JP2008111684A - Satellite signal tracker and satellite signal receiver with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a satellite signal tracker having the S/N ratio improved by extending the coherent addition time of the tracking means, continuously monitoring the signal tracking state, enabling retaining of synchronization, and capable of suppressing increase of the circuit size and current consumption. <P>SOLUTION: In the Costas loop, its carrier frequency control signal is corrected by extending the coherent addition time to the period of navigation data from a satellite, converting the I and Q correlation signals into multiple nominated frequencies, performing coherent and non-coherent additions on each of the nominated frequencies, and continuously calculating frequency deviations from a signal power distribution. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is installed in a mobile body such as a mobile phone or a car, and performs stable frequency tracking even in a very weak environment such as a satellite signal from a navigation satellite such as GPS indoors or under an overhead, resulting in stable The present invention relates to a satellite signal tracking device capable of outputting a positioning position, and a satellite signal receiver including a plurality of channels of the satellite signal tracking device.

  A system for determining the position, velocity, etc. of objects on the earth (hereinafter referred to as “users”) using information on the distance to navigation satellites (artificial satellites) that orbit the earth and the orbits of the navigation satellites. When a satellite signal receiver of a Global Navigation Satellite System (GNSS) such as the Global Positioning System (GPS) captures the satellite signal, the satellite signal is sequentially searched even in an environment where the received satellite signal is very weak. Therefore, although there are restrictions such as a low acceleration state and an observation time of several seconds or more, it is possible to use a capturing means that captures a satellite signal and obtains a positioning position. However, it is desired to realize a high-sensitivity tracking means with a simple configuration that allows positioning in real time even when the acceleration of the satellite signal is high (when the received carrier frequency changes).

  First, when searching for a satellite signal in an environment where the satellite signal is very weak, the addition time for adding the correlation signal obtained from the PN code correlation and the carrier frequency correlation to the received signal that has received the satellite signal is lengthened. Thus, an added correlation signal having an improved signal-to-noise ratio (S / N ratio) is obtained, and the frequency (and phase) of the oscillation frequency signal of the local oscillator (carrier NCO) used for carrier frequency correlation based on the added correlation signal. ) Is necessary to control. For this purpose, Patent Document 1 shows that two types of addition processing, coherent addition and non-coherent addition, are used in combination.

  Coherent addition is an addition method in which an I (carrier positive phase) correlation signal and a Q (carrier 90 ° phase shift) correlation signal are added as they are, and a method capable of greatly improving the S / N ratio. In GPS, inversion of the I and Q correlation signals occurs only every 20 ms, so that coherent addition can be performed up to 20 ms.

Non-coherent addition is a method of adding the signal power P (= I ² + Q ² or = (I ² + Q ² ) ^1/2 ) of an I, Q correlation signal or a signal obtained by coherent addition of these signals. Although the degree of improvement in the S / N ratio of this method is inferior to coherent addition, it is not affected by the inversion of the I and Q correlation signals, so the S / N ratio is improved even when the inversion pattern of the navigation message from the satellite is unknown There is an advantage that can be done.

  When searching for (acquiring) a satellite signal, it is necessary to ensure carrier frequency synchronization as well as PN code synchronization for the received signal. In order to shorten the time required for this search, as shown in Patent Document 2 (particularly FIG. 2), a carrier frequency including a local oscillator (carrier NCO) for each of a plurality of different frequency ranges with respect to the same PN code. In some cases, correlation means is provided to search a plurality of frequency ranges simultaneously. Further, in Patent Document 2 (particularly, paragraph “0007”), instead of using carrier frequency correlating means each including a carrier NCO, a frequency may be obtained by using Fast Fourier Transform within a section where navigation data does not change. is there. These are all related to satellite signal search. As a configuration, a plurality of sets of carrier frequency correlation means including a carrier NCO are required, or a large circuit scale and processing load are required to perform fast Fourier transform. Become heavier. In Patent Document 2 (particularly, paragraph “0019”), when tracking, only one carrier frequency correlation means (orthogonal frequency conversion means) is used for tracking, and other carrier frequency correlation means (orthogonal frequency) Conversion means) is used for searching and is used to shorten the search time.

