EP2525519B1 - Method for synchronising jammers - Google Patents

Description

The invention relates to a method for time synchronization of jamming devices according to the features of patent claim 1.

Generally, radio signal jammers make it difficult or impossible to properly receive radio messages. The jammer, like the transmitter to be disturbed, emits energy in the form of electromagnetic waves and superimposes all or part of the original waves. It can operate at the same center frequency as the failed receiver or at an adjacent center frequency. The field strength, the modulation of the interfering signal and the disturbed message are important.

From the DE 10 2008 038 315 A1 For example, a method is known that allows efficient and reliable interference of a target signal within geographic limits.

From the US 2006/0153281 A1 jamming devices are known, comprising a detection device for detecting a target signal described, which is exchanged between a transmitting device and a receiving device, and a jamming device that interferes with a detection of a target signal to be disturbed this. These systems are also referred to as reactive interference systems.

Conventional 'open-loop' interferers, on the other hand, continuously emit interference signals on predefined frequency bands, regardless of whether signal activity is present there or not. Reactive interference systems thus generally lead to a significantly improved interference efficiency in comparison to 'open-loop' interferers.

Reactive interference systems first check the received frequency spectrum for potentially dangerous signals and then send targeted interference signals to prevent the detected communications. The cycles between observation and evaluation of the spectrum until the emission of the corresponding interference signals are relatively short. Reactive interference systems are used, inter alia, in mobile vehicles for convoy protection against radio-controlled detonators. If several reactive interference systems travel within a convoy, then the lookthrough (LT) phases, ie the phases in which the interference systems scan a given frequency spectrum for potentially dangerous signals, have to be synchronized in time with the individual interference systems (see, for example, US Pat US 2009/0611759 A1 ). Otherwise, the interference systems would respond to the emitted interference signals of the other interference systems, instead of concentrating their resources on actual threat signals (so-called ring-around effect).

The object of the invention is to specify a method for the synchronization of a plurality of reactive interference systems combined in a convoy.

This object is achieved with the features of the valid claim 1. Advantageous embodiments of the invention are the subject of further subclaims.

• Senden eines ersten Synchronisationssignals mit einer Zeitdauer T₁ und mit einer vorgebbaren Frequenz f_a,
• die kooperierenden reaktiven Störsender schalten im Falle einer Detektion des Synchronisationssignals in der LT-Phase in einen Synchronisationszyklus um, wobei der Synchronisationszyklus eine Folge einer vorgebbaren Anzahl von aufeinander folgenden LT-Phasen umfasst,
• Senden eines zweiten Synchronisationssignals mit einer Zeitdauer T₂ und mit einer vorgebbaren Frequenz f_b,
• die kooperierenden reaktiven Störsender schätzen durch Auswertung des in einer oder mehreren aufeinanderfolgenden LT-Phasen gemessenen spektralen Leistungspegels des zweiten Synchronisationssignals die zeitliche Position t₀ des Einschaltzeitpunkts des zweiten Synchronisationssignals,
• die kooperierenden reaktiven Störsender synchronisieren sich, wobei die zeitliche Position t₀ als gemeinsamer Ankerpunkt für das zeitliche Raster des Störzyklus verwendet wird.

According to the invention, one or more jammers are switched from a jamming operation to a synchronization mode for the time synchronization of a plurality of cooperating jamming transmitters, the jamming operation of a jamming transmitter comprising a continuous series of jamming cycles with a predetermined time frame. The switchover takes place according to the following steps:

• Transmitting a first synchronization signal having a time duration T ₁ and a presettable frequency f _a ,
• the cooperating reactive jammers switch to a synchronization cycle in the event of detection of the synchronization signal in the LT phase, the synchronization cycle comprising a series of a predefinable number of successive LT phases,
• Sending a second synchronization signal having a time duration T ₂ and having a predefinable frequency f _b ,
• the cooperating reactive jammers estimate the temporal position t _{0 of} the switch-on time of the second synchronization signal by evaluating the spectral power level of the second synchronization signal measured in one or more successive LT phases;
• the cooperating reactive jammers synchronize using the temporal position t ₀ as the common anchor point for the temporal grid of the jamming cycle.

The method according to the invention serves to synchronize in time two or more mobile reactive radio interference systems for the protection of convoys or individual vehicles against radio-controlled bombs. Such a reactive interference system regularly broadband scans the frequency spectrum - during the LT phases - to detect potential threat signals. For this purpose, during a separate calculation phase, preferably in real time, a spectral analysis of the frequency band of interest is performed. In the subsequent disturbance phase, the interference system then reacts with corresponding interference signals in order to prevent the possible triggering of a radio-controlled bomb in the vicinity of the convoy or individual vehicle to be protected.

