JP2001153942A - Spectrum spreading demodulator and gps receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make recoverable from an interruption in tracking due to a tunnel, etc., more speedily than before. SOLUTION: This modulator is provided with two correlators 18 and 20, two code/carrier generators 26 and 28, and a wide-area error range computing circuit 32 and narrow-area error range computing circuit 34 each corresponding to the code/carrier generators 26 and 28. When the reception of signals from a GPS satellite 10 and tracking are interrupted due to entrance into a tunnel, etc., a code phase on the code/carrier generator 26 is swept and changed in a wide rang according to the result of computations by the wide-area error range computing circuit 32 on one hand, and a code phase on the code/carrier generator 28 is swept and changed in a narrow range according to the result of computations by the narrow-area error range computing circuit 34. Then it becomes possible to resume tracking in a short time by the sweeping/changing control of the code phase in a narrow range. By a wide-range sweeping/changing control, it is possible to cope with conditions which can not be coped with by a narrow-range sweeping/changing control.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a GPS (Global Pos
The present invention relates to a spread spectrum demodulator mounted on a receiver and other devices, and particularly to a code phase search method executed by the spread spectrum demodulator. In the present application, a signal for positioning is transmitted from a positioning satellite existing in an orbit around the earth after spread spectrum modulation, and received and spread spectrum demodulated by a receiver on the earth. G is a system that determines the current position of
Called PS. Therefore, the GPS in the present application includes NAVSTAR / GPS developed and implemented in the United States as one embodiment, but should not be construed as being limited thereto. In addition, the expression “mounted” on a moving object is to be understood as including mobile by humans and transportation by animals.

[0002]

2. Description of the Related Art A GPS receiver utilizes a GPS,
It is widely used as a device capable of detecting the position of a vehicle, a ship, an aircraft, and other moving objects in real time and accurately. GPS wirelessly transmits signals for positioning from GPS satellites, which are positioning satellites placed in orbit around the earth,
This is a system in which a GPS receiver mounted on a mobile object on the earth receives and demodulates the information, and obtains the current position, speed, and the like of the target mobile object. As a basic function, a GPS receiver receives and demodulates a signal transmitted from a GPS satellite, and executes an arithmetic operation, that is, a positioning operation, for obtaining a current position, a speed, and the like of a mounted mobile body based on the result. Function to perform

A signal transmitted from a GPS satellite has 157
5.42 MHz L1 carrier and 1227.60 MH
transmitted by the z L2 carriers. Further, these carriers are spread-spectrum modulated using a spreading code defined for each GPS satellite, and then transmitted from the GPS satellite. As the spreading code, a C / A code having a chip rate of 1.023 MHz, 10.23 MHz
P code having the following chip rate. for that reason,
In the GPS receiver, a predetermined number or more of GPS satellites in operation that are within the line-of-sight range are selected, and a spread code for correlation detection corresponding to the spread code related to the selected GPS satellite is generated. The spread spectrum demodulation of the received signal is performed by establishing and maintaining the synchronization between the spread code and the received signal.

For this spread spectrum demodulation, a GPS receiver is usually provided with a correlator, a code generator and a control member such as a CPU. The code generator generates a spread code for correlation detection. The correlator obtains a correlation value between the correlation detection spreading code and the received signal. The control member determines the correlation value while sweeping and changing the code phase of the correlation detection spread code, and detects the appearance of a peak in the correlation value (code phase search), thereby detecting the code in the received signal from the GPS satellite. Capture phase (establish code synchronization). Once captured, the control member tracks the change in the code phase in the received signal from the GPS satellite by controlling the code phase in the spread code for correlation detection so that the correlation value continues to maintain a peak (code synchronization). Maintenance). In the tracking state, the positioning operation is performed using information included in the received signal subjected to spread spectrum demodulation and information such as a code phase (and a carrier phase) obtained by code synchronization (and a carrier synchronization). .

However, if the code phase of a received signal is acquired from an unknown state,
A long time is required from the start of the search for the code phase to the acquisition, and the real-time operation of the positioning operation is impaired. Therefore, in order to resume tracking in a relatively short time in the case of a temporary tracking interruption, based on the situation before the tracking interruption and the like, at the time of the code phase search, estimate the target or reference code phase and its error range, The code phase (chip number) of the spread code for correlation detection is swept and changed within the estimation error range with the code phase estimation value interposed therebetween. Thus, for example, when the GPS receiver enters the garage, in the tunnel, under the bridge, etc.
When a building, a tree, a mountain, or the like is occupied between the receiver and the GPS satellite, or the like, the time from the return to the receivable state (for example, when leaving a tunnel) to the restart of tracking can be reduced. In other words, in the best case, the search time is one chip, and in the worst case, the tracking can be resumed until the search of the entire estimation error range is completed.

