U.S. patent application number 17/160964 was filed with the patent office on 2021-08-19 for communication device, information processing method, and storage medium.
This patent application is currently assigned to KABUSHIKI KAISHA TOKAI RIKA DENKI SEISAKUSHO. The applicant listed for this patent is KABUSHIKI KAISHA TOKAI RIKA DENKI SEISAKUSHO. Invention is credited to Kenichi KOGA, Tatsuya KOIKE, Satoshi MORI, Yoshiki OISHI.
Application Number | 20210258912 17/160964 |
Document ID | / |
Family ID | 1000005750123 |
Filed Date | 2021-08-19 |
United States Patent
Application |
20210258912 |
Kind Code |
A1 |
OISHI; Yoshiki ; et
al. |
August 19, 2021 |
COMMUNICATION DEVICE, INFORMATION PROCESSING METHOD, AND STORAGE
MEDIUM
Abstract
A communication device includes: a plurality of wireless
communication sections, each configured to be capable of wirelessly
transmitting and receiving a signal to and from another
communication device; and a control section configured to detect a
specific element with regard to each of a plurality of correlation
computation results that are obtained by correlating a first signal
that is transmitted from the other communication device and that
includes change in amplitude with respective second signals
obtained when the plurality of wireless communication sections
receive the first signal, calculate a reliability parameter that is
an indicator indicating whether the detected specific element is
appropriate for a processing target, and control a positional
parameter determination process on the basis of the reliability
parameter, the positional parameter determination process being a
process of estimating a positional parameter indicating a position
of the other communication device on the basis of the detected
specific element.
Inventors: |
OISHI; Yoshiki; (Aichi,
JP) ; MORI; Satoshi; (Aichi, JP) ; KOGA;
Kenichi; (Aichi, JP) ; KOIKE; Tatsuya; (Aichi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KABUSHIKI KAISHA TOKAI RIKA DENKI SEISAKUSHO |
Aichi |
|
JP |
|
|
Assignee: |
KABUSHIKI KAISHA TOKAI RIKA DENKI
SEISAKUSHO
Aichi
JP
|
Family ID: |
1000005750123 |
Appl. No.: |
17/160964 |
Filed: |
January 28, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 1/0003 20130101;
H04W 64/003 20130101; H04L 25/0222 20130101 |
International
Class: |
H04W 64/00 20060101
H04W064/00; H04L 25/02 20060101 H04L025/02; H04L 1/00 20060101
H04L001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 14, 2020 |
JP |
2020-023217 |
Claims
1. A communication device comprising: a plurality of wireless
communication sections, each of which is configured to be capable
of wirelessly transmitting and receiving a signal to and from
another communication device; and a control section configured to
correlate a first signal that is transmitted from the other
communication device and that includes change in amplitude with
respective second signals obtained when the plurality of wireless
communication sections receive the first signal, at a designated
interval after the other device transmits the first signal, detect,
on a basis of a first threshold, a specific element that is one or
more of a plurality of elements included in a correlation
computation result, with regard to each of a plurality of the
correlation computation results that are results obtained by
correlating the first signal and the respective second signals at
the designated interval and that includes a correlation value
indicating magnitude of correlation between the first signal and
the second signal as the element obtained at each delay time
serving as time elapsed after the other communication device
transmits the first signal at the designated interval, calculate a
reliability parameter that is an indicator indicating whether the
detected specific element is appropriate for a processing target,
and control a positional parameter determination process on a basis
of the reliability parameter, the positional parameter
determination process being a process of estimating a positional
parameter indicating a position of the other communication device
on a basis of the detected specific element.
2. The communication device according to claim 1, wherein, to
detect the specific element on a basis of the first threshold, the
control section detects an element having a correlation value that
exceeds the first threshold for first time, as the specific
element.
3. The communication device according to claim 1, wherein the
reliability parameter includes a difference between delay time of a
first element and delay time of a second element in the correlation
computation result, the first element having a peak correlation
value for the first time after the specific element, the second
element having a peak correlation value for second time after the
specific element.
4. The communication device according to claim 3, wherein, to
control the positional parameter estimation process on a basis of
the reliability parameter, the control section estimates the
positional parameter on a basis of the specific element whose
difference indicated by the reliability parameter is larger than a
second threshold.
5. The communication device according to claim 4, wherein the
second threshold is any value that is less than or equal to width
of the change in amplitude in time direction, which is included in
the first signal.
6. The communication device according to claim 1, wherein the
reliability parameter includes a correlation coefficient between
the correlation computation result obtained on a basis of the
second signal received by a first wireless communication section
among the plurality of wireless communication sections, and the
correlation computation result obtained on a basis of the second
signal received by a second wireless communication section that is
different from the first wireless communication section among the
plurality of wireless communication sections.
7. The communication device according to claim 6, wherein the
reliability parameter includes a correlation coefficient between
chronological change in correlation value of a portion including
the specific element in the correlation computation result obtained
on a basis of the second signal received by a first wireless
communication section among the plurality of wireless communication
sections, and chronological change in correlation value of a
portion including the specific element in the correlation
computation result obtained on a basis of the second signal
received by a second wireless communication section that is
different from the first wireless communication section among the
plurality of wireless communication sections.
8. The communication device according to claim 6, wherein the
correlation computation result includes a complex number, which is
the correlation value, as the element obtained at each delay time,
and the control section calculates the correlation coefficient by
correlating complex numbers obtained at respective delay times,
which are included in the two correlation computation results.
9. The communication device according to claim 6, wherein, to
control the positional parameter estimation process on a basis of
the reliability parameter, the control section estimates the
positional parameter on a basis of the specific element whose
correlation coefficient indicated by the reliability parameter is
higher than a third threshold.
10. The communication device according to claim 1, wherein the
reliability parameter includes a difference between the delay time
of the specific element and the delay time of the element having a
maximum correlation value in the correlation computation
result.
11. The communication device according to claim 10, wherein, to
control the positional parameter estimation process on a basis of
the reliability parameter, the control section estimates the
positional parameter on a basis of the specific element whose
difference indicated by the reliability parameter is smaller than a
fourth threshold.
12. The communication device according to claim 1, wherein the
reliability parameter includes a difference between electric power
corresponding to the specific element in the correlation
computation result obtained on a basis of the second signal
received by a first wireless communication section among the
plurality of wireless communication sections, and electric power
corresponding to the specific element in the correlation
computation result obtained on a basis of the second signal
received by a second wireless communication section that is
different from the first wireless communication section among the
plurality of wireless communication sections.
13. The communication device according to claim 12, wherein, to
control the positional parameter estimation process on a basis of
the reliability parameter, the control section estimates the
positional parameter on a basis of the specific element whose
difference indicated by the reliability parameter is smaller than a
fifth threshold.
14. An information processing method that is executed by a
communication device including a plurality of wireless
communication sections, each of which is configured to be capable
of wirelessly transmitting and receiving a signal to and from
another communication device, the information processing method
comprising: correlating a first signal that is transmitted from the
other communication device and that includes change in amplitude
with respective second signals obtained when the plurality of
wireless communication sections receive the first signal, at a
designated interval after the other device transmits the first
signal; detecting, on a basis of a first threshold, a specific
element that is one or more of a plurality of elements included in
a correlation computation result, with regard to each of a
plurality of the correlation computation results that are results
obtained by correlating the first signal and the respective second
signals at the designated interval and that includes a correlation
value indicating magnitude of correlation between the first signal
and the second signal as the element obtained at each delay time
serving as time elapsed after the other communication device
transmits the first signal at the designated interval; calculating
a reliability parameter that is an indicator indicating whether the
detected specific element is appropriate for a processing target;
and controlling a positional parameter determination process on a
basis of the reliability parameter, the positional parameter
determination process being a process of estimating a positional
parameter indicating a position of the other communication device
on a basis of the detected specific element.
15. A non-transitory computer readable storage medium having a
program stored therein, the program causing a computer for
controlling a communication device including a plurality of
wireless communication sections, each of which is configured to be
capable of wirelessly transmitting and receiving a signal to and
from another communication device, to function as a control section
configured to correlate a first signal that is transmitted from the
other communication device and that includes change in amplitude
with respective second signals obtained when the plurality of
wireless communication sections receive the first signal, at a
designated interval after the other device transmits the first
signal, detect, on a basis of a first threshold, a specific element
that is one or more of a plurality of elements included in a
correlation computation result, with regard to each of a plurality
of the correlation computation results that are results obtained by
correlating the first signal and the respective second signals at
the designated interval and that includes a correlation value
indicating magnitude of correlation between the first signal and
the second signal as the element obtained at each delay time
serving as time elapsed after the other communication device
transmits the first signal at the designated interval, calculate a
reliability parameter that is an indicator indicating whether the
detected specific element is appropriate for a processing target,
and control a positional parameter determination process on a basis
of the reliability parameter, the positional parameter
determination process being a process of estimating a positional
parameter indicating a position of the other communication device
on a basis of the detected specific element.
Description
CROSS REFERENCE TO RELATED APPLICATION(S)
[0001] This application is based upon and claims benefit of
priority from Japanese Patent Application No. 2020-023217, filed on
Feb. 14, 2020, the entire contents of which are incorporated herein
by reference.
BACKGROUND
[0002] The present invention relates to a communication device, an
information processing method, and a storage medium.
[0003] In recent years, technologies that allow one device to
estimate a position of another device in accordance with a result
of transmitting/receiving a signal between the devices have been
developed. As an example of the technologies of estimating a
position, WO 2015/176776 A1 discloses a technology that allows an
UWB (ultra-wideband) receiver to estimate an angle of incidence of
a wireless signal from an UWB transmitter by performing wireless
communication section using UWB.
[0004] However, the technology disclosed by WO 2015/176776 A1 does
not deal with reduction in accuracy of estimating the angle of
incidence of the wireless signal in an environment where an
obstacle is interposed between the transmitter and the receiver, or
other environments. In addition to dealing with the above-described
issue, it has been desired to improve accuracy of the position
estimation technologies more.
[0005] Accordingly, the present invention is made in view of the
aforementioned issues, and an object of the present invention is to
provide a mechanism that makes it possible to improve accuracy of
estimating a position.
SUMMARY
[0006] To solve the above described problem, according to an aspect
of the present invention, there is provided a communication device
comprising: a plurality of wireless communication sections, each of
which is configured to be capable of wirelessly transmitting and
receiving a signal to and from another communication device; and a
control section configured to correlate a first signal that is
transmitted from the other communication device and that includes
change in amplitude with respective second signals obtained when
the plurality of wireless communication sections receive the first
signal, at a designated interval after the other device transmits
the first signal, detect, on a basis of a first threshold, a
specific element that is one or more of a plurality of elements
included in a correlation computation result, with regard to each
of a plurality of the correlation computation results that are
results obtained by correlating the first signal and the respective
second signals at the designated interval and that includes a
correlation value indicating magnitude of correlation between the
first signal and the second signal as the element obtained at each
delay time serving as time elapsed after the other communication
device transmits the first signal at the designated interval,
calculate a reliability parameter that is an indicator indicating
whether the detected specific element is appropriate for a
processing target, and control a positional parameter determination
process on a basis of the reliability parameter, the positional
parameter determination process being a process of estimating a
positional parameter indicating a position of the other
communication device on a basis of the detected specific
element.
[0007] To solve the above described problem, according to another
aspect of the present invention, there is provided an information
processing method that is executed by a communication device
including a plurality of wireless communication sections, each of
which is configured to be capable of wirelessly transmitting and
receiving a signal to and from another communication device, the
information processing method comprising: correlating a first
signal that is transmitted from the other communication device and
that includes change in amplitude with respective second signals
obtained when the plurality of wireless communication sections
receive the first signal, at a designated interval after the other
device transmits the first signal; detecting, on a basis of a first
threshold, a specific element that is one or more of a plurality of
elements included in a correlation computation result, with regard
to each of a plurality of the correlation computation results that
are results obtained by correlating the first signal and the
respective second signals at the designated interval and that
includes a correlation value indicating magnitude of correlation
between the first signal and the second signal as the element
obtained at each delay time serving as time elapsed after the other
communication device transmits the first signal at the designated
interval; calculating a reliability parameter that is an indicator
indicating whether the detected specific element is appropriate for
a processing target; and controlling a positional parameter
determination process on a basis of the reliability parameter, the
positional parameter determination process being a process of
estimating a positional parameter indicating a position of the
other communication device on a basis of the detected specific
element.
