JP3115090B2 - Setting method of search bandwidth in GPS receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for setting a search bandwidth in a GPS receiver. GPS (Global Posi
The Positioning System (Global Positioning System) is a satellite-based positioning system that sets up six orbits around the earth above an altitude of about 20,200 km and launches multiple satellites in each orbit. A GPS signal containing navigation data for positioning is transmitted from each satellite to the earth in a spread spectrum system, and a GPS receiver on the ground (or sea or air) is required for positioning.
By receiving radio waves from one or four satellites, it is possible to calculate in real time necessary positional information such as the latitude, longitude and altitude of a receiving point using navigation data included in GPS signals from each satellite. Things.

[0002]

2. Description of the Related Art GPS signals that are open to the public are C /
This signal is called an A code, and is transmitted at 1575.42 MHz. Therefore, in order to acquire a satellite, in principle, it is sufficient to wait for reception at 15575.42 MHz. However, since the GPS satellite is not a geostationary satellite, its reception frequency fluctuates due to the Doppler effect, and the oscillation frequency of the oscillator of the GPS receiver also fluctuates due to its offset.

Therefore, in order to actually acquire a satellite,
The deviation of the reception frequency due to the Doppler effect (hereinafter, referred to as
"Doppler frequency deviation") and the offset of the oscillator to set the search center frequency of satellite radio waves, set an appropriate search bandwidth, and set the search frequency within the search bandwidth starting from the search center frequency. The satellite is searched while swinging up and down, and the acquisition of the satellite is completed when the oscillator locks to the satellite radio wave.
By repeating such a capturing operation, the number of satellites required for positioning is captured.

[0004] During the satellite acquisition operation, the narrower the search bandwidth, the shorter the satellite acquisition time. This search bandwidth can be set narrower as the offset value of the oscillator is smaller. Therefore, in order to set the search bandwidth as narrow as possible, it is desirable to minimize the error of the offset value of the oscillator of the GPS receiver.

Therefore, the conventional GPS receiver uses an extremely accurate crystal oscillator with temperature compensation (hereinafter referred to as "TCXO") as an oscillator, and calculates the final calculation when the power of the receiver is turned off after the positioning is completed. The obtained offset value of the oscillator is backed up in a memory and used as an initial offset value of the oscillator at the start of the next positioning.

[0006] TCXO is -40 ° C to + 85 ° C by compensating the temperature characteristic of the crystal unit in an electric circuit.
Very high precision of about ± 2 to ± 5 [ppm] (± 3 [KHz] to ± 8 [KHz] in frequency conversion) is provided over a wide temperature range. Note that the offset accuracy of an oscillator used in ordinary communication equipment is ± 50 to ± 10.
0 [ppm], and at best ± 20 [p
pm].

[0007]

Since the conventional GPS receiver employs the above-described high-precision TCXO, the offset of the oscillator due to a temperature change inside the receiver while the power of the receiver is turned off. The change in the value does not need to be considered, and the offset value backed up in the memory is used as it is as the initial offset value at the start of the next positioning. If the data in the memory has disappeared or the backup data has been invalidated due to an error in the memory, the variation range of the TCXO offset value is set as the entire search range.

However, when a low-precision oscillator is used, a change in the offset value due to a temperature change is large,
The offset value backed up in the memory cannot be used as it is as the offset value of the oscillator at the start of the next positioning. Therefore, when a low-precision oscillator is used, it is necessary to search the satellite radio wave in a wide band over the entire range of the offset change of the oscillator, and there is a problem that it takes much time to acquire the satellite. Such a problem is the same even when the backup value of the offset value is used.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a GPS capable of shortening a satellite acquisition time even when a low-precision oscillator is used.
An object of the present invention is to provide a method for setting a search bandwidth in a receiver.

[0010]

In order to achieve the above object, a method of the present invention is to provide a GPS receiver which searches for a satellite radio wave over a predetermined search bandwidth starting from a search center frequency. If the calculated offset value of the oscillator exceeds a predetermined reference value, the calculated time is backed up in a memory, and when the power is turned on at the next positioning, a predetermined time is calculated from the backed-up calculation time. Only when the reference time has not elapsed, the initial search bandwidth at the start of positioning is set to a wide band.

[0011]

[Operation] If the offset value backed up in the memory is not used as the initial offset at the start of positioning, basically, the entire variation range of the offset value of the oscillator becomes the search bandwidth. Also, even if the backed up value is used as the initial offset, it is necessary to set the search bandwidth in consideration of the accuracy of the oscillator. In this case, if a low-precision oscillator is used for the receiver, the search band becomes too wide, so it is necessary to limit the search bandwidth by some method.

