JPH07140224A - Spread spectrum signal tracking device - Google Patents

Abstract

PURPOSE:To enable spread spectrum signals to be tracked in a shorter time by dynamically determining a correlation measuring time according to the relationship between the signal level of an estimated spread spectrum signal and an anticipated correlation noise level. CONSTITUTION:A spread spectrum signal received by a receiver is inputted to multipliers 1a and 1b, where the carrier components of the signal for an I channel and a Q channel are eliminated independently. Correlators 3a and 3b measure respective correlation values (i) and (q) according to the inputted base band signals of the I and Q channels and a PN code from a PN code generator 11, and the correlation values are inputted to respective cyclic integrators 4a and 4b. The integrators 4a, 4b perform addition of the correlation values (i) and (q) according to the number of cycles which is transmitted from a correlation measuring requirement computing portion 18, and the values are squared by squarers 5a and 5b and added together through an adder 6. These signals squared and added together are inputted to a synchronization recognition portion 8 to determine whether or not the signals are in synchronization with the PN code.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum signal acquisition device suitable for use in a GPS (Global Positioning System) receiver, and more particularly to a device configuration for shortening the acquisition time of a spread spectrum signal. Regarding improvement.

[0002]

2. Description of the Related Art As is well known, GPS is a three-dimensional position (reception of only three satellites) for 24 hours in the world and in all weather by receiving radio waves from three or more satellites in the field of view. In the case of, it is a system that enables measurement of two-dimensional position), speed, and time. For this reason, much research is being conducted to utilize this GPS for navigation of automobiles and the like.

By the way, when the GPS is used for navigation of an automobile in this way, it is necessary to keep the navigation information as highly reliable information by shortening the so-called positioning start time and the recovery time from the satellite radio wave interruption as much as possible. You will need it to do this. The positioning start time is the time required to start positioning by capturing the radio waves of the above three or more satellites, and the return time from the satellite radio wave interruption is the time from the satellites due to, for example, a high-rise building. It is the time until the radio waves of these three or more satellites are captured again and the positioning becomes possible after the radio waves are blocked.

In order to shorten the positioning start time and the recovery time from the satellite radio wave cutoff, it is absolutely necessary to first capture the radio waves of each satellite in the field of view in the shortest possible time.

On the other hand, in such GPS, the signal transmitted from the satellite is spread spectrum modulated. Therefore, in order to capture the satellite signal, not only the carrier frequency is accurately predicted, but also a PN code having the same pattern as the PN (pseudo noise) code included in the satellite signal is generated in the receiver. It is necessary to synchronize the PN codes with each other. The synchronization can be obtained by measuring the correlation between the baseband signal obtained by removing the carrier component from the received spread spectrum signal and the PN code generated in the receiver. Here this P
It is known that the autocorrelation value of the N code has a peak every code period when the correlation measurement section is one cycle of the PN code, and is almost zero at other phases.

Therefore, in the past, for example, Japanese Patent Laid-Open No. 64-269 was used.
As also seen in Japanese Patent Publication No. 76, etc., the time for measuring the correlation between the baseband signal and the PN code generated in the receiver, that is, the correlation measurement time is the PN code cycle time. By the way, in the case of GPS receiver,
C / A code cycle time (=
1 msec) is the correlation measurement time.

[0007]

As long as the carrier frequency of the satellite signal can be accurately predicted and the PN code phase of the satellite signal can be accurately matched, the PN code cycle time can be correlated. By setting the measurement time, it is possible to capture the satellite signal in a short time.

For example, when the GPS receiver is composed of a Costas loop, the sum of squares (correlation power) of the correlation values i and q measured from the I channel and the Q channel has the same PN code phase and carrier frequency. Peaks when you do. At this time, the peak correlation power is also sufficiently larger than the peak correlation noise power, so that it is easy to determine that the PN codes are synchronized with each other based on the peak correlation power. .

However, even if the PN code phases match, the peak correlation power decreases if the carrier frequencies differ. When the carrier frequency error is close to 1 KHz, the peak correlation power becomes lower than the peak correlation noise power. In such a state, it is difficult to determine the peak correlation power, let alone the synchronization determination of the PN code.

As described above, in order to stably acquire the spread spectrum signals of all the satellites, at least the carrier frequencies of the satellite signals and the carrier frequencies generated in the receiver must be exactly matched. . However, as a practical matter, there is often a difference between the carrier frequency set as a target in the GPS receiver and the carrier frequency actually output from the generator,
It has been considered extremely difficult to match this with the carrier frequency of the satellite signal. When such a shift in carrier frequency cannot be ignored, carrier search will be repeated many times, which will prolong the positioning start time and the recovery time from the satellite radio wave interruption described above.

On the other hand, if the signal level of the received GPS satellite signal is strong, the carrier frequency prediction error is 1
It is possible to capture this, even near KHz. If the signal level of the satellite signal is strong in this way, the peak correlation power will also be maintained at a value larger than the peak correlation noise power, and the presence or absence of synchronization of the PN code will be determined based on the peak correlation power. It becomes possible to do.

However, GPS satellite signals arriving on the ground are not always received at such a strong signal level. The signal level of a satellite usually has a strong dependence on the satellite elevation angle, and when this becomes a low elevation angle, there is almost no difference between the peak correlation power and the peak correlation noise power, and the allowance for the carrier frequency prediction error naturally becomes "0". Get closer. Therefore, even in such a case, the carrier search will be repeated many times, which will prolong the positioning start time and the recovery time from the satellite radio wave interruption described above.

The present invention has been made in view of such circumstances, and captures a spread spectrum signal transmitted from a satellite in a shorter time even when the allowable amount of a carrier frequency prediction error is small. It is an object of the present invention to provide a spread spectrum signal capturing device capable of performing the above.

[0014]

In order to achieve these objects, the present invention removes a carrier component from a received spread spectrum signal to extract a baseband signal, and at the same time a required correlation measurement time is obtained. While performing a correlation calculation using the extracted baseband signal and a predetermined pseudo noise code, the pseudo noise is calculated until the correlation power obtained based on the correlation calculation reaches a predetermined value indicating synchronization with the pseudo noise code. In a spread spectrum signal capturing device for sliding the phase of a code, a received signal level estimating means for estimating a signal level of the received spread spectrum signal, and a signal level of the estimated spread spectrum signal and a correlation noise predicted in advance. Correlation measurement condition calculation means for dynamically determining the correlation measurement time based on the relationship with the level Unisuru.

