JPH0996668A - Gps receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize the effect of error when error or noise inherent to each satellite is present in the position or a pseudo distance of satellite. SOLUTION: The GPS receiver comprises a pseudo distance bias calculating means 17 for determining the difference between the previous pseudo distance and the distance between an estimated receiving position and the previous position of satellite, a means 18 for calculating the angle of elevation when a current satellite is observed from a current or previous estimated receiving position, and a means 19 for calculating the propagation delay of ionospheric layer or atmospheric layer. The GPS receiver further comprises a means 16 for calculating the weight by method of least squares from the pseudo distance bias, angle of elevation, propaqation delay and the accuracy information of satellite carried on the navigation message, and a means 15 for determining an estimated receiving position closer to the true receiving position than previously estimated receiving position through combination of the weight calculated by the weight calculating means 16 and the method of least squares.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a GPS receiving apparatus for determining its own position by receiving and decoding signal radio waves from a plurality of GPS (Global Positioning System) artificial satellites. It is widely used when it is desired to obtain the current position of a ship as an absolute position on the earth.

[0002]

2. Description of the Related Art A conventional GP will now be described with reference to the drawings.
An example of the S receiver will be described. Figure 2 is the conventional GP
It is a schematic diagram of an S receiver. In FIG.
Reference numeral 1 is detection means, 2 is satellite data analysis means, 3 is pseudorange residual calculation means, 4 is direction cosine matrix calculation means, and 5 is estimated reception position calculation means.

The operation of the conventional GPS receiver having the above structure will be described below. The radio waves of each GPS satellite are transmitted by being carried on a carrier wave of L1 (1575.42 Hz), for example.
Pseudo Random Noi called a code
se) is phase-modulated, and is characterized by including frequency error due to Doppler shift due to movement of satellite and user. Therefore, the detection means 1 demodulates the signal radio wave of each satellite by the despreading process and the frequency and phase matching process for the PRN code spread radio wave of each satellite, and extracts the data signal.

The satellite data analysis means 2 assembles a navigation message from the signal data detected by the detection means 1,
Information useful for the subsequent calculation of the estimated reception position is extracted. For example, the satellite position and satellite accuracy information is obtained from the orbit information and status information included in the message, or the propagation time is obtained from the time when the message with the signal transmission time and its transmission time arrives at the receiving device. By multiplying the propagation time by the speed of light, the distance estimated to be the distance between the current satellite position and the reception position, that is, the pseudo distance is calculated.

Next, the pseudorange residual calculation means 3 calculates the difference between the pseudorange obtained by the satellite data analysis means 2 and the distance between the estimated reception position read last time or from the backup memory and the current satellite position. A certain pseudorange residual is obtained, and n (n> 3) is obtained by the direction cosine matrix calculation means 4.
Then, a 4 * n direction cosine matrix Hn consisting of direction cosine vectors for the estimated reception position of each satellite position is calculated.

Next, the estimated reception position calculation means 5 makes n
From the pseudorange residual vector PD obtained from the pseudorange residual calculating means 3 and the direction cosine matrix obtained from the direction cosine matrix calculating means 4 for each satellite, the previous estimated reception position Xo (X: 3: The difference dX between the dimensional position vector) and the current estimated reception position Xn is obtained. Actually, the clock bias, which is an error included in each pseudo distance, is equal to dX.
Since it is obtained at the same time, there are four unknowns. If n = 4, the position difference dX can be obtained by multiplying the inverse matrix of the direction cosine matrix by the pseudorange residual vector, but generally, the number of satellites that can be received may be four or more. In that case, of course, since the inverse matrix of the direction cosine matrix does not exist, it cannot be normally solved. Therefore,
Choose 4 out of n by some standard, or
Since there is a least-squares solution, it will be solved by the least-squares method as shown in equation (1). dX = (H ^T · H) ⁻¹ H ^T · PD ………… (1)

The least-squares method is particularly effective in GPS positioning in which noise and errors are likely to occur because the solution is determined so as to minimize the square of noise or errors contained in the pseudorange residual vector. Therefore, the conventional estimated reception position calculation means 5
However, there are many methods that use the least squares method to calculate the estimated reception position.

