EP1577679A1 - Search device for the localisation of a transmitter, in particular search device for avalanche victims - Google Patents

Abstract

The device (1) is swiveled within an angular range of search angles covering a search region and has search antennas for receiving transmitter signals radiated by the transmitter from instantaneous search directions, a signal processor for producing processing signals from the transmitter signals and an output unit. A magnetic field sensor outputs sensor signals related to the earth's magnetic field to the signal processor that are fed as processing signals to the output unit and associate each search direction with a fixed search angle relative to the earth's magnetic field. An independent claim is also included for a method of locating a transmitter, especially one buried in an avalanche.

Description

The invention relates to a search device for locating a transmitter, in particular an avalanche transceiver, wherein for searching a search area, the search device by Panning a user in an angular range that covers the search area.

Avalanche burial seekers work with an unmodulated transmit signal 457 kHz. All skiers in a group switch on their devices in normal operation Broadcasting. If a part of the group is buried in an avalanche, the other people receive their devices on receipt and try to cover the burials of the transmitted signal.

The transmission signal is clocked at a frequency of about one hertz. The broadcasting time at the frequency of 457 kHz, the so-called duty cycle, is ten to 30 percent.

For locating by ear (or maximum / minimum field strength) conventional devices from the transmit signal at 457 kHz by downmixing one Audible sound at a frequency of about 2 kHz. Since the built-in antenna a has pronounced directional characteristics, can by turning the receiver and Find the volume maximum or minimum the direction of the maximum field strength the spilled transmitter to be determined. This technique requires of the Seek high concentration, exercise, and small at larger distances Ambient noise.

In order to simplify the search even without practice and in stress situations the search, were devices with several antennas arranged at right angles to each other developed. By switching between these antennas, the receiving direction of the transmission signal are determined.

This method has a number of disadvantages in practice. On the one hand influence the antennas mutually, even if they are turned off, so that the receiver sensitivity of the device suffers altogether. In particular, a direction determination at long distances over 50 meters almost impossible, the thus won Direction indicator so not useful. On the other hand, this technique is very sensitive to interference, so the direction indication is not optimal Conditions strongly scatters.

A special challenge for the seeker is when he receives the signals receives several victims at the same time. The location purely by ear requires here a lot of practice and a cumbersome search strategy.

The object of the invention is therefore to provide a generic search device, which the position of at least one buried on reliable and cost-effective Way determined automatically.

This object is achieved by a search device with the features of claim 1 and a Locating method with the features of claim 17 solved.

• eine Suchantenne zum Empfang von Sendersignalen, die vom Sender aus momentanen Suchrichtungen ausgestrahlt werden,
• eine Signalverarbeitungseinrichtung zur Erzeugung von Verarbeitungssignalen aus den Sendersignalen und
• eine Ausgabeeinheit, der die Verarbeitungssignale zugeführt werden, zur Ausgabe von Ergebnissignalen, welche die Verarbeitungssignale repräsentieren, an den Benutzer.

A search device for locating (at least) one transmitter, in particular an avalanche victim search device, wherein for searching a search area, the search device is pivoted by a user in an angular range of search angles covering the search area, conventionally comprises:

• a search antenna for receiving transmitter signals which are broadcast by the transmitter from current search directions,
• a signal processing device for generating processing signals from the transmitter signals and
• an output unit, to which the processing signals are supplied, for outputting result signals representing the processing signals to the user.

According to the invention, such a search device further comprises a magnetic field sensor on, the earth magnetic field related sensor signals to the signal processing device outputs, which are supplied as a processing signal of the output unit and each Search direction assign a fixed search angle, relative to the Earth's magnetic field.

An essential idea of the invention is that a search device, which the above task solves, ideally, how a radar works and the antenna constantly by an angular range, for example. 180 degrees, would rotate. Because it's known at which angle the antenna is standing, can at any time a received Signal with the respective field strength assigned to the current angle of the antenna become. This is of course not feasible in practice. After all, will but the rotation by 180 degrees achieved by the person seeking the device while walking in the hand holds and swings left and right, a procedure like this is known in the application of search devices according to the prior art. The The problem then is to determine the angle to an external reference coordinate system the device is at a given time.

In principle, it is conceivable information about the current search angle through the To obtain evaluation of the signals from acceleration sensors or rotation sensors. In practice, initial value problems and the constant gravitational acceleration result here too big mistakes.

Also, information about the search angle might be from the evaluation of the GPS signal. This is the relatively high cost of a GPS Receiver and, for rescue applications, generally inadequate availability sufficient GPS signals.

According to the earth's magnetic field as such, solid and permanently available Reference coordinate system used. This is the assignment at any time the received transmitter signal of a transmitter to a fixed search angle possible.

In a preferred embodiment of the search device according to the invention gives the Magnetic field sensor three sensor signals relating to the earth's magnetic field to the signal processing device out. This allows the solid angle of the device relative to the Determine field lines in which the field strength components of the earth's magnetic field in three measured perpendicular to each other axes.

In addition, magnetic field sensors with a precision of 1 degree are cheaper as a GPS receiver, so that the search device according to the invention made cheaper can be.

In a further embodiment inclination sensors are provided, the sensor signals output the signal processing device, which related to the location of the search device represent on a horizontal plane. From the sensor signals of the tilt sensors can be the sensor signals of the magnetic field sensor advantageously correct so that the relative position of the search device to the earth's magnetic field very accurate and independent of the horizontal position of the search device can be determined.

