JP2020122683A - Gnss receiver and method for calculating ionosphere delay amount - Google Patents

Abstract

To obtain an ionosphere delay amount accurately and promptly for a satellite that can use only one frequency band, and use it for high-accuracy positioning.SOLUTION: An ionospheric delay coefficient estimation unit 51 obtains an ionospheric delay amount from a satellite capable of using two frequencies L1 and L2, and uses the parameters of an ionospheric delay amount model to obtain an ionospheric delay coefficient K common to the signals from all observable satellites. An ionosphere delay amount calculation unit 52 uses the ionosphere delay coefficient K to obtain an ionosphere delay amount of signals from a satellite capable of using only one frequency band L1 with high accuracy and quickly. Therefore, it is possible to use signals from the satellite capable of using only one frequency band for high-accuracy positioning.SELECTED DRAWING: Figure 1

Description

The present invention relates to an ionospheric delay amount calculation method in a GNSS receiver.

In GNSS satellite positioning, positioning accuracy depends on how various error factors can be estimated and reduced. There are several factors that cause error in satellite positioning, and typical ones are satellite clock error, satellite position error, ionospheric delay amount, tropospheric delay amount, multipath, and receiver noise. Correcting the amount error is an important issue in high-accuracy positioning.

The ionosphere is a region where ionized gas spreads from about 50km to about 1000km above the earth, that is, free electrons and ions, and the state of the ionosphere largely depends on solar activity. Change. Generally, when the sun rises, the electron density rises and reaches its peak around 14:00. It decreases after that, and ionization hardly occurs at night, and the electron density decreases.

The propagation velocity of a radio wave that passes through the ionosphere depends on the total amount of electrons in its path. Become. The ionospheric delay I in the L-band microwave used as the radio wave of the GPS satellite can be expressed by the following equation.
I=(40.3/f ² )TEC
Here, f is the frequency (Hz) of the radio wave, and TEC is the total number of free electrons (total amount of electrons) on the line connecting the receiver and the satellite.

In positioning by a satellite, there is a problem that the positioning accuracy is deteriorated due to a delay in propagation time generated when a radio wave transmitted from the satellite passes through the ionosphere, so-called ionospheric delay.

Therefore, in conventional satellite positioning receivers, a model formula for the ionospheric delay amount is incorporated in the software inside the receiver, and the ionospheric delay amount is estimated by predicting the delay amount according to the elevation angle of the satellite. Was there.

A typical ionospheric delay amount model formula is an ionospheric delay amount correction model called a Klobuchar model, and the ionospheric delay amount is corrected using the parameters of the Klobuchar model transmitted from GPS satellites. That is, the receiver measures the code pseudoranges with multiple satellites, estimates the position and time error of the receiver at that time, and corrects the ionospheric delay amount with the parameter given from the Klobuchar model sent from the satellite. (See Non-Patent Document 1).

Further, as a method of performing ionosphere delay correction with higher accuracy, an ionosphere delay correction method using an ionosphere-free linear combination method is known. Since the ionospheric delay is almost inversely proportional to the square of the carrier frequency f, most of the influence can be eliminated by multiplying the carrier phase of two frequencies by a certain coefficient and adding them. In the GNSS receiver that can receive two frequencies L1 and L2 by utilizing this, the ionosphere delay amount is canceled by the two frequencies L1 and L2 transmitted from the satellite by using the ionosphere-free linear combination method. (See Non-Patent Document 2).

By the way, in the GNSS positioning by satellite, as a method of improving the accuracy, the accuracy is improved by obtaining the precise position and the observation data of the adjacent reference station, and the position of the mobile station is obtained by obtaining the three-dimensional vector between the reference station and the mobile station. Relative positioning is known. The relative positioning method includes RTK (Real-Time-Kinematic)-GNSS. As shown in FIG. 6, there is a reference station R and a mobile station r, each of which receives radio waves from a plurality of satellites S, and the mobile station r observes both the pseudo range and the carrier phase observed by the reference station R. Is obtained from the reference station R, a new observation value is generated together with the observation data of the user side mobile station r, and the position of the mobile station r is obtained with an accuracy of about 1 cm. Since this RTK positioning measures the position by the carrier phase, it is necessary to correctly solve the integer bias of the carrier phase, which is the ambiguity of the carrier phase. That is, in order to determine the position of the receiver by the carrier wave phase, it is necessary to obtain an integer value bias indicating how many sine waves are included between the satellite and the receiver. In order to obtain the integer value bias, it is necessary to know the rough position of the receiving antenna from the pseudo distance information, and if the accuracy of the pseudo distance is high, the integer value bias candidates can be narrowed down. If there is an error of several cm in the carrier wave phase, the integer value bias cannot be correctly obtained, and therefore the error due to the ionospheric delay is also required to be highly accurate within 1 cm.

