WO2007015188A1

WO2007015188A1 - Method, apparatus and system for localization in a wireless network

Info

Publication number: WO2007015188A1
Application number: PCT/IB2006/052527
Authority: WO
Inventors: Ningjiang Chen; Xin Chen
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2005-08-01
Filing date: 2006-07-24
Publication date: 2007-02-08
Also published as: EP1961254A1

Abstract

A method, apparatus and system for localization in wireless network are disclosed in the present invention for localizing one mobile node in a wireless network. The method comprises the steps of: acquiring a transmission power level, which is related to location of the mobile node; comparing the transmission power level with a location mapping information, wherein the location mapping information comprises at least a known location and its corresponding transmission power level; determining the location of the mobile node, according to the comparison result. The present invention can achieve broader applications for localization, and make the localization result for a mobile node more accurate and more efficient, since it utilizes the transmission power level to localize a mobile node, which makes the localization results insensitive to the influence of the complex environment.

Description

METHOD, APPARATUS AND SYSTEM FOR LOCALIZATION IN A WIRELESS NETWORK

FIELD OF THE INVENTION The invention relates to a wireless network, in particularly, to a method, apparatus and system for localizing a mobile node in a wireless network.

BACKGROUND OF THE INVENTION

In a wireless network, Radio Signal Strength (RSS) is widely used as an approach to measure the distance between nodes, for instance, a wireless sensor network (WSN) may generally include several sensor nodes, each of which normally has the capability to perform short-haul wireless communication and communicates with each other via Radio Frequency information. Based on the Radio Path Loss model, the distance between two sensor nodes can be calculated. In theory, if the distances between a mobile node and three stationary nodes are known, the location of the mobile node can be calculated in 3-D coordinate system with 3-D coordinates of three stationary nodes.

However, since the wireless signal is liable to suffering interferences, thereby being not stable and even erroneous, it is unreliable to use RSS to measure the distance between two nodes. A solution is to combine TOF (Time of Flight) method with RSS, namely utilizing the propagation speed of wireless signal and the relay-time between transmitter and receiver, to measure the distance between two nodes.

However, the TOF method also has some shortcomings: firstly, TOF method requires accurate time synchronization, which requires extra effort of WSN to maintain synchronization information; and in real applications, it will consume the limited resources of WSN; secondly, for indoor distance measurement, the complex situation of reflection wave caused by walls and furniture considerably degrades the accuracy of TOF.

In conclusion, a method and apparatus for localization in wireless network with stable measurement result insensitive to indoor complex environmental interference is therefore needed.

OBJECT AND SUMMARY OF THE INVENTION

The present invention provides a method, apparatus and system for localization in wireless network, which achieves stable measurement result insensitive to indoor environment.

According to an embodiment of the present invention, a method for localizing a mobile node in a wireless network is provided, wherein the method comprises the steps of: acquiring a transmission power level, which is related to location of the mobile node; comparing the transmission power level with a location mapping information, wherein the location mapping information comprises at least a known location and its corresponding transmission power level; and determining the location of the mobile node, according to the comparison result.

According to another embodiment of the present invention, an apparatus for localizing a mobile node in a wireless network is provided, wherein the apparatus comprises: an acquiring device, for acquiring a transmission power level, which is related to location of the mobile node; a comparing device, for comparing the transmission power level with a location mapping information, which comprises of at least a known location and its corresponding transmission power level; and a determining device, for determining the location of the mobile node according to the comparison result.

According another embodiment of the present invention, a wireless network system for localizing a mobile node in the wireless network is provided, wherein the wireless network system comprises: at least a receiving device, for receiving a group of localization messages with at least two localization messages from the mobile node, wherein the group of localization messages includes a transmission power level respectively different from each other; an acquiring device, for acquiring a lower transmission power level in the group of localization messages, and the transmission power level is related to the location of the mobile node; a comparing device, for comparing the transmission power level and a location mapping information, which comprises at least a known location and its corresponding transmission power level; and a determining device, for determining the location of the mobile node according to the comparison result.

