JP2000266836A - Method for compensating for gps multipath - Google Patents

Abstract

PROBLEM TO BE SOLVED: To compensate for a multipath without increasing a sampling frequency and without adding hardware. SOLUTION: With a movement velocity (v) of a mobile station in the range of a lower limit velocity (vmin) and an upper limit velocity (vmax) (No in S1 and No in S3), a loop bandwidth (Bl) of a DLL is increased in proportion to the movement velocity (v) (S6). When the movement velocity (v) of the mobile station is not lower than the upper limit velocity (vmax) (Yes in S1), the loop bandwidth (Bl) of the DLL is set to its upper limit (Blmax) (S2). When the movement velocity (v) of the mobile station is not higher than the lower limit velocity (vmin) (Yes in S3), the loop bandwidth (Bl) of the DLL is set to its lower limit (Blmin) (S4). When the movement velocity (v) of the mobile station is not higher than the lower limit velocity (vmin), waves from GPS satellites of a low angle of elevation are cut (S5).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a GPS (Global Positioning System) for a plurality of
m) GPS for detecting the current position of the user's mobile station by receiving radio waves radiated on the earth from a satellite
More particularly, the present invention relates to a method for compensating for a multipath that receives not only a direct wave directly received from a GPS satellite but also a reflected wave received with a slight delay via various reflection paths.

[0002]

2. Description of the Related Art As is well known, GPS (Global Positio
ning System) is a satellite positioning system using military satellites managed by the United States Department of Defense composed of a total of 24 non-geostationary satellites, four in each of six orbital planes at an altitude of about 20,000 km. The non-geostationary satellite (military satellite) is called a GPS satellite. If radio waves (signals) from four GPS satellites are received, three-dimensional positioning becomes possible. By the way, three GPS
If radio waves (signals) from satellites are received, two-dimensional positioning is possible.

[0003] In other words, GPS is a global positioning system that has been launched by the United States Department of Defense, consisting of 24 artificial satellites (GPS satellites), ground control stations, and user mobile stations. By using this global positioning system, the distance between a mobile station and three or more GPS satellites is measured from the time required for radio waves to arrive, and the position of the mobile station, and further, the moving direction and speed are obtained. be able to. This global positioning system was originally intended for military use, but today,
Widely applied to car navigation systems and the like.

[0004] Here, car navigation refers to the display of the position of the car being driven in real time on the map of the onboard vehicle, the display of road traffic information such as travel time, and the optimization of the destination. This means calculating the route and providing it to the driver.

A car navigation system currently used calculates the latitude, longitude, altitude and time when four or more GPS satellites are captured, and when only three GPS satellites can be captured, the altitude is fixed. Calculate latitude, longitude and time. When only two GPS satellites can be captured, the time of the internal clock is used, the latitude and longitude are calculated with the altitude fixed, and one GPS satellite is calculated.
An error display is provided when only a satellite or no GPS satellite can be acquired (Japanese Patent Application Laid-Open No. 9-1990).
-236650).

[0006] Japanese Patent Application Laid-Open Nos. 10-48311, 10-48312, 10-48313
JP-A-10-48314, JP-A-10-48314
No. 48315, JP-A-10-48316, and the like describe a GPS satellite.

That is, the GPS satellite is equipped with an atomic clock of a highly stable rubidium oscillator of 10 ^-13 / day (10 nanoseconds / day) and a cesium oscillator as a precision time standard.
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.

The navigation signal transmitted from the GPS satellite is a PSK (Phase Shift Keying) wave that is spread spectrum modulated by a PN (Pseudo Noise) code, and a carrier wave of the PSK wave. Has a first carrier (L.sub.L) having a carrier frequency of 1575.42 MHz.
1) and the carrier frequency is 60/77 times that of 1227.
Two types of 6 MHz second carrier (L2) are used. On the other hand, P code (Precision Code) is used for PN code.
And C / A code (Clear and Acquisition Code). The C / A code has a bit rate (chip rate) of 1.023 Mbps, a period of about 1 millisecond, and a first rate.
Only the carrier L1 is used. P code is 1 of C / A code
It has a bit rate of 10.23 Mbps which is 0 times,
A cycle of one week uses not only the first carrier L1 but also the second carrier L2. By using the P code, ionospheric propagation delay correction is performed, and precise positioning is enabled.

