JP2011196807A - False signal cross correlation detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent or reduce a failure caused by a position jump or the like resulting from a false signal cross correlation which excludes a satellite having a lower probability for obtaining an erroneous false signal cross correlation from the selection of a satellite.SOLUTION: In a false signal cross correlation detection method, it is determined whether a difference between Doppler frequency measurement values (difference between receive frequencies) is within a predetermined range in a plurality of the satellites for receiving and capturing signals (S201). It is checked whether a receive level difference of a satellite combination within the predetermined range is a predetermined value or larger (S205, S206). If the condition is met, the satellite having a low receive level is considered as a false image caused by the false signal cross correlation, and excluded from subsequent positioning calculation (S208).

Description

The present invention relates to a radio system that transmits a spectrum spread signal from a plurality of transmission sources that perform transmission at the same carrier frequency to a receiver while moving relative to each other. For example, a plurality of positioning satellites The present invention relates to a positioning system that transmits at the same carrier frequency while moving relative to each other and transmits a spread spectrum positioning signal to a receiver.

As a system related to a positioning system in which a plurality of positioning satellites transmit at the same carrier frequency while moving relative to each other and transmit a spread spectrum positioning signal to a receiver, a GPS satellite in an earth orbit is used as a transmission source. There is a GPS (Global Positioning System) that measures the position, velocity, etc. of a receiver that exists in a space where a predetermined number of GPS satellites can be seen.

The present invention particularly relates to a false signal cross-correlation detection method and a transmission source selection restriction method executed by a receiver that wirelessly captures a transmission source such as a positioning satellite through carrier frequency synchronization control and code phase synchronization control in such a system. And a satellite selection restriction method.

In GPS, a GPS receiver detects its position, velocity, and the like by positioning calculation based on satellite signals received from GPS satellites in orbit around the earth. In order to perform positioning calculations with a GPS receiver, it is necessary to select more than the number of GPS satellites required in principle, capture and track satellite signals from those GPS satellites, and demodulate data from the satellite signals. is there.

Since the satellite signal transmitted from the GPS satellite is a signal that is modulated by 50 bps data indicating the transmission time, detailed orbit information, orbital calendar information, and the like, and further spread spectrum by a spread spectrum code determined for each satellite. The GPS receiver despreads the received satellite signal with a spectrum despreading code corresponding to the selected target satellite, and demodulates data from the resulting signal.

The GPS receiver executes positioning calculation based on the demodulated data related to each selected target satellite and the code phase obtained as phase control information through spectrum despreading.

However, during acquisition and tracking of a certain target satellite, the reception level of the signal received from the target satellite is low, while the reception level of the other satellite is high, and the frequency of the target satellite and the frequency of the other satellite are high. When the difference of 0 is close to 0 Hz or N kHz (N is an integer), the receiver may falsely track the other satellites due to the false signal cross-correlation of each signal.

Therefore, in Patent Document 1, it is determined whether or not the frequency difference between the satellites being tracked by the receiver is within a predetermined range, and the correlation peak value is a false signal in the satellite combination within the predetermined range. If both the low level obtained by the cross-correlation shows the following correlation and the high level correlation not obtained by the false signal cross-correlation are included, the correlation below the maximum threshold is calculated. It has been proposed to exclude the indicated satellites from acquisition targets for satellite selection until power is turned on again.

JP 2003-98244 A

However, in Patent Document 1, since the correlation peak value is determined based on the maximum threshold value of the weak signal and the minimum threshold value of the strong signal and regarded as a false signal cross-correlation, a false signal cross-correlation may occur by mistake. There is a risk of excluding satellites from satellite selection.

Different GPS signals have a cross-correlation that is at most −21.1 dB lower than the autocorrelation. For example, when the maximum reception level of the GPS signal is about −120 dBm, the maximum reception level of the false signal cross-correlation is −141.1 dBm, and the low level and the high level are correlation peaks corresponding to around −141.1 dBm. Therefore, there is a case where the weak signal satellite having the smaller correlation peak value out of the satellite combinations having the correlation peak value in the vicinity of −141.1 dBm is excluded from the satellite selection. .

However, since the reception level difference between the satellite combinations is low, the false signal cross-correlation by the strong signal satellite having a large correlation peak value among the satellite combinations is smaller than the correlation peak value of the weak signal satellite, and erroneous tracking is performed. It does not occur.