According another embodiment of the present invention, a wireless network system for localizing a mobile node in the wireless network is provided, wherein the wireless network system comprises: at least a transmitting device, for sending a group of localization messages with at least two localization messages, wherein the group of localization messages includes a transmission power level respectively different from each other; an acquiring device, for acquiring a lower transmission power level in the group of localization messages, and the transmission power level is related to the location of the mobile node; a comparing device, for comparing the transmission power level with a location mapping information, which comprises at least a known location and its corresponding transmission power level; and a determining device, for determining the location of the mobile node according to the comparison result. In conclusion, a method, apparatus and system for localization in wireless networks proposed in the present invention can achieve broader applications for localization, and make the localization for mobile node more accurate and more efficient since it utilizes the transmission power level message to localize mobile nodes, which makes the localization results insensitive to the influence of complex environment. Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic diagram illustrating a sensor network according to an embodiment of the present invention;

Figure 2 is a schematic diagram in statistics format illustrating all beacon messages received by a mobile node according to an embodiment of the present invention;

Figure 3 is a flowchart illustrating a method for disposing a sensor network according to an embodiment in the present invention;

Figure 4 is a flowchart illustrating a method for localizing a mobile node in a sensor network according to an embodiment of the present invention;

Figure 5 is a functional block diagram of a fixed node in a sensor network according to an embodiment of the present invention. Figure 6 is a schematic diagram illustrating a sensor network according to another embodiment of the present invention;

Figure 7 is a schematic diagram illustrating a sensor network according to another embodiment in the present invention.

Throughout the drawing figures, like reference numerals will be understood to refer to like parts and components.

DETAILED DESCRIPTION OF THE INVENTION Next, the embodiments of the present invention will describe in detail in conjunction with figures.

Figure 1 is a schematic diagram illustrating a sensor network according to an embodiment of the present invention, and the sensor network includes four beacon nodes 110,120,130 and 140, each of the beacon nodes may be a sensor, which broadcasts beacon message at different transmission power level every one second respectively, for instance, as shown in figure 1, the beacon node 110, 120, 130 and 140 broadcast beacon messages at transmission power level from 1 to 4 separately, and the transmission power level is included in corresponding broadcasted beacon message. One beacon message is comprised of two parts, beacon node ID and transmission power level, and the transmission power level denotes the transmission power level when a beacon transmits the beacon message. For instance, the beacon message sent by the beacon node 110 with beacon ID = 1 at transmission power level 2 is shown in table 1: Table 1

Besides, the whole area within the radio coverage of WSN includes many sub-areas partitioned by users, sub-area 151, 152, 153, 154,155 and 156. The sub-areas can be partitioned based on the functional areas in a specific application environment, which could be an area where users require for behavior monitoring performed by the WSN, such as an office. Sub-areas can also be appropriately partitioned according to the number and locations of beacon nodes 110,120,130 and 140.

Each of sub-areas 151,152,153,154,155 and 156 has one location respectively which is different from each other, so that one mobile node 160 that enters each of above sub- areas can utilize the location of the sub-area where the node resides to carry out localization, in other word, the mobile node 160 can implement localization according to the location of the sub-area closest to itself.

Figure 2 shows the schematic diagram in statistic format illustrating all beacon messages received by a mobile node according to an embodiment of the present invention. For example, there are 4 beacon nodes in a WSN, then for a specific mobile node in the WSN, the beacon message with lowest received transmission power level (LRTPL) 2, 2, 3 and 4 are received from the beacon nodes with beacon ID 1,2,3,4 at each fixed interval respectively. The final statistic result is shown in table 2. Table 2:

Figure 3 shows the flowchart of a method for disposing a sensor network according to an embodiment of the present invention. Firstly, at step S310, a user disposes sensor nodes as beacon nodes in a application environment, which could be an area where the user requires for the sensor network to perform user's behavior monitoring, e.g. an office. The number and location of the beacons can be determined according to the size of the application environment and the partition of the functional areas (e.g., office desk area, demonstration area beside whiteboard.)

And then, at step S320, the user sets the relating parameters of the beacons. The parameters may include: Timer_interval, denoting the desired time interval between two adjacent beacon messages sent from a beacon node); Min_power_level, denoting the lowest transmission power level of a beacon node; Max_power_level, denoting the highest transmission power level of a beacon node; Power_level_interval, denoting the increasing amplitude between two adjacent transmission power levels of a beacon node, etc.

Subsequently, at step S330, according to locations and parameters of above beacon nodes, the user partitions the whole application environment into several sub-areas, which may be partitioned according to the functional areas in the application environment, e.g. the office desk functional area, demonstration area beside whiteboard. In different functional areas, the user will take on different behaviors, e.g. standing up, sitting down, typing or making a phone call in office desk functional area. Partitioning sub-areas according to the functional areas in the application environment can make the judgment on the user's behaviors more accurate. At step S340, the user starts the test by using a mobile node to receive the beacon messages from each of beacon nodes in each sub-area, so as to obtain the LRTPL of beacon message from each of beacon nodes in each sub-area.

The LRTPL' s location mapping information of each corresponding beacon node shown in figure 1 is listed in table 3.

