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JPH09200100

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Notice
This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
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DESCRIPTION JPH09200100
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
method and apparatus for wireless transmission of a signal S1 between a transmitter and at least
one receiver. The invention relates in particular to a method and an apparatus for radio
transmission of an audio signal between a television set and at least two speakers at a distance
from the television set.
[0002]
Prior art wireless transmission methods have been based on modulating a carrier whose
frequency is in the infrared (1R) range. The wave representing the 1R signal has unidirectional
propagation and is therefore blocked by an obstacle between the transmitter and the receiver.
Furthermore, in order to make a good transmission in this frequency domain, the transmitter and
receiver must be very well aligned. Thus, using a 1R frequency carrier is not compatible in an
environment such as a television room, for example, to obtain a good acoustic distribution in the
room, as schematically shown in FIG. And it needs to be located some distance from the television
set.
[0003]
Another drawback of the method using the 1R carrier is due to the sensitivity of the 1R signal to
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ambient light. Furthermore, this type of transmission requires the use of high sensitivity light
emitting diodes (LEDs) with considerable power consumption, in addition to its high cost.
[0004]
SUMMARY OF THE INVENTION The object of the present invention is to eliminate the drawbacks
of the conventional method by using a method of wireless transmission.
[0005]
According to the method of the present invention, at the transmitting end: a first signal S1 of
frequency F2 in the region of -VHF (very high frequency) is frequency-modulated by the signal
S1 to be transmitted, The second signal S3 of frequency F3 in the SHF (super high frequency)
region is amplitude-modulated by the modulation signal S2m obtained from the frequency
modulation of the carrier S2, and transmits the amplitude-modulated signal S3m to the receiver,
And: amplitude demodulation of signal S3m to obtain signal S2m, and frequency demodulation of
signal S2m to obtain signal S1.
[0006]
Using carriers S2 and S3 whose frequencies are respectively in the VHF and SHF bands avoids
the damage caused by ambient light affecting the 1R signal, while the SHF signal propagates
along a plurality of separate paths As far as possible it is possible to increase the possibility of
affecting the link between the transmitter and the receiver.
It is very unlikely that this path will be protected at the same time, so that the signal S3m can
reach the receiver via one or more non-protected paths.
In addition, the propagation of the SHF signal through the wall is very weak compared to the
near frequency, thus minimizing the risk of interference between users.
[0007]
Another advantage of the method according to the invention is obtained by the implementation
of both FM-AM modulation, which can considerably simplify the receiver. Thus, the regeneration
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of the signal S3m is done by means of conventional amplitude modulation which does not
require expensive parts. Furthermore, according to the method of the present invention, the
transmission of the SHF signal has a relatively modest frequency stability compared to that
required by the oscillator used in the conventional frequency modulation scheme at both the
transmitting and receiving ends. Use an inexpensive local oscillator.
[0008]
The method according to the invention is implemented by an apparatus for wireless transmission
between a transmitter and a receiver. The transmitter comprises three stages connected in
cascade: a first stage for amplification / filtering of the signal S1, a second stage for frequency
modulation of the carrier S2, and a third stage for amplitude modulation of the carrier S3. While
the receiver comprises three cascaded stages: a first stage for amplitude demodulation of the
signal S3m, a second stage for frequency demodulation of the signal S2m, and amplification /
filtering of the received signal S1. And the third stage.
[0009]
Other features and advantages of the present invention will become apparent from the following
description taken together with the drawings (examples are not limited thereto).
[0010]
3A and 5C show the spectrum of a signal S1 transmitted between a transmitter 10 and a receiver
12 according to the method of the present invention, wherein at the transmitting end: The first
signal S1 of frequency F2 in the VHF range is frequency-modulated by the signal S1 to be
transmitted, and then the second signal S3 of frequency F3 in the -SHF range is the modulation
obtained from the frequency modulation of the carrier S2. The amplitude modulated and
amplitude modulated signal S3m is transmitted to the receiver by the signal S2m, and at the
receiving end, the amplitude demodulation of the signal S3m is performed to obtain the signal
S2m, and the frequency demodulation of the signal S2m is performed to the signal S1. obtain.
[0011]
DESCRIPTION OF THE PREFERRED EMBODIMENT In an example of application of the method
according to the invention shown in FIG. 1, a carrier S2 of frequency 1 MHz is emitted by a
television set 14 to two speakers 16 and 18 at a distance from the television set. It is modulated
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by the audio signal S1.
As shown in FIGS. 3B and 5B, frequency modulation of the carrier S2 by the signal S1 makes it
possible to obtain a maximum frequency deviation of. +-. 100 kHz for the frequency F2.
Since the frequency deviation .DELTA.F is proportional to the amplification of the signal S1,
adjustment of the acoustic levels of the speakers 16 and 18 will be achieved by adjusting the
frequency deviation .DELTA.F. In this way, it is not necessary to use an additional channel to
control the sound level of the loudspeaker.
[0012]
According to a preferred embodiment of the method according to the invention, the carrier S3
has a frequency F3 equal to 5.8 GMz. The spectrum of the signal S3m shown in FIGS. 3C and 5A
obtained by amplitude modulation of the carrier S3m is a center line representing the frequency
F3 and 2 representing the 15 modulation signals S2m at the frequency F2. And two sidebands.
