Description

A locating method and a locating system

Technical Field

The present invention relates to locating field, particularly to a locating method and a locating system.

Background Art In a locating system, a real-time locating system (RTLS) mainly comprises a tag and a locating infrastructure, wherein, the tag is disposed on an object to be located, the locating infrastructure comprises a plurality of access points (AP) for communicating with the tag and other locating devices (the locating devices comprised in the locating infrastructure are different for different locating systems), when the tag enters into the coverage area of the AP of the locating infrastructure, the tag communicates with the AP, and then the locating infrastructure can calculate the position of the tag.

There are many types of locating technologies in the prior art, some of the locating technologies, such as the locating technology of the received signal strength indication (RSSI) method based on wireless local area network (WLAN) can calculate the position of the tag by measuring the field strength of the wireless signals received by the tag, or by measuring the field strength of the wireless signals transmitted from the tag and received by the AP of the infrastructure. Some other locating technologies, such as the locating technology of the time difference of arrival (TDOA) method based on ISO 24730 standards, can calculate the position of a tag by measuring the propagation delay of radio frequency (RF) signals at the tag and a reference point at a given position. In addition, there are other locating technologies such as dead-reckoning (DR) locating technology, etc. The currently available locating technologies usually use only one single locating method, such locating

technologies using a single locating method have advantages and disadvantages, for example, some locating methods are only suitable for indoor applications, while some locating methods may need a sight distance circumstance between the tag and the AP, while still some other locating methods can realize successive autonomous locating.

However, in practical application situations, the distribution area of a locating system may involve various types, and the wireless propagation condition of RF signals in each area may vary with time, therefore when employing the prior art locating technology using a single locating method, the locating precision and validity of the tag can be different at different positions and times, and sometimes it may even be the case that the locating precision is unable to meet the requirement or to work out a location, etc., while in practical applications, it is desirable to be able to obtain a tag's satisfactory locating precision, and it can be seen that the abovementioned locating technologies in the prior art are not capable of meeting this requirement.

Contents of the invention

The present invention provides a locating method on one hand, and provides a locating system on the other hand, so as to obtain a tag's satisfactory locating precision in various areas .

The present invention provides a locating method, which method is for use in a locating system comprising a tag and a locating infrastructure, said locating infrastructure comprising an access point AP and a server, the method comprising: providing by the AP, upon detecting the tag, the information of the tag to the server; sending by said server characteristic parameter adjustment information to the tag corresponding to said tag information via said AP according to a locating requirement;

adjusting by said tag its characteristic parameter according to said characteristic parameter adjustment information; and locating the tag with the adjusted characteristic parameter.

Preferably, said step of sending by said server characteristic parameter adjustment information to the tag corresponding to said tag information via said AP according to a locating requirement involves the following: said server determines the characteristic parameter information that said tag is to be adjusted to and sends the characteristic parameter adjustment information to said tag via said AP according to one of or any combination of such conditions as a locating precision requirement in a current area in which the tag is located, the locating precision requirement of at a current time, the AP deployed in the current area, a locating technology supported by or determined to be used by the locating infrastructure, whether or not to maximize the service life of the battery in the tag and a signal propagation condition.

Preferably, said characteristic parameter adjustment information comprises one of or any combination of the tag's transmission parameter information, information about an antenna used for locating, information about the mode of signal propagation and information about a locating technology adopted.

Preferably, said tag's transmission parameter information comprises one of or any combination of such pieces of information as a transmission power, a flicker frequency, flicker data's format/packet length, a signal structure, a modulation parameter, the type and number of measurement extracted from the tag and triggering and triggered specific tag characteristics.

Preferably, said information of the antenna used for locating comprises one of such pieces of information for indicating the use of a specific antenna, for indicating the switching between different antennas, and for indicating the use of a plurality of antennas at the same time.

Preferably, said mode information about signal propagation comprises information about a multicasting mode or a broadcasting mode.

Preferably, said information about the adopted locating technology is the information of a single locating technology; said locating the tag with the adjusted characteristic parameter involves the server controling the AP to collect the location information of said tag, and calculating the location of said tag according to said location information.