[0015]

According to the received signal level estimation means and the correlation measurement condition calculation means, the correlation measurement time is dynamically determined according to the signal level of the received spread spectrum signal at each time, and the determined correlation measurement is performed. Over time, the extracted baseband signal and a predetermined pseudo noise code (PN
Code) and the correlation calculation is performed. Incidentally, as the correlation measurement time is set shorter, the characteristic of the correlation power obtained by the correlation calculation changes in the direction of widening the allowable amount with respect to the prediction error of the carrier frequency.

For this reason, even when the carrier frequency prediction error is small due to reasons such as incomplete removal of the carrier component or a small signal level of the received spread spectrum signal, By setting a shorter correlation measurement time by the correlation measurement condition calculation means, the allowable amount of the carrier frequency prediction error is expanded.

By thus increasing the allowable amount of the carrier frequency prediction error, the level of the correlation power obtained based on the above correlation calculation is also substantially increased in the direction in which the carrier frequency error increases. Therefore, the determination that the same correlation power has a predetermined value indicating synchronization with the PN code can be made at a relatively early stage. Therefore, the time required to capture the spread spectrum signal is naturally shortened.

The received signal level estimating means may be, for example, (a) elevation angle calculating means for obtaining the received elevation angle of the spread spectrum signal, and (b) estimation of the same spread spectrum signal corresponding to the obtained received elevation angle. A signal level estimation table in which the signal level is preset and registered can be provided. As mentioned above, the signal level of the spread spectrum signal strongly depends on its reception elevation angle. Therefore, by calculating the reception elevation angle of the spread spectrum signal and estimating the signal level of the spread spectrum signal from the calculated value, a highly reliable value can be obtained as the received signal level.

Further, the correlation calculation by the baseband signal and a predetermined pseudo noise code is a cyclic integral for each correlation value between the I component and the Q component of the baseband signal and the pseudo noise code, and 2 of these integral values. In the case of the multiply-and-accumulate operation, this is (
c) Means for determining the correlation measurement time as the number of cycles in this cyclic integration. For this purpose, for example, prepare a map in which the relationship between the expected peak correlation noise power and the number of rounds corresponding to them is set based on preliminary experiments, etc., and the estimated received signal level is minimized. The number of cycles corresponding to the recognizable peak correlation noise power is obtained from this map.

Further, in place of the above configuration, (A) received signal level estimating means for estimating the signal level of the received spread spectrum signal with a predetermined width, and (B) estimation with this predetermined width. Based on the relationship between the signal level of the spread spectrum signal and the correlation noise level predicted in advance, as the correlation measurement time, each different time corresponding to the level width of the spread spectrum signal estimated with the same predetermined width is dynamically set. (C) The correlation calculation by the extracted baseband signal and a predetermined pseudo-noise code is simultaneously performed over each of the determined correlation measurement times. Meanwhile, the phase of the pseudo noise code is slid until one of the correlation powers obtained based on the correlation calculation reaches a predetermined value indicating the synchronization with the pseudo noise code. In the structure that can be made more reliable acquisition of spread spectrum signals mentioned above. That is, in this case, in addition to the basic operation described above by the received signal level estimating means and the correlation measuring condition calculating means, the correlation measuring time for each phase is set for each phase setting value of the pseudo noise code (PN code). Thus, the synchronization determination based on is executed in parallel. Therefore, even if the reception environment is further deteriorated, the probability that the spread spectrum signal will be captured will be kept high.

In this case, the received signal level estimating means (A) also includes, for example, (a ') elevation angle calculating means for obtaining the reception elevation angle of the spread spectrum signal, and (b') the obtained reception angle. The estimated signal level of the spread spectrum signal corresponding to each elevation angle may be configured to include a signal level estimation table in which a critical level corresponding to the predetermined width is preset and registered.

Further, the correlation calculation by the baseband signal and a predetermined pseudo noise code is performed by a plurality of systems of cyclic integration for each correlation value between the I component and the Q component of the baseband signal and the pseudo noise code, and a plurality of them. When the square sum calculation of multiple systems for each integrated value of the system, this is also used as the correlation measurement condition calculation means in (B) above.
(c ') It may be configured as a means for determining each of the different correlation measurement times as the number of cycles in cyclic integration of these plural systems. Also in this case, it is possible to use a map in which the relationship between the expected number of peak correlation noise powers and the number of rounds corresponding to them is set in advance.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the configuration of an embodiment of a spread spectrum signal capturing apparatus according to the present invention.

The apparatus of this embodiment is a GPS receiver embodying the spread spectrum signal acquisition apparatus according to the present invention. The GPS receiver itself is assumed to be mounted on a vehicle such as an automobile. And in the device of this embodiment,
The PN code (pseudo noise code) generated from the inside of the receiver is slid to detect the synchronization of the spread spectrum signal received by the sliding.

Now, in the spread spectrum signal capturing apparatus of the embodiment shown in FIG. 1, the signals are transmitted from GPS satellites,
The spread spectrum signal received by the receiver is input to the multipliers 1a and 1b, where the carrier component of the I channel and the Q channel is removed.

Incidentally, the multiplier 1a removes the carrier component of the phase "0 °" from this spread spectrum signal to obtain I
The baseband signal of the channel is extracted, and the extracted baseband signal of the I channel is the LPF.
After the high frequency component is removed by the (low pass filter) 2a, it is input to the correlator 3a. The multiplier 1b removes the carrier component of the phase "90 °" from the spread spectrum signal to extract the Q-channel baseband signal. The extracted Q-channel baseband signal is the LPF. (Low pass filter) 2b
After the high frequency component is removed by, it is input to the correlator 3b.

