JPH1172549A - Gps correction calculation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the accuracy degradation by continuous use of past pseudo distance correction information in a position measurement calculation method using a differential GPS. SOLUTION: After starting a position measurement operation, when valid information is present, correction calculation by obtained pseudo distance correction information is performed (S2), the obtained pseudo distance correction information is stored (S3) and a counter value is set at 0, further (S5). When no valid information is present, whether or not the counter value is below a stipulated value, is judged (S6). When it is below the stipulated value, the correction calculation by the stored pseudo distance correction information is performed (S4) and a fixed value is added to the counter value further (S7). When it is larger than the stipulated value, the correction calculation by the correction information stored in S3 is not performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position detecting apparatus using a GPS (Global Positioning System) receiver for obtaining a receiver position and speed from a differential GPS satellite orbiting the earth.

[0002]

2. Description of the Related Art A GPS receiver simultaneously receives radio waves from a plurality of satellites, acquires navigation messages (ephemeris and time information) from artificial satellites, and measures the signal propagation time to the receivers of each satellite. This is a system that can calculate a pseudo distance and calculate an absolute position on the earth by the following equation (1) (hereinafter referred to as positioning).

However, the pseudorange to be measured has various errors due to ionospheric delay, atmospheric delay, and artificially degraded accuracy (referred to as SA) by the US Department of Defense. Therefore, an error occurs in positioning using a satellite including those errors.

Therefore, the differential GPS measures a pseudo distance correction value (pseudo distance error, signal propagation time error) of each GPS satellite at a fixed reference station (base station) whose exact position is known by surveying or the like. This is a system that enables high-precision positioning of a mobile by transmitting a pseudo-range correction value (correction information) of each satellite measured by a base station to each mobile. A mobile phone, FM multiplex broadcasting, and the like are used for transmitting the correction information, and the correction information is updated at intervals of several seconds. The following formulas (2) and (3) are used to calculate the correction value.
Is used.

Equation (1) ｛(X ₁ -X ₀ ) ² + (Y ₁ -Y ₀ ) ² + (Z ₁ -Z ₀ ) ² ｝ ^1/2 = (C × r ′ ₁ ) ｛(X ₂ -X ₀ ) ² + (Y ₂ -Y ₀ ) ² + (Z ₂ -Z ₀ ) ² ｝ ^1/2 = (C × r ' ₂ ) ｛(X ₃ -X ₀ ) ² + (Y ₃ -Y ₀ ) ² + (Z ₃ -Z ₀ ) ² ｝ ^1/2 = (C × r ' ₃ ):: ｛(Xn-X ₀ ) ² + (Yn-Y ₀ ) ² + (Zn-Z ₀ ) ² ｝ ^1/2 = (C × r'n) (Xi, Yi, Zi): satellite position r ' _i : measured propagation time (X ₀ , Y ₀ , Z ₀ ): receiver position C: speed of light

Equation (2) ｛(X ₁ -X ₀ ) ² + (Y ₁ -Y ₀ ) ² + (Z ₁ -Z ₀ ) ² ｝ ^1/2 = ｛C × r ” ₁ ｝ X (X ₂ -X ₀ ) ² + (Y ₂ -Y ₀ ) ² + (Z ₂ -Z ₀ ) ² ｝ ^1/2 = ｛C × r '' ₂ ｝ X (X ₃ -X ₀ ) ² + (Y ₃ -Y ₀ ) ² + (Z ₃ -Z ₀ ) ² ｝ ^1/2 = ｛C × r " ₃ ｝:: ｛(Xn-X ₀ ) ² + (Yn-Y ₀ ) ² + (Zn-Z ₀ ) ² ｝ ^1/2 = ｛C × r "n｝ (Xi, Yi, Zi): satellite position r" _i = r ' _i + RRCi _i : corrected propagation time (ionospheric delay,
RRCi _i : Propagation time error or propagation time correction value r ' _i : Measured propagation time (X ₀ , Y ₀ , Z ₀ ): Receiver position C: Light speed

[0007] Equation _{(3) RRC L = RRC T} × C RRC L: pseudorange correction value or pseudo range error RRC _T: propagation time correction value or propagation time error C: velocity of light

