NAVIGATION SATELLITE SYSTEM RECEPTION DEVICE, METHOD FOR PROCESSING NAVIGATION SATELLITE SIGNAL FROM SAME, AND PROGRAM

Abstract

A navigation satellite system reception apparatus including a satellite orbit information acquisition unit that acquires orbit information of a navigation satellite, an installation position information acquisition unit that acquires position information of an installation position, an azimuth meter that acquires azimuth information of an azimuth in which a wall surface of a nearby obstruction extends, and an azimuth mask generation unit that calculates a mask region for selecting a navigation satellite to be a target of processing based on the azimuth information. A positioning and time synchronization processing unit calculates an azimuth and an angle of elevation of each navigation satellite based on the orbit information and the position information, selects a navigation satellite to be a target of processing, and performs at least one of the positioning processing or the time synchronization processing based on a received navigation satellite signal.

Claims

1. A navigation satellite system reception apparatus for performing at least one of positioning processing or time synchronization processing with a navigation satellite based on a navigation satellite signal received from a plurality of navigation satellites, the navigation satellite system reception apparatus comprising: an orbit information acquisition unit, implemented with one or more processors, configured to acquire orbit information of a navigation satellite of the plurality of navigation satellites; a position information acquisition unit, implemented with one or more processors, configured to acquire position information of an installation position of the navigation satellite system reception apparatus; an azimuth information acquisition unit, implemented with one or more processors, configured to acquire azimuth information of an azimuth perpendicular to a wall surface of an obstruction present adjacent to the navigation satellite system reception apparatus; a mask region calculating unit, implemented with one or more processors, configured to calculate a mask region for selecting a navigation satellite of the plurality of navigation satellites to be a target of processing in the positioning processing or the time synchronization processing, based on the azimuth information; and a navigation satellite signal processing unit, implemented with one or more processors, configured to: calculate an azimuth and an angle of elevation of each of the plurality of navigation satellites with reference to the navigation satellite system reception apparatus based on the orbit information and the position information; select a navigation satellite of the plurality of navigation satellites to be a target of processing based on the azimuth and the angle of elevation that are respectively calculated and the mask region; and perform at least one of the positioning processing or the time synchronization processing based on the navigation satellite signal received from the navigation satellite that is selected.

2. The navigation satellite system reception apparatus according to claim 1, wherein the mask region is identical to or is included in a region on a side opposite to a region in an azimuth toward an open space side with respect to the wall surface of the obstruction with a boundary being both azimuths perpendicular to the azimuth toward the open space side with respect to the wall surface of the obstruction in polar coordinates with a center being the installation position of the navigation satellite system reception apparatus.

3. The navigation satellite system reception apparatus according to claim 1, wherein the mask region includes a boundary being defined by a threshold with respect to at least an azimuth in polar coordinates with a center being the installation position of the navigation satellite system reception apparatus.

4. The navigation satellite system reception apparatus according to claim 3, wherein the mask region includes a boundary being defined by a threshold with respect to an angle of elevation in polar coordinates with a center being the installation position of the navigation satellite system reception apparatus.

5. The navigation satellite system reception apparatus according to claim 1, wherein the azimuth information acquisition unit includes an azimuth meter installed toward a predetermined azimuth with respect to the wall surface of the obstruction.

6. The navigation satellite system reception apparatus according to claim 5, wherein the azimuth information acquisition unit includes a support base for supporting an antenna of the navigation satellite system reception apparatus, and the azimuth meter is provided at the support base.

