WO2016062337A1

WO2016062337A1 - Method and system for locating avalanche victims equipped with a transceiver

Info

Publication number: WO2016062337A1
Application number: PCT/EP2014/072550
Authority: WO
Inventors: Pau CLOSAS GÓMEZ; Nicola Baldo
Original assignee: Fundació Centre Tecnològic De Telecomunicacions De Catalunya
Priority date: 2014-10-21
Filing date: 2014-10-21
Publication date: 2016-04-28

Abstract

Present invention refers to a system and a method for locating buried transceivers which are emitting a wireless rescue signal. The invention comprises at least two searching transceivers configured to detect said rescue signals. The searching transceivers obtain some information about the rescue signals and exchange said information with other searching transceivers by means of a communication module. Finally, a processing module estimates a location of the transceiver emitting rescue signals based on the information of the position, orientation, the information about detected rescue signals and the information received from other searching transceivers through the communication module.

Description

METHOD AND SYSTEM FOR LOCATING AVALANCHE VICTIMS EQUIPPED

WITH A TRANSCEIVER

DESCRIPTION

TECHNICAL FIELD OF THE INVENTION

Present invention generally relates to radio-locating lost people and more specifically relates to locating missing people because of an avalanche with the highest accuracy and speed.

BACKGROUND OF THE INVENTION

Avalanche transceivers or avalanche beacon are a class of active radio beacon transceivers specialized for the purpose of finding people or equipment buried under snow as they are emitting a low-power pulsed beacon signal. Therefore, an avalanche beacon cannot be considered a preventative measure for possible avalanche burial, but rather it is a way to reduce the amount of time buried.

Current state-of-the-art avalanche transceivers are digital transceivers that take the strength of the signal and the emitted dipole flux pattern and compute distance and direction to the buried transceiver. Then, digital beacons indicate the direction to the victim's beacon as an arrow on the display or providing audio cues such as varying pitch or frequency.

Most of low- to mid-range beacons have a segmented arrow capable of pointing in five to eight forward directions only, displaying a 'U-Turn' indicator if the user is traveling away from the victim. However, higher end beacons are equipped with a digital compass and free-flowing arrow, facilitating more exact direction finding, even rotating to maintain direction between pulses of the transmitting beacon (a feature that is impossible without a digital compass or sophisticated accelerometer).

Due to the nature of the 457 kHz signal (frequency international standard) at the ranges common for avalanche burial (and the range specified in the standards), there have been many techniques developed to search for buried beacons as for example Grid search, Induction search, or Circle method. Thus, good beacon search abilities are required for participating in a search mission of buried people after an avalanche (recreational backcountry skiers, mountaineers as well as avalanche professionals such as ski guides, ski patrollers, search and rescue volunteers and professionals).

Therefore, a major drawback of the solutions known from the state of the art is that they require extensive training for rescuers in order to be able to use the avalanche transceiver effectively, being an untrained person not expected to participate in the search phase of a "search and rescue" (SAR) mission in an avalanche scenario.

Taking into account that an avalanche can drag people for a significant distance, there is often a big area to be covered by the rescuers. The lack of visual references makes hard to orient yourself even with the assistance of navigation systems, so the rescuers spread themselves over the area looking for emitting signals from the victims. With prior art technical solutions, human communication and action coordination is required to benefit from the presence of multiple rescuers; however, effective coordination requires extensive training and cannot be performed well by untrained personnel. The reason of this limitation is that solutions from prior art are based on avalanche transceiver devices that are designed to work for a single rescuer only, and do not take advantage of the presence of multiple avalanche transceiver being simultaneously used by multiple rescuers. An autonomous collaborative method that improves the speed and accuracy of the location of a victim by taking advantage of the simultaneous presence and movement of multiple avalanche receivers operated by rescuers spread over the area, without the need for human coordination, would be a big contribution.

As the probability of a victim surviving an avalanche quickly diminishes as the time spent buried increases, the reduction of the time an avalanche victim stays buried is the main concern of any search mission; for this reason, any improvement of existing techniques that yields a reduction in the time an avalanche victim stays buried may save lives. This is especially the case for avalanches where several people are buried, where the presence of multiple signals makes the search more difficult and time consuming. Untrained rescue personnel using prior art avalanche transceivers is typically not able to coordinate with other rescuers to discriminate among the different buried transceivers and parallelize search operations; in fact, untrained personnel typically ends up gathering in groups that search for the same signal (typically, the strongest one), with each rescuer in the group repeating the same steps to locate the same device, thus wasting precious time that could be instead be spent to search and rescue another person by going after another signal.

