JP2008191068A - Noise estimation device for satellite signal, noise-to-signal ratio computation device, and satellite signal receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To find a noise distribution value (noise average and noise dispersion) and a noise-to-signal ratio, when tracking a satellite signal from a navigation satellite such as a GPS under a very weak environment thereof in an indoor space, under a high-level structure or the like, and to allow stable frequency tracking. <P>SOLUTION: A non-correlative signal not correlated with a reception signal from a satellite is carrier-correlated by a 1 ms correlation channel circuit 1n for a noise, to be output in every 1 ms, and a noise power dispersion σ<SP>2</SP>during the 1 ms in every 1 ms by a noise dispersion measuring instrument 4. A prescribed time (N) coherent addition is executed using the noise power dispersion σ<SP>2</SP>during the 1ms, so as to find the noise distribution value including the noise average and the noise dispersion, corresponding to the case when added by a prescribed frequency (M). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a noise estimation device that is installed in a mobile body such as a mobile phone or a car, and performs frequency tracking stably even in a very weak environment such as a satellite signal from a navigation satellite such as GPS indoors or under an overhead. The present invention relates to a signal-to-noise ratio calculation device and a satellite signal reception 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 is received by a Global Navigation Satellite System (GNSS) satellite signal receiver such as the Global Positioning System (GPS), the satellite signal is searched sequentially 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 (high-sensitivity search), a correlation signal obtained by taking a PN code correlation and a carrier frequency correlation is added to the received signal. The added correlation signal with improved signal-to-noise ratio (S / N ratio) is obtained by lengthening the addition time, and the oscillation frequency signal of the local oscillator (carrier NCO) used for carrier frequency correlation based on the added correlation signal It is necessary to control the frequency (and phase). 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.

  In order to improve sensitivity, it is desirable to increase the addition time, but in terms of following the acceleration, it is desirable that the addition time is short. However, the signal power fluctuation and the movement acceleration accompanying the reception environment change due to movement or the like are generally unknown before measurement. Therefore, the first method having a long addition time and a high improvement in the S / N ratio and the second method having a short addition time and a low improvement in the S / N ratio but good acceleration follow-up are performed simultaneously. From the first method and the second method, for example, it is conceivable to use an addition result of a method suitable for the S / N ratio during the measurement period. For this purpose, it is necessary to obtain the S / N ratio during the measurement period.

  At the time of high sensitivity search, the correlation power distribution as shown in FIG. 2A can be obtained by sequentially shifting the start timing of the internal spreading code (PN code) with respect to the received signal related to the specific satellite signal. . In FIG. 2A, the horizontal axis indicates the code offset value (chip), and the strongest autocorrelation power (ie, when the phase of the spreading code of the received signal matches the phase of the internal spreading code) , Signal power) Smes, and the autocorrelation power other than the signal power Smes is noise. If autocorrelation power other than the signal power Smes is used, the noise average Nmean and its noise variance Nrms can be calculated simultaneously as shown in FIGS. Using these measurement results and calculation results, the S / N ratio at the time of high sensitivity search can be obtained by “S / N = (Smes−Nmean) / Nrms”.

Also, the S / N ratio at the time of tracking is [coherent for the I and Q correlation signals used for tracking frequency control within the same interval (time) where coherent addition is performed (time) and noncoherent addition (interval). Non-Patent Document 1 describes that the S / N ratio is obtained from “added value / non-coherent added value”].
US Pat. No. 6,724,343 GLOBAL POSITIONING SYSTEM: Theory and Applications Vol.1, Bradford W. Parkinson, James J. Spilker Jr., pp391-393

  Considering that the method of FIG. 2 implemented for the high-sensitivity search is also performed in tracking, the signal power Smes is naturally obtained because tracking is in progress, but noise information cannot be obtained only by the tracking channel. In order to obtain noise information, a noise estimation channel is provided to obtain a noise level, and the signal power Smes in the tracking channel is determined based on the noise level, as shown in the republished patent application WO01 / 094972. Are known. However, in this re-published patent, only the noise level is obtained, and the noise variance Nrms cannot be obtained. In addition, in order to obtain the noise variance Nrms, it is impossible to calculate in real time, and it is not possible to calculate the S / N ratio in this method practically because it is affected by fluctuations other than the observation interval. .

  Further, in the case of the method shown in Non-Patent Document 1 used for general tracking, as shown in FIG. 39 of Non-Patent Document 1, as the signal power becomes weaker, the S / N ratio. In the case of high sensitivity (signal-to-noise ratio of about 20 dB or less), there is a drawback that it cannot be used practically.