Alternatively, said information about the locating technology is the information about a plurality of locating technologies being adopted according to a time multiplexing mode; and said locating the tag with the adjusted characteristic parameter involves the server controling the AP to collect the location information of said tag when it uses different locating technologies, incorporating said location information at a location level or at a measurement level, and calculating the location of said tag.

Preferably, said information about the adopted locating technology is about a locating technology for indicating RSSI based on the intensity of the received signals of a wireless local area network WLAN, and/or a locating technology based on a method of time difference of arrival TDOA.

Preferably, said information about the adopted locating technology is the information of a dead-reckoning locating technology;

and said locating the tag with the adjusted characteristic parameter is by said tag's autonomous locating.

Preferably, the method further comprises: choosing a reference tag serving as a reference point for locating; and the step of locating the tag with the adjusted characteristic parameter is by using said reference tag to communicate with said tag with the adjusted characteristic parameter so as to determine the relative location information therebetween; and the server collects the relative location information between said reference tag and said tag with the adjusted characteristic parameter via the AP, and calculates the location of said tag with the adjusted characteristic parameter according to said relative location information and the known location information of said reference tag.

Preferably, after said tag has adjusted its own characteristic parameter, it further comprises sending by the tag via the AP the result of adjustment to the server.

Preferably, after having carried out said locating the tag with the adjusted characteristic parameter, it further comprises the server evaluating the locating precision after the locating has been carried out, and sending warning information to a client end when the locating precision is lower than a preset threshold.

A locating system provided by the present invention comprises: a tag and a locating infrastructure; said tag is for adjusting its own characteristic parameter according to characteristic parameter adjustment information from said locating infrastructure; and said locating infrastructure comprises an access point AP and a server, said AP is for providing tag information to said server when it detects a tag, and said server sends characteristic parameter adjustment information to the tag corresponding to said tag information via said AP according

to a locating requirement, and locates the tag of which the characteristic parameter has been adjusted.

Preferably, said system further comprises: a reference tag serving as a locating reference point, for communicating with said tag of which the characteristic parameter has been adjusted, so as to determine the relative location information therebetween; and the server of said locating infrastructure further collects via said AP the relative location information between said reference tag and said tag of which the characteristic parameter has been adjusted, and calculates the location of said tag of which the characteristic parameter has been adjusted according to said relative location information and the known location information of said reference tag.

Preferably, said tag is further used for, after the characteristic parameter having been adjusted, sending the result of the adjustment to the server of said locating infrastructure via the AP of said locating infrastructure.

Preferably, the server of said locating infrastructure is further used for evaluating the locating precision after the locating has been carried out, and sending warning information to a client end when the locating precision is lower than a preset threshold.

Preferably, said AP comprises an AP supporting only locating access, and/or an AP supporting both locating access and communication .

It can be seen from the solutions above solutions that the technical solutions of the present invention are applied in the locating system comprising a tag and an infrastructure, said locating infrastructure comprises an AP and a server, and the server of the present invention sends characteristic parameter adjustment information to the tag via the AP

according to a locating requirement, wherein, the characteristic parameter adjustment information comprises one piece of or any combination of information associated with locating precision, such as the propagation parameter information of the tag, information about antennas used for locating, information about the mode of signal propagation and information about the adopted locating technology, so as to adjust the tag's characteristic parameter to the state meeting the locating requirement according to the characteristic parameter adjustment information, then to enable the locating of the tag with the characteristic parameter adjusted, so as to obtain satisfactory tag locating precision no matter in which area the tag is located.

Description of the Drawings

The abovementioned and other features and advantages of the present invention will become more apparent to those skilled in the art by the detailed description of the exemplary embodiments of the present invention herembelow with reference to the accompanying drawings, in which:

Fig. 1 is a schematic structural diagram of the locating system in an embodiment of the present invention.

Fig. 2 is another schematic structural diagram of the locating system in the embodiment of the present invention. Fig. 3 is a schematic flowchart of the locating method in the embodiment of the present invention.