[0010] As described above, in order for the user's mobile station to determine its almost accurate current position, it is sufficient to capture at least four GPS satellites. On the other hand, mobile stations move not only in suburbs but also in urban areas. In the suburbs, there are few buildings such as high-rise buildings, there are few objects blocking the radio wave propagation path, and it is easy for mobile stations to capture four or more GPS satellites.

On the other hand, in urban areas, buildings such as high-rise buildings are densely packed and there are many objects blocking the radio wave propagation path, so that it is extremely difficult for a mobile station to capture four or more GPS satellites. It is. Also, in an urban area, even if a GPS satellite can be captured, if the elevation angle of the GPS satellite is low, the mobile station will not only receive direct waves (desired waves) from the low-elevation GPS satellites but also high-rise buildings. Also receives the reflected waves reflected by the building. Therefore, the mobile station often measures an incorrect current position. This is called a positioning error due to multipath.

FIG. 4 shows a case where a positioning error occurs due to multipath. As shown in FIG. 4, mobile station M and building B
Are separated by a distance of 150 m, and the path difference, that is, the multipath delay is 300 m. In such a situation, the mobile station M receives the direct wave Wd from the GPS satellite S.
It is also assumed that not only the reflected wave Wr reflected by the building B is received. In such a case, the mobile station M cannot determine the position of the true position, and as the measured position, the position of the mobile station M is 1 position from the true position.
A position distant by 50 m will be erroneously measured.

The reason why such a multipath causes a positioning error will be described below in detail.

As described above, the PSK from the GPS satellite
A PN code (C / A code) is transmitted on a wave, but a GPS receiver mounted on a mobile station receives the transmitted PN code as a received PN code, and receives the received PN code and the received PN code. Local PN code generated inside the receiver (C /
(A code) for synchronization. To achieve this synchronization, a delay locked loop (DLL) is employed. In other words, the received PN code is tracked using the DLL.

[0015] As shown in FIG.
A first multiplier 11 for correlating the N code with the local PN code and outputting a first correlation signal a; a delay unit 12 for delaying the local PN code by a predetermined delay time and outputting a delayed PN code A second multiplier 13 for correlating the received PN code and the delayed PN code and outputting a second correlation signal b;
And a low-pass filter (not shown) that obtains the difference between the correlation signal and the second correlation signal and outputs a difference signal c, and a low-pass filter that outputs only a low-frequency component of the difference signal and outputs a filter output signal ( LPF) 15 ', a clock source 16 for outputting a clock signal whose clock frequency changes in response to the filter output signal, and a C / A code generator 17 for generating the internal PN code in response to the clock signal It is composed of

As the predetermined delay time of the delay unit 12, a time Δ (about 0.9775 μsec) corresponding to the reciprocal of the chip rate (1.023 Mbps) is usually selected.
The time Δ is called one chip. A delay device having a one-chip delay time is called a one-chip delay device, and a DLL having a one-chip delay device as a delay device is 1Δ-DLL.
Called. The speed (light speed) of radio waves is about 300,000 km /
Seconds, one chip Δ corresponds to a distance of about 294 m.

On the other hand, when a tracking operation is performed using such a 1Δ-DLL, the above-described positioning error due to multipath is determined by the value of the path difference (multipath delay) between the direct wave and the reflected wave. It does not necessarily occur in the case of. In other words, the actual tracking operation using the 1Δ-DLL is an operation of first bringing up to within ± 0.5 chip in the initial search and following up by tracking. From this, tracking is shifted when there is a multipath delay within one chip as a path difference,
It is not expected to be affected if there is more multipath delay.

This will be described with reference to FIG. 6 and FIG. FIG. 6 shows the response of 1Δ-DLL when there is no multipath, and FIG. 7 shows the response of 1Δ-DLL when a reflected wave having a multipath delay of one chip is added at the same level as the direct wave. 6 and 7, the horizontal axis indicates the relative time (relative distance) in units of one chip of the C / A code, and the vertical axis indicates the normalized size. In FIGS. 6 and 7, a is the first multiplier 1
1, a first correlation signal output from the second multiplier 13, a second correlation signal output from the second multiplier 13, and a subtractor 14
5 shows the difference signal output from the.

