Telecommunications – Receiver or analog modulated signal frequency converter – Noise or interference elimination
Patent
1997-09-25
2000-06-20
Trost, William G.
Telecommunications
Receiver or analog modulated signal frequency converter
Noise or interference elimination
455 63, 455 121, 348 21, H04B 110
Patent
active
060788003
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method and a device for reducing RF transmission interference in a monofrequency or multifrequency network.
Transmission networks, such as radio broadcasting or TV broadcasting networks include a source terrestrial station from which the radio broadcast or TV broadcast programs are compiled, transmitted to a telecommunications satellite, this telecommunications satellite forwarding these programs on to terrestrial stations for receiving/retransmitting on a terrestrial RF network. The terrestrial RF network comprises a plurality of retransmitting stations each equipped with an SA satellite receiving antenna, a receiver and a transmitter linked to a transmission aerial covering a specified terrestrial geographical area. Two retransmitting stations S.sub.1, S.sub.2 are normally spaced a distance of the order of at most 150 km apart. In the case of an interactive television RF network, a user, located between two retransmitting stations S.sub.1, S.sub.2, is required to transmit interactive signals at a frequency F.sub.1 to the closer transmitting station S.sub.1 so as to allow the interactive screening of a TV program for example with the source terrestrial station, or any intermediate station provided, as the case may be, for this purpose. The user receives the TV program at a frequency F.sub.2 from the closer transmitting station S.sub.2.
However, the signals transmitted by the user at the frequency F.sub.1 are subject, from the distant transmitting stations S.sub.2, to a phenomenon of interference at a similar or identical frequency, by virtue of the much greater transmitting power of these transmitting stations and of the limited frequency space allocated to these terrestrial RF networks. The transmitting station which is pertinent to the relevant user, the station S.sub.1, therefore receives the wanted signal at the frequency F.sub.1 generated by the user and an interfering signal at this same frequency F.sub.1 or at a very similar frequency.
At the present time, there is no device or technique making it possible to ensure a systematic reduction of the aforesaid interference, other than those which employ rejector systems creating a filtering in the wanted frequency band received or causing a rejection with regard to the antenna pattern in the direction of the interferer. These rejector systems are however inefficient if the signal due to the interferer exhibits a frequency bandwidth greater than that of the wanted signal or if the wanted signal originates from the same direction as the interferer.
The present invention aims to remedy the aforesaid drawback.
Its object is the implementation of a device for reducing RF interference exploiting the fact of the simultaneous presence of the same signal, contributing to the interference signal, on two different transmission media, these signals, although generally possessing different spectral characteristics, nevertheless transport the same information.
The method and the device for reducing the RF transmission interference to a wanted signal, transmitted to a receiver, this wanted signal being impaired by an interfering signal, present simultaneously, to within the propagation time, on a terrestrial and satellite RF network, which are the subjects of the present invention, are noteworthy in that they implement, at reception level, a first path for receiving the wanted signal in the presence of the interfering signal, delivering a wanted signal received in the presence of the interferer, a second path for receiving the interfering signal generated by delayed duplication of the interfering signal transmitted by the satellite network, delivering a received interfering signal similar to the interfering signal present in the first path with the wanted signal and means subtracting the received interfering signal from the wanted signal in the presence of the interfering signal, this making it possible to deliver a received wanted signal free of interfering signal.
The device for reducing RF interference, which is the subject of the present
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patent: 5093839 (1992-03-01), Kohno et al.
patent: 5440308 (1995-08-01), Dybdal et al.
patent: 5535432 (1996-07-01), Dent
patent: 5568523 (1996-10-01), Tsujimoto
patent: 5818517 (1998-10-01), Hudson et al.
Telediffusion de France
Trost William G.
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