Field of the Invention
The present invention relates to a wireless
communication system for transmitting and receiving a radio
signal between multiple wireless communications stations,
and a wireless transceiver used therefor.
Background of the Invention
Conventionally, there have been disclosed various
types of wireless transceivers employing a superheterodyne
scheme that converts a radio frequency signal into a
relatively low frequency signal (intermediate frequency
signal), and amplifying and detecting the same. For example,
a wireless receiver disclosed in Patent Document 1 includes
a local oscillator which outputs a signal (i.e., a local
oscillation signal) of a frequency (local oscillation
frequency) that is an integer multiple of the frequency of
an input signal (reference oscillation signal).
In the wireless receiver, a reception signal (RF
signal) received by an antenna and the local oscillation
signal outputted from the local oscillator are mixed by a
mixer and converted into a signal having a frequency
(intermediate frequency) lower than that of the RF signal.
Further, various wireless transceivers using a phase locked
loop (PLL) circuit as a local oscillator have also been
provided.
As for a wireless communications station, there may be
cases where characteristics (RF characteristics) of radio
waves in use such as an occupied frequency bandwidth, an
adjacent channel leakage power or the like should meet the
rules of Radio Regulation Law. For example, in Japan Radio
Regulation Law, a different standard (communication
standards) is prescribed for each of usage purposes. In
particular, a 'low power radio station' is prescribed as one
of radio stations not requiring license in a provisory
clause, article 4 of Japan Radio Regulation Law.
The 'low power radio station' includes a 'radio
station for a cordless phone', a 'particular low power radio
station', a 'low power security system', a 'radio station
for a low power data communication system' and the like.
Standards for radio facilities of each radio station are
prescribed by facility regulation of enforcement regulations
of the same Law.
As a wireless communication system including a
particular low power radio station, for example, a fire
warning system disclosed in Patent Document 2 was already
proposed. This fire warning system includes multiple fire
alarms as radio stations installed in multiple locations.
Each of the fire alarms includes a fire detection unit
for detecting a fire, an alarm unit for generating an alarm
sound, a wireless transmission/reception unit for
transmitting and receiving fire notification information
notifying about the occurrence of a fire through radio
signals, and an operation controller (or a microcomputer)
for controlling operations of the alarm unit and the
wireless transmission/reception unit.
When a fire detection unit of a fire alarm detects the
occurrence of a fire, an operation controller of the fire
alarm outputs an alarm sound from an alarm unit and,
simultaneously, a wireless transmission/reception unit
thereof transmits fire notification information to other
fire alarms. When wireless transmission/reception units of
the other fire alarms receive the fire notification
information from the fire alarm at the origin of fire, alarm
units of the other fire alarms make an alarm sound loudly.
Thus, when a fire alarm at a certain location detects the
occurrence of a fire, alarm sounds are outputted from all
multiple fire alarms including the fire alarm at the origin
of fire, thereby quickly and reliably notifying about the
occurrence of fire.
As the above, the fire alarm transmits the fire
notification information through a radio signal and uses a
battery as a power source. This eliminates a necessity of
wiring and increases freedom of installation position.
However, since a fire alarm is usually installed at a high
location (e.g., the ceiling) where it is not easy to access
in maintenance (e.g., battery replacement), preferably, the
fire alarm can be used for a long period of time, e.g., for
years, without maintenance and power consumption thereof is
reduced to thereby lengthen a life span of the battery.
To this end, in each fire alarm, the operation
controller including a microcomputer is switched into a
sleep state consuming less power and a
transmission/reception operation of the wireless
transmission/reception unit is stopped, except for a case of
detecting a fire and sounding an alarm, and wirelessly
transmitting fire notification information. However, when.
the operation controller is in the sleep state except for
the case of the fire detection, fire notification
information wirelessly transmitted from another fire alarm
cannot be received. For that reason, each fire alarm
intermittently starts the operation controller in the sleep
state to execute an operation of receiving a wireless signal.
Specifically, when a start signal is inputted to the.
operation controller from a timer, the operation controller
checks whether or not it can receive a radio wave (i.e.,
fire notification information wirelessly transmitted from
another fire alarm). That is, the operation controller
controls the wireless transmission/reception unit to perform
a receiving operation, and determines whether or not the
strength of a reception signal received by the wireless
transmission/reception unit exceeds a certain reference
value.
When the reception signal strength does not exceed the
reference value, the operation controller stops the
transmission and reception operation of the wireless
transmission/reception unit, sets an intermittent reception
time period in the timer for next intermittent reception,
starts counting, and transitions to the sleep state. On the
other hand, when the reception signal strength exceeds the
reference value, the operation controller continues the
reception state of the wireless transmission/reception unit,
analyzes the reception signal received by the wireless
transmission/reception unit, and determines whether or not
there is any communications to the fire alarm itself. When
there is any communications to the fire alarm, the operation
controller of the fire alarm executes corresponding
processing.
Thus, the operation controller operates intermittently,
and checks the signal strength of a radio wave received by
the wireless transmission/reception unit. When the
operation controller determines that the radio wave cannot
be received, the operation controller stops the transmission
and reception operation of the wireless
transmission/reception unit, thereby reducing power
consumption and lengthening a life span of a battery.
Meanwhile, a conventional wireless communication
DEVICE is disclosed in Patent Document 1. As shown in Fig.
15, the wireless communication DEVICE includes an antenna
1000, an RF unit 1100, an interface unit 1200, and a
microcomputer unit 1300. The RF unit 1100 includes a
demodulation unit 111 for demodulating reception data (a
demodulation signal) from a radio signal received via the
antenna 1000 and a sampling clock generating unit 112 for
generating a sampling clock from a synchronization bit
stream of the demodulation signal.
The interface unit 12 00 includes a frame code register
121 for storing a frame synchronization part (a unique word),
a frame synchronization shift register 122 for sequentially
storing the reception data demodulated by the demodulation
unit 111 in synchronization with the sampling clock, a frame
synchronization detection unit 12 3 for outputting a frame
synchronization detection signal when bit streams of the
frame code register 121 and the frame synchronization shift
register 122 are identical, and a reception buffer 12 4 for
storing the reception data in synchronization with the
sampling clock when a frame synchronization is detected by
the frame synchronization detection unit 123.
The microcomputer unit 1300 includes a RAM 131 for
storing reception data, a controller 132 for decoding an
original message from the reception data stored in the RAM
131, and a transmission unit 133 for transmitting the
reception data stored in the reception buffer 124 to the RAM
131 by the number of times designated by the controller 132,
and outputting a transmission completion signal to the
controller 132 when the transmission of the reception data
is completed.
Hereinafter, a reception operation of the conventional
example will be described with reference to a time chart
shown in Fig. 16. Also, a communications frame exchanged in
the conventional example includes a synchronization bit
stream (preamble) for allowing bit synchronization, a frame
synchronization bit stream (unique word) for allowing frame
synchronization, data including a communications message, a
check code (e.g., a CRC) for an error detection, and the
like.
First, the microcomputer unit 1300 awaits in a sleep
mode until a frame synchronization detection signal is
outputted from the frame synchronization detection unit 123
of the interface unit 1200. And, when the RF unit 1100
receives a radio signal and a frame synchronization
detection signal is outputted from the frame synchronization
detection unit 12 3 of the interface unit 12 00, the
microcomputer unit 1300 starts a rising edge interrupt
process in synchronization with rising of the frame
synchronization detection signal.
When the microcomputer unit 130 0 starts the rising
edge interrupt process, the controller 132 thereof instructs
the interface unit 1200 to output the reception data stored
in the reception buffer 124. In the microcomputer unit 1300,
the reception data outputted from the reception buffer 12 4
is transmitted to the RAM 131 by the transmission unit 133,
and the controller 132 decodes it into the original message.
Further, when a bit stream of a prescribed length is
received from the reception buffer 132, the controller 132
outputs a reset signal to the RF unit 1100 and the interface
unit 12 00. When the RF unit 110 0 and the interface unit
1200 receive the reset signal from the controller 132, the
sampling clock generating unit 112 and the frame
synchronization detection unit 123 are reset.
In the above conventional example, normally, only the
RF unit 1100 and the interface unit 1200 operate and the
microcomputer unit 1300 is in a sleep mode, thereby reducing
power consumption. Further, since a processing load of the
microcomputer unit 1300 is reduced during standby, an
inexpensive (low performance) microcomputer may be used.
Herein, it happens that the demodulation unit 111 of
the RF unit 1100 outputs a signal such as a random bit
stream due to the influence of thermal noise or radio wave
noise even while the antenna 1000 is not receiving a radio
signal. Further, the likelihood is that the random bit
stream includes the same bit stream as the bit stream
(unique word) of the frame synchronization part.
Accordingly, the frame synchronization detection unit 123
may erroneously detect a frame synchronization part and
output a frame synchronization detection signal.
Even in this case, the microcomputer unit 1300 starts
a rising edge interrupt process in synchronization with
rising of the frame synchronization detection signal and the
controller 132 instructs the interface unit 12 00 to output
the reception data stored in the reception buffer 124.
Further, in the microcomputer unit 1300, the reception data
outputted from the reception buffer 12 4 is transmitted to
the RAM 131 by the transmission unit 133, and the controller
132 decodes it into the original message (see Fig. 17).
In the meantime, the sampling clocking generating unit
112 of the RF unit 1100 continuously monitors a bit stream
of the demodulation signal demodulated by the demodulation
unit 111. Since a bit width (pulse width) of the random bit
stream is not uniform, the sampling clock generating unit
112 determines soon that there is out of synchronization and
stops outputting of the sampling clock. When outputting of
the sampling clock is stopped, the frame synchronization
detection unit 123 also stops outputting of the frame
synchronization detection signal.
Further, when the frame synchronization detection
signal falls before a bit stream having a prescribed length
is received from the reception buffer 124, the microcomputer
unit 1300 starts a falling edge interrupt process in which
the data (bit stream) received from the reception buffer 124
is discarded and a reset signal is outputted to the RF unit
1100 and the interface unit 1200, and then turns to be in
standby status (see Fig. 17).
[Patent Document 1] Japanese Patent Application
Publication No. 2010-28331
[Patent Document 2] Japanese Patent Application
Publication No. 2008-176515
[Patent Document 3] Japanese Patent Application
Publication No. 2006-239731
By the way, among the two types of local oscillators
described above, the local oscillator using a frequency
multiplier circuit advantageously consumes less power in
comparison to the local oscillator using a PLL circuit. On
the contrary, the latter local oscillator has a wider
variable range of frequency than that of the former local
oscillator. In many cases, general wireless transceivers
employ the local oscillator using a PLL circuit in
consideration of the fact that the variable range of
frequency is wide. However, the use of the PLL circuit
increases power consumption in comparison to the case of
using a frequency multiplier circuit. Especially, in case
where a wireless transceiver is mounted in the device which
uses a battery as a power source, it is preferred that the
former local oscillator (i.e., the local oscillator using a
frequency multiplier circuit) which consumes less power is
employed, to thereby lengthening a life span of the battery.
In the fire warning system of Patent Document 2, the
operation controller is intermittently operated in order to
reduce power consumption, and the operation controller
started up by a timer checks a state of the reception signal
received by the wireless reception/transmission unit, i.e.,
determines whether or not a radio wave can be received based
on a measurement result of a reception signal strength.
Here, when it is determined that the radio wave cannot
be received, the operation controller stops a
transmission/reception operation of the wireless
transmission/reception unit and then transits its operation
state to a sleep state, However, the operation controller
keeps operating while the wireless transmission/reception
unit is measuring the reception signal strength, which
results in unnecessary power consumption and reducing a life
span of the battery as much.
Further, in Patent Document 3, if a regular radio
signal is received immediately after an erroneous
synchronization occurs due to thermal noise or radio wave
noise, there is a possibility that the regular radio signal
is not received normally. The case in which such a
phenomenon occurs will be described with reference to the
time chart shown in Fig. 18. In Fig. 18, N is a random
value obtained by demodulating thermal noise, P is a
preamble, U is a unique word, and 1,2,3... are data.
It is assumed that a frame synchronization detection
signal rises due to an error detection at the time of tl,
the microcomputer unit 1300 starts a rising edge interrupt
process, and a regular radio signal is received in
succession. Since a pulse width of a bit stream of a
demodulation signal change at the time of t9 when the
regular radio signal is inputted, the sampling clock
generating unit 112 often determines that it is a
synchronization loss.
Here, there may occur a case where the frame
synchronization detection signal falls due to a
synchronization loss at the time t2 before the controller
132 outputs, at the time t3, a control signal for
instructing the interface unit 120 to output the reception
data stored in the reception buffer 12 4. In this case,
since the control signal is outputted from the microcomputer
unit 1300 although the frame synchronization detection
signal has fallen due to the synchronization loss, reception
data is outputted from the reception buffer 12 4 to the
microcomputer unit 13 00 in synchronization with falling of
the control signal at the time t4.