These correlators 3a and 3b respectively have correlation values i and q on the basis of the input I-channel and Q-channel baseband signals and a PN code generated from a PN code generator 11 described later. Is to measure. The measured correlation value i of the I channel is measured by the cyclic integrator 4a, and the correlation value q of the Q channel is measured by the cyclic integrator 4a.
Input to b. The correlators 3a and 3b are assumed to measure the correlation values i and q at a time such as at least PN code period / n (where n is a natural number of 2 or more).

The cyclic integrators 4a and 4b successively add the input correlation values i and q m times on the basis of the number of cycles m given from a correlation measurement condition calculating unit 18 described later. , The addition results are
After being squared by the squarers 5a and 5b, the sums are added through the adder 6.

Then, the signal obtained by the square addition, that is, the correlation power of the received signal is further input to the synchronization determination unit 8 after its noise component is smoothed through the filter 7, and in the synchronization determination unit 8. The presence or absence of synchronization with the PN code is determined based on comparison with the capture determination threshold TH.

Here, the filter 7 is usually constructed as a means for repeatedly executing the cyclic integration similar to the cyclic integrators 4a and 4b, and by adding and averaging the correlation powers, variations due to noises, measurement errors, etc. are generated. It works to mitigate.

The synchronization determination unit 8 monitors the level of the filtered correlation power based on the capture determination threshold TH given from the correlation measurement condition calculation unit 18 described later, and the correlation power level is equal to or higher than the threshold TH. When this occurs, it is determined that the PN code generated is synchronized.

When it is determined that the synchronization has been achieved, that is, that the synchronization has been captured, the synchronization determination unit 8 outputs the true signal Tr to the demodulator 9 to activate the demodulation function.

The demodulator 9 demodulates the transmission data from the captured spread spectrum signal based on the correlation value i of the I channel measured through the correlator 3a. The demodulated data is The GPS data will be used for positioning calculation of the vehicle.

On the other hand, when the level of the input correlation power is less than the threshold value TH, the synchronization determination unit 8 determines that the synchronization is not yet established, and the PN code control unit 10
A fail signal F is output to

The PN code control section 10 is a section for controlling the code pattern and the generation timing (code phase) of the PN code generated by the PN code generator 11, and the failure signal F is added from the synchronization determination section 8 in this way. Thus, the phase of the PN code generated at that time is changed by, for example, (1/2) chip. P
As described above, the PN code generated from the N code generator 11 is given to the correlators 3a and 3b. Therefore, by changing the phase of the PN code in this way, the correlation values i and q of the I channel and Q channel are also changed, and thus the level of the correlation power filtered and squared is changed.

If the level of the changed correlation power is equal to or higher than the capture determination threshold value TH, the synchronization determination unit 8
It is determined that the synchronization has been achieved in step S3, and the acquisition process for the received signal is ended.

However, even if the level of the same correlation power changes, if the threshold value TH is not satisfied, the synchronization determination unit 8 is again activated.
A fail signal F is sent from the PN code control unit 10 to the PN code control unit 10, and the PN code phase changing process is repeated.

Even if the PN code phase changing process is repeated for one cycle of the PN code phase, if the correlation power above the threshold value TH cannot be detected, then the synchronization judgment is made at that time. Based on the fail signal F output from the unit 8, the PN code control unit 10 outputs a signal requesting the carrier control unit 12 to change the carrier frequency. That is, in this case, it is considered that the carrier signal frequency output from the carrier generator 13 did not exist in the main lobe of the correlation power.

The carrier control unit 12 includes the carrier generator 1.
3 is a part for controlling the frequency of the carrier signal generated, and the frequency of the carrier signal being generated at that time is changed by the addition of the signal requesting the change of the carrier frequency from the PN code controller 10.

From the carrier generator 13, the multiplier 1
A carrier frequency signal having a phase of "0 °" is applied to a and a carrier frequency signal having a phase of "90 °" is applied to the multiplier 1b. Therefore, by changing the frequencies of the carrier signals in this way, the basebands of the I channel and Q channel are also changed, and consequently the main lobe of the correlation power is changed.

However, at this time, as shown in FIG.
When the carrier frequency is changed so that the main lobe of the correlation power changes in (2 / measurement time) [Hz] cycle,
In the valley portion of the main lobe, the carrier frequency cannot be searched based on the acquisition determination threshold value TH.

Therefore, in the carrier control unit 12, as shown in FIG. 2B, the carrier frequency to be changed is set so that the valley of the main lobe of the correlation power becomes larger than the capture determination threshold TH. Shall be controlled.

If the carrier frequency is changed in this way,
Even if the correlation power equal to or higher than the capture determination threshold TH cannot be detected by the previous PN code search, the capture determination threshold TH may be detected by the subsequent PN code search.
The above correlation power may be detected.

On the other hand, in the apparatus of the embodiment, the data memory 14 stores the satellite orbit information (almanac data) or contained in the previously demodulated GPS data and the own position information ps calculated based on the GPS data. At least memory that is stored. The satellite orbit information or and the position information ps thus stored are read out from the same data memory 14 at the time of initial setting of the device, and given to the elevation angle calculation unit 15.

The elevation angle calculation unit 15 uses the data memory 14
This is a part for calculating the satellite elevation angle e based on the position of the vehicle (receiver) based on the satellite orbit information or and position information ps read from and the time information t output from the clock 16. The elevation angle calculation method itself is well known, and a description thereof is omitted here. The value of the elevation angle e obtained through the elevation angle calculation unit 15 is input to the correlation power estimation table 17.

The correlation power estimation table 17 is shown in FIG.
As shown in FIG. 5, for example, a ROM (read-only memory) in which the relationship of the estimated peak correlation power A ^ 2 (A square: "^" represents a power) is preset with respect to the value of the elevation angle e is registered. It is a table consisting of. As shown in FIG. 3, in the correlation power estimation table 17, the value of the estimated peak correlation power A ^ 2 corresponding to the elevation angle value e is read out by accessing with the elevation angle value e and the correlation is calculated. The data is output to the measurement condition calculation unit 18. As described above, the signal level of the spread spectrum signal, that is, the value of the estimated peak correlation power A ^ 2 depends strongly on the reception elevation angle, that is, the satellite elevation angle e.