  The present invention has been made in view of the above points, and at the time of tracking in a very weak environment such as a satellite signal from a navigation satellite such as GPS indoors or under an overpass, a noise distribution value (noise average and noise variance). An object of the present invention is to provide a noise estimation device, a signal-to-noise ratio calculation device, and a satellite signal reception device for obtaining a signal-to-noise ratio and performing frequency tracking stably.

The noise estimation apparatus according to claim 1, wherein a carrier correlation between a received signal related to a specific satellite signal input by converting a satellite signal and a non-correlated signal that cannot be correlated with the received signal is taken. A 1 ms correlation channel circuit 1n for noise that outputs the I correlation signal I0n and the Q correlation signal Q0n simultaneously every 1 ms;
A noise variance measuring device 4 for measuring a variance σ ² of noise power between 1 ms from the I correlation signal I0n and the Q correlation signal Q0n from the 1 ms correlation channel circuit 1n for noise;
The noise power variance σ ² for 1 ms is used for coherent addition for a predetermined time (N), and the noise average Nmean and noise variance Nrms corresponding to the case where the coherent addition result is added a predetermined number of times (M) are included. And a noise distribution calculator 5 for obtaining a noise distribution value.

The noise estimation apparatus according to claim 2 converts a satellite signal and receives a carrier correlation between a received signal related to a specific satellite signal input and a non-correlated signal that cannot be correlated with the received signal. A 1 ms correlation channel circuit 1n for noise that outputs the I correlation signal I0n and the Q correlation signal Q0n simultaneously every 1 ms;
A noise variance measuring device 4 for measuring a variance σ ² of noise power between 1 ms from the I correlation signal I0n and the Q correlation signal Q0n from the 1 ms correlation channel circuit 1n for noise;
A first noise average N1mean corresponding to a case where the coherent addition is performed for the first predetermined time (N1) using the noise power variance σ ² for 1 ms and the result of the coherent addition is added for the first predetermined number of times (M1). And a first noise distribution calculator 51 for obtaining a first noise distribution value including the first noise variance N1rms;
The noise power variance σ ² for 1 ms is used for coherent addition for a second predetermined time (N2 <N1) shorter than the first predetermined time (N1), and the coherent addition result is a second predetermined number of times (M2). And a second noise distribution calculator 52 for obtaining a second noise distribution value including a second noise average N2mean and a second noise variance N2rms, which corresponds to the case of addition.

The signal-to-noise ratio calculation apparatus according to claim 3 includes a carrier local oscillator (carrier NCO) 1a that receives a frequency control signal Fout and generates a carrier frequency signal, and relates to a specific satellite signal that is input after converting the satellite signal. A 1 ms correlation channel circuit 1s for a signal that takes a code correlation between a received signal and a PN code and a carrier correlation with the carrier frequency signal and outputs an I correlation signal I0i and a 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 from the signal 1 ms correlation channel circuit 1s are subjected to coherent addition for a predetermined time (N) in synchronization with the navigation data switching timing of the specific satellite signal, and the I coherent addition value is obtained. A coherent adder 2 that outputs Ici and a Q coherent addition value Qci;
Non-coherent that obtains signal power P in a coherent addition section from the I coherent addition value Ici and Q coherent addition value Qci, obtains the accumulated signal power P by performing cumulative addition of the signal power a predetermined number of times (M), and outputs it Adder 3;
A carrier correlation between the received signal and a non-correlated signal that cannot be correlated with the received signal, and a 1 ms correlation channel for noise that simultaneously outputs an I correlation signal I0n and a Q correlation signal Q0n for 1 ms every 1 ms. Circuit 1n;
A noise variance measuring device 4 for measuring a variance σ ² of noise power between 1 ms from the I correlation signal I0n and the Q correlation signal Q0n from the 1 ms correlation channel circuit 1n for noise;
Noise average variance Nrms and noise variance Nrms corresponding to the case where the coherent addition for the predetermined time (N) is performed using the noise power variance σ ² for 1 ms and the coherent addition result is added for the predetermined number of times (M). A noise distribution calculator 5 for obtaining a noise distribution value including
Using the cumulative signal power P, the noise average Nmean, and the noise variance Nrms, the signal-to-noise ratio S / N is calculated as [signal-to-noise ratio S / N = (cumulative signal power P−noise average Nmean) / noise variance. Nrms] is calculated.

