JP2003098244A - False signal cross-correlation detection method, transmission source selection restriction method, and satellite selection restriction method - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To prevent or reduce a failure such as position jump due to a false signal cross-correlation. SOLUTION: For a plurality of satellites received / acquired, a difference between Doppler frequency measurement values (reception frequency difference).
It is determined whether or not is within a predetermined range (202). Among the satellites within the predetermined range, the smallest correlation peak value indicates a weak signal (203) and the largest correlation peak value indicates a strong signal. It is checked whether or not it is indicated (204). When those conditions are satisfied, the satellite exhibiting the largest correlation peak value is a true satellite, the other satellites are not actually true satellites, but are actually false signals due to strong received signals from other satellites. It is assumed that the image is merely a false image due to cross-correlation. Satellites found to be false images are excluded from targets for subsequent satellite selection (205).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio system for transmitting a spread spectrum signal from a plurality of transmission sources to a receiver while transmitting relative to each other and / or at the same carrier frequency, for example, The present invention relates to a positioning system in which a plurality of positioning satellites move relative to each other and transmit at the same carrier frequency to transmit a spread spectrum positioning signal to a receiver. This type of system uses a GPS satellite that is in an orbit around the earth as a transmission source, and a GPS that measures the position, speed, etc. of a receiver in a space in which a predetermined number of GPS satellites can be seen as a positioning target.
(Global Positioning System). The present invention particularly relates to a false signal cross-correlation detection method and a transmission source selection limiting method executed by a receiver that wirelessly captures a transmission source, for example, a positioning satellite through carrier frequency synchronization control and code phase synchronization control in such a system. And a satellite selection restriction method.

[0002]

2. Description of the Related Art In GPS, GP in orbit around the earth
The GPS receiver detects its own position, speed, etc. by the positioning calculation based on the satellite signal received from the S satellite. G
In order to perform the positioning calculation with the PS receiver, it is necessary to select more than the number of GPS satellites required in principle, capture satellite signals from those GPS satellites, and demodulate data from the captured satellite signals. is there. The satellite signal transmitted from the GPS satellite is a signal that is modulated by data of 50 bps indicating the transmission time, detailed orbit information, ephemeris information, etc., and is further spread spectrum by the spread spectrum code determined for each satellite. The GPS receiver despreads the received satellite signal with a spectrum despreading code corresponding to the selected GPS satellite, and demodulates the data from the resulting signal. With a GPS receiver,
Positioning calculation is performed based on the demodulated data of each selected GPS satellite and the code phase obtained as phase control information through spectrum despreading. The spread spectrum code used in GPS is C / A (Coarse).
There are two types, Acquisition code and P (Precision) code, and there are design differences between the two, such as the number of chips per epoch, code speed, and epoch length.
All of them are pseudo-noise codes composed of a predetermined number of chips, and each chip takes a binary value of 1,0. For example,
C / A code is 102 chips per epoch
3, the code rate is 1.023 MHz, and thus the Gold code has a repetition cycle (epoch length) of 1 msec.

Spectrum despreading in a GPS receiver is performed by detecting a correlation value between a spectrum despreading code and a satellite signal, comparing the detected correlation value with a predetermined threshold,
In addition, the phase control of the spectrum despreading code, that is, the code phase control based on the result of this comparison is also involved. First,
The correlation value between the spectrum despread code and the satellite signal is information indicating the degree of matching / mismatch between the value of the pseudo noise code related to the satellite signal and the value of the spectrum despread code. When the value and the value of the spectrum despreading code are the same over the entire epoch, that is, when the chip position of the spectrum despreading code, that is, the code phase, is synchronized with the satellite signal, compared to other states. Noticeably larger. Therefore, in the GPS receiver, the detected correlation value is compared with the threshold value, and when the former exceeds the latter, it is determined that "the code phase is synchronized". It should be noted that this threshold is set in advance so that the code phase synchronization state can be detected separately from other states. In the GPS receiver, while shifting the code phase of the spectrum despreading code by, for example, one chip until the code phase is synchronized, that is, until the satellite signal is captured, and the entire one epoch is checked, Perform correlation value detection and threshold comparison. When the code phase was shifted over one epoch and examined, but if the judgment of "synchronization" cannot be obtained, the local oscillation frequency may be slightly shifted because it may not be frequency synchronized with the carrier of the satellite signal. try again. In the code phase locked state, it is possible to despread the satellite signal and demodulate the data, and at the same time, the code phase at that time, that is, the code phase at which the correlation value reaches a peak, can be used for deriving the pseudorange. After capturing the satellite signal once, the satellite (signal) is tracked by changing the code phase so as to follow the phase change of the pseudo noise code related to the satellite signal.