The correlation measurement condition calculating unit 18 uses the peak correlation noise power map 19 to calculate the correlation measurement time, that is, the previous cyclic integrators 4a and 4b from the value of the estimated peak correlation power A ^ 2 input. On the other hand, it is a part that determines the number of rounds m to be designated and the capture determination threshold TH that is a reference for the synchronization determination unit 8 to perform the synchronization determination described above.

The number of rounds m and the acquisition determination threshold TH
In determining, the correlation measurement condition calculation unit 18 first executes the following calculation so that the estimated peak correlation power A ^ 2 input as described above has a width corresponding to the carrier frequency error Δf. Even in the following, "^" represents exponentiation. Ap ^ 2 = [A.sin (πΔfT) / πΔfT] ^ 2 (1) where Ap ^ 2 is the peak correlation power obtained by adding the carrier frequency error Δf to the estimated peak correlation power A ^ 2. Is. In the equation, A indicates the correlation peak value of this correlation power, and T indicates the correlation measurement time. The relationship between the estimated peak correlation power A ^ 2 and the obtained peak correlation power Ap ^ 2 is shown in FIG. 4 for reference. Previous,
The peak correlation power obtained as the sum of squares (i ^ 2 + q ^ 2) of the correlation value i of the I channel and the correlation value q of the Q channel is also the above (1) because the predicted carrier frequency shifts by Δf. The equation or the relationship similar to that shown in FIG. 4 changes.

On the other hand, the peak correlation noise power map 19
For example, as shown in FIG. 5, expected peak correlation noise powers An1 ^ 2, An2 ^ 2, An3 ^ 2, and An4 ^ 2 and the number of rounds m corresponding to them (m = 1, m =
2, m = 3, and m = 4) is a map set in advance based on experiments and the like.

Also, each of these peak correlation noise powers An1
It is assumed that the relationship between the number of cycles m and the correlation measurement time T set corresponding to ^ 2, An2 ^ 2, An3 ^ 2, and An4 ^ 2 is as follows. (1) Peak correlation noise power An1 ^ 2 Number of rounds m = 1 Correlation measurement time T = 0.25 × PN code cycle time (2) Peak correlation noise power An2 ^ 2 Number of rounds m = 2 Correlation measurement time T = 0. 5 × PN code cycle time (3) Peak correlation noise power An3 ^ 2 Number of cycles m = 3 Correlation measurement time T = 0.75 × PN code cycle time (4) Peak correlation noise power An4 ^ 2 Number of cycles m = 4 Correlation Measurement time T = 1.0 × PN code cycle time In the correlation measurement condition calculation unit 18, the peak correlation noise powers An1 ^ 2, An2 ^ 2, An3 predicted and set in this way for the peak correlation noise power map 19 are set. ^ 2 and An
4 ^ 2 and the peak correlation power Ap ^ 2 obtained above are sequentially compared, and the peak correlation noise power at which the peak correlation power Ap ^ 2 can be recognized at least and the number of rounds corresponding to the peak correlation noise power are determined. decide.

For example, the peak correlation power Ap ^ found above
2 is each peak correlation noise power An1 ^ 2, An2 ^ 2, A
As shown in FIG. 5, it is determined that n3 ^ 2 and An4 ^ 2 have a relationship such as An1 ^ 2 ≥ Ap ^ 2> An2 ^ 2> An3 ^ 2> An4 ^ 2 (2). In this case, "peak correlation noise power An2 ^ 2" is determined as the peak correlation noise power at which the same peak correlation power Ap ^ 2 can be recognized at least, and the number of rounds m corresponding to the peak correlation noise power An2 ^ 2 is determined. As a result, “m = 2” with the correlation measurement time T being (0.5 × PN code cycle time) is determined.

In the case of this example, the correlation measurement condition computing unit 18 instructs the previously determined "cyclic number m = 2" to the cyclic integrators 4a and 4b, and also to the synchronization determining unit 8. The above-determined “peak correlation noise power An2
A value corresponding to “2” will be designated as the capture determination threshold TH.

Incidentally, conventionally, the correlation measurement time T has been fixed to the PN code cycle time (in the example of the peak correlation noise power map 19 described above, the time corresponding to the number of cycles m = 4). However, in this way, the correlation measurement time T is “0.5 × P
Correlation obtained as the sum of squares (i ^ 2 + q ^ 2) of the correlation value i of the I channel and the correlation value q of the Q channel by being shortened to "N code cycle time (number of cycles m = 2)". For example, as shown in FIG. 6, the electric power changes so as to increase the permissible amount with respect to the carrier frequency prediction error Δf. Also in the above formula (1), it can be understood that the reduction rate of the correlation power with respect to the carrier frequency error Δf can be reduced by shortening the correlation measurement time T.

Incidentally, in FIG. 6, the broken line shows the characteristic of the correlation power when the correlation measurement time T = PN code cycle time (the number of cycles m = 4), and the solid line shows the correlation measurement time T = 0. 5 × PN code cycle time (number of patrols m = 2)
The characteristics of the correlation power are shown below. If the same level of correlation power is assumed, it is clear that a larger carrier frequency error can be expected with the correlation power characteristic shown by the solid line with a short correlation measurement time T, as noted as Δf and Δf ′. . In addition, changing the point of view, point pt1
And pt2, assuming allowable values for the same carrier frequency error, the allowable value pt1 is captured on the side of the correlation power characteristic indicated by a broken line with a long correlation measurement time T (= PN code cycle time). Disabled (threshold TH
However, on the other hand, on the side of the correlation power characteristic shown by the short solid line of the correlation measurement time T on the other side, it is possible to sufficiently capture even with the allowable value pt2.

However, if the correlation measurement time T is shortened in this way, the peak correlation noise power also increases accordingly. For example, when looking at the above correlation power with respect to the PN code phase, when the correlation measurement time T is selected as the PN code cycle time, the peak correlation noise power An ^ 2 is as shown in FIG. The value is kept sufficiently small compared to the peak correlation power. However, the correlation measurement time T is PN
When (1 / n) time of the code period (n is a natural number of 2 or more) is selected, as shown in FIG. 7B, the peak correlation noise power (An ') ^ 2 and the peak correlation power The level difference with Then, the correlation measurement time T is P
If it is not a natural number multiple of the N code cycle time, or if the same time T is set to be extremely short, it becomes impossible to capture the satellite signal having a small peak correlation power.

