Optical communications – Optical communication over freee space
Reexamination Certificate
2000-03-06
2003-09-23
Pascal, Leslie (Department: 2733)
Optical communications
Optical communication over freee space
C398S099000, C398S167500, C398S058000, C398S180000, C370S330000
Reexamination Certificate
active
06623187
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical communication system and a wireless optical communication method used in the technical field of wireless communication using infrared and other light.
2. Description of the Related Art
In the field of wireless communication using infrared ray, the International Electrotechnical Commission (IEC) and, in Japan, the Electronic Industries Association of Japan (EIAJ) assign sub-carrier frequency hands.
There are various optical communication devices for unwired communication using infrared rays. For example, there are remote controls for remote control of television sets, video cassette recorders, etc. using infrared rays, cordless headphones receiving audio signals etc. by wireless communication using infrared rays from audio players, etc.
The sub-carrier frequency band assigned for use in infrared communication in a remote control is 33 kHz to 40 kHz (specifically, not less than 33 kHz and less than 40 kHz), while the sub-carrier frequency band assigned for use in transmission of audio signals in the above cordless headphones etc. 2 MHZ to 6 MHZ (specifically, not less than 2 MHZ and less than 6 MHZ).
Here, as shown in
FIG. 18
, assume an infrared optical communication system which comprises one control node (device)
200
and a plurality of controlled nodes
260
, for example, three controlled nodes
260
A to
260
C. Also, as shown in
FIG. 19
, assume that the optical communication system performs optical communication by the time-division multiplex system.
In FIG.
18
and
FIG. 19
, a control block B
1
is used for transmitting control information from a control node
200
to the controlled nodes.
The control block B
1
is periodically transmitted. A plurality of time slots SL (four time slots SL
1
to SL
4
in the example shown in
FIG. 19
) are provided between one control block and the next control block.
The nodes transmit data by sending transfer blocks B
2
(transfer blocks B
2
A, B
2
B, and B
2
C in the example shown in
FIG. 19
) in the time slots (communication time slot) SL.
As shown in
FIG. 20
, part of the above control block B
1
is used as an enabling signal (transmission-enablng signal) indicating information on the assignment of the time slots and indicating approval of use of the time slots SL. The control node
200
transmits the enabling signal to the controlled nodes
260
.
In the example of FIG.
19
and
FIG. 20
, referring to the enabling signal in the control block B
1
, first the controlled node
260
A transfers a transfer block (communication block) B
2
A to the control node
200
. Next, the control node
200
transfers the transfer block B
2
B to all of the controlled nodes
260
. Then, the controlled node
260
C transfers the transfer block B
2
C to the control node
200
.
This optical communication system uses a wide band for attaining high speed communication. Further, to enable use without interfering with remote controls, cordless headphones, and other systems, it uses a sub-carrier frequency of not less than 6 MHZ and less than 60 MHZ (or not less than 6 MHZ and less than 50 MHZ) shown by the hatched portion in FIG.
21
.
FIG. 22
is a schematic block diagram for explaining the configuration of the control node
200
and the controlled nodes
260
.
In
FIG. 22
, the control node
200
comprises a transmission device (transmitter)
210
and a reception device (receiver)
220
. A controlled node
260
comprises a transmission device (transmitter)
240
and a reception device (receiver)
250
.
The transmission device
210
of the control node
200
comprises a quadrature modulation circuit
211
and a light emission circuit
212
, while the reception device
220
comprises a light reception circuit
221
and a quadrature demodulation circuit
222
.
Similarly, the transmission device
240
of a controlled node
260
comprises a quadrature modulation circuit
241
and a light emission circuit
242
, while the reception device
250
comprises a light reception circuit
251
and a quadrature demodulation circuit
252
.
The quadrature modulation circuit
211
of the control node
200
modulates a transmission signal S
201
and outputs a modulated signal (carrier modulated signal) S
202
composed of a frequency component of not more than 6 MHZ and less than 60 MHZ (or not less than 6 MHZ and less than 50 MHZ). The modulated signal S
202
is input to the light emission circuit
212
.
The light emission circuit
212
performs amplitude modulation on infrared rays based on the modulated signal S
202
. Namely, the light emission circuit
212
comprises a light emitting diode for emitting an infrared ray and drives the light emitting diode based on the modulated signal S
202
. As a result, an infrared ray S
203
which is amplitude-modulated based on the modulated signal S
202
is output from the light emission circuit
212
.
On the other hand, the reception device
250
of the controlled node
260
receives the infrared ray S
203
output from the control node
200
at the reception circuit
251
. Namely, the light reception circuit
251
comprises a photodiode which receives the infrared ray S
203
and converts it to an electric signal. Also, the reception circuit
251
has, for example, a high-pass filter which cuts a low frequency component such as the direct current component of the electric signal. An output signal S
204
of the reception circuit
251
is input to the quadrature demodulation circuit
252
.
The quadrature demodulation circuit
252
performs quadrature demodulation on the signal S
204
to reproduce a reception signal S
205
the same as the transmission signal S
201
.
Note that the transmission device
240
of the controlled node
260
has the same configuration as the transmission device
210
of the control node
200
, and the reception device
220
of the control node
200
has the same configuration as the reception device
250
of the controlled node
260
.
Namely, the quadrature modulation circuit
241
of the controlled node
260
modulates a transmission signal S
211
and outputs a modulated signal S
212
composed of a frequency component of not less than 6 MHZ and less than 60 MHZ (or not less than 6 MHZ and less than 50 MHZ). The light emission circuit
242
performs amplitude modulation on an infrared ray based on the modulated signal S
212
. As a result, an infrared ray S
213
amplitude-modulated based on the modulated signal S
212
is output from the light emission circuit
242
.
On the other hand, the reception device
220
of the control node
200
receives the infrared ray from the controlled node
260
at the light reception circuit
221
, converts it into an electric signal, and cuts the direct current component of the electric signal. It performs quadrature modulation on the output signal S
214
of the reception circuit
221
to reproduce a reception signal S
215
the same as the transmission signal S
211
.
The emission intensity (amplitude) of the infrared ray S
203
amplitude-modulated based on the modulated signal S
202
is shown as an example in FIG.
23
. In
FIG. 23
, a control block B
1
and a transfer block B
2
B transmitted by the control node
200
are shown.
The transfer block B
2
B is transferred in a time slot SL
2
.
Summarizing the disadvantages of the above system, when performing high speed wireless communication using an infrared ray as explained above, there are the following disadvantages in the transmission device for emitting the infrared ray:
Since the light emission circuit of the above transmission device produces an amplitude-modulated infrared ray as explained above, as shown in
FIG. 23
, it constantly emits an infrared ray of a certain level (having a signal strength) even when there is no transmission signal. Namely, even a node which for example transmits once in 1000 cycles constantly emits an infrared ray. Therefore, it emits a wasted infrared ray in the remaining 999 cycles. As a result, the power consumption of the transmission device becomes large.
By modifying the output level of the in
Fahmy Sherif R.
Maioli Jay H.
Pascal Leslie
Sony Corporation
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