JP2006258735A - Positioning system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positioning system capable of reducing influences by reflected waves, without heavily loading on the user, and capable of narrowing a positionable area. <P>SOLUTION: The positioning system includes a speed calculating section 5 for calculating the moving speed, based on vehicle speed pulses output from a vehicle, a satellite signal selecting section 6 for selecting satellite signals, by comparing signal levels and thresholds of satellite signals transmitted by a plurality of satellites, and a position-calculating section 7 for calculating the position of the positioning system, based on the selected satellite signals. The satellite signal selecting section 6 changes the threshold, in response to the moving speed calculated by the speed-calculating section 5. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a positioning device applied to a satellite positioning system (Global Navigation Satellite System, hereinafter simply referred to as “GNSS”) represented by GPS (Global Positioning System).

  As shown in FIG. 6, the conventional positioning apparatus includes an antenna unit 11 that receives radio waves transmitted from a satellite, a signal processing unit 12 that demodulates received received signals, and a satellite signal obtained by demodulating. And a positioning unit 13 for positioning based on the map, and corresponding map data is read from the map data storage unit 17 and displayed on the display device with reference to the measured position.

  The positioning unit 13 includes a satellite signal selection unit 15 that selects a satellite signal, and a position calculation unit 16 that calculates the position of the positioning device based on the selected satellite signal. The position calculation unit 16 performs positioning by deriving the intersection of each sphere centered on the position of each satellite that has transmitted the satellite signal selected by the satellite signal selection unit 15 and having a propagation distance from each satellite to the positioning device. The position of the device is calculated.

  In an environment where radio waves transmitted from satellites are likely to be reflected, such as in a building town, the position calculation unit 16 may not be able to correctly measure the propagation distance due to the influence of the reflected wave, and the calculation result by the position calculation unit 16 A positional shift of several tens of meters may occur.

  This reflected wave is strongly influenced by surrounding buildings, and is greatly different between a place with a good view and a building street. Therefore, the satellite signal selection unit 15 determines the signal level of the satellite signal transmitted by the satellite. By comparing with the threshold value, the satellite signal that is considered to increase the measurement error of the propagation distance is not selected.

  However, depending on the surrounding environment of the positioning device, even a satellite signal whose signal level exceeds the threshold value may be strongly influenced by the reflected wave, and in this case, a large positioning error occurs.

In order to reduce the influence of this reflected wave, the conventional positioning device stores information that is a measure of the ease of occurrence of the reflected wave in the map data in advance, and the threshold value that is compared with the signal level by the satellite signal selection unit 15. In an area where reflected waves are likely to be generated, positioning is performed using only a satellite signal having a high signal level and stable by relatively lowering the reception sensitivity (see, for example, Patent Document 1).
JP 2001-264076 A (page 3-4, FIG. 1)

  However, in the conventional positioning device, in order to manage whether or not the reflected wave is likely to be generated in the map data for each region divided in a grid pattern, the reception sensitivity is set over the entire area where the reflected wave is likely to be generated. As a result, the area where positioning is possible becomes narrower.

  Also, with conventional positioning devices, the map data must be kept up-to-date, which entails enormous costs for surveying the whole country and updating the map data, placing a heavy burden on the user. There was a problem.

  The present invention has been made to solve the conventional problems, and provides a positioning device that can reduce the influence of reflected waves without placing a heavy burden on the user and without narrowing the area where positioning is possible. For the purpose.

  The positioning device of the present invention is a positioning device that selects the satellite signal by comparing a signal level of a satellite signal transmitted by a plurality of satellites with a threshold value, and performs positioning based on the selected satellite signal. It has the structure provided with the threshold value change means which changes the said threshold value according to the moving speed of.

  For example, the threshold value changing unit lowers the threshold value as the moving speed increases, and increases the threshold value as the moving speed decreases.

  With this configuration, the positioning device of the present invention increases the threshold during low-speed movement that is easily affected by reflected waves, and lowers the threshold during high-speed movement that is not easily affected by reflected waves. Therefore, the influence of the reflected wave can be reduced without imposing a heavy burden on the user and narrowing the area where positioning can be performed.

  The threshold changing means may calculate the moving speed based on a vehicle speed pulse output by a vehicle provided with the positioning device, and the moving speed is calculated based on a positioning result of the positioning device. You may make it calculate.

  The present invention can provide a positioning device that has the effect of reducing the influence of reflected waves without placing a heavy burden on the user and without narrowing the area where positioning can be performed.

  Embodiments of the present invention will be described below with reference to the drawings.