In further embodiments of the search device according to the invention, the signal processing device designed to from the transmitter signals and the sensor signals To generate angle signals that have a reception field strength as a function of a Represent search angle. The application of signal processing mechanisms to the Angular signals according to the invention allows in a particularly simple and reliable Way the determination of the transmitter location.

In a further embodiment, in particular the aforementioned embodiment, the Signal processing device for calculating a transmitter search angle, in which the Transmitter is formed based on the angle signals. This can be done by the search device The location of the transmitter can be determined as the determination of the distance between Transmitter and search device by conventional methods is easily possible. A provision the station by ear is therefore not required. The station search angle can after one or more panning of the search device according to the invention be determined, even if the device is already back in a completely different Direction shows.

In a further embodiment of this embodiment, the signal processing device formed to at least two angle signals the transmitter search angle to determine.

A problem with transmitters to find buried victims is that the transmitter signal the transmitter is clocked. In a random pivoting movement, it is so common happen that the transmitter is currently in a transmission pause when the searcher is in the direction of maximum or minimum field strength (during the times when the Sender sends) is held. The sequence of angle signals, d. H. the function of Receive field strength above the search angle, therefore, is generally only in sections available. Advantageously, therefore, an algorithm is implemented in the search device to to extrapolate from the intervening values maximum and minimum. in the The principle for this are only two arbitrary points of the field strength curve (that is, two Angle signals) required when the directivity of the search antenna known is.

These are the - as before for the search angle and subsequently for the field strength described - obtained images (time -> search angle) and (time -> field strength) in transformed an image (search angle -> field strength). In a particularly advantageous Embodiment of the search device according to the invention is the extrapolation or Interpolation of the complete course of the image (search angle -> field strength) Application of least squares method performed. this makes possible a constant improvement of the estimated field strength over the search angle with further measured values.

In further embodiments of the search device according to the invention, the output unit formed for the graphic output of result signals that the transmitter search angle represent, and in particular a display panel for the graphical display of Sender location in the search area includes. This will be advantageous the fast and intuitive recording of the transmitter by the user allows.

In further embodiments of the search device according to the invention, the signal processing device comprises a filter correlation unit configured to generate angle signals by correlation of the transmitter signals (received signal or mixed down Received signal) with predetermined pattern or filter signals to detect. hereby the detection of weak transmitter signals of a transmitter is made possible, for example, in long distance from the search device. This corresponds to finding a signal with known form in noise. On the filter correlation unit can, for example, a so-called matched-filter mechanism be implemented, wherein a cross-correlation between the searched and the received signal is performed.

In a further embodiment of this embodiment, the filter correlation unit formed to the angle signals with a sinusoidal and with a cosinusoidal Filter signal sequence to correlate. Especially with a cosinusoidal filter signal, d .h. if a cosinusoidal transmitter signal is expected, the computational cost be significantly reduced compared to a matched filter method when the transmitter signal is decomposed into a sine and a cosine component. In this case, all that is needed instead of the cross-correlation a simple multiplication with the sine and the Cosine component of the pattern or filter signal with subsequent absolute value formation and moving average filtering.

In further embodiments, the signal processing device comprises an inventive Seeker an autocorrelation unit, which is designed to be in stored signals by autocorrelation to detect periodic signal components. If the signals of multiple stations are received, the transmitter signals of the Transmitters superimpose each other and also mutually cancel. Because two devices always have slightly different from each other repetition rates and / or duty cycles, is However, in principle, an assignment of the respective received signal to the one or other stations possible. The superposition of signals from multiple stations is is the sum of several periodically switched on and off signals. Therefore, it is suitable the autocorrelation function adjusts itself to the periodic components of this sum signal detect. For example, from the measured reception field strengths by threshold decision an on / off function are formed whose autocorrelation function Contains spectral lines at the frequencies occurring. Thus, one is Separation of the signals of several transmitters by providing an autocorrelation unit in Search device possible.

In further embodiments of the search device according to the invention is the autocorrelation unit downstream of a filter correlation unit. As a result, the structure designed of the search device particularly advantageous because initially all detectable (possibly weak) transmitter signals are identified and then in a simple way these signals can be assigned to different stations.

In further embodiments, the search antenna of the search device according to the invention comprises a ferrite antenna, preferably with a cosinusoidal directional characteristic. Ferrite Antenna are special because of their pronounced directional characteristic for transmitter location suitable. A cosinusoidal directional characteristic allows, for example, training the filter correlation unit as stated above, wherein the angle signals correlated with a sinusoidal and with a cosinusoidal filter signal sequence become.

In further embodiments of the invention, the search device comprises a transmitter for Transmitting transmitter signals, the transmitter signals preferably by a transmitter identifier are individualized. As a result, group functions can be realized be in which of a plurality of stations at least one by his individualized identifier is identifiable, for example, the group leader one Group of skiers.

In certain other embodiments of the invention, the signal processing device is for generating processing signals corresponding to a transmitter search angle assign a transmitter identifier, wherein a transmitter is designed such that Transmitter signals of this transmitter can be customized with respect to transmitter signals of other transmitters are. As a result, the user of the search device according to the invention in advantageous simply the option to become one of a plurality located transmitter in a prominent manner.

