CN109782305B - Method for generating RTK message by receiver optimization strategy under multi-reference condition - Google Patents

Abstract

The present invention provides a method for generating RTK messages with a receiver optimization strategy under multiple reference conditions, which can select a reference receiver with high data quality and balanced state stability index from multiple reference receivers in a reference station as the carrier phase The reference source for differential message transmission ensures that the mobile station receives differential messages with the best data quality, thereby ensuring the integrity of the reference station and the positioning accuracy and positioning success rate of the mobile station. Based on the hardware of a reference station composed of a plurality of reference receivers, the present invention optimizes one reference receiver as the reference source of the carrier phase difference message so that the mobile station can perform RTK positioning, which can not only solve the problem of integrity, but also It enables the mobile station to perform RTK positioning, improves positioning accuracy, and can better provide effective guarantee for aircraft landing or high-precision positioning requirements in other industries.

Description

The Method of Generating RTK Messages Based on Receiver Optimal Strategy under Multiple Reference Conditions

technical field

The invention relates to a method for optimizing a reference source, which belongs to the field of high-precision relative positioning of carrier phase of satellite navigation.

Background technique

RTK positioning in the conventional field can be realized by configuring one receiver each for the base station and the mobile station, but when there is an integrity risk in the navigation system or the reference receiver of the base station fails, this hardware configuration mode will cause RTK The fixed rate and positioning accuracy of positioning will be greatly reduced, what's more, its positioning mode will directly exit RTK positioning, and the positioning mode will be degraded. However, in fields that are closely related to life safety, such as aircraft surface guidance and landing, conventional configurations obviously cannot meet functional performance indicators such as integrity, availability, and continuity. Therefore, a base station composed of multiple reference receivers (for example: LAAS and GBAS) came into being. This type of reference station broadcasts the pseudo-range differential enhancement information to the outside, which is used for the mobile station to perform pseudo-range differential positioning. Although this type of reference station has functional performance indicators such as integrity, continuity, and availability, it only has the ability to broadcast pseudo-range differential enhanced messages. The accuracy of pseudo-range differential positioning mode is at the meter level, which obviously cannot match the positioning accuracy. Compared with the sub-meter-level RTK positioning mode, in order to improve the positioning accuracy of the mobile station, the base station composed of multiple reference receivers will inevitably broadcast carrier phase difference messages, but the problem introduced is the normal situation of multiple reference receivers The monitoring and isolation of the integrity algorithm will pass through the monitoring and isolation of the integrity algorithm, so how to choose the best among the reference receivers as the reference source of the carrier phase difference message and how to avoid unnecessary switching of the reference receiver is a problem that must be considered.

Contents of the invention

In order to overcome the deficiencies in the prior art, the present invention provides a carrier phase difference multi-reference receiver optimization method, which can select one with high data quality and state stability index balance (excellent measurement residual error) from the multiple reference receivers of the reference station. The reference receiver with the highest star search score) is selected from the average value as the reference source for sending carrier phase difference messages to ensure that the mobile station receives differential messages with the best data quality, thereby ensuring the integrity of the reference station and the positioning of the mobile station Accuracy and positioning success rate.

The technical solution adopted by the present invention to solve its technical problems comprises the following steps:

1) Perform SQM, DQM, MQM and residual monitoring on each reference receiver, mark and isolate the corresponding faulty satellite channel, and the reference receiver with more than 2 satellites marked out of use;

2) Determine whether the number of BDS/GPS dual-system four-frequency points of each reference receiver is not less than 4, and if it is less than 4, the receiver will exit;

3) Judging whether the difference between the number of satellites searched by dual-frequency points of each navigation system exceeds 3 satellites; if more than 3, the receiver exits;

4) Calculate the mean value μ and the standard deviation σ of the number of satellites searched at each dual-frequency point of the BDS/GPS dual system, and count the μ _BDS -2σ _BDS and μ _GPS -2σ _GPS of each navigation system of each reference receiver;

其中，n为该基准接收机锁定卫星个数，residual_{sat i}为该卫星的残差值；计算所有可用基准接收机残差平均值

其中，m是可用基准接收机个数；如果某基准接收机的单个基准接收机锁定卫星残差平均值大于所有可用基准接收机残差平均值，则该接收机退出；5) Calculate the average value of the residual error of a single reference receiver locking the satellite

Among them, n is the number of satellites locked by the reference receiver, and residual _{sat i} is the residual value of the satellite; calculate the average value of the residuals of all available reference receivers

Among them, m is the number of available reference receivers; if the average value of the residual error of a single reference receiver locked by a reference receiver is greater than the average value of the residual error of all available reference receivers, the receiver will exit;