The method according to the invention is implemented by an apparatus for wireless
communication comprising a transmitter 10 and a receiver 12 which are schematically shown in
FIGS. 2 and 6 respectively. As shown in FIG. 2, the transmitter 10 is arranged in cascade in three
stages: a first stage 20 for amplification / filtering of the signal S1 to be transmitted, and a
second stage for frequency modulation of the carrier S2. 22 and a third stage 24 for amplitude
modulation of the carrier S3.
[0013]
In the particular application shown in FIG. 2, stage 20 includes a first audio amplifier 30 and a
second audio amplifier 38, the input 32 of the first audio amplifier receiving signal S1 and its
output being the first Of the second audio amplifier receives the preamplified and filtered signal
S1 from the filtering means 36, the output of which is coupled to the frequency modulation stage
22. The frequency modulation stage 22 comprises a voltage controlled RF (radio frequency)
oscillator (VCO) 50 adapted to generate the signal S2, whose input 51 receives the signal S1,
while the output 52 carries the frequency of the signal S2 according to the signal S1. The
modulated signal S2m is supplied to a first RF amplifier 57, the output 58 of said first RF
amplifier 57 being coupled to the input 60 of the second filtering means 62, the output 64 of
which is the second RF. Coupled to the input 66 of the amplifier 68. The output 70 of the second
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RF amplifier 68 is coupled to the amplitude modulation stage 24.
[0014]
The amplitude modulation stage 24 comprises an SHF (super high frequency) oscillator 80 which
is adapted to generate a carrier wave S3 and which supplies at its output 82 a signal S3m
obtained from amplitude modulation by the signal S2m of the carrier wave S3. The output 82 of
the SHF oscillator 80 is coupled to an antenna 84 adapted to send the signal S3m to the receiver
12. According to the preferred embodiment of the present invention shown in FIG. 4, the receiver
12 has three cascaded stages: a first stage 90 for amplitude demodulation of the signal S3m and
a second stage for frequency demodulation of the signal S2m. 92 and a third stage 94 for
amplification / filtering of the received signal S1.
[0015]
Stage 90 includes an antenna 96 coupled to preamplification means 98 for receiving signal S2m,
the output 100 of the preamplification means being coupled to a first terminal 102 of AM
detector 104, and The second terminal 106 is coupled to the input 108 of the high impedance
amplification means 110, the output of which is coupled to the stage 92. This stage 92 comprises
a third filtering means 112 coupled to the input 116 of the frequency demodulator 114, the
output 118 of the demodulator 114 providing the signal S1 to the stage 94.
[0016]
The stage 94 comprises a fourth filtering means 120 coupled to the input 122 of the third audio
amplifier 124, the output 126 of said amplifier 124 being coupled to the loudspeaker 16. Thus,
after filtering and amplification at stage 20, the signal S1 to be transmitted is applied to the input
51 of the RF oscillator 50 to frequency modulate the carrier S2 generated by the RF oscillator 50.
The resulting signal S2m is then amplified and filtered and applied to the input of SHF oscillator
80 to amplitude modulate the signal S3 generated by oscillator 80. The resulting signal S3m is
then sent by antenna 84 to antenna 96. On the receive side, the signal S3m is preamplified by the
preamplifier 98 and applied to the AM detector 104 to regenerate the demodulated signal S2m
of the spectrum shown in FIG. 5B.
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[0017]
The signal S2m is then applied to the frequency demodulator 114 via the filtering means 112.
The demodulator 114 sends a signal S1 at its output 118, which signal S1 is sent to the
loudspeaker 16 via the filtering means 120.
[0018]
The method and apparatus according to the invention allow the transmitted signal S1 to be free
from disturbances such as ambient light and such disturbances which result in the blocking of
the transmitter-receiver link. Furthermore, the amplitude demodulation of the SHF carrier is
used, which considerably simplifies the structure of the receiver used.
[0019]
Brief description of the drawings
[0020]
1 schematically shows an example of an environment using the method according to the
invention.
[0021]
2 schematically shows a transmitter which can implement the method according to the invention.
[0022]
3A, 3B and 3C respectively amplitude-modulate the carrier S3 with the signals S2 and S2
obtained by frequency-modulating the carrier with the signals S1 and S1 on the transmission side
according to the method of the present invention. Fig. 6 shows the respective spectra of the
signal S3m obtained by
[0023]
4 schematically shows an FM-AM receiver which can implement the method according to the
invention.
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[0024]
FIGS. 5A, 5B and 5C show the spectra of the signal S3m, the signal S2m and the signal S1 on the
receiving side according to the method of the present invention, respectively.
[0025]
Explanation of sign
[0026]
DESCRIPTION OF REFERENCE NUMERALS 10 transmitter 12 receiver 14 television set 16, 18
speaker 20 first stage 22 second stage 24 third stage 30 audio amplifier 36 filtering means 50
voltage control oscillator 57 RF amplifier 62 filtering means 68 RF amplifier 80 SHF oscillator 84
antenna 90 first stage 92 second stage 94 third stage 96 antenna 98 preamplification means
104 AM detector 110 amplification means 112 filtering means 114 frequency demodulator 120
filtering means 124 voice amplifier
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