[0008] To solve the above described problem, according to another
aspect of the present invention, there is provided a storage medium
having a program stored therein, the program causing a computer for
controlling a communication device including a plurality of
wireless communication sections, each of which is configured to be
capable of wirelessly transmitting and receiving a signal to and
from another communication device, to function as a control section
configured to correlate a first signal that is transmitted from the
other communication device and that includes change in amplitude
with respective second signals obtained when the plurality of
wireless communication sections receive the first signal, at a
designated interval after the other device transmits the first
signal, detect, on a basis of a first threshold, a specific element
that is one or more of a plurality of elements included in a
correlation computation result, with regard to each of a plurality
of the correlation computation results that are results obtained by
correlating the first signal and the respective second signals at
the designated interval and that includes a correlation value
indicating magnitude of correlation between the first signal and
the second signal as the element obtained at each delay time
serving as time elapsed after the other communication device
transmits the first signal at the designated interval, calculate a
reliability parameter that is an indicator indicating whether the
detected specific element is appropriate for a processing target,
and control a positional parameter determination process on a basis
of the reliability parameter, the positional parameter
determination process being a process of estimating a positional
parameter indicating a position of the other communication device
on a basis of the detected specific element.
[0009] As described above, according to the present invention, it
is possible to provide the mechanism that makes it possible to
improve accuracy of estimating a position.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a diagram illustrating an example of a
configuration of a system according to an embodiment of the present
invention.
[0011] FIG. 2 is a diagram illustrating an example of arrangement
of a plurality of antennas installed in a vehicle according to the
embodiment.
[0012] FIG. 3 is a diagram illustrating an example of a positional
parameter of a portable device according to the embodiment.
[0013] FIG. 4 is a diagram illustrating an example of a positional
parameter of the portable device according to the embodiment.
[0014] FIG. 5 is a diagram illustrating an example of processing
blocks for signal processing in a communication unit according to
the embodiment.
[0015] FIG. 6 is a graph illustrating an example of a CIR according
to the embodiment.
[0016] FIG. 7 is a sequence diagram illustrating an example of a
flow of a ranging process executed by the system according to the
embodiment.
[0017] FIG. 8 is a sequence diagram illustrating an example of a
flow of an angle estimation process executed by the system
according to the embodiment.
[0018] FIG. 9 is a graph illustrating an example of a CIR.
[0019] FIG. 10 is a graph illustrating an example of a CIR.
[0020] FIG. 11 is graphs illustrating examples of CIRs with regard
to a plurality of wireless communication sections.
[0021] FIG. 12 is a graph illustrating an example of a CIR with
regard to the wireless communication section in an LOS
condition.
[0022] FIG. 13 is a graph illustrating an example of a CIR with
regard to the wireless communication section in an NLOS
condition.
[0023] FIG. 14 is diagrams for describing examples of reliability
parameters according to the embodiment.
[0024] FIG. 15 is diagrams for describing examples of reliability
parameters according to the embodiment.
[0025] FIG. 16 is a flowchart illustrating an example of a flow of
a control process of a positional parameter estimation process
executed by the communication unit according to the embodiment on
the basis of the reliability parameters.
[0026] FIG. 17 is a flowchart illustrating an example of a flow of
a control process of a positional parameter estimation process
executed by the communication unit according to the embodiment on
the basis of the reliability parameters.
[0027] FIG. 18 is a flowchart illustrating an example of a flow of
a control process of a positional parameter estimation process
executed by the communication unit according to the embodiment on
the basis of the reliability parameters.
DETAILED DESCRIPTION OF THE EMBODIMENT(S)
[0028] Hereinafter, referring to the appended drawings, preferred
embodiments of the present invention will be described in detail.
It should be noted that, in this specification and the appended
drawings, structural elements that have substantially the same
function and structure are denoted with the same reference
numerals, and repeated explanation thereof is omitted.
[0029] Further, in the present specification and the drawings,
different alphabets are suffixed to a same reference numeral to
distinguish elements which have substantially the same functional
configuration. For example, a plurality of elements which have
substantially the same functional configuration are distinguished
such as wireless communication sections 210A, 210B, and 210C, as
necessary. However, when there is no need in particular to
distinguish elements that have substantially the same functional
configuration, the same reference numeral alone is attached. For
example, in the case where it is not necessary to particularly
distinguish the wireless communication sections 210A, 210B, and
210C, the wireless communication sections 210A, 210B, and 210C are
simply referred to as the wireless communication sections 210.
1. Configuration Example
[0030] FIG. 1 is a diagram illustrating an example of a
configuration of a system 1 according to an embodiment of the
present invention. As illustrated in FIG. 1, the system 1 according
to the present embodiment includes a portable device 100 and a
communication unit 200. The communication unit 200 according to the
present embodiment is installed in a vehicle 202. The vehicle 202
is an example of a usage target of the user.
[0031] A communication device of an authenticate and a
communication device of an authenticator are involved in the
present embodiment. In the example illustrated in FIG. 1, the
portable device 100 is an example of the communication device of
the authenticate, and the communication unit 200 is an example of
the communication device of the authenticator.
[0032] When a user (for example, a driver of the vehicle 202)
carrying the portable device 100 approaches the vehicle 202, the
system 1 performs wireless communication for authentication between
the portable device 100 and the communication unit 200 installed in
the vehicle 202. Next, when the authentication succeeds, the
vehicle 202 becomes available for the user by unlocking a door lock
of the vehicle 202 and starting an engine of the vehicle 202. The
system 1 is also referred to as a smart entry system. Next,
respective structural elements will be described sequentially.
[0033] (1) Portable Device 100
[0034] The portable device 100 is configured as any device to be
carried by the user. Examples of the any device include an
electronic key, a smartphone, a wearable terminal, and the like. As
illustrated in FIG. 1, the portable device 100 includes a wireless
communication section 110, a storage section 120, and a control
section 130.
[0035] The wireless communication section 110 has a function of
performing wireless communication with the communication unit 200
installed in the vehicle 202. The wireless communication section
110 wirelessly receives a signal from the communication unit 200
installed in the vehicle 202. In addition, the wireless
communication section 110 wirelessly transmits a signal to the
communication unit 200.
[0036] For example, wireless communication is performed between the
wireless communication section 110 and the communication unit 200
by using an ultra-wideband (UWB) signal, for example. In the
wireless communication of the UWB signal, it is possible for
impulse UWB to measure propagation delay time of a radio wave with
high accuracy by using the radio wave of ultra-short pulse width of
a nanosecond or less, and it is possible to perform ranging with
high accuracy on the basis of the propagation delay time. Note
that, the propagation delay time is time from transmission to
reception of the radio wave. The wireless communication section 110
is configured as a communication interface that makes it possible
to perform communication by using the UWB signals, for example.
[0037] Note that, the UWB signal may be transmitted/received as a
ranging signal, an angle estimation signal, and a data signal, for
example. The ranging signal is a signal transmitted and received in
the ranging process (to be described later). The ranging signal may
be configured in a frame format that does not include a payload
part for storing data or in a frame format that includes the
payload part. The angle estimation signal is a signal transmitted
and received in an angle estimation process (to be described
later). The angle estimation signal may be configured in a way
similar to the ranging signal. The data signal is preferably
configured in the frame format that includes the payload part for
storing the data.
[0038] Here, the wireless communication section 110 includes at
least one antenna 111. In addition, the wireless communication
section 110 transmits/receives a wireless signal via the at least
one antenna 111.
[0039] The storage section 120 has a function of storing various
kinds of information for operating the portable device 100. For
example, the storage section 120 stores a program for operating the
portable device 100, and an identifier (ID), password, and
authentication algorithm for authentication, and the like. For
example, the storage section 120 includes a storage medium such as
flash memory and a processing device that performs
recording/playback on/of the storage medium.
[0040] The control section 130 has a function of executing
processes in the portable device 100. For example, the control
section 130 controls the wireless communication section 110 to
perform communication with the communication unit 200 of the
vehicle 202. The control section 130 reads information from the
storage section 120 and writes information into the storage section
120. The control section 130 also functions as an authentication
control section that controls an authentication process between the
portable device 100 and the communication unit 200 of the vehicle
202. For example, the control section 130 may include a central
processing unit (CPU) and an electronic circuit such as a
microprocessor.
[0041] (2) Communication Unit 200
[0042] The communication unit 200 is prepared in association with
the vehicle 202. Here, it is assumed that the communication unit
200 is installed in the vehicle 202 in such a manner that the
communication section 200 is installed in a vehicle interior of the
vehicle 202, the communication section 200 is built in the vehicle
202 as a communication module, or in other manners. Alternatively,
the communication unit 200 may be prepared as a separate object
from the vehicle 202 in such a manner that the communication unit
200 is installed in a parking space for the vehicle 202 or in other
manners. In this case, the communication unit 200 may wirelessly
transmit a control signal to the vehicle 202 on the basis of a
result of communication with the portable device 100 and may
remotely control the vehicle 202. As illustrated in FIG. 1, the
communication unit 200 includes a plurality of wireless
communication sections 210 (210A to 210D), a storage section 220,
and a control section 230.
[0043] The wireless communication section 210 has a function of
performing wireless communication with the wireless communication
section 110 of the portable device 100. The wireless communication
section 210 wirelessly receives a signal from the portable device
100. In addition, the wireless communication section 210 wirelessly
transmits a signal to the portable device 100. The wireless
communication section 210 is configured as a communication
interface that makes it possible to perform communication by using
the UWB, for example.
[0044] Here, each of the wireless communication sections 210
includes an antenna 211. In addition, each of the wireless
communication sections 210 transmits/receives a wireless signal via
the antenna 211.
[0045] The storage section 220 has a function of storing various
kinds of information for operating the communication unit 200. For
example, the storage section 220 stores a program for operating the
communication unit 200, an authentication algorithm, and the like.
For example, the storage section 220 includes a storage medium such
as flash memory and a processing device that performs
recording/playback on/of the storage medium.
[0046] The control section 230 has a function of controlling
overall operation performed by the communication unit 200 and
in-vehicle equipment installed in the vehicle 202. For example, the
control section 230 controls the wireless communication sections
210 to perform communication with the portable device 100. The
control section 230 reads information from the storage section 220
and writes information into the storage section 220. The control
section 230 also functions as an authentication control section
that controls the authentication process between the portable
device 100 and the communication unit 200 of the vehicle 202. In
addition, the control section 230 also functions as a door lock
control section that controls a door lock of the vehicle 202, and
opens and closes the door lock. The control section 230 also
functions as an engine control section that controls the engine of
the vehicle 202, and starts/stops the engine. Note that, a motor or
the like may be installed as a power source in the vehicle 202 in
addition to the engine. For example, the control section 230 is
configured as an electronic circuit such as an electronic control
unit (ECU).
2. Estimation of Positional Parameter
[0047] <2.1. Positional Parameter>
[0048] The communication unit 200 (specifically, control section
230) according to the present embodiment performs a positional
parameter estimation process of estimating a positional parameter
that represents a position of the portable device 100. Hereinafter,
with reference to FIG. 2 to FIG. 4, various definitions related to
the positional parameter will be described.
[0049] FIG. 2 is a diagram illustrating an example of arrangement
of the plurality of antennas 211 (wireless communication sections
210) installed in the vehicle 202 according to the present
embodiment. As illustrated in FIG. 2, the four antennas 211 (211A
to 211D) are installed on a ceiling of the vehicle 202. The antenna
211A is installed on a front right side of the vehicle 202. The
antenna 211B is installed on a front left side of the vehicle 202.
The antenna 211C is installed on a rear right side of the vehicle
202. The antenna 211D is installed on a rear left side of the
vehicle 202. Note that, distances between adjacent antennas 211 are
set to a half or less of wavelength .lamda. of a carrier wave of an
angle estimation signal (to be described later). A local coordinate
system of the communication unit 200 is set as a coordinate system
based on the communication unit 200. An example of the local
coordinate system of the communication unit 200 has its origin at
the center of the four antennas 211. This local coordinate system
has its X axis along a front-rear direction of the vehicle 202, its
Y axis along a left-right direction of the vehicle 202, and its Z
axis along an up-down direction of the vehicle 202. Note that, the
X axis is parallel to a line connecting a pair of the antennas in
the front-rear direction (such as a pair of the antenna 211A and
the antenna 211C, and a pair of the antenna 211B and the antenna
211D). In addition, the Y axis is parallel to a line connecting a
pair of the antennas in the left-right direction (such as a pair of
the antenna 211A and the antenna 211B, and a pair of the antenna
211C and the antenna 211D).
[0050] Note that, the arrangement of the four antennas 211 is not
limited to the square shape. The arrangement of the four antennas
211 may be a parallelogram shape, a trapezoid shape, a rectangular
shape, or any other shapes. Of course, the number of antennas 211
is not limited to four.
[0051] FIG. 3 is a diagram illustrating an example of a positional
parameter of the portable device 100 according to the present
embodiment. The positional parameter may include a distance R
between the portable device 100 and the communication unit 200. The
distance R illustrated in FIG. 3 is a distance from the origin of
the local coordinate system of the communication unit 200 to the
portable device 100. The distance R is estimated on the basis of a
result of transmission/reception of a ranging signal (to be
described later) between the portable device 100 and one of the
plurality of wireless communication sections 210. The distance R
may be a distance between the portable device 100 and one of the
wireless communication sections 210 that transmit/receive the
ranging signal (to be described later).
