EP0486368A1 - Verfahren und Vorrichtung zum Schutz gegen Störungen von Richtfunkverbindungen - Google Patents

Verfahren und Vorrichtung zum Schutz gegen Störungen von Richtfunkverbindungen Download PDF

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Publication number
EP0486368A1
EP0486368A1 EP91402992A EP91402992A EP0486368A1 EP 0486368 A1 EP0486368 A1 EP 0486368A1 EP 91402992 A EP91402992 A EP 91402992A EP 91402992 A EP91402992 A EP 91402992A EP 0486368 A1 EP0486368 A1 EP 0486368A1
Authority
EP
European Patent Office
Prior art keywords
channel
information
pseudo
transmission
signal
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP91402992A
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English (en)
French (fr)
Inventor
Pierre Le Seigneur
Pierre-André Laurent
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Thales SA
Original Assignee
Thomson CSF SA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Thomson CSF SA filed Critical Thomson CSF SA
Publication of EP0486368A1 publication Critical patent/EP0486368A1/de
Withdrawn legal-status Critical Current

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04K—SECRET COMMUNICATION; JAMMING OF COMMUNICATION
    • H04K3/00—Jamming of communication; Counter-measures
    • H04K3/20—Countermeasures against jamming
    • H04K3/22—Countermeasures against jamming including jamming detection and monitoring
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04K—SECRET COMMUNICATION; JAMMING OF COMMUNICATION
    • H04K3/00—Jamming of communication; Counter-measures
    • H04K3/20—Countermeasures against jamming
    • H04K3/22—Countermeasures against jamming including jamming detection and monitoring
    • H04K3/224—Countermeasures against jamming including jamming detection and monitoring with countermeasures at transmission and/or reception of the jammed signal, e.g. stopping operation of transmitter or receiver, nulling or enhancing transmitted power in direction of or at frequency of jammer
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04K—SECRET COMMUNICATION; JAMMING OF COMMUNICATION
    • H04K3/00—Jamming of communication; Counter-measures
    • H04K3/20—Countermeasures against jamming
    • H04K3/25—Countermeasures against jamming based on characteristics of target signal or of transmission, e.g. using direct sequence spread spectrum or fast frequency hopping
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04K—SECRET COMMUNICATION; JAMMING OF COMMUNICATION
    • H04K3/00—Jamming of communication; Counter-measures
    • H04K3/20—Countermeasures against jamming
    • H04K3/25—Countermeasures against jamming based on characteristics of target signal or of transmission, e.g. using direct sequence spread spectrum or fast frequency hopping
    • H04K3/255—Countermeasures against jamming based on characteristics of target signal or of transmission, e.g. using direct sequence spread spectrum or fast frequency hopping based on redundancy of transmitted data, transmission path or transmitting source
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04K—SECRET COMMUNICATION; JAMMING OF COMMUNICATION
    • H04K2203/00—Jamming of communication; Countermeasures
    • H04K2203/10—Jamming or countermeasure used for a particular application
    • H04K2203/14—Jamming or countermeasure used for a particular application for the transfer of light or images, e.g. for video-surveillance, for television or from a computer screen
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04K—SECRET COMMUNICATION; JAMMING OF COMMUNICATION
    • H04K2203/00—Jamming of communication; Countermeasures
    • H04K2203/30—Jamming or countermeasure characterized by the infrastructure components
    • H04K2203/36—Jamming or countermeasure characterized by the infrastructure components including means for exchanging jamming data between transmitter and receiver, e.g. in forward or backward direction