[0004]

However, in order to always correctly establish the code phase synchronization of the spectrum despread code with respect to the received signal (satellite signal in the case of GPS), the method of simply comparing the correlation value with the threshold is not enough. This is because (1) a weak correlation value, that is, a false signal cross-correlation value generated for a reception signal from a transmission source (satellite in the case of GPS) different from the transmission source corresponding to the spectrum despreading code, and (2) the correlation value Weak correlation values that occur at phases other than the peak code phase, that is, false position autocorrelation values, (3) Correlation with the transmission source and the code phase are correct, but the correlation level of the correlator is low. This is because the signal correlation value and the like cannot be identified by a simple threshold comparison.

First, considering the C / A code in GPS as an example, there is no distortion in the satellite signal waveform, and the input level of the received satellite signal to the correlator is, for example, -110 dB.
When the spectrum despreading code corresponding to the transmission source of the satellite signal is used and the spectrum despreading code is accurately code-phase-synchronized with the satellite signal under the quasi-ideal situation with a high ratio of about m. The number of matching chips per epoch is 1023. When the absolute value of the difference between the number of matching chips and the number of non-matching chips is referred to as a correlation value, it can be said that the correlation value in this case, that is, the strong signal correlation value is 1023. However, since the actual satellite signal waveform is distorted, the strong signal correlation value is lower than this ideal value, for example, about 1023 × 40.0% = 409.2.

Next, the satellite signal reception level is further increased to 23.7.
If it is lower by dB and −133.7 dBm, then 23.7 dB =
As can be read from the equation of −20 × log (2.6 / 40.0), the correlation value, that is, the correlation value at the time of weak signal is 1023 × 2.
6% = 26.2.

On the other hand, if the satellite signal reception level is sufficiently high, the false signal cross-correlation value may be approximately the same as the above weak signal correlation value. That is, in GPS, different GPS
Since the correlation value between the C / A codes related to the satellite may increase up to 33, if the signal strength and distortion are similar to those at the time of the strong signal, the false signal cross-correlation value is 33 at maximum. × 40.0% = 26.0 can be obtained. This false signal cross-correlation value is almost equal to the weak signal correlation value due to the satellite signal having a level lower than that of the strong signal by 23.7 dB, that is, 26.2 described above.

As described above, the weak signal correlation value and the false signal cross-correlation value can be close to each other, and the latter may be larger depending on the radio wave environment. Therefore, the correlation value at the time of weak signal is definitely judged as "synchronous" and the false signal cross-correlation value is "asynchronous"
It is difficult to set the threshold so that it can be judged. As a result, in the past, the risk of determining "code phase = asynchronous" based on the weak signal correlation value and the risk of determining "code phase = synchronization" based on the false signal cross-correlation value was considered in the receiver design. It was included. A similar problem occurs between the weak signal correlation value and the false position autocorrelation value.

The present invention has been made to solve the above problems, and a signal spread spectrum is transmitted by a different spread spectrum code for each transmission source, and a predetermined number of transmission signals are transmitted to a receiver. In a wireless system in which the source is selected and the received signal is despread by the corresponding spectrum despreading code, the weak signal correlation value and false signal cross-correlation value (and false position autocorrelation value) appearing in the correlation detection value at the receiver ) And so that they can be identified more reliably.