7. A navigation satellite signal processing method used in a navigation satellite system reception apparatus for performing at least one of positioning processing or time synchronization processing with a navigation satellite based on a navigation satellite signal received from a plurality of navigation satellites, the navigation satellite signal processing method comprising: acquiring, by an orbit information acquisition unit, orbit information of a navigation satellite of the plurality of navigation satellites; acquiring, by a position information acquisition unit, position information of an installation position of the navigation satellite system reception apparatus; acquiring, by an azimuth information acquisition unit, azimuth information of an azimuth perpendicular to a wall surface of an obstruction present adjacent to the navigation satellite system reception apparatus; calculating, by a mask region calculating unit, a mask region for selecting a navigation satellite of the plurality of navigation satellites to be a target of processing in the positioning processing or the time synchronization processing, based on the azimuth information; calculating, by a navigation satellite signal processing unit, an azimuth and an angle of elevation of each of the plurality of navigation satellites with reference to the navigation satellite system reception apparatus based on the orbit information and the position information; selecting, by a navigation satellite signal processing unit, a navigation satellite of the plurality of navigation satellites to be a target of processing based on the azimuth and the angle of elevation that are respectively calculated and the mask region; and performing, by a navigation satellite signal processing unit, at least one of the positioning processing or the time synchronization processing based on the navigation satellite signal received from the navigation satellite that is selected.

8. A non-transitory computer-readable storage medium storing a navigation satellite signal processing program for causing one or more computer to function as the orbit information acquisition unit, the position information acquisition unit, the mask region calculating unit, and the navigation satellite signal processing unit according to claim 1.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0037] FIG. 1 is a configuration diagram of an overall system including a navigation satellite signal reception apparatus.

[0038] FIG. 2 is a functional block diagram of a navigation satellite signal reception apparatus.

[0039] FIG. 3 is a flowchart for describing an operation of a navigation satellite signal reception apparatus.

[0040] FIG. 4 is an example of a reception environment in which a navigation satellite antenna is installed toward outside of a room from a window.

[0041] FIG. 5 is a schematic diagram for describing setting of an azimuth mask.

[0042] FIG. 6 is a diagram illustrating a reception environment in which a navigation satellite antenna is installed at a room window and a skyward image.

[0043] FIG. 7 is a diagram illustrating a reception state of a GPS satellite signal in a reception environment of FIG. 6.

[0044] FIG. 8 is a diagram illustrating positions of GPS satellites at time (a) of FIG. 7.

[0045] FIG. 9 is a diagram illustrating positions of GPS satellites at time (b) of FIG. 7.

[0046] FIG. 10 is a screenshot of software that observes a reception state of navigation satellite signals (without an azimuth mask).

[0047] FIG. 11 is a screenshot of software that observes a reception state of navigation satellite signals (with an azimuth mask).

[0048] FIG. 12 shows measurement results of improvement of time synchronization accuracy in a multipath reception environment.

[0049] FIG. 13 illustrates a modification of an azimuth mask.

[0050] FIG. 14 illustrates a modification of an azimuth mask.

[0051] FIG. 15 illustrates a modification of an azimuth mask.

[0052] FIG. 16 is a schematic diagram for describing an occurrence state of multipath signals.

[0053] FIG. 17 is a diagram for describing an environment in which multipath signals are received.

[0054] FIG. 18 is a diagram for describing a reception state of multipath signals.

[0055] FIG. 19 is a configuration diagram illustrating a measurement system of time accuracy in a multipath reception environment.

[0056] FIG. 20 shows deterioration of time accuracy in a multipath reception environment and measurement results of an improvement effect with an SNR mask.

[0057] FIG. 21 is a schematic diagram illustrating a relationship between an angle of elevation of a navigation satellite and a reflected wave.

[0058] FIG. 22 shows deterioration of time accuracy in a multipath reception environment and measurement results of an improvement effect with an angle of elevation mask.

DESCRIPTION OF EMBODIMENTS

[0059] An overall configuration of a system including a navigation satellite signal reception apparatus according to one embodiment of the present disclosure is illustrated in FIG. 1. The present system includes a navigation satellite antenna 1, a support base 2, an azimuth meter 3, and a navigation satellite signal reception apparatus 4.

[0060] The navigation satellite antenna 1 is an antenna for receiving navigation satellite signals. The support base 2 is a function unit for fixing the navigation satellite antenna 1 and the azimuth meter 3 to a wall surface, a window frame, or the like. The azimuth meter 3 is a function unit for measuring an azimuth at which the support base 2 is installed. The navigation satellite signal reception apparatus 4 is a function unit that sets an azimuth mask to be described below, performs positioning by using filtered navigation satellite signals, and performs time synchronization, based on information of the azimuth measured in the azimuth meter 3. The configuration and the operation of each of the function units will be described below in detail.