Once the position difference dX is obtained, the current estimated reception position Xn can be obtained as follows: Xn = Xo + dX (2)

With the above method, the estimated reception position can be obtained using the signal radio waves received from a plurality of satellites.

[0010]

However, with the above configuration alone, even if the least-squares method is used in the process due to the effects of satellite position calculation, satellite-specific errors included in the pseudorange, and noise. The required inverse matrix operation became unstable, and the accuracy of the solution sometimes deteriorated.

Further, in order to avoid the deterioration, there has been a method of performing the least squares method by giving a weight so that the influence can be changed for each satellite, but a factor that determines the weight is included in the navigation message. Satellite reliability, ionosphere,
Since the amount of information is small, such as only the delay information of the atmospheric layer, it was difficult to perform effective weighting.

[0012] The present invention solves such a conventional problem, and an object of the present invention is to provide a GPS receiver capable of obtaining an estimated reception position with high accuracy.

[0013]

In order to achieve the above object, the GPS receiver of the present invention uses a pseudorange bias, satellite accuracy information, elevation angle, and radio wave propagation so as to cancel the influence of errors peculiar to the satellite. It is provided with a weight calculation means for calculating the weight of the least square method from the delay.

[0014]

Therefore, according to the present invention, by calculating the weight and obtaining the solution by the least squares method by multiplying the weight, the effectiveness of the weight can be enhanced and an estimated reception position with high accuracy can be obtained.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the GPS receiver according to claim 1 of the present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic configuration of the GPS receiver in this embodiment. In FIG. 1, 11 is detection means, 12 is satellite data analysis means, 13 is pseudo-range residual calculation means, 14 is direction cosine matrix calculation means, 15 is estimated reception position calculation means, 16 is weight calculation means, and 17 is pseudo. Distance bias calculation means, 18 is an elevation angle calculation means, and 19 is a radio wave propagation delay means.

The detection means 11, the data analysis means 12, the pseudo distance residual calculation means 13, and the direction cosine matrix calculation means 14 are the same as those described in the conventional example, and therefore their duplicated description will be omitted.

In this embodiment, the pseudo distance bias calculating means 17 is a difference between the distance between the previous estimated receiving position obtained by the least squares method and the previous position of the satellite i and the pseudo distance of the previous time. The distance bias PRBi is calculated. This pseudorange bias PRBi represents the error included in the pseudorange of the satellite i corresponding to the previous least squares solution. Therefore, the smaller the PRBi, the higher the reliability of the satellite.

Further, the elevation angle calculating means 18 calculates the elevation angle ELi when the satellite i is looked up from the current or previous estimated reception position. Generally, the lower the elevation angle ELi, the higher the positional accuracy in the horizontal direction. It is easy to understand, for example, if we consider the earth as one of the satellites. That is,
Ideally, the point of intersection between the sphere centered on the satellite and the radius of the pseudorange and the surface of the earth intersect at one point, but if there is an error included in the pseudorange, they do not intersect at one point. The effect of the intersection point of the error on the deterioration of accuracy is obviously lower when the elevation angle is lower. Therefore, the smaller the ELi, the higher the reliability for the satellite.

Next, the radio wave propagation delay means 19 obtains the propagation delay due to the ionosphere from the ionospheric delay information extracted from the navigation message analyzed by the satellite data analysis means 12 and the elevation angle of the satellite i obtained by the elevation angle calculation means 18, and Propagation delay due to the atmospheric layer is calculated according to the elevation value from a table prepared in advance or an approximate expression. The delay amount obtained by adding the propagation delay due to the ionosphere and the propagation delay due to the atmosphere layer is output as the radio wave propagation delay DLi for the satellite i. This delay DLi can only be an approximate expression as long as it is a single positioning, and accuracy cannot be expected in many cases. Therefore, the smaller the DLi, the higher the reliability of the information of the satellite i in general.

Further, from the navigation message analyzed by the satellite data analyzing means 12, the accuracy information ACCi (called accuracy) called by the satellite itself can be known, but if the data of the satellite is trusted, , ACCi is smaller, the reliability of the information of the satellite i is higher.

