U.S. patent application number 14/519224 was filed with the patent office on 2015-02-05 for radio communication system, radio communication method, and data transmitter.
This patent application is currently assigned to RENESAS ELECTRONICS CORPORATION. The applicant listed for this patent is Renesas Electronics Corporation. Invention is credited to Haruya ISHIZAKI, Masayuki MIZUNO.
Application Number | 20150038088 14/519224 |
Document ID | / |
Family ID | 46880585 |
Filed Date | 2015-02-05 |
United States Patent
Application |
20150038088 |
Kind Code |
A1 |
ISHIZAKI; Haruya ; et
al. |
February 5, 2015 |
RADIO COMMUNICATION SYSTEM, RADIO COMMUNICATION METHOD, AND DATA
TRANSMITTER
Abstract
Disclosed is a radio communication system capable of reducing
the cost for introducing a system utilizing RFID technology into a
radio network environment. A radio communication system pertaining
to the present invention includes a first radio equipment that
transmits first data using a first radio wave; a data transmitter
that outputs a second radio wave generated by modulating the first
radio wave depending on second data which is an object for
transmission; and a second radio equipment that receives the first
and second radio waves and includes a separation and demodulation
circuit that separates and demodulates the first data transmitted
from the first radio equipment and the second data transmitted from
the data transmitter included in the received radio waves. The data
transmitter includes an amplifier for generating the second radio
wave by amplifying the first radio wave.
Inventors: |
ISHIZAKI; Haruya;
(Kawasaki-shi, JP) ; MIZUNO; Masayuki;
(Kawasaki-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Renesas Electronics Corporation |
Kawasaki-shi |
|
JP |
|
|
Assignee: |
RENESAS ELECTRONICS
CORPORATION
Kawasaki-shi
JP
|
Family ID: |
46880585 |
Appl. No.: |
14/519224 |
Filed: |
October 21, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13566107 |
Aug 3, 2012 |
8891413 |
|
|
14519224 |
|
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|
Current U.S.
Class: |
455/63.1 ;
455/66.1 |
Current CPC
Class: |
H04B 7/24 20130101; H04W
4/80 20180201; H04B 2001/0408 20130101; H03F 3/24 20130101; H04B
1/3822 20130101; H04B 15/00 20130101; H04B 1/04 20130101 |
Class at
Publication: |
455/63.1 ;
455/66.1 |
International
Class: |
H04B 15/00 20060101
H04B015/00; H04B 7/24 20060101 H04B007/24; H04B 1/04 20060101
H04B001/04; H04B 1/38 20060101 H04B001/38 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 6, 2011 |
JP |
2011-194265 |
Claims
1. A radio communication system in an in-vehicle network of a motor
vehicle comprising: a first radio equipment in the motor vehicle
that transmits first data as a first signal using a first radio
wave; a data transmitter in the motor vehicle that comprises: an
amplifier that generates a second signal by modulating the first
radio wave based on second data received from a sensor in the motor
vehicle, and transmits the second signal as a second radio wave;
and a second radio equipment in the motor vehicle that receives the
first radio wave and the second radio wave, and separates and
demodulates the first data transmitted from the first radio
equipment and the second data transmitted from the data
transmitter.
2. The radio communication system in the in-vehicle network of the
motor vehicle according to claim 1, wherein, if a gain control
signal corresponding to the second data is active, the amplifier
amplifies an amplitude the first signal so that the second radio
wave acts as a disturbance to the first radio wave that is received
by the second radio equipment.
3. The radio communication system in the in-vehicle network of the
motor vehicle according to claim 1, wherein the data transmitter
further comprises: a signal antenna for receiving the first radio
wave and transmitting the second radio wave; and a duplexing
element that separates a path for transferring the first signal
corresponding to the received first radio wave to an input of the
amplifier and a path for transferring the second signal to be
transmitted as the second radio wave from an output of the
amplifier to the antenna.
4. The radio communication system in the in-vehicle network of the
motor vehicle according to claim 1, wherein the data transmitter
further comprises: a receiving antenna for receiving the first
radio wave; and a transmitting antenna for transmitting the second
radio wave.
5. The radio communication system in the in-vehicle network of the
motor vehicle according to claim 4, wherein the receiving antenna
and the transmitting antenna are configured as loop antennas and
arranged so as to be rotated 90 degrees relative to each other in
the same plane.
6. The radio communication system in the in-vehicle network of the
motor vehicle according to claim 1, wherein the amplifier
comprises: a first amplifier receives and amplifies the first
signal; a second amplifier that further amplifies the amplified
first signal output from the first amplifier and outputs the second
signal; and a switch provided between the first amplifier and the
second amplifier, wherein the amplifier generates the second signal
by switching the switch between a conducting state and a
non-conducting state depending on the second data.
7. The radio communication system in the in-vehicle network of the
motor vehicle according to claim 1, wherein the data transmitter
further comprises: an attenuator that attenuates the second signal
and generates a third signal, which is the second signal output
from the amplifier fed back via the attenuator, wherein the
amplifier receives input of the first signal and the third signal
and generates the amplified second signal depending on the second
data, and wherein an amount of attenuation by the attenuator is
determined based on an amplitude of the first signal and an
amplitude of the third signal.
8. The radio communication system in the in-vehicle network of the
motor vehicle according to claim 7, wherein the amplifier is
configured as a differential amplifier that takes the respective
inputs of the first signal and the third signal, and wherein an
amount of attenuation by the attenuator is determined so that the
amplitude of the first signal equals the amplitude of the third
signal.
9. The radio communication system in the in-vehicle network of the
motor vehicle according to claim 1, wherein the amplifier is
provided with an amplitude limiting function that limits the power
level of the generated second signal below a prescribed value.
10. The radio communication system in the in-vehicle network of a
motor vehicle according to claim 1, wherein the amplifier includes
a harmonic elimination circuit that eliminates harmonics generated
when generating the second signal.
11. The radio communication system in the in-vehicle network of the
motor vehicle according to claim 1, wherein the data transmitter
further comprises a sensor for acquiring the second data which is
the object for transmission.
12. The radio communication system in the in-vehicle network of the
motor vehicle according to claim 1, wherein the data transmitter
further comprises a data storage unit for storing the second data
which is the object for transmission.
13. The radio communication system in the in-vehicle network of the
motor vehicle according to claim 1, wherein the data transmitter
externally acquires the second data which is the object for
transmission via an input terminal.
14. The radio communication system in the in-vehicle network of the
motor vehicle according to claim 1, wherein the data transmitter
changes the bit error rate of the first radio wave by causing a
disturbance to the first radio wave depending on the second data,
and wherein the second radio equipment demodulates the second data
transmitted from the data transmitter based on changes in the bit
error rate of the first radio wave.
15. The radio communication system in the in-vehicle network of the
motor vehicle according to claim 14, wherein the data transmitter
changes the bit error rate of the first radio wave within a range
lower than a radio standard value of bit error rate.
16. The radio communication system in the in-vehicle network of the
motor vehicle according to claim 14, wherein a modulation cycle of
bit error rate for transmitting the second data is longer than a
modulation cycle of the first radio wave for transmitting the first
data.
17. The radio communication system in the in-vehicle network of the
motor vehicle according to claim 1, wherein the radio communication
system includes a plurality of data transmitters and the second
radio equipment distinguishes a source of the second data based on
respective identification information added to the second data by
each of the data transmitters.
18. A data transmitter in a motor vehicle comprising: an amplifier
that: receives a first data as a first signal transmitted using a
first radio wave by a radio equipment in a motor vehicle; generates
a second signal by modulating the first radio wave based on second
data received from a sensor in the motor vehicle, and outputs the
second signal as a second radio wave.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation Application of U.S.
application Ser. No. 13/566,107, filed Aug. 3, 2012, which is based
on Japanese Patent Application No. 2011-194265 filed on Sep. 6,
2011 including the specification, drawings and abstract, the
disclosures of which are incorporated herein by reference in their
entirety.
BACKGROUND
[0002] The present invention relates to a radio communication
system and method and, particularly, to a radio communication
system and method making it possible to introduce a system
utilizing RFID (Radio Frequency IDentification) technology into a
radio network environment.
[0003] Lately, systems utilizing RFID attract attention and have
begun to be applied for various uses. A basic configuration of a
system using RFID includes an RFID reader/writer that performs data
communication with an RFID radio tag via radio and a computer
terminal that controls the RFID reader/writer. The RFID
reader/writer can read data stored on the radio tag or write data
into the radio tag (see Non-patent Document 1).
[0004] An RFID radio tag does not have a built-in battery, since it
generates a power supply voltage using radio waves when
transmitting and receiving data to and from the RFID reader/writer.
Such a radio tag is generally called "passive-type". Specifically,
in the RFID radio tag, a radio wave (a part of a carrier) supplied
from the RFID reader/writer is rectified from AC to DC by a
full-wave rectifier. The DC voltage is stepped up or down to a
suitable voltage as a circuit power supply by an internal voltage
control circuit or a booster circuit, and then the power is
supplied as a power supply to internal circuits such as a current
mode demodulator and a logic circuit. In this case, the efficiency
of AC to DC conversion in the RFID radio tag can be enhanced by
optimizing the size of a PMOS/NMOS rectifying diode included in the
full-wave rectifier or reducing a loss due to parasitic capacitance
or the like before input to the rectifying diode and a loss due to
mismatch between an antenna and an input of the rectifier.
[0005] A technology concerning an indoor intruder detection
apparatus is disclosed in Patent Document 1. The indoor intruder
detection apparatus disclosed therein includes a transmitting
device, a receiving device, and an alarm device. The transmitting
device transmits an unmodulated radio signal with a given carrier
frequency. The receiving device includes a receiving unit that
receives a signal output from the transmitting device, a detecting
unit that detects the received signal, and a level fluctuation
detecting unit that outputs a detection signal when the level of
the detected signal exceeds a predetermined range. The alarm device
sounds an alarm based on the detection signal output from the level
fluctuation detecting unit of the receiving device. The indoor
intruder detection apparatus disclosed in Patent Document 1 detects
an indoor intruder based on a fluctuation in the received electric
field of radio waves output from the transmitting device and a
fluctuation in the bit error rate of demodulated signals.
[Patent Document 1]
[0006] Japanese Unexamined Patent Application Publication No. Hei7
(1995)-141577
[Non-Patent Document 1]
[0006] [0007] International Solid-State Circuits Conferences 2006
Proceedings, Lecture No. 17.2
SUMMARY
[0008] As described in the Background section, in order to read
data stored in an RFID radio tag (which is also referred to as a
data transmitter), a special RFID reader/writer is required.
Therefore, in order to read data stored in an RFID radio tag under
a radio network (WLAN) environment, for example, a special RFID
reader/writer wired to or wirelessly connected the radio network is
required. Consequently, a problem lies in that it takes cost to
introduce a system utilizing RFID technology into a radio network
environment.
[0009] According to one aspect of the present invention, a radio
communication system includes a first radio equipment that
transmits first data using a first radio wave; a data transmitter
that outputs a second radio wave generated by modulating the first
radio wave depending on second data which is an object for
transmission; and a second radio equipment that receives the first
and second radio waves and includes a separation and demodulation
circuit that separates and demodulates the first data transmitted
from the first radio equipment and the second data transmitted from
the data transmitter included in the received radio waves. The data
transmitter includes an amplifier for generating a second signal by
amplifying a first signal corresponding to the first radio wave,
depending on the second data, and outputs the second signal as the
second radio wave.
[0010] According to another aspect of the present invention, a
radio communication method is used to transmit second data by a
data transmitter over a radio network including a first radio
equipment that transmits first data and a second radio equipment
that receives the first data. The radio communication method
includes the steps of: transmitting the first data from the first
radio equipment using a first radio wave; at the data transmitter,
modulating the first radio wave depending on the second data, thus
generating a second radio wave, and outputting the second radio
wave; and, at the second radio equipment, receiving the first and
second radio waves and separating and demodulating the first data
transmitted from the first radio equipment and the second data
transmitted from the data transmitter included in the received
radio waves. The step of generating and outputting the second radio
wave at the data transmitter includes amplifying a first signal
corresponding to the first radio wave depending on the second data,
thus generating a second signal, and outputting the second signal
as the second radio wave.
[0011] In the radio communication system and method according to
another aspect of the present invention, the data transmitter
modulates the first radio wave depending on second data which is an
object for transmission and outputs the modulated radio wave as the
second radio wave. The thus modulated second radio wave acts as a
disturbance to the first radio wave. Then, the second radio
equipment separates the first data transmitted from the first radio
equipment and the second data transmitted from the data transmitter
by exploiting the presence or absence of a disturbance to the first
radio wave 12 and demodulates the first and second data. Thus,
because there is no need for providing a special RFID reader/writer
to read data stored on the data transmitter, it is possible to
reduce the cost for introducing a system utilizing RFID technology
into a radio network environment. Also, because the second radio
wave yielded by amplifying the first radio wave is output from the
data transmitter, the second data can be transmitted from the data
transmitter to the second radio equipment even if there is some
distance between the data transmitter and the second radio
equipment.
