JP2009281844A - Gps (global positioning system) receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To remove an influence of a strong signal on a weak signal ch by estimating a strong signal mutual correlation value of the weak signal ch without acquiring an amplitude in the strong signal ch, under an environment wherein a synthesized signal of a satellite signal of the strong signal and a satellite signal of the weak signal is received. <P>SOLUTION: The ratio of strong signal mutual correlation included in an output of the weak signal ch is estimated by means of a least-squares method from an output of mutual correlation ch. The output of the mutual correlation ch is multiplied by the estimated ratio, to thereby acquire a mutual correlation component included in the output of the weak signal ch. The mutual correlation component is subtracted from the output of the weak signal ch, to thereby acquire a mutual correlation component. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a GPS (Global Positioning System) receiver that receives a signal obtained by synthesizing a strong satellite signal and a weak satellite signal, and in particular, prevents erroneous acquisition and erroneous tracking in a weak signal reception channel. It relates to a GPS receiver.

  A GPS satellite (hereinafter also referred to as a satellite) spreads information with a spread code different for each satellite, modulates it with a common carrier frequency, and transmits it as a satellite signal. A GPS receiver (hereinafter sometimes referred to as a receiver) receives a combination of satellite signals transmitted from each satellite. When the GPS receiver starts receiving, it cannot receive the satellite signals of the satellites located behind the earth, so it searches the receivable visible satellites and continues to receive signals from the satellites found as a result. Do tracking so you can.

  The search is a process of searching for a receivable satellite signal from the received signals from the currently launched GPS satellites. Although the spread code for each satellite is known, it is necessary to determine the frequency and spread code phase in order to receive the satellite signal.

  The carrier frequency is known (for example, 1575.42 MHz in GPS L1), but because of the influence of the Doppler effect due to the movement of the satellite and the receiver, the frequency for accurate reception varies from satellite to satellite. Further, although the spreading code sequence for each satellite is known, it is necessary to determine the spreading code phase in order to perform despreading on the received signal.

  For this reason, in the search process, the spread code phase is assigned to each satellite in a round-robin manner, and each correlation value is calculated. If the peak correlation value obtained as a result exceeds a predetermined threshold value, it is determined that the satellite signal of the satellite can be received, and the frequency and spreading code phase at which the peak correlation value is obtained are determined. Note that determining that the satellite signal can be received as a result of the search and determining the frequency and the spread code phase is called acquisition.

  For the satellite signal determined to be receivable by the search process, a tracking process is performed in order to continue reception. Since the positional relationship between the satellite and the receiver changes from moment to moment, in the tracking process, the reception frequency, code phase, and the like are controlled periodically to continue stable reception.

  FIG. 6 shows a schematic configuration of a GPS receiver that has been conventionally used. The antenna 1 receives satellite signals from a plurality of satellites. The frequency converter 2 converts the satellite signal modulated at the carrier frequency to an intermediate frequency (IF). The A / D conversion unit 3 converts the frequency-converted satellite signal from an analog signal to a digital signal to obtain a received signal.

  The signal processing unit 4 performs signal processing on the received signal according to the control content from the control unit 20. Generally, it is often implemented by hardware, and is mainly composed of a search unit and a plurality of tracking channels.

  The search unit 10 performs a search process on the satellite number designated by the control unit 20, determines whether the satellite is receivable, determines the frequency and spreading code phase at which the peak correlation value is obtained, and determines the result as the control unit 20 Notify

  The tracking channels 11 to 1N perform correlation processing of received signals according to the satellite number, frequency, and spreading code phase specified by the control unit 20. The control unit 20 is notified of a correlation value obtained as a result of the correlation processing.

  One tracking channel performs correlation processing on satellite signals from one satellite. In order to perform positioning with a GPS receiver, since the reception results of satellite signals from at least four satellites are necessary, generally, a tracking channel of 4 channels or more is mounted.

  The control unit 20 is generally executed by software. The hardware processing in the signal processing unit 4 is controlled, the hardware processing result is acquired, and the following search unit control and tracking channel control are performed based on the hardware processing result. As described above, the hardware in the control unit 20 and the signal processing unit 4 has a processing loop.

  The search unit 10 is caused to execute a search by designating a satellite number from the control unit 20, and information on the result is acquired. Then, the information obtained as a result of the search, that is, the receivable satellite number, frequency, and spreading code phase are sequentially set in the tracking channels 11 to 1N, and processing is instructed. Based on the correlation value acquired from each tracking channel, an optimal reception frequency or the like is calculated and periodically reset to the tracking channel.

  A specific configuration example of the search unit 10 is shown in FIG. In FIG. 7, an input received signal is phase-shifted by mixing with a frequency from a carrier NCO 102 by a mixer 101 and supplied to a code correlator 103. In the code correlator 103, the correlation between the signal from the mixer 101 and the spread code from the code GEN (code generator) 105 is taken. The code phase of the spread code from the code GEN 105 is scanned by the control from the code NCO 104.

The signal that has undergone phase rotation and has been subjected to code correlation is integrated every predetermined time by the integrator 106, and further, the power generation unit 107 obtains power from the I signal and the Q signal (I ² + Q ² ), and the buffer and It supplies to the sort part 108. The buffer and sort unit 108 sorts the correlation power for each code phase, finds the maximum correlation power and its code phase, and supplies the result to the control unit 20. From the control unit 20, the frequency is set to the carrier NCO 102, and the code number is set to the code GEN.

  In the search unit 10, the code correlator 103 performs code correlation calculation on the code number designated by the control unit 20. Correlation calculation is performed while shifting the code phase, and the correlation power for all code phases is calculated. When correlation powers for all codes are obtained, sorting is performed based on the correlation powers, code phases for obtaining maximum correlation powers and their correlation powers are determined, and output to the control unit 20. This process is called code phase scanning.

