JP6305011B2 - Satellite signal tracking device - Google Patents

Description

  The present invention relates to a satellite signal tracking device capable of tracking even in a case where a satellite moving from a navigation satellite including GPS is weak in a moving body moving at high acceleration.

  For example, as a car navigation system uses a GPS (Global Positioning System) to acquire a current position, a highly sensitive satellite that can perform signal tracking even in a place where the signal level is low, such as indoors. There is a need for a signal tracking device.

  In order to achieve high sensitivity, it is necessary to lengthen the coherent addition time, and it is necessary to stabilize the frequency oscillator inside the receiver. For this purpose, a technique related to a reference oscillator frequency correction system that corrects the frequency of a frequency oscillator by using an external reference having a stable frequency such as the frequency of a radio device provided therewith is known (see, for example, Patent Document 1). ).

  Further, a technique related to a tracking method of a radio frequency signal for calculating an acceleration for each satellite with an accelerometer provided outside is known (see, for example, Patent Document 2).

  Furthermore, a technique for increasing the PLL (Phase Locked Loop) bandwidth according to the acceleration calculated from the received GPS signal to improve the acceleration response (see, for example, Patent Document 3), or a high speed to cope with high acceleration. A technique using a next PLL loop is known (see, for example, Patent Document 4).

  Furthermore, a technique for tracking a signal even when the signal level is extremely weak, such as at an indoor window (see, for example, Patent Document 5).

Special table 2008-522157 gazette Special Table 2007-535839 US Pat. No. 5,703,597 Japanese translation of PCT publication No. 2002-500773 JP 2008-111684 A

  The technique described in Patent Document 1 requires an external reference having a stable frequency, such as the frequency of a radio device provided therewith, and the technique described in Patent Document 2 requires an external accelerometer.

  The technique described in Patent Document 3 is effective when the signal level is strong and the mobile object acceleration can be calculated correctly, but when the signal level is weak, increasing the PLL bandwidth makes it easier to follow the noise. It becomes impossible to follow.

  The technique described in Patent Document 4 can be applied only when the signal level is strong and the coherent addition time of the PLL can be shortened. That is, when the signal level is weak, the higher-order part is more susceptible to noise and cannot follow correctly.

  Although the technique described in Patent Document 5 exemplifies the case of one signal, the tracking circuit includes a number of satellites to be tracked (for example, 10 satellites or more).

  Here, FIG. 3 shows a configuration of a conventional satellite signal tracking device. When the signal level is high, the N1ms coherent adder 102 and the first Costas loop computing unit 103 track the signal level by well-known PLL control. Here, N1 is specifically, for example, 1 ms, 4 ms, and 5 ms.

  When the signal level is low, for example, −140 dBm or less, the N2ms coherent adder 104 and the second Costas loop computing unit 105 track the signal level by well-known PLL control. Since the signal inversion by data such as transmission time and detailed orbit information is added to the satellite signal, a period in which the data inversion does not occur, that is, 20 ms is selected as the GPS signal as the coherent addition time N2. .

  In this case, the sensitivity can be increased by extending the coherent addition time, but tracking cannot be performed when the frequency changes suddenly in the acceleration state. Therefore, when a plurality of frequency candidates in the vicinity of the tracking frequency are compared at regular intervals, for example, every 100 ms or every 500 ms, and the current frequency deviation amount is measured, and the frequency deviation is equal to or greater than a threshold value. In this case, the frequency of the second Costas loop calculator 105 is corrected.

  When the moving body maintains a high acceleration state, as shown by the tracking frequency 1 in FIG. 4, it is determined that there is a frequency shift by the frequency correction determiner 107, and at the timing when the frequency is corrected, the true frequency is obtained. But otherwise does not match the true frequency. Moreover, as shown in the tracking frequency 2, if the frequency deviation amount measurement range is exceeded, tracking cannot be performed.

  Accordingly, an object of the present invention is to provide a satellite signal tracking device that can solve the above-described problems and can track a mobile object that moves at high acceleration even when the satellite signal from a navigation satellite including GPS is weak. There is.