Therefore, in the apparatus of this embodiment, the peak correlation noise powers An1 ^ 2, An2 ^ 2, An3 with respect to the peak correlation noise power map 19 are sufficiently taken into consideration based on preliminary experiments and the like. ^ 2 and An4 ^ 2
Also, the registration setting of the correlation measurement time T (the number of rounds m) corresponding to them is performed.

FIG. 8 and FIG. 9 show a procedure for capturing a spread spectrum signal by the apparatus of this embodiment. Next, with reference to FIG. 8 and FIG. 9 together, the operation of the entire apparatus of the embodiment will be described in more detail.

The apparatus of this embodiment captures the spread spectrum signal transmitted from the GPS satellite by the procedure listed below. First, the apparatus performs initial setting (step 100) for the satellite signal to be captured, in order to obtain the most suitable correlation measurement condition in the position / environment of the vehicle. The procedure for this initial setting is shown in FIG.
The details are shown in.

That is, in the initialization routine shown in FIG. 9, the device of the embodiment first sets the data memory 1
4, the latest satellite orbit information or and the position information ps of the vehicle and the current time information t output from the clock 16 are read into the elevation angle calculation unit 15 to calculate the elevation angle value e of the capture target satellite. (Step 101). The same apparatus that has obtained the elevation value e in this way next performs correlation power estimation table 1
7, the received signal level (peak correlation power) A ^ 2 corresponding to the obtained elevation angle value e is estimated (step 10
2) Based on this estimated peak correlation power A ^ 2, the number of rounds m and the acquisition determination threshold TH are determined through the correlation measurement condition calculation unit 18 (step 103). The determination of the number of rounds m and the acquisition determination threshold TH is based on the peak correlation noise power map 19 and the modified peak correlation power Ap ^.
2 is executed in the manner described with reference to FIG. 5 above, as described above.

On the other hand, the apparatus of this embodiment further controls the frequency of the carrier signal to be generated from the carrier generator 13 to the predicted carrier frequency as the initialization routine (step 104), and the PN code generator. The PN code pattern to be generated from 11 is controlled to the PN code pattern of the satellite signal to be captured (step 10).
5).

For example, as a spread spectrum signal (satellite signal) to be captured, S (t) = AP (t) D (t) cosωi t (3) where S (t): spread spectrum signal A: amplitude If a signal such as P (t): PN code (-1, + 1) D (t): data (-1, + 1) cos ωi t: carrier is received, the frequency of the carrier signal to be generated is It is controlled to a frequency such as “cos (ωt + φ)” through the control unit 12,
One PN code is controlled by the PN code control unit 10 into a pattern such as “P (t + τ)”.

By the way, the spread spectrum signal is multiplied by the carrier signal through the multipliers 1a and 1b and the high frequency components thereof are removed through the LPFs 2a and 2b. The signal will be extracted. I channel signal = AP (t) D (t) cos (Δωt + φ) Q channel signal = AP (t) D (t) sin (Δωt + φ) (4) where Δω = ω−ωi Also, these I channel and Q The channel signals are measured by the correlators 3a and 3b based on the PN code, so that the respective correlation values i and q take the following values. i = (1 / T) A∫_ {T0} ^ {T + T0} P (t + τ) P (t) D (t) cos (Δωt + φ) dt q = (1 / T) A∫_ { T0} ^ {T + T0} P (t + τ) P (t) D (t) sin (Δωt + φ) dt (5) where T: correlation measurement time (= PN code cycle time /
n, n ≧ 2) T0: Correlation measurement start time In the equation, “∫_ {T0} ^ {T + T0}” means “integration from“ T0 ”to“ T + T0 ””. And In the main routine shown in FIG. 8, the apparatus of this embodiment which has completed the initial setting in this way, through the cyclic integrators 4a and 4b based on the determined number of cycles m (for example, m = 2), the I channel Cyclic integration is performed on the correlation value i and the correlation value q of the Q channel (step 110). In addition, in the same device, after the respective integrated values thus obtained are squared through the squarers 5a and 5b, they are added through the adder 6,
Calculate the correlation power of the satellite signal (step 12)
0).

The apparatus of the embodiment, which has thus obtained the correlation power of the satellite signal, further passes the correlation power through the filter 7,
After alleviating the variations (steps 130 and 14)
0), the synchronization determination unit 8 determines whether or not the correlation power P is synchronized, based on the comparison with the determined capture determination threshold TH (step 150). Note that the filtering by the filter 7 is normally performed in step 14 shown in FIG.
0 → step 110 → step 120 → step 130
As described above, it is realized as a process of repeating the cyclic integration similar to the cyclic integrators 4a and 4b, and averaging the obtained correlation powers, as in the above loop.

In the apparatus of this embodiment, when it is determined by the synchronization determination unit 8 that the value of the obtained correlation power P is equal to or greater than the capture determination threshold TH (when the true signal Tr is output). Ends the acquisition processing for the satellite signal, assuming that the satellite signal has been acquired. It has also been described above that the demodulator 9 is activated by achieving the target acquisition of the satellite signal, and then the GPS data demodulation for the satellite signal becomes possible.

On the other hand, when it is determined by the synchronization determination unit 8 that the value of the obtained correlation power P is less than the capture determination threshold TH (when the failure signal F is output), the apparatus of the embodiment is , PN code control unit 10
The phase of the PN code generated from the code generator 11 is changed by, for example, (1/2) chip (step 16).
0). Such a phase change of the PN code is performed until the value of the correlation power P that changes due to the phase change of the PN code becomes equal to or larger than the capture determination threshold TH.
It is repeated for a period (step 170). If the level of the correlation power changed due to the phase change of the PN code becomes equal to or higher than the acquisition determination threshold TH during that time, it is determined at that point that synchronization has been established, and the acquisition processing for the satellite signal is terminated. It

On the other hand, even if such a search (code search) with changing the phase of the PN code is repeated for one cycle of the same PN code phase, the value of the correlation power P still satisfies the threshold value TH. If not, the device of the same embodiment then:
The carrier frequency is changed (step 180).
The carrier control unit 13 changes the carrier frequency.
Through, for example, in the manner shown in FIG. 2 (b), and by changing the carrier frequency,
Even if the correlation power above the capture determination threshold TH cannot be detected by the previous code search, the correlation power above the threshold TH may be detected by the subsequent code search. And so on, as mentioned above.