  In the search process, the frequency is also determined. For this purpose, the control unit 20 predicts the Doppler frequency of the search target satellite based on the almanac (rough satellite orbit information) acquired from the already received satellite signal. The code phase is scanned at several frequencies around the predicted frequency to determine the frequency at which the maximum correlation value is obtained. This process is called frequency scanning.

  That is, the frequency and code phase at which the maximum correlation value is obtained are determined by frequency scanning and code phase scanning.

  A specific configuration example of the tracking channel #n is shown in FIG. The GPS receiver includes a plurality of tracking channels as shown in FIG. 6, but FIG. 8 shows only one of them, and the other plurality of tracking channels have the same configuration.

  In FIG. 8, an input received signal is phase-rotated by mixing with a frequency from a carrier NCO 1 n 2 (set by the control unit 20) by a mixer 1 n 1 and supplied to a code correlator 1 n 3. In the code correlator 1n3, a correlation between the signal from the mixer 1n1 and the spread code from the code GEN (code generator) 1n5 is taken. The code phase of the spreading code from the code GEN1n5 is controlled by the code phase from the code NCO1n4 (set by the control unit 20).

  The signal whose phase correlation has been obtained by phase rotation is integrated by the integrator 1n6 for each I component and Q component of the correlation value every predetermined time and supplied to the control unit 20. From the control unit 20, the frequency is set to the carrier NCO1n2, and the code number is set to the code GEN.

  The control unit 20 sets the frequency, code number, and code phase obtained as a result of the search process for a certain satellite in the tracking channel #n. The tracking channel #n performs a correlation operation with the specified frequency, code number, and code phase, outputs the I component and Q component of the correlation result to the control unit 20, and the control unit 20 continues stable reception. The optimal frequency and code phase are calculated as needed and set to tracking channel #n.

  The correlation calculation is to perform a convolution calculation with a spreading code on a signal obtained by multiplying the received signal by IF frequency + Doppler frequency to baseband, and the calculation result is called a correlation value. Autocorrelation is a correlation calculation performed at a frequency, a spread code sequence, and a spread code phase corresponding to a satellite signal to be received. The peak of the autocorrelation value is obtained by frequency scanning and code phase scanning.

  On the other hand, performing a correlation operation with another spreading code sequence on a satellite signal to be received is called cross-correlation. The correlation value by cross-correlation is (1) the difference between the Doppler frequency of the input signal and the Doppler frequency used in the correlation calculation, (2) the code sequence and code phase of the input signal, and the code sequence and code phase used in the correlation calculation. , Depending on.

  In the case of a C / A code in GPS, the maximum correlation value of cross-correlation is about −21.6 dB compared to the autocorrelation value. That is, when the autocorrelation value is −120 dBm in the tracking channel that receives the signal of a certain satellite SV # 1, the cross-correlation value of the signal of the satellite SV # 1 is a maximum of −141 dBm in the tracking channel that receives another satellite signal. Appears in the size of.

  Then, based on the reception results of GPS signals from four or more satellites, the position (latitude, longitude, altitude) of the receiver is measured (positioning process).

  By the way, when a GPS receiver is incorporated in a mobile phone, it is necessary to increase the sensitivity of the GPS receiver that is assumed to be used indoors. This is because a weak signal greatly attenuated by passing through a building wall is received, and positioning is possible. It is expected that signals from many satellites will be blocked by walls and become weak signals indoors. On the other hand, if the propagation path is an opening such as a window, it will be received as a strong signal at the same level as outdoor reception. There is a possibility that. That is, when the GPS receiver is used indoors, the level difference between the strong signal and the weak signal may be very large compared to the case of outdoor use. When a weak signal is received in such an environment, there is a risk of erroneous tracking for the following reason.

  Assuming an environment where two satellites are received, one is a strong signal and the other is a weak signal. That is, received signal = strong signal + weak signal. The search for the strong signal satellite is performed without any problem by the conventional method because the signal level is high.

Considering the weak signal satellite search, the received signal is despread with the spreading code of the weak signal satellite, and the result is the following two sums.
-Strong signal cross-correlation with strong signal despread with weak signal code-Weak signal autocorrelation with weak signal de-spread with weak signal code

  The following shows how the weak signal search results will be divided into the case where the level difference between the strong signal and the weak signal is not so large.

  When the level difference between the strong signal and the weak signal is not so large, the weak signal autocorrelation peak level is stronger than the strong signal cross-correlation level as shown in the code phase-correlation level characteristic diagram of FIG. Become. For this reason, the weak signal auto-correlation peak level is captured as a result of the weak signal search, and the normal tracking of the weak signal is possible. Note that a plurality of levels of strong signal cross-correlation occur at different code phases (three are illustrated in the example of FIG. 9).

  When the level difference between the strong signal and the weak signal is large, the strong signal cross-correlation is higher than the autocorrelation peak level of the weak signal ((A) in FIG. 10) as shown in the code phase-correlation level characteristic diagram of FIG. The peak level ((B) in FIG. 10) may become stronger.

  When the level difference between the strong signal and the weak signal is large, acquisition is performed at the code phase of the strong signal cross-correlation peak ((B) in FIG. 10), and tracking is started. This state is incorrect tracking.

  The correlation result of the channel that caused the erroneous tracking is clearly different from the result of the autocorrelation calculation of the weak signal. Therefore, if the information is used for positioning, the position jump may be caused.

  Therefore, a method of leaving a weak signal autocorrelation value by subtracting a strong signal cross-correlation value from an output correlation value of a weak signal channel (hereinafter sometimes abbreviated as “ch”) is disclosed in Patent Document 1. (Patent Document 1 mainly performs processing by hardware, and Patent Document 2 mainly performs processing by software).