[0012] According to a further aspect of the present invention, a
data transmitter includes a modulation circuit that modulates a
first radio wave being used in a radio network depending on
transmission data which is an object for transmission, thereby
generating a second radio wave that causes a disturbance to the
first radio wave. The modulation circuit includes an amplifier for
generating a second signal by amplifying a first signal
corresponding to the first radio wave, depending on the
transmission data, and outputs the second signal as the second
radio wave.
[0013] According to the aspects of the present invention, it is
possible to provide a radio communication system and method capable
of reducing the cost for introducing a system utilizing RFID
technology into a radio network environment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a block diagram representing a radio communication
system pertaining to a first embodiment;
[0015] FIG. 2 is a block diagram representing a data transmitter
for use in the radio communication system pertaining to the first
embodiment;
[0016] FIG. 3A is a diagram for explaining operation of the data
transmitter shown in FIG. 2;
[0017] FIG. 3B is a diagram for explaining operation of the data
transmitter shown in FIG. 2;
[0018] FIG. 4 is a circuit diagram showing a concrete example of
the data transmitter shown in FIG. 2;
[0019] FIG. 5 is a block diagram showing another example of the
data transmitter for use in the radio communication system
pertaining to the first embodiment;
[0020] FIG. 6 is a block diagram showing yet another example of the
data transmitter for use in the radio communication system
pertaining to the first embodiment;
[0021] FIG. 7 is a diagram for explaining a bit error rate of radio
waves that are received by a second radio equipment pertaining to
the first embodiment;
[0022] FIG. 8 is a block diagram showing another example of the
radio communication system pertaining to the first embodiment;
[0023] FIG. 9 is a diagram showing another example of a second
radio equipment included in the radio communication system
pertaining to the first embodiment;
[0024] FIG. 10 is a block diagram representing a data transmitter
used in a radio communication system pertaining to a second
embodiment;
[0025] FIG. 11A is a diagram for explaining operation of the data
transmitter shown in FIG. 10;
[0026] FIG. 11B is a diagram for explaining operation of the data
transmitter shown in FIG. 10;
[0027] FIG. 12 is a block diagram representing a data transmitter
used in a radio communication system pertaining to a third
embodiment;
[0028] FIG. 13 is a circuit diagram showing a concrete example of
the data transmitter shown in FIG. 12;
[0029] FIG. 14 is a block diagram representing a data transmitter
used in a radio communication system pertaining to a fourth
embodiment;
[0030] FIG. 15 is a diagram for explaining the effect of the
invention pertaining to the fourth embodiment;
[0031] FIG. 16 is a block diagram representing a data transmitter
used in a radio communication system pertaining to a fifth
embodiment;
[0032] FIG. 17 is a diagram for explaining the effect of the
invention pertaining to the fifth embodiment;
[0033] FIG. 18 is a block diagram representing a radio
communication system pertaining to a sixth embodiment;
[0034] FIG. 19 is a block diagram representing a data transmitter
used in the radio communication system pertaining to the sixth
embodiment;
[0035] FIG. 20A is a diagram for explaining operation of the data
transmitter shown in FIG. 19;
[0036] FIG. 20B is a diagram for explaining operation of the data
transmitter shown in FIG. 19;
[0037] FIG. 21 is a circuit diagram showing a concrete example of
the data transmitter shown in FIG. 19;
[0038] FIG. 22 is a diagram for explaining the arrangement of a
receiving antenna and a transmitting antenna of the data
transmitter shown in FIG. 19;
[0039] FIG. 23 is a block diagram representing a radio
communication system pertaining to a seventh embodiment;
[0040] FIG. 24 is a block diagram representing a second radio
equipment used in the radio communication system pertaining to the
seventh embodiment;
[0041] FIG. 25 is a flowchart for explaining operation of the radio
communication system pertaining to the seventh embodiment;
[0042] FIG. 26 is a diagram for explaining noise removal by a
finite impulse response filter;
[0043] FIG. 27 is a diagram representing a relationship between
carrier frequency and data rate of the radio communication
system;
[0044] FIG. 28 is a flowchart for explaining operation of a radio
communication system pertaining to an eighth embodiment.
[0045] FIG. 29A is a block diagram representing a radio
communication system pertaining to a ninth embodiment;
[0046] FIG. 29B is a diagram showing an example of disturbances to
the first radio waves created by each of a plurality of data
transmitters;
[0047] FIG. 30 is diagram representing SN ratio when M-sequence PN
codes are used;
[0048] FIG. 31 is diagram for explaining an example in which the
present invention is applied to an in-vehicle network;
[0049] FIG. 32A is a diagram for explaining a data transmitter
installed on an adhesive member; and
[0050] FIG. 32B is a cross-sectional view for explaining a data
transmitter installed on an adhesive member.
DETAILED DESCRIPTION
First Embodiment
[0051] In the following, embodiments of the present invention will
be described with reference to the drawings. FIG. 1 is a block
diagram representing a radio communication system pertaining to a
first embodiment. As shown in FIG. 1, the radio communication
system pertaining to the first embodiment includes a first radio
equipment 1, a second radio equipment 2, and a data transmitter
(corresponding to an RFID radio tag) 3. The first radio equipment 1
transmits first data using first radio waves 12, 13. The data
transmitter 3 modulates a first radio wave 13 depending on second
data which is an object for transmission and thus generates and
outputs a second radio wave 14. The second radio equipment 2
receives a first radio wave 12 and the second radio wave 14 and
includes a separation and demodulation circuit 24 that separates
and demodulates first data transmitted from the first radio
equipment 1 and second data transmitted from the data transmitter 3
included in the received radio waves. A feature of the radio
communication system pertaining to the present embodiment resides
in that a disturbance from the data transmitter 3 such as an RFID
tag, which was removed as noise in related art, can be isolated and
extracted as data by the separation and demodulation circuit 24 of
the second radio equipment 2. Each of the constituent elements of
the radio communication system pertaining to the present embodiment
will be detailed below.
[0052] The first radio equipment 1 includes internal circuitry (not
shown) and an antenna 11 for implementing radio communication with
the second radio equipment 2 and transmits first data using first
radio waves 12, 13. Here, one first radio wave 12 is a direct radio
wave that is directly transmitted to the second radio equipment 2.
The other first radio wave 13 is received by the data transmitter
3.
[0053] The second radio equipment 2 includes internal circuitry
(not shown) and an antenna 23 for implementing radio communication
with the first radio equipment 1. The separation and demodulation
circuit 24 provided in the second radio equipment 2 separates first
data transmitted from the first radio equipment 1 and second data
transmitted from the data transmitter 3 included in the received
first and second radio waves. Further, the separation and
demodulation circuit 24 demodulates the first data transmitted from
the first radio equipment 1 and the second data transmitted from
the data transmitter 3, respectively.
[0054] Here, the first radio equipment 1 and the second radio
equipment 2 forms a radio network (WLAN). For example, it can be
assumed that the first radio equipment 1 is a base station in WLAN
(a parent node in WLAN) and the second radio equipment 2 is a
receiver in WLAN (a child node in WLAN). Alternatively, for
example, the first radio equipment 1 and the second radio equipment
2 may be configured to enable bidirectional communication. In the
present embodiment, normal data communication between the first
radio equipment 1 and the second radio equipment 2 is performed
through the use of the internal circuitry included each of the
first radio equipment 1 and the second radio equipment 2. Aspects
of the normal data communication between the first radio equipment
1 and the second radio equipment 2 are the same as for related art
and, therefore, detailed explanation thereof is here dispensed
with.
[0055] The radio communication system pertaining to the present
embodiment is not limited to WLAN and can also be widely applied to
any equipment pursuant to existing radio standards such as
Bluetooth (a registered trademark) and mobile or cellular phones,
besides WLAN.
[0056] The data transmitter 3 includes an antenna 31, a modulation
circuit 32, and a sensor 33. The data transmitter 3 receives a
first radio wave 13 output from the first radio equipment 1,
modulates the first radio wave 13 depending on second data which is
an object for transmission by means of the modulation circuit 32,
and thus generates and outputs a second radio wave 14. Here, the
second data that is transmitted by the data transmitter 3 is, for
example, data acquired with the sensor 33. The sensor 33 may be,
for example, a temperature sensor which measures someone's
temperature, a pressure sensor which measures someone's blood
pressure, etc. For example, a data transmitter with a built-in
temperature sensor is attached to a measurement subject and
temperature information for the measurement subject is transmitted
by radio and received over the radio network, so that the
temperature of the measurement subject can be checked
consecutively.
[0057] The sensor 33 is not limited to the temperature sensor or
the pressure sensor and may be any sensor that is capable of
acquiring intended data.
[0058] The modulation circuit 32 generates a second radio wave 14
by modulating the first radio wave 13 depending on second data
which is an object for transmission. Here, for example, the
modulation circuit 32 can generate a second radio wave 14 by load
modulating the first radio wave depending on the second data which
is an object for transmission. That is, the modulation circuit 32
coupled to the antenna 31 of the data transmitter 3 is configured
with a load modulation circuit. By changing matching to the first
radio wave 13 received by the antenna 31, data can be transmitted
to the second radio equipment 2.
[0059] For example, impedance setting for the modulation circuit 32
is set such that an output impedance of the antenna 31 and an input
impedance of the modulation circuit 32 match in a real part and the
absolute values of both impedances match with sign inversion in an
imaginary part. Then, the efficiency of power transfer from the
antenna 31 to the inside of the data transmitter 3 is maximized
and, ideally, radio wave received by the antenna 31 is not
reflected again. In other words, the second radio wave is not
output from the antenna 31.
[0060] On the other hand, when the above impedance setting with
regard to the output impedance of the antenna 31 and the input
impedance of the modulation circuit 32 is cleared, the first radio
wave 13 which has been input from the antenna 31 is reflected by
impedance mismatch. This reflected wave is radiated as the second
radio wave 14.
[0061] Then, this reflected wave (second radio wave 14) acts as a
disturbance to the first radio wave 12. Thus, by detecting whether
this disturbance is present at the second radio equipment 2, binary
data can be transmitted from the data transmitter 3 to the second
radio equipment 2.
[0062] However, the load modulation as above is performed on the
data transmitter 3 without being supplied with external power.
Hence, it is impossible to transmit from the antenna 31 the second
radio wave 14 with a strength larger than the strength of the first
radio wave 13 received by the antenna 31. In other words, the
reflected wave (second radio wave 14) reflected by impedance
mismatch becomes weaker in strength than the first radio wave 13
received by the antenna 31. Therefore, in a case where a load
modulation circuit is used as the modulation circuit 32, power
consumption can be kept low, but there is a problem in which the
communication distance between the data transmitter 3 and the
second radio equipment 2 is restricted to a short distance.
[0063] In order to solve this problem, accordingly, a data
transmitter 3 that is shown in FIG. 2 can be used as the data
transmitter 3 in the radio communication system pertaining to the
present embodiment. The data transmitter 3 shown in FIG. 2 includes
an antenna 31, a modulation circuit 32, and a sensor 33. The
modulation circuit 32 includes an amplifier (variable gain
amplifier) 35 and a duplexing element 37. The modulation circuit 32
generates a second radio wave 14 by modulating the first radio wave
13 depending on second data which is an object for
transmission.
[0064] In particular, the amplifier 35 provided in the modulation
circuit 32 amplifies a first signal 15 corresponding to the first
radio wave 13 received by the antenna 31, depending on second data,
and thus generates a second signal 16. The generated second signal
16 is radiated as the second radio wave 14 from the antenna 31. The
amplifier 35 is capable of changing its amplification factor
according to a gain control signal 36. Here, a value of the gain
control signal 36 corresponds to second data which is an object for
transmission.
[0065] The duplexing element 37 has a function of separating a path
17 (see FIG. 3A) for inputting the first signal 15 corresponding to
the first radio wave 13 received by the antenna 31 to the amplifier
35 and a path 18 (see FIG. 3A) for outputting the second signal 16
amplified by the amplifier 35 from the amplifier 35 to the antenna
31. As the duplexing element 37, for example, a directional coupler
can be used. That is, the duplexing element 37 is configured to
allow power transfer from the antenna 31 to the input of the
amplifier 35 and power transfer from the output of the amplifier 35
to the antenna 31. In other words, the duplexing element 37 is
configured such that it can close off power transfer from the
output of the amplifier 35 to the input of the amplifier 35, power
transfer from the input of the amplifier 35 to the output of the
amplifier 35, power transfer from the input of the amplifier 35 to
the antenna 31, and power transfer from the antenna 31 to the
output of the amplifier 35.
