JP5375774B2 - Code phase error calculation method and code phase calculation method - Google Patents

Description

The present invention relates to a technique for determining the reliability of a multipath signal .

  As a positioning system using a positioning signal, a GPS (Global Positioning System) is widely known and used by being incorporated in a mobile phone, a car navigation device, or the like. In the GPS, a position calculation process for obtaining the position of the position calculation device is performed based on information such as the position of a plurality of GPS satellites and a pseudo distance from each GPS satellite to the position calculation device.

  Multipath is one of the main factors that cause errors in position calculation using positioning signals. An environment in which multipath occurs is called a “multipath environment”. A multipath environment is a direct wave signal from a positioning signal source (or GPS satellite if GPS), a reflected wave reflected on a building or the ground, a transmitted wave transmitted through an obstacle, or an obstacle diffracted. This is an environment in which an indirect wave signal such as a diffracted wave is superimposed and received as a multipath signal. This is a phenomenon in which the indirect wave signal becomes an error signal and it is difficult to decode the code.

  In order to solve the problem of the error caused by the multipath, for example, in Patent Document 1, a positioning satellite that is highly likely to be affected by the multipath is determined to be a positioning unsuitable satellite, and the positioning unsuitable satellite is excluded. A technique for calculating a position is disclosed.

JP 2008-170214 A

  As one of the ideas of multipath countermeasures, there is an idea of performing position calculation by removing multipath signals from the captured positioning signals. However, in an urban canyon environment where high-rise buildings are adjacent, the majority of received positioning signals may be multipath signals, and if all multipath signals are eliminated, position calculation is necessary. There arises a problem that the number of satellites cannot be secured. For this reason, there is a demand to use a highly reliable positioning signal that can be used for position calculation, even if it is a multipath signal, for position calculation as much as possible.

  The present invention has been made in view of the above-described problems, and an object thereof is to propose a new mechanism for determining whether a multipath signal is good or bad.

  A first form for solving the above-described problem is that a correlation calculation process is performed on a received signal that has received a satellite signal transmitted from a position calculation satellite, and a peak correlation value obtained by the correlation calculation process. And determining the reliability of the multipath signal when the received signal is a multipath signal using a correlation value of a phase delayed by a predetermined phase from the peak phase indicating the peak correlation value. It is a multipath signal reliability determination method including.

  As another form, a correlation calculation unit that performs a correlation calculation process on a received signal received from a satellite signal transmitted from a position calculation satellite, a peak correlation value obtained by the correlation calculation process, and the peak A determination unit that determines the reliability of the multipath signal when the received signal is a multipath signal, using a correlation value of a phase delayed by a predetermined phase from the peak phase indicating the correlation value. A path signal reliability determination device may be configured.

  According to the first embodiment and the like, the correlation calculation process is performed on the received signal received from the satellite signal transmitted from the position calculating satellite. Then, using the peak correlation value obtained by the correlation calculation process and the correlation value of the phase delayed by a predetermined phase from the peak phase indicating the peak correlation value, the multipath when the received signal is a multipath signal Determine the reliability of the signal.

  A multipath signal is an indirect wave such as a reflected wave reflected from a building or the ground, a transmitted wave transmitted through an obstacle, or a diffracted wave diffracted from an obstacle to a direct wave signal transmitted from a positioning satellite. The signal is a superimposed signal. The indirect wave signal is a signal delayed from the direct wave signal because the propagation distance from the positioning satellite to the receiver is longer than the direct wave signal. For this reason, when the received signal is a multipath signal, the influence of the indirect wave signal appears greatly in the phase delayed from the peak phase, and the absolute value of the correlation value increases. Therefore, by referring to the peak correlation value and the correlation value of the phase delayed by a predetermined phase from the peak phase, the degree of influence of the indirect wave signal on the direct wave signal can be grasped, and the quality of the multipath signal can be determined. Can be determined.

  Further, as a second mode, the multipath signal reliability determination method according to the first mode, wherein the predetermined phase is not less than 1 chip and less than 2 chips, may be configured. .

  According to the second aspect, the reliability of the multipath signal is determined using a phase delayed by one chip or more and less than two chips from the peak phase as the predetermined phase. As a result of experiments by the inventor of the present application, the correlation value of the phase delayed by 1 chip or more and less than 2 chips compared to the correlation value in the phase where the delay from the peak phase is less than 1 chip or the phase delayed by 2 chips or more However, it turned out that it is easy to determine the influence of an indirect wave signal. Therefore, it is more preferable to determine the reliability of the multipath signal by using the correlation value of the phase delayed by one chip or more and less than two chips.

  Further, as a third mode, executing the multipath signal reliability determination method of the first or second mode, and an indirect wave signal indirectly receiving the satellite signal with respect to the direct wave signal directly receiving the satellite signal Determining whether the correlation value is intensifying or weakening in accordance with the delay of the peak using a peak correlation value and a correlation value of a phase advanced by a predetermined phase from the peak phase indicating the peak correlation value; A code phase error calculation method including: calculating an error included in the code phase obtained from the result of the correlation calculation process using an error calculation method determined according to the reliability and the determined state May be configured.

  According to the third embodiment, whether the correlation value is intensifying or weakening in accordance with the delay of the indirect wave signal with respect to the direct wave signal is determined based on the peak correlation value and the peak phase indicating the peak correlation value. Judgment is made using the correlation value of the advanced phase. Then, an error included in the code phase obtained from the result of the correlation calculation process is calculated using an error calculation method determined according to the reliability of the multipath signal and the determined strength or weakness state.

  As will be described in detail later, depending on the phase difference between the direct wave signal and the indirect wave signal, whether the correlation value is in an intensifying state or a weakening state changes, and the change in this state causes a code phase error. It was found that the sign of changed. It was also found that the width (amplitude) of the change in the code phase error changes depending on the reliability of the multipath signal. From this, it is possible to appropriately calculate the code phase error by making the error calculation method variable according to the reliability of the multipath signal and the strength / weakness of the correlation value. .

  Further, as a fourth mode, from the result of the correlation calculation process using the code phase error calculation method of the third mode and using the code phase error obtained by the code phase error calculation method A code phase calculation method including calculating a corrected code phase obtained by correcting the obtained code phase may be configured.

  According to the fourth embodiment, the correction code phase obtained by correcting the code phase obtained from the result of the correlation calculation process is calculated using the code phase error obtained by the code phase error calculation method of the third embodiment described above. To do. As a result, position calculation can be performed using a more accurate correction code phase in which the error is corrected, and the accuracy of position calculation is improved.

  As a fifth mode, receiving satellite signals from a plurality of position calculating satellites, and executing the multipath signal reliability determination method according to the first or second mode for each received signal of the satellite signals. Selecting the satellite signal used for position calculation using the reliability obtained by executing the multipath signal reliability determination method, and calculating the position using the received signal of the selected satellite signal. Performing a position calculation method.

  According to the fifth embodiment, the satellite signal used for position calculation is selected using the reliability obtained by executing the multipath signal reliability determination method of the first or second embodiment described above. Then, position calculation is performed using the received signal of the selected satellite signal. For example, when the number of satellites necessary for position calculation is insufficient, among satellite signals determined to be multipath signals, satellite signals with high reliability are used for position calculation. As a result, even in an environment where a sufficient number of satellites cannot be secured if multipath signals are excluded, it is possible to perform position calculation using satellite signals that are multipath signals but have high reliability. .

Explanatory drawing of the peak detection of a correlation value. Explanatory drawing of the peak detection of a correlation value. Explanatory drawing of the peak detection of a correlation value. The figure which shows the correlation result with respect to a multipath signal. Explanatory drawing of code phase error ERR. Explanatory drawing of code phase error ERR. Explanatory drawing of code phase error ERR. Explanatory drawing of the calculation method of PE value. The relationship figure of PE value and code phase error ERR. The figure which shows the correlation result with respect to a direct wave signal. The figure which shows the correlation result with respect to a direct wave signal. The figure which shows the correlation result with respect to a multipath signal. The figure which shows the correlation result with respect to a multipath signal. Illustration of vector angle. Illustration of vector angle. FIG. 6 is a relationship diagram between a vector angle and a code phase error. Explanatory drawing of determination whether a received signal is a multipath signal. Explanatory drawing of the calculation method of PL value. Explanatory drawing of PL value. Explanatory drawing of PL value. Explanatory drawing of PL value. Explanatory drawing of PL value. The relationship figure of PL value and code phase error. The relationship figure of (DELTA) PL value and a code phase error. Explanatory drawing of the determination method of the reliability of a multipath signal. The relationship figure of (DELTA) PE value and a code phase error. The block diagram which shows the function structure of a mobile telephone. The block diagram which shows the circuit structure of a baseband process circuit part. The figure which shows the data structure of ROM. The figure which shows the data structure of RAM. The figure which shows the data structure of a flag determination range table. The figure which shows the data structure of an offset table. The figure which shows the data structure of an error model type | formula table. The figure which shows the data structure of the acquisition object satellite database. The flowchart which shows the flow of a position calculation process. The flowchart which shows the flow of a multipath detection process. The flowchart which shows the flow of a multipath signal reliability determination process. The flowchart which shows the flow of a code phase correction process. The flowchart which shows the flow of a 2nd position calculation process. The flowchart which shows the flow of a position calculation use satellite signal determination process. Explanatory drawing of the calculation method of PE value in a modification. Explanatory drawing of the calculation method of PL value in a modification.