Patent Document 3 (particularly, FIGS. 5 and 8) shows that the signal vector Ae ^{j (} ω ^{NT +} φ ⁾ is multiplied by the reverse unit vector e ^−j ω ^NT to remove the phase rotation of the signal in the baseband. Has been. The actual inversion operation of the I and Q components (I + jQ) is performed by expressing the multiplier part (cos ωNT−jsin ωNT) as a real part and an imaginary part and using the following equation (1).
(I + jQ) (cosωNT−jsinωNT)
= Icos ωNT + Qsin ωNT + jQcos ωNT−jIsin ωNT (1)
The rotation angle ωNT is given as a digital word from a numerically controlled oscillator, and the cos ωNT and sin ωNT values are obtained from a PROM table.

Further, in the GPS receiver, when the synchronization of the PN code (spreading code) is maintained, the frequency deviation amount X of the carrier frequency and the signal power (regardless of whether the synchronization of the carrier frequency is maintained). There is a relationship of P∝ (sinX / X) ² between the reception levels) P. That is, the reception level P becomes maximum when the carrier frequency completely matches the received signal, and becomes minimum at a frequency shifted by a predetermined frequency from the carrier frequency (Patent Document 4, particularly FIG. 10).

In Patent Document 4, when the signal power from the tracking satellite becomes weak, the normal tracking operation in which the synchronization is held by one channel circuit is switched to the operation in which the synchronization is held by two channel circuits. The synchronization holding operation by the two-channel circuit secures two channel circuits for the synchronization holding of the GPS satellite. A frequency higher by a predetermined frequency β than the expected carrier frequency expected to be the original carrier frequency is set in one channel circuit C1, and a frequency lower by the predetermined frequency β is set in the other channel circuit C2. The reception levels P1 and P2 of the first and second channel circuits C1 and C2 are compared, and the expected carrier frequency is adjusted by trial and error so that the reception levels P1 and P2 are equal. The expected carrier frequency when the reception levels P1 and P2 are equal is tracked as a correct carrier frequency.
US Pat. No. 6,724,343 Patent No. 3,106,829 Patent No. 2,620,219 JP 2003-255036 A

  When the tracking means of a satellite signal receiver such as GPS is made highly sensitive, generally the inversion pattern of the navigation data from the satellite is unknown, so that the coherent addition is performed up to the navigation data period (eg, 20 ms for GPS). It can be performed. However, extending the coherent addition time makes it impossible to detect an abrupt frequency change and makes it impossible to satisfy the acceleration tracking specification. Conventionally, a coherent time of 5 ms or less is normally used from the viewpoint of satisfying the acceleration tracking specification. . Therefore, the S / N ratio cannot be sufficiently improved.

  As for frequency changes, it is possible to cope with sudden frequency changes as long as signal powers of a plurality of frequencies near the expected carrier frequency can be compared. However, in order to constantly monitor the tracking state, it is necessary to add two channel circuits for maintaining synchronization together with the channel circuit that performs normal tracking operation, and to operate all the channel circuits at all times during tracking. . Since these channel circuits have a local oscillator or the like, the circuit scale becomes large and the current consumption becomes excessive.

  The present invention has been made in view of the above points. The coherent addition time of the tracking means is increased to improve the S / N ratio, and synchronization can be maintained while constantly monitoring the tracking state. It is an object of the present invention to provide a satellite signal tracking device that can suppress an increase in circuit scale and current consumption by eliminating the need for a local oscillator in an additional circuit for holding. Another object of the present invention is to provide a satellite signal receiver including a plurality of the satellite signal tracking devices.