[0061] The navigation satellite antenna 1 is connected to the navigation satellite signal reception apparatus 4 with a coaxial cable or the like, and transmits received navigation satellite signals to the navigation satellite signal reception apparatus 4. The navigation satellite antenna 1 may be an active antenna with an embedded amplifier for navigation satellite signals, or may be a passive antenna without such an embedded amplifier. The navigation satellite antenna 1 may have directivity in the vertically upward direction with an embedded ground plane or the like, and may have isolation characteristics of received navigation satellite signals in a gyration direction.

[0062] The support base 2 is fixed in a direction perpendicular to a wall surface or a window, and fixes relative positions of the navigation satellite antenna 1, the azimuth meter 3, and the wall surface being an obstruction. Although the distance between the navigation satellite antenna 1 and the wall surface or the window may be any distance, a longer distance provides a wider region including the periphery of the zenith of an open space in which navigation satellite signals can be received in the line of sight state by the navigation satellite antenna 1, and enables reception of a larger number of navigation satellite signals as visible satellite signals.

[0063] The azimuth meter 3 measures an installation azimuth of the support base 2. The azimuth meter 3 and the navigation satellite signal reception apparatus 4 are connected together with a wired or wireless transmission medium, and information of the measured azimuth is transmitted to the navigation satellite signal reception apparatus 4. Examples of the wired medium include a LAN cable and a serial transmission cable. Examples of the wireless medium include Wi-Fi (trade name) (IEEE802.11), Bluetooth (trade name), specified low power radio, and infrared light. The azimuth meter 3 performs measurement of the azimuth by using a magnetic sensor, a gyrocompass, or the like. In addition, a method of measuring the azimuth by measuring a relative reception position based on navigation satellite signals received from two navigation satellite antennas mounted on the support base may be used. A terminal such as a smartphone may be used as an azimuth meter.

[0064] The navigation satellite signal reception apparatus 4 performs positioning and time synchronization by using navigation satellite signals received by the navigation satellite antenna 1. In this case, filtering of navigation satellite signals is performed based on the installation azimuth of the support base 2 measured in the azimuth meter 3. The function and the operation of the navigation satellite signal reception apparatus 4 will be described with reference to FIGS. 2 and 3. FIG. 2 is a functional block diagram of the navigation satellite signal reception apparatus, and FIG. 3 is a flowchart for describing the operation of the navigation satellite signal reception apparatus.

[0065] As illustrated in FIG. 2, the navigation satellite signal reception apparatus 4 includes a navigation satellite signal reception unit 41 that receives navigation satellite signals transmitted from the navigation satellite antenna 1, a satellite orbit information acquisition unit 42, an installation position information acquisition unit 43, an azimuth mask generation unit 44, a positioning and time synchronization processing unit 45, a time information generation unit 46, and a position information generation unit 47. The navigation satellite signal reception apparatus 4 may be implemented in any form. The navigation satellite signal reception apparatus 4 may be implemented by installing a program in a computer, or may be implemented as a dedicated hardware apparatus.

[0066] The satellite orbit information acquisition unit 42 acquires satellite orbit information through the navigation satellite signals received by the navigation satellite antenna 1 (see Step S2 of FIG. 3). When GPS satellites are used, data of the satellite orbit information includes two types, called the Almanac and the Ephemeris, which can be acquired from navigation messages included in the navigation satellite signals. In addition to the method of acquiring from navigation messages, examples of methods of acquiring the satellite orbit information include a method of acquiring satellite orbit information by using a Secure User Plane Location (SUPL) server via a mobile network by means of Assisted GNSS and a method of acquiring orbit information available on the Internet (see Step S2a of FIG. 3). One example of a website that shows orbit information of navigation satellites is given below:

URL: http://sys.qzss.go.jp/dod/archives/pnt.html

[0067] The installation position information acquisition unit 43 calculates, based on received navigation satellite signals from four or more satellites, a reception position that is specifically an installation position of the navigation satellite signal reception apparatus 4, and more specifically an installation position of the navigation satellite antenna 1 (see Step S3 of FIG. 3). For the acquisition of the reception position, values of three-dimensional coordinates may be set (see Step S3a of FIG. 3). As the values of three-dimensional coordinates, data of latitude, longitude, altitude, is used, for example.