In addition, the process of excluding satellites that are considered to have been mistracked from the capture targets for satellite selection until the receiver is turned on again is an opportunity to capture when the reception level of the weak signal satellites increases. You will lose.

The present invention has been made in consideration of such a problem, and an object thereof is to execute a determination of a false signal cross-correlation that does not include a satellite combination with a small reception level difference.

In order to achieve such an object, the false signal cross-correlation detection method according to the present invention includes:
In a wireless system that transmits a spectrum spread signal from a plurality of transmission sources that perform transmission while moving relative to each other to a receiver, by a receiver that wirelessly captures the transmission source through carrier frequency synchronization control and code phase synchronization control, Executed,
Based on the information obtained through carrier frequency synchronization control, measure the Doppler frequency of the received signal for each captured transmission source, and detect the combinations where the measured Doppler frequency difference is within the specified range. Receiving frequency difference determining step,
Among the transmission sources belonging to the above combinations, the reception level is measured based on the correlation peak value obtained by the code phase synchronization control, and among the above combinations, there are combinations in which the difference in the measurement value of the reception level is within a predetermined range. A reception level difference determining step for checking whether or not it is included,
If it is found that it is included in the reception level difference determination step, carrier frequency synchronization control and code phase synchronization control for a transmission source with a low reception level are actually cross-correlated with the spectrum despread code of the transmission source with a high reception level. It is determined that it corresponds to the false signal cross-correlation, and is excluded from the object of positioning calculation (position / velocity).

The false signal cross-correlation detection method according to the present invention includes:
In a positioning system that transmits a spectrum-spread positioning signal from multiple positioning satellites that transmit at the same carrier frequency while moving relative to each other, the positioning satellite is wirelessly transmitted through carrier frequency synchronization control and code phase synchronization control. Executed by the capturing receiver,
Based on the information obtained through carrier frequency synchronization control, the carrier frequency and Doppler frequency of the received signal are measured for each captured positioning satellite, and the difference between the measured values of the Doppler frequency is within a predetermined range from the captured positioning satellites. A reception frequency difference determination step for detecting a combination;
A reception level difference determining step for measuring a reception level based on a correlation peak value obtained by code phase synchronization control and checking whether a combination in which a difference in the measurement value of the reception level is within a predetermined range is included from the above combinations. And
If it is found that it is included in the reception level difference determination step, carrier frequency synchronization control and code phase synchronization control for positioning satellites with low reception levels are actually cross-correlated with the spectrum despreading codes of positioning satellites with high reception levels. It is determined that it corresponds to a false signal cross-correlation, and is excluded from the object of positioning calculation (position / velocity).

This invention does not compare the correlation peak value of each satellite with the low level threshold that can also be obtained by false signal cross-correlation and the high level threshold that cannot be obtained by false signal cross-correlation. Therefore, it is possible to avoid the problem of erroneously detecting a combination having a small reception level difference.

In addition, by removing the satellite determined to support the false signal cross-correlation from the acquisition target of the satellite selection until the power is turned on again, by excluding it from the target of the positioning calculation, When the frequency difference is outside the predetermined range, the satellite can be used.

It is a block diagram which shows the function structure of the GPS receiver which concerns on one Embodiment of this invention. It is a flowchart which shows an example of the positioning use prohibition satellite setting procedure for weak signal separation in this embodiment.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

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, down-converted by the frequency converter 102, 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 necessary for positioning calculation, the number of chips per epoch of the spread spectrum code related to the satellite signal to be acquired and tracked, and the allowable device size and cost, etc. In addition, n are provided corresponding to each of the I and Q phases, and are operated in parallel or sequentially.

The reception control unit 106 operates according to the information from the position / velocity calculation unit 112 and based on the output of the correlator 104, the operation of the signal generator 105, particularly the frequency of the local oscillation signal to be generated, and the spectrum despread code to be generated (pseudo). Noise code) type, code phase of each spectrum despread code to be generated, and the like are controlled.

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

First, the reception control unit 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 calculation unit 112, and the code phase is output from the correlator 104. The correlation value is controlled to be a peak (“capture”).