Further, the microcomputer unit 1300 detects falling
of the frame synchronization detection signal since the
rising edge interrupt processing is finished, starts a
falling edge interrupt process, and discards accumulated
reception data (t=t6).
Meanwhile, after the time t2 at which the
synchronization loss is determined, the frame
synchronization detection unit 123 detects a unique word
from the demodulation signal of the regular radio signal and
accordingly the frame synchronization detection signal rises
(t=t5), while the microcomputer unit 1300 is executing the
falling edge interrupt process at the time t5. When the
falling edge interrupt process is terminated (t=t6) , the
microcomputer unit 1300 detects rising of the frame
synchronization detection signal and starts a rising edge
interrupt process, and the controller 132 outputs a control
signal for instructing the interface unit 1200 to output the
reception data stored in the reception buffer 124 (time
t=t8) . Accordingly, the reception data starts to be
accumulated at the time t8. However, the reception data is
continuously outputted from the time t4 of the output
instruction caused by the erroneous detection.
That is, the reception data of the regular radio
signal had already been started to be outputted from the
buffer 124 at the time t8 when the control signal is output
from the microcomputer unit 130 0. Therefore, although the
microcomputer unit 1300 starts to receive data at the time
t7 when the control signal falls, data corresponding to 3
bits already outputted cannot be received. Further, since
contents of the reception buffer 124 is deleted when the
microcomputer unit 130 0 discards the reception data, the
reception data may not exist in the reception buffer 124
when a control signal for instructing to accumulate
reception data after a next frame synchronization detection
is outputted after the rising of the frame synchronization
detection signal (the time t=t5), since the frame
synchronization detection signal has already risen,.
Summary of the Invention
In view of the above, the present invention provides a
wireless transceiver capable of securing a variable range of
frequency while reducing power consumption in a local
oscillator.
Further, the present invention provides a wireless
communication system in which power consumption of a
wireless communications station is further reduced.
Furthermore, the present invention provides a wireless
communication system capable of properly receiving a regular
radio signal even immediately after erroneous
synchronization.
In accordance with a first aspect of the present invention,
there is provided a wireless transmitter/receiver,
including: a local oscillator which oscillates at a
predetermined local oscillation frequency; a mixer for
mixing a local oscillation signal having the local
oscillation frequency outputted from an output terminal of
the local oscillator and a radio signal received by an
antenna; a modulation circuit for modulating the local
oscillation signal to generate a radio signal; and a
transmission/reception switching unit which selectively
switches over between a reception state in which the output
terminal of the local oscillator is connected to the mixer
and a transmission state in which the output terminal is
connected to the antenna without passing through the mixer.
Further, the local oscillator includes: a reference
oscillation unit which oscillates at a predetermined
reference oscillation frequency lower than the local
oscillation frequency; a first frequency conversion unit and
a second frequency conversion unit which convert a reference
oscillation signal having the reference oscillation
frequency outputted from an output terminal of the reference
oscillation unit into the local oscillation signal; a first
switching unit which selectively switches over between a
first input state in which the output terminal of the
reference oscillation unit is connected to an input terminal
of the first frequency conversion unit and a second input
state in which the output terminal of the reference
oscillation unit is connected to an input terminal of the
second frequency conversion unit; and a second switching
unit which selectively switches over between a first output
state in which the output terminal of the local oscillator
is connected to the output terminal of the first frequency
conversion unit and a second output state in which the
output terminal of the local oscillator is connected to an
output terminal of the second frequency conversion unit,
while cooperating with switching operation of the first
switching unit, and wherein the second frequency conversion
unit includes a voltage controlled oscillator, a phase
comparator, a divider, a loop filter, a phase locked loop
circuit having a charge pump, and the first frequency
conversion unit includes a frequency multiplying circuit
having power consumption smaller than that of the phase
locked loop circuit.
With this configuration, a variable range of frequency
can be secured while reducing power consumption in a local
oscillator.
In accordance with a second aspect of the present
invention, there is provided a wireless communication system
for transmitting and receiving a radio signal by a radio
wave between multiple wireless stations, each of the
wireless stations including: a wireless
transmission/reception unit which transmits and receives the
radio signal; a radio level measuring unit which measures a
received signal strength of the radio signal received by the
wireless transmission/reception unit; a timer which outputs
a start-up signal whenever a predetermined intermittent
reception time is lapsed; and an operation controller which
analyzes the reception signal received by the wireless
transmission/reception unit to obtain information related to
the wireless transmission/reception unit itself.
Further, the wireless transmission/reception unit
autonomously executes an operation of receiving the radio
signal based on an operation command set by the operation
controller, and the radio level measuring unit autonomously
executes an operation of measuring the received signal
strength of the radio signal received by the wireless
transmission/reception unit based on an operation command
set by the operation controller; the operation controller
sets an operation command in the wireless
transmission/reception unit and the radio level measuring
unit when the operation controller in a sleep state is
activated by the start-up signal from the timer, and shifts
to the sleep state until the measuring of the received
signal strength by the radio level measuring is completed;
and, when the measurement result of the received signal
strength by the radio level measuring unit is equal to or
greater than a predetermined reference value, the wireless
transmission/reception unit continuously performs a
reception operation and the operation controller analyzes
the reception signal; and, when the measurement result is
smaller than the reference value, the wireless
transmission/reception unit stops the reception operation.
With this configuration, the wireless communication
system can be realized which allows power consumption of a
wireless communications station to be further reduced by
decreasing power consumption of an operation controller.
In accordance with a third aspect of the present
invention, there is provided a wireless communication system,
including: a wireless transmission/reception unit which
processes a radio signal received by an antenna to convert
it into a bit stream of a pulse signal; and an operation
controller which obtains information included in the radio
signal from the bit stream outputted from the wireless
transmission/reception unit, wherein a communications frame
of the radio signal includes a synchronization bit stream
for bit synchronization, a frame synchronization bit stream
for frame synchronization, and data corresponding to the
information.
Further, the wireless transmission/reception unit
includes: a demodulation unit which demodulates the radio
signal into a demodulation signal formed of a bit stream of
a pulse signal; a frame synchronization detection unit which
detects the frame synchronization bit stream from the bit
stream of the demodulation signal and outputs a frame
synchronization detection signal; a reception data buffer
which temporarily accumulates the demodulation signal
outputted from the demodulation unit when the frame
synchronization detection signal is outputted; and a command
processing unit for outputting the reception data
accumulated in the reception data buffer to the operation
controller when a reception data output command is received
from the operation controller.
Furthermore, the operation controller includes: an
interface unit which communicates a signal with the wireless
transmission/reception unit; and a central processing unit
which executes processing of obtaining information included
in the radio signal from the bit stream outputted from the
wireless transmission/reception unit, or processing of
outputting the reception data output command to the wireless
transmission/reception unit while the frame synchronization
detection signal is being output. In addition, when the
reception data output command is not received until the
frame synchronization detection unit stops outputting of the
frame synchronization detection signal after starting to
output the frame synchronization detection signal, the
command processing unit controls the reception data buffer
not to output the reception data accumulated therein even if
the reception data output command is outputted from the
central processing unit of the operation controller before
the frame synchronization detection unit starts to output a
next frame synchronization detection signal.
With this configuration, even immediately after
erroneous synchronization, a regular radio signal can be
properly received.
Brief Description of the Drawings
The above and other objects and features of the
present invention will become apparent from the following
description of embodiments, given in conjunction with the
accompanying drawings, in which:
Fig. 1 is a block diagram schematically showing a
wireless communication system in accordance with the present
invention;
Fig 2 is a block diagram showing a wireless
transceiver in accordance with a first embodiment of the
present invention;
Figs. 3A and 3B are circuit diagrams of major parts of
a local oscillator in the wireless transceiver;
Figs. 4A and 4B are circuit diagrams of major parts of
another example of the local oscillator in the wireless
transceiver;
Fig. 5 is a view showing a configuration of a wireless
communication system constituted by wireless communication
DEVICES each mounting the wireless transceiver thereon;
Fig. 6 is a block diagram of a fire alarm (a master
station and a slave station) in accordance with a second
embodiment of the present invention;
Fig. 7 is a flow chart for explaining an intermittent
reception operation of the fire alarm in accordance with the
second embodiment;
Fig. 8 is a flow chart for explaining an intermittent
reception operation of the fire alarm in accordance with a
modification of the second embodiment;
Fig. 9 is a view showing configuration of a facility
control system using the wireless transceiver in accordance
with the first embodiment;
Fig. 10 is a block diagram of major parts of a
wireless communication system in accordance with a third
embodiment of the present invention;
Figs. 11 to 14 are time charts for explaining the
operation of the third embodiment of the present invention;
Fig. 15 is a block diagram showing a conventional
example; and
Figs. 16 to 18 is time charts for explaining the
operation of the conventional example.
Detailed Description of the Embodiments
Hereinafter, embodiments of the present invention will
be described in more detail with reference to the
accompanying drawings which form a part hereof. In the
drawings, the same reference numerals are used for the same
or like parts throughout the drawings, and a redundant
description thereof will be omitted.
(Embodiment 1)
A first embodiment of the present invention will be
described in detail with reference to Figs. 1 to 5. Fig. 1
illustrates a wireless communication system employing a
wireless transceiver in accordance with the first embodiment
of the present invention.
As shown in Fig. 2, the wireless transceiver
(transmitter/receiver) of the present embodiment includes a
local oscillator 1, an antenna 2, an RF filter 3, a low
noise amplifier (LNA) 4, and a mixer 5. Further, the
wireless transceiver includes an intermediate frequency (IF)
filter 6, an IF amplifier 7, a demodulation unit 8, a
transmission unit 9, an antenna switching unit 10, a
transmission/reception switching unit 11, and a controller
12 (which corresponds to an operation controller in Fig. 1).
Here, the wireless transceiver of the present
embodiment employs, for example, a frequency modulation
{frequency shift keying (FSK)) scheme as a modulation scheme.
When it transmits a radio signal from the antenna 2, it
executes modulation by changing a dividing ratio m of a
programmable divider 32 (to be described later) according to
a signal to be transmitted and transmits it. Further, when
it receives the radio signal by the antenna 2, it converts
the radio signal into a signal having an IF frequency lower
than that (radio frequency) of the radio signal and then
executes demodulation on the signal by the demodulation unit
8.
However, the modulation method is not limited to the
foregoing modulation processing. For example, a signal
(local oscillation signal) outputted from the local
oscillator 1 may be mixed with the modulation signal by the
transmission unit 9, a capacity of a variable capacitance
unit such as a switched capacitor or a variable capacitance
diode (to be described later) may be changed based on a
modulation signal. Further, the modulation scheme is not
limited to the frequency modulation scheme, and for example,
a phase modulation (phase shift keying) scheme such as a
binary phase shift keying (BPSK) or the like may be used.
The local oscillator 1 includes a reference
oscillation unit 20, a multiplying unit 21, a PLL unit 22, a
first switching unit 23, and a second switching unit 24.
The reference oscillation unit 20 oscillates at a reference
oscillation frequency fx lower than the radio frequency to
output a reference oscillation signal. Herein, the
reference oscillation unit 20 includes a variable
capacitance unit (not shown) having a switched capacitor, a
variable capacitance diode or the like which is not shown.
Accordingly, the controller 12 can select the reference
oscillation frequency fx from among multiple frequencies fxl,
fx2, fx3,... by changing a capacity of the variable
capacitance unit.
The multiplying unit 21, which corresponds to a first
frequency conversion unit, frequency-converts the reference
oscillation signal outputted from the reference oscillation
unit 2 0 into a signal (local oscillation signal) having a
local oscillation frequency fy. Similarly, the PLL unit 22,
which corresponds to a second frequency conversion unit,
frequency-converts the reference oscillation signal
outputted from the reference oscillation unit 20 to the
local oscillation signal having the local oscillation
frequency fy.
The first switching unit 23 selectively switches
between a first input state in which an output terminal of
the reference oscillation unit 2 0 is connected to an input
terminal of the multiplying unit 21 and a second input state
in which the output terminal of the reference oscillation
unit 20 is connected to an input terminal of the PLL unit 22.
The second switching unit 24 selectively switches between a
first output state in which an output terminal of the local
oscillator 1 is connected to an output terminal of the
multiplying unit 21 and a second output state in which the
output terminal of the local oscillator 1 is connected to an
output terminal of the PLL unit 22.
The multiplying unit 21 includes a frequency
multiplier circuit outputting a signal (i.e., the local
oscillation signal) having a frequency (the local
oscillation frequency fy) of an integer multiple of the
frequency fx of the input signal (i.e., the reference
oscillation signal) by using non-linearity of input/output
characteristics of, e.g., a transistor or the like. Here,
since the multiplying unit 21 has been known, a description
of a detailed configuration and operation thereof will be
omitted. Alternatively, a known delay locked loop circuit
may also be used as the multiplying unit 21.