Embodiments

In order to make the object, technical solution and advantages of the present invention more apparent, the present invention will be further described in detail below by reference to the accompanying drawings and embodiments.

As shown in Fig. 1, it shows a schematic structural diagram of a locating system 1 in the embodiment of the present invention, wherein it comprises a tag T and a locating infrastructure. In the figure, the coverage area 3 shown comprises three sub-areas (that is, area I, area II, area III

in Fig. 1), and in the coverage areas shown are arranged a plurality of APs Al, A2 of the locating infrastructure, for establishing connection between the tag T and the locating infrastructure, and each AP can be an AP specially for locating (Al in Fig. 1), such as an AP based on ISO 24730 standards etc., and it can also be an AP capable of both communicating and locating (A2 in Fig. 1), such as the equipment of WLAN 7 and so on which can be used not only as ordinary communication equipment, but also as an AP for locating. Furthermore, the locating infrastructure also comprises at least one server 5, for evaluating tag messages, calculating tag positions and performing system control and management, etc., and furthermore, it can also interact with application software.

In the embodiment, in order to improve the applicability of the locating technology and further to ensure locating precision according to actual situations, the tag T and locating infrastructure can be made to support at least one locating technology, such as the locating technology of RSSI based on WLAN, the locating technology based on a TDOA method, and the dead-reckoning locating technology. In this case, the dead-reckoning locating technology is a commonly used navigation locating technology, of which the principle is that a tag T calculates its own instant position by utilizing the data measured by a direction sensor (such as a gyroscope) , a velocity sensor (such as an accelerometer) and other sensors (such as a barometer or a thermometer) , and it can realize the tag's successive autonomous locating.

When in practical implementation, various types of interfaces can be arranged for the AP Al, A2 of the tag T and of the locating infrastructure, including therein several types of air interface (for example, RFLS wireless interface, RFID wireless interface, sensor interface, etc.) and corresponding periphery interfaces. These interfaces and memory, microcontroller cores are integrated into a chip for a microchip (similar to the system on the chip G2C501 of G2

Microsystems Company) , which can be used on a tag T and/or an AP Al, A2, and the tag T and/or the AP Al, A2 can be switched selectively among several interfaces, thereby realizing the integrated operation based on wireless communication, real- time location, RFID, etc.

The tag supporting multiple locating technologies can flexibly interact with various types of locating infrastructures, and is capable of using corresponding interfaces to realize the locating in all types of RFLS system, likewise, the locating infrastructure supporting multiple types of locating technologies is capable of locating various types of tags.

In real applications, at the locating infrastructure side, the server 5 is capable of obtaining the locating precision requirement of different sub-areas in the coverage area, and already knows the case of the AP Al, A2 deployed in each area and the locating technologies supported by the locating infrastructure or the currently used locating technologies determined from the supported locating technologies by the locating infrastructure. To meet the precision requirement, the server 5 can determine the characteristic parameter suitable for the tag T in a current area, such as the propagating parameter of the tag T, the locating technology used by the tag T, etc., according to the locating requirement of one or more situations in these areas, and further it can inform the tag T by the AP Al, A2 via a wireless downlink, according to which the tag T adjusts its own characteristic parameter, so as to meet different locating requirements and locating precisions. During practical implementations, the server 5 can send characteristic parameter adjustment information to the tag T via the AP Al, A2, for example, the characteristic parameter information comprising information about transmission parameters and/or information about the adopted locating technology. In this case, the tag's transmission parameter information can comprise one piece of or any combination of

information such as transmission power, flicker frequency, flicker data's format/packet length, signal structure, modulation parameter, measurement type and number extracted from the tag T and the triggering and the triggered specific tag characteristics (for example, sensor, energy management, etc. ) .

Furthermore, sometimes it should be taken into account whether or not to maximize the service life of the tag's battery, because different tag transmission parameters such as locating technologies and transmission power lead to different loss of the service life of battery. For example, locating with the locating infrastructure may consume comparatively more energy from the battery, while locating with the dead-reckoning locating technology can consume relatively less energy from the battery.

