JPH0797131B2 - 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
When the satellite that has been captured up to that point is blocked by a building or the like and remains incapable of reception for a certain period of time (for example, 1 minute) or more, the S receiver receives GPS signals as shown in the outline of its operation in Fig. 3.
We are trying to start reacquisition of satellites.

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 maximum change in Doppler frequency of this GPS satellite is about ± 5 [KHz] on the ground.

On the other hand, the GPS receiver causes Doppler change due to movement of the receiver itself, for example, in the case of a vehicle-mounted GPS receiver, movement of the vehicle. The maximum Doppler frequency change due to vehicle movement is ± 600 [Hz] (vehicle speed 60 m / sec). In addition, the frequency shift of the GPS receiver oscillator is ± 3
About [KHz] occurs. When these changes are added, 5,
000 + 600 + 3,000 = 8,600 [Hz], and the reception frequency of the satellite radio wave is ± 8,600 at the maximum around 1575.42 [MHz].
It will change in the range of [Hz]. If you try to reacquire the satellite while covering the maximum change range of this reception frequency ± 8,600 [Hz], the GPS receiver will have a range of ± 8,600 [Hz] above and below the satellite radio wave transmission frequency of 1575.42 [MHz]. It is necessary to search the satellite radio wave while waving the search frequency over a wide band.

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 frequency of satellite radio waves. There is no problem if the capture range of this PLL is wide enough to cover the maximum change range ± 8,600 [Hz], but the capture range of the normal PLL is
The range must be narrow band, for example, about 300 [Hz] due to restrictions on the circuit configuration. Therefore, in order to search while covering the maximum variation range of the reception frequency of the satellite radio wave ± 8,600 [Hz], it is necessary to search while switching the PLL search frequency in several steps. For example, if the capture range of the PLL is 300 [Hz],
It becomes 8,600 / 300 ≈ 28, 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 described above, since satellite radio waves are transmitted by the spread spectrum method, when receiving them, it is necessary to first despread the received radio waves and identify whether or not they are the radio waves of the target satellite. This judgment requires about 1 second. Therefore, it takes at least about 56 seconds to search the 56 steps, and the original positioning calculation cannot be performed during this period.

Furthermore, the GPS needs to acquire a minimum of three satellites, preferably four satellites, in its positioning. The most desirable GPS receiver is to have one reception channel for one satellite. However, in the consumer equipment such as the in-vehicle navigation device described above, in consideration of downsizing, cost reduction, positioning accuracy, etc., normally, the receiving channel is set to one channel, and this one channel is time-division multiplexed. It is usually configured to receive three or four satellite radio waves sequentially. Therefore, in the case of using the conventional GPS receiver, for example, when reacquiring N satellites, the reacquisition operation is completed for N satellites as shown in FIG.
It takes at least 56 × N seconds.

Also, if the satellite radio wave happens to be blocked by a building when the PLL search frequency is exactly the same as the satellite radio wave reception frequency, another 56 × until the next search frequency matches the satellite radio wave. There was a problem that it took a long time to wait N seconds, it took a lot of time to reacquire satellites, and the original positioning calculation could not be restarted quickly.

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

[Means for Solving the Problems]

In order to achieve the above object, the satellite radio wave capturing method of the present invention, when the satellite radio wave being captured becomes unreceivable for a certain period of time or more, the entire range of the maximum change range of the reception frequency of the satellite radio wave of the PLL. In a GPS receiver that searches the satellite radio wave in a wide band while changing the search frequency, when the satellite radio wave becomes unreceivable, first, the capture range of the PLL is set by the Doppler change rate of the reception frequency by the satellite. During the predetermined time obtained by dividing, within the range of the frequency change due to the Doppler change rate and the Doppler frequency change due to the moving speed of the GPS receiver, centering on the reception frequency of the satellite radio wave at the time when it becomes unreceivable Narrow band search of satellite radio waves is performed while changing the search frequency, and if satellite radio waves cannot be re-acquired after the predetermined time, it is stored in the GPS receiver. The satellite Doppler frequency at the time when the predetermined time has elapsed is recalculated from the satellite orbit information to obtain an expected reception frequency, and the satellite reception is searched by switching to the wideband search mode with the estimated reception frequency as the center frequency. It is the one.

[Work]

Taking the case of an in-vehicle GPS receiver as an example, the maximum Doppler frequency change by satellite is ± 5 [KHz] as described above.
The maximum Doppler change rate is about 40 [Hz / min]. Therefore, for example, assuming that the PLL capture range is 300 Hz = ± 1500 [Hz], it will take about 150/40 = 3 minutes and 45 seconds for the satellite radio wave reception frequency to change Doppler beyond this capture range. become.

In other words, until the time of 3 minutes and 45 seconds has passed, the change in the Doppler frequency due to the satellite is centered on the reception frequency that was received until then, and the capture range of the PLL is ± 1.
It is within the range of 50Hz. In addition to this, the GPS signal reception frequency changes as described above.
Although there is a Doppler frequency change due to the moving speed of the receiver itself and a frequency shift of the GPS receiver oscillator, the frequency shift changes slowly over a long period of time and is ignored in a short time unit of about several minutes. can do. Therefore, the maximum change range of the reception frequency of the satellite radio wave within the above 3 minutes and 45 seconds is the capture range of the PLL ± 150 [Hz] and the Doppler change due to the moving speed of the GPS receiver ± 600 [Hz], that is, ± 750 [Hz]. It is very likely that it exists in the range of [Hz].