In the case of multiple reactive interferers, which are active in a composite - for example, a convoy - a temporal synchronization is essential. Otherwise, a ring-around effect occurs in which the individual jamming systems respond to the jamming signals of the other jamming systems instead of concentrating their resources on actual threat signals (since they detect the jamming signals of the other jammers during their LT phases). To avoid the ring-around effect, all participating cooperative reactive interferers can use the same duration of an LT phase or the same duration of an interference phase.

The deployment scenario in which several mobile jamming systems move within a convoy to be protected is in Fig. 1 to see. The convoy, for example, consists of a plurality of vehicles F, some vehicles are equipped with a reactive interferer S. The interferers S themselves comprise several transmission and receiving means for transmitting interfering signals or for scanning the received frequency spectrum.

Fig. 1

beispielhafter Fahrzeugkonvoi mit mehreren mobilen Störsystemen zum Schutz gegen per Funk ferngezündete Bomben,

Fig. 2

beispielhafte Abfolge von LT-/Berechnungsphasen und Störphasen a) im normalen operativen Betrieb und b) bei kurzzeitigem Wechsel in den Synchronisationszyklus,

Fig. 3

beispielhafte Darstellung des Ablaufs eines Synchronisationszyklus,

Fig. 4

beispielhafte Darstellung einer digitalen Signalverarbeitung im Empfangszweig eines reaktiven Störers.

The invention will be explained in more detail with reference to figures. Show it:

Fig. 1

exemplary vehicle convoy with several mobile jamming systems for protection against remote radio controlled bombs,

Fig. 2

exemplary sequence of LT / calculation phases and interference phases a) in normal operative operation and b) in the case of a brief change to the synchronization cycle,

Fig. 3

exemplary representation of the sequence of a synchronization cycle,

Fig. 4

exemplary representation of a digital signal processing in the receiving branch of a reactive interferer.

The method according to the invention uses the LT phases as well as the spectral analysis in the reception branches of the reactive interference systems. The basis here is a synchronization signal, which is expediently within the scan bandwidths of all interfering systems involved. Suitably, this synchronization signal is sent from a cooperating reactive jammer selected as a pilot transmitter or a separate transmitter. A separate transmitter here means a transmitter which is either outside the convoy or inside the convoy, but without disturbance tasks.

To switch to the synchronization mode and to activate the synchronization of the pilot transmitter two synchronization signals are sent out. The first activation of the pilot transmitter, that is, the transmission of the first synchronization signal, takes place at a fixed, known frequency f _a and signals in each case the beginning of a new synchronization cycle. The normal operative operation of the reactive interference systems is characterized by the continuous change between LT phases (plus calculation phases) and interference phases (s. Fig. 2a ). As soon as the changeover to the synchronization mode is signaled by the first activation of the pilot transmitter, the participating reactive interference systems briefly change into a special synchronization cycle (see FIG. Fig. 2b ), which are several consecutive contains the following LT phases (without time gaps, ie the calculation phases must be processed parallel to the LT phases). The normal fault operation is therefore only temporarily interrupted.

In the Fig. 2a and 2b are marked with "b" the interference phases, with "o" the LT phases and with "g" the calculation phases.

The second activation of the pilot transmitter also takes place at a fixed, known frequency f _b and serves for the actual time synchronization of the individual reactive interference systems. To do so, the reactive interferers involved observe the spectral power level of the pilot carrier during the successive LT phases and, based thereon, estimate the exact timing position t _{0 of} the turn-on edge of the second synchronization signal. This then serves as an anchor point for the nominal temporal grid of LT / calculation phases and interference phases. Finally, all reactive interference systems synchronize themselves to this grid by adjusting the length of the next interference phase accordingly. The proposed sequence of temporal synchronization is in Fig. 3 shown schematically.

The first and second synchronization signals may either originate from a separate source or be provided by one of the participating reactive interferers.

The number of LT phases within a synchronization cycle can either be fixed or parameterizable.

For the execution of the individual synchronization cycles, for example, a fixed flowchart can be used which depends on the expected temporal drift of the participating reactive interferers. Alternatively, synchronization cycles may also be started as needed, provided there is a suitable control mechanism that monitors the timing of all reactive interferers.