When there is no multipath, as is apparent from FIG. 6, the first correlation signal a and the second correlation signal b have a triangular similar shape, but the second correlation signal b Is delayed by a time corresponding to one chip from the first correlation signal. More specifically, the first correlation signal a gradually increases from the point of -1.5 chips, reaches a peak 1 at the point of -0.5 chips, and then gradually decreases to a point of 0.5 chips. It has a waveform that becomes zero. On the other hand, the second correlation signal b gradually increases from the point of −0.5 chip delayed by a time corresponding to one chip from the first correlation signal a,
The waveform has a peak of 1 at the time of 0.5 chip, and then gradually decreases to become zero at the time of 1.5 chip.

Therefore, the difference signal c obtained by subtracting the second correlation signal b from the first correlation signal a is the first correlation signal from the time point of -1.5 chips to the time point of -0.5 chips. As in the case of a, the value increases to 1, but from the time of −0.5 chip to the time of 0.5 chip, the value is obtained by subtracting the second correlation signal b from the first correlation signal a. 1
, Gradually becomes zero at the time point of 0 chip, and further decreases to −1, and becomes 1.
Until the time of 5 chips, the waveform is such that the second correlation signal is reduced to 0 in an inverted form.

Therefore, when there is no multipath, the difference signal c becomes zero at the time of 0 chip (true time), so that 1
Δ-DLL can accurately track the received PN code.

On the other hand, when the reflected wave has a one-chip multipath delay, as shown in FIG. 7, the first correlation signal a and the second correlation signal b have a trapezoidal similarity. Although the second correlation signal b is delayed from the first correlation signal by a time corresponding to one chip. More specifically, the first correlation signal a gradually increases from the point of −1.5 chips, reaches a peak of 1 at the point of −0.5 chips, and reaches 0.5 at the point of −0.5 chips. Maintain peak 1 until time point and then gradually decrease to 1.5
It has a waveform that becomes zero at the time of a chip. On the other hand, the second
The correlation signal b gradually increases from the point of −0.5 chip delayed by a time corresponding to one chip from the first correlation signal a, reaches a peak 1 at the point of 0.5 chip, and becomes 0.5 at the point of 0.5 chip.
1 peak from chip to 1.5 chip
, And then gradually decreases to become zero at 2.5 chips.

Therefore, the difference signal c obtained by subtracting the second correlation signal b from the first correlation signal a is the first correlation signal from the time point of -1.5 chips to the time point of -0.5 chips. As in the case of a, the value increases to 1, but from the time of −0.5 chip to the time of 1.5 chip, the value becomes the value obtained by subtracting the second correlation signal b from the first correlation signal a. ,
It gradually decreases from 1 and becomes zero at 0.5 chip,
Then, the waveform further decreases to −1, and becomes a waveform in which the second correlation signal is reduced to zero in an inverted form from the time point of 1.5 chips to the time point of 2.5 chips.

Therefore, when there is a one-chip multipath delay, the difference signal c becomes zero at a time point shifted by 0.5 chip from the true time point, and the 1Δ-DLL shifts the received PN code in this shifted state. You will be tracking. That is, if the reflected wave has a one-chip multipath delay, a distance equivalent to 0.5 chip as a pseudo distance from the true position, that is, a value added by 147 m is obtained. The above is the reason why a positioning error occurs when there is a multipath. Therefore, as shown in FIG. 4, the distance between the direct wave and the reflected wave is 300 m corresponding to almost one chip.
It will be appreciated that a path difference of 150 m will result in a positioning error of 150 m.

Conventionally, as a method for reducing the positioning error due to such multipath, the following two methods are used.
Two methods are employed. A first conventional method is to reduce the bandwidth of a delay locked loop (DLL), and a second method is to reduce the bandwidth of a delay locked loop (DLL).
In the conventional method, the slope of the correlation signal is obtained and driven to a true synchronization point.