Liu Xiu, "Study on ionospheric model using single-frequency pseudorange single positioning", [online], [Search on December 21, 2018], Internet <URL: http://www.denshi.e.kaiyodai .ac.jp/jp/assets/files/pdf/content1/2012ryu_m.pdf> Tomoji Takasu, "Theory and analysis processing of precise positioning by carrier wave phase measurement value", [online], [Search on December 21, 2018], Internet <URL: http://gpspp.sakura.ne.jp/ tutorial/html/gps_symp_2005_2.htm〉

However, the correction by the Klobuchar model assumes that the ionosphere is a single layer existing only at an altitude of 350 km, the nighttime ionospheric delay amount is a constant flat, and the daytime approximation is represented by a half-wave cosine curve with a maximum local time of 14:00. Since it is a model (see FIG. 5), only about 50% accuracy was obtained, and it was not possible to endure high-accuracy positioning such as RTK positioning.

Since ionospheric delay is an error factor that greatly affects GNSS surveying, it is required for high-precision positioning represented by RTK positioning to quickly and accurately determine the amount of ionospheric delay. The GNSS receiver uses GPS satellites capable of simultaneously receiving L1 and L2 signals to perform positioning by canceling the ionosphere delay amount for each satellite by an ionosphere-free linear coupling method.

However, there is a problem that the ionospheric delay correction method using the ionosphere-free linear combination method cannot be performed unless two frequencies L1 and L2 from the satellites can be received, and the number of satellites that can be used for positioning is limited. .. Also, if the data from many satellites can be used, it becomes easy to determine the integer bias, but with the data from few satellites, it takes time to determine the integer bias, which is an obstacle to high-accuracy positioning. In addition, since the carrier phase bias is not an integer, it is not possible to directly determine an integer value bias, which is another factor that requires a long time for the RTK positioning calculation.

In addition, the correction data of the MADOCA (Multi-GNSS Advanced Demonstration tool for Orbit and Clock Analysis) method, which is a highly accurate positioning correction technology that is currently being developed, is basically only the correction information on the satellite side. High-accuracy error correction on the GNSS receiver side is an issue for accurate positioning.

Therefore, the present invention obtains the ionospheric delay coefficient K common to the signals from all the satellites at the observation point, calculates the ionospheric delay amount using the ionospheric delay coefficient K for satellites that can use only one frequency band, An object of the present invention is to provide a GNSS receiver and an ionosphere delay amount calculation method capable of obtaining an ionosphere delay amount with high accuracy and quickly.

In order to achieve the above object, the invention described in claim 1 of the present application is a GNSS receiver for performing positioning based on signals transmitted from a plurality of satellites, and two different frequency bands transmitted from the satellites. Ionosphere delay coefficient estimator that receives the signal of the above and estimates the ionosphere delay coefficient at the observation point, and the ionospheric delay that calculates the ionospheric delay amount of the signal received from the satellite that can use only one frequency using the ionosphere delay coefficient. And a quantity calculator.

The invention according to claim 2 is a method for calculating an ionospheric delay amount in a GNSS receiver for performing positioning based on signals transmitted from a plurality of satellites, wherein signals of two different frequency bands transmitted from the satellites. And an ionospheric delay coefficient estimation step for estimating an ionospheric delay coefficient at the observation point, and an ionospheric delay amount calculation for calculating an ionospheric delay amount of a signal received from a satellite that can use only one frequency using the ionospheric delay coefficient And a step.