The satellite signal tracking device according to claim 1 includes a carrier local oscillator (carrier NCO) 2 that receives a frequency control signal Fout and generates a carrier frequency signal, and converts a satellite signal into a received signal related to a specific satellite signal that is input. A 1 ms correlation channel circuit 1 that outputs the I correlation signal I0i and the Q correlation signal Q0i for 1 ms at the same time every 1 ms.
The I correlation signal I0i and the Q correlation signal Q0i are subjected to coherent addition in synchronization with the navigation data switching timing of the specific satellite signal, and the I coherent addition value Ici and the Q coherent addition value of the I, Q correlation signals I0i, Q0i A coherent adder 3 that outputs Qci;
A Costas loop calculator 4 for determining the frequency control signal Fout based on the I and Q coherent addition values Ici and Qci;
A frequency for calculating and outputting frequency-converted I-correlation signals I0c1-Iock and frequency-converted Q-correlation signals Q0c1-Qock that are frequency-converted with respect to the plurality of frequency candidates Fc1-Fck with respect to the I correlation signal I0i and the Q correlation signal Q0i Computing units 5 and 6;
The frequency conversion I correlation signals I0c1 to Iock and the frequency conversion Q correlation signals Q0c1 to Qock are received, and a plurality of accumulated signal powers P1 to Pk obtained by accumulating signal powers for a predetermined period for each frequency candidate Fc1 to Fck are obtained. A plurality of signal power integrators 71 to 7k and 81 to 8k to be output;
Based on the distribution state of the plurality of accumulated signal powers P1 to Pk, a frequency shift amount between the current tracking frequency and the true tracking frequency to be tracked in the frequency control signal Fout is calculated, and according to the frequency shift amount And a frequency shift / tracking frequency calculator 9 for correcting the frequency control signal Fout.

The satellite signal tracking device according to claim 2 is the satellite signal tracking device according to claim 1, wherein the plurality of signal power integrators 71 to 7k and 81 to 8k are:
The frequency conversion I correlation signals I0c1 to Iock and the frequency conversion Q correlation signals Q0c1 to Qock are synchronized with the navigation data switching timing of the specific satellite signal, and the frequency conversion I correlation signals I0c1 to Iock and the frequency conversion Q correlation signal Q0c1 are synchronized. A plurality of frequency candidate coherent adders 71 to 7k that perform coherent addition for each ~ Qock and store and output the frequency transformed I coherent added value and the frequency transformed Q coherent added value obtained by the coherent addition;
The signal power in the coherent addition interval is obtained for each frequency candidate Fc1 to Fck from the frequency conversion I coherent addition value and the frequency conversion Q coherent addition value, and a predetermined number M of the signal power is obtained for each frequency candidate Fc1 to Fck. It includes a plurality of frequency candidate non-coherent adders 81 to 8k that perform cumulative addition to obtain and output cumulative signal powers P1 to Pk.

  According to a third aspect of the present invention, there is provided a satellite signal receiver including two or more satellite signal tracking devices according to the first or second aspect according to the satellite to be tracked.

  According to the satellite signal tracking device and the satellite signal receiver of the present invention, the coherent addition time of the tracking means can be increased to improve the S / N ratio, and synchronization can be maintained while constantly monitoring the tracking state. Furthermore, a local oscillator is not required for the additional circuit for maintaining synchronization, and an increase in circuit scale and current consumption can be suppressed.

  Hereinafter, an embodiment for carrying out the present invention will be described using GPS as an example. The satellite signal tracking device of the present invention relates to tracking of satellite signals, in particular, carrier frequency tracking. The frequency check range of the carrier frequency at the time of tracking and the frequency check range of the carrier frequency at the time of acquisition (during search) are: The differences are first explained.

