JPH09145819A - GPS receiver - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To provide a GPS receiver capable of synchronizing with a satellite radio wave in a short time and shortening a time until a position is detected. SOLUTION: The amount of change Δf in the offset frequency of the oscillation frequency of the oscillator, which greatly varies depending on the temperature of the receiver after the power is turned on until the temperature inside the receiver stabilizes
_The value ofs is stored in the memory in correspondence with the elapsed time T1 to T5 since the power was turned on, and in the next process, the oscillation center frequency f _c is set using the oscillation frequency fluctuation according to that time. .

Description

Detailed Description of the Invention

[0001]

The present invention relates to a plurality of GPS (Gl
obal Positioning System) The present invention relates to a GPS receiver capable of shortening the time required to detect a position by receiving radio waves from a satellite.

[0002]

2. Description of the Related Art A GPS system is a satellite navigation system capable of positioning independently from any point on the earth by receiving radio waves from a plurality of satellites. Recently, receivers have been widely used in car navigation systems and the like because both the antenna and the device are made compact.

G for position detection in the GPS system
The PS signal is a signal called C / A code,
It is transmitted in the band frequency band (1575.42 MHz). This carrier frequency (1575.42MHz) is GPS
The frequency fluctuates due to the Doppler effect that occurs because the satellite is moving. Further, the oscillator in the GPS receiver also has an offset, and its oscillation frequency changes with temperature.

Therefore, in order to actually synchronize with the radio waves of the satellite, the following method is adopted.

First, the fluctuation of the reception frequency due to the Doppler effect (hereinafter referred to as the Doppler shift frequency) and the offset of the oscillator are added together with respect to the carrier wave, and the obtained frequencies are added for synchronization (hereinafter referred to as the frequency for synchronization). , Scan center frequency). Next, an appropriate bandwidth is set around this scanning center frequency, and the frequency is changed within that bandwidth so as to synchronize with the radio waves of the satellite.

In the conventional GPS receiver, the offset frequency of the last operating oscillator is backed up in a memory, and when the power is turned on next time, the offset frequency of the backed up oscillator and the satellite orbit data are used. The scanning center frequency was determined by adding the calculated Doppler shift frequency, and based on this, the satellite radio waves were synchronized.

[0007]

However, in the above-mentioned conventional GPS receiver, the temperature inside the receiver is lowered while the power is off, the offset frequency of the oscillator is also changed, and the backup is stored in the memory. There may be a large difference between the offset frequency being set and the actual offset frequency, and it may take time between the next power-on and the synchronization with the satellite radio wave. That is, in the conventional GPS receiver, since the offset frequency of the oscillator at the time of the last operation is backed up, the offset frequency of the oscillator also changes when the temperature inside the receiver decreases while the power is off. Therefore, due to the difference between the offset frequency backed up in the memory and the actual offset frequency, there is a problem that it takes time from the power-on to the synchronization with the satellite radio wave.

The present invention solves such a problem of the conventional GPS receiver, can synchronize with the satellite radio wave in a short time, and can shorten the time until the position is detected.
It is an object to provide a receiver.

[0009]

In order to achieve the above object, the present invention has a reference internal oscillator, and scans a fixed frequency range with reference to the oscillation frequency of the reference internal oscillator, thereby providing a plurality of GPSs. In a GPS receiver that synchronizes with radio waves from satellites and receives radio waves from the plurality of GPS satellites to perform position detection, a frequency range to be scanned according to the elapsed time after turning on the power of the receiver It has a scanning center frequency transition means for changing the center frequency of.

According to the present invention, it is possible to shorten the time until the position is detected despite the fluctuation of the oscillation frequency of the reference internal oscillator due to the elapsed time.

Here, the scanning center frequency transition means has a storage means for storing a change in the oscillation frequency of the internal oscillator with respect to an elapsed time since the power of the receiver was turned on last time, and the storage means stores the change. The center frequency of scanning is changed based on the change of the oscillation frequency of the internal oscillator.

According to the present invention, the time until the position is detected can be further shortened on the basis of the history of changes in the oscillation frequency of the reference internal oscillator due to the elapsed time at the previous reception.

Further, the scanning center frequency transition means determines the scanning center frequency in consideration of a frequency change due to the Doppler effect caused by the movement of the GPS satellite.

According to the present invention, the time taken to detect the position can be further shortened by taking into consideration the fluctuation of the reception frequency due to the movement of the satellite.

[0015]

The invention according to claim 1 of the present invention has a reference internal oscillator, and scans a constant frequency range with reference to the oscillation frequency of the reference internal oscillator, so that a plurality of GPS satellites are transmitted. Synchronize with the radio wave,
In a GPS receiver that receives a radio wave from the S satellite and performs position detection, it has a scanning center frequency transition means for changing the center frequency of the frequency range to be scanned according to the elapsed time after the power of the receiver is turned on. With this feature, it is possible to synchronize with the satellite radio wave in a short time in consideration of the change in the offset frequency due to the temperature inside the receiver after turning on the power, and shorten the time to detect the position. can do.

According to a second aspect of the present invention, there is provided storage means for storing a change in the oscillation frequency of the internal oscillator with respect to an elapsed time since the scanning center frequency transitioning means last turned on the power supply of the receiver. However, since the center frequency of the scanning is changed based on the change of the oscillation frequency of the internal oscillator stored in the storage means, the change history of the oscillation frequency of the reference internal oscillator due to the elapsed time at the previous reception. It is possible to further shorten the time from power-on to synchronization with the satellite radio wave, and further shorten the time to detect the position.

