JP7814732B2 - Location estimation device, location estimation system and mobile node - Google Patents

Description

Article 30, paragraph 2 of the Patent Act applies 1. Date held: September 16, 2021 2. Institute of Electronics, Information and Communication Engineers Society Conference 2021 (correspondence lecture) 3. Preliminary manuscript published: August 31, 2021 [Publications, etc.] 1. Date held: November 12, 2021 2. AXIES High-Quality and Security ICT Workshop 2021 3. Preliminary manuscript published: None [Publications, etc.] 1. Date held: November 26, 2021 2. Institute of Electronics, Information and Communication Engineers Network System Study Group 2021 3. Preliminary manuscript published: November 18, 2021

This disclosure relates to a location estimation device, a location estimation system, and a mobile node.

Various methods have been proposed for estimating location indoors, where GPS signals are difficult to reach, using wireless communication technologies such as Wi-Fi, Bluetooth, and BLE (Bluetooth Low Energy).

Non-Patent Document 1 describes a method in which multiple signal sources (beacons) that transmit wireless signals are installed indoors, the distance from each signal source is estimated based on the received signal strength indicator (RSSI) of the wireless signals, and the estimated distance is used to estimate location.

However, the relationship between RSSI and distance from the signal source varies depending on the radio wave propagation environment. Therefore, in reality, it is difficult to accurately estimate the distance from the signal source based on RSSI, and a location estimate using an inaccurate distance will also be inaccurate. Furthermore, the error in the distance estimated based on RSSI increases in proportion to the distance from the signal source. Therefore, in order to improve the accuracy of location estimation, it is necessary to install a large number of signal sources closely together, which is costly.

Non-Patent Document 1 also describes a method (fingerprinting) for estimating location by dividing an indoor area into multiple sections, pre-measuring the RSSI for each section, and selecting the RSSI closest to the current RSSI from the pre-measured RSSIs. However, even with the fingerprinting method, improving the accuracy of location estimation requires the installation of multiple signal sources, which is similarly costly.

F. Zafari, A. Gkelias, K.K. Leung, "A Survey of Indoor Localization Systems and Technologies," IEEE Communications Surveys & Tutorials, Vol. 21, No. 3, pp. 2568-2599, 2019.

The present disclosure aims to solve the above-mentioned problems and provide a location estimation device, location estimation system, and mobile node that perform location estimation with high accuracy.

To solve the above problems, the position estimation device disclosed herein is a position estimation device that estimates the position of a mobile node, wherein each of the mobile and fixed nodes broadcasts a wireless signal containing an identifier assigned to that node, and the position estimation device includes: a receiving unit that receives proximity information from each of the mobile and fixed nodes, the proximity information including identifiers of other nodes contained in the wireless signal received by that node with a received signal strength equal to or greater than a predetermined threshold; a proximity relationship identifying unit that identifies the proximity relationship between each of the nodes based on the proximity information; and a position estimation unit that estimates the position of the mobile node based on the proximity relationship between each of the nodes and the positions of the fixed nodes.

Furthermore, the position estimation system according to the present disclosure includes a mobile node capable of transmitting and receiving wireless signals, a fixed node capable of transmitting and receiving wireless signals, and a position estimation device. Each of the mobile node and the fixed node includes a broadcast unit that broadcasts a wireless signal including an identifier assigned to the node, a first receiving unit that receives wireless signals broadcast by other nodes, a creating unit that creates proximity information including identifiers of other nodes included in wireless signals received by the first receiving unit with a received signal strength equal to or greater than a predetermined threshold, and a transmitting unit that transmits the proximity information to the position estimation device. The position estimation device includes a second receiving unit that receives the proximity information from the mobile node and the fixed node, a proximity relationship identifying unit that identifies a proximity relationship between the nodes based on the proximity information, and a position estimation unit that estimates the position of the mobile node based on the proximity relationship between the nodes and the positions of the fixed nodes.

