JPH04326079A - Gps receiver - Google Patents

Abstract

PURPOSE:To shorten the time till the catching of a satellite radio wave and to rapidly start the measurement of a position by calculating the Doppler quantity of the satellite radio wave due to the motion of an artificial satellite and altering search frequency on the basis of said Doppler quantity. CONSTITUTION:The transmission radio waves from a plurality of artificial satellites are received by an antenna 1 and converted in frequency in a frequency converting part 5. In a signal processing part 6, search frequency is set on the basis of the reference frequency from a reference frequency oscillator 3 and the Doppler quantity of satellite radio waves due to the motion of the artificial satellites to a receiver is calculated and the search frequency is altered on the basis of the calculated Doppler quantity. The receiving processing of the receiving signal converted in the frequency converting part 5 on the basis of the altered search frequency.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a GPS receiver that detects the position of the receiver by receiving radio waves transmitted from an artificial satellite.

0002

[Prior Art] Conventionally, in this type of GPS receiver,
As shown in Japanese Unexamined Patent Publication No. 63-308587, temperature sensors etc. are placed near a reference frequency oscillator (hereinafter referred to as TCXO), and the outputs of these sensors are used to determine whether the TCXO
The amount of deviation in the output frequency of the satellite is predicted to shorten the time it takes to acquire satellite radio waves.

0003

[Problems to be Solved by the Invention] However, the amount of deviation between the output of the temperature sensor and the output frequency of the TCXO is not a simple relationship. It is necessary to divide the output of the sensor into an appropriate range and store the amount of deviation in the output frequency of the TCXO within this range, which requires a large amount of storage area. Furthermore, since the characteristics of both the temperature sensor and the TCXO change over time, the stored information may have a large error. Furthermore, if such an error occurs, this error will not be detected until positioning is performed, and this error will lengthen the time it takes to acquire satellite radio waves for three or more satellites.

[0004] Therefore, the present invention focuses on the fact that the factor that lengthens the time until satellite radio wave acquisition is not only the deviation of the output frequency of the TCXO, but also the Doppler shift due to the movement of the artificial satellite. The purpose of this is to obtain the Doppler amount of satellite radio waves due to the movement of the satellite, and use this to change the search frequency to shorten the time it takes to acquire satellite radio waves and to start positioning earlier.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an antenna for receiving transmitted radio waves from a plurality of artificial satellites, and an antenna for receiving transmitted radio waves from a plurality of artificial satellites received via this antenna. In a vehicle GPS receiver, the receiving means includes a reference frequency oscillation means for setting a reference frequency, and the reference frequency oscillation means sets a reference frequency. means for setting a search frequency based on the frequency and receiving the transmitted radio waves from the artificial satellite at this search frequency, and calculating the Doppler amount of the satellite radio waves due to the movement of the artificial satellite with respect to the receiver; , and means for changing the search frequency based on the obtained Doppler amount.

[0006]

[Embodiments] The present invention will be described below with reference to embodiments shown in the drawings. FIG. 1 is a block diagram of a vehicle GPS receiver showing an embodiment of the present invention. Antenna 1 captures satellite radio waves from GPS satellites and converts them into electrical signals. This electrical signal is sufficiently amplified by the amplifier 2 and input to the frequency converter 5. In the frequency converter 5, a reference frequency oscillator (hereinafter, TC
The local oscillation frequency obtained by multiplying the output of the XO (XO) 3 by a frequency multiplier circuit 4 and the received signal are combined to perform frequency conversion.

[0007] Note that the frequency conversion is performed not only once but twice.
A configuration may be adopted in which conversion is performed more than once. In the signal processing unit 6, the frequency-converted received signal is processed by a TCXO.
3 is used to demodulate the carrier component and demodulate the pseudo-noise code. This operation is called a search operation, and the state in which demodulation is successful and tracking is called the state in which satellite radio waves are captured. Furthermore, the signal processing unit 6 demodulates the orbit data.
Performs positioning calculation processing.

[0008] The present invention is characterized in that in the signal processing section 6, the process from the search operation to the acquisition of satellite radio waves is made fast. This signal processing section 6 is configured using a microcomputer in order to execute its operations, and executes its operations according to programs for performing various operations described below.

