values ​​of multiple epochs of the same satellite to calculate the initial value of the L1 frequency carrier phase ambiguity through formula (13), and then take the average.

[0141] For the GPS system, the accuracy of the initial value of the L1 frequency carrier phase ambiguity is fully satisfactory. For the case with different residual error terms, the residual error term 0.00907·N′ is also eliminated within the accuracy range of the initial value of the L1 frequency carrier phase ambiguity. GPS , then formula (11) is simplified to:

[0142]

[0143] Where N′ BDS -N′ GPS is the integer ambiguity parameter of the intersatellite difference of the BDS BeiDou system B1 and the GPS system LI carrier phase. The integer ambiguity parameter N′ BDS -N′ GPS The solution of is the same as the traditional baseline ambiguity resolution method;

[0144] The GPS system L1 frequency carrier phase wavelength is used as the coefficient of the Beidou system B1 and GPS system L1 carrier phase inter-satellite differential ambiguity parameter, and the integer characteristics of the inter-satellite differential ambiguity parameter are restored, including the following steps: 【5】:After calculating the initial integer value of the B1 frequency carrier phase ambiguity of the BeiDou system and GPS system L1 frequency carrier phase ambiguity integer initial value In the case of , the initial integer value of the carrier phase ambiguity is taken as a known value, and the integer correction value N′ in formula (6) is BDS , N′ GPS The two carrier phase integer ambiguity parameters in formula (5) are used as the integer correction N′ of the B1 frequency carrier phase ambiguity of a satellite in the BeiDou system. BDS , the integer correction N′ of the L1 frequency carrier phase ambiguity of a satellite in the GPS system GPS A carrier phase ambiguity parameter is synthesized through inter-satellite difference grouping, and the GPS system L1 frequency carrier phase ambiguity wavelength is used as the coefficient. The formula is as follows;

[0145]

[0146] Then for formula (5), we have:

[0147]

[0148] In formula (15) and formula (16), It is the ambiguity parameter of the inter-satellite difference between the B1 frequency carrier phase of the Beidou system and the L1 frequency carrier phase of the GPS system.

[0149] 【6】: Recover the mixed inter-satellite difference between the BDS Beidou system B1 frequency carrier phase and the GPS system L1 frequency carrier phase

[0150] The inter-satellite differential ambiguity parameter in the observation equation (16) is The integer characteristics of , the specific process is:

[0151] Since the wavelengths of the carrier phases of the BDS BeiDou system Β1 and the GPS system L1 are different, the wavelength λ of the carrier phase of the BeiDou system Β1 is BDS = 0.19203 m, the wavelength λ of the GPS system L1 carrier phase GPS = 0.19029 m. Therefore, the B1 and L1 carrier phase intersatellite differential ambiguity parameters It does not have integer characteristics. Based on the wavelength of the B1 frequency carrier phase of the BeiDou system and the wavelength of the L1 frequency carrier phase of the GPS system, the B1 carrier phase ambiguity parameter N′ in equation (16) is calculated BDS Department

[0152] The number is the wavelength ratio of the carrier phase of the Beidou system B1 and the GPS system L1, then:

[0153]

[0154] According to equation (17), the carrier phase inter-satellite differential ambiguity in equation (15) is Further written as;

[0155]

[0156] Where, the initial integer values ​​of the B1 and L1 carrier phase ambiguity are The integer correction N′ BDS and N′ GPS are all unknown integer weeks, namely N′ BDS -N′ GPS is the ambiguity parameter after the intersatellite difference between the B1 frequency carrier phase of the BeiDou system and the L1 frequency carrier phase of the GPS system, 0.00914·N′ BDS is the inter-satellite differential ambiguity parameter N′ of the B1 and LI carrier phases BDS -N′ GPS The residual error term of , for formula (16) is:

[0157]

[0158] If we want to make the B1 and LI carrier phase inter-satellite differential ambiguity parameters N′ BDS -N′ GPS To restore the integer characteristics, in order to resolve the B1 and L1 carrier phase intersatellite differential integer ambiguity, the residual error term 0.00914·N′ needs to be BDS The impact is reduced to no impact on N′ BDS -N′GPS The whole week characteristics;

[0159] 【7】: Determine the integer initial value of the BDS BeiDou system B1 frequency carrier phase ambiguity so that the residual error term is 0.00914·N′ BDS It does not affect the solution of the carrier phase ambiguity parameter in equation (19), that is, the residual error term is 0.00914·N′ BDS The size of can restore and maintain the integer characteristics of the ambiguity parameters;

