Offshore long baseline positioning method based on multi-frequency signals of beidou-3

Abstract

The application discloses a near-sea long baseline positioning method based on multi-frequency signals of Beidou-3, comprising the following steps: a multi-frequency combination observation value combination coefficient constraint condition suitable for long baseline is proposed, and the optimal observation value combination coefficient of Beidou-3 is selected according to the constraint condition; after the received carrier observation data is pre-combined and processed by a reference station system, the data is broadcast in one direction according to an improved new type of coding protocol, so that the communication burden is reduced under the condition of ensuring the data resolution; a positioning solution terminal analyzes the combined carrier data of the reference station and the carrier observation value received by the terminal to form a combined observation equation with weak ionospheric influence, simultaneously solves a self-ionosphere-eliminating combined pseudorange single-point positioning observation equation, estimates the position parameters and the tropospheric wet delay parameters by using Kalman filtering, and realizes near-sea high-precision positioning solution.

Description

Technical Field

[0001] This invention belongs to the field of GNSS (Global Navigation Satellite System) positioning and navigation technology, and relates to a multi-frequency combined observation value combined positioning solution model, specifically to a near-shore long baseline positioning method based on BeiDou-3 multi-frequency signals. Background Technology

[0002] To better apply BeiDou PNT services in the maritime field, the Maritime Safety Administration of the Ministry of Transport of my country has built the China Coastal Radio Beacon-Differential Global Positioning System (RBN-DGPS) network, providing complete signal coverage along the Chinese coast and establishing it as an internationally standardized and modern navigation aid system. In recent years, the construction of the coastal RBN differential BeiDou system has been carried out, achieving BDS / GPS dual-mode compatibility at 22 differential stations along the Chinese coast and promoting the standardization of the coastal BeiDou high-precision positioning and navigation system. It is currently widely used in various operations such as ship navigation, marine surveying, maritime law enforcement, and emergency search and rescue.

[0003] However, due to the poor stability of mobile communication signals in maritime areas and the lack of sufficient reference station network support, the application of BeiDou positioning at sea still lags significantly behind that on land. This is mainly reflected in lower positioning accuracy, poor reliability, and the long time required for high-precision positioning. Currently, the mainly used coastal beacon differential technology can only support meter-level to sub-meter-level positioning, while real-time precise point positioning technology requires the support of real-time clock difference orbit products, and its application at sea is not yet mature.

[0004] my country's BeiDou-3 system, launched in 2020, provides five frequency signals: B1I, B3I, B1C, B2a, and B2b. Utilizing this five-frequency observation information, a series of excellent observation combinations with low noise and weak ionospheric influence can be constructed, offering significant advantages in implementing one-way real-time long-baseline (RTK) positioning. This provides a new direction for solving the challenges of maritime positioning. This paper, based on the BeiDou five-frequency observation combination, focuses on addressing the difficulties of long-baseline positioning at sea, proposing a new RTK positioning mode suitable for one-way broadcasting of small amounts of data from wireless beacons, thus providing a new technical means for high-precision positioning in near-shore areas. Summary of the Invention

[0005] To address the aforementioned issues, this invention discloses a near-shore long baseline positioning method based on BeiDou-3 multi-frequency signals. It proposes a multi-frequency combined observation model suitable for long baselines, which can alleviate the pressure on mobile communication in maritime areas and reduce signal propagation errors under long baseline conditions, thereby meeting the need for high-precision near-shore long baseline positioning.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] The near-shore long baseline positioning method based on BeiDou-3 multi-frequency signals includes the following steps:

[0008] Step 1: Propose a constraint condition for the combination coefficients of multi-frequency combined observations applicable to long baselines, and select the optimal combination coefficients of BeiDou-3 observations based on this constraint.

[0009] Step 2: The reference station system pre-combines and processes the received carrier observation data, and then broadcasts it unidirectionally according to the improved new coding protocol of this invention, which reduces the communication burden while ensuring data resolution.