[0052] In addition, as illustrated in FIG. 3, the positional
parameter may include an angle of the portable device 100 based on
the communication unit 200, the angle including an angle .alpha.
between the X axis and the portable device 100 and an angle .beta.
between the Y axis and the portable device 100. The angles .alpha.
and .beta. are angles between the coordinate axes of a first
predetermined coordinate system and a straight line connecting the
portable device 100 with the origin of the first predetermined
coordinate system. For example, the first predetermined coordinate
system is the local coordinate system of the communication unit
200. The angle .alpha. is an angle between the X axis and the
straight line connecting the portable device 100 with the origin.
The angle .beta. is an angle between the Y axis and the straight
line connecting the portable device 100 with the origin.
[0053] FIG. 4 is a diagram illustrating an example of the
positional parameter of the portable device 100 according to the
present embodiment. The positional parameter may include
coordinates of the portable device 100 in a second predetermined
coordinate system. In FIG. 4, a coordinate x on the X axis, a
coordinate y on the Y axis, and a coordinate z on the Z axis of the
portable device 100 are an example of such coordinates. In other
words, the second predetermined coordinate system may be the local
coordinate system of the communication unit 200. Alternatively, the
second predetermined coordinate system may be a global coordinate
system.
[0054] <2.2. CIR>
[0055] (1) CIR Calculation Process
[0056] In the positional parameter estimation process, the portable
device 100 and the communication unit 200 communicate with each
other to estimate the positional parameter. At this time, the
portable device 100 and the communication unit 200 calculates
channel impulse responses (CIRs).
[0057] The CIR is a response obtained when an impulse is input to
the system. In the case where a wireless communication section of
one of the portable device 100 and the communication unit 200
(hereinafter, also referred to as a transmitter) transmits a signal
including a pulse as a first signal, the CIR according to the
present embodiment is calculated on the basis of a second signal
that corresponds to the first signal and that is received by a
wireless communication section of the other (hereinafter, also
referred to as a receiver). The pulse is a signal including change
in amplitude. It can be said that the CIR indicates characteristics
of a wireless communication path between the portable device 100
and the communication unit 200. Hereinafter, the first signal is
also referred to as a transmission signal, and the second signal is
also referred to as a reception signal.
[0058] For example, the CIR may be a correlation computation result
that is a result obtained by correlating the transmission signal
with the reception signal at each delay time that is time elapsed
after the transmitter transmits the transmission signal. Here, the
correlation may be sliding correlation that is a process of
correlating the transmission signal with the reception signal by
shifting relative positions of the signals in a time direction. The
correlation computation result includes a correlation value
indicating a degree of the correlation between the transmission
signal and the reception signal as an element obtained at each
delay time. Each of a plurality of the elements included in the
correlation computation result is information including a
combination of the delay time and the correlation value. The
correlation may be calculated at each delay time between designated
intervals. In other words, the CIR may be a result of correlating
the transmission signal with the reception signal at the designated
interval after the transmitter transmits the transmission signal.
Here, the designated interval is an interval between timings at
which the receiver samples the reception signal, for example.
Therefore, an element included in the CIR is also referred to as a
sampling point. The correlation value may be a complex number
including IQ components. In addition, the correlation value may be
a phase or amplitude of the complex number. In addition, the
correlation value may be electric power that is a sum of squares of
an I component and a Q component of the complex number (or square
of amplitude).
[0059] For another example, the CIR may be the reception signal
itself (complex number including IQ components). Alternatively, the
CIR may be a phase or amplitude of the reception signal.
Alternatively, the CIR may be electric power that is a sum of
squares of an I component and a Q component of the reception signal
(or square of amplitude).
[0060] A value obtained at each delay time of the CIR is also
referred to as a CIR value. In other words, the CIR is
chronological change in the CIR value. In the case where the CIR is
the correlation computation result, the CIR value is a correlation
value obtained at each delay time. In the case where the CIR is the
reception signal itself, the CIR value is the reception signal
received at each delay time. In the case where the CIR is the phase
or amplitude of the reception signal, the CIR value is the phase or
amplitude of the reception signal received at each delay time. In
the case where the CIR is the electric power of the reception
signal, the CIR value is the electric power of the reception signal
received at each delay time.
[0061] In the case where the CIR is the correlation computation
result, the receiver calculates the CIR by correlating the
transmission signal with the reception signal through the sliding
correlation. For example, the receiver calculates a value obtained
by correlating the reception signal with the transmission signal
delayed by a certain delay time, as characteristics (that is, CIR
value) obtained at the delay time. Next, the receiver calculates
the CIR value at each delay time to calculate the CIR. Hereinafter,
it is assumed that the CIR is the correlation computation
result.
[0062] Note that, the CIR is also referred to as delay profile in a
ranging technology using the UWB. In particular, the CIR using
electric power as the CIR value is referred to as power delay
profile.
[0063] Hereinafter, with reference to FIG. 5 to FIG. 6, a CIR
calculation process performed in the case where the portable device
100 serves as the transmitter and the communication unit 200 serves
as the receiver will be described in detail.
[0064] FIG. 5 is a diagram illustrating an example of processing
blocks for signal processing in the communication unit 200
according to the present embodiment. As illustrated in FIG. 5, the
communication unit 200 includes an oscillator 212, a multiplier
213, a 90-degree phase shifter 214, a multiplier 215, a low pass
filter (LPF) 216, an LPF 217, a correlator 218, and an integrator
219.
[0065] The oscillator 212 generates a signal of same frequency as
frequency of a carrier wave that carries a transmission signal, and
outputs the generated signal to the multiplier 213 and the
90-degree phase shifter 214.
[0066] The multiplier 213 multiplies a reception signal received by
the antenna 211 by the signal output from the oscillator 212, and
outputs a result of the multiplication to the LPF 216. Among input
signals, the LPF 216 outputs a signal of lower frequency than the
frequency of the carrier wave that carries the transmission signal,
to the correlator 218. The signal input to the correlator 218 is an
I component (that is, a real part) among components corresponding
to an envelope of the reception signal.
[0067] The 90-degree phase shifter 214 delays the phase of the
input signal by 90 degrees, and outputs the delayed signal to the
multiplier 215. The multiplier 215 multiplies the reception signal
received by the antenna 211 by the signal output from the 90-degree
phase shifter 214, and outputs a result of the multiplication to
the LPF 217. Among input signals, the LPF 217 outputs a signal of
lower frequency than the frequency of the carrier wave that carries
the transmission signal, to the correlator 218. The signal input to
the correlator 218 is a Q component (that is, an imaginary part)
among the components corresponding to the envelope of the reception
signal.
[0068] The correlator 218 calculates the CIR by correlating a
reference signal with the reception signals including the I
component and the Q component output from the LPF 216 and the LPF
217 through the sliding correlation. Note that, the reference
signal described herein is the same signal as the transmission
signal before multiplying the carrier wave.
[0069] The integrator 219 integrates the CIRs output from the
correlator 218, and outputs the integrated CIRs.
[0070] Here, the transmitter may transmit a signal including a
preamble as the transmission signal. The preamble is a sequence
known to the transmitter and the receiver. Typically, the preamble
is arranged at a head of the transmission signal. The preamble
includes one or more preamble symbols. The preamble symbol is a
pulse sequence including one or more pulses. The pulse sequence is
a set of the plurality of pulses that are separate from each other
in the time direction.
[0071] The preamble symbol is a target of integration performed by
the integrator 219. Therefore, the correlator 218 calculates the
CIR for each of the one or more preamble symbols by correlating a
portion corresponding to a preamble symbol with a preamble symbol
included in the transmission signal with regard to each of portions
corresponding to the one or more preamble symbols included in the
reception signal, at the designated intervals after the portable
device 100 transmits the preamble symbol. Next, the integrator 219
obtains integrated CIRs by integrating the CIRs of the respective
preamble symbols with regard to the one or more preamble symbols
included in the preamble. Next, the integrator 219 outputs the
integrated CIRs. Hereinafter, the CIR means the integrated CIRs
unless otherwise noted.
[0072] As described above, the CIR includes a correlation value
indicating a degree of the correlation between the transmission
signal and the reception signal as an element obtained at each
delay time, which is time elapsed after the transmitter transmits
the transmission signal. From a viewpoint of the preamble symbol,
the CIR includes the correlation value indicating a degree of the
correlation between the transmission signal and the reception
signal as an element obtained at each delay time, which is time
elapsed after the transmitter transmits each preamble symbol.
[0073] (2) Example of CIR
[0074] FIG. 6 illustrates an example of the CIR output from the
integrator 219. FIG. 6 is a graph illustrating the example of the
CIR according to the present embodiment. The graph includes a
horizontal axis representing delay time. The graph includes a
vertical axis representing absolute values of CIR values (such as
amplitude or electric power). Note that, the shape of CIR, more
specifically, the shape of chronological change in the CIR value
may also be referred to as a CIR waveform. Typically, a set of
elements obtained between a zero-crossing and another zero-crossing
corresponds to a single pulse with regard to the CIR. The
zero-crossings are elements whose value is zero. However, the same
does not apply to an environment with noise. For example, a set of
elements obtained between intersections of a standard with
chronological change in the CIR value may be treated as
corresponding to the single pulse. The CIR illustrated in FIG. 6
includes a set 21 of elements corresponding to a certain pulse, and
a set 22 of elements corresponding to another pulse.
[0075] For example, the set 21 corresponds to a signal (such as
pulse) that reaches the receiver through a first path. The first
path is a shortest path between the transmitter and the receiver.
In an environment that includes no obstacle, the first path is a
straight path between the transmitter and the receiver. For
example, the set 22 corresponds to a signal (such as pulse) that
reaches the receiver through a path other than the first path. As
described above, the signals that have passed through different
paths are also referred to as multipath waves.
[0076] (3) Detection of First Incoming Wave
[0077] Among wireless signals received from the transmitter, the
receiver detects a signal that meets a predetermined detection
standard as a signal that reaches the receiver through the first
path. Next, the receiver estimates the positional parameter on the
basis of the detected signal.
[0078] Hereinafter, the signal detected as the signal that reaches
the receiver through the first path is also referred to as the
first incoming wave. The first incoming wave may be any of a direct
wave, a delayed wave, or a combined wave. The direct wave is a
signal that passes through a shortest path between the transmitter
and the receiver, and is received by the receiver. In other words,
the direct wave is a signal that reaches the receiver through the
first path. The delayed wave is a signal that passes through a path
different from the shortest path between the transmitter and the
receiver, that is, through a path other than the first path, and
reaches the receiver. The delayed wave is received by the receiver
after getting delayed in comparison with the direct wave. The
combined wave is a signal received by the receiver in a state of
combining a plurality of signals that have passed through a
plurality of different paths.
[0079] The receiver detects the signal that meets the predetermined
detection standard as the first incoming wave, among the received
wireless signals. For example, the predetermined detection standard
is a condition that the CIR value (such as amplitude or electric
power) exceeds a predetermined threshold for the first time. In
other words, the receiver may detect a pulse corresponding to a
portion of the CIR obtained when the CIR value exceeds the
predetermined threshold for the first time, as the first incoming
wave.
[0080] Here, it should be noted that the signal detected as the
first incoming wave is not necessarily the direct wave. For
example, if the direct wave is received in a state where the direct
wave and the delayed wave annihilate each other, sometimes the CIR
value falls below the predetermined threshold and the direct wave
is not detected as the first incoming wave. In this case, the
combined wave or the delayed wave coming while being delayed behind
the direct wave is detected as the first incoming wave.
[0081] Hereinafter, the predetermined threshold used for detecting
the first incoming wave is also referred to as a first path
threshold.
[0082] --Reception Time of First Incoming Wave
[0083] The receiver may treat the time of meeting the predetermined
detection standard as reception time of the first incoming wave.
For example, the reception time of the first incoming wave is time
corresponding to delayed time of an element having a CIR value that
exceeds the first path threshold for the first time.
[0084] Alternatively, the receiver may treat time of obtaining a
peak of the detected first incoming wave as the reception time of
the first incoming wave. In this case, for example, the reception
time of the first incoming wave is time corresponding to delayed
time of an element having highest amplitude or electric power as
the CIR value, among the set of elements corresponding to the first
incoming wave with regard to the CIR.
[0085] Hereinafter, it is assumed that the reception time of the
first incoming wave is time corresponding to delayed time of an
element having a CIR value that exceeds the first path threshold
for the first time.
[0086] --Phase of First Incoming Wave
[0087] The receiver may treat a phase obtained at time of meeting
the predetermined detection standard as a phase of the first
incoming wave. For example, the phase of the first incoming wave is
a phase serving as a CIR value of an element having the CIR value
that exceeds the first path threshold for the first time.