  In Patent Documents 1 and 2, first, an input signal is received by a strong signal ch, the amplitude, code phase, and carrier frequency of the strong signal included in the input signal are measured, and the waveform of the strong signal is reproduced. The strong signal included in this input signal becomes an interference signal in the weak signal ch.

  Next, the cross-correlation value between the reproduced strong signal, the code phase set by the weak signal ch and the set signal expressed by the carrier frequency is calculated.

Then, a correlation value between the input signal and the set signal expressed by the set code phase and carrier frequency is obtained with the weak signal ch. Since the correlation value in the weak signal ch includes the correlation value of the cross correlation between the strong signal and the setting signal in addition to the autocorrelation value of the weak signal originally desired, the correlation value in the weak signal ch is reproduced. The cross-correlation value between the set strong signal waveform and the set strong signal is subtracted. In this way, the interference signal component (strong signal cross-correlation value) in the weak signal ch is removed.
US7,064,707B2 US6,282,231B1

  However, in order to obtain the weak signal autocorrelation value by subtracting the strong signal cross-correlation value from the output correlation value of the weak signal ch by the methods of Patent Documents 1 and 2, it is necessary to obtain the amplitude at the strong signal ch. However, in recent receivers, the input signal is usually quantized for digital processing. When the number of quantization bits is small, particularly when 1-bit quantization is performed, the amplitude measured in the strong signal ch has a relatively large error, so that the interference signal component (strong signal cross-correlation value in the weak signal ch). ) Is difficult to remove correctly, and the suppression performance deteriorates.

  The present invention has been made in view of the above points, and in an environment where a signal obtained by combining a strong satellite signal and a weak satellite signal is received, the amplitude of the strong signal ch is not obtained. An object of the present invention is to provide a GPS receiver capable of estimating the strong signal cross-correlation value of the weak signal ch and eliminating the influence of the strong signal on the weak signal ch.

The GPS receiver according to claim 1, wherein a reception signal is inputted and acquisition and / or tracking is performed with a frequency and a spread code type / phase corresponding to different satellite signals, and receives a strong signal satellite signal. A plurality of reception channels that are weak signal channels for receiving strong signal channels or weak satellite signals;
A first signal having a frequency and a spreading code type / phase of one strong signal channel of the plurality of reception channels is input, and the first signal and one weak signal channel of the plurality of reception channels Having at least one cross-correlation channel that performs cross-correlation with the frequency including the Doppler component and the type / phase of the spreading code and outputs a cross-correlation channel correlation component that is the second signal,
The strong signal and the one weak signal channel included in the third signal (IPW = x1 * IPC + x2) that is the output of the one weak signal channel and acquired or tracked in the one strong signal channel The cross-correlation ratio (x1) of the second signal (IPC) with respect to the cross-correlation component (x1 * IPC) with the weak signal to be acquired or tracked is estimated using the second signal and the third signal. And
Multiplying the second signal (IPC) by the cross-correlation ratio (x1) to determine a cross-correlation component included in the third signal (IPW);
Subtracting the cross-correlation component (x1 * IPC) included in the third signal from the third signal (IPW) to obtain a weak signal component x2 included in the third signal (IPW). To do.

The GPS receiver according to claim 2, wherein a reception signal is inputted and acquisition and / or tracking is performed at a frequency and a type / phase of a spreading code corresponding to different satellite signals, and receives a strong signal satellite signal. A plurality of N reception channels that are strong signal channels or weak signal channels that receive weak satellite signals;
A first signal having a frequency of a strong signal channel and a type / phase of a spreading code of any one of the plurality of reception channels is input, and the first signal and a weak one of the plurality of reception channels are input. A predetermined number of mutual channels corresponding to the number N of reception channels for performing cross-correlation with the frequency including the Doppler component of the signal channel and the type / phase of the spreading code and outputting the cross-correlation channel correlation component as the second signal A correlation channel,
If one or more N-1 or less strong signal channels are formed,
A strong signal included in the third signal (IPW = x11 * IPC1 + x12 * IPC2 +... + X2) that is the output of one weak signal channel and acquired or tracked in one strong signal channel and the weak signal For the cross-correlation component (x11 * IPC1, or x12 * IPC2, or...) With the weak signal to be acquired or tracked in the channel, the weak signal channel and the one strong signal channel The cross-correlation ratio (x11, x12, or...) Of the second signal is set as the second signal (IPC1, IPC2, or...) Related to the weak signal channel and the one strong signal channel. ) And the third signal (IPW) for each strong signal component included in the third signal (IPW) ,
The cross-correlation ratio (x11, x12,...) For each strong signal component included in the third signal (IPW) is multiplied by the second signal (IPC1, IPC2,...) Related to the weak signal channel. Cross-correlation components (x11 * IPC1, x12 * IPC2,...) Included in the third signal (IPW)
The cross-correlation components (x11 * IPC1, x12 * IPC2,...) Included in the third signal (IPW) are subtracted from the third signal (IPW), and are included in the third signal (IPW). A weak signal component (x2) is obtained.

  The GPS receiver according to claim 3 is the GPS receiver according to claim 1 or 2, wherein the second signal is a strong signal related to the channel in a cross-correlation channel correlation component obtained in the cross-correlation channel. It is characterized in that the influence of data modulation is removed by multiplying the output code of the channel.

  According to the GPS receiver of the present invention, the strong signal cross-correlation value of the weak signal ch is estimated and obtained in an environment where a signal obtained by combining the strong satellite signal and the weak satellite signal is received. By subtracting the strong signal cross-correlation value from the output correlation value of the weak signal ch, the influence of the strong signal on the weak signal ch can be eliminated without obtaining the amplitude on the strong signal ch.