[0068] The azimuth mask generation unit 44 generates and sets a mask (hereinafter referred to as an azimuth mask) for navigation satellite signals using a combination of thresholds of the azimuth and the angle of elevation for filtering navigation satellite signals of a specific azimuth, based on the installation azimuth of the support base 2 measured in the azimuth meter 3 (see Steps S5 and S6 of FIG. 3). The azimuth mask is set in the following manner: the mask is set on a side opposite to the direction in which the navigation satellite antenna 1 is installed, i.e., the azimuth in which the open space is limited with the wall surface, with an azimuth perpendicular to the azimuth of the azimuth meter 3 being a threshold (boundary), in polar coordinates with the center being the installation position of the navigation satellite signal reception apparatus 4. In this case, an offset value of the azimuth determined by relative positions between the azimuth meter 3 and the support base 2 is corrected as appropriate in setting of the mask. In the example of FIG. 1, the azimuth meter 3 is installed in an azimuth perpendicular to the wall surface being an obstruction. However, the azimuth meter 3 may be installed in another predetermined azimuth. In this case, predetermined correction processing is performed on an azimuth detected in the azimuth meter 3 in setting of the mask.

[0069] An example of setting the azimuth mask is illustrated in FIGS. 4 and 5. FIG. 4 is an example of a reception environment in which the navigation satellite signal reception apparatus 4 is located inside a room and the support base 2 is fixed to a window frame toward the outside of the room. FIG. 5(a) illustrates an example of a skyward image in the reception environment of FIG. 4. FIG. 5(b) illustrates an example of an azimuth mask in the reception environment. The azimuth mask has a semicircular shape as illustrated in FIG. 5(b).

[0070] The positioning and time synchronization processing unit 45 performs positioning processing and time synchronization processing with navigation satellites, based on a plurality of navigation satellite signals received in the navigation satellite antenna 1. Here, the positioning and time synchronization processing unit 45 selects navigation satellite signals to be a target of processing out of all of the received navigation satellite signals by using the azimuth mask. Specifically, the positioning and time synchronization processing unit 45 calculates an azimuth and an angle of elevation of each navigation satellite signal received by the navigation satellite antenna 1, based on the satellite orbit information acquired by the satellite orbit information acquisition unit 42 and the reception position acquired by the installation position information acquisition unit 43 (see Step S4 of FIG. 3). Then, based on the azimuth and the angle of elevation of each navigation satellite signal and the azimuth mask generated in Step S6, the positioning and time synchronization processing unit 45 selects navigation satellite signals to be a target of processing (see Step S7 of FIG. 3), and performs the positioning processing and the time synchronization processing based on the selected navigation satellite signals (see Step S8 of FIG. 3). In the example of FIG. 5, navigation satellite signals plotted at positions other than the azimuth mask (hatched part) are used as a target of processing.

[0071] The time information generation unit 46 outputs results of the time synchronization in a predetermined format. In one example, as the time information, timecode data in a format of National Marine Electronics Association (NMEA) 0183 or the like for reporting timing signals in a signal format of one Pulse Per Second (PPS) or the like in synchronization with navigation satellite signals and information (Time of the Day (ToD)) related to absolute time such as hour and second is used.

[0072] The position information generation unit 47 outputs results of the positioning in a predetermined format. The results of the positioning are output in a format such as NMEA 0183.

[0073] Note that, as attached information of the results of time synchronization and the results of positioning, the positioning and time synchronization processing unit 45 can output a navigation satellite system type, a satellite number, or the like in a format such as NMEA 0183 as information related to a navigation satellite.