According to the first and second aspects of the present invention, the ionospheric delay coefficient common to all satellites at the time of observation is estimated from the signals of the satellites that are able to receive signals in two different frequency bands, and By calculating the current amount of ionospheric delay for satellites that can use only one frequency band from the estimated ionospheric delay coefficient, and performing positioning calculation based on the observation value that subtracts the amount of ionospheric delay, data regarding the amount of ionospheric delay can be obtained. High-accuracy positioning can be performed even in an environment where no signal is sent, and even satellites that can use only one frequency band signal can be used for high-accuracy positioning such as RTK positioning.

Furthermore, although the carrier phase bias becomes a real value in the conventional ionosphere-free coupling method, according to the inventions of claims 1 and 2, the RTK can be handled by an integer value. Positioning calculation etc. can be performed quickly.

It is a schematic block diagram of the GNSS receiver which concerns on this Embodiment. It is a flowchart which shows operation|movement of a GNSS receiver. It is a flowchart which shows operation|movement of the ionosphere delay coefficient estimation part of a GNSS receiver. It is a flowchart which shows operation|movement of the ionosphere delay amount calculation part of a GNSS receiver. It is a graph showing the half-wave cosine curve of the Klobuchar model. It is a schematic diagram showing composition of an RTK positioning system.

The present invention will be described below based on the illustrated embodiments.

FIG. 1 is a schematic configuration diagram showing a GNSS receiver 1 according to an embodiment of the present invention. This GNSS receiver 1 is a conventional GNSS receiver in that an observation data output unit 5 that outputs observation data necessary for positioning calculation includes an ionosphere delay coefficient estimation unit 51 and an ionosphere delay amount calculation unit 52 described later. The configuration is different, and other configurations are the same as those of the conventional GNSS receiver, and thus detailed description thereof will be omitted, but the configuration is roughly as follows.

The GNSS receiver 1 correlates the antenna 2 that receives a signal from the satellite, the high frequency unit 3 that converts the frequency of the received signal into a digital signal, and the code of the signal from the satellite, estimates the Doppler frequency, and estimates the signal. A signal processing unit 4 that continuously captures signals and outputs signals, an observation data output unit 5 that outputs observation data necessary for positioning calculation, and a positioning calculation unit 6 that calculates position and speed using the observation data. Prepare

Although not shown, the GNSS receiver 1 receives from the reference station data receiving antenna 21 and the reference station data receiving antenna 21, which are antennas for receiving the carrier wave phase data and the like transmitted from the reference station, which are necessary for RTK positioning. A reference station data receiving unit 31 for demodulating carrier phase data of the reference station and the like.

In this embodiment, the high frequency unit 3, the signal processing unit 4, the observation data output unit 5, the positioning calculation unit 6, and the reference station data reception unit 31 (not shown) are configured as one module unit. An antenna 2 and an antenna 21 (not shown) are connected to this module unit.

The observation data output unit 5 includes an ionosphere delay coefficient estimator 51 and an ionosphere delay amount calculator 52.

The ionosphere delay coefficient estimator 51 incorporates a task program executed by the ionosphere delay coefficient estimator 51 to obtain an ionosphere delay coefficient K. The ionospheric delay coefficient K is a coefficient for obtaining the ionospheric delay amount of each satellite, and is derived using an ionospheric delay amount correction model. Specifically, the ionosphere delay coefficient estimator 51 extracts satellite data that can use two frequencies L1 and L2, and calculates the amount of ionospheric delay at the frequency L1.

That is, for satellites that can utilize the frequencies of L1 and L2, the ionospheric delay amount of L1 can be calculated by the following formula.
IL1_i=(PL1_i-PL2_i)/(1-γ) (1)
Here, I is an ionospheric delay amount, P is a pseudorange observation value, L1 and L2 represent frequencies, and i represents a satellite transmitting the signal. Further, when the code bias correction values cbias_L1i and cbias_L2i of the satellite i are obtained from the augmentation information by MADOCA or the like, the above formula (1) can be expressed as the following formula (1′) considering the code bias correction value of the satellite i. Good.
IL1_i=( (PL1_i+cbias_L1i)-(PL2_i+cbias_L2i) )/(1-γ) (1')

Next, the ionospheric delay coefficient K is calculated using the ionospheric delay correction model. In this embodiment, the Klobuchar model in which the navigation message of the GPS satellite includes parameters is adopted as the ionosphere delay correction model.