  Embodiments of a GPS receiver according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram for explaining a GPS receiver according to the present invention. In order to perform positioning with a GPS receiver, the reception results of satellite signals from at least four satellites are necessary, and therefore, reception channels (hereinafter referred to as “ch”) of 4ch or more are generally mounted. Depending on the satellite signal reception status, for example, when the reception channel is 4 channels, the strong signal channel is 4, the weak signal channel is 0, the strong signal channel is 3, the weak signal channel is 1, and the strong signal channel is 2. A pattern in which the weak signal ch is 2, the strong signal ch is 1, the weak signal ch is 3, and the strong signal ch is 0 and the weak signal ch is 4 is considered. The strong signal that is tracked by the strong signal ch, for example, interferes with the weak signal ch when both the strong signal ch and the weak signal ch exist.

  In FIG. 1, in order to explain the present invention, an example is shown in which one strong signal ch and one weak signal ch are provided and a total of two reception channels are provided. In FIG. 1, a strong signal ch11 that is a reception channel for searching or tracking one strong signal and a weak signal ch12 that is a reception channel for searching or tracking one weak signal are shown. A cross-correlation ch30 for performing cross-correlation with the weak signal is provided.

  Although not shown in FIG. 1, a control unit (processor) 20, an antenna 1, a frequency conversion unit 2, an A / D conversion unit 3, and the like are provided as described with reference to FIG. 6.

  The operation principle of the present invention will be described below. As in the conventional description, assume an environment in which signals from two satellites are received, one being a strong signal and the other being a weak signal. Here, the strong signal ch11 is devoted to a channel having a sufficiently large power detected in the search or a channel having a sufficiently large power detected in the tracking channel determination process. Further, the weak signal ch12 indicates a channel in which the satellite signal is weak, but an undecided channel that is not determined to be a strong signal channel may be assumed.

  The strong signal ch11 is one of normal reception channels and receives a strong signal. Although there are usually a plurality of strong signals ch, only one is shown here for explanation. The strong signal ch11 has the same configuration (111 to 116) as the tracking channel described in FIG. 8, and the input IF reception signal is the mixer 111, and the frequency from the carrier NCO 112 (set by the control unit 20). The phase is rotated by mixing with the code correlator 113 and supplied to the code correlator 113. In the code correlator 113, the correlation between the signal from the mixer 111 and the spread code from the code GEN (code generator) 115 is taken. The code phase of the spread code from the code GEN 115 is controlled by the code phase from the code NCO 114 (set by the control unit 20). From the carrier NCO 112, the IF frequency + the strong signal Doppler frequency is supplied to the mixer 111, and from the code NCO 114 and the code GEN 115, the strong signal code phase whose phase is synchronized with the strong signal is supplied to the code correlator 113. ing.

  The signal whose code correlation has been obtained after the phase rotation is integrated by the integrator 116 for each I component and Q component of the correlation value every predetermined time and supplied to the control unit 20. From the control unit 20, the frequency is set to the carrier NCO 112, and the code number is set to the code GEN115.

  The strong signal ch11 outputs strong signal autocorrelation power and weak signal crosscorrelation power. However, since the strong signal autocorrelation power >> weak signal crosscorrelation power, the strong signal autocorrelation power is substantially satisfied. Is output.

  FIG. 2 is a diagram showing a more specific circuit configuration of the strong signal ch of FIG. In order to perform phase rotation in the mixer separately for the in-phase component I and the quadrature component Q, a mixer 111I and a mixer 111Q are provided, and a frequency signal obtained from the carrier NCO 112 via the sin table 112I is supplied to the mixer 111I, and the mixer 111Q is supplied. A frequency signal obtained from the carrier NCO 112 via the cos table 112QI is supplied.

  Further, in order to configure a DLL circuit that performs tracking, in the shift register 115S based on the code NCO 114 and the code generator 115, the half-chip phase is advanced from the synchronization code P-code of the phase that is actually synchronized and the synchronization code. The leading code E-code and the delayed code L-code whose half chip phase is delayed from the synchronization code are generated, and the code correlator 113IE, 113IP, 113IL, 113QE, 113QP, 113QL, the I signal from the mixer 111I, By multiplying the Q signal from the mixer 111Q, the correlation values ie, ip, il, qe, qp, and ql are obtained. These correlation values ie to ql are integrated by integrators 116IE, 116IP, 116IL, 116QE, 116QP, and 116QL for a predetermined time, for example, 1 / n [ms], and the integrated correlation values IE, IP, IL, QE, QP, Get QL.

  The buffer 119 has n or more (at least n) storage areas for each correlation value for sequentially storing the integrated correlation values IE to QL, and stores n correlation values IE to QL in those storage areas. To do.

  As “n” is increased, the measurement accuracy is improved, but the processing load of the control unit is increased.

  In the correlation value processing, instead of the correlation values IE, IL, QE, QL, the correlation values IEL, QEL with IE-IL = IEL, QE-QL = QEL may be processed.

  For example, the control unit 20 sets the frequency, code number, and code phase obtained as a result of the search process for a certain satellite in the tracking ch. The tracking ch performs a correlation operation at a specified frequency, code number, and code phase, outputs the I component and Q component of the correlation result to the control unit 20, and the control unit 20 is optimal so that stable reception is continued. The frequency and code phase are calculated as needed and set to the tracking ch. In addition, the control unit 20 performs control processing for the present invention. The control unit 20 may be provided in common for all the channels.

  Further, the strong signal ch11 that is the reception channel is multiplied by the synchronization code P-code of the shift register 115S and the frequency signal from the carrier NCO 112 (which may be a frequency signal obtained via the sin table 112I) by the mixer 111S, The first signal having the frequency of the strong signal ch and the type / phase of the spreading code is output. This first signal is supplied to the cross-correlation ch30.

