EP1577679B1 - 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 victim search device, wherein for searching a search area, the search device is pivoted by a user in an angular range, which covers the search area.

Avalanche searchers work with an unmodulated transmit signal at 457 kHz. All skiers in a group switch their equipment to normal operation. If a part of the group is buried in an avalanche, the other people switch their equipment to receive and try to locate the victims on the basis of the emitted signal.

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

For localization by ear (or maximum / minimum field strength) conventional devices generate from the transmission signal at 457 kHz by downmixing an audible sound at a frequency of about 2 kHz. Since the built-in antenna has a pronounced directional characteristic, the direction of the maximum field strength of the buried transmitter can be determined by turning the receiver and searching for the maximum or minimum volume. This technique requires of the Seek high concentration, exercise, and low ambient noise especially at longer distances.

In order to simplify the search even without practice and in stressful situations, devices were developed with several antennas arranged at right angles to each other. By switching between these antennas, the direction of reception of the transmission signal can be determined (see also AT 006 120 U2, DE 101 09 284 A1).

This method has a number of disadvantages in practice. On the one hand, the antennas influence each other even if they are switched off, so that the receiver sensitivity of the device as a whole suffers. In particular, a determination of the direction at long distances over 50 meters is almost impossible, so the direction indicator thus obtained not useful. On the other hand, this technique is very sensitive to disturbances, so that the direction indicator scatters greatly under non-optimal conditions.

A special challenge for the seeker is when he receives the signals of several victims at the same time. The location purely by ear here requires a lot of practice and a cumbersome search strategy. A corresponding procedure is described in EP 0 733 916 A2, wherein a better location is achieved in that the transmitter transmits with three antennas that are orthogonal to one another. After determining the search direction, this direction can be followed by means of an electronic compass.

The DE 299 22 217 U1 are busy with the search of buried. GPS coordinates are compared here. To search for avalanche victims GPS receivers are too inaccurate and prone to failure.

Starting from EP 0 733 916 A2 it is an object of the present invention to specify a generic search device which automatically determines the position of at least one buried subject in a reliable and cost-effective manner.

This object is achieved by a search device having the features of claim 1 and a positioning method having the features of claim 16.

An essential idea of the invention is that a search device which achieves the above-mentioned object would ideally work like a radar and would constantly rotate the antenna by an angular range, for example 180 degrees. Because it is known at which angle the antenna is currently standing, a received signal with the respective field strength can be assigned to the instantaneous angle of the antenna at any time. This is of course not feasible in practice. After all, but the rotation is achieved by 180 degrees in that the searching person holds the device while walking in the hand and swings to the left and right, a procedure as it is known in the application of search devices according to the prior art. The problem then is to determine what angle to an external reference coordinate system the device is at a given time.

The idea to generate angle signals from the transmitter signals and the sensor signals, which represent a reception field strength as a function of a search angle, solves this problem. The application of signal processing mechanisms to the angle signals according to the invention allows the determination of the transmitter location in a particularly simple and reliable manner.

In principle, it is conceivable to obtain information about the current search angle by evaluating the signals from acceleration sensors or rotation sensors. In practice, initial value problems and the constant gravitational acceleration lead to large errors.

Also, information about the search angle could possibly be obtained from the evaluation of the GPS signal. This is offset by the relatively high cost of a GPS receiver and - for rescue applications - generally insufficient availability of sufficient GPS signals.

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

In a preferred embodiment of the search device according to the invention, the magnetic field sensor outputs three sensor signals relating to the earth's magnetic field to the signal processing device. Thus, the solid angle of the device can be determined relative to the field lines, in which the field strength components of the geomagnetic field are measured in three mutually perpendicular axes.

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

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

In a further embodiment, in particular of the aforementioned embodiment, the signal processing device is designed for calculating a transmitter search angle, in which the transmitter is located, on the basis of the angle signals. As a result, the locator of the transmitter can be determined by the search device, since the determination of the distance between the transmitter and the search device by conventional methods is easily possible. A provision the station by ear is therefore not required. The station search angle can be determined after one or more panning of the search device according to the invention, even if the device already shows again in a completely different direction.