In some cases, the characteristic parameter adjustment information can also comprise the antenna information used for locating, since the tag T generally comprises more than one antennae, so the server can designate the tag T to do the locating with a specific antenna, or to switch among different antennae, or to use multiple antennae simultaneously, and which antennae are practically employed can be determined according to actual situations.

After having received said characteristic parameter adjustment information, the tag T can adjust its characteristic parameter according to the characteristic parameter adjustment information, and if the characteristic parameter adjustment information comprises information such as increasing transmission power and switching the locating technology to an RSSI locating technology based on WLAN, the tag T will accordingly increase the propagation power and switch the adopted locating technology to the RSSI locating technology based on WLAN. Further, the tag T can send the adjustment result to the server 5 via the AP Al, A2. For example, if the tag T is unable to adjust the corresponding

characteristic parameter according to the characteristic parameter adjustment information, it can return an error message to the server 5, so the server 5 re-adjusts the characteristic parameter adjustment information according to the error information. Alternatively, furthermore, if the tag is able to adjust the corresponding characteristic parameter according to the adjustment information, correct information can be sent to the server.

In this case, when the tag T is instructed to adopt a different locating technology, in the case that in some areas locating with the locating infrastructure can achieve a relatively higher locating precision, the locating infrastructure can be used to do the locating and, correspondingly, the tag T is instructed to utilize the locating technology in which the locating infrastructure is used, then the server of the locating infrastructure controls the AP Al, A2 to collect the tag's position information, and calculates the position of the tag according to the position information, thereby accomplishing the locating of the tag T. As to the cases that in some areas, the locating precision is relatively lower via the locating by the locating infrastructure or it is not possible to locate by using the locating infrastructure, the tag can be instructed to adopt the dead-reckoning locating technology to realize autonomous locating. However, when considering using this locating technology, since its reckoning process is an accumulation process and the measurement error of the direction sensor is accumulated along with time delay, and only relative position and navigation direction can be determined according to the reckoning result, then, when the locating is again appropriate to be performed via the locating infrastructure, the tag T can be instructed to switch to corresponding locating technology supporting the locating by the locating infrastructure, or to use the locating results (absolute location) obtained by the locating infrastructure to correct the locating result (relative location) obtained by the dead- reckoning locating technology. Furthermore, for decreasing

the energy consumption of the batteries, sometimes the dead- reckoning locating technology can also be adopted.

Furthermore, simultaneously applying different locating technologies is feasible too, for example, for the purpose of increasing locating precision, multiple locating technologies can be adopted according to a time multiplexing mode, at this time, the server 5 controls the AP Al, A2 to collect the position information of the tag T by using different locating technologies, combines all the collected position information at a position level or at a measurement level, and calculates the position of the tag T, so as to realize the location of the tag T. In which case, in the case of combining at the position level, the position calculation results by different locating technologies can be carried out after the processing such as averaging or combined smoothing; and when combining at the measurement level, the results measured by using different locating technology, such as the distance between the tag T and the AP Al, A2, can firstly be performed after processing such as averaging or combined smoothing, then the position of the tag T is calculated. Certainly, when simultaneously using different locating technologies, it can increase the power consumption of the tag battery, so as to decrease the service life of the tag battery.

In some cases, for meeting the requirements of simultaneous change of the characteristic parameters of all tags T or a specific tag group (for example, corresponding climate changes propagation condition, or different precision requirements at different times, etc.), the tags T can be set in a multicasting or broadcasting mode, correspondingly, the characteristic parameter adjustment information from the server can comprise the mode information of signal propagation, then the tags T enter into the multicasting or broadcasting mode according to the adjustment information, and a tag T can return error information to the server when the tag cannot follow the instruction from the server.