  GNSS, represented by GPS, is a satellite positioning system that can be used on the entire earth using satellites. In addition to GPS managed by the United States, GLONASS (Global Orbiting Navigation Satellite System) in Russia is known. The European Galileo is also planned for practical use. For these satellite positioning systems, single or integrated positioning devices have been developed and are expected to be used in various places in land, sea and air.

  Today, vehicle navigation devices using GPS are widely used. In this embodiment, an example in which the positioning device of the present invention is applied to a GPS and mounted on a vehicle will be described. The present invention can also be applied to GNSS, and is not limited to GPS.

  FIG. 1 shows a positioning apparatus according to an embodiment of the present invention.

  The positioning device 1 includes an antenna unit 2 that receives radio waves transmitted from a satellite, a signal processing unit 3 that demodulates a reception signal received by the antenna unit 2, and a positioning based on a satellite signal obtained by the demodulation process. And a speed calculation unit 5 that calculates a moving speed of the positioning device 1 based on a vehicle speed pulse output from the vehicle.

  The signal processing unit 3, together with the positioning unit 4 and the speed calculation unit 5, is integrally configured by an LSI (Large Scale Integration) or a CPU (Central Processing Unit) that executes a program.

  The signal processing unit 3 has channels (generally 8 to 16 channels) that can be received simultaneously, and demodulates signals transmitted from different satellites in each channel.

  The positioning unit 4 includes a satellite signal selection unit 6 that selects a satellite signal, and a position calculation unit 7 that calculates the position of the positioning device 1 based on the selected satellite signal. The speed calculation unit 5 and the satellite signal selection unit 6 constitute threshold value changing means in the present invention.

  The operation of the positioning device 1 configured as described above will be described.

  In GPS, the carrier frequency of the L1 band (1.57542 GHz) is released for consumer use, and in the future, the carrier frequency of the L2 band (1.2276 GHz) and L5 band (1.17645 GHz) is also released for consumer use. Is going to be.

  Signals transmitted from the satellite at these carrier frequencies are received by the antenna unit 2.

  The signal transmitted from the satellite includes a satellite signal that is spectrum-spread with a code unique to the satellite called a C / A (Clear and Acquisition or Coarse and Access) code and spread to a level below noise.

  When a C / A code is correlated with a signal spread with the same C / A code (hereinafter simply referred to as “autocorrelation”), the correlation value at the same phase is maximum and the phase is shifted by 1 bit or more. The correlation value is almost zero. In addition, the C / A code has a feature that the correlation value is almost zero when the correlation (also referred to as “cross-correlation”) is taken with a signal whose spectrum is spread with different C / A codes. Further, the C / A code is characterized in that the correlation value is proportional to the phase difference in the range where the phase difference of autocorrelation is 0 to 1 bit.

  Therefore, the satellite signal of each channel can be acquired by despreading the received signal received by the antenna unit 2 in accordance with the phase of each C / A code.

  As a method for adjusting the phase of the C / A code, a DLL (Delay Lock Loop) method is generally used. As shown in FIG. 2, the DLL is based on the phase of the synchronized C / A code. By simultaneously obtaining autocorrelation values shifted by ± 0.5 bits and controlling the correlation values to be the same, the phases of the C / A codes are matched.

  On the other hand, since the satellite moves at a speed of orbiting the earth in about 12 hours, a maximum Doppler shift frequency of ± 5000 Hz is generated with this movement.

  The signal processing unit 3 despreads the received signal received by the antenna unit 2 by using the DLL to match the phase of the C / A code, and obtains a satellite signal by detecting and removing the Doppler shift frequency. .

  Here, the satellite signal includes navigation data including satellite orbit information and the like, and the navigation data is broadcast from the satellite at a speed of 50 bps. These navigation data are acquired from the satellite signal by the signal processing unit 3.

  The navigation data is configured in units called subframes every 300 bits, and five types of subframes 1 to 5 are broadcast from the satellite in order.

  A bit string called a preamble pattern indicating the head is stored in the subframe, and in order to acquire data of the subframe, first, the preamble pattern is detected.

  The sub-frames 1 to 5 are collectively called a main frame, and 25 types of main frames are broadcast in order. That is, subframe 1 constituting main frame 1, subframe 2 constituting main frame 1,..., Subframe 5 constituting main frame 1, subframe 1 constituting main frame 2,. The broadcast is performed in the order of the subframe 5 constituting the main frame 25, and the subframe 1 constituting the main frame 1 is broadcast again.

  Subframes 1 to 3 mainly store detailed orbit information of satellites being broadcast, correction values of satellite management times, and the like, and are indispensable for positioning. Subframes 1 to 3 basically have an expiration date of 4 hours, and the same one is broadcast for 2 hours. On the other hand, the subframes 4 to 5 mainly store orbit information and health information of other satellites.