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

A problem with transmitters to find victims is that the transmitter signal of the transmitter is clocked. Thus, in a random panning motion, it will often happen that the station is currently in a pause when the searcher is held in the direction of maximum or minimum field strength (during the times the station is transmitting). The sequence of angle signals, d. H. the function of the reception field strength above the search angle, therefore, will generally be present only in sections. Advantageously, therefore, an algorithm is implemented in the search device to extrapolate from the intermediate values maximum and minimum. In principle, only two arbitrary points of the field strength curve (i.e., two angle signals) are required for this, if the directional characteristic of the search antenna is known.

For this purpose, the images obtained (as described above for the search angle and subsequently for the field strength) (time -> search angle) and (time -> field strength) are transformed into an image (search angle -> field strength). In a particularly advantageous embodiment of the search device according to the invention, the extrapolation or interpolation of the complete course of the image (search angle -> field strength) is carried out by applying the method of least squares. This allows a continuous improvement of the estimated field strength profile over the search angle with further measured values.

In further embodiments of the search device according to the invention, the output unit is designed for graphic output of result signals which represent the transmitter search angle, and in particular a display field for graphic display of the Sender location in the search area includes. As a result, the fast and intuitive detection of the transmitter location by the user is advantageously made possible.

In further embodiments of the search device according to the invention, the signal processing device comprises a filter correlation unit which is designed to detect angle signals by correlation of the transmitter signals (received signal or reduced received signal) with predetermined pattern or filter signals. This allows the detection of weak transmitter signals of a transmitter, which is, for example, located at a great distance from the search device. This corresponds to finding a signal of known form in noise. For example, a so-called matched-filter mechanism can be implemented on the filter correlation unit, whereby a cross-correlation is carried out between the searched and the received signal.

In a further embodiment of this embodiment, the filter correlation unit is designed to correlate the angle signals with a sinusoidal and with a cosinusoidal filter signal sequence. Especially with a cosinusoidal filter signal, i. E. if a cosinusoidal transmitter signal is expected, the computational overhead of a matched-filter method can be significantly reduced if the transmitter signal is decomposed into a sine and a cosine component. In this case, a simple multiplication with the sine and cosine components of the pattern or filter signal with subsequent magnitude formation and moving average filtering is sufficient instead of the cross-correlation.

In further embodiments, the signal processing device of a search device according to the invention comprises an autocorrelation unit, which is designed to detect periodic signal components in stored signals by autocorrelation. If the signals of several transmitters are received, the transmitter signals of the transmitters can overlap each other and also cancel each other out. Since two devices always have slightly different repetition rates and / or duty cycles, however, an assignment of the respectively received signal to the one or the other transmitter is possible in principle. The superimposition of signals from several transmitters is the sum of several signals that are periodically switched on and off. Therefore, the autocorrelation function is suitable for the periodic contributions of this sum signal detect. For example, an on / off function can be formed from the measured reception field strengths by thresholding whose autocorrelation function contains spectral lines at the frequencies occurring. Thus, a separation of the signals of multiple transmitters by providing an autocorrelation unit in the search device is possible.

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

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 antennas are particularly suitable for transmitter location because of their pronounced directional characteristic. A cosinusoidal directional characteristic makes it possible, for example, to form the filter correlation unit as stated above, wherein the angle signals are correlated with a sinusoidal and with a cosinusoidal filter signal sequence.

In further embodiments of the invention, the search device comprises a transmitter for transmitting transmitter signals, wherein the transmitter signals are preferably individualized by a transmitter identifier. In this way, group functions can be realized in which at least one of a plurality of transmitters is identifiable by its individualized identifier, for example the group leader of a group of skiers.

In certain further embodiments of the invention, the signal processing device is designed to generate processing signals which associate a transmitter identifier with a transmitter identifier, a transmitter being designed such that transmitter signals of this transmitter can be individualized with respect to transmitter signals of further transmitters. As a result, the user of the search device according to the invention in advantageous a simple way the option be made available to display one of a plurality of located stations in a prominent way.

• 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 developed further in such a way that sensor signals which relate to the earth's magnetic field are displayed to the users as a processing signal by result signals, and a fixed search angle relative to the earth's magnetic field is assigned to each search direction. Thus, the geomagnetic field is used as a fixed reference coordinate system, and it is possible at any time the assignment of the measured transmitter signal of a transmitter to a fixed search angle.