[0006]

However, conversely, this means that, in the worst case, even after returning to the receivable state, tracking cannot be resumed unless the search for the entire estimated error range is completed. The present invention has been made to solve such a problem, and has been made.
In a spread spectrum demodulator used in a PS receiver or the like, when tracking of a code phase in a received signal or an input signal is interrupted, the tracking can be resumed as soon as possible after returning to a reception or input enabled state. That is its purpose.

[0007]

In order to achieve the above object, a spread spectrum demodulator according to the present invention comprises: (1) a code corresponding to a spread code used when an input signal is subjected to spread spectrum modulation; (2) a plurality of code generators each generating a correlation detection spreading code
Each is provided corresponding to one of the code generators,
A plurality of correlators for determining a correlation value between the correlation signal and a spread code for correlation detection generated by a code generator and the input signal,
(3) The code phase of the input signal is captured by controlling the code phase of the spread code for correlation detection so that the correlation value in any of the correlators becomes a peak, and thereafter, the correlation detection is performed so that the peak is continuously obtained. Control means for tracking a change in the code phase in the input signal by controlling a code phase in the spread code for use. (4) When the control means stops the tracking state, at least one of the Until the correlation value in the correlator reaches a peak, (5) the center guess value, which is the guess value of the code phase in the input signal that would have been captured at the current time if tracking was continued to the present time, is included in the center guess value. The value of the code phase that was tracked before the tracking was suspended in the wide-range error range that is the estimated maximum range of the error Is a process of deriving based on the change tendency and the elapsed time after the tracking is interrupted, and (6) a wide-range error range across a central estimated value of a code phase in a spread code for correlation detection generated by at least one code generator. In parallel with this, the code phase of the spread code for correlation detection generated by at least one other code generator is swept within a narrow-range error range across the center estimated value. The method is characterized in that a process for causing the image to be executed is executed. Further, the GPS receiver according to the present invention receives a signal transmitted on spread spectrum modulation by a GPS satellite in orbit around the earth, performs spread spectrum demodulation of the received signal, and obtains information obtained as a result. A GPS receiver for performing a predetermined positioning operation based on the above-mentioned method, characterized in that the spread spectrum demodulator of the present invention is used to spread spectrum demodulate a signal received from a GPS satellite.

As described above, in the present invention, a plurality of correlators and code generators are provided, and
After the tracking is interrupted, the wide area search and the narrow area search are executed in parallel. Here, the wide area search is performed by causing at least one of a plurality of code generators to sweep and change the code phase of the spread code for correlation detection within a wide area error range with the center estimated value interposed therebetween. Is to search for a code phase at which a peak occurs. The narrow area search is performed by sweeping the code phase of the spread code for correlation detection in at least one of the plurality of code generators within the narrow area error range with the center estimated value interposed therebetween. , Searching for a code phase having a peak correlation value. In the present invention, the wide area search and the narrow area search are executed in parallel, and when a peak is detected by any of the correlators (that is, by any of the searches), re-acquisition and tracking restart are performed. .

The center estimated value in the present invention is an estimated value of the code phase that would have been captured at the present time if tracking was continued to the present. This is based on the code phase or the change tendency thereof in the input signal or the received signal which was acquired before the tracking interruption and the elapsed time from the tracking interruption to the present, and is known theoretically, experimentally or empirically. What is necessary is just to guess according to the guessing logic. In the case of a GPS receiver,
It is also desirable to take into account the ability of a local oscillator, such as TCXO, to down convert the received signal. In estimating, it is desirable to make a realistic assumption that the mounting destination moving body maintains the moving speed at the time of tracking suspension. The wide-range error range is a maximum estimated range of an error included in the central estimated value. This corresponds to the estimated error range in the related art, but need not be the same. In the case of the GPS receiver, the wide-range error range is calculated by calculating a relative position change of the GPS satellite with respect to the GPS receiver which is expected when the mounted mobile body moves at the maximum moving speed, and sequentially determining the error based on the result. preferable. The narrow error range is a range narrower than the wide error range. The width or the time change rate of the width may be constant,
The temporal change rate of the width may be changed according to the passage of time. In the case of the GPS receiver, the narrow-range error range is based on the assumption that the moving speed of the target moving body before stopping the tracking is not significantly changed, and the GPS satellite for the GPS receiver expected under the assumption is not changed. It is preferable to calculate the relative position change and the like, and determine them sequentially based on the result.