[0088] Alternatively, the receiver may treat a phase of the peak of
the detected first incoming wave as the phase of the first incoming
wave. In this case, for example, the reception time of the first
incoming wave is the phase serving as a CIR value of an element
having highest amplitude or electric power as the CIR value, among
the set of elements corresponding to the first incoming wave with
regard to the CIR.
[0089] Hereinafter, it is assumed that the phase of the first
incoming wave is a phase serving as a CIR value of an element
having the CIR value that exceeds the first path threshold for the
first time.
[0090] --Width of First Incoming Wave
[0091] The width of the set of elements corresponding to the first
incoming wave in the time direction is also referred to as the
width of the first incoming wave. For example, the width of the
first incoming wave is the width between a zero-crossing and
another zero-crossing of the CIR in the time direction. For another
example, the width of the first incoming wave is width between
intersections of a standard with chronological change in the CIR
value in the time direction.
[0092] The width of a pulse included in the transmission signal in
the time direction is also referred to as the width of the pulse.
For example, the width of the pulse is the width between a
zero-crossing and another zero-crossing of chronological change in
the CIR value in the time direction. For another example, the width
of the pulse is width between intersections of a standard with
chronological change in the CIR value in the time direction.
[0093] In the case where only the direct wave is detected as the
first incoming wave, the first incoming wave of the CIR has an
ideal width. The ideal width obtained when only the direct wave is
detected as the first incoming wave can be calculated through
theoretical calculation using the waveform of the transmission
signal, a reception signal processing method, and the like. On the
other hand, in the case where the combined wave is received as the
first incoming wave, the width of the first incoming wave of the
CIR may be different from the ideal width. For example, in the case
where a combined wave obtained by combining a direct wave and a
delayed wave having a same phase as the direct wave is detected as
the first incoming wave, a portion corresponding to the direct wave
and a portion corresponding to the delayed wave are added in a
state where they are shifted in the time direction. Therefore, the
portions reinforce each other, and the first incoming wave in the
CIR has a wider width. On the other hand, in the case where a
combined wave obtained by combining a direct wave and a delayed
wave having an opposite phase from the direct wave is detected as
the first incoming wave, the direct wave and the delayed wave
annihilate each other. Therefore, the first incoming wave in the
CIR has a narrower width.
[0094] <2.3. Estimation of Positional Parameter>
[0095] (1) Ranging
[0096] The communication unit 200 performs the ranging process. The
ranging process is a process of estimating a distance between the
communication unit 200 and the portable device 100. For example,
the distance between the communication unit 200 and the portable
device 100 is the distance R illustrated in FIG. 3. The ranging
process includes transmission/reception of a ranging signal and
calculation of the distance R based on propagation delay time of
the ranging signal. The ranging signal is a signal used for ranging
among signals transmitted/received between the portable device 100
and the communication unit 200. The propagation delay time is time
from transmission to reception of the signal.
[0097] Here, the ranging signal is transmitted/received by one of
the plurality of wireless communication sections 210 of the
communication unit 200. Hereinafter, the wireless communication
section 210 that transmits/receives the ranging signal is also
referred to as a master. The distance R is a distance between the
wireless communication section 210 serving as the master (more
precisely, the antenna 211) and the portable device 100 (more
precisely, the antenna 111). In addition, the wireless
communication sections 210 other than the wireless communication
section 210 that transmits/receives the ranging signal are also
referred to as slaves.
[0098] In the ranging process, a plurality of the ranging signals
may be transmitted and received between communication unit 200 and
the portable device 100. Among the plurality of ranging signals, a
ranging signal transmitted from one device to the other device is
also referred to as a first ranging signal. Next, a ranging signal
transmitted as a response to the first ranging signal from the
device that has received the first ranging signal to the device
that has transmitted the first ranging signal is also referred to
as a second ranging signal. In addition, a ranging signal
transmitted as a response to the second ranging signal from the
device that has received the second ranging signal to the device
that has transmitted the second ranging signal is also referred to
as a third ranging signal.
[0099] Next, with reference to FIG. 7, an example of a flow of the
ranging process will be described.
[0100] FIG. 7 is a sequence diagram illustrating the example of the
flow of the ranging process executed in the system 1 according to
the present embodiment. The portable device 100 and the
communication unit 200 are involved in this sequence. It is assumed
that the wireless communication section 210A functions as the
master in this sequence.
[0101] As illustrated in FIG. 7, the portable device 100 first
transmits the first ranging signal (Step S102). When the wireless
communication section 210A receives the first ranging signal, the
control section 230 calculates a CIR of the first ranging signal.
Next, the control section 230 detects a first incoming wave of the
first ranging signal of the wireless communication section 210A on
the basis of the calculated CIR (Step S104).
[0102] Next, the wireless communication section 210A transmits the
second ranging signal in response to the first ranging signal (Step
S106). When the second ranging signal is received, the portable
device 100 calculates a CIR of the second ranging signal. Next, the
portable device 100 detects a first incoming wave of the second
ranging signal on the basis of the calculated CIR (Step S108).
[0103] Next, the portable device 100 transmits the third ranging
signal in response to the second ranging signal (Step S110). When
the wireless communication section 210A receives the third ranging
signal, the control section 230 calculates a CIR of the third
ranging signal. Next, the control section 230 detects a first
incoming wave of the third ranging signal of the wireless
communication section 210A on the basis of the calculated CIR (Step
S112).
[0104] The portable device 100 measures a time period T.sub.1 from
transmission time of the first ranging signal to reception time of
the second ranging signal, and a time period T.sub.2 from reception
time of the second ranging signal to transmission time of the third
ranging signal. Here, the reception time of the second ranging
signal is reception time of the first incoming wave of the second
ranging signal detected in Step S108. Next, the portable device 100
transmits a signal including information indicating the time period
T.sub.1 and the time period T.sub.2 (Step S114). For example, such
a signal is received by the wireless communication section
210A.
[0105] The control section 230 measures a time period T.sub.3 from
reception time of the first ranging signal to transmission time of
the second ranging signal, and a time period T.sub.4 from
transmission time of the second ranging signal to reception time of
the third ranging signal. Here, the reception time of the first
ranging signal is reception time of the first incoming wave of the
first ranging signal detected in Step S104. In a similar way, the
reception time of the third ranging signal is reception time of the
first incoming wave of the third ranging signal detected in Step
S112.
[0106] Next, the control section 230 estimates the distance R on
the basis of the time periods T.sub.1, T.sub.2, T.sub.3, and
T.sub.4 (Step S116). For example, the control section 230 estimates
propagation delay time .tau..sub.m by using an equation listed
below.
.tau. m = T 1 .times. T 4 - T 2 .times. T 3 T 1 + T 2 + T 3 + T 4 (
1 ) ##EQU00001##
[0107] Next, the control section 230 estimates the distance R by
multiplying the estimated propagation delay time .tau..sub.m by
speed of the signal.
[0108] --Cause of Reduction in Accuracy of Estimation
[0109] The reception times of the ranging signals serving as start
or end of the time periods T.sub.1, T.sub.2, T.sub.3, and T.sub.4
are reception times of the first incoming waves of the ranging
signals. As described above, the signals detected as the first
incoming wave are not necessarily the direct waves.
[0110] In the case where the combined wave or the delayed wave
coming while being delayed behind the direct wave is detected as
the first incoming wave, reception time of the first incoming wave
varies in comparison with the case where the direct wave is
detected as the first incoming wave. In this case, an estimation
result of the propagation delay time .tau..sub.m is changed from a
true value (an estimation result obtained in the case where the
direct wave is detected as the first incoming wave). In addition,
this change deteriorates accuracy of estimating the distance R
(hereinafter, also referred to as ranging accuracy).
[0111] (2) Angle Estimation
[0112] The communication unit 200 performs the angle estimation
process. The angle estimation process is a process of estimating
the angles .alpha. and .beta. illustrated in FIG. 3. An angle
acquisition process includes reception of an angle estimation
signal and calculation of the angles .alpha. and .beta. on the
basis of a result of reception of the angle estimation signal. The
angle estimation signal is a signal used for estimating an angle
among signals transmitted/received between the portable device 100
and the communication unit 200. Next, with reference to FIG. 8, an
example of a flow of the angle estimation process will be
described.
[0113] FIG. 8 is a sequence diagram illustrating the example of the
flow of the angle estimation process executed in the system 1
according to the present embodiment. The portable device 100 and
the communication unit 200 are involved in this sequence.
[0114] As illustrated in FIG. 8, the portable device 100 first
transmits the angle estimation signals (Step S202). Next, when the
wireless communication sections 210A to 210D receive respective
angle estimation signals, the control section 230 calculates CIRs
of the respective angle estimation signals received by the wireless
communication sections 210A to 210D. Next, the control section 230
detects first incoming waves of the respective angle estimation
signals on the basis of the calculated CIRs with regard to the
wireless communication sections 210A to 210D (Step S204A to Step
S204D). Next, the control section 230 detects respective phases of
the detected first incoming waves with regard to the wireless
communication sections 210A to 210D (Step S206A to Step S206D).
Next, the control section 230 estimates the angles .alpha. and
.beta. on the basis of the respective phases of the detected first
incoming waves with regard to the wireless communication sections
210A to 210D (Step S208).
[0115] Next, details of the process in Step S208 will be described.
P.sub.A represents the phase of the first incoming wave detected
with regard to the wireless communication section 210A. P.sub.B
represents the phase of the first incoming wave detected with
regard to the wireless communication section 210B. P.sub.C
represents the phase of the first incoming wave detected with
regard to the wireless communication section 210C. P.sub.D
represents the phase of the first incoming wave detected with
regard to the wireless communication section 210D. In this case,
antenna array phase differences Pd.sub.AC and Pd.sub.BD in the X
axis direction and antenna array phase differences Pd.sub.BA and
Pd.sub.DC in the Y axis direction are expressed in respective
equations listed below.
Pd.sub.AC=(P.sub.A-P.sub.C)
Pd.sub.BD=(P.sub.B-P.sub.D)
Pd.sub.DC=(P.sub.D-P.sub.C)
Pd.sub.BA=(P.sub.B-P.sub.A) (2)
[0116] The angles .alpha. and .beta. are calculated by using the
following equation. Here, .lamda. represents wavelength of a
carrier wave of the angle estimation signal, and d represents a
distance between the antennas 211.
.alpha. or .beta.=arccos(.lamda.Pd/(2.pi.d)) (3)
[0117] Therefore, respective equations listed below represent
angles calculated on the basis of the respective antenna array
phase differences.
.alpha..sub.AC=arccos(.lamda.Pd.sub.AC/(2.pi.d))
.alpha..sub.BD=arccos(.lamda.Pd.sub.BD/(2.pi.d))
.beta..sub.DC=arccos(.lamda.Pd.sub.DC/(2.pi..pi.d))
.beta..sub.BA=arccos(.lamda.Pd.sub.BA/(2.pi.d)) (4)
[0118] The control section 230 calculates the angles .alpha. and
.beta. on the basis of the calculated angles .alpha..sub.AC,
.alpha..sub.BD, .beta..sub.DC, and .beta..sub.BA. For example, as
expressed in the following equations, the control section 230
calculates the angles .alpha. and .beta. by averaging the angles
calculated with regard to the two respective arrays in the X axis
direction and the Y axis direction.
.alpha.=(.alpha..sub.AC+.alpha..sub.BD)/2
.beta.=(.beta..sub.DC+.beta..sub.BA)/2 (5)
[0119] --Cause of Reduction in Accuracy of Estimation
[0120] As described above, the angles .alpha. and .beta. are
calculated on the basis of the phases of the first incoming waves.
As described above, the signals detected as the first incoming
waves are not necessarily the direct waves.
[0121] In other words, sometimes the delayed wave or the combined
wave may be detected as the first incoming wave. Typically, phases
of the delayed wave and the combined wave are different from the
phase of the direct wave. This difference deteriorates accuracy of
angle estimation.
[0122] --Supplement
[0123] Note that, the angle estimation signal may be
transmitted/received during the angle estimation process, or at any
other timings. For example, the angle estimation signal may be
transmitted/received during the ranging process. Specifically, the
third ranging signal illustrated in FIG. 7 may be the same as the
angle estimation signal illustrated in FIG. 8. In this case, it is
possible for the communication unit 200 to calculate the distance
R, the angle .alpha., and the angle .beta. by receiving a single
wireless signal that serves as both the angle estimation signal and
the third ranging signal.
[0124] (3) Coordinate Estimation
[0125] The control section 230 performs a coordinate estimation
process. The coordinate estimation process is a process of
estimating three-dimensional coordinates (x, y, z) of the portable
device 100 illustrated in FIG. 4. As the coordinate estimation
process, a first calculation method and a second calculation method
listed below may be adopted.