The signal-to-noise ratio calculation apparatus according to claim 4 includes a carrier local oscillator (carrier NCO) 1a that receives a frequency control signal Fout and generates a carrier frequency signal, and relates to a specific satellite signal that is input after converting a satellite signal. A 1 ms correlation channel circuit 1s for a signal that takes a code correlation between a received signal and a PN code and a carrier correlation with the carrier frequency signal and outputs an I correlation signal I0i and a 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 from the signal 1 ms correlation channel circuit 1s are coherently added for a first predetermined time (N1) in synchronization with the navigation data switching timing of the specific satellite signal, and the first I A first coherent adder 21 that outputs a coherent addition value Ici1 and a first Q coherent addition value Qci1;
The signal power in the first coherent addition interval is obtained from the first I coherent addition value Ici1 and the first Q coherent addition value Qci1, and the first accumulated signal power is accumulated for the first predetermined number of times (M1). A first non-coherent adder 31 for obtaining and outputting P1,
The I correlation signal I0i and the Q correlation signal Q0i from the signal 1 ms correlation channel circuit 1s are subjected to a second predetermined time (N2 <N1) shorter than the first predetermined time (N1), and the second I coherent is obtained. A second coherent adder 22 that outputs the addition value Ici2 and the second Q coherent addition value Qci2,
The signal power in the second coherent addition interval is obtained from the second I coherent addition value Ici2 and the second Q coherent addition value Qci2, and the signal power is accumulated for a second predetermined number of times (M2) to obtain the second accumulated signal power. A second non-coherent adder 32 for determining and outputting P2,
A carrier correlation between the received signal and a non-correlated signal that cannot be correlated with the received signal, and a 1 ms correlation channel for noise that simultaneously outputs an I correlation signal I0n and a Q correlation signal Q0n for 1 ms every 1 ms. Circuit 1n;
A noise variance measuring device 4 for measuring a variance σ ² of noise power between 1 ms from the I correlation signal I0n and the Q correlation signal Q0n from the 1 ms correlation channel circuit 1n for noise;
A first noise corresponding to the case where coherent addition is performed for the first predetermined time (N1) using the noise power variance σ ² for 1 ms and the result of the coherent addition is added for the first predetermined number of times (M1). A first noise distribution calculator 51 for obtaining a first noise distribution value including an average N1 mean and a first noise variance N1rms;
Using the noise power variance σ ² for 1 ms, the coherent addition is performed for the second predetermined time (N2 <N1), and the coherent addition result corresponds to the second predetermined number of times (M2). A second noise distribution calculator 52 for obtaining a second noise distribution value including a two-noise average N2mean and a second noise variance N2rms;
Using the first and second accumulated signal powers P1 and P2, the first and second noise averages N1mean and N2mean and the first and second noise variances N1rms and N2rms, the first and second signal-to-noise ratio S1. / N1, S2 / N2, [first signal-to-noise ratio S1 / N1 = (first cumulative signal power P1−first noise average N1mean) / first noise variance N1rms], and [second signal-to-noise ratio S2] / N2 = (second cumulative signal power P2−second noise average N2mean) / second noise variance N2rms].

The satellite signal receiving apparatus according to claim 5 includes a carrier local oscillator (carrier NCO) 1a that receives a frequency control signal Fout and generates a carrier frequency signal, and converts the satellite signal into a received signal related to a specific satellite signal that is input. A 1 ms correlation channel circuit 1s for a signal 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 from the signal 1 ms correlation channel circuit 1s are coherently added for a first predetermined time (N1) in synchronization with the navigation data switching timing of the specific satellite signal, and the first I A first coherent adder 21 that outputs a coherent addition value Ici1 and a first Q coherent addition value Qci1;
From the first I coherent addition value Ici1 and the first Q coherent addition value Qci1, the signal power in the first coherent addition interval is obtained, and the first predetermined signal power is accumulated for the first predetermined number of times (M1). A first non-coherent adder 31 for obtaining and outputting P1,
A Costas loop computing unit 4 for determining the frequency control signal Fout based on the first I and Q coherent addition values Ici1 and Qci1;
The I correlation signal I0i and the Q correlation signal Q0i from the signal 1 ms correlation channel circuit 1s are subjected to a second predetermined time (N2 <N1) shorter than the first predetermined time (N1), and the second I coherent is obtained. A second coherent adder 22 that outputs the addition value Ici2 and the second Q coherent addition value Qci2,
The signal power in the second coherent addition interval is obtained from the second I coherent addition value Ici2 and the second Q coherent addition value Qci2, and the signal power is accumulated for a second predetermined number of times (M2) to obtain the second accumulated signal power. A second non-coherent adder 32 for determining and outputting P2,
A carrier correlation between the received signal and a non-correlated signal that cannot be correlated with the received signal, and a 1 ms correlation channel for noise that simultaneously outputs an I correlation signal I0n and a Q correlation signal Q0n for 1 ms every 1 ms. Circuit 1n;
A noise variance measuring device 4 for measuring a variance σ ² of noise power between 1 ms from the I correlation signal I0n and the Q correlation signal Q0n from the 1 ms correlation channel circuit 1n for noise;
A first noise corresponding to the case where coherent addition is performed for the first predetermined time (N1) using the noise power variance σ ² for 1 ms and the result of the coherent addition is added for the first predetermined number of times (M1). A first noise distribution calculator 51 for obtaining a first noise distribution value including an average N1 mean and a first noise variance N1rms;
Using the noise power variance σ ² for 1 ms, the coherent addition is performed for the second predetermined time (N2 <N1), and the coherent addition result corresponds to the second predetermined number of times (M2). A second noise distribution calculator 52 for obtaining a second noise distribution value including a two-noise average N2mean and a second noise variance N2rms;
Using the first and second accumulated signal powers P1 and P2, the first and second noise averages N1mean and N2mean and the first and second noise variances N1rms and N2rms, the first and second signal-to-noise ratio S1. / N1, S2 / N2, [first signal-to-noise ratio S1 / N1 = (first cumulative signal power P1−first noise average N1mean) / first noise variance N1rms], and [second signal-to-noise ratio S2] / N2 = (second cumulative signal power P2−second noise average N2mean) / second noise variance N2rms], and based on the first and second signal-to-noise ratios S1 / N1 and S2 / N2. And calculating / controlling means 6 for controlling the frequency control signal Fout by changing the characteristic or input of the Costas loop calculator 4.

