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Title:
METHOD AND SYSTEM FOR THE LOCALISATION OF OBJECTS WITHIN AN ENVIRONMENT TO BE MONITORED
Document Type and Number:
WIPO Patent Application WO/2015/092825
Kind Code:
A1
Abstract:
The present invention concerns a method and system for the short-range localization, i.e. within tens of meters, of collaborative (active) objects, i.e. with communication means associated, and non-collaborative (passive) objects, i.e. without communication means associated. The method uses both radio ranging and ultrasonic ranging in order to determine presence and distances within and with respect of a network of anchor nodes. Radio ranging is used for active objects and ultrasonic ranging is used both for passive and active localization. The system can be used for localization in logistic, short-range navigation, security and surveillance, entertainment, tracking of goods and personnel, sensible area monitoring etc.

Inventors:
CHIANI MARCO (IT)
MAZZOTTI MATTEO (IT)
Application Number:
PCT/IT2014/000339
Publication Date:
June 25, 2015
Filing Date:
December 18, 2014
Export Citation:
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Assignee:
ALMA MATER STUDIORUM UNIVERSITY DL BOLOGNA (IT)
International Classes:
G01S1/20; G01S1/68; G01S1/72; G01S1/80; G01S5/02; G01S11/08; G01S15/00
Domestic Patent References:
WO2013008169A12013-01-17
Foreign References:
US20070265004A12007-11-15
US20050135292A12005-06-23
Attorney, Agent or Firm:
PERRONACE Andrea (ROMA S.p.A. Via Piemonte 26 -, ROMA, IT)
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Claims:
CLAIMS

1. Method for monitoring an environment, utilizing a network comprising a plurality of anchor nodes (1, 2a, 2b, 2n) synchronized with each other, each comprising a radio transceiver and an ultrasonic transceiver, characterised in that it comprises the execution of the following steps:

A. determining the topology of said network by means of a measurement of the mutual distances between nodes, as obtained by means of radio ranging and ultrasonic signal exchange techniques, further determining the acoustic visibility of each node with respect to all the other anchor nodes (1, 2a, 2b, 2n) , i.e. the absence of obstacles which interrupt the direct path of the ultrasonic signal between nodes;

B. sending ultrasonic signals from each anchor node of said plurality of anchor nodes (1, 2a, 2b, 2n) and detect the acoustic responses of said environment ;

C. on the basis of the responses of the environment in step B and said topology of step A:

CI. Obtaining at least an acoustic visibility map (V ap) , including information about the area reachable by the ultrasonic waves emitted by each node of said plurality of anchor nodes (1, 2a, 2b, 2n) ;

C2. Obtaining at least an objects map (iMap) including position of static and/or dynamic objects (O, N, A) in said environment;

D. sending radio waves from at least a subset of anchor nodes of said plurality of anchor nodes (1, 2a, 2b, 2n) and detecting the responses of possible radio transceiver devices (A) in said environment ;

E. on the basis of the radio responses obtained in step D:

El. identifying the positions of said radio transceiver devices (A) ;

E2. Combining the positions of step El with the positions of the objects in said at least an objects map (iMap) , associating each of said radio transceiver devices (A) to an object detected by- ultrasonic waves and including such an association in said at least an objects map (iMap) ;

F. continuously updating said at least an objects map (iMap) and said acoustic visibility map (VMap) by executing the following steps:

Fl. Selecting at least an object (O, N) contained in said at least an objects map (iMap) ;

F2. Sending ultrasonic and/or radio waves from a subset of said plurality of anchor nodes (1, 2a, 2b, 2n) that are acoustically visible with said at least an object selected in step Fl, according to said at least an acoustic visibility map ( VMap) ;

F3. Detecting the signals returned by said at least an object selected and updating said at least an objects map (iMap) and said at least an acoustic visibility map (VMap) accordingly.

2. Method according to claim 1, characterised in that in said step E2 said radio transceiver devices (A) are associated to persons authorised to access said environment .

3. Method according to any claim 1 to 2 , characterised in that in step A the distances between said anchor nodes (1, 2a, 2b, 2n) are estimated utilizing Ultra-Wideband (UWB) radio signals.

4. Method according to any claim 1 to 3 , characterised in that said plurality of anchor node (1, 2a, 2b, 2n) comprises a master anchor node (1) and a plurality of slave anchor nodes (2a, 2b, 2n) , the synchronisation operations preceding step A being performed by said master anchor node (1) , the mutual distances of step A being the distances between said master node (1) and said slave nodes (2a, 2b, 2n) .

5. Method according to claim 3 , characterised in that all the steps are executed using the subdivision of master anchor node and slave anchor nodes, in such a way that the master node organises the actions of and collects the information from the slave anchor nodes.

6. Method according to any claim 1 to 5 , characterised in that in step A each of said anchor nodes (1, 2a, 2b, 2n) sends, on a rotating basis, to each other anchor node (1, 2a, 2b, 2n) ultrasonic pulse-type signals, according to the principle of operation of the multi-static sonars.