  Preferred embodiments of the present invention will be described below with reference to the drawings. Hereinafter, a case where the present invention is applied to a mobile phone including a GPS receiver will be described as an example. In this embodiment, the GPS receiver functions as a multipath signal detection device that detects a multipath signal, and also determines the reliability of the multipath signal when the received signal is a multipath signal. Also functions as a degree determination device. The embodiment to which the present invention is applicable is not limited to this.

[principle]
(A) Detection of multipath signal First, the principle of detecting a multipath signal will be described. In the GPS receiver, a GPS satellite signal as a positioning signal transmitted from a GPS satellite which is a kind of positioning satellite is captured using a spreading code called a C / A code. Specifically, the GPS satellite signal is a 1.57542 [GHz] communication modulated by a direct spread spectrum method with a C / A (Coarse and Acquisition) code that is a unique modulation code assigned to each GPS satellite. Signal. The C / A code is a pseudo random noise code having a repetition period of 1 ms with a code length of 1023 chips as one PN frame.

  The GPS satellite signal received signal and the C / A code of the GPS satellite signal (hereinafter referred to as “capture target satellite signal”) of the GPS satellite to be captured (hereinafter referred to as “capture target satellite”). Correlation with the simulated replica code is performed. At this time, correlation calculation is performed while shifting the frequency and phase of the replica code. The correlation value obtained by the correlation calculation is maximized when the frequency of the replica code matches the frequency of the received signal and the phase of the replica code matches the phase of the received signal. By detecting the phase and frequency with the maximum correlation value, the phase and carrier frequency (Doppler frequency) of the C / A code included in the GPS satellite signal are obtained, and the GPS satellite signal is captured.

  In addition, a different code for each GPS satellite is defined in advance as the C / A code, so that a desired GPS satellite signal can be separated and captured from the received signal. If the maximum correlation value is less than a certain value, it is not determined to be a peak, and it is determined that it is not a capture target satellite signal. In this case, the capture target satellite is changed, and the correlation calculation is performed again to try to capture the signal.

  By the way, the position of the GPS satellite is constantly changing, and the distance between the GPS satellite and the GPS receiver (that is, the pseudorange) is also changed accordingly. For this reason, the GPS receiver performs a process of tracking the captured GPS satellite signal in order to cope with a change in the pseudorange.

  1 to 3 are diagrams for explaining detection of a phase having a maximum correlation value (peak) (hereinafter referred to as “peak phase”). In FIG. 1, an example of the autocorrelation value of the C / A code is shown with the horizontal axis representing the code phase and the vertical axis representing the correlation value. In the following description, the correlation value means the magnitude (absolute value) of the correlation value.

  The autocorrelation value of the C / A code is represented by a substantially symmetrical triangle shape with the peak value as a vertex. That is, the correlation value at the phase delayed by the same amount from the peak phase is equal to the correlation value at the advanced phase.

  Therefore, a phase advanced by a certain amount (hereinafter referred to as “Early phase”) with respect to the currently tracked code phase (hereinafter referred to as “Punctual phase”) and delayed by a certain amount. A correlation value in each phase (hereinafter referred to as “late phase”) is calculated. A certain amount can be, for example, 1/3 chip. The punctual phase is set such that the correlation value of the Late phase (hereinafter referred to as “Late correlation value”) Pl and the correlation value of the Early phase (hereinafter referred to as “Early correlation value”) Pe are equal. Control.

  Specifically, as shown in FIG. 1, when the Early correlation value Pe and the Late correlation value Pl match, it is considered that the punctual phase Pp matches the peak phase. Further, as shown in FIG. 2, when the Early correlation value Pe is larger than the Late correlation value Pl, the punctual phase is delayed because the punctual phase is behind the peak phase. Further, as shown in FIG. 3, when the Early correlation value Pe is smaller than the Late correlation value Pl, the punctual phase is advanced from the peak phase, so that the punctual phase is delayed. In the following description, “Punctual phase” refers to a punctual phase when the Early correlation value Pe and the Late correlation value Pl match, that is, the peak phase that is considered to match the peak phase.

  By the way, in a multipath environment, a signal (received signal) received by a GPS receiver is a direct wave signal that is a GPS satellite signal transmitted from a GPS satellite, and a reflected wave or an obstacle reflected on a building, the ground, or the like. It becomes a signal (multipath signal) in which an indirect wave signal such as a transmitted wave that has been transmitted or a diffracted wave that is diffracted by an obstacle is superimposed.

  FIG. 4 is a diagram illustrating a correlation result with respect to a multipath signal, and each correlation value of a direct wave signal, an indirect wave signal, and a multipath signal obtained by combining (superimposing) the direct wave signal and the indirect wave signal. The graph is shown. In FIG. 4, the horizontal axis indicates the code phase, and the vertical axis indicates the correlation value.

  The correlation value for the indirect wave signal has a substantially triangular shape like the correlation value for the direct wave signal, but the magnitude of the peak value (correlation peak value) of the correlation value of the indirect wave signal is It is smaller than the correlation peak value. This is due to the fact that the GPS satellite signal transmitted from the GPS satellite is weakened at the time of reception because the GPS satellite signal is reflected on the building or the ground or transmitted through an obstacle. .

  The peak phase of the indirect wave signal is delayed from the peak phase of the direct wave signal. This is because the propagation distance from the GPS satellite to the GPS receiver is increased by the GPS satellite signal transmitted from the GPS satellite being reflected on the building or the ground or diffracting an obstacle.

  Since the correlation value for the multipath signal is the sum of the correlation value of the direct wave signal and the correlation value of the indirect wave signal, the triangular shape is distorted and is not symmetrical with respect to the peak value. For this reason, as shown in FIG. 5, the punctual phase in the multipath signal does not coincide with the peak phase. Hereinafter, the phase difference between the peak phase and the punctual phase is referred to as “code phase error” and is expressed as “ERR”. Further, the sign of the code phase error when the punctual phase is delayed from the peak phase is defined as “positive”, and the sign of the code phase error when the punctual phase is advanced from the peak phase is defined as “negative”. The positive / negative code phase error is the type of interference between the direct wave signal and the indirect wave signal caused by the difference in phase between the direct wave signal and the indirect wave signal, that is, the state in which the direct wave signal and the indirect wave signal strengthen (so-called increase) Depending on whether it is in a destructive state (so-called destructive interference).

  FIG. 6 is a diagram illustrating an example of a correlation result when the direct wave signal and the indirect wave signal are in phase, and FIG. 7 illustrates a correlation result when the direct wave signal and the indirect wave signal are in reverse phase. It is a figure which shows an example. When the direct wave signal and the indirect wave signal that have arrived at the GPS receiver are in phase, the direct wave signal and the indirect wave signal strengthen each other, so the correlation value of the synthesized wave signal is the correlation value with respect to the direct wave signal. And the sum of the correlation value for the indirect wave signal. That is, the correlation value is intensified according to the delay of the indirect wave signal with respect to the direct wave signal. In this case, as shown in FIG. 6, since the punctual phase is delayed from the peak phase, the code phase error ERR has a positive value.

  On the other hand, when the direct wave signal and the indirect wave signal that have arrived at the GPS receiver have opposite phases, the direct wave signal and the indirect wave signal weaken each other, so the correlation value of the synthesized wave signal is the direct wave signal. Is expressed as a subtraction value obtained by subtracting the correlation value for the indirect wave signal from the correlation value for. That is, the correlation value is weakened according to the delay of the indirect wave signal with respect to the direct wave signal. In this case, as shown in FIG. 7, since the punctual phase is a leading phase with respect to the peak phase, the code phase error ERR has a negative value. When the correlation value of the indirect wave signal is larger than the correlation value of the direct wave signal, the subtraction value of the correlation value is a negative value, but since the absolute value is calculated, it is shown as a positive value. Yes.

  When the direct wave signal and the indirect wave signal are intensified, the correlation value of the synthesized wave signal is expressed as the sum of the correlation value for the direct wave signal and the correlation value for the indirect wave signal, so the correlation value is intensified. It means a state. When the direct wave signal and the indirect wave signal are weakened, the correlation value of the synthesized wave signal is expressed as a subtraction value obtained by subtracting the correlation value for the indirect wave signal from the correlation value for the direct wave signal. It means a state. That is, the strengthening / weakening state of the direct wave signal and the indirect wave signal is equivalent to the strengthening / weakening state of the correlation value.

  In this embodiment, two parameters, “PE value” and “vector angle θ”, are defined. The multipath signal is detected by determining whether or not the received signal is a multipath signal using the values of these two parameters.

FIG. 8 is an explanatory diagram of a PE value calculation method and shows an example of a correlation result for a received signal. In the figure, the PE value is calculated from the punctual correlation value Pp, the correlation value Pn at the phase advanced by one chip or more from the punctual phase, and the correlation value Pa at the phase advanced by N chips from the punctual phase according to the following equation (1). To do.
PE = (Pp-Pn) / (Pa-Pn) (1)

  However, in Expression (1), 0 <N <1, and as shown in FIG. 8, for example, N = 2/3. That is, the PE value represents the ratio between the punctual correlation value Pp for the correlation value Pn and the correlation value Pa for the correlation value Pn. Since the correlation value Pn is a correlation value of a phase that is one chip or more away from the punctual phase, it can be said to be a correlation value for the noise floor (correlation value of a signal regarded as noise).