Autonomous collaborative methods have not been developed as a way for discriminating more quickly the different buried transceivers, and reducing the searching time. Prior art is then missing a solution to this problem, where untrained people is not able to effectively contribute in search missions to reduce the time required to finding and rescue avalanche victims.

SUMMARY OF THE INVENTION

Present invention solves the aforementioned problems by a system for locating transceivers which are emitting a wireless rescue signal, the system comprising at least two searching transceivers configured to detect said rescue signals wherein each one of the searching transceivers. The system comprises:

- a location module, configured for providing information of a position of the searching transceiver;

- an orientation module, configured for providing information of an orientation of the searching transceiver;

- a communication module configured for exchanging information about detected rescue signals and the position and orientation of the receiver with other searching transceivers, through a wireless communication network;

- a processing module configured for estimating a location of the transceiver emitting rescue signals based on the information of the position, the information of the orientation and the information, received from other searching transceivers through the communication module, about detected rescue signals, position and orientation. The searching devices may comprise a display for showing, through a graphical user interface, a map of the search area.

According to one particular embodiment of the invention, the processing module may further comprise a clustering module configured for organizing into clusters the information about each one of detected rescue signals emitted from different transceivers, wherein each cluster corresponds to one emitting transceiver.

The processing module may comprise the step of estimating a location of a transceiver emitting rescue signals and sequentially updating the estimation as new information is received.

A second aspect of the invention refers to a searching device for locating transceivers which are emitting a wireless rescue signal, the searching device is characterized by comprising:

- a measurement module configured to detect said wireless rescue signals

- a location module, configured for providing information of a position of the searching device;

- an orientation module, configured for providing information of an orientation of the searching device;

- a communication module configured for exchanging information about detected rescue signals, position and orientation with other searching devices, through a wireless communication network;

- a processing module configured for estimating a location of the transceiver emitting rescue signals based on the information of the position, the information of the orientation and the information, received from other searching devices through the communication module, about detected rescue signals, position and orientation.

Another aspect of the invention refers to a method for locating transceivers which are emitting a wireless rescue signal, wherein at least two searching transceivers configured to detect said rescue signals are involved. The method comprises the following steps: a) receiving, by a first searching transceiver, at least a wireless rescue signal emitted from a transceiver, through a wireless communication network;

b) obtaining information of its own position, through a first location module, its own orientation, through a first orientation module, and obtaining information about received wireless rescue signal, by the first searching transceiver;

c) receiving, by at least a second searching transceiver, the same wireless rescue signal through a wireless communication network;

d) obtaining information of second searching transceiver position, through a second location module, information of second searching transceiver orientation, through a second orientation module, and obtaining information about received wireless rescue signal, by the at least second searching transceiver;

e) broadcasting the obtained information through a second communication module of the second searching transceiver;

f) receiving, the first searching transceiver, the information broadcast by the at least second searching transceiver through a first communication module;

g) estimating, by a processing module of the first searching transceiver, a location of the transceiver, being the estimation based on the information of its own position, the information about received wireless rescue signal and information received from the at least second searching transceiver.

According to one particular embodiment, when the first searching transceiver detects two or more rescue signals, the invention may further comprise organizing into clusters the information about each one of detected rescue signals emitted from different transceivers, by a clustering module of the processing module.

Additionally, when more than one victim is involved in the rescue and the information about different rescue signals of different transceivers is gathered in two or more clusters by means of a clustering module, the invention may further comprise estimating, by the processing module of the first searching transceiver, a separate location for each one of the transceivers emitting said different rescue signals. Then, a separate instance of the location module is run for each buried transceiver identified by the clustering module.

The information about received wireless rescue signals may comprise, according to different embodiments of the invention, measurements of signal strength and electromagnetic field direction.

The information broadcast by a searching transceiver may be provided with a numeric identifier which uniquely identifies the searching transceiver.

The step of estimating a location of the transceiver may be based on modeling the information about received wireless rescue signals obtained by the searching transceiver with predetermined propagation models to set out a system of equations to be solved.