[0066] For example, as shown in FIG. 3A, if second data which is an
object for transmission is "1" (i.e., the gain control signal 36 is
"1" (active state)), the amplifier 35 amplifies the first signal 15
corresponding to the first radio wave 13 received by the antenna 31
and generates the second signal 16 with a larger amplitude. The
generated second signal 16 is radiated from the antenna 31 as the
second radio wave 14 which acts as a disturbance to the first radio
wave 12. At this time, it is possible to output a stronger second
radio wave 14 from the antenna 31 by increasing the amplification
factor of the amplifier 35. In this way, data of "1" is transmitted
from the data transmitter 3 to the second radio equipment 2.
[0067] On the other hand, as shown in FIG. 3B, if second data which
is an object for transmission is "0" (i.e., the gain control signal
36 is "0" (inactive state)), the amplifier 35 regulates the
amplitude of the first signal 15 corresponding to the first radio
wave 13 received by the antenna 31 to a sufficiently small
amplitude. Thus, in this case, because the second signal 16 with a
sufficiently small amplitude is output from the amplifier 35, the
second radio wave 14 radiated from the antenna 31 does not act as a
disturbance to the first radio wave 12. In this way, data of "0" is
transmitted from the data transmitter 3 to the second radio
equipment 2. If the gain control signal 36 is "0", the amplifier 35
may regulate the amplitude of the first signal 15 corresponding to
the first radio wave 13 received by the antenna 31 to zero. At this
time, no second signal 16 is output from the amplifier 35 and,
thus, no second radio wave 14 is output from the antenna 31.
[0068] FIG. 4 is a circuit diagram representing a concrete example
of the data transmitter 3 shown in FIG. 2. The data transmitter 3
shown in FIG. 4 is one example and, in the present embodiment, any
data transmitter that can implement the operation described above
can be used, not limited to the data transmitter shown in FIG.
4.
[0069] As shown in FIG. 4, the amplifier (single-end amplifier) 35
includes N-type transistors Tr1, Tr2, capacitors C1, C2, and
resistors R1, R2, R3. To one end of a capacitor C1, the first
signal 15 corresponding to the first radio wave 13 received by the
antenna 31 is supplied. The other end of the capacitor C1 is
coupled to one end of a resistor R1 and a gate of an N-type
transistor Tr2. A bias voltage bias_1 is supplied to the other end
of the resistor R1. A drain of the N-type transistor Tr2 is coupled
to a source of an N-type transistor Tr1 and a source of the N-type
transistor Tr2 is grounded.
[0070] The gain control signal 36 is supplied to a gate of the
N-type transistor Tr1. A drain of the N-type transistor Tr1 is
coupled to one end of a resistor R2 and one end of a capacitor C2.
The other end of the resistor R2 is coupled to a power supply VDD.
The other end of the capacitor C2 is coupled to one end of a
resistor R3. A bias voltage bias_2 is supplied to the other end of
the resistor R3. The second signal 16 amplified by the amplifier 35
is output from a node node_1 at which the other end of the
capacitor C2 and the one end of the resistor R2 are coupled.
[0071] In the amplifier 35 shown in FIG. 4, if the gain control
signal 36 is "0", the N-type transistor Tr1 is put in an off state
and, thus, no amplified signal is output from the node node_1. On
the other hand, if the gain control signal 36 is "1", the N-type
transistor Tr1 is put in an on state. At this time, the first
signal 15 increased as much as the bias voltage bias_1 is supplied
to the gate of the N-type transistor Tr2. Thereby, the N-type
transistor Tr2 operates in response to the first signal 15 and,
thus, the second signal 16 yielded by amplifying the first signal
15 is output from the node node_1. The amplified signal is supplied
via the duplexing element 37 to the antenna 31 and radiated as the
second radio wave 14 from the antenna 31.
[0072] By using the data transmitter 3 equipped with the amplifier
35 described above, it is possible to transmit second data from the
data transmitter 3 to the second radio equipment 2 even if there is
some distance between the data transmitter 3 and the second radio
equipment 2. For example, let us assume the following: the gain of
the amplifier 35 is 10 dB, the communication distance between the
data transmitter 3 and the second radio equipment 2 when the
amplifier 35 is not used is r, the communication distance between
the data transmitter 3 and the second radio equipment 2 when the
amplifier 35 is used is r'. Besides, assuming that a difference
between the attenuations by the respective communication distances
is 10 dB and the attenuations by the distances are in accordance
with a Friis transmission equation, the following equation can be
derived.
20 log(4.pi.r'/.lamda.)-20 log(4.pi.r/.lamda.)=10 Equation 1
[0073] Hence, r'=3.2r is calculated from the above equation. In the
case where the amplifier 35 is used in the modulation circuit 32,
the communication distance between the data transmitter 3 and the
second radio equipment 2 can be increased by a factor of 3.2.
[0074] Second data that is transmitted by the data transmitter 3
may be data provided beforehand in the data transmitter 3. In this
case, the data transmitter 3 does not need to include a sensor and
can be configured including a data storage unit 38 for storing
data, as shown in FIG. 5. Also, second data that is transmitted by
the data transmitter 3 may be externally acquired data. In this
case, the data transmitter 3 includes an input terminal 39, as
shown in FIG. 6, and the data transmitter 3 can acquire external
data 40 via the input terminal 39. Here, a value of the acquired
external data 40 corresponds to the gain control signal 36.
[0075] The data transmitter 3 may include a power generating
circuit 34 as in another example of the radio communication system
pertaining to the present embodiment, which is shown in FIG. 8.
That is, the power generating circuit 34 provided in a data
transmitter 30 shown in FIG. 8 receives a first radio wave
(environmental radio wave) 13 through an antenna 31 and rectifies
the first radio wave (environmental radio wave) 13 from AC to DC by
a full-wave rectifier. After the voltage of the resulting DC power
is increased or decreased to a voltage suitable for a circuit power
supply by using an internal voltage control circuit and a booster
circuit, the power generating circuit 34 can supply this power to
the modulation circuit 3, sensor 33, and other components. In this
case, the data transmitter 30 does not need a battery installed
therein and is configured as a so-called passive-type data
transmitter. On the other hand, the data transmitter 3 may have a
built-in battery and, in this case, it is configured as a so-called
active-type data transmitter. In the case of the active type, the
remaining amount of the battery may be included as second data that
is transmitted by the data transmitter 3. In this case also, by
providing the amplifier 35 in the modulation circuit 32, the
communication distance between the data transmitter 3 and the
second radio equipment 2 can further be extended.
[0076] Then, descriptions are provided for operation of the radio
communication system pertaining to the present embodiment. The
first radio equipment 1 and the second radio equipment 2 shown in
FIG. 1 forms a radio network (WLAN). In particular, the first radio
equipment 1 and the second radio equipment 2 are configured to
enable communication using the first radio wave 12 having
components modulated in accordance with a standard.
[0077] FIG. 7 is a diagram for explaining a bit error rate of radio
waves (the first radio wave 12 and second radio wave 14) that are
received by the second radio equipment. If there is not data
transmission from the data transmitter 3, the first radio wave 12
is not affected by the second radio wave 14 transmitted from the
data transmitter 3. That is, in this case, the second radio wave 14
transmitted from the data transmitter 3 does not act as a
disturbance to the first radio wave 12 and, thus, the bit error
rate does not rise, as indicated by a reference numeral 71 in FIG.
7. Therefore, the first radio equipment 1 and the second radio
equipment 2 can perform communication at a low bit error rate
(reference numeral 71) shown in FIG. 7. The second radio equipment
2 receives the first radio wave 12 by the antenna 23 and the
separation and demodulation circuit 24 demodulates first data
transmitted from the first radio equipment 1.
[0078] Next, a case where the data transmitter 3 transmits data is
discussed. In this case, the data transmitter 3 first receives a
first radio wave 13 which has been output from the first radio
equipment 1. Also, the sensor 33 outputs data acquired by the
sensor 33 to the modulation circuit 32. Then, the modulation
circuit 32 modulates the received first radio wave 13 depending on
the data acquired by the sensor 33 (second data which is an object
for transmission) and outputs the modulated radio wave as the
second radio wave 14.
[0079] In the case where the data transmitter 3 transmits data, the
first radio wave 12 is affected by the second radio wave 14
transmitted from the data transmitter 3, as shown in FIG. 7.
Therefore, in this case, the second radio wave 14 transmitted from
the data transmitter 3 acts as a disturbance to the first radio
wave 12 and, consequently, the bit error rate rises, as indicated
by a reference numeral 72 in FIG. 7.
[0080] That is, the second radio wave generated by undergoing
modulation in the data transmitter 3 disturbs the first radio wave
12 transmitted from first radio equipment 1 and deteriorates the
received SN ratio, thus causing the bit error rate to rise. That
is, on/off keying modulation, if applied in the data transmitter 3,
enables the transmission of second data, exploiting fluctuations in
the bit error rate over time as shown in FIG. 7. By detecting these
fluctuations in the bit error rate over time at the second
receiving equipment 2, it is possible to demodulate the second data
transmitted from the data transmitter 3.
[0081] The bit error rate 72 which is raised should fall within a
range lower than a radio standard value of bit error rate, so that
it does not have an adverse effect on the communication between the
first radio equipment 1 and the second radio equipment 2. That is,
both the bit error rate 71 and the bit error rate 72 should fall
within a range lower than a radio standard value of bit error rate.
In general, a communication environment changes at all times and is
subjected to various disturbances and, thus, radio standards are
established to ensure robustness of communication against such
disturbances.
[0082] The second radio equipment 2 receives the first radio wave
12 and the second radio wave 14 by the antenna 23. Then, the
separation and demodulation circuit 24 separates and demodulates
first data transmitted from the first radio equipment 1 and second
data transmitted from the data transmitter 3 included in these
received radio waves and generates demodulated data 25 from the
first radio equipment 1 and demodulated data 26 from the data
transmitter 3.
[0083] Here, the first data which is transmitted by the first radio
equipment 1 is carried on the first radio wave 12 having components
modulated in accordance with a standard supported by the first
radio equipment 1 and the second radio equipment 2 (that is, the
radio wave having a carrier frequency pursuant to a standard). On
the other hand, the second data which is transmitted by the data
transmitter 3 is conveyed by exploiting changes in the bit error
rate (i.e., fluctuations in the bit error rate) of the radio waves
(first and second radio waves) received by the second radio
equipment 2.
[0084] When the second radio equipment 2 receives the radio waves,
a cycle of changes in the bit error rate of the radio waves (that
is, a modulation cycle of bit error rate) is longer than a
modulation cycle of the first radio wave 12 having a carrier
frequency pursuant to a standard. Accordingly, it is possible to
separate the first data transmitted from the first radio equipment
1 and the second data transmitted from the data transmitter 3 by
means of the separation and demodulation circuit 24. For example,
the separation and demodulation circuit 24 has a low-pass filter
(LPF) and can isolate the second data for which the modulation
cycle of bit error rate is longer by using the low-pass filter
(LPF). Alternatively, for example, the separation and demodulation
circuit 24 may be provided with a band-pass filter (BPF); in this
case also, it can isolate the second data for which the modulation
cycle of bit error rate is longer by using the band-pass filter
(BPF). Here, the band-pass filter (BPF) can be configured by
combining a low-pass filter (LPF) and a high-pass filter (HPF). At
the same time, by using the high-pass filter (HPF), fluctuating
components of environmental radio waves, which have a modulation
cycle longer than a fluctuation cycle of second data, can be
removed from the second data. The separation and demodulation
circuit 24 may be a filtering circuit for analog signals or a
filtering circuit for digital signals after A/D conversion.
[0085] FIG. 8 is a block diagram showing another example of the
radio communication system pertaining to the present embodiment. As
shown in FIG. 8, a first radio wave 12 and a second radio wave 14
received by the antenna 23 of the second radio equipment 2 may be
amplified by an amplifier 27. Also as shown in FIG. 8, a baseband
filter 28 may be used as the separation and demodulation circuit
24. An additional filter may be provided, as appropriate, depending
on radio wave conditions in surroundings. Filtering may be
performed for a frequency band in which the second radio wave 14 is
strong. By the amplifier 27 and the filtering, the signal amplitude
can be increased to a level that separation and demodulation
processing can be performed by the following separation and
demodulation circuit 24 (baseband filter 28).
[0086] The separation and demodulation circuit 24 provided in the
second radio equipment 2 shown in FIG. 1 can be configured as
follows. FIG. 9 is a diagram showing a configuration of a second
radio equipment 22 in the radio communication system pertaining to
the present embodiment. The second radio equipment 22 shown in FIG.
8 includes an antenna 23, a receiving circuit 81, and a protocol
processing unit 82 and this configuration is the same as for
existing radio equipment. Now, the protocol processing unit 82 is
customized by software implementation so that the protocol
processing unit 82 of the second radio equipment 22 operates as the
separation and demodulation circuit 24 described above. In this
way, by software implementation to customize the protocol
processing unit 82, the second radio equipment 2 shown in FIG. 1
can be configured using existing radio equipment. In the present
embodiment, a part of the protocol processing unit shown in FIG. 9
may be configured by hardware. In this case, the remaining part of
the protocol processing unit other than the part configured by
hardware is customized by software implementation. The second radio
equipment 2 can also be configured in this way.