  As a result of an experiment conducted by the inventor of the present application, it was found that there is the following relationship between the PE value and the code phase error ERR. FIG. 9 is a diagram illustrating the relationship between the PE value of the received signal and the code phase error ERR when the multipath effect is changed from the “none” state to the “present” state. In FIG. 9, with the horizontal axis as a common time axis, the solid line shows the time change of the PE value, and the broken line shows the time change of the code phase error ERR.

  When the influence of multipath is “none”, the received signal at the GPS receiver is only a direct wave signal. In this case, the code phase error ERR is almost zero, and the PE value is a constant value. This is because the shape of the correlation curve of the direct wave signal does not change with time. Hereinafter, the PE value when the influence of the multipath is “none”, that is, when there is no indirect wave signal, will be described as “PE offset value”.

  Since the degree of inclination of the triangle of the correlation value differs depending on the PRN code of the GPS satellite signal, the PE offset value differs for each GPS satellite. In addition, since the triangle height of the correlation value varies depending on the signal strength of the GPS satellite signal, the PE offset value also varies depending on the signal strength of the GPS satellite signal. That is, the PE offset value can be said to be a value that depends on the GPS satellite number and the signal strength of the GPS satellite signal.

  On the other hand, when the multipath influence is “present”, the received signal is a multipath signal in which an indirect wave signal is superimposed on a direct wave signal. In this case, both the code phase error ERR and the PE value vary with time. This is because the indirect wave signal changes due to the relative positional relationship between the GPS satellite signal and the GPS receiver changing as the GPS satellite or GPS receiver moves, and the shape of the correlation value of the curve of the multipath signal changes. It is to do. That is, the correlation values Pp and Pa of the received signal in FIG. 8 change. The fluctuation of the PE value can be approximated by a sin wave, and the amplitude is determined by the signal intensity relationship between the direct wave signal and the indirect wave signal and the difference in carrier frequency.

  It can be seen from FIG. 9 that the PE value and the code phase error ERR have substantially the same time variation. That is, when the code phase error ERR increases, the PE value also increases. Conversely, when the code phase error ERR decreases, the PE value also decreases. As described above, when the direct wave signal and the indirect wave signal are strengthened, the code phase error ERR has a positive value. When the direct wave signal and the indirect wave signal are weakened, the code phase error ERR is negative. Value. Therefore, when the direct wave signal and the indirect wave signal strengthen each other, the PE value changes in the increasing direction, and when the direct wave signal and the indirect wave signal weaken each other, the PE value changes in the decreasing direction.

Next, an index value called a vector angle θ is defined. The vector angle θ is defined as follows. 10 and 11 are diagrams showing correlation results of direct wave signals. FIG. 10 shows a graph of the correlation value with respect to the code phase of the direct wave signal. FIG. 11 shows the correlation value P of each code phase in FIG. 10, the horizontal axis is the Q component (orthogonal component) of the correlation value, and the vertical axis is It is the figure plotted on the IQ coordinate plane made into I component (in-phase component) of a correlation value. Incidentally, the correlation value P = (I ² + Q ² ) ^1/2 .

  Referring to FIG. 11, the correlation value P of the direct wave signal is distributed in a substantially straight line passing through the origin O on the IQ coordinate plane. That is, the correlation values P0 and P4 of the code phases CP0 and CP4 have zero I and Q components, and are plotted at the origin O on the IQ coordinate plane. Further, the correlation values P1 to P3 of the code phases CP1 to CP3 are plotted at positions away from the origin O because both the I component and the Q component are not zero, and in particular, the code phase (peak phase) at which the correlation value P is maximum. ) The correlation value P2 of CP2 is plotted at a position farthest from the origin O.

  That is, the correlation value P from the phase CP0 advanced by 1 chip or more from the peak phase CP2 to the phase CP4 delayed by 1 chip or more moves away from the origin O on the IQ coordinate plane and reaches the farthest position in the peak phase. After that, a substantially linear locus that returns to the origin O is drawn again. Note that the substantially linear locus drawn by the correlation value P forms an angle of about 45 degrees with respect to the Q axis in the figure, but it depends on the phase of the carrier wave of the direct wave signal, how to take the IQ coordinate system, etc. Depending on it.

  12 and 13 show the correlation results of the multipath signal obtained by synthesizing the indirect wave signal with the direct wave signal shown in FIGS. 4 and 5. FIG. 12 shows a graph of the correlation value with respect to the code phase of the multipath signal, and FIG. 13 is a diagram in which the correlation value of each code phase in FIG. 12 is plotted on the IQ coordinate plane.

  According to FIG. 13, the correlation value P of the multipath signal is distributed so as to draw a locus of a closed curve on the IQ coordinate plane. That is, the code phase CP0 has both the I component and the Q component of the correlation value P0, and is plotted at the origin O of the IQ coordinate plane. The correlation values P1 to P4 of the code phases CP1 to CP4 are plotted at positions away from the origin O because both the I component and the Q component are not zero. In particular, the correlation value P2 of the peak phase CP2 is from the origin O. The farthest position is plotted. That is, the correlation value P of the multipath signal moves away from the origin O and draws a locus of a closed curve that returns to the origin O again after reaching the farthest position in the peak phase.

  Further, among the correlation values P of the multipath signal, when the Early and Late correlation values P are plotted on the IQ coordinate plane, they are as shown in FIGS. FIG. 14 shows the correlation values for the multipath signal, and FIG. 15 is a diagram in which the correlation values of the respective code phases in FIG. 14 are plotted on the IQ coordinate plane.

  In FIG. 15, a position vector from the origin O toward the position of the Early correlation value Pe is referred to as “Early correlation vector”, and a position vector toward the position of the Late correlation value Pl is referred to as “Late correlation vector”. The angle θ formed by the early correlation vector and the late correlation vector is defined as a “vector angle”. Since the correlation values Pl and Pe are equal, the magnitudes of the Early correlation vector and the Late correlation vector in the IQ coordinate plane are equal.

  The vector angle θ and the code phase error ERR have the following relationship. FIG. 16 is a diagram illustrating the relationship between the vector angle θ and the code phase error ERR when the multipath effect is changed from the “present” state to the “not present” state. In FIG. 16, with the horizontal axis as the common time, the solid line indicates the time change of the vector angle θ, and the broken line indicates the time change of the code phase error ERR.

  When the influence of multipath is “none”, the received signal is only a direct wave signal. In this case, the code phase error ERR is zero, and the vector angle θ is a constant value (theoretically zero). This is because the correlation value P of the direct wave signal is distributed so as to draw a substantially linear locus on the IQ coordinate plane, as shown in FIG. Theoretically, since the Early correlation value and the Late correlation value for the direct wave signal are equal, the vector angle θ is zero. However, in practice, the correlation calculation is performed while shifting the phase by a predetermined phase width. The value is determined according to the performance of the hardware.

  On the other hand, when the multipath effect is “present”, the received signal is a multipath signal, and the code phase error ERR and the vector angle θ both vary with time. The change in the vector angle θ can be approximated by a sine wave, and its amplitude is determined by the relationship between the signal intensity of the direct wave signal and the indirect wave signal and the difference in carrier frequency. In the state where the multipath effect is “present”, the vector angle θ is “not present” as the code phase error ERR increases between the vector angle θ and the code phase error ERR. The vector angle θ changes so as to approach the state (a constant value close to zero), and conversely, the smaller the code phase error ERR.

  Based on the relationship between each PE value and vector angle θ and the code phase error ERR, it is determined whether the received signal is a multipath signal. If the code phase error ERR is sufficiently large, it is determined to be a multipath signal.

  Specifically, as shown in FIG. 17, a determination range is defined for the PE value and the vector angle θ. FIG. 17 is a diagram showing changes over time in the code phase error ERR, the PE value, and the vector angle θ when the influence of the multipath is changed from the “none” state to the “present” state. With the common time axis, the broken line indicates the time change of the code phase error ERR, the solid line indicates the time change of the PE value, and the alternate long and short dash line indicates the time change of the vector angle θ.

  As shown in FIG. 17, determination ranges B and C for the PE value are determined. The determination ranges B and C are ranges having a common center value, and the center value corresponds to the PE value (that is, the C / A code included in the direct wave signal) when the received signal is only the direct wave signal. Equal to a predetermined value). Further, the width of the determination range C is set larger than the width of the determination range B.

  By the way, the PE value for the direct wave signal differs according to the C / A code of the GPS satellite signal included in the direct wave signal. For this reason, the center values of the determination ranges B and C are different values depending on the GPS satellites to be captured. Further, a determination range A for the vector angle θ is determined. The center value of this determination range A is equal to the value of the vector angle θ when the received signal is a direct wave signal.

  Then, at least one of the conditions “Condition A: PE value is outside determination range B and vector angle θ is outside determination range A” or “Condition B: PE value is outside determination range C” is satisfied. If satisfied, the received signal is determined to be a multipath signal, and if none is satisfied, it is determined not to be a multipath signal. This is due to the following reason.

