JPH0756509B2 - Satellite radio wave capturing method of GPS receiver - Google Patents

Description

The present invention relates to a satellite radio wave capturing method for a GPS receiver.

[Conventional technology]

As a satellite positioning system using artificial satellites,
GPS (Global Positioning System: Global P
ositioning System).

As its name suggests, this positioning system is a satellite positioning system that covers the entire globe. It sets six satellite orbits that orbit the earth above an altitude of about 20,200 km, and finally four orbits on each orbit. A total of 24 GPS satellites are launched each, and GPS signals containing navigation data for positioning are transmitted from each satellite toward the earth by a spread spectrum method, and multiple GPS receivers are placed on the ground (or at sea or in the air). The GPS of each satellite is received by receiving the radio waves of one satellite, for example, the radio waves of three satellites in the case of two-dimensional positioning and the radio waves of four satellites in the case of three-dimensional positioning.
Based on the navigation data contained in the signal, the required position information such as latitude, longitude and altitude of the receiving point at that time can be measured in real time.

This GPS was originally developed for the US military, but some of its radio waves (C / A code) have been released to the private sector, and this radio wave can be used by automobiles, ships, aircraft, etc. It is possible to build a navigation device.

[Problems to be Solved by the Invention]

For example, GP used in car navigation systems
If the satellite that has been captured until then is blocked by a building or the like and the unreceivable state continues for a certain period of time (for example, 1 minute), the S receiver will receive GPS satellites as shown in the flowchart of its operation in Fig. 6. To start recapture.

By the way, the GPS satellite transmits radio waves at 1575.42 [MHz], but since it is not a geostationary satellite, its reception frequency changes due to the Doppler effect. The change in Doppler frequency by this GPS satellite is about ± 5 [KHz] on the ground.

On the other hand, the GPS receiver produces the Doppler effect even when the receiver itself moves, for example, when the vehicle-mounted GPS receiver moves. The maximum Doppler frequency change due to vehicle movement is ± 600 [Hz] (vehicle speed 60 m / sec).
Furthermore, the frequency shift of the GPS receiver oscillator is ± 3 [KH
z] occurs. If these changes are added, the reception frequency of satellite radio waves will change within a range of ± 8,600 [Hz] at maximum.

Therefore, the maximum change range of this reception frequency is ± 8,600 [Hz]
When trying to reacquire the satellite while covering the above, the GPS receiver swings the search frequency over a wide range of 8,600 [Hz] above and below the satellite radio wave transmission frequency of 1575.42 [MHz], Have to search.

Generally, in a GPS receiver, a PLL is used for a receiving circuit so that the reception frequency of the GPS receiver is accurately synchronized with the reception frequency of satellite radio waves.

The capture range of this PLL is the maximum change range ±
There is no problem if it can be widely adopted so as to cover all of 8,600 [Hz], but the capture range of the PLL has to be a narrow band of, for example, about ± 150 [Hz] due to restrictions on the circuit configuration.

Therefore, to search while covering the maximum variation range of the reception frequency of the satellite radio wave ± 8,600 [Hz],
As shown in the figure, it is necessary to search the PLL search frequency in several steps. For example, when the PLL capture range is ± 150 [Hz], 8,600 / 300 ≈ 28.6
It becomes 6 and it is necessary to switch the search frequency by 28 steps on one side and 56 steps in total in the upper and lower ranges.

As mentioned above, satellite radio waves are sent by the spread spectrum method, so when receiving them, it is necessary to despread the received radio waves first and identify whether or not they are the radio waves of the target satellite. Takes about 1 second. Therefore,
It takes at least 56 seconds to search the above 56 steps, and the original positioning calculation cannot be performed during this time.

Furthermore, the GPS needs to acquire a minimum of three satellites, preferably four satellites, in its positioning. The most desirable GPS receiver is to provide one satellite with one reception channel for reception, but in consumer equipment such as the in-vehicle navigation device described above, positioning accuracy, cost reduction, Due to demands for miniaturization and the like, it is usual that only one receiving channel is provided and the one channel is time-division multiplexed to sequentially receive the radio waves of a plurality of satellites. Therefore, for example, when reacquiring N satellites using such a sequential type receiver, it takes at least 56 × N seconds for the reacquisition operation of N satellites to complete one cycle. .

If the satellite happens to be blocked by a building while waiting for a signal, etc., when the PLL search frequency matches the satellite radio wave reception frequency, wait until the next search frequency match. × It takes a lot of time to reacquire satellites, for example, it can only be acquired after waiting N seconds.
There was a problem that the original positioning calculation could not be restarted quickly.

The present invention has been made based on the above circumstances, and an object thereof is to provide a satellite radio wave capturing method for a GPS receiver capable of recapturing a satellite as quickly as possible.