FIG. 5 shows the relationship between -40 ° C. and + 85 °.
6 shows an example of the temperature characteristic of an oscillator that realizes an offset value of ± 20 [ppm] in a temperature range of C. As is apparent from FIG. 5, the offset value (absolute value)
Has a large value at both ends of the operating temperature range (+ 85 °
C, around -40 ° C).

It can be said that such a high or low temperature of the receiver hardly occurs in a normal use state, and it is considered that the receiver concentrates on a specific case from a seasonal and regional viewpoint. That is, it does not occur at a place where it does not occur, or at a time when it does not occur, and once it occurs, such a state is expected to continue for a while.

The present invention has been made in view of the above,
When it is necessary to search a wide band, such as when using a low-precision oscillator, instead of always searching the entire range of the temperature change of the offset value as in the past, the oscillator becomes large at that time. A wide band is searched only when it is expected to have an offset value.

That is, according to the method of the present invention, when the power supply is turned on for the next positioning, the power supply is turned on at the next positioning from the time when the offset value backed up in the memory has exceeded a predetermined reference value in the past. If the predetermined reference time has not passed by the time when is turned on, it is determined that the offset value of the oscillator is likely to continue to have a large value exceeding the reference value, and the initial search bandwidth at the start of positioning is determined. The search band is set wide, otherwise the search band is set narrow.

By using such a method, even when a low-precision oscillator is used, the initial search bandwidth can be set narrower in a situation where use in a normal temperature range is continued, and the satellite search bandwidth can be reduced accordingly. Acquisition time can be reduced. Further, even in a situation where the offset value of the oscillator has a large value, the initial search bandwidth can be appropriately set, and the acquisition time can be shortened accordingly.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method of the present invention will be described below with reference to the drawings. FIG. 1 is a flowchart of the operation of the first embodiment of the method of the present invention, FIG. 3 is an explanatory diagram of switching the search bandwidth when the initial search bandwidth is set to a narrow band in the embodiment, and FIG. FIG. 7 is an explanatory diagram of switching of a search bandwidth when an initial search bandwidth is set to a wide band in an example.

In the following description, the description will be simplified.
Backup value Δf _OSCUnit of
In some cases, [ppm], and in some cases,
[Hz]. In actual processing,
Needless to say, the positions should be unified.

In the case of the present invention, first, a reference value for judging whether or not the offset value exceeds a value in a normal operating temperature range during the positioning calculation, and a time when the offset value exceeds the reference value are determined. A reference time for determining whether the order time has elapsed is set. For example, taking the case of the temperature characteristic in FIG. 5 as an example, the offset value is within ± 5 [ppm] in the range of −20 ° C. to + 70 ° C., which is considered to almost cover the normal operating temperature range. ± 5 [ppm] is set as the reference value. Further, as the reference time, in consideration of the use environment and the like,
For example, one week is set.

Now, when the power of the GPS receiver is turned on to perform positioning, the receiver receives the offset value of the oscillator backed up in the memory at the end of the previous positioning (hereinafter, referred to as the offset value).
It is determined whether or not Δf _OSC is used as the initial offset value of the oscillator in the current positioning (step S1 in FIG. 1).

When the backup value Δf _OSC is used as the initial offset value, the process proceeds to step S2, where a predetermined initial search bandwidth is set (step S2), and the satellite Doppler frequency calculated from the orbit data is set. After setting the search center frequency f _S from the deviation Δf _d and the backup value Δf _OSC (step S
3), start a search (step S10).

If the backup value Δf _OSC is not used as the initial offset value, the process proceeds to step S4, where the offset value calculated in the past is set to the reference value (eg ±
5 [ppm]) is determined.
If the reference value has been exceeded, the process proceeds to step S
Proceeding to 5, it is determined whether or not the elapsed time from the time when the offset value exceeding the reference value is calculated has exceeded a predetermined reference time (for example, one week).

If it is determined in step S5 that the current time does not exceed the reference time, the current use environment of the receiver is almost unchanged from the previous positioning, and the change of the offset value of the oscillator is the same as the previous positioning. Since it is expected to be as large as the end time, the process proceeds to step S6, and FIG.
, The initial search bandwidth W ₀ is set to a wide band.