  In a state where the influence of multipath is “none”, the PE value is a constant value according to the acquisition target satellite, and the vector angle θ is a constant value (theoretically zero). That is, both “condition A” and “condition B” are not satisfied, and it is determined that the signal is not a multipath signal. On the other hand, in a state where the influence of multipath is “present”, the PE value changes substantially in accordance with the code phase error ERR, and the absolute value of the vector angle θ increases as the absolute value of the code phase error ERR increases. As the absolute value of the code phase error ERR decreases, the code phase error ERR changes as it decreases.

  That is, “condition A” may not be satisfied even with a multipath signal due to the relationship between the code phase error ERR and the vector angle θ. For example, in FIG. 17, a period in the vicinity of each of the times t1, t3, and t5 is a period in which the “condition A” is not satisfied but the absolute value of the code phase error ERR is large. Therefore, according to “Condition B”, when the PE value is large to some extent regardless of the value of the vector angle θ, it is determined that the signal is a multipath signal.

(B) Determination of reliability of multipath signal Next, the principle of determining the reliability of the multipath signal will be described. The reliability of the multipath signal is used as an index value indicating the degree to which the multipath signal can be used for position calculation. In other words, the higher the reliability of the multipath signal, the higher the degree to which the multipath signal can be used for position calculation. In the present embodiment, the smaller the change width of the code phase error ERR (the amplitude of the code phase error) is, the easier it is to approach the true value of the code phase by correcting the error. Therefore, it is determined that the reliability of the multipath signal is high. . The reliability of the multipath signal is determined using an index value called “PL value”.

FIG. 18 is a diagram for explaining a method of calculating a PL value, and shows an example of a correlation result with respect to a received signal. In FIG. 18, the PL value is calculated according to the following equation (2) using the punctual correlation value Pp and the correlation value Pb at a phase delayed by M chips from the punctual phase.
PL = Pb / Pp (2)
However, 1 ≦ M <2, and as shown in FIG. 18, for example, M = 1.4. That is, the PL value indicates the ratio between the correlation value Pb and the punctual correlation value Pp.

  As a result of experiments conducted by the inventor of the present application, the influence of the indirect wave signal is greater in the phase delayed by 1 chip or more and less than 2 chips compared to the phase delayed from the punctual phase by less than 1 chip or the phase delayed by 2 chips or more It was found that the absolute value of the correlation value tends to increase. For this reason, in this embodiment, the PL value is calculated using the correlation value of the phase (1 ≦ M <2) delayed by one chip or more and less than two chips.

  19-22 is a figure for demonstrating the meaning which PL value represents. FIG. 19 shows a case where the GPS satellite signal transmitted from the GPS satellite is reflected by the building and reaches the GPS receiver, so that the received signal of the GPS receiver becomes a multipath signal. Here, the illustration and explanation will be made focusing on the case where the direct wave signal and the indirect wave signal are intensified. In FIG. 19, it is assumed that the propagation distance difference between the direct wave signal and the indirect wave signal is “ΔL1”.

  FIG. 20 is a diagram illustrating a correlation result with respect to the multipath signal of FIG. 19, and shows graphs of correlation values of the direct wave signal, the indirect wave signal, and these combined wave signals. A value obtained by converting the phase shift between the direct wave signal and the indirect wave signal into a distance corresponds to the propagation distance difference “ΔL1” in FIG. In FIG. 20, when the PL value is calculated using the punctual correlation value Pp1 and the correlation value Pb1 at a phase delayed by 1.4 chips from the punctual phase, PL1 = Pb1 / Pp1.

  FIG. 21 shows a case where the GPS satellite signal transmitted from the GPS satellite is reflected on the building and reaches the GPS receiver, so that the received signal of the GPS receiver becomes a multipath signal, as in FIG. Yes. Here, the description will be focused on the case where the direct wave signal and the indirect wave signal strengthen each other. In FIG. 21, compared with FIG. 19, the time (propagation time) until the GPS satellite signal transmitted from the GPS satellite is reflected by the building and reaches the GPS receiver is longer. Thereby, the propagation distance difference “ΔL2” between the direct wave signal and the indirect wave signal is longer than the propagation distance difference “ΔL1” in FIG. 19 (ΔL2> ΔL1).

  FIG. 22 is a diagram illustrating a correlation result with respect to the multipath signal of FIG. 21, and shows a graph of correlation values of the direct wave signal, the indirect wave signal, and these combined wave signals. A value obtained by converting the phase shift between the direct wave signal and the indirect wave signal into a distance corresponds to the propagation distance difference “ΔL2” in FIG. In FIG. 22, when the PL value is calculated using the punctual correlation value Pp2 and the correlation value Pb2 at a phase delayed by 1.4 chips from the punctual phase, PL2 = Pb2 / Pp2.

  As described above, since the propagation distance to the GPS receiver is increased due to the reflection of the GPS satellite signal to the building, the peak phase of the indirect wave signal is delayed from the peak phase of the direct wave signal. Furthermore, since ΔL2> ΔL1, the peak phase delay of the indirect wave signal in FIG. 22 is larger than the peak phase delay of the indirect wave signal in FIG. Therefore, in FIG. 22, the influence of the indirect wave signal in the phase separated from the punctual phase by M (= 1.4) chips is larger than that in FIG. 20, and the magnitude of the correlation value Pb2 is the correlation value. It is larger than Pb1.

  Since the relationship of Pb2> Pb1 is established, PL2> PL1 is satisfied from the PL value definition equation of Equation (2). Therefore, if ΔL2> ΔL1, then PL2> PL1, and the PL value increases as the propagation distance difference ΔL between the direct wave signal and the indirect wave signal increases. That is, it can be said that there is a positive correlation between the propagation distance difference ΔL and the PL value.

  Further, there is the following relationship between the PL value and the code phase error ERR. FIG. 23 is a diagram illustrating a relationship between the PL value of the received signal and the code phase error ERR when the simulation experiment is performed by changing the influence of the multipath from the “none” state to the “present” state. . In FIG. 23, with the horizontal axis as a common time axis, the solid line indicates the time change of the PL value, and the broken line indicates the time change of the code phase error ERR.

  Referring to this figure, when the influence of multipath is “none”, the received signal at the GPS receiver is only a direct wave signal. In this case, the code phase error ERR is almost zero, and the PL value is also almost zero. This is because, when the received signal is only a direct wave signal, as shown in FIG. 18, the correlation value becomes almost zero at a phase separated by 1 chip or more from the punctual phase, and in the PL value definition equation of equation (2), This is because Pb≈0. Hereinafter, the PL value when the multipath effect is “none”, that is, when there is no indirect wave signal, will be described as “PL offset value”.

  Since the degree of inclination of the triangle of the correlation value differs depending on the PRN code of the GPS satellite signal, the PL offset value differs for each GPS satellite. In addition, since the triangle height of the correlation value varies depending on the signal strength of the GPS satellite signal, the PL offset value also varies depending on the signal strength of the GPS satellite signal. That is, the PL offset value is a value that depends on the GPS satellite number and the signal strength of the GPS satellite signal.

  On the other hand, when the multipath influence is “present”, the received signal is a multipath signal in which an indirect wave signal is superimposed on a direct wave signal. In this case, both the code phase error ERR and the PL value vary with time. The fluctuation of the PL value can be approximated by a sine wave, and the amplitude is determined by the difference in signal strength and carrier distance between the direct wave signal and the indirect wave signal.

  Further, it can be seen from FIG. 23 that the PL value and the code phase error ERR fluctuate substantially in reverse time. That is, when the code phase error ERR increases, the PL value decreases. Conversely, when the code phase error ERR decreases, the PL value increases. As described above, when the direct wave signal and the indirect wave signal are strengthened, the code phase error ERR has a positive value. When the direct wave signal and the indirect wave signal are weakened, the code phase error ERR is negative. Value. Therefore, when the direct wave signal and the indirect wave signal strengthen each other, the PL value changes in a decreasing direction. When the direct wave signal and the indirect wave signal weaken each other, the PL value changes in an increasing direction. .

  As described above, the direction of increase / decrease of the PL value changes depending on the type of interference (strengthening / weakening) between the direct wave signal and the indirect wave signal. Further, the signal strength of the received signal changes from moment to moment, and the increase / decrease in the PL value also changes depending on the signal strength relationship between the direct wave signal and the indirect wave signal. Therefore, even if the PL value is observed, it cannot be distinguished whether the change is caused by a difference in interference between the direct wave signal and the indirect wave signal or a change in signal intensity. . Therefore, the inventor of the present application defined an “ΔPL value” as a value obtained by subtracting the PL offset value from the PL value, and conducted an experiment for examining the time change of the ΔPL value.

  FIG. 24 is a diagram illustrating the relationship between the code phase error ERR and the ΔPL value. The result of the simulation experiment in the case where the reception signal is only the direct wave signal until time t1 and the indirect wave signal is superimposed on the direct wave signal at time t1 is shown. Further, the relationship between the ΔPL value and the code phase error ERR was examined by changing the propagation distance difference ΔL between the direct wave signal and the indirect wave signal. The code phase error ERR and ΔPL values when the propagation distance difference ΔL is 0.6 chips (= about 180 m) are diamond and square, respectively, and the propagation distance difference ΔL is 1.1 chips (= about 330 m). In this case, the code phase error ERR and the ΔPL value are indicated by a triangle and a cross, respectively.