[0010] Step 3: The positioning and calculation terminal analyzes the combined carrier data of the reference station and the carrier observations it receives to form a combined observation equation with weak ionospheric influence. At the same time, it establishes its own combined pseudorange single-point positioning observation equation with ionospheric depletion. Kalman filtering is used to estimate the position parameters and tropospheric wet delay parameters to achieve high-precision positioning and calculation in the nearshore area.

[0011] The specific steps are as follows:

[0012] Step 1. Propose a constraint condition for the combination coefficients of multi-frequency combined observations applicable to long baselines, and select the optimal combination coefficients of BeiDou-3 observations based on this constraint.

[0013] First, consider the double-difference observation model as shown in equation (1):

[0014]

[0015] In the formula,

[0016] subscript i k (k = 1, 2, ..., 5) represents the frequency identifier; c represents the speed of light;

[0017] Indicates the combined frequency of the five frequencies.

[0018] Indicates the ambiguity of the five-frequency combination.

[0019] This indicates the noise level measured using a five-frequency combination.

[0020] This represents the sum of other errors.

[0021] The first-order ionospheric delay effect coefficient (unit: cycle / m) is related to the ambiguity fixation rate and success rate.

[0022] related:

[0023]

[0024] Multiply equation (2) by the combined wavelength The ionospheric delay coefficient, expressed in meters, is shown in equation (3). This value affects the accuracy of distance measurement.

[0025]

[0026] Assuming all observation noise is white noise and that each observation is independent, the combined carrier observation noise amplification factor, expressed in meters, can be calculated as follows:

[0027]

[0028] Based on the aforementioned observation model, and considering the near-shore long baseline positioning environment, the multi-frequency combined observation value combination coefficient constraint condition proposed in this invention first considers the complex ionospheric situation of long baselines, selecting a relatively large ionospheric delay under extreme conditions as a reference, requiring that the influence of ionospheric delay on ranging is less than 1 cm and on ambiguity resolution is less than 0.1 weeks. Therefore, Secondly, the performance of the multi-frequency observation combination proposed in this invention is required to be superior to that of the ionosphere de-combination, thus there is

[0029] When selecting the optimal combination coefficients, based on the above constraints, and considering that the noise amplification factor per week should not be too large, we traverse all coefficient combinations within the limited range of [-5, 5] and select the combination that meets the requirements.

[0030] Step 2. The reference station system pre-processes the received carrier observation data and then broadcasts it according to the novel radio communication protocol proposed in this invention.

[0031] This protocol is an improvement on the standard radio broadcast protocol framework. It fully complies with the standard radio broadcast protocol's format requirements of 30 bits per word and 32 words per frame, and adopts the standard radio broadcast protocol's common message header. This means that when developing software using this protocol, there is no need to redevelop the decoding module. You only need to add a new message type to the protocol decoding module.

[0032] To adapt to the current situation of a large number of satellites in multiple systems, the communication protocol designed in this invention adds a frame end identifier and a sequence number field to ensure the integrity of data transmission before and after transmission. In the event of a discrepancy in the sequence number count, the subsequent erroneous frames can be discarded, maximizing the preservation of the received intact sub-epochs.

[0033] To improve the resolution of broadcast observations while compressing the required data volume, the communication protocol designed in this invention employs a separation of coarse distance and precise distance for carrier observations in one-meter units, and transmits data in milliseconds (ms). Its distance resolution is 0.00014 m, a 64% improvement compared to standard radio broadcast protocols; for transmitting observation data from 10 satellites, its data transmission volume is reduced by 26% compared to standard radio broadcast protocols.

[0034] Step 3. The positioning and calculation terminal combines the differential combination observation equations of the weak ionospheric influence with its own ionospheric desiccation combination pseudorange single-point positioning observation equations to estimate parameters.

[0035] When estimating location parameters, the positioning solution terminal analyzes the combined carrier data of the reference station and performs differential analysis with its own received carrier observations to form a combined observation equation with weak ionospheric influence. At the same time, it combines its own ionospheric pseudorange single-point positioning observation equation, which greatly reduces the number of observations that need to be transmitted in terms of communication, while ensuring centimeter-level positioning accuracy.