According to one particular embodiment of the invention, when new information is received by the first searching transceiver, the invention may further comprise processing the new information to estimate a more accuracy estimation of the location by applying a Recursive Least Squares or a Kalman filter.

Optionally, present invention may comprise estimating a confidence region for the estimated position of each buried transceiver based on a measure of probability. For example an ellipsoid may be used.

Additionally, present invention may show in a display the first searching transceiver, a graphical representation of the search area with the estimated location of one or more transceivers emitting wireless rescue signals, the position of other rescue transceivers in the search area, and the confidence region for the estimated position of each buried transceiver.

A last aspect of the invention refers to a computer program product comprising computer program code adapted to perform the method of the invention when said program code is executed on a computer, a digital signal processor, a field- programmable gate array, an application-specific integrated circuit, a micro- processor, a micro-controller, or any other form of programmable hardware.

Therefore, present invention take advantage of the presence of multiple avalanche transceivers being simultaneously used by multiple rescuers. The autonomous collaborative method takes advantage of the simultaneous presence and movement of multiple avalanche receivers operated by rescuers spread over the area. Thanks to this autonomous collaborative methods allows, even untrained rescue personnel using the present invention can collaborate in the search of buried victims, achieving an automatic improvement of the accuracy of the estimated position of the victim as rescuers move within the area, with the improvement being larger and faster over time the more rescuers are involved in the search. Even an untrained rescuer wandering randomly over the search area and using the present invention would yield a positive contribution to the accuracy of the location of the victim. This improvement yields a reduction in the time an avalanche victim stays buried. Moreover, in case of avalanches where several people are buried and the presence of multiple signals makes the search more difficult and time consuming, present invention allows the automatic discrimination of multiple buried victims, and the simultaneous automatic estimation of their position. This allows even untrained rescue personnel using the present invention to collaborate in the search of multiple buried victims, without the need for human coordination.

DESCRIPTION OF THE DRAWINGS

To complete the description that is being made and with the object of assisting in a better understanding of the characteristics of the invention, in accordance with a preferred example of practical embodiment thereof, accompanying said description as an integral part thereof, is a drawing wherein, by way of illustration and not restrictively, the following has been represented:

Figure 1.- shows a typical scenario where one embodiment of the invention may operate.

Figure 2.- shows the modules comprised by a searching transceiver according to one embodiment of the invention. Figure 3.- shows the processing module according to one embodiment of the invention, where the clustering module allows locating more than one victim at the same time.

Figure 4.- shows a graphical user interface according to one embodiment of the invention, for an example avalanche rescue scenario.

DETAILED DESCRIPTION OF THE INVENTION

Present invention discloses a process and a system for estimating a location of buried avalanche victims, equipped with regular avalanche beacons, by means of a cooperative technique which may involve several users (trained or untrained). This cooperative search approach greatly improves the accuracy and speed of the search, thanks to a much more accurate estimate of the position of each buried transceiver and to a novel method to discriminate among multiple signals from different buried transceivers and estimate their positions in parallel. With present invention, users may find buried people by following the indications of an intuitive interface without the need to use specific search patterns and/or human coordination among rescuers that only trained rescue personnel could perform effectively.

Figure 1 represents a typical scenario where present invention may operate, it can be seen: a buried user (1 1 ) (although other scenarios may comprise several buried users), equipped with a common avalanche transceiver emitting standard distress or rescue signals (12). The goal of present invention is the fast and accurate estimation of the location of the transceiver, which along this description is referred as: b^k = [b_x,b ,b_z]^' in Cartesian coordinates, where k e {l,...,K} , and

K is the total number of buried devices. The position is assumed to be static, as typically verified in avalanche SAR missions; and - a set of M people (13, 14) forming the Search and Rescue (SAR) team. Each person in the team is equipped with a searching transceiver of present invention. The time-varying position of the SAR team member ^{z e} {1> ···> Λ^} _wj|| _De referred from now on as: »'⁽ = ^{( ,}^^{( ,}^⁽ r _{in Cartesian coordinateS!} ^ { -. } , where ^ denotes the time. This assumption of time-varying position is consistent with the typical behavior of rescuers in an avalanche SAR mission, as rescuers are moving in the attempt of trying to locate the buried person. The example of figure 1 takes M=2, which means that there are two searching devices (13, 14) surrounding the area of the buried user (1 1 ) with trajectories represented by s¹ ^) and s²(t) at time instant t and an orientation d¹(f and d²(t) associated.