  According to the noise estimation device, the signal-to-noise ratio calculation device, and the satellite signal reception device of the present invention, the noise distribution value is obtained when the satellite signal from the navigation satellite such as GPS is tracked in a very weak environment such as indoors or under an overhead. (Noise average and noise variance) and signal-to-noise ratio can be obtained in real time, and frequency tracking can be performed stably.

  Hereinafter, with reference to FIG. 1 and FIG. 2, embodiments of the noise estimation device, the signal-to-noise ratio calculation device, and the satellite signal reception device of the present invention will be described using GPS as an example.

  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 NCO 1a is received as a received signal. The input signal is input to the 1 ms correlation channel circuit 1s. The received signal is also input to the 1 ms correlation channel 1n for noise.

  The 1 ms correlation channel circuit 1s includes a carrier local oscillator 1a that receives a frequency control signal Fout and generates a carrier frequency signal. The 1ms correlation channel circuit 1s converts the satellite signal and receives the code correlation between the received signal and the PN code related to the input specific satellite signal. 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 1s 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 the code correlator is correlated with the I carrier frequency signal generated by the carrier NCO 1a by the I carrier correlator and the Q carrier frequency signal generated by the carrier NCO 1a 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 1s 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 NCO 1a 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.

  In the N1ms coherent adder 21 that is the first coherent adder, the I addition correlation value I0i and the Q addition correlation value Q0i are output every time I, Q addition correlation values I0i, Q0i are output from the 1 ms correlation channel circuit 1s for 1 ms. Coherent addition is performed for N1 ms. 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 I and Q coherent addition values Ici1 and Qci1 as the coherent addition results are output every N1 ms (for example, 20 ms), and then added internally for integration in the next coherent interval. Reset the result.

  Edge information is supplied from the edge information generator 8. This edge edge information is a general user position (that is, the position where the satellite signal receiving apparatus is present), satellite orbit information is known, and all satellites are tracked under the condition of tracking one or more satellites with 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 7 normally determines the carrier frequency control signal Fout to be given to the carrier NCO 1a based on the I and Q coherent addition values Ici1 and Qci1 whose S / N ratio is improved by the coherent addition time. The carrier frequency control signal Fout is controlled by changing the characteristic or input of the Costas loop calculator 4 by a control signal (weight value w or switching signal cos) from the S / N calculation / control device.

  A Costas loop is formed by the Costas loop calculator 7, the 1 ms correlation channel circuit 1 s including the carrier NCO 1 a, and the N 1 ms coherent adder 21. This Costas loop is closed loop control, and since the S / N ratio is improved because the coherent addition time is N1 ms (= 20 ms), the carrier frequency control signal Fout with high accuracy even when the satellite signal is weak, An accurate carrier frequency can be obtained.

  The M1-th non-coherent adder 31 as the first non-coherent adder obtains the signal power in the first coherent addition section from the first I coherent addition value Ici1 and the first Q coherent addition value Qci1, and the first power of the signal power is calculated. Accumulative addition is performed a predetermined number of times (for example, M1 = 25 times) to obtain and output the first cumulative signal power P1. The accumulated signal power P1 is reset every time it is output.