• zum Absuchen eines Suchgebietes wird ein Suchgerät durch einen Benutzer in einem Winkelbereich von Suchwinkeln geschwenkt, der das Suchgebiet überdeckt,
• Sendersignale, die vom Sender ausgestrahlt werden, werden aus momentanen Suchrichtungen von einer Suchantenne des Suchgerätes empfangen,
• Verarbeitungssignale werden aus den Sendersignalen erzeugt und
• Ergebnissignale, welche die Verarbeitungssignale repräsentieren, werden an den Benutzer ausgegeben.

A method for locating a transmitter, in particular the transmitter of an avalanche victim, conventionally comprises the following steps:

• to search a search area, a search device is panned by a user in an angular range of search angles that covers the search area,
• Transmitter signals emitted by the transmitter are received from current search directions by a search antenna of the searcher,
• Processing signals are generated from the transmitter signals and
• Result signals representing the processing signals are output to the user.

According to the invention, such a method is further developed in such a way that Sensor signals related to the earth's magnetic field, as a processing signal through Result signals are displayed to the users and each search direction a solid Search angle, relative to the earth's magnetic field, is assigned. This turns the Earth's magnetic field used as a fixed reference coordinate system, and it is at any time the assignment the measured transmitter signal of a transmitter to a fixed search angle possible.

In preferred embodiments of the method according to the invention are for the Assignment of search direction and angle Field strength components of the Earth's magnetic field measured in three mutually perpendicular directions. This can be the solid angle of the device relative to the field lines are determined.

In further preferred embodiments of the method according to the invention The inclinations of the search device are measured against the horizontal plane and the Sensor signals corrected accordingly. Thus, the direction can be advantageous exactly be determined.

In further embodiments of the method according to the invention, angle signals, each indicating a reception field strength at a search angle, from the Transmitter signals and the assignments of search direction and search angle generated. To Generating the angle signals is advantageous the application of signal processing Mechanisms on these signals possible, resulting in particularly simple and reliable Way the destination of the transmitter allowed.

In further embodiments of the method according to the invention, a transmitter search angle, in which the transmitter is located, calculated from the angle signals and a Output result signal representing the station search angle. This allows the Location of the transmitter to be determined, since the determination of the distance between transmitters and search device is easily possible by conventional methods. A provision of the Sender location by ear is therefore not required. The station search angle can after one or more times pivoting of the search device according to the invention are determined even if the device is already pointing in a completely different direction.

In a further embodiment of the invention, the transmitter search angle is at least two, in particular at least three, angle signals determined. For clocked transmitter signals a transmitter, it is often the case in a random pivoting movement that the station is currently in a pause when the searcher is in the direction of maximum or minimum field strength. The sequence of angle signals, d. H. the Function of the reception field strength above the search angle, therefore, becomes general only available in sections. The process of the invention is therefore advantageous designed to maximum and minimum from the intermediate values extrapolate. In principle, two arbitrary points of the field strength curve (i.e. H. two angle signals) is sufficient if the directional characteristic of the search antenna is known. For a robust approximation, the use is at least three Angle signals advantageous.

In further embodiments of the aforementioned embodiments, an estimated angle signal sequence according to the least squares method from the angle signals calculated and the station search angle from the maximum of the estimated angle signal sequence is determined. From the present, sectional consequences of the angle signals can with the least squares method the determining parameters of the whole Curves are estimated. This can easily be the estimated angle signal sequence calculated as previously stated above.

In further embodiments of this embodiment are used in the calculation of Estimated angle signal sequence angle signals differently weighted, in particular according to the time since a reception of the angular signals underlying transmitter signals has passed. Using the least squares method, the Estimate can be constantly improved by using new readings. This results even at a great distance from the buried and accordingly weak transmitter signal quickly a relatively accurate location estimate. On the other leaves by weighting older people in relation to the current ones Measured values or the angle signals derived therefrom a jumping or excessive Reliably suppress instability of the calculated transmitter search angle.

In further embodiments of the method according to the invention are estimated transmitter signals by correlation of transmitter signals with predetermined filter signals determined and determined angle signals from the estimated transmitter signals. Becomes a cross-correlation between the filter signals and the transmitter signals, the Detection of weak transmitter signals of a transmitter allows, for example. In large Distance from the locator, this finding a signal with known form in the noise corresponds.

In a further embodiment of this embodiment is for determining the Transmitter signal from noise interference by correlation of received transmitter signals with a sinusoidal and a cosinusoidal filter signal sequence one each Sine and a cosine signal sequence determined. In principle, the above-mentioned cross-correlation be performed by means of a matched filter mechanism. The disadvantage However, the matched filter is very expensive. This is due to the fact that the pattern function represented by the filter signals in all possible phase positions the sequence of received transmitter signals must be compared. This computational effort can be significantly reduced if the sequence of transmitter signals in a sine and a cosine component is decomposed.

In a further embodiment of this embodiment, reception field strengths the signals of the estimated transmitter signal sequence from the summation of the products of the (if previously down-mixed) received signal sequence with a sine and a cosine signal sequence determined. The argument (angle) of the above-mentioned sine and cosine component formed complex number describes the phase position of the received signal in Ratio to the cosine pattern function, while the amount of the complex number is a measure for the reception field strength.

In preferred embodiments of the method according to the invention is for detection from several transmitters a periodic signal component of stored transmitter signals or processing signals, in particular estimation transmitter signals, by autocorrelation determined. If the signals of several victims are received, the Transmitter signals of the transmitter superimpose each other and also mutually extinguished. There two stations always slightly different from each other repetition rates and / or duty cycles However, in principle, an assignment of the respective received signal to the one or the other transmitter possible. When superposing signals of several Sender is the sum of several periodically on and off Signals. Therefore, the autocorrelation function is suitable for the periodic contributions to recognize this sum signal. For example, from the measured reception field strengths Threshold decision an on / off function formed whose autocorrelation function spectral lines at the frequencies occurring contains. Thus, a separation of the signals of several transmitters is possible. By averaging The autocorrelation function over several observation periods can be dominant periodic components relatively independent of the respective orientation of the transmitter be determined to the receiver very reliable.