However, in the apparatus of this embodiment, as described above, the optimum correlation measurement condition (correlation measurement time, that is, the number of integration cycles m) for each target satellite signal is calculated.
Also, since the acquisition determination threshold TH) is initialized in advance, the allowable amount of the carrier frequency prediction error is suitably expanded, and this acquisition process is also ended at a relatively early stage.

By the way, in the apparatus of the above embodiment, the peak correlation power A ^ 2 (A) estimated from the calculated satellite elevation angle e.
(Square) is almost uniquely determined as shown in FIG. However, there is a considerable variation in the peak correlation power of the satellite signals actually received, and the estimated peak correlation power (correctly, the peak correlation power is corrected by taking into account the carrier frequency error Δf Ap ^
If there is no significant difference between 2) and the capture determination threshold TH, capture may fail.

In order to avoid such a situation, it is only necessary to measure a plurality of correlation values having different correlation measurement times and perform the synchronization determination. FIG. 10 shows, as another embodiment of the spread spectrum signal capturing apparatus according to the present invention, an example of an apparatus configured to measure a plurality of correlation values having different correlation measurement times and perform synchronization determination. In the apparatus of the embodiment shown in FIG. 10, the same elements as those of the apparatus shown in FIG. 1 above are designated by the same or related reference numerals, and duplicate description of these elements will be omitted. .

In the apparatus of this embodiment, as shown in FIG. 10, different correlation measurement times (the number of rounds m1 and m2) for each of the correlation value i of the I channel and the correlation value q of the Q channel. It is configured by including two systems of correlation power calculation circuits in which is set. Incidentally, the correlation power calculation circuit of the first system includes cyclic integrators 4a and 4b, and squarers 5a and 5
b, an adder 6a, and a filter 7a. The correlation power calculation circuit of the second system includes cyclic integrators 4c and 4d, 2
It comprises multipliers 5c and 5d, an adder 6b, and a filter 7b. Further, the correlation powers P1 and P2 obtained through these two systems of correlation power calculation circuits are subjected to synchronization determination in the synchronization determination unit 8 ′ based on the different capture determination thresholds TH1 and TH2. . On the other hand, the latest satellite orbit information o stored in the data memory 14
Although the satellite elevation angle e is calculated by the elevation angle calculation unit 15 based on r and the position information ps of the vehicle and the current time information t output from the clock 16, the same applies to the device of this embodiment. In the case of the device of the embodiment, as shown in FIG. 11, for example, the estimated peak correlation power value is set in the correlation power estimation table 17 ′ with a predetermined width with respect to the calculated elevation angle value e. Has been done. In the example of FIG. 11, the peak correlation power A1 ^ 2 and the peak correlation power A2 ^ smaller than the peak correlation power A1 ^ 2 for a certain elevation angle e.
It is shown that two types of peak correlation power with 2 are estimated.

In addition, in the apparatus of the same embodiment, the correlation measurement condition calculation unit 18 'has the estimated peak correlation power A
From the correction values Ap1 ^ 2 and Ap2 ^ 2 in which the carrier frequency error Δf of 1 ^ 2 and A2 ^ 2 is taken into consideration, the peak correlation noise power map 19 is used to enter the cyclic integrators 4a and 4b of the first system. The number of patrols that should be specified for m
1 and the number of cycles m2 to be specified for the second system cyclic integrators 4c and 4d, and the capture determination thresholds TH1 and TH2 that are the reference for the synchronization determination unit 8 ′ to perform the synchronization determination. It is the part that determines. The peak correlation noise power map 19 shows the expected peak correlation noise power An1 ^ 2 in several steps even in the device of this embodiment.
, An2 ^ 2, An3 ^ 2, and An4 ^ 2 and the corresponding number of rounds m (m = 1, m = 2, m = 3, and m =
4) is a map that is set in advance based on experiments, etc., and corresponds to each of these peak correlation noise powers An1 ^ 2, An2 ^ 2, An3 ^ 2, and An4 ^ 2. It is also assumed that the relationship between the number m of patrols set by the above and the correlation measurement time T is as follows. (1) Peak correlation noise power An1 ^ 2 Number of rounds m = 1 Correlation measurement time T = 0.25 × PN code cycle time (2) Peak correlation noise power An2 ^ 2 Number of rounds m = 2 Correlation measurement time T = 0. 5 × PN code cycle time (3) Peak correlation noise power An3 ^ 2 Number of cycles m = 3 Correlation measurement time T = 0.75 × PN code cycle time (4) Peak correlation noise power An4 ^ 2 Number of cycles m = 4 Correlation Measurement time T = 1.0 × PN code cycle time In the correlation measurement condition calculation unit 18 ′, the peak correlation noise powers An1 ^ 2, An2 ^ 2, An3 predicted and set in this way with respect to the peak correlation noise power map 19 are set. ^ 2 and An4
^ 2 and the above-mentioned corrected values of peak correlation power Ap1 ^ 2 and Ap
2 ^ 2 are sequentially compared, and their peak correlation powers Ap1
The peak correlation noise power that can recognize at least each of ^ 2 and Ap2 ^ 2 and the number of rounds corresponding to the peak correlation noise power are determined.