Definitions

  • the present invention relates to a method and a device for protecting radio-relay systems against jamming. It relates more particularly to radio-relay systems and satellite-protected transmissions which must be capable of withstanding malicious electronic interference aimed at breaking communications.
  • pseudo-random sequence also called PN sequence
  • the multiplication or over-modulation of the current binary information symbol or Mayor of useful bit rate D transmitted by a series of pseudo-random bit rate N times higher determines the pseudo-random sequence actually transmitted.
  • the process of extraction by correlation of the symbol in the received stream has the effect of improving by a factor N the signal / (noise + jammer) ratio between the input of the correlator and its output.
  • each M-ary symbol is considered as an element of information resulting from an M-ary coding which consists, as opposed to binary coding, of transmitting the useful bits in packets of m bits and which is of interest to provide a transmission quality, characterized by a low error rate, all the better as m is large for a given signal-to-noise energy ratio.
  • a first aim of the invention is to improve the resistance of radio links produced in direct view or supported by a tropospheric propagation channel in the ranges of the usual frequencies SHF to EHF with respect to MRE Electronic Research Means in the field.
  • passive electronic countermeasures including those relating to the analysis of emissions and, consecutively, vis-à-vis the CME Electronic Countermeasures active in particular those relating to intrusion which could be attempted by a third party, this improvement cannot be obtained only by full encryption of the beams.
  • a second object of the invention is to improve the hardening against CME interference actions (by spectrum spreading) of the part of the beam reserved for the low capacity (or "survival") transmission channel as well as for frame synchronizations of the radio beam, the rest of the beam itself, unprotected in a nominal mode, being assigned to the high-capacity transmission channel supporting the flow of information of the users of the system, the whole being produced by means of the use of means preserving the fundamental characteristic of hermeticity expressed above.
  • a third object of the invention is to authorize an operation of the beam in a "fallback" mode according to which the anti-jamming hardening can also be applied to the transmission channel supporting the information flow of the users of the system.
  • the anti-jamming hardening can also be applied to the transmission channel supporting the information flow of the users of the system.
  • which can be considered in this case as a channel of reduced capacity so that, the synchronizations for the extraction of the information during the nominal switchover / fallback are ensured or at least facilitated by the permanence of a hardened survival channel, so as to preserve the fundamental characteristic of previous hermeticity.
  • the subject of the invention is a method of protecting a radio-relay system against interference, characterized in that it consists in adding to the transmission channel information of the users of the beam, a low-speed channel relatively to that of transmission of user information to transmit beam synchronization and service information, spreading the signal spectrum of the low-speed transmission channel by applying to this signal a sequence of pseudo-random signals, multiplexing during periods of frames of determined duration T o the information passing over the low-speed transmission channel, with the information of the beam users, and applying the signal resulting from the multiplexing onto the beam.
  • the multiplexing of the bit stream takes place between pseudo-random sequences transmitted on an information channel Ci of rate R 1 with very low capacity.
  • an information channel Ci of rate R 1 with very low capacity.
  • the frequency spectrum of the bit rate information R 1 applied to the channel Ci is widened by application of a pseudo-random PN sequence before being introduced into the transmission channel.
  • the bit rate information R 2 applied on the channel C 2 is encrypted before being transmitted on the transmission channel.
  • Multiplexing between the channels Ci and C 2 takes place alternately during respective time intervals T 1 and T 2 per time frame of duration T o such that:
  • the total bit rate R T obtained on the transmission channel is equal to:
  • This second mode in fact constitutes a fallback solution which can be used in the case where the interference is significant enough to prohibit the operation of the C 2 channel.
  • channel C 3 appears as a subset of channel C 2 .
  • the second mode of implementation of the method according to the invention allows for example, for a bit rate of 1 Kbits / s of the channel Ci, transmission by frame of duration T 2 of 30 binary information symbols from channel C 3 with a bit rate of 30 Kbits / s.
  • the spreading gain BT M 2/30 + 900, or 29.54 dB.
  • the anti-jamming protection of the channels Ci and C 3 can also include interleaving and / or coding devices for the correction of errors so as to ensure better resistance to certain types of jammers, of the pulse type. for example.
  • FIGS. 3 and 4 Transmission and reception devices allowing dual mode operation, in nominal mode and in fallback mode, in accordance with the transmission methods described above are shown in FIGS. 3 and 4 respectively.
  • the transmission device which is represented in FIG. 3 comprises a pseudo-random generator 1, a multiplier circuit 2, a synchronization device 3 and storage devices 4, 5 and 6 respectively dedicated to the signals coming from the information channels C 2 , Ci and C 3 .
  • the pseudo-random generator 1 supplies to the multiplier 2, with a rhythm Rt (Rt being the rhythm which modulates the RF carrier), a signal 7 intended, on the one hand, for the encryption of the information coming from the unprotected information channel C 2 of the nominal mode and, on the other hand, to the spreading of the PN spectrum of the information originating from the channel Ci protected in the two modes and from the channel C 2 protected in fallback mode.
  • the operating rhythm of the generator 1 is determined by a clock signal 8 which it receives from the synchronization device 3.
  • a current key is applied to an input 9 of the generator 1.