In addition, in some cases, it is possible to use air interfaces to perform tag-to-tag locating. As shown in Fig. 2, it is another structure diagram of the locating system 1 of the embodiment of the present invention (in Fig. 2, only communication and locating APs A2 are illustrated, certainly the locating APs can also be comprised) . In Fig. 2, assuming that the fixed locating infrastructure can only achieve high locating precision in some areas of the coverage area 3 (such as the high precision or accuracy area IV in Fig. 2), and cannot achieve in some other area satisfactory locating precision, that is, the low locating precision (such as the area V with low precision or accuracy in Fig. 2), then, the server 5 can designate the tag T capable of obtaining higher locating precision as a reference tag RT, which is used as the reference point for locating. Then the reference tag RT (there can be several of them) can be used to communicate with the tag T to be located, so as to determine the relative position information between the two, subseguently, the server 5 of the locating infrastructure collects the relative position information between the reference tag RT and the tag T to be located via the AP A2, and calculates the position of the tag to be located according to the relative position information and to the known position information of the reference tag RT.

Taking RSSI locating technology based on WLAN as an example, a fingerprint identification technology based on RSSI can be used to perform tπangulation, wherein the reference tag RT collects the RSSI value of the tag T to be located, reports the collected RSSI value to the AP AP2, or after having determined the relative distance between the reference tag RT and the tag T to be located according to the RSSI value, the reference tag RT reports the relative distance to the AP A2 ; the AP A2 provides the received information to the server 5, and the server 5 calculates the position of the tag T to be located according to the information and the known position information of the reference tag RT. In which case, if what the reference tag reports RT is the RSSI value, the server 5

can determine the relative distance between the reference tag RT and the tag T to be located according to the RSSI value, then calculate the position of the tag T to be located, so as to increase the locating precision in the area with low locating precision V.

In the above process, the RSSI value of the reference tag RT can also be collected by the tag T to be located, then the tag T to be located reports the collected RSSI value to the AP A2, or after the tag T to be located having determined the relative distance between the reference tag RT and the tag T to be located according to the RSSI value, and the tag T to be located reports the relative distance to the AP A2.

The above tag-to-tag locating scheme can significantly reduce the number of APs; therefore it can effectively reduce the dependence on the network framework, and facilitate the deployment of access points.

Furthermore, the server 5 of the locating infrastructure in the embodiment can also evaluate the location precision after the locating has been performed, and send warning information to a client end when the locating precision is lower than a preset threshold. In which case, when evaluating the locating precision after the locating has been performed, the server 5 can evaluate according to empirical knowledge; or it can also evaluate according to the analysis of the RF signals. When evaluating on the basis of the analysis of RF signals, the server 5 can extract from the RF signals quality indication information (for example, RSSI information) or the intermediate results of position calculation by using locating geometry to carry out the evaluation; Furthermore, it can also evaluate on the basis of previous statistical information and additional state information, such as the tag's motion information (for example, measured by mobile sensor) .

Furthermore, the tag T and locating infrastructure of the

embodiment can provide a set of redundant locating service systems based on an independent sensor or equipment, when failure occurs to one of the locating service systems, it can switch to another locating service system to carry out locating.

The above detailed description is made to the locating system of the embodiment of the present invention; the locating method of the embodiment of the present invention will be described in detail below.

Fig. 3 is an exemplary flowchart of the locating method of the embodiment of the present invention. The locating method in the embodiment is mainly used in a locating system 1 comprising a T tag and a locating infrastructure, the tag T and the locating infrastructure support at least one locating technology, and the locating infrastructure comprises an access point (AP) Al, A2 and a server 5, as shown in Fig. 3, which flow procedure comprises: Step 301, when the AP Al, A2 detects the tag T, it provides the tag information to the server 5.

In which case, the tag information comprises at least identification information of the tag T (for example, ID of the tag T), and it can also comprise the tag's measurement information (for example, RSSI), etc.

Step 302, the server 5 sends characteristic parameter adjustment information to the tag T corresponding to said tag information via said AP Al, A2 according to a locating requirement .