Figure 2 represents, according to one embodiment of the invention, a searching transceiver proposed by the present invention comprising the following modules:

An avalanche transceiver module (ATM) (21 ) that is able to receive beacons from other transceivers and provide information on such signals. According to one possible embodiment of the invention, the ATM can be based on a state-of-the-art avalanche transceiver operating at the 457 kHz frequency and providing information on signal strength and electromagnetic field direction information of other similar transceivers. According to another possible embodiment of the invention, the ATM can be based on a transceiver for other wireless technologies, such as for example I EEE 802.1 1 or Bluetooth, and measure received signal strength of other similar transceivers.

A Location Module (LM)(22), that provides information of its absolute position, based on, for example, a Global Navigation Satellite System (GNSS) receiver, possibly coupled with an inertial measurement unit.

An Orientation Module (OM) (23) that provides information on its orientation, based on a compass, inertial measurement unit, or other similar technology. A Search and Rescue Communication Module (SARCOMM) (24) that exchanges the above information with other identical searching transceivers participating in the search and rescue operation.

A processing module (25), also called "Buried Transceiver Location Module" (BTLM) that continuously receives as input the above described information, and provides as output the current best estimated position of the buried transceivers.

A Graphical User Interface (GUI) (26) that shows a map of the area pointing the position of the buried transceivers as well as of all the search devices in the area.

Present invention operates, according to one preferred embodiment of the invention, following different stages: measurement, communication, estimation, and visualization. Each one of the searching transceivers owned by a member of the SAR team iteratively repeats each of these stages during the SAR mission.

The measurement stage starts by receiving a distress or rescue signal transmitted by a buried avalanche transceiver, a beacon for example. One embodiment of the invention comprises wireless rescue signals transmitted through a wireless channel. The searching transceiver of one member of the SAR team is configured to detect said wireless rescue signals and obtained some information about said signals. The following measures are taken according to one embodiment of the invention: the absolute time reference t provided by the location module (22), for example a GNSS module, and corresponding to the time at which the rescue signal is received; its own geographical position at time t provided by the location module (22), for example a GNSS module, denoted as s'( = [s t _y it it)]^' e R³ in Cartesian coordinates for the member /^' of the SAR team; its own orientation at time t provided by the OM (23), denoted as: d'(t) = [ά_φ' (ί), ά_θ' (ί)]^' <Ξ [-π/2,π/2] χ [-π, π] in spherical coordinates; the received signal strength (RSS) corresponding to the received distress signal, denoted as r^l(t) R ; and

- the magnetic field direction vector ⁱ(t) = [h_x ⁱ (t),h_y ⁱ (t),hi(t)] corresponding to the received distress signal in Cartesian coordinates.

Then, the measurements related to the reception of one particular distress/rescue signal are represented by a tuple [i, t, s'(t), d^l(t), r^l(t), h'(t)]-

When a new tuple is gathered by the ATM of the searching transceiver, said tuple is sent to both the SARCOMM module and the BTLM module.

Communication stage comprises two different processes: sending and receiving. Both processes may be carry out independently as any searching transceiver involved in the SAR mission may receive messages from other searching devices at any time.

Independently, according to one embodiment of the invention, a searching transceiver detecting a wireless rescue signal and gathering a tuple, sends the tuple to its embedded communication module, which broadcasts said tuple immediately or after a short time. According to one embodiment of the invention, the communication module can aggregate several tuples in a single transmission. Any searching transceiver, within a certain range, is then receiving the information contained in the tuple. The communication between two communication modules, according to one embodiment of the invention, is a wireless communication and the messages are exchanged through a wireless communication channel or a wireless communication network. For example, different embodiments of the invention can be realized based on the IEEE 802.1 1 WLAN (a.k.a. Wi-Fi) and the IEEE 802.15.1 WPAN (a.k.a. Bluetooth) technologies.

According to one embodiment of the invention, the previously mentioned tuples are encoded for transmission as an information packet by specifying for each variable in the tuple a suitable binary representation format, defining a data structure for the tuple that includes the binary representation of each variable in the tuple, and including in the information packet a binary representation of the number of tuples transmitted plus an instance of the aforementioned data structure for each tuple to be transmitted.