For example, the peak correlation powers Ap1 ^ 2 and Ap2 ^ 2 are respectively the peak correlation noise powers An1 ^ 2, A2.
As shown in FIG. 12, for n2 ^ 2, An3 ^ 2, and An4 ^ 2, An1 ^ 2> Ap1 ^ 2 ≥An2 ^ 2> An3 ^ 2> Ap2 ^ 2> An4 ^ 2 (6) When it is determined that the peak correlation power Ap1 ^ 2 is at least recognizable, "peak correlation noise power An2 ^ 2" is determined as the peak correlation noise power An2 ^ 2, and the peak correlation noise power An2 ^ 2 is determined. As the number of rounds m corresponding to 2, “m1 = 2” with the correlation measurement time T being (0.5 × PN code cycle time) is determined. Similarly, "peak correlation noise power An4 ^ 2" is determined as the peak correlation noise power capable of recognizing the peak correlation power Ap2 ^ 2, and the correlation measurement is performed as the number of rounds m corresponding to the peak correlation noise power An4 ^ 2. Time T (1.0 x P
"M2 = 4", which is N code cycle time) is determined.

In the case of this example, the correlation measurement condition calculating unit 18 'gives the determined "cycle number m1 = 2" to the cyclic integrators 4a and 4b of the first system, and the cyclic system of the second system. The above determined “number of rounds m2 = 4” is instructed to the integrators 4c and 4d, and the determined “peak correlation noise power A
Values corresponding to "n2 ^ 2" and "peak correlation noise power An4 ^ 2" are designated as capture determination thresholds TH1 and TH2, respectively.

As described above, on the one hand, the correlation measurement time T is “0.5 × PN code cycle time (number of rounds m1 = 2)”.
On the other hand, the correlation measurement time T on the other hand is “1.0 × P
The correlation obtained as a square sum (i ^ 2 + q ^ 2) of the correlation value i of the I channel and the correlation value q of the Q channel is maintained by "N code cycle time (number of cycles m2 = 4)". The electric powers P1 and P2 have characteristics shown by, for example, a solid line and a dashed line in FIG. 13 for the corresponding capture determination thresholds TH1 and TH2, respectively.

As is apparent from FIG. 13, even if the actually measured correlation power is small, even if the carrier frequency error Δf is small, rather, with the level of the correlation power P2 of the second system, for example, as the point P0,
It is possible to capture the correlation power P1 before the first system. In other words, although a large allowance can be taken for the carrier frequency error Δf, there is a possibility that the acquisition will fail with the correlation power P1 of the first system having a small difference from the corresponding acquisition determination threshold TH1. Even in some cases, in a range where the carrier frequency error Δf is small, the acquisition can be performed earlier based on the correlation power P2 of the second system having a relatively large difference from the acquisition determination threshold TH2.

FIGS. 14 and 15 show a procedure for capturing a spread spectrum signal by the apparatus of the embodiment shown in FIG. 10. Hereinafter, with reference to FIGS. The operation of the entire example apparatus will be described.

Even in the apparatus of this embodiment, the initial setting (step 200) is executed for the satellite signal to be captured so as to obtain the most suitable correlation measurement condition in the position and environment of the vehicle. The details of the procedure for this initial setting are shown in FIG.

That is, in the initialization routine shown in FIG. 15, the apparatus of this embodiment also outputs the latest satellite orbit information or and the position information ps of the vehicle and the clock 16 stored in the data memory 14. The current time information t to be read is read into the elevation angle calculation unit 15 and the elevation angle value e of the capture target satellite is calculated (step 201). The apparatus that has obtained the elevation value e in this way then uses the correlation power estimation table 17 ′ to obtain the above-mentioned two types of received signal levels (peak correlation powers) A1 ^ 2 and A corresponding to the obtained elevation value e.
Estimate 2 ^ 2 (steps 202 and 203). Then, the estimated peak correlation powers A1 ^ 2 and A2 ^
Based on 2, the number of rounds m1 and m2 and the capture determination thresholds TH1 and TH2 are passed through the correlation measurement condition calculation unit 18.
Is determined (step 204). Number of rounds m1
And m2, and the determination of the capture decision thresholds TH1 and TH2, using the peak correlation noise power map 19 and the modified peak correlation powers Ap1 ^ 2 and Ap2 ^ 2 as described above, and refer to FIG. 12 above. Is performed in the manner described above.

Also in the apparatus of this embodiment, as in the previous case, the frequency of the carrier signal generated from the carrier generator 13 is further set to the predicted carrier frequency through the carrier control unit 12 as the same initialization routine. Controlled (step 205) and PN code control unit 1
PN generated from the PN code generator 11 through 0
The code pattern is controlled to the PN code pattern of the satellite signal to be captured (step 206).

The apparatus of this embodiment, which has thus completed the initial setting, has determined the number of rounds m1 and m2 (for example, m1 = 2, m2 =) determined in the main routine shown in FIG.
4), the correlation powers P1 and P2 of the two systems having different correlation measurement times for the satellite signal are calculated through the correlation calculation circuits of the first and second systems (step 2).
10).

The apparatus of the embodiment, which has obtained the correlation powers P1 and P2 of these two systems for the satellite signal, then compares the obtained correlation determination powers TH1 and TH2 with the synchronization determination unit 8 '. And these correlation powers P1 and P
The presence or absence of synchronization is determined for each of the two (steps 220 and 230). If it is determined that either one of the correlation powers P1 and P2 is equal to or more than the corresponding capture determination threshold value, it is determined that the satellite signal has been captured, and the capture processing for the satellite signal is performed. To finish.

Further, the correlation powers P1 and P2 of the above two systems
If any of the above is less than the corresponding capture determination threshold value, similar to the device of the previous embodiment: Process for changing PN code phase (step 240),
When the change of the PN code phase reaches one cycle of the same PN code phase and still cannot be captured, the following processing is executed: changing the carrier frequency (steps 250 and 260). It

Even in the case of the apparatus of this embodiment, however, as described above, the optimum correlation measurement condition for the target satellite signal is initialized in advance each time, and within the range where the carrier frequency error Δf is small, Since the capture probability is further increased based on the correlation power having a long correlation measurement time, the capture time is surely shortened.

In the apparatus of the embodiment shown in FIG. 10, for convenience sake, 2 having a predetermined width with respect to the calculated elevation angle value e.
It is assumed that two peak correlation powers are estimated and that the number of rounds and two acquisition determination thresholds are determined based on each of the estimated peak correlation powers. , And the number of the same peak correlation powers selected from them are arbitrary, and the number of rounds and the number of capture determination thresholds determined based on the peak correlation powers are also arbitrary. In short, a plurality of systems of the above correlation power arithmetic circuit including a cyclic integrator, a squarer, an adder, a filter, etc. may be prepared corresponding to the set number of cycles and the number of capture determination thresholds. .