7. Method according to any claim 5 to 6, characterised in that, for the synchronisation, said master anchor node (1) sends suitable periodic synchronisation radio signals termed "beacons" , said beacons signals containing the behaviour mode of each node of the network, i.e. the time information of the synchronisation steps that the node must perform.

8. Method according to any claim 1 to 7, characterised in that, in step B, each anchor node (1, 2a, 2b, 2n) is configured to receive and sample both the response to pulses sent from itself, as a mono- static sonar, and the response to pulses sent from other nodes, as multi-static sonar, utilising predefined information of synchronisation.

9. Method according to any claim 1 to 8, characterised in that said objects map and/or said visibility map in step C is three-dimensional.

10. Method according to any claim 1 to 9, characterised in that in step A the measurement of said distances by radio ranging is compared with the measurement of the same distances by ultrasounds according to the following steps:

- if a distance measured by radio ranging is substantially equal to the same distance as measured by ultrasounds, one assumes as valid measurement of the distance the value as measured by ultrasounds;

- if a distance measured by radio ranging is smaller than the same distance as measured with ultrasounds by a certain pre-defined quantity Δ, then the distance as measured by radio ranging is assumed as valid and one derives an acoustic visibility between nodes;

- if a distance measured by radio ranging is larger than the same distance as measured by ultrasounds by a certain pre-defined quantity Δ, an acoustic visibility between nodes is derived and the value measured by ultrasounds is assumed as valid.

11. Method according to claim 10, characterised in that :

to each anchor node (1, 2a, 2b, 2n) a ultrasonic transducer (T)is associated, which is oriented with respect to a reference direction, and in that:

for the calculation of said mutual distances between anchor nodes of step A, the orientation information of each node is used, in particular provided by orientation sensors associated to said anchor nodes (1, 2a, 2b, 2n) , which detect the acoustic emission direction with respect to said reference direction, as well as the temperature information provided by the temperature sensor associated to said nodes.

12. System (S) for the monitoring of an environment, comprising a network which includes a plurality of anchor nodes (1, 2a, 2b, 2n) synchronised with each other, a control unit for the control of said anchor nodes and a central processing unit (U) configured to process the data coming from said control unit and provide control information to said control unit, characterised in that said central processing unit comprises a series of processing modules (2, 3, 4, 5, 6, 7, 8, 9, 10, 11) installed on it and configured to obtain at least an objects map (iMap) containing the position of static and/or dynamic objects (0, N, A) in said monitored environment and at least a acoustic visibility map (VMap) representing the acoustic visibility field of the nodes of said plurality of anchor nodes (1, 2a, 2b, 2n) , according to steps A-F of the method of any claim 1 to 10.

13. System (S) according to claim 12, characterised in that to each anchor node (1, 2a, 2b,

2n) an ultrasonic transducer (T) is associated, oriented with respect to a reference direction, as well as a temperature sensor, and in that said series of processing modules comprises a processing module configured to use the orientation information of each node as provided by said orientation sensors and the temperature information provided by temperature sensors to execute step A.

Description:
Method and system for the localisation of objects within an environment to be monitored

*****

The present invention concerns a method for the localisation of objects within an environment to be monitored. The present invention further concerns a system which allows to implement the method.

More in detail, the invention concerns a method and a system of the above-mentioned type, designed and realised in particular for the short-range localisation, i.e. within some tens of metres, of collaborative (active) and non-collaborative (passive) objects, i.e. without communication means, both in internal and external localisation contexts, such as logistics, short-range navigation, security and monitoring, entertainment, goods tracking, personal tracking in risk areas, monitoring of sensible areas, safety at work, and that can be used for any other type of short-range localization.

In the following, the description will be directed to active and passive short-range localisation in closed environments, but it is evident that the same must not be considered limited to this specific application.

As it is well known, the today's short-range localisation networks are designed and configured to separately localise radio-transmitting devices, which are termed also collaborative or active or "tag" devices, and non-collaborative units as persons or things, therefore not provided with transmitting units, which are termed also passive or "targets", within an area to be monitored, giving rise therefore to the active localisation in the first case and the passive localisation in the second case.

Nowadays, there are different high precision localisation systems, for short-range applications, in real-time, which are termed "real-time locating systems" (RTLS) , having the only active localisation functionality.

These systems can be wired or wireless.

The wired systems comprise a network of "anchor" nodes, i.e. a network of receiving and transmitting units, connected with each other by means of a series of wired connections, which are needed for the synchronisation of the same anchor nodes, and a central node for the processing and fusion of the information, which exchanges information with the anchor nodes . These systems allow high precision position estimates of objects that are present in the environment to be monitored, because they are based on the time difference of arrival (TDoA) of the signals .

The wireless systems instead present the same infrastructure but are able to function without the need of synchronisation between the anchor nodes (for example the techniques utilised can be based on the estimate of the Time of Flight (ToF) or the Angle of Arrival (AoA) of the exchanged signals) . However, they allow to achieve a precision of localisation of objects present in the environment to be monitored, which is of medium quality, of the order of few metres.