[Means for Solving the Problems]

In order to achieve the above object, the first satellite radio wave capturing method of the present invention is a GPS receiver which recaptures a satellite when the radio wave of the satellite being captured becomes unreceivable for a certain time or longer. , The search frequency is repeated with the center frequency of the PLL search frequency being fixed to the reception frequency of the satellite radio wave at the time when the reception becomes impossible, and the bandwidth of the PLL search frequency in each of the repeated searches is set to 1
It is designed to gradually widen the bandwidth of the previous search.

A second satellite radio wave capturing method of the present invention is a GPS receiver configured to re-capture a satellite when the radio wave of the satellite being captured becomes unreceivable for a certain time or longer. The search is repeated with the bandwidth of fixed to a predetermined narrow band, and the center frequency of the search frequency of the PLL in each of the repeated searches is set to the satellite radio wave starting from the reception frequency of the satellite radio wave at the time when the reception becomes impossible. It is configured to gradually shift along the Doppler change curve of the reception frequency of.

[Work]

Taking the case of the in-vehicle GPS receiver mentioned above as an example, the maximum change range of the reception frequency of satellite radio waves is about ± 8,600 [Hz], and the Doppler change rate of the reception frequency at this time is up to 40%.
It is about [Hz / min].

Therefore, the reception frequency of the satellite radio wave after it becomes unreceivable in the tunnel or the like gradually deviates from the reception frequency of the satellite radio wave at the time when it becomes unreceivable with the passage of time according to the Doppler change rate. Therefore, when reacquiring the satellite, the search frequency is wideband from the beginning to the maximum change range of the satellite frequency of ± 8,600 [Hz] like the conventional GPS receiver shown in Fig. 7. Rather than searching the satellite radio wave while swinging, the search range is gradually widened as the number of searches progresses, or the search range remains narrow and the center frequency of the search frequency is increased as the number of searches progresses. It is more likely that satellite radio waves can be recaptured more quickly if the reception frequency is changed according to the Doppler change.

The present invention has been made in view of the above points, and the first satellite radio wave capturing method increases the probability of finding a satellite by gradually increasing the search range of the PLL that searches for satellite radio waves to a wide band. The acquisition time was shortened.

In the second satellite radio wave capturing method, the probability of finding a satellite is increased by changing the center frequency of the PLL search frequency along the Doppler change curve of the reception frequency of the satellite radio wave, and the capture time is shortened.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory diagram of search frequency switching showing an embodiment of a first satellite radio wave capturing method of the present invention, and FIG. 2 is a flowchart of its operation. Incidentally, GPS receiver is assumed at the receiving frequency f _r is in capture satellite radio waves.

Now, in the midst of receiving a radio wave of a predetermined satellite reception frequency f _r, for example, the car becomes impossible reception enters the like shadow of a building (FIG. 2 step [1]), this unreceivable state When a certain fixed time, for example, one minute has passed (step [2]), the GPS receiver receives the time T _{1 when the} one minute has passed.
The satellite reacquisition operation according to the present invention is started from the position.

The PLL capture range of the GPS receiver is ± 150 [Hz],
The maximum change range of the reception frequency of satellite radio waves is ± 8,600 [Hz]
The maximum change range of the reception frequency is ± 8,60
To search the whole range of 0 [Hz], as described above,
It is necessary to switch the search frequency by ± 28 steps and a total of 56 steps up and down, but in the case of the present invention, the number n of search steps is set to a predetermined initial value, for example, n = ± 2 steps during the first search. (Step [3]),
As shown in FIG. 1, centering on the reception frequency f _r at the time when reception becomes impossible, first within this range of n = ± 2 steps.
The satellite radio wave search is repeated a predetermined number of times k, for example, k = 2 times, while switching the PLL search frequency (step [4]).

If the satellite radio wave cannot be received in the first search, it is determined that the satellite radio wave reception frequency does not exist within the range of n = ± 2 steps, and the search step number n is increased by a predetermined number. Number of steps S, for example S =
Increase by ± 2 steps to make n = ± 4 steps (step [5]).

Then, after determining whether or not the number of search steps n exceeds a predetermined limit number (step [6]),
The operation moves to the second search operation (step [3]), n
The search operation is repeated k = 2 times while switching the PLL search frequency in the range of ± 4 steps (step [4]).

Each time the satellite reacquisition fails as described above, the satellite radio wave search is repeatedly executed while increasing the search step number n by a predetermined increase step number S until the predetermined limit step number is reached (step [6 ]).

As described above, since the reception frequency of the satellite radio wave gradually changes at a predetermined Doppler change rate, the satellite is highly likely to be reacquired at any timing position of the search operation. Therefore, in the case of FIG.
The satellite can be reacquired in a short time without having to swing the search frequency switching step from the beginning over the entire band of the maximum change range of the reception frequency ± 8,600 [Hz].