The weight calculation means 16 calculates the pseudo range bias PRBi calculated by the pseudo range bias calculation means 17 and the elevation angle EL calculated by the elevation angle calculation means 18 for each satellite i.
i, the radio wave propagation delay DL obtained by the radio wave propagation delay means 19
i and the accuracy information ACCi are used to calculate the weight Wi while considering the characteristics of each data.

The estimated reception position calculation means 15 is calculated by the weight Wi calculated by the weight calculation means 16, the pseudo distance residual vector PD calculated by the pseudo distance residual calculation means 13, and the direction cosine matrix calculation means 14. From the direction cosine matrix and
Previous estimated reception position Xo (X: three-dimensional position vector)
The difference dx between the current estimated reception position Xn and the current estimated reception position Xn is obtained by the method of least squares. The reason for solving by the method of least squares is as described in the conventional example.

The weight calculating means 16 may be the weight calculating means described in claim 2, and the estimated receiving position calculating means 15 may be the estimated receiving position calculating means described in claim 3.

By adopting the above configuration, it is possible to realize a GPS receiving device which can determine the weight from four pieces of information, enhance the effectiveness of the weight, and obtain an estimated reception position with high accuracy.

Next, the weight calculating means means according to claim 2 of the present invention will be described. The pseudorange bias for satellite i is PRBi, the elevation angle is ELi, and the radio wave propagation delay is DL.
i, AC accuracy information of the satellite notified by the navigation message
In the case of Ci, as described in the above embodiments, the smaller the value, the higher the reliability of the satellite in obtaining the estimated reception position.

Therefore, the weight Wi when the information of a certain satellite i is used for the calculation of the estimated reception position is the sum of the absolute values of the above four data multiplied by some adjustment coefficient (positive), or
Alternatively, as the sum of squares, Wi = a * | PRBi | + b * | ELi | + c * | DLi | + d * | ACCi | (a, b, c, d are positive constants) (3) or ^{, Wi = a * PRBi 2 +} b * ELi 2 + c * DLi 2 + d * ACCi 2 (a, b, c, d is a positive constant) is calculated as ............ (4).

This weight is a value that decreases as the reliability of the satellite in obtaining the estimated reception position becomes higher, and care must be taken when using the least squares method. Needless to say, if the reciprocal of Wi is set to Wi again as a weight, the opposite characteristic is exhibited.

As described above, according to the weight calculating means of this embodiment, the pseudo range bias, the elevation angle, the radio wave propagation delay, and the accuracy information of the satellite notified by the navigation message are effectively combined, and the least square method is used. It is possible to calculate weights that are effectively used to obtain accurate estimated reception positions.

Next, the estimated reception position calculation means according to claim 3 of the present invention will be described. The weight W of each satellite obtained by the weight calculation means 16 for all the detected satellites
A weight matrix in which i is diagonally arranged is I, and a vector in which n pseudo distance residuals PDi, which is the difference between the distance between the previous estimated reception position and the current position of the satellite i and the pseudo distance, are combined is PD.
Further, when H is a 4 * n direction cosine matrix consisting of direction cosine vectors for the estimated reception positions of n (n> 3) satellites, the previous estimated reception position Xo (X: three-dimensional The difference dx between the position vector) and the current estimated reception position Xn is calculated by dX = (H ^t H + I) ⁻¹ H ^t · PD (5).

When the position difference dx is obtained, the previous estimated reception position Xo (X: three-dimensional position vector) and the current estimated reception position are set as Xn, and the current estimated reception position Xn is Xn = Xo + dX .... … (6) can be obtained.

As described above, according to the estimated reception position calculating means of the present embodiment, if each component of I is minute with respect to each component of H, the inverse matrix of H ^t H itself is unstable. Even if there is, it has the effect of regularization, and the solution dX can be stably obtained.

Further, the contribution to the estimated reception position which is the final result of each satellite is changed by incorporating the weight Wi described in claims 1 and 2 into the least squares method as shown in the equation (5). As a result, the accuracy of the estimated reception position can be improved.