[0010]

In order to achieve such an object, the false signal cross-correlation detection method according to the present invention comprises:
(1) In a radio system that transmits spread spectrum signals from a plurality of transmission sources that perform transmission while moving relative to each other, reception that wirelessly captures the transmission sources through carrier frequency synchronization control and code phase synchronization control The Doppler frequency of the received signal is measured for each of the captured transmission sources based on the information obtained through (2) carrier frequency synchronization control, and the difference in the measured values of the Doppler frequency from the captured transmission sources is measured. A step of determining a reception frequency difference for detecting a combination in which is within a predetermined range, and (3)
Among the transmission sources belonging to the above combinations, the correlation peak value obtained by the code phase synchronization control shows a low level correlation that can be obtained even by the false signal cross correlation and cannot be obtained by the false signal cross correlation. The above-mentioned low level is provided when it is found in (4) the correlation comparison step that a correlation comparison step for checking whether or not a high level correlation is included is included. The correlation peak value indicating the correlation is actually a cross-correlation between the received signal from the transmission source related to the above high-level correlation and the spectrum despreading code corresponding to the transmission source different from the transmission source. It is characterized as being the result of the correlation.

The false signal cross-correlation detection method according to the present invention comprises:
Alternatively, (1) in a wireless system that transmits spread spectrum signals from multiple transmission sources that transmit at the same carrier frequency to a receiver, the transmission sources are wirelessly captured through carrier frequency synchronization control and code phase synchronization control. (2) The carrier frequency of the received signal is measured for each transmission source captured based on the information obtained through the carrier frequency synchronization control, and the measured value of the carrier frequency is selected from the captured transmission sources. A receiving frequency difference determining step of detecting a combination in which the difference of is within a predetermined range,
(3) Among the transmission sources belonging to the above combination, the correlation peak value obtained by the code phase synchronization control shows a low level correlation obtained also by the false signal cross correlation and the false signal cross correlation. In the case where it is found in (4) the correlation comparison step that a high level correlation that cannot be obtained is included in the correlation comparison step for checking whether or not both are included, The correlation peak value indicating the low-level correlation is actually the cross-correlation between the received signal from the transmission source relating to the high-level correlation and the spectrum despreading code corresponding to the transmission source different from the transmission source. It is characterized as being the result of false signal cross-correlation.

The false signal cross-correlation detection method according to the present invention comprises:
(1) In the correlation comparing step, among the transmission sources belonging to the above combination, one in which the correlation peak value obtained by the code phase synchronization control is smaller than the weak signal maximum threshold value representing the above low level correlation and the above low level. It is a step of checking whether or not a value greater than the strong signal minimum threshold value indicating the correlation is included, or (2) the correlation comparing step is performed by the code phase synchronization control between the transmission sources belonging to the combination. This is a step of checking whether or not there is a significant difference in the obtained correlation peak value, and the smallest correlation peak value among the transmission sources having a significant difference in the correlation peak value is actually the result of the above false signal cross-correlation. The feature is that it is considered to be.

The transmission source selection limiting method according to the present invention is
(1) a step of executing the false signal cross-correlation detection method according to the present invention; and (2) a selection exclusion step of excluding a transmission source corresponding to the spectrum despread code that has caused the false signal cross correlation from the subsequent capture targets. And are included.

The satellite selection limiting method according to the present invention is (1)
A positioning system that transmits positioning signals spread spectrum to a receiver from multiple positioning satellites that transmit at the same carrier frequency while moving relative to each other, and wirelessly transmits positioning satellites through carrier frequency synchronization control and code phase synchronization control. The Doppler frequency in the carrier of the received signal is measured based on the information obtained through (2) carrier frequency synchronization control, which is executed by the capturing receiver, and the Doppler frequency is acquired from the captured positioning satellites. And (3) a correlation peak value obtained by code phase synchronization control is a false signal in the positioning satellites belonging to the above combination. A low level of correlation that can also be obtained by cross-correlation and a false signal that cannot be obtained by cross-correlation Present the correlation levels, a correlation comparison step checks if it contains both
(4) When it is determined that the correlation peak value is included in the correlation comparison step, the correlation peak value indicating the low level correlation is actually the received signal from the positioning satellite related to the high level correlation, and the positioning thereof. The positioning satellite corresponding to the spectrum despreading code that caused the false signal cross-correlation is regarded as the result of the false signal cross-correlation that is the cross-correlation with the spectrum despreading code corresponding to the positioning satellite different from the satellite. And a selection exclusion step of excluding from the capture target of.