The operation of the microcomputer in the signal processing section 6 will be explained next. FIG. 2 is a flowchart showing the calculation process. First, in step 100, processing for selecting a satellite and calculating the position of the satellite is performed. In this case, different operations are performed during a warm start or hot start and during a cold start. A warm start is a state in which the approximate trajectory data (ormanac data) and the approximate receiver position are stored in the receiver, and the current time is also approximately known. Hot start refers to a state in which detailed orbit data (ephemeris data) is also stored in the receiver. A cold start refers to a state other than the above two states. These ormanac data, approximate receiver position, and ephemeris data have been obtained and stored in the previous processing, and according to the stored information, it is determined which of the above three cases it is.

[0010] At the time of a warm start or a hot start, satellite positions are first calculated from the approximate orbit data, and visible satellites (receivable satellites) are determined from among them. Combinations of these visible satellites that improve positioning accuracy are selected as many as possible to track.

[0011] Furthermore, at the time of a cold start, it is impossible to optimally select a satellite because the satellite position cannot be calculated. Therefore, the selection is such that the satellites with satellite numbers 1 to 32 are sequentially searched.

In the following step 110, step 100
Predict the frequency of satellite radio waves for the satellite selected in . In the case of a warm start or a hot start, the satellite position can be calculated from the approximate orbit data, so the satellite position after an appropriate minute time is calculated from the satellite position determined in step 100, and the satellite/receiver (receiver) position at this minute time is calculated. The velocity vSi of the satellite is determined by the change in the distance between (using approximate receiver position data onboard), and the Doppler amount Δfsi is determined by the following equation based on this velocity vSi of the satellite.

[0013]

[Equation 1] ΔfSi=vSi·fO /C where fO is the satellite radio wave transmission frequency (1575.42 MHz), and C is the speed of light (299892458 m/s).

[0014] Also, step 160 or 1, which will be described later,
TCXO deviation amount △f calculated by the TCXO deviation calculation means of 80 and the Doppler amount △f due to the motion of the satellite.
Considering Si, the predicted frequency f of the satellite radio wave is calculated using the following formula:
Find ri. (ΔfTCXO is set to 0 until it is calculated.)

[0015]

[Equation 2]fri=fO +ΔfSi−ΔfTCXO In this embodiment, the TCXO deviation amount ΔfTCXO refers to the value after frequency multiplication. Therefore, the actual frequency deviation amount of the TCXO is the amount obtained by dividing ΔfTCXO by the multiplier.

Furthermore, in the case of a cold start, it is not possible to obtain the Doppler amount ΔfS due to the motion of the satellite, so the predicted frequency fri of the satellite radio wave is obtained using the following formula.

[0017]

[Math. 3] fri=fO −△fTCXO Followed step 1
In step 20, a search operation is performed for the satellite selected in step 100 and whose frequency of satellite radio waves was predicted in step 110. This step involves acquiring satellite radio waves or
Even if we perform correlation measurements on all phases of the pseudo-noise code,
Terminates if no correlation is obtained.

In the following step 130, processing is distributed according to the result of step 120. That is,
If the satellite radio waves can be captured in the search operation in step 120, the process proceeds to step 150, and if the satellite radio waves cannot be captured, the process proceeds to step 140.

If the acquisition of the satellite radio wave fails and the process proceeds to step 140, an operation is performed to control the search frequency in the vicinity of the predicted satellite radio frequency obtained in step 110. The Doppler amount due to satellite motion causes errors depending on the accuracy of the approximate orbit data, receiver clock, and approximate position data of the receiver. Furthermore, the amount of deviation of the TCXO cannot be corrected for short-term fluctuations caused by factors such as temperature. Furthermore, satellite radio waves may not be captured because an error occurs between the predicted frequency of the satellite radio waves and the actual frequency due to Doppler of the satellite radio waves caused by the movement of the vehicle. For this reason, it is necessary to perform a search operation centered on the predicted satellite radio wave frequency to the range of accuracy of the prediction. Furthermore, the frequency at which the search is performed is determined by the performance of determining the correlation of pseudo-noise codes up to how many Hz shifted signals.

The method of controlling the search frequency differs in the following three states. The first is at a warm start or hot start, the second is at a cold start, and the third is after positioning has started.