  Referring to FIG. 24, it can be seen that the waveform of the code phase error ERR oscillates around a value near zero when the propagation distance difference ΔL is 0.6 chip or 1.1 chip. Further, when comparing the change width (amplitude) of the code phase error ERR, the case where the propagation distance difference ΔL is 1.1 chips is smaller. From this, it is likely that the amplitude of the code phase error ERR tends to decrease as the propagation distance difference ΔL increases. Actually, as a result of detailed experiments performed by the present inventor, the amplitude of the code phase error ERR decreases as the propagation distance difference ΔL increases, particularly in the range of the propagation distance difference ΔL = 0.6 to 1.5 chips. It was confirmed.

  From this, the larger the propagation distance difference ΔL, the smaller the amplitude of the code phase error ERR. Therefore, if the code phase error ERR is corrected, the code phase error ERR can be easily approached. If it is possible to approximate the true code phase, even a multipath signal can be used for position calculation. In the present embodiment, a multipath signal having a high degree of approach to the true code phase by correcting the code phase error ERR is referred to as a highly reliable multipath signal. Therefore, it can be said that the greater the propagation distance difference ΔL, the higher the reliability of the multipath signal.

  Focusing on the ΔPL value, the waveform of the ΔPL value oscillates up and down regardless of whether the propagation distance difference ΔL is 0.6 chip or 1.1 chip. What is characteristic is that the distribution of the ΔPL value in the case of ΔL = 1.1 chip is concentrated at the top of the graph, and has a value as if biased. That is, the ΔPL value is generally larger when the propagation distance difference ΔL is 1.1 chips than when 0.6 chips. From this, it can be seen that the ΔPL value generally increases as the propagation distance difference ΔL increases.

  Note that there is a phenomenon in which the increase / decrease change in the ΔPL value shown in FIG. 24 and the increase / decrease change in the PL value shown in FIG. 23 are reversed. This is a filter provided in the receiving circuit of the GPS receiver. The phenomenon itself is not significant. In a GPS receiver, a received signal may be passed through a filter such as a low-pass filter in a preceding stage in the receiving circuit to attenuate a signal having a high frequency. At this time, if the cut-off frequency of the low-pass filter is set high, the influence of the direct wave signal is large in the phase delayed by M chips from the punctual phase when the correlation calculation is performed on the received signal after passing through the filter. May appear. Then, due to the magnitude relationship between the PL value and the PL offset value calculated in this case, the increase / decrease change in the ΔPL value and the increase / decrease change in the PL value may be reversed. Of course, depending on the filter characteristics, the increase / decrease change of the ΔPL value may coincide with the increase / decrease change of the PL value. However, as the propagation distance difference ΔL increases, the ΔPL value generally increases. That is no different.

  Based on the experimental result of FIG. 24, the reliability of the multipath signal is determined as follows. That is, as shown in FIG. 25, threshold determination is performed on the ΔPL value. When the ΔPL value is equal to or greater than a predetermined threshold, the propagation distance difference ΔL is large and the code phase error ERR is estimated to be small. Therefore, the reliability of the multipath signal is determined to be “high”. This corresponds to a long delay distance of the indirect wave signal with respect to the direct wave signal.

  On the other hand, when the ΔPL value is less than the threshold value, it is estimated that the propagation distance difference ΔL is small and the code phase error ERR is large. Therefore, the reliability of the multipath signal is determined to be “low”. This corresponds to a short delay distance of the indirect wave signal with respect to the direct wave signal.

  The ΔPL value threshold value may be selected and set in advance by a simulation experiment or the like. For example, in the result of the simulation experiment of FIG. 24, if the threshold determination is performed with the threshold of the ΔPL value being “10”, the waveform of the ΔPL value in the case of ΔL = 0.6 chip and the case of ΔL = 1.1 chip The waveform of the ΔPL value can be separated, and the reliability of the multipath signal can be determined.

(C) Correction of Code Phase Next, the principle of correcting the code phase when it is determined that the received signal is a multipath signal will be described. It has been explained that the code phase error ERR is a positive value when the direct wave signal and the indirect wave signal are intensified, and the code phase error ERR is negative when the direct wave signal and the indirect wave signal are weakened. . This means that the code of the code phase error ERR changes according to the type of interference between the direct wave signal and the indirect wave signal.

  In FIG. 24, particularly in the range of the propagation distance difference ΔL = 0.6 to 1.5 chips, the amplitude of the code phase error ERR decreases as the propagation distance difference ΔL between the direct wave signal and the indirect wave signal increases. I explained that there is a tendency. In the above-described range, the ΔPL value tends to increase as the propagation distance difference ΔL increases. That is, there is a positive correlation between the propagation distance difference ΔL and the ΔPL value. Therefore, the larger the ΔPL value, the smaller the amplitude of the code phase error ERR. As described with reference to FIG. 25, the greater the ΔPL value, the higher the reliability of the multipath signal. Therefore, the higher the reliability of the multipath signal, the smaller the amplitude of the code phase error ERR. This means that the amplitude of the code phase error ERR changes according to the reliability of the multipath signal. In other words, the amplitude of the code phase error ERR changes according to the length of the delay distance of the indirect wave signal relative to the direct wave signal.

  Based on these findings, the inventor of the present application (a) reliability of the multipath signal, (b) a state of strengthening or weakening of the correlation value (a kind of interference between the direct wave signal and the indirect wave signal), It was determined that it is appropriate to calculate the code phase error ERR by changing the calculation method according to the two factors.

  (A) As described above, the reliability of the multipath signal can be determined based on the magnitude of the ΔPL value. However, (b) how to determine whether the correlation value is strengthened or weakened (the type of interference between the direct wave signal and the indirect wave signal) is a problem. That is, an index value is required to determine whether the correlation value is in a state of strengthening or a state of weakening.

  Accordingly, the inventors of the present application have focused on (A) the PE value defined by the principle of multipath signal detection. The PE value increases or decreases depending on the phase difference between the direct wave signal and the indirect wave signal, but also increases or decreases depending on the signal strength of the received signal. Therefore, even if only the PE value is observed, whether the change in increase / decrease is due to the difference in interference between the direct wave signal and the indirect wave signal or the change in the signal strength of the received signal. It cannot be distinguished. Therefore, an experiment was performed in which a value obtained by subtracting the PE offset value from the PE value is defined as “ΔPE value”, and the time change of the ΔPE value is examined.

  FIG. 26 is a diagram illustrating the relationship between the code phase error ERR and the ΔPE value. The result of the simulation experiment is shown in the case where the reception signal is only the direct wave signal until time t2, and the indirect wave signal is superimposed on the direct wave signal at time t2. Also, the relationship between the ΔPE value and the code phase error ERR was examined by changing the propagation distance difference ΔL between the direct wave signal and the indirect wave signal. When the propagation distance difference ΔL is 0.6 chips (= about 180 m), the code phase error ERR and ΔPE values are diamond and square, respectively, and the propagation distance difference ΔL is 1.1 chips (= about 330 m). In this case, the code phase error ERR and the ΔPE value are indicated by a triangle and a cross, respectively.

  From this figure, it can be seen that the ΔPE value and the code phase error ERR fluctuate in substantially the same manner regardless of the propagation distance difference ΔL. That is, when the code phase error ERR increases, the ΔPE value increases. Conversely, when the code phase error ERR decreases, the ΔPE value also decreases. That is, when the direct wave signal and the indirect wave signal are strengthened by interference, the ΔPE value changes in a direction to increase, and when the direct wave signal and the indirect wave signal are weakened by interference, the ΔPE value is decreased. To change.

  Focusing on the waveform of the ΔPE value, the ΔPE value oscillates around a value near zero, and the waveform is different depending on whether the propagation distance difference ΔL is 0.6 chip or 1.1 chip. It turns out that it has almost overlapped. Therefore, it can be said that the ΔPE value exhibits almost the same characteristics regardless of the propagation distance difference ΔL.

  According to this experimental result, when the direct wave signal and the indirect wave signal are strengthened by interference (in the case of incremental interference), the ΔPE value becomes a positive value, and the direct wave signal and the indirect wave signal are weakened by the interference. If they match (in the case of destructive interference), the ΔPE value is negative. Therefore, the state of correlation value strengthening / weakening (the type of interference between the direct wave signal and the indirect wave signal) can be determined based on the sign of the ΔPE value.

  Based on the above experimental results, in the present embodiment, an expression for correcting the code phase error ERR based on the sign of the ΔPE value and the reliability of the multipath signal (hereinafter referred to as “error model expression”). .) Is variably selected to correct the code phase. This is because the type of interference between the direct wave signal and the indirect wave signal (= difference in the sign of the ΔPE value), the length of the delay distance of the indirect wave signal relative to the direct wave signal (= difference in the reliability of the multipath signal), and Accordingly, this corresponds to correcting the code phase by making the error model equation variable.