  • the synchronization device 3 ensures all the synchronizations (rhythm and frame) necessary for the various signal processing functions from a signal 10 supplied by an ultra stable reference source not shown and common to the whole of the transmitter.
  • the nominal or fallback operating mode is controlled by a signal 11 coming from a management device not shown.
  • the storage device 4 ensures the adaptation of the flow rate between the flow at the input 12 coming from the channel C 2 and the flow at the output 13 imposed by the output flow Rt. It receives from the synchronization device 3 on a link 14 a clock signal H 2 of rhythm equal to rhythm R 2 of channel C 2 and, during time T 2 on a link 15, a clock signal H ' 2 of rhythm equal to Rt, T 2 being the transmission time of channel C 2 in the output multiplex.
  • the storage device 5 plays a role similar to the storage device 4 with regard to the protected channel Ci applied to its input 16.
  • the device 5 furthermore integrates, in a known manner, an error correction function.
  • All the signals from the storage devices 4 and 5 are applied to the second input of the multiplier circuit 2.
  • the circuit 2 outputs a modulation signal from the transmitter on a link 22.
  • the initial synchronization is carried out according to a method known to those skilled in the art, by means of a correlator which takes advantage of the presence of the channel Ci where the useful binary rhythm is low and the spreading sequences known, at an offset temporal close.
  • the receiver sees arriving every millisecond a known binary sequence or its opposite, according to the value of the current bit of the channel Ci and of duration equal to 0.1 ms, the binary sequence varying according to the hour and the ( or) encryption key (s).
  • the initial synchronization is made by correlating the received signal with its expected value at times between TO-Dt and T0 + Dt around the time nominal TO of its appearance. This time range is explored in 2-chip steps, or approximately 16.6 ns with the numerical values mentioned above.
  • the synchronization instant corresponds to the instant when the output of the correlator used exceeds a given threshold, fixed as a function of the desired false alarm rate.
  • Dt is 1 ms maximum
  • 60,000 possible positions are to be tested in the worst case, which represents a maximum synchronization time of one minute, knowing that it is only possible to do a correlation in 1 ms increments (period of appearance of the known sequence).
  • This process allows synchronization to be obtained even under extreme conditions, where the interference power can exceed the useful signal power by 20 dB (this value being closely linked to the spreading factor N, which is here in the example of 3000).
  • the synchronization can be continued, for example, by means of an advance-delay loop, well known to those skilled in the art, which compares the results of correlations made slightly in advance and in delay by compared to the ideal position to deduce the correction to be made.
  • an advance-delay loop well known to those skilled in the art, which compares the results of correlations made slightly in advance and in delay by compared to the ideal position to deduce the correction to be made.
  • the reception device of FIG. 4 comprises a first and a second correlation channel.
  • the first correlation path comprises in known manner a multiplier circuit 23, an integrator circuit 24, a square elevation device 25, and a sampler circuit 26.
  • the second correlation channel also comprises, in a known manner, a multiplier circuit 27, a integrator circuit28, a square elevation device 29 and a sampler circuit 30.
  • the received signal is applied to first operand inputs of multiplier circuits 23 and 27 and is the subject of a first correlation with the expected sequence applied on a second operand input of the multiplier circuit 23.
  • the square of the module of the output signal obtained at the output of the integrator circuit 24 is performed by the square elevation device 25, the output of which is sampled at the end of period d integration by the sampler circuit 26.
  • the sampled signal is then filtered by a low pass filter 31 which acts as an averaging device capable of monitoring the evolution of the useful signal with a certain time constant.
  • the received signal is correlated with the expected sequence or every other bit is reversed by a multiplier circuit 32 receiving on a first operand input the expected sequence and on a second operand input one CHIP clock signal divided by two by a divider by two circuit 32 bis.
  • the output of the second correlation channel is filtered using a low-pass filter 33 coupled to the output of the sampler circuit 30.
  • the filtered output signal obtained at the output of the filter 33 is compared by a subtractor 34 and a comparator 35 to a threshold value provided by the output of a multiplier circuit 36 performing the multiplication by a constant k of the average value of the signal obtained at the output of the filter 31 composing the first correlation channel.
  • the constant k is adjusted as a function of the interference threshold beyond which the channel C 2 must be protected.
  • the signal obtained at the output of the comparator circuit 35 is in turn filtered by a low-pass filter 37, the output of which is connected to the input of a hysteresis device 38, the role of which is to prevent the device from too often and / or accidentally switches from the unprotected state to the protected state and vice versa, and thus improve the sensitivity of the device.
  • the interference detector which has just been described can in practice be produced by means of elements already existing in the receivers.
  • the correlators can have a different structure, without calling into question the very principle of the invention.
  • the protection can be further adjusted more gradually depending on the level of interference.
  • a variable number of detection channels operating in parallel, these channels comprising elements similar to those numbered 36 to 37 on FIG. 4 and however differing from each other by the value of the constant k.
  • the synchronization acquired on the signals of the protected channel Ci can also be used for the separation of the signals of the unprotected transmission channel C 2 and, in the second operating mode, for the extraction (despreading) of the signals of the second protected channel C 3 .