In preferred embodiments of the method according to the invention, field strength components of the geomagnetic field are measured in three mutually perpendicular directions for the assignment of search direction and angle. Thus, the solid angle of the device can be determined relative to the field lines.

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 are corrected accordingly. Thus, advantageously, the direction can be determined exactly.

In further embodiments of the method according to the invention, angle signals which in each case indicate a reception field strength at a search angle are generated from the transmitter signals and the assignments of search direction and search angle. To Generation of the angle signals is advantageous the application of signal processing mechanisms to these signals possible, which allows the determination of the transmitter location in a particularly simple and reliable manner.

In further embodiments of the method according to the invention, a transmitter search angle in which the transmitter is located is calculated on the basis of the angle signals and a result signal is output which represents the transmitter search angle. In this way, the location of the transmitter can be determined, since the determination of the distance between the transmitter and the search device by conventional methods is easily possible. A determination of the transmitter location by ear is therefore not required. The station search angle can be determined after one or more panning of the search device according to the invention, even if the device already shows again in a completely different direction.

In a further embodiment of the invention, the transmitter search angle is determined from at least two, in particular at least three, angle signals. With clocked transmitter signals of a transmitter, it is often the case with a random pivoting movement that the transmitter is currently in a transmission pause, when the search device is held 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, will generally be present only in sections. Advantageously, therefore, the inventive method is designed to extrapolate from the intermediate values maximum and minimum. For this purpose, in principle any two points of the field strength profile (i.e., two angle signals) are sufficient if the directional characteristic of the search antenna is known. For a robust approximation, the use of at least three angle signals is advantageous.

In further embodiments of the aforementioned embodiments, 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. From the present sections of the angle signals, the least squares method can be used to estimate the determining parameters of the entire curve. From this, the estimation angle signal sequence can be calculated in a simple manner, as has already been explained above.

In further embodiments of this embodiment, angle signals are weighted differently in the calculation of the estimated angle signal sequence, in particular in accordance with the time that has elapsed since receipt of the transmitter signals underlying the angle signals. Using the least squares method, the estimate can be continuously improved by using new measurements. This results in a relatively accurate location estimate even at a great distance from the buried and correspondingly weak transmitter signal. On the other hand, jumping or excessive instability of the calculated transmitter search angle can be reliably suppressed by a corresponding weighting of older persons in relation to the current measured values or the angle signals determined therefrom.

In further embodiments of the method according to the invention, estimated transmitter signals are determined by correlation of transmitter signals with predetermined filter signals and angle signals are determined from the estimated transmitter signals. If a cross-correlation between the filter signals and the transmitter signals is performed, the detection of weak transmitter signals of a transmitter is, for example, located at a great distance from the searcher, which corresponds to finding a signal of known form in the noise.

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

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

In preferred embodiments of the inventive method, a periodic signal component of stored transmitter signals or processing signals, in particular estimated transmitter signals, is determined by autocorrelation for the detection of a plurality of transmitters. If the signals of several buried victims received, the transmitter signals of the transmitter can overlap each other and also mutually cancel. However, since two transmitters always have slightly different repetition rates and / or duty cycles from each other, it is possible in principle to assign the respectively received signal to the one or the other transmitter. The superimposition of signals from several transmitters is the sum of several signals that are periodically switched on and off. Therefore, the autocorrelation function is useful to detect the periodic components of this sum signal. For example, an on / off function can be formed from the measured reception field strengths by thresholding whose autocorrelation function contains spectral lines at the frequencies occurring. Thus, a separation of the signals of several transmitters is possible. By averaging the autocorrelation function over several observation periods, dominant periodic components can be determined very reliably, relatively independent of the respective orientation of the transmitter to the receiver.

In one embodiment of this embodiment, a determined periodic signal component, which can be assigned to a transmitter, is masked out of transmitter signals or processing signals in order to determine further periodic signal components. Due to noise and inaccuracies, the periodic components of weaker received signals are often obscured. In order to be able to detect these components, it is advantageous if signal components which can be assigned to a dominant received signal are masked out (set to zero).

