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Title:
METHOD AND SYSTEM FOR THE LOCALIZATION OF OBJECTS IN WIRELESS SPONTANEOUS NETWORKS
Document Type and Number:
WIPO Patent Application WO/2009/061259
Kind Code:
A1
Abstract:
The invention relates to a method and a system for the localisation of objects in wireless spontaneous networks where the said objects carry a target unit PTR (10). The method is characterised in that spontaneous networks are formed during the use of at least one search unit SSR (20) and one second search unit (30) designed for contact not only with the target unit PTR but also with each other through wireless short-range communication, a search application server SAS (40) designed to administer search tasks to and from the spontaneous networks via the first search unit SSR, that each target unit PTR (10) has been assigned a unique identity that can be registered and in that when contact is established with any one of the search units (20, 30) a message (3) is generated to which data is associated based on the identity of the target unit PTR from the search unit that has made contact, including its position (80:1 ) when the contact was established, that the second search unit DSR moves around the said first search unit SSR and that the message that is generated when contact is established with the target unit PTR is transported backwards to the search application server SAS via the first search unit SSR.

Inventors:
MALM THOMAS (SE)
JAKOBSSON ADRIAN (SE)
Application Number:
PCT/SE2008/051098
Publication Date:
May 14, 2009
Filing Date:
September 29, 2008
Export Citation:
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Assignee:
MALM THOMAS (SE)
JAKOBSSON ADRIAN (SE)
International Classes:
G06K7/00; G01S13/74
Domestic Patent References:
WO2005065363A22005-07-21
WO2007006085A12007-01-18
Foreign References:
US20050246248A12005-11-03
US20030137968A12003-07-24
US20060253590A12006-11-09
Other References:
See also references of EP 2212826A4
Attorney, Agent or Firm:
ZACCO SWEDEN AB (Sveavägen 151, Stockholm, SE)
Download PDF:
Claims:

CLAIMS

1. A method for the localisation of objects in wireless spontaneous networks in which each object carries a passive target unit PTR (10) with a unique identity that can be electronically registered, whereby:

- a number of first search units SSR (20) are arranged;

- a number of second search units DSR (30) are arranged to be mobile, moving along pathways or in a similar manner, relative to the first search units;

- that the first search units SSR, the second search units DSR and the target units PTR are designed for their mutual contact and the formation of spontaneous networks through short-range communication;

- that either the first search units SSR (20) or the second search units DSR (30) is equipped for the generation of electronic messages and the determination of the geographical position of the search unit; - that a search application server SAS (40) is arranged for communication with the first search units SSR; c h a r a c t e r i s e d i n that in the event of spontaneous contact between any one of the search units (20, 30) and a passive target unit PTR (10) a message (3) is generated by the search unit making the contact; that based on the unique identity of the relevant target unit PTR, associated data is attached to the message from the search unit that is making contact, including the position

(80:1) of the search unit when contact was made; that the. message that is generated on contact is transmitted backwards through the network over short-range communication to a first search unit SSR (20) and subsequently from this search unit to the search application server SAS (40).

2. The method according to claim 1 , whereby the message (3) is transmitted from the first search unit SSR (20) to the search application server SAS (40) along a fixed line (110) or over the internet.

3. The method according to either claim 1 or 2, whereby not only information about the geographical location (80:1) at which contact was established with the target unit PTR (10) is added to the message (3), but also information about the geographical location (80:2) at which contact was lost.

4. The method according to claim 3, whereby several supplementary geographical points (80:1a, 80:1 b-80:1 n) are periodically logged during the interval between contact being

established (80:1) and contact being lost (80:2) between the target unit PTR (10) and the search unit (20, 30), and that these supplementary geographical points are used for calculation of the geographical position of the target unit PTR.

5. The method according to claim 4, whereby the strength of signal between the second search unit DSR (30) and the target unit PTR (10) is measured at the logged geographical points (80:1a, 80:1 b-80:1 n) and in that the distance between the passing second search unit DSR and the target unit PTR is calculated based on the measured strength of signal at the logged points.