6) If the maximum values of μ _BDS -2σ _BDS and μ _GPS -2σ _GPS are on the same reference receiver, then select the reference receiver; otherwise, calculate the μ _BDS -2σ _BDS and μ _GPS -2σ of each reference receiver The mean and variance of the sum of _GPS are recorded as α and β respectively, and α-2β is calculated, and the reference receiver with the maximum value of α-2β is selected;

7) If there are multiple reference receivers with the same maximum value of α-2β at the same time in the reference receiver, then the reference receiver with the smallest average value of the residual error of the locked satellite is preferred;

8) Accumulate the data of the set number of epochs, if the selected receiver can continuously meet the steps 1)~3), then do not switch the reference receiver; otherwise, return to step 1) and select a reference receiver again;

9) Real-time statistics of the mean value μ _state and standard deviation σ _state of each reference receiver α-2β;

10) After setting the number of epochs, assume that the mean value μ _state and standard deviation σ _state conform to the Gaussian distribution, and normalize it;

11) If the normalized value of each epoch falls within the 2σ interval of the standard Gaussian distribution, do not switch the reference receiver, otherwise return to step 1) and select a reference receiver again.

The beneficial effects of the present invention are: on the basis of the hardware of the reference station composed of multiple reference receivers, one reference receiver is selected as the reference source of the carrier phase difference message so that the mobile station can perform RTK positioning, which can solve the problem of integrity It can also enable the mobile station to perform RTK positioning, improve positioning accuracy, and better provide effective guarantee for aircraft landing or high-precision positioning requirements in other industries.

Description of drawings

Fig. 1 is a schematic diagram of a method for generating a carrier phase difference message;

Fig. 2 is a schematic diagram of carrier phase difference multi-reference receiver optimization method;

Fig. 3 is a schematic diagram of the preferred strategy of the reference receiver;

Fig. 4 is a schematic diagram of B1 pseudorange deviation 300 meters height positioning result (without optimization method);

Figure 5 is a schematic diagram of the height positioning results after the strategy is introduced;

Figure 6 is a schematic diagram of the positioning results of the mobile station after 2 satellites are added with a carrier cycle jump;

Figure 7 is a schematic diagram of the height positioning results after the strategy is introduced.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments, and the present invention includes but not limited to the following embodiments.

The present invention is based on a differential reference station composed of multiple reference receivers, an optimal method for selecting a reference receiver with excellent performance and stable state as a reference source from multiple reference receivers, and using the data of the reference receiver Packing and broadcasting are performed for the mobile station to perform carrier phase differential positioning (hereinafter referred to as RTK positioning).

The present invention mainly comprises the following aspects:

(1) Carrier Phase Difference Message Generation Method

The data quality and the number of satellites contained in the carrier phase difference message generated by the ground reference station play an important role in improving the accuracy. The mechanism mainly includes three steps: integrity monitoring, residual monitoring, and statistically-based optimal strategy. The carrier phase difference message generation mechanism is shown in Figure 1.

a) Integrity monitoring.

Integrity monitoring is performed on the original observations and ephemeris of locked satellites output by available reference receivers. The integrity algorithms used are signal quality monitoring (SQM), data quality monitoring (DQM) and measurement quality monitoring (MQM).

Among them, signal quality monitoring (SQM) mainly detects and identifies anomalies in the received GPS/BDS ranging signals, and it mainly consists of three parts: correlation peak monitoring, signal power monitoring and code carrier divergence monitoring.

Data Quality Monitoring (DQM) is mainly to monitor the reliability of the satellite navigation message data received by the receiver. The data center of the ground-based augmentation system mainly checks the correctness of the updated GPS satellite ephemeris and satellite clock data through the data quality monitoring algorithm.

Measurement quality monitoring (MQM) mainly monitors the step and impact changes of measurement values caused by clock anomalies and reference receiver failures by using the consistency of multiple epoch pseudoranges and carrier phase measurements, which mainly includes three Section: receiver lock time monitoring, carrier acceleration ramp step monitoring and innovative monitoring of carrier smoothed code pseudorange.

b) Residual monitoring.

The accuracy of the original observations is monitored by calculating satellite residuals. If the residual of a certain satellite is greater than the threshold (250 meters), it is determined that the satellite of the receiver is unavailable.

The residual calculation formula is as follows:

是卫星钟差，

是基准接收机钟差。Among them, r is the true range, ρ is the pseudo-range,

is the satellite clock,

is the reference receiver clock error.

c) fault isolation

Three kinds of QM monitoring and residual monitoring As long as there is one method to monitor the abnormality of the corresponding satellite of the corresponding frequency point, the corresponding satellite of the corresponding frequency point of the receiver will be isolated. If there are more than 2 satellites of the corresponding frequency point of each receiver If the satellite is marked abnormally, the corresponding frequency point of the receiver will be judged as unavailable

d) Optimizing strategies based on statistics.