Furthermore, the mobile node according to the present disclosure is a mobile node capable of transmitting and receiving wireless signals, and includes a broadcast unit that broadcasts wireless signals including an identifier assigned to the mobile node, a first receiving unit that receives wireless signals broadcast by other nodes, a creating unit that creates proximity information including identifiers of other nodes included in wireless signals received by the first receiving unit with a received signal strength equal to or greater than a predetermined threshold, a transmitting unit that transmits the proximity information to other nodes, a second receiving unit that receives the proximity information from other nodes, a proximity relationship identifying unit that identifies proximity relationships between nodes based on the proximity information, and a position estimating unit that estimates the position of the mobile node based on the proximity relationships between nodes and the positions of fixed nodes.

Furthermore, another mobile node according to the present disclosure is a mobile node capable of transmitting and receiving wireless signals, and includes: a memory unit that stores the number of hops from a fixed node to the mobile node and the position of the fixed node; a broadcast unit that broadcasts the number of hops from the fixed node to the mobile node and the position of the fixed node stored in the memory unit; a receiver unit that receives wireless signals broadcast by other nodes; an adder unit that adds the number of hops from the fixed node to the mobile node and the position of the fixed node to the memory unit based on either or both of the number of hops from the fixed node to the mobile node and the position of the fixed node contained in wireless signals received by the receiver unit with a received signal strength equal to or greater than a predetermined threshold; and a position estimation unit that estimates the position of the mobile node based on the number of hops from the fixed node to the mobile node and the position of the fixed node stored in the memory unit.

1 is a diagram showing a configuration of a position estimation system according to a first embodiment; FIG. 2 illustrates an example of proximity information transmitted by a mobile node. FIG. 2 is a block diagram showing the functional configuration of a mobile node. FIG. 2 is a block diagram showing the functional configuration of a location estimation server. 10 is a flowchart detailing the processing performed by the mobile node and the anchor node; 10A and 10B are diagrams illustrating examples of proximity information created by a mobile node and an anchor node. 10 is a flowchart illustrating details of a process executed by a location estimation server. FIG. 1 is a diagram illustrating an example of an undirected graph representing the proximity relationships of each node. FIG. 8B illustrates a matrix representation of the undirected graph of FIG. 8A. FIG. 10 is a diagram illustrating an example of a distance matrix of the number of hops. FIG. 10 is a diagram illustrating a method for calculating an average distance per hop. FIG. 10 is a diagram illustrating an example of an estimated distance matrix. FIG. 10 is a diagram illustrating a configuration of a position estimation system according to a second embodiment. 10 is a diagram showing an example of the number of hops of a mobile node and the position of an anchor node stored in a memory unit of the mobile node; FIG. FIG. 2 is a block diagram showing the functional configuration of a mobile node. 10 is a flowchart illustrating the details of a process executed by a mobile node. FIG. 1 illustrates the steps of a process performed by a mobile node. FIG. 1 illustrates the steps of a process performed by a mobile node. FIG. 1 illustrates the steps of a process performed by a mobile node. FIG. 1 illustrates the steps of a process performed by a mobile node.

Embodiments of the present disclosure will be described below with reference to the drawings. Identical or corresponding elements in the drawings are designated by the same reference numerals, and detailed descriptions will be omitted where appropriate.

(Embodiment 1)
Fig. 1 is a diagram illustrating a configuration of a position estimation system 100 according to a first embodiment of the present disclosure. Fig. 1 illustrates an indoor monitoring area S. Specific examples of facilities having the monitoring area S include manufacturing facilities (such as manufacturing sites, warehouses, and offices), hospitals, large-scale commercial facilities, and public facilities (such as train stations, airports, and city halls).

Three fixed nodes (anchor nodes) A to C, which are wireless communication devices capable of sending and receiving wireless signals, are installed in the monitoring area S. The positions (X and Y coordinates) of anchor nodes A to C on a two-dimensional plane are known. There are no particular limitations on how anchor nodes A to C are installed, but they may be installed on the floor of monitoring area S or attached to the wall or ceiling. Anchor nodes A to C are assigned unique identifiers ID_A to ID_C, respectively, that allow them to be uniquely identified. Note that the number of anchor nodes is not limited to three; any number greater than three is sufficient. The reason for the number of anchor nodes being three or more is that three or more signal sources with known positions are required when using the multilateration technique described below.

