JP2001264409A - Multipass judgement method for car navigation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To directly judge whether a received GPS signal is a multipass or not by observing the signal, thereby eliminating the influence of the multipass from the positioning solution of GPS. SOLUTION: The estimated Doppler shift amount Δfr of a received GPS signal is calculated based on the position and velocity victor (ud) of an own vehicle calculated by a dead reckoning function according to the definition, represented by Δfr=-fT. (v-ud).a/c} (wherein v is the velocity vector of a GPS satellite; a is a unit directional vector; and c is the velocity of light). The carrier wave of the received GPS signal is measured to obtain a measured Doppler shift amount Δf. A difference Δf' between Δf and Δfr is calculated, and when Δf' is equal to or larger than a prescribed threshold value, it is judged that the received signal is a multipass, and a GPS positioning operation is performed after eliminating the GPS signal judged as a multipass.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for determining whether or not a received GPS signal is multipath in a car navigation system.

[0002]

2. Description of the Related Art GPS in car navigation systems
The receiver measures the distance (pseudo distance) between the GPS satellite and the GPS receiver itself (own vehicle) using the GPS signal, and calculates the position of the host vehicle geometrically using the obtained pseudo distance. It is carried out. However, in receiving a GPS signal in a car navigation device, a GPS receiver may receive a GPS signal reflected by a building or the like (hereinafter, referred to as a multipath). When a GPS receiver measures a pseudorange by a multipath signal, a pseudorange different from a pseudorange measured by a signal directly coming from a GPS satellite (hereinafter, referred to as a direct signal) is measured, and as a result, an erroneous pseudorange is measured. A positioning solution is calculated. This phenomenon is called a multipath failure, and is a problem in receiving a GPS signal of a car navigation device.

[0003] It is extremely difficult to observe the GPS signal itself received by the GPS receiver and determine whether or not the signal is multipath, and conventionally, it has not been possible to make an accurate determination. . On the other hand, in car navigation systems, G such as dead reckoning (autonomous navigation)
The accuracy as a car navigation device is improved by providing positioning means different from PS positioning and comprehensively judging these positioning results. However, even when such a determination method is used, it is not possible to directly determine whether or not the GPS positioning solution includes the influence of multipath.
The PS positioning solution may be selected as the position of the own vehicle.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and directly determines whether or not a received GPS signal is a multipath signal by observing the GPS signal. To eliminate the effects of multipath from

[0005]

Means for Solving the Problems The conceptual diagram of multipath is as follows.
It is shown as in FIG. As shown in the figure, a multipath that reflects a building or the like and arrives at the own vehicle arrives at the own vehicle through a path different from the direct signal.

FIG. 2 shows a state in which the own vehicle is receiving a multipath while traveling. In FIG. 2, the GPS satellite 2 moves at a speed vector v, and the vehicle 1 moves from a position P ₀ to a position P _0.
Moving at velocity vector u _d towards _1. GPS
Focusing on the relationship between the satellite 2 and the own vehicle 1, the own vehicle 1 and the GPS satellite 2 are approaching, and the length of the path of the direct signal coming from the GPS satellite 2 is decreasing. On the other hand, the vehicle 1 as the distance from the mobile to building 3 to P ₁ from the position P _0, the length of the path of the multipath is increasing. That is, in this case, the Doppler shift amount obtained by observing the carrier frequency of the multipath signal, the Doppler shift amount in the state where the vehicle is moving at a velocity vector u ₁ towards the position S0 in Fig. 2 to S1 Is equivalent to Therefore, the Doppler shift amount of the carrier when observing the multipath is different from the Doppler shift amount of the carrier when observing the direct signal.

Here, the GPS signal is observed and the measured
The shift amount Δf is determined, and the distance between the GPS satellite and the own vehicle is determined.
Based on the relative velocity vector,
Estimated Doppler shift amount Δf_rAnd the difference Δ
f ′, Δf ′ = Δf−Δf_r  Is obtained, the received GPS signal is a multipath signal
If there is, Δf becomes Δf_rAnd a different value. Therefore, Δ
f ′ is set to a predetermined threshold value, and Δf ′ is equal to or larger than the predetermined threshold value.
Received, the received GPS signal is a multipath signal.
Can be determined.