  At the time of the search, as described in Patent Document 2, since the period of the PN code is 1 ms, a frequency check is performed in kHz units (for example, in 1 kHz increments) from the relationship between the frequency and the correlation output value. . In this case, as shown in FIG. 2 of Patent Document 2, carrier frequency correlation means including a plurality of local oscillators (carriers NCO) is provided in increments of 1 kHz with respect to the same PN code, and a plurality of frequency ranges are searched simultaneously. Since the added correlation value for 1 ms greatly fluctuates with the frequency change of 1 kHz, local oscillators operating at a sampling frequency (local oscillation frequency) of several tens of MHz or more are required as many as the carrier frequency correlation means.

  On the other hand, at the time of tracking, even if the true frequency to be tracked changes suddenly due to movement of a mounted vehicle or the like, it is usually within several tens of Hz / sec. Therefore, it is only necessary to measure the tracking frequency deviation within a range of several tens of Hz. If the tracking frequency is a frequency deviation within about several tens of Hz, the influence on the addition correlation value for 1 ms is several% or less, and it can be said that there is almost no problem.

  For example, when performing 20 ms coherent addition in frequency tracking of a satellite signal, an addition result obtained by coherently adding an addition correlation value obtained by performing frequency conversion for, for example, 10 Hz on a 1 ms addition correlation value, and a local oscillator The addition result obtained by coherently adding the addition correlation values obtained by shifting the frequency by 10 Hz using (carrier NCO) for a predetermined time is almost the same result.

  Based on this knowledge, the satellite signal tracking device of the present invention provides a plurality of summed correlation values obtained by performing frequency conversion for several Hz to several tens of Hz with respect to a 1 ms added correlation value, respectively, by coherent addition for a predetermined time. Is used to obtain a frequency shift amount between the true frequency to be tracked and the currently tracked frequency, and the current tracked frequency is corrected according to the frequency shift amount. In the present invention, the additive correlation value for 1 ms obtained by the conventional tracking device is simply frequency-converted and used, so that no additional local oscillator (carrier NCO) or the like is required, and the circuit scale and current consumption are reduced. Significant reduction has been achieved.

  Hereinafter, an embodiment of the satellite signal tracking device of the present invention will be described with reference to FIGS. In FIG. 1, a satellite signal arriving at an antenna 101 from a satellite is converted to an intermediate frequency by a down converter 102, converted to a digital signal for digital processing by an A / D conversion circuit 103, and a carrier NCO2 is received as a received signal. The 1 ms correlation channel circuit 1 is input.

  The 1 ms correlation channel circuit 1 includes a carrier local oscillator 2 that receives a frequency control signal Fout and generates a carrier frequency signal. The 1 ms correlation channel circuit 1 converts a satellite signal and receives a code correlation between a received signal and a PN code related to a specific satellite signal that is input. The carrier correlation with the carrier frequency signal is taken, and the I correlation signal I0i and the Q correlation signal Q0i for 1 ms are simultaneously output every 1 ms. The 1 ms correlation channel circuit 1 may be the same as that used in a conventional GPS receiver. As a precaution, the main configuration is illustrated.

  That is, a PN code identical to the PN code of the satellite to be received is generated by the code generator, and the received signal and the generated PN code are correlated by the code correlator. A delay lock loop (DLL) is configured so that the code NCO controls the PN code phase of the code generator so that the correlation value of the code correlator is maximized. The output of this code correlator is correlated with the I carrier frequency signal generated at the carrier NCO2 by the I carrier correlator and the Q carrier frequency signal generated at the carrier NCO2 by the Q carrier correlator. Is output. The output of the I carrier correlator is integrated by an I1 ms integrator composed of a register or the like, and output as an I addition correlation value I0i for 1 ms every 1 ms. Similarly, the output of the Q carrier correlator is integrated by a Q1 ms integrator and is output every 1 ms as a Q addition correlation value Q0i for 1 ms.

  The I and Q addition correlation values I0i and Q0i output from the 1 ms correlation channel circuit 1 are the frequency difference and phase difference between the true tracking frequency to be truly tracked and the current tracking frequency output from the carrier NCO2 at that time. It has a frequency component corresponding to. When the current tracking frequency is equal to the true tracking frequency, the frequency components of the I and Q addition correlation values I0i and Q0i are ideally zero.