In each of the above embodiments, the peak correlation noise power map shows four levels of peak correlation noise power and four cycles corresponding to those peak correlation noise powers. The setting example of the peak correlation noise power and the number of rounds is also only an example. If more values are set for the peak correlation noise power and the number of rounds based on experiments, etc., it is expected that desirable values suitable for the environment will be obtained even under the correlation measurement conditions. To be done. As a result, it becomes possible to further shorten the above-mentioned capture time.

Further, in each of the above-described embodiments, the capture determination threshold value TH referred to in the synchronization determination unit is set to the value of the predicted peak correlation noise power that can recognize the estimated peak correlation power at least. However, the capture determination threshold TH does not necessarily have to be set to such a value of the predicted peak correlation noise power. The capture determination threshold TH need only be a value near the same peak correlation noise power or a value higher than that.

Also, the correlation measurement time is dynamically calculated based on the means for estimating the signal level of the received spread spectrum signal and the relationship between the estimated signal level of the spread spectrum signal and the predicted correlation noise level. The method of realizing the means for determining is not limited to that of the above-described embodiment, but is arbitrary. Particularly, regarding the correlation power estimation table, the correlation measurement condition calculation unit, and the peak correlation noise power map shown in the apparatus of the embodiment, these are configured as one calculation circuit or a ROM table, and the correlation is directly obtained from the obtained elevation angle value. It is of course possible to adopt a configuration in which the correlation measurement conditions such as the measurement time (number of rounds) and the capture determination threshold value are obtained.

[0088]

As described above, according to the present invention, the carrier frequency prediction error is not allowed because the carrier component is not completely removed or the received spread spectrum signal has a low signal level. Even if the capacity is small, it is possible to accurately determine the synchronization with the PN code. As a result, the time required to capture the spread spectrum signal can be shortened.

[Brief description of drawings]

FIG. 1 is a block diagram showing a device configuration of an embodiment of a spread spectrum signal capturing device according to the present invention.

FIG. 2 is a diagram showing an example of setting a receiver-side carrier frequency with respect to a threshold.

FIG. 3 is a diagram showing an example of a correlation power estimation table shown in FIG.

FIG. 4 is a diagram showing a characteristic of correlation power.

FIG. 5 is a diagram showing an example of the peak correlation noise power map shown in FIG. 1 and a manner of setting the number of rounds using the map.

FIG. 6 is a diagram showing how the allowable value of the carrier frequency error changes in correlation power characteristics depending on the length of the correlation measurement time.

FIG. 7 is a diagram showing a transition of peak correlation noise power caused by a difference in correlation measurement time together with a synchronization characteristic of correlation power with respect to a PN code phase.

FIG. 8 is a flowchart showing a procedure for capturing a spread spectrum signal by the apparatus of the embodiment shown in FIG.

9 is a flowchart showing a specific processing procedure of the initial setting processing shown in FIG.

FIG. 10 is a block diagram showing an apparatus configuration of another embodiment of the spread spectrum signal acquisition apparatus according to the present invention.

FIG. 11 is a diagram showing an example of a correlation power estimation table of the apparatus of the embodiment shown in FIG.

FIG. 12 is a diagram showing an example of a peak correlation noise power map of the apparatus of the embodiment shown in FIG. 10 and a manner of setting the number of rounds using the map.

FIG. 13 is a diagram showing how the carrier frequency error changes according to the length of the correlation measurement time and the threshold value for the synchronization determination changes in the correlation power characteristic.

FIG. 14 is a flowchart showing a procedure for capturing a spread spectrum signal by the apparatus of the embodiment shown in FIG.

FIG. 15 is a flowchart showing a specific processing procedure of the initialization processing shown in FIG.

[Explanation of symbols]

1 (1a, 1b) ... Multiplier, 2 (2a, 2b) ... LPF
(Low-pass filter), 3 (3a, 3b) ... Correlator, 4 (4a, 4b, 4c, 4d) ... Cyclic integrator, 5
(5a, 5b, 5c, 5d) ... Squarer, 6 (6a, 6
b) ... adder, 7 (7a, 7b) ... filter, 8, 8 '
... Synchronization determination unit, 9 ... Demodulator, 10 ... PN code control unit,
11 ... PN code generator, 12 ... Carrier control unit, 13
... Carrier generator, 14 ... Data memory, 15 ... Elevation angle calculation unit, 16 ... Clock, 17, 17 '... Correlation power estimation table, 18, 18' ... Correlation measurement condition calculation unit, 19 ... Peak correlation noise power map.

Claims (3)

[Claims] 1. A baseband signal is extracted by removing a carrier component from a received spread spectrum signal, and a correlation between the extracted baseband signal and a predetermined pseudo noise code is obtained over a required correlation measurement time. While performing the operation, until the correlation power obtained based on the correlation operation reaches a predetermined value indicating synchronization with the pseudo noise code,
In a spread spectrum signal capturing device for sliding the phase of the pseudo noise code, a received signal level estimating means for estimating a signal level of the received spread spectrum signal, and a signal level of the estimated spread spectrum signal are predicted in advance. And a correlation measurement condition calculating means for dynamically determining the correlation measurement time based on the relationship with the correlation noise level. 2. The received signal level estimation means has an elevation angle calculation means for obtaining a received elevation angle of the spread spectrum signal, and an estimated signal level of the same spread spectrum signal corresponding to the obtained received elevation angle is preset and registered. The spread spectrum signal capturing apparatus according to claim 1, comprising: a signal level estimation table. 3. Correlation calculation using the baseband signal and a predetermined pseudo noise code is performed by cyclic integration of each correlation value between the I component and the Q component of the base band signal and the pseudo noise code, and the integral value of these integration values. The spread spectrum signal capturing apparatus according to claim 1, wherein the correlation measurement condition calculating means determines the correlation measurement time as the number of cycles in the cyclic integration.