  In the N2ms coherent adder 22 as the second coherent adder, the I addition correlation value I0i and the Q addition correlation value Q0i are output each time the I, Q addition correlation values I0i and Q0i are output from the 1 ms correlation channel circuit 1s for 1 ms. Coherent addition is performed for N2 ms (for example, 5 ms). Also in this case, it is desirable to perform coherent addition in accordance with the switching timing (edge information) of the navigation data from the satellite. However, since N2ms is much shorter than N1ms, it is not always necessary to synchronize with the edge information. Then, I and Q coherent addition values Ici2 and Qci2 as the coherent addition results are output, and the internal addition results are reset for integration in the next coherent interval.

  The M2 non-coherent adder 32, which is the second non-coherent adder, obtains the signal power in the second coherent addition interval from the second I coherent addition value Ici2 and the second Q coherent addition value Qci2, and obtains the second of the signal power. Accumulative addition is performed a predetermined number of times (for example, M2 = 40 times) to obtain and output the second cumulative signal power P2. The accumulated signal power P2 is reset every time it is output.

  The N1ms coherent adder 21 uses a long coherent addition time N1 = 20 ms for tracking with a long addition time and a high improvement in the S / N ratio, and the N2ms coherent adder 22 has a short addition time and an improved S / N ratio. A short addition time N2 = 5 ms is used to perform tracking with a low degree of acceleration but good acceleration tracking. That is, N1 ≧ N2 (the case where N1 and N2 are equal may be included), and it is preferable that N1 * M1> N2 * M2 considering the number of non-coherent times.

  The 1 ms correlation channel circuit 1n for noise takes a carrier correlation between a received signal and a non-correlated signal that cannot be correlated with the received signal, and simultaneously outputs an I correlated signal I0n and a Q correlated signal Q0n for 1 ms every 1 ms. Output to.

  The 1 ms correlation channel circuit 1n for noise does not have a carrier NCO and performs carrier correlation at a fixed frequency. A frequency different from the conversion frequency (for example, several tens of MHz) of the down converter 102 by about several MHz may be set as the fixed frequency.

  The purpose of the code correlation in the 1 ms correlation channel circuit 1n for noise is to obtain a correlation with noise. Therefore, if the correlation with the PN code of a positioning satellite not in the sky is taken, the correlation with noise can be obtained. However, if you select a positioning satellite that is not in the sky, if the almanac information used to select the positioning satellite is incorrect (for example, immediately after startup or when the almanac information has not been updated), positioning in the sky There is a possibility of selecting a satellite code. In order to avoid such a situation, it is preferable to use a code different from the code of the navigation system of the satellite receiver. As a different code, when the navigation system of the satellite receiver is a GPS system, for example, a code of a GLONASS system may be used, or a simple repetitive signal may be used. Moreover, you may use the signal which added the received signal only for 1 ms, without using such a different code | cord | chord.

The noise variance measuring device 4 observes the I correlation signal I0n and the Q correlation signal Q0n output every 1 ms from the 1 ms correlation channel circuit 1n for noise for a certain period (for example, 500 ms), and disperses the noise power σ between 1 ms. ² is measured every 1 ms.

The noise distribution calculator 51 of method 1 which is a first noise distribution calculator performs coherent addition for a first predetermined time (N1 = 20 ms) using the noise power variance σ ² for 1 ms, and the coherent addition result is obtained. A first noise distribution value including a first noise average N1mean and a first noise variance N1rms, corresponding to a case where the first predetermined number of times (M1 = 25) is added, is obtained.

In addition, the noise distribution calculator 52 of the method 2, which is the second noise distribution calculator, uses the noise power variance σ ² for 1 ms, and the second predetermined time (N2 = 5 ms) shorter than the first predetermined time (N1). <N1) Coherent addition is performed, and a second noise distribution value including the second noise average N2mean and the second noise variance N2rms corresponding to a case where the coherent addition result is added a second predetermined number of times (M2 = 40 times) is obtained. .

When obtaining the first and second noise distribution values, if the coherent addition time Nms and the non-coherent number M are given, and if the noise is Gaussian noise of the normal distribution (0, σ ² ), the coherent addition time Nms and the non-coherent addition time Nms. A noise distribution when the number of coherent times M is added is statistically obtained. That is, the noise average Nmean of the noise distribution and its noise variance Nrms are functions of Nmean = F1 (N, M, σ ² ) and Nrms = F2 (N, M, σ ² ).

Although the parts related to N and M in the function of this noise average Nmean and its noise variance Nrms are complicated, in reality, N and M take only predetermined values, so that the noise average Nmean and its noise variance Nrms are eventually ,
Nmean = Fnm (σ ² ) ≈Anmσ ² + Bnm,
Nrms = Fnm (σ ² ) ≈Cnmσ ² + Dnm,
Can be approximated by The noise average Nmean and the noise variance Nrms obtained by this approximate expression correspond to the values obtained by the original function, respectively.