  The Nms coherent adder 3 performs coherent addition of the I addition correlation value I0i and the Q addition correlation value Q0i only for Nms every time the I, Q addition correlation values I0i and Q0i are output from the 1 ms correlation channel circuit 1 for 1 ms. Do. Specifically, coherent addition is performed only during the switching timing (edge information) of the navigation data from the satellite. When the edge timing is reached, the coherent addition results I and Q coherent addition values Ici and Qci are output every Nms (for example, 20 ms), and the internal addition result for subsequent integration in the next coherent interval. To reset.

  Edge information is supplied from the edge information generator 11. This edge edge information is a general user position (that is, the position where the satellite signal tracking device is present), satellite orbit information is known, and all satellites are tracked under the condition of tracking one or more strong satellite signals. The edge position of is accurately determined. For example, (1) the GPS time is obtained by tracking one or more satellites of normal sensitivity, and (2) the GPS satellite position at the current time using the ephemeris information (satellite orbit information) obtained from the assist information. (3) Using the approximate user position, the distance difference between the GPS satellite and the current position is obtained, and divided by the speed of light to obtain the time until the signal from the GPS satellite arrives. (4) The time Is obtained by determining the time T2 that is excessively divided by the edge interval and storing the value as the switching timing, and (5) switching when the remainder obtained by dividing the GPS time by the edge interval becomes the value T2.

  The Costas loop calculator 4 determines the carrier frequency control signal Fout to be given to the carrier NCO2 based on the I and Q coherent addition values Ici and Qci whose S / N ratio is improved by the coherent addition time.

  A Costas loop is formed by the Costas loop calculator 4, the 1 ms correlation channel circuit 1 including the carrier NCO 2, and the Nms coherent adder 3. This Costas loop is a closed loop control, and since the S / N ratio is improved because the coherent addition time is Nms (= 20 ms), the carrier frequency control signal Fout with high accuracy even when the satellite signal is weak, ie, high An accurate carrier frequency can be obtained, and real-time frequency tracking can be performed.

  The frequency calculator composed of the frequency conversion device 5 and each candidate frequency setting device 6 is a frequency conversion I correlation obtained by performing frequency conversion on each of the plurality of frequency candidates Fc1 to Fck with respect to the I correlation signal I0i and the Q correlation signal Q0i. The signals I0c1 to Iock and the frequency converted Q correlation signals Q0c1 to Qock are calculated and output.

  Each candidate frequency setting device 6 instructs the frequency conversion device 5 on a plurality of candidate frequencies Fc1 to Fck to be added to or subtracted from the correlation signal frequency Ft included in the I and Q correlation signals I0i and Q0i. As candidate frequencies Fc1 to Fck, positive and negative frequencies are prepared at intervals of several Hz to several tens of Hz centering on 0 Hz. The plurality of candidate frequencies Fc1 to Fck are preferably prepared for each frequency interval B [Hz].

  The frequency conversion device 5 performs frequency conversion on the I and Q correlation signals I0i and Q0i from the 1 ms correlation channel 1 based on the candidate frequencies Fc1 to Fck set by each candidate frequency setting device 6, and the frequency conversion is performed. The I and Q correlation signals I0c1 to k and Q0c1 to k are output for each frequency, for example, F1 = Ft−Fc1, F2 = Ft−Fc2, F3 = Ft + Fc3, F4 = Ft + Fc4, and F5 = Ft + Fc5.

  The frequency conversion in this frequency conversion device 5 is shown in FIG. 8 of Patent Document 3, for example, and similarly to the expression (1), the I correlation signal I0i and the Q correlation signal Q0i are multiplied by a multiplier (cosωNT−jsinωNT). The real part is multiplied by frequency conversion I correlation signals I0c1 to Iock, and the imaginary part is frequency conversion Q correlation signals Q0c1 to Qock. The rotation angle ωNT is given by a digital word from a numerically controlled oscillator in accordance with each candidate frequency, and the values of cos ωNT and sin ωNT can use a ROM table.

