JP3302404B2 - GPS receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a GPS (Global Posit
GPS equipped with a function to search for satellites to be used for positioning using almanac data from satellites and a function to search all satellites over the entire frequency range in which reception is possible without using almanac data (search the sky mode) Regarding the receiver.

[0002]

2. Description of the Related Art A GPS is a mobile object (user) on the earth using a GPS satellite launched in orbit around the earth.
Is a system that performs positioning. FIG. 3 shows a configuration of a GPS receiver according to one conventional example.

As shown in FIG. 1, the GPS receiver includes an antenna 10, a preamplifier 12, and a frequency converter 14. The antenna 10 receives a signal transmitted from a GPS satellite, and the preamplifier 12 amplifies the signal at a high frequency. The frequency conversion unit 14 converts the frequency of the high-frequency amplified signal into an intermediate frequency, and the obtained intermediate frequency signal is input to the receiving unit 16.

A receiving unit 16 connected to the subsequent stage of the frequency converting unit 14 is configured as, for example, a PLL.
It has a function of N code synchronization. Here, since the signal transmitted from the GPS satellite is spread spectrum, it is necessary to synchronize a PN code (pseudo noise code) in order to demodulate data from this signal. From the PN code phase information, the satellite time (GP
Time when the signal was transmitted from the S satellite).
The pseudorange calculation unit 18 connected to the reception unit 16 executes this calculation, that is, the calculation for obtaining the satellite time from the phase information of the PN code, and further calculates the pseudorange of the satellite (error of the clock of the receiver and the like). Including distance).

[0005] The receiving section 16 has a function of carrier synchronization. That is, P for synchronization of the PN code
A PLL for carrier synchronization is provided in addition to the LL. The receiving unit 16 converts the intermediate frequency signal into a baseband signal by carrier synchronization, and measures a Doppler frequency included in a carrier related to transmission from a satellite. The receiving unit 16 supplies the baseband signal thus obtained to the satellite orbit data decoding unit 20 and outputs the Doppler frequency to the Doppler calculating unit 22.

The satellite orbit data decoding unit 20 decodes almanac data and ephemeris data from data bits of the supplied baseband signal. Here, the almanac data is data indicating the orbit history of each satellite constituting the GPS, and by using this data, the approximate position and speed of each satellite at the satellite time can be known. The ephemeris data is data relating to the orbit of the GPS satellite that transmitted the signal, and by using this data, the position and speed of the GPS satellite that transmitted the signal at the satellite time can be accurately known. The almanac data decoded by the satellite orbit data decoding unit 20 is stored in the almanac memory 24 and the ephemeris data is stored in the ephemeris memory 26, respectively.

The almanac data stored in the almanac memory 24 is stored in an almanac satellite position / velocity calculation unit 2
8 is used to calculate the position and velocity of the GPS satellites. That is, the almanac satellite position / velocity calculation unit 28
Calculates the position and speed of each GPS satellite at the satellite time obtained by the pseudo distance calculation unit 18 based on the almanac data. The satellite selection calculator 30 connected to the subsequent stage of the almanac satellite position / velocity calculator 28 determines which GPS is currently used based on the satellite position calculated by the almanac satellite position / velocity calculator 28 when the user's position exists. It is determined whether the satellite is a visible satellite, that is, at a position visible to the user, and a predetermined number of satellites (four in the case of three-dimensional positioning) suitable for positioning calculation are selected. The satellite selection calculator 30 sets the carrier frequency of the selected satellite in the receiver 16.

As described above, a GPS satellite to be used for positioning is selected using almanac data. However, when the position of the user is unknown, satellite selection cannot be performed based on the position of the user. If the position of the user has a significant error, it may be unclear whether the GPS satellite is visible or not even if the selection is made using the almanac data, and the calculation carrier frequency may be incorrect so that the GPS satellite cannot be received. Occurs. In such a case, a mode in which all satellites are searched over the entire receivable frequency range without using almanac data (search the sky mode)
to go into.