[0087] More specifically, the first data which is transmitted by
the first radio equipment 1 is carried on the first radio wave 12
having components modulated in accordance with a standard supported
by the first radio equipment 1 and the second radio equipment 2
(that is, the radio wave having a carrier frequency pursuant to a
standard). On the other hand, the second data which is transmitted
by the data transmitter 3 is conveyed by exploiting changes in the
bit error rate (i.e., fluctuations in the bit error rate) of the
radio waves (first and second radio waves) received by the second
radio equipment 2. And the protocol processing unit 82 is
customized by software implementation to separate and demodulate
the first data transmitted by the first radio equipment 1 (that is,
data transmitted with a carrier frequency pursuant to a standard)
and the second data transmitted by the data transmitter 3 (that is,
data transmitted by exploiting a bit error rate modulated by a
given modulating frequency), respectively. Thereby, demodulated
data 25 from the first radio equipment 1 and demodulated data 26
from the data transmitter 3 can be acquired. Such processing in the
protocol processing unit 82 is performed in a baseband domain.
[0088] Under a radio network environment, heretofore, a special
RFID reader/writer wired to or wirelessly connected to the radio
network was needed to read data stored on an RFID radio tag (data
transmitter). Consequently, a problem existed in which the
introduction of a system utilizing an RFID technology into a radio
network environment is costly.
[0089] However, in the radio communication system pertaining to the
present embodiment, under the environment of the radio network
formed by the first radio equipment 1 and the second radio
equipment 2, the data transmitter 3 generates and outputs the
second radio wave 14 by modulating the first radio wave 13
depending on second data which is an object for transmission. Here,
the modulated second radio wave 14 acts as a disturbance to the
first radio wave 12. Then, the separation and demodulation circuit
24 of the second radio equipment 2 separates the first data
transmitted from the first radio equipment 1 and the second data
transmitted from the data transmitter 3 by exploiting the presence
or absence of a disturbance to the first radio wave 12 and
demodulates the first and second data.
[0090] In the thus configured radio communication system pertaining
to the present embodiment, there is no need for providing a special
RFID reader/writer to read data stored on an RFID radio tag (data
transmitter 3). Therefore, according to the invention pertaining to
the present embodiment, it is possible to provide a radio
communication system capable of reducing the cost for introducing a
system utilizing RFID technology into a radio network
environment.
[0091] Further, in the radio communication system pertaining to the
present embodiment, it is possible to configure the second radio
equipment by software implementation to customize the protocol
processing unit 82 of the second radio equipment 22 having an
existing hardware structure shown in FIG. 9 to operate as the
separation and demodulation circuit 24 shown in FIG. 1. Therefore,
because the second radio equipment pertaining to the present
embodiment can be configured only by introducing software into the
existing hardware structure, it is possible reduce the cost for
introducing a system utilizing RFID technology into a radio network
environment.
[0092] Further, in the radio communication system pertaining to the
present embodiment, the amplifier 35 is provided in the modulation
circuit 32 of the data transmitter 3, as shown in FIG. 2. In this
way, the provision of the amplifier 35 in the modulation circuit 32
can boost the output of the generated second radio wave 14. Thus,
the second data can be transmitted from the data transmitter 3 to
the second radio equipment 2, even if there is some distance
between the data transmitter 3 and the second radio equipment
2.
[0093] For a passive-type data transmitter 3 which generates a
power supply voltage using radio waves, when radio waves are
transmitted by a special RFID reader/writer to supply power to the
data transmitter 3, some of the radio waves is not directed to the
data transmitter 3. That is, if the RFID reader/writer has a
non-directional antenna, there is wasted power of radio waves not
directed to the data transmitter 3. Even though the RFID
reader/writer has a directional antenna and the efficiency of power
transfer is enhanced, wasted and lost power in air still remains as
long as power is carried on radio waves.
[0094] By contrast, in the radio communication system pertaining to
the present embodiment shown in FIG. 8, the power generating
circuit 34 of the data transmitter 30 generates power using radio
waves (environmental radio waves) that are used for communication
between the first radio equipment 1 and the second radio equipment
2. Therefore, because there is no need for newly introducing an
RFID reader/writer to output radio waves for power supply, it is
possible to reduce power consumption of the radio communication
system.
[0095] The technology disclosed in Patent Document 1 only detects
the presence or absence of a disturbance, but is incapable of
discriminating between a disturbance fluctuating over time and data
and discriminating between an undesired disturbance source and a
desired disturbance. Stated differently, such a radio communication
system is subjected to various disturbances due to a changing
communication environment, which results in a changing bit error
rate. The art disclosed in Patent Document 1 only detects whether a
disturbance has changed simply based on the bit error rate, but
does not extract a desired disturbance as significant data. By
contrast, in the radio communication system pertaining to the
present embodiment, second data (data transmitted from the data
transmitter) for which the modulation cycle of bit error rate is
longer is isolated by means of the separation and demodulation
circuit and the second data is demodulated. Thus, it become
possible to derive communication data from a desired disturbance,
remove noise, which is requisite for fulfilling radio data
communication, and select a communication partner in
one-to-multiple communication (for detail, see a ninth embodiment),
which were impossible in the art disclosed in Patent Document
1.
[0096] Another aspect of the present invention relates to a radio
communication method for transmitting second data by a data
transmitter 3 over a radio network including a first radio
equipment 1 that transmits first data and a second radio equipment
2 that receives the first data. The radio communication method
includes the following steps: (1) transmitting the first data from
the first radio equipment 1 using first radio waves 12, 13; (2) at
the data transmitter 3, modulating a first radio wave 13 depending
on second data, thus generating a second radio wave 14, and
outputting the second radio wave 14; and (3) at the second radio
equipment 2, receiving the first radio wave 12 and the second radio
wave 14 and separating and demodulating the first data transmitted
from the first radio equipment 1 and the second data transmitted
from the data transmitter 3 included in the received radio waves.
When generating and outputting the second radio wave 14, the data
transmitter 3 amplifies a first signal 15 corresponding to the
first radio wave 13 depending on the second data, thus generates a
second signal 16, and radiates the second signal 16 as the second
radio wave 14. In order to amplify the first radio wave 13
depending on the second data, the amplifier 35, for example, shown
in FIG. 2 can be used.
[0097] According to the embodiment of the present invention
described in the foregoing context, it is possible to provide a
radio communication system and a radio communication method capable
of reducing the cost for introducing a system utilizing RFID
technology into a radio network environment. Further, in the
present invention pertaining to the present embodiment, because the
amplifier 35 is provided in the modulation circuit 32 of the data
transmitter 3, the second data can be transmitted from the data
transmitter 3 to the second radio equipment 2, even if there is
some distance between the data transmitter 3 and the second radio
equipment 2.
Second Embodiment
[0098] Next, a second embodiment of the present invention is
described. FIG. 10 is a block diagram representing a data
transmitter 503 included in a radio communication system pertaining
to the second embodiment. In the radio communication system
pertaining to the present embodiment, the modulation circuit 532 of
the data transmitter 503 is provided with two amplifiers 534, 535
and a switch 536, which differs from the radio communication system
of the first embodiment (particularly, see FIG. 2). Because others
are the same as the radio communication system of the first
embodiment and, the same components are assigned the same reference
numerals and duplicative description is dispensed with.
[0099] The data transmitter 503 shown in FIG. 10 includes an
antenna 31, a modulation circuit 532, and a sensor 33. The
modulation circuit 532 includes two amplifiers (variable gain
amplifiers) 534. 534, a switch 536, and a duplexing element 538.
The duplexing element 538 is basically the same as the duplexing
element 37 described in the first embodiment. That is, the
duplexing element 538 has a function of separating a path 517 (see
FIG. 11A) for inputting a first signal 515 corresponding to the
first radio wave 13 received by the antenna 31 to an amplifier 534
and a path 518 (see FIG. 11A) for outputting an amplified second
signal 516 from an amplifier 535 to the antenna 31. As the
duplexing element 538, for example, a directional coupler can be
used.
[0100] Besides, the switch 536 is provided between the amplifier
534 and the amplifier 535. The switch 536 makes and breaks an
electrical contact between the amplifier 534 and the amplifier 535
according to a control signal 537 corresponding to second data
which is an object for transmission.
[0101] For example, as shown in FIG. 11A, if second data which is
an object for transmission is "1" (i.e., the control signal 537 is
"1"), the switch 536 is put in a conducting state and the amplifier
534 and the amplifier 535 are coupled to each other via the switch
536. At this time, the amplifier 534 and the amplifier 535 amplify
the first signal 515 corresponding to the first radio wave 13
received by the antenna 31 and thus generates the second signal
516. The generated second signal 516 is radiated from the antenna
31 as the second radio wave 14 which acts as a disturbance to the
first radio wave 12. At this time, by amplifying the amplitude of
the first radio wave 13 using the amplifier 534 and the amplifier
535, the stronger second radio wave 14 can be output from the
antenna 31. In this way, data of "1" is transmitted from the data
transmitter 503 to the second radio equipment 2.
[0102] On the other hand, as shown in FIG. 11B, if second data
which is an object for transmission is "0" (i.e., the control
signal 36 is "0"), the switch 536 is put in a non-conducting state
and the amplifier 534 and the amplifier 535 are uncoupled. Thus,
because the signal amplified by the amplifier 534 is not supplied
to the amplifier 535, the second signal 516 is not output from the
amplifier 535. Therefore, the second radio wave 14 is not radiated
from the antenna 31. In this way, data of "0" is transmitted from
the data transmitter 503 to the second radio equipment 2.
[0103] In this case, the amplifier 534 following the antenna 31 is
configured as a low noise amplifier and the amplifier 535 that
outputs the second signal 516 to the antenna 31 is configured as a
high gain amplifier matched with the antenna 31. Thereby, the SN
ratio of a signal can be minimized and it is possible to extend the
communication distance between the data transmitter 503 and the
second radio equipment 2.
[0104] As described above, in the radio communication system
pertaining to the present embodiment, the amplifiers 534, 535 are
provided in the modulation circuit 532 of the data transmitter 503,
as shown in FIG. 10. In this way, the provision of the amplifiers
534, 535 in the modulation circuit 532 can boost the output of the
generated second radio wave 14. Thus, the second data can be
transmitted from the data transmitter 503 the second radio
equipment 2, even if there is some distance between the data
transmitter 503 and the second radio equipment 2.
Third Embodiment
[0105] Next, a third embodiment of the present invention is
described. In the data transmitter 3 shown in FIG. 2, the second
signal 16 is prevented from being fed back to the amplifier 35 by
means of the duplexing element 37. However, if the function of the
duplexing element 37 is insufficient, a part of the second signal
16 might be fed back to the amplifier 35. In such a case, the
modulation circuit might oscillate depending on setting of circuit
design parameters (amplification factor or the like, phase margin,
etc.)
[0106] In the radio communication system pertaining to the third
embodiment, a data transmitter is described in which the
oscillation of a modulation circuit can be avoided. Because others
are the same as the radio communication system of the first
embodiment and, the same components are assigned the same reference
numerals and duplicative description is dispensed with.
[0107] FIG. 12 is a block diagram representing a data transmitter
used in the radio communication system pertaining to the present
embodiment. The data transmitter 603 shown in FIG. 12 includes a
modulation circuit 632 and a sensor 33. The modulation circuit 632
includes a duplexing element 633, an amplifier 634, an attenuator
635, signal strength detectors 638, 639, and an operational
amplifier AMP11.
[0108] The duplexing element 633 is basically the same as the
duplexing element 37 described in the first embodiment. That is,
the duplexing element 633 has a function of separating a path for
inputting a first signal 611 corresponding to the first radio wave
13 received by the antenna 31 to the amplifier 634 and a path for
outputting an amplified second signal 613 from the amplifier 634 to
the antenna 31. As the duplexing element 633, for example, a
directional coupler can be used.
[0109] As the amplifier 634, for example, a variable gain amplifier
with two inputs can be used. The amplifier 634 takes the inputs of
a first signal 611 corresponding to the first radio wave 13
received by the antenna 31 and a signal (third signal) which has
been output from the attenuator 635 and generates an amplified
second signal 613 according to a gain control signal 637. The
generated second signal 613 is supplied via the duplexing element
633 to the antenna 31 and radiated as the second radio wave 14 from
the antenna 31.
[0110] For example, if the gain control signal 637 is "1", the
amplifier takes the inputs of the first signal 611 corresponding to
the first radio wave 13 received by the antenna 31 and the signal
612 output from the attenuator 635 and generates the amplified
second signal 613. The generated second signal 613 is radiated from
the antenna 31 as the second radio wave 14 which acts as a
disturbance to the first radio wave 12. In this way, data of "1" is
transmitted from the data transmitter 603 to the second radio
equipment.