The PLL unit 22, which is well known, includes a
voltage controlled oscillator (VOC) 30, a 1/n divider 31, a
programmable divider 32, a phase comparator 33, a loop
filter 34, and a charge pump 35. The 1/n divider 31 divides
the reference oscillation signal by n (where n is a positive
integer). Further, the programmable divider 32 divides an
output signal from the VCO 30 by m (where m is a positive
integer which is different from n, or a fractional number).
The phase comparator 33 detects a phase difference between
the two dividers 31 and 32 and outputs a signal
corresponding to the phase difference.
The charge pump 35 charges or discharges electric
charges based on a signal outputted from the phase
comparator 33. The loop filter 34 smoothes a signal
outputted by charging or discharging of the charge pump 35.
The VCO 30 is controlled by a DC signal outputted from the
loop filter 34, and a local oscillation signal having the
local oscillation frequency fy (=m/nxfx) is outputted from
the PLL unit 22. Here, the dividing numbers n and m of the
two dividers 31 and 32 may be set to arbitrary integer
values (here, m may be a fractional number) by the
controller 12, respectively, and the local oscillation
frequency fy of the local oscillator 1 can be changed by
setting the dividing numbers n and m as appropriate integer
values (here, m may be a fraction number).
Here, when comparing the multiplying unit 21 and the
PLL unit 22 having the configuration as mentioned above,
power consumption of the multiplying unit 21 is smaller than
that of the PLL unit 22, and a variable range of the local
oscillation frequency fy of the PLL unit 22 is wider than
that of the multiplying unit 21.
In case of the PLL unit 2, an operation power of the
VCO 3 0 is supplied from an external power source (system
power source) Vcc, and a switch SW1 is provided to turn on
or off power supply to the VCO 30 from the system power
source Vcc. That is, when the switch SW1 is turned off by
the controller 12, a power terminal is separated from the
system power source Vcc, turning off the VCO 30, and when
the switch SW1 is turned on, the power terminal is connected
to the system power source Vcc, operating the VCO 30.
Further, a bypass capacitor Cl electrically connects the
power terminal of the VCO 30 with a ground with respect to
an alternating current to thereby stabilize a power source
voltage.
In the first switching unit 23, a common terminal 23c
connected to the output terminal of the reference
oscillation unit 20 is selectively switched between a
switching terminal 2 3a connected to an input terminal of the
multiplying unit 21 and a switching terminal 2 3b connected
to the input terminal of the PLL unit 22 (an input terminal
of the 1/n divider 31). Also, in the second switching unit
24, a common terminal 2 4c connected to a common terminal lie
of the transmission/reception switching unit 11 is
selectively switched between a switching terminal 24a
connected to the output terminal of the multiplying unit 21
and a switching terminal 24b connected to the output
terminal of the PLL unit 22 (the output terminal of the VCO
30) .
In the transmission/reception switching unit 11, a
common terminal lie is selectively switched between a
switching terminal 11a connected to an input terminal of the
mixer 5 and a switching terminal lib connected to an input
terminal of the transmission unit 9. Further, in the
antenna switching unit 10, a common terminal 10c connected
to the antenna 2 is selectively switched between a switching
terminal 10a connected to an input terminal of the RF filter
3 and a switching terminal 10b connected to an output
terminal of the transmission unit 9.
The antenna switching unit 10, the
transmission/reception conversion unit 11, the first and
second switching units 23 and 24 are controlled to be
switched by the controller 12. The controller 12
substantially simultaneously controls switching of the first
switching unit 23 and the second switching unit 24, and
substantially simultaneously controls switching of the
antenna switching unit 10 and the transmission/reception
switching unit 11.
Here, in terms of preventing undesirable erroneous
operation, the four units of the first switching unit 23,
the second switching unit 24, the antenna switching unit 10,
and the transmission/reception switching unit 11 may be
substantially simultaneously controlled to be switched, or
preferably, the antenna switching unit 10 and the
transmission/reception switching controller 11 are
substantially simultaneously controlled to be switched after
the first switching unit 23 and the second switching unit 24
are first substantially simultaneously controlled to be
switched.
The transmission unit 9 includes an amplifier for
amplifying a radio signal (RF signal) after modulation, and
amplifies the radio signal (RF signal) outputted from the
local oscillator 1 and outputs the same to the antenna
switching unit 10. And, a radio signal inputted through the
antenna switching unit 10 is radiated as a radio wave from
the antenna 2. The transmission unit 9 is well known, so a
description of a detailed configuration and operation
thereof will be omitted.
Here, the local oscillator 1 selectively outputs a
local oscillation signal having a receiving local
oscillation frequency (i.e., a frequency equal to a
difference between a radio frequency and an intermediate
frequency) which is used in receiving and is lower than a
radio frequency of a radio signal, and a local oscillation
signal having a transmitting local oscillation frequency
which is used in transmitting and is equal to a radio
frequency. In the wireless transceiver in accordance with
the present embodiment, the first frequency conversion unit
(the multiplying unit 21) outputs the local oscillation
signal which is relatively frequently selected among the
receiving local oscillation signal and the transmitting
local oscillation signal, while the second frequency
conversion unit (the PLL unit 22) outputs the local
oscillation signal which is less frequently selected
thereamong.
For example, when the frequency of receiving a radio
signal (including an standby operation in which a radio
signal to be received is being awaited, and this is also
applied in the same manner hereinafter) is higher than the
frequency of transmitting a radio signal, it is possible to
reduce power consumption by outputting the receiving local
oscillation signal through the multiplying unit 21 rather
than through the PLL unit 22. Conversely, when the
frequency of transmitting a radio signal is higher than the
frequency of receiving a radio signal, it is possible to
reduce power consumption by outputting the transmitting
local oscillation signal through the multiplying unit 21
rather than through the PLL unit 22. The conditions of
using the multiplying unit 21 and the PLL unit 22 are not
limited to the frequencies of the transmission and the
reception.
For example, as described later, in case where
multiple frequency channels are selectable as a radio
frequency, the multiplying unit 21 may be used as a
frequency conversion unit of the local oscillator 1 when a
default (initial state) frequency channel is selected, while
the PLL unit 22 may be used as the frequency conversion unit
of the local oscillator 1 when channels other than the
default frequency channel are selected. This can also
reduce power consumption.
The wireless transceiver in accordance with this
embodiment may be used in a wireless communication device Xj
(where j is a natural number) as shown in Fig. 5, for
example. The wireless communication device Xj includes at
least one of various types of environment measurement
sensors Sk (where k is a natural number irrelevant to j)
such as an optical sensor SI, a thermal sensor S2, a
chemical sensor S3, a pressure sensor S4,... and the like.
Further, when the wireless communication device Xj, in
a state of being attached to a ceiling surface, a wall
surface or the like, senses a change in a surrounding
environment of an installation location, it transmits a
radio signal to inform other wireless communication device
Xj of the change. Here, wireless communication device Xj
all may have the same type of environment measurement sensor
Sk or each may have different type of environment
measurement sensor Sk.
For example, a wireless communication device XI
activates a wireless transceiver thereof (the wireless
transceiver in accordance with the present embodiment) at a
constant intermittent reception interval, and receives a
first radio signal Sigl sent out from one of the other
wireless communication devices X2, X3, X4, .... In this case,
when the wireless communication device XI cannot receive the
first radio signal Sigl having a certain time period from
any one of the other wireless communication devices X2, X3,
X4, ..., the wireless communication device XI immediately
stops the wireless transceiver to prevent battery
consumption.
On the other hand, when the wireless communication
device XI can receive the first radio signal Sigl, the
wireless communication device XI transmits a second radio
signal Sig2 from the wireless transceiver of the wireless
communication device XI itself, the second radio signal Sig2
indicating that the first radio signal Sigl could be
received by wireless communication device XI itself and the
first radio signal Sigl is being transmitted to the other
unspecified wireless communication devices X2, X3, X4, ....
As shown in Fig. 5, each of the wireless communication
devices Xj includes at least one of a visual notification
unit X100 sensed visually by human and a sound alarming unit
X101 sensed acoustically. Thus, when one (the wireless
communication device XI in Fig, 5) of the wireless
communication devices Xj senses the abnormal occurrence
therearound, it operates the visual notification unit X100
or the sound alarming unit X101 to notify surroundings of
the abnormal occurrence and simultaneously transmit the
first radio signal Sigl.
Further, when another wireless communication device
(in Fig. 5, only the wireless communication device X2
closest to the wireless communication device XI) receives
the first radio signal Sigl, it analyzes an address of the
first radio signal Sigl, and transmits a second radio signal
Sig2 to the other wireless communication devices (in Fig. 5,
wireless communication devices X3 and X4 other than XI and
X2) which have not received the first radio signal Sigl.
The wireless communication device X3 cannot recognize
whether or not the wireless communication device X4 has
received the second radio signal Sig2 from the wireless
communication device X2, so the wireless communication
device X3, upon receiving the second radio signal Sig2,
continuously transmits the second radio signal Sig2 to the
wireless communication device X4 .
As a result, in addition to the single wireless
communication device (the wireless communication device XI)
which has firstly sensed the abnormal occurrence, all the
pre-registered wireless communication devices (the wireless
communication devices XI, XI, X3, and X4) can cooperate and
notify the surroundings of the abnormal occurrence.
An operation of the wireless transceiver of the
present embodiment will be described in more detail with
relation to the foregoing operation of the wireless
communication device.
First, while no the wireless communication devices
senses a change in a surrounding environment of an
installation location, the controller 12 repeatedly counts
intermittent reception intervals by a timer (not shown), and
activates the wireless transceiver in a receivable state
whenever the counting of the intermittent reception interval
is completed.
Specifically, when the counting of intermittent
reception interval is completed, the controller 12 connects
the common terminal 10c of the antenna switching unit 10 to
the switching terminal 10a of the RF filter 3 and
simultaneously connects the common terminal lie of the
transmission/reception switching unit 11 to a switching
terminal 11a of the mixer 5. Further, the controller 12
connects the common terminal 23c of the first switching unit
23 to the switching terminal 23a connected to the input
terminal of the multiplying unit 21, and simultaneously
connects the common terminal 24c of the second switching
unit 2 4 to the switching terminal 24a connected to the
output terminal of the multiplying unit 21. In the meantime,
the controller 12 turns off the switch SW1 and separates the
power source terminal of the VCO 30 from the system power
source Vcc to thereby stop the PLL unit 22.
In the receivable state, the IF amplifier 7 amplifies
an intermediate frequency (IF) signal and outputs a received
signal strength indication (RSSI) signal indicating a signal
strength of an input signal (IF signal before being
amplified) to the controller 12. When the RSSI signal is
smaller than a threshold value, the controller 12 determines
that the radio wave received by the antenna 2 is not a
desired wave (a radio wave transmitted from another wireless
communication device), and immediately stops the wireless
transceiver. On the other hand, when the RSSI signal is
equal to or greater than the threshold value, the controller
12 determines that the received radio wave is highly likely
to be a desired wave, and demodulates it by the demodulation
unit 8 without stopping the wireless transceiver.
When the radio signal demodulated by the demodulation
unit 8 is the first radio signal transmitted from another
wireless communication device, the controller 12 connects
the common terminal 10c of the antenna switching unit 10 to
the switching terminal 10b of the transmission unit 9 and
simultaneously connects the common terminal lie of the
transmission/reception switching unit 11 to the switching
terminal lib of the transmission unit 9. Further, the
controller 12 connects the common terminal 23c of the first
switching unit 23 to the switching terminal 23b connected to
the input terminal of the PLL unit 22 and simultaneously
connects the common terminal 24c of the second switching
unit 24 to the switching terminal 24b connected to the
output terminal of the PLL unit 22. Then, the controller 12
turns on the switch SW1 and connects the power source
terminal of the VCO 30 to the system power source Vcc to
thereby operate the PLL unit 22.
In this case, the controller 12 encodes a transmission
frame including a signal indicating that the first radio
signal to be transmitted to the other wireless communication
devices is transmitted, and generates a signal to be
wirelessly transmitted by modulating the local oscillation
signal with the frame by using the PLL unit 22 of the local
oscillator 1. Then, the signal is amplified by the
transmission unit 9, and is outputted to the antenna 2
through the antenna switching unit 10. Thus, the second
radio signal is transmitted from the antenna 2.
When the wireless communication device intermittently
performs reception, power consumption can be reduced by
operating the first frequency conversion unit (the
multiplying unit 21) as the frequency conversion unit of the
local oscillator 1. Further, when the wireless
communication device transmits the first or the second radio
signal, as described above, the second frequency conversion
unit (the PLL unit 22) is selected as a frequency conversion
unit of the local oscillator 1 and serves as a modulation
circuit, thereby covering a frequency (radio frequency) that
the multiplying unit 21 cannot cope with. As a result, a
variable range of frequency can be secured while reducing
power consumption of the local oscillator 1.