  For each satellite signal selected by the satellite signal selection unit 6, the position calculation unit 7 is expressed by Equation 1 with the radius of the propagation distance of the signal transmitted from the satellite centered on the position of the satellite that transmitted the satellite signal. The position of the positioning device 1 is calculated by setting up the equations of the spheres and solving the simultaneous equations composed of these equations.

The position (X _i , Y _i , Z _i ) of the satellite i can be accurately calculated from the detailed orbit information of each satellite included in the navigation data acquired by the signal processing unit 3. The propagation distance L _i can be calculated as “(signal reception time of the positioning device 1−signal transmission time of the satellite i) × light speed”, but at the signal reception time of the positioning device 1, Since a time error due to the internal clock is included, an accurate distance cannot be calculated. However, since this time error is the same amount for all satellites, it can be treated as one unknown.

Therefore, there are four unknowns in the simultaneous equations, that is, the position (X _r , Y _r , Z _r ) of the positioning device 1 and the time error of the positioning device 1, and the position calculation unit 7 is for four or more satellites. The position of the positioning device 1 and the exact time are calculated by solving simultaneous equations consisting of the standing sphere equations.

Specifically, the signal transmission time of the satellite i based on the calculation of the propagation distance L _i can be calculated from the satellite signal.

  For example, time information in units of 6 seconds is stored at the head of the subframe, and this time represents the time at which the head of the subframe is transmitted. That is, if a preamble pattern stored at the head of a subframe is detected and time data in units of 6 seconds is acquired, an accurate time can be calculated in units of 6 seconds.

  Further, as described above, since the navigation data is transmitted at 50 bps from the top of the subframe, the time in units of 20 msec can be calculated by counting the number of data from the top of the subframe.

  Furthermore, since the beginning of the navigation data and the beginning of the C / A code are completely synchronized and the C / A code period is 1 msec, the number of occurrences of the C / A code from the bit edge of the navigation data is counted. Thus, the time in units of 1 msec can be calculated. Also, a time of 1 msec or less can be calculated based on the phase from the beginning of the C / A code.

  As described above, the signal processing unit 3 accurately adjusts the phase of the C / A code, so that the positioning unit 4 can accurately determine the signal transmission time of the satellite and improve the positioning accuracy of the positioning device 1. Can do.

  The satellite signal selection unit 6 selects a satellite signal by comparing the signal level of the satellite signal with a threshold value.

  Since the signal processing unit 3 performs control so that the correlation value between the C / A code whose phase is shifted by ± 0.5 bit and the received signal are the same using a DLL, as shown in FIG. When the synthesized wave 23 obtained by synthesizing the reflected wave 21 with the direct wave 22 is received by the antenna unit 2, the C / A code is shifted by ± 0.5 bits when the phase of the C / A code is in phase. The correlation values are not the same, and the C / A code phase cannot be matched.

  As can be seen from FIG. 3, the C / A code is hardly affected by the reflected wave delayed by 1.5 bits or more. Therefore, since the C / A code is propagated at the speed of light at a bit rate of 1.023 Mbps, the C / A code is hardly affected by the reflected wave delayed by about 450 m or more. In other words, the C / A code is more strongly influenced by the reflected wave reflected by a nearby building than the reflected wave reflected by a distant building.

  For this reason, when the positioning device 1 is moving at high speed, the positional relationship with surrounding buildings always changes, so even if there is an influence of reflected waves, the influence is eliminated in a short time, and positioning is performed. The influence on the calculation accuracy of the position of the device 1 is extremely small.

  On the other hand, when the positioning device 1 is moving at a low speed or is stopped, the positional relationship with the surrounding building is hardly changed, and therefore the influence of the reflected wave is long, and the position of the positioning device 1 The calculation accuracy of becomes worse.

  Therefore, the satellite signal selection unit 6 changes the threshold according to the speed calculated by the speed calculation unit 5. For example, the satellite signal selection unit 6 lowers the threshold during high-speed movement that is not easily affected by the reflected wave, and increases the threshold during low-speed movement or when the vehicle is stopped that is easily affected by the reflected wave.

  From a general vehicle, pulse information is output in a form that is proportional to the number of rotations of the tire for the purpose of integrating the total travel distance or displaying a speed meter. The speed calculation unit 5 reads the pulse information and multiplies it by a certain coefficient to calculate the moving speed of the positioning device 1.

  FIG. 4 is a conceptual diagram for explaining the relationship between the elevation angle of the satellite and the reflected wave as viewed from the positioning device 1.