There are moreover some RTLS ultrasounds systems, for example "Active Bat" or "Cricket" which exploit similar radio synchronisation mechanisms for the active localisation, i.e. the mobile active devices, which are synchronised by radio, and emit ultrasounds impulses in order to be localised by a fixed nodes network which receives the ultrasounds signals emitted by the active devices. The radio signals are not utilised instead for the active localisation (of the nodes or mobile active devices) and the ultrasounds signals are not utilised for the passive localisation.

It is evident that the known systems present different disadvantages.

A first disadvantage is represented by the separation of the active and passive localisations, the today's systems do not allow indeed to manage both localisations at the same time.

A further disadvantage, for some systems, is represented by the need of connecting the anchor nodes by connection and synchronisation cables, which require the proximity of the same anchor nodes . It is evident that it is expensive to connect consecutive anchor nodes in the presence of physical obstacles in the environment to be monitored.

In the light of the foregoing, it is therefore object of the present invention to realise a method and a system able to manage in a unified fashion the active and passive localisation of objects present in the same area, by means of heterogeneous technologies integration.

Another object of the invention is to realise a system devoid of cable connections between anchor nodes of the localisation network.

Another object of the invention is to speed up and reduce the exchange of data between the anchor nodes and the central processing node.

These and other results are obtained by the invention using a method and system of localisation of active and passive objects within an area to be monitored by means of the integration of different technologies.

It is therefore subject matter of the present invention a method for monitoring an environment, utilizing a network comprising a plurality of anchor nodes synchronized with each other, each comprising a radio transceiver and an ultrasonic transceiver, characterised in that it comprises the execution of the following steps:

A. determining the topology of said network by means of a measurement of the mutual distances between nodes, as obtained by means of radio ranging and ultrasonic signal exchange techniques, further determining the acoustic visibility of each node with respect to all the other anchor nodes, i.e. the absence of obstacles which interrupt the direct path of the ultrasonic signal between nodes;

B. sending ultrasonic signals from each anchor node of said plurality of anchor nodes and detect the acoustic responses of said environment;

C. on the basis of the responses of the environment in step B and said topology of step A:

CI. Obtaining at least an acoustic visibility map, including information about the area reachable by the ultrasonic waves emitted by each node of said plurality of anchor nodes;

C2. Obtaining at least an objects map including position of static and/or dynamic objects in said environment;

D. sending radio waves from at least a subset of anchor nodes of said plurality of anchor nodes and detecting the responses of possible radio transceiver devices in said environment;

E. on the basis of the radio responses obtained in step D:

El. identifying the positions of said radio transceiver devices;

E2. Combining the positions of step El with the positions of the objects in said at least an objects map, associating each of said radio transceiver devices to an object detected by ultrasonic waves and including such an association in said at least an objects map;

F. continuously updating said at least an objects map and said acoustic visibility map by executing the following steps:

Fl . Selecting at least an object contained in said at least an objects map;

F2. Sending ultrasonic and/or radio waves from a subset of said plurality of anchor nodes that are acoustically visible with said at least an object selected in step Fl, according to said at least an acoustic visibility map;

F3. Detecting the signals returned by said at least an object selected and updating said at least an objects map and said at least an acoustic visibility map accordingly.

According to an aspect of the invention, step E2 said radio transceiver devices are associated to persons authorised to access said environment.

According to an aspect of the invention, in step A the distances between said anchor nodes are estimated utilizing Ultra-Wideband radio signals.

According to an aspect of the invention, said plurality of anchor nodes comprises a master anchor node and a plurality of slave anchor nodes, the synchronisation operations preceding step A being performed by said master anchor node, the mutual distances of step A being the distances between said master node and said slave nodes.

According to an aspect of the invention, all the steps are executed using the subdivision of master anchor node and slave anchor nodes, in such a way that the master node organises the actions of and collects the information from the slave anchor nodes.

According to an aspect of the invention, in step A each of said anchor nodes sends, on a rotating basis, to each other anchor node ultrasonic pulse-type signals, according to the principle of operation of the multi-static sonars.

According to an aspect of the invention, for the synchronisation, said master anchor node sends suitable periodic synchronisation radio signals termed "beacons", said beacons signals containing the behaviour mode of each node of the network, i.e. the time information of the synchronisation steps that the node must perform.

According to an aspect of the invention, in step B, each anchor node is configured to receive and sample both the response to pulses sent from itself, as a mono-static sonar, and the response to pulses sent from other nodes, as multi-static sonar, utilising predefined information of synchronisation.

According to an aspect of the invention, said objects map and/or said visibility map in step C is three-dimensional .