In one embodiment of the invention, a plurality of synchronization cycles can be performed in quick succession, so that also those reactive

Synchronize interferers that could not detect the start signal of the first synchronization cycle - either because of destructive propagation conditions or due to an unfavorable position of the LT phase. The number of short consecutive synchronization cycles can be parametrizable or dynamically controlled.

The frequency f _{b of} the second synchronization signal used in the second activation of the pilot transmitter may be either equal to or different from the frequency f _{a of} the first synchronization signal. The latter variant allows the participating reactive interferers to distinguish the start signal for a new synchronization cycle from the actual synchronization signal.

The period of time T ₁ during which the first synchronization signal is transmitted at the frequency f _a can be chosen so that the participating reactive interferers can detect it with an arbitrary temporal position of its LT phase. In this case, T ₁ depends on the type of interference used.

The delay .DELTA.T at which the second synchronization signal is transmitted on the frequency _f.sub.b after the end of the first synchronization signal can be tuned to the total length of the LT phases used in the synchronization cycle. It can thereby be ensured that each of the reactive interferers involved can detect the switch-on edge within its successive LT phases.

In the following, the method according to the invention will be explained in more detail using an example. Here, the first and second synchronization signal, referred to below synonymously as a pilot signal, provided by one of the participating reactive interferers. That is, at the beginning of the mission, a disturber in the convoy is declared as a so-called 'master' disturber. In the estimation of the position of the switch-on edge t _{0 of} the second synchronization signal, a method which is particularly easy to implement is selected.

The pilot signal of the master interferer is based on the same internal signal generator that is also used to generate the interfering signals ('Exciter'). This allows one particularly low-cost implementation of the method according to the invention for switching from interference mode to a synchronization mode. As soon as a synchronization cycle is to be completed, the master interferer reserves one of its exciter for the pilot signal ('pilot exciter'). This is then no longer available for the reactive interference mode (due to the fixed frequency f _a ). In order to initiate the synchronization cycle, the master interferer activates the pilot signal, ie the first synchronization signal is sent for a complete interference phase (ie in this case T ₁ corresponds to the used disturbance duration, cf. Fig. 3 ). In the next interference phase, the pilot signal (second synchronization signal) for the actual synchronization is then sent (ie .DELTA.T corresponds to the sum of LT and calculation duration).

• Da der Master-Störer während des gesamten Synchronisationszyklus das herkömmliche Raster aus LT/Berechnungsphasen und Störphasen verwendet, kann der Störbetrieb auf Basis der verbleibenden Exciters unverändert fortgesetzt werden. Der Master-Störer kann somit zumindest einen Teilschutz realisieren, während die übrigen reaktiven Störer ('Slave-Störer') ihren normalen Störbetrieb kurzzeitig unterbrechen (vgl. Fig. 2b bzw. Fig. 3), um in den Synchronisationsmodus zu wechseln.
• Die Einschaltflanke des Pilotsignals liegt sowohl bei der ersten als auch bei der zweiten Aktivierung auf dem nominellen zeitlichen Raster für die LT-/Berechnungsphasen und Störphasen. Somit ist es nicht erforderlich, dass die "Slave"-Störer, d.h. die übrigen kooperativen reaktiven Störsysteme im Konvoi, das Startsignal von dem eigentlichen Synchronisationssignal unterscheiden können müssen. Man kann für die zweite Aktivierung des Pilotsignals daher die selbe Frequenz wählen wie für die erste Aktivierung (f_b=f_a).
• Fig. 3 zeigt ein Beispiel für eine Grobsynchronisation, wie sie zum Beispiel zu Beginn einer Mission durchgeführt werden kann. Im laufenden Betrieb hingegen wird in der Regel lediglich eine Feinsynchronisation nötig sein. In diesem Fall können die in Fig. 3 dargestellten aufeinander folgenden LT-Phasen der Slave-Störer teilweise durch eine weitere Störphase ersetzt werden (unmittelbar zu Beginn des Synchronisationszyklus). Auf diese Weise kann die Unterbrechung des normalen Störbetriebs bei den Slave-Störern weiter verkürzt werden. Die während der Feinsynchronisation verwendete Anzahl aufeinander folgender LT-Phasen-im Folgenden mit N bezeichnet - richtet sich dabei nach dem zu erwartenden zeitlichen Drift der beteiligten Störer. Während eines Synchronisationszyklus ergibt sich für die Slave-Störer abhängig vom Parameter N eine prozentuale Einschränkung des normalen Störbetriebs von $$\frac{{\mathit{NT}}_{\mathit{LT}}}{{\mathit{T}}_{\mathit{Jam}}}\cdot 100\%$$
  