Anchor nodes A to C may be dedicated wireless communication devices or IoT (Internet of Things) devices. The wireless communication method of anchor nodes A to C is not particularly limited, but may be, for example, Wi-Fi, Bluetooth, BLE, RFID (Radio Frequency Identifier), ZigBee, or UWB (Ultra Wide Band).

Furthermore, there are six people in the monitored area S, each carrying mobile nodes 1 to 6, which are wireless communication devices capable of sending and receiving wireless signals. The positions (X and Y coordinates) of mobile nodes 1 to 6 on a two-dimensional plane change as the people carrying mobile nodes 1 to 6 move around within the monitored area S. Mobile nodes 1 to 6 are assigned unique identifiers ID_1 to ID_6, respectively, which allow each mobile node to be uniquely identified. Note that the number of mobile nodes is not limited to six, as long as it is one or more.

Mobile nodes 1-6 may be dedicated wearable terminals or IoT devices, or may be portable devices with wireless communication capabilities, such as mobile phones, smartphones, tablets, PDAs (Personal Digital Assistants), or personal computers. The wireless communication method used by mobile nodes 1-6 is not particularly limited, but may be, for example, Wi-Fi, Bluetooth, BLE, ZigBee, or UWB.

Mobile nodes 1-6 and anchor nodes A-C constantly broadcast wireless signals containing their own node identifiers to the surrounding area at a predetermined transmission power. Furthermore, mobile nodes 1-6 and anchor nodes A-C acquire the identifiers contained in wireless signals broadcast by other nodes that are received by the own node with an RSSI above a predetermined threshold.

Mobile nodes 1-6 and anchor nodes A-C transmit "proximity information" containing identifiers of other nodes contained in wireless signals received by the own node with an RSSI above a predetermined threshold to location estimation server 20 at a predetermined first period. Note that the fact that the proximity information contains only identifiers of other nodes received by the own node with an RSSI above a predetermined threshold means that it contains only identifiers of other nodes that are relatively close to the own node.

Figure 2 is a diagram showing an example of proximity information transmitted by mobile node 1. The first identifier in the proximity information is the identifier of the local node. Therefore, in the example of Figure 2, ID_1, the identifier of mobile node 1, is stored. However, if the location estimation server 20 can identify the node that sent the proximity information by other means, such as by referring to header information included in the wireless signal, the identifier of the local node may be omitted. The second and subsequent identifiers in the proximity information are identifiers of other nodes received by the local node with an RSSI above a predetermined threshold, i.e., identifiers of other nodes located relatively close to the local node. In the example of Figure 2, ID_3, the identifier of mobile node 3, ID_5, the identifier of mobile node 5, and ID_C, the identifier of anchor node C, are stored.

Location estimation server 20 is installed near monitoring area S and receives proximity information transmitted from mobile nodes 1-6 and anchor nodes A-C at a predetermined first cycle. When location estimation server 20 receives proximity information from mobile nodes 1-6 and anchor nodes A-C, it estimates the positions of mobile nodes 1-6 on a two-dimensional plane based on the proximity information and the positions of anchor nodes A-C, whose positions are known. Note that location estimation server 20 does not have to be installed near monitoring area S, but may be installed within monitoring area S.

Figure 3 is a block diagram showing the functional configuration of mobile node 1. Mobile nodes 2-6 and anchor nodes A-C also have similar functional configurations. Mobile node 1 comprises a broadcast unit 11, a receiving unit 12, a creating unit 13, a transmitting unit 14, and a wireless communication interface 15. However, the configuration shown in Figure 3 is a functional configuration, and the hardware configuration may differ.