When ephemeris data is obtained from a predetermined number of satellites, positioning calculation can be performed based on the data. That is, the ephemeris memory 26
By calculating the position and speed of the GPS satellites using the ephemeris data stored in the satellite, the position and speed of each satellite designated by the satellite selection calculation unit 30 for search can be known. This calculation is performed by the ephemeris position / velocity calculation unit 32. Positioning calculation unit 34
Calculates the position and speed of the user based on the satellite position and speed obtained by the ephemeris position and speed calculation unit 32, the pseudorange obtained by the pseudorange calculation unit 18, and the added Doppler obtained by the Doppler calculation unit 22. . Note that the Doppler calculator 22 adds the Doppler frequency obtained by the receiver 16 for a predetermined period, and outputs the addition result as an added Doppler.

[0010] The position and speed of the user obtained in this way are displayed on the display unit 36, used for the user, and supplied to the satellite selection calculation unit 30.

[0011]

However, in the conventional GPS receiver, if the position of the user is unknown or the error is large even if the user holds almanac data, the search-the-sky mode may continue for a long time. . That is, when the search-the-sky mode is executed, the position of the user cannot be obtained until ephemeris data of four satellites necessary for the positioning calculation is collected.
If the power is cut off before that or if any of the satellites instructed to search become unreceivable, the time-consuming search-the-sky mode must be executed.

An object of the present invention is to solve such a problem, and an object of the present invention is to enable the search-the-sky mode to be terminated early.

[0013]

In order to achieve such an object, the present invention provides a method based on received almanac data.
GPS satellite position and velocity and positioning calculation
Frequency of 3 GPS satellites other than 1 satellite required for GPS
Approximately calculate the position of the moving object by recursive calculation based on
Means .

[0014]

According to the present invention, when almanac data is held, a radio wave is received from a certain GPS satellite, thereby obtaining satellite time and receiving three satellites other than the one required for positioning calculation. When the Doppler frequency is obtained, the approximate position of the user is obtained. By using this position for the selection calculation of the satellite and the setting of the reception frequency, the search-the-sky mode can be terminated early.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. The same components as those in the conventional example shown in FIG.

FIG. 1 shows a GPS according to an embodiment of the present invention.
The configuration of the receiver is shown. The feature of this embodiment is that an almanac positioning calculation unit 38 is provided.
The almanac positioning calculation unit 38 obtains the satellite time for one satellite, and the almanac satellite selection calculation unit 28 determines the satellite position and speed based on the almanac data, and can receive three satellites other than the one required for the positioning calculation. When the Doppler frequency is obtained, this is a member that calculates the approximate position of the user based on the satellite position and speed based on almanac data and the added Doppler. The calculation in the almanac positioning calculation unit 38 is performed as follows, and the obtained position has accuracy that can be used for the satellite selection calculation in the satellite selection calculation unit 30, the frequency setting for the reception unit 16, and the like. Therefore, by using this position, the search-the-sky mode can be terminated early.

First, a calculation formula in the almanac positioning calculation unit 38 is derived. Now, i (i = 1,
The added Doppler di of the (2, 3, 4) th GPS satellite is approximately expressed by the following equation (1).

[0018]

(Equation 1) The equation (1) is an equation that ignores the speed of the user, the clock frequency error of the GPS satellite, the ionospheric delay, and the like.
(*, *) Indicates the inner product of the vectors.

By transforming equation (1),

(Equation 2) Becomes here,

(Equation 3) Therefore, the left side of the equation (2) is further transformed as follows.

[0020]

(Equation 4) Therefore, if the right side of Expression (2) is represented by bi,

(Equation 5) Therefore, considering a 4 × 4 matrix A and a vector b (→) having Ai in Expression (5) and bi in Expression (8) as components,

(Equation 6) Is obtained. In the present embodiment, the following expression obtained by modifying this expression (9)

(Equation 7) By performing a recursive calculation by using, the approximate position of the user is calculated from the position and the speed calculated based on the almanac data.