As described above, in the present invention, the wide area search and the narrow area search are executed in parallel. Usually, the frequency of occurrence of such a situation that the mounting destination moving at the maximum moving speed is not high, and it can be considered that the true code phase is likely to be located at or near the center guess value. The probability that the tracking can be restarted early by the narrow area search is higher than in the case of the conventional search only or the wide area search only. That is, the average required time until the tracking restarts becomes shorter. Furthermore, since the wide area search is also executed in parallel rather than simply narrowing the search range, error factors in the apparatus when the moving speed of the mounting target moving body is extremely high or low, or inside the apparatus. When it becomes apparent,
The tracking can be resumed in the same required time as the conventional search.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a GPS according to an embodiment of the present invention.
2 shows a configuration of a receiver. In this figure, for simplification of illustration, only a circuit for one channel is shown. The GPS receiver shown in this figure is a GPS receiver in orbit around the earth.
A signal transmitted from the satellite 10 is received using the antenna 12, the received signal is amplified by the amplifier 14, and further down-converted by the mixer 16, and the two correlators 1
8 and 20 are provided. The local oscillation signal for down-conversion in mixer 16 is TC
An XO (temperature compensated crystal oscillator) 22 is supplied to the mixer 16 via an n-multiplier 24.

Further, code and carrier generators 26 and 28 are provided corresponding to the correlators 18 and 20. These are the code and carrier generators 26 and 28
Operates on the basis of a clock supplied from the TCXO 22, generates a carrier and a correlation detection spread code under the control of the CPU 30 as a control member, and supplies the spread code to the corresponding correlator 18 or 20. In the correlator 18 or 20, the corresponding code and carrier generator 26 or 2
8 and the carrier in the received signal are frequency- and phase-synchronized, and when the corresponding code and the spread code for correlation detection from the carrier generator 26 or 28 and the spread code related to the received signal are phase-synchronized, The correlation value obtained by the correlator 18 or 20 becomes a peak. The CPU 30 is a GPS satellite 10 used for positioning operation.
, The code and carrier generators 26 and 28 are controlled (captured) such that the correlation value in the correlator 18 or 20 is peaked, and the code and carrier generators 26 and 28 are controlled such that the correlation value is kept peaked. (Tracking).

[0014] However, for example, when the target mobile unit enters the tunnel, it becomes impossible to receive the signal from the GPS satellite 10, and accordingly, the tracking is interrupted. At this time, in the worst case, in the code phase search within the estimation error range described in the related art, tracking cannot be resumed until the entire estimation error range is searched after returning to a receivable state (exiting the tunnel). Therefore, in the present embodiment, after the tracking is suspended, the wide-range error range calculation circuit 32 and the narrow-range error range calculation circuit 34 determine the search range under the control of the CPU 30, and the two sets of code generators and correlators are used. By executing the wide-area search and the narrow-area search in parallel with each other, the time required for restarting tracking by the code phase search is reduced.

In FIG. 2, as shown by the broken line, the change in the code phase of the received signal after the tracking is interrupted may be regarded as having the same tendency as before the tracking was interrupted. That is, the main factor of the change of the code phase in the received signal is the GPS
Movement of the moving body on which the receiver is mounted, and thus GPS
It can be considered that it is a relative position change with respect to the satellite 10,
Also, when traveling in a tunnel, etc., it is usually good to maintain the speed before entering the tunnel without suddenly increasing the speed, so under the assumption that the speed at the time of tunnel entry is maintained, In addition, the code phase in the received signal after the tracking suspension can be estimated based on the code phase value until the tracking suspension or its change tendency, the elapsed time since the tracking suspension, and the like. The broken line in FIG. 2 indicates the value obtained as a result of this estimation, that is, the central estimated value.

In FIG. 2, the range indicated by the dashed line is
The range to be subjected to the wide area search, that is, the wide area error range,
The wide-range error range in the present embodiment corresponds to the estimated error range in the related art. The wide-range error range is caused by a change in the relative position of the GPS satellite 10 with respect to the GPS receiver and a change in the frequency of the Doppler component included in the received signal from the GPS satellite 10 which may occur when the mounted mobile body moves at its maximum moving speed. , TCXO 22 in consideration of fluctuations in oscillation frequency and the like.