In order to achieve the above object, the invention of claim 1 is directed to a high-sensitivity coherent adder, a Costas loop computing unit that calculates a PLL frequency from a correlation value output from the coherent adder, and frequency control. A frequency change amount corrector connected to the Costas loop arithmetic unit and calculating a final frequency output based on a PLL frequency calculated by the Costas loop arithmetic unit, and performing correlation calculation for a plurality of frequency candidates for a certain period of time. The frequency deviation measuring device for determining the true frequency deviation amount is compared with the frequency obtained by the frequency deviation measuring device and the frequency calculated by the frequency change amount correcting device to determine whether the deviation is equal to or greater than a threshold value. Store the frequency obtained by the frequency correction determiner and the frequency deviation measuring device, and calculate the difference between the previous stored value and the current measured value. A frequency change measuring device that calculates a wave number change amount and, when instructed to update the frequency change amount from the frequency correction determiner, changes the frequency change amount given to the frequency change amount corrector to a calculated value. When the Costas loop computing unit is instructed to correct the frequency from the frequency correction determiner, the Costas loop computing unit replaces the PLL frequency with the frequency, and the frequency change amount corrector measures the frequency change amount measurement. When the Costas loop is performed, the final frequency output is calculated by adding the frequency change amount in the acceleration state given from the device, and when the frequency correction determiner determines that the deviation is greater than or equal to the threshold value, Instructing the loop computing unit to change the frequency and instructing the frequency variation measuring instrument to update the frequency variation. A satellite signal receiver, characterized.

In this invention, when the Costas loop arithmetic unit instructs the frequency correction determiner to correct the frequency, the PLL frequency is replaced with the frequency , and the frequency connected to the Costas loop arithmetic unit for frequency control. The change amount corrector adds the frequency change amount in the acceleration state given from the frequency change amount measuring instrument , and the final frequency output is calculated every time the Costas loop is performed . The deviation is equal to or greater than the threshold by the frequency correction determiner. When it is determined that the frequency change amount is instructed to the Costas loop computing unit, the frequency change amount measuring device is instructed to update the frequency change amount.

  According to the first aspect of the present invention, in a moving body that moves at high acceleration, tracking is possible even when the satellite signal from the navigation satellite including GPS is weak.

1 is a schematic block diagram showing a satellite signal tracking device according to an embodiment of the present invention. It is a figure for demonstrating the change of a tracking frequency and the change of a true frequency in the satellite signal tracking apparatus of FIG. It is. It is a schematic block diagram which shows the conventional satellite signal tracking apparatus. It is a figure for demonstrating the change of the tracking frequency in the tracking circuit of FIG. 3, and the change of a true frequency.

  The present invention will be described below based on the illustrated embodiments.

  1 and 2 show an embodiment of the present invention. In this embodiment, the satellite signal tracking device 1 in the satellite signal receiver of the Global Navigation Satellite System (GNSS) including the Global Positioning System (GPS) will be described as an example.

  The satellite signal tracking device 1 is installed in a moving body having a high acceleration state, such as a racing car, for tracking satellite signals. As shown in FIG. 1, the satellite signal tracking device 1 mainly includes a 1 ms correlation circuit 10, a switch 11, an N1 ms coherent adder 12, a first Costas loop calculator 13, an N2 ms coherent adder 14, A second Costas loop computing unit 15, a frequency change amount corrector 16, a frequency deviation measuring unit 17, a frequency correction determining unit 18, and a frequency change amount measuring unit 19 are provided.

  The 1 ms correlation circuit 10 has the same function as that used in a conventional GPS signal receiver, and outputs an I addition correlation value and a Q addition correlation value for 1 ms. Here, a satellite signal received from a GPS satellite via an antenna (not shown) is converted into a digital signal and input to the 1 ms correlation circuit 10 as a received signal.

  The switch 11 is a switch for switching the tracking circuit in accordance with the signal level. When the signal level is high, the N1 ms coherent adder 12 and the first Costas loop calculator 13 are used to change the signal level to the signal level by well-known PLL control. Switch circuits to track. Here, the coherent addition time N1 ms is specifically set to 1 ms, 4 ms, and 5 ms, for example. When the signal level is low, for example, −140 dBm or less, the circuit is switched by the N2ms coherent adder 14 and the second Costas loop calculator 15 so that the signal level is tracked by well-known PLL control. Here, since the signal inversion by the data such as the transmission time and detailed orbit information is added to the satellite signal, the coherent addition time N2 is set to a period in which the data inversion does not occur, that is, 20 ms in the case of the GPS signal. To do.