That is, in the first conventional method, not one-chip delay unit 12 but one-chip delay unit
This is a method using a delay device shorter than the chip Δ. Thereby, the time difference between the first correlation signal a and the second correlation signal b in FIG. 6 is shortened, and the positioning error can be reduced accordingly. For example, the delay time of the delay unit is set to 0.
By setting 1Δ to 0.05Δ, the positioning error is reduced to 1/1.
It can be reduced from 0 to 1/20.

The second conventional method is a method in which a slope of a correlation curve between a first correlation signal a and a second correlation signal b is obtained, and a true synchronization point is obtained from an intersection of the curves. According to the second conventional method, when a multipath occurs, the slope of the correlation curve differs between the first correlation signal a and the second correlation signal b, and the normal D curve assumes that the slope is the same.
LL can improve that a true synchronization point cannot be found.

[0028]

However, in the first and second conventional methods described above, both increase the sampling frequency and require additional hardware. As a result, these conventional methods can be said to be methods that go against the requirements for miniaturization, low cost, and low power consumption, which are required for GPS receivers.

Accordingly, it is an object of the present invention to provide a GPS receiver capable of compensating for multipath without increasing the sampling frequency.

Another object of the present invention is to provide a GP that can compensate for multipath without adding hardware.
An S receiver is provided.

Still another object of the present invention is to provide a GPS receiver capable of compensating for multipath even if the size, cost and power consumption are reduced.

[0032]

Means for Solving the Problems The present inventor has made intensive studies on how to compensate for multipath without increasing the sampling frequency and without adding hardware. . The present inventor has proposed a fluctuating period (fading bandwidth) Bf of a reflected wave of a radio wave from a GPS satellite.
And the following well-known relation between the loop bandwidth Bl of the DLL and the positioning error due to multipath, and conceived to use this relation.

That is, when Bf / Bl is large, no positioning error occurs, and when Bf / Bl is small, a positioning error occurs. on the other hand,
It is also known that the fading bandwidth (Bf) is proportional to the moving speed of the mobile station (GPS receiver).

Therefore, when the moving speed of the mobile station is low, a positioning error occurs, so that the DLL loop bandwidth B
By reducing l, it is possible to prevent a positioning error from occurring. That is, the multipath resistance can be improved.

When the moving speed of the mobile station is lower than the predetermined speed, the positioning is performed at a predetermined frequency, so that the DL is required.
It is difficult to reduce the loop bandwidth B1 of L below a predetermined limit. Therefore, when the moving speed of the mobile station is lower than the predetermined speed, the loop bandwidth Bl of the DLL is fixed to a predetermined limit. In this case, low-elevation angle GPS satellites are cut to ensure multipath tolerance.

That is, according to the present invention, a GPS for detecting the current position of a user's mobile station by receiving radio waves radiated on the earth from a plurality of GPS satellites orbiting the earth A method for compensating a multipath in a receiver for receiving not only a direct wave directly received from a GPS satellite but also a reflected wave received with a slight delay through various reflection paths. Loop (DL
L), and a GPS multipath compensation method characterized by changing the loop bandwidth of the DLL according to the moving speed of the mobile station is obtained.

In the above GPS multipath compensation method,
When the moving speed of the mobile station is low, it is preferable to reduce the loop bandwidth of the DLL. When the moving speed of the mobile station is higher than the lower limit speed, the loop bandwidth of the DLL is increased in proportion to the moving speed. When the moving speed of the mobile station is lower than the lower limit speed, the loop bandwidth of the DLL is increased. It is preferable to keep it constant at a predetermined limit. In this case, when the moving speed of the mobile station is equal to or lower than the lower limit speed, it is desirable to cut off radio waves from GPS satellites having a low elevation angle.

According to the present invention, there is provided a method of compensating for multipath in a receiver mounted on a mobile station of a spread spectrum communication system and using a delay locked loop (DLL) for correlation detection. A multipath compensation method characterized by changing the loop bandwidth of the delay locked loop according to the speed is obtained.

[0039]

Embodiments of the present invention will be described below in detail with reference to the drawings.