6. The method according to claim 5, whereby the distance is calculated by a CPU (34) that is a component of the second search unit DSR (30), and in that the said distance data is added to the message (3).

7. The method according to any one of claims 1-6, whereby search tasks are administered to the spontaneous network as a search lists (2) that are transferred via a first line (110) or over the internet from the search application server SAS (40) to the first search unit SSR (20).

8. The method according to claim 7, whereby the search list (2) is transmitted through the spontaneous network from the first search unit SSR (20) to the second search unit (30) via short-range communication.

9. The method according to any one of claims 1-8, whereby ZigBee, Z-wave, WPAN (wireless personal area network), Bluetooth or a similar standard is used for short-range communication between the search units SSR (20) and DSR (30) and with the target unit PTR (IO).

10. The method according to any one of claims 1-9, whereby the first search unit SSR (20) is arranged to be stationary with a location at a building such as a house or similar.

11. The method according to any one of claims 1-10, whereby the second search unit DSR (30) is arranged to be mobile with a location at a moving object such as a vehicle, a hire car, a postal vehicle or similar distribution vehicle, or a bus, tram or train.

12. The method according to any one of claims 1-11 , whereby each one of the search units SSR and DSR is arranged to permit "anchoring" of the target unit PTR (10) and that in

the event that radio contact with the target unit PTR is lost to generate a message that is transported back to the search application server (40).

13. A system for the localisation of objects in wireless spontaneous networks comprising: several passive target units PTR (10) each one of which has a unique electronic identity that can be registered, and which are intended to be arranged to be carried by the objects; a number of first search units SSR (20); a number of second search units (30) arranged to be mobile, moving along a pathway or in a similar manner, relative to the first search units; a search application server SAS (40) designed for communication with the first search units SSR (20); that each passive target unit PTR (10), the first search units SSR (20) and the second search units (30) comprise a radio module (11 , 21 , 31 ) that allows spontaneous short-range communication between the units; that either one of the first search units SSR (20) and the second search units DSR (30) comprises a CPU (34) for the generation of a message (3), and a GPS module (33) for the generation of information about the position of the search unit, c h a r a c t e r i s e d i n that the message is arranged to be generated on spontaneous contact between any one of the search units SSR, DSR (20, 30) and a target unit PTR (10), that based on the identity of the target unit PTR information about the position (80:1) of the search unit that is making contact when contact was established is added, whereby the message generated is arranged to be transmitted backwards through the spontaneous network that has formed to any one of the first search units SSR and from this search unit onwards to the search application server SAS (40).

14. The system according to claim 13, whereby both the first search unit SSR (20) and the second search unit DSR (30) comprise a CPU (24) for the generation of a message (3) and a GPS module (23) for the generation of information about the position of the search unit.

15. The system according to either claim 13 or 14, whereby the arrangement for communication between the first search unit SSR (20) and the search application server (40) comprises a first line (110) or the internet.

16. The system according to any one of claims 13-15, whereby the second search unit

DSR (30) comprises protocols that allow the transport of the message (3) that has been generated on contact between the target unit PTR (10) and the second search unit (30) such

that this is transmitted backwards to the first search unit SSR (20) via wireless short-range communication in the spontaneous network that has formed.

17. The system according to claim 15, whereby the arrangement for communication is designed for the transfer of search tasks and the searching for specific target units PTR (10) in the spontaneous network that has formed, which search tasks, administered in the form of search lists (2), are transferred from the search application server SAS (40) to the first search unit SSR (20).

18. The system according to any one of claims 13-17, whereby each search unit SSR

(20) and DSR (30) has been assigned an electronic identity that can be registered.

19. The system according to claim 18, whereby the search units SSR, DSR comprise protocols that add information about the position (80:1) of the relevant search unit when spontaneous contact is established with a target unit PTR (10).