FIG. 2 shows the flow of this calculation, that is, the operation of the almanac positioning calculation unit 38. As shown in this figure, the almanac positioning calculation unit 38 first initializes the user position Pu (→) and the clock error Δf (100), and thereafter executes steps 102 to 106 relating to recursive calculation. ing.

In step 102, the satellite position Pi obtained by the almanac satellite position / velocity calculation unit 28 is calculated.
Each component of the matrix A and the vector b (→) is calculated based on (→), the speed vi (→), and the added Doppler di (i = 1, 2, 3, 4) calculated by the Doppler calculation unit 22. Each component of the matrix A is represented by a vector b
Each component of (→) is calculated by equation (8). In step 104, the vector C is calculated based on the equation ( 12 ).
(→) is calculated. The vector C (→) has a user position Pu (→) and a clock error Δf as components as shown in Expression (6).

Therefore, in step 104,
It can be seen that the position Pu (→) of the user and the clock error Δf are determined. At this point, they have not been determined with good accuracy. Therefore, the calculations after step 102 are repeated using the user position Pu (→) and the clock error Δf obtained in step 104. That is, a recursive calculation is performed.

In step 106, the vector C
It is determined whether all the changes of each component (→) are equal to or smaller than a preset threshold, that is, whether the calculation has converged. If it is determined that the convergence has been achieved, the calculation result is output to the positioning calculation unit 34 and the satellite selection calculation unit 30 and the process ends.

As described above, since the approximate position of the user is obtained while determining the convergence by the recursive calculation, the satellite selection calculation unit 30 is used regardless of the satellite position and the speed calculated based on the almanac data. The position of the user can be obtained with accuracy that can be used for the satellite selection calculation in, the frequency setting for the receiving unit 16, and the like. Therefore, by using this position, the search-the-sky mode can be terminated early.

[0026]

As described above, according to the present invention,
GPS satellite calculated based on received almanac data
The position and velocity of the star and the satellites other than the one required for the positioning calculation
Based on the Doppler frequencies of the three GPS satellites,
Since the position is roughly calculated by recursive calculation , the search-the-sky mode can be terminated early by using this position for selection calculation of a satellite and setting of a reception frequency.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a GPS receiver according to one embodiment of the present invention.

FIG. 2 is a flowchart illustrating an operation of an almanac positioning calculation unit in the embodiment.

FIG. 3 is a block diagram showing a configuration of a GPS receiver according to one conventional example.

[Explanation of symbols]

 16 Receiving part 18 Pseudorange calculating part 20 Satellite orbit data decoding part 22 Doppler calculating part 28 Almanac satellite position and speed calculating part 30 Satellite selection calculating part 32 Ephemeris satellite position and speed calculating part 34 Positioning calculating part 38 Almanac positioning calculating part

Continuation of front page (58) Fields investigated (Int.Cl. ⁷ , DB name) G01S 5/00-5/14 G01C 21/00-21/24 G01C 23/00-25/00

Claims (1)

(57) [Claims] 1. A means for measuring a satellite time which is a transmission time of a radio wave from a GPS satellite and calculating a pseudorange of the GPS satellite based on the time, a means for measuring a Doppler frequency of a radio wave from the GPS satellite, and a GPS satellite Means for calculating the position and velocity of GPS satellites based on almanac data received from
Position and speed of GPS satellites and one satellite required for positioning calculation
Based on the Doppler frequencies of three non-star GPS satellites,
Means for roughly calculating the position of a moving object by recursive calculation, and the position and speed of a GPS satellite calculated based on almanac data and the rough calculation by the rough calculation means
Means for selecting a GPS satellite to be used for positioning based on the position of the moving object; means for calculating the position and speed of the selected GPS satellite based on ephemeris data received from each selected GPS satellite; A GPS receiver comprising: means for calculating a position of a moving object mounted on the basis of a pseudorange, a Doppler frequency, and a position and a speed calculated based on ephemeris data for each selected GPS satellite.