Telecommunications – Transmitter
Reexamination Certificate
2002-02-13
2004-09-21
Tran, Cong Van (Department: 2683)
Telecommunications
Transmitter
C455S024000, C455S428000, C375S140000, C375S219000
Reexamination Certificate
active
06795691
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a transmission device of variable power. More particularly, the invention pertains to a transmission device having a very wide range of power variation.
Within the framework of wide-bandwidth wireless networks, it is known practice to use ever higher frequencies in order to allow the transmission of high bit rate applications such as video. These networks are also intended to allow data exchanges between at least one base station and a plurality of subscribers. These networks are commonly referred to as point-multipoint networks.
The point-multipoint type radio transmission systems are known to the person skilled in the art by the acronyms MMDS (standing for Microwave Multipoint Distribution System), LMDS (standing for Local Multipoint Distribution System) and MVDS (standing for Multipoint Video Distribution System). These systems used for the broadcasting of programmes permit a return path to the subscriber terminals which allows the subscriber to interact with the programme received. At present, the MPT-1560-RA standard provides for the use of frequencies situated between 40.5 and 42.5 GHz.
FIG. 1
illustrates an LMDS type system. A broadcasting station
1
furnished with a transmission/reception antenna
2
broadcasts information destined for a plurality of subscribers
3
. Each subscriber
3
has an external unit
4
, consisting of an antenna and means for transposing the signal received or the signal to be transmitted to an intermediate frequency, and an internal unit
5
which comprises means of channel selection in transmission and in reception as well as various means of coding/decoding for exchanging data with at least one user apparatus
6
, for example a television set, a telephone or a personal computer.
Transmissions in millimetre bands are strongly dependent on time, on atmospheric conditions, and on the distance D separating the subscriber
3
from the broadcasting station
1
.
FIG. 2
represents the attenuation to a 40 GHz (giga Hertz) transmission as a function of distance. Curve
7
represents the attenuation in good weather and curve
8
represents the attenuation during rain. As may be observed by the person skilled in the art, the attenuation varies by around 50 dB as the distance varies from 50 m to 2 km.
Now, a base station is used for several subscribers and the subscribers must transmit with the least power so as not to saturate the reception of the base station and jam the other subscribers. It is therefore necessary to have an adjustment of the transmission power level for each subscriber. A dialogue between the broadcasting station and the device placed at the subscriber's home makes it possible to adjust the transmission power.
FIG. 3
represents an exemplary embodiment of the transmitter part of the device placed at the subscriber's home, according to the state of the art. The internal or first unit
5
comprises means of modulation
10
which receive a signal to be modulated. A mixer
11
is connected to the modulation means
10
so as to transpose the modulated signal into an intermediate frequency band, a voltage-controlled oscillator
12
delivering the transposition signal. The output of the mixer
11
is coupled to an amplification facility which comprises one or more amplifiers
13
and a variable-gain attenuation circuit
14
. A supervisory circuit
15
sends the various control signals to the modulation means
10
to the controlled oscillator
12
and to the attenuation circuit
14
. A coaxial cable is connected at the output of the amplification facility so as to transport the signal to the external or second unit
4
. The external unit
4
comprises a first filter
16
connected to the coaxial cable and to a mixer
17
. A local oscillator
18
delivers a transposition frequency to the mixer. A second filter
19
eliminates the image frequencies originating from the mixer
17
. An amplifier of SSPA type (standing for Solid State Power Amplifier) amplifies the signal before delivering it to an antenna
21
.
In the circuit of
FIG. 3
, the adjustment of the transmission gain is carried out in the internal unit
5
with the aid of the attenuation circuit
14
. One problem is that the adjustment of the power with the aid of the attenuator
14
alters the signal-to-noise ratio. It is not possible to have more than 35 dB of power variation if one wishes to comply with a signal-to-noise ratio of at least 25 dB.
SUMMARY OF THE INVENTION
The invention proposes a transmission path structure which makes it possible to increase the range of variation of the transmission power without degrading the signal-to-noise ratio. The attenuation is carried out in part in the internal unit and in part in the external unit by switching an amplifier.
In a first inventive arrangement a transmission device comprising: an internal unit which modulates data to be transmitted and transposes them into an intermediate frequency band and which comprises means of variable attenuation; an external unit which transposes at least one intermediate band signal into a transmission frequency band, the said external unit comprising at least one amplifier linked to an antenna; and a linking cable which links the external unit and the internal unit. The external unit comprises a switching circuit arrangement for coupling the amplifier output to the antenna or coupling the amplifier input to the antenna.
In a second inventive arrangement a transmission/reception device comprising: an internal unit which, on the one hand, modulates data to be transmitted and transposes them into an intermediate frequency band and which comprises means of variable attenuation, and, on the other hand, transposes and demodulates data received; an external unit which transposes at least one intermediate band signal into a transmission frequency band and at least one signal received in a reception band into the intermediate band, the external unit comprising at least one amplifier linked to an antenna for the transmission of data; a linking cable which links the external unit and the internal unit. The external unit comprises a switching circuit for selectably coupling or bypassing the amplifier to the antenna.
According to a particular embodiment, the internal unit comprises means for delivering a switching signal to the external unit and the external unit comprises means for receiving the switching signal and controlling the switching circuit. This embodiment permits the control of switching in the external unit by the internal unit.
Preferably, the means of variable attenuation make it possible to have a greater range of variation of attenuation than the amplification change achieved by the amplifier bypass switch. Thus, it is possible to switch the external unit between two signal bursts without impeding transmission.
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Bouvet Sophie
Robert Jean-Luc
Levy Robert B.
Thomson Licensing S.A.
Tran Cong Van
Tripoli Joseph S.
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