The server 5 identifies the tag T according to the tag information reported by the AP Al, A2 ; further sends the characteristic parameter adjustment information to the tag T via the AP Al, A2 according to the locating requirement, and the particular procedure can be that the server 5 determines the characteristic parameter information to which the tag T

should be adjusted according to one of or to any combination of conditions such as the locating precision requirement of a current area in which the tag T is located, the locating precision requirement at a current time, the AP Al, A2 deployed in the current area, the locating technology supported by or determined to be used by the locating infrastructure, whether or not to maximize the service life of the battery of the tag and signal propagation condition; and sends the characteristic parameter adjustment information to the tag T via a wireless downlink by the AP Al, A2. In which case, the characteristic parameter adjustment information can comprise one of, or any combination of the tag' s transmission information, information about the antenna used for locating, the mode information of signal propagation and the information about the adopted locating technology.

In which case, the transmission parameter information can comprise one of or any combination of information such as a transmission power, a flicker frequency, flicker data's format/packet length, a signal structure, a modulation parameter, the type and number of measurement extracted from the tag and triggering and triggered specific tag characteristics (such as sensors, energy management, etc.) .

The antenna information used for location can comprise: information for indicating the use of a specific antenna, or for indicating the switching between different antennas, or for indicating the use of a plurality of antennas at the same time .

The mode information of signal propagation can comprise: the information about a multicasting mode and the information about a broadcasting mode.

The information of adopted locating technology can comprise: the information of a locating technology or a plurality of locating technologies used in a time multiplex mode. In which case, the locating technology can be the locating technology

of indicating RSSI based on the intensity of received signals of a wireless local area network WLAN 7, it can also be the locating technology based on the TDOA method, and yet it can also be the dead-reckoning locating technology, etc.

In the case that it can obtain a higher locating precision with locating by the locating infrastructure in some areas, the locating infrastructure can be used to do the locating, correspondingly, the tag is instructed to adopt the locating technology where the locating infrastructure performs the locating, and in the case that it is can obtain a lower locating precision with locating by the locating infrastructure in some areas or the locating infrastructure is unable to carry out the locating, the tag T can be instructed to adopt the dead-reckoning locating technology to achieve autonomous location. However, in view of when this locating technology is adopted, the measurement errors by direction sensors accumulate over a prolonged period of time due to an accumulation process of the reckoning process, and the reckoning process can only determine relative position and direction, the tag T can be instructed to switch to a corresponding locating technology supporting the locating by the locating infrastructure when the locating infrastructure is once again available for locating, or the tag T can also be instructed to correct the locating results (the relative location) by the dead-reckoning locating technology by using the locating result (the absolute location) obtained by the locating infrastructure. Furthermore, sometimes the dead- reckoning locating technology can also be adopted in order to reduce the consumption of the battery energy.

Step 303, the tag T adjusts its characteristic parameter according to the characteristic parameter adjustment information from the server 5.

In this step, after having received the abovementioned characteristic parameter adjustment information, the tag T can adjust its characteristic parameter according to the

adjustment information, for example, if the characteristic parameter adjustment information comprises increasing transmission power and switching the locating technology to the RSSI locating technology based on WLAN, the tag T correspondingly increases the transmission power and switches the adopted locating technology to the RSSI locating technology based on WLAN. Furthermore, the tag T can send the adjustment results to the server 5 via the AP Al, A2. For example, if the tag T cannot complete the corresponding adjustment of the characteristic parameter, it can return an error message to the server 5, and then the server 5 readjusts the characteristic parameter adjustment information according to the error message. Alternatively, furthermore, if the tag T can complete the adjustment of a corresponding characteristic parameter according to the adjustment information, it can return correct information to the server 5.

Step 304, locating the tag T with the characteristic parameter adjusted.