Table 3

Since the beacon message may be not well-received due to some unexpected reasons, the node in the same location will receive the beacon message with two different transmission power levels sent from the same beacon. The values of LRTPL have statistical property, for instance, sub-area 1 receives two beacon messages sent from the beacon 110 (beacon ID is 1) in certain time period: the LRTPL value of one beacon message is 2 and the LRTPL value of another beacon message is 3, in which the percentage of the number of beacon messages with LRTPL value 2 is 80%, with LRTPL value 3 is 20%. When determining the LRTPL value corresponding to each of sub-areas, only the LRTPL with larger percentage is referenced, for instance, the LRTPL value corresponding to Beacon ID 1 in sub-area 1 is 2.

At step S350, the LRTPL of each sub-area is analyzed. According to the information in table 2, the LRTPL corresponding to each beacon node in each sub-area will be finally obtained after analysis. For example, the LRTPL value corresponding to the beacon 110

(Beacon ID 1) in sub-area 1 is 2, the LRTPL value corresponding to the beacon 120

(Beacon ID 2) is 2, etc.

At step S360, the user judges whether each sub-area has different localization information, if so, then stores each LRTPL corresponding to each sub-area into a database at step S370.

Finally, at step S380, all location mapping information (table 3) will be stored in the data base, and the location mapping information may include the name of each sub-area, corresponding functional areas and their corresponding transmission power levels, etc.

At above step S360, if the judgment result is no, namely, at least two sub-areas have the same localization information, then at step 390, the user readjusts the relating parameters of beacon nodes, and further at step S395, readjusts the location of beacon nodes, then repeats procedures from step S330 to step S350 until each sub-area has unique localization information.

Figure 4 shows a flowchart illustrating the method for localizing a mobile node in a sensor network according to an embodiment of the present invention.

Firstly, at step S410, beacon node 110 monitors whether new mobile node (e.g. one user carrying sensor) enters the WSN. If the sensor network comprises multiple beacon nodes, the beacon node 110 among which can be selected as monitoring node, which monitors if new mobile node enters the WSN by monitoring whether the presence information is received from the mobile node.

Before the monitoring beacon node receives presence information from the mobile node, other beacon nodes could be in "hibernation" state; after receiving the presence information, the monitoring beacon node "wakes up" other beacon nodes Then, at step S420, a mobile node 160 enters into the sensor network, and then sends a presence message, which is used to inform the beacon node 110 that the mobile node 160 needs to be localized. Moreover, the presence message may also include the ID information of the mobile node 160, such as the personal ID information of the user carrying sensors, so that the corresponding ID authentication can be carried out firstly when the mobile node 160 enters the sensor network.

At step S430, the beacon node 110 judges whether it receives the presence message sent from the mobile node 160, if so, then the beacon node 110 "wakes up" other beacon nodes at step S440, otherwise, the beacon 110 continues judging whether it receives the presence message sent from the mobile node 160.

At step S450, the beacon node 110 sends beacon message to the mobile node 160, which includes the ID of the beacon node and the transmission power level for transmitting the beacon message. For instance, beacon node 110 with beacon ID 1 broadcasts the beacon message at different transmission power levels ranging from 1 to 4. The higher the transmission power level is, the broader range can the beacon message be broadcasted. The

LRTPL needed for receiving the beacon message at the location of the mobile nodelόO is 2, that is for beacon node 110, the LRTPL of the mobile node is 2.

At step S460, after receiving the beacon message, the mobile node 160 sends the LRTPL corresponding to each beacon node to a fixed node 170 in the sensor network, which is used to compare the similarity between LRTPL of the mobile node 160 and the

LRTPL of each sub-area in location mapping information table (table 3). Each sub-area's LRTPL is pre-stored in a data base included in the fixed node, (as step S370 shown in figure 4)

At step S470, fixed node 170 uses Euclidean distance to calculate the similarity between the LRTPL of mobile node and that of each sub-area.

}

Wherein, i denotes the ith known sub-area L₁; j denotes the jth beacon node B_j; k=l or 2, denote two different LRTPL values; PERyt denotes the percentage of each LRTPL;

PL_yk denotes the LRTPL corresponding to the beacon node B_j; RPL, denotes the LRTPL of the mobile node with respect to the jth beacon node; arg HUn₁ denotes the sub-area No. i L = arg min _: {∑ RPL _l - ∑ (PL _≠ * PER _≠ ) \ } with minimum A * ⁾ value, namely the most fitted sub-area to the location of mobile node 110.