According to a third aspect of the present invention, the scanning center frequency transition means determines the scanning center frequency in consideration of a frequency change due to the Doppler effect caused by the movement of the GPS satellite. Because,
In consideration of fluctuations in the reception frequency due to movement of the satellite, the time from power-on to synchronization with the satellite radio wave can be further shortened, and the time until position detection can be shortened.

A GPS receiver according to the present invention will be described below in detail with reference to the accompanying drawings. In the present invention, a plurality of amounts of change over time of the offset frequency of the oscillator in the previous operation are stored in the memory together with the time history after the power is turned on, and in accordance with the time history in this operation, This is to select and use a plurality of offset frequency variations having the same time history.

FIG. 1 shows a flowchart of the synchronous scanning process in one embodiment of the GPS receiver of the present invention. Also,
FIG. 2 is a diagram for explaining the setting operation of the scanning center frequency and the scanning band in the processing of the flowchart shown in FIG.

First, the processing procedure will be described with reference to FIG.
When the GPS receiver is powered on for position detection, the GPS receiver reads from the memory the offset frequency of the oscillator when it was first synchronized with the previous operation backed up in the memory, and The offset frequency is Δf _ini (step 1).

Next, the Doppler shift frequency Δf _dop of the signal carrier from the satellite is calculated from the navigation data of the GPS satellite (step 2).

On the other hand, the elapsed time from when the power of the GPS receiver is turned on to this time is calculated by the real time clock (RTC) held in the GPS receiver (step 3).

Next, the change amount Δf _ofs of the offset frequency over time is read and set from the backup contents of the memory (step 4).

[0024] To set the carrier frequency (1575.42 MHz) initial offset frequency Delta] f _ini, as the Doppler shift frequency Delta] f _dop and alignment scanning center plus the variation Delta] f _ofs offset frequency frequency f _c (Step 5).

Scan center frequency f _c thus obtained
The scanning is started with the start point as the starting point (step 6), and if the synchronization is obtained, the synchronous scanning is ended there (step 7). If the synchronization is not obtained, the width of the scanning frequency is sequentially expanded within the preset maximum scanning width. Then, it synchronizes with the radio waves of the satellite (step 9).

At this time, if the sequentially widened scanning width reaches the preset maximum scanning width but the synchronization cannot be established (step 8), the process returns to step 3 again, and at that time, again. The process of obtaining the scanning center frequency f _c and scanning is repeated.

The contents of this scanning can be easily understood by referring to the explanatory view of FIG. When the power is turned on, the GPS receiver first starts scanning with the scanning center frequency f _c = f _c0 . However, f _c0 is a value obtained by adding the initial offset frequency Δf _ini and the Doppler shift frequency Δf _dop to the carrier frequency (1575.42 MHz) represented by f _c0 = 1575.42 MHz + Δf _ini + Δf _dop . The scanning is started from this scanning center frequency f _c0, and the scanning width is sequentially increased on both the positive and negative sides to try to synchronize with the satellite.

When the expanded scan width reaches the preset scan width but the synchronization is not achieved, the change amount Δf of the offset frequency at the elapsed time T1 at that time.
_A new scanning center frequency f _c is obtained by adding _ofs1 to the previous f _c0 , and the processing is repeated while the scanning width is sequentially widened to the positive and negative sides with this as the starting point and synchronization with the satellite is repeated.

In FIG. 2, the elapsed times are T1, T2, T3, and T.
4 shows how the scanning processing range changes as time passes.

By this method, the synchronization should actually be _achieved by that time, but the change amount Δf _ofs of the offset frequency converges to a constant value after a certain period of time, so that the scanning center frequency f _c is It doesn't change over time.

[0031]

As described above, according to the present invention, the amount of offset of the oscillation frequency of the oscillator, which greatly fluctuates depending on the temperature of the receiver until the temperature inside the receiver stabilizes after the power is turned on, is turned on. The scanning center frequency is set by using the oscillation frequency fluctuation due to that time in the next processing, so that it is stored in the memory in correspondence with the passage of time after that. The time can be shortened and it is extremely effective in practice.

[Brief description of the drawings]

FIG. 1 is a flowchart of a scanning center frequency setting process in an embodiment of a GPS receiver of the present invention.

FIG. 2 is a characteristic diagram showing a scanning center frequency and a scanning band when an oscillator whose oscillator offset frequency changes with time is used.

[Explanation of symbols]

f _c Scan center frequency f _c0 Scan center frequency when power is turned on Δf _dop Doppler shift frequency Δf _ini Initial offset frequency Δf _ofs Offset frequency change amount T1, T2, T3, T4 Elapsed time after power on

Claims (3)

[Claims] 1. A plurality of GPS satellites having a reference internal oscillator and synchronizing with radio waves from a plurality of GPS satellites by scanning a fixed frequency range with the oscillation frequency of the reference internal oscillator as a reference. In a GPS receiver that receives a radio wave from the device and detects a position, a GPS center frequency transition unit that changes the center frequency of the frequency range to be scanned according to the elapsed time after the power of the receiver is turned on is provided. Characteristic GPS receiver. 2. The scanning center frequency transition means has a storage means for storing a change in the oscillation frequency of the internal oscillator with respect to an elapsed time after the power source of the receiver is turned on last time.
2. The GPS receiver according to claim 1, wherein the center frequency of scanning is changed based on a change in the oscillation frequency of the internal oscillator stored in the storage means. 3. The scanning center frequency transition means is the GP.
The GPS according to claim 1 or 2, wherein the scanning center frequency is determined in consideration of a frequency change due to the Doppler effect caused by the movement of the S satellite.
Receiving machine.