As described above, in the present invention, by detecting the false signal cross-correlation in the reception frequency discrimination step and the correlation comparison step, and by enabling the selection exclusion process of the transmission source, for example, the positioning satellite, the false signal mutual correlation is achieved. The influence of correlation is suppressed. First, if the signal from a certain transmission source (for example, positioning satellite; the same applies in this section below) is sufficiently strong, the correlation peak value with the spectrum despreading code corresponding to that transmission source will be sufficiently strong. It is highly possible that a strong signal will cause a correlation peak value with a spectrum despreading code corresponding to a transmission source other than the transmission source to be comparable to that obtained by the weak signal cross-correlation. . In other words, when the false signal cross-correlation occurs, the source of the signal that has caused the false signal cross-correlation is often correctly captured separately. On the other hand, if the signals are from the same transmission source, their Doppler frequencies or carrier frequencies should be almost the same. In the present invention, focusing on these points, regarding the combination of “transmission sources” with a sufficiently small difference in the measured values of the Doppler frequency or the carrier frequency, the presence or absence of false signal cross-correlation is detected through the determination of the correlation peak value. I am trying. As described above, according to the present invention, it is possible to easily identify the false signal cross-correlation with respect to the weak signal time correlation and take countermeasures against the latter easily by a simple method and promptly in actual use.

[0016]

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

(1) Overall Function and Operation FIG. 1 shows a schematic functional configuration of a GPS receiver according to an embodiment of the present invention. In the receiver shown in this figure, the satellite signal is received by the antenna 101, and the frequency conversion unit 10
2 is down-converted, sampled by the A / D converter 103, and input to the correlator 104. The correlator 104 and the signal generator 105 depend on the number of satellites required for positioning calculation, the number of chips per epoch of the spread spectrum code related to the satellite signal to be captured / tracked, and the allowable device size / cost. In addition, a plurality of I, Q phases are provided and operated in parallel or sequentially. The reception control unit 106 includes the position / speed calculation unit 1
In accordance with the information from 12 and the output of the correlator 104, the operation of the signal generator 105, particularly the frequency of the local oscillation signal to be generated, the type of spectrum despreading code (pseudo noise code) to be generated, each spectrum inverse to be generated It controls the code phase etc. of the spreading code.

The correlator 104, the reception control unit 106 and the signal generator ("pseudo noise code and local oscillation signal generator" in the figure) 105 constitute a synchronous loop for satellite signals with respect to both carrier frequency and code phase. ing.

First, the reception controller 106 causes the signal generator 105 to generate a spectrum despread code corresponding to each satellite belonging to the combination selected by the position / velocity calculator 112, and the code phase thereof to the correlator 104. Control is performed so that the correlation value that is the output of is at a peak (“capture”).
By this control, the code phase synchronization of the spectrum despreading code with respect to the satellite signal is established. Therefore, when the satellite signal is spectrum despread, the data demodulation unit 1
At 10, data can be demodulated from the satellite signal. The demodulated data, for example, the detailed orbit information of the transmission source satellite and the data regarding the transmission time are stored in the position / speed calculation unit 112.
Is supplied to. The reception control unit 106 controls the code phase in the signal generator 105 (“tracking”) based on the correlation values that are sequentially obtained so that this state, that is, the code phase synchronization state is maintained.

In a member (or frequency converter 102) (not shown) before the input stage of the correlator 104, the satellite signal is converted to a lower frequency by the local oscillation signal supplied from the signal generator 105. The satellite signal for which the code phase synchronization is established is the satellite signal after this frequency conversion. Here, if the local oscillation frequency in the signal generator 105 is deviated, even if the code phase synchronization is once established, the synchronization easily deviates with the passage of time. It cannot track satellite signals. Reception control unit 1
Reference numeral 06 indicates a local phase based on the correlation value, such as slightly adjusting the local oscillation frequency in the signal generator 105 when the code phase is shifted over one epoch of the spectrum despreading code and the code phase synchronization cannot be established. Oscillation frequency control is performed to synchronize the local oscillation frequency with the carrier frequency of the satellite signal (carrier frequency synchronization loop).