  The frequency conversion process in the frequency conversion device 5 may be performed with a very slow cycle of the target I and Q correlation signals I0i and Q0i every 1 ms, and each candidate frequency is sequentially time-divided by one conversion circuit. Therefore, it can be executed with an extremely small circuit, and the current consumption can be extremely reduced. This is clearly superior in comparison with the case where frequency conversion is performed for a plurality of candidate frequencies using a local oscillator (carrier NCO).

  A plurality of signal power accumulators composed of a plurality of frequency candidate Nms coherent adders 71 to 7k and a plurality of frequency candidate M times non-coherent adders 81 to 8k are frequency converted I correlation signals I0c1 to I0ck and frequency conversion Q correlation. In response to the signals Q0c1 to Q0ck, accumulated signal powers P1 to Pk obtained by accumulating the signal powers of a predetermined period for each frequency candidate Fc1 to Fck are obtained and output.

  Similar to the Nms coherent adder 3, the plurality of frequency candidate Mms coherent adders 71 to 7k convert the frequency conversion I correlation signals I0c1 to Iock and the frequency conversion Q correlation signals Q0c1 to Qock into the navigation data switching timing of satellite signals ( The frequency conversion I coherent addition value and the frequency conversion Q coherent addition value obtained by performing coherent addition for each of the frequency conversion I correlation signals I0c1 to Iock and the frequency conversion Q correlation signals Q0c1 to Qock in synchronization with the edge information). Is stored and output.

In addition, the M-time non-coherent adders 81 to 8k for each frequency candidate convert the signal power in the coherent addition interval for each frequency candidate Fc1 to Fck from the frequency conversion I coherent addition value and the frequency conversion Q coherent addition value to “I”. ² + Q ² ”or“ (I ² + Q ² ) ^1/2 ”, and for each frequency candidate Fc1 to Fck, the signal power is accumulated a predetermined number M (for example, M is several tens of times or more). Accumulated signal powers P1 to Pk are obtained and output to the frequency shift & tracking frequency calculator 9.

  The candidate frequencies Fc1 to Fck include the case of the candidate frequency “0”, and one of the frequency candidate coherent adders 71 to 7k and one of the M candidate non-coherent adders 81 to 8k of the frequency candidates are the candidate frequency “ It was described as corresponding to “0”. However, the candidate frequencies Fc1 to Fck do not include the case of the candidate frequency “0”, and the frequency candidate coherent adders 71 to 7k do not have one corresponding to the candidate frequency “0”. Instead, Nms The I and Q coherent addition values Ici and Qci output from the coherent adder 3 may be input to one of the M times non-coherent adders 81 to 8k of the frequency candidates as corresponding to the candidate frequency “0”. good.

  The frequency shift / tracking frequency calculator 9 calculates a frequency shift amount with the true tracking frequency to be tracked in the frequency control signal Fout based on the distribution state of the accumulated signal powers P1 to Pk, and according to the frequency shift amount. The frequency control signal Fout is corrected. An average frequency Fmean of the frequency control signal Fout is obtained by the average frequency calculator 10 over a predetermined averaging time, for example, 20 × M [ms].

  The frequency shift / tracking frequency calculator 9 first obtains the frequency shift amount between the average frequency Fmean and the true frequency to be tracked based on the distribution of the signal powers P1 to Pk corresponding to each frequency candidate for each NxMms, A corrected frequency control signal Fmod to be newly tracked is determined in consideration of the amount of frequency deviation and the magnitude of signal power. This corrected frequency control signal Fmod is given to the Costas loop computing unit 4, and the subsequent tracking is continued as a new frequency control signal Fout.