20. The system according to claim 19, whereby the protocol is a ZigBee or Bluetooth protocol.

21. The system according to any one of claims 13-20, comprising a user terminal UT (50) such as a normal personal computer PC that is connected to the search application server SAS (40) via a first line or the internet.

22. The system according to any one of claims 13-21 , comprising a database (60) for the storage of verification lists (4) containing the results of searches carried out.

23. The system according to claim 22, whereby the verification list (4) comprises information about location, date and time that has been delivered by the search application server (40).

24. The system according to either claim 22 or 23, comprising a password associated with the identity of the target unit PTR (10) and which password must be specified for logging in to the database (60).

Description:

Method and system for the localization of objects in wireless spontaneous networks

The present invention concerns a method for the localisation of objects in wireless spontaneous networks according to the introduction to claim 1 and a system for the localisation of objects in wireless spontaneous networks according to the introduction to claim 16.

BACKGROUND TO THE INVENTION

The localisation of objects such as, for example, stolen goods; missing persons and animals; persons, goods or vehicles for which the police are searching and that are in motion or stationary, etc., is a technical area that has developed in parallel with the development of an improved GPS system (where "GPS" is an abbreviation for "global positioning system") and refined radio and mobile technology. Modern technology makes possible, among other operations, the rapid and efficient localisation of an object if this has been equipped with a suitably designed mobile telecommunication unit. In order to transfer information about the location, position, status and possibly other information about an object, conventional localisation systems use the global positioning system, GPS, and conventional mobile telephone technology, GSM and 3G. The position and location of the object in question can be transmitted to its owner, relatives, authorities, etc., by the determination of its position and the placing of a telephone call over the mobile telephone network. One disadvantage of known systems is that they require a subscription with a third party operator, such as a mobile telephone operator that owns the mobile telephone network and that receives and processes the signals. This in turn leads to the systems becoming unnecessarily expensive and complicated, and to all extents and purposes available solely for a few stakeholders and authorities. The Involvement of a third party and the insight and supervision that such parties obtain into one's own operations may in certain cases lead to a reluctance of certain stakeholders to use such conventional localisation systems.

Since known localisation systems use conventional mobile communication systems such as GSM and 3G for the wireless transfer of information, these systems have the disadvantage that they require relatively high transmitter powers, and this in turn means that the systems consume relatively large amounts of energy, and have a limited operating period. The target units of known localisation systems are provided with timers, with which it

is possible for them to work intermittently, in order to reduce the of consumption of energy. The timer enables the unit to be switched on and switched off at suitable intervals.

THE PURPOSE OF THE INVENTION

The purpose of the present invention is thus to achieve a method and a system for the localisation of objects in wireless spontaneous networks that make it possible to simplify the technology and provide it more cheaply. In particular, a system is aspired to that makes it possible to search efficiently for objects in formed wireless spontaneous networks with the aid of the cheap short-range technology WPAN technology (where "WPAN" is an abbreviation for "wireless personal area network"), and technology in which the user does not depend on mobile telephony cover and a subscription with any third party operator. It would be possible in this way not only to hold the investment costs at a low level, but also to obtain a system that not only consumes very little power but also provides a long operating period.

SUMMARY OF THE INVENTION

The purpose of the invention is achieved according to the properties and characteristics that are specified by claim 1 and 13, respectively.

According to one aspect of the present invention, a method for the localisation of objects in wireless spontaneous networks is achieved where the said objects incorporate a passive target radio, PTR. The spontaneous network is formed during the use of at least one stationary search unit SSR and one distributed search unit designed for contact not only with the target unit PTR but also with each other through wireless short-range communication, a search application server SAS designed to administrate search tasks to and from the spontaneous network though the stationary search unit SSR. Each target unit PTR has been assigned a unique searchable identity such as, for example, a MAC address, a radio node ID, an RNID address or similar, and when contact is established with any one of the search units a message is generated to which associated data is attached that is based on the electronic network identity of the PTR of the target unit, from the search unit that is seeking contact, including its geographical position when the contact is established. The distributed search units DSR are arranged to move in pathways around the said stationary search unit SSR and the message that is generated when contact is established with the target unit PTR

is transported backwards to the search application server SAS via the stationary search unit SSR.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows schematically the units that are components of the system for the localisation of objects according to the present invention.

