JPH1048312A - Apparatus and system for reception from satellite - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an apparatus and a system in which the time required for searching a receiving frequency from an artificial frequency is shortened, in which a processing operation to obtain positioning data from the turning-on operation of a power supply is performed at higher speed than in conventional cases and in which a present position can be calculated in a short time. SOLUTION: A GPS receiving apparatus 3 is constituted of an antenna unit 4 which receives radio waves from a plurality of GPS satellites, of a GPS body unit 5 which computes a present position on the basis of signals received by the antenna unit 4 and of an operating and display part 6 which displays a map around the present position. The GPS body unit 5 is composed of an RF converter 9 and of a GPS demodulation and computing part 10. A CPU 14 at the GPS demodulation and computing part 10 stores the past deviation of a temperature-compensated crystal oscillator (TCXO) 16, it estimates the deviation between frequencies of the GPS satellites 2 on the basis of the mean value of the past deviation, and it sets frequency search ranges of the radio waves from the GPS satellites 2 according to the estimates deviation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a satellite receiver and a satellite communication system which receive radio waves from artificial satellites and detect the current position based on the received signals.

[0002]

2. Description of the Related Art A global positioning system: GPS (Gl) is used as a satellite receiver for receiving a radio wave from an artificial satellite to determine the current position and a satellite communication system using the satellite receiver.
Product development using an obal positioning system (for example, a surveying system or a navigation system) is underway. This GPS is a non-geostationary satellite communication system that receives radio waves radiated from a non-geostationary satellite launched outside the earth's atmosphere and obtains a reception position. The GPS has an orbit altitude of about 20,000 km, a period of about 12 hours, and an inclination of orbit. Twenty-four satellites are arranged in six orbit planes at an angle of 55 degrees.

[0003] Artificial satellites used in GPS (hereinafter referred to as "GP
S satellite)) is 10 ^-13 /
It is equipped with a highly stable rubidium oscillator (10 nanoseconds / day) and an atomic clock of cesium oscillator. The time signals of all the GPS satellites are synchronized with the time managed as the entire GPS system.

Therefore, the atomic clock mounted on each GPS satellite is constantly monitored by a ground control station.
Periodically updated time correction data is transmitted to each GPS satellite together with the satellite orbit prediction data, and each GPS satellite transmits the orbit prediction data to the ground by radio waves.

[0005] A navigation signal transmitted from a GPS satellite is 1575.42 MHz (L1) as a PSK wave (Phase Shift Keying) subjected to spread spectrum modulation with a PN (Pseudo Noise) code. 1
Two types of radio waves of 227.6 MHz (L2) are transmitted. This code consists of P code (Precision Code) and C /
There are two types of A code (Clear and Acquisition Code). P code is 10.23 Mbps, L1 in one week cycle
And L2 are used to perform ionospheric correction, thereby enabling precise positioning. The C / A code is 1.023Mbp
s, using only L1 with a period of about 1 ms.

There are two types of positioning methods using the GPS, which differ in principle from each other as follows. As
A method to directly calculate the receiving position by receiving radio waves from multiple satellites by direct method positioning and decoding its navigation information (satellite time, orbital elements, etc.) There is a method of receiving radio waves from GPS satellites with a receiver placed and performing relative positioning based on a difference in arrival time between signals reaching the two receivers.

In the above direct method, the receiving device receives navigation signals transmitted from three or more GPS satellites, and calculates the difference between the time of the quartz clock built in the receiving device and the satellite time obtained from the navigation information. The three-dimensional position of the receiving point can be obtained by measuring the distance to the satellite. Actually, since the clock of the receiving apparatus itself may be shifted, the error of the clock can be calculated together with the position coordinates of the receiving apparatus from observation data transmitted from four or more GPS satellites.

The positioning accuracy by the direct method is within 10 m for the P code and about 30 to 100 m for the C / A code. Note that the positioning accuracy of the C / A code is SA (Selective) that intentionally causes an error in the navigation information (orbit, time) of the satellite.
Availability: selective use) is used to reduce the positioning accuracy. Is generally C
A method using the / A code is used as a positioning method for a mobile object such as an automobile.

Further, in the above-described interference method, relative positioning is performed based on the arrival time difference between signals arriving at the two receivers. Since it has the advantage of being able to cancel and can be positioned with higher accuracy than positioning by the direct method, development for geodetic and surveying is under way.