In further embodiments of the method according to the invention, the transmitter signals of a transmitter are compared with transmitter signals of further transmitters by a transmitter identifier individualized and processing signals are generated, which assign a sender search angle this sender identification. In this way, group functions can be realized in which at least one of a plurality of transmitters is 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, like reference numerals are used for the same and like-acting elements.

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). Communication with the user is via an illuminated display 10 and two control buttons 12, 13. The display 10 allows the graphic display of the position of one or more spillers relative to their own location. The device 1 additionally has a loudspeaker 14 for outputting a synthetically generated sound to the user as acoustic feedback and an LED 15, as is known for conventional devices. The loudspeaker 14 and the red LED 15 enable a conventional search even 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 for true to scale representation of the location of the geordeten transmitter Spilled, a status line 18 with the respective most important information and labeling fields 20 for the two control buttons 12th

The device 1 is designed as a combined search and transmit device. The housing has the form of a folding mobile phone. The hinge is indicated in Fig. 1 by a dashed line 21. If the device 1 is in search mode, closing the device automatically switches back to the transmission mode. As a result, an emergency downshift is realized in an advantageous manner, as it is, for example, in the case of a later avalanche, required in the standards.

The device 1 is equipped with an outwardly invisible antenna for transmitting and searching at a search frequency of 457 kHz. The specified frequency is standardized for avalanche transceivers (EN 282). An automatic location of the buried is done from the natural pivoting movement of the seeker or user. According to the invention, however, no manual bearing is required as in conventional devices. In addition, the illustrated device 1 has a bearing mode for concentrating on a selected victim.

A search process is carried out in such a way that the searcher turns the device 1 back and forth several times after switching from transmit to search mode by about 180 degrees. The achievable DF or search accuracy is initially ± 10 degrees. When panning, all transmitter or transmitter signals of transmitters are detected by those who are in range. The range of the device is about 80 m. The transmitters may be conventional avalanche transceivers, or devices identical to the device 1. A manual bearing, i. holding the device 1 in the direction of the strongest signal is not required.

The detected transmitters 22 are displayed in direction and distance on the display 10, with the scale representation of the distance of the transmitter 22 from the searcher (in the center of the coordinate field 16, i.e. the crosshair 23) being specified by distance indications 24 in meters.

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

Target search in the near range can be supported by the red LED 15. Moreover, for precise point location, a zoom function may be activated in the display 10 (not shown). As the seeker approaches a transmitter location 22, i. the suspected resting point of a buried, a circle is displayed on the display 10, which is concentric with the resting point 22 and concentrically shrinks on further approach. Experience has shown that the circle is fade in from a distance of three meters, but the fade-in can also take place at greater or smaller distances. Instead of a circle, a square or similar symbol could also be used.

By means of the search device according to the invention, the exact burial depth can be determined in a simple manner. For this purpose, the seeker brings the detected transmitter 22 (the suspected resting point of the victim) with the center of the crosshairs 23 (the position of the seeker) in cover, so that the seeker is vertically above the victim. 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.

Once a buried person has been found and recovered, the seeker picks up the bearing and devotes himself to the next victim.

The search device 1 is equipped with a motion sensor (not shown). This detects whether the device 1 is moved. If the device is in any mode that is not the send mode and the device is not moved for 90 seconds, it automatically switches to the send mode. As a result, the above-mentioned emergency downshift is triggered safely even if the seeker due to a post avalanche or the like surprising event has no opportunity to close the search device.

The search device 1 has in the embodiment described here in addition to the search function on other functions that can be selected via the main menu to be reached with the key 13. This includes an electronic compass, a temperature gauge and inclination measurement to assess the avalanche danger, an indication of the battery condition and a remaining time indicator for transmit and search operation. When the battery level is low, a warning is issued regardless of the operating mode.

For safety reasons, the standard does not allow any additional functions (compass, temperature display, inclination measurement). However, the search device according to the invention, for example, requires the inclination sensors for its functionality. Then only care must be taken that the display of the additional data obtained does not increase the power consumption in such a way that the safety of the mission is no longer guaranteed. Therefore, a safety circuit is provided in the search device 1 (not shown) which turns off the display of the additional functions when the battery capacity falls below 50% of the maximum value. Thus, the requirements of the standard to the reliability of the device are met.