Figure 2 shows schematically a typical design of the system according to the invention. Figure 3 shows a block diagram for a target unit PTR, a component of the system according to the invention.

Figure 4 shows a functional diagram for the target unit PTR according to Figure 3. Figure 5 shows a block diagram for a stationary search unit SSR 1 a component of the system according to the invention. Figure 6 shows a functional diagram for the stationary search unit SSR according to

Figure 5.

Figure 7 shows a block diagram for a distributed search unit DSR 1 a component of the system according to the invention.

Figure 8 shows a functional diagram for the distributed search unit DSR according to Figure 7.

Figure 9 shows a search list generated by a search application server that is a component of the system.

Figure 10 shows a message generated by a search unit that is a component of the system following contact with a target unit that is in the same way also a component of the system and that is carried by the search object.

Figure 11 shows a verification list with data that has been inserted and stored in a database that is a component of the system.

DETAILED DESCRIPTION OF THE INVENTION

A system is described below that uses any suitable short-range system of the type that offers licence-free frequency bands and the establishment of a spontaneous wireless personal data network, a "wireless personal area network" (abbreviated as "WPAN") of, for example, IEEE 802.15 standard, ZigBee or Bluetooth. Such system have the advantage that they allow the transfer of simple messages and data between different digital active radio units, known as "nodes", with a low consumption of energy. The system is described in detail based on the use of what are known as "ad hoc" protocols in urban environments such as a

town, built-up area, or community. It should, however, be understood that the system can be used within a number of different environments and regions where vehicles, mobile units, people or other objects move along pathways, for example at different types of terminal and warehouses, bus and train stations, large office buildings, etc. The nodes in spontaneous wireless networks do not need to know in advance the topology of the network that surrounds them: they must determine this. The principle is based on new nodes (at freely chosen times) broadcasting their presence and attempting to detect messages sent out (known as "hello" messages) from their neighbours. The nodes obtain in this way knowledge of the new nodes and one or several ways of reaching them. Such systems are built up as distributed networks of radio units in which each unit has a unique identity (an id number) in the form of a suitable electronic network address, such as, for example, 0.0.12.117.65.32, and properties adapted for its role in the system. The system communicates over longer distances by the information being sent onwards between the radio units (the nodes) with the aid of the "mouth-to-mouth" method. The protocol of the system is constructed with short, simple commands that control the various functions in the network. All search units that are included in the system have a search list of objects whose position is desired.

An example of such a search list is shown in Figure 9 denoted by the reference number 1. The search list 1 contains information about the identity of the search object, the search priority, the remaining duration of the search period, and the geographical limits of the search region. The search list 1 can be distributed among the mobile units, and this means that they do not need to be in direct contact with a supervisory system.

The system consists principally of four types of unit, illustrated in Figure 1.

- a target unit 10, a "passive target radio", PTR - search units 20, 30, a stationary search radio, SSR, and a distributed search radio,

DSR

- a server unit, 40, a search application server, SAS.

Figure 3 shows the target units PTR 10 in more detail. The target unit PTR 10 is used to label an object. The target unit PTR 10 is to demonstrate low consumption of power and it is to operate for at least 3 years. It is furthermore to demonstrate a range of radio communication of 50 to 1 ,000 metres. In order to function in the manner intended, the target unit PTR 10 comprises the following parts:

- a System-on-Chip radio transceiver module 11 (a radio module) that includes a CPU and protocol stack 12 - a battery with its associated power supply electronic circuits 14.