In one embodiment of this embodiment, a determined periodic signal component, which can be assigned to a transmitter, from transmitter signals or processing signals hidden to determine further periodic signal components. By Noise and inaccuracies become the periodic components of weaker received signals often obscured. In order to detect these components, it is advantageous when signal components that can be assigned to a dominant received signal, hidden (set to zero).

In further embodiments of the method according to the invention, the transmitter signals a transmitter to transmitter signals of other stations by a transmitter identifier individualized and processing signals are generated which correspond to a station search angle assign this sender identification. This allows group functions be realized in which of a plurality of transmitters at least one optionally identifiable by its individualized identifier, for example the Group leader of a group of skiers.

Fig. 1

ein Ausführungsbeispiel eines erfindungsgemäßen Suchgerätes;

Fig. 2a, 2b

jeweils eine Ansicht der Anzeige des Suchgerätes aus der Fig. 1;

Fig. 3

in schematisierter Form ein funktionales Blockschaltbild des Suchgerätes der Fig. 1.

Other aspects, advantages and advantages of the invention will become apparent from the following description of an embodiment of the invention with reference to the accompanying drawings, in which:

Fig. 1

an embodiment of a search device according to the invention;

Fig. 2a, 2b

in each case a view of the display of the search device of FIG. 1;

Fig. 3

in schematic form a functional block diagram of the search device of FIG. 1.

In the figures, the same reference numerals for the same and the same effect elements used.

1 shows an exemplary embodiment of a search device 1 designed according to the invention for use as an avalanche victim search device (avalanche transceiver). The communication with the user via a backlit display 10 and two control buttons 12, 13th The display 10 allows the graphic display of the position of one or more buried relative to your own location. The device 1 also has a loudspeaker 14 for outputting a synthetically generated search sound to the user as Acoustic feedback and an LED 15, as is known for conventional devices. The speaker 14 and the red LED 15 also allow a conventional search without using the graphic display via the display 10.

As shown in detail in Fig. 2a, the display of the display 10 is divided into a Coordinate field 16 to the true to scale representation of the location of the located transmitter of Spilled, a status line 18 with the most important information and labeling fields 20 for the two control buttons 12.

The device 1 is designed as a combined search and transmit device. The case has the Shape of a folding mobile phone. The hinge is indicated by a dashed line in FIG Line 21 indicated. If the device 1 is in search mode, it is closed by closing the Device automatically returns to the transmission mode. This will open Advantageously, an emergency downshift realized as they, for example. In the case of After avalanche, in the standards is required.

The device 1 is equipped with an antenna not visible to the outside for sending and searching equipped on a search frequency of 457 kHz. The specified frequency is for Avalanche victim search devices standardized (EN 282). An automatic location of the Burial takes place from the natural pivoting movement of the seeker or User. According to the invention, however, no manual bearing as in conventional Devices required. In addition, the illustrated device 1 has a DF mode to focus on a selected victim.

A search process is carried out so that the searcher the device 1 after switching from transmit to seek mode, swings back and forth by about 180 degrees several times. The achievable DF or search accuracy is initially ± 10 degrees. When panning All transmitter or transmitter signals of transmitters are detected by buried persons who are in Range are located. The range of the device is about 80 m. At the stations can they are conventional avalanche transceivers or identical to device 1 Equipment. A manual bearing, i. holding the device 1 in the direction of the strongest Signal is not required.

The detected transmitters 22 become on the direction and distance on the display 10th displayed, wherein the scale representation of the distance of the transmitter 22 from Searcher (in the center of the coordinate field 16, i.e. the crosshairs 23) Distances 24 in meters is specified.

The seeker can now find himself by requesting the victim, the first and press the button 12 "PEILEN" focus on this and the hide further transmitter 22. During the search process, distance information is displayed 24 and position information 22 constantly adapted to the current position of the searcher.

Target search in the near range can be supported by the red LED 15. In addition, for a precise point location, a zoom function in the display 10 be activated (not shown). When the seeker approaches a transmitter location 22, i.e. the suspected resting place of a buried person, becomes a circle on the display 10 superimposed, which is concentric to the base 22 and on closer approach concentrically reduced. According to experience, an insertion of the circle is from a Distance of three meters advantageous, but the overlay can be synonymous with larger or only at smaller distances. Instead of a circle could also be a square or the like symbol.

By means of the search device according to the invention can easily the exact Spill depth can be determined. For this purpose, the searcher brings the detected transmitter 22 (the presumed resting place of the victim) with the center of the crosshairs 23 (the position of the seeker) to cover, so that the searcher vertically above the Spilled is located. The distance indication 24 then indicates the burial depth. In known search devices, the determination of the burial depth is only indirect and results in greater burial depth unreliable values, since the display at greater depth often remains the same over a diameter of up to several meters and over the depth no more accurate information is possible.

If a buried person is found and saved, the seeker picks up the bearing and dedicates it to the next victim.