A GPS receiver to which the multipath compensation method according to the present invention is applied will be described with reference to FIG.
The illustrated GPS receiver has a DLL for eight channels so that at most eight GPS satellites can be acquired.
Since each channel has the same configuration, only the DLL of channel 1 is shown in detail here.
Details of the other channels 2 to 8 are omitted, and only the blocks are shown. In addition, this GPS receiver
It is assumed that it is installed on a moving body such as a car and used as a part of a car navigation device. Therefore, the mobile operates as a mobile station.

A radio wave emitted from a GPS satellite (not shown) is received by an antenna 21 and a low noise amplifier (LN).
A) After being amplified at 22, a local oscillator 24 is
And is converted into an intermediate frequency signal by mixing with the local oscillation signal of the radio frequency. This intermediate frequency signal is supplied to the amplifier 2
The signal is amplified at 5 and the gain is controlled by an automatic gain controller (AGC) 26, and then supplied to the DLL 10 of each channel.

The DLL includes a first multiplier 11, a one-chip delay unit 12, a second multiplier 13, a subtractor 14, a low-pass filter (LPF) 15, and a first numerically controlled oscillator (LPF) serving as a clock source. In addition to the NCO 16 and the C / A code generator 17, a second numerically controlled oscillator (NCO) 18 and a mixer 19 are provided. The illustrated DLL has substantially the same configuration as that shown in FIG. 5 except for the second numerically controlled oscillator 18 and the mixer 19. Therefore, in the following, for the sake of simplicity, only the differences will be described.

The signal output from the automatic gain controller 26 is mixed by the mixer 19 with the intermediate frequency local signal output from the second numerically controlled oscillator 19 and converted into a baseband signal. This baseband signal is a signal representing a reception PN code (C / A code). The part for processing the baseband signal is substantially the same as the DLL shown in FIG. 5 described above, and thus the description thereof will be omitted. However, the low-pass filter 15 is configured so that the bandwidth Bl of the DLL 10 can be varied.

Next, the configuration of the low-pass filter 15 for varying the bandwidth Bl of the DLL 10 will be described.

The difference signal output from the subtractor 14 indicates the phase difference between the transmitting PN code and the receiving PN code. The value of the phase difference is in the range of −1023 to 1023, and corresponds to a phase error of −π to π [rad], respectively. Although not shown, the low-pass filter 15 includes a first multiplier for multiplying the difference signal output from the subtractor 14 by a coefficient (2π / 1023) to obtain the phase error. A phase error is obtained from the output of the first multiplier. The low-pass filter 15 also includes a second multiplier (not shown) for multiplying the obtained phase error by a coefficient (B1 · T) that determines the bandwidth of the loop.
Here, B1 represents a loop bandwidth to be varied as described above, and T represents a sampling period (in this example, 1 millisecond). The low-pass filter 15 further adds the carrier frequency error component fe obtained from the carrier lock loop (not shown) and the sampling period T
Is provided with an adder (not shown) for adding the multiplication result (fe · T). The addition result output from the adder is applied to a phase setting input terminal of a first numerically controlled oscillator (NCO) 16 as an output signal of the low-pass filter 15.

Next, an example of the operation of 1Δ-DLL when the loop bandwidth Bl is made variable will be described.

First, the case where Bl = 1 kHz will be described. In this case, the coefficient (Bl · T) becomes 1, and all the phase errors are applied to the phase setting input terminal of the first numerically controlled oscillator (NCO) 16 in one sampling.
For this reason, the phase error is immediately tracked, but actually, the operation of the loop becomes unstable due to the presence of noise and the like. Therefore, no such loop bandwidth is used. In other words, the case where Bl = 1 kHz is equivalent to the case where there is no loop filter.

Next, the case where B1 = 10 Hz will be described. In this case, the coefficient (Bl · T) is 0.01,
1/100 of the phase error will be updated by one sampling. In other words, by performing sampling 100 times, all the phase errors have finally been updated. That is, it takes 100 milliseconds to finish following the instantaneous phase error.

Finally, the case where Bl = 1 Hz will be described. In this case, the coefficient (B1 · T) becomes 0.001, and when considered in the same way as the case of B1 = 10 Hz, 1/1000 of the phase error is updated by one sampling, and the instantaneous phase error is It will take one second to follow.