Using this, specific coefficients A1 nm, B1 nm, C1 nm, and D1 nm are assigned to the noise distribution calculator 51 of method 1, and specific coefficients A2 nm, B2 nm, C2 nm, and D2 nm are assigned to the noise distribution calculator 52 of method 2, respectively. Set in advance. Then, in the noise distribution calculator 51 of method 1, N1mean≈A1 nmσ ² + B1 nm, N1rms≈C1 nmσ ² + D1 nm, and in the noise distribution calculator 52 of method 2, N2mean≈A2 nmσ ² + B2 nm, N2rms≈C2 nmσ ² + D2 nm Ask.

  The S / N calculation / control device 6 serving as calculation / control means includes first and second cumulative signal powers P1, P2, first and second noise averages N1mean and N2mean, and first and second noise variances N1rms and N2rms. Are used, and the first and second signal-to-noise ratios S1 / N1 and S2 / N2 are used as [first signal-to-noise ratio S1 / N1 = (first accumulated signal power P1−first noise average N1mean ) / First noise variance N1rms] and [second signal-to-noise ratio S2 / N2 = (second accumulated signal power P2−second noise average N2mean) / second noise variance N2rms]. From the S / N calculation / control device 6, the first and second signal-to-noise ratios S1 / N1, S2 / N2, the first and second accumulated signal powers P1, P2, the first and second noise averages N1mean, N2mean, the first and second noise variances N1rms and N2rms are output to the outside and can be used in another device (not shown).

In the present invention, the first and second signal-to-noise ratios S1 / N1, S2 / N2, the noise averages N1mean and N2mean and their noise variances N1rms and N2rms are the sources of their calculation. since variance sigma ² of are constantly updated by the noise variance measuring device 4 is accurately determined in real time. Also, a plurality of addition methods can be obtained simultaneously by simply setting a coefficient for noise distribution calculation.

  The S / N calculation / control device 6 controls the frequency control signal Fout by changing the characteristic or input of the Costas loop calculation unit 4 based on the signal-to-noise ratios S1 / N1 and S2 / N2.

  The first signal-to-noise ratio S1 / N1 obtained by the S / N arithmetic / control device 6 and having a long addition time and a high S / N improvement degree, and an acceleration follow-up property although the addition time is short and the S / N improvement degree is low. The weight value w is supplied to the Costas loop computing unit 7 in consideration of both the second signal-to-noise ratio S2 / N2 that is good. The Costas loop calculator 7 weights the frequency control signal Fout by the I and Q coherent addition values Ici1 and Qci1 using the weight value w. For example, weighting by the weight value w is performed when the noise component obtained by considering both the first and second signal-to-noise ratios S1 / N1 and the second signal-to-noise ratio S2 / N2 is large. 7 may be increased, and when small, the response of the Costas loop calculator 7 may be decreased.

  Further, as control by the S / N calculation / control device 6, as shown by a broken line in FIG. 1, the Costas loop calculation unit 7 is supplied with the first I coherent addition value Ici1 and the first Q coherent addition value Qci1 together with the second coherent adder. The second I coherent addition value Ici2 and the second Q coherent addition value Qci2 from 22 are also input. Then, the first coherent addition values Ici1, Qci1 and the second coherent addition values Ici2, Qci2 are switched by the switching signal cos obtained in the same manner as the weight value w obtained by the S / N calculation / control device 6. use. That is, the frequency control signal Fout is changed by switching the input to the Costas loop calculator 4 from the first coherent addition value Ici1, Qci1 that is always used to the second coherent addition value Ici2, Qci2, or vice versa. Control. For example, in the switching, the first and second signal-to-noise ratios S1 / N1 and S2 / N2 are taken into account when the noise component obtained is small, the addition time is long and the S / N improvement degree is high. The coherent addition values Ici1 and Qci1 may be used. When the coherent addition values Ici1 and Qci1 are large, the second coherent addition values Ici1 and Qci2 having a short addition time and low S / N improvement but good acceleration follow-up may be used.

  In the embodiment of FIG. 1, a first sequence for determining a first signal-to-noise ratio S1 / N1 by an N1 ms coherent adder 21, an M1 non-coherent adder 31, and a noise distribution calculator 51 of method 1; and an N2 ms coherent adder 22, M2 times non-coherent adder 32, and the second series for obtaining the second signal-to-noise ratio S2 / N2 by the noise distribution computing unit 52 of method 2 are provided. Of these, the second series is omitted, You may comprise only the 1st series. However, as in the embodiment of FIG. 1, by providing both the first sequence and the second sequence, two types of signal-to-noise ratios S1 / N1 and S2 / N2 with different addition results (time and frequency) are obtained. Therefore, it is possible to grasp in more detail the situation such as the signal level and noise level in the received signal, and their temporal variation. Note that a third series or the like may be added to the first and second series to obtain three or more types of signal-to-noise ratios.