[0010]

SUMMARY OF THE INVENTION In this way, the GPS
In a satellite receiving system that receives radio waves from satellites to determine the current position, each GPS satellite is equipped with a precise atomic clock, whereas the satellite receiver only has a clock with a crystal oscillator. It is. Therefore, a clock offset easily occurs in the time information of the satellite receiver. Therefore, in a satellite receiver, three or more (about four to twelve)
Simultaneously received radio waves transmitted from GPS satellites
The position of the receiving point is calculated from the pseudo distance data including the clock offset between the PS satellite and the receiving point and the orbital position data of each receiving satellite. Therefore, in the satellite receiver,
Four to twelve reception channels are provided.

However, in the satellite receiver, each G
Since the frequency of the radio wave from the PS satellite changes due to the Doppler shift, the previous reception position is stored when the power is turned off, and the almanac, the previous reception position and time are stored when the power is turned on. More Doppler shift was predicted. A temperature-compensated crystal oscillator (hereinafter, referred to as a reference oscillator) is used as a reference oscillator with the predicted frequency as a center frequency.
The error range due to the maximum deviation of "TCXO" was searched.

Since TCXO has a characteristic that the oscillation frequency changes depending on the temperature, if the temperature is not the same, the TCXO deviation differs, and it takes time to search for the reception frequency. Then, this invention was made in view of the said subject, and an object of this invention is to provide the satellite receiver and the satellite receiving system which solved the said problem.

[0013]

Means for Solving the Problems The present invention has the following features in order to solve the above problems. According to the first aspect of the present invention, a crystal oscillator for generating a reference frequency, and a deviation of a reception frequency of a radio wave transmitted from a plurality of artificial satellites based on the reference frequency output from the crystal oscillator, is predicted from the artificial satellite. A receiver for receiving the radio waves of
A satellite receiving apparatus comprising: a calculating means for calculating a current position from a signal received by the receiver; a storing means for storing a past deviation of the crystal oscillator; and an average of the past deviation stored in the storing means. Deviation prediction means for predicting the deviation of the frequency of the artificial satellite received this time using a value, and a frequency search range setting for setting a frequency search range of radio waves from the artificial satellite in accordance with the deviation predicted by the deviation prediction means Means.

Therefore, according to the present invention, the deviation of the frequency of the artificial satellite received this time is predicted using the average value of the past deviation of the crystal oscillator, and the radio wave from the artificial satellite is predicted according to the predicted deviation. Since the frequency search range is set, the deviation of the reference frequency can be predicted to a value corresponding to the use environment, and the time until capturing radio waves from each artificial satellite can be reduced.

According to a second aspect of the present invention, there is provided a satellite receiving apparatus for predicting frequencies of radio waves transmitted from a plurality of artificial satellites based on a reference frequency output from a crystal oscillator and receiving radio waves from the artificial satellites. In the satellite receiving system having the satellite receiving device, the satellite receiving device stores a past deviation of the crystal oscillator, and an average value of the past deviation stored in the storing unit, and uses the average value of the frequency of the artificial satellite received this time. Deviation prediction means for predicting the deviation, and frequency search range setting means for setting a frequency search range of radio waves from the other artificial satellite according to the deviation predicted by the deviation prediction means. Things.

Therefore, according to the second aspect, the deviation of the frequency of the artificial satellite received this time is predicted using the average value of the past deviation of the crystal oscillator, and the radio wave from the artificial satellite is predicted according to the predicted deviation. Since there is a satellite receiver that sets the frequency search range, the deviation of the reference frequency can be predicted to a value according to the usage environment, and the time required for capturing radio waves from each artificial satellite can be reduced.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing one embodiment of the present invention. GPS receiving system (satellite receiving system) 1
Is a non-geostationary satellite communication system that receives a radio wave transmitted from a non-geostationary satellite launched out of the earth's atmosphere and obtains a reception position.
GPS satellites 2 are arranged.

The GPS receiver (satellite receiver) 3 includes an antenna unit 4 for receiving radio waves from at least four GPS satellites 2 (2a to 2d), and an antenna unit 4
A GPS main unit (receiver) 5 for calculating the current position from the signal received by the controller 5 and an operation / display unit 6 for displaying a map around the current position.

The antenna unit 4 is connected to the GPS satellite 2 (2
The antenna 7 includes an antenna 7 for receiving radio waves from a to 2d) and an LNA (low noise amplifier) 8 for amplifying a signal received by the antenna 7. In addition, the GPS main unit 5
An RF converter 9 for converting an RF signal into an intermediate frequency signal (IF), and an intermediate frequency signal (I
After generating digital data obtained by demodulating F), arithmetic processing is performed using the digital data to obtain position data,
It comprises a GPS demodulation / arithmetic unit 10 for generating positioning data such as speed data.