The broadcast unit 11 broadcasts a wireless signal containing its own node identifier, ID_1, to the surrounding area via the wireless communication interface 15 at a predetermined transmission power. The receiver 12 receives wireless signals broadcast by other nodes via the wireless communication interface 15. The creator 13 acquires the identifiers of other nodes contained in wireless signals received by the receiver 12 with an RSSI equal to or greater than a predetermined threshold, and creates proximity information containing the identifiers of the other nodes. The transmitter 14 transmits the proximity information created by the creator 13 to the location estimation server 20 via the wireless communication interface 15. Note that anchor nodes A to C may further be provided with a wired communication interface (not shown), and may transmit the proximity information created by the creator 13 to the location estimation server 20 via wired communication.

Figure 4 is a block diagram showing the functional configuration of the location estimation server 20. The location estimation server 20 includes a wireless communication interface 21, a receiving unit 22, a proximity relationship identification unit 23, a location estimation unit 24, and a display unit 25. However, the configuration shown in Figure 4 is a functional configuration, and the hardware configuration may differ. Furthermore, each function of the location estimation server 20 may be implemented in multiple physically separated components.

The receiver 22 receives proximity information from mobile nodes 1-6 and anchor nodes A-C via the wireless communication interface 21. As described above, the proximity information includes the identifiers of other nodes contained in wireless signals received by the node with an RSSI equal to or greater than a predetermined threshold. If anchor nodes A-C have a wired communication interface, the location estimation server 20 may also have a wired communication interface (not shown) and receive proximity information from anchor nodes A-C via wired communication.

The proximity relationship identification unit 23 creates an undirected graph representing the proximity relationships between each node based on the proximity information. The position estimation unit 24 estimates the positions of each of the mobile nodes 1 to 6 based on the undirected graph representing the proximity relationships between each node and the positions of anchor nodes A to C, whose positions are known.

The position estimation unit 24 includes a hop count calculation unit 24a, a distance estimation unit 24b, a position memory unit 24c, an individual position estimation unit 24d, and a cooperative position estimation unit 24e. The hop count calculation unit 24a calculates the number of hops between each node based on an undirected graph representing the proximity relationships between each node. The distance estimation unit 24b estimates the actual distance between each node based on the number of hops between each node and the positions of anchor nodes A to C, whose positions are known. In this embodiment 1, the distance estimated by the distance estimation unit 24b is referred to as the "estimated distance." The position memory unit 24c pre-stores the positions of anchor nodes A to C. The individual position estimation unit 24d individually estimates the position of each of mobile nodes 1 to 6 using a multilateration technique based on the estimated distance between the mobile node and anchor nodes A to C. The cooperative position estimation unit 24e simultaneously estimates the positions of mobile nodes 1-6 by solving an optimization problem that includes the positions of mobile nodes 1-6 as variables, using the positions of mobile nodes 1-6 estimated by the individual position estimation unit 24d as initial estimated positions. The display unit 25 is configured, for example, with a liquid crystal display panel, and displays the positions of mobile nodes 1-6 estimated by the cooperative position estimation unit 24e.

Next, we will explain the process for estimating the positions of mobile nodes 1-6 in position estimation system 100 according to embodiment 1. The process for estimating the positions of mobile nodes 1-6 is divided into a process performed by mobile nodes 1-6 and anchor nodes A-C, and a corresponding process performed by position estimation server 20.

Figure 5 is a flowchart that details the processing performed by mobile nodes 1-6 and anchor nodes A-C.

In step S101, the broadcast unit 11 of each of mobile nodes 1-6 and anchor nodes A-C begins broadcasting a wireless signal containing the node's identifier via the wireless communication interface 15. The transmission power at this time is the same for all of mobile nodes 1-6 and anchor nodes A-C, for example, 2.5 mW.

In step S102, the receiver 12 of each of the mobile nodes 1-6 and anchor nodes A-C receives all wireless signals with an RSSI above a predetermined threshold via the wireless communication interface 15 and acquires the identifiers of other nodes contained in each received signal. Here, the predetermined threshold is, for example, -50 dBm. However, this predetermined threshold may be adjusted as appropriate depending on the number or density of mobile nodes within the monitoring area S. For example, if there are many mobile nodes within the monitoring area S and the distances between the mobile nodes are short, the predetermined threshold may be set higher than -50 dBm. Conversely, if there are few mobile nodes within the monitoring area S and the distances between the mobile nodes are long, the predetermined threshold may be set lower than -50 dBm. Furthermore, to deal with cases where the RSSI fluctuates slightly, the receiver 12 may acquire all identifiers of other nodes contained in wireless signals received with an RSSI above a predetermined threshold at least once within a predetermined period, for example, 100 ms.

