Measurement device and method for detection of simultaneous duplicate transmission

0001The invention relates to a measuring device and a measuring method for detecting the simultaneous presence of at least one first signal and one second signal in a measuring signal.

0002In aeronautical radio, amplitude-modulated signals are still common. A major problem with the use of such signals is that if signals are randomly transmitted simultaneously by two aircraft, for example, the weaker signal arriving at the receiver remains undetected. This can lead to safety-related errors.

0003For the detection of such double transmissions, a method is known in which a received signal is distorted non-linearly and is then transmitted into the frequency range. Symmetrical spectral components in the distorted spectrum are then determined and removed. On the basis of the remaining signal components, it is then concluded that a second signal transmitted at the same time is present. This is how the German Offenlegungsschrift shows<patcit id="pcit0001" dnum="DE102011080999A1"><text>DE 10 2011 080 999 A1</text></patcit> a non-linear distortion method described above. However, this method is disadvantageous because it requires a high level of computational effort due to the non-linear distortion. In addition, it is problematic in use with CLIMAX operation. It is not able to differentiate between several transmitters in simulcast operation of the CLIMAX system and an actual, recognizable double transmission.

0004Another method is from the patent application <patcit id="pcit0002" dnum="DE102007037105A1"><text>DE 10 2007 037105 A1</text></patcit> known. The invention is based on the object of creating a simple and reliable measuring device and measuring method which are able to reliably detect double transmissions.

0005According to the invention, the object is achieved for the measuring device by the features of independent claim 1 and for the method by the features of independent claim 3. Advantageous further developments are the subject of the dependent claims which refer back to them. The inventive measuring device is used to detect the simultaneous presence of at least a first signal and a second signal in a measurement signal, preferably a received signal of a radio device in aeronautical radio. The measuring device contains a receiving device for receiving the measurement signal as a digital measurement signal and a processing device. The processing device has a transformation device for transforming the digital measurement signal into a measurement signal in the frequency range. The processing device also includes a subtraction device for subtracting a first sideband of the measurement signal in the frequency range from a second sideband of the measurement signal in the frequency range. Both sidebands are the same signal component - the strongest carrier. The subtraction device generates a residual signal. Based on the residual signal, it is very easy to infer the presence of a double transmission.

0006Preferably, only the receiving device processes the measurement signal before digitization by the receiving device. The receiving device then processes the measurement signal only by means of linear operations before it digitizes the measurement signal into the digital measurement signal. Since no non-linear operations are necessary, processing that conserves computing resources can be guaranteed.

0007The first signal and the second signal are preferably amplitude-modulated signals, each with a carrier. In this way, the predominant transmission method in aeronautical radio can be used.

0008The subtraction device is preferably designed to detect a strongest carrier present in the measurement signal, the sidebands of the measurement signal being separated by the strongest carrier present in the measurement signal. A reliable differentiation of the sidebands to be subtracted can thus be ensured.

0009The subtraction device is preferably designed to mirror one of the sidebands of the measurement signal in the frequency domain at a position of a strongest carrier present in the measurement signal before the subtraction. This ensures that the measuring device functions reliably for any transmission signal.

0010The processing device advantageously includes a detection device for detecting the presence of the second signal in the measurement signal based on remaining signal components of the residual signal. An automatic evaluation that is very simple for the user of the measuring device can thus be achieved.

0011The detection device is preferably designed to determine the presence of the second signal in the measurement signal by means of a threshold value comparison of remaining signal components or by means of a threshold value comparison of a signal derived from the remaining signal components in the residual signal. This means that the derived useful signal is compared against the noise. A very simple detection can thus be ensured.

0012The detection device is preferably designed to determine the presence of the second signal in the measurement signal by means of a threshold value comparison of summed powers of the remaining signal components in the residual signal. The presence of the second signal can thus be detected with increased accuracy.

0013The detection device is preferably designed to detect rotor modulations of the first signal and / or the second signal and to remove detected rotor modulations of the first signal and / or the second signal from the first signal or the second signal. Alternatively, it is designed to disregard detected rotor modulations of the first signal and / or of the second signal when the presence of the second signal is detected in the measurement signal. In this way, errors caused by rotor modulations in the detection of a double transmission can be avoided. The measurement method according to the invention is used to detect the simultaneous presence of at least one first signal and a second signal in a measurement signal. The measurement signal is received as a digital measurement signal. The digital measurement signal is then transformed into a measurement signal in the frequency range. This is followed by a subtraction of a first sideband of the measurement signal in the frequency range from a second sideband of the measurement signal in the frequency range, a residual signal being generated in the process. Based on the residual signal, it is very easy to infer the presence of a double transmission.

0014The measuring device according to the invention and the measuring method according to the invention can preferably detect double transmissions when the level difference between the two signals is from 0 to 20 dB, particularly preferably from 0 to 40 dB. Reliable detection of a double transmission is thus possible even with a very strong and a very weak signal.

0015The measuring device and the measuring method are particularly preferably suitable for distinguishing actual double transmissions by different participants from supposed double transmissions in the CLIMAX method.