The radio module 11 of the target unit 10 is normally maintained in a listening mode, known as "hibernation", which means that the radio transmitter is inactive and that the unit listens for

incoming activation signals from any one of the search units SSR 20 or DSR 30. The radio module 11 of the target unit PTR 10 is activated when radio contact is established, and it responds with its identification, after which it returns to hibernation mode. The target unit PTR 10 is so designed that it can be simply used for labelling different objects by being applied to the object. The design of the target unit PTR 10 can be varied, in particular with respect to its format and lifetime, depending on the intended area of application. It is appropriate in certain contexts to attach the target unit PTR 10 to the object when it is manufactured, and this may be relevant for the manufacture of theft-prone objects such as bicycles, portable computers, machines and motor vehicles. Each owner of each target unit PTR 10 that is sold receives an identification number (an id number) in the form of a certificate giving the electronic network address of the unit, and a security code that is intended to be used for searching for or localisation of the target unit PTR 10.

Figure 5 shows the stationary search unit SSR 20 in more detail, and the figure shows that the unit comprises principally the following parts: - a radio transceiver module 21 (a radio module) with its associated protocol stack 22

- a GPS module 23 for determining position (optional)

- a CPU 24 with a unit 25 for connection to the internet and for reporting back to the search application server SAS 40

- electronic circuits 26 for power supply. The stationary search unit SSR 20 is a stationary search station intended to receive search orders in the form of search lists 2 from the supervisory search application server 40 of the system and to begin searching for target units PTR 10. Figure 9 shows examples of such search lists. It is the task of the stationary search unit SSR 20 also to forward search lists 2 to other search units in its vicinity, i.e. to transfer information not only to other stationary search units SSR 20 but also to distributed search units DSR 30 located in the vicinity. The stationary search unit SSR 20 has been designed to be powered by a 10-30 volt DC supply, and it has a range of radio communication of at least 1 ,000 metres. The stationary search unit SSR 20 has been designed such that it can be located on fixed objects such as, for example, buildings. It has also the ability to be in permanent internet contact for reporting back to the search application server 40. It is not necessary that the stationary search unit SSR be equipped with a GPS module 23: it can be arranged at a position determined in advance, or it may receive its position from a distributed search unit DSR 30 that passes by. Furthermore, the stationary search unit SSR 20 has been designed to allow remote updating, and to allow "anchoring" of target units PTR 10, followed by the monitoring of these units such that they do not disappear out from the range of radio contact. Anchoring involves the generation of a message that is transported back to the search application server 40 in the event that radio contact with the target unit PTR is lost.

As is illustrated in Figure 9, the stationary search unit SSR 20 receives a request for searching from the search application server 40 of the supervisory system via the internet connection. As is shown in Figure 6, searching is started through the stationary search unit SSR 20 periodically transmitting the electronic id number of the target unit that is being sought (PTR #x) using short-range radio. The stationary search unit SSR can also forward the search enquiry if it comes into contact with other search units, such as, for example, a distributed search unit DSR 30, whereby also this unit starts to search for the relevant target unit PTR 10. An example of this is shown in Figure 8. In the event of a reply being received from the target unit PTR 10, a message 3 is generated to which the stationary search unit SSR 20 adds information about its own position with the aid of the GPS module 23. Figure 10 shows an example of such a message 3. The message 3 is transmitted backwards via the internet to the search application server SAS 40 of the supervisory system, which receives in this way information that the approximate position of the sought target unit PTR 10 has been determined. With the aid of pre-determined time limits TTL (time to live) and by carrying out a number of subsequent searches, the search result can be further confirmed in the case in which the target unit PTR 10 is moving. Should the target unit PTR 10 disappear from the total area of short-range radio coverage of the system, the stationary search unit SSR will continue to search for a period that has been determined in advance. It will then terminate the search when the time limit TTL set for searching has been reached.