  (NT_LT < T_Jam), wobei T_LT die Dauer der LT-Phase und T_Jam die Dauer der Störphase bezeichnet. Typischerweise ist die Störphase deutlich länger als die LT-Phase, z.B. T_Jam=10T_LT. Somit ergeben sich z.B. für N=3 typische Werte von 30%. Diese Einschränkung des Störbetriebs betrifft nur einen einzigen LT-/Störzyklus der Slave-Störer.
• Um allen Slave-Störern die Möglichkeit zur Synchronisation zu ermöglichen (auch denjenigen, deren LT-Phase beispielsweise mit der Berechnungsphase des Master-Störers zusammen fällt), können pro Synchronisation mehrere aufeinander folgende Synchronisationszyklen durchgeführt werden, unter Umständen mit leicht variierender Stördauer des Master-Störers. Dies kann zum Beispiel dann geschehen, wenn der Master-Störer feststellt, dass sich nach dem ersten Synchronisationszyklus nicht alle Slave-Störer hinreichend genau synchronisieren konnten.

The above definitions have the following consequences:

• Since the master interferer uses the conventional grid of LT / calculation phases and disturbance phases throughout the synchronization cycle, the disturbance operation can be continued unchanged based on the remaining exciters. The master interferer can thus realize at least partial protection, while the other reactive interferers ('slave interferers') interrupt their normal interference operation for a short time (cf. Fig. 2b respectively. Fig. 3 ) to switch to synchronization mode.
• The switch-on edge of the pilot signal is at the nominal time grid for the LT / calculation phases and interference phases both in the first and in the second activation. Thus, it is not necessary that the "slave" interferers, ie the other cooperative reactive interference systems in the convoy, be able to distinguish the start signal from the actual synchronization signal. It is therefore possible to select the same frequency for the second activation of the pilot signal as for the first activation (f _b = f _a ).
• Fig. 3 shows an example of a coarse synchronization, as it can be done for example at the beginning of a mission. On the other hand, during normal operation, only a fine synchronization will usually be necessary. In this case, the in Fig. 3 shown successive LT phases of the slave interferers are partially replaced by another disturbance phase (immediately at the beginning of the synchronization cycle). In this way, the interruption of the normal fault operation with the slave interferers can be further shortened. The number of successive LT phases used during the fine synchronization, hereinafter referred to as N, depends on the expected temporal drift of the interferers involved. During a synchronization cycle, depending on the parameter N, the slave interferers have a percentage limitation of the normal disturbance operation of $$\frac{{\mathit{NT}}_{\mathit{LT}}}{{\mathit{T}}_{\mathit{Jam}}}\cdot 100\%$$
  
  (NT _LT <T _Jam ), where T _{LT is} the duration of the LT phase and T _{Jam is} the duration of the spurious phase. Typically, the spurious phase is significantly longer than the LT phase, eg T _Jam = 10T _LT . Thus, for example, for N = 3, typical values are 30%. This restriction of disturbance operation concerns only a single LT / disturb cycle of the slave interferers.
• In order to enable all slave interferers to synchronize (even those whose LT phase coincides, for example, with the computation phase of the master interferer), several consecutive synchronization cycles can be performed per synchronization, possibly with slightly varying disturbance duration of the master jammer. This can happen, for example, when the master interferer determines that not all slave interferers could synchronize sufficiently precisely after the first synchronization cycle.

For the actual time synchronization (at the second activation of the pilot signal), the slave interferers use the same signal processing that is also used to analyze potential threat signals. Similar to the master interferer, this allows a particularly low-cost implementation of the synchronization mechanism. A corresponding digital signal processing chain is in Fig. 4 shown. It typically includes essentially the blocks of 'digital filtering', 'fenestration' and 'spectral analysis' (based on Fast Fourier Transform (FFT), for example).

For synchronization in time, the slave interferers observe the spectrum of the second pilot signal emitted by the master interferer and estimate its starting time t ₀ on the basis of the spectral power level (magnitude square of the calculated FFT spectrum). For this purpose, they first determine in which of the successive LT phases the switch-on edge of the pilot signal is located (cf. Fig. 3 ). This can be achieved, for example, by finding a series of three successive LT phases in which the pilot signal is initially absent (first LT phase), having a medium power level in the second LT phase, and in the third LT Phase has a maximum power level. The switch-on edge is then in the middle LT phase. On the basis of the exact spectral power level in the middle LT phase, the exact position of the switch-on edge is then estimated. This exploits the fact that the greater the active part of the pilot signal during the LT phase, the greater the spectral power level.