0016The invention is described by way of example below with reference to the drawing, in which an advantageous exemplary embodiment of the invention is shown. In the drawing show:<dl id="dl0001"><dt>Fig. 1</dt><dd>a schematic representation of the problem underlying the present invention;</dd><dt>Fig. 2a</dt><dd>a spectral representation of two simultaneously transmitted signals in the frequency domain;</dd><dt>Figure 2b</dt><dd>a spectral sum display of the simultaneously transmitted signals <figref idref="f0001">Fig. 2a</figref>;</dd><dt>Fig. 3</dt><dd>an embodiment of the measuring device according to the invention in a block diagram;</dd><dt>Fig. 4</dt><dd>a detailed view of the embodiment of the measuring device according to the invention in a block diagram;</dd><dt>Fig. 5</dt><dd>a spectral representation of a signal used by the exemplary embodiment of the measuring device according to the invention, and</dd><dt>Fig. 6</dt><dd>an embodiment of the measuring method according to the invention in a flowchart.</dd></dl>

0017First, the <figref idref="f0001">Figures 1-2b</figref> explains the problem underlying the present invention. Then, using <figref idref="f0002 f0003">Fig. 3-4</figref> an embodiment of the measuring device according to the invention and its function explained in detail. Finally, using<figref idref="f0004">Fig. 6</figref> dealt with the functioning of an exemplary embodiment of the method according to the invention. Identical elements have in some cases not been shown and described repeatedly in similar figures.

0018In <figref idref="f0001">Fig. 1</figref> the problem underlying the invention is shown schematically. A first aircraft 10 sends a first signal 11 to a receiver 14. At the same time, a second aircraft 12 sends a second signal 13 to the receiver 14. Due to the significantly smaller distance between the second aircraft 12 and the receiver 14, the second signal 13 comes out clearly higher level at the receiver 14 than the first signal 11. Due to the amplitude modulation and the use of the nominally identical transmission frequency, the first signal 11 disappears in the stronger second signal 13 and cannot be detected by the receiver 14 without further measures. A message sent by the aircraft 10 to the receiver 14 therefore does not arrive. Of course, the measuring device according to the invention and the measuring method according to the invention can also be used with a different constellation of the participants. So is for example a double transmission of an aircraft and a ground station is conceivable when received by an aircraft or a ground station. In general terms, each of the participants shown can be replaced by an aircraft or a ground station.

0019In <figref idref="f0001">Fig. 2a</figref> is the in <figref idref="f0001">Fig. 1</figref> The situation shown in the frequency domain. The first signal 11 off<figref idref="f0001">Fig. 1</figref> The left side band 20b, the right side band 21b and the carrier 22b correspond here. The second signal 13 off<figref idref="f0001">Fig. 1</figref> The left side band 20a, the right side band 21a and the carrier 22a correspond here. It can be clearly seen here that the components corresponding to the first signal 11 have a significantly lower level than the components corresponding to the second signal 13. That is to say, the components of the first signal 11 in the second signal 13 disappear.

0020In <figref idref="f0001">Figure 2b</figref> is on at the receiver 14 off <figref idref="f0001">Fig. 1</figref> incoming total signal shown spectrally. Due to slight frequency differences between the two signals, there is a slight asymmetry of the sum signal, which in<figref idref="f0001">Figure 2b</figref> is shown. A left side band 30 and a right side band 31 can be seen around a recognizable central support 32. The contributions of the first signal 11 from can hardly be seen here<figref idref="f0001">Fig. 1</figref>. Only in the left foot area of ​​the left sideband 30 and the right sideband 31 and at the foot point of the carrier 32 can small changes be seen in relation to a single signal. However, it is not possible to infer a double transmission directly from these areas. Of course, the entire received signal can also contain only one useful signal, for example the first signal 11 or the second signal 13 and noise. This case must therefore be distinguished from the case presented above in the context of double transmission detection.

0021<figref idref="f0002">Fig. 3</figref> shows an embodiment of the measuring device according to the invention in a block diagram. The first signal 11 off<figref idref="f0001">Fig. 1</figref> and the second signal 13 off <figref idref="f0001">Fig. 1</figref> together form a measurement signal 50. The measuring device 2 includes a receiving device 3, a digital processing device 7, an output device 8 and a control device 9. The receiving device 3 also includes an antenna 4, an analog processing device 5 and an analog-digital converter 6. The antenna 4 is connected to the analog processing device 5, which in turn is connected to the analog-digital converter 6. This in turn is connected to the digital processing device 7. The analog processing device 5, the digital processing device 7 and the output device 8 are further connected to a control device 9. Only the components of the measuring device relevant to the invention are shown here. Usual reception technology, as used in an aircraft radio, is not shown in detail here.