Hereinafter, an example of a conventional differential GPS correction calculation will be described with reference to the drawings.
FIG. 3 is a flowchart of a conventional differential GPS correction calculation process. In FIG. 3, first, it is determined in step S1 whether there is differential GPS pseudo-range correction information (hereinafter referred to as DGPS correction information or pseudo-range correction information) that is valid during the current positioning calculation. If there is valid DGPS correction information, the pseudo distance for each satellite measured in the process of step S2 is corrected with the pseudo distance correction information of the same satellite number. Next, the effective DGPS correction information used this time in the process of step S3 is stored. For explanation,
In Equations (1) and (2), the propagation time error is used instead of the pseudo distance correction value, but the meaning of the correction information is the same as shown in Equation (3). When there is valid DGPS correction information, a highly accurate position can be obtained by solving the simultaneous equations of the equation (2). Valid DGPS
If there is no correction information, in step S4, the DGPS correction information stored in step S3 is used as valid correction information in the current positioning calculation, and the measured pseudorange for each satellite is stored with the same satellite number. Is corrected using the pseudo distance correction information. Even when there is no effective DGPS correction information, a highly accurate position can be obtained by solving the simultaneous equations of Expression (2).

Therefore, in an environment with poor communication conditions, D
GPS correction information cannot be updated continuously, and effective DGP
Even if acquisition of S correction information is intermittent, DGPS
, The correction process is not intermittent, and high-accuracy positioning results are continuously obtained.

Since the DGPS correction information is updated at intervals of several seconds, if the latest correction information can be acquired at each update timing, it is determined that “valid correction information exists”, and if the acquisition fails, “valid correction information does not exist”. And When the valid time is set in the DGPS correction information, it is determined that “valid correction information exists” or “no valid correction information exists” depending on whether or not correction information within the valid time exists. For example, when updated at 5 second intervals, the effective time can be considered to be 5 seconds. The pseudo distance correction amount is calculated from the DGPS correction information.

[0011]

However, in the above-described calculation processing method, if the DGPS correction information is not updated for a long time, the pseudo distance correction amount is continuously calculated with the old DGPS correction information. As the accuracy decreases, the accuracy deteriorates. When the deteriorated correction information is used, the position accuracy is deteriorated as compared with the case where the single positioning is performed.

An object of the present invention is to solve such a problem, and an object of the present invention is to provide a GPS correction calculation method capable of reducing remarkable deterioration of accuracy due to use of past DGPS correction information. .

[0013]

SUMMARY OF THE INVENTION The GPS correction calculation method of the present invention is intended to limit the use of past DGPS correction information by time. It becomes possible to reduce.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the first aspect of the present invention, if there is valid differential GPS pseudo-range correction information, positioning calculation is performed using the obtained correction information,
Furthermore, the acquired pseudo distance correction information is stored, and if there is no valid differential GPS pseudo distance correction information, the latest pseudo GPS correction calculation method for performing positioning calculation using the pseudo distance correction information stored when valid is used. When the pseudo distance correction information is stored, the counter value is set to 0, and the effective differential GPS
This is a GPS correction calculation method in which a counter that counts up when there is no pseudo distance correction information is set, and the use of the stored pseudo distance correction information is limited by the counter value. When valid DGPS correction information cannot be obtained continuously By setting a time limit to the old DGP
It has the function of preventing the position accuracy from being degraded by the S correction information.

According to a second aspect of the present invention, there is provided the differential GPS correction calculation method according to the first aspect, wherein there is no effective differential GPS pseudo-range correction information, and the stored pseudo-range information cannot be used. The correction amount calculated from the stored pseudo distance correction information,
GPS used by updating to a value attenuated by an arbitrary time constant
This is a correction calculation method, and it is possible to obtain a positioning result that changes smoothly without abrupt position jump when the DGPS correction information is interrupted and returns to normal single positioning.

An embodiment of the present invention will be described below with reference to FIGS. (Embodiment 1) FIG. 1 is a flowchart of a GPS correction calculation process according to a first embodiment of the present invention, and the same steps as those in the conventional example shown in FIG. First, in the process of step S1, it is determined whether there is differential GPS pseudo-range correction information (hereinafter referred to as DGPS correction information or pseudo-range correction information) valid at the time of the current positioning calculation. If there is valid DGPS correction information, the pseudo distance for each satellite measured in the process of step S2 is corrected with the pseudo distance correction information of the same satellite number. Next, the effective DGPS correction information used this time in the process of step S3 is stored. Further, the counter value is set to 0 in the process of step S5. For the sake of explanation, a propagation time error is used instead of the pseudo distance correction value in the above equations (1) and (2), but the meaning of the correction information is the same as shown in the equation (3).
When there is valid DGPS correction information, a highly accurate position can be obtained by solving the simultaneous equations of the equation (2). If there is no valid DGPS correction information, step S
In the process of 6, it is determined whether the counter value is within the specified value,
If it is within the specified value, in step S4, the DGPS correction information stored in the processing in step S3 is used as the correction information effective in the current positioning calculation, and the pseudo distance measured for each satellite is stored in the same satellite number. The correction is performed using the pseudo distance correction information. Even when there is no effective DGPS correction information, a highly accurate position can be obtained by solving the simultaneous equations of Expression (2). Here, step S7 is further performed.
In step (3), a constant value is added to the counter value. Valid DGP
If there is no S information and the counter value becomes larger than the specified value, the DGPS correction value stored in the process of step S3 is also treated as invalid and no correction process is performed. If valid DGPS correction information cannot be obtained continuously, the counter value is accumulated, so that it is possible to prevent deterioration of position accuracy due to old DGPS correction information that has passed for a long time.

For example, FM multiplex D updated every 5 seconds
In the case of the GPS correction information (having the initial value and the inclination of the correction amount due to the lapse of time as data), it does not need to be updated every time.
Correction information that is effective for a certain period of time can be acquired by acquiring information twice. However, if the pseudo distance correction amount is calculated with the old DGPS correction information as time elapses, the accuracy deteriorates. Therefore, by setting a time limit as in the present embodiment, it is possible to reduce the deterioration in accuracy due to the use of past DGPS correction information.

(Embodiment 2) FIG. 2 is a flowchart of a GPS correction calculation process according to a second embodiment of the present invention. In the present embodiment, steps S8 and S9 are added to the first embodiment shown in FIG. 1, and the same reference numerals as those in FIG. The processing in step S8 is the same as the DG stored in the processing in step S3.
This is a process of attenuating the pseudo distance correction amount calculated from the PS correction information with an arbitrary time constant. The processing in step S9 is
This is a process for performing pseudo distance correction using the pseudo distance correction amount after the attenuation process calculated in the process of step S8.

If the counter value is larger than the specified value in the processing in step S6, the pseudo distance correction calculation is performed in the processing in step S9 based on the pseudo distance correction amount attenuated in the processing in step S8. An example of how to make attenuation will be described below. When the process of step S8 is continuously selected, the absolute value of the pseudo distance correction amount gradually decreases. For example, if the initial value of the pseudo distance correction amount is 1, the first step S
The value is multiplied by 0.9, for example, 0.9 in the process of 8, and 0.81 if the process of step S8 is successively selected. If the process of step S8 is not continuously selected, the process starts from the initial value. Step S is continuously performed in this manner.
When the process of step 8 is performed, the pseudo-range correction amount based on the DGPS correction information stored in the process of step S3 is attenuated. Positioning results that change smoothly without position jumps can be obtained.

[0020]

As described above, according to the present invention, the stored DG
By setting the time limit of the PS correction information, there is an effect of preventing deterioration of position accuracy due to old DGPS correction information that has passed for a long time.

Further, when the DGPS correction information is interrupted and the operation returns to the normal single positioning, the correction amount calculated from the stored DGPS correction information is updated to a value attenuated by an arbitrary time constant and the correction calculation is performed. Thus, a positioning result that changes smoothly without abrupt position jump can be obtained.

[Brief description of the drawings]

FIG. 1 is a flowchart of a GPS correction calculation process according to a first embodiment of the present invention.

FIG. 2 is a flowchart of a GPS correction calculation process according to a second embodiment of the present invention.

FIG. 3 is a flowchart of a conventional GPS correction calculation process.

Claims (2)

[Claims] If there is valid differential GPS pseudo-range correction information, a positioning operation is performed using the obtained correction information, and the obtained pseudo-range correction information is stored, and the effective differential GPS pseudo-range correction information is stored. If there is no valid differential GPS pseudo distance correction information, when the latest pseudo distance correction information is stored, the counter value is set to 0 when the latest pseudo distance correction information is stored. A GPS correction calculation method comprising: setting a counter that counts up when there is no data, and limiting the use of the stored pseudo distance correction information by the counter value. 2. The GPS correction calculation method according to claim 1, wherein when there is no valid differential GPS pseudo distance correction information and the stored pseudo distance information becomes unavailable, the stored pseudo distance correction information is used. A GPS correction calculation method, wherein a correction amount to be calculated is updated to a value attenuated by an arbitrary time constant and used.