In a situation where the GPS satellite and the own vehicle move, the Doppler-shifted carrier frequency f _R of the GPS signal received by the own vehicle is expressed by the following equation (1).

[Number 1] _{f R = f T {1- (} v r · a) / c} , however, _{f T} is not the Doppler shift, the original carrier frequency. v _r is the relative velocity vector between the GPS satellite and the vehicle. a is a unit direction vector from the own vehicle to the satellite. c is the speed of light.

If the speed vector of the GPS satellite is v and the speed vector of the own vehicle is u, the relative speed vector v _r
Can be expressed as v _r = v−u. Therefore, the Doppler shift amount of the carrier wave is expressed by the following equation (2) from the above equation (1).

## EQU2 ## Doppler shift amount = f _R −f _T = −f _T ·
{(vu) a / c}

[0010] Next, as shown in FIG.
Signal is being received, the direct signal
The estimation of the puller shift amount is performed as follows. Car of own car 1
-Navigation devices include vehicle speed pulse signals, gyrosa
The position of the vehicle by the dead reckoning function using sensors
And the velocity vector can be calculated. This dead
Vehicle speed vector calculated by the reckoning function
U _dfar. Also, even for multipath signals,
Obtain orbit information (ephemeris) of GPS satellites from signals
It is possible to get GPS satellites from this ephemeris.
Calculate the velocity vector v. Also this ephemeris
And the vehicle position calculated by the dead reckoning function
Gives a unit direction vector a toward the GPS satellites.
You. By substituting these values into the right side of Equation 2,
Estimated Doppler shift amount Δf of direct signal_r, Below
Notation 3

Equation 3] obtained by calculation of _{Δf r = -f T · {(} v-u d) · a / c}.

According to the above equation 3, the estimated signal of the direct signal is obtained.
Puller shift amount Δf_rCan be calculated by
Measured Doppler obtained by observing GPS signals
The difference Δf ′ from the shift amount Δf is obtained as follows. Δf ′ = Δf−Δf_r  Δf_rIs the Doppler shift for the direct signal
And the measured Doppler shift amount Δf
Is the case where multipath is observed, Δf and Δ
f_rWill be different. Therefore, a predetermined value for Δf ′
By setting a threshold of Δf ′, when Δf ′ is larger than this threshold,
If the received signal is multipath
Can be.

When the absolute value of .DELTA.f 'exceeds a predetermined value, it is determined that the path is a multipath. For a GPS satellite having .DELTA.f' equal to or less than the predetermined value, it is determined that the path is not a multipath. By performing the GPS positioning operation using only the GPS satellites determined as above, a GPS positioning solution free from multipath effects can be obtained.

[0013]

FIG. 3 shows a configuration of a car navigation apparatus for executing a multipath determination method and a positioning GPS satellite determination method according to the present invention. The car navigation device 20 in FIG. 3 includes the GPS antenna 8, the GPS receiver 21, and the NAVI_CPU1.

In the GPS receiver 21, the RF unit 12
Mixes the GPS signal captured by the GPS antenna 8 with the frequency of the local oscillator 13, downconverts the signal, and converts the signal into an intermediate frequency signal. The arithmetic unit 22 synchronizes with the carrier of the GPS signal, further demodulates the signal, obtains ephemeris and other data from the GPS message included in the GPS signal, and executes a GPS positioning operation. The arithmetic unit 22 includes a plurality of control units (channels) for synchronizing and demodulating a GPS signal, and simultaneously captures a plurality of GPS satellites.

The operation unit 22 receives the output signal of the gyro sensor 5, the vehicle speed pulse signal, and the back signal, performs dead reckoning based on these signals, and calculates the position and speed vector of the own vehicle. The calculation unit 22 also calculates the positioning result of the vehicle position based on the dead reckoning function and the GP.
By estimating the error value included in each positioning result and comparing the positioning result of the own vehicle position based on the S positioning, the positioning result determined to be more accurate is determined by NAVI_CPU1 together with the error estimation value and other information. Output to

The NAVI_CPU 1 reads map information from a map database (not shown), performs map matching on the positioning result input from the GPS receiver 21, and determines the final position of the vehicle. Also, NA
The VI_CPU 1 executes all processes required for a car navigation device, such as a route search.