[0111] On the other hand, if the gain control signal 637 is "0",
the amplifier 634 takes the inputs of the first signal 611
corresponding to the first radio wave 13 received by the antenna 31
and the signal 612 output from the attenuator 635 and generates a
second signal 613 with a reduced amplitude. In this case, the
second signal 613 that is output from the amplifier 634 is a signal
with a sufficiently small amplitude and, thus, does not act as a
disturbance to the first radio wave 12. In this way, data of "0" is
transmitted from the data transmitter 603 to the second radio
equipment. If the gain control signal 637 is "0", the amplifier 634
may regulate the amplitude of the first signal 611 corresponding to
the first radio wave 13 received by the antenna 31 to zero. At this
time, no second signal 613 is output from the amplifier 634 and,
thus, no second radio wave 14 is radiated from the antenna 31.
[0112] The attenuator 635 attenuates the second signal 613 which
has been output from the amplifier 634 to a level that is as strong
as the first signal 611 and outputs the attenuated signal 612 to
the amplifier 634. That is, the second signal 613 which has been
output from the amplifier 634 is fed back via the attenuator 635 to
the amplifier 634.
[0113] A signal strength detector 638 detect the strength of the
signal 612 that has been output from the attenuator 635 and outputs
a signal corresponding to the detected signal strength to an
inverting input terminal of the operational amplifier AMP11. A
signal strength detector 639 detects the strength of the first
signal 611 corresponding to the first radio wave 13 received by the
antenna 31 and outputs a signal corresponding to the detected
signal strength to a non-inverting input terminal of the
operational amplifier AMP11. The signal strength detectors 638, 639
are, for example, the circuits capable of converting an amplitude
level of the signals 611, 612 to a DC voltage.
[0114] The operational amplifier AMP11 adjusts the amount of
attenuation by the attenuator 635 so that the strength of the first
signal 611 detected by the signal strength detector 639 equals the
strength of the signal 612 detected by the signal strength detector
638.
[0115] Stated differently, in the modulation circuit 632 shown in
FIG. 12, the second signal 613 that has been output from the
amplifier 634 is attenuated to be as strong as the first signal 611
and the attenuated signal 612 is fed back to the amplifier 634.
Then, the output of the amplifier 634 is decreased by the signal
612. Thereby, a feedback loop through the amplifier 634 can be
stabilized and it is possible to avoid the oscillation of the
modulation circuit 632. In this case, the signal strength detectors
638, 639, the operational amplifier AMP11, and the attenuator 635
form a feedback loop so that the strength of the first signal 611
corresponding to the first radio wave 13 received by the antenna 31
equals the strength of the signal 612 that has been output from the
attenuator 635.
[0116] FIG. 13 is a circuit diagram showing a concrete example of
the data transmitter 603 shown in FIG. 12. The data transmitter 603
shown in FIG. 13 is one example and, in the present embodiment, any
data transmitter that can implement the operation described above
can be used, not limited to the data transmitter shown in FIG.
13.
[0117] As shown in FIG. 13, the amplifier 634 includes P-type
transistors Tr11, Tr12 and N-type transistors Tr13 to Tr15. A
source of a P-type transistor Tr11 is coupled to a power supply VDD
and its gate and drain are coupled to a gate of a P-type transistor
Tr12. For the P-type transistor Tr12, its source is coupled to the
power supply VDD, its gate is coupled to the gate and drain of the
P-type transistor Tr11, and its drain is coupled to a drain of an
N-type transistor Tr14.
[0118] A drain of an N-type transistor Tr13 is coupled to the gate
and drain of the P-type transistor Tr11 and to the gate of the
P-type transistor Tr12. The first signal 611 is supplied to a gate
of the N-type transistor Tr13. The drain of the N-type transistor
Tr14 is coupled to the drain of the P-type transistor Tr12. The
signal 612 is supplied to a gate of the N-type transistor Tr14. The
sources of the N-type transistor Tr13 and the N-type transistor
Tr14 are coupled to a drain of an N-type transistor Tr15. A source
of the N-type transistor Tr15 is grounded and its gate is supplied
with the gain control signal 637. The second signal 613 is output
from a node at which the drain of the P-type transistor Tr12 and
the drain of the N-type transistor Tr14 are coupled. In other
words, the amplifier 634 is configured as a differential
amplifier.
[0119] The signal strength detector 638 is configured with a diode
D11 for half-wave rectification and a capacitor C11. The signal 612
is supplied to an anode of the diode D11 and its cathode is coupled
to one end of the capacitor C11. The other end of the capacitor C11
is grounded.
[0120] The signal strength detector 639 is configured with a diode
D12 for half-wave rectification and a capacitor C12. The first
signal 611 is supplied to an anode of the diode D12 and its cathode
is coupled to one end of the capacitor C12. The other end of the
capacitor C12 is grounded.
[0121] The attenuator 635 is configured with a variable resistor
VR11. The second signal 613 is supplied to one end of the variable
resistor VR11 and the signal 612 is output from its other end. A
resistance value of the variable resistor VR11 is adjusted based on
a signal that is output from the operational amplifier AMP11.
[0122] In the data transmitter 603 shown in FIG. 13, if the gain
control signal 637 is "0", the N-type transistor Tr15 is put in an
off state. In this case, no amplified second signal 613 is output
from the amplifier 634. On the other hand, if the gain control
signal 637 is "1", the N-type transistor Tr15 is put in an on
state. In this case, the second signal 613 amplified depending on
the first signal 611 and the signal 612 is output from the
amplifier 634. The amplified second signal 613 is supplied via the
duplexing element 633 to the antenna 31 and radiated as the second
radio wave 14 from the antenna 31
[0123] The signal strength detector 638 converts the amplitude of
the signal 612 to a strength signal (DC component) and outputs the
strength signal to the inverting input terminal of the operational
amplifier AMP11. The signal strength detector 639 converts the
amplitude of the first signal 611 to a strength signal (DC
component) and outputs the strength signal to the non-inverting
input terminal of the operational amplifier AMP 11. The operational
amplifier AMP11 adjusts the resistance value of the attenuator 635
so that the strength of the first signal detected by the signal
strength detector 639 equals the strength of the signal 612
detected by the signal strength detector 638. Although the signals
that are handled by the signal strength detectors 638, 639, the
operational amplifier AMP11, and the variable resistor VR11 are
assumed to be analog values, these components may be changed to a
circuit that handles digital values.
[0124] As described above, in the radio communication system
pertaining to the present embodiment, the second signal 613 that is
output from the amplifier 634 is attenuated to be as strong as the
first signal 611 and the attenuated signal 612 is fed back to the
amplifier 634. Then, the output of the amplifier 634 is decreased
by the signal 612. Thereby, a feedback loop through the amplifier
634 can be stabilized and it is possible to avoid the oscillation
of the modulation circuit 632.
[0125] Also in the radio communication system pertaining to the
present embodiment, the amplifier 634 is provided in the modulation
circuit 632 of the data transmitter 603, as shown in FIG. 12. In
this way, the provision of the amplifier 634 in the modulation
circuit 632 can boost the output of the generated second radio wave
14. Thus, the second data can be transmitted from the data
transmitter 603 to the second radio equipment 2, even if there is
some distance between the data transmitter 603 and the second radio
equipment 2.
Fourth Embodiment
[0126] Next, a fourth embodiment of the present invention is
described. In the data transmitter 3 shown in FIG. 2, the
transmission of the second radio wave 14 with a large strength is
made possible by using the amplifier 35 provided inside the data
transmitter 3. However, the strength of the second radio wave 14
that is output from the data transmitter 3 may become too large
depending on setting of the amplifier 35 and may have an impact on
other electronic devices.
[0127] In the radio communication system pertaining to the present
embodiment, a data transmitter is described in which the second
radio wave that is output from the data transmitter can be
constrained to a prescribed strength. Because others are the same
as the radio communication system of the first embodiment and, the
same components are assigned the same reference numerals and
duplicative description is dispensed with.
[0128] FIG. 14 is a circuit diagram representing a data transmitter
703 used in the radio communication system pertaining to the
present embodiment. The data transmitter 703 shown in FIG. 14
includes a modulation circuit 732 and a sensor 33. The modulation
circuit 732 includes amplifiers (single-end amplifier) 733, 734, a
voltage down converter 735, and a duplexing element 737. Here, the
amplifiers (single-end amplifier) 733, 734 and the voltage down
converter 735 form a variable gain amplifier with an amplitude
limiting function.
[0129] The duplexing element 737 is basically the same as the
duplexing element 37 described in the first embodiment. That is,
the duplexing element 737 has a function of separating a path for
inputting a first signal 711 corresponding to the first radio wave
13 received by the antenna 31 to an amplifier 733 and a path for
outputting an amplified second signal 713 from an amplifier 734 to
the antenna 31. As the duplexing element 737, for example, a
directional coupler can be used.
[0130] As shown in FIG. 14, the amplifier 733 includes N-type
transistors Tr21, Tr22, capacitors C21, C22, and resistors R21,
R22, R23. The first signal 711 corresponding to the first radio
wave 13 received by the antenna 31 is supplied to one end of a
capacitor C21. The other end of the capacitor C21 is coupled to one
end of a resistor R21 and to a gate of an N-type transistor Tr22. A
bias voltage bias_21 is supplied to the other end of the resistor
R21. For the N-type transistor Tr22, its drain is coupled to a
source of an N-type transistor Tr21 and its source is grounded.
[0131] For the N-type transistor Tr21, its gate is supplied with a
gain control signal 736 and its drain is coupled to one end of a
resistor R22 and to one end of a capacitor C22. The other end of
the resistor R22 is coupled to a power supply VDD_1. The other end
of the capacitor C22 is coupled to one end of a resistor R23. A
bias voltage bias_22 is supplied to the other end of the resistor
R23. A signal 712 amplified by the amplifier 733 is output from a
node node_21 at which the other end of the capacitor C22 and the
one end of the resistor R23 are coupled and to the amplifier
734.
[0132] The amplifier 734 includes N-type transistors Tr23, Tr24, a
capacitor C23, and resistors R24, R25. For an N-type transistor
Tr24, its drain is coupled to a source of an N-type transistor
Tr23, its gate is supplied with the signal 712 output from the
amplifier 733, and its source is grounded. For the N-type
transistor Tr23, its gate is supplied with the gain control signal
736 and its drain is coupled to one end of a resistor R24 and to
one end of a capacitor C23. The other end of the resistor R24 is
coupled to a power supply VDD_2. The other end of the capacitor C23
is coupled to one end of a resistor R25. A bias voltage bias_23 is
supplied to the other end of the resistor 25. A second signal 713
amplified by the amplifier 734 is output from a node node_22 at
which the other end of the capacitor 23 and the one end of the
resistor R25 are coupled.
[0133] The voltage down converter 735 converts a power supply
voltage VDD_1 to a power supply voltage VDD_2 that is lower than
the power supply voltage VDD_1.
[0134] In the amplifiers 733, 734 shown in FIG. 14, if the gain
control signal 736 is "0", the N-type transistor Tr21 of the
amplifier 733 and the N-type transistor Tr23 of the amplifier 734
are put in an off state and, thus, no amplified second signal 713
is output from the amplifier 734.
[0135] On the other hand, if the gain control signal 736 is "1",
the N-type transistor Tr21 of the amplifier 733 is put in an on
state. At this time, the first signal 711 increased as much as the
bias voltage bias_21 is supplied to the gate of the N-type
transistor Tr22. Thereby, the N-type transistor Tr22 operates in
response to the first signal 711 and, thus, the signal 712 yielded
by amplifying the first signal 711 is output from the node
node_21.
[0136] If the gain control signal 736 is "1", the N-type transistor
Tr23 of the amplifier 734 is also put in an on state. At this time,
the signal 712 output from the amplifier 733 is supplied to the
gate of the N-type transistor Tr24. Thus, the N-type transistor
Tr24 operates in response to the signal 712 and the second signal
713 yielded by amplifying the signal 712 is output from the node
node_22. At this time, because the power supply voltage VDD_2 is
lower than the power supply voltage VDD_1, the amplitude of the
second signal that is output from the node node_22 is smaller than
the amplitude of the signal 712 output from the amplifier 733. The
amplified second signal 713 is supplied via the duplexing element
737 to the antenna 31 and radiated as the second radio wave 14 from
the antenna 31
[0137] In the data transmitter 703 pertaining to the present
embodiment, the power supply voltage VDD_2 of the amplifier 734 is
set lower than the power supply voltage VDD_1 by means of the
voltage down converter 735. Thereby, the amplitude of the second
signal 713 amplified by the amplifier 734 can be made smaller than
the power supply voltage VDD_2. Thus, it is possible to constrain
the strength of the second radio wave that is output from the data
transmitter to a prescribed strength.
[0138] FIG. 15 is a diagram for explaining the effect of the
invention pertaining to the present embodiment. In the case of the
data transmitter 3 pertaining to the first embodiment, the strength
of the second radio wave 14 that is output from the data
transmitter 3 may become larger than a standard value in some
circumstances, depending on setting of the amplifier 35 (see a part
marked with a reference numeral 715). By contrast, because the
variable gain amplifier with an amplitude limiting function is used
in the data transmitter pertaining to the present embodiment, the
strength of the second radio wave 14 can be kept below the standard
value (see a part marked with a reference numeral 716). In this
case, the strength of the second radio wave that is output from the
data transmitter can be adjusted by modifying a value of the power
supply voltage VDD_2 that is set by the voltage down converter
735.