In the above-described wireless communication system,
since it is determined that the frequency that the wireless
transceiver of each wireless communication device Xj
operates in a receivable state is higher than the frequency
that it operates in a transmittable state, as described
above, power consumption can be reduced by selecting the
multiplying unit 21 in the receivable state. Further, in
the transmittable state, the PLL unit 22 is selected so that
a selectable range (variable range) of the local oscillation
frequency can be secured, which makes it possible to
transmit a signal at a desired radio frequency.
As described above, it is preferred that the frequency
(radio frequency) of the radio wave used by the wireless
communication device can be appropriately selected based on
an environment of an installation location among multiple
radio frequencies (frequency channels). When a frequency
channel changes, the local oscillation frequency fy of the
local oscillator 1 needs to be changed depending on a
frequency channel. In the PLL unit 22, the local
oscillation frequency fy can be easily changed by adjusting
the dividing numbers j and k, but it is not easy to adjust
the multiplier of the multiplying unit 21 to change the
local oscillation frequency fy in comparison to the
adjustment of the dividing numbers j and k of the PLL unit
22.
To that end, in the present embodiment, a variable
capacitance unit (not shown) including a switched capacitor,
a variable capacitance diode or the like is provided in the
reference oscillation unit 20. Accordingly, the controller
12 selects the reference oscillation frequency fx of the
reference oscillation unit 20 among multiple frequencies fxl,
fx2, fx3,... by changing a capacity of the variable
capacitance unit. As a result, the local oscillation
frequency fy can be easily changed while fixing the
multiplier of the multiplying unit 21. Further, even when a
frequency channel of a radio frequency is changeable, the
multiplying unit 21 can be used as a frequency conversion
unit of the local oscillator 1 in the receivable state.
Therefore, even in the receivable state, power consumption
of the wireless transceiver (the local oscillator 1) can be
reduced by deleting a need for using the PLL unit 22.
Meanwhile, in case where the wireless transceiver is
activated to perform a receiving operation at an
intermittent reception interval and power supply to the
local oscillator 1 is turned on and off accordingly,
charging current flows into the bypass capacitor CI
connected to the power terminal of the VCO 30 in the PLL
unit 22, thereby unnecessarily consuming power. However, in
the present embodiment, the connection between the bypass
capacitor CI and the system power source Vcc is switched by
a opening/closing unit (the switch SWl) . Accordingly, the
controller 12 closes (turns on) the switch SWl only when the
PLL unit 22 is used as a frequency conversion unit of the
local oscillator 1. Thus, it is possible to prevent the
bypass capacitor CI from being charged or discharged when
the PLL unit 22 is not used, thereby suppressing unnecessary
power consumption.
Further, as shown in Fig. 3A, an additional switch SW2
may be added between the power terminal of the VCO 30 and
the bypass capacitor CI, and be turned on and off to operate
in conjunction with the switch SWl provided between the
power terminal of the VCO 30 and the system power source Vcc.
Herein, when the switch SWl (or the switch SW2) is
closed and the bypass capacitor CI is connected to the
system power source Vcc, an inrush current (charging
current) may flow, which results into a temporal drop in a
voltage of the system power source Vcc. To cope with this,
preferably, a current limiting resistor R is provided
between the bypass capacitor CI and the system power source
Vcc to limit the inrush current, as shown in Fig. 3B,
thereby reducing a temporary drop in the voltage of the
system power source Vcc.
In case of a normal state in which an inrush current
does not flow, however, since power is unnecessarily
consumed by the current limiting resistor R and the voltage
applied to the power terminal of the VCO 30 is dropped, as
shown in Figs. 4A and 4B, preferably, a short-circuit unit
(the SW3) for connecting the system power source Vcc and the
power terminal of the VCO 30 is provided. Accordingly, the
controller 12 closes the switch SWl in a state in which the
switch SW3 is open to thus limit an inrush current by the
current limiting resistor R (see Fig. 4A), and, after
closing the switch SW3, the controller 12 opens the switch
SWl to thus separate the current limiting resistor R from
circuit (see Fig. 4B) . As a result, since a current does
not flow through the current limiting resistor R in a normal
state, unnecessary power consumption and voltage drop can be
avoided. Here, the switch SWl may be in a closed state.
By the way, a condition for switching over, as the
frequency conversion unit of the local oscillator 1, between
the multiplying unit 21 to the PLL unit 22 is not limited to
the above-described reception and transmission frequency.
As described above, the multiplying unit 21 generates a
local oscillation signal by obtaining a frequency of an
integer multiple of a reference oscillation frequency by
using the delay locked loop circuit or by using non-
linearity. For that reason, comparing to a local
oscillation signal outputted from the PLL unit 22, the local
oscillation signal outputted from the multiplying unit 21
includes a great amount of unnecessary frequency components
which are an integer multiple of the reference oscillation
frequency besides the desired local oscillation frequency.
Accordingly, if the multiplying unit 21 is used as a
frequency conversion unit of the local oscillator 1, there
is a high probability that a radio wave (interference wave)
having a frequency different from that of a target radio
wave (radio signal) is received and interfering waves
(specifically, interfering waves having frequency components
of IF ± an integer multiple of reference oscillation
frequency) is easy to be received. On the contrary, if the
PLL unit 22 is used, relatively small unnecessary frequency
components are included in the oscillation frequency after
the frequency conversion, so it is advantageously hardly
affected by interfering waves as compared to the multiplying
unit 21. However, since the battery is used as a power
source in the foregoing wireless communication device, the
life span of the battery is reduced in comparison to the
case of using the multiplying circuit when the PLL circuit
is used as a frequency conversion unit of a local oscillator.
In this case, only when the reception signal (IF
signal) outputted from the mixer 5 is not normally
demodulated by the demodulation unit 8, the controller 12
may switch the first switching unit 23 to the second input
state and simultaneously switch the second switching unit 24
to the second output state. Specifically, when a bit
synchronization of the reception signal (IF signal) is not
achieved by the demodulation unit 8 though the R3SI signal
is greater than a threshold value, the controller 12 may
determines that a radio signal is not normally received due
to an influence of interfering waves, and adjusts the first
and second switching units 23 and 24 to switch over from the
multiplying unit 21 to the PLL unit 22 as the frequency
conversion unit of the local oscillator 1. By doing so, the
life span of the battery can be lengthened and an influence
of interfering waves can be avoided.
Here, if switching over is performed from the
multiplying unit 21 to the PLL unit 22 during reception, a
radio signal cannot be normally received until a circuit
operation of the PLL unit 22 is stabilized. When a
intensity of an interfering wave is high in a usage
environment of the wireless transceiver (an installation
environment of the wireless communication device), the
frequency conversion unit of the local oscillator 1 may be
frequently switched from the multiplying unit 21 to the PLL
unit 22. However, when the intensity of the interfering
wave is low in the usage environment, it is expected that a
radio signal can be normally received by using the
multiplying unit 21 as the frequency conversion unit of the
local oscillator 1.
In this regard, the controller 12 may perform a
switching control on the first and second switching units 23
and 2 4 as describe above, during a certain time period from
a time point at which the wireless transceiver is started up
(i.e., a time point at which the operation of the wireless
communication system is started up by the wireless
communication device group), and, after a lapse of the
certain time period, the controller 12 may keep the state of
the first and second switching units 23 and 24 at the time
point when the certain time period expires.
Further, when a certain time period (e.g., several
hours) has passed after switching from the multiplying unit
21 to the PLL unit 22 during reception, the controller 12
may check whether or not reception is available if the PLL
unit 2 2 is switched from the PLL unit 22 to the multiplying
unit 21. When the reception is available, the multiplying
unit 21 is used. In this case, when the number of switching
the first switching unit 23 to the second input state and
simultaneously switching the second switching unit 24 to the
second output state exceeds a certain number of times, the
controller 12 may switch the first switching unit 23 to the
second input state switch and simultaneously the second
switching unit 2 4 to the second output state when starting
an intermittent reception.
By doing so, it is possible to further lengthen the
life span of the battery by using the multiplying unit 21 as
the frequency conversion unit of the local oscillator 1, in
an environment in which an influence of interfering wave is
small. Further, in an environment in which an influence of
interfering wave is large, it is possible to normally and
rapidly receive a radio signal by using the PLL unit 22 as
the frequency conversion unit of the local oscillator 1.
Generally, an influence of an interfering wave is
larger at daytime than during nighttime. In light of this,
a clock for counting time may be provided in the controller
12. Accordingly, in a time zone in which a counting time of
the clock is daytime, the controller 12 may switch the first
switching unit 23 to the second input state and
simultaneously switches the second switching unit 24 to the
second output state, and, in a time zone of the nighttime,
may switch the first switching unit 23 to the first input
state and simultaneously switch the second switching unit 24
to the first output state.
By doing so, it is possible to lengthen the life span
of the battery by using the multiplying unit 21 as a
frequency conversion unit of the local oscillator 1 in the
time zone (nighttime) in which an influence of interference
is small. Further, it is possible to normally and quickly
receive a radio signal by using the PLL unit 22 as a
frequency conversion unit of the local oscillator 1 in the
time zone (daytime) in which an influence of interference is
large.
Meanwhile, the reference oscillation unit 20 may be
configured such that multiple types of reference oscillation
signals each having different reference oscillation
frequencies fxl, fx2,.„ are selectively switched to be output,
and the first frequency conversion unit may include a
plurality of multiplying circuits 1 - i(where i^2) each
having a different multiplier. Accordingly, when a
reception signal is not normally demodulated in a state in
which the controller 12 has switched the first switching
unit 23 to the first input state and simultaneously the
second switching unit 2 4 to the first output state,
combinations of the reference oscillation frequencies
fxi (i=l, 2, . ) of the reference oscillation signals and the
multipliers of the multiplying circuits may be sequentially
changed without changing the local oscillation frequency fy.
For example, 420 MHz of the local oscillation
frequency fy is obtained by multiplying the reference
oscillation frequency fxl=52.5 MHz by 8, or multiplying the
reference oscillation frequency fx2=70 MHz by 6. In the
former case, frequency components of the interfering wave
mainly include frequencies of an integer multiple of 52.5
MHz+IF, while, in the latter case, they mainly include
frequencies an integer multiple of 7 0 MHz ± IF. That is,
the frequencies of the interfering waves are different, and
the influence of interfering waves can be reduced by
selecting a combination of a reference oscillation frequency
and a multiplier in order to avoid an influence of an
existing interfering wave.
In this manner, a reception signal may be normally
received by changing the combinations of the reference
oscillation frequency fxi and the multiplier of the
multiplying circuits without changing the local oscillation
frequency fy. However, when a reception signal is not
normally demodulated by any combination, the controller 12
may switch the first switching unit to the second input
state and simultaneously switch the second switching unit 24
to the second output state to thereby select the PLL unit 22.
Hereinafter, in accordance with a second embodiment of
the present invention, a wireless communication system (a
fire alarm system) will be described where a fire alarm
which makes an alarm sound upon detecting a fire and
transmits a radio signal (including fire notification
information) by using a radio wave serves as a wireless
communications station, with reference to Figs. 6 to 8.
(Second Embodiment)
Fig 6 is a view showing the configuration of a
wireless communication system to which the second embodiment
is applicable, which corresponds to a simplified
illustration of Fig. 1. In the present embodiment, a fire
alarm system includes multiple (two in the drawing) fire
alarms TR. In the following description, respective fire
alarms will be denoted by fire alarms TR1, TR2, ..., TRn
(where n Is a positive integer) , and in case of generally
describing a fire alarm, a fire alarm TR will be denoted.
The fire alarm TR includes an operation controller 100,
a wireless transmission/reception unit 200, a radio level
measuring unit 300, a timer 400, a fire detection unit 500,
an alarm unit 600, and a battery power unit 700.
The wireless transmission/reception unit 200 transmits
a radio signal through a radio wave from an antenna 2a and
receives a radio signal transmitted from a different fire
alarm TR by the antenna 2a. The wireless
transmission/reception unit 200 has a function of
autonomously executing a certain operation, namely/ an
operation of receiving a radio signal when an operation
command is set by the operation controller 100. Further,
the wireless transmission/reception unit 200 may be used,
for example, based on ^wireless communications station of a
small power security system' prescribed in Subparagraph 3,
Paragraph 4, Article 6 of enforcement regulations, Japan
Radio Law.
The radio level measuring unit 300 measures a
reception signal strength of a radio signal received by the
wireless transmission/reception unit 200. The radio level
measuring unit 300 has a function of autonomously executing
a certain operation, namely, an operation of measuring a
reception signal strength of a radio signal when an
operation command is set by the operation controller 100.
The timer 4 00 repeatedly performs a counting operation
of a time interval (this time interval is called an
intermittent reception time) of an intermittent reception
operation as described later, and whenever a counting
operation is completed, the timer 400 outputs a start-up
signal to the operation controller 100.