The search device 1 is equipped with a motion sensor (not shown). This detects whether the device 1 is being moved. If the device is in any mode, which is not the transmit mode, and will power the device for 90 seconds not moved, it automatically switches to the transmission mode. This will be the above-mentioned emergency downshift also safely triggered when the seeker due to a post-avalanche or the like surprising event no opportunity has more to close the search device.

The search device 1 has in the embodiment described here in addition to the Search function via further functions, which can be reached via the key 13 Main menu are selectable. This includes an electronic compass, a temperature gauge and inclination measurement to assess the avalanche danger, a display of the Battery status and a remaining time display for transmit and search mode. At low Battery level is a warning regardless of the operating mode.

For safety reasons, the standard does not allow any additional functions (Compass, temperature display, inclination measurement). However that requires For example, the inclination sensors according to the invention for its functionality. Then only care must be taken that the display of the additional Data obtained does not increase the power consumption so much that the safety of the Use is no longer guaranteed. Therefore, a security circuit in the search device 1 provided (not shown), which turns off the display of the additional functions when the Battery capacity drops below 50% of the maximum value. Thus, the requirements of Standard complies with the operational safety of the device.

In other search devices according to the invention are only some or none of these Additional functions available; Thus, a safety circuit of the above described type omitted.

Furthermore, via the main menu of the search device 1 is a quick guide for the device and configuration displays and configuration settings for language and Display illumination accessible.

The integrated sensors, which are described in more detail below, can do this Device 1 at any time determine in which direction the seeker is currently holding it. So that can the location of the located transmitter of the buried at any time correct relative to own point of view.

From the display shown in Fig. 2a is intuitively clear that the in the coordinate field 16 highlighted spills 26 at 30m distance exactly in the direction lies in which the device 1 is held straight. The closest in a straight line lying - shown highlighted - burial can by pressing the button 12 ("PEILEN") are selected for further search. As shown in Fig. 2b, is Thus, the information in the display 10 to the data of the targeted buried 26th reduced. The loudspeaker 14 (see Fig. 1) is only in a distance-dependent manner the search tone of the targeted victim 26 again. The bearing can be done at any time Press button 13 ("ALL") to cancel. A multiple search is for up to six burials possible simultaneously.

The technical realization in the search device 1 takes place in principle such that the received 457 kHz signals digitized and processed with a powerful microprocessor become. Digital signal processing algorithms enable search sounds, i. Sender signals even then filter out of the noise, if they are already below the perceptibility limit of human hearing. This allows a The range comparable to conventional, analogue devices.

From the received signals, the positions of the victims are calculated. The The algorithms used are robust against individual faults or measurement errors. There over the whole search phase the positions are constantly being recalculated, which improves the Accuracy of estimated positions for the buried quickly over time.

In Fig. 3, the functional structure of the device 1 of Fig. 1 is shown schematically. In addition to the receiver 28 with search antenna and mixing stage for the addon are a Earth magnetic field sensor 30, which provides a sensor signal for each rotational degree of freedom (X, Y, vertical) outputs, and tilt sensors 32 for the two tilt axes available. In addition, another sensor 34 for one of the above-mentioned additional functions of Device, the temperature measurement, drawn.

The microprocessor-controlled sample manager 36 carries the current sample to the correct destination and selects the channel for the next sample. The time behavior is designed so that the maximum possible sample clock essentially for the Sampling of the reception or transmitter signals is available. For the scanning of the Sensor data, the receive signal is faded out about every 32nd time slot and held whose one of the sensor channels for temperature, magnetic field and inclination read.

In the angle estimation module 38, from the samples of the magnetic sensor 30 and the Tilt sensors 32 determines the spatial position to the Earth's magnetic field exactly. such Methods are known per se to those skilled in the art and therefore will not be further described. By the use of these sensors 30, 32 according to the invention everyone Direction in which the search device 1 is held, with respect to the measured magnetic field vector μ assigned a fixed search angle φ.

The sin / cos correlator 40 is for the detection of transmitter signals at the sensitivity limit intended. Basically, the task consists in one

Spilled to be able to locate as far away as possible. This matches with finding a signal of known shape in noise.

Finding such a search sound in the noise is - in the sense of a hypothesis test - Optimal with a "matched filter" possible, where basically a cross-correlation between the searched and the received signal is performed.

The matched filter has as impulse response exactly the mirrored along the time axis searched function. The gain of the matched filter is due to the fact that Nutzsignalanteile be added constructively by the impulse response, while noise components add up in performance.

The disadvantage of the matched filter is the very high computational effort. This one is stirring Therefore, the pattern function in all possible phase positions with the consequence of Receive or transmitter signals must be compared.

From the transmitter signal sequence is known that it is a cosinusoidal signal sequence with constant frequency. Any scaled and phase-shifted sine wave can be divided into a cosine and a sine component. The performance of searched signal is the sum of the power of sine and cosine. Therefore, it is sufficient, the transmitter signal sequence with a cosine and a sinusoidal Filter sequence to multiply, the sequence of transmitter signals so in a sine and to decompose a cosine component. The argument (angle) of the sine and Cosine component complex number describes the phase angle of the Receive or transmitter signal sequence in relation to the cosine pattern function, while the amount of the complex number is a measure of the reception field strength.

