JPH1048311A - Satellite receiving device and satellite receiving system - Google Patents

Abstract

(57) [Summary] An object of the present invention is to take a long frequency search time when receiving radio waves from a plurality of satellites. A GPS receiving device includes: an antenna unit for receiving radio waves from a plurality of GPS satellites; a GPS main unit for calculating a current position from a signal received by the antenna unit; It comprises an operation / display unit 6 for displaying a map. The GPS main unit 5 includes an RF converter 9 and a GPS demodulation / arithmetic unit 10.
Consists of The CPU 14 of the GPS demodulation / arithmetic unit 10
The frequency of the radio wave from the first GPS satellite 2 is stored, and other GPs are stored based on the frequency of the first GPS satellite 2.
The frequency of the radio wave from the S satellite 2 is predicted, and the frequency search range of the radio wave from another GPS satellite 2 is set according to the predicted frequency.

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. 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.

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 using 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 device itself may be shifted, the error of the clock can be calculated from the observation data transmitted from the four GPS satellites together with the position coordinates of the receiving device.

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, so that the propagation delay of radio waves radiated from GPS satellites, the time error of GPS satellites, and the like are determined. Since it has the advantage of being able to cancel and can be positioned with higher accuracy than the 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. Then, an error range due to the maximum deviation of the reference oscillator (TCXO) is searched using the predicted frequency as the center frequency.

For example, in the case of a receiving device mounted on a car, the receiving device moves while the power is on.
The vehicle may pass through a long tunnel that cannot receive radio waves from PS satellites, or enter a building or an underground parking lot. However, even when passing through a tunnel while the power is on, or when parking in a building or underground parking lot, the GPS satellites move in the same manner as above and the relative speed changes, and the frequency increases. Doppler shift.

For this reason, when the vehicle moves again to a position where it can receive radio waves from GPS satellites, the Doppler shift has been predicted from the almanac and the previous reception position and time. In order to search the error range due to the maximum deviation of the reference oscillator (TCXO) using the predicted frequency as the center frequency, it takes a considerable time to receive radio waves from all receivable GPS satellites.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to provide a satellite receiving apparatus and a satellite receiving system which solve the above problems.

[0015]

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 receiver for searching each frequency of radio waves transmitted from a plurality of artificial satellites to receive radio waves from the artificial satellites, and calculating a current position from a signal received by the receiver. In a satellite receiving apparatus including an arithmetic unit, a storage unit that stores a frequency of a radio wave from the one artificial satellite, and a frequency of a radio wave from another artificial satellite is predicted based on the frequency stored in the storage unit. Frequency prediction means, and frequency search range setting means for setting a frequency search range of radio waves from the other artificial satellite according to the frequency predicted by the frequency prediction means, characterized by comprising: is there.

Therefore, according to the first aspect, when a radio wave from one artificial satellite is captured, the frequency is stored, the frequency of the radio wave from another artificial satellite is predicted based on the stored frequency, and Since the frequency search range of radio waves from other artificial satellites can be set according to the predicted frequency, the time required to capture radio waves from the second and subsequent artificial satellites can be reduced.

According to a second aspect of the present invention, in a satellite receiving system having a satellite receiving device for predicting a frequency of a radio wave transmitted from an artificial satellite and receiving a radio wave from the artificial satellite, the satellite receiving device includes: Storage means for storing a frequency of a radio wave from one artificial satellite; frequency prediction means for predicting a frequency of a radio wave from another artificial satellite based on the frequency stored in the storage means; Frequency search range setting means for setting a frequency search range of radio waves from the other artificial satellite in accordance with the set frequency.

Therefore, according to the second aspect, when a radio wave from one artificial satellite is captured, the frequency is stored, and based on the stored frequency, the frequency of the radio wave from another artificial satellite is predicted. Since the frequency search range of radio waves from other artificial satellites can be set according to the predicted frequency, the time required to capture radio waves from the second and subsequent artificial satellites can be reduced.

[0019]

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.

A 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
It is composed of an LL circuit and the like. 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 speed 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 (2a to 2d) 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 the intermediate frequency signal (IF) from the RF converter 9 and the 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.

In this configuration, the frequency conversion of the RF converter 9 is fixed, and tuning is performed by the NCO 23.
Then, the reception frequency is obtained by the following equation. Receiving frequency = VCO + TCXO + NCO = 84.5 × TCXO + TCXO + Tune × TCXO (1) The nominal oscillation frequency of TCXO16 is 18.414 MH.
z, the IF of the RF converter 9 is 1.023 MHz.

Here, when trying to receive a radio wave emission frequency of 1575.42 MHz from the GPS satellite 2, GP
The value when locking the radio wave from S satellite 2 is Tune =
1.023 / 18.414. However, TCXO
When the deviation ΔF is included in the 16 reference frequencies, it can be expressed as the following equation.

TCXO = tcxo + ΔF (2) The reference frequency is tcxo = 18.414 MHz. Therefore, the actual reception frequency is 1575.42 + 8
It stops at 5.555 × ΔF [MHz]. However, TCXO
Since the deviation is unknown, it is necessary to search the reception frequency error range caused by the TCXO deviation.