  The weak signal ch12 is one of normal tracking channels, and receives a weak signal. The weak signal ch12 has the same configuration (121 to 126) as the strong signal ch11, and outputs a signal of “weak signal autocorrelation power + strong signal cross-correlation power”. The IF frequency + the weak signal Doppler frequency is supplied to the mixer 121 from the carrier NCO 122, and the weak signal code is supplied to the code correlator 123 from the code NCO 124 and the code GEN 125. When the weak signal code phase is normally tracked by the weak signal, phase synchronization is achieved. Since the weak signal ch12 is also a single reception channel, it may be used as a strong signal ch. Therefore, as in FIG. 2, the shift register synchronization code P-code and the frequency signal from the carrier NCO are multiplied by a mixer. Can be output. However, when used as a weak signal ch, the output is not performed. Further, when the reception channel is dedicated to the weak signal channel, a configuration capable of outputting the reception channel is not necessary.

  The cross-correlation ch30 specializes in actual measurement of the strong signal cross-correlation and has the same configuration (301 to 306) as the strong signal ch11, but the input signal is not an IF reception signal, The first signal having the frequency of the strong signal ch11 and the type / phase of the spreading code is supplied. The carrier NCO 302 supplies a frequency obtained by adding the weak signal Doppler frequency to the IF frequency to the mixer 301, and the code NCO 304 and the code GEN 305 supply the weak signal code to the code correlator 303. The integrator 306 outputs a second signal that is a strong signal cross-correlation power. Unlike FIG. 2, the cross-correlation ch30 does not require a configuration that can output the shift register synchronization code P-code and the frequency signal from the carrier NCO by a mixer.

  A processing procedure in the configuration of FIGS. 1 and 2 will be described. First, as a first stage, outputs of strong signal ch11, weak signal ch12, and cross-correlation ch30, that is, integrated correlation values IE, IP, IL, QE, QP, and QL are obtained. These correlation values IE to QL or IEL and QEL are stored in a buffer 117 having N storage areas for each correlation value. In order to distinguish the correlation values of the strong signal ch11, the weak signal ch12, and the cross-correlation ch30, the correlation value of the strong signal ch11 is denoted by S to be IPS, IELS, QPS, QELS, and the correlation value of the weak signal ch12 is W. Is attached to IPW, IELW, QPW, QELW, and the correlation value of the cross-correlation ch30 is attached with C to represent IPC, IELC, QPC, QELC. The values stored in the buffer 117 are expressed as an array. For example, the value of the IPS buffer 117 is expressed as IPS (1), IPS (2),..., IPS (n), or IPS (i), i = 1,. The same applies to other correlation values.

  Next, as a second step, the output IPC, IELC, QPC, and QELC of the cross-correlation ch30 are multiplied by the sign of the output IPS of the strong signal ch in order to remove the influence of the data modulation of the strong signal. That is, IPC (i) * SGN (IPS (i)), IELC (i) * SGN (IPS (i)), QPC (i) * SGN (IPS (i)), QELC (i) * SGN (IPS ( i)), i = 1,..., n are calculated. The strong signal included in the input signal is data-modulated, but the reproduced first signal, which is the strong signal, is not data-modulated, so the influence of the data modulation is removed by multiplying the sign of the output IPS representing the data modulation. Is.

  Next, as a third stage, the cross-correlation ratio x1 included in the outputs IPW and QPW of the weak signal ch12 is determined using the outputs IPC and QPC of the cross-correlation ch30 and the outputs IPW and QPW of the weak signal ch12. presume. This estimation is preferably a least square estimation. This cross-correlation ratio x1 indicates how many times the output IPC and QPC are included in the cross-correlation component included in the outputs IPW and QPW of the weak signal ch, that is, the auto-correlation portion removed from the outputs IPW and QPW. It is a coefficient to represent. x1 = “cross-correlation component included in output of weak signal ch” / “output of cross-correlation ch”.

The input signal consists of a data-modulated strong and weak signal and noise. Therefore, the following relationship is obtained when correlation is obtained with the weak signal ch12.
IPW (i) = x1 * (IPC (i) * SGN (IPS (i))) + x2 + v1
QPW (i) = x1 * (QPC (i) * SGN (IPS (i))) + x3 + v2
Here, IPW (i), QPW (i): the correlation between the input signal and the frequency / spreading code (hereinafter, weak signal setting value) of the carrier NCO 122 and the code GEN 125, the output of the weak signal ch12,
IPC (i) * SGN (IPS (i)), QPC (i) * SGN (IPS (i)): cross-correlation component between strong signal and weak signal set value,
x2, x3: autocorrelation component between weak signal and weak signal set value,
v1, v2: correlation component between noise and weak signal setting value, noise component,

In order to estimate the least squares of the unknowns x1, x2, and x3, the following h1, h2, h3, y1, y2, and y3 are calculated. Σ represents the sum of i = 1,..., N. By this least square estimation, the square sum of the prediction error is minimized, so that the unknown including the noise components v1 and v2 is estimated.
h1 = Σ (IPC (i) ² ) + QPC (i) ² )
h2 = Σ (IPC (i) * SGN (IPS (i))
h3 = Σ (QPC (i) * SGN (IPS (i))
y1 = Σ (IPC (i) * SGN (IPS (i)) * IPW (i)
+ QPC (i) * SGN (IPS (i)) * QPW (i))
y2 = ΣIPW (i)
y3 = ΣQPW (i)

The following matrix operation is performed. x _e 1 is an estimated cross-correlation ratio obtained by estimating the cross-correlation ratio x1, and when expressed in a simplified form using the in-phase component and omitting the SGN component
x _e 1 = “IPW−x _e 2” / “IPC”. X _e 2 is an estimated auto-correlation component obtained by estimating the auto-correlation component x 2, and the other “x _e ...” Used thereafter represents an estimated value of “x.