The reception control unit 106 causes the correlation value storage unit 107 to store the peak of the correlation value obtained from the correlator 104 for each satellite, that is, the correlation peak value. Further, in a state where both carrier frequency synchronization and code phase synchronization with the satellite signal are established, that is, in a state where the satellite signal subjected to spectrum despreading is obtained via the correlator 104, the reception control unit 106 causes the correlator 104 to operate. The satellite signal subjected to spectrum despreading is supplied to the data demodulation unit 110 to demodulate data such as detailed orbit information, while the code phase in the signal generator 105 among the information obtained through the synchronization control is calculated by the pseudo distance measurement unit 109 and The pseudo-oscillation measuring unit 108 is supplied with the local oscillation signal frequency in the signal generator 105, and the local oscillation signal frequency is supplied to the Doppler frequency measuring unit 111. The pseudo distance measuring unit 109 obtains a pseudo distance to the transmission source of the satellite signal, that is, a code pseudo distance based on the code phase. The pseudo speed measuring unit 108 detects the time change of the code phase and obtains the moving speed of the receiver with respect to the transmission source of the satellite signal, that is, the pseudo speed. The Doppler frequency measuring unit 111 obtains the Doppler shift of the satellite signal carrier frequency, and thus the moving speed of the receiver with respect to the transmission source, that is, the Doppler speed, from the change of the local oscillation frequency.

The position / velocity calculator 112 calculates the position of the receiver by using the code pseudo distance obtained by the pseudo distance measuring unit 109 in addition to the data demodulated by the data demodulator 110. In addition, the position / speed calculation unit 112
Calculates the moving speed of the receiver with respect to the earth surface or the center based on the pseudo speed obtained by the pseudo speed measuring unit 108 and the measurement result by the Doppler frequency measuring unit 111. The position / speed calculation unit 112 notifies the user of the calculation result and the like via a display device, a voice output device, a communication line, etc., which are not shown. The position / velocity calculation unit 112 further selects and selects a combination of satellites used for positioning based on the information demodulated by the data demodulation unit 110, the information acquired and calculated in the past, and the like. The reception control unit 106 is instructed to receive (capture / track) satellite signals from GPS satellites.

(2) Countermeasures against false signal cross-correlation Further, the position / velocity calculation unit 112 determines the output of the Doppler frequency measurement unit 111, reads the correlation value from the correlation value storage unit 107 according to the result, The positioning prohibited satellite setting and the like based on the read correlation value are executed according to the procedure shown in FIG. As a result, in the present embodiment, the correlation peak value (false signal cross-correlation value) generated by the false signal cross-correlation is comparable to the correlation peak value (weak signal correlation value) generated by the weak signal, or We're dealing with things that reach higher levels.

The point that the inventor has focused on is that when the correlation peak value caused by the false signal cross correlation has a relatively high value,
The received signal that generated the false signal cross-correlation is usually at a high level, and therefore it is possible that the received signal can be correctly captured separately by the correct spectrum despreading code corresponding to the source satellite of the received signal. It is expensive.

On the one hand, the received signal is correctly (that is, using the spectrum despreading code corresponding to the transmission source satellite), and on the other hand it is mistaken (that is, the spectrum despreading code corresponding to the satellite other than the transmission source satellite is acquired. Under this circumstance of being acquired, the stored contents by the correlation value storage unit 107, the measurement result in the pseudo velocity measuring unit 108, the pseudo distance measuring unit 109 and the Doppler frequency measuring unit 111, and the data demodulating unit 110 in The demodulation result is
There must be more than one type of satellite.
However, of these two or more types of stored contents, measurement results and demodulation results, at most one is correct, that is, one that is associated with the source satellite, and the rest is erroneously satellites other than the source satellite. (That is, to the satellite corresponding to the spectrum despread code used in the synchronization loop). If positioning calculation is performed based on the stored contents, measurement results, and demodulation results obtained in this situation, and satellite selection is performed for that purpose, correct information due to strong signals and incorrect information due to false signal cross-correlation are mixed. Since these processes are performed after that, an inaccurate positioning result or a sudden change in the positioning result (so-called “position skip”) will occur.

However, of the information obtained by the respective functions shown in the figure, the Doppler frequency measurement value in the Doppler frequency measuring section 111 is obtained through control of the carrier frequency locked loop, and what kind of code phase locked loop is used. It does not depend on whether the spectrum despread code is used. Therefore, if there is a combination having substantially the same value among a plurality of Doppler frequency measurement values obtained as frequency shifts appearing in received signal carriers from different satellites, if there is a Doppler associated with that combination, The frequency measurements may actually be the frequency shifts that have appeared on the received signal carrier from the same satellite. If the carrier is 1.57542 GHz in GPS, for example, the difference in Doppler frequency measurement value is ± 20 Hz.
Within the range, it may be said that the values are substantially the same. Of course, the criterion for determining whether or not the values are substantially the same should be appropriately set depending on what carrier, system, and receiver the present invention is applied to.