[0126] --First Calculation Method
[0127] The first calculation method is a method of calculating the
coordinates x, y, and z on the basis of results of the ranging
process and the angle estimation process. In this case, the control
section 230 first calculates the coordinates x and y by using
equations listed below.
x=Rcos .alpha.
y=Rcos .beta. (6)
[0128] Here, the distance R, the coordinate x, the coordinate y,
and the coordinate z have a relation represented by an equation
listed below.
R= {square root over (x.sup.2+y.sup.2+z.sup.2)} (7)
[0129] The control section 230 calculates the coordinate z by using
the above-described relation and an equation listed below.
z= {square root over
(R.sup.2-R.sup.2cos.sup.2.alpha.-Rcos.sup.2.beta.)} (8)
[0130] --Second Calculation Method
[0131] The second calculation method is a method of calculating the
coordinates x, y, and z while omitting estimation of the angles
.alpha. and .beta.. First, the above-listed equations (4), (5),
(6), and (7) establish a relation represented by equations listed
below.
x/R=cos .alpha. (9)
y/R=cos .beta. (10)
x.sup.2+y.sup.2+z.sup.2=R.sup.2 (11)
dcos .alpha.=.lamda.(Pd.sub.AC/2+Pd.sub.BD/2)/(2.pi.) (12)
dcos .beta.=.lamda.(Pd.sub.DC/2+Pd.sub.BA/2)/(2.pi.) (13)
[0132] The equation (12) is rearranged for cos .alpha., and cos
.alpha. is substituted into the equation (9). This makes it
possible to obtain the coordinate x by using an equation listed
below.
x=R.lamda.(Pd.sub.AC/2+Pd.sub.BD/2)/(2.pi.d) (14)
[0133] The equation (13) is rearranged for cos .beta., and cos
.beta. is substituted into the equation (10). This makes it
possible to obtain the coordinate y by using an equation listed
below.
y=R.lamda.(Pd.sub.DC/2+Pd.sub.BA/2)/(2.pi.d) (15)
[0134] Next, the equation (14) and the equation (15) are
substituted into the equation (11), and the equation (11) is
rearranged. This makes it possible to obtain the coordinate z by
using an equation listed below.
z= {square root over (R.sup.2-x.sup.2-y.sup.2)} (16)
[0135] The process of estimating the coordinates of the portable
device 100 in the local coordinate system has been described above.
It is also possible to estimate coordinates of the portable device
100 in the global coordinate system by combining the coordinates of
the portable device 100 in the local coordinate system and
coordinates of the origin of the local coordinate system relative
to the global coordinate system.
[0136] --Cause of Reduction in Accuracy of Estimation
[0137] As described above, the coordinates are calculated on the
basis of the propagation delay time and phases. In addition, they
are estimated on the basis of the first incoming waves. Therefore,
accuracy of estimating the coordinates may deteriorate in a way
similar to the ranging process and the angle estimation
process.
[0138] (4) Estimation of Existence Region
[0139] The positional parameter may include a region including the
portable device 100 among a plurality of predefined regions. For
example, in the case where the region is defined by a distance from
the communication unit 200, the control section 230 estimates the
region including the portable device 100 on the basis of the
distance R estimated through the ranging process. For another
example, in the case where the region is defined by an angle with
respect to the communication unit 200, the control section 230
estimates the region including the portable device 100 on the basis
of the angles .alpha. and .beta. estimated through the angle
estimation process. For another example, in the case where the
region is defined by the three-dimensional coordinates, the control
section 230 estimates the region including the portable device 100
on the basis of the coordinates (x, y, z) estimated through the
coordinate estimation process.
[0140] Alternatively, in a process specific to the vehicle 202, the
control section 230 may estimate the region including the portable
device 100 among the plurality of regions including the vehicle
interior and the vehicle exterior of the vehicle 202. This makes it
possible to provide courteous service such as providing different
serves in the case where the user is in the vehicle interior and in
the case where the user is in the vehicle exterior. In addition,
the control section 230 may estimate the region including the
portable device 100 among nearby region and faraway region. The
nearby region is a region within a predetermined distance from the
vehicle 202, and the faraway region is the predetermined distance
or more away from the vehicle 202.
[0141] (5) Use of Result of Estimating Positional Parameter
[0142] For example, a result of estimating the positional parameter
may be used for authentication of the portable device 100. For
example, the control section 230 determines that the authentication
is successful and unlock a door in the case where the portable
device 100 is in a region close to the communication unit 200 on a
driver seat side.
3. Technical Problem
[0143] The plurality of wireless communication sections 210 may
include both a wireless communication section 210 in a
line-of-sight (LOS) condition and a wireless communication section
210 in a non-line-of-sight (NLOS) condition.
[0144] The LOS condition means that the antenna 111 of the portable
device 100 and the antenna 211 of the wireless communication
section 210 are visible from each other. In the case of the LOS
condition, a highest reception electric power of the direct wave is
obtained. Therefore, there is a high possibility that the receiver
succeeds in detecting the direct wave as the first incoming
wave.
[0145] The NLOS condition means that the antenna 111 of the
portable device 100 and the antenna 211 of the wireless
communication section 210 are not visible from each other. In the
case of the NLOS condition, reception electric power of the direct
wave may become lower than the others. Therefore, there is a
possibility that the receiver fails in detecting the direct wave as
the first incoming wave.
[0146] In the case where the wireless communication section 210 is
in the NLOS condition, reception electric power of the direct wave
is smaller than noise among signals came from the portable device
100. Accordingly, even if detection of the direct wave as the first
incoming wave is successful, the phase and reception time of the
first incoming wave may be changed due to an effect of the noise.
In this case, accuracy of ranging and accuracy of angle estimation
deteriorate.
[0147] In addition, in the case where the wireless communication
section 210 is in the NLOS condition, reception electric power of
the direct wave becomes lower than the case where the wireless
communication section 210 is in the LOS condition, and detection of
the direct wave as the first incoming wave may end in failure. In
this case, accuracy of ranging and accuracy of angle estimation
deteriorate.
[0148] Therefore, according to the present embodiment, there is
provided the technology that makes it possible to improve the
accuracy of estimating the positional parameter by estimating the
positional parameter on the basis of a first incoming wave in the
case where there is a high possibility that the direct wave is
successfully detected as the first incoming wave.
4. Technical Features
[0149] (1) Overview
[0150] The control section 230 detects a specific element on the
basis of a first threshold with regard to each of CIRs respectively
obtained from the plurality of wireless communication sections 210.
The specific element is one or more of a plurality of elements
included in the CIR. Specifically, to detect the specific element
on the basis of the first threshold, the control section 230
detects one or more element whose amplitude component included in
the CIR value exceeds the first threshold, as the specific element.
The amplitude component included in the CIR value may be amplitude
itself or electric power obtained by squaring the amplitude.
[0151] The specific element is an element corresponding to the
first incoming wave. Time corresponding to delay time of the
specific element serves as time of receiving the first incoming
wave and is used for ranging. In addition, the phase of the
specific element serves as the phase of the first incoming wave and
is used for angle estimation. In other words, the control section
230 detects the specific element to be used for the positional
parameter estimation with regard to the plurality of wireless
communication sections 210.
[0152] For example, to detect the specific element on the basis of
the first threshold, the control section 230 detects an element
having amplitude or electric power that exceeds the first threshold
for the first time, as the specific element. The amplitude or
electric power serves as the CIR value. In this case, the specific
elements are detected one by one with regard to the plurality of
CIR s obtained with regard to the plurality of wireless
communication sections 210. The first threshold is the
above-described first path threshold. In other words, the specific
element is an element whose CIR value exceeds the first path
threshold for the first time, among the plurality of elements
included in the CIR. This makes it possible to reduce computational
load for detecting the specific elements in comparison with the
case of detecting the plurality of specific elements from a single
CIR.
[0153] The control section 230 calculates the reliability
parameter. The reliability parameter is an indicator indicating
whether the detected specific element is appropriate for a
processing target. More specifically, the reliability parameter is
an indicator indicating whether it is appropriate to use the
detected specific element for estimating the positional parameter.
When mention is made of a plurality of the specific elements
detected with regard to the respective wireless communication
sections 210, the reliability parameter is an indicator indicating
whether each of the detected specific elements is appropriate for
the processing target.
[0154] When the specific element is appropriate for the processing
target, the specific element corresponds to a direct wave. On the
other hand, when the specific element is inappropriate for the
processing target, the specific element does not correspond to the
direct wave. In other words, the reliability parameter can be
treated as an indicator that indicates suitability of the detected
specific element for an element corresponding to the direct wave.
In the case where the detected specific element corresponds to a
delayed wave or a combined wave, that is, in the case where the
delayed wave or the combined wave is detected as the first incoming
wave, the accuracy of estimating the positional parameter
deteriorates as described above. Therefore, it is possible to
evaluate the accuracy of estimating the positional parameter on the
basis of the reliability parameter.
[0155] For example, the reliability parameters are continuous
values or discrete values. As the reliability parameter has a
higher value, the reliability parameter may indicate that the
specific element is appropriate for the processing target. In a
similar way, if the reliability parameter has a lower value, the
reliability parameter may indicate that the specific element is
inappropriate for the processing target, and vice versa.
Hereinafter, a degree of appropriateness of the specific element as
the processing target may also be referred to as reliability. In
addition, high reliability means that the specific element is
appropriate for the processing target, and low reliability means
that the specific element is inappropriate as the processing
target.
[0156] The control section 230 detects the specific elements and
calculates the reliability parameters on the basis of the
transmission signal transmitted from the portable device 100 in the
positional parameter estimation process and the respective
reception signal obtained when the plurality of wireless
communication sections 210 receive the transmission signal. Such a
transmission signal may be the ranging signal or the angle
estimation signal. For example, such a transmission signal may be a
signal that is the third ranging signal illustrated in FIG. 7 and
that also serves as the angle estimation signal.
[0157] Details of a method of calculating the reliability parameter
will be described later.
[0158] The control section 230 controls a positional parameter
determination process on the basis of the reliability parameter.
The positional parameter determination process is a process of
estimating a positional parameter indicating a position of the
portable device 100 on the basis of the detected specific element.
Specifically, the control section 230 selects a specific element
corresponding to a reliability parameter with the highest
reliability, or a reliability parameter indicating reliability that
exceeds a predetermined threshold. Next, the control section 230
estimates a positional parameter on the basis of the selected
specific element.
[0159] For example, the control section 230 performs ranging on the
basis of delay time of the selected specific element. For another
example, the control section 230 estimates an angle on the basis of
the phase of the selected specific element. For another example,
the control section 230 estimates coordinates on the basis of the
phase and the delay time of the selected specific element. Anyway,
it is possible to estimate the positional parameter on the basis of
the specific element with high reliability. This makes it possible
to improve accuracy of estimating the positional parameter. Note
that, details of a process of controlling the positional parameter
estimation process on the basis of the reliability parameter will
be described later.
[0160] (2) Reliability Parameter
[0161] --First Reliability Parameter
[0162] The reliability parameter may include a first reliability
parameter that is a difference between delay time of a first
element and delay time of a second element of the CIR. The first
element has a peak CIR value for the first time after the specific
element, and the second element has the peak CIR value for the
second time after the specific element. Details of the first
reliability parameter will be described with reference to FIG. 9
and FIG. 10.
[0163] FIG. 9 and FIG. 10 are graphs illustrating examples of the
CIR s. The graph includes a horizontal axis representing delay
time. The graph includes a vertical axis representing absolute
values of CIR values (such as electric power or amplitude).
[0164] The CIR illustrated in FIG. 9 include a set 21 of elements
corresponding to the direct wave, and a set 22 of elements
corresponding to the delayed wave. The set 21 includes a specific
element SP.sub.FP that is an element whose CIR value exceeds a
first path threshold TH.sub.FP for the first time. In other words,
the set 21 corresponds to the first incoming wave. The set 21
includes a first element SP.sub.P1 having a peak CIR value for the
first time after the specific element SP.sub.FP. On the other hand,
the set 22 includes a second element SP.sub.P2 having a peak CIR
value for the second time after the specific element SP.sub.FP.
[0165] The CIR illustrated in FIG. 10 includes a set 23 of elements
corresponding to the combined wave received in a state where the
direct wave is combined with the delayed wave having a different
phase from the direct wave. The CIR waveform of the set 23 has two
peaks because two waves having different phases are combined. The
CIR waveform of the set 23 has two peaks because two waves having
different phases are combined. The set 23 includes a specific
element SP.sub.FP that is an element whose CIR value exceeds a
first path threshold TH.sub.FP for the first time. In other words,
the set 23 corresponds to the first incoming wave. The set 23
includes a first element SP.sub.P1 having a peak CIR value for the
first time after the specific element SP.sub.FP. The set 23
includes a second element SP.sub.P2 having a peak CIR value for the
second time after the specific element SP.sub.FP.