The present invention focuses on the above point, and when the satellite radio wave cannot be received, first, during a predetermined time obtained by dividing the PLL capture range by the Doppler change rate of the satellite radio wave reception frequency. Is the capture range of the PLL and GPS centered on the reception frequency of the satellite radio wave when it becomes unreceivable.
Narrow band search of satellite radio waves is performed within the range of maximum frequency change expected from the moving speed of the receiver. If the satellite radio waves cannot be captured even after the predetermined time has passed,
The Doppler frequency of the satellite at the lapse of the predetermined time is recalculated from the satellite orbit information stored in the GPS receiver to obtain the expected reception frequency, and the PLL search frequency is set to the satellite radio wave centering on the expected reception frequency. The wideband search of satellite radio waves is performed while changing over the entire width of the maximum change range of the reception frequency of. As a result, the satellite radio wave recapture time is shortened in both narrow band search and narrow band search.

〔Example〕

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

FIG. 1 is an explanatory view of switching search frequencies showing an embodiment of the method of the present invention, and FIG. 2 is a flowchart of the operation. The GPS receiver is assumed to be capturing satellite radio waves at the reception frequency f _r in FIG.

Now, while receiving a predetermined satellite radio wave at the reception frequency f _r , for example, a vehicle enters the shadow of a building and the satellite radio wave becomes unreceivable (step [1] in FIG. 2). When the disabled state has passed a predetermined time, for example, one minute (step [2]), the GPS receiver performs the one minute, and from time T ₁ position, the narrow band search which is a feature of the present invention is performed. Start the satellite reacquisition operation.

That is, as described above, assuming that the capture range of the PLL of the GPS receiver is 300 [Hz] = ± 150 [Hz] and the Doppler change rate of the reception frequency of satellite radio waves is 40 [Hz / min], During the period of 2 minutes and 45 seconds from time T ₁ to time T ₂ , the PLL search center frequency is ± 300 [Hz] centered on the reception frequency f _r at the time when reception becomes impossible, as shown in FIG. , ±
Switching to two stages of 600 [Hz], centering on f _r ± 750 [Hz]
Search for satellite radio waves in the range. Therefore, since the search range is narrow, the satellite can be reacquired earlier.

When the satellite reacquisition is successful within the time of 3 minutes and 45 seconds, there is no need to perform a wideband search subsequent to the satellite reacquisition, so the satellite reacquisition operation ends (Yes in step [4]).

On the other hand, if the satellite could not be recaptured even after the time of 3 minutes and 45 seconds, the process proceeds to step [5] (No in step [4]), and the satellite stored in the CPS receiver. The Doppler frequency of the satellite at that point in time is recalculated using the orbital information of 3 and as shown in FIG.
The expected reception frequency _frr after 45 minutes has passed is calculated (step [5]). Then, when this 3 minutes and 45 seconds have elapsed, the GPS receiver is switched from the narrow band search mode to the wide band search mode, and thereafter, the maximum change range ± of the reception frequency of the satellite radio wave with the expected reception frequency _frr as the center frequency. 8,60
Wideband search of satellite radio waves is performed by sequentially switching the PLL search frequency over the entire width of 0 [Hz] (step [6]). Therefore, after 3 minutes and 45 seconds have elapsed, the satellite radio wave reception frequency is reached at that time. A wideband search is performed centered on the frequency position that is expected to be closest to. This allows the satellite to be reacquired sooner.

〔The invention's effect〕

As is clear from the above description, according to the satellite radio wave capturing method of the present invention, when the satellite radio wave being captured cannot be received for a certain period of time or longer, first, the capture range of the PLL is set. A narrow band search is performed for a predetermined time obtained by dividing by the Doppler change rate of the reception frequency of the satellite radio wave, and if the satellite radio wave cannot be captured by the narrow band search, the satellite at the time is determined from the orbit information of the satellite. Recalculate the Doppler frequency of to obtain the expected reception frequency,
Since the wide band search is performed with the expected reception frequency as the center frequency, satellite radio waves can be recaptured more quickly in both narrow band search and wide band search, and the original positioning calculation as GPS can be performed faster. It can be restarted.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of switching of search frequencies according to one embodiment of the method of the present invention, FIG. 2 is a flowchart of operation of the above embodiment, FIG. 3 is a flowchart of operation of a conventional method, and FIG. 4 is a search of conventional method. It is a frequency switching explanatory drawing. f _r …… Reception frequency when reception is no longer possible f _rr …… Expected reception frequency after elapse of a predetermined time

Claims (1)

[Claims] 1. When the satellite radio wave being captured becomes unreceivable for a certain period of time or longer, the satellite radio wave is searched for in a wide band while changing the PLL search frequency over the entire range of the maximum change in the reception frequency of the satellite radio wave. When the satellite radio wave becomes unreceivable in the GPS receiver,
During the predetermined time obtained by dividing the capture range of by the Doppler change rate of the reception frequency by the satellite, the reception frequency of the satellite radio wave at the time when reception becomes impossible
Narrow band search of satellite radio waves is performed while changing the search frequency within the range of frequency change due to the Doppler change rate and Doppler frequency change due to the moving speed of the GPS receiver, and satellite radio waves can be recaptured even after the lapse of the predetermined time. If not, from the orbit information of the satellite stored in the GPS receiver to obtain the expected reception frequency by recalculating the Doppler frequency of the satellite at the time of the predetermined time, the expected reception frequency as the center frequency, It is characterized by switching to the wideband search mode and searching for satellite radio waves.
How to capture satellite radio waves from GPS receivers.