Therefore, radio waves radiated from the GPS satellites 2 (2a to 2d) to the ground are received by the antenna unit 4, amplified, and then supplied to the RF converter 9. R
Although not shown, the F converter 9 includes an RF amplifier, first and second mixers, first and second IF circuits, VCO and P
An LL circuit and the like are provided. And the RF converter 9
Converts an RF signal into an intermediate frequency signal (IF),
It is supplied to the S demodulation / arithmetic unit 10.

Further, the GPS demodulation / arithmetic unit 10 outputs positioning data such as position data and velocity data for specifying the current position to the operation / display unit 6, and the operation / display unit 6
Positioning data (reception position) supplied from the GPS demodulation / arithmetic unit 10 in response to an operation performed on the keyboard of the operation unit
Is displayed. When the GPS receiver 3 has map data by a memory card or the like, the operation / display unit 6
And the current location on the map.

FIG. 2 is a block diagram showing the configuration of the GPS demodulation / arithmetic unit 10. The GPS demodulation / arithmetic unit 10 has a CP
U14, a custom LSI 15, and a TCXO (temperature compensated crystal oscillator) 16. The CPU 14 performs satellite search control, carrier synchronization control, and C / A code synchronization control by operating the keys on the operation / display unit 6, and displays the GPS satellites 2 (2 a to 2 d) and the current position of the user on the operation / display unit 6. The pseudo distance data indicating the distance (without correction) is output. The custom LSI 15 receives an intermediate frequency signal (IF) from the RF converter 9 and a temperature-compensated clock from the TCXO 16, and includes a baseband converter, a carrier synchronization circuit, a correlation processing circuit,
It includes a C / A code generation circuit, a C / A code synchronization circuit, a baseband filter, a PSK (phase shift keying) data demodulation circuit, and CPU peripheral logic.

FIG. 3 is a block diagram showing a circuit configuration for performing frequency conversion of a signal received by the antenna 7. VCO
(Voltage Controlled Oscillator) 22 is provided in the RF converter 9 and changes the oscillation frequency according to the voltage output from the TCXO 16. The NCO 23 is provided in the GPS demodulation / arithmetic unit 10 and performs tuning by changing the frequency oscillated from the TCXO 16.

The satellite receiving system 1 which receives the radio waves transmitted from the GPS satellites 2 and obtains the current position as described above
In each of the GPS satellites 2 (2a to 2d), a precise atomic clock is mounted, while the GPS receiver 3 has a TC clock.
Only a crystal oscillation clock using the clock from the XO 16 is mounted. Therefore, a clock offset easily occurs in the time information of the GPS receiver 3.

Therefore, the GPS receiver 3 simultaneously receives radio waves transmitted from three or more GPS satellites 2, and includes a pseudo-clock including a clock offset between each of the GPS satellites 2 (2a to 2d) and the receiving point. The position of the receiving point is calculated from the distance data and the orbital position data of each of the received GPS satellites 2 (2a to 2d).

As described above, the memory 21 of the CPU 14
A deviation prediction program (deviation prediction unit) that functions as a storage unit that stores the past deviation of the CXO 16 and that uses the average value of the past deviation to predict the deviation of the frequency of the GPS satellite 2 received this time; GP according to deviation
A frequency search range setting program (frequency search range setting means) for setting a frequency search range of a radio wave from the S satellite 2 is stored.

When the power supply voltage Vcc is supplied, the CPU 14 starts the above-described receiving operation, performs an operation based on the pseudo distance data of the demodulated signal supplied from the RF converter 9, and obtains position data, It generates positioning data such as speed data and time data. Further, the CPU 14 performs image processing based on the main program and data from a map CD-ROM (not shown).

FIG. 4 is a flowchart for explaining the processing executed by the CPU 14. In step S1 (hereinafter, "step" is omitted), the CPU 14 sets the search center frequency using the deviation of the reference oscillator (TCXO16) at the time of the last positioning and the Doppler prediction.

Next, the received center frequency is searched by searching the search center frequency set in S1, and the current position is measured from the frequency to determine the deviation of the TCXO16 (TCXOnew).
Is determined (S2). Then, the difference (TCXOold) previously stored is added with a fraction of the difference (TCXOnew) of the TCXO16 measured this time and stored (stored in the memory 21) (S3). That is, in S3, the value of the reference frequency (TC
XOkeep). TCXOkeep = TCXOold + (TCXOold−TCXOnew) / A (1) where A is a storage coefficient and is statistically determined.

The TCXO 16 has a characteristic that the oscillation frequency changes with temperature.
The O deviation is different and it takes time to search for the reception frequency. In this way, by adding 1 / A of the difference between the past deviation TCXOold and the currently measured TCXOnew to the past deviation TCXOold, A value obtained by averaging past deviations is calculated. For example, even when the temperature of the TCXO 16 suddenly changes, the influence of the deviation due to the temperature change can be reduced.