When the fire detection unit 500 detects a fire, for
example, by detecting smoke, heat, a spark or the like that
is generated due to a fire, it activates the operation
controller 100 which is in a sleep state, and outputs a fire
detection signal to the operation controller 100. Further,
a detailed configuration of the fire detection unit 50 0 is
well known, so a detailed description thereof will be
omitted.
The alarm unit 600 outputs a fire alarm (hereinafter,
referred to as an 'alarm sound' ) by a sound (a buzzer sound,
a voice message or the like) from a speaker (not shown),
thus notifying ambient people of the outbreak of a fire.
The battery power unit 7 00 supplies each part with
operation power by using, as a power source, a battery such
as a dry cell or the like.
The operation controller 10 0 includes a microcomputer
(not shown) or a memory unit 100a {e.g., a rewritable non-
volatile semiconductor memory) as main components. The
operation controller 100 performs various functions as
described later by executing programs stored in a memory
(ROM, EEPROM or the like) (not shown) by the microcomputer.
Also, when a fire is not detected or when the intermittent
reception operation is not executed by controlling the timer
4 00, the operation controller 100 may stop a
transmission/reception operation of the wireless transceiver
2 00 to thereby save power and changes its operation state to
a sleep state consuming low power.
When the fire detection unit 500 detects a fire while
the operation state of the operation controller 100 is in
the sleep state, the fire detection unit 500 outputs a
start-up signal to the operation controller 100 to activate
the operation controller 100. Being activated from the
sleep state, the operation controller 10 0 performs a
notification operation by using, e.g., a buzzer provided in
the alarm unit 600 based on the fire detection signal
inputted from the fire detection unit 500. Further, instead
of buzzing sound, the operation controller 100 may output a
voice message (e.g. 'fire broke out' , etc.) previously
stored in a memory (or the memory unit 10 0a) through the
speaker to thus execute a notification operation.
Furthermore, in order for a different fire alarm TR to
perform the notification operation in cooperation, the
operation controller 100 transmits a radio signal including
fire notification information notifying the outbreak of fire
from the wireless transmission/ reception unit 2 00. In the
different fire alarm TR, when the operation controller 10 0
receives the fire notification information included in the
radio signal through the wireless transmission/reception
unit 200, the operation controller 100 controls the alarm
unit 600 to perform a notification operation. Herein, a
unique identification code is assigned to each fire alarm
TRn, and is stored in the memory unit la, so a destination
of a radio signal and a source fire alarm TRn (an origin of
fire) thereof can be specified by using the identification
code.
Here, the operation controller 100 is constituted by a
low power consuming microcontroller which is driven by, e.g.,
a battery, and this type of microcontroller may be, e.g.,
MSP4340 (Registered Trademark) available from Texas
Instruments Inc. Alternatively, there is disclosed ASIC for
communications as a single chip in which an intermittent
reception function is provided by timer function or wireless
transmission/reception unit according to a particular small
power wireless communications station. Such ASIC is
available from, e.g., ML7 066 of OKI Semiconductor Co., Ltd.
or the like, and the wireless transmission/reception unit
2 00, the radio level measuring unit 300, or the timer 4 is
realized by using such ASIC.
The operation controller 100 is powered by the battery
power unit 700, and reduces power consumption to thereby
lengthen a life span of the battery. That is, except for
the case of fire detection, an operation state of the
operation controller 100 is shifted to a sleep state and the
wireless transmission/reception unit 2 00 also stops a
transmission/reception operation. Also, in order to receive
a radio signal transmitted from the different fire alarm TR,
the operation controller 100 is activated to check whether
or not a desired radio wave {a radio signal transmitted from
the different fire alarm TR) can be received (intermittent
reception) whenever a certain intermittent reception time
has lapsed.
When a desired radio wave can be received in the
intermittent reception, the operation controller 100
controls the wireless transmission/reception unit 200 to
continue a reception operation, and analyzes a signal
received by the wireless transmission/reception unit 200.
On the other hand, when it is not received in the
intermittent reception, the operation controller 100
immediately stops the reception operation of the wireless
transmission/reception unit 2 00 and enters a standby state.
Further, checking of radio wave reception is executed by the
radio level measuring unit 300 based on a received signal
strength indication (RSSI) signal outputted from the
wireless transmission/reception unit 200. Here, the RSSI
signal is a DC voltage signal proportional to a magnitude of
a received signal strength.
For example, vRadio facility of wireless
communications station of small power security system'' in
Paragraph 17, Article 49 of radio facility regulations of
enforcement regulation, Japan Radio Law, provides that the
emission of a radio wave should be terminated within three
seconds after the radio wave is emitted, and a radio wave
cannot be emitted until two seconds have been lapsed
therefrom (see Paragraph 5 of the same Article).
That is, it is prescribed that a time period for which
a radio wave is transmitted is within three seconds and a
pause period of at least two seconds after a transmission is
provided. Thus, each fire alarm TR finishes transmission
within the transmission time period in conformity with the
radio facility regulation, stops transmission during the
pause period and is switched to a reception available state.
Here, the intermittent reception time, which is a time
interval of the intermittent reception operation, is set to
be longer than the transmission time (within three seconds)
prescribed in the radio facility regulation.
Next, the intermittent reception operation will be
described in detail with reference to a flow chart of Fig. 7.
Before entering the sleep state, the operation controller
100 sets an intermittent reception time in the timer 400,
starts a counting operation {step SI) and then enters the
sleep state (step S2) . When the timer 4 00 completes the
counting operation (counts up) of the intermittent reception
time (Yes in step S3) , the timer 4 00 outputs a start-up
signal to the operation controller 10 0 to activate the
operation controller 100 from the sleep state (step S4).
Being activated from the sleep state, the operation
controller 100 sets an operation command in each of the
wireless transmission/reception unit 200 and the radio level
measuring unit 300 (step S5), and shifts to the sleep state
(step S6) until a measuring operation by the radio level
measuring unit 3 00 is completed.
When an operation command is set by the operation
controller 10 0, the wireless transmission/reception unit 200
autonomously executes a reception operation (step S7). Also,
when the operation command is set by the operation
controller 100, the radio level measuring unit 300
autonomously executes an operation of measuring a received
signal strength of the signal received by the wireless
transmission/reception unit 200 (step S8) . When the radio
level measuring unit 300 completes the measuring operation,
it outputs a start-up signal to the operation controller 100
to activate the operation controller 100 from the sleep
state (step S9) . Activating from the sleep state, the
operation controller 100 obtains the measurement result of
the received signal strength from the radio level measuring
unit 300, and compares the measurement result of the
received signal strength with a certain reference value
(step S10). Here, the reference value is set to be a value
which is higher than a received signal strength in a state
in which a radio signal is not transmitted from another fire
alarm TR, and lower than a received signal strength in a
state in which a radio signal is transmitted from another
fire alarm TR.
When the measurement result of the received signal
strength is equal to or greater than the reference value
(Yes in step S10), the operation controller 100 determines
that a radio signal is transmitted from the other fire alarm
TR, controls the wireless transmission/reception unit 200 to
continue the reception operation {step Sll), and analyzes
the received signal (step S12). When the received signal
includes fire notification information, the operation
controller 100 controls the alarm unit 600 to perform the
above-described alarming operation based on the fire
notification information, and executes a notification
operation by cooperating with the fire alarm TR at the
origin of the fire (step S13).
When the measurement result of the received signal
strength is smaller than the reference value (No in step
S10) , the operation controller 100 determines that a radio
signal is not transmitted from the other fire alarm TR and
stops the reception operation of the wireless
transmission/reception unit 2 00 (step S14). Thereafter, the
operation controller 100 is returned to the operation of
step SI, sets the intermittent reception time in the timer
4 00 to start a counting operation, and shifts to a sleep
state until the timer 4 counts up the intermittent reception
time (step S2).
As described above, in case of the intermittent
reception, when the operation controller 100 is activated
upon receiving a start-up signal from the timer 4 00, the
operation controller 100 sets an operation command in the
wireless transmission/reception unit 200 and the radio level
measuring unit 300, and shifts to the sleep state. Thus,
while the wireless transmission/reception unit 200 executes
a reception operation and the radio level measuring unit 300
measures the received signal strength, the operation
controller 100 is shifted to the sleep state, so power
consumption in the operation controller 100 can be further
reduced.
Accordingly, if the wireless station (the fire alarm
TR) is driven by a battery, a life span of the battery can
be lengthened and a replacement cycle of the battery can be
lengthened, thereby reducing the burden of a maintenance
operation. Also, the wireless transmission/reception unit
2 00 and the radio level measuring unit 300 autonomously
operates when an operation command is set by the operation
controller 100, and the wireless transmission/reception unit
2 00 continue to perform reception operation when the
received signal strength is equal to or greater than a
reference value. Thus, it is possible to reliably receive a
radio signal transmitted from another wireless station (the
fire alarm TR).
Further, in the present embodiment, in case of the
intermittent reception, when the radio level measuring unit
300 completes measurement of a received signal strength, the
radio level measuring unit 300 activates the operation
controller 100 from a sleep state and the operation
controller 10 0 determines whether or not there is a
reception signal based on the measurement result of the
received signal strength. Thus, in case of the intermittent
reception, since the operation controller 100 is in the
sleep state between a time at which the operation command is
set in the wireless transmission/reception unit 200 and the
radio level measuring unit 300 and a time at which the
measurement of the received signal strength is completed,
power consumption by the operation controller 100 can be
reduced in the corresponding time duration.
Further, the operation controller 100 compares the
received signal strength measured by the radio level
measuring unit 300 with the reference value. In the present
embodiment, when the measurement result of the received
signal strength is equal to or greater than the reference
value, the operation controller 100 continues the reception
operation of the wireless transmission/reception unit 2 00
and executes analyzation of the reception signal, thereby
reliably receiving a radio signal from another fire alarm TR.
Also, when the received signal strength is smaller than the
reference value, the operation controller 10 0 stops the
reception operation of the wireless transmission/reception
unit 200, thus reducing power consumption of the wireless
transmission/reception unit 200.
Further, in a wireless communication system including
a plurality of fire alarms TR, a particular fire alarm TRl
(hereinafter, referred to as a ^master station')
periodically monitors to check whether or not the other fire
alarms TR2~TRn (hereinafter, referred to as a xslave
station') normally operates. That is, in the fire alarm TRl
as a master station, the operation controller 100
periodically (e.g., at every 24 hours) activates the
wireless transmission/reception unit 200 and transmits a
radio signal including a periodic monitoring message to the
slave stations.
In each of the slave stations TR2~TRn, the operation
controller 100 monitors whether or not the fire detection
unit 500 is out of order and whether or not remaining
capacity of the battery power unit 7 00 is lowered
periodically (e.g., at every one hour) and stores the
monitoring results (device error and lowering of the
remaining capacity) in the memory unit 100a. Further, when
the operation controller 100 of each of the slave stations
TR2~TRn receives the periodic monitoring message from the
master station TRl, it transmits a radio signal including
fire notification information for notifying the monitoring
results stored in the memory unit 100a to the master station
TRl .
After the operation controller 100 of the master
station TRl transmits the radio signal including fire
notification information, it switches the wireless
transmission/reception unit 200 to a reception state and
receives radio signals transmitted from the respective slave
stations TR2~TRn. Further, when there is any slave station
TR2,... which does not return fire notification information
within a certain time period after the periodic monitoring
message is transmitted, the operation controller 100 of the
master station TRl controls the alarm unit 600 to notify a
fault of the slave station TR2,... (communications error) .
Further, when fire notification information including
a fault occurrence or lowered remaining capacity of a
battery is returned from any slave station TR2,..., the
operation controller 100 of the master station TRl controls
the alarm unit 600 to notify a fault (generation of
breakdown, a lowered remaining capacity of battery, etc.) of
the slave station TR2,.... Also, when a breakdown of the fire
detection unit 500 or a lowered remaining capacity of the
battery is detected, the operation controller 100 of each of
the master station TRl and the slave station TR2,...
immediately drives the alarm units 600 to notify the
occurrence of the fault, respectively.
Further, after the operation controller 100 of the
master station TRl transmits a radio signal including fire
notification information from the wireless
transmission/reception unit 200 when detecting a fire, or
receives a radio signal including fire notification
information from another slave station TR2,..., it transmits a
synchronization beacon at a time period from the wireless
transmission/reception unit 200. The synchronization beacon
is a signal defining a time slot required for performing
wireless communications (hereinafter, referred to as
'synchronization communication' ) based on time division
multiple access (TDMA) among multiple fire alarms TR.
One period of the synchronization beacon is divided
into multiple time slots so that each of the time slots is
allocated to each of the slave stations TR2, .... And, a
message from the master station TR1 to the slave station
TR2,... is included in the synchronization beacon and
transmitted, so a radio signal including a message from the
slave stations TR2,... to the master station TR1 is carried in
the time slot allocated to each slave station and
transmitted. Thus, a collision between the radio signals
transmitted from the fire alarms TR (the master station TR1
and the slave stations TR2,...) can be reliably prevented.