Next, as a fourth stage, the estimated cross-correlation ratio x _e 1 is multiplied by the output IPC, IELC, QPC, QELC of the cross-correlation ch30 and included in the outputs IPW, IELW, QPW, QELW of the weak signal ch12. Estimate the cross-correlation component. The output IPW weak signal ch12, IELW, QPW, from QELW, by subtracting the estimated cross-correlation component, the weak signal component x _e 2, x _e 3 a is corrected correlation value IPWX (i), IELWX ( i), QPWX (i), QELWX (i).
IPWX (i) = IPW (i) -x _e 1 * IPC (i) * SGN (IPS (i))
IELWX (i) = IELW (i) −x _e 1 * IELC (i) * SGN (IPS (i))
QPWX (i) = QPW (i) -x _e 1 * QPC (i) * SGN (IPS (i))
QELWX (i) = QELW (i) -x _e 1 * QELC (i) * SGN (IPS (i))

In this way, included in the third signal that is the output of one weak signal ch12 (hereinafter, the parenthesized notation using the in-phase component and omitting the SGN component; IPW = x _e 1 * IPC + x _e 2) And a second signal (x _e 1 * IPC) for a cross-correlation component (x _e 1 * IPC) between a strong signal tracked by one strong signal channel 11 and a weak signal to be tracked by one weak signal channel 12 IPC) cross-correlation ratio (x _e 1) is estimated using the second signal and the third signal. Then, the cross-correlation ratio (x _e 1) is multiplied by the second signal (IPC) to determine a cross-correlation component included in the third signal (IPW), and is included in the third signal from the third signal (IPW). By subtracting the cross-correlation component (x _e 1 * IPC), the weak signal component (x _e 2) included in the third signal (IPW) can be obtained.

In the search mode, acquisition is performed, but corrected correlation values IPWX (i), IEWX (i), ILWX (i), QPWX (i), QEWX (i), QLWX (i) Are obtained by the following equation.
IPWX (i) = IPW (i) -x _e 1 * IPC (i) * SGN (IPS (i))
IEWX (i) = IEW (i) -x _e 1 * IEC (i) * SGN (IPS (i))
ILWX (i) = ILW (i) -x _e 1 * ILC (i) * SGN (IPS (i))
QPWX (i) = QPW (i) -x _e 1 * QPC (i) * SGN (IPS (i))
QEWX (i) = QEW (i) −x _e 1 * QEC (i) * SGN (IPS (i))
QLWX (i) = QLW (i) -x _e 1 * QLC (i) * SGN (IPS (i))

  FIG. 3 is a diagram showing a configuration in which there are three reception channels, two of which are formed as strong signal channels and one as a weak signal channel.

  The outputs IPW (i) and QPW (i) of the weak signal ch12 include the cross-correlation component 1 due to the strong signal 1 being tracked by the strong signal ch11-1 and the strong signal 2 being tracked by the strong signal ch11-2. And the cross-correlation component 2 is included. Therefore, in order to remove the interference signal due to the strong signals 1 and 2, the cross-correlation ch30-1 that performs the cross-correlation between the strong signal 1 of the strong signal ch11-1 and the weak signal set value of the weak signal ch12, and the strong signal ch11 -2 is provided as a cross-correlation ch30-2 that performs cross-correlation between the strong signal 2 of -2 and the weak signal set value of the weak signal ch12.

  Based on the following equation, the weak signal of the weak signal ch12 is obtained in the same manner as in the case where there is one strong signal ch described above. In the following expression, the meaning of each symbol is the same as in the case of one strong signal ch already described, but the subscript 1 represents the strong signal 1 and the subscript 2 represents the strong signal 2. Represents. For example, x11 is the cross-correlation ratio 1, and x11 = “cross-correlation component due to the strong signal 1 included in the output of the weak signal ch” / “output of the cross-correlation ch1”. Further, x12 is the cross-correlation ratio 2, and x12 = “cross-correlation component due to the strong signal 2 included in the output of the weak signal ch” / “output of the cross-correlation ch2”.

IPW (i) = x11 * (IPC1 (i) * SGN (IPS1 (i))
+ X12 * (IPC2 (i) * SGN (IPS2 (i)) + x2 + v1
QPW (i) = x11 * (QPC1 (i) * SGN (IPS1 (i))
+ X12 * (QPC2 (i) * SGN (IPS2 (i)) + x3 + v2

In order to estimate the least squares of the unknowns x11, x12, x2, and x3, the following h11, h12, h22, h13, h23, h14, h24, y11, y12, y2, and y3 are calculated.
h11 = Σ (IPC1 (i) ² + QPC1 (i) ² )
h12 = Σ (IPC1 (i) * IPC2 (i) + QPC1 (i) * QPC2 (i))
h22 = Σ (IPC2 (i) ² + QPC2 (i) ² )
h13 = Σ (IPC1 (i) * SGN (IPS1 (i))
h23 = Σ (IPC2 (i) * SGN (IPS2 (i))
h14 = Σ (QPC1 (i) * SGN (IPS1 (i))
h24 = Σ (QPC2 (i) * SGN (IPS2 (i))
y11 = Σ (IPC1 (i) * SGN (IPS1 (i)) * IPW (i)
+ QPC1 (i) * SGN (IPS1 (i)) * QPW (i))
y12 = Σ (IPC2 (i) * SGN (IPS2 (i)) * IPW (i)
+ QPC2 (i) * SGN (IPS2 (i)) * QPW (i))
y2 = ΣIPW (i)
y3 = ΣQPW (i)

The following matrix operation is performed. x _e 11 and x _e 12 are the estimated cross-correlation ratios.