Regarding the Klobuchar model, the following equation is defined when the ionospheric delay coefficient K common to all satellites is defined as a correction coefficient for the ionospheric delay width Ai from the satellites.
IL1_i=(A ₀ +K×Ai×Ci)×Si (2)
Ci=cos(2π(ti-T ₀ )/Tn) (3)
Si=(1.0+16.0(0.53-elevi/π) ³ ) (4)
Here, A ₀ is the ionosphere delay value in the midnight zone, A i is the ionosphere delay amplitude of satellite i (calculated by the coefficient broadcast from the satellite), ti is the time of crossing the ionosphere of satellite i, T ₀ is the time at which the maximum amplitude is 14:00, Tn is the time width that is not in the middle of the night (calculated by the coefficient broadcast from the satellite), and elevi is the elevation angle of the satellite i.
Therefore, the ionospheric delay coefficient K is obtained by the following equation.
K = ((IL1_i / Si) -A 0) / Ai × Ci) (5)
Thus, if the ionospheric delay amount of L1 is known, the ionospheric delay coefficient K can be obtained from the observed value and the parameter sent from the satellite.

Further, if K is a correction coefficient for Ai, correction cannot be performed at midnight, and the value of K in a time zone close to midnight may easily become abnormal. Therefore, depending on the state of the positioning environment, the equation (2) below is used. The expression (2′) may be used.
IL1_i=K×(A ₀ +Ai×Ci)×Si (2′)
The ionospheric delay coefficient K in the above equation (2′) is given by the following equation.
_{K = IL1_i / ((A 0} + Ai × Ci) × Si) (5')
That is, the ionospheric delay coefficient estimator 51 uses the parameters of the Klobuchar model included in the navigation message of the GPS satellite from the L1 ionospheric delay amount of the satellite where L1 and L2 can be observed, and the above equation (5) or The ionospheric delay coefficient K is obtained from the equation (5').

Although the amount of ionospheric delay differs for each satellite, the ionospheric delay coefficient K is a coefficient common to all signals from satellites that can be observed at the observation point. If this ionospheric delay coefficient K is known, L2 is not received, that is, L1. The ionospheric delay amount of a satellite that can use only the frequency of can be calculated by the equation (2) or the equation (2').

The ionosphere delay amount calculation unit 52 incorporates a task program executed by the ionosphere delay amount calculation unit 52 to obtain the ionosphere delay amount of the signal from each satellite using the ionosphere delay coefficient K obtained by the ionosphere delay coefficient estimation unit 51. Has been.

That is, the ionosphere delay amount calculation unit 52 obtains the ionosphere delay amount of the satellite L1, which can use only the frequency of L1, by the above equation (2) or (2′) using the ionosphere delay coefficient K.

In this way, the ionospheric delay coefficient K common to all observable satellites is obtained, the ionospheric delay amount is obtained for satellites that can use only L1 signals, and the observation data necessary for positioning is output. Different from

Next, the operation of the GNSS receiver 1 will be described with reference to the flowchart of FIG.

When the GNSS receiver 1 is activated, the antenna 2 receives signals from a plurality of satellites. (Step S1). The signal received by the antenna 2 is converted into predetermined digital data that can be easily processed by the high frequency section 3, and is sent to the signal processing section 4. The signal processing unit 4 supplements and tracks signals. When the signal can be captured and tracked, the obtained signal is sent to the observation data output unit 5. Note that this flow is the same as in the GNSS receiver of the conventional art.

When signals are obtained from a plurality of satellites, the task program of the ionosphere delay coefficient estimator 51 of the observation data output unit 5 is activated to extract satellites that can use frequencies that can receive L1 and L2 and obtain the ionospheric delay coefficient K (step S2).

Here, the operation of the ionosphere delay coefficient estimator 51 will be described in detail with reference to the flowchart of FIG. 3. The task program incorporated in the ionosphere delay coefficient estimator 51 is activated when a plurality of satellite signals can be tracked. , Satellites that can use two frequencies L1 and L2 are extracted (step S21). Next, it is determined whether or not there are a plurality of satellites that can use L1 and L2 (step S22). If there is only one satellite that can use L1 and L2, the amount of ionospheric delay of L1 of that satellite is calculated (step S23). If there are a plurality of satellites, the ionospheric delay amount of L1 of each satellite that can utilize L1 and L2 is calculated (step S25).