According to one embodiment of the invention, the IEEE 802.1 1 technology is used for communication among searching transceivers, by having each transceiver incorporating an IEEE 802.1 1 network interface card, by configuring such card in Independent basic service set (IBSS mode) with a pre-determined Extended Service Set Identification (ESSID), with the ESSID being the same for all rescuer devices operating in the same area, and by using the WLAN MAC broadcast address to exchange information packets among searching transceivers.

According to one embodiment of the invention, the Internet Protocol version 4 (IPv4) is used for communications among searching transceivers, by configuring each searching transceiver on the same IPv4 subnet and by using the IPv4 broadcast address 255.255.255.255 to perform broadcast communications among searching transceivers.

According to one embodiment of the invention, the User Datagram Protocol (UDP) is used to transport information packets among searching transceivers, with one or more tuples included in the information packets,

When a new tuple is provided by the avalanche transceiver module (ATM) of a user / to the SARCOMM module of the searching transceiver/ , the SARCOMM module broadcasts the following information to the other devices of the SAR team: a numeric identifier may be added by the communication module in one embodiment of the invention before broadcasting a tuple for identification purpose. This numeric identifier may be set by default by the manufacturer and it is a permanent numeric identifier which uniquely identifies the device i . According to an embodiment of the invention, the unique identifier could be the MAC address of the network interface card used by the SARCOMM module, the absolute time reference t

- the position ^s ^

- the orientation d' (t)

the received signal strength r^l (t)

the magnetic field direction vector ' (t)

The SARCOMM module of searching transceiver i receives similar information gathered by other devices in the SAR team and broadcasted by their corresponding SARCOMM modules. The inclusion of the numeric identifier allows the discrimination of the searching transceiver that generated each piece of information. In detail, for searching transceiver j = \, ...,M , j≠i , the SARCOMM module of searching transceiver i shall be able to receive a set of measurement tuples [j, t, s^J(t), d^J(t), r^J(t), h^J (t)] that were obtained at different time values t by other searching transceiver j = \ ...M, j≠i . As soon as one of such tuples is received, it is passed to the processing module (BTLM module). Because of communication impairments it is possible that not all of the measurement tuples transmitted by other devices are received by device i .

Estimation stage computes a location of the victim as the position of the buried transceiver emitting rescue signals. Processing module (25) of each searching transceiver takes advantage of its own measurements (27) and the measurement provided by other searching transceivers (28) within a certain range to make the estimation as accurate and fast as possible.

Upon receiving new information by either the ATM module or the SARCOMM module, the BTLM module of searching transceiver i elaborates a new estimation of the location of the buried transceiver. This is performed by gathering together the measurements tuples generated by the ATM of the searching transceiver i with the measurement tuples received by the SARCOMM and originated from the other searching transceivers j = \...M,j≠ i , being the format of these two categories of measurement tuples exactly the same.

The processing module, according to one embodiment of the invention, comprises two sub-modules: a Clustering Module (CM) (31 ) and one or more Location Estimation Modules (LEM) (32), as shown in Figure 3.

Embodiments comprising the clustering module consider scenarios with more than one buried victims, so the Clustering Module leverages the time and device identifier information in the measurement tuples to partition all the available measurement tuples into clusters corresponding to different buried transceivers. This operation is performed, according to one embodiment of the invention, by using a train pulse deinterleaving algorithm, which allow to detect the number of sources (K in this case) based on the analysis of the Time Of Arrival (TOA) of each received signal ( t in this case), and hence to assign to each measurement tuple an index k = l ...K that identifies the buried transceiver which originated the signal.

After the clustering module organizes into clusters the information about each one of detected rescue signals emitted from different transceivers, the CM provides to the LEM a set of per-buried-transceiver tuples [k, n, s^k(n), d^k(n), r^k(n), h^k(n)] (33), where the index k denotes the buried transceiver and the index n is incremented per each new tuple associated with that buried transceiver. In other words, the CM reorganize the measurement tuples (34) that were previously indexed by the receiver device i and the time t so that they are now indexed by the buried device k and the per-buried device tuple number n . In the reorganized tuples, the information on i and t is removed since it is not needed by the LEM.