[0160] Residual error term 0.00914·N′ BDS When the absolute value is less than 0.5, the residual error term is 0.00914·N′ BDS It does not affect the resolution of B1 and LI carrier phase intersatellite differential ambiguity parameters, and can restore the integer characteristics of carrier phase ambiguity parameters:

[0161] For the current BeiDou system, this implementation uses the pseudo-range observations of the BeiDou system BI frequency to calculate the integer initial value of the carrier phase ambiguity of the B1 frequency. The formula of the observation equation of the pseudo-range observations of the BeiDou system L1 frequency after the undifference error correction of the external reference station is:

[0162] P BDS +COR BDS =ρ BDS +C·t REV +M BDS +Δ BDS (20)

[0163] Where P BDS is the pseudorange observation value of the B1 frequency of the BeiDou system; COR BDS is the error correction number of the pseudorange observation value, which is provided by the external reference station and has the same source as the undifference error correction number of the user receiver in [1]; ρ BDS is the geometric distance from the BeiDou system satellite to the receiver, t REV is the receiver clock error, in seconds, and their meanings are the same as in formula (1); M BDS is the multipath effect error of the pseudorange observation value of the B1 frequency of the BeiDou system; Δ BDS is the pseudorange observation noise and unmodeled error of BeiDou system B1.

[0164] The integer initial value of the B1 frequency carrier phase ambiguity is calculated by using the pseudo-range observation value of the B1 frequency of the BeiDou system after the undifference error correction of the external reference station. According to formula (3) and formula (20), ignoring the multipath effect, observation noise and non-modeled error, the formula for calculating the integer initial value of the LI frequency carrier phase ambiguity is:

[0165] Where INT is the integer symbol, that is, the value in the bracket on the right side of the equation is taken to the nearest integer. The accuracy of the initial integer value of the B1 frequency carrier phase ambiguity calculated using equation (21) mainly depends on the B1 frequency pseudorange observation value P of the BeiDou system. BDS accuracy.

[0166] For the current BeiDou system, the residual error term is 0.00914·N′ BDS When the absolute value of the value is less than 0.5: the absolute value of the integer correction of the initial value of the BDS Beidou system B1 frequency carrier phase ambiguity calculated by formula (21) should be less than 54 cycles, that is, the integer correction N′ BDS The absolute value of is less than 54, and the B1 frequency pseudorange observation value P in formula (21) BDS The equivalent distance accuracy is 10.36 meters. Then -0.5<0.00914·N′ BDS <0.5, that is, the inter-satellite differential ambiguity parameter N′ between the frequency carrier phase of the Beidou system B1 and the GPS system L1 BDS -N′ GPS The residual error term does not exceed 0.5 cycles and does not affect the inter-satellite differential ambiguity parameter N′ BDS -N′ GPS The integer characteristics of and the resolution of integer ambiguities;

[0167] For the current BeiDou system, the residual error term is 0.00914·N′ BDS When the absolute value is less than 0.25: The initial value of the BDS Beidou system B1 carrier phase ambiguity calculated using formula (21) The integer correction N′ BDS The absolute value of should be less than 27 weeks. The pseudorange observation value P in formula (21) BDS The equivalent distance accuracy is 5.18 meters, and the residual error term is 0.00914·N′ BDS , then -0.25<0.00914·N′ BDS <0.25, does not affect the inter-satellite differential ambiguity parameter N′ between the Beidou system B1 and the GPS system L1 frequency carrier phase BDS -N′ GPS The integer properties of

[0168] There are two methods to calculate the integer initial value of the B1 frequency carrier phase ambiguity using the B1 frequency pseudorange observation value of the BeiDou system. One is to use the B1 frequency pseudorange observation value of one epoch to calculate the integer initial value of the B1 frequency carrier phase ambiguity, and its accuracy is mainly affected by the observation noise of the B1 frequency pseudorange observation value. For the BDS BeiDou system, the accuracy of the above B1 frequency carrier phase ambiguity initial value is fully satisfactory.

[0169] This method uses the B1 frequency pseudorange observation value of one epoch to calculate the integer initial value of the B1 frequency carrier phase ambiguity through formula (21); the second method is to improve the accuracy of the B1 frequency pseudorange observation value in calculating the integer initial value of the B1 frequency carrier phase ambiguity by using the B1 frequency pseudorange observation value of multiple epochs before the current epoch to calculate the integer initial value of the B1 frequency carrier phase ambiguity, and then take the average of multiple identical integer initial values ​​of the B1 frequency carrier phase ambiguity to improve the accuracy of the integer initial value of the B1 frequency carrier phase ambiguity, that is, use the B1 frequency pseudorange observation value of multiple epochs of the same satellite to calculate the initial value of the B1 frequency carrier phase ambiguity through formula (21), and then take the average.