Further, even if a combination of Doppler frequency measurement values such that the difference is within the criterion is obtained from the output of the Doppler frequency measuring unit 111, the Doppler frequencies are simply coincident or close to each other. It may not be too much. Therefore, in the present embodiment, when a combination of the Doppler frequency measurement values is found by the determination regarding the difference between the Doppler frequency measurement values, the false signal cross-correlation is determined by performing the determination regarding the combination of the correlation peak values corresponding to the combination. Check whether or not. That is, if one of the correlation peak values is a strong signal correlation value and the rest are weak signal correlation values, the satellite corresponding to the spectrum despreading code for which the strong signal correlation value is obtained is obtained. Can be recognized as the cause of the false signal cross-correlation that resulted in a correlation peak value of about the weak signal correlation value. In other words, while the true satellite is being captured by the strong signal time correlation, the false signal cross-correlation by the strong received signal from that satellite gives the result as if it were capturing another satellite. Can be admitted. In the present embodiment, not only the occurrence of the false signal cross-correlation phenomenon is detected by the correlation peak value threshold determination in addition to the Doppler frequency measurement value difference determination, but which satellite is a true satellite and which satellite is a false satellite of the true satellite. It also detects whether it is an image.

The procedure shown in FIG. 2 is performed by the position / speed calculator 112.
Among the processes executed by, the process is based on the above-mentioned viewpoint and principle, and is executed at a predetermined frequency. In the positioning prohibited satellite setting procedure shown in this figure, first, the position / velocity calculation unit 112 inputs from the Doppler frequency measurement unit 111 a plurality of Doppler frequencies that are measured values for different satellites. The difference between the input Doppler frequency measurement values is calculated (201). G
In PS, since the carrier frequencies used in each satellite are the same, the difference in Doppler frequency is the difference in carrier frequency of the received signal. Therefore, this is referred to as "received frequency difference" in FIG.

The position / speed calculator 112 determines whether or not there is a combination in which the difference is within ± 20 Hz among the input Doppler frequency measurement values (202). As a result, if it is found that there is no such combination, it can be considered that all satellites are true satellites, not false images, and no false signal cross-correlation has occurred. Therefore, the position / velocity calculation unit 11
The operation of 2 shifts to a procedure not shown. Conversely, if it is found that the difference between any two minimum Doppler frequency measurement values is within ± 20 Hz, one of those Doppler frequency measurement values is due to the false signal cross-correlation. Therefore, the operation of the position / velocity calculation unit 112 shifts to the threshold determination regarding the correlation peak value.

In the procedure shown in FIG. 2, the position / velocity calculation unit 112 stores the correlation peak value of at least the satellite corresponding to each of the Doppler frequency measurement values whose difference is within ± 20 Hz. The minimum correlation peak value is compared with the weak signal maximum threshold value (203), and the maximum correlation peak value is compared with the strong signal minimum threshold value (204). It should be noted that the weak signal maximum threshold is set to be equal to or higher than the maximum correlation peak value that can occur due to false signal cross-correlation, and the strong signal minimum threshold is
It is assumed that the value is set to be equal to or higher than the minimum correlation peak value that cannot occur in the false signal cross-correlation.

When it is found in step 203 that "minimum correlation peak value> weak signal maximum threshold" is satisfied, it is determined that all of the above-mentioned plurality of correlation peak values are so large that they cannot be obtained by the false signal cross-correlation. Regard,
The operation of the position / velocity calculation unit 112 goes out of the illustrated procedure.
Further, when it is found in step 204 that “maximum correlation peak value <strong signal minimum threshold” is established, any of the received signals that have produced the above-described plurality of correlation peak values will cause false signal cross-correlation. Assuming that the position / speed calculator 112 is not strong, the operation of the position / speed calculator 112 goes out of the illustrated procedure.