[0036] The observation equation for the weak ionospheric effect of the double-difference carrier wave is as follows:

[0037]

[0038] In the formula, These are combined carrier observations in meters. represents the wetted delay component of the tropospheric zenith; el represents the residual error term considered in the position.

[0039] The pseudorange single-point positioning observation equation for the deionization combination is as follows:

[0040]

[0041] Linearizing the observation equations in equations (5) and (6) using Taylor expansion yields:

[0042]

[0043] In the formula, PIF represents the pseudorange observation value of the ionosphere-free combination; ep represents the residual pseudorange error term that has not been considered. and δX, δY, and δZ represent the coefficients of the coordinate corrections, respectively; LIR is the combined carrier observation value affected by the weak ionosphere; δX, δY, δZ, dtrop, N1, ..., Nn are the estimation parameters of the Kalman filter.

[0044] The beneficial effects of this invention include:

[0045] This invention proposes a near-shore long baseline positioning method based on BeiDou-3 multi-frequency signals. It details a method for selecting the combination coefficients of multi-frequency combined observations suitable for long baselines. The solution obtained using the selected optimal combination coefficients is superior to that of dual-frequency ionospheric desiccation combinations in terms of solution efficiency, data transmission volume, and positioning accuracy. Furthermore, a novel wireless communication protocol is proposed, adaptable to the broadcasting of multi-frequency combined observation data under long baseline conditions, and achieving higher broadcasting accuracy than standard radio broadcasting protocols. This provides a solution to the challenges of poor communication stability and low positioning accuracy in near-shore long baseline positioning. Attached Figure Description

[0046] Figure 1 This is a flowchart illustrating the implementation of the near-shore long baseline positioning method based on BeiDou-3 multi-frequency signals described in this invention.

[0047] Figure 2 This is a structural diagram of the improved communication protocol of this invention;

[0048] Figure 3 It is the error curve of the fixed solution obtained by performing positioning calculation using the method described in this invention;

[0049] Figure 4 It is a real-time positioning and calculation software implemented using the method described in this invention. Detailed Implementation

[0050] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0051] As shown in the figure, this embodiment discloses a near-shore long baseline positioning method based on BeiDou-3 multi-frequency signals. The specific steps are as follows:

[0052] Step 1: Propose a constraint condition for the combination coefficients of multi-frequency combined observations applicable to long baselines, and select the optimal combination coefficients of BeiDou-3 observations.

[0053] First, consider the double-difference observation model as shown in equation (1):

[0054]

[0055] In the formula,

[0056] subscript i k (k = 1, 2, ..., 5) represents the frequency identifier; c represents the speed of light;

[0057] Indicates the combined frequency of the five frequencies.

[0058] Indicates the ambiguity of the five-frequency combination.

[0059] This indicates the noise level measured using a five-frequency combination.

[0060] This represents the sum of other errors.

[0061] The first-order ionospheric delay effect coefficient (unit: cycle / m) is related to the ambiguity fixation rate and success rate.

[0062] related:

[0063]

[0064] Multiply equation (2) by the combined wavelength The ionospheric delay coefficient, expressed in meters, is shown in equation (3). This value affects the accuracy of distance measurement.

[0065]

[0066] Assuming all observation noise is white noise and that each observation is independent, the combined carrier observation noise amplification factor, expressed in meters, can be calculated as follows:

[0067]

[0068] Based on the aforementioned observation model, and considering the near-shore long baseline positioning environment, the multi-frequency combined observation value combination coefficient constraint condition proposed in this invention first considers the complex ionospheric situation of long baselines, selecting a relatively large ionospheric delay under extreme conditions as a reference, requiring that the influence of ionospheric delay on ranging is less than 1 cm and on ambiguity resolution is less than 0.1 weeks. Therefore, Secondly, the performance of the multi-frequency observation combination proposed in this invention is required to be superior to that of the ionosphere de-combination, thus there is

[0069] When selecting the optimal combination coefficients, based on the above constraints, and considering that the noise amplification factor per week should not be too large, the coefficient combinations are traversed within a limited range of [-5, 5]. The resulting combination coefficients are shown in Table 1.