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

Furthermore, a short guide for the device and configuration displays and Konfigurationseinstellmöglichkeiten for language and display lighting can be reached via the main menu of the search device 1.

The integrated sensors, which are described in more detail below, the device 1 can determine at any time, in which direction the seeker keeps it straight. Thus, the location of the located transmitters of the victims can be displayed correctly at any time relative to their own point of view.

From the display shown in FIG. 2a, it is intuitively clear that the spill 26 shown highlighted in the coordinate field 16 lies exactly 30m away in the direction in which the device 1 is held straight. The nearest buried victim highlighted - highlighted - can be selected by pressing key 12 ("PEILEN") for further search. As shown in Fig. 2b, so that the information in the display 10 is reduced to the data of the targeted spill 26. The loudspeaker 14 (see Fig. 1) only reproduces the search sound of the targeted victim 26 in a distance-dependent manner. The bearing can be canceled at any time by pressing button 13 ("ALL"). A multiple search is possible for up to six burials simultaneously.

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

From the received signals, the positions of the victims are calculated. The algorithms used are robust against individual faults or measurement errors. As the positions are constantly being recalculated throughout the search phase, the accuracy of the estimated positions for the victims will improve rapidly over time.

In Fig. 3, the functional structure of the device 1 of Fig. 1 is shown schematically. In addition to the search antenna receiver 30 and the search sound mixing stage, there are provided a geomagnetic field sensor 30 which outputs a sensor signal for each rotational degree of freedom (X, Y, vertical) and tilt sensors 32 for the two tilt axes. In addition, a further sensor 34 for one of the above-mentioned additional functions of the device, the temperature measurement, located.

The microprocessor-controlled sample manager 36 supplies the current sample to the correct destination and selects the channel for the next sample. The timing is designed so that the maximum possible sample clock essentially for the Sampling of the reception or transmitter signals is available. For the sampling of the sensor data, the received signal is faded out approximately every 32nd time slot and instead one of the sensor channels for temperature, magnetic field and inclination is read.

In the angle estimation module 38, the spatial position relative to the earth's magnetic field is determined exactly from the sampled values of the magnetic sensor 30 and the inclination sensors 32. Such methods are known per se to those skilled in the art and are therefore not described further. By using these sensors 30, 32, according to the invention, each direction in which the search device 1 is held is assigned a fixed search angle φ with respect to the measured magnetic field vector μ.

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

Spilled to be able to locate as far away as possible. This corresponds to finding a signal of known form in noise.

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

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

The disadvantage of the matched filter is the very high computational effort. This is due to the fact that the pattern function must be compared in all possible phase positions with the sequence of the reception or transmitter signals.

From the transmitter signal sequence is known that it is a cosinusoidal signal sequence with a constant frequency. Any scaled and phase-shifted sine wave can be divided into a cosine and a sine wave. The performance of searched signal is the sum of the power of sine and cosine. Therefore, it is sufficient to multiply the transmitter signal sequence with a cosine and a sinusoidal filter signal sequence, ie to break the sequence of transmitter signals into a sine and a cosine component. The argument (angle) of the complex number formed by sine and cosine components describes the phase position of the receiver 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 buried people is particularly difficult if at the same time the signals of several victims are received. The transmitter signals of the transmitters can overlap each other and also mutually cancel out. Since two devices always have slightly different repetition rates and / or duty cycles, however, an assignment of the respectively received signal to the one or the other transmitter is possible in principle.

The superimposition of signals from several transmitters is the sum of several signals that are periodically switched on and off. In principle, therefore, an autocorrelation function is suitable in order to detect the periodic components of this summation signal.

In the simplest case, an on / off function, whose autocorrelation function should contain spectral lines at the frequencies occurring, is formed from the measured field strength values by thresholding. The disadvantage of this method is that just at low field strengths or imperfect orientation of the receiving antenna to the transmitter, the on / off times can be determined only insufficiently accurate. These inaccuracies smear the spectral lines of the autocorrelation function, i. out of focus, and quickly unusable.

As in the ideal on-off function, the information about the periodicity is of course also present in the analog field strength function. This is calculated as the magnitude of the output of the sin / cos correlator 40, i. H. won as the output of the RSS module 42. By averaging the autocorrelation function over several observation periods, dominant periodic components can be determined very reliably, relatively independent of the respective orientation of the transmitter to the receiver.