[0166] In the case where the direct wave is detected as the first
incoming wave, the first incoming wave has a CIR waveform with a
single peak as illustrated in FIG. 9. On the other hand, in the
case where the combined wave is detected as the first incoming
wave, the first incoming wave has a CIR waveform with multiple
peaks as illustrated in FIG. 10. In addition, it is possible to
determine whether the first incoming wave has the CIR waveform with
the single peak or the multiple peaks on the basis of a difference
T.sub.P1-P2 between the delay time T.sub.P1 of the first element
SP.sub.P1 and the delay time T.sub.P2 of the second element
SP.sub.P2. This is because a large difference T.sub.P1-P2 is
obtained in the case where the first incoming wave has the CIR
waveform with the single peak. In addition, a smaller difference
T.sub.P1-P2 is obtained in the case where the first incoming wave
has the CIR waveform with the multiple peaks.
[0167] In the case where the combined wave is detected as the first
incoming wave, accuracy of estimating the positional parameter
deteriorates in comparison with the case where the direct wave is
detected as the first incoming wave. Therefore, it can be said that
the larger difference T.sub.P1-P2 means higher reliability. As
described above, it is possible to evaluate reliability by using
the difference T.sub.P1-P2. The difference T.sub.P1-P2 is the first
reliability parameter.
[0168] Therefore, to control the positional parameter estimation
process on the basis of the reliability parameter, the control
section 230 estimates the positional parameter on the basis of the
specific element whose difference T.sub.P1-P2 indicated by the
reliability parameter is larger than a second threshold. For
example, the control section 230 determines that the difference
T.sub.P1-P2 illustrated in FIG. 9 is larger than the second
threshold, and estimates the positional parameter on the basis of
the specific element SP.sub.FP illustrated in FIG. 9. For another
example, the control section 230 determines that the difference
T.sub.P1-P2 illustrated in FIG. 10 is smaller than the second
threshold, and does not estimate the positional parameter on the
basis of the specific element SP.sub.FP illustrated in FIG. 10.
Such a configuration makes it possible to estimate the positional
parameter on the basis of the specific element obtained in the case
where there is a high possibility that the direct wave is detected
as the first incoming wave. This makes it possible to improve
accuracy of estimating a positional parameter.
[0169] Here, an interval between a plurality of peaks included in
the CIR waveform of the combined wave is smaller than the width of
the single pulse. On the other hand, an interval between respective
peaks of two separate waves is larger than the width of the single
pulse. Therefore, the second threshold may be set to any value that
is less than or equal to the width of the pulse. This makes it
possible to determine whether or not the combined wave is detected
as the first incoming wave.
[0170] --Second Reliability Parameter
[0171] The reliability parameter may include a second reliability
parameter derived from correlation between CIR waveforms of the
wireless communication sections 210 in a pair. Details of the
second reliability parameter will be described with reference to
FIG. 11.
[0172] FIG. 11 is graphs illustrating examples of CIRs with regard
to the plurality of wireless communication sections 210. A CIR 20A
illustrated in FIG. 11 is a graph illustrating an example of a CIR
with regard to a wireless communication section 210A. A CIR 20B
illustrated in FIG. 11 is a graph illustrating an example of a CIR
with regard to a wireless communication section 210B. Each graph
includes a horizontal axis representing delay time. It is assumed
that a time axis of the CIR 20A is synchronous with a time axis of
the CIR 20B. The graph includes a vertical axis representing
absolute values of CIR values (such as amplitude or electric
power).
[0173] The CIR 20A includes a set 23A of elements corresponding to
the combined wave received in a state where the direct wave is
combined with the delayed wave having a different phase from the
direct wave. The CIR waveform of the set 23A has two peaks because
two waves having different phases are combined. The set 23A
includes a specific element SP.sub.FP that is an element whose CIR
value exceeds the first path threshold TH.sub.FP for the first
time. In other words, the set 23A corresponds to the first incoming
wave.
[0174] On the other hand, the CIR 20B includes a set 23B of
elements corresponding to the combined wave received in a state
where the direct wave is combined with the delayed wave having a
same phase as the direct wave. The CIR waveform of the set 23 has a
single large peak because two waves having the same phase are
combined. The set 23B includes a specific element SP.sub.FP that is
an element whose CIR value exceeds the first path threshold
TH.sub.FP for the first time. In other words, the set 23B
corresponds to the first incoming wave.
[0175] In the case where the plurality of wireless communication
sections 210 receive signals in the state where the direct wave is
combined with the delayed wave, the wireless communication sections
210 have different relations of phases of the direct wave and the
delayed wave even if a distance between the wireless communication
sections 210 is short. As a result, different CIR waveforms are
obtained as illustrated in the CIR 20A and CIR 20B. In other words,
the different CIR waveforms between the wireless communication
sections 210 in a pair mean that a combined wave is received by at
least one of the wireless communication sections 210 in the pair.
In the case where the combined wave is detected as the first
incoming wave, that is, in the case where detection of the specific
element corresponding to the direct wave ends in failure, accuracy
of estimating the positional parameter deteriorates.
[0176] Accordingly, the second reliability parameter may be a
correlation coefficient between a CIR obtained on the basis of
reception signal received by a first wireless communication section
210 among the plurality of wireless communication sections 210, and
a CIR obtained on the basis of a reception signal received by a
second wireless communication section 210 that is different from
the first wireless communication section 210 among the plurality of
wireless communication sections 210. In other words, the second
reliability parameter may be a correlation coefficient between a
waveform of the entire CIR calculated with regard to the first
wireless communication section 210 and a waveform of the entire CIR
calculated with regard to the second wireless communication section
210. In addition, the control section 230 determines that
reliability gets higher as the correlation coefficient increases.
On the other hand, the control section 230 determines that
reliability gets lower as the correlation coefficient decreases.
Such a configuration makes it possible to evaluate reliability from
a viewpoint of correlation between CIR waveforms.
[0177] Here, the delay time and the phase of the specific element
is used for the process of estimating the positional parameter.
Therefore, the reliability parameter may be derived from
correlation between CIR waveforms close to the specific
element.
[0178] In other words, the second reliability parameter may be a
correlation coefficient between chronological change in CIR value
of a portion including the specific element in the CIR obtained on
the basis of reception signal received by the first wireless
communication section 210 among the plurality of wireless
communication sections 210, and chronological change in CIR value
of a portion including the specific element in the CIR obtained on
the basis of the reception signal received by the second wireless
communication section 210 that is different from the first wireless
communication section 210 among the plurality of wireless
communication sections 210. Here, the portion means a set including
the specific element and one or more elements that exist before
and/or after the specific element. In other words, the second
reliability parameter may be a correlation coefficient between a
waveform obtained in a vicinity of the specific element in the CIR
calculated with regard to the first wireless communication section
210, and a waveform obtained in a vicinity of the specific element
in the CIR calculated with regard to the second wireless
communication section 210. In addition, the control section 230
determines that reliability gets higher as the correlation
coefficient increases. On the other hand, the control section 230
determines that reliability gets lower as the correlation
coefficient decreases. Such a configuration makes it possible to
evaluate reliability from a viewpoint of correlation between CIR
waveforms obtained in the vicinity of the specific element. In
addition, such a configuration makes it possible to reduce an
amount of calculation in comparison with the case of correlating
waveforms of the entire CIRs.
[0179] To control the positional parameter estimation process on
the basis of the reliability parameter, the control section 230
estimates the positional parameter on the basis of the specific
element whose correlation coefficient indicated by the reliability
parameter is higher than a third threshold. For example, the
control section 230 calculates the correlation coefficient with
regard to one or more pairs of any wireless communication sections
210. Next, in the case where all of the one or more correlation
coefficients that have been calculated are higher than the third
threshold, the control section 230 estimates the positional
parameter on the basis of the specific elements detected with
regard to the plurality of wireless communication sections 210. In
other cases, the control section 230 does not estimate the
positional parameter. Such a configuration makes it possible to
estimate the positional parameter on the basis of the specific
element obtained in the case where there is a high possibility that
the direct wave is detected as the first incoming wave with regard
to each of the plurality of wireless communication sections 210.
This makes it possible to improve accuracy of estimating a
positional parameter.
[0180] Note that, the correlation coefficient may be the Pearson
correlation coefficient.
[0181] The CIR may include amplitude or electric power, which is a
CIR value, as an element obtained at each delay time. In this case,
the control section 230 calculates a correlation coefficient by
correlating respective amplitudes or electric powers obtained at
corresponding delay times, which are included in the two CIRs. Note
that, the corresponding delay times indicates a same delay time in
an environment where the time axes of the two CIRs are synchronous
with each other.
[0182] The CIR may include a complex number, which is a CIR value,
as the element obtained at each delay time. In this case, the
control section 230 calculates a correlation coefficient by
correlating respective complex numbers obtained at corresponding
delay times, which are included in the two CIRs. The complex number
includes a phase component in addition to an amplitude component.
Therefore, it is possible to calculate a more accurate correlation
coefficient than the case of calculating a correlation coefficient
on the basis of amplitude or electric power.
[0183] --Third Reliability Parameter
[0184] The reliability parameter may include a third reliability
parameter that is a difference between delay time of a specific
element and delay time of an element having a maximum CIT value in
a CIR. Details of the third reliability parameter will be described
with reference to FIG. 12 and FIG. 13.
[0185] FIG. 12 is a graph illustrating an example of a CIR with
regard to the wireless communication section 210 in the LOS
condition. FIG. 13 is a graph illustrating an example of a CIR with
regard to the wireless communication section 210 in the NLOS
condition. The graph includes a horizontal axis representing delay
time. The graph includes a vertical axis representing absolute
values of CIR values (such as electric power or amplitude).
[0186] The CIR illustrated in FIG. 12 include a set 21 of elements
corresponding to the direct wave, and a set 22 of elements
corresponding to the delayed wave. The set 21 includes a specific
element SP.sub.FP that is an element whose CIR value exceeds a
first path threshold TH.sub.FP for the first time. In other words,
the set 21 corresponds to the first incoming wave. In addition, the
set 21 includes an element SP.sub.PP having a maximum CIR value in
the CIR.
[0187] The CIR illustrated in FIG. 13 include a set 21 of elements
corresponding to the direct wave, and a set 22 of elements
corresponding to the delayed wave. The set 21 includes a specific
element SP.sub.FP that is an element whose CIR value exceeds a
first path threshold TH.sub.FP for the first time. In other words,
the set 21 corresponds to the first incoming wave. On the other
hand, the set 22 includes an element SP.sub.PP having a maximum CIR
value in the CIR.
[0188] In the case of the LOS condition, the direct wave has the
largest CIR value. Therefore, as illustrated in FIG. 12, the set 21
corresponding to the direct wave includes the element SP.sub.PP
having the maximum CIR value in the CIR.
[0189] On the other hand, in the case of the NLOS condition, a CIR
value of the delayed wave may be larger than a CIR value of the
direct wave. In the case of the NLOS condition, this is because
there is an obstacle in the first path. In particular, in the case
where a human body is interposed in the first path, the direct wave
drastically attenuates when the direct wave passes through the
human body. In this case, as illustrated in FIG. 13, the set 21
corresponding to the direct wave does not include the element
SP.sub.PP having the maximum CIR value in the CIR.
[0190] It is possible to determine whether the wireless
communication section 210 is in the LOS condition or the NLOS
condition, on the basis of a difference T.sub.FP-PP between delay
time T.sub.FP of the specific element SP.sub.FP and delay time
T.sub.PP of the element SP.sub.PP having the maximum CIR value in
the CIR. This is because the difference T.sub.FP-PP may be small in
the case where the wireless communication section 210 is in the LOS
condition as illustrated in FIG. 12. In addition, the difference
T.sub.FP-PP may be large in the case where the wireless
communication section 210 is in the NLOS condition as illustrated
in FIG. 13.
[0191] In the case of the NLOS condition, the accuracy of
estimating the positional parameter deteriorates in comparison with
the case of the LOS condition. Therefore, it can be said that
higher reliability is obtained as the difference T.sub.FP-PP
decreases. As described above, it is possible to evaluate
reliability by using the difference T.sub.FP-PP. The difference
T.sub.FP-PP is the third reliability parameter.
[0192] Therefore, to control the positional parameter estimation
process on the basis of the reliability parameter, the control
section 230 estimates the positional parameter on the basis of the
specific element whose difference T.sub.FP-PP indicated by the
reliability parameter is smaller than a fourth threshold. For
example, the control section 230 determines that the difference
T.sub.FP-PP illustrated in FIG. 12 is smaller than the fourth
threshold, and estimates the positional parameter on the basis of
the specific element SP.sub.FP illustrated in FIG. 12. For another
example, the control section 230 determines that the difference
T.sub.FP-PP illustrated in FIG. 13 is larger than the fourth
threshold, and does not estimate the positional parameter on the
basis of the specific element SP.sub.FP illustrated in FIG. 13.
Such a configuration makes it possible to estimate the positional
parameter on the basis of the specific element that is likely to be
detected with regard to the wireless communication section 210 in
the LOS condition. This makes it possible to improve accuracy of
estimating a positional parameter.