If the minimum correlation peak value of the plurality of correlation peak values is the weak signal maximum threshold or less and the maximum correlation peak value is the strong signal minimum threshold or more, the strong signal minimum threshold or more is reached. It may be admitted that the correlation peak value is, so to speak, a correct correlation peak value due to strong signal correlation, and that the received signal that caused the correlation peak value caused false signal cross-correlation. In the present embodiment, in order to prevent the above-mentioned position skip due to the influence of the false signal cross-correlation, when such a condition is satisfied (203, 204), the position / speed calculation unit 11
2 thereafter prohibits the satellite selection procedure (not shown) corresponding to the satellites corresponding to the spectrum despread codes that have produced the above-described plural correlation peak values for a predetermined time or until the power is turned on again (205). . That is, in order to prevent a false image from being captured, it is prohibited to establish synchronization by the spectrum despreading code in the synchronization loop. However, satellites corresponding to the spectrum despreading code that has produced a correlation peak value equal to or higher than the strong signal minimum threshold value can be regarded as being correctly synchronized with the received signal from that satellite, and are not excluded from the selection target.

As described above, among a plurality of Doppler frequency measurement values whose difference is within ± 20 Hz, the Doppler frequency measurement value whose corresponding correlation peak value is equal to or higher than the strong signal minimum threshold is related to the strong signal. It is a measurement value, and other Doppler frequency measurement values (including those below the maximum weak signal threshold) are regarded as measurement values related to false signal cross-correlation, and the spectrum despreading code used to obtain the latter is not used. By doing so, it is possible to eliminate or at least reduce problems such as position skipping due to false signal cross-correlation. It should be noted that, instead of the method of excluding from the selection target, a method of prohibiting the use of the measurement value and demodulated data regarding the satellite may be used.

In the above embodiment, the combination of satellites in which the difference between the measured Doppler frequencies is within 20 Hz (2
02) By comparing the correlation peak value with the weak signal maximum threshold and the strong signal maximum threshold (2
03, 204), and false signal cross-correlation was detected. Instead, a detection method in which the satellite with the smallest correlation peak value is selected from the combination of satellites in which the difference in the Doppler frequency measurement values is within the predetermined range and the correlation peak value related to that satellite is regarded as a false signal cross-correlation May be adopted. At that time, the process of selecting the minimum correlation peak value by performing a simple comparison between the correlation peak values may be used, but more preferably, it is limited to the case where there is a significant difference between the correlation peak values, , It is possible to prevent the situation that "there is really a weak signal correlation, but it was mistakenly treated as a false signal cross correlation".

(3) Addendum Regarding false position autocorrelation value and weak signal correlation value, all chips belonging to one epoch (1023 in C / A code)
By detecting the correlation value for
It is possible to discriminate between the 023 different code phases by checking the correlation values and selecting the code phase showing the maximum correlation value and having a sufficiently large correlation value among them. This processing can be executed by the reception control unit 106.

The present invention is not limited to the C / A code, but can be applied to the P code in principle. The present invention can be applied to a GPS receiver having various reinforcements or modifications, for example, a GPS receiver having a DGPS function. Further, not only the GPS receiver, but also a receiver that receives a spread spectrum signal by selectively using a plurality of types of spread spectrum codes, especially a receiver whose reception level may be extremely low The invention can be applied. The present invention has a large number of chips per epoch,
The effect becomes remarkable when it is applied to the one in which the false signal cross-correlation value is relatively large, the one in which the transmitter and the receiver are asynchronous, and the like.

In addition, the applicant of the present application filed Japanese Patent Application No. 2000-34.
No. 3056 proposes a method of changing the threshold for determining the correlation value in accordance with the result of the correlation value determination. Although this method can also deal with a part of the trouble caused by the weak signal, the present invention is superior in terms of speed and reliability. That is, in the present invention, since the false signal cross-correlation value and the weak signal correlation value can be discriminated without using the positioning result regarding the position of the receiver, the false signal cross correlation value at the time before the positioning result to be used is obtained. The influence of the correlation value can be prevented.

[Brief description of drawings]

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

FIG. 2 is a flowchart showing an example of a positioning prohibited satellite setting procedure for weak signal separation according to the present embodiment.

[Explanation of symbols]

101 antenna, 104 correlator, 105 pseudo noise code and local oscillation signal generator, 106 reception control unit, 1
07 Correlation value storage unit, 111 Doppler frequency measurement unit, 112 Position / speed calculation unit.