For example, when trying to receive an L1 carrier that is spread spectrum modulated by a C / A code, 1
One of the L1 carriers having a frequency of 575.25 MHz
The wavelength is 3 × 10 ⁸ (m / sec) /1575.25 (M
Hz) = 0.19 (m) or a chip rate of 1.023 MHz in which the C / A code has 1023 chips.
Therefore, one chip length of the C / A code is 0.19 (m) × 157.25 (MHz) /1.02
3 (MHz) = 292.6 (m). The vehicle on which the vehicle is mounted is an automobile, and its maximum moving speed is 216 km / h = 6.
If it is 0 m / sec, the error range of the code phase in the received signal is 60 (m / s) at the maximum after the tracking is interrupted.
ec) /292.6 (m) = approximately 0.21 (chip / sec)
It may be inferred that it spreads as fast as c). However,
Other factors such as changes in Doppler frequency and TCXO2
The error of 2 also acts. It is approximately 0.04 chip / s
If it is ec, the range indicated by the one-dot chain line in FIG. 2, that is, the wide-range error range to be subjected to the wide-range search, will increase at a speed of approximately 0.25 chips / sec over time. .

In the wide area search according to the present embodiment, the CPU 30 and the wide area error range calculation circuit 32 change the code phase of the correlation detection spread code supplied to the correlator 18 so as to sweep within the wide area error range with the center estimated value interposed therebetween. Is an operation of controlling the code and carrier generator 26 and trying to detect the peak of the correlation value in the correlator 18. When performing the wide area search, the CPU 30 instructs the wide area error range calculation circuit 32 about the carrier frequency, that is, the reception frequency of the GPS satellite 10 to be captured, and the estimated center value shown in FIG. The elapsed time from the tracking interruption is supplied as information from the CPU 30 to the wide-range error range calculation circuit 32 and the narrow-range error range calculation circuit 34, or from the signal supplied from the CPU 30 indicating the tracking interruption. Elapsed time is counted in these circuits or either. The wide-range error range calculation circuit 32 performs control related to carrier synchronization based on the reception frequency, and sequentially calculates a wide-range error range based on the elapsed time since the tracking was interrupted and the maximum moving speed of the target mobile body, and based on the result. The code phase of the spread code for correlation detection is controlled. That is, the wide area error range calculation circuit 32 transmits the correlation detection diffusion code to the code and carrier generator 26 so as to sandwich the center estimated value and to perform a sweep change within the wide area error range based on the center estimated value and the wide area error range. Command the code phase at. While this control is being performed, the code phase of the spread code for correlation detection according to the code and carrier generator 26 changes as shown by the curve I in FIG. In FIG. 2, the curve I has a constant frequency, but this is not necessary. Also, a spreading code, for example, a C / A code is composed of 1023 chips, and therefore, the code phase can be represented by the number of this chip. Therefore, in FIG. 1, the code phase is represented by “chip number”. I have.

Even with such a wide area search alone, in the worst case, the time required for searching the entire wide area error range is
Tracking can be resumed. For example, suppose a case in which the mounting destination mobile body has passed through a tunnel having a length of 500 m at a speed of 10 m / sec, that is, a case where it has been inside the tunnel for 50 sec. While the target mobile unit is in the tunnel, the code phase of the received signal is 0.25 (chip / sec) at the maximum.
c) × 50 (sec) = approximately 13 (chips). Taking into account that there is a shift to positive and negative and that there is a state of shift = 0, the spread of the wide area error range immediately after exiting the tunnel is 13 (chips) × 2 + 1 (chips) = 27.
(Chip). If it takes 15 (msec) time to check the correlation value for a certain code phase, 27 (chips) × 15 (sec) = 27 (chips) to search the entire wide-range error range having a spread of 27 chips. 4
A time of 05 (msec) is required. In other words, in the case of wide area search only, from exiting the tunnel to resuming tracking,
It takes 405 msec at worst. In the best case where the code phase of the spread code for correlation detection at the time of exit from the tunnel coincides with the code phase of the received signal, the required time is 15 msec, so the average of the worst case and the best case is In other words, (405 (m
sec) +15 (msec)) / 2 = 210 (msec)
c) Some time is required.

In the present embodiment, the significance of performing a narrow search is 405 msec at worst and 210 msec on average.
That is, the time required for restarting tracking can be reduced. Further, in this embodiment, the wide area search is also executed in parallel with the narrow area search, and when the peak of the correlation value is detected in one of the narrow area search and the wide area search, the tracking is restarted. To compensate for the limitation of the principle of narrow-range search that does not cover the entire error range (wide-range error range) caused by the movement of the body, but to search only a part of the error range. is there.