Also, the allocation of the time slots to the respective
fire alarms TR may be fixed, or allocation information of
the time slots may be notified to the respective slave
stations TR2,... through the synchronization beacon
transmitted from the master station TRl.
(Modified embodiment of Second Embodiment)
A modified embodiment of the wireless communication
system in accordance with the second embodiment will be
described with reference to Fig 8. In the second
embodiment, in case of intermittent reception, when the
radio level measuring unit 300 completes measuring of a
received signal strength, the radio level measuring unit 300
activates the operation controller 100 from the sleep state,
such that the operation controller 100 compares the
measurement result of the received signal strength with the
reference value. In case of intermittent reception of the
present modified embodiment, when the radio level measuring
unit 300 completes measuring of a received signal strength,
the radio level measuring unit 300 compares the measurement
result of the received signal strength with the reference
value.
Further, only when the measurement result of the
received signal strength is equal to or greater than the
reference value, the radio level measuring unit 300
activates the operation controller 100 from the sleep state
to analyze the reception signal. When the measurement
result of the received signal strength is smaller than the
reference value, the radio level measuring unit 300 does not
activate the operation controller 10 0 and the operation
controller 100 is maintained in the sleep state until the
timer 4 00 completes counting. Also, the configuration of
the system of the present example is the same as that of the
second embodiment, so the same reference numerals are used
for the same or similar components and a description thereof
will be omitted.
Fig. 8 is a flow chart illustrating an operation of
intermittent reception, and an operation of the present
example will be described based on the flow chart.
Before shifting to the sleep state, the operation
controller 100 sets an intermittent reception time period in
the timer 4 00, starts a counting operation by the timer 4 00
(step S21) and then shifts to the sleep state.
When the timer 4 00 completes the counting (Yes in step
S22) , a start-up signal is outputted to the operation
controller 100 from the timer 400 to activate the operation
controller 100 from the sleep state {step S23) . Being
activated from the sleep state, the operation controller 100
sets an operation command in each of the wireless
transmission/reception unit 200 and the radio level
measuring unit 300 (step S24), and then shifts to the sleep
state (step S25).
When the operation command is set by the operation
controller 100, the transmission/reception unit 200
autonomously executes a reception operation {step S26).
Further, when the operation command is set by the operation
controller 100, the radio level measuring unit 30 0
autonomously executes an operation of measuring a received
signal strength of the signal received by the wireless
transmission/reception unit 200 (step S27) . When the radio
level measuring unit 300 measures a received signal strength,
it compares the measurement result of the received signal
strength with a reference value (step S28).
When the measurement result of the received signal
strength is equal to or greater than the reference value in
step S2 8 (Yes in step S28) , the radio level measuring unit
300 determines that a radio signal is transmitted from
another fire alarm TR, and outputs a start-up signal to the
operation controller 10 0 (step S29) . Starting up from the
sleep state, the operation controller 10 0 controls the
wireless transmission/reception unit 2 00 to continue the
reception operation depending on the start-up signal from
the radio level measuring unit 300 (step S30), and analyzes
a received signal from the wireless transmission/reception
unit 2 00 (step S31) . When the received signal includes fire
notification information, the operation controller 100
controls the alarm unit 600 to perform the alarming
operation as described earlier in the second embodiment
based on the fire notification information, and executes a
notification operation by cooperating with the fire alarm TR
at the origin of the fire (step S32).
On the other hand, when the measurement result of the
received signal strength is smaller than the reference value
in step S28 (No in step S28), the radio level measuring unit
300 determines that a radio signal is not transmitted from
another fire alarm TR and stops the reception operation of
the wireless transmission/reception unit 200 (step S33).
Thereafter, the radio level measuring unit 300 is returned
to step SI, sets the intermittent reception time period in
the timer 400 to start a counting operation and then repeats
the operations after step S2 .
As described above, the operation controller 100 sets
an operation command in the wireless transmission/reception
unit 2 00 and the radio level measuring unit 300, and shifts
to the sleep state, in case of the intermittent reception.
Accordingly, the wireless transmission/reception unit 200
and the radio level measuring unit 300 autonomously perform
an operation, respectively. That is, the radio level
measuring unit 300 compares the measurement result of the
received signal strength with a reference value and
determines whether or not there is a reception signal based
on the comparison result.
When the measurement result of the received signal
strength is equal to or greater than the reference value,
the radio level measuring unit 300 activates the operation
controller 10 0 and the operation controller 10 0 analyzes the
received signal received by the wireless
transmission/reception unit 200, thereby reliably receiving
a radio signal from another fire alarm TR. Further, when
the measurement result of the received signal strength is
smaller than the reference value, the radio level measuring
unit 30 0 stops the reception operation of the wireless
transmission/reception unit 2 00, thereby reducing power
consumption of the wireless transmission/reception unit 200.
In addition, since the radio level measuring unit 300
does not activate the operation controller 100 and the
operation controller 10 0 is maintained in the sleep state
until the timer 4 00 completes the counting, power
consumption of the operation controller 100 can be further
reduced. Thus, when the wireless station (the fire alarm
TR) is driven by a battery, a life span of the battery can
be lengthened and the replacement cycle of the battery can
be lengthened, and thus, the burden of a maintenance
operation can be reduced.
Although the wireless transceiver in accordance with
the present invention is applied in the wireless
communication system including the wireless communication
device group in the above embodiments, the wireless
transceiver in accordance with the present invention may be
applied to a wireless transmitter Yl and a wireless receiver
Y2 of a wireless remote control system as illustrated in Fig.
9. In addition to transmission function of the wireless
transceiver of the embodiments as described above, the
wireless transmitter Yl includes an object detection sensor
YS capable of detecting the presence of an object such as a
human body, an obstacle or the like in proximity by a
manipulation input detection sensor, a pressure sensor or
the like in a contact manner, or by a manual detection
sensor based on heat, light, or vibration in a contactless
manner.
Besides the reception function of the foregoing
wireless transceiver, the wireless receiver Y2 also includes
a facility control unit YC for executing a remote
communications with an air-conditioner, an illumination
system, or a facility equipment such as a facility power
source which is responsible for controlling an environment
of a particular location, without interfering wireless
communications with the wireless transmitter Yl. A signal
transmission between the facility control unit YC and the
facility equipment may be a wired transmission or a wireless
transmission.
Accordingly, when the wireless transmitter detects the
presence of an object such as a human body, an obstacle or
the like therearound by the object detection sensor YS, the
wireless transmitter transmits a radio signal Sig3
representing an event detected by the object detection
sensor YS, to the wireless receiver Y2 through the wireless
transceiver. When the wireless receiver Y2 receives the
radio signal Sig3, it determines a lighting system or the
like) previously provided in the facility control unit YC, a
target facility equipment to be driven among a facility
equipment group including the air-conditioner, the lighting
system and the facility power source, and an operation mode
thereof based on the contents of the received radio signal
Sig3, and remotely controls the target facility equipment
based on the determination results, by executing a facility
control algorithm (which may just turn ON or OFF facility
equipments such as an air-conditioner.
In this case, the wireless receiver Y2 may transmit to
the wireless transmitter Yl a signal Sig4 as an answer back
(which is good in a so-called ACK signal) representing that
the radio signal Sig3 is successfully received or the
contents thereof is analyzed, from the wireless transceiver
of the wireless receiver Y2 itself. Herein, each of the
wireless transmitter Yl and the wireless receiver Y2 is
required to have a wireless transmission function and a
wireless reception function. The wireless transceiver in
accordance with the present invention is capable of handling
different radio frequencies for transmission and reception,
and thus, it can be preferably used.
(Third Embodiment)
Next, a third embodiment in accordance with the
present invention will be described in detail with reference
to Figs. 10 to 15. As shown in Fig. 10, a wireless
communication system of the third embodiment includes a
wireless transmission/reception unit 200 for processing a
radio signal received via the antenna 2 to convert it into a
bit stream of a pulse signal, and an operation controller
100 for obtaining information (data) included in the radio
signal from the bit stream outputted from the wireless
transmission/reception unit 200. Also, like the
conventional example, a communications frame of the radio
signal is configured to include in a synchronization bit
stream (preamble) for bit synchronization, a frame
synchronization bit stream (unique word) for frame
synchronization, data corresponding to the information, a
check code (e.g., CRC) for error detection, and the like.
The wireless transmission/reception unit 2 00 includes
an amplifying unit 2000 (which corresponds to the LNA 4 in
Fig. 1), a frequency conversion unit 2100 (which corresponds
to the mixer 5 in Fig. 1) , a frequency selecting unit 220 0
(which corresponds to the IF filter 6 and the IF amplifier 7
in Fig. 1) , a demodulation unit 2300, a sampling clock
generating unit 2 40, a reception data buffer 25 0, a shift
register 260, a frame synchronization detection unit
(hereinafter, referred to as a 'synchronization detection
unit') 270, a unique word (UW) register 280, and a command
processing (command decoding) unit 2 90. In the present
embodiment, the wireless transmission/reception unit 200 is
provided as a large-scale integration circuit (LSI) in which
the respective parts are integrated in a single chip.
The radio signal received by the antenna 2 is
amplified by the amplifying unit 2 000, and then converted
into IF lower than RF by the frequency conversion unit 2100.
The frequency conversion unit 2100 includes a local
oscillator (not shown) for oscillating a signal having a
local oscillation frequency which is the same as a frequency
of a difference between the RF and the IF, and a frequency
adjustment unit (not shown) for controlling a frequency
deviation in the local oscillator.
In a general wireless communication system, when a
frequency deviation occurs in the local oscillator, a
reference frequency is not settled due to a remaining
frequency error caused by the frequency offset, and the
frequency error may cause erroneous demodulation when a
frequency-modulated radio signal is demodulated. To cope
with this, there is provided a function of correcting the
frequency deviation of the local oscillator to automatically
cancel an influence of the frequency deviation, that is, a
function, which is a so-called auto frequency control (AFC).
In the present embodiment, the frequency control
circuit is provided in the frequency conversion unit 2100 to
realize the automatic frequency control function. This
frequency control circuit controls a frequency by
controlling a frequency synthesizer (e.g., a frequency
synthesizer using a fractional PLL circuit) provided in the
local oscillator. Further, the frequency conversion unit
2100 is well known, so a description of a detailed
configuration and operation thereof will be omitted.
The frequency selecting unit 22 00 includes a band pass
filter to select only a signal component (reception signal)
having a desired frequency band from an IF signal which is
frequency-converted by the frequency conversion unit 2100,
and output the same. The reception signal is demodulated
into a demodulation signal (baseband signal) by the
demodulation unit 2300. The sampling clock generating unit
240 generates a sampling clock, adjusts a phase of the
sampling clock such that the demodulation signal can be
sampled in the middle of rising and falling of the
demodulation signal, and outputs the same. Further, the
demodulation signal is sampled in synchronization with the
sampling clock and, at the same time, the sampled bit stream
(reception data) is stored in the shift register 2 60. The
'shift register 260 has a capacity having bits equal to the
number of bits of the unique word.
The synchronization detection unit 27 0 compares the
reception data stored in the shift register 260 and the
unique word stored in the UW register 28 0. When the bit
streams of the both are identical, the synchronization
detection unit 270 determines that they are synchronized,
and outputs a frame synchronization detection signal (having
a high (H) level). Further, the unique word previously
designated by the operation controller 10 0 is stored in the
UW register 180.
In the meantime, the sampling clock generating unit
240 continuously monitors rising and falling of the
demodulation signal, and the sampling clock generating unit
240 determines that the bit synchronization is deviated when
timings of rising and falling are rapidly changed, and
outputs a synchronization deviation signal to the
synchronization detection unit 27 0. When the
synchronization detection unit 270 receives the
synchronization deviation signal from the sampling clock
generating unit 240, it stops outputting of the frame
synchronization detection signal (turning into a low (L)
level).
When the synchronization detection unit 270 starts to
output the frame synchronization detection signal (rising
from the L level to the H level), the reception data buffer
250 samples the demodulation signal in synchronization with
the sampling clock and accumulates the sampled bit streams
(reception data).
Meanwhile, the operation controller 100 includes a
central processing unit (CPU) 1000, a RAM 110, a ROM 120, an
I/O unit 130, a first serial communication unit 14 0, a
second serial communication unit 150, a data bus 160, and
the like. The CPU 1000 performs various processes as
described later by executing programs stored in the ROM 120.
The I/O unit 130 detects rising and rising of the frame
synchronization detection signal outputted from the
synchronization detection unit 27 0 of the wireless
transmission/reception unit 200, and informs the CPU 1000 of
a rising interruption and a falling interruption through the
data bus 160. When a rising interruption is notified by the
I/O unit 130, the CPU 1000 starts a rising edge interruption
process and sends a reception data output command to the
second serial communication unit 150 through the data bus
160. Further, the second serial communication unit 150
transmits the reception data output command applied from the
CPU 10 00 to the command decoding unit 2 90 of the wireless
transmission/reception unit 200.