The illustrated GPS receiver further includes a CPU 3
1, ROM 32, RAM 33, and clock generator 3
4 is provided. The clock generator 34 supplies a clock signal for internal timing to the CPU 31. CPU31
Are the ROM 32, the RAM 33, and the D of each channel.
It is connected to the LL10 and to an external electronic device (not shown) via an external interface.
The CPU 31 performs processing according to a program stored in the ROM 32. For example, the CPU 31 supplies a control signal to the second numerically controlled oscillator 18 of the DLL 10 of each channel and fetches a filter output signal output from the low-pass filter 15. Further, the CPU 31 determines the bandwidth Bl of the DLL 10 and sets the bandwidth Bl in the low-pass filter 15 as described later.

Next, a GPS multipath compensation method according to the present invention will be described. Here, the fluctuation period (fading bandwidth) of the reflected wave of the radio wave from the GPS satellite is Bf, D
Let the loop bandwidth of LL10 be denoted by B1. Fading bandwidth Bf and DLL 10 loop bandwidth Bl
It is known that the following relationship exists between the position error and the positioning error due to multipath.

That is, when Bf / Bl is large (for example,
(Bf / Bl ≧ 5) No positioning error occurs, and if Bf / Bl is small (for example, Bf / Bl <5), a positioning error occurs.

On the other hand, it is also known that the fading bandwidth Bf has the following relationship with the moving speed v of the mobile station (GPS receiver).

Bf ∝ (v / λ) where λ is the wavelength of the radio wave emitted from the GPS satellite, and is equal to the speed (light speed) C of the radio wave divided by the carrier frequency f 0 of the radio wave (λ = C / F0). This is due to the Doppler effect. That is, the fading bandwidth Bf is proportional to the moving speed v of the mobile station.

Therefore, when the moving speed v of the mobile station is low, a positioning error occurs. By narrowing the loop bandwidth Bl of the DLL, it is possible to prevent the positioning error from occurring. That is, the multipath resistance can be improved.

When the moving speed v of the mobile station becomes lower than a predetermined speed (hereinafter referred to as a lower limit speed vmin),
In order to perform positioning at a predetermined frequency, it is difficult to narrow the loop bandwidth Bl of the DLL 10 below a predetermined limit. Therefore, when the moving speed v of the mobile station is lower than the lower limit speed vmin, the DLL loop bandwidth Bl is fixed to a predetermined limit. In this case, it is preferable to cut low-elevation angle GPS satellites in order to secure multipath resistance.

Here, how to cut a low-elevation angle GPS satellite will be described. As previously mentioned,
When actually performing positioning, if radio waves from four or more GPS satellites can be received, positioning is performed by selecting a combination of GPS satellites that provides the highest accuracy from the position of each GPS satellite. At this time, since the GPS satellites with a low elevation angle (5 ° or less) pass obliquely through the atmosphere, there is a large error in the radio wave propagation time, so that the radio waves from other GPS satellites with a high elevation angle can be received. In such a case, the radio wave from the GPS satellite with the low elevation angle is not used for the position calculation. In the “multipath compensation” according to the present invention, radio waves from GPS satellites having an elevation angle range of 5 ° to 10 °, which would normally be used, are not adopted for position calculation. That is, "cutting low-elevation angle GPS satellites" actually means that "radio waves from GPS satellites in the elevation angle range of 5 to 10 degrees are not used for positioning". However, if only four GPS satellites can be captured, it is more important to perform positioning than "multipath compensation", so even low-elevation GPS satellites use radio waves from them for positioning. .

Next, a GPS multipath compensation method according to the present invention will be described with reference to FIGS. FIG.
3 is a flowchart showing a part of a program stored in the ROM 32 for performing GPS multipath compensation. FIG. 3 is a diagram showing a relationship between the moving speed v of the mobile station and the loop bandwidth Bl of the DLL 10. Here, the case where the lower limit speed vmin is 3.5 km / h is shown, and the case where the upper limit speed vmax of the moving speed v of the mobile station is 35 km / h will be described as an example. Further, the lower limit Blmin and the upper limit Blmax of the loop bandwidth Bl of the DLL 10 are 1H, respectively.
z and 10 Hz.