[0074] As described above, by setting an azimuth mask in a reception environment in which an open space in which the navigation satellite antenna 1 is installed at a window frame or a wall surface is significantly limited according to the present disclosure, invisible satellite signals of the invisible satellite located at skyward positions blocked by a structure can be effectively eliminated, thus allowing for enhancement of accuracy in positioning and time synchronization. In the conventional method using an SNR mask, when interference waves are received, the SNR of received navigation satellite signals may be lowered as a whole, and accordingly, the number of satellites equal to or greater than a threshold of the SNR may be reduced, and positioning and time synchronization may be hindered. In the present disclosure; however, interference waves do not affect selection of navigation satellite signals.

[0075] Note that the reception position calculated in the process of Step S3 of FIG. 3 may include errors due to limitation on the open space and reception of multipath signals. However, considering a relative positional relationship with satellites located on an orbit at a high altitude (when using GPS satellites, approximately 20000 km above the ground), there is only a slight influence on errors at the time of calculating an azimuth and an angle of elevation of each navigation satellite signal.

[0076] An example of improvement of time synchronization accuracy using an azimuth mask of the navigation satellite signal reception apparatus will be described. In the present example, an example of improvement of time synchronization accuracy in a multipath reception environment in which the navigation satellite antenna is installed at a room window will be described. FIG. 6 is a diagram illustrating a reception environment in which the navigation satellite antenna is installed at a room window and a skyward image, FIG. 7 is a diagram illustrating a reception state of GPS satellite signals in the reception environment of FIG. 6, FIG. 8 is a diagram illustrating positions of GPS satellites at time (a) of FIG. 7, and FIG. 9 is a diagram illustrating positions of GPS satellite at time (b) of FIG. 7. Note that, in the present example, signals of GPS satellites and quasi-zenith satellites (Quasi-Zenith Satellite System (QZSS)) are received. In the present reception environment, a window faces an azimuth of approximately 30 degrees. Specifically, a value indicated by the azimuth meter 3 is approximately 30 degrees.

[0077] FIGS. 10 and 11 are screenshots of software that observes a reception state of navigation satellite signals in the present reception environment described above. FIG. 10 illustrates an example of a reception state of GPS signals and QZSS signals in a case of observation using the navigation satellite signal reception apparatus in which an azimuth mask is not set and FIG. 11 illustrates an example of a reception state of GPS signals and QZSS signals in a case of observation using the navigation satellite signal reception apparatus in which an azimuth mask is set for the sake of comparison of both the cases. Note that, in FIGS. 10 and 11, satellites with a satellite number of less than 40 represent GPS satellites, and satellites with a satellite number of 90 or greater represent GZSS satellites.

[0078] In the navigation satellite signal reception apparatus (FIG. 10) in which an azimuth mask is not set, regarding the 14th, 16th, 27th, 32nd GPS satellite signals and the 93rd QZSS signal, invisible satellite signals of the invisible satellite located at positions blocked by a structure are received as multipath signals, and are used for positioning and time synchronization. Although the 95th satellite located at a position close to the zenith and having a large angle of elevation is not used for positioning and time synchronization, it is thought that other invisible satellite signals are reflected and diffracted by a nearby structure and reach the navigation satellite antenna. In contrast, it can be understood that, in the navigation satellite signal reception apparatus (FIG. 11) in which the navigation satellite signals of the navigation satellite located at positions in an azimuth of from 120 degrees to 300 degrees corresponding to an azimuth of 30 degrees of the window are masked, these invisible satellite signals are not used for positioning and time synchronization.

[0079] FIG. 12 illustrates measurement results of time errors measured by using a measurement system illustrated in FIG. 19 described above regarding the navigation satellite signal reception apparatus in which the azimuth mask is set and the navigation satellite signal reception apparatus in which the azimuth mask is not set. In the navigation satellite signal reception apparatus in which the azimuth mask is not set, a maximum value of an absolute value of time errors (max|TE|) within a 24-hour continuous measurement period is approximately 150 ns, whereas the navigation satellite signal reception apparatus in which the azimuth mask is set, by contrast, it is significantly reduced to as small as approximately 30 ns, and an effect of improvement of time synchronization accuracy by virtue of the setting of the azimuth mask is therefore confirmed.