Due to noise and inaccuracies, the periodic components of weaker received signals are often obscured. In order to be able to detect these components, signal components which can be assigned to a dominant received signal are masked out (set to zero).

The assignment of individual signal sections to different transmitters is performed by the heuristic segmentation in the segmentation module 46. For this purpose, those signal elements which contribute to the maximum of the ACF are essentially determined by threshold value decision. If necessary, the signal elements determined in this way are separated again by analysis of jumps in the correlation values and assigned to different transmitters. For example, a signal element may be subdivided into two individual regions at the edges, starting from the left and right boundaries, and a central overlay region, which can not be used for the location estimation. For segmentation, jumps and discontinuities in the sin and cos correlation values can be used.

In the location estimation module 48, the location of the at least one received transmitter is determined. The distance of the transmitter can be reliably determined in a conventional manner by applying a power law to the measured or determined field strength. At the same time, in module 48, the assignment of the search angle φ obtained according to the invention from the sensor data to the processing signals σ resulting from the currently measured transmitter signals, which indicate the instantaneous reception field strength of a transmitter, takes place.

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 angle signals σ (φ), which in each case indicate a reception field strength at a search angle, are generally present only in sections. From these sections, however, the least squares method can be used to estimate the determining parameters of the entire curve. From this it is easy to calculate the angle and distance of the transmitter.

In a fault-free case, the entire field strength profile as a result of estimated angle signals could be calculated from the field strength profile of the received transmitter signal sequence. For calculation, two arbitrary points of the transmitter signal sequence were sufficient. In practice, however, the received signal is more or less noisy. The two points used for the approximation can then be randomly strongly corrupted by noise samples, so that the parameters of the actual angular signal sequence are very erroneous to be appreciated. In order to achieve an unbiased estimate, all available points of the received field strength curve or transmitter signal sequence should be included and the searched parameters optimized so that the total deviation of the calculated course of the estimated angular signal sequence from the portion of the sequence of angular signals determined from the transmitter signals and search angles is minimal becomes.

Using the least squares method, the estimate can be continuously improved by using new measurements. On the one hand, this results in a relatively accurate location estimate even at a great distance from the victim and correspondingly weak search or reception signal. On the other hand, jumping or excessive instability of the determined transmitter search angle can be reliably suppressed by a corresponding weighting of older persons in relation to the current values of the measured search or determined angle signals.

Thus, with a sufficient number of measured values, a reliable determination of the position of the transmitter is possible. This applies in particular even if the maximum itself can not be detected, since just at the times at which the searching device points in the direction of the transmitter, this is located in the scanning intervals. The data of the real received signal gives indications of the necessary number of samples for a sufficiently accurate determination.

The object of the location estimation is also the solution of the problem of resolving the 180 degree ambiguity of the angle estimate from the field strength differences of two or more successive recording intervals and assigning the transmitter to the front (in the direction of movement) or rear (opposite to the direction of movement) half-plane.

Thus, the position of a victim, in particular the transmitter search angle, even then fully and reliably calculated if his transmitter at the time when the device 1 of the seeker points in his direction, is currently in the transmission break. This is achieved with an inventively designed search device which has only a single search antenna and therefore be correspondingly lighter and less expensive can (of course, the use of multiple antennas in a search device according to the invention 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 search device according to the invention described here by way of example is based on modules, which are shown in FIG. 3 as separate units. 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 fully-equipped search device such as that illustrated by the figures, a processor with 30 MIPS computing power and 8 KB of working memory would be 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 separating the signal components of multiple transmitters may be formed. Such a device can be used in situations where only one transmitter is to be located. An example of this is a group of skiers on a secured track, in which the finding of the group leader is made possible by the search devices of the group members, whereby only the transmitter of the conductor is in the transmission mode.

Likewise, a search device according to the invention can be designed without a module for carrying out the cross-correlation of a filter signal with weak search or reception signals. 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 memory, processor processing capacity) are available for other functions, for example, the AKF module may be configured to separate a larger number of transmitters from each other. Also, a lower-powered device may have an extended operating time for the same battery capacity, such as when a 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. The viewpoint of the searcher and the sender location detected by the searcher, i. the suspected lying points of the victims are superimposed on the representation of the GPS system. Such a system allows the seeker to intuitively, i.e., intuitively determine, the position of the reclining point from any prominent terrain points present. quickly detect, so that he can visit the resting point with the least possible delay.