First, the CPU 31 determines the moving speed v of the mobile station.
Is greater than or equal to the upper limit speed vmax (35 km / h) (step S1). If the moving speed v is the upper limit speed vma
If x or more (v ≧ vmax) (Ye in step S1)
s), since it is not affected by multipath, the CPU 31
Sets the loop bandwidth Bl of the DLL 10 to the upper limit Blmax (10 Hz) which is a normal loop bandwidth (Bl = Bl
max) (step S2). That is, when the moving speed v is 35
At km / h, the fading bandwidth Bf is equal to 50 Hz, and Bf / Blmax = 5.
km / h or more, the loop bandwidth Bl of the DLL 10
Is set to 10 Hz, which is the upper limit, so that B
This is because f / Bl ≧ 5.

On the other hand, if the moving speed v is lower than the upper limit speed vmax (v <vmax) (No in step S1), C
The PU 31 has a moving speed v of the lower limit speed vmin (3.5 km).
/ H) It is determined whether it is less than or equal to (step S3). if,
If the moving speed v is equal to or lower than the lower limit speed vmin (v ≦ vmin) (Yes in step S3), the CPU 31
Is set to its lower limit Blmin (1 Hz) (Bl = Blmin) (step S4). This is because when the moving speed v is equal to or less than 3.5 km / h, the position information needs to be updated every second, so that the loop bandwidth Bl of the DLL 10 can no longer be reduced.
The loop bandwidth Bl of 10 is kept constant at 1 Hz. In this case, radio waves from GPS satellites having a low elevation angle are not used in this range because the possibility of multipath influence is high (step S5). For example, positioning is usually performed using a radio wave from a GPS satellite having an elevation angle of 5 ° or more, but when the moving speed v is 3.5 km / h or less,
Positioning is performed using only radio waves from GPS satellites having an elevation angle of 10 ° or more.

Next, how to know the elevation angle of a GPS satellite in a GPS receiver will be described. GPS
It is assumed that the receiver has captured one GPS satellite. In this case, the signal (radio wave) from the captured GPS satellite includes data (almanac) for calculating the approximate orbit of all GPS satellites. The GPS receiver calculates the orbit of all GPS satellites from this data,
It determines which GPS satellites can be captured from the approximate current location, and attempts to receive signals (radio waves) from each GPS satellite in sequence.

Once the GPS receiver has been able to receive the almanac, the almanac (data) is stored in a non-volatile memory, so that a significant movement (for example, 1000 km or more) with the power turned off is made. Unless you do it,
When the power is turned on next time, it is possible to immediately determine which GPS satellite can be captured.

As described above, since the orbits of all the GPS satellites can be calculated from the almanac, the G at a certain time from this orbit can be calculated.
The position of the PS satellite can be obtained in a coordinate system (geocentric coordinate system) with the current position of the GPS receiver as the center. That is,
You can know the elevation angle of each GPS satellite.

In step S3, the moving speed v
Is higher than the lower limit speed vmin (v> vmin) (No in step S3). That is, it is assumed that the moving speed v is in the range between the lower limit speed vmin and the upper limit speed vmax (vmax>v> vmin). In this case, the CPU 31
The loop bandwidth Bl of L10 is set in proportion to the moving speed v (Bl = αv) (step S6). Here, α is a coefficient equal to (1 / 3.5).

With such a configuration, when it is desired to know the current position accurately using a car navigation device including this GPS receiver mounted on a moving body,
When the vehicle is traveling at a low speed of 35 km / h or less in a building that is most likely to be affected by the multipath in an actual use state, the influence of the multipath can be reduced.

The present invention is not limited to the above-described embodiment, and it goes without saying that various changes can be made without departing from the spirit of the present invention. For example, in the above embodiment, the case where the present invention is applied to a GPS receiver has been described as an example.
(Spread spectrum) It goes without saying that the present invention can be applied to a communication system.

[0067]

As described above, according to the present invention, when the moving speed of the mobile station is low, the loop bandwidth of the delay locked loop is narrowed, so that the multipath resistance can be improved. When the moving speed of the mobile station is equal to or lower than the predetermined lower limit speed, the loop bandwidth of the delay locked loop is kept constant to a certain limit. In this case, radio waves from low-elevation angle GPS satellites are cut off. Thereby, multipath resistance can be ensured.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a GPS receiver to which a GPS multipath compensation method according to an embodiment of the present invention is applied.