  Specifically, (1) the sign of the ΔPE value is “positive” and the reliability of the multipath signal is “high”, and (2) the sign of the ΔPE value is “positive” and the reliability of the multipath signal is “low”. (3) The sign of the ΔPE value is “negative” and the multipath signal reliability is “high”, and (4) the sign of the ΔPE value is “negative” and the reliability of the multipath signal is “low”. An error model formula corresponding to each of the patterns is determined in advance. For example, four types of error model equations as shown in the following equations (3) to (6) are determined.

ERR = a ₁ · ΔPE + b ₁ (ΔPE ≧ 0 and ΔPL ≧ threshold) (3)
ERR = a ₂ · ΔPE + b ₂ (ΔPE ≧ 0 and ΔPL <threshold) (4)
ERR = a ₃ · ΔPE + b ₃ (ΔPE <0 and ΔPL ≧ threshold) (5)
ERR = a ₄ · ΔPE + b ₄ (ΔPE <0 and ΔPL <threshold) (6)
However, “a ₁ ” to “a ₄ ” and “b ₁ ” to “b ₄ ” are coefficients corresponding to the respective error model expressions. These error model equations can be obtained, for example, by fitting a function using the least square method to the sampling data of the ΔPE value and the ERR value.

  When the above error model expression is defined, the code phase error ERR is calculated by alternatively selecting the error model expression based on the magnitudes of the ΔPE value and the ΔPL value. That is, the code phase error ERR is calculated by substituting the ΔPE value into the selected error model equation. Then, the code phase error ERR is corrected by adding the calculated code phase error ERR to the code phase acquired by performing the correlation calculation process.

1. 1. First embodiment 1-1. Functional Configuration FIG. 27 is a block diagram showing an internal configuration of the mobile phone 1. The cellular phone 1 includes a GPS antenna 10, a GPS receiving unit 20, a host CPU (Central Processing Unit) 51, an operation unit 52, a display unit 53, a ROM (Read Only Memory) 54, and a RAM (Random Access Memory). ) 55, a mobile phone radio communication circuit unit 60, and a mobile phone antenna 70.

  The GPS antenna 10 is an antenna that receives an RF (Radio Frequency) signal including a GPS satellite signal transmitted from a GPS satellite. The GPS satellite signal is a signal that is spectrum-modulated by a C / A code that is a PRN code, and is superimposed on an L1 band carrier wave having a carrier frequency of 1.57542 [GHz].

  The GPS receiving unit 20 captures and extracts a GPS satellite signal from the RF signal received by the GPS antenna 10, and performs a positioning calculation based on a navigation message or the like extracted from the GPS satellite signal to calculate a current position. The GPS receiving unit 20 includes an RF receiving circuit unit 30 and a baseband processing circuit unit 40. In the present embodiment, the GPS receiver 20 is a functional block corresponding to a multipath signal detection device and a multipath signal reliability determination device.

  The RF receiving circuit unit 30 includes a SAW (Surface Acoustic Wave) filter 31, an LNA (Low Noise Amplifier) 32, a local oscillation signal generation unit 33, a multiplication unit 34, an amplification unit 35, and an A / D conversion unit 36. And performs signal reception by a so-called superheterodyne method.

  The SAW filter 31 is a band-pass filter, passes a signal in a predetermined band with respect to the RF signal input from the GPS antenna 10, and blocks and outputs a frequency component outside the band.

  The LNA 32 is a low noise amplifier, and amplifies the signal input from the SAW filter 31 and outputs the amplified signal.

  The local oscillation signal generation unit 33 is configured by an oscillator such as an LO (Local Oscillator) and generates a local oscillation signal.

  The multiplication unit 34 is configured to include a multiplier that synthesizes a plurality of signals, and multiplies (synthesizes) the RF signal input from the LNA 32 by the local oscillation signal generated by the local oscillation signal generation unit 33 to generate an intermediate frequency. Down-converted to a signal (IF signal). Although not shown, the multiplication unit 34 multiplies the local oscillation signals whose phases are shifted from each other by 90 degrees with the RF signal, thereby down-converting the received signal into an IF signal, and in-phase component (I signal). And quadrature component (Q signal).

  The amplification unit 35 amplifies the IF signal (I signal and Q signal) input from the multiplication unit 34 with a predetermined amplification factor. The A / D converter 36 converts the signal (analog signal) input from the amplifier 35 into a digital signal. Therefore, the RF receiving circuit unit 30 outputs the I signal and Q signal of the IF signal.

  The baseband processing circuit section 40 captures and tracks a GPS satellite signal from the IF signal input from the RF receiving circuit section 30, and calculates a pseudo distance based on a navigation message, time information, and the like obtained by decoding the data. And positioning calculation.

  FIG. 28 is a diagram illustrating an example of a circuit configuration of the baseband processing circuit unit 40. The baseband processing circuit unit 40 includes a memory 41, a replica code generation unit 42, a correlation calculation unit 43, a CPU 44, a ROM 45, and a RAM 46.

  The memory 41 samples and stores the I signal and Q signal of the IF signal input from the RF receiving circuit unit 30 at predetermined time intervals.

  The replica code generation unit 42 generates and outputs a replica code (replica signal) simulating the PRN code of the GPS satellite signal of the GPS satellite to be captured in accordance with the control signal from the CPU 44.

  The correlation calculation unit 43 shifts the phase of the replica code to perform the correlation calculation between the sampling data of each of the I signal and Q signal of the IF signal stored in the memory 41 and the replica code input from the replica code generation unit 42. While doing.

  The CPU 44 is a processor that comprehensively controls each unit of the baseband processing circuit unit 40 and performs various arithmetic processes including a position calculation process. The CPU 44 causes the replica code generation unit 42 to generate a C / A code replica code of the capture target satellite. Based on the correlation calculation result (correlation value) by the correlation calculation unit 43, the C / A code and code phase included in the GPS satellite signal are detected, and the GPS satellite signal is captured and tracked. The tracking of the GPS satellite signal is performed by variably controlling the currently tracked phase (Puncture phase) so that the Late correlation value and the Early correlation value described above coincide with each other.

  The ROM 45 is a read-only non-volatile storage device for realizing various processes including a system program for the CPU 44 to control each part of the baseband processing circuit unit 40 and the RF receiving circuit unit 30 and a position calculation process. Various programs and data are stored.

  The RAM 46 is a readable / writable volatile storage device, used as a work area for the CPU 44, and temporarily stores programs and data read from the ROM 45, calculation results executed by the CPU 44 according to various programs, and the like.

  The host CPU 51 is a processor that comprehensively controls each unit of the mobile phone 1 according to various programs such as a system program stored in the ROM 54. Specifically, mainly the telephone function as a telephone is realized, and a position display screen in which the current position of the mobile phone 1 input from the baseband processing circuit unit 40 is plotted on a map is displayed on the display unit 53. The processing for realizing various functions including the position display function is performed.

  The operation unit 52 is an input device including operation keys, button switches, and the like, and outputs an operation signal corresponding to an operation by a user to the host CPU 51. By operating the operation unit 52, various instructions such as a position calculation start / end instruction are input.

  The display unit 53 is a display device configured by an LCD (Liquid Crystal Display) or the like, and displays a display screen (for example, a position display screen or time information) based on a display signal input from the host CPU 51.

  The ROM 54 stores a system program for the host CPU 51 to control the mobile phone 1 and various programs and data for realizing the position display function.

  The RAM 55 is used as a work area of the host CPU 51, and temporarily stores programs and data read from the ROM 54, data input from the operation unit 52, calculation results executed by the host CPU 51 according to various programs, and the like.

  The mobile phone radio communication circuit unit 60 is a mobile phone communication circuit unit configured by an RF conversion circuit, a baseband processing circuit, and the like, and transmits and receives radio signals under the control of the host CPU 51.

  The cellular phone antenna 70 is an antenna that transmits and receives cellular phone radio signals to and from a radio base station installed by a communication service provider of the cellular phone 1.

1-2. Data Configuration FIG. 29 is a diagram illustrating an example of data stored in the ROM 45 of the baseband processing circuit unit 40. The ROM 45 stores a position calculation program 451, a flag determination range table 453, an offset table 455, and an error model formula table 457 that are read by the CPU 44 and executed as position calculation processing (see FIG. 35). Yes.

  In the position calculation process, the CPU 44 acquires and calculates a measurement for position calculation for each capture target satellite based on the correlation result with respect to the received signal. The measurement is information related to the received signal used by the CPU 44 in the position calculation calculation, and includes information on the received frequency and code phase of the received signal.

  Then, for each GPS satellite signal that has been successfully captured, the CPU 44 determines whether or not the GPS satellite signal is a multipath signal. If the CPU 44 determines that the GPS path is a multipath signal, the reliability of the multipath signal is determined. Determine. Then, based on the reliability determination result, a process of correcting the code phase included in the measurement is performed, and a predetermined position calculation calculation is performed using the corrected code phase (hereinafter referred to as “corrected code phase”). By doing so, the position of the mobile phone 1 is calculated. This position calculation process will be described later in detail using a flowchart.

  FIG. 31 is a diagram illustrating an example of a data configuration of the flag determination range table 453. In the flag determination range table 453, the central value of each of the determination ranges A to C and the width in the positive direction and the negative direction based on the central value are stored in association with each GPS satellite. ing. This flag determination range table 453 is used in the multipath detection process to determine whether or not the GPS satellite signal to be determined is a multipath signal.

