Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
  • H04B1/06—Receivers
  • H04B1/10—Means associated with receiver for limiting or suppressing noise or interference
  • H04B1/12—Neutralising, balancing, or compensation arrangements
  • H04B1/123—Neutralising, balancing, or compensation arrangements using adaptive balancing or compensation means
  • H04B1/126—Neutralising, balancing, or compensation arrangements using adaptive balancing or compensation means having multiple inputs, e.g. auxiliary antenna for receiving interfering signal

Definitions

• the invention relates to a method and a device for reducing interference from radio transmission in a single-frequency or multi-frequency network.
• Transmission networks such as radio or television networks, include a source earth station from which the radio or television programs are produced, transmitted to a telecommunications satellite, this telecommunications satellite retransmitting these programs to reception-retransmission earth stations on a terrestrial radio network.
• the terrestrial radio network comprises a plurality of retransmission stations each equipped with a satellite reception antenna AS, a receiver and a transmitter connected to a transmitting aerial covering a determined terrestrial geographical area.
• Two retransmission stations S lr S 2 are normally spaced apart by a distance of about 150 km maximum.
• a user placed between two re-transmission stations S ,, S 2 , is required to transmit interactive signals at a frequency F ⁇ to the nearest transmitting station in order to allow the interactive sequence of a TV program, for example with the source earth station, or any intermediate station provided for this purpose if necessary.
• the user receives from the nearest transmitting station If the TV program has a frequency F 2 .
• the signals transmitted by the user at the frequency F x are subjected, on the part of the distant transmitting stations S 2 , to an interference phenomenon at a frequency close to or identical, due to the transmitting power much most of these transmitting stations and the limited frequency space allocated to these terrestrial radio networks.
• the station S 1 ( therefore receives the useful signal at the frequency F x generated by the user and an interfering signal at this same frequency Fi or at a very close frequency.
• the station S 1 there is no no device or technique exists for ensuring a systematic reduction of the above-mentioned interference, except those which use rejection systems creating filtering in the useful frequency band received or causing rejection on the antenna pattern in the direction
• rejector systems are however ineffective if the signal due to the jammer has a frequency bandwidth greater than that of the wanted signal or if the wanted signal comes from the same direction as the jammer. 'inconvé ⁇ deny the above.
• Radio interference reduction device taking advantage of the fact of the simultaneous presence of the same signal, contributing to the interference signal, on two different transmission media, these signals, although generally having different spectral characteristics, nevertheless carry the same information.
• the radio interference interference reduction method and device of a useful signal transmitted to a receiver are remarkable in that they implement, at the reception level, a first channel for receiving the useful signal in the presence of the interfering signal, delivering a useful signal received in the presence of the interfering second channel 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 their present in the first channel with the useful signal and means subtracting the interfering signal received from the useful signal in the presence of the interfering signal, which makes it possible to deliver a useful signal received free of interfering signal.
• the radio interference reduction device, object of the present invention finds application in the implementation and management of radio networks or radio broadcasting of radio or television programs.
• FIG. 2a shows a block diagram of a radio interference reduction device installed in a multi-frequency type transmission network
• - Figure 2b shows a detail of the device, object of the present invention
• - Figure 2c shows an illustrative diagram of implementation of the radio interference reduction method, object of the present invention
• - Figure 3 shows, in an ampli ⁇ tude-frequency diagram the shape of the frequency spectra of the signals obtained at different test points of Figure 2b, in the case where these signals are TV signals.
• the device, object of the present invention comprises at the reception level of the above-mentioned transmitting station S x a first channel V ⁇ for receiving the useful signal, in the presence of the interfering signal, this first channel delivering a useful signal received in the presence of the interferer and a second channel V 2 for receiving the interfering signal generated by delayed duplication of the interfering signal transmitted by the satellite network.
• the second channel V 2 delivers a received interfering signal similar to the interfering signal present in the first channel V x with the useful signal.
• the device, object of the invention comprises a module subtracting the interfering signal received from the useful signal in the presence of the interfering signal, which makes it possible to deliver, for example to a transmitter of the transmitting station S ! a useful signal received free of any scrambling signal for the retransmission of this useful signal received towards the source ground station, for example, or towards an intermediate station.
• the device, object of the present invention is composed of two aerial systems, an aerial AT for reception of terrestrial radio signals receiving the signal transmitted by the user, it is i.e. the useful signal at the frequency F 1 and the signal emitted by the jammer, i.e. the signal emitted at the same frequency F x or at a frequency very close by the jammer, either by the station transmission S 2 of the same radio network, and an aerial for reception of radio signals transmitted by the satellite, the antenna AS in FIG. 2a, normally present, for example, in the installations of the transmission station S x .
• each channel v lr V 2 also includes corresponding demodulation equipment as will be described later in the description.
• the signals thus received by the channels V : and V 2 are demodulated in baseband, then aligned in time by a delay compensating device, calibrated exactly on the difference of the propagation time of the signals.