The initial frequency search is performed in the same manner as in the conventional case. However, when the first GPS satellite 2 is locked, the TCXO deviation can be known from the oscillation frequency of the NCO 23 and the Doppler shift prediction (Dopp) of the channel locking the radio wave from the GPS satellite 2 based on the following equation. it can. 1575.42 + Dopp = 85.5 × TCXO + Tune × TCXO (3) Then, the search center frequency of another channel which is not locked yet is set to a value including the TCXO deviation correction. As a result, it is possible to reduce the time from locking the first GPS satellite 2 to locking the second and subsequent GPS satellites 2.

The satellite receiving system 1 which receives the radio wave transmitted from the GPS satellite 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 receiving device 3 simultaneously receives radio waves transmitted from three or more GPS satellites 2 and includes a pseudo-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 frequency prediction program (frequency prediction) that functions as a storage unit that stores the frequency of the radio wave from the first GPS satellite 2 and that predicts the frequency of the radio wave from another GPS satellite 2 based on the frequency of the first GPS satellite 2 Means) and
A frequency search range setting program (frequency search range setting means) for setting a frequency search range of a radio wave from another GPS satellite 2 according to the predicted frequency 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 satellite locking process executed by the CPU 14. CP
In step S1 (hereinafter, "step" is omitted), U14 reads the frequency at the time of previous reception stored in the memory 21 and performs the Doppler shift of the GPS satellite 2 desired to be received from the approximate reception position and time. Predict.

Next, a reception frequency within an error range due to the maximum deviation of the reference oscillator (TCXO16) is searched as the expected center frequency (S2). Subsequently, it is determined whether there is a channel on which the radio wave from the GPS satellite 2 is locked (S3). If there is no channel that has locked the satellite, the frequency search is continued. When the radio wave from the GPS satellite 2 is locked, the frequency is stored, and the process proceeds to S4.

In S4, the deviation of the reference oscillator (TCXO16) is calculated from the carrier NCO set value of the channel on which the radio wave from the GPS satellite 2 is locked and the Doppler predicted value. Then, the search center frequency of the channel which has not been locked is calculated based on the Doppler prediction value from the reference oscillator (TCX).
The received frequency is searched by replacing the frequency including the deviation of O16) (S5). When a radio wave from the GPS satellite 2 is received, the channel is locked by the satellite.

Next, it is determined whether or not there is an unlocked channel (S6). If there is an unlocked channel, the process returns to S5, and the processes of S5 and S6 are repeated. At this time, the search center frequency of another channel which is not yet locked is calculated from the Doppler prediction value in S4.
The received frequency is searched by replacing the frequency including the deviation of the reference oscillator (TCXO16) calculated in step (1). As described above, since the search center frequency and the frequency search range obtained based on the deviation of the reference oscillator (TCXO16) calculated for the first time are set for the radio waves from the second and subsequent GPS satellites 2, the other GPS The reception frequency can be searched and locked in a short time by predicting the Doppler shift of the satellite 2.

When all the channels are locked, for example, radio waves from all of the 4 to 12 GPS satellites 2 are received, the positioning data can be calculated, and a series of satellite lock processing ends. As described above, when receiving the radio waves from the second and subsequent GPS satellites 2, the search center frequency and the frequency search range are set based on the deviation of the reference oscillator (TCXO16) calculated for the first time. Can be shortened until a radio wave from the GPS satellite 2 is captured. In particular, the time from when the power of the GPS receiver 3 is turned on to when the radio waves from all receivable GPS satellites 2 are received can be greatly reduced.

For example, in the case of a receiver mounted on a car, the receiver may pass through a long tunnel that cannot receive radio waves from the GPS satellites 2, or enter a building or an underground parking lot. However, when a car comes out of a tunnel, a building, an underground parking lot, or the like to a receivable position, it is possible to shorten the time required to receive radio waves from the second and subsequent GPS satellites 2 as described above. When moving from a place where radio waves from the GPS satellite 2 cannot be received to a receivable position, the current position can be known 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.

[0043]

As described above, according to the first and second aspects, when a radio wave from one artificial satellite is captured, its frequency is stored, and based on the stored frequency, a signal from another artificial satellite is stored. Since the frequency of the radio wave can be predicted and the frequency search range of the radio wave from another satellite can be set according to the predicted frequency, the time until the radio wave from each of the second and subsequent satellites is captured is reduced. Can be shortened,
In particular, when receiving radio waves from a large number of artificial satellites, it is possible to greatly shorten the search time required until receiving radio waves from all the artificial satellites, thereby speeding up the search operation.

[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 22 VCO 23 NCO

Claims (2)

[Claims] 1. A receiver for searching each frequency of radio waves transmitted from a plurality of artificial satellites and receiving radio waves from the artificial satellites, and a calculating means for calculating a current position from a signal received by the receiver. Storage means for storing a frequency of a radio wave from the one artificial satellite; and frequency prediction means for predicting a frequency of a radio wave from another artificial satellite based on the frequency stored in the storage means. And a frequency search range setting means for setting a frequency search range of radio waves from the other artificial satellite in accordance with the frequency predicted by the frequency prediction means. 2. A satellite receiving system having a satellite receiving device for predicting the frequency of a radio wave transmitted from an artificial satellite and receiving a radio wave from the artificial satellite, wherein the satellite receiving device includes a radio wave from the one artificial satellite. Storage means for storing the frequency of the above, frequency prediction means for predicting the frequency of radio waves from other satellites based on the frequency stored in the storage means, and said frequency prediction means according to the frequency predicted by the frequency prediction means A frequency search range setting unit for setting a frequency search range of a radio wave from another artificial satellite.