  FIG. 32 is a diagram illustrating an example of a data configuration of the offset table 455. In the offset table 455, a PE offset value 4555 and a PL offset value 4557 are stored for each signal intensity 4553 of the received signal in association with each GPS satellite 4551. This offset table 455 is used to calculate the ΔPE value and the ΔPL value.

  FIG. 33 is a diagram showing an example of the data configuration of the error model formula table 457. As shown in FIG. The error model formula table 457 is a table in which error model formulas for use in correcting the code phase are defined. Four types of error model formulas are defined according to the positive / negative of the ΔPE value and the reliability of the multipath signal. It has been.

  FIG. 30 is a diagram illustrating an example of data stored in the RAM 46 of the baseband processing circuit unit 40. The RAM 46 stores a capture target satellite database 461 and an output position 463.

  FIG. 34 is a diagram showing an example of the data configuration of the capture target satellite database 461. As shown in FIG. The acquisition target satellite database 461 is a database in which acquisition target satellite data 462 (462-1, 462-2, 462-3,...) That is data about each acquisition target satellite is accumulated and stored.

  Each capture target satellite data 462 includes a satellite number 4621, IQ correlation value data 4622 as a result of correlation calculation for the capture target satellite, and a reception frequency and code phase acquired and calculated for the capture target satellite. A measurement 4623, a vector angle 4624, a PE value 4625, a ΔPE value 4626, a PL value 4627 and a ΔPL value 4628 calculated for the acquisition target satellite, and a flag 4629 of F1 to F3 are stored.

  The output position 463 is position data determined as a position to be finally output by performing position calculation calculation.

1-3. Process Flow FIG. 35 is a flowchart showing a position calculation process executed when the position calculation program 451 stored in the ROM 45 is read by the CPU 44.
First, the CPU 44 determines a capture target satellite based on satellite orbit information such as almanac and ephemeris (step A1). Then, the process of loop A is executed for each determined satellite to be captured (steps A3 to A19).

  In the process of loop A, the CPU 44 causes the replica code generation unit 42 to generate a C / A code replica code of the capture target satellite, and the received signal from the capture target satellite input from the correlation calculation unit 43. A measurement is calculated based on the correlation calculation result and stored in the capture target satellite data 462 of the capture target satellite (step A5). That is, the reception frequency and phase at which the correlation value takes the peak correlation value are identified and used as the measurement of the capture target satellite. In this case, the phase obtained as a measurement is a punctual phase that is regarded as being coincident with the above-described peak correlation value, and may include a code phase error ERR.

  Next, the CPU 44 measures the signal intensity of the received signal from the capture target satellite (step A7). Then, the CPU 44 determines whether or not the acquisition target satellite has been successfully acquired (step A9). If it is determined that acquisition has been successful (step A9; Yes), a multipath detection process is performed (step A11). ).

FIG. 36 is a flowchart showing the flow of multipath detection processing.
First, the CPU 44 initializes all the flags F1 to F3 to “0” (step B1). Subsequently, the PE value is calculated based on the correlation result for the received signal from the capture target satellite output from the correlation calculation unit 43 (step B3). Further, the vector angle θ is calculated based on the Early correlation value and the Late correlation value input from the correlation calculation unit 43 (step B5).

  Next, the CPU 44 refers to the flag determination range table 453 of the ROM 45, compares the calculated PE value with each of the predetermined determination ranges B and C, and if the PE value is outside the determination range B (step B7: Yes). The flag F2 is set to “1” (step B9), and if it is outside the determination range C (step B11: Yes), the flag F3 is set to “1” (step B13). Further, the calculated vector angle θ is compared with a predetermined determination range A, and if it is outside the determination range A (step B15: YES), the flag F1 is set to “1” (step B17).

  Then, based on the set values of the flags F1 to F3, it is determined whether or not the received signal from the target captured satellite is a multipath signal. That is, if at least one of “condition A: flags F1 and F2 are both“ 1 ”or“ condition B: flag F3 is “1” ”(step B19: Yes), the received signal is multi If it is determined that the signal is a path signal (step B21) and both are not satisfied (step B19: No), it is determined that the signal is not a multipath signal (step B23). When the above processing is performed, the multipath detection processing is terminated.

  Returning to the position calculation process of FIG. 35, after performing the multipath detection process, if it is determined that the received signal from the capture target satellite is a multipath signal (step A9: Yes), the CPU 44 A signal reliability determination process is performed (step A15).

FIG. 37 is a flowchart showing a flow of multipath signal reliability determination processing.
First, the CPU 44 calculates a PL value based on the correlation result for the received signal from the capture target satellite output from the correlation calculation unit 43 (step C1). Then, referring to the offset table 455 of the ROM 45, the PL offset value corresponding to the satellite number of the capture target satellite and the signal intensity of the received signal from the capture target satellite measured in step A7 is read (step C3).

  Next, the CPU 44 calculates a ΔPL value by subtracting the PL offset value read in step C3 from the PL value calculated in step C1 (step C5). Then, the CPU 44 performs threshold determination for the ΔPL value, and determines the reliability of the multipath signal (step C7). Specifically, when ΔPL value ≧ threshold, the reliability is determined as “high”, and when ΔPL value <threshold, the reliability is determined as “low”. Then, the CPU 44 ends the multipath signal reliability determination process.

  Returning to the position calculation process of FIG. 35, after performing the multipath signal reliability determination process, the CPU 44 performs a code phase correction process (step A17).

FIG. 38 is a flowchart showing the flow of the code phase correction process.
First, the CPU 44 reads the PE offset value corresponding to the satellite number and signal strength of the capture target satellite with reference to the offset table 455 of the ROM 45 (step D1). Then, the CPU 44 calculates a ΔPE value by subtracting the PE offset value read in step D1 from the PE value calculated in step B3 of the multipath detection process (step D3).

  Thereafter, the CPU 44 refers to the error model equation table 457 of the ROM 45, and determines the error based on the ΔPE value calculated in step D3 and the reliability of the multipath signal determined in step C7 of the multipath signal reliability determination process. One model formula is selected (step D5).

  Next, the CPU 44 calculates the code phase error ERR by substituting the ΔPE value into the selected error model equation (step D7). Then, the CPU 44 corrects the code phase by adding the code phase error ERR calculated in step D7 to the code phase included in the measurement calculated in step A5, thereby calculating a corrected code phase (step D9). Then, the CPU 44 ends the code phase correction process.

  Returning to the position calculation process of FIG. 35, after performing the code phase correction process, the CPU 44 shifts the process to the next acquisition target satellite. Then, when the processing of the loop A is completed for all acquisition target satellites (step A19), the CPU 44 executes position calculation calculation for calculating the position of the mobile phone 1 using the measurement of each acquisition satellite (step A21). In particular, the pseudo distance is calculated using the correction code phase and used for the position calculation calculation.

  The CPU 44 stores the calculated position in the RAM 46 as the output position 463, and outputs it to the host CPU 51 (step A23). Thereafter, the CPU 44 determines whether or not to end the position calculation (step A25). If not (step A25: No), the CPU 44 returns to step A1. If the position calculation is to be ended (step A25: Yes), the position calculation process is ended.

1-4. In the cellular phone 1, the correlation calculation unit 43 performs a correlation calculation process of multiplying the reception signal received from the GPS satellite signal transmitted from the GPS satellite by the replica code generated by the replica code generation unit 42. A correlation value is calculated. The CPU 44 calculates the PL value using the peak correlation value obtained by the correlation calculation process and the correlation value of the phase delayed by M (1 ≦ M <2) chips from the peak phase indicating the peak correlation value, Based on the calculated PL value, the reliability of the multipath signal when the received signal is a multipath signal is determined.

  More specifically, the CPU 44 measures the signal strength of the received GPS satellite signal. Then, a GPS satellite that has transmitted the GPS satellite signal and a PL offset value corresponding to the measured signal strength are read out from the PL offset values determined for each GPS satellite. Then, the ΔPL value is calculated by subtracting the PL offset value from the PL value, and the threshold value determination for the ΔPL value is performed to determine the reliability of the multipath signal.

  A multipath signal is a direct wave signal that is a GPS satellite signal transmitted from a GPS satellite, an indirect wave such as a reflected wave reflected by a building or the ground, a transmitted wave that has passed through an obstacle, or a diffracted wave that has been diffracted by an obstacle. The signal is a superimposed signal. The indirect wave signal is a signal delayed from the direct wave signal because the propagation distance from the GPS satellite to the GPS receiver is longer than the direct wave signal. Therefore, when the received signal is a multipath signal, the influence of the indirect wave signal appears greatly in the phase delayed from the peak phase, more specifically, in the phase delayed by 1 chip or more and less than 2 chips from the peak phase. The experiment revealed that the absolute value of the correlation value increased. Therefore, by observing the PL value calculated using the peak correlation value and the correlation value of the phase delayed by 1 chip or more and less than 2 chips from the peak phase, the degree of influence of the indirect wave signal on the direct wave signal can be determined. And can determine whether the multipath signal is good or bad.

2. Second Embodiment In the second embodiment, the mobile phone 1 selects a satellite signal used for position calculation (hereinafter referred to as “position calculation use satellite signal”) using the reliability of the multipath signal, and This is an embodiment in which position calculation is performed using a selected position calculation use satellite signal.