  Instead of the configuration in which the noise estimation device, signal-to-noise ratio calculation device, and satellite signal reception device of the present invention are implemented by hardware, some or all of the processing may be performed by software processing.

1 is an overall configuration diagram of a satellite signal receiving device according to an embodiment of the present invention. Diagram for explaining correlation power distribution obtained during high-sensitivity search

Explanation of symbols

101 antenna, 102 down converter, 103 A / D converter 1 s 1 ms correlation channel circuit for signal, 1 n 1 ms correlation channel circuit for noise 1 a carrier NCO, 21 N1 ms coherent adder, 22 N2 ms coherent adder, 31 M1 times non-coherent addition , 32 M2 times non-coherent adder 4 Noise variance measuring device, 51 Method 1 noise distribution calculator, 52 Method 2 noise distribution calculator, 6 S / N calculation / control device, 7 Costas loop calculator, 8 Edge Information generator

Claims (5)

The carrier correlation between the received signal related to the specific satellite signal that is converted from the satellite signal and the uncorrelated signal that cannot be correlated with the received signal is taken, and the I correlation signal and the Q correlation signal for 1 ms are simultaneously converted to 1 ms. 1 ms correlation channel circuit for noise to be output every time,
A noise variance measuring device for measuring the variance of noise power between 1 ms from the I correlation signal and the Q correlation signal from the 1 ms correlation channel circuit for noise every 1 ms;
A noise distribution computing unit that obtains a noise distribution value including noise average and noise variance corresponding to a case where coherent addition is performed for a predetermined time using the noise power variance for 1 ms and the coherent addition result is added a predetermined number of times; And a noise estimation device. The carrier correlation between the received signal related to the specific satellite signal that is converted from the satellite signal and the uncorrelated signal that cannot be correlated with the received signal is taken, and the I correlation signal and the Q correlation signal for 1 ms are simultaneously converted to 1 ms. 1 ms correlation channel circuit for noise to be output every time,
A noise variance measuring device for measuring the variance of noise power between 1 ms from the I correlation signal and the Q correlation signal from the 1 ms correlation channel circuit for noise every 1 ms;
First including a first noise average and a first noise variance corresponding to a case where coherent addition is performed for a first predetermined time using the noise power variance for 1 ms and the coherent addition result is added for a first predetermined number of times. A first noise distribution calculator for determining a noise distribution value;
Using the noise power variance for 1 ms, a second predetermined time shorter than the first predetermined time is coherently added, and the coherent addition result is added a second predetermined number of times. And a second noise distribution calculator for obtaining a second noise distribution value including two noise variances. 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 for a signal that simultaneously outputs an I correlation signal and a Q correlation signal for 1 ms every 1 ms;
The I correlation signal and the Q correlation signal from the 1 ms correlation channel circuit for signals are subjected to coherent addition for a predetermined time in synchronization with the navigation data switching timing of the specific satellite signal, and the I coherent addition value and the Q coherent addition value are A coherent adder that outputs
A non-coherent adder for obtaining a signal power in a coherent addition section from the I coherent addition value and the Q coherent addition value, performing a cumulative addition of the signal power a predetermined number of times, and obtaining and outputting the accumulated signal power;
A 1 ms correlation channel circuit for noise that takes a carrier correlation between the received signal and a non-correlated signal that cannot be correlated with the received signal, and simultaneously outputs an I correlation signal and a Q correlation signal for 1 ms every 1 ms; ,
A noise variance measuring device for measuring the variance of noise power between 1 ms from the I correlation signal and the Q correlation signal from the 1 ms correlation channel circuit for noise every 1 ms;
Noise distribution calculation for obtaining a noise distribution value including noise average and noise variance corresponding to the case where the coherent addition is performed for the predetermined time using the noise power variance for 1 ms and the coherent addition result is added for the predetermined number of times. And
And a calculation means for calculating a signal-to-noise ratio by [signal-to-noise ratio = (cumulative signal power−noise average) / noise variance] using the accumulated signal power and the noise average and noise variance. A signal-to-noise ratio calculation device. 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 for a signal that simultaneously outputs an I correlation signal and a Q correlation signal for 1 ms every 1 ms;
The I correlation signal and the Q correlation signal from the signal 1 ms correlation channel circuit are subjected to coherent addition for a first predetermined time in synchronization with the navigation data switching timing of the specific satellite signal, and the first I coherent addition value and the first Q A first coherent adder that outputs a coherent addition value;
From the first I coherent addition value and the first Q coherent addition value, the signal power in the first coherent addition interval is obtained, the first predetermined number of times of cumulative addition of the signal power is performed, and the first cumulative signal power is obtained and output. A first non-coherent adder;