At step S480, according to the pre-stored name information of each sub-area and the name information of their corresponding functional areas, fixed node 170 obtains the name of the most fitted (i.e the closest) sub-area to the mobile node 160 (e.g. sub-area 3) and the name of corresponding functional area (e.g. office desk area). In this way, the sensor network can know the functional area where the user resides and the possible behaviors taken by the user in the functional area so that the sensor network can make more accurate judgment for the user behaviors. At step S490, fixed node 170 will send the calculated location of the mobile node

160 (e.g. coordinate (89.235), the name of the sub-area corresponding to mobile node 160 and the name of corresponding functional areas, to a target node 180, which can be connected with an equipment (e.g. a lamp) to control the equipment.

At step S495, according to received above information, target node 180 can acquire the location of the mobile node, the name of corresponding sub-area and the name of corresponding functional area, and then take activities accordingly, e.g. increasing the brightness of the lamp.

Figure 5 shows the schematic diagram illustrating the functional block of a fixed node in a sensor network according to an embodiment of the present invention.

The fixed node 500 comprises an acquiring device 510, for acquiring the LRTPL of the beacon message sent from each of beacon node to a mobile node in the sensor network (as shown in figure 2);

The fixed node 500 further comprises a storage device 540, for storing the LRTPL location mapping information for each sub-area with known location with respect to each beacon node in the sensor network (as shown in table 3), name of each sub-area and the sub-area information of corresponding functional area name. Moreover, the storage device 540 is also used to store the user ID information of a mobile node and cipher information, etc. The fixed node 500 further comprises a comparing device 522 and a determining device 524, in which the comparing device 522 is used to compare the similarity between the LRTPL of a mobile node acquired by the acquiring device 510 and the LRTPL location mapping information of each sub-area with respect to each beacon node stored in the storage device 540, so as to obtain the most fitted sub-area to the mobile node 160. The comparing method can be referred to the illustration of step S570 in figure 5.

Based on the comparison result and the name, location and name of corresponding functional areas of each sub-area stored in the storage device 540, the determining device

524 determines the specific location of the mobile node 160.

The fixed node 500 also comprises an actuator 530, which could be connected with an equipment (e.g. a lamp) in cable or wireless way. After processor 520 calculates out the location of the mobile node, the fixed node can control the equipment to make corresponding adjustment through actuator 530. (e.g. increasing the brightness of the lamp)

It is to be understood by those skilled in the art that the actuator 500 can be also included in another node independent from the fixed node 500, and receive the location information of the mobile node sent from the fixed node 500, and also control an equipment(e.g. a lamp) according to the location information. The fixed node 500 further comprises a transmitting device 580 and a receiving device 590, in which transmitting device 590 is used to broadcast the calculated location information of the mobile node in the sensor network.

It is to be understood by those skilled in the art that each functional module contained in the fixed node 500 in the present invention can also be allocated in each different node (e.g. each beacon node or target node) in the sensor network in integrated or distributed manner, for instance, full functions of the fixed node 500 can also be realized in each beacon node or target node. It is evident that the functions of the fixed node 500 can also be fulfilled by the mobile node.

The method and apparatus for localization in a wireless network according to an embodiment of the present invention can be applied in an office environment equipped with sensor network, through the sensor carried by the user (namely a mobile node), can the location of the user be calculated out. Also, according to the location of the user, the identification of frequent activities of the user in the area can be fulfilled, and furthermore, intelligently adjusting and controlling indoor lighting system can also be achieved according to user's behavior status.

Figure 6 is a schematic diagram illustrating a sensor network according to another embodiment of the present invention. As shown in figure 6, according to another embodiment of the present invention, the sensor network may comprise a beacon node 110 as minimum, which broadcasts the beacon message at four different transmission power levels ranging from 1 to 4, and then the value of LRTPL received at mobile node 160 is 2. Correspondingly, a user uses the mobile node to perform the test to receive the beacon message sent from beacon node 110 in sub-area 151,153,154 and 156, so as to obtain the beacon message's LRTPL received from each beacon node in each sub-area.

For example, the LRTPL of each beacon node corresponding to each sub-area is shown in table 4 Table4:

Then, following the method illustrated in figure 4, we can use Euclidean distance to calculate the similarity between the LRTPL of mobile node and that of sub-area, and get the most fitted sub-area to the mobile node 160 (sub-area 156), so as to determine the location of the mobile node 160.

Figure 7 is a schematic diagram illustrating a sensor network according to another embodiment of the present invention.