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  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Synchronisation In Digital Transmission Systems (AREA)
  • Mobile Radio Communication Systems (AREA)
EP91402992A 1990-11-16 1991-11-07 Verfahren und Vorrichtung zum Schutz gegen Störungen von Richtfunkverbindungen Withdrawn EP0486368A1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR9014293 1990-11-16
FR9014293A FR2669485B1 (fr) 1990-11-16 1990-11-16 Procede et dispositif de protection de faisceaux hertziens contre le brouillage.

Publications (1)

Publication Number Publication Date
EP0486368A1 true EP0486368A1 (de) 1992-05-20

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EP91402992A Withdrawn EP0486368A1 (de) 1990-11-16 1991-11-07 Verfahren und Vorrichtung zum Schutz gegen Störungen von Richtfunkverbindungen

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EP (1) EP0486368A1 (de)
FR (1) FR2669485B1 (de)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1098469A1 (de) * 1999-11-03 2001-05-09 Infineon Technologies AG Kodiervorrichtung

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1546628A (fr) * 1966-08-27 1968-11-22 Philips Nv Système pour la transmission d'information dans une bande de fréquences prescrite

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS61225936A (ja) * 1985-03-30 1986-10-07 Nec Corp スクランブル方式

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1546628A (fr) * 1966-08-27 1968-11-22 Philips Nv Système pour la transmission d'information dans une bande de fréquences prescrite

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
CONFERENCE PROCEEDINGS MILITARY MICROWAVES '88 Juillet 1988, LONDRES pages 33 - 42; REISCH ET AL: 'A three channel ECM-resistant microwave data link' *
EUROCON '86 Avril 1986, NEW YORK pages 632 - 636; KOWATSCH ET AL: 'Spread-spectrum signal processing with surface acoustic wave convolvers' *
PATENT ABSTRACTS OF JAPAN vol. 11, no. 70 (E-485)(2517) 3 Mars 1987 & JP-A-61 225 936 ( NEC CORP. ) 7 Octobre 1986 *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1098469A1 (de) * 1999-11-03 2001-05-09 Infineon Technologies AG Kodiervorrichtung
US7127620B2 (en) 1999-11-03 2006-10-24 Infineon Technologies Ag Power analysis resistant coding device

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FR2669485A1 (fr) 1992-05-22
FR2669485B1 (fr) 1993-01-22

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