[0170] For the BDS BeiDou system, the accuracy of the initial value of the B1 frequency carrier phase ambiguity is fully satisfactory. For the above cases with different residual error terms, the residual error term 0.00914·N′ is also eliminated within the range of the initial value accuracy requirement of the B1 frequency carrier phase ambiguity. BDS , then formula (19) is simplified to;

[0171]

[0172] Where N′ BDS -N′ GPS This is the integer ambiguity parameter of the observation equation (22). The integer ambiguity N′ at this time is BDS -N′ GPS The solution of is the same as the traditional baseline ambiguity resolution method;

[0173] Step 4: Mix the inter-satellite differential integer ambiguity N′ between the BDS BeiDou system B1 frequency and the GPS system L1 frequency carrier phase observations BDS -N′ GPS After the determination, the station location parameters are calculated using formula (14) or formula (22), and then the initial integer solutions of the BDS Beidou system B1 frequency carrier phase ambiguity and the GPS system L1 frequency carrier phase ambiguity are calculated using formula (3) and formula (4) through the station location parameters, where the receiver clock error of formula (3) and formula (4) is calculated by formula (12) or formula (20). That is, the determined integer ambiguity is used to iteratively calculate the initial integer solution of the ambiguity to determine the final integer ambiguity, and then the inter-satellite differential BDS Beidou system B1 frequency and GPS system L1 frequency carrier phase observation value Φ and ambiguity N are used to determine the distance from the user Beidou / GPS receiver to the satellite. The inter-satellite differential combination method of the BDS Beidou system B1 and the GPS system L1 carrier phase and the receiver position calculation are realized.

[0174] Although specific embodiments of the present invention have been described above, they are merely examples and many changes or modifications may be made to these embodiments without departing from the principles and essence of the present invention.

Claims

1. A low-cost, high-precision positioning RTK system based on the BDS+GPS dual-system carrier phase inter-satellite mixing differential algorithm, characterized by: The hardware platform includes an LTE Cat1 wireless communication module with an embedded OPENSOURCE microprocessor, a multi-mode satellite signal receiving module, and a power module. The multi-mode satellite signal receiving module is connected to an external high-gain GNSS spiral antenna; the GNSS spiral antenna is used to receive BDS and GPS satellite signals. After the satellite signal is received by the satellite signal receiving module, the satellite signal raw data is transmitted to the OPENSOURCE microprocessor; the power module provides stable voltage for each functional module of the embedded platform; the serial port communication module is used for communication of data related to the embedded hardware platform and the local device, and the LTE Cat1 communication is used to obtain base station data from the network in real time.

2. According to claim 1, a low-cost, high-precision positioning RTK system based on the BDS+GPS dual-system carrier phase inter-satellite mixing differential algorithm is characterized by: The LTE CAT1 communication module is embedded with the OPENSOURCE microprocessor. The wireless communication LTE Cat1 module adopts the lowest cost Hezhou Air724.

3. The low-cost, high-precision positioning RTK system based on the BDS+GPS dual-system carrier phase inter-satellite mixing differential algorithm according to claim 1 is characterized in that: The satellite signal receiving module adopts Unicore's UM20 single-frequency module, which supports BDS B1 / B2 and GPS L1 / L2 satellite signals.

4. A low-cost, high-precision positioning RTK system based on the BDS+GPS dual-system carrier phase inter-satellite mixing differential algorithm, characterized by: The RTOS embedded operating system is selected as the operating system of the device. A low-cost, high-precision positioning RTK system based on the BDS+GPS dual-system carrier phase inter-satellite mixing differential algorithm based on this embedded platform includes the following steps: Step 1: The system first receives the raw observation data broadcast by the satellites of the BDS+GPS dual systems and transmits it to the OPENSOURCE microprocessor of the system; Step 2, respectively confirming the BDS carrier phase integer ambiguity and the GPS carrier phase integer ambiguity through the carrier phase observation equation of the embedded software program; Step 3: Use the carrier phase inter-satellite mixing differential algorithm to perform RTK; Step 4: According to the obtained RTK result, the microprocessor performs the integer characteristic of the ambiguity parameter of the carrier phase mixing inter-satellite differential recovery in the updating process, and further obtains the result of RTK high-precision positioning.