• this delay is only related to time propagation and processing between the interfering transmitter site of the transmitting station S 2 and the receiving site, the transmitting station S x , due to the almost synchronous supply of the two transmitting station sites by the same satellite signal. It is indeed indicated that the distance of 150 km which separates the transmitting stations S : and S 2 is negligible compared to the distance of a satellite such as a geostationary satellite, for example, compared to the terrestrial surface.
• the aforementioned delay for two transmitting sites or stations separated by a distance of between 100 and 150 km can be of the order of 500
• the signal received by satellite under good propagation conditions, at the transmitting station S lr is preferably delayed because this signal is received with an optimal quality, superior to that of the signal transmitted by the terrestrial radio network.
• each channel V x and V 2 are then temporally aligned baseband signals, which are added in phase opposition by means of a 0-u coupler, for example.
• the first channel V ⁇ comprises, for example, advantageously, connected in cascade: the terrestrial reception antenna denoted AT, a baseband demodulator of conventional type, a device for equalization for performing an equalization treatment of conventional type, that is to say of amplitude and frequency equalization.
• the equalization circuit is followed by a gain-inverting circuit -1.
• the second channel comprises, connected in cascade, the satellite reception antenna AS, a demodulator of the satellite channel in baseband of conventional type, this demodulator being followed by an equalization device also making it possible to achieve an equalization processing of the demodulated signals both in amplitude and in frequency.
• the equalization circuit is then followed by a delay circuit making it possible to compensate for the propagation time of the interfering signal transmitted and to deliver the interfering signal received.
• a 0- ⁇ coupler receives on its input ports the interfering signal received and the interfering signal plus the useful signal delivered respectively by the second channel V 2 and the first channel V x to deliver the useful signal, that is to say the signal transmitted by the user initially.
• This useful signal can then be delivered for example to a collection network, not shown, for transmission to the source station or to any suitable intermediate station in order to ensure the interactive progress of the TV program thus broadcast.
• an equalization device In order to align in amplitude the received interfering signals having undergone different channel distortions, it is preferable to use an equalization device allowing an efficient alignment processing of the levels of the signals to be subtracted over the useful signal bandwidth to get back.
• the effective gain on the interference depends strongly on the alignment in amplitude and in frequency of the received signals, as well as, of course, that of the compensation or of the time offset. operated on the interfering signal received by the satellite radio network.
• the aforementioned alignments can advantageously be implemented with good precision thanks to the presence of the test signals, which then make it possible to calibrate the equalization and delay compensation processing perfectly.
• the method which is the subject of the invention consists in simultaneously receiving the useful signal in the presence of the interfering signal in order to obtain a useful signal received in the presence of the jammer, receiving the interfering signal generated by delayed duplication of the interfering signal transmitted by the satellite network to obtain a received interfering signal, similar to the interfering signal present with the wanted signal.
• the received interfering signal is subtracted from the useful signal in the presence of the interfering signal to deliver a received useful signal free of an interfering signal.
• test points A to F have been represented, placed respectively in alphabetical order at the output of the terrestrial antenna AT, at the output of the satellite antenna AS, at the output of the terrestrial demodulator of the first channel , at the output of the gain amplifier -1 of this same first channel, at the output of the delay compensation circuit on the second channel and delivering the interfering signal received and finally, at the output of the coupler 0-r ⁇ deli ⁇ vrant the useful signal after rejection of the interfering signal received.
• FIG 3 there is shown, by way of non-limiting example, the frequency spectrum of the signal received at the aforementioned test point A, that is to say at the output of the terrestrial antenna AT.
• This signal is shown for a conventional terrestrial television channel, modulated in MABLR modulation for "reduced sideband modulation".
• the spectrum of the jammer is superimposed on the spectrum of television signals for the high frequencies thereof.
• the spectrum of the interfering signal obtained at the output of the satellite antenna AS is represented for a satellite TV channel modulated in frequency modulation.
• the aforementioned signal is followed by a representation of the spectrum of the useful signal emitted by the user, that is to say of the useful digital signal transmitted in the band of the terrestrial TV channel at the frequency F, towards the transmitting station S :.
• the spectrum of the video baseband signal is shown for the interfering signal plus the useful signal after phase shift of 180 °, i.e. application of a gain equal to -1, the sign - at point D in FIG. 3, symbolizing the amplification by a gain equal to -1.
• the sum has been represented, using the 0- ⁇ coupler, an algebraic sum between the signal represented at point D and the signal represented at point E, the signal delivered at point F corresponding to that of the spectrum of the only useful signal, the digital signal cleared of the interfering TV spectrum, after subtraction, this signal then being able to be demodulated for its use or application within the framework of the broadcasting of the interactive TV program mentioned above.
• the device, object of the present invention makes it possible to improve the spectral efficiency of a broadcasting band by making it suitable for the transmission of new services, whatever its occupation.

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Radio Relay Systems (AREA)

Applications Claiming Priority (3)

Publications (1)

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• 1995
  • 1995-12-06 FR FR9514417A patent/FR2742283B1/fr not_active Expired - Fee Related
• 1996
  • 1996-12-03 EP EP96941099A patent/EP0808529A1/de not_active Withdrawn
  • 1996-12-03 WO PCT/FR1996/001917 patent/WO1997021277A1/fr not_active Application Discontinuation
  • 1996-12-03 US US08/875,774 patent/US6078800A/en not_active Expired - Fee Related

Non-Patent Citations (1)

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