Through this strategy, a receiver with a large number of search satellites and excellent data quality is selected from multiple reference receivers as a reference to ensure the RTK positioning accuracy and positioning success rate of the mobile station. This strategy will be carried out in the second part of this chapter Details.

_e ) Switch suppression strategy

This strategy can suppress unnecessary switching between reference receivers. Due to the hardware of each reference receiver or other reasons, different receivers will have differences in the measurement values of the same satellite at the same epoch. Once the reference receiver is switched, it may cause the dual-frequency carrier broadcast by the reference station The integer cycle and fractional cycle of the carrier of the phase difference message jump, which causes the positioning result of the mobile station to jump. In severe cases, the positioning accuracy may exceed the target. Therefore, it is necessary to select not only the best performance but also the stable reference receiver. machine. This handover suppression strategy solves the problem of selecting a reference receiver with a stable state. For a detailed introduction, see the third part of this chapter. If there is a switch judgment condition, it will jump to the first step of the preferred strategy to start execution.

(2) Optimization strategy based on statistics

After integrity monitoring and residual monitoring, it is necessary to optimize the reference receiver with the best state through correlation results. A core point of this patent is to propose a corresponding strategy to ensure that the selected reference receiver has good data quality and a large number of satellite searches.

In order to comprehensively consider the ability of multi-reference receivers of ground reference stations to operate GPS and BDS systems, it is necessary to comprehensively evaluate the satellite search situation of each reference receiver dual system and the quality of data measurement when selecting a reference receiver. Only the dual system of BDS and GPS Only the reference receiver with the largest number of integrated frequency search satellites and the best data quality can be used as the reference position of RTK, and the original observations of the reference receiver are packaged as carrier phase difference messages and broadcast to the mobile station.

The preferred strategy based on statistics is as follows:

1) BDS/GPS dual-system four-frequency point, the number of search satellites is not less than 4;

2) The difference between the number of satellites searched by dual-frequency points of each navigation system does not exceed 3 satellites;

3) Calculate the mean value μ and standard deviation σ of the number of satellites searched at each dual-frequency point of the BDS/GPS dual system, and count the μ _BDS -2σ _BDS and μ _GPS -2σ _GPS of each navigation system of each reference receiver;

4) The average residual error of each available reference receiver to lock the satellite is less than or equal to the average residual error of all available reference receivers;

The average residual error for a single reference receiver locked to a satellite is calculated as follows:

Among them, n is the number of satellites locked by the reference receiver, residual _{sat i} is the residual value of the satellite, and the calculation formula is shown in residual monitoring.

The average of all available reference receiver residuals is calculated as follows:

Among them, m is the number of available reference receivers.

5) If the maximum values of μ _BDS -2σ _BDS and μ _GPS -2σ _GPS are on the same reference receiver, then select the reference receiver; otherwise, calculate the μ _BDS -2σ _BDS and μ _GPS - The mean value and variance of the sum of 2σ _GPS are recorded as α and β respectively, and α-2β is calculated, then the reference receiver with the maximum value of α-2β is selected.

6) If there are multiple reference receivers with the same maximum value of α-2β at the same time, the reference receiver with the smallest average residual error of the locked satellite is preferred.

(3) Multi-reference receiver switching suppression strategy

A reference station composed of multiple reference receivers, each reference receiver has different measurement errors due to equipment hardware or other reasons, so the measurement results of each reference receiver for each satellite are different at the same time. Therefore, once the reference receiver is switched, it may cause the carrier integer cycle and fractional cycle of the dual-frequency carrier phase difference message broadcast by the reference station to jump, thereby causing the positioning result of the mobile station to jump. The positioning accuracy exceeds the target.

The above step (2) focuses on how to select the receiver with the best state at this moment, but in order to avoid the carrier cycle jump caused by unnecessary reference receiver switching, the reference receiver with excellent state and stable state should be selected in a balanced manner as The reference source of the carrier phase difference of the ground station, the two complement each other to ensure the excellent accuracy index and integrity performance of the real-time dynamic differential positioning. Therefore, how to avoid unnecessary switching of multiple reference receivers is another core of the present invention.