The command decoding unit 290 decodes the reception
data output command received from the second serial
communication unit 150 and outputs the same to the reception
data buffer 250. When the reception data buffer 250
receives the reception data output command from the command
decoding unit 290, it transmits reception data (bit stream)
accumulated in the reception data buffer 250 and the
sampling clock inputted from the sampling clock generating
unit 240, to the first serial communication unit 14 0 of the
operation controller 100.
The first serial communication unit 14 0 transmits the
reception data and the sampling clock received from the
reception data buffer 250 of the wireless
transmission/reception unit 200 to the CPU 1000 through the
data bus 160. The CPU 1000 decodes the reception data
transmitted from the first serial communication unit 14 0 to
obtain information (message) included in the radio signal,
and executes various processes based on the obtained
information. Further, when the CPU 1000 obtains information
(message) having a prescribed length (which corresponds to ¦
one frame), it issues a reset command to the second serial
communication unit 150 through the data bus 160.
Furthermore/ the second serial communication unit 150
transmits the reset command applied from the CPU 1000 to the
command decoding unit 2 90 of the wireless
transmission/reception unit 200.
The command decoding unit 2 90 decodes the reset
command received from the second serial communication unit
150 and outputs the same to the sampling clock generating
unit 240 and the synchronization detection unit 270. When
the sampling clock generating unit 240 receives the reset
command, it stops generating of the sampling clock and is
returned to an initial state. Similarly, when the
synchronization detection unit 270 receives the reset
command, it stops outputting of the frame synchronization
detection signal and is returned to an initial state. In
the present embodiment, the I/O unit 130, and the first and
second serial communication units 14 0 and 150 are equivalent
to an interface unit.
By the way, even in the wireless communication system
in accordance with the third embodiment of the present
invention like the conventional example, the demodulation
unit 2300 of the wireless transmission/reception unit 200
may output a signal formed of a random bit stream due to an
influence of thermal noise or radio wave noise although a
radio signal is not received by the antenna 2. In this case,
the same bit stream as that of the unique word may be
contained in the random bit stream and, accordingly, the
synchronization detection unit 270 erroneously detects frame
synchronization and outputs a frame synchronization
detection signal. Further, the CPU 1000 of the operation
controller 100 starts rising edge interruption process in
synchronization with rising of the frame synchronization
detection signal, and transmits a reception data output
command through the second serial communication unit 150.
Accordingly, the reception data and the sampling clock are
transmitted from the reception data buffer 250 of the
wireless transmission/reception unit 200, and the CPU 1000
executes decoding of the reception data.
Here, the sampling clock generating unit 240 of the
wireless transmission/reception unit 200 continuously
monitors a bit stream of the demodulation signal demodulated
by the demodulation unit 2300. Since a bit width (pulse
width) of the random bit stream is not uniform, the sampling
clock generating unit 240 determines that there is a
synchronization deviation not before long and stops
outputting of the sampling clock. When outputting of the
sampling clock is stopped, the synchronization detection
unit 270 also stops outputting of the frame synchronization
detection signal. Further, when the outputting of the frame
synchronization detection signal is stopped (falling from
the H level to the L level) before a bit stream having a
prescribed length is received from the reception data buffer
250, the CPU 1000 of the operation controller 100 starts
falling edge interruption process to cancel the data (bit
stream) received from the reception data buffer 250 and to
output a reset command.
As described above, in the conventional example, if a
normal radio signal is received immediately after an
erroneous synchronization occurs due to thermal noise or
radio wave noise, there is a possibility that the radio
signal cannot be received normally. However, in the
wireless communication system of the third embodiment, even
when the regular radio signal is received immediately after
erroneous synchronization occurs due to the thermal noise or
the radio wave noise, the normal radio signal can be
reliably received.
Hereinafter, an operation of the wireless
communication system of the third embodiment in case where a
normal radio signal is received immediately after erroneous
synchronization occurs due to thermal noise or radio wave
noise and a synchronization deviation is shortly detected
will be described in detail with reference to the time chart
of Fig. 11. In Fig. 11, 'N' denotes noise, *P' denotes a
preamble, *U' denotes a unique word, numbers ^1', *2',...
indicate data, and voutput' represents a reception data
output command.
It is assumed that an error detection of
synchronization occurs at the time t=tl so a frame
synchronization detection signal rises, the CPU 1000 of the
operation controller 100 starts accordingly a rising edge
interruption process, and a synchronization deviation is
determined so the frame synchronization detection signal
falls at the time t=t2 before the time t=t3 when a reception
data output command is transmitted to the wireless
transmission/reception unit 2 00 through the second serial
communication unit 15 0 from the CPU 1000. In this case, in
the conventional example, a control signal is outputted from
the microcomputer 1300 before the frame synchronization
detection signal falls, and the reception data is outputted
to the microcomputer 1300 from the reception buffer 124 in
synchronization with the falling of the control signal (see
the time t=t4 in Fig. 18) although the synchronization
deviation has been determined and the frame synchronization
detection signal has fallen.
However, in the present embodiment, as shown in Fig.
10, the frame synchronization detection signal outputted
from the synchronization detection unit 270 is also inputted
to the command decoding unit 2 90, and the command decoding
unit 290 performs a logical-AND operation of the reception
data output command (the output signal in Fig. 1) and the
frame synchronization detection signal. Further, only when
the frame synchronization detection signal and the reception
data output command all are inputted (when the both have the
H level), the reception data output command is outputted to
the reception data buffer 250. Thus, in Fig. 11, since the
synchronization deviation occurs and the frame
synchronization detection signal is stopped (having the L
level) at the time t=t3 at which the command decoding unit
2 90 receives the reception data output command, the
reception data output command is not outputted from the
command decoding unit 290 and the reception data is not
outputted from the reception data buffer 250.
Further, when the transmitting of the reception data
output command is completed (time t=t4), the CPU 1000 starts
a falling edge interruption process depending on a falling
interruption from the I/O unit 130, and outputs a reset
command. In this case, since the reception data is not
outputted from the reception data buffer 250, the CPU 1000
is not required to discard the data received from the
reception data buffer 2 50 in the falling edge interrupt
process.
On the other hand, when a normal radio signal is
received by the antenna 2 after the time t=t2 at which the
synchronization deviation occurs and the frame
synchronization detection signal rises (time t=t5), the CPU
1000 starts a rising edge interruption process in response
to a rising interruption from the I/O unit 130 (time t=t6)
and transmits a reception data output command through the
second serial communication unit 150 to the command decoding
unit 290 (time t=t7~t8). Since the frame synchronization
detection signal is a High (H) level at the time point when
the reception data output command (ACT signal) is received,
the command decoding unit 2 90 outputs the reception data
output command to the reception data buffer 250.
Further, when receiving the reception data output
command, the reception data buffer 250 outputs the reception
data and a sampling clock (time t=t8). Herein, the
reception data buffer 250 starts to output the reception
data from the time point when the reception data output
command has been received, and the reception data is not
outputted before the reception data output command is
received, unlike the conventional example illustrated in Fig.
18. Thus, the first serial communication unit 140 of the
operation controller 100 can receive sequentially the data
accumulated in the reception data buffer 250 from the
beginning data (i.e., ^l').
In the wireless communication system in accordance
with the present embodiment, if the command decoding unit
2 90 of the operation controller 100 does not receive a
reception data output command until the synchronization
detection unit 270 stops output ting of the frame
synchronization detection signal after starting to output
the frame synchronization detection signal, the reception
data accumulated in the reception data buffer 2 50 is not
outputted even though the reception data output command is
outputted from the CPU 1000 of the operation controller.
Thus, even immediately after the erroneous synchronization,
a regular radio signal can be properly received as described
above.
Further, in the present embodiment, the command
decoding unit 2 90 performs logical-AND operation of the
reception data output command and the frame synchronization
detection signal and, when the frame synchronization
detection signal and the reception data output command all
are not inputted (i.e., when at least one of them is in a
Low (L) level) , the reception data output command is not
outputted to the reception data buffer 250. This can be
realized through the relatively simple configuration.
As described above, if the normal radio signal is
received, erroneous synchronization can be shortly dissolved
hy detecting synchronization deviation. However, when
erroneous synchronization occurs due to thermal noise or the
like, there is a high possibility that a local oscillation
frequency controlled by a frequency control circuit of the
frequency conversion unit 2100 has been greatly deviated
from a local oscillation frequency corresponding to the
original radio signal (see 'AFC frequency' in Fig. 12).
In this case, as shown in Fig. 12, it is possible to
reduce a time required for the frequency control circuit to
complete adjustment of the frequency deviation with respect
to a normal radio signal by initialing an AFC frequency for
frequency deviation control in the frequency control circuit
of the frequency conversion unit 2100 of the wireless
transmission/reception unit 2 00 at the time t=t2 when
synchronization deviation is determined.
Alternatively, as shown in Fig. 13, when outputting of
the frame synchronization detection signal is stopped at the
time t=t4) when the reception data output command is
outputted, the CPU 1000 may transmit an initialization
command through the second serial communication unit 150 to
initialize the AFC frequency for frequency deviation control
of the frequency control circuit.
In the above embodiment, although the command decoding
unit 2 90 performs logical-AND operation of the reception
data output command and the frame synchronization detection
signal and determines whether or not the reception data
output command is outputted to the reception data buffer 250,
the present invention is not limited thereto. That is, as
shown in Fig. 14, an output of the frame synchronization
detection signal may be checked (see time t=t3) immediately
before a reception data output command is outputted based on
the frame synchronization detection signal.
In this case, when outputting of the frame
synchronization detection signal is stopped, the CPU 1000
may not output the reception data output command from the
command decoding unit 2 90. Further, a dotted line of
'output' at the interval of t3 to t4 in Fig. 14 indicates
that outputting of the reception data output command is
stopped. By doing so, as shown in Fig. 14, the falling edge
interruption process is not executed even though a falling
interruption of the frame synchronization detection signal
is received from the I/O unit 130, and the rising edge
interruption process can be executed immediately after the
rising of the frame synchronization detection signal. Thus,
a maximum length of the reception data buffer 250 can be
shortened in comparison to the configuration illustrated in
Fig. 11.
While the invention has been shown and described with
respect to the embodiments, it will be understood by those
skilled in the art that various changes and modifications
may be made without departing from the scope of the
invention as defined in the following claims.
We claim:
1. A wireless transmitter/receiver, comprising:
a local oscillator which oscillates at a predetermined
local oscillation frequency;
a mixer for mixing a local oscillation signal having
the local oscillation frequency outputted from an output
terminal of the local oscillator and a radio signal received
by an antenna;
a modulation circuit for modulating the local
oscillation signal to generate a radio signal; and
a transmission/reception switching unit which
selectively switches over between a reception state in which
the output terminal of the local oscillator is connected to
the mixer and a transmission state in which the output
terminal is connected to the antenna without passing through
the mixer,
wherein the local oscillator includes:
a reference oscillation unit which oscillates at a
predetermined reference oscillation frequency lower than the
local oscillation frequency;
a first frequency conversion unit and a second
frequency conversion unit which convert a reference
oscillation signal having the reference oscillation
frequency outputted from an output terminal of the reference
oscillation unit into the local oscillation signal;
a first switching unit which selectively switches over
between a first input state in which the output terminal of
the reference oscillation unit is connected to an input
terminal of the first frequency conversion unit and a second
input state in which the output terminal of the reference
oscillation unit is connected to an input terminal of the
second frequency conversion unit; and
a second switching unit which selectively switches
over between a first output state in which the output
terminal of the local oscillator is connected to the output
terminal of the first frequency conversion unit and a second
output state in which the output terminal of the local
oscillator is connected to an output terminal of the second
frequency conversion unit, while cooperating with switching
operation of the first switching unit, and
wherein the second frequency conversion unit includes
a voltage controlled oscillator, a phase comparator, a
divider, a loop filter, a phase locked loop circuit having a
charge pump, and the first frequency conversion unit
includes a frequency multiplying circuit having power
consumption smaller than that of the phase locked loop
circuit.
2. The wireless transmitter/receiver of claim 1, wherein
the reference oscillation unit selects and outputs one among
multiple types of reference oscillation signals having
different reference oscillation frequencies from each other.
3. The wireless transmitter/receiver of claim 1 or 2,
wherein the local oscillator includes a bypass capacitor
electrically connecting a power terminal of the voltage
controlled oscillator with a ground with respect to an
alternating current, the voltage controlled oscillator being
connected to an external power source, and an
opening/closing unit for switching over between connections
of the bypass capacitor and the external power source or the
power terminal,
wherein, only when the first switching unit is
switched to the second input state and the second switching
unit is switched to the second output state, the
opening/closing unit connects the bypass capacitor to the
external power source or the power terminal.