5. A low-cost, high-precision positioning RTK system based on the BDS+GPS dual-system carrier phase inter-satellite mixing differential algorithm, characterized by: Firstly, the non-error correction numbers at two frequencies, BDS Beidou satellite frequency and GPS satellite frequency, are provided by external reference stations to eliminate the satellite orbit error, tropospheric delay error and ionospheric delay error in the carrier phase measurement values ​​of BDS Beidou and GPS respectively. Then, the respective carrier phase measurement values ​​of the BDS Beidou system and the GPS system are subtracted to eliminate the receiver error in the carrier phase measurement values ​​of different satellites by the same satellite receiver, and the integer characteristics of the inter-satellite differential ambiguity of the BDS Beidou system frequency and GPS system frequency carrier phase measurement values ​​are confirmed, thereby confirming the integer ambiguity of the inter-satellite differential measurement values ​​of the BDS Beidou satellite system carrier and the GPS system carrier phase; Finally, the measured value is used to confirm the distance between the BDS Beidou system and the GPS system satellite and the satellite receiver.

6. The BDS+GPS dual-system carrier phase inter-satellite mixing differential algorithm as claimed in claim 5, characterized in that: The method for eliminating the receiver error in the carrier phase measurement values ​​of the B1 / B2 and L1 / L2 frequencies of different satellites by the same satellite receiver is to combine the carrier phase ambiguity parameters of the BDS Beidou satellite system B1 / B2 frequency and the carrier phase ambiguity parameters of the GPS satellite system L1 / L2 frequency into one ambiguity parameter, using either of the following two methods: (1) The integer correction of the initial integer solution of the B1 / B2 frequency carrier phase ambiguity of a satellite in the BDS BeiDou satellite system and the integer correction of the initial integer solution of the L1 / L2 frequency carrier phase ambiguity of a satellite in the GPS satellite system are formed into an ambiguity parameter through inter-satellite difference, and then converted into inter-satellite difference ambiguity using the B1 / B2 frequency carrier phase ambiguity wavelength of the BDS BeiDou satellite system as the coefficient. The formula is: In the formula, λ BDS is the wavelength of the BDS BeiDou system B1 / B2 frequency carrier phase; N BDS is the integer ambiguity of the BDS BeiDou satellite system B1 / B2 frequency carrier phase measurement value; GPS is the wavelength of the GPS satellite system L1 / L2 frequency carrier phase, N GPS is the integer ambiguity of the L1 / L2 frequency carrier phase measurement of the GPS satellite system; is the initial integer solution of the GPS system L1 / L2 frequency carrier phase ambiguity, is the initial integer solution of the BDS system B1 / B2 frequency carrier phase ambiguity, N′ BDS N′ is the integer correction value of the B1 / B2 frequency carrier phase integer ambiguity of the BeiDou system. GPS is the integer correction of the L1 / L2 frequency carrier phase ambiguity of the GPS system. The size of the integer correction of the B1 / B2 and L1 / L2 frequency carrier phase ambiguity is related to the integer initial value of the ambiguity. In formula (1), is the ambiguity parameter of the inter-satellite difference between the BDS system B1 / B2 frequency carrier phase and the GPS system L1 / L2 frequency carrier phase, (2) The integer correction of the initial integer solution of the B1 / B2 frequency carrier phase ambiguity of a satellite in the BDS BeiDou system and the integer correction of the initial integer solution of the L1 / L2 frequency carrier phase ambiguity of a satellite in the GPS satellite system are combined into one ambiguity after inter-satellite difference and the L1 / L2 frequency carrier phase ambiguity wavelength of the GPS satellite system is used as the coefficient to form the inter-satellite difference ambiguity. The formula is as follows: In the formula, It is the ambiguity parameter of the inter-satellite differential combination of the carrier phase of the BDS system B1 / B2 frequency and the carrier phase of the GPS system L1 / L2 frequency.