According to an aspect of the invention, in step A the measurement of said distances by radio ranging is compared with the measurement of the same distances by ultrasounds according to the following steps:

- if a distance measured by radio ranging is substantially equal to the same distance as measured by ultrasounds, one assumes as valid measurement of the distance the value as measured by ultrasounds;

- if a distance measured by radio ranging is smaller than the same distance as measured with ultrasounds by a certain pre-defined quantity Δ, then the distance as measured by radio ranging is assumed as valid and one derives an acoustic visibility between nodes;

- if a distance measured by radio ranging is larger than the same distance as measured by ultrasounds by a certain pre-defined quantity Δ, an acoustic visibility between nodes is derived and the value measured by ultrasounds is assumed as valid.

According to an aspect of the invention:

to each anchor node a ultrasonic transducer is associated, which is oriented with respect to a reference direction, and in that:

for the calculation of said mutual distances between anchor nodes of step A, the orientation information of each node is used, in particular provided by orientation sensors associated to said anchor nodes, which detect the acoustic emission direction with respect to said reference direction, as well as the temperature information provided by the temperature sensor associated to said nodes .

It is further specific subject-matter of the invention a system for the monitoring of an environment, comprising a network which includes a plurality of anchor nodes synchronised with each other, a control unit for the control of said anchor nodes and a central processing unit configured to process the data coming from said control unit and provide control information to said control unit, characterised in that said central processing unit comprises a series of processing modules installed on it and configured to obtain at least an objects map containing the position of static and/or dynamic objects in said monitored environment and at least a acoustic visibility map representing the acoustic visibility field of the nodes of said plurality of anchor nodes, according to steps A-F of the method of the invention.

According to an aspect of the invention, to each anchor node an ultrasonic transducer is associated, oriented with respect to a reference direction, as well as a temperature sensor, and in that said series of processing modules comprises a processing module configured to use the orientation information of each node as provided by said orientation sensors and the temperature information provided by temperature sensors to execute step A.

The present invention will be now described by way of illustration but not by way of limitation, according to its preferred embodiments, with particular reference to the figures of the enclosed drawings, wherein:

figure 1 shows the architecture of the system of the invention during a step of self-configuration and initial synchronisation of the units composing it;

figure 2 shows the architecture of the system of figure 1 during a step of virtual reconstruction of the environment wherein it is placed;

figure 3 shows the architecture of the previous system during a step of identification of passive objects, or targets, which have smaller dimensions and are moving, and are in the environment wherein it is placed;

figure 4 shows the architecture of the previous system during a step of identification of active objects, or tags, which are in the environment wherein it is placed;

figure 5 shows a functional block diagram of a processing unit of the system that is subject matter of the invention.

In the various figures, similar parts will be indicated by the same reference numbers.

The system S is placed within an environment to be monitored and possibly to be represented graphically, and comprises a wireless fixed or moving localisation network. Such network can have different topologies, for example it can be star-shaped, or cluster-shaped, in order to manage multi-cell localisation systems.

The network is composed by a plurality of master and slave anchor nodes, in particular a master anchor node 1, and a plurality of slave anchor nodes 2a, 2b, ... , 2n.

The system S further comprises a central processing unit U which processes the information received by the master anchor node 1 by using a set of processing modules comprised by it, as it will be widely described in the following.

An anchor node at a time transmits an acoustic impulse, whilst all the nodes "hear" the environment response. Once the anchor nodes have sampled such a response, the data must be processed together by the central processor in order to execute imaging and localisation. Such data are therefore transmitted by each slave anchor node to the master anchor node, and from the latter to the central processing unit (by means of the channel C) . Such transmissions of data occur by radio, and they have been shown in the figure by unidirectional arrows, from the slave anchor nodes to the master anchor node.

As it is shown in figures 3 and 4, within the environment to be monitored a plurality of passive targets N is present, as fixed or moving objects or persons without communication units, and a plurality of active tags A is also present, usually electronic devices, which should be localised and possibly represented graphically.

The master anchor node 1 processes and reorganises the information acquired by the slave anchor nodes 2a, 2b, ... , 2n and by tags A present in the environment by means of known algorithms of imaging, trilateration and triangulation, filtering, tracking, identification and the like, as will it be described in detail in the following.

The slave anchor nodes 2a, 2b, ... , 2n deal with acquiring information on the surrounding environment by means of heterogeneous technologies working in close synergy, as it will be described in the following.

The electronic devices A, usually battery-powered, exchange information with the slave anchor nodes 2a, 2b, ... , 2n in order to allow to be detected, identified and localised in the environment. Such electronic devices A are provided with a radio interface which is able to communicate and perform range estimate operations with the slave anchor nodes 2a, 2b, ... , 2n of the network. Each master anchor node 1 and slave anchor node 2a, 2b, ... , 2n comprises in turn an internal processing unit, for example a microcontroller, not shown in figure, a radio communication interface R comprised of an antenna, which is used for the active localisation, the identification and the data exchange between nodes, and is also provided with a functionality of ranging, between the transmitting node and the receiving node, and an acoustic transceiver which receives and transmits ultrasonic signals of the impulsive type and is utilised for the passive localisation, the representation of the environment and the refining of the active localisation.

The radio interface R allows performing the information exchange without the necessity of using cable connections between the network nodes.