In step S8, a search center frequency f _S is set using the Doppler frequency deviation Δf _d of the satellite calculated from the orbit data and a predetermined offset value α prepared in advance. The process starts (steps S10 and S11).

On the other hand, in step S4, the offset calculated in the past is a reference value (for example, ± 5 [ppm]).
If the receiver environment has not exceeded
It shows that the temperature characteristic of the sample falls within the range of ± 5 [ppm]. Therefore, the change range of the offset value at that time is expected to be small, and the process proceeds to step S7.

Similarly, if it is determined in step S5 that the reference time (for example, one week) has elapsed, the surrounding use environment is expected to have changed from the time of the previous positioning, so the processing is performed. Moves to step S7.

Then, after resetting the flag indicating the reference value over in step S7, the process proceeds to step S8, and the initial search bandwidth W ₀ is set to a narrow band as shown in FIG. after setting the search center frequency f _S using a fixed offset value α which had been prepared in advance and the Doppler frequency deviation Delta] f _d of the satellite computed from the data, it starts searching (step S10).

The set initial search bandwidth W ₀
3 and 4 when the satellite cannot be captured even if the search is repeated for a predetermined time or a predetermined number of times in
As shown in, while expanding gradually the search bandwidth as W ₁ to _W-4, it repeats the search until capturing satellite.

When the search is completed and a predetermined number of satellites are captured, positioning is started based on the navigation data sent from the satellites (step S11), and the current position is calculated and the offset value is calculated (step S12). ). Then, it is determined whether or not the calculated offset value exceeds the reference value (step S13). If the calculated offset value exceeds the reference value, an over-reference value flag is set (step S1).
4), the time at which the offset value was calculated is backed up in the memory (step S15). Steps S12 to S1
Step 5 is repeated until the measurement operation is completed (step S16).

In the embodiment of FIG. 1 described above, the method of the present invention is applied only when the backup value Δf _OSC is not used, and the initial search band is set to either a wide band or a narrow band. It goes without saying that the method of the present invention can be applied even when the backup value Δf _OSC is used. FIG. 2 is a flowchart of the operation when the backup value is used. In the case of FIG. 1, when the backup value is not used, the process branches at step S1 to shift to step S2 to set a predetermined initial search bandwidth. In the case of FIG. 2, however, the initial search bandwidth is set. Is the step S23 or S2 in all cases
5 is set to either a wide band or a narrow band. The processing of other parts is the same.

[0031]

As is apparent from the above description,
In the method of the present invention, when the offset value of the oscillator calculated during the positioning exceeds a predetermined reference value, the calculated time is backed up in a memory, and the power is turned on at the next positioning. Only when the predetermined reference time has not elapsed from the backup calculation time, the initial search bandwidth at the start of positioning is set to a wide band, so even when using a low-precision oscillator, a normal In a situation where the use in the temperature range is continued, the initial search bandwidth can be set to be narrow, and the satellite acquisition time can be reduced as compared with the conventional case where the search bandwidth is always set to be wide. Further, the initial search bandwidth can be appropriately set even in an extreme temperature environment, and the acquisition time can be shortened.

[Brief description of the drawings]

FIG. 1 is a flowchart of the operation of a first embodiment of the method of the present invention.

FIG. 2 is a flowchart of the operation of the second embodiment of the method of the present invention.

FIG. 3 is an explanatory diagram of search bandwidth switching when an initial search bandwidth is set to a narrow bandwidth in the embodiment.

FIG. 4 is an explanatory diagram of search bandwidth switching when an initial search bandwidth is set to a wide band in the embodiment.

FIG. 5 is a diagram illustrating an example of a temperature characteristic of an oscillator.

[Explanation of symbols]

f _S search center frequency Delta] f _OSC backup offset value (backup value) Delta] f _d the Doppler frequency deviation W ₀ initial acquisition bandwidth

Continuation of front page (58) Fields investigated (Int. Cl. ⁷ , DB name) G01C 21/00-21/36 G01C 23/00-25/00 G01S 5/00-5/14 WPI (DIALOG)

Claims (1)

(57) [Claims] 1. A GPS receiver in which satellite radio waves are searched over a predetermined search bandwidth starting from a search center frequency, wherein an offset value of an oscillator calculated during positioning exceeds a predetermined reference value. Then, the calculated time is backed up in the memory, and only when the predetermined reference time has not elapsed from the backed-up calculation time at the time when the power is turned on at the next positioning, the initial time at the start of positioning is initialized. A method for setting a search bandwidth in a GPS receiver, wherein the search bandwidth is set to a wide band.