[0080] One embodiment of the present disclosure has been described in detail above. The present disclosure; however, is not limited to this. For example, in the above embodiment, the navigation satellite antenna 1, the azimuth meter 3, the navigation satellite signal reception apparatus 4, and the support base 2 are separated from each other. However, a part or all of these components may be integrated together.

[0081] Setting of the azimuth mask may be adjusted in consideration of the length of the support base 2 and the height of the wall surface from the installation position of the support base 2 with respect to the wall surface.

[0082] For example, in the above embodiment, as the azimuth mask, a semicircular region on a side opposite to a region in an azimuth toward an open space side with respect to a wall surface of an obstruction with a boundary being both azimuths perpendicular to the azimuth toward the open space side with respect to the wall surface of the obstruction in polar coordinates with the center being the installation position of the navigation satellite signal reception apparatus 4 is used. However, a region included in the semicircular region may be used. Specifically, as illustrated in FIG. 13, a region having an arc shape with its chord being in parallel with the semicircular region in a skyward image may be used.

[0083] In the above embodiment, as the azimuth mask, a semicircular region defined by a threshold solely with respect to an azimuth in polar coordinates with the center being the installation position of the navigation satellite signal reception apparatus 4 is used. However, as illustrated in FIG. 14, a region including a boundary defined by a threshold with respect to an angle of elevation may be used. Note that the example of FIG. 14 is also an example of a region included in a semicircular region.

[0084] A margin may be set to a threshold of an azimuth or an angle of elevation that may be used for defining a region of an azimuth mask. For example, as illustrated in FIG. 15, a margin with respect to an azimuth may be set for the azimuth mask of the semicircular region. Note that the example of FIG. 15 is also an example of a region included in a semicircular region. In a similar manner, the example of FIG. 15 is also an example of a region defined by a threshold solely with respect to an azimuth.

[0085] A mask having any shape can be set by setting a threshold of an angle of elevation for each azimuth, other than the above azimuth mask.

[0086] In the above embodiment, as a measure for acquiring azimuth information of an azimuth in which a wall surface of an obstruction present near the navigation satellite signal reception apparatus 4 extends from the installation position of the navigation satellite signal reception apparatus 4, the support base 2 and the azimuth meter 3 are used. However, the support base 2 can be omitted if the azimuth meter 3 can be installed toward a predetermined azimuth with respect to the wall surface of the obstruction.

[0087] The above embodiment illustrates as example in which both the positioning processing and the time synchronization processing are performed by the navigation satellite signal reception apparatus 4. However, the present disclosure can be applied also with a configuration in which either the positioning processing or the time synchronization processing is performed.

[0088] In above embodiment, the position of the navigation satellite antenna 1 is fixed. However, the present disclosure can be applied in a form of moving the navigation satellite antenna. In one example, time synchronization accuracy and positioning accuracy can be improved over time by applying the present disclosure to a side surface of a mobile object such as a monorail and adaptively setting an azimuth mask for the state of an open space that varies over time.

[0089] In the above embodiment, the present disclosure can be applied also in a form of using multi-GNSS. In this case, enhancement of accuracy is expected since the number of visible satellite signals is increased. As targets of combinations, not only a global navigation satellite system, but also a local navigation satellite system can be used. Examples of the global navigation satellite system include GPS, GLONASS, Galileo, and Beidou, and examples of the local navigation satellite system include QZSS.

Reference Signs List

[0090] 1 . . . Navigation satellite antenna [0091] 2 . . . Support base [0092] 3 . . . Azimuth meter [0093] 4 . . . Navigation satellite signal reception apparatus [0094] 41 . . . Navigation satellite signal reception unit [0095] 42 . . . Satellite orbit information acquisition unit [0096] 43 . . . Installation position information acquisition unit [0097] 44 . . . Azimuth mask generation unit [0098] 45 . . . Positioning and time synchronization processing unit [0099] 46 . . . Time information generation unit [0100] 47 . . . Position information generation unit