By this control, code phase synchronization of the spectrum despread code with respect to the satellite signal is established. Therefore, in the state where the satellite signal is spectrum despread, the data demodulator 110 can demodulate the data from the satellite signal.

Demodulated data, for example, detailed orbit information of the transmission source satellite and data related to transmission time are supplied to the position / velocity calculation unit 112. The reception control unit 106 controls the code phase in the signal generator 105 based on the sequentially obtained correlation values (“tracking”) so that this state, that is, the code phase synchronization state is maintained.

In addition, a satellite signal is converted to a lower frequency by a local oscillation signal supplied from the signal generator 105 in a member (or frequency converter 102) (not shown) before the input stage of the correlator 104. The satellite signal for which the code phase synchronization is established is the satellite signal after the frequency conversion.

Here, if the local oscillation frequency in the signal generator 105 is deviated, even if the code phase synchronization is established once, the synchronization is easily deviated with the passage of time. The satellite signal cannot be tracked.

The reception control unit 106 checks the code phase by shifting the code phase over one epoch of the spectrum despread code, but when the code phase synchronization cannot be established, the correlation value such as slightly adjusting the local oscillation frequency in the signal generator 105, etc. The local oscillation frequency control based on the above 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 are established with respect to the satellite signal, that is, in a state where a satellite signal whose spectrum is despread through the correlator 104 is obtained, the reception control unit 106 sends the correlation signal to the correlator 104. Then, the spectrum signal despread satellite signal is supplied to the data demodulator 110 to demodulate the data such as detailed orbit information, while the code phase in the signal generator 105 of the information obtained through the synchronization control is changed to the pseudorange measuring unit 109 and The signal is supplied to the pseudo speed measuring unit 108 and the local oscillation signal frequency in the signal generator 105 is supplied to the Doppler frequency measuring unit 111.

The pseudorange measuring unit 109 obtains a pseudorange with respect to the source of the satellite signal, that is, a code pseudorange based on the code phase. The pseudo speed measuring unit 108 detects a change in the code phase over time and obtains the moving speed of the receiver with respect to the satellite signal transmission source, that is, the pseudo speed.

The Doppler frequency measuring unit 111 obtains the Doppler shift of the satellite signal carrier frequency from the change of the local oscillation frequency, and thus the moving speed of the receiver with respect to the transmission source, that is, the Doppler speed.

The position / velocity calculation unit 112 calculates the position of the receiver using the code pseudorange obtained by the pseudorange measurement unit 109 in addition to the data demodulated by the data demodulation unit 110.

Further, the position / velocity 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 measurement unit 108 and the measurement result in the Doppler frequency measurement unit 111.

The position / velocity calculation unit 112 notifies the user of the calculation result and the like via a display device, a sound output device, a communication line, etc. (not shown). The position / velocity calculation unit 112 further selects and selects a combination of satellites used for positioning based on information demodulated by the data demodulation unit 110, information acquired and calculated in the past, and the like. The reception control unit 106 is instructed to receive (capture / track) a satellite signal from a GPS satellite.

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, and sets the positioning use prohibition satellite setting based on the calculated reception level. This is executed according to the procedure shown in FIG.

The point of the present invention is that when the correlation peak value generated by the false signal cross-correlation takes a relatively high value, the received signal that has generated the false signal cross-correlation is usually at a high level. There is a high possibility that the received signal is correctly captured by the correct spectrum despread code corresponding to the transmission source satellite of the received signal.

The received signal is captured correctly on the one hand (ie using a spectrum despread code corresponding to the source satellite), but erroneously on the other side (ie using a spectrum despread code corresponding to a satellite other than the source satellite). Under this situation, the content stored in the correlation value storage unit 107, the measurement result in the pseudo speed measurement unit 108, the pseudo distance measurement unit 109, and the Doppler frequency measurement unit 111, and the demodulation result in the data demodulation unit 110 are obtained. There must be more than one type of the satellite.

However, among these two or more stored contents, measurement results and demodulation results, there is at most one correct one, that is, one corresponding to the source satellite, and the rest are satellites other than the source satellite by mistake. (Ie, 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 under 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 obtained. Since these processes are performed in a mixed manner, an inaccurate positioning result or a sudden change in the positioning result (so-called “position skip”) will occur.