It is appropriate that the stationary search unit SSR 20 be distributed together with a number of distributed search units DSR 30 such that these units together offer added value for positioning services for several stakeholders and users, in association with the construction of infrastructure for short-range radio. The construction of the infrastructure that is necessary for the function of the present system is facilitated by ensuring that such added value is received. One example of such added value is the case in which a car rental firm installs a stationary search unit SSR 20 at its office and equips the hired-out objects, in the form of cars, with search units 30 of DSR-type. The distributed search units DSR 30 thus continuously log their geographical positions, after which stored data is transferred to the stationary search unit SSR 20 when the cars with the search units DSR 30 are in radio contact with the stationary search unit SSR 20 at the office. The stationary search unit SSR 20 in turn transfers information via the internet backwards to the search application server SAS 40 of the system. At the same time as the car hire firm receives information about the geographical movements of their own hired-out objects, the system can be used for searching for specific target units PTR 10 within the mobile infrastructure that has formed in this way.

Figure 7 shows the distributed search unit DSR 30 in more detail, which search unit comprises the following parts:

- a radio transceiver module 31 (a radio module) with its associated protocol stack 32

- a GPS module 33 for determining position - a CPU 34

- electronic circuits 35 for power supply.

In contrast to the stationary search unit SSR 20, the distributed search unit DSR 30 lacks the possibility of connection to the internet, and it thus has no direct link backwards to the search application server SAS 40. The distributed search units DSR 30 use instead other search units as informers. The distributed search units DSR 30 are used in principle exclusively as distributed search stations that receive orders from the search application server SAS 40 of the supervisory system via the stationary search unit SSR 20 and via other distributed search units DSR 30. A distributed search unit DSR receives its own list 2 of search objects of the type that is shown in Figure 9 updated through continually forming networks with other search units within range for short-range communication by radio and by continually asking these units: "Which id numbers do you have on your list?". Since the stationary search unit SSR 20 has direct contact backwards with the search application server 40 of the supervisory system and thus always has updated search lists, a distributed search unit DSR 30 receives an updated search list as soon as it comes into radio contact with a stationary search unit SSR 20 or into radio contact with another distributed search unit DSR 30 that has recently been in contact with a stationary search unit SSR 20 and has received an updated search list 2. The distributed search unit DSR 30 has been arranged to be powered by a 10-30 volt DC supply, and it has a range of radio communication of at least 1 ,000 metres. It is also appropriate that the unit be designed to allow remote updating. In the same way as that used for the stationary search unit SSR 20, also the distributed search unit may "anchor" target units PTR 10 and monitor these units such that they do not disappear out from the range of radio contact. A message is generated in the event of loss of contact with an anchored target unit PTR 10, which message is transported back to the search application server 40. As is illustrated in Figure 9 with dashed lines, the distributed search unit DSR receives a request for searching in the form of a search list 2 via communication with a stationary search unit SSR. A continual searching is started through the distributed search unit DSR attempting to contact the sought target unit (PTR #x) by periodically transmitting via short- range radio the id number of the target unit that is sought. See also Figure 8, which illustrates this part. The distributed search unit DSR can also forward the search enquiry if it comes into contact with other distributed search units 30, whereby also this unit starts to search for the relevant target unit. When a reply is received from the sought target unit PTR 10, a message

3 is generated to which the distributed search unit DSR 30 adds information about its own position during its contact with the target unit PTR 10. Figure 10 shows an example of such a message 3. The message 3 is transmitted to the search application server 40 of the supervisory system as soon as the distributed search unit DSR 30 establishes contact with a stationary search unit SSR 20, which in turn, as is illustrated in Figure 2, forwards the message backwards via the internet to the search application server 40 of the supervisory system. Thus the approximate position of the sought target unit PTR 10 has been determined. The accuracy of the localisation can be gradually improved with the aid of set time limits and repeated searches and replies. This is particularly important in the case in which the sought target unit PTR 10 is moving.