Suppression strategy:

1) Accumulate at least 600 epochs of data (reference receiver output frequency: 1Hz), and if the receiver selected within 600 epochs can continuously meet the first 3 steps of the optimization strategy based on statistics, it will not switch the reference receiver , go to the next step; otherwise, skip to step 1 of the preferred strategy;

2) Real-time statistics of the mean value μ _state and standard deviation σs _state of each reference receiver α-2β (see the sixth step of the optimization strategy based on statistics for the calculation method);

3) After 600 epochs, assuming that the mean value μ _state and standard deviation σ _state of the third step statistics conform to the Gaussian distribution, normalize it.

4) If the normalized value of each epoch falls within the 2σ interval of the standard Gaussian distribution, no switching will be performed; otherwise, a reference receiver will be selected again according to the optimization strategy.

Embodiments of the present invention relate to a reference station equipment composed of multiple reference receivers, and from multiple reference receivers, the reference receiver with the best state and the most stable state and excellent comprehensive performance index is selected as a reference source, and then the reference receiver Machine data is packaged and broadcast.

Implementation steps of the present invention are as follows:

1) Carry out SQM, DQM, MQM and residual monitoring on 4 reference receivers to monitor faults and isolate corresponding faulty satellite channels. If more than 2 satellites are marked, determine the frequency point of the reference receiver If it is unavailable, the receiver will exit; otherwise, enter the next step;

2) Determine whether the number of BDS/GPS dual-system four-frequency points of each reference receiver is less than 4, and if it is less than 4, the receiver will exit; otherwise, enter the next step;

3) Judging whether the difference between the number of satellites searched by dual-frequency points of each navigation system exceeds 3 satellites; if more than 3, the receiver exits; otherwise, enters the next step;

4) Calculate the mean value μ and the standard deviation σ of the number of satellites searched at each dual-frequency point of the BDS/GPS dual system, and count the μ _BDS -2σ _BDS and μ _GPS -2σ _GPS of each navigation system of each reference receiver;

5) The average residual error of each available reference receiver to lock the satellite is less than or equal to the average residual error of all available reference receivers; if it is greater than the average residual error of all available reference receivers, the receiver exits; otherwise, enter the next step;

The average residual error for a single reference receiver locked to a satellite is calculated as follows:

Among them, n is the number of satellites locked by the reference receiver, residual _{sat i} is the residual value of the satellite, and the calculation formula is shown in residual monitoring.

The average of all available reference receiver residuals is calculated as follows:

Among them, m is the number of available reference receivers.

6) If the maximum values of μ _BDS -2σ _BDS and μ _GPS -2σ _GPS are on the same reference receiver, then select the reference receiver; otherwise, calculate the μ _BDS -2σ _BDS and μ _GPS - The mean value and variance of the sum of 2σ _GPS are recorded as α and β respectively, and α-2β is calculated, then the reference receiver with the maximum value of α-2β is selected;

7) If there are multiple reference receivers with the same maximum value of α-2β in the reference receiver, then choose the reference receiver with the smallest average value of the residual error of the locked satellite;

8) At least 600 epochs of accumulated data (reference receiver output frequency: 1Hz), and the receiver selected within 600 epochs will not switch the reference receiver if it can continuously meet the first 3 steps; otherwise, it will pass the selection again Strategy selects a reference receiver, skip to step 1;

9) Real-time statistics of the mean value μ _state and standard deviation σ _state of each reference receiver α-2β;

10) After 600 epochs, assume that the mean value μ _state and standard deviation σ _state conform to Gaussian distribution, and normalize it.

11) If the normalized value of each epoch falls within the 2σ interval of the standard Gaussian distribution, no switching is performed, otherwise, skip to step 1 and select a reference receiver again.

In the embodiment of the present invention, the mobile station remains stationary, and the location of the mobile station is (34.2378728571, 108.909674311, 388.0335).

Using 4 reference receivers (reference station) and one mobile receiver (mobile station), if you do not add the optimal method, and add +300m deviation to the pseudo-range of the two satellites B1 frequency point locked by the reference source, the increase will be Large pseudorange residuals.

As can be seen from Figure 4, there is a jump of about 2-3 meters in height. According to the statistics of the positioning mode, the success rate of RTK fixed solution is reduced to 98.22%, and the mean and standard deviation of positioning are shown in Table 1

Table 1 B1 pseudo-range deviation 300 meters longitude and latitude height positioning mean and standard deviation

Four reference receivers (base station) and one mobile receiver (rover station) are used. Before fault injection, reference receiver 1 was the reference for RTK. Add +300m deviation to the pseudo-range of the two satellites B1 locked by reference receiver 1. It can be seen that this strategy judges reference receiver 1 as abnormal, and selects reference receiver 2 as the reference for carrier phase difference. As shown in table 2.