Alternatively or additionally, the search device can be combined with a voice control, as is known for example in GPS systems for motor vehicles. In this case, the searcher receives acoustic instructions, for example in the form of a voice generated by the search device. 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. In this case, the terrain view recorded by the camera is advantageously reproduced on the display of the search device. The detected transmitter locations are superimposed on the terrain view. The view on the display is broadly consistent with the view the seeker has of his environment. Thus, the orientation of the seeker is facilitated, especially in contour-rich terrain.

A combination of a search device according to the invention with a GPS system and camera is also possible. In doing so, the GPS system and camera would work together to achieve a detailed and contour rich representation of the terrain.

Instead of being used only as an avalanche victim search device, a search device designed according to the invention can also be advantageously used for further applications. As an example, a group of skiers are called, which are based on their group leader, for example. In poor visibility or otherwise confusing conditions. All participants have transceivers. The device of the conductor has a transmitter whose transmitter signal is provided with an individual transmitter identification. The search devices of the group participants are designed to evaluate the received sender identification, so that the located transmitter of the conductor is identifiable among the plurality of located transmitters. The display of the search devices of the participants 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 station identifiers on the standard signal at 457 kHz is not provided. However, in addition to the otherwise standard-compliant transmitter in a transmitter, a second transmitter may be provided which emits the signals with transmitter identifiers.

In addition, within the scope of the invention, which is indicated solely by the following claims, many other embodiments by skilled action 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 (28)

1. A search device for locating a transmitter, in particular avalanche-victim search device (1),
   wherein for scanning a search area the search device (1) is swivelled by a user through a range of search angles that covers the region to be searched,
   with

   - a search antenna (28) for receiving signals being sent out by a transmitter from a momentary search direction,

   - a signal-processing means for generating processed signals from the transmitter signals,

   - an output unit (14, 15) to which the processed signals are sent for outputting result signals representing the processed signals to the user, and

   - a magnetic-field sensor (30) that outputs to the signal-processing means (36-48) sensor signals regarding the earth's magnetic field, which are sent on as processed signals to the output unit (10),

   characterized in that
   a fixed search angle (ϕ) relative to the earth's magnetic field (µ) is assigned to each received signal, wherein the signal-processing means (48) is designed to generate angle signals from the transmitter signals and the sensor signals, wherein the angle signals represent a reception field strength in dependence on a search angle (ϕ).
2. The search device according to claim 1,
   characterized in that
   the magnetic-field sensor (30) sends to the signal-processing means (36-40) three sensor signals related to the earth's magnetic field.
3. The search device according to claim 1 or 2,
   characterized in that
   inclination sensors (32) are provided, that send to the signal-processing means (36-40) sensor signals representing the orientation of the search device (1) with respect to a horizontal plane.
4. The search device according to one of the preceding claims,
   characterized in that
   the signal-processing means (48) is designed to calculate a transmitter search angle at which the transmitter is located, by means of the angle signals.
5. The search device according to claim 4,
   characterized in that
   the signal-processing means (48) is designed to derive the transmitter search angle from at least two angle signals.
6. The search device according to claims 4 or 5,
   characterized in that
   the output unit (10) is designed for the graphic output of result signals that represent the transmitter search angle, and in particular comprises a display field (10) for the graphic display (16) of the transmitter site (22) in the search area.
7. The search device according to one of the preceding claims,
   characterized in that
   the signal-processing means comprises a filter correlation unit (40) that is designed to detect angle signals by correlating the transmitter signals with preset filter signals.
8. The search device according to claim 7,
   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.
9. The search device according to one of the preceding claims,
   characterized in that
   the signal-processing means comprises an autocorrelation, unit (44) that is designed to detect, by autocorrelation, periodic signal components in stored signals.
10. The search device according to claim 9,
    characterized in that
    the autocorrelation unit (44) is placed after a filter correlation unit (40).
11. The search device according to one of the preceding claims,
    characterized in that
    the search antenna (28) comprises a ferrite antenna, preferably with cosinusoidal directional characteristic.
12. Search device according to one of the preceding claims,
    characterized by
    a transmitter to send out transmitter signals, such that the transmitter signals are individualized preferably by a transmitter identification code.
13. The search device according to claim 12,
    characterized by
    a movement sensor that detects the movements of the search device (1), and an emergency switchback connected to the movement sensor, which switches the search device (1) into a transmission mode, in which the transmitter sends out transmission signals, whenever the movement sensor detects no movement of the search device (1) within a pre-specified period of time, for example 90 seconds.
14. The search device according to one of the claims 6 to 13,
    characterized by
    a GPS system and/or a camera to represent the surroundings on the display field (10).
15. The sarch device according to one of the preceding claims,
    characterized in that
    the signal-processing means is designed to generate processed signals that assign a transmitter identifier to a transmitter search angle, in which case a transmitter is so constructed that the signals sent out by this transmitter can be individualized with respect to the signals from other transmitters.
16. A method of localizing a transmitter, in particular the transmitter of an avalanche victim,