The I correlation signal and the Q correlation signal from the 1 ms correlation channel circuit for signal are subjected to coherent addition for a second predetermined time shorter than the first predetermined time, and the second I coherent addition value and the second Q coherent addition value are output. A second coherent adder,
The signal power in the second coherent addition interval is obtained from the second I coherent addition value and the second Q coherent addition value, and the second predetermined signal power is accumulated for a second predetermined number of times to obtain and output the second accumulated signal power. A second non-coherent adder;
A 1 ms correlation channel circuit for noise that takes a carrier correlation between the received signal and a non-correlated signal that cannot be correlated with the received signal, and simultaneously outputs an I correlation signal and a Q correlation signal for 1 ms every 1 ms; ,
A noise variance measuring device for measuring the variance of noise power between 1 ms from the I correlation signal and the Q correlation signal from the 1 ms correlation channel circuit for noise every 1 ms;
The first noise average and the first noise variance corresponding to the case where the coherent addition is performed for the first predetermined time using the noise power variance for the 1 ms and the coherent addition result is added for the first predetermined number of times are included. A first noise distribution calculator for obtaining a first noise distribution value;
The second noise average and the second noise variance corresponding to the case where the coherent addition is performed for the second predetermined time using the noise power variance for 1 ms and the coherent addition result is added for the second predetermined number of times are included. A second noise distribution calculator for obtaining a second noise distribution value;
Using the first and second accumulated signal powers, the first and second noise averages, and the first and second noise variances, the first and second signal-to-noise ratios are expressed as [first signal-to-noise ratio = (First cumulative signal power-first noise average) / first noise variance] and [second signal-to-noise ratio = (second cumulative signal power-second noise average) / second noise variance]. And a signal-to-noise ratio calculation device. 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 for a signal that simultaneously outputs an I correlation signal and a Q correlation signal for 1 ms every 1 ms;
The I correlation signal and the Q correlation signal from the signal 1 ms correlation channel circuit are subjected to coherent addition for a first predetermined time in synchronization with the navigation data switching timing of the specific satellite signal, and the first I coherent addition value and the first Q A first coherent adder that outputs a coherent addition value;
From the first I coherent addition value and the first Q coherent addition value, the signal power in the first coherent addition interval is obtained, and the signal power is accumulated for a first predetermined number of times to obtain and output the first accumulated signal power. A first non-coherent adder;
A Costas loop computing unit that determines the frequency control signal based on the first I and Q coherent addition values;
The I correlation signal and the Q correlation signal from the 1 ms correlation channel circuit for signal are subjected to coherent addition for a second predetermined time shorter than the first predetermined time, and the second I coherent addition value and the second Q coherent addition value are output. A second coherent adder,
The signal power in the second coherent addition interval is obtained from the second I coherent addition value and the second Q coherent addition value, and the second predetermined signal power is accumulated for a second predetermined number of times to obtain and output the second accumulated signal power. A second non-coherent adder;
A 1 ms correlation channel circuit for noise that takes a carrier correlation between the received signal and a non-correlated signal that cannot be correlated with the received signal, and simultaneously outputs an I correlation signal and a Q correlation signal for 1 ms every 1 ms; ,
A noise variance measuring device for measuring the variance of noise power between 1 ms from the I correlation signal and the Q correlation signal from the 1 ms correlation channel circuit for noise every 1 ms;
The first noise average and the first noise variance corresponding to the case where the coherent addition is performed for the first predetermined time using the noise power variance for the 1 ms and the coherent addition result is added for the first predetermined number of times are included. A first noise distribution calculator for obtaining a first noise distribution value;
The second noise average and the second noise variance corresponding to the case where the coherent addition is performed for the second predetermined time using the noise power variance for 1 ms and the coherent addition result is added for the second predetermined number of times are included. A second noise distribution calculator for obtaining a second noise distribution value;
Using the first and second accumulated signal powers, the first and second noise averages, and the first and second noise variances, the first and second signal-to-noise ratios are expressed as [first signal-to-noise ratio = (First cumulative signal power-first noise average) / first noise variance] and [second signal-to-noise ratio = (second cumulative signal power-second noise average) / second noise variance]. And an arithmetic / control means 6 for controlling the frequency control signal by changing characteristics or inputs of the Costas loop arithmetic unit based on the first and second signal-to-noise ratios. Satellite signal receiver.

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