The estimated cross-correlation ratios x _e 11 and x _e 12 are multiplied by the outputs IPC1, IELC1, QPC1, QELC1, IPC2, IELC2, QPC2, and QELC2 of the cross-correlation ch30-1 and 30-2, and the weak signal ch12 is obtained. The cross-correlation components included in the output IPW, IELW, QPW, QELW are estimated. The output IPW weak signal ch12, IELW, QPW, from QELW, by subtracting the estimated cross-correlation component, the weak signal component x _e 2, x _e 3 a is corrected correlation value IPWX (i), IELWX ( i), QPWX (i), QELWX (i).

  In the above description, the present invention relates to the case where there are two received channels, the strong signal ch is 1, and the weak signal ch is 1, and the case where there are three received channels, the strong signal ch is 2, and the weak signal ch is 1. Explained. As described above, since the reception result of satellite signals from at least four satellites is necessary for positioning with a GPS receiver, generally, reception channels of 4 channels or more are mounted.

  4 and 5 are diagrams illustrating possible patterns according to the reception status of the satellite signal when the reception channel is 4 channels, for example. 4 and 5, a pattern in which the strong signal ch is 4 and the weak signal ch is 0 (FIG. 4A), and a pattern in which the strong signal ch is 3 and the weak signal ch is 1 (FIG. 4B). )), A pattern in which the strong signal ch is 2 and the weak signal ch is 2 (FIG. 4C), a pattern in which the strong signal ch is 1 and the weak signal ch is 3 (FIG. 5A), and a strong signal A pattern in which ch is 0 and weak signal ch is 4 ((b) in FIG. 5) is conceivable.

  In FIG. 4A, each received channel tracks strong signals 1 to 4 and becomes strong signal ch1 to strong signal ch4, so there is no need to use a cross-correlation channel.

  In FIG. 4B, the three received channels track the strong signals 1 to 3, become the strong signal ch1 to the strong signal ch3, and one received channel becomes the weak signal ch1 to be tracked to the weak signal 1. In this case, the strong signals 1 to 3 tracked by the strong signal ch1 to the strong signal ch3 interfere with the weak signal ch1. Therefore, the cross-correlation between the strong signal 1 and the weak signal 1 is performed using the cross-correlation ch1, the cross-correlation between the strong signal 2 and the weak signal 1 is performed using the cross-correlation ch3, and the cross-correlation between the strong signal 3 and the weak signal 1 is performed. This is performed with the cross-correlation ch4. Then, each cross-correlation ratio is obtained by the same method as described with reference to FIG. 3, and the weak signal component of the weak signal ch1 is obtained.

  In FIG. 4C, the two received channels track the strong signals 1 and 2 to become the strong signal ch1 and the strong signal ch2, and the two received channels should track the weak signals 1 and 2, respectively. ch2. In this case, the strong signals 1 and 2 being tracked by the strong signal ch1 and the strong signal ch2 interfere with the weak signal ch1, and the weak signal ch2 is also tracked by the strong signal ch1 and the strong signal ch2. The strong signals 1 and 2 that are present interfere with each other. Therefore, the cross-correlation between the strong signal 1 and the weak signal 1 is performed with the cross-correlation ch1, the cross-correlation between the strong signal 2 and the weak signal 1 is performed with the cross-correlation ch2, and the mutual correlation between the strong signal 1 and the weak signal 2 is performed. The correlation is performed with the cross-correlation ch3, and the cross-correlation between the strong signal 2 and the weak signal 2 is performed with the cross-correlation ch4. Then, by using the same method as described with reference to FIG. 3, the respective cross-correlation ratios are obtained, and the weak signal component of the weak signal ch1 and the weak signal component of the weak signal ch2 are obtained.

  In FIG. 5A, one received channel tracks the strong signal 1 and becomes the strong signal ch1, and the three received channels become the weak signal ch1 to the weak signal ch3 to be tracked to the weak signals 1 to 3. In this case, the strong signal 1 tracked by the strong signal ch1 interferes with the weak signal ch1, the weak signal ch2, and the weak signal ch3. Therefore, the cross-correlation between the strong signal 1 and the weak signal 1 is performed using the cross-correlation ch1, the cross-correlation between the strong signal 1 and the weak signal 2 is performed using the cross-correlation ch2, and the cross-correlation between the strong signal 1 and the weak signal 3 is performed. This is performed with the cross-correlation ch4. Then, each cross-correlation ratio is obtained by the same method as described with reference to FIG. 3, and the weak signal component of the weak signal ch1 is obtained.

  In FIG. 5B, each reception channel tracks weak signals 1 to 4 and becomes weak signal ch1 to weak signal ch4, and there is no strong signal that interferes with these weak signals ch1 to 4. There is no need to use it.

  4 and 5, the supply of each first signal from the strong signal ch to the cross-correlations ch1 to ch4 is provided with a selection switch, and the selection switch is appropriately switched according to the reception status of the satellite signal. As a result, the number of cross-correlation channels is limited to four.

In general, the number of cross-correlation channels is a predetermined number corresponding to the number N of received channels. When N is a plurality of received channels, (N / 2) ² cross-correlation channels when N is an even number, and (N + 1) * (N-1) / 4 when N is an odd number. If there is a cross-correlation channel of. That is, the predetermined number of cross-correlation channels is “(N / 2) ² (when N is an even number)” or “(N + 1) * (N−1) / 4 (when N is an odd number)”. For example, when N = 4, the present invention can be realized by providing four cross-correlation channels as shown in FIGS.