Claims (6)

[Claims] 1. A wireless system for transmitting a spectrum-spread signal from a plurality of transmission sources that perform transmission while moving relative to each other to wirelessly capture a transmission source through carrier frequency synchronization control and code phase synchronization control. The Doppler frequency of the received signal is measured for each of the acquired transmission sources based on the information obtained through the carrier frequency synchronization control performed by the receiver. The reception frequency difference determination step of detecting a combination within a predetermined range, and among the transmission sources belonging to the above combination, the correlation peak value obtained by the code phase synchronization control is of a low level obtained by false signal cross-correlation. Are both those that show correlation and those that show high-level correlation that cannot be obtained by false signal cross-correlation included? If it is found that the correlation peak is included in the correlation comparison step, the correlation peak value indicating the low level correlation is actually the transmission source related to the high level correlation. And a false signal cross-correlation detection method, which is a result of a false signal cross-correlation that is a cross-correlation between a received signal from the device and a spectrum despread code corresponding to a transmission source different from the transmission source. 2. In a radio system for transmitting a spread spectrum signal from a plurality of transmission sources transmitting at the same carrier frequency to a receiver, the transmission sources are wirelessly captured through carrier frequency synchronization control and code phase synchronization control. The carrier frequency of the received signal is measured based on the information obtained through the carrier frequency synchronization control performed by the receiver and for each captured transmission source, and the difference in the measured carrier frequency from the captured transmission sources is The reception frequency difference determination step of detecting a combination within a predetermined range, and among the transmission sources belonging to the above combination, the correlation peak value obtained by the code phase synchronization control is of a low level obtained by false signal cross-correlation. Whether both those showing correlation and those showing high-level correlation that cannot be obtained by false signal cross-correlation are included The correlation peak value indicating the low-level correlation is actually obtained from the transmission source related to the high-level correlation when it is found that the correlation peak is included in the correlation comparison step. The false signal cross-correlation detection method, which is regarded as a result of a false signal cross-correlation that is a cross-correlation between the received signal and the spectrum despread code corresponding to a transmission source different from the transmission source. 3. The false signal cross-correlation detection method according to claim 1, wherein in the correlation comparing step, among the transmission sources belonging to the combination, the correlation peak value obtained by the code phase synchronization control is the low value. False signal cross-correlation, characterized in that it is a step of checking whether or not both a weak signal maximum threshold value representing a level correlation and a strong signal minimum threshold value representing a low level above are included. Detection method. 4. The false signal cross-correlation detection method according to claim 1, wherein the correlation comparison step has a significant difference in correlation peak value obtained by code phase synchronization control between transmission sources belonging to the combination. Is a step of checking whether or not there is present, and is characterized in that the smallest correlation peak value among transmission sources having a significant difference in correlation peak value is actually regarded as a result of the false signal cross-correlation. False signal cross-correlation detection method. 5. A step of executing the false signal cross-correlation detection method according to any one of claims 1 to 4, and a transmission source corresponding to a spectrum despreading code that has caused the false signal cross correlation from a target to be captured thereafter. And a source selection limiting method, which comprises: 6. A carrier frequency synchronization control and a code phase synchronization control in a positioning system for transmitting a spread spectrum positioning signal from a plurality of positioning satellites that transmit at the same carrier frequency while moving relative to each other to a receiver. Is performed by a receiver that wirelessly captures positioning satellites through, based on the information obtained through carrier frequency synchronization control, and measures the Doppler frequency in the carrier of the received signal for each captured positioning satellite, and from the captured positioning satellites, The reception frequency difference determination step of detecting a combination in which the difference between the measured values of the Doppler frequency is within the predetermined range, and the correlation peak value obtained by the code phase synchronization control in the positioning satellites belonging to the above combination Corresponding low level correlations obtained by correlation and false signal cross correlations Correlation peaks that show low level correlations when it is found in the correlation comparison step that checks whether or not high level correlations are included, and correlation correlation step. The value is actually the result of a false signal cross-correlation that is a cross-correlation between the received signal from the positioning satellite related to the above high-level correlation and the spectrum despreading code corresponding to a positioning satellite different from the positioning satellite, And a selection exclusion step of excluding positioning satellites corresponding to the spectrum despreading code that has caused the false signal cross-correlation from the subsequent acquisition target.