4. The wireless transmitter/receiver of claim 3, wherein
the local oscillator includes a current limiting resistor
for limiting an inrush current flowing into the bypass
capacitor from the external power source.
5. The wireless transmitter/receiver of claim 4, wherein
the local oscillator further includes a short-circuit unit
connected in parallel to the current limiting resistor,
wherein the short-circuit unit connects the external
power source to the power terminal after the opening/closing
unit connects the bypass capacitor to the external power or
the power terminal.
6. The wireless transmitter/receiver of any one of claims
1 to 5, wherein the local oscillator selectively outputs a
local oscillation signal having a receiving local
oscillation frequency different from a radio frequency of
the radio signal and a local oscillation signal having a
transmitting local oscillation frequency equal to the radio
frequency, and the local oscillation signal selected
relatively frequently from among the local oscillation
signal having the receiving local oscillation frequency and
the local oscillation signal having the transmitting local
oscillation frequency is outputted by the first frequency
conversion unit and the local oscillation signal selected
relatively less frequently is outputted by the second
frequency conversion unit.
7 . The wireless transmitter/receiver of any one of claims
1 to 6, further comprising a controller for controlling the
first switching unit and the second switching unit, and
wherein, in case where the transmission/reception
switching unit is switched to the reception state, the
controller switches the first switching unit to the second
input state and switches the second switching unit to the
second output state only when a reception signal outputted
from the mixer is not normally demodulated in a state in
which the first switching unit is switched to the first
input state and the second switching unit to the first
output state by the controller.
8 . The wireless transmitter/receiver of claim 7, wherein,
after a predetermined period of time has passed in the
reception state, the controller keeps states of the first
and second switching units at the time point when the
predetermined period of time has passed.
23. The wireless transmitter/receiver of claim 7 or 8,
wherein, when the transmission/reception switching
unit is switched to the reception state, the local
oscillator performs an intermittent operation in
which an operation period and a pause period are
repeated at a predetermined interval, and
the controller switches the first switching unit to
the first input state and switches the second switching unit
to the first output state when the operation period starts.
10. The wireless transmitter/receiver of claim 9, wherein,
after the number of switching the first switching unit to
the second input state and the second switching unit to the
second output state exceeds a predetermined number of times,
the controller switches the first switching unit to the
second input state and switches the second switching unit to
the second output state when the operation period starts.
23. The wireless transmitter/receiver of any one of
claims 7 to 10,
wherein the reference oscillation unit selects and
outputs one among multiple types of reference oscillation
signals having different reference oscillation frequencies
from each other,
wherein the first frequency conversion unit includes a
plurality of multiplying circuits having different
multipliers from each other, and
wherein, when the reception signal outputted from the
mixer is not normally demodulated in a state in which the
controller switches the first switching unit to the first
input state and the second switching unit to the first
output state, the controller sequentially changes
combinations of the reference oscillation frequencies of the
reference oscillation signals and the multipliers of the
multiplying circuits without changing the local oscillation
frequency; and, when the reception signal is not normally
demodulated in every combination, the controller switches
the first switching unit to the second input state and
switches the second switching unit to the second output
state.
2 3. The wireless transmitter/receiver of any one of
claims 7 to 10,
wherein the controller includes a clock for counting
time, and
wherein the controller switches the first switching
unit to the second input state and the second switching unit
to the second output state during a time zone of daytime,
and switches the first switching unit to the first input
state and the second switching unit to the first output
state during a time zone of nighttime.
13. A wireless communication system for transmitting and
receiving a radio signal by a radio wave between multiple
wireless stations, each of the wireless stations comprising:
a wireless transmission/reception unit which transmits
and receives the radio signal;
a radio level measuring unit which measures a received
signal strength of the radio signal received by the wireless
transmission/reception unit;
a timer which outputs a start-up signal whenever a
predetermined intermittent reception time is lapsed; and
an operation controller which analyzes the reception
signal received by the wireless transmission/reception unit
to obtain information related to the wireless
transmission/reception unit itself,
wherein the wireless transmission/reception unit
autonomously executes an operation of receiving the radio
signal based on an operation command set by the operation
controller, and the radio level measuring unit autonomously
executes an operation of measuring the received signal
strength of the radio signal received by the wireless
transmission/reception unit based on an operation command
set by the operation controller,
wherein the operation controller sets an operation
command in the wireless transmission/reception unit and the
radio level measuring unit when the operation controller in
a sleep state is activated by the start-up signal from the
timer, and shifts to the sleep state until the measuring of
the received signal strength by the radio level measuring is
completed, and
wherein, when the measurement result of the received
signal strength by the radio level measuring unit is equal
to or greater than a predetermined reference value, the
wireless transmission/reception unit continuously performs a
reception operation and the operation controller analyzes
the reception signal; and, when the measurement result is
smaller than the reference value, the wireless
transmission/reception unit stops the reception operation.
14. The wireless communication system of claim 13,
wherein the radio level measuring unit outputs a
start-up signal to the operation controller when the
measuring of the received signal strength based on the
operation command is completed; and the operation controller
compares the measurement result of the received signal
strength by the radio level measuring unit and the reference
value when the operation controller in the sleep state is
activated by the start-up signal from the radio level
measuring unit; and, when the measurement result is equal to
or greater than the reference value, the operation
controller controls the wireless transmission/reception unit
to continue the reception operation and analyzes the
reception signal, and, when the measurement result is
smaller than the reference value, the operation controller
stops the reception operation of the wireless
transmission/reception unit.
15. The wireless communication system of claim 13, wherein
the radio level measuring unit compares the measurement
result of the received signal strength and the reference
value, and when the measurement result is smaller than the
reference value, the radio level measuring unit stops the
reception operation of the wireless transmission/reception
unit.
16. The wireless communication system of claim 15, wherein
the radio level measuring unit outputs a start-up signal to
the operation controller when the measurement result of the
received signal strength is equal to or greater than the
reference value, and, the operation controller analyzes a
signal received by the wireless transmission/reception unit
when the operation controller in the sleep state is
activated by the start-up signal from the radio level
measuring unit.
17. The wireless communication system of claim 13, wherein
the wireless transmission/reception unit includes:
a local oscillator which oscillates at a predetermined
local oscillation frequency;
a mixer for mixing a local oscillation signal having
the local oscillation frequency outputted from an output
terminal of the local oscillator and a radio signal received
by an antenna;
a modulation circuit for modulating the local
oscillation signal to generate a radio signal; and
a transmission/reception switching unit which
selectively switches over between a reception state in which
the output terminal of the local oscillator is connected to
the mixer and a transmission state in which the output
terminal is connected to the antenna without passing through
the mixer,
wherein the local oscillator includes:
a reference oscillation unit which oscillates at a
predetermined reference oscillation frequency lower than the
local oscillation frequency;
a first frequency conversion unit and a second
frequency conversion unit which convert a reference
oscillation signal having the reference oscillation
frequency outputted from an output terminal of the reference
oscillation unit into the local oscillation signal;
a first switching unit which selectively switches over
between a first input state in which the output terminal of
the reference oscillation unit is connected to an input
terminal of the first frequency conversion unit and a second
input state in which the output terminal of the reference
oscillation unit is connected to an input terminal of the
second frequency conversion unit; and
a second switching unit which selectively switches
over between a first output state in which the output
terminal of the local oscillator is connected to the output
terminal of the first frequency conversion unit and a second
output state in which the output terminal of the local
oscillator is connected to an output terminal of the second
frequency conversion unit, while cooperating with switching
operation of the first switching unit, and
wherein the second frequency conversion unit includes
a voltage controlled oscillator, a phase comparator, a
divider, a loop filter, a phase locked loop circuit having a
charge pump, and the first frequency conversion unit
includes a frequency multiplying circuit having power
consumption smaller than that of the phase locked loop
circuit.
18. A wireless communication system, comprising:
a wireless transmission/reception unit which processes
a radio signal received by an antenna to convert it into a
bit stream of a pulse signal; and
an operation controller which obtains information
included in the radio signal from the bit stream outputted
from the wireless transmission/reception unit,
wherein a communications frame of the radio signal
includes a synchronization bit stream for bit
synchronization, a frame synchronization bit stream for
frame synchronization, and data corresponding to the
information,
wherein the wireless transmission/reception unit
includes:
a demodulation unit which demodulates the radio signal
into a demodulation signal formed of a bit stream of a pulse
signal;
a frame synchronization detection unit which detects
the frame synchronization bit stream from the bit stream of
the demodulation signal and outputs a frame synchronization
detection signal;
a reception data buffer which temporarily accumulates
the demodulation signal outputted from the demodulation unit
when the frame synchronization detection signal is
outputted; and
a command processing unit for outputting the reception
data accumulated in the reception data buffer to the
operation controller when a reception data output command is
received from the operation controller,
wherein the operation controller includes:
an interface unit which communicates a signal with the
wireless transmission/reception unit; and
a central processing unit which executes processing of
obtaining information included in the radio signal from the
bit stream outputted from the wireless
transmission/reception unit, or processing of outputting the
reception data output command to the wireless
transmission/reception unit while the frame synchronization
detection signal is being output, and
wherein, when the reception data output command is not
received until the frame synchronization detection unit
stops outputting of the frame synchronization detection
signal after starting to output the frame synchronization
detection signal, the command processing unit controls the
reception data buffer not to output the reception data
accumulated therein even if the reception data output
command is outputted from the central processing unit of the
operation controller before the frame synchronization
detection unit starts to output a next frame synchronization
detection signal.
19. The wireless communication system of claim 18, wherein
the command processing unit controls the reception data
buffer to output the reception data accumulated therein to
the operation controller only when the frame synchronization
signal and the reception data output command are input
simultaneously.
2 0. The wireless communication system of claim 18 or 19,
wherein the central processing unit checks whether or not
the frame synchronization detection signal is outputted
immediately before it outputs the reception data output
command based on the frame synchronization detection signal,
and does not output the reception data output command when
outputting of the frame synchronization detection signal is
stopped.
21. The wireless communication system of claim 18 or 19,
wherein the wireless transmission/reception unit further
includes a frequency conversion unit for converting the
radio signal received by the antenna into a signal having an
intermediate frequency lower than a radio frequency of the
radio signal,
wherein the frequency conversion unit includes:
a local oscillator which oscillates a signal having a
local oscillation frequency that is the same as a difference
between the radio frequency and the intermediate frequency;
and
a frequency control circuit which controls a frequency
deviation in the local oscillator, and
wherein the frequency control circuit initializes a
control of the frequency deviation when outputting of the
frame synchronization detection signal is stopped.
22. The wireless communication system of claim 18 or 19,
wherein the wireless transmission/reception unit further
includes a frequency conversion unit for converting the
radio signal received by the antenna into a signal having an
intermediate frequency lower than that of the radio
frequency,
wherein the frequency conversion unit includes:
a local oscillator which oscillates a signal having a
local oscillation frequency that is the same as a difference
between the radio frequency and the intermediate frequency;
and
a frequency control circuit which controls a frequency
deviation in the local oscillator, and
wherein the central processing unit outputs a command
of initializing a control of the frequency deviation by the
frequency control circuit when outputting of the frame
synchronization detection signal is stopped at a time point
when the reception data output command is outputted.
23. The wireless communication system of claim 18, wherein
the wireless transmission/reception unit includes:
a local oscillator which oscillates at a predetermined
local oscillation frequency;
a mixer for mixing a local oscillation signal having
the local oscillation frequency outputted from an output
terminal of the local oscillator and a radio signal received
by an antenna;
a modulation circuit for modulating the local
oscillation signal to generate a radio signal; and
a transmission/reception switching unit which
selectively switches over between a reception state in which
the output terminal of the local oscillator is connected to
the mixer and a transmission state in which the output
terminal is connected to the antenna without passing through
the mixer,
wherein the local oscillator includes:
a reference oscillation unit which oscillates at a
predetermined reference oscillation frequency lower than the
local oscillation frequency;
a first frequency conversion unit and a second
frequency conversion unit which convert a reference
oscillation signal having the reference oscillation
frequency outputted from an output terminal of the reference
oscillation unit into the local oscillation signal;
a first switching unit which selectively switches over
between a first input state in which the output terminal of
the reference oscillation unit is connected to an input
terminal of the first frequency conversion unit and a second
input state in which the output terminal of the reference
oscillation unit is connected to an input terminal of the
second frequency conversion unit; and
a second switching unit which selectively switches
over between a first output state in which the output
terminal of the local oscillator is connected to the output
terminal of the first frequency conversion unit and a second
output state in which the output terminal of the local
oscillator is connected to an output terminal of the second
frequency conversion unit, while cooperating with switching
operation of the first switching unit, and
wherein the second frequency conversion unit includes
a voltage controlled oscillator, a phase comparator, a
divider, a loop filter, a phase locked loop circuit having a
charge pump, and the first frequency conversion unit
includes a frequency multiplying circuit having power
consumption smaller than that of the phase locked loop
circuit.