FIG. 4 shows an operation flowchart for determining whether or not the received GPS signal is to be subjected to the GPS positioning calculation in the GPS receiver 21. G
In the PS receiver 21, the arithmetic unit 22 obtains the frequency of the carrier by synchronizing with the carrier of the GPS signal, and calculates the difference from the original carrier frequency of the GPS signal to obtain the measured Doppler shift amount Δf. Calculate (S30
1). Next, the arithmetic unit 22 calculates the velocity vector u _d of the vehicle by dead reckoning capabilities, to calculate the velocity vector v of the GPS satellite from the ephemeris obtained from the GPS signals. Further, a unit direction vector a from the own vehicle to a GPS satellite is obtained from the own vehicle position calculated by the dead reckoning function and the ephemeris. Furthermore, based on these values, the definition of the number 3, and calculates the estimated Doppler shift Delta] f _r according _{Δf r = -f T · {(} v-u d) · a / c} (S
302).

Next, the arithmetic unit 22 calculates the measured Doppler shift.
Δf and estimated Doppler shift Δf_rΔf ′ = Δf−Δf_r  (S303), and when Δf ′ is equal to or larger than a predetermined threshold value,
(S304: YES), the received GPS signal
It is determined to be a multipath and is excluded from the target of GPS positioning calculation.
Removed (S305). When Δf ′ is less than a predetermined threshold
(S304: NO), the received GPS signal is
It is determined that it is not a chip path, and it is targeted for GPS positioning calculation
(S306).

The arithmetic unit 22 performs the processing shown in FIG. 4 on each of the received GPS signals, and executes the GPS positioning operation using only the GPS signals that have been subjected to the positioning operation (ie, non-multipath). Therefore, the influence of multipath is excluded from the GPS positioning solution calculated by the calculation unit 22.

[0020]

As described above, according to the present invention,
The presence or absence of multipath can be determined based on the difference between the measured Doppler shift amount obtained by observing the GPS signal and the estimated Doppler shift amount for the direct signal. In this case, the estimated Doppler shift amount can be calculated from the dead reckoning function in accordance with the definition of Equation (3). By performing the GPS positioning operation using the GPS signal determined not to be multipath by this determination method, the influence of multipath is excluded from the GPS positioning solution,
A highly accurate GPS positioning solution can be obtained.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a multipath.

FIG. 2 is a conceptual diagram for explaining a multipath Doppler shift.

FIG. 3 is a block diagram of a car navigation device that executes the multipath determination method of the present invention.

FIG. 4 is a flowchart illustrating an operation for determining whether a received GPS signal is to be subjected to GPS positioning calculation.

[Explanation of symbols]

 Reference Signs List 1 own vehicle 2 GPS satellite 3 building 5 gyro sensor 8 GPS antenna 12 RF unit 13 local oscillator 21 GPS receiver 22 operation unit 25 NAVI_CPU1

Claims (3)

[Claims] 1. A GPS signal obtained by measuring a carrier of a GPS signal.
Calculated based on the measured Doppler shift amount Δf of the carrier wave and the relative velocity vector between the GPS satellite and the vehicle
Estimated Doppler shift amount Δf of carrier_rDifference with
Minute Δf ′, Δf ′ = Δf−Δf_r  Is used to determine the presence or absence of multipath based on
Multi-pass judgment in car navigation system
Method. 2. A vehicle speed vector u _d calculated based on a dead reckoning function, a GPS satellite speed vector v calculated based on a GPS satellite orbital information (ephemeris), based on the dead reckoning function. vehicle position calculated is calculated from the GPS satellite ephemeris, unit direction vector a from the vehicle to the GPS satellite, on the basis of, the estimated Doppler shift _{Δf r, Δf r = -f T} · { _{(v-u d) · a} / c} , _however, f T: the original carrier frequency c of the GPS signal: of claim 1, wherein the calculating at the speed of light definitions,
A multipath determination method in a car navigation device. 3. A determination method according to claim 1 or 2, wherein it is determined whether or not the received GPS signal is multipath, and only the GPS satellites determined to be non-multipath are subjected to positioning calculation. A method for determining a positioning GPS satellite.