When the satellite cannot be reacquired even if the number of search steps is increased until the predetermined limit number of steps is reached (step [6]), the search mode is changed from the present invention to the conventional wideband as shown after time T _2. Return to the search mode (step [7]) and search frequency is ± 28 steps over the entire range of the maximum change range of the reception frequency ± 8,600 [Hz], sum up and down
It is sufficient to search for satellite radio waves while switching to 56 steps.

FIG. 3 is an explanatory diagram of search frequency switching showing an embodiment of the second satellite radio wave capturing method of the present invention, and FIG. 4 is a flowchart of the operation.

As described above, the reception frequency of the satellite radio wave is, for example, the fifth frequency.
As shown in the figure, it changes over time based on a predetermined Doppler change rate. Therefore, in the embodiment of FIG. 3, the PLL along the Doppler change curve L of FIG.
The narrow band search of satellite radio waves is performed while changing the center frequency of the search frequency of.

Now, in the midst of receiving a radio wave of a predetermined satellite reception frequency f _r, for example, the car becomes impossible reception enters the like shadow of a building (FIG. 4 step [11]), the unreceivable state When a predetermined fixed time, for example, 1 minute has passed (step [12]), the GPS receiver starts the satellite reacquisition operation according to the present invention from the time T ₁ position when 1 minute has passed.

First, the Doppler change frequency at the start of the search is calculated (step [13]).

In the first round of search operation, the reception frequency f _r of the satellite radio wave at the time became the unreceivability the Doppler variation frequency, as shown in FIG. 3, PL around this frequency f _r
While oscillating the L search frequency in a predetermined step range, for example, ± 3 steps, the satellite radio wave search operation is repeated a predetermined number of times k, for example, k = 2 times (steps [14] [15]).

When the satellite cannot be reacquired in the first search operation, the process returns to step [13] again, and the Doppler change frequency f _r2 for the second search operation along the Doppler change curve L is calculated. . Then, the second search operation of the satellite radio wave is repeated twice while swinging the PLL search frequency in the range of ± 3 steps around the Doppler change frequency _fr2 (steps [14] and [15]).

Each time the satellite re-acquisition fails as described above, new Doppler change frequencies f _r3 , f _r4 , f _r5 , f _r6 , f _r7 ... along the Doppler change curve L are sequentially obtained and obtained. The satellite radio wave search is repeatedly executed while swinging the PLL search frequency in the range of ± 3 steps centering on each Doppler change frequency.

As described above, since the reception frequency of the satellite radio wave gradually changes at a predetermined Doppler change rate, the satellite is highly likely to be reacquired at any timing position of the search operation. Therefore, in the case of FIG.
Without changing the search frequency switching step over the entire receiving frequency maximum change range ± 8,600 [Hz],
It is possible to reacquire satellites in a short time with the narrow band search.

〔The invention's effect〕

As is clear from the above description, when the satellite radio wave capturing method of the present invention is used, recapture of the satellite after passing through the satellite radio wave unreceivable area such as a tunnel becomes quicker,
The original GPS positioning calculation can be resumed sooner.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of search frequency switching showing an embodiment of the first satellite radio wave capturing method of the present invention, FIG. 2 is a flowchart of the operation of the above embodiment, and FIG. 3 is a second satellite of the present invention. Explanatory diagram for switching the search frequency showing an embodiment of the radio wave capturing method, FIG. 4 is a flowchart of the operation of the above embodiment, FIG. 5 is a diagram showing an example of the Doppler change curve of the reception frequency of the satellite radio wave, and FIG. Is a flowchart of the operation of the conventional method, and FIG. 7 is an explanatory diagram of switching of the search frequency of the conventional method.

Claims (2)

[Claims] 1. A GP which reacquires a satellite when the radio wave of the satellite being acquired becomes unreceivable for a certain time or longer.
In the S receiver, the search is repeated with the center frequency of the PLL search frequency fixed to the reception frequency of the satellite radio wave at the time when the reception becomes impossible, and the bandwidth of the PLL search frequency in each of the repeated searches is set. A satellite radio wave capturing method for a GPS receiver, which is characterized by gradually expanding the bandwidth of the previous search. 2. A GP which recaptures a satellite when the radio wave of the satellite being captured becomes unreceivable for a certain time or longer.
In the S receiver, the search is repeated with the bandwidth of the PLL search frequency fixed at a predetermined narrow band, and the satellite at the time when the central frequency of the PLL search frequency in each of the repeated searches becomes unreceivable. A satellite radio wave capturing method for a GPS receiver, which is characterized by gradually shifting along the Doppler change curve of the satellite radio wave reception frequency starting from the radio wave reception frequency.