If there is a combination where the frequency difference is substantially 0 Hz or N kHz (N is an integer), the Doppler frequency measurement for that combination may actually be a frequency shift appearing on the received signal carrier from the same satellite. There is.

In the case of a 1.57542 GHz carrier in GPS, for example, if the absolute value of the difference in Doppler frequency measurement value is 20 Hz or less, or within NkHz ± 20 Hz, there is a high possibility of a received signal carrier from substantially the same satellite. Of course, the substantial criteria should be set as appropriate depending on the carrier, system, and receiver to which the present invention is applied. In FIG. 2, values corresponding to 20 Hz and NkHz ± 20 Hz are THR 1 Hz. , NkHz ± THR2Hz.

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 measurement unit 111, the difference in Doppler frequency is close to 0 Hz or N kHz by chance. Maybe it is only.

Therefore, in the present embodiment, when a combination of the Doppler frequency measurement values is found by the determination regarding the difference in the Doppler frequency measurement values, it is possible to determine whether the false signal cross-correlation is performed by determining the combination of the reception levels corresponding to the combination. Check for no.

That is, if the difference between the reception levels of these combinations is approximately equal to or greater than the difference between autocorrelation and cross-correlation, the satellite corresponding to the spectrum despread code from which the strong signal correlation value is obtained is It can be recognized that this is the cause of the false signal cross-correlation that resulted in the correlation peak value of the weak signal correlation value.

In other words, while a true satellite is captured by a strong signal, the result is as if another satellite was captured by a false signal cross-correlation by a strong received signal from that satellite. be able to.

In the present embodiment, not only the occurrence of a false signal cross-correlation phenomenon is detected by determining a difference in received level measurement values in addition to determining a difference in Doppler frequency measurement values, but also which satellite is a true satellite and which satellite is the true satellite. Whether it is a false image is also detected.

The procedure shown in FIG. 2 is a process based on the above-mentioned attention point and principle among the processes executed by the position / velocity calculation unit 112, and is executed at a predetermined frequency.

In the positioning use prohibition satellite setting procedure shown in FIG. 2, first, the position / velocity calculation unit 112 calculates the absolute value of the difference between a plurality of Doppler frequencies and the measurement values, which are measured values for different satellites. Is calculated. The Doppler frequency is input from the Doppler frequency measurement unit 111 to the position / velocity calculation unit 112. (S201).

The position / velocity calculation unit 112 determines whether the difference in the input Doppler frequency measurement value is THR 1 Hz or less, N kHz ± THR 2 Hz, or another value (S202).

As a result, when it is determined as another value, it can be assumed that any satellite is not a false image but a true satellite and no false signal cross-correlation occurs. Transition.

Conversely, if it is found that the absolute value of the difference between any two combinations of Doppler frequency measurements is less than or equal to THR1 Hz or within NkHz ± THR2 Hz, one of those Doppler frequency measurements May be due to a false signal cross-correlation, the operation of the position / velocity calculation unit 112 shifts to reception level difference comparison determination.

In the procedure shown in FIG. 2, the position / velocity calculation unit 112 calculates the correlation peak value for each satellite combination corresponding to each Doppler frequency measurement value whose absolute value of the difference is equal to or less than THR1 Hz or within NkHz ± THR2 Hz. From the correlation value storage unit 107, the reception level is calculated, and the absolute value of the reception level difference between the satellites is calculated (S203, S204). The absolute value of the reception level difference is compared with THR3 and THR4 (S205, S206).

When it is determined in steps S205 and S206 that the absolute value of the reception level is equal to or lower than THR3 and THR4, it is assumed that none of the satellite combinations is a false signal cross-correlation, and the position / velocity calculation unit 112 The operation leaves the procedure shown in FIG.

If it is found in steps S205 and S206 that "absolute value of reception level> THR3 or THR4" holds, the correlation peak value of the strong signal satellite of the above satellite combination is correct by the strong signal time correlation. It may be appreciated that this is a correlation peak value and that the received signal that resulted in the correlation peak value caused a false signal cross-correlation.

In the present embodiment, in order to prevent the above-described position jump due to the influence of the false signal cross-correlation, when such a condition is satisfied (S205, S206), the position / velocity calculation unit 112 determines the reception level of the satellite combination. The low satellite is excluded from the use of the position / velocity calculation (S208).