  In this way, a strong signal channel or weak signal that receives and receives a strong satellite signal and receives and / or tracks the frequency and type and phase of a spreading code corresponding to different satellite signals when the received signal is input. A plurality of N reception channels, which are weak signal channels for receiving the satellite signal, and a first signal having a frequency and a spreading code type / phase of any strong signal channel among the plurality of reception channels; A cross-correlation channel correlation that is a second signal is performed by cross-correlating the first signal with the frequency and Doppler component type / phase of the weak signal channel of any one of the plurality of reception channels. A GPS receiver having a predetermined number of cross-correlation channels according to the number of reception channels N for outputting components is configured. .

And when one or more N-1 or less strong signal channels are formed,
(1) Included in the third signal that is the output of one weak signal channel (hereinafter, parenthesized notation using the in-phase component and omitting the SGN component; IPW = x11 * IPC1 + x12 * IPC2 +... + X2) Cross-correlation component between a strong signal being acquired or tracked in one strong signal channel and a weak signal to be acquired or tracked in the weak signal channel (x11 * IPC1, or x12 * IPC2, or ... )), The cross-correlation ratio (x11, x12,...) Of the second signal related to the weak signal channel and the one strong signal channel is set to the weak signal channel and the one strong signal channel. Second signal (IPC1, or IPC2, or...) Related to the strong signal channel and the third signal (IPW) Was used to estimate for each strong signal component included in the third signal (IPW),
(2) The cross-correlation ratio (x11, x12,...) For each strong signal component included in the third signal (IPW) is used as the second signal (IPC1, IPC2,...) Related to the weak signal channel. To determine cross-correlation components (x11 * IPC1, x12 * IPC2,...) Included in the third signal (IPW),
(3) The third signal (IPW) is obtained by subtracting the cross-correlation components (x11 * IPC1, x12 * IPC2,...) Included in the third signal (IPW) from the third signal (IPW). To obtain a weak signal component (x2).

  Further, when other weak signal ch is present, similarly, the interference component due to the strong signal can be removed to obtain the weak signal component in the other weak signal ch.

  In the present invention, even when the interference signal (strong signal) is a sine wave that is not code-modulated, the influence of the sine wave can be removed by the same method.

The figure for demonstrating the GPS receiver of this invention The figure which shows the more concrete circuit structure of receiving ch (strong signal ch, weak signal ch). Configuration diagram when there are three reception channels (strong signal ch; two, weak signal ch; one) The figure which shows the pattern 1-3 in case a receiving channel is 4ch The figure which shows the patterns 4 and 5 when receiving channel is 4ch The figure which shows schematic structure of the GPS receiver generally used conventionally The figure which shows the specific structural example of a search part Diagram showing a specific configuration example of the tracking channel Characteristic diagram of code phase-correlation level when the level difference between strong and weak signals is small Characteristic diagram of code phase-correlation level when the level difference between strong and weak signals is large

Explanation of symbols

1: antenna, 2: frequency conversion unit, 3: A / D conversion unit, 4: signal processing unit, 10: search unit 11, 12: tracking ch, 101-1n1: mixer 102-1n2: carrier NCO, 103-1n3 : Code correlator 104-1n4: code NCO, 105-1n5: code generator 106-1n6: integrator, 107: power generation unit, 108: buffer and sorting unit, 119: buffer, 20: control unit, 30: mutual Correlation ch

Claims (3)

Received signals are input and tracked with frequency and spreading code type / phase corresponding to different satellite signals, receiving strong signal satellite signals or weak satellite signals. A plurality of receiving channels to be weak signal channels,
A first signal having a frequency and a spreading code type / phase of one strong signal channel of the plurality of reception channels is input, and the first signal and one weak signal channel of the plurality of reception channels Having at least one cross-correlation channel that performs cross-correlation with the frequency including the Doppler component and the type / phase of the spreading code and outputs a cross-correlation channel correlation component that is the second signal,
The strong signal that is included in the third signal that is the output of the one weak signal channel and is acquired or tracked in the one strong signal channel and should be acquired or tracked in the one weak signal channel Estimating a cross-correlation ratio of the second signal with respect to a cross-correlation component with a weak signal using the second signal and the third signal;
Multiplying the second signal by the cross-correlation ratio to determine a cross-correlation component included in the third signal;
A GPS receiver, wherein a weak signal component included in the third signal is obtained by subtracting a cross-correlation component included in the third signal from the third signal. Received signals are input and tracked with frequency and spreading code type / phase corresponding to different satellite signals, receiving strong signal satellite signals or weak satellite signals. A plurality of N reception channels to be weak signal channels,
A first signal having a frequency of a strong signal channel and a type / phase of a spreading code of any one of the plurality of reception channels is input, and the first signal and a weak one of the plurality of reception channels are input. A predetermined number of mutual channels corresponding to the number N of reception channels for performing cross-correlation with the frequency including the Doppler component of the signal channel and the type / phase of the spreading code and outputting the cross-correlation channel correlation component as the second signal A correlation channel,
If one or more N-1 or less strong signal channels are formed,
A mutual relationship between a strong signal included in a third signal that is an output of one weak signal channel and being acquired or tracked in one strong signal channel and a weak signal to be acquired or tracked in the weak signal channel. For the correlation component, the cross-correlation ratio of the second signal related to the weak signal channel and the one strong signal channel is set to the second signal and the third signal related to the weak signal channel and the one strong signal channel. And for each strong signal component included in the third signal,
Multiplying the second signal related to the weak signal channel by the cross-correlation ratio for each strong signal component included in the third signal to determine a cross-correlation component included in the third signal;
A GPS receiver, wherein a weak signal component included in the third signal is obtained by subtracting a cross-correlation component included in the third signal from the third signal.   3. The GPS receiver according to claim 1, wherein the second signal is obtained by multiplying a cross-correlation channel correlation component obtained by the cross-correlation channel by a sign of an output of the strong signal channel related to the channel. A GPS receiver, wherein the influence of modulation is removed.

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