0022The measurement signal 50, which contains at least one signal, for example from an aircraft - but can alternatively contain a first and a second signal in the case of double transmission - is received by the antenna 4 and transmitted as a received signal 51 to the analog processing device 5. This performs analog processing steps, such as filtering and amplification, and outputs a processed measurement signal 52 to the analog-digital converter 6. This digitizes the signal and transmits it as a digital measurement signal 53 to the digital processing device 7. This detects the double transmission and communicates a result to the control device 9. In the case of a double transmission, the control device 9 controls the output device 8 in order to indicate the double transmission, for example by means of an acoustic warning signal or an optical warning signal. The analog processing device 5, the digital processing device 7 and the output device 8 are controlled by the control device 9. The detailed function of the digital processing device 7 is based on<figref idref="f0003">Fig. 4</figref> entered into more detail.

0023In <figref idref="f0003">Fig. 4</figref> FIG. 3 is a detailed view of the digital processing device 7 from FIG <figref idref="f0002">Fig. 3</figref> shown. The digital processing device 7 receives the digital measurement signal 53 from the analog-digital converter 6. The digital processing device 7 contains a transformation device 70, a subtraction device 71 and a detection device 72. The transformation device 70 is made up of the analog-digital converter 6<figref idref="f0002">Fig. 3</figref> connected. The subtraction device 71 is connected to the transformation device 70 and to the detection device 72. The detection device 72 is connected to the control device 9<figref idref="f0002">Fig. 3</figref> connected. The digital measurement signal is fed to the transformation device 70 and transformed by it into a measurement signal in the frequency range 54. A Fast Fourier Transformation is used for this purpose, for example. The measurement signal in the frequency range 54 corresponds to that in<figref idref="f0001">Figure 2b</figref> overall signal shown. The measurement signal in the frequency range 54 is then fed to the subtraction device 71, which subtracts a first sideband of the overall signal from a second sideband of the overall signal.

0024Since the two sidebands of an amplitude-modulated signal are symmetrical with respect to the carrier, this results in a complete cancellation of the signal if only one signal was part of the measurement signal. However, this asymmetry can be found in<figref idref="f0001">Figure 2b</figref> cannot be easily recognized. In particular shows<figref idref="f0001">Figure 2b</figref> an ideal signal without noise. In a real signal, the slight asymmetries of the signal would appear<figref idref="f0001">Figure 2b</figref> disappear in the stronger signal.

0025The subtraction device 71 thus first determines the exact carrier position in the frequency range of the measurement signal in the frequency range 54. A sideband is then mirrored at this determined carrier position. The mirrored sideband is subtracted from the non-mirrored sideband. A residual signal 55 resulting in the case of double transmission is in<figref idref="f0003">Fig. 5</figref> shown.

0026A residual signal 55 generated in this way is then transmitted to the detection device 72 which, from the signal components present in the residual signal 55, concludes the presence or absence of a double transmission. A threshold value comparison can be used for this purpose, for example. Alternatively, the residual signal 55 can first be processed, for example by calculating the amount or calculating the power. The processed residual signal can then be examined by means of a threshold value comparison. If the threshold is exceeded, the presence of a double transmission is deduced and the control device 9 detects this<figref idref="f0002">Fig. 3</figref> communicated. The control device 9 is also informed of the absence of a double transmission.

0027In previous systems for the detection of double transmissions, rotor modulations, ie modulations which arise from the rotating rotor blades in a propeller-driven aircraft, are often detected as double transmissions. Such rotor modulations generate periodic continuations of the transmission signal in the frequency range. The periodicity is given by the number of blades of the rotor and the speed. In order to exclude such rotor modulations and thus not to detect them as double transmissions, the detection device 72 additionally carries out a rotor modulation compensation. In this case, the detection device 72 searches specifically for rotor modulations which are recognized on the basis of the known periodicity and removes these periodic repetitions of the signal in the frequency range before the threshold value comparison is carried out.

0028In <figref idref="f0003">Fig. 5</figref> the residual signal 55 is off <figref idref="f0003">Fig. 4</figref> shown in the case of a double broadcast. The residual signal 55 here contains two signal components 40, 41, which correspond to the in<figref idref="f0001">Figure 2b</figref> correspond to difficult to detect asymmetries of the overall signal. Now that the symmetrical signal components have been removed, these asymmetrical signal components can easily be detected. In<figref idref="f0003">Fig. 5</figref> a threshold value 42 is also drawn in, on the basis of which, for example, the presence of the double transmission is detected.

0029In <figref idref="f0004">Fig. 6</figref> an embodiment of the method according to the invention is shown. In a first step 100, a measurement signal is received. This measurement signal contains at least a first signal, but optionally a second signal. In a second step 101, the measurement signal is transformed into the frequency range. In a third step 102, a strongest carrier is detected within the received signal. In a fourth step 103, the two sidebands, which are defined by the two spectral sides of the strongest carrier detected, are subtracted from one another. First, one of the sidebands is mirrored at the carrier position. In a fifth step 104, remaining signal components are detected after the subtraction. In a sixth step 105, a double transmission is determined. With regard to the function of the individual steps, please refer to the corresponding sections <figref idref="f0002">Fig. 3</figref> and <figref idref="f0003">Fig. 4</figref> referenced.

0030The invention is not limited to the illustrated embodiment. All of the features described above or shown in the figures can be advantageously combined with one another as desired within the scope of the invention.