That is, the value of TCXOkeep is determined on the basis of the average deviation in the past, and the deviation of the most frequently used temperature can be obtained and stored in the memory 21. Therefore, when the past deviation stored in the memory 21 is read, the TCX suitable for the use environment is read.
A reference frequency of O16 is obtained. As a result, the time required to search for the reception frequency from the GPS satellite 2 is shortened, the processing from when the power is turned on until the positioning data is obtained is faster than in the past, and the current position is determined in a short time. .

FIG. 5 is a flowchart showing a process for displaying the current position from the positioning data obtained from the GPS satellite 2. The CPU 14 determines in step S11 that the GPS satellite 2
When the radio waves from (2a to 2d) are synchronized with the frequency, GP
Radio waves from the S satellite 2 (2a to 2d) can be received.
Then, the intermediate frequency signal (IF) from the RF converter 9
After generating digital data obtained by demodulating the data, arithmetic processing is performed using the digital data to generate positioning data such as position data and speed data.

Thereafter, the positioning data is read, and the position data (latitude, longitude) in the positioning data indicates the current position (S12). Subsequently, screen data for displaying a mark indicating the current position on the display of the operation / display unit 6 is generated (S13). The current position is latitude and longitude data, whereas the map data in the map CD-ROM is
It is stored in association with the coordinates of the vertical axis and the horizontal axis. The latitude and longitude data of the current position are converted into coordinate data of map data (S14).

The area of the map to be displayed on the display of the operation / display unit 6 is obtained by coordinates corresponding to the coordinates of the current position in accordance with the scale factor specified by the key operation of the operation / display unit 6. The map data of the obtained area is stored in a map CD-RO.
Read from M (S15). Further, based on the map data read in S15, screen data for displaying a map on a display is generated (S16). Subsequently, using the screen data for displaying the current position generated in S7 and the screen data for displaying the map generated in S16, a map and a mark of the current position are displayed on the display by overlapping both screen data ( S17). After the display corresponding to the positioning data read in S11 is completed, the process returns to S11 again and repeats the processing of S11 to S17.

[0035]

As described above, according to the first and second aspects, the deviation of the frequency of the artificial satellite received this time is predicted using the average value of the past deviation of the crystal oscillator, and the predicted deviation is calculated. Since the frequency search range of the radio wave from another artificial satellite is set accordingly, a reference frequency suitable for the use environment can be obtained, and the reception frequency of the other satellite can be predicted to a value corresponding to the use environment. Therefore, the time required to search for the reception frequency from the artificial satellite is shortened, the processing from the time when the power is turned on until the positioning data is obtained can be accelerated, and the current position can be determined in a short time.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a GPS demodulation / arithmetic unit in FIG. 1;

FIG. 3 is a block diagram showing a circuit configuration for performing frequency conversion of a received signal.

FIG. 4 is a flowchart illustrating a satellite locking process executed by a CPU.

FIG. 5 is a flowchart showing a process for displaying a current position from positioning data obtained from a GPS satellite.

[Explanation of symbols]

 Reference Signs List 1 GPS receiving system 2 (2a to 2d) GPS satellite 3 GPS receiving device 4 Antenna unit 5 GPS main unit 7 Antenna 9 RF converter 10 GPS demodulation / arithmetic unit 14 CPU 15 Custom LSI 16 TCXO (Temperature compensated crystal oscillator) 21 Memory

Claims (2)

[Claims] 1. A crystal oscillator for generating a reference frequency, and a deviation of a reception frequency of radio waves transmitted from a plurality of artificial satellites is predicted based on the reference frequency output from the crystal oscillator to generate a radio wave from the artificial satellite. A satellite receiver comprising: a receiver for receiving; and a calculating means for calculating a current position from a signal received by the receiver; a storage means for storing a past deviation of the crystal oscillator; Deviation prediction means for predicting the deviation of the frequency of the artificial satellite received this time using the average value of the past deviations, and a frequency search range of the radio wave from the artificial satellite according to the deviation predicted by the deviation prediction means. A satellite receiving apparatus comprising: a frequency search range setting means for setting. 2. A satellite receiving system comprising a satellite receiving device for predicting the frequency of radio waves transmitted from a plurality of artificial satellites based on a reference frequency output from a crystal oscillator and receiving radio waves from artificial satellites, A satellite receiver configured to store a past deviation of the crystal oscillator; and a deviation prediction unit that predicts a deviation of the frequency of the artificial satellite received this time using an average value of the past deviation stored in the storage unit. And a frequency search range setting means for setting a frequency search range of a radio wave from the artificial satellite according to the deviation predicted by the deviation prediction means.