The exact characteristic curve for the relationship between the spectral power level and the time component of the active pilot signal depends strongly on the window function used and the pilot frequency used. This characteristic can be recorded, for example, in the implementation stage of the synchronization method according to the invention. During operation, the estimation of the start time t _{0 can} then be based on a simple comparison of the observed power level versus the characteristic, which means a very low implementation effort. Finally, based on the estimation of the start time t ₀ , the time synchronization with the master interferer takes place as described.

The master interferer (as well as the other interferers) each have several exciters available for interfering with target signals. The synchronization method according to the invention is tailored to the boundary conditions in a composite of reactive interferers.

• erhält der Master-Störer seinen Störbetrieb während des Synchronisationszyklus weitest gehend aufrecht, während für die Slave-Störer die Einschränkung des normalen Störbetriebs zeitlich auf ein Minimum beschränkt wird,
• basiert das Verfahren zu einem großen Teil auf der bestehenden Signalverarbeitung eines reaktiven Störers, was den zusätzlichen Implementierungsaufwand gering hält,
• wird für die Schätzung des Zeitversatzes eine sehr einfache Methode eingesetzt, was hinsichtlich einer Echtzeitimplementierung von Vorteil ist,
• benötigt der Master-Störer lediglich einen einzigen Exciter für Synchronisationszwecke (Pilot-Exciter), wodurch auch im Synchronisationsmodus eine hohe Störeffizienz gewährleistet wird.

Especially

• the master interferer maintains its disturbance operation as far as possible during the synchronization cycle, while for the slave interferers the limitation of the normal disturbance operation is kept to a minimum,
• the method is based to a large extent on the existing signal processing of a reactive interferer, which minimizes the additional implementation effort,
• a very simple method is used for the estimation of the time offset, which is advantageous in terms of a real-time implementation,
• requires the master interferer only a single exciter for synchronization purposes (pilot exciter), whereby a high interference is ensured even in the synchronization mode.

Claims (9)

1. Method for temporally synchronizing a plurality of cooperating reactive jammers for interfering with one or more target signals,
   characterized in that
   for the purpose of temporal synchronization, one or more jammers are changed over from an interference mode to a synchronization mode, the interference mode of a jammer comprising a continuous sequence of interference cycles with a predefined temporal pattern, each interference cycle comprising a look-through (LT) phase for detecting one or more target signals, a calculation phase for calculating corresponding interference signals and an interference phase for transmitting the interference signals,
   the changeover to the synchronization mode being effected by means of the following steps:

   - a first synchronization signal with a duration T₁ and with a predefinable frequency f_a is transmitted,

   - the cooperating reactive jammers change over to a synchronization cycle if the synchronization signal is detected in the LT phase, the synchronization cycle comprising a sequence of a predefinable number of successive LT phases,

   - a second synchronization signal with a duration T₂ and with a predefinable frequency f_b is transmitted,

   - the cooperating reactive jammers estimate the temporal position to of the switch-on time of the second synchronization signal by evaluating the spectral power level of the second synchronization signal, which level is measured in one or more successive LT phases,

   - the cooperating reactive jammers synchronize, the temporal position to being used as a common anchor point for the temporal pattern of the interference cycle.
2. Method according to Claim 1,
   characterized in that
   the first and second synchronization signals are transmitted by a cooperating reactive jammer selected as the pilot transmitter or by a separate transmitter.
3. Method according to either of Claims 1 and 2, characterized in that
   the frequency f_a of the first synchronization signal is the same as or different from the frequency f_b of the second synchronization signal.
4. Method according to one of the preceding claims, characterized in that
   the second synchronization signal is transmitted with a delay ΔT after the switch-off time of the first synchronization signal.
5. Method according to one of the preceding claims, characterized in that
   the duration T₁ of the first synchronization signal is greater than or equal to the temporal duration of an interference cycle.
6. Method according to one of the preceding claims, characterized in that
   the duration of the LT phase and the duration of the interference phase are the same for all cooperating jammers.
7. Method according to one of the preceding claims, characterized in that
   the first and second synchronization signals are within a frequency range which can be detected during the look-through phases of the interference systems involved.
8. Method according to one of the preceding claims, characterized in that
   a plurality of synchronization cycles can be carried out in quick succession.
9. Method according to one of the preceding claims, characterized in that
   a plurality of synchronization cycles are carried out in succession or in that the synchronization cycles are carried out as required.

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