    - wherein to scan a search region a search device (1) is swiveled by a user through a range of search angles that covers the search region,

    - transmitter signals sent out by the transmitter are received from momentary search directions by a search antenna (28) of the search device (1),

    - processed signals are generated from the transmitter signals,

    - result signals that represent the processed signals are output to the user, and

    - sensor signals related to the earth's magnetic field are displayed to the users as processed signals by way of result signals,

    characterized in that
    a fixed search angle (ϕ) relative to the earth's magnetic field (µ) is assigned to each received transmitter signal,
    wherein the angle signals, each of which indicates a received field strength (σ) at a search angle (ϕ), are generated from the transmitter signals (r) and the assignment of search direction and search angle.
17. The method according to claim 16,
    characterized in that
    for the purpose of assigning search direction and angle, field-strength components (µ) of the earth's magnetic field are measured in three mutually perpendicular directions (X, Y, vertical).
18. The method according to claim 16 or 17,
    characterized in that
    the inclinations of the search device with respect to the horizontal plane are measured (32) and the sensor signals are correspondingly corrected (38).
19. The method according to claims 16 or 18,
    characterized in that
    a transmitter search angle, at which the transmitter is situated, is calculated with reference to the angle signals and a result signal is sent out (10, 16) that represents the transmitter search angle (22).
20. The method according to one of the claims 16 to 19,
    characterized in that
    the transmitter search angle is determined by at least two, in particular at least three angle signals.
21. The method according to one of the claims 19 or 20,
    characterized in that
    an estimated angle-signal sequence is calculated from the angle signals by the method of least error squares, and the transmitter search angle is specified from the maximum of the estimated angle-signal sequence.
22. The method according to claim 21,
    characterized in that
    during calculation of the estimated angle-signal sequence the angle signals are weighted differently, in particular according to the time that has elapsed since reception of the transmitter signals on which the angle signals are based.
23. The method according to one of the claims 16 to 22,
    characterized in that
    estimated transmitter signals (40: a, b) are derived by correlation of transmitter signals (r) with pre-specified filter signals, and angle signals are derived from the estimated transmitter signals.
24. The method according to claim 23,
    characterized in that
    to distinguish 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 one sine and one cosine signal sequence (a, b) is derived.
25. The method according to claim 24,
    characterized in that
    reception field strengths of the signals in the estimated transmitter-signal sequence are derived by summation of the products of the received transmitter-signal sequence with a sine and a cosine signal sequence (a and b).
26. The method according to one of the claims 16 to 25,
    characterized in that
    to detect several transmitters a periodic signal component of stored transmitter signals or processed signals, in particular estimated transmitter signals, is found by autocorrelation (44).
27. The method according to claim 26,
    characterized in that
    a detected periodic signal component (σ) that can be assigned to a transmitter is blanked out of transmitter signals or processed signals, in order to detect other periodic signal components.
28. The method according to one of the claims 16 to 27,
    characterized in that
    the transmitter signals from a transmitter are individualized by a transmitter identification code, compared to the signals sent by other transmitters, and processed signals are generated that assign this transmitter identifier to a transmitter search angle.

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