[0070] Table 1 Search Results for BDS-3 Five-Frequency Combination Coefficients

[0071]

[0072] As shown in the table, the optimal combination coefficient of BDS-3 is (2,2,-3,0,0), and its corresponding ionospheric delay coefficient is 10⁻³, which is almost negligible.

[0073] Step 2: After pre-processing the received carrier observation data, the reference station system broadcasts it according to the improved radio communication protocol for multi-system five-frequency combined observation data, as described in this invention. This protocol is based on the standard radio broadcast protocol framework and fully conforms to the standard radio broadcast protocol's format requirements of 30 bits per word and 32 words per frame. It also uses the standard radio broadcast protocol's common message header. This eliminates the need to redevelop the decoding module when using this protocol for software development; only a new message type needs to be added to the protocol decoding module. The specific protocol structure is as follows: Figure 2 As shown in Table 2, the meanings of each field are as follows:

[0074] Table 2. Meaning of each field in the communication protocol

[0075]

[0076] To adapt to the current situation of a large number of satellites in multiple systems, the communication protocol designed in this invention adds a frame end identifier and a sequence number field to ensure the integrity of data transmission before and after transmission. In the event of a discrepancy in the sequence number count, the subsequent erroneous frames can be discarded, maximizing the preservation of the received intact sub-epochs.

[0077] To improve the resolution of broadcast observations while compressing the required data volume, the communication protocol designed in this invention employs a separation of coarse distance and precise distance for carrier observations in one-meter units, and transmits data in milliseconds (ms). Its distance resolution is 0.00014 m, a 64% improvement compared to standard radio broadcast protocols; for transmitting observation data from 10 satellites, its data transmission volume is reduced by 26% compared to standard radio broadcast protocols.

[0078] Step 3: When estimating the location parameters, the positioning solution terminal analyzes the combined carrier data of the reference station and performs differential analysis with the carrier observations it receives to form a combined observation equation with weak ionospheric influence. At the same time, it combines its own combined pseudorange single-point positioning observation equation to eliminate ionospheric influence. This method greatly reduces the number of observations that need to be transmitted in terms of communication, while ensuring centimeter-level positioning accuracy.

[0079] The observation equation for the weak ionospheric effect of the double-difference carrier wave is as follows:

[0080]

[0081] In the formula, These are combined carrier observations in meters. represents the wetted delay component of the tropospheric zenith; el represents the residual error term considered in the position.

[0082] The pseudorange single-point positioning observation equation for the deionization combination is as follows:

[0083]

[0084] Linearizing the observation equations in equations (5) and (6) using Taylor expansion yields:

[0085]

[0086] In the formula, PIF represents the pseudorange observation value of the ionosphere-free combination; ep represents the residual pseudorange error term that has not been considered. and δX, δY, and δZ represent the coefficients of the coordinate corrections, respectively; LIR represents the combined carrier observations affected by the weak ionosphere; δX, δY, δZ, dtrop, N1, ..., Nn are the estimated parameters of the Kalman filter.

[0087] It should be noted that the above content merely illustrates the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. For those skilled in the art, various improvements and modifications can be made without departing from the principle of the present invention, and all such improvements and modifications fall within the scope of protection of the claims of the present invention.