Here, the following principle is used to obtain the ionospheric delay amount for the satellite i that can utilize L1 and L2.
The pseudorange residual between L1 and L2 of the satellite i and the GNSS receiver 1 is obtained by the following formula.
ΔρL1_i =PL1_i-(Ri+IL1_i+Di+cTi+ct) (6)
ΔρL2_i=PL2_i-(Ri+IL2_i+Di+cTi+ct) (7)
Where ΔρL1_i is the pseudorange residual of L1 of satellite i, ΔρL2_i is the pseudorange residual of L2 of satellite i, P is the pseudorange observation value, and R is the satellite and GNSS receiver 1. , I is the ionospheric delay, D is the troposphere delay, T is the satellite time error, t is the user time error, and c is the speed of light.
If you draw both,
ΔρL1_i-ΔρL2_i=PL1_i-PL2_i-(IL1_i-IL2_i) (8)
Next to
At the true position, ΔρL1_i−ΔρL2_i=0, so IL1_i-IL2_i=PL1_i-PL2_i (9)
The ionosphere correction value is inversely proportional to frequency, so
IL2_i=IL1_i×γ (10)
γ=fL1 ² /fL2 ²
Therefore,
PL1_i-PL2_i=PL1_i(1-γ) (11)

From equations (9) and (11),
IL1_i=(PL1_i-PL2_i)/(1-γ) (12)
Therefore, the ionospheric delay amount (IL1_i) of L1 can be obtained by obtaining the observed value of the pseudo range of L1 and L2 on the satellite i in which the frequencies of L1 and L2 can be used. Here, when the code bias correction values cbias_L1i and cbias_L2i of the satellite i are obtained from the reinforcement information by MADOCA or the like, the above equation (12) is expressed as the following equation (12′) considering the code bias correction value of the satellite i. Good.
IL1_i=((PL1_i+cbias_L1i)-(PL2_i+cbias_L2i) )/(1-γ) (12')

Next, the ionosphere delay coefficient estimator 51 calculates the ionosphere delay coefficient K based on the calculated L1 ionosphere delay amount (IL1_i) (step S26). In the present embodiment, the Klobuchar model is used as the ionospheric delay correction model for obtaining the ionospheric delay coefficient K.

The ionospheric delay coefficient estimator 51 calculates the ionospheric delay amount (IL1_i) of L1 of the satellite i in which L1 and L2 can be observed and the parameter of the Klobuchar model included in the navigation message of the GPS satellite from the equation (5) above. , or (5 ') equation K = ((IL1_i / Si) -A 0) / Ai × Ci) (5)
_{K = IL1_i / ((A 0} + Ai × Ci) × Si) (5')
Then, the ionospheric delay coefficient K is calculated.

When the ionospheric delay coefficient K is obtained from a plurality of satellites, the obtained ionospheric delay coefficient K is weighted or averaged by observation conditions such as the elevation angle of the satellite to obtain a more accurate coefficient (step S27). .. Then, the obtained ionosphere delay coefficient K is transmitted to the ionosphere delay amount calculation unit. When the ionosphere delay coefficient K can be obtained from only one satellite, the ionosphere delay coefficient K is transmitted to the ionosphere delay amount calculator 52 without being weighted or averaged (step S28).

Here, the operation of the ionosphere delay amount calculation unit 52 will be described with reference to the flowchart of FIG.

The task program incorporated in the ionosphere delay amount calculation unit 52 is activated by the data of the ionosphere delay coefficient K transmitted from the ionosphere delay coefficient estimation unit 51. Upon activation, the ionosphere delay amount calculation unit 52 extracts satellites that can use only L1 from the observed satellites (step S31). When the ionosphere delay amount calculation unit 52 can extract a satellite that can use only L1, it acquires data necessary for calculating the ionosphere delay amount from the signal of the satellite (step S32). Then, based on the acquired data and the ionosphere delay coefficient K, the L1 ionosphere delay amount of the satellite is obtained (step S33).