The master anchor node 1 is further equipped with a communication interface C, for example USB, Ethernet or the like, to exchange information with the central processing unit U.

The information flow between the nodes is based on communication standards for wireless sensors network (WSN) , for example of the IEE 802.15.4 or IEEE 802.15.4a type.

The master anchor node 1 and slave anchor node 2a, 2b, ... , 2n allow direct construction of the virtual image of the surrounding environment, individuating possible objects/persons which are in the environment, as it will be described in detail in the following.

As a result of the localisation process, the system allows to map objects and persons of the real world with precise references to their current geographical position and, therefore, to place them within a virtual space representing the area to be monitored.

As described above, the system S according to an embodiment of the invention employs integrated heterogeneous technologies .

In particular, the radio communication interface R allows to synchronise the ultrasonic modules T of the master anchor nodes 1 and slave anchor nodes 2a, 2b, ... , 2n, enabling the functionality of monostatic/multistatic sonar even in the absence of direct acoustic visibility between the anchor nodes.

In particular, in order to correctly combine the acoustic responses of the master anchor nodes 1 and slave anchor nodes 2a, 2b, ... , 2n, it is necessary that these responses are synchronised with each other, i.e., if any anchor node of the network transmits an acoustic impulse, all the other anchor nodes of the network must begin to sample at the same time the received signal, starting in the same time instant.

If the anchor nodes are in direct acoustic visibility with each other (i.e. if the ultrasounds can run without obstacles between the nodes) , they can synchronise with each other also a posteriori, i.e. being known the reciprocal positions between the anchor nodes and the instant of reception of the impulse emitted by one of the anchor nodes, it is possible to calculate the instant in which the impulse has been emitted by that anchor node.

If instead the anchor nodes are not in direct visibility with each other, they fail to receive directly the impulse emitted by a certain anchor node but they receive only reflected echoes. In such a case, the radio communication interface R can emit a radio signal in order to synchronise the anchor nodes of the network even in the absence of mutual direct visibility.

Besides the data acquired by means of the ultrasonic sensors and the radio ranging interfaces, other information can be communicated by the master anchor nodes 1 and slave anchor nodes 2a, 2b, ... , 2n, of the network to the central processing unit U, such as the orientation of the nodes or the ambient temperature .

These collateral information are available if the nodes are equipped with suitable sensors, such as inclinometer, electronic compass and temperature sensor, and can be utilised by the central processing unit U in order to improve the detection of network configuration and the estimate of the ambient parameters influencing the localisation process, such as for example the sound propagation speed.

Making now reference to fig 5, as described above, the central processing unit U comprises a set of processing modules.

A first module 2 for the processing of the ultrasonic responses and the data of radio ranging or "raw data processing module" processes and conditions in real time the input data; a second module 3 of estimate of the network geometry or "inter-A ranging module" estimates the relative distances between all the anchor nodes of the network, on the basis of the received ultrasonic and radio ranging data; a third module 4 for the processing of the network geometry or "AN network geometry estimation module" calculates exactly the network geometry on the basis of the data received by the second module 3; a fourth module 5 for the management of the control signals to the network or "sensor Network Manager module" manages the functioning of the network in a dynamic and adaptive way; a fifth module 6 for the construction of a map or "quasi-static image formation module" constructs a three-dimensional map of the environment by means of imaging operations of the known type; a sixth module 7 for the detection of the targets N or "dynamic target localisation module" detects the position and the displacement of the targets N within the environment to be monitored, as it will be explained in detail in the following; a seventh module 8 for the detection of tags A or "radio identification and localisation module" processes the radio ranging information received by the tags A; a eighth module 9 for the integration of the data or "object shape processing and data fusion module" combines and integrates the ultrasonic data with the radio data to provide indication about the presence of targets N and tags A in the environment to be monitored; a ninth module 10 for the optimisation of the localisation or "multi-target tracking module" improves the accuracy of the localisation of the targets N and tags A consequent to the reception of the information transmitted by the eighth module 9; finally, a tenth module 11 for the visualisation or "viewer module" allows to make visible and enjoyable the information about the position and identity of tags A and targets N present in the environment to be monitored and allows moreover to visualise the three- dimensional map of the surrounding environment, termed "iMap" .

Functioning of the system The functioning of the above described system S is as follows according to certain steps.

When it is necessary to monitor an environment, the master node 1 and slave nodes 2a, 2b, .. , 2n of the system S are positioned according to a suitable topography, within the same environment.

Initially, the system S must auto-configure, during a step of auto-configuration. Making reference to figure 1, the master anchor node 1 works as coordinator of the network because it sends signals, such as functioning and synchronisation parameters, to the slave anchor nodes 2a, 2b, ... 2n.

The auto-configuration step, consists of automatic procedures for the measurement of the reciprocal distances between the master node 1 and the slave nodes 2a, 2b, ... , 2n of the network.