2 shows a G according to the invention in the GPS receiver of FIG. 1;
6 is a flowchart for explaining a PS multipath compensation method.

FIG. 3 is a diagram illustrating a relationship between a moving speed of a moving object and a loop bandwidth of a delay locked loop in the GPS multipath compensation method of FIG. 2;

FIG. 4 is a diagram illustrating a case where a positioning error occurs due to multipath.

FIG. 5 shows a delay locked loop (D) used for a GPS receiver.
LL) is a block diagram showing the configuration of FIG.

FIG. 6 is a waveform chart showing waveforms at various parts of the delay locked loop shown in FIG. 5 when there is no multipath.

FIG. 7 is a waveform chart showing waveforms at various parts of the delay locked loop shown in FIG. 5 when there is a multipath.

[Explanation of symbols]

 Reference Signs List 10 delay locked loop (DLL) 11 multiplier 12 one-chip delay unit 13 multiplier 14 subtractor 15 low-pass filter (LPF) 16 numerically controlled oscillator (NCO) 17 C / A code generator 18 numerically controlled oscillator (NCO) 19 Mixer

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[Procedure amendment]

[Submission date] March 16, 1999 (1999.3.1.
6)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 8

[Correction method] Change

[Correction contents]

Claims (8)

[Claims] 1. GPs of multiple aircraft orbiting the earth
A GPS receiver for detecting a current position of a user's mobile station by receiving radio waves radiated on the earth from an S (Global Positioning System) satellite.
A method for compensating for a multipath that receives not only a direct wave directly received from a PS satellite but also a reflected wave that is received with a slight delay through various reflection paths, wherein the GPS receiver includes a delay locked loop (DLL). ), Wherein the loop bandwidth (Bl) of the DLL is changed according to the moving speed (v) of the mobile station.
Multipath compensation method. 2. The GPS multipath compensation method according to claim 1, wherein the loop bandwidth (B1) of the DLL is narrowed when the moving speed (v) of the mobile station is low. 3. When the moving speed (v) of the mobile station is higher than a lower limit speed (vmin), the loop bandwidth (B1) of the DLL is increased in proportion to the moving speed (v). The moving speed (v) of the station is the lower limit speed (v
min) or less, the DLL loop bandwidth (B
The GP according to claim 1, wherein l) is fixed to a predetermined limit.
S multipath compensation method. 4. The method according to claim 3, wherein when the moving speed (v) of the mobile station is equal to or lower than the lower limit speed (vmin), radio waves from GPS satellites having a low elevation angle are cut off. GPS multipath compensation method. 5. When the moving speed (v) of the mobile station is within a range between a lower limit speed (vmin) and an upper limit speed (vmax), the loop bandwidth (B1) of the DLL is changed to the moving speed (v). ), And the moving speed (v) of the mobile station is increased to the upper limit speed (vmax).
In the above case, the loop bandwidth (Bl) of the DLL is set to its upper limit (Blmax), and the moving speed (v) of the mobile station is set to the lower limit speed (vmin).
The GPS multipath compensation method according to claim 1, wherein in the following cases, the DLL loop bandwidth (Bl) is set to its lower limit (Blmin). 6. The radio communication system according to claim 5, wherein when the moving speed (v) of the mobile station is equal to or lower than the lower limit speed (vmin), radio waves from low-elevation GPS satellites are cut off. GPS multipath compensation method. 7. The minimum speed (vmin) is 3.5 km /
h, the upper limit speed (vmax) is equal to 35 km / h, and the lower limit (Blmin) and the upper limit (Blmax) of the loop bandwidth (Bl) of the DLL are 1 respectively.
Hz and 10 Hz.
2. The GPS multipath compensation method according to 1. 8. A method for compensating for multipath in a receiver mounted on a mobile station of a spread spectrum communication system and using a delay locked loop (DLL) for correlation detection, the method comprising: A GPS multipath compensation method, wherein the loop bandwidth (B1) of the delay locked loop is changed accordingly.