The Location Estimation Module (32), as part of the processing module, is in charge of providing the output with the estimation of victims' location. Embodiments where a clustering module is included, and more than one victim is involved, have a separate instance of the LEM for each buried transceiver identified by the CM. But in the following, it is describes the operation of a single LEM instance which operates on the tuples [k, n, s^k (n), d^k(n), r^k(n), h^k(n)] (33) provided by the CM and relative only to a single buried transceiver ( k = const). Let N be the number of tuples received by the LEM so far relative to the buried device k . The purpose of the LEM is to determine the estimated position of the Λ: -th buried device.

The operation of the LEM of the processing module is based on modeling the received signal strength (RSS) measurements and magnetic field direction measurements with predetermined propagation models. For the RSS, this model is, according to one embodiment of the invention, a log-normal model or others coming from ad-hoc experimental campaigns. Therefore, the assumed model for RSS observations is

where f_rfi (-) : R³ x R³ χ[-π/2,π/2] χ [-π,π] -» R is a function that maps the relative position between the /-th searching transceiver and the buried transceiver to RSS values. Only the first variable of the function is unknown, which belongs to the position of the buried device, and the rest of variables are fed by the CM. This function is in general parameterized by Θ which might be known a priori or might be estimated jointly with b^k(n) .

v^k(n) is a random term gathering all effects misspecified in the model as well as the noisy nature of the RSS observations. Typically it is assumed zero-mean Gaussian distributed with a certain variance, although it is not strictly necessary here.

For the magnetic field direction, the model according to one embodiment of the invention is in the form: h_x ^k{n) = f_h ;*^k( )A^k{n)) +v_hk {n) (2) h^k(n) = f_h ^b^k;s^k(n),d^k(n))+v_hk (n) (3) M^k

+v_hk {n) (4) where the functions /_¾;θ (·) . Λ ,Θ Ο ^ar,d fi, ,ΘΟ ^'- R^{3 χ} &^{3 χ} &^2→ R ^are an expression of the magnetic field component on the x , y and z direction respectively, and can be determined from Maxwell's equations or using numerical approximations, e.g., obtained from field measurements.

Applying the model to all the tuples relative to the buried transceiver k , the following system of equations is obtained:

that can be written in compact vectorial form as: y = /_e(b*) +v (6) where y,f_e (b^k),v R AN

The goal is thus to infer b^k from y which can be achieved by several criteria according to different embodiments of the invention. For instance, one of the solutions is based on the Least Squares (LS) principle by minimization of the residual b^k = arg iiiin j) y—

or the Weighted Least Squares (WLS) criteria, that coincides with the Maximum Likelihood estimator, where: h^k = argminfy - fg (h^k) ) '∑^{_ 1} (y— #(b^'fc))

(8) and ∑ is the covariance matrix of the noise term v that can be jointly estimated.

These computations become cumbersome as the number of measurements N increase. Present invention solves this problem computing an estimate for the unknown buried's position sequentially, that is processing the new tuple N as it arrives accounting for all previous tuples 1, 2, ..., N - 1 but avoiding reprocessing all the sets of observations which might be computationally demanding and very costly in terms of memory usage. This is done, according to different embodiments, using different techniques as for example the Recursive Least Squares (RLS) or the Kalman filter (KF), the latter requiring an additional equation modeling the evolution of the position of buried device k from b*(« -l) to b^k(n) . In general, the Kalman Filter solution can be implemented by means of any Bayesian filtering method, trading off between accuracy and computational complexity. It can be seen that in this case where the buried device is assume to be moving only slightly, both solutions are almost equivalent.

According to one embodiment of the invention, the LEM module additionally estimates, for each buried device k, the confidence region of the estimated position b^k(n), which can be expressed as, for example, the ellipsoid that is estimated to contain the actual position b^k at a certain probability, for example at a 95% confidence level. This confidence region can be computed by means of the confidence intervals in frequentist statistics or from the covariance matrix of the posterior distribution in Bayesian statistics.

One embodiment of the invention comprises a Graphical User Interface (GU I) which is depicted in Figure 4. The GUI provides the user (40) with information on the position of the detected avalanche victims (41 , 42) and the other rescuers (43, 44, 45) participating in the search operations and operating the same invention that are present in the area. The GUI uses distinct symbols to represent 1 ) buried transceivers and 2) devices of the type described in the present invention which are operated by rescuers to locate buried transceivers. Reference signals may also be provided by the GUI in order to assist the user to easily estimate distances and be aware of the area. Reference signals can be for example dash-lined concentric circumferences marking ten meters intervals (46), or any other visual marks.