[0193] --Fourth Reliability Parameter
[0194] The reliability parameter may include a fourth reliability
parameter that is between electric power corresponding to a
specific element in a CIR obtained on the basis of reception signal
received by a first wireless communication section 210 among the
plurality of wireless communication sections 210, and electric
power corresponding to a specific element in a CIR obtained on the
basis of a reception signal received by a second wireless
communication section 210 that is different from the first wireless
communication section 210 among the plurality of wireless
communication sections 210. Next, details of the fourth reliability
parameter will be described.
[0195] Hereinafter, the electric power corresponding to the
specific element will be referred to as first-path-compliant
electric power. For example, the first-path-compliant electric
power may be electric power of an element having a peak CIR value
for the first time after the specific element. The electric power
serves as the CIR value. For another example, the
first-path-compliant electric power may be a sum of electric powers
of the specific element and one or more element subsequent to the
specific element. The electric power serves as the CIR value.
[0196] A difference in the first-path-compliant electric power
between the wireless communication sections 210 in a pair is
decided by a difference between propagation distances from the
portable device 100 to the respective wireless communication
sections 210. This is because the radio wave attenuates in
proportion to a square of the propagation distance. Note that,
distances between the wireless communication sections 210 are set
to a half or less of wavelength .lamda. of a carrier wave of an
angle estimation signal. Therefore, there is little difference in
the propagation distances from the portable device 100 to the
respective wireless communication sections 210. In other words,
ideally, the first-path-compliant electric powers do not differ
greatly between the wireless communication sections 210 in a
pair.
[0197] However, first-path-compliant electric powers may differ
greatly between the wireless communication sections 210 in the case
where the combined wave is detected as the first incoming wave with
regard to one of the wireless communication sections 210 in the
pair. This is because the wireless communication sections 210 may
have different relations of phases of two pulses to be combined
even if a distance between the wireless communication sections 210
is short. For example, in the case where the two pulses to be
combined have a same phase, the two pulses reinforce each other.
Therefore, large first-path-compliant electric power is obtained
with regard to the combined wave detected as the first incoming
wave. For another example, in the case where the two pulses to be
combined have opposite phases, the two pulses annihilate each
other. Therefore, small first-path-compliant electric power is
obtained with regard to the combined wave detected as the first
incoming wave.
[0198] In the case where the combined wave is detected as the first
incoming wave, accuracy of estimating the positional parameter
deteriorates in comparison with the case where the direct wave is
detected as the first incoming wave. Therefore, it can be said that
higher reliability is obtained as a difference in the
first-path-compliant electric power between the wireless
communication sections 210 reduces. As described above, it is
possible to evaluate reliability by using the difference in the
first-path-compliant electric power between the wireless
communication sections 210. The difference in the
first-path-compliant electric power between the wireless
communication sections 201 is the fourth reliability parameter.
[0199] Therefore, to control the positional parameter estimation
process on the basis of the reliability parameter, the control
section 230 estimates the positional parameter on the basis of the
specific element whose difference in the first-path-compliant
electric power between the wireless communication sections 210
indicated by the reliability parameter is smaller than a fifth
threshold. For example, the control section 230 calculates the
difference in the first-path-compliant electric power with regard
to one or more pairs of any wireless communication sections 210.
Next, in the case where all of the one or more differences in the
first-path-compliant electric power are lower than the fifth
threshold, the control section 230 estimates the positional
parameter on the basis of the respective specific elements detected
with regard to the plurality of wireless communication sections
210. In other cases, the control section 230 does not estimate the
positional parameter. Such a configuration makes it possible to
estimate the positional parameter on the basis of the specific
element obtained in the case where there is a high possibility that
the direct wave is detected as the first incoming wave with regard
to each of the plurality of wireless communication sections 210.
This makes it possible to improve accuracy of estimating a
positional parameter.
[0200] --Fifth Reliability Parameter
[0201] The fifth reliability parameter is an indicator that
indicates whether the first incoming wave itself is the appropriate
detection target. In other words, the fifth reliability parameter
is an indicator that indicates whether the specific element itself
is the appropriate detection target. Higher reliability is obtained
as the first incoming wave is more appropriate for the processing
target, and lower reliability is obtained as the first incoming
wave is more inappropriate for the processing target.
[0202] Specifically, the fifth reliability parameter may be an
indicator that indicates magnitude of noise. In this case, the
fifth reliability parameter is calculated on the basis of at least
any of a signal-to-noise ratio (SNR) and electric power of the
first incoming wave. In the case where the electric power is high,
influence of the noise is small. Therefore, the fifth reliability
parameter indicating that the first incoming wave is appropriate
for the detection target is calculated. On the other hand, in the
case where the electric power is low, influence of the noise is
small. Therefore, the fifth reliability parameter indicating that
the first incoming wave is inappropriate for the detection target
is calculated. In the case where the SNR is high, the influence of
the noise is small. Therefore, the fifth reliability parameter
indicating that the first incoming wave is appropriate for the
detection target is calculated. On the other hand, in the case
where the SNR is low, effects of the noise are large. Therefore,
the fifth reliability parameter indicating that the first incoming
wave is inappropriate for the detection target is calculated.
[0203] By using the fifth reliability parameter, it is possible to
evaluate reliability on the basis of whether the first incoming
wave itself is appropriate for the detection target.
[0204] --Sixth Reliability Parameter
[0205] The sixth reliability parameter is an indicator that
indicates adequacy of a direct wave for the first incoming wave. In
other words, the sixth reliability parameter is an indicator that
indicates suitability of the specific element for an element
corresponding to the direct wave. Higher reliability is obtained as
the adequacy of the direct wave for the first incoming wave gets
higher, and lower reliability is obtained as the adequacy of the
direct wave for the first incoming wave gets lower.
[0206] The sixth reliability parameter may be calculated on the
basis of consistency between the respective first incoming waves of
the plurality of the wireless communication sections 210.
Specifically, the sixth reliability parameter is calculated on the
basis of at least any of reception time and electric power of the
first incoming wave with regard to each of the plurality of
wireless communication sections 210. By the effect of multipath, a
plurality of wireless signals coming through different paths may be
combined and received by the wireless communication sections 210 in
a state where the signals are amplified or offset. Next, in the
case where ways of amplifying and offsetting the wireless signals
are different between the plurality of wireless communication
sections 210, different reception times and different electric
power values may be obtained with regard to the first incoming
waves between the wireless communication sections 210. When
considering that distances between the wireless communication
sections 210 are short distances that are a half or less of the
wavelength .lamda. of the angle estimation signal, a large
difference in the reception times and electric powers of the first
incoming waves between the wireless communication sections 210
means low suitability of the direct waves for the first incoming
waves.
[0207] Therefore, a sixth reliability parameter is calculated in
such a manner that the sixth reliability parameter indicates that
the suitability of the direct waves for the first incoming waves
gets lower as the difference in reception time of the first
incoming wave (that is, delay time of the specific element) between
the wireless communication sections 210 gets larger. On the other
hand, the sixth reliability parameter is calculated in such a
manner that the sixth reliability parameter indicates that the
suitability of the direct waves for the first incoming waves gets
higher as the difference in reception time of the first incoming
wave between the wireless communication sections 210 gets smaller.
In addition, the sixth reliability parameter is calculated in such
a manner that the sixth reliability parameter indicates that the
suitability of the direct wave for the first incoming wave gets
lower as the difference in electric power of the first incoming
wave between the wireless communication sections 210 gets larger.
On the other hand, the sixth reliability parameter is calculated in
such a manner that the sixth reliability parameter indicates that
the suitability of the direct wave for the first incoming wave gets
higher as the difference in electric power of the first the first
incoming wave between the wireless communication sections 210 gets
smaller.
[0208] The sixth reliability parameter may be calculated on the
basis of consistency between positional parameters indicating
positions of the portable device 100 estimated on the basis of the
respective first incoming waves received by the plurality of
wireless communication sections 210 in pairs. Each of the pair
includes two different wireless communication sections 210 among
the plurality of wireless communication sections 210. Here, the
positional parameters are the angles .alpha. and .beta. illustrated
in FIG. 3 and the coordinates (x, y, z) illustrated in FIG. 4. In
the case where the first incoming waves are the direct waves, same
or substantially same results are obtained with regard to the
angles .alpha. and .beta. and the coordinates (x, y, z) even if
different combinations are used as the pairs of the wireless
communication sections 210 for calculating the angles .alpha. and
.beta. and the coordinates (x, y, z). However, in the case where
the first incoming waves are not the direct waves, different
results may be obtained from the different pairs of the wireless
communication sections 210 with regard to the angles .alpha. and
.beta. and the coordinates (x, y, z).
[0209] Accordingly, the sixth reliability parameter is calculated
in such a manner that the sixth reliability parameter indicates
that the adequacy of the direct waves for the first incoming waves
gets higher as the difference in positional parameter calculation
result between different combinations of the antenna pairs. For
example, the sixth reliability parameter is calculated in such a
manner that the sixth reliability parameter indicates that the
adequacy of the direct waves for the first incoming waves gets
higher as an error between .alpha..sub.AC and .alpha..sub.BD gets
smaller and as an error between .beta..sub.DC and .beta..sub.BA
gets smaller. On the other hand, the sixth reliability parameter is
calculated in such a manner that the sixth reliability parameter
indicates that the adequacy of the direct waves for the first
incoming waves gets lower as the difference in positional parameter
calculation result between different combinations of the antenna
pairs gets larger. For example, the sixth reliability parameter is
calculated in such a manner that the sixth reliability parameter
indicates that the adequacy of a direct waves for the first
incoming waves gets lower as an error between .alpha..sub.AC and
.alpha..sub.BD gets larger and as an error between .beta..sub.DC
and .beta..sub.BA gets larger. These angles have been described
above with regard to the angle estimation process.
[0210] By using the sixth reliability parameter, it is possible to
evaluate the reliability on the basis of the adequacy of the direct
waves for the first incoming waves.
[0211] --Seventh Reliability Parameter
[0212] The seventh reliability parameter is an indicator that
indicates inadequacy of a combined wave for the first incoming
wave. In other words, the seventh reliability parameter is an
indicator that indicates unsuitability of the specific element for
the combined wave. Higher reliability is obtained as the
unsuitability of the combined wave for the first incoming wave gets
higher, and lower reliability is obtained as the suitability of the
combined wave for the first incoming wave gets lower.
[0213] Specifically, the seventh reliability parameter is
calculated on the basis of at least any of width of the first
incoming wave in the time direction and a state of the phase of the
first incoming wave.
[0214] First, with reference to FIG. 14, calculation of the seventh
reliability parameter based on the width of the first incoming wave
in the time direction will be described. Here, the width of the
first incoming wave in the time direction may be width of an
element corresponding to the first incoming wave in the time
direction, with regard to the CIR.
[0215] FIG. 14 is diagrams for describing examples of the
reliability parameter according to the present embodiment. In the
case where the direct wave is independently received as illustrated
in the top of FIG. 14, width W of a set 21 of elements
corresponding to the direct wave in the CIR serves as an ideal
width obtained when only the direct wave is detected as the first
incoming wave. Here, the width W is width of a set of elements
corresponding to a single pulse in the time direction. For example,
the width W is width between a zero-crossing and another
zero-crossing. For another example, the width W is width between
intersections of a standard and varied CIR values. On the other
hand, when the wireless communication sections 210 receive the
plurality of wireless signals came through different paths in a
state where the plurality of pulses are combined, the width W of a
set of elements corresponding to the combined wave in the CIR may
be different from the ideal width obtained when only the direct
wave is detected as the first incoming wave, due to influence of
multipath. For example, when a delayed wave having a same phase as
the direct wave is received in such a manner that the delayed wave
is combined with the direct wave as illustrated in the bottom of
FIG. 14, the set 21 of elements corresponding to the direct wave
and the set 22 of elements corresponding to the delayed wave are
added in a state where they are shifted in the time direction.
Therefore, the set 23 of elements corresponding to the combined
wave in the CIR has a wide width W. On the other hand, when a
delayed wave having an opposite phase from the direct wave is
received in such a manner that the delayed wave is combined with
the direct wave, the direct wave and the delayed wave annihilate
each other. Therefore, a set of elements corresponding to the
combined wave in the CIR has a narrow width W.
[0216] As described above, the seventh reliability parameter is
calculated in such a manner that the seventh reliability parameter
indicates that the inadequacy of the combined wave for the first
incoming wave gets higher as the difference between the width of
the first incoming wave and the ideal width obtained when only the
direct wave is detected as the first incoming wave gets smaller. On
the other hand, the seventh reliability parameter is calculated in
such a manner that the seventh reliability parameter indicates that
the inadequacy of the combined wave for the first incoming wave
gets lower as the difference between the width of the first
incoming wave and the ideal width obtained when only the direct
wave is detected as the first incoming wave gets larger.