In a first part of the first step, termed radio ranging, the measurement of the distances occurs by means of known radio ranging operations, according to which two nodes estimate the reciprocal distance by transmitting to each other data packets and by estimating their time of flight (ToF) , i.e. the time needed by the data packets in order to travel from one node of the network to the other.

Starting from the ToF and knowing the value of the light propagation speed, it is possible to estimate the distance between nodes. By knowing all the relative distances between the nodes, it is possible therefore to estimate the relative position of the nodes of the network, drawing its topology which precise metric references.

The radio ranging step gives back a measurement Dr expressed in metres or centimetres. In order to estimate with good precision the distances between the nodes, ultra-wide band (UWB) radio signals are used, because they allow to identify with high precision the instant of reception of the signal .

Once the ranging radio step is terminated, the system S executes a second ultrasonic estimate, or ultrasonic ranging, wherein a further estimate of the distances between the nodes is effected by acoustic measurements, in order to make more accurate the estimate of the reciprocal distances obtained in the previous radio ranging.

In particular, coordinated by the master anchor node 1, each slave anchor node 2a, 2b, 2n of the network sends in rotation ultrasonic signals of the impulsive type which are received by the other slave anchor nodes 2a, 2b, ... , 2n of the network, according to the functioning principle of the known sonar multi- static systems.

Being all the slave anchor nodes 2a, 2b, ... , 2n synchronised with each other, each nodes can estimate a ToF, i.e. the time elapsed between the emission of the signal and its reception.

Starting from this acoustic ToF and the knowledge of the sound propagation speed, it is possible to estimate the distance between the transmitting node and any receiving node with a precision of the order of centimetres .

The ultrasonic ranging step gives back a measurement Ds in metres or centimetres.

Once all the values Dr and Ds have been obtained, one performs a comparison between them.

If Dr is approximately equal to Ds, one assumes as valid measurement of the distance between the nodes the value Ds because it represents a more accurate measurement .

If Dr is smaller than Ds by a certain predefined quantity Δ, then one assumes as valid measurement of the distance between the nodes the value Dr because in this case one assumes that there is no acoustic visibility between the nodes.

The case wherein Dr is larger than Ds by a certain predefined quantity Δ, is not very significant because it happens when there is already an acoustic visibility between the nodes, therefore one presumes there is also radio visibility.

In such a way, by comparing the relative distance estimates obtained by the two signal typologies, radio and ultrasonic type, it is possible to recognise automatically whether two slave anchor nodes 2a, 2b, ... , 2n are in acoustic visibility with each other or there are obstacles impeding the direct path of the signal.

It is possible to install temperature sensors on the slave anchor nodes 2a, 2b, ... , 2n to correct the propagation speed utilised in the distance calculation, with the known formula space = speed x time, in order to further improve the accuracy of the estimate.

All the data obtained in the radio ranging step and ultrasonic ranging step are transmitted to the master anchor node 1 and, thereby, to the data processing central server U and in particular to the first module 2, second module 3, and third module 4.

The first module 2 processes in real time the ultrasonic responses and the data relevant to the radio rangings received by the master anchor node 1. In particular, these received data are suitably- filtered and averaged in order to reduce the effects of the random disturbances. The impulsive multistatic and monostatic responses coming from the ultrasonic transducers T are elaborated by eliminating possible disturbances of self-coupling that are in the signal. Moreover, residual time deviations between the signals are eliminated by applying known techniques for the estimate of the time of arrival ToA.

The second module 3, starting from the data of the first module 2, estimates the relevant distances between all the master anchor node 1 and slave anchor nodes 2a, 2b, ... , 2n.

Finally, the third module 4, on the basis of relative distance information provided by the second module 3, elaborates the overall geometry of the network .

This third module 4, moreover, during the construction of the geometry of the network, takes into account the additional information relevant to the inclination or orientation of the nodes. Such information can be provided automatically by the sensors network or inserted manually by the technician or user of the system S.

In this first step of auto-configuration, as well as in the other steps, the coordination performed by the master anchor node 1 by the radio transmission of suitable synchronisation or periodic beacon signals is important .

Particular, each slave anchor node 2a, 2b, ... , 2n, consequent to the reception of a periodic beacon, synchronises its own time reference or clock with that of all the others. Moreover, within the beacon packets the behaviour mode of each network node is contained, i.e. when each node must transmit a ultrasonic signal and when instead it must receive signals from other nodes, when it must re-tune and when it must transmit by radio the collected information and the samples, allowing the multistatic functioning of the network by means of exchanges without any cable.

Making now reference to figure 2, subsequently to the first step, the system S executes a step B of three-dimensional reconstruction of the environment wherein the system S is positioned, i.e. a 3D imaging, in order to detect the position of stationary objects 0 that are in the environment.

Once the positions of all the network nodes are known, following the first step, it is possible to estimate the presence and the position of walls, shelves, furniture, obstacles and other static objects 0 within the monitored area and to represent these objects graphically.

The second step consists of an environment inspection procedure or sounding and an environment image reconstruction procedure.