[0139] The above-described variable gain amplifier with an
amplitude limiting function, which is formed of the amplifiers 733,
4 and the voltage down converter 735, is one example.
[0140] Any amplifier that can constrain the strength of the second
radio wave to a prescribed strength may be used.
Fifth Embodiment
[0141] Next, a fifth embodiment of the present invention is
described. In the data transmitter 3 shown in FIG. 2, a harmonic
distortion might occur when the amplifier 35 provided inside the
data transmitter 3 operates in a nonlinear domain. When the power
level of such a harmonic distortion is too large, it might have an
impact on other electronic devices.
[0142] In the radio communication system pertaining to the present
embodiment, a data transmitter is described in which the power
level of a harmonic distortion can be constrained below a standard
value. Because others are the same as the radio communication
system of the first embodiment and, the same components are
assigned the same reference numerals and duplicative description is
dispensed with.
[0143] FIG. 16 is a circuit diagram representing a data transmitter
803 used in the radio communication system pertaining to the
present embodiment. The data transmitter 803 shown in FIG. 16
includes a modulation circuit 832 and a sensor 33. The modulation
circuit 832 includes an amplifier (single-end amplifier) 833, a
harmonic elimination circuit (low-pass filter) 834, and a duplexing
element 837. Here, the amplifier 833 and the harmonic elimination
circuit 834 form a variable gain amplifier with a harmonic
elimination function.
[0144] The duplexing element 837 is basically the same as the
duplexing element 37 described in the first embodiment. That is,
the duplexing element 837 has a function of separating a path for
inputting a first signal 811 corresponding to the first radio wave
13 received by the antenna 31 to the amplifier 833 and a path for
outputting an amplified second signal 813 from the harmonic
elimination circuit 834 to the antenna 31. As the duplexing element
837, for example, a directional coupler can be used.
[0145] As shown in FIG. 16, the amplifier 833 includes N-type
transistors Tr31, Tr32, capacitors C31, C32, and resistors R31,
R32, R33. The first signal 811 corresponding to the first radio
wave 13 received by the antenna 31 is supplied to one end of a
capacitor C31. The other end of the capacitor C31 is coupled to one
end of a resistor R31 and to a gate of an N-type transistor Tr32. A
bias voltage bias_31 is supplied to the other end of the resistor
R31. For the N-type transistor Tr32, its drain is coupled to a
source of an N-type transistor Tr31 and its source is grounded.
[0146] For the N-type transistor Tr31, its gate is supplied with a
gain control signal 836 and its drain is coupled to one end of a
resistor R32 and to one end of a capacitor C32. The other end of
the resistor R32 is coupled to a power supply VDD. The other end of
the capacitor C32 is coupled to one end of a resistor R33. A bias
voltage bias_32 is supplied to the other end of the resistor R33. A
signal 812 amplified by the amplifier 833 is output from a node
node_31 at which the other end of the capacitor C32 and the one end
of the resistor R33 are coupled and to the harmonic elimination
circuit 834.
[0147] The harmonic elimination circuit 834 includes P-type
transistors Tr33, Tr34, N-type transistors Tr35 to Tr37, a
capacitor C33, and a resistor 34. For a P-type transistor Tr33, its
source is coupled to a power supply VDD and its gate and drain are
coupled to a gate of a P-type transistor Tr34. For the P-type
transistor Tr34, its source is coupled to the power supply VDD, its
gate is coupled to the gate and drain of the P-type transistor
Tr33, and its drain is coupled to a drain of an N-type transistor
Tr36.
[0148] For an N-type transistor Tr35, its drain is coupled to the
gate and drain of the P-type transistor Tr33 and to the gate of the
P-type transistor Tr34 and its gate is grounded. The drain of the
N-type transistor Tr36 is coupled to the drain of the P-type
transistor Tr34. The signal 812 is supplied via the resistor R34 to
a gate of the N-type transistor Tr36. The sources of the N-type
transistor Tr35 and the N-type transistor Tr36 are coupled to a
drain of an N-type transistor Tr37. For the N-type transistor Tr37,
its source is grounded and its gate is coupled to the power supply
VDD. The capacitor C33 is coupled between the gate and drain of the
N-type transistor Tr36. The harmonic elimination circuit (low-pass
filter) shown in FIG. 16 is configured to have a frequency
characteristic marked with a reference numeral 815 in FIG. 17.
[0149] In the amplifier 833 shown in FIG. 16, if the gain control
signal 836 is "0", the N-type transistor Tr31 is put in an off
state and, thus, no amplified second signal 813 is output.
[0150] On the other hand, if the gain control signal 836 is "1",
the N-type transistor Tr31 of the amplifier 833 is put in an on
state. At this time, the first signal 811 increased as much as the
bias voltage bias_31 is supplied to the gate of the N-type
transistor Tr32. Thereby, the N-type transistor Tr32 operates in
response to the first signal 811 and, thus, the signal 812 yielded
by amplifying the first signal 811 is output from the node
node_31.
[0151] For the signal 812 that has been output from the amplifier
833, its harmonic component is eliminated by the harmonic
elimination circuit 834 having the frequency characteristic marked
with the reference numeral 815 in FIG. 17. Then, the second signal
813 amplified by the amplifier 833 and whose harmonic component was
eliminated by the harmonic elimination circuit 834 is output from
the node node_32. The second signal 813 is supplied via the
duplexing element 837 to the antenna 31 and radiated as the second
radio wave 14 from the antenna 31.
[0152] FIG. 17 is a diagram for explaining the effect of the
invention pertaining to the present embodiment. In the data
transmitter 3 pertaining to the first embodiment, when the
amplifier 35 provided inside the data transmitter 3 operates in a
nonlinear domain, a harmonic distortion (marked with a reference
numeral 816) might occur. When the power level of this harmonic
distortion is too large, it might have an impact on other
electronic devices. By contrast, because the variable gain
amplifier with a harmonic elimination function is used in the data
transmitter 803 pertaining to the present embodiment, the power
level of the harmonic distortion can be constrained below a
standard value. That is, as shown in FIG. 17, the power level of a
second-order harmonic can be kept below the standard value (see a
part marked with a reference numeral 817) and the electric field
strength of a third-order harmonic can be nullified.
[0153] The above-described variable gain amplifier with a harmonic
elimination function, which is formed of the amplifier 833 and the
harmonic elimination circuit 834, is one example. Any amplifier
that can constrain the power level of a harmonic distortion below a
standard value may be used.
Sixth Embodiment
[0154] Next, a sixth embodiment of the present invention is
described. FIG. 18 is a block diagram representing a radio
communication system pertaining to the sixth embodiment. FIG. 19 is
a block diagram representing a data transmitter 903 used in the
radio communication system pertaining to the sixth embodiment. In
the radio communication system pertaining to the present
embodiment, the first radio wave 13 is received by a receiving
antenna 931_1 of the data transmitter 903 and the second radio wave
14 is transmitted from a transmitting antenna 931_2, which differs
from the radio communication system pertaining to the first
embodiment. Because others are the same as the radio communication
system of the first embodiment and, the same components are
assigned the same reference numerals and duplicative description is
dispensed with.
[0155] The data transmitter 903 shown in FIG. 19 includes the
receiving antenna 931_1, the transmitting antenna 931_2, a
modulation circuit 932, and a sensor 33. The modulation circuit 932
includes an amplifier (variable gain amplifier) 935. The modulation
circuit 932 generates the second radio wave 14 by modulating the
first radio wave 13 depending on second data which is an object for
transmission.
[0156] In particular, the amplifier 935 provided in the modulation
circuit 932 amplifies a first signal 915 corresponding to the first
radio wave 13 received by the receiving antenna 931_1, depending on
second data, and thus generates a second signal 916. The generated
second signal 916 is radiated as the second radio wave 14 from the
transmitting antenna 931_2. The amplifier 935 is capable of
changing its amplification factor according to a gain control
signal 936. Here, a value of the gain control signal 936
corresponds to second data which is an object for transmission.
[0157] For example, as shown in FIG. 20A, if second data which is
an object for transmission is "1" (i.e., the gain control signal
936 is "1"), the amplifier 935 amplifies the first signal 915
corresponding to the first radio wave 13 received by the receiving
antenna 931_1 and generates the second signal 916 with a larger
amplitude. The generated second signal 916 is radiated from the
transmitting antenna 931_2 as the second radio wave 14 which acts
as a disturbance to the first radio wave 12. At this time, it is
possible to output a stronger second radio wave 14 from the
transmitting antenna 931_2 by increasing the amplification factor
of the amplifier 935. In this way, data of "1" is transmitted from
the data transmitter 903 to the second radio equipment 2.
[0158] On the other hand, as shown in FIG. 20B, if second data
which is an object for transmission is "0" (i.e., the gain control
signal 936 is "0"), the amplifier 935 regulates the amplitude of
the first signal 915 corresponding to the first radio wave 13
received by the receiving antenna 931_1 to a sufficiently small
amplitude. Thus, in this case, because the second signal 916 with a
sufficiently small amplitude is output from the amplifier 935, the
second radio wave 14 that is output from the transmitting antenna
931_2 does not act as a disturbance to the first radio wave 12. In
this way, data of "0" is transmitted from the data transmitter 903
to the second radio equipment 2. If the gain control signal 936 is
"0", the amplifier 935 may regulate the amplitude of the first
signal 915 corresponding to the first radio wave 13 received by the
antenna 31 to zero. At this time, no second signal 916 is output
from the amplifier 935 and, thus, no second radio wave 14 is output
from the transmitting antenna 931_2.
[0159] FIG. 21 is a circuit diagram showing a concrete example of
the data transmitter 903 shown in FIG. 19. The data transmitter 903
shown in FIG. 21 is one example and, in the present embodiment, any
data transmitter that can implement the operation described above
can be used, not limited to the data transmitter shown in FIG.
21.
[0160] As shown in FIG. 21, the amplifier (single-end amplifier)
935 includes N-type transistors Tr41, T42, capacitors C41, C42, and
resistors R41, R42, R43. The first signal 915 corresponding to the
first radio wave 13 received by the receiving antenna 931_1 is
supplied to one end of a capacitor C41. The other end of the
capacitor C41 is coupled to one end of a resistor R41 and to a gate
of an N-type transistor Tr42. A bias voltage bias_41 is supplied to
the other end of the resistor R41. For the N-type transistor Tr42,
its drain is coupled to a source of an N-type transistor Tr41 and
its source is grounded.
[0161] For the N-type transistor Tr41, its gate is supplied with
the gain control signal 936 and its drain is coupled to one end of
a resistor R42 and to one end of a capacitor C42. The other end of
the resistor R42 is coupled to a power supply VDD. The other end of
the capacitor C42 is coupled to one end of a resistor R43. A bias
voltage bias_42 is supplied to the other end of the resistor R43.
The second signal 916 amplified by the amplifier 935 is output from
a node node_41 at which the other end of the capacitor C42 and the
one end of the resistor R43 are coupled and to the transmitting
antenna 931_2.
[0162] In the amplifier 935 shown in FIG. 21, if the gain control
signal 936 is "0", the N-type transistor Tr41 is put in an off
state and, thus, no amplified signal is output from the node
node_41. On the other hand, if the gain control signal 936 is "1",
the N-type transistor Tr41 is put in an on state. At this time, the
first signal 915 increased as much as the bias voltage bias_41 is
supplied to the gate of the N-type transistor Tr42. Thereby, the
N-type transistor Tr42 operates in response to the first signal 915
and, thus, the second signal 916 yielded by amplifying the first
signal 915 is output from the node node_41. The amplified signal is
supplied to the transmitting antenna 931_2 and radiated as the
second radio wave 14 from the transmitting antenna 931_2.
[0163] By using the data transmitter 903 equipped with the
amplifier 935 described above, it is possible to transmit second
data from the data transmitter 903 to the second radio equipment 2
even if there is some distance between the data transmitter 903 and
the second radio equipment 2. The data transmitter 903 pertaining
to the present embodiment is also equipped with the receiving
antenna 931_1 and the transmitting antenna 931_2. Thus, the
duplexing element 37 used in the modulation circuit 32 of the first
embodiment can be dispensed with. Besides, it is possible to
prevent the oscillation of the amplifier 935.
[0164] Because the data transmitter 903 in the present embodiment
is equipped with the receiving antenna 931_1 and the transmitting
antenna 931_2, it is needed to avoid that the second radio wave 14
radiated from the transmitting antenna 931_2 is received by the
receiving antenna 931_1 again. That is, if the second radio wave 14
radiated from the transmitting antenna 931_2 is received by the
receiving antenna 931_1 again, a loop through the receiving antenna
931, amplifier 935, and transmitting antenna 931_2 is formed, and
the modulation circuit 932 is at risk for oscillating.