Claims

1. - A system for locating transceivers which are emitting a wireless rescue signal, the system comprising at least two searching transceivers configured to detect said rescue signals wherein each one of the searching transceivers is characterized by comprising:

- a processing module configured for estimating a location of the transceiver emitting rescue signals based on the information of the position, the information of the orientation and the information, received from other searching transceivers through the communication module, about detected rescue signals, position and orientation.

2. - The system of claim 1 wherein the searching devices further comprising a display for showing, through a graphical user interface, a map of the search area.

3. - The system of any one of the previous claims wherein the processing module further comprising a clustering module configured for organizing into clusters the information about each one of detected rescue signals emitted from different transceivers, wherein each cluster corresponds to one emitting transceiver.

4. - The system of any one of previous claims wherein the processing module estimating a location of a transceiver emitting rescue signals is further configured for sequentially updating the estimation as new information is received.

5. - A searching device for locating transceivers which are emitting a wireless rescue signal, the searching device is characterized by comprising:

- a measurement module configured to detect said wireless rescue signals - a location module, configured for providing information of a position of the searching device;

6. - Method for locating transceivers which are emitting a wireless rescue signal, wherein at least two searching transceivers configured to detect said rescue signals are involved, the method is characterized by comprising the following steps: a) receiving, by a first searching transceiver, at least a wireless rescue

signal emitted from a transceiver, through a wireless communication network; b) obtaining information of its own position, through a first location module, its own orientation, through a first orientation module, and obtaining information about received wireless rescue signal, by the first searching transceiver; c) receiving, by at least a second searching transceiver, the same wireless rescue signal through a wireless communication network; d) obtaining information of second searching transceiver position, through a second location module, information of second searching transceiver orientation, through a second orientation module, and obtaining information about received wireless rescue signal, by the at least second searching transceiver; e) broadcasting the obtained information through a second communication module of the second searching transceiver; f) receiving, the first searching transceiver, the information broadcast by the at least second searching transceiver through a first communication module; g) estimating, by a processing module of the first searching transceiver, a location of the transceiver, being the estimation based on the information of its own position, the information about received wireless rescue signal and information received from the at least second searching transceiver.

7. - Method of claim 6 wherein the first searching transceiver detects two or more rescue signals, further comprising organizing into clusters the information about each one of detected rescue signals emitted from different transceivers, by a clustering module of the processing module.

8. - Method of claim 7, wherein two or more clusters gather the information about different rescue signals of different transceivers, further comprising estimating, by the processing module of the first searching transceiver, a separate location for each one of the transceivers emitting said different rescue signals.

9. - Method of any one of previous claims 6 - 8 wherein the information about received wireless rescue signals comprising measurements of signal strength and electromagnetic field direction.

10. - Method of any one of previous claims 6 - 9 wherein the information broadcast by a searching transceiver is provided with a numeric identifier which uniquely identifies the searching transceiver.

11. - Method of any of the previous claims 6 - 10 wherein estimating a location of the transceiver is based on modeling the information about received wireless rescue signals obtained by the searching transceiver with predetermined propagation models to set out a system of equations to be solved.

12. - Method of any one of the previous claims 6-1 1 wherein, when a new information is received by the first searching transceiver, further comprising processing the new information to estimate a more accuracy estimation of the location by applying a Recursive Least Squares or a Kalman filter.

13. - Method of any one of the previous claims 6-12 further comprising estimating a confidence region for the estimated position of each buried transceiver based on a measure of probability.

14. - Method of any one of the previous claims 6-13 further comprising showing in a display of the first searching transceiver, a graphical representation of the search area with the estimated location of one or more transceivers emitting wireless rescue signals, the position of other rescue transceivers in the search area, and the confidence region for the estimated position of each buried transceiver

15. - A computer program product comprising computer program code adapted to perform the method according to any of the claims 6-14 when said program code is executed on a computer, a digital signal processor, a field-programmable gate array, an application-specific integrated circuit, a micro-processor, a micro-controller, or any other form of programmable hardware.