Table 2 Selection results of reference receivers after strategy introduction

Under the strategy proposed in this paper, taking the height positioning result as an example, the positioning result of the mobile station is shown in Figure 5.

It can be seen from Figure 5 that there is no jump in the height value. According to the statistics of the positioning mode, the success rate of RTK fixed solution is 100%, and the mean value and standard deviation of positioning are shown in Table 3.

Table 3 The mean value and standard deviation of latitude and longitude positioning after the introduction of the strategy

average standard deviation 34.2378728306026 1.2108486574906E-8 108.909674274428 1.5773786094586E-8 388.0250883984521 0.0037271655203

When the reference receiver is switched, it will cause a certain degree of carrier cycle jump, so add cycle slip to the reference source to simulate the switching situation of the reference receiver.

Remove the preferred method setting, randomly add 2 stars to the reference source in the whole week and fractional weeks, and the RTK fixed solution success rate is 99.94%. The overall positioning results are as follows, and the height is shown in Figure 6.

Table 4 Positioning results of the mobile station

mean Standard Deviation 34.237872858813 1.2090192902624E-7 108.9096742809958 1.3355133880312E-7 388.0163054695202 0.0366298572962

Start the optimization method logic, the same fault filling method, the simulation results are shown in Figure 7.

It can be seen from Figure 7 that there is no jump in the height value. According to the statistics of the positioning mode, the success rate of RTK fixed solution is 100%, and the mean value and standard deviation of positioning are shown in Table 5.

Table 5 The average value and standard deviation of latitude and longitude positioning after the introduction of the strategy

average standard deviation 34.2378728306026 1.2108486574906E-8 108.909674274428 1.5773786094586E-8 388.0250883984521 0.0037271655203

Through the above carrier phase difference multi-reference receiver optimization method, it is ensured that under the multi-reference condition, the reference receiver with the best state and the most stable and balanced state is selected as the reference source, and then broadcast to the mobile station for RTK positioning, ensuring that the broadcast message has Certain integrity and precision make the positioning result of the mobile station more reliable and improve its positioning accuracy.

Claims (1)

1. A method for generating an RTK message by a receiver with an optimal strategy under a multi-reference condition is characterized by comprising the following steps:

1) Respectively carrying out SQM, DQM, MQM and residual error monitoring on each reference receiver, marking and isolating corresponding fault satellite channels, and quitting the use of more than 2 satellites by the marked reference receivers;

2) Judging whether the number of the four-frequency points of the BDS/GPS dual system of each reference receiver is not less than 4, and if the number of the four-frequency points of the BDS/GPS dual system of each reference receiver is less than 4, the receiver exits;

3) Judging whether the difference of the number of the double-frequency point satellite searches of each navigation system exceeds 3 satellites or not; if more than 3, the receiver exits;

4) Calculating the mean value mu and the standard deviation sigma of the number of the double-frequency point satellite searches of the BDS/GPS double system, and counting the mu of each navigation system of each reference receiver _BDS -2σ _BDS And mu _GPS -2σ _GPS ；

5) Computing mean residual values for single reference receiver locked satellites

Where n is the reference receiver lockNumber of satellites, residual _{sat i} Is the residual value of the satellite; computing the mean of all available reference receiver residuals

Wherein m is the number of available reference receivers; if the mean value of the residual errors of a single reference receiver locking satellite of a certain reference receiver is larger than the mean value of the residual errors of all the available reference receivers, the receiver exits;

6) Mu.f _BDS -2σ _BDS And mu _GPS -2σ _GPS If the maximum value of the reference receiver is on the same reference receiver, selecting the reference receiver; otherwise, mu of each reference receiver is calculated _BDS -2σ _BDS And mu _GPS -2σ _GPS Respectively recording the mean value and the variance of the sum as alpha and beta, calculating alpha-2 beta, and selecting a reference receiver with the maximum value of the alpha-2 beta;

7) If the maximum values of a plurality of reference receivers alpha-2 beta are the same at the same time, the reference receiver with the minimum residual average value of the locked satellite is preferred;

8) Accumulating the data of the set epoch number, and if the optimized receiver can continuously meet the steps 1) to 3), not switching the reference receiver; otherwise, returning to the step 1) to select a reference receiver again;

9) Real-time statistics of mean value mu of alpha-2 beta of each reference receiver _state And standard deviation σ _state ；

10 After setting the epoch number, assume the mean μ _state And standard deviation σ _state Normalizing the Gaussian distribution;

11 Not switching the reference receiver if the normalized value of each epoch falls within the standard Gaussian distribution 2 sigma interval, otherwise returning to the step 1) to select a certain reference receiver again.

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