  Here, the average frequency Fmean is used because there is a change in Doppler frequency due to the movement of the object to be measured (automobile or the like) and the satellite, and the deviation amount obtained by the frequency deviation & tracking frequency calculator 9 is between NxM [ms]. This is to cope with the average frequency deviation amount.

  The reason why the magnitude of the signal power is also considered in the frequency deviation amount is that the reliability of the frequency deviation amount obtained by the frequency deviation & tracking frequency calculator 9 depends on the signal power. For example, the correction frequency control signal Fmod = Average frequency Fmean + Kw · frequency deviation amount. That is, when the signal power is high, the reliability of the frequency deviation amount is high, so the weighting value Kw is increased. Conversely, when the signal power is low, the reliability of the frequency deviation amount is low, so the weighting value Kw is reduced. Is good.

  An example of how to determine the amount of frequency deviation in the frequency deviation / tracking frequency calculator 9 will be described based on the distribution of the signal powers P1 to P5 of the frequencies F1 to F5 corresponding to the five frequency candidates Fc1 to Fc5 in FIG. To do.

The signal powers P1 to P5 are ideally distributed as shown in FIG. 2 according to the theoretical formula of (sin W / W) ² . Here, W is a variable corresponding to the frequency.

  As shown in FIG. 2, it is assumed that signal powers P1 to P5 with respect to the frequencies F1 to F5 are obtained. First, the maximum power Pmax (here P3) and the second largest power P2nd (here P2) are obtained. These actual power ratios Er = P2nd / Pmax depend on the frequency deviation amount. On the other hand, frequency deviation amounts corresponding to various simulated power ratios Ei (E1, E2, E3,...) Are calculated in advance from the signal power distribution, or approximate expressions thereof are stored.

  Then, a simulated power ratio Ei close to the actually obtained power ratio Er is searched, and a frequency shift amount corresponding to the simulated power ratio Ei is determined as a required frequency shift amount.

  When the frequency F3 at which the maximum power Pmax (P3) is obtained is the frequency currently being tracked, the frequency shift amount corresponding to the simulated power ratio Ei close to the actual power ratio Er may be obtained. However, when the frequency F3 at which the maximum power Pmax (P3) is obtained is a frequency F4 or F2 that is, for example, ± B away from the currently tracked frequency, it corresponds to the simulated power ratio Ei that is close to the actual power ratio Er. The frequency deviation amount to be obtained is determined by adding or subtracting the frequency ± B away from the frequency deviation amount to be obtained.

  As described above, in the present invention, since the frequency deviation amount is immediately obtained using the ratio of the signal powers of a plurality of frequencies, it is determined even when compared with the case where the expected carrier frequency is adjusted by trial and error as in Patent Document 4. It is clear that the present invention is superior in that the time required is short and a correlator of another channel circuit is unnecessary.

  In the satellite signal tracking device of the present invention, in the Costas loop, the S / N ratio is improved by extending the coherent addition time until the navigation data period from the satellite (for example, 20 ms for GPS), thereby receiving satellite signals such as GPS. We are improving the sensitivity of the machine tracking method.

  On the other hand, extending the coherent addition time makes it impossible to detect an abrupt frequency change in the conventional apparatus and satisfies the acceleration tracking specification. In the present invention, this disadvantage is solved by a frequency calculator (frequency conversion device 5, each candidate frequency setting device 6), a plurality of signal power integrators (frequency candidate Nms coherent adders 71 to 7k, frequency candidate M times non-coherent adder 81). ˜8k), a frequency deviation & tracking frequency calculator 9 is provided to always obtain the frequency deviation amount regardless of the strength of the satellite signal.

  Therefore, even if a sudden frequency change occurs and the tracking frequency of the Costas loop is tracked to a frequency that is different from the frequency to be truly tracked, the amount of frequency deviation is detected immediately, Automatically tracks to the frequency that should be truly tracked. Moreover, it is not necessary to use a local oscillator for the frequency calculator (frequency conversion device 5, each candidate frequency setting device 6) for that purpose.