  As shown in FIG. 4, a radio wave transmitted from a satellite with a low elevation angle generates a reflected wave having a wider influence range than a radio wave transmitted from a satellite with a high elevation angle as viewed from the positioning device 1. To do. For example, the reflected wave 31 of the radio wave transmitted from the satellite SV1 at the zenith has a narrow range of influence, but the reflected wave 32 of the radio wave transmitted from the satellite SV2 at a position where the elevation angle viewed from the positioning device 1 is low is , The range of influence is widened.

  FIG. 5 is a conceptual diagram for explaining the relationship between the elevation angle viewed from the positioning device 1 and the distance to the satellite. In FIG. 5, for simplicity of explanation, the earth 41 is a sphere having a radius of about 6370 km, and the orbit of the satellite 42 is a circular orbit having an altitude of about 20000 km.

  As can be seen from FIG. 5, the distance to the observation point 43 becomes longer as the satellite 42 has a larger elevation angle 44 than the observation point 43 where the positioning device 1 is located. When the directivity of the antenna unit 2 is not taken into account, the signal level is inversely proportional to the square of the distance, so that the signal level of the satellite signal transmitted from the satellite 42 at a position where the elevation angle 44 is small with respect to the observation point 43 is higher. Lower.

  As described above, the satellite that is easily affected by the reflected wave is a satellite at a position where the elevation angle is small, and the satellite signal selection unit 6 controls the influence of the reflected wave because the signal level becomes smaller as the satellite is located at a position where the elevation angle is small. By increasing the threshold value during low-speed movement or when the vehicle is easily stopped, it is possible to prevent the position calculation unit 7 from calculating the position of the positioning device 1 based on the satellite signal transmitted from the satellite at a position where the elevation angle is small.

  Such a positioning device 1 according to an embodiment of the present invention increases the threshold during low-speed movement that is easily affected by reflected waves, and lowers the threshold during high-speed movement that is not easily affected by reflected waves. The optimum threshold value according to the speed can be determined, and the influence of the reflected wave can be reduced without imposing a heavy burden on the user and narrowing the area where positioning is possible.

  As described above, when the satellite signal is received, the Doppler shift frequency is being detected, and the Doppler shift frequency is equal to the relative speed between the satellite and the positioning device 1, and The moving speed can be calculated based on satellite orbit information.

  Therefore, the speed calculation unit 5 may calculate the moving speed of the positioning device 1 by subtracting the moving speed of the satellite calculated based on the orbit information from the detected Doppler shift frequency. This moving speed is a speed vector in the satellite direction, and the moving direction can be calculated in addition to the moving speed of the positioning device 1 by obtaining the speed vector for a plurality of satellites.

  For example, in a positioning device 1 that does not receive a vehicle speed pulse, such as portable navigation, a moving speed for determining a threshold value cannot be acquired. The positioning device of the present invention is assumed to be for a vehicle, and the moving speed of the vehicle does not change greatly when viewed in time. Therefore, when the vehicle speed pulse is not input, the speed calculation unit 5 may determine the threshold value using, for example, the moving speed calculated based on the trajectory information obtained one second before.

  As described above, the positioning device according to the present invention has an effect that the influence of the reflected wave can be reduced without placing a heavy burden on the user and without narrowing the area where positioning can be performed. It is useful as a positioning device applied to GNSS represented by

The block diagram of the positioning apparatus in one embodiment of this invention Conceptual diagram for explaining the characteristics of C / A code Conceptual diagram for explaining the influence of reflected waves on the C / A code Conceptual diagram for explaining the relationship between the elevation angle of the satellite and the reflected wave as seen from the positioning device Conceptual diagram for explaining the relationship between the elevation angle of the satellite and the distance to the satellite as seen from the positioning device Block diagram of a conventional positioning device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positioning device 2, 11 Antenna part 3, 12 Signal processing part 4, 13 Positioning part 5 Speed calculation part 6, 15 Satellite signal selection part 7, 16 Position calculation part 17 Map data storage part

Claims (5)

In a positioning device that selects the satellite signal by comparing the signal level of a satellite signal transmitted by a plurality of satellites with a threshold value, and performs positioning based on the selected satellite signal,
A positioning device comprising threshold changing means for changing the threshold according to a moving speed of the positioning device. The positioning device according to claim 1, wherein the threshold value changing unit lowers the threshold value as the moving speed increases. The positioning device according to claim 1, wherein the threshold value changing unit increases the threshold value as the moving speed decreases. The positioning device according to any one of claims 1 to 3, wherein the threshold value changing means calculates the moving speed based on a vehicle speed pulse output by a vehicle provided with the positioning device. The positioning device according to any one of claims 1 to 3, wherein the threshold value changing unit calculates the moving speed based on a positioning result of the positioning device.

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