[0217] Next, with reference to FIG. 15, calculation of the seventh
reliability parameter based on a state of phase of the first
incoming wave will be described. Here, the state of the phase of
the first incoming wave may be a degree of difference in phase
between elements corresponding to the first incoming wave in the
received wireless signal. Alternatively, the state of the phase of
the first incoming wave may be a degree of difference in phase
between elements corresponding to the first incoming wave in the
CIR.
[0218] FIG. 15 is diagrams for describing examples of the
reliability parameter according to the present embodiment. In the
case where only the direct wave is independently received as
illustrated in the top of FIG. 15, respective phases .theta. of a
plurality of elements belonging to the set 21 corresponding to the
direct wave in the CIR are a same or substantially same phase (that
is, .theta.1.apprxeq..theta.2.apprxeq..theta.3). Note that, the
phase is an angle between IQ components of a CIR and an I axis on
an IQ plane. This is because distances of paths of direct waves are
the same with regard to the respective elements. On the other hand,
in the case where the combined wave is received as illustrated in
the bottom of FIG. 15, respective phases .theta. of a plurality of
elements belonging to the set 23 of elements corresponding to the
combined wave in the CIR are different phases (that is,
.theta.1.noteq..theta.2.noteq..theta.3). This is because pulses
having different distances between the transmitter and the
receiver, that is, the pulses having different phases are combined.
As described above, the seventh reliability parameter is calculated
in such a manner that the seventh reliability parameter indicates
that the unsuitability of the combined wave for the first incoming
wave gets higher as the difference between the phases of elements
corresponding to the first incoming wave gets smaller. On the other
hand, the seventh reliability parameter is also calculated in such
a manner that the seventh reliability parameter indicates that the
unsuitability of the combined wave for the first incoming wave gets
lower as the difference between the phases of the elements
corresponding to the first incoming wave gets larger.
[0219] By using the seventh reliability parameter, it is possible
to evaluate the reliability on the basis of the unsuitability of
the combined wave for the first incoming wave.
[0220] (3) Flow of Process
[0221] Various kinds of methods can be used for controlling the
positional parameter estimation process on the basis of the
reliability parameter. Next, two specific examples will be
described with regard to the control methods.
First Example
[0222] The control section 230 may repeatedly perform position
estimation communication N number of times. The position estimation
communication means that the plurality of wireless communication
sections 201 receive a wireless signal (ranging signal and/or angle
estimation signal) from the portable device 100. N is an integer
that is two or more.
[0223] The control section 230 calculates respective CIR s with
regard to the plurality of wireless communication sections 210 on
the basis of the reception signals received by the plurality of
wireless communication sections 210 through single position
measurement communication. Next, the control section 230 detects
the specific elements with regard to the plurality of wireless
communication sections 210. In addition, the control section 230
calculates the reliability parameters.
[0224] By repeatedly performing the position estimation
communication N number of times, it is possible for the
communication unit 200 to obtain N number of combinations of the
plurality of specific elements and reliability parameters detected
with regard to the respective wireless communication sections
210.
[0225] The control section 230 performs the positional parameter
estimation process on the basis of the specific element in a
combination. The combination includes a reliability parameter with
the highest reliability or a reliability parameter indicating
higher reliability than a predetermined threshold, among the N
number of combinations. Such a configuration makes it possible to
estimate the positional parameter on the basis of a specific
element with the highest reliability or a specific element with
higher reliability than the predetermined threshold, among specific
elements obtained through N number of times of the position
estimation communication. This makes it possible to improve
accuracy of estimating a positional parameter.
[0226] Next, with reference to FIG. 16, a flow of a process will be
described with regard to such an example. FIG. 16 is a flowchart
illustrating an example of a flow of a control process of a
positional parameter estimation process executed by the
communication unit 200 according to the present embodiment on the
basis of the reliability parameters.
[0227] As illustrated in FIG. 16, the communication unit 200 first
repeatedly performs the position estimation communication N number
of times (Step S302).
[0228] Next, the control section 230 detects the specific elements
and calculates the reliability parameters on the basis of CIR s
obtained through the N number of times of position estimation
communication (Step S304). This makes it possible to obtain N
number of combinations of the plurality of specific elements and
reliability parameters detected with regard to the respective
wireless communication sections 210.
[0229] Next, the control section 230 estimates a positional
parameter of the portable device 100 on the basis of N number of
combinations of the specific elements and the reliability
parameters obtained in Step S304 (Step S306). Specifically, the
control section 230 performs the positional parameter estimation
process on the basis of the specific element in a combination
including a reliability parameter with the highest reliability or a
reliability parameter indicating higher reliability than the
predetermined threshold, among the N number of combination.
Second Example
[0230] The control section 230 may repeatedly perform the
positional estimation communication until a reliability parameter
indicating higher reliability than the predetermined threshold is
obtained. In this case, the control section 230 performs the
positional parameter estimation process on the basis of a specific
element detected through position estimation communication through
which the reliability parameter indicating the higher reliability
than the predetermined threshold is obtained. Such a configuration
makes it possible to estimate the positional parameter on the basis
of the specific element with the higher reliability than the
predetermined threshold. This makes it possible to improve accuracy
of estimating a positional parameter.
[0231] Next, with reference to FIG. 17, a flow of a process will be
described with regard to such an example. FIG. 17 is a flowchart
illustrating an example of a flow of a control process of a
positional parameter estimation process executed by the
communication unit 200 according to the present embodiment on the
basis of the reliability parameters.
[0232] As illustrated in FIG. 17, the communication unit 200 first
performs the position estimation communication (Step S402).
[0233] Next, the control section 230 detects the specific element
and calculates the reliability parameter on the basis of a CIR
obtained through the position estimation communication (Step
S404).
[0234] Next, the control section 230 determines whether or not a
reliability parameter indicating higher reliability than the
predetermined threshold is obtained (Step S406).
[0235] The process returns to Step S402 in the case where it is
determined that the reliability parameter indicating higher
reliability than the predetermined threshold is not obtained (NO in
Step S406).
[0236] On the other hand, in the case where it is determined that
the reliability parameter indicating higher reliability than the
predetermined threshold is obtained (YES in Step S406), the
positional parameter of the portable device 100 is estimated on the
basis of the specific element detected through the position
estimation communication through which the reliability parameter is
obtained (Step S408).
Third Example
[0237] The control section 230 does not have to always repeat the
position estimation communication. The control section 230 may
perform the positional parameter estimation process on the basis of
a specific element corresponding to a reliability parameter
indicating higher reliability than the predetermined threshold, at
least with regard to the reliability parameter that is calculable
for each wireless communication section 210. For example, there may
be a situation where only a specific element detected with regard
to the wireless communication section 210A has low reliability
among the specific elements detected with regard to the wireless
communication sections 210A to 210D. In such a situation, the
control section 230 may estimate the positional parameter of the
portable device 100 on the basis of the specific elements detected
with regard to the wireless communication sections 210B to
210D.
[0238] Next, with reference to FIG. 18, a flow of a process will be
described with regard to such an example. FIG. 18 is a flowchart
illustrating an example of a flow of a control process of a
positional parameter estimation process executed by the
communication unit 200 according to the present embodiment on the
basis of the reliability parameters.
[0239] As illustrated in FIG. 18, the communication unit 200 first
performs the position estimation communication (Step S502).
[0240] Next, the control section 230 detects the specific element
and calculates the reliability parameter on the basis of a CIR
obtained through the position estimation communication (Step
S504).
[0241] Next, the control section 230 estimates the positional
parameter on the basis of a specific element corresponding to a
reliability parameter indicating higher reliability than the
predetermined threshold among the specific elements detected in
Step S504 (Step S506).
5. Supplement
[0242] Heretofore, preferred embodiments of the present invention
have been described in detail with reference to the appended
drawings, but the present invention is not limited thereto. It
should be understood by those skilled in the art that various
changes and alterations may be made without departing from the
spirit and scope of the appended claims.
[0243] For example, it is also possible to use a combination of any
two or more reliability parameters among the plurality of
reliability parameters described in the above embodiment.
[0244] For example, in the above-described embodiment, the specific
element is an element whose CIR value exceeds the first path
threshold for the first time. However, the present invention is not
limited thereto. For example, the specific element may be an
element whose CIR value exceeds the first path threshold for the
second time.
[0245] For example, in the above-described embodiment, the receiver
calculates the CIR and calculates the first incoming wave. However,
the present invention is not limited thereto. The receiver may
detect the first incoming wave on the basis of the reception signal
without calculating the CIR. For example, the receiver may use a
condition that the amplitude or reception electric power of the
received wireless signal exceeds a predetermined threshold for the
first time, as the predetermined detection standard for detecting
the first incoming wave. In this case, the receiver may detect a
signal having amplitude or reception electric power that exceeds
the predetermined threshold for the first time, as the first
incoming wave among reception signals.
[0246] For example, in the above-described embodiment, the control
section 230 calculates the CIR, detects the first incoming wave
(that is, specific element), and estimates the positional
parameter. However, the present invention is not limited thereto.
Any of the above-described processes may be performed by the
wireless communication section 210. For example, each of the
plurality of wireless communication sections 210 may calculate the
CIR and detect the first incoming wave on the basis of the
reception signal received by each of the plurality of wireless
communication sections 210. In addition, the positional parameter
may be estimated by the wireless communication section 210 that
functions as the master.
[0247] For example, according to the above-described embodiment,
the description has been given with reference to the example in
which the angles .alpha. and .beta. are calculated on the basis of
antenna array phase differences between antennas in a pair.
However, the present invention is not limited thereto. For example,
the communication unit 200 may calculate the angles .alpha. and
.beta. through beamforming using the plurality of antennas 211. In
this case, the communication unit 200 scans main lobes of the
plurality of antennas 211 in all the directions, determines that
the portable device 100 exists in a direction with largest
reception electric power, and calculates the angles .alpha. and
.beta. on the basis of this direction.
[0248] For example, according to the above-described embodiment, as
described with reference to FIG. 3, the local coordinate system has
been treated as a coordinate system including coordinate axes
parallel to axes connecting the antennas in the pairs. However, the
present invention is not limited thereto. For example, the local
coordinate system may be a coordinate system including coordinate
axes that are not parallel to the axes connecting the antennas in
the pairs. In addition, the origin is not limited to the center of
the plurality antennas 211. The local coordinate system according
to the present embodiment may be arbitrarily set on the basis of
arrangement of the plurality of antennas 211 of the communication
unit 200.
[0249] For example, although the example in which the portable
device 100 serves as the authenticate and the communication unit
200 serves as the authenticator has been described in the above
embodiment, the present invention is not limited thereto. The roles
of the portable device 100 and the communication unit 200 may be
reversed. For example, the positional parameter may be estimated by
the portable device 100. In addition, the roles of the portable
device 100 and the communication unit 200 may be switched
dynamically. In addition, a plurality of the communication units
200 may determine the positional parameters, and perform
authentication.
[0250] For example, although the example in which the present
invention is applied to the smart entry system has been described
in the above embodiment, the present invention is not limited
thereto. The present invention is applicable to any system that
estimates the positional parameter and performs the authentication
by transmitting/receiving signals. For example, the present
invention is applicable to a pair of any two devices selected from
a group including portable devices, vehicles, smartphones, drones,
houses, home appliances, and the like. In this case, one in the
pair operates as the authenticator, and the other in the pair
operates as the authenticate. Note that, the pair may include two
device of a same type, or may include two different types of
devices. In addition, the present invention is applicable to a case
where a wireless local area network (LAN) router estimates a
position of a smartphone.
[0251] For example, in the above embodiment, the standard using UWB
has been exemplified as the wireless communication standard.
However, the present invention is not limited thereto. For example,
it is also possible to use a standard using infrared as the
wireless communication standard.
[0252] Note that, a series of processes performed by the devices
described in this specification may be achieved by any of software,
hardware, and a combination of software and hardware. A program
that configures software is stored in advance in, for example, a
recording medium (non-transitory medium) installed inside or
outside the devices. In addition, for example, when a computer
executes the programs, the programs are read into random access
memory (RAM), and executed by a processor such as a CPU. The
recording medium may be a magnetic disk, an optical disc, a
magneto-optical disc, flash memory, or the like. Alternatively, the
above-described computer program may be distributed via a network
without using the recording medium, for example.
[0253] Further, in the present specification, the processes
described using flowcharts are not necessarily executed in the
order illustrated in the drawings. Some processing steps may be
executed in parallel. In addition, additional processing steps may
be employed and some processing steps may be omitted.
REFERENCE SIGNS LIST
[0254] 1 system [0255] 100 portable device [0256] 110 wireless
communication section [0257] 111 antenna [0258] 120 storage section
[0259] 130 control section [0260] 200 communication unit [0261] 202
vehicle [0262] 210 wireless communication section [0263] 211
antenna [0264] 220 storage section [0265] 230 control section
* * * * *