[0165] Therefore, in the present embodiment, the receiving antenna
931_1 and the transmitting antenna 931_2 of the data transmitter
903 should preferably be configured as shown in FIG. 22. That is,
the receiving antenna 931_1 and the transmitting antenna 931_2 are
configured as loop antennas and the receiving antenna 931_1 and the
transmitting antenna 931_2 are arranged so as to be rotated 90
degrees relative to each other in the same plane. By arranging the
receiving antenna 931_1 and the transmitting antenna 931_2 in this
way, it can be avoided that the second radio wave 14 radiated from
the transmitting antenna 931_2 is received by the receiving antenna
931_1 again. Shown in FIG. 22, reference numerals 951, 952 denote
the spatial radiation characteristic of the receiving antenna 931_1
and reference numerals 953, 954 denote the spatial radiation
characteristic of the transmitting antenna 931_2.
[0166] The invention pertaining to the present embodiment may
appropriately be combined with the invention of any of the second
through fifth embodiments described previously.
Seventh Embodiment
[0167] Next, a seventh embodiment of the present invention is
described. FIG. 23 is a block diagram representing a radio
communication system pertaining to the seventh embodiment. In the
radio communication system pertaining to the present embodiment,
the second radio equipment 21 includes a demodulation circuit 41
and an error rate evaluating circuit 42 as the separation and
demodulation circuit 24, which differs from the radio communication
system pertaining to the first embodiment described with FIG. 1.
Because others are the same as in the first embodiment, the same
components are assigned the same reference numerals and duplicative
description is dispensed with.
[0168] As shown in FIG. 23, the second radio equipment 21 in the
radio communication system pertaining to the present embodiment
includes an amplifier 27, a demodulation circuit 41, and an error
rate evaluating circuit 42. The amplifier 27 can be dispensed with,
as appropriate, if the signal level of the first radio wave 12 and
the second radio wave 14 is high, that is, at such a level that
received radio wave signals can be processed by the following
separation and demodulation circuit 24.
[0169] The demodulation circuit 41 demodulates first data
transmitted from the first radio equipment 1 included in the
received radio waves and outputs the demodulated data as
demodulated data 25 from the first radio equipment 1. After the
first data transmitted from the first radio equipment 1 has been
demodulated, the error rate evaluating circuit 42 evaluates the bit
error rate. Based on fluctuations in the bit error rate over time,
the error rate evaluating circuit 42 reads and demodulates data
from the data transmitter 3 and generates demodulated data 26 from
the data transmitter 3. In the radio communication system
pertaining to the present embodiment, a circuit that executes
demodulation is only the demodulation circuit 41 that demodulates
the first data transmitted from the first radio equipment 1. Data
transmitted from the data transmitter 3 is demodulated in baseband
processing in the following stage.
[0170] The received SN ratio for second data from the data
transmitter 3 deteriorates, for example, in a case where an
interfering wave from a third party has further come in the radio
communication system configured as above, or in a case where the
first radio wave (direct wave) 12 from the first radio equipment 1
is dominant over the second radio wave 14 from the data transmitter
3 because of their positional relation. In such a case, by carrying
out decision by majority processing and code spreading, the
received SN ratio for second data from the data transmitter 3 can
be enhanced, so that the second radio equipment 21 can receive
second data from the data transmitter 3.
[0171] For example, let us assume that the first radio equipment 1,
the second radio equipment 21, and the data transmitter 3 are
placed in the form of an isosceles triangle; i.e., a distance
between the first radio equipment 1 and the second radio equipment
21 equals a distance between the first radio equipment 1 and the
data transmitter 3 and a distance from the second radio equipment
21 to the data transmitter 3 is a half of the distance from the
second radio equipment 21 to the first radio equipment 1. Also, let
us assume an attenuation coefficient of about 0.5 for the second
radio wave generated by modulating the radio wave from the first
radio equipment 1 and radiated by the data transmitter 3 (here, the
attenuation coefficient of the second radio wave is set low for the
purpose of illustrating the case where the SN ratio of the signal
transmitted from the data transmitter 3 deteriorates). In this
case, the distance of an indirect travel of a radio wave from the
first radio equipment 1 via the data transmitter to the second
radio equipment 21 is 1.5 times the distance of a direct travel of
a radio wave from the first radio equipment 1 to the second radio
equipment 21. Assuming that the power of the arrived radio wave is
proportional to a reciprocal of the square of the distance, the
indirect wave is more attenuated by a distance attenuation of
10*log (1/(1.5*1.5))=-4 dB as compared with the direct wave. The
indirect wave is further attenuated by 10*log(0.5)=-3 dB due to its
attenuation coefficient of 0.5. Thereby, the ratio between the
power N of the radio wave arrived as noise at the second radio
equipment 21 directly from the first radio equipment 1 and the
power S of the radio wave arrived as data at the second radio
equipment 21 via the data transmitter 3 is S/N=-3 dB+-4 dB=-7 dB,
assuming that signal attenuation=distance attenuation+modulation
attenuation and the noise power is constant. In consequence, data
is buried in noise.
[0172] However, if, for example, same data is transmitted 12 times
from the data transmitter 3 and decision by majority processing is
performed at the second radio equipment 2 to suppress a random
noise, the S/N ratio is improved 7.6 dB by filtering with a 12-tap
finite impulse response filter, which is defined by
H(z.sup.-1)=1+z.sup.-1+z.sup.-2+ . . . +z.sup.-11, as shown in FIG.
26. Thus, it is possible to receive data with S/N=-7 dB.
[0173] Here, as shown in FIG. 27, in a WLAN carrier frequency band
of 2.4 GHz, the data rate is at least 1 Mbps or more. Thus, there
is no periodicity at a low frequency for which the data rate is
below 1 Mbps in environmental radio waves, white noise is
considered to spread sufficiently over the communication band of
the data transmitter 3. Therefore, it is possible to improve the SN
ratio by carrying out the decision by majority processing. Because
the decision by majority processing and code spreading require
redundancy, the effective data communication rate decreases. In
this case, data size that can be handled becomes smaller as
compared with existing RFID systems.
[0174] Then, the second radio equipment 21 used in the radio
communication system pertaining to the present embodiment is
described specifically, using FIG. 24. The demodulation circuit 41
of the second radio equipment 21 shown in FIG. 24 includes a
demodulating unit 51, a demapping unit 52, a soft-decision
deinterleaving and Viterbi demodulating unit 53, and a frame
processing unit 54.
[0175] A demapped output from the demapping unit 52 is output to
the soft-decision deinterleaving and Viterbi demodulating unit 53
and the error rate evaluating circuit 42. A soft-decision
deinterleaved and Viterbi demodulated output from the soft-decision
deinterleaving and Viterbi demodulating unit 53 is output to the
frame processing unit 54 and the error rate evaluating circuit 42.
A frame processed output from the frame processing unit 54 is
output as demodulated data 25 from the first radio equipment 1. The
frame processed output from the frame processing unit 54 is also
output to the error rate evaluating circuit 42.
[0176] The error rate evaluating circuit 42 also includes a storage
61. The error rate evaluating circuit 42 demodulates second data
from the data transmitter 3 based on at least one of the demapped
output, the soft-decision deinterleaved and Viterbi demodulated
output, and the frame processed output and outputs demodulated data
26 from the data transmitter 3.
[0177] FIG. 25 is a flowchart for explaining operation of the
second radio equipment 21 shown in FIG. 24. First, first data
transmitted from the first radio equipment 1 is demodulated by the
demodulating unit 51. Data demodulated by the demodulating unit 51
is output from the demodulation circuit 41, diverging from each
layer of protocol processing, such as a demapped bit sequence, a
soft-decision deinterleaved and Viterbi demodulated bit sequence,
and a frame processed bit sequence. As the demodulated data
undergoes protocol processing in the demapping unit 52, further in
the soft-decision deinterleaving and Viterbi demodulating unit 53,
and further in the frame processing unit 54, the influence of a
disturbance such as an interfering wave is alleviated. Therefore,
the influence of a disturbance on a demapped bit sequence is larger
than that on a frame processed bit sequence.
[0178] Then, sampling of bit error rate (BER) of the frame
processed output is performed (step S1). This BER sampling is
performed at a rate higher than the symbol rate of data transmitted
from the data transmitter 3. The sampled BER sequence is held in
the storage (step S2).
[0179] Then, code despreading is performed for the sequence
obtained through the steps S1, S2 to improve the SN ratio (step
S3). In particular, this step obtains a correlation between a
spread code previously stored in the second radio equipment 21 and
the sampled BER sequence and performs despreading. The resulting
bit sequence is held again in the storage. Same data is repeatedly
transmitted from the data transmitter 3. Thus, the decision by
majority processing among such data is performed and the result is
held in the storage (step S4).
[0180] Next, it is decided whether there is a distinct error such
as parity bit inversion in the result obtained by the decision by
majority processing (step S5). If there is no distinct error, as
decided at step S5, the obtained result is output as data (second
data) transmitted from the data transmitter 3 (step S6). Otherwise,
if there is a distinct error, as decided at step S5, data from the
data transmitter 3 is regarded as being transmitted in an
environment in which the data tends to be buried in noise.
[0181] In such a case, sampling of BER of the soft-decision
deinterleaved and Viterbi demodulated output that is more affected
by a disturbance is performed (step S7). Then, the same processing
as the above steps S2 to S4 is performed for a sampled BER sequence
obtained from the soft-decision deinterleaved and Viterbi
demodulated output (step S8). Further, it is decided whether there
is a distinct error such as parity bit inversion in the result
obtained by the decision by majority processing (step S9). If there
is no distinct error, as decided at step S9, the obtained result is
output as data (second data) transmitted from the data transmitter
3 (step S6).
[0182] Otherwise, if there is a distinct error, as decided at step
S9, sampling of BER of the demapped output that is even more
affected by a disturbance is performed (step S10). Then, the same
processing as the above steps S2 to S4 is performed for a sampled
BER sequence obtained from the demapped output (step S11). The thus
obtained result is output as data (second data) transmitted from
the data transmitter 3 (step S6).
[0183] As the object for BER sampling is changed from the frame
processed output to the soft-decision deinterleaved and Viterbi
demodulated output, and to the demapped output, the sensitivity to
noise increases. In this case, the influence of noise can be
reduced by increasing the length of the above spread code or
increasing the number of times of sampling in the decision by
majority processing. If the system is only used in a low noise
environment, for example, in an environment where the distance
between the data transmitter 3 and the second radio equipment 2 is
short, it is not necessary to follow such a complex procedure as
described above and it is possible to demodulate second data
transmitted from the data transmitter 3 by tracing only the BER of
the frame processed output.
[0184] In the radio communication system pertaining to the present
embodiment as well, it is possible to provide a radio communication
system capable of reducing the cost for introducing a system
utilizing RFID technology into a radio network environment.
[0185] The second radio equipment 21 in the radio communication
system pertaining to the present embodiment can also be configured
by software implementation to customize existing radio equipment.
That is, because demapping and subsequent processing in the second
radio equipment 21 shown in FIG. 24 are protocol processing, the
second radio equipment 21 shown in FIG. 24 can be configured by
software implementation to customize the protocol processing unit,
for example, shown in FIG. 9. In the present embodiment, a part of
the protocol processing unit shown in FIG. 9 may be configured by
hardware. In this case, the remaining part of the protocol
processing unit other than the part configured by hardware is
customized by software implementation. The second radio equipment
21 can also be configured in this way.
Eighth Embodiment
[0186] Next, an eighth embodiment of the present invention is
described. In the radio communication system pertaining to the
present embodiment, processing that is performed by the second
radio equipment 21 shown in FIG. 24 differs from that in the
seventh embodiment. Because others are the same as in the seventh
embodiment and, the same components are assigned the same reference
numerals and duplicative description is dispensed with.
[0187] FIG. 28 is a flowchart for explaining processing that is
performed by the second radio equipment 21 pertaining to the
present embodiment. A difference of the flowchart shown in FIG. 28
from the flowchart shown in FIG. 25 and described in the seventh
embodiment lies in that the decisions by parity bit (S5, S9) are no
longer needed.
[0188] Specifically, in the flowchart shown in FIG. 28, sampling of
BER of the frame processed output is first performed (step S21).
The sampled BER sequence is stored in the storage (step S22).
[0189] Then, code despreading is performed for the sequence
obtained through the steps S21, S22 to improve the SN ratio (step
S23). In particular, this step obtains a correlation between a
spread code previously stored in the second radio equipment 21 and
the sampled BER sequence and performs despreading. The resulting
bit sequence is held again in the storage. Decision by majority
processing is performed for data that is repeatedly transmitted
from the data transmitter 3 and the result (result 1) is held in
the storage (step S24).
[0190] In parallel with the processing from the above steps S1 to
S24, the following processing is performed. First, sampling of BER
of the demapped output is performed (step S25). The sampled BER
sequence is held in the storage (step S26).