In the narrow search, the narrow error range is set smaller than the wide error range targeted for the sweep change in the wide search, and the code and carrier generator are set within the set narrow error range. 28, the code phase of the spread code for correlation detection generated in
This operation is to detect a peak correlation value at zero. When executing the narrow-range search, the CPU 30 instructs the narrow-range error range calculation circuit 34 with the reception frequency and the estimated center value. The operations of the narrow-range error range calculation circuit 34, the code and carrier generator 28, and the correlator 20, which are members for executing the narrow-range search, are based on the logic that determines the narrow-range error range and the logic that determines the wide-range error range Except for the differences,
The operation is the same as the operation of the member for executing the wide area search.

The narrow-range error range is calculated on the basis of, for example, the width of a given narrow-range error range or its time rate of change and the elapsed time from the interruption of tracking. For example, in a case such as entry into a tunnel, entry into a garage, or the like, usually, the moving speed of the loading destination moving body is sufficiently lower than its maximum moving speed. As described above, when the mounting target moving body enters the tunnel having a total length of 500 m at a speed of 36 km / h = 10 m / sec, the speed of the mounting target moving body in the tunnel is likely to be lower than that. Assuming that, the code phase error in the received signal is 10 (m
/Sec)/292.6 (m) = 0.03 (chip / s
ec) It can be seen that it spreads at a certain speed. Even if error factors such as the Doppler frequency and the local oscillation frequency are taken into account, it is appropriate to set the narrow-range error range to a range that spreads at a speed of 0.04 chips / sec. In FIG. 2, the change indicated by the spread code for correlation detection related to the output of the code and the carrier generator 28 is represented by II.

Assuming that the code phase search is performed only by the narrow area search, the worst case is 0.04 (chip / sec) × 50 (s) in the above example of tunnel passage.
ec) × 2 + 1 (chips) = 5 (chips) must be searched, and therefore, 5 (chips) × 15 (mse)
c) = 75 (msec) is required. On the average with the best case, (75 (msec) +15 (ms
ec)) / 2 = 45 (msec), and the tracking can be resumed. The worst required time and the average required time listed here are shorter than those in the case of only the wide area search. Therefore,
In many cases, tracking is restarted based on the result of the narrow area search, and the time required for tracking restart is shorter than in the past.

Further, the CPU 30 includes the correlators 18 and 20.
Until the peak correlation is obtained in any of
Perform a wide area search and a narrow area search in parallel. That is,
The moving object is moving at extremely high speed or G
In the present embodiment, even in a situation in which a narrow error search alone cannot cope, such as when a significant error factor occurs in the circuit operation in the PS receiver, this situation can be dealt with by a wide area search executed in parallel. It is possible to resume tracking at least in the same time as the prior art.

Although one set of circuits for the wide area search and one circuit for the narrow area search are shown, at least one set of these circuits may be provided, and two or more sets may be provided.

[Brief description of the drawings]

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

FIG. 2 is a timing chart for conceptually explaining a wide area search and a narrow area search in the embodiment.

[Explanation of symbols]

10 GPS satellites, 18,20 correlators, 26,28
Code and carrier generator, 30 CPU, 32 wide-range error range calculation circuit, 34 narrow-range error range calculation circuit.

Claims (2)

[Claims] 1. A plurality of code generators each for generating a correlation detection spreading code which is a code corresponding to a spreading code used when an input signal is subjected to spread spectrum modulation, and any one of the code generators Provided in response to
A plurality of correlators for obtaining a correlation value between the correlation detection spreading code generated by the corresponding code generator and the input signal; and a code in the correlation detection spreading code such that the correlation value in any one of the correlators becomes a peak. The code phase in the input signal is captured by controlling the phase, and thereafter, the change in the code phase in the input signal is tracked by controlling the code phase in the spread code for correlation detection so that a peak is continuously obtained. Control means, the control means, when the tracking state is cut off, at least until the correlation value in any one of the correlators reaches a peak, and if the tracking is continued to the present, the control means has captured at the current time. The center guess value, which is the estimated value of the code phase in the input signal, A process of deriving a narrow-range error range narrower than the wide-range error range and the wide-range error range based on the code phase value tracked before the tracking suspension or its change tendency and the elapsed time after the tracking suspension, and at least one code While the code phase of the spread code for correlation detection generated by the generator is swept within a wide error range with the center guess value interposed therebetween,
In parallel with this, executing a process of sweeping and changing the code phase of the spread code for correlation detection generated by at least one other code generator within a narrow-range error range across the center estimated value. Spread spectrum demodulator characterized. 2. A signal transmitted by spread spectrum modulation by a GPS satellite in orbit around the earth is received, spread spectrum demodulation of the received signal is performed, and a predetermined positioning operation is performed based on information obtained as a result. A GPS receiver, comprising: a GPS receiver that performs spread spectrum demodulation on a signal received from a GPS satellite.