[0034]

As described above, according to the GPS receiver of the present invention, the estimated receiving position accuracy of each satellite is calculated from the pseudo range bias, the elevation angle, the radio wave propagation delay, and the accuracy information of the satellite notified by the navigation message. It is possible to provide a GPS receiver that calculates the weight indicating the contribution and improves the accuracy of the estimated reception position obtained as the least squares solution.

Further, according to the weight calculation means of the present invention, the pseudo range bias, the elevation angle, the radio wave propagation delay, and the accuracy information of the satellite notified by the navigation message are effectively combined to make a minimum of 2.
It is possible to calculate the weight effectively used for obtaining the accurate estimated reception position by the multiplication method. Further, according to the estimated reception position calculation means of the present invention, the weight Wi can be effectively incorporated into the least squares method to change the contribution to the estimated reception position which is the final result of each satellite. As a result, the accuracy of the estimated reception position can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a GPS receiver according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a schematic configuration of a conventional GPS receiver.

[Explanation of Codes] 11 Detection means 12 Satellite data analysis means 13 Pseudo distance residual calculation means 14 Directional cosine matrix calculation means 15 Estimated reception position calculation means 16 Weight calculation means 17 Pseudo distance bias calculation means 18 Elevation angle calculation means 19 Radio wave propagation delay means

Claims (3)

[Claims] 1. A detection means for detecting signal radio waves transmitted by a plurality of GPS satellites, a navigation message is assembled from the detected data, and the time information contained in the message is used until the signal radio waves reach the current reception position. The satellite data analysis means for calculating the propagation time of the satellite and the pseudo distance obtained by converting the time into a distance, and further obtaining the satellite position and the satellite accuracy information from the orbit information and the status information included in the message, the pseudo distance and the estimated reception. Pseudo-range residual calculation means for obtaining pseudo-range residual from position and direction cosine matrix calculation for obtaining 4 * n direction cosine matrix Hn consisting of direction cosine vectors for estimated reception positions of n (n> 3) satellites A GPS receiving device having means for determining a difference between a previous estimated receiving position and a previous satellite position and a previous pseudo distance. Distance bias calculation means, elevation angle calculation means for calculating the elevation angle when the current satellite is looked up from the current or previous estimated reception position, the navigation message obtained by the satellite data analysis means and the ionosphere from the elevation angle. Based on the accuracy information of the satellite obtained from the radio wave propagation delay calculating means for calculating the radio wave propagation delay of the atmosphere layer, the pseudo range bias, the elevation angle, the radio wave propagation delay, and the data analyzing means, the least squares method weight is calculated. An estimated reception position closer to the true reception position than the previous estimated reception position is calculated by the least square method from the weight calculation means for calculation, the direction cosine matrix Hn and the pseudo distance residual, and the weight calculated by the weight calculation means. GP having an estimated reception position calculating means for obtaining
S receiver. 2. When the weight calculation means sets PRBi as the pseudorange bias for satellite i, ELi as the elevation angle, DLi as the radio wave propagation delay, and ACCi as the accuracy information of the satellite notified by the navigation message, Weight Wi
Wi = a * | PRBi | + b * | ELi | + c * | DL
i | + d * | ACCi | (a, b, c, d are positive constants)
Alternatively, Wi = a * PRBi ² + b * ELi ² + c * DLi ² +
The GPS receiver according to claim 1, wherein d * ACCi ² (a, b, c, d are positive constants) is calculated. 3. The estimated reception position calculation means has a weight matrix in which the weights Wi obtained by the weight calculation means for the satellite i are diagonally arranged, and I is the distance between the previous estimated reception position and the current position of the satellite i. Pseudorange residual PD, which is the difference between the distance and the pseudorange
PD is a vector of n i, and n (n
> 3) When the 4 * n direction cosine matrix consisting of the direction cosine vector for the estimated reception position of each satellite is H, the previous estimated reception position Xo (X: three-dimensional position vector) and the current estimated reception position the difference dx between the position ^{Xn, dX = (H t H} + I) -1 H determined by ^t · PD, the estimated received position Xn from the dx, GPS receiving apparatus according to claim 1, obtained by Xn = Xo + dX.