As shown in Figure 7, it is to be understood by those skilled in the art that the method and apparatus for localization in wireless network as disclosed in this invention can also be used by the mobile node 160 to be localized, wherein the mobile node 160 can broadcast the location information at different transmission power levels (e.g. from 1 to 4), and beacon node 110, 120,130 and 140, as receiving devices, receive the LRTPL of the location information with value 2, 2, 3 and 4 respectively, same as in table 2. Accordingly, when disposing such kind of sensor network, a user uses one mobile node to perform the message-sending test in each sub-area to obtain the LRTPL of each sub-area. Following the same way can the data shown in figure 3 be obtained. Then, following the method shown in figure 4, Euclidean distance is used to calculate the similarity between the LRTPL of mobile node and that of sub-area to obtain the most fitted sub-area to the mobile node 160 ( sub-area 156), thereby determining the location of the mobile node 160.

It is to be understood by those skilled in the art that the method and apparatus for localization in wireless network as disclosed in this invention can not only be applied in sensor network, but also be made of various modifications without departing from the spirit and scope of the invention so as to be applied in other kinds of wireless networks, e.g.

Blue Tooth Piconet, etc.

It is to be understood by those skilled in the art that the method and apparatus for localization in wireless network as disclosed in this invention can be made of various modifications without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

CLAIMS:

1. A method for localizing a mobile node in a wireless network, comprising the steps of:

(a) acquiring a transmission power level, which is related to location of the mobile node;

(b) comparing the transmission power level with a location mapping information, wherein the location mapping information comprises at least a known location and its corresponding transmission power level; and

(c) determining the location of the mobile node, according to the comparison result.

2. The method according to claim 1, further comprising the step of: receiving a group of localization messages with at least two localization messages from a signal source, wherein the group of localization messages includes a transmission power level respectively different from each other; wherein the step (a) comprises the step of: acquiring a lower transmission power level in the group of localization messages, and the transmission power level is related to the location of the mobile node.

3. The method according to claim 2, further comprising the steps of: receiving a group of localization messages with at least two localization messages from another different signal source, wherein the group of localization messages includes a transmission power level respectively different from each other; wherein the step (a) comprises the step of: acquiring a lower transmission power level in the group of localization messages, and the transmission power level is related to the location of the mobile node.

4. The method according to claim 1, further comprising the step of: acquiring the location mapping information, which comprises at least a known location and its corresponding transmission power level.

5. The method according to claim 1, further comprising the step of: sending a location message of the mobile node to a target node, which can control an equipment according to the location message.

6. The method according to claim 1, wherein the known location is a sub-area, and the step (c) comprises the step of: determining a most fitted sub-area to the acquired transmission power level.

7. The method according to claim 6, wherein the step (c) further comprises the step of: determining a name of the sub-area.

8. The method according to claim 6, wherein the step (c) further comprises the step of: determining a functional area of the sub-area.

9. An apparatus for localizing a mobile node in a wireless network, comprising: an acquiring device, for acquiring a transmission power level, which is related to location of the mobile node; a comparing device, for comparing the transmission power level with a location mapping information, which comprises of at least a known location and its corresponding transmission power level; and a determining device, for determining the location of the mobile node according to the comparison result.

10. The apparatus according to claim 9, wherein the determining device is used to determine the most fitted sub-area to the transmission power level of the mobile node.

11. The apparatus according to claim 9, further comprising a storage device, for storing the location mapping information, which includes at least a known location and its corresponding transmission power level.

12. The apparatus according to claim 11, wherein the storage device is used to store user's ID of the mobile node and cipher information.

13. The apparatus according to claim 9, further comprising an actuator, for controlling an equipment according to the location of the mobile node.

14. A wireless network system for localizing a mobile node in the wireless network, comprising: at least a receiving device, for receiving a group of localization messages with at least two localization messages from the mobile node, wherein the group of localization messages includes a transmission power level respectively different from each other; an acquiring device, for acquiring a lower transmission power level in the group of localization messages, and the transmission power level is related to the location of the mobile node; a comparing device, for comparing the transmission power level and a location mapping information, which comprises at least a known location and its corresponding transmission power level; and a determining device, for determining the location of the mobile node according to the comparison result.

15. A wireless network system for localizing a mobile node in the wireless network, comprising: at least a transmitting device, for sending a group of localization messages with at least two localization messages, wherein the group of localization messages includes a transmission power level respectively different from each other; an acquiring device, for acquiring a lower transmission power level in the group of localization messages, and the transmission power level is related to the location of the mobile node; a comparing device, for comparing the transmission power level with a location mapping information, which comprises at least a known location and its corresponding transmission power level; and a determining device, for determining the location of the mobile node according to the comparison result.