In particular, during the sounding, coordinated by the master anchor node 1, in rotation each slave anchor node 2a, 2b, ... 2n sends acoustic signals of the impulsive type. Each network node samples the received response and transmits it by radio to the master anchor node 1 which, in turn, forwards it to the central processing unit U and in particular to the module 6.

In this step, each slave anchor node 2a, 2b, ... , 2n is able to receive and sample both the response to impulses sent by itself, as monostatic sonar, and the response to impulses sent by other nodes, as multistatic sonar (each node listens to the signals emitted by each node) .

The responses to the impulses sent by different nodes do not superimpose thanks to the synchronisation and coordination functions executed by the master anchor node 1.

In the reconstruction procedure, by means of suitable known algorithms of signal processing, it is possible to construct three-dimensional maps, or 3D images, by the fifth module 6.

In particular, a map is constructed, termed "iMap", of the monitored area, which represents the geography of the environment wherein the position of obstacles or static objects 0 or moving objects N is represented, and a map, termed VMap is constructed, which keeps track of the visibility of the points in space in relation to the anchor nodes and represents the acoustic visibility field of the anchor nodes 1, 2a, 2b, ... , 2n, wherein the environment acoustic response to ultrasound emitted by each anchor node 1, 2a, 2b, ... , 2n is utilized.

These maps are updated continuously on the basis of the changes detected within the area to be monitored by the anchor nodes, during further steps which are described in detail in the following.

In order to construct these maps, the fifth module 6 combines the ultrasonic signals received by the various anchor nodes by means of known techniques derived from the decision and estimate theory, from the information theory and from machine learning algorithms . The environment to be monitored is discretised into a set of points, uniformly distributed or not, for each of them being evaluated the probability that an object is present, which reflects the impinging signal, and the probability that the condition of visibility with the different anchor nodes of the network is verified. In order to calculate the probability that in a given point of the space an object is present, information about the visibility from the same point to the different anchor nodes of the network is needed. Vice versa, in order to estimate the probability that a point is in visibility with a given anchor node, one needs to know which objects are present in the area and prevent the propagation of the signal. The utilised techniques are the estimate iterative techniques and the statistical inference techniques for the determination of such 3D maps, such as known algorithms of message passing between space points or of expectation-maximisation.

Making reference now to figure 3, once the second 3D imaging step B is terminated, the system S proceeds with the detection and localisation of the non- collaborative targets N, during step C of non- collaborative identification.

With reference to figure 3, during step B, also the identification and the localisation of the moving target objects N occurs, therefore the acquisition and the transmission of the information from the slave anchor nodes 2a, 2b, ... , 2n to the master node 1 and to the central processing unit U occurs in a way analogous to the foregoing, it is then the task of the central processing unit U to process information with different modes, depending on whether one wishes to localise static or dynamic objects.

In particular, the sixth module 7 for the detection of the targets N operates on the basis of the ultrasonic responses received by the anchor nodes . The utilised techniques are known and belong to the field of decision and estimate theory which allow to combine in an optimal way the received ultrasonic signals, constructing, for the various points of the discretised space, optimal or sub-optimal detection metrics. Alternatively, traditional algorithms in the field of sonar/radar detection can be used, which are based on the estimate of ToA of the reflected signals and on trilateration techniques. In both cases, it is of fundamental importance the knowledge of the visibility map, VMap, provided by the fifth module 6, which allows to identify the information coming from those anchor nodes that are effectively useful for the localisation and to discard the useless signals.

In order to highlight the signals reflected by the moving targets N and discard the echoes due to the other static objects 0, one can use known techniques for the removal of the clutter, such as high-pass filters. When considerable changes in the geometry of the surrounding environment are detected, for example because of big moving targets N, an update request is sent to the fifth module 6, forcing the updating of the static image of the surrounding environment and therefore of the VMap and iMap maps, as it will be explained in detail in the following.

Once the map creation step is terminated, this step of continuous updating of the maps iMap and VMap begins .

In particular, the updating step provides the following sub-steps:

a first sub-step wherein the first static object O or a moving target N is selected, which is contained in the objects iMap map;

a second sub-step wherein one has the emission of ultrasounds from a subset of anchor nodes 1, 2a, 2b, ... , 2n which are in visibility, according to the map VMap of visibility with the object selected in the first sub-step;

and a third sub-step of detection of the backward ultrasounds and calculation of the position of the static objects O or the moving targets N in the environment to be monitored.

Once the updating step is terminated, one proceeds with the step wherein the objects map iMap is continuously updated by executing the following sub- steps :

a first sub-step of identification of at least a collaborative object tag A, i.e. a device provided with means of communication with the anchor nodes 1, 2a, 2b, ... , 2n, contained in the objects map iMap;

a second sub-step of emission of radio signals from a subset of anchor nodes 1, 2a, 2b, ... , 2n which come out to be close to the collaborative tag A;

a third sub-step of calculation of the position of the collaborative tag A for the exact localisation within the environment to be monitored.