  The N1 ms coherent adder 12 outputs a coherent addition of the I addition correlation value and the Q addition correlation value to N1 ms, for example, 5 ms each time an I addition correlation value and a Q addition correlation value are output from the 1 ms correlation circuit 10 for 1 ms. The I-coherent addition value and the Q-coherent addition value are output after the interval. Then, the I coherent addition value and the Q coherent addition value are output, and the internal addition result is reset for the subsequent integration in the next coherent interval.

  Similarly to the N1 ms coherent adder 12, the N2 ms coherent adder 14 outputs the I addition correlation value and the Q addition correlation value each time the 1 ms correlation circuit 10 outputs an I addition correlation value and a Q addition correlation value. Coherent addition is performed for N2 ms, which is the switching timing (edge information) of navigation data from the satellite, for example, for 20 ms, and an I coherent addition value and a Q coherent addition value are output. The signal-to-noise ratio (S / N ratio) is improved by coherently adding the I-added correlation value and the Q-added correlation value by the N2 ms coherent adder 12. Then, the I coherent addition value and the Q coherent addition value are output, and the internal addition result is reset for the subsequent integration in the next coherent interval.

  In the N2 ms coherent adder 14, only a low frequency component appears in the actual frequency change. For example, if the coherent addition time N2ms is 20 ms, even if the frequency deviation amount is 55 Hz, the N2ms coherent adder 14 can only observe a frequency deviation amount obtained by subtracting a frequency that is an integral multiple of 50 Hz, that is, 5 Hz. The low frequency component is correctly detected.

  The second Costas loop calculator 15 calculates a high-sensitivity PLL frequency based on the correlation value from the N2 ms coherent adder 14 in the same manner as the first Costas loop calculator 13.

  The frequency change amount corrector 16 adds the frequency change amount that cannot be detected by the N2 ms coherent adder 14 to the PLL frequency from the second Costas loop calculator 15 and outputs the final frequency output. As a result, the frequency difference in the 1 ms correlation circuit 10 becomes only the low frequency component, which is the difference between the true frequency and the frequency change amount corrected by the frequency change amount corrector 16, and the frequency shift occurs in the N2 ms coherent adder 14. It is detected correctly, and as a result, frequency tracking can be performed stably.

  The frequency deviation measuring device 17 performs correlation calculation for a plurality of frequency candidates for a certain period, for example, every 100 ms, every 500 ms, and obtains a true frequency deviation amount.

  The frequency correction determination unit 18 compares the frequency F1 obtained from the frequency deviation measuring unit 17 with the frequency Fout from the frequency variation correction unit 16, and if the deviation is a threshold value, for example, 10 Hz or more, the frequency correction determination unit 18 The Costas loop computing unit 15 is instructed to change the frequency, and the frequency variation measuring unit 19 described later is instructed to update the frequency variation.

  The frequency variation measuring device 19 stores the frequency F1 obtained from the frequency deviation measuring device 17, and calculates the frequency variation from the difference between the previous stored value and the current measured value. When the frequency change measuring device 19 is instructed to update the frequency change amount from the frequency correction determiner 18, the frequency change amount measuring device 19 obtains a value corresponding to the control cycle of the Costas loop system based on the updated frequency change amount, and the frequency change amount. Is output to the frequency change amount corrector 16. For example, when a change of 50 Hz is observed every 500 ms and the Costas loop is performed every 5 ms, a value of 0.5 Hz / 5 ms is set in the Costas loop.

  Next, the satellite signal tracking method and operation by the satellite signal tracking apparatus 1 having such a configuration will be described.

  First, the power of the satellite signal receiving device and the satellite signal tracking device 1 is turned on, and the satellite signal received by the antenna of the satellite signal receiving device is searched. When the satellite signal is acquired by the search, frequency tracking is performed as described above in order to track the acquired satellite signal. At this time, when the signal level is high by the switch 11, the signal level is tracked by the N1 ms coherent adder 12 and the first Costas loop calculator 13, and the signal level is low, for example, −140 dBm or less. N2ms coherent adder 14 and second Costas loop calculator 15 track the signal level.