  Note that when the signal powers P1 to Pk are low, the reliability of the frequency shift amount obtained by the frequency shift & tracking frequency calculator 9 is low, so the frequency change amount from the previous frequency shift amount measurement value is A restriction may be provided according to the magnitude of the signal power.

  Further, the frequency Fmod output to the Costas loop calculator 4 may be determined in consideration of the acceleration change of the frequency shift amount.

  Instead of the configuration in which the satellite signal tracking device of the present invention is realized by hardware, part or all of the processing may be performed by software processing.

  The above description relates to one satellite signal tracking device, but the same satellite signal tracking device is further added, and the received signal from the A / D converter 103 is supplied to the added satellite signal tracking device. To do. A satellite signal receiver having a plurality of satellite signal tracking devices is configured by tracking satellite signals from different satellites in the plurality of satellite signal tracking devices.

1 is a diagram showing the overall configuration of a satellite signal tracking device according to an embodiment of the present invention. The figure for demonstrating an example of how to obtain | require frequency deviation amount

Explanation of symbols

101 antenna 102 down converter 103 A / D converter 1 1 ms correlation channel circuit 2 carrier NCO
3 Nms coherent adder 4 Costas loop calculator 5 Frequency converter 6 Each candidate frequency setting device 71-7k Nms coherent adder 81-8k of frequency candidate M times non-coherent adder 9 of frequency candidate 9 Frequency shift & tracking frequency calculator 10 Average frequency calculator 11 Edge information generator

Claims (3)

It includes a carrier local oscillator that receives a frequency control signal and generates a carrier frequency signal, and takes the code correlation between the received signal and the PN code related to the input specific satellite signal after converting the satellite signal and the carrier correlation with the carrier frequency signal. A 1 ms correlation channel circuit that simultaneously outputs an I correlation signal and a Q correlation signal for 1 ms every 1 ms;
Coherent addition of the I correlation signal and the Q correlation signal in synchronization with the navigation data switching timing of the specific satellite signal, and outputting the I coherent addition value and the Q coherent addition value of the I and Q correlation signals And
A Costas loop computing unit that determines the frequency control signal based on the I and Q coherent addition values;
A frequency calculator that calculates and outputs a frequency-converted I-correlation signal and a frequency-converted Q-correlation signal that are respectively frequency-converted for a plurality of frequency candidates with respect to the I-correlation signal and the Q-correlation signal;
A plurality of signal power integrators that receive the frequency-transformed I correlation signal and the frequency-transformed Q correlation signal, and obtain and output a plurality of accumulated signal powers obtained by accumulating the signal power of a predetermined period for each frequency candidate;
Based on the distribution status of the plurality of accumulated signal powers, a frequency shift amount between a current tracking frequency and a true tracking frequency to be tracked in the frequency control signal is calculated, and the frequency control signal is calculated according to the frequency shift amount. A satellite signal tracking device, comprising: a frequency shift / tracking frequency calculator for correcting The plurality of signal power integrators are:
The frequency conversion I correlation signal and the frequency conversion Q correlation signal are coherently added to each of the frequency conversion I correlation signal and the frequency conversion Q correlation signal in synchronization with the switching timing of the navigation data of the specific satellite signal. A plurality of frequency candidate coherent adders for storing and outputting the added frequency transformed I coherent sum and frequency transformed Q coherent sum;
The signal power in the coherent addition interval is obtained for each frequency candidate from the frequency conversion I coherent addition value and the frequency conversion Q coherent addition value, and the accumulated signal is obtained by performing a predetermined number of additions of the signal power for each frequency candidate. The satellite signal tracking device according to claim 1, further comprising: a plurality of frequency candidate non-coherent adders that obtain and output power. A satellite signal receiver comprising two or more satellite signal tracking devices according to claim 1 or 2 according to the satellite to be tracked.

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