An embodiment will be described below, with reference to Figure 2, of a wireless infrastructure denoted by reference number 1 formed by distributed search units as described above and denoted by DSR 30:1 -DSR 30:3. Stationary search units denoted SSR 20:1-SSR 20:3 form nodes in a wireless network system for short-range radio communication. It should, however, be understood that a wireless network of the present type may be constituted by a freely chosen number of search units. The target units that it is desired to locate are shown in the drawing denoted by reference numbers PTR 10:1 and PTR 10:2. The said target units PTR are provided with their own battery and short-range radio for communication over short distances using the standard that is specified by ZigBee and the IEEE 802.15.4 standard. Each search and each target unit has, in accordance with ZigBee, a unique electronic identifier, for example a 64-bit MAC address.

The target units PTR are normally in hibernation in order in this way to conserve the battery and to be able to live for a long time. The target units can be awakened to form radio contact with any one of the search units SSR, DSR with the aid of "hello" messages. The units that are components of the system include a user terminal UT 50 connected to the search application server SAS 40. The user terminal UT 50 may be constituted by a normal PC and an associated database system DB 60 of suitable design.

Each search unit DSR 30:1-30:3, SSR 20:1-20:3 contains search lists 2 with sought target units PTR 10:1-10:2 and thus of those objects to which the target units have been attached. As is shown in Figure 9, each search list 2 can contain information about the identity of the relevant target unit PTR 10:1-10:2, the search priority, the remaining duration of the search period, and the geographical limits of the search region. The search protocol and the search lists 2 provide a distributed spontaneous network system for searching for objects in which the mobile search units DSR 30:1-30:3 do not need to be in direct contact with any supervisory system. The stationary search units 20:1-20:3 in the wireless infrastructure .1 that is formed are provided for short-range radio communication with protocols of, for example, Bluetooth type or ZigBee type, and they form wireless access

points that may be, but are not necessarily, located at such a distance from each other that they also can communicate with each other. Figure 2 illustrates the range of radio communication between the stationary search units SSR 20 with dashed radio rings 70. Communication backwards from the stationary search units SSR 20:1-20:3 to the search application server SAS 40, and communication from this server to the user terminal UT 50 and the database DB 60, takes place in any suitable manner, but it takes place preferably via Ethernet or the internet, and by the use of any known network technology for data transfer such as, for example, IEEE 802.11a.

The wireless infrastructure includes also the distributed search units DSR 30:1-30:3 that form nodes and that move when carried by mobile objects along pathways within a limited geographical region. The said objects may, for example, be constituted by any mobile object that can carry a search unit DSR 30 with a suitable power supply for powering this unit. Such objects as, for example, taxis, buses, post vehicles and distribution vehicles may be considered as carriers. The communication between the stationary search units SSR 20:1- 20:3 and the distributed search units DSR 30:1-30:3 takes place spontaneously when the units by chance are located sufficiently close to each other that they come into radio contact, and in accordance with a communication protocol that has been determined in advance.

As it moves along a pathway, the distributed search unit DSR1 will come into radio contact with the target unit PTR1 , which thereby is awakened from its hibernation. The location at which contact is established is denoted in the drawing as the point 80:1. Contact is broken at the location that is denoted by point 80:2. On establishment of the said contact, a message 3 is transmitted from the target unit PTR1 to the distributed search unit DSR1 containing information of the network identity of the target unit, such as 0.0.12.117.65.32 in decimal form, and possibly other data associated with it, for example the times during which the radio contact was maintained. See also Figure 10. The distributed search unit DSR1 adds information about PTR1 to the message 3, supplemented by information about the time at which contact was established at 80:1 and the time at which contact was lost at 80:2 with the associated locations and positioning data for the said times generated by the built-in GPS module 33 of the search unit DSR1. In order to make possible more accurate calculations of the geographical position and motion of the target unit PTR1 when spontaneous contact with the distributed search unit DSR1 is achieved, it is appropriate to design the protocol in the manner that is shown in Figure 2. This design is namely such that not only one, but several supplementary geographical points 80:1a, 80:1b-80:1n can be periodically logged with the aid of the GPS module 33 of the search unit DSR1 while contact is held between the search unit DSR1 and the target unit PTR1. The said geographical points 80:1a, 80:1 b-80:1 n are logged during the interval between contact being established and contact being broken at the points 80:1 and