Claims

1. A near-shore long baseline positioning method based on BeiDou-3 multi-frequency signals, characterized in that, include: Step 1: Propose a constraint condition for the combination coefficients of multi-frequency combined observations applicable to long baselines, and select the optimal combination coefficients of BeiDou-3 observations based on this constraint. The constraint conditions for the combination coefficients of the multi-frequency combined observations are first considered in the double-difference observation model shown in equation (1): ； In the formula, subscript i k This represents the frequency identifier, where k = 1, 2, ..., 5; c represents the speed of light; Indicates the combined frequency of the five frequencies. ; Indicates the ambiguity of the five-frequency combination. ; This indicates the noise level measured using a five-frequency combination. ; This represents the sum of other errors. ; This is the first-order ionospheric delay effect coefficient, in units of cycles / m. This value is related to the fixation rate and success rate of ambiguity. ； Multiply equation (2) by the combined wavelength The ionospheric delay coefficient, expressed in meters, is shown in equation (3). This value affects the accuracy of distance measurement. ； Assuming all observation noise is white noise and that each observation is independent, the combined carrier observation noise amplification factor in meters is obtained: ； Based on the above observation model, and considering the near-shore long baseline positioning environment, the multi-frequency combined observation combination coefficient constraint condition proposed in step 1 first considers the complex ionospheric situation of long baselines, selecting a large ionospheric delay under extreme conditions as a reference. It requires that the ionospheric delay has an impact of less than 1 cm on ranging and less than 0.1 weeks on ambiguity resolution. Therefore, we have... Secondly, it is required that the performance of the multi-frequency observation combination proposed in step 1 is superior to that of the ionospheric desiccation combination, thus there is , When selecting the optimal combination coefficients, based on the above constraints, and considering that the noise amplification factor per cycle should not be too large, a finite number of coefficients should be selected. Iterate through all coefficient combinations within the range and select the combination that meets the requirements. Step 2: The reference station system pre-processes the received carrier observation data and then broadcasts it unidirectionally according to the new coding protocol, which reduces the communication burden while ensuring data resolution. Step 3: The positioning and calculation terminal analyzes the combined carrier data of the reference station and the carrier observations it receives to form a combined observation equation for the weak ionospheric influence. At the same time, it establishes its own combined pseudorange single-point positioning observation equation for the ionospheric elimination. Kalman filtering is used to estimate the position parameters and tropospheric wet delay parameters to achieve high-precision positioning and calculation in the nearshore area.

2. The near-shore long baseline positioning method based on BeiDou-3 multi-frequency signals as described in claim 1, characterized in that, Step 2: The reference station system pre-processes the received carrier observation data and then broadcasts it according to a new radio communication protocol applicable to multi-system five-frequency combined observation data. This protocol is an improvement on the standard radio broadcasting protocol framework, fully conforming to the standard radio broadcasting protocol's format requirements of 30 bits per word and 32 words per frame, and adopts the standard radio broadcasting protocol's common message header. This means that when using this protocol for software development, it is not necessary to redevelop the decoding module; only a new message type needs to be added to the protocol decoding module. To adapt to the current situation of a large number of satellites in multiple systems, the improved communication protocol adds frame end identifier and sequence number fields to ensure the integrity of data transmission before and after transmission. If a sequence number discrepancy occurs, the erroneous frames that follow are discarded immediately, preserving as many intact sub-epochs as possible. To improve the resolution of broadcast observations while compressing the amount of data required, the improved communication protocol adopts a form that separates the coarse distance from the precise distance of carrier observations in one meter units, and uses time units in milliseconds for transmission. Its distance resolution is 0.00014m.

3. The near-shore long baseline positioning method based on BeiDou-3 multi-frequency signals as described in claim 1, characterized in that, In step 3, during the estimation of position parameters, the positioning terminal analyzes the combined carrier data of the reference station and performs differential analysis with its own received carrier observations to form a combined observation equation affected by the weak ionosphere. At the same time, it establishes its own combined pseudorange single-point positioning observation equation for the ionosphere, and uses Kalman filtering to estimate the position parameters and tropospheric wet delay parameters. This saves the number of observations that need to be transmitted in terms of communication, while ensuring centimeter-level positioning accuracy. The combined observation equations for the effects of the weak ionosphere are as follows: ； In the formula, ρ represents the distance between the station and the satellite; These are combined carrier observations in meters. This represents the wetted delay component of the tropospheric zenith. This indicates the remaining error term considered by the bit. The pseudorange single-point positioning observation equation for the deionization combination is as follows: ； Linearizing the observation equations in equations (5) and (6) using Taylor expansion yields: ； In the formula, These are pseudorange observations for ionospheric combination; This indicates the unconsidered pseudorange residual error term; , and These represent the coordinate correction amounts. , and The coefficient; These are combined carrier observations influenced by the weak ionosphere; These are the estimated parameters for the Kalman filter.

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