System-theoretically, the sin / cos correlator 40 operating in this manner effects a demodulation of the search sound into the baseband (multiplication by sin or cos) and subsequent low-pass filtering for suppressing the image frequencies at twice the signal frequency. An essential advantage of the sin / cos correlator 40 is that it can be constructed in a simple and resource-saving manner. Compared to a matched filter, the detection performance is 3 dB worse.
In the RSS module 42, values are obtained from the output values a (amplitude estimate of the sine component) and b (amplitude estimate of the cosine component) of the correlator 40 by means of square mean RSS ("received signal strength") values. The AKF module 44 then calculates the autocorrelation function (AKF) of the RSS values. The output of the AKF module 44 serves as the basis for the separation of the signal components in the case of several simultaneously active transmitters.

The search for the buried is then particularly difficult, if at the same time the signals of several victims are received. The transmitter signals of the transmitter can overlap each other and also mutually cancel out. Because two devices always have slightly different repetition rates and / or duty cycles from each other, However, in principle, an assignment of the respective received signal to the one or the other transmitter possible.

The superposition of signals from multiple stations is the sum several periodically on and off signals. Basically, a suitable Autocorrelation function to detect the periodic components of this sum signal.

In the simplest case, the measured field strength values are determined by thresholding an on / off function is formed, their autocorrelation function Spectral lines should contain at the frequencies occurring. The disadvantage of this Method is that, especially at low field strengths or imperfect Align the receiving antenna with the transmitter's ON / OFF times only can be determined with insufficient accuracy. These inaccuracies are the Spectral lines of the autocorrelation function smeared, i. out of focus, and fast unusable.

As well as in the ideal on-off function, the information about the Periodicity of course also in the analog field strength function available. This is called Amount of the output of the sin / cos correlator 40, d. H. as the output of the RSS module 42 won. By averaging the autocorrelation function over several observation periods can dominante periodic proportions relatively independent of the respective Alignment of the transmitter to the receiver can be determined very reliable.

Due to noise and inaccuracies, the periodic components become weaker Receiving signals often obscured. To be able to detect these components, be Signal components that can be assigned to a dominant received signal, hidden (set to zero).

The assignment of individual signal sections to different transmitters is determined by the heuristic segmentation in segmentation module 46. This will be in the Essentially by thresholding those signal elements determined that the Maximum of the AKF contribute. The signal elements determined in this way are possibly transmitted Analysis of jumps in the correlation values again separated and different Assigned to senders. A signal element may, for example, starting from the left and right boundary into two separate areas at the edges and one - for the location estimation unusable - overlay area can be divided in the middle. For segmentation can jumps and discontinuities in the sin and cos correlation values be used.

In the location estimation module 48, the location of the at least one received station is determined determined. The distance of the transmitter can be in a conventional manner on application a power law on the measured or determined field strength reliable be determined. At the same time in the module 48, the assignment of the invention obtained from the sensor data search angle φ to those from the currently measured Transmitter signals resulting processing signals σ, the current reception field strength specify a sender.

The ferrite receiving antenna used in the receiving unit 28 has a cosine-shaped directivity. With a fixed transmitter, the received field strength thus changes with the cosine of the double search angle. If the device is swiveled back and forth by the searcher during the search, ie if the angle is continuously changed, then the field estimation module 48 can easily form the field strength σ as a function of the search angle φ.
For all angle signal elements of a recording interval (from which exactly one AKF was calculated), the searcher angle and thus the location of the transmitter is estimated by linking with the search angles φ. The coordinates obtained from successive recording intervals for the same transmitters can be continuously improved by weighted averaging.

Due to the timing of the search tone, i. the received transmitter signal sequence, the Field strength function, d. H. the sequence of angular signals σ (φ), each one receiving field strength specify at a search angle, generally only partially available. However, from the given sections, you can use the least squares method the determining parameters of the entire curve are estimated. From this it is easy to calculate the angle and distance of the transmitter.

In the case of trouble could from the field strength curve of the received transmitter signal sequence the total field strength curve is calculated as a sequence of estimated angle signals become. For calculation, two arbitrary points of the transmitter signal sequence were sufficient. In the Practice is the received signal, however, more or less noisy. The approximation used two points can then be randomly corrupted by noise samples so that the parameters of the actual angular signal sequence are severely flawed to be appreciated. To achieve a robust estimate, all available Points of the received field strength curve or the transmitter signal sequence included and the searched parameters are optimized so that the total deviation of the calculated course of the estimated angle signal sequence from the portion of the sequence of the Transmitter signals and search angles determined angle signals is minimal.

Using the least squares method, the estimate may be by Use of new readings can be constantly improved. First, it results thereby also at a great distance from the buried and correspondingly weak Search or receive signal quickly a relatively accurate location estimate. On the other leaves by a corresponding weighting of older ones in relation to the current values the measured search or detected angle signals a jumping or excessive Instability of the determined station search angle reliably suppress.

Thus, with a sufficient number of measured values a reliable determination of the Position of the transmitter possible. This is especially true even if the maximum itself can not be detected, since just at the times at which the seeker Device pointing in the direction of the transmitter, this is in the pauses. The data of the real received signal give clues for the necessary number of samples for a sufficiently accurate determination.

Another task of the local estimation is the solution of the problem, from the field strength differences two or more consecutive recording intervals the 180 degree ambiguity of the angle estimate dissolve and the transmitter of the front (in Movement direction) or rear (opposite to the direction of movement) half-plane assign.

Thus, the location of a victim, especially the station search angle, even then completely and reliably calculable if its transmitter at that time, to the the device 1 of the searcher points in his direction, is currently in the transmission pause. This is achieved with a inventively designed search device, which only one has only search antenna and therefore be correspondingly easier and cheaper can (of course, the use of multiple antennas in an inventive Search device also possible).