Here, as a feature of the present case, the search frequency is not controlled uniformly within the search range, but as shown in FIG. Reduce frequency accordingly. This is in consideration of the environment unique to vehicles, such as buildings blocking satellite radio waves. (1) At the time of warm start or hot start, search is performed alternately in the ± direction in units of fstp1 from fri to fri±fnlmt1, centering on the predicted frequency fri of the satellite radio wave.

■Fri ± fnlmt1, mainly fri
Search alternately in ± direction in units of fstp1 until f
ri+(2+i)・fcstp〜fri+(3+i)・
fcstp and fri-(2+i)・fcstp~fri
−(3+i)・fcstp frequency band alternately fstp
Search by 1 unit. (i=0) ■■ processing i=1,
Increase by 2 or 3. (The carrier frequency shift amount is up to ±fwlmt) Return to ■■.

Actual control is performed according to the flowchart shown in FIG. Note that fnlmt1 indicates a range to be searched frequently, and is set based on the accuracy of fri and the short-term fluctuation amount of the TCXO frequency.

[0024] fstp1 indicates a search unit, and is set based on the amount of carrier frequency shift within a captureable range. fc
stp indicates a division unit of a frequency band that is searched infrequently.

[0025] fwlmt is set from the maximum value of the Doppler amount and the TCXO shift amount due to satellite motion. The search frequency is changed within the range shown in FIG. 5 by the above-mentioned processes (1) to (2). (2) At the time of cold start, assuming that the satellite radio frequency prediction value fri of all satellites is 0, fs
Search in ± direction in units of tp2 up to maximum fwlmt. In this case, the search is performed in the numerical order shown in FIG. Note that fstp2 indicates a search unit, and fstp2>
fstp1.

[0026] At this cold start, it is not possible to obtain the predicted frequency fri of the satellite radio wave, so the search width must be the width of all possible Doppler amounts. Furthermore, if the amount of deviation of the TCXO has not been determined, the search width must include the predicted maximum value of the amount of deviation. Therefore, the search time becomes very long. For this reason, the search unit is set larger than at warm start and hot start (f
stp2>fstp1). As a result, satellites with weak signals cannot be captured, but satellites with strong signals can be captured at high speed. Once one satellite is captured, the TCXO shift amount calculation means 1, which will be described later, calculates the TCXO shift amount. By determining this and collecting approximate orbit data from this satellite, it becomes possible to shorten the time it takes to capture the satellite thereafter.

Actual control is performed according to the flowchart shown in FIG. (3) After positioning starts, ±fnlmt2 is set around the predicted satellite radio frequency fri.
The search is performed alternately in both directions up to fstp1. In this case, the search is performed in the numerical order shown in FIG. Note that fnlmt2 indicates the search range, and fnlm
t2 >fnlmt1.

When positioning is performed, the clock of the receiver is accurately corrected and the receiver position is also accurate. moreover,
Since the TCXO deviation amount can also be accurately determined by the TCXO deviation calculation means 2, which will be described later, the search width can be narrowed and the time required to capture a new satellite's radio wave can be sped up.

The actual control is similar to that shown in the flowchart of FIG. 7, but fstp2 is changed to fstp1, fw
The difference is that the process is executed with lmt set to fnlmt2. The above is the operation of step 140, but the search width, unit, etc. values fstp1, fstp2, fn
lmt1 and fnlmt2 can be set in various ways depending on the system.

As described above, steps 120, 130, 14
The operation 0 is repeated until the satellite radio wave is successfully acquired. If the satellite radio wave acquisition is successful, control continues with step 1
Moved to 50. In step 150, the number of satellites whose satellite radio waves have been successfully captured is managed, and processing is divided depending on whether the number is two or less or three or more. If there are two or less, the process moves to step 160, and if there are three or more, the process moves to step 170.

In step 160, the receiver clock is approximately corrected using the time information contained in the satellite radio wave, and the Doppler amount due to the satellite motion is determined from this and the above-mentioned general or detailed orbit data. The difference between this Doppler amount and the actually measured frequency is determined as the amount of deviation of the TCXO. Furthermore, if there are two satellites that have been successfully captured, the average of the TCXO deviations determined for each satellite is calculated, and this value is taken as the TCXO deviation amount. Further, in this step, the search frequency control in step 140 is also initialized. Initialization means returning the search frequency to the predicted satellite radio frequency value.