For false position autocorrelation values and weak signal correlation values, correlation values are detected for all chips belonging to one epoch (1023 in the case of C / A code), that is, correlation values for all 1023 code phases. And the code phase having the maximum correlation value and having a sufficiently large correlation value can be identified. This process can be executed by the reception control unit 106.

The present invention is not limited to the C / A code, and can be applied to the P code in principle. The present invention can also be applied to a GPS receiver to which various reinforcements or modifications are made, for example, a GPS receiver having a DGPS function.

Furthermore, not only a GPS receiver, but a receiver that selectively uses a plurality of types of spread spectrum codes to receive a spectrum spread signal, particularly a receiver whose reception level may be very low. The invention can be applied.

The present invention is particularly effective when applied to a chip having a large number of chips per epoch, a pseudo signal cross-correlation value that tends to be relatively large, and a transmitter / receiver that is asynchronous.

101 ... antenna, 102 ... frequency converter,
103 ... A / D converter, 104 ... n correlators,
105 ... n pseudo-noise codes and local oscillation signal generators 106 ... Reception control unit,
107 ... correlation value storage unit, 108 ... pseudo speed measurement unit,
109: Pseudo distance measuring unit, 110: Data demodulation,
111: Doppler frequency measurement unit 112: Position / speed calculation unit

Claims (6)

By a radio system that moves relative to each other and transmits a spectrum spread signal from a plurality of transmission sources that perform transmission to a receiver, by a receiver that wirelessly captures the transmission source through carrier frequency synchronization control and code phase synchronization control, Executed,
Based on information obtained through carrier frequency synchronization control, the carrier frequency and Doppler frequency of the received signal are measured for each acquired transmission source, and the difference in measured values of Doppler frequency is within a predetermined range from the acquired transmission sources. A reception frequency difference determination step for detecting a combination;
A reception level difference determining step for measuring a reception level based on a correlation peak value obtained by code phase synchronization control and checking whether a combination in which a difference in the measurement value of the reception level is within a predetermined range is included from the above combinations. And
If it is found that it is included in the reception level difference determination step, carrier frequency synchronization control and code phase synchronization control for a transmission source with a low reception level are actually cross-correlated with the spectrum despread code of the transmission source with a high reception level. A false signal cross-correlation detection method for determining that it corresponds to a false signal cross-correlation. In a positioning system that transmits a spectrum-spread positioning signal from multiple positioning satellites that transmit at the same carrier frequency while moving relative to each other, the positioning satellite is wirelessly transmitted through carrier frequency synchronization control and code phase synchronization control. Executed by the capturing receiver,
Based on the information obtained through carrier frequency synchronization control, the carrier frequency and Doppler frequency of the received signal are measured for each captured positioning satellite, and the difference between the measured values of the Doppler frequency is within a predetermined range from the captured positioning satellites. A reception frequency difference determination step for detecting a combination;
A reception level difference determining step for measuring a reception level based on a correlation peak value obtained by code phase synchronization control and checking whether a combination in which a difference in the measurement value of the reception level is within a predetermined range is included from the above combinations. And
If it is found that it is included in the reception level difference determination step, carrier frequency synchronization control and code phase synchronization control for positioning satellites with low reception levels are actually cross-correlated with the spectrum despreading codes of positioning satellites with high reception levels. A false signal cross-correlation detection method for determining that it corresponds to a false signal cross-correlation. 3. The false signal cross-correlation detection method according to claim 1, further comprising a reception frequency difference determination step using a carrier frequency instead of a Doppler frequency. 4. The false signal cross-correlation detection method according to claim 1, further comprising a reception level difference determination step using a correlation peak value instead of a reception level. A step of executing the false signal cross-correlation detection method according to any one of claims 1 to 4, and a transmission source or a positioning satellite corresponding to the spectrum despread code that has caused the false signal cross-correlation from a subsequent acquisition target. And a selection exclusion step of excluding the transmission source selection limiting method. A step of executing the false signal cross-correlation detection method according to any one of claims 1 to 4, and a transmission source or a positioning satellite corresponding to the spectrum despread code that has caused the false signal cross-correlation, A positioning calculation use restricting method, comprising: a positioning calculation use exclusion step for excluding the target from the target.