  As described above, according to the satellite signal tracking device 1, tracking is possible even in a moving body that moves at a high acceleration even when the satellite signal from the navigation satellite including the GPS is weak.

  That is, the frequency difference in the 1 ms correlation circuit 10 is only the low frequency component, which is the difference between the true frequency and the frequency change corrected by the frequency change corrector 16, and the frequency shift is correct in the N2 ms coherent adder 14. As a result, the frequency tracking can be stably performed.

  In addition, when the frequency change measuring device 19 is instructed to update the frequency change amount from the frequency correction determiner 18, the frequency change amount measuring device 19 obtains a value corresponding to the control period of the Costas loop system based on the updated frequency change amount. Since the change amount is output to the frequency change amount corrector 16, the frequency tracking can always be performed stably.

  Although the embodiment of the present invention has been described above, the specific configuration is not limited to the above embodiment, and even if there is a design change or the like without departing from the gist of the present invention, Included in the invention. For example, in the above-described embodiment, the frequency variation measuring device 19 is changed only when instructed by the frequency correction determiner 18, but when the change in the frequency variation is equal to or greater than the threshold value even when constantly changed. It may be changed.

  Moreover, although the frequency deviation measuring instrument 17 for high sensitivity is one system, for example, two systems of 100 ms and 500 ms are prepared, and when the signal level is relatively high, the frequency deviation measuring range is widened in the 100 ms system and responds. If the signal level is close to the noise level, the selection may be made according to the signal level, such as increasing the frequency estimation accuracy in a 500 ms system.

  In the frequency change amount measuring device 19, the frequency change is obtained from the change from the previous time, but when the signal level is low, the reliability of the measurement value is low, so an LPF corresponding to the signal level is added or the signal level is changed. Weighting (applied frequency change amount = (weight amount corresponding to signal level) * (current frequency change amount measurement value)) may be performed.

  The amount of frequency change is obtained only from the output of the frequency deviation measuring device 17, but the amount of frequency change in a state where the signal level is high and the N1ms coherent adder 12 and the first Costas loop calculator 13 are used is separately provided. The measured value may be the initial value of the amount of frequency change used when the signal level becomes low.

  The frequency change instruction from the frequency correction determiner 18 to the second Costas loop calculator 15 may be a case where it is determined that the frequency deviation is continuously equal to or more than a threshold value plural times.

DESCRIPTION OF SYMBOLS 1 Satellite signal tracking apparatus 10 1ms correlation circuit 12 N1ms coherent adder 13 1st Costas loop computing unit 14 N2ms coherent adder 15 2nd Costas loop computing unit 16 Frequency change amount corrector 17 Frequency deviation measuring device 18 Frequency correction determination 19 Frequency change measuring instrument

Claims (1)

A coherent adder for high sensitivity,
A Costas loop calculator that calculates a PLL frequency from the correlation value output from the coherent adder;
A frequency change amount corrector connected to the Costas loop computing unit for frequency control and calculating a final frequency output based on a PLL frequency calculated by the Costas loop computing unit;
A frequency deviation measuring device that performs correlation calculation for a plurality of frequency candidates for a certain period to obtain a true frequency deviation amount;
A frequency correction determiner that compares the frequency obtained by the frequency deviation measuring device with the frequency calculated by the frequency change amount corrector and determines whether the deviation is equal to or greater than a threshold value;
When the frequency obtained by the frequency deviation measuring device is stored, the amount of frequency change is calculated from the difference between the previously stored value and the current measured value, and the frequency correction amount is instructed to be updated by the frequency correction determiner Is a frequency change amount measuring device that changes the frequency change amount given to the frequency change amount corrector to a calculated value;
With
When the Costas loop calculator is instructed to correct the frequency from the frequency correction determiner, it replaces the PLL frequency with that frequency,
The frequency change amount corrector adds a frequency change amount in an acceleration state given from the frequency change amount measuring device, and calculates a final frequency output every time a Costas loop is performed ,
If the frequency correction determiner determines that the deviation is greater than or equal to a threshold, the frequency correction determiner issues a frequency change instruction to the Costas loop arithmetic unit and updates the frequency change amount to the frequency change amount measuring device. Instruct
A satellite signal receiver characterized by that.