The amount of deviation of the TCXO obtained here includes errors due to reasons such as the movement of the vehicle not being taken into account and the receiver position being inaccurate. In step 150,
If it is determined that there are three or more satellites that have been successfully captured,
In step 170, satellite radio wave tracking and positioning processing is performed. Positioning is similar to that described in Japanese Patent Laid-Open No. 198887/1987.

At step 180, the latest receiver position determined at step 170 is used to accurately determine the amount of deviation of the TCXO. For example, after three-dimensional positioning using four satellites to determine latitude, longitude, and altitude, the determination is performed as follows. The position of the receiver determined by positioning is used as the origin of the coordinates, and the ENU coordinates are determined with the east as the E axis, the north as the N axis, and the upward direction as the U axis. Find the position of each satellite on this ENU coordinate,
Find the direction cosine of the unit vector from the receiver to the satellite to each coordinate axis and create the following matrix.

[0034]

[Equation 4] However, n1 represents the direction cosine of the unit vector toward the satellite in the ENU coordinate system toward the N axis, and ei represents the EN
In the U coordinate system, ui indicates the direction cosine of a unit vector toward the satellite toward the e-axis, and ui indicates the direction cosine of the unit vector toward the satellite toward the u-axis in the ENU coordinate system.

The difference between the actually measured frequency of the radio wave of satellite i and the Doppler amount Δfsi due to the movement of the satellite described above is caused by the movement of the vehicle and the deviation of the TCXO. fdu this
When i is assumed, this fdui can be obtained by the following equation.

[0036]

[Equation 5] fdui=actual frequency−(fo+Δfsi) From equations 2 and 3,

[0037]

[Equation 6] However, fn, fe, fu are vehicle speeds n, e,
This is the Doppler-converted value of the u-axis component.

Therefore, the TCXO deviation amount ΔfTCXO can be accurately determined using the above equation. Furthermore, after two-dimensional positioning using three satellites to determine latitude and longitude while fixing the altitude, the following equation is used in the same way as three-dimensional positioning.

[0039]

[Equation 7] Note that the TCXO obtained in step 180
The deviation amount ΔfTCXO is stored in a storage device (backed up by a battery) in the signal processing unit 6, and this stored value is used in the frequency prediction calculation in step 110 when the vehicle is started next time. .

In the above embodiment, a TCXO is used as the reference frequency oscillator, but other oscillation means such as a crystal oscillator may be used instead. Furthermore, the above-mentioned device that accurately predicts the frequency of satellite radio waves can be applied to GPS receivers for uses other than vehicles.

[0041]

[Effects of the Invention] As described above, according to the present invention, the Doppler amount of satellite radio waves due to the motion of an artificial satellite is determined, and the search frequency is changed based on this to perform a search operation for radio waves from the artificial satellite. This has the advantage of being able to obtain a search frequency appropriate for the deviation of the reference frequency, shorten the time it takes to acquire satellite radio waves, and speed up the start of positioning.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a GPS receiver to which the present invention is applied.

FIG. 2 is a flowchart showing arithmetic processing by a microcomputer in a signal processing section.

FIG. 3 is an explanatory diagram for explaining search frequency control.

[Figure 4] Thermostat at warm start and hot start
3 is a flowchart showing frequency control.

[Figure 5] Thermostat at warm start and hot start
FIG. 2 is an explanatory diagram for explaining frequency control.

FIG. 6 is an explanatory diagram for explaining search frequency control at the time of cold start.

FIG. 7 is a flowchart showing search frequency control at the time of cold start.

FIG. 8 is an explanatory diagram for explaining search frequency control after starting positioning.

[Explanation of symbols]

1 Antenna 2 Amplification section 3 Reference frequency oscillator 6 Signal processing section

Claims (1)

[Claims] [Claim 1] An antenna for receiving transmitted radio waves from a plurality of artificial satellites, and a receiving means for receiving and processing the transmitted radio waves from the plurality of artificial satellites received via the antenna to determine the position of a vehicle. In the GPS receiver, the receiving means includes a reference frequency oscillation means for setting a reference frequency, sets a search frequency based on the reference frequency set by the reference frequency oscillation means, and uses the search frequency to A device for receiving radio waves transmitted from a satellite, comprising means for obtaining a Doppler amount of the satellite radio wave due to the movement of the artificial satellite with respect to the receiver, and means for changing the search frequency based on the obtained Doppler amount. A GPS receiver characterized by: