JP3626814B2 - Initial radio wave capture method for GPS receiver - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an initial radio wave capturing method in a GPS receiver, and more particularly to an initial radio wave capturing method capable of adjusting an observation posture in a short time.
[0002]
[Prior art]
Recently, mobile navigation systems using GPS satellites and precision survey systems have attracted attention. In this type of system, the GPS receiver receives the radio wave transmitted from the GPS satellite, decodes the information contained in the received radio signal, and the necessary location information such as the latitude, longitude, altitude, etc. of the receiving point Get.
[0003]
By the way, in order to start observation with a GPS receiver, it is necessary to capture a radio signal transmitted from one of the satellites, and capturing such a radio wave is usually called an initial radio wave capturing method. Conventionally, one of the two methods described below has been adopted.
The first method is to calculate satellites that should be receivable based on (1) the approximate location of the reception point, (2) almanac data, and (3) the approximate time, and assign them to the receiver channels. The second method is a method in which satellites are sequentially assigned to receiver channels in random order, such as in ascending order of PRN numbers.
[0004]
However, the technical problems described below have been pointed out in such initial radio wave capturing methods.
[0005]
[Problems to be solved by the invention]
In other words, in the former acquisition method, it is possible to calculate a satellite that should be able to be received even if any one of (1) approximate position of receiving point, (2) almanac data, and (3) approximate time is missing. As a result, it becomes impossible to assign a satellite that can capture the initial radio wave to the channel of the receiver, and it is impossible to determine when the observation can be started.
[0006]
Also, in the latter acquisition method, satellites that can be reliably received are not necessarily allocated, and since satellites are searched one by one in sequence, it takes time until initial radio wave acquisition.
The present invention has been made in view of such conventional problems, and the object of the present invention is (1) the approximate position of the receiving point, (2) the almanac data, and (3) the approximate time. An object of the present invention is to provide an initial radio wave capturing method in a GPS receiver that can be prepared for observation in a short time even if it is unknown.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, in a method of capturing an initial radio wave in a GPS receiver having a channel number of 8 channels or more, all of the channels are divided into groups of 2 channels at the time of initial radio wave capture. Two satellites orbiting the same orbital plane and located at 180 ° different positions on the orbit are assigned to the channels.
A total of 24 GPS satellites are arranged, 4 each on a total of 6 orbital planes, and it is possible to capture 5 or more satellites in any region for about 24 hours and to perform 3D positioning. .
According to the present invention, the GPS receiver has the number of channels of 8 channels or more, and divides this into a set of 2 channels, so that satellites of at least four orbital planes can be assigned. At this time, since two satellites orbiting the same orbital plane and 180 degrees different from each other in the orbital plane are assigned to each set of channels, one satellite in the same orbital plane must be It is in a position where it can receive radio waves.
In other words, the earth is a sphere of approximately 360 °, and when a GPS receiver is installed at an arbitrary position on the earth, the radio waves of satellites that are within a range of approximately 180 ° are received at that position. It is possible.
In this case, according to the present invention, when one channel of a set of two channels cannot receive radio waves from a satellite in a certain area, the satellite assigned to this channel is positioned behind the earth in that area. Will be.
However, since the satellite assigned to the other channel is at a position different by 180 °, radio waves from the satellite can be reliably captured on the other channel.
Such a situation is the same for the four orbits. Therefore, in the present invention, the four satellites necessary for positioning are immediately acquired even if the approximate position of the receiving point, almanac data, and approximate time are unknown. can do.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows the positioning principle of the present invention. As shown in the figure, four satellites A1 to A4 arranged at equiangular intervals along the orbital plane move on the orbit A of the earth in about 12 hours.
[0009]
In the figure, the trajectory A is drawn as a circular trajectory, but in reality, it is an elliptical trajectory of about 20,200 km on the earth and an inclination angle of 55 °, and includes six trajectories B including the trajectory A shown in the figure. Four satellites are assigned to each of .about.F at equiangular intervals.
Assuming that a certain position on the earth is a reception point B, two satellites A3 and A4 of the four satellites A1 to A4 are behind the earth when viewed from the reception point B as shown by the hatched lines in the figure. Hidden and unable to receive radio waves. Therefore, at this measurement point B, the observable satellites are A1 and A2.
[0010]
Here, the satellite A1 is at a position 180 ° opposite to the satellite A3 across the center of the earth, and the satellite A2 is also at a position opposite to the satellite A4 180 ° across the center of the earth. Is in a position where the other cannot be received reliably, and both cannot receive simultaneously.
That is, when the satellite A1 and the satellite A3 or the satellite A2 and the satellite A4 are combined with respect to one orbit A, one of them can be reliably captured. This state is the same for the other tracks B to F.
[0011]
Therefore, in this embodiment, in the initial radio wave capturing method in the GPS receiver having the number of channels of 8 channels or more, at the time of initial radio wave capture, all the channels are divided into groups of 2 channels, and the same channel is used for each channel. Two satellites orbiting the orbital plane and being 180 degrees different from each other on the orbital plane are assigned.
[0012]
More specifically, FIG. 2 shows an example of allocation for each channel of the digital signal processor in the GPS receiver having eight channels. In the figure, the eight channels are divided into four groups of two, two channels 1, two channels, three channels 4, four... Channels 7, 8. Channel 1 is assigned satellite A1 in orbit A, and channel 2 is assigned satellite A3 in the same orbit A at a position opposite to 180 °.
[0013]
Similarly, satellites B1 and B3 in orbit B are assigned to channels 3 and 4, satellites C1 and C3 in orbit C are assigned to channels 5 and 6, and satellites D1 and D3 in orbit D are assigned to channels 7 and 8, respectively. D3 is assigned to each.
When satellites are assigned to the respective channels in this manner, spectrum despreading and data demodulation are performed while switching sequentially according to a command from a CPU (not shown), and positioning is performed while capturing all available satellites.
[0014]
FIG. 3 shows the initial radio wave capturing procedure of the GPS receiver assigned as described above. When the power of the GPS receiver is turned on, the CPU built in the receiver is stored in the built-in backup memory. Access and check whether valid navigation data such as almanac data necessary for initial acquisition of the satellite is stored at that time, and if it is stored, use that data to determine the position of each satellite. Can be calculated, the initialization ends (steps 1 to 3 above).
[0015]
On the other hand, when necessary data is not stored in the backup memory, the initial acquisition operation of the satellite according to the present invention is started.
As described above, there are 8 GPS receiver channels, and if satellites that are 180 ° opposite to each orbital A to D are assigned to each channel, each satellite is captured for each channel. The information is collected by dividing a predetermined elapsed time (steps 4 to 6 above).
[0016]
In this case, as described above, one satellite in each of the orbits A to D is surely captured within the elapsed time, so that information from a total of four satellites can be obtained.
Next, the satellites that can be captured at the current time are recalculated from the almanac information in the navigation data of each captured satellite (steps 7 and 8 above), and the initialization is completed (step 3).
[0017]
According to the initial radio wave capturing method configured as described above, the GPS receiver has a channel number of 8 channels or more, and divides this into groups of 2 channels. Satellites can be assigned. At this time, since two satellites orbiting the same orbital plane and 180 degrees different from each other in the orbital plane are assigned to each set of channels, one satellite in the same orbital plane must be It is in a position where it can receive radio waves.
[0018]
Therefore, in the present invention, four satellites necessary for positioning can be acquired immediately even if the approximate position of reception points, almanac data, and approximate time are unknown.
In the above embodiment, the eight channels are the minimum channels for capturing at least four satellites that can be used for positioning calculation, and the number of channels having the highest cost performance. Incidentally, 12 channels are required for initial acquisition of the satellites in all six orbits. Of course, each channel may be assigned to a combination of A2-A4, B2-B4, C2-C4, and D2-D4.
[0019]
【The invention's effect】
As described in detail above with reference to the embodiments, the initial radio wave capturing method in the GPS receiver according to the present invention is the minimum in surveying even if there is no data such as the approximate position of the reception position, almanac data, and approximate time. Since the limited four satellites can be received in a short time, it is suitable for shortening the positioning work.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a positioning principle of the present invention.
FIG. 2 is an explanatory diagram showing allocations to orbits and satellites corresponding to receiver channels.
FIG. 3 is a flowchart showing a procedure for initial radio wave acquisition;
[Explanation of symbols]
A to D Orbits A1, A3 180 ° facing satellites

Claims (1)

In a method of capturing an initial radio wave in a GPS receiver having a channel number of 8 channels or more,
At the time of initial radio wave capture, all of the above channels are divided into groups of 2 channels,
An initial radio wave capturing method in a GPS receiver, wherein two satellites orbiting the same orbital plane and located at 180 ° different positions on the orbit are assigned to each set of channels.

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