In this step, when the locating technology based on the locating infrastructure is adopted, the server 5 of the locating infrastructure controls a corresponding AP Al, A2 to collect the position information of the tag T (for example, when using the RSSI locating technology based on WLAN, it may need one AP Al, A2 ; when using the locating technology based on TDOA, it may need a plurality of APs Al, A2), and calculates the position of the tag T according to the collected position information. When different locating technologies are adopted at the same time (for example, when using a plurality of locating technologies in a time multiplexing mode) , the server 5 controls the corresponding APs Al, A2 to collect the position information when the tag T uses different locating technologies, and combines the collected position information at a position level or at a measurement level, so as to calculate the position of said tag T. In which case, when combining at the position level,

the position calculation results using different locating technologies can be processed by, e.g. averaging or combined smoothing; and in the case of combining at the measurement level, the result measured by using different locating technologies, such as the distance between the tag T and AP Al, A2, can be processed first, by for example averaging or combined smoothing, and then the position of the tag T is calculated. Certainly, simultaneously using different locating technologies can increase the power consumption of tag battery, thus reducing the service life of the tag battery.

When using the dead-reckoning locating technology, the tag T can perform the autonomous locating.

Furthermore, the embodiment can further choose a reference tag RT as a reference point for the locating, then in this step, the chosen reference tag RT can be utilized to communicate with the tag T to be located, and to determine the relative position information between two of them; the server 5 collects said reference tag RT and the relative position information between said tags after the characteristic parameter adjustment via the AP Al, A2, and calculates the position of the tag T to be located according to the collected relative position information and the known position information of the reference tag RT.

Taking the RSSI locating technology based on WLAN as an example, the fingerprint identification technology based on RSSI can be utilized to perform triangulation, and the reference tag RT collects the RSSI value of the tag T to be located, reports the collected RSSI value to the AP Al, A2, or after having determined the relative distance between the reference tag RT and the tag T to be located according to the RSSI value, the reference tag RT reports the relative distance to the AP Al, A2 ; the AP Al, A2 provides the received information to the server 5, and the server 5 calculates the position of the tag T to be located according

to the information and the known position information of the reference tag RT. In which case, if the reference tag RT reports the RSSI value, the server 5 can determine the relative distance between the reference tag RT and the tag T to be located according to the RSSI value, and then calculate the position of the tag T to be located, so as to increase the locating precision in the area with a low locating precision V.

In the abovementioned process, the RSSI value of the reference tag can also be collected by the tag T to be located, then the tag T to be located reports the collected RSSI value to the AP Al, A2 or after having determined the relative distance between the reference tag RT and the tag T to be located according to the RSSI value, the tag T to be located reports the relative distance to the AP Al, A2.

Furthermore, after having located the tag T with the characteristic parameter adjusted the server 5 in the embodiment can further evaluate the locating precision after the locating, and send warning information to a client end when the locating precision is lower than a preset threshold.

In which case, when evaluating the locating precision after the locating, the server 5 can evaluate according to empirical knowledge; or evaluate according to the analysis of the RF signals. When evaluating based on the analysis of the RF signals, the server can extract from the RF signals quality indication information (for example, the RSSI information) or the intermediate results of position calculation by using locating geometry; Furthermore, it can also evaluate on the basis of previous statistical information and additional state information, such as the tag's motion information (for example, that measured by a mobile sensor) .

Furthermore, the tag T and the locating infrastructure of the embodiment can provide a set of redundant locating service

systems based on independent sensors or equipment, when the failure occurs with one of the locating service systems, the server 5 can switch to another locating service system to perform the locating.

The locating infrastructure in the embodiment of the present invention can be an infrastructure supporting at the same time a plurality of locating technologies, and can also be an integration of a plurality of infrastructures supporting respectively different locating technologies, in the case of the integration of a plurality of infrastructures supporting different locating technologies, the advantageous conditions of existing different infrastructures can be utilized to reduce the installation costs in adding new infrastructures.

It can be seen that in the embodiment of the present invention the locating infrastructure and tag T can be flexibly utilized to do the locating according to specific application requirements and specific external environments, and the locating can be implemented in different sub-areas in the coverage area 3 according to different precision requirements in a cost-effective manner. Furthermore, considering service life of the tag battery, it can make the service life of the battery optimized and the maintenance costs are reduced.

What is described above is only the preferred embodiments of the present invention, but they are not intended to limit the protective scope of the present invention. Any modification, equivalent substitution and improvement within the spirit and principle of the present invention are to be covered in the protective scope of the present invention.