The observation data output unit 5 obtains the pseudorange residual and the integrated phase residual with each satellite (step S4). For example, the following equation is used to obtain the pseudorange residual and the residual of the integrated phase of satellite i during RTK positioning.
ΔρL1_i=Pi−(Ri+IL1_i+Di+c×Ti+c×t)
ΔφL1_i=λL1×Li− (Ri−IL1_i+Di+c×Ti+c×t+λL1×BL1_i)
ΔρL2_i=Pi-(Ri+γ×IL1_i+Di+c×Ti+c×t)
ΔφL2_i=λL2×Li-(Ri-γ×IL1_i+Di+c×Ti+c×t+λL2×BL2_i)
Here, ΔρL1_i is the residual of the pseudorange of L1 of the satellite i, ΔφL1_i is the residual of the integrated phase of the L1 of the satellite i, ΔρL2_i is the residual of the pseudorange of L2, and ΔφL2_i is the L2 of the satellite i. Is the residual of the integrated phase of Pi, Pi is the pseudorange observation value of satellite i, Li is the integrated phase of satellite i, R is the geometric distance between satellite receivers, and I is the ionospheric delay (ionosphere delay). The value of IL1_i obtained by the delay amount calculation unit 52 is used, provided that the expression for obtaining the residual of the integrated phase has the opposite sign.), and D is the tropospheric delay (uses the same model expression as for independent positioning). Yes, T is the satellite clock error (using the correction value transmitted from the satellite), t is the user clock error, and c is the speed of light.

The observation data output unit 5 calculates and outputs observation data using the ionospheric delay amount thus obtained (step S5).

The positioning calculation unit 6 uses the observation data transmitted from the observation data output unit 5 to perform positioning calculation by a method such as RTK (step S6).

When the positioning calculation unit 6 finishes the positioning calculation, it is output as position information (step S7). For example, it is displayed on a display device or position information is transmitted to an external device.

According to the GNSS receiver 1 and the ionosphere delay amount calculation method having such a configuration, it is possible to obtain the ionosphere delay amount with high accuracy and fast even for a satellite that can use only one frequency band signal. As a result, satellites receiving only L1 can be used for RTK positioning, and non-GPS satellite systems, such as Galileo satellites, can also be used for positioning. Also, unlike the ionosphere-free linear combination method, integer value bias is guaranteed by the flow of the conventional RTK positioning routine, and wide lanes of L1 and L2 can be used, so RTK positioning can be performed earlier than the ionosphere-free linear combination method. Is possible.

Although the embodiments of the present invention have been described above, the specific configuration is not limited to the above-mentioned embodiments, and even if there is a design change or the like within a range not departing from the gist of the present invention, Included in the invention. In the above embodiment, the Klobuchar model is used as the ionosphere delay amount correction model, but the ionosphere delay coefficient K may be obtained using another ionosphere delay amount correction model.

1 GNSS receiver 2 antenna 3 high frequency unit 4 signal processing unit 5 observation data output unit 51 ionosphere delay coefficient estimation unit 52 ionosphere delay amount calculation unit 6 positioning calculation unit K ionosphere delay coefficient

Claims (2)

A GNSS receiver for performing positioning based on signals transmitted from a plurality of satellites,
An ionospheric delay coefficient estimator that receives signals in two different frequency bands transmitted from the satellite and estimates an ionospheric delay coefficient common to signals from all satellites at the observation point;
An ionospheric delay amount calculation unit that calculates an ionospheric delay amount of a signal received from a satellite that can use only one frequency using the ionospheric delay coefficient;
A GNSS receiver comprising: A method for calculating an ionospheric delay amount in a GNSS receiver for performing positioning based on signals transmitted from a plurality of satellites,
An ionospheric delay coefficient estimation step of receiving signals of two different frequency bands transmitted from the satellite and estimating an ionospheric delay coefficient common to signals from all satellites at the observation point;
An ionospheric delay amount calculation step for calculating an ionospheric delay amount of a signal received from a satellite that can use only one frequency, using the ionospheric delay coefficient;
A method for calculating an ionospheric delay amount, comprising:

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