7. The BDS Beidou satellite system B1 / B2 frequency and GPS satellite system L1 / L2 frequency carrier phase RTK method according to claim 6, characterized in that: For the inter-satellite differential ambiguity determined in (1), The method to restore its integer characteristics is: the wavelength of the carrier phase of the BDS Beidou satellite system B1 / B2 and the GPS satellite system L1 / L2 is different, and the wavelength ratio is obtained. The formula is: Where A represents the wavelength ratio of the carrier phase of the GPS satellite system L1 / L2 and the BDS BeiDou satellite system B1 / B2, and A∈(0,1); Then the inter-satellite differential ambiguity parameter in equation (1) is Further replaced with: Where N′ BDS and N′ GPS are all unknown integer weeks, namely N′ BDs -N′ GPS is the ambiguity parameter after the inter-satellite difference between the BDS BeiDou satellite system B1 / B2 frequency carrier phase and the GPS satellite system L1 / L2 frequency carrier phase, (1-A)·N′ GPS is the inter-satellite differential ambiguity parameter N′ BDS -N′ GPS The residual error term is: Where φ BDS is the BDS BeiDou satellite system B1 / B2 frequency carrier phase measurement value, the subscript BDS represents the BDS BeiDou system; φ GPS It is the L1 / L2 frequency carrier phase measurement value of the GPS satellite system. The subscript GPS represents the GPS satellite system. COR BDS It is the non-error correction value of the BDS Beidou system B1 / B2 frequency carrier phase provided by the external reference station; COR GPS is the non-error correction value of the L1 / L2 frequency carrier phase of the GPS satellite system; P BDS is the geometric distance from the BDS BeiDou satellite system to the receiver; P GPS is the geometric distance from the GPS satellite to the receiver; Determine the initial integer value of the GPS satellite system L1 / L2 frequency carrier phase ambiguity so that the residual error term is (1-A)·N′ GPS Eliminate and restore the ambiguity parameter N′ BDS -N′ GPS The integer property of .

8. The BDS Beidou satellite system B1 / B2 frequency and GPS satellite system L1 / L2 frequency carrier phase RTK method according to claim 6, characterized in that: For the confirmed inter-satellite differential ambiguity described in (2), The method to restore its integer characteristics is: the wavelength of the carrier phase of the BDS Beidou satellite system B1 / B2 frequency and the GPS satellite system L1 / L2 frequency is different, and the wavelength ratio is obtained. The formula is: Where B represents the B1 / B2 frequency carrier phase wavelength ratio of the BDS BeiDou satellite system and the L1 / L2 frequency carrier phase wavelength ratio of the GPS satellite system, and B∈(1,2); Intersatellite differential ambiguity Further written as: In the formula, (B-1)·N' BDS is the unknown number N′ BDS -N′ GPS The residual error term is: Confirm the integer initial value of the BDS BeiDou satellite system B1 / B2 frequency carrier phase ambiguity so that the residual error term (B-1) · N' BDS Eliminate and restore the ambiguity parameter N' BDS -N′ GPS The integer property of .

9. The BDS Beidou satellite system B1 / B2 frequency and GPS satellite system L1 / L2 frequency carrier phase RTK method according to claim 7, characterized in that: The method for confirming the integer initial value of the L1 / L2 frequency carrier phase ambiguity of the GPS satellite system is: For the current GPS satellite system, the residual error term (1-A)·N′ GPS When the absolute value is less than 0.5: If the L1 / L2 frequency carrier phase ambiguity integer initial value is calculated using the pseudo-range measurement value of the GPS satellite system L1 / L2 frequency, the deviation of the GPS satellite system L1 / L2 frequency carrier phase ambiguity initial value should be less than 55 cycles; for the current GPS satellite system, in the residual error term (1-A)·N′ GPS When the absolute value is less than 0.25, the initial value deviation of the L1 / L2 frequency carrier phase ambiguity of the GPS satellite system should be less than 27 weeks.

10. The BDS Beidou satellite system B1 / B2 frequency and GPS satellite system L1 / L2 frequency carrier phase RTK method according to claim 8, characterized in that: The method for confirming the integer initial value of the BDS Beidou satellite system B1 / B2 frequency carrier phase ambiguity is: The BDS BeiDou satellite system B1 / B2 frequency pseudorange measurement value is used to calculate the integer initial value of the BDS BeiDou satellite system B1 / B2 frequency carrier phase ambiguity. The minimum requirement that the initial value should meet is: For the current BDS BeiDou satellite system, the residual error term (B-1)·N′ BDS When the absolute value is less than 0.5: If the integer initial value of the B1 / B2 frequency carrier phase ambiguity is calculated using the pseudo-range measurement value of the BDS Beidou satellite system B1 / B2 frequency, the deviation of the initial value of the ambiguity of the BDS Beidou satellite system B1 / B2 frequency carrier phase should be less than 54 weeks; for the current BDS Beidou satellite system, in the residual error term (B-1)·N′ BDS When the absolute value is less than 0.25, the deviation of the initial value of the B1 / B2 frequency carrier phase ambiguity of the BDS Beidou satellite system should be less than 27 weeks.

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