2-1. Process Flow FIG. 39 is a flowchart showing a second position calculation process performed by the CPU 44 of the baseband processing circuit unit 40 in the second embodiment. Note that the same steps as those of the position calculation process of FIG.

  In the process of loop A, the CPU 44 performs the multipath signal reliability determination process in step A15, and then shifts the process to the next acquisition target satellite. Then, after performing the processing of loop A for all the capture target satellites, the position calculation use satellite signal determination processing is performed (step E20).

FIG. 40 is a flowchart showing a flow of position calculation use satellite signal determination processing.
First, the CPU 44 selects a satellite signal determined not to be a multipath signal from the captured satellite signals and sets it as a position calculation use satellite signal (step F1). That is, satellite signals that are not multipath signals are preferentially used for position calculation.

  Next, the CPU 44 determines whether or not the number of position calculation use satellite signals has reached the number of position calculation necessary satellites that is the number of satellites necessary for position calculation (step F3). The number of satellites required for position calculation is four for three-dimensional positioning for calculating latitude, longitude, and altitude, and three for two-dimensional positioning for calculating latitude and longitude. When it is determined that the number of position calculation use satellite signals has reached the number of position calculation necessary satellites (step F3; Yes), the CPU 44 ends the position calculation use satellite signal determination process.

  On the other hand, if it is determined in step F3 that the number of satellite signals used for position calculation has not reached the number of satellites required for position calculation (step F3; No), the CPU 44 determines that the number of satellite signals determined to be multipath signals. Then, the satellite signal having the reliability of “high” is selected and added to the position calculation use satellite signal (step F5). If position calculation cannot be performed using only a signal that has not been determined to be a multipath signal, position calculation is also performed using a highly reliable signal that is determined to be a multipath signal.

  Then, the CPU 44 again determines whether or not the number of position calculation use satellite signals has reached the number of position calculation necessary satellites (step F7). If it is determined that it has reached (step F7; Yes), The calculation use satellite signal determination process is terminated. If it is determined that the position has not been reached (step F7; No), the host CPU 51 is notified that the position cannot be calculated (step F9), and the process proceeds to step A25.

2-2. In the second embodiment, when the number of signals determined not to be multipath signals among the acquired GPS satellite signals is less than the number of satellites necessary for position calculation, it is determined to be multipath signals. Among satellite signals, position calculation is performed using satellite signals with high reliability. As a result, even in an environment where many received signals are multipath signals, such as an urban canyon environment surrounded by high-rise buildings, it is possible to perform position calculation using highly reliable signals. It becomes.

3. Modifications It should be noted that embodiments to which the present invention can be applied are not limited to the above-described embodiments, and can of course be changed as appropriate without departing from the spirit of the present invention.

3-1. Electronic Device In the above-described embodiment, the case where the present invention is applied to a mobile phone that is a kind of electronic device has been described, but in addition, a car navigation device, a portable navigation device, a personal computer, a PDA (Personal Digital Assistants), The same applies to other electronic devices such as wristwatches.

3-2. Satellite Position Calculation System In the above-described embodiment, the case where GPS is used has been described. However, for example, the present invention can be similarly applied to other satellite positioning systems such as GALILEO using the same CDMA method as GPS. Furthermore, the present invention is not limited to a satellite positioning system, but can be applied to a system that transmits a signal modulated by a direct spread spectrum method, for example, a system that uses a wireless LAN wireless signal of the IEEE802.11b standard as a positioning signal.

3-3. In the above-described embodiments, the CPU 44 of the baseband processing circuit unit 40 performs the position calculation process. However, the host CPU 51 may perform the position calculation process. In addition, the CPU 44 and the host CPU 51 share the processing such that the multipath detection process, the multipath signal reliability determination process, and the code phase correction process are performed by the CPU 44 and the position calculation calculation is performed by the host CPU 51. Good.

3-4. Determination of multipath signal For example, in the above-described embodiment, when at least one of the two conditions (conditions A and B) is satisfied, the received signal is determined to be a multipath signal. The determination may be made using only one condition. In this case, the ranges of the determination ranges A, B, and C may be determined to be increased or may be determined to be decreased.

3-5. PE Value and PL Value In the above-described embodiment, FIG. 8 illustrates the PE value calculation method and FIG. 18 illustrates the PL value calculation method. The PE value and PL value calculation method is as follows. It is also possible.

FIG. 41 is an explanatory diagram of a PE value calculation method in the modification. In FIG. 8, the PE value is calculated using the punctual correlation value Pp, the correlation value Pn at the phase advanced by one chip or more from the punctual phase, and the correlation value Pa at the code phase advanced by N chips from the punctual phase. The PE value may be calculated according to the following equation (7) without using the value Pn.
PE = Pp / Pa (7)

FIG. 42 is an explanatory diagram of a PL value calculation method according to the modification. In FIG. 18, the PL value is calculated using the punctual correlation value Pp and the correlation value Pb at a phase delayed by M chips from the punctual phase, but the correlation value Pm at a phase delayed by less than one chip from the punctual phase is also used. Then, the PL value may be calculated according to the following equation (8).
PL = (Pm−Pb) / (Pp−Pb) (8)

3-6. Error Model Formula In the above-described embodiment, the error model formula indicating the relationship between the ΔPE value and the code phase error ERR has been described as being approximated by a linear function. However, functions such as quadratic functions, exponential functions, logarithmic functions, etc. It is also possible to approximate using various functions.

  In addition, as a result of numerical experiments conducted by the inventor of the present application, when an error model equation is determined, if the error model equation is determined by simply performing function fitting using the least square method, the error model equation is calculated. It has been found that the code phase error ERR (code phase calculation error) is larger than the error actually included in the code phase (actual error of the code phase), and correction may be strongly applied. Therefore, the error model formula may be determined so that the correction amount of the code phase is reduced. For example, it is possible to apply a method of shifting an error model expression obtained using the least square method in a direction in which the correction amount of the code phase is reduced.

3-7. In the second embodiment described above, the case where the position calculation use satellite signal is determined using the reliability of the multipath signal has been described. However, in addition to the reliability of the multipath signal, the received signal The satellite signal for position calculation may be determined using information such as the signal intensity and the elevation angle of the satellite.

  For example, in step F5 in FIG. 40, when selecting a satellite signal to be added to the position calculation use satellite signal from among the multipath signals, among the satellite signals having high reliability, the satellite signal having a high signal strength. Alternatively, a satellite signal transmitted from a GPS satellite having a high elevation angle may be preferentially selected and added to the position calculation use satellite signal.

3-8. Multipath signal reliability In the above-described embodiment, when the ΔPL value is greater than or equal to the threshold, the multipath signal reliability is “high”, and when the ΔPL value is less than the threshold, the multipath signal reliability is “low”. However, the reliability may be determined more finely. As the ΔPL value is larger, the reliability only needs to be higher. Therefore, by setting a plurality of reliability determination thresholds, it is possible to determine the reliability of three or more levels.

  Also in this case, a plurality of types of error model equations corresponding to the difference in reliability are determined in advance, and if the received signal is a multipath signal, the error model equation corresponding to the reliability of the multipath signal is selected. Used to correct the code phase. Further, when the position calculation use satellite signal is determined based on the reliability of the multipath signal, the satellite signal may be added to the position calculation use satellite signal in order from the satellite signal having the highest reliability.

1 mobile phone, 20 GPS receiver, 30 RF receiver circuit,
40 baseband processing circuit section, 41 memory, 42 replica code generation section,
43 correlation calculation unit, 44 CPU, 45 ROM, 46 RAM,
51 host CPU, 52 operation unit, 53 display unit, 54 ROM,
55 RAM, 60 wireless communication circuit for mobile phone, 70 antenna for mobile phone

Claims (3)

Performing correlation calculation processing on the received signal received from the satellite signal transmitted from the position calculating satellite;
The value of the change component of the time change of the first relative ratio between the peak correlation value obtained by the correlation calculation process and the correlation value of the phase delayed by the first phase from the peak phase indicating the peak correlation value is By comparing with a predetermined threshold condition, the reliability indicating the tolerance used for calculating the position of the multipath signal when the received signal is a multipath signal including a direct wave signal and an indirect wave signal is determined. When,
Whether the correlation value is strengthened or weakened according to the delay of the indirect wave signal indirectly received from the satellite signal with respect to the direct wave signal directly received from the satellite signal, the peak correlation value and the peak correlation value Determining based on the sign of the change component of the time change of the second relative ratio with the correlation value of the phase advanced by the second phase from the peak phase indicating
An error calculation method corresponding to the determined reliability and the determined state is selected from error calculation methods predetermined according to the reliability and the state, and the selected error calculation method is selected. with a said calculating the error contained in the code phases determined from the result of the correlation operation,
Code phase error calculation method including The error calculation method is a method of calculating the error by using a model expression whose coefficient is different depending on the reliability and the state , using the value of the change component of the second relative ratio with time as a variable. ,
The code phase error calculation method according to claim 1. Executing the code phase error calculation method according to claim 1 or 2,
Using the code phase error obtained by the code phase error calculation method to calculate a corrected code phase obtained by correcting the code phase obtained from the result of the correlation calculation process;
Code phase calculation method including

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