[0191] Then, code despreading is performed for the sequence
obtained through the steps S25, S26 to improve the SN ratio (step
S27). In particular, this step obtains a correlation between a
spread code previously stored in the second radio equipment 21 and
the sampled BER sequence and performs despreading. The resulting
bit sequence is held again in the storage. Decision by majority
processing is performed for data that is repeatedly transmitted
from the data transmitter 3 and the result (result 2) is held in
the storage (step S28).
[0192] Finally, a difference between the decision by majority
processing results 1 and 2 is output as data (second data)
transmitted from the data transmitter (step S29).
[0193] In this way, by obtaining a difference between the frame
processed output that is less affected by a disturbance than the
demapped output and the demapped output, it is possible to extract
data transmitted as the disturbance from the data transmitter 3. In
the radio communication system pertaining to the present, the
processing that is performed by the second radio equipment 21 can
be made simpler than that in the seventh embodiment.
Ninth Embodiment
[0194] Next, a ninth embodiment of the present invention is
described. The radio communication system pertaining to the present
embodiment includes a plurality of data transmitters 3_1 to 3_N,
which differs from the radio communication systems described in the
first through eighth embodiments. Because others are the same as in
the first through eighth embodiments, the same components are
assigned the same reference numerals and duplicative description is
dispensed with.
[0195] FIG. 29A is a block diagram representing the radio
communication system pertaining to the present embodiment. As shown
in FIG. 29A, the radio communication system pertaining to the
present embodiment has a plurality of data transmitters 3_1 to 3_N
within a receivable range of first radio waves output from the
first radio equipment 1. A data transmitter 3_1 receives a first
radio wave 13_1 output from the first radio equipment 1, modulates
the first radio wave 13_1 depending on second data which is an
object for transmission, and outputs a second radio wave 14_1.
Similarly, a data transmitter 3_2 receives a first radio wave 13_2
output from the first radio equipment 1, modulates the first radio
wave 13_2 depending on second data which is an object for
transmission, and outputs a second radio wave 14_2. Similarly, a
data transmitter 3_N receives a first radio wave 13_N output from
the first radio equipment 1, modulates the first radio wave 13_N
depending on second data which is an object for transmission, and
outputs a second radio wave 14_N.
[0196] FIG. 29B is a diagram showing an example of disturbances to
the first radio waves 13_1 to 13_N created by each of the data
transmitters 3_1 to 3_N. As shown in FIG. 29B, each of the data
transmitters 3_1 to 3_N adds identification information such as a
spread code, as a header, to data which is an object for
transmission.
[0197] The second radio equipment 2 receives the first radio wave
12 and the second radio waves 14_1 to 14_N and separates and
demodulate first data transmitted from the first radio equipment 1
and each data transmitted from each of the data transmitters 3_1 to
3_N included in the received radio waves by means of the separation
and demodulation circuit 24. Here, the separation and demodulation
circuit 24 can distinguish each data transmitted from each data
transmitter 3_1 to 3_N based on the identification information
added as the header to the data which is an object for
transmission. Data separated and demodulated by the separation and
demodulation circuit 24 is output as demodulated data 25 from the
first radio equipment 1 and demodulated data 26_1 to 26_N from each
data transmitter 3_1 to 3_N.
[0198] Although a spread code is used as identification information
in the above example, any identification information by which each
data can be distinguished may be used. As the spread code, for
example, an M-sequence code can be used. However, not limited to
the M-sequence code, any pseudo random number code with a high
autocorrelation, for example, a GOLD code can also be used.
Although the examples in which despreading is performed have been
described in the seventh and eighth embodiments, spreading for data
identification needs to be done before such despreading in this
case.
[0199] For example, assuming that a pseudo random number pattern
which is a code sequence with a small autocorrelation, e.g., PN4 is
used as the spread code, there is one pseudo random number sequence
according to an initial value permitted for M sequences. However,
if PN5 or PN7 is used, the pseudo random number sequences increase
to three or nine, respectively. If autocorrelations of PN5 and PN7
each are profiled, as shown in FIG. 30, differences between the
peak and bottom of correlation strength are 16 and 32,
respectively, which correspond to 24 dB and 30 dB, respectively.
Thus, data with such a spread code can be distinguished from data
with another spread code at an accuracy higher than the SN ratio
required for on/off keying modulation, where BER >10.sup.-2.
[0200] If PN5 is used as the above header and matched filtering is
initially performed when receiving data to synchronize a desired
data transmitter with the second radio equipment 2, it is possible
to selectively receive data only from a single desired data
transmitter, even if three radio chips exist in the second radio
equipment 2. If there are more than three data transmitters, it is
possible to selectively receive data from each data transmitter by
using a spread code of PN7 or higher.
[0201] By the radio communication system as described above, even
in a case where a plurality of data transmitters 3_1 to 3_N exist,
it is possible to avoid crosstalk and distinguish and receive each
data transmitted from each data transmitter.
Tenth Embodiment
[0202] Next, a tenth embodiment of the present invention is
described. In the tenth embodiment, a case is described in which
the radio communication system described in any of the first
through ninth embodiments is applied to an in-vehicle network of a
motor vehicle.
[0203] In the present embodiment, as shown in FIG. 31, the
in-vehicle network of a motor vehicle 90 is built using the first
radio equipment 1 and the second radio equipment 2 described in any
of the first through ninth embodiments. The first radio equipment 1
transmits first data to the second radio equipment 2, using a first
radio wave 12. Here, the first radio wave 12 is a direct wave that
is directly transmitted from the first radio equipment 1 to the
second radio equipment 2.
[0204] For example, a system may be configured in which the first
radio equipment 1 is connected to an ECU for engine control, an ECU
for transmission control, an ECU for air-conditioner control, etc.,
and control information on these ECUs is transmitted by the first
radio equipment 1 to the second radio equipment 2. For example, a
system may be configured in which the second radio equipment 2 is
connected to a car navigation system and control information
transmitted from the first radio equipment 1 is displayed on the
screen of the car navigation system.
[0205] The above examples are exemplary and any in-vehicle network
may be built using the first radio equipment 1 and the second radio
equipment 2 in the present embodiment.
[0206] In the present embodiment, a data transmitter 3 can be
placed in any location in the motor vehicle. For example, a data
transmitter A (3_1) may be placed on a tire 91 to monitor the air
pressure of the tire 91 of the motor vehicle. This data transmitter
A (3_1) may be equipped with a pressure sensor and may transmit
information on the air pressure of the tire 91 acquired by the
pressure sensor to the second radio equipment 2.
[0207] When air pressure information is transmitted from the data
transmitter A (3_1) to the second radio equipment 2, the method
described in any of the first through ninth embodiments can be
used. That is, the data transmitter A (3_1) modules the first radio
wave 13_1 transmitted from the first radio equipment 1 depending on
air pressure information which is an object for transmission and
outputs the modulated radio wave as a second radio wave 14_1. The
thus modulated second radio wave 14_1 acts as a disturbance to the
first radio wave (direct wave) 12 transmitted from the first radio
equipment 1 to the second radio equipment 2. Then, the second radio
equipment 2 determines the presence or absence of a disturbance to
the first radio wave 12, separates data transmitted from the first
radio equipment 1 and air pressure information transmitted from the
data transmitter A (3_1), and demodulates them.
[0208] For example, a data transmitter B (3_2) may be placed on a
window 92 to monitor whether the window 92 of the motor vehicle is
open or closed. This data transmitter B (3_2) may be equipped with
a position sensor to detect whether the window 92 is open or closed
and may transmit information as to whether the window 92 is open or
closed, acquired by the position sensor, to the second radio
equipment 2.
[0209] When information as to whether the window 92 is open or
closed is transmitted from the data transmitter B (3_2) to the
second radio equipment 2, the method described in any of the first
through ninth embodiments can be used. That is, the data
transmitter B (3_2) modulates the first radio wave 13_2 transmitted
from the first radio equipment 1 depending on information as to
whether the window 92 is open or closed, which is an object for
transmission, and outputs the modulated radio wave as the second
radio wave 14_2. Thus modulated second radio wave 14_2 acts as a
disturbance to the first radio wave (direct wave) 12 transmitted
from the first radio equipment 1 to the second radio equipment 2.
Then, the second radio equipment 2 determines the presence or
absence of a disturbance to the first radio wave 12, separates data
transmitted from the first radio equipment 1 and information as to
whether the window 92 is open or closed transmitted from the data
transmitter B (3_2), and demodulates them.
[0210] For example, a data transmitter C (3_3) may be placed in any
location in the motor vehicle to monitor in-vehicle temperature.
This data transmitter C (3_3) may be equipped with a temperature
sensor and may transmit information on in-vehicle temperature
acquired by the temperature sensor to the second radio equipment
2.
[0211] When information on in-vehicle temperature is transmitted
from the data transmitter C (3_3) to the second radio equipment 2,
the method described in any of the first through ninth embodiments
can be used. That is, the data transmitter C (3_3) modulates the
first radio wave 13_3 transmitted from the first radio equipment 1
depending on information on in-vehicle temperature which is an
object for transmission and outputs the modulated radio wave as the
second radio wave 14_3. The thus modulated second radio wave 14_3
acts as a disturbance to the first radio wave (direct wave) 12
transmitted from the first radio equipment 1 to the second radio
equipment 2. Then, the second radio equipment 2 determines the
presence or absence of a disturbance to the first radio wave 12,
separates data transmitted from the first radio equipment 1 and
information on in-vehicle temperature transmitted from the data
transmitter C (3_3), and demodulates them.
[0212] For example, when information indicative of abnormality has
been transmitted from any of the data transmitters 3_1 to 3_3, the
second radio equipment 2 can notify the driver of the abnormality
by displaying an alert on the car navigation system connected to
the second radio equipment 2.
[0213] The locations where the data transmitters 3 are placed,
described above, are exemplary and the data transmitters 3 can be
placed in any other locations. In such a case that a plurality of
data transmitters 3 are placed, it is required to distinguish data
transmitted from each data transmitter 3_1 to 3_3. In this case,
for example, as described in the ninth embodiment, it is possible
to distinguish the source of data transmitted from the data
transmitter 3_1 to 3_3 by adding identification information such as
a spread code as a header to data which is an object for
transmission.
[0214] In the present embodiment, the data transmitters 3 are able
to operate without being supplied with external power. Thus, the
present invention is beneficial particularly in a case where the
condition of a part in a location where power supply wiring is
difficult is measured by a sensor, for example, the air pressure of
a tire is measured.
Other Embodiments
[0215] Other embodiments are described below. The data transmitter
described in any of the foregoing embodiments may be fabricated on
a semiconductor chip. That is, all circuits (modulation circuit,
sensor, etc.) constituting the data transmitter may be fabricated
on a semiconductor chip. In this case, an antenna may be formed on
the same semiconductor chip having the data transmitter's circuits
formed thereon. Or an antenna may be formed separately from the
semiconductor chip having the data transmitter's circuits formed
thereon.
[0216] As shown in FIG. 32A, a data transmitter 591 fabricated
using a semiconductor chip can be attached to a measurement subject
using an adhesive member 594. As the adhesive member 594, for
example, adhesive tape can be used. Here, the data transmitter 591
includes all circuits 592 constituting the data transmitter and an
antenna 593. For example, if the data transmitter 591 is equipped
with a temperature sensor, it is possible to measure the
temperature of a measurement subject easily by placing the chip of
the data transmitter 591 on the adhesive member 594 and attaching
the adhesive member 594 to the measurement subject.
[0217] Because the tack strength of the adhesive member decreases
over time, the adhesive member cannot be used after a given time
has elapsed. By contrast, the product lifetime of the data
transmitter 591 is long. Therefore, the data transmitter 591 can be
reused by configuring the adhesive member 594 so that the data
transmitter 591 can be removed from it. For example, by forming a
pocket on the adhesive member 594, the data transmitter 591 can be
removed.
[0218] FIG. 32B is cross-sectional view of an adhesive member. If
the data transmitter 591 is equipped with a temperature sensor, as
shown in FIG. 32B, as a member 595 that is positioned between the
data transmitter 591 attached to the adhesive member 594 and the
measurement subject, a material having a high thermal conductivity
is preferably used. By using a material having a high thermal
conductivity, it is possible to measure the temperature of the
measurement subject accurately. As the material having a high
thermal conductivity, inter alia, a metal material such as copper
and a resin material having a high thermal conductivity can be
used.
[0219] Also, a data transmitter may be installed to a thermometer.
In this case, a temperature sensor that the thermometer has may be
used as a sensor of the data transmitter. By installing the data
transmitter to the thermometer, history data on the temperature of
the measurement subject can be transmitted to the second radio
equipment 2.
[0220] While the present invention has been described in accordance
with the foregoing embodiments, it will be appreciated that the
invention is not limited to only the configurations of the
described embodiments and embraces variants, modifications, and
combinations that can be achieved by those skilled in the art
within the scope of the invention encompassed by the claims of the
present application.
* * * * *