In particular, in the first sub-step each tag A coming in radio visibility of the network synchronises with the beacon signal emitted by the master anchor node 1 and sends a join request to the network, which the master anchor node 1 receives and processes. If the tag A is recognised and accepted, the master anchor node 1 and the central processing unit U know the presence and the identity of the tag A in the monitored environment . Once the tag A is recognised, the second sub-step is initiated in order to localise the tag A within the environment .

To this end, with reference to figure 4, the master anchor node 1 starts periodically the procedure of radio ranging between the tag A and the slave anchor nodes 2a, 2b, 2n of the network.

When authorised by the master anchor node 1, the tag A exchanges information of radio ranging with the subset of slave anchor nodes 2a, 2b, ... , 2n indicated by the master anchor node 1.

The reciprocal distances between the tag A and the slave anchor nodes 2a, 2b, ... , 2n are calculated on the basis of the estimate of the ToF of the exchanged packets and are then communicated from the tag A to the master anchor node 1, which forward them to the central processing unit U, in particular to the eighth module 8 which processes the information of radio ranging.

By knowing the positions of the slave anchor nodes 2a, 2b, ... , 2n of the network, the eighth module 8 is able to localise the tag A by means of known operations of triangulation/trilateration.

Both during the execution of step B and step D, the system S uses the support of the fourth module 5 to manage the anchor nodes network in a dynamic and adaptive way.

In particular, the fifth module 5 coordinates the frequencies with which the tags A are to be interrogated and specifies the list of the anchor nodes that have to be involved in the identification and localisation of the different tags A which are present. In such a way, one can select in a dynamic way the optimal subset of anchor nodes which the tag A has to interrogate in order to make itself localise by the system S.

Analogously, the fourth module 5 can request that only some anchor nodes of the network transmit ultrasonic signals for the localisation of targets N and tags A. By an adaptive management of this type, the transmissions of the radio and ultrasonic signals in the proximity of the detected targets N and/or tags A can be intensified, avoiding to waste resources in the zones wherein no activity has been detected.

In particular, one can disable the transmission of ultrasonic pulses, or one can reduce the number thereof, for those anchor nodes which are not in direct visibility with the detected object.

The identification of an optimal subset of network anchor nodes allows also to realise a visibility map V ap optimised on the basis of the most important information.

Once the tags updating step is terminated, for the applications of the system S to surveillance or video- surveillance of environments, this system S executes a step of integration of radio and ultrasonic data, by means of the eighth module 9, wherein the collaborative tags A are associated to moving persons detected by means of ultrasounds, thus identifying the persons authorised to transit in the monitored zone.

In particular, the input data from the seventh module 8, relevant to the tags A, are associated to the input data of the sixth module 7, relevant to moving persons or targets N, detected by ultrasounds, thus identifying the persons authorised to stay in the monitored zone.

The information on the position of the various targets N detected by means of ultrasounds signals is combined with the positions estimated for the tags A by means of known techniques of data association, mainly based on the proximity.

The information about the objects moving in the monitored environment are merged by means of known algorithms of clustering, which are able to distinguish and separate the single targets N.

This integration allows to differentiate between authorised and unauthorized targets N.

At this point the module 9 is able to provide information about the presence and position of collaborative and non-collaborative targets N within the area.

By the radio identification of the collaborative tags A, it is possible moreover to distinguish between authorised and unauthorised subjects.

The last described step comprises a step of optimisation of the localisation realised by the ninth module 10.

To the end of improving the accuracy of localisation, the information provided by the eighth module 9 are processed by means of tracking algorithms exploiting knowledge of the trajectories followed by the various targets N.

To this end, there are various known solutions characterised by different performances and computational complexity, such as Kalman filters, Bayesian tracking, particle filters, PHD filters and like.

The output of these ninth module 10 is constituted by the information about the identity and the position of the various tags A and targets N within the environment .

Such information are provided to the fourth module 5 to the end of coordinating the future detections, and to the tenth module 11 of visualisation.

Said tenth module 11 allows the visualisation of the position and identity of the tags A and targets N present in the environment. It allows moreover to visualise the three-dimensional map of the surrounding environment, the iMap. This module can also be interrogated remotely, for example by means of a web server to allow the access from Internet.

As it is evident, the subject system S allows to realise, with an only integrated network, functionalities of active and passive localisation and imaging of the environmental be monitored.

Having recourse to different technologies, such as radio and ultrasounds, allows to take advantage from the different physical characteristics of the signals, such as propagation speed, bandwidth, in order to realise a localisation system with low complexity and extremely low development and implementation costs.

Another advantage is represented by the possibility of synchronising the nodes of the network without the use of cables.

Another advantage is represented by the simplicity of installation of the network by means of auto- configuration procedures .

Finally, the costs of the hardware and software components and the costs for the installation of the network are definitely low.

The present invention has been described by way of illustration, but not by a way of limitation, according to its preferred embodiments, but it is to be understood that variations and/or modifications can be made by those skilled in the art without thereby- falling outside the relevant scope of protection, as defined in the enclosed claims.