80:2, and it is also appropriate that the distance between the passing distributed search unit DSR 30 and the target unit PTR 10 is calculated based on the strength of the signals at the logged points for accurate determination of the position of the target unit. The said calculation takes place immediately in the CPU 34 of the distributed search unit, whereby the logged and the calculated values are included in the message 3.

As the distributed search unit DSR1 subsequently moves along its pathway 90, it will come into contact with the distributed search unit DSR2 at the point 90:1 and it will loose contact at point 90:2. The list with data and information collected about the target unit PTR1 that has been detected is thus transferred from DSR1 to DSR2. The list with information about the target unit PTR1 that has been found is subsequently transferred in a similar manner from DSR2 and backwards to the distributed search unit DSR3 when these come into and out of radio contact with each other. The distributed search unit DSR3 comes into contact with the radio coverage area 70 of the stationary search unit SSR2 at the point 100:1 and it looses contact at the point 100:2, whereby the message 3 with information about the target unit PTR1 that has been located is transferred backwards to the supervisory computer SAS 40 of the infrastructure via the fixed line 110 and the internet.

The supervisory computer SAS 40 of the infrastructure receives the message with information about the target unit PTR1 that has been located and after addition of the data with the time and date at which the message was received stores it in the database in the form of a verification list 4.

Figure 11 shows an example of the said verification list 4 with the associated data generated by the supervisory computer 40 of the infrastructure in the embodiment described. The verification list 4 originates from the spontaneous detection of the target unit PTR with the unique network identifier 0.0.12.117.65.32, the table comprises the identity of the search unit SSR, DSR that detected the target unit, in this case 0.0.14.119.65.32, the location at which the detection took place received, for example, from infrastructure stored in the database 60 and presented in a suitable graphical form in the form of a local map of the region or similar. The verification list 4 in Figure 11 illustrates that the search object PTR has the id 0.0.12.117.65.32 and that it has been contacted by search unit DSR 0.0.14.119.65.32 at location 80:1 on 18 August 2007 at 18:35, and that the contact was lost at location 80:2 on 18 August 2007 at 18:40. When the messages 3 and their associated data are received, the data is organised in the search application server SAS 40 and stored in the database DB 60. The database 60 in this example stores lists of data collected where each list originates from a particular target object with its specific network identifier. The verification list 4 shown in Figure 11 belongs to the identification arrangement 0.0.12.117.65.32. The verification list 4 may contain location, date and time that have been delivered by the search application server SAS 40. The database may be accessed with the aid of the computer terminal 50,

which may be a personal computer or any suitable computer that is connected to the internet.

The user connects to the database DB 60 with the aid of a standard internet connection and web browser interface, and feeds in the unique network identifier of the sought object, after logging in and specifying a security code. It can be conceived that a user registers with the database using an anonymous login in the form of a user name and password for improved security. The user specifies when logging into the database the network identifier of his or her own arrangements, whereby the database 60 searches for lists that originate from the specified identifier. In this example, the target object with identifier 0.0.12.117.65.32 would present the list that is shown in Figure 11.

The information in the list may be presented for the user in any suitable manner that is compatible with the positioning information, i.e. if, for example, the positioning data is constituted by a postcode, the data can be presented graphically in the form of a map of the local region. The present invention is not limited to that which has been described above and presented in the drawings: it can be changed and modified in a number of different ways within the scope of the innovative concept specified in the attached patent claims.