The determined location of a transmitter is then displayed on the display 10, as described above with reference to FIGS. 1, 2a and 2b.

The representation of the functions of the invention described here by way of example Search device is based on modules that in Fig. 3 as separate units are drawn. These units may be in the search device in the form of software, Firmware and / or hardware. Preferably, the modules are in the form of Software on a microprocessor / DSP. For a full featured searcher like the illustrated by the figures would be a processor with 30 MIPS computing power and 8 KB RAM is suitable.

Numerous modifications of the search device described here by way of example are conceivable. Thus, an inventive device without AKF module or module for the separation of Be formed signal components of several transmitters. Such a device is in situations can be used in which only one transmitter is to be located. An example of this is a group of skiers on secured runway, in which the finding of the group leader by the search devices of the group members is made possible, whereby only the transmitter of the conductor is in transmission mode.

Likewise, a search device according to the invention without a module for the implementation of Cross correlation of a filter signal formed with weak search or received signals be. Then weak signals in the noise are no longer detectable, the Sensitivity of the search device is reduced accordingly. However, then the Resources of the device (available space, processor processing capacity) for Other functions available, for example, the AKF module can be designed to a larger number of transmitters to separate. Also can be a functionally poorer device have the same battery capacity over a prolonged period of use, if about one smaller processor is used.

It is conceivable to combine a search device according to the invention with a GPS system. The GPS system provides a true-to-nature representation of the terrain. Of the Viewpoint of the searcher and the sender location detected by the searcher, i. the Suspected lying points of the buried, will be the representation of the GPS system superimposed. Such a system allows the searcher to know the position of the person Liegepunktes on the basis of any existing landmark terrain points intuitively, i. to quickly grasp, so that he with the least possible delay the lounger can visit.

Alternatively or additionally, the search device can be combined with a voice control as is known in car GPS systems. This receives the Searching acoustic instructions, such as in the form of a voice generated by the searcher. This allows the seeker to focus on the terrain.

A search device according to the invention can furthermore be combined with a camera, as is known for mobile phones. This is advantageous from the camera recorded terrain view is displayed on the display of the search device. The detected transmitter locations are superimposed on the terrain view. The view on the display is largely consistent with the view the seeker has of his environment. Thus, the orientation of the searcher is facilitated, especially in contour rich Terrain.

Also a combination of a search device according to the invention with a GPS system and camera is possible. This would be GPS system and camera to achieve a interact in a detailed and contour-rich representation of the site.

Instead of only as an avalanche victim search device can be inventively trained Search device also be used advantageously for other applications. As an example a group of skiers who are guided by their group leader, eg. in poor visibility or otherwise confusing conditions. All participants have via transmitting / searching devices. The device of the conductor has a transmitter whose Transmitter signal is provided with an individual station identifier. The search devices of the Group participants are designed to evaluate the received sender identification, such that the located transmitter of the conductor is identifiable among the plurality of located transmitters is. The display of the participants' search devices identifies the location of the group leader by specifying the identifier. In a further development of this method all transmitters of a group can be individualized by transmitter identifications.

Although the transmission of transmitter detections on the standard signal at 457 kHz not provided. However, besides the otherwise standard compliant sender in a transmitter, a second transmitter may be provided, the signals with transmitter identifiers radiates.

In addition, are within the scope of the invention, exclusively by the following claims is given, by expert action many more further embodiments conceivable.

LIST OF REFERENCE NUMBERS

1

detector

10

display

12, 13

Control buttons

14

speaker

15

LED

16

coordinate field

18

status bar

20

Labeling field for control buttons

21

Klappscharnier

22

Symbol detected station in the coordinate field 16

23

crosshairs

24

Distance information in the coordinate field 16

26

highlighted geordeter transmitter shown

28

Receiver with search antenna

30

Sensor for the Earth's magnetic field

32

inclinometers

34

temperature sensor

36

Sample Manager

38

Angle estimation module

40

Sin / cos correlator

42

RSS module

44

AKF module

46

Segmentation module for heuristic segmentation

48

Location estimation module

a

Amplitude estimate of the cosine component

b

Amplitude estimate of the sine component

r

Receive or transmitter signal

R

Output signal of the RSS module

μ

magnetic field vector

φ

search angle

σ

determined reception field strength of a transmitter

Claims (30)

Search device for locating a transmitter, in particular an avalanche victim search device (1),
wherein for searching a search area, the search device (1) is panned by a user in an angular range of search angles covering the search area,
With a search antenna (28) for receiving transmitter signals emitted by the transmitter from current search directions, a signal processing device for generating processing signals from the transmitter signals and an output unit (14, 15) to which the processing signals are supplied for outputting result signals representing the processing signals to the user, marked by
a magnetic field sensor (30) for outputting sensor signals related to the earth magnetic field to the signal processing means (36-48) supplied as a processing signal to the output unit (10) and associating each search direction with a fixed search angle (φ) relative to the geomagnetic field (μ). Search device according to claim 1,
characterized in that
the magnetic field sensor (30) outputs three sensor signals relating to the earth's magnetic field to the signal processing device (36-40). Search device according to claim 1 or 2,
characterized in that
Inclination sensors (32) are provided which output sensor signals to the signal processing device (36 - 40), which represent the position of the search device (1) relative to a horizontal plane. Search device according to one of the preceding claims,
characterized in that
the signal processing means (48) is adapted to generate from the transmitter signals and the sensor signals angle signals representing a reception field strength in dependence on a search angle (φ). Search device according to one of the preceding claims, in particular according to claim 4,
characterized in that
the signal processing means (48) for calculating a transmitter search angle, in which the transmitter is located, based on the angle signals is formed. Search device according to one of the preceding claims, in particular according to claim 5,
characterized in that
the signal processing device (48) is designed to determine the transmitter search angle from at least two angle signals. Search device according to one of the preceding claims, in particular according to claim 5 or 6,
characterized in that
the output unit (10) is designed to graphically output result signals representing the transmitter search angle and, in particular, a display field (10) for graphically displaying (16) the transmitter location (22) in the search area. Search device according to one of the preceding claims,
characterized in that
the signal processing device comprises a filter correlation unit (40) which is designed to detect angle signals by correlation of the transmitter signals with predetermined filter signals. Search device according to one of the preceding claims, in particular according to claim 8,
characterized in that
the filter correlation unit (40) is designed to correlate the transmitter signals with a sinusoidal and with a cosinusoidal filter signal sequence. Search device according to one of the preceding claims,
characterized in that
the signal processing device comprises an autocorrelation unit (44) which is designed to detect periodic signal components in stored signals by autocorrelation. Search device according to claim 10,
characterized in that
the autocorrelation unit (44) is connected downstream of a filter correlation unit (40). Search device according to one of the preceding claims,
characterized in that
the search antenna (28) comprises a ferrite antenna, preferably with a cosinusoidal directional characteristic. Search device according to one of the preceding claims,
characterized by t
a transmitter for transmitting transmitter signals, wherein the transmitter signals are preferably individualized by a transmitter identifier. Search device according to claim 13,
characterized by t
a motion sensor that detects movements of the search device (1), and
an emergency downshift connected to the motion sensor which switches the searcher (1) to a transmit mode at which the transmitter transmits transmitter signals when the motion sensor does not detect movement of the searcher (1) within a predetermined time period, for example 90 seconds. Search device according to one of claims 7 to 14,
characterized by t
a GPS system and / or a camera for displaying the environment on the display panel (10). Search device according to one of the preceding claims,
characterized in that
the signal processing device is designed to generate processing signals which associate a transmitter identifier with a transmitter identifier, wherein a transmitter is embodied such that transmitter signals of this transmitter can be individualized with respect to transmitter signals of further transmitters. Method for locating a transmitter, in particular the transmitter of an avalanche victim, in which, for searching a search area, a search device (1) is swiveled by a user in an angular range of search angles that covers the search area, Transmitter signals emitted by the transmitter are received from current search directions by a search antenna (28) of the search device (1), Processing signals are generated from the transmitter signals and Result signals representing the processing signals are output to the user, characterized in that
Sensor signals which relate to the earth's magnetic field, as a processing signal by result signals to the users are displayed and each search direction, a fixed search angle (φ), relative to the Earth's magnetic field (μ), is assigned. Method according to claim 17,
characterized in that
for the assignment of search direction and angle field strength components (μ) of the geomagnetic field in three mutually perpendicular directions are measured (X, Y, vertical). Method according to claim 17 or 18,
characterized in that
the inclinations of the search device are measured against the horizontal plane (32) and the sensor signals are corrected accordingly (38). Method according to one of claims 17 to 19,
characterized in that
Angle signals, each indicating a reception field strength (σ) at a search angle (φ), are generated from the transmitter signals (r) and the assignments of search direction and angle. Method according to one of claims 17 to 20, in particular according to claim 20,
characterized in that
a transmitter search angle in which the transmitter is located is calculated from the angle signals and a result signal is output (10, 16) representing the transmitter search angle (22). Method according to one of claims 17 to 21, in particular according to claim 21,
characterized in that
the station search angle is determined from at least two, in particular at least three, angle signals. Method according to one of claims 15 to 22, in particular according to one of claims 219 or 22,
characterized in that
an estimated angle signal sequence is calculated from the angle signals according to the method of least squares and the transmitter search angle is determined from the maximum of the estimated angle signal sequence. Method according to claim 23,
characterized in that
in the calculation of the estimated angle signal sequence angle signals are weighted differently, in particular according to the time that has elapsed since receipt of the angular signals underlying transmitter signals. Method according to one of claims 17 to 24,
characterized in that
Estimated transmitter signals (40: a, b) are determined by correlation of transmitter signals (r) with predetermined filter signals and angle signals are determined from the estimated transmitter signals. Method according to claim 25,
characterized in that
For determining the transmitter signal from noise interference by correlation of received transmitter signals (r) with a sinusoidal and with a cosinusoidal filter signal sequence in each case a sine and a cosine signal sequence (a, b) is determined. Method according to claim 26,
characterized in that
Receiving field strengths of the signals of the estimated transmitter signal sequence from the summation of the products of the received transmitter signal sequence with a sine and a cosine signal sequence (a and b) are determined. Method according to one of claims 17 to 27,
characterized in that
for detecting a plurality of transmitters, a periodic signal component of stored transmitter signals or processing signals, in particular estimated transmitter signals, is determined by autocorrelation (44). Method according to claim 28,
characterized in that
a determined periodic signal component (σ), which can be assigned to a transmitter, is masked out of transmitter signals or processing signals in order to determine further periodic signal components. Method according to one of the preceding claims,
characterized in that
the transmitter signals of a transmitter are compared with transmitter signals of further transmitters by a transmitter identification and
Processing signals are generated, which assign a station search angle this sender identification.

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