For example, suppose that receiver 12 of mobile node 1 is able to receive the wireless signals broadcast by mobile node 3, mobile node 5, and anchor node C at least once within a specified time period with an RSSI above a specified threshold. This means that mobile node 3, mobile node 5, and fixed node C are present in the vicinity of mobile node 1 (for example, within a radius of about 4 m). At this time, mobile node 1 acquires ID_3, the identifier of mobile node 3, ID_5, the identifier of mobile node 5, and ID_C, the identifier of anchor node C. The same applies to mobile nodes 2-6 and anchor nodes A-C.

In step S103, the creation units 13 of mobile nodes 1-6 and anchor nodes A-C create proximity information based on the identifiers of other nodes acquired in step S102 above. As mentioned above, the proximity information includes the identifier of the node itself (optional) and the identifiers of other nodes located near the node itself. Figure 6 shows an example of a list of each piece of proximity information created by the creation units 13 of mobile nodes 1-6 and anchor nodes A-C.

In step S104, the transmitters 14 of the mobile nodes 1-6 and anchor nodes A-C transmit the proximity information created in step S103 to the position estimation server 20 via the wireless communication interface 15. In particular, the transmitters 14 of the mobile nodes 1-6 and anchor nodes A-C transmit the proximity information to the position estimation server 20 via the wireless communication interface 15. If wired communication is possible between the anchor nodes A-C and the position estimation server 20, the transmitters 14 of the anchor nodes A-C may transmit the proximity information to the position estimation server 20 via wired communication.

In step S105, mobile nodes 1-6 and anchor nodes A-C wait for a predetermined time, for example, 100 ms. This wait time corresponds to the aforementioned predetermined first period during which mobile nodes 1-6 and anchor nodes A-C transmit proximity information to location estimation server 20. When the predetermined wait time expires, the processing of the flowchart in FIG. 5 returns to step S102.

By performing the above process, mobile nodes 1-6 and anchor nodes A-C can repeatedly transmit proximity information, including identifiers of other nodes present in the vicinity of the node, to the location estimation server 20 at a predetermined first period.

Figure 7 is a flowchart that details the processing performed by the location estimation server 20, corresponding to the processing performed by mobile nodes 1-6 and anchor nodes A-C in Figure 6.

In step S201, the receiver 22 of the location estimation server 20 receives, via the wireless communication interface 21, the proximity information transmitted by mobile nodes 1-6 and anchor nodes A-C in step S104 of FIG. 5 for a predetermined period of time, for example, one second. That is, the receiver 22 of the location estimation server 20 receives all of the proximity information for each node shown in FIG. 6. However, if the same proximity information is received multiple times, only the proximity information received first is retained and the proximity information received later is discarded. Note that if wired communication is possible between anchor nodes A-C and the location estimation server 20, the receiver 22 of the location estimation server 20 may receive proximity information from anchor nodes A-C via wired communication.

In step S202, the proximity relationship identification unit 23 of the location estimation server 20 creates an undirected graph, such as that shown in Figure 8A, that represents the proximity relationships of each node based on the proximity information of mobile nodes 1 to 6 and anchor nodes A to C received in step S201 above.

In more detail, in this first embodiment, a pair of nodes that can receive each other's identifier with an RSSI above a predetermined threshold is defined as a "neighboring node pair." For example, when mobile node 1 can receive mobile node 3's identifier with an RSSI above a predetermined threshold, and mobile node 3 can receive mobile node 1's identifier with an RSSI above a predetermined threshold, mobile node 1 and mobile node 3 become a "neighboring node pair." By linking these neighboring node pairs, an undirected graph such as that shown in Figure 8A is created. Figure 8B is a matrix representation of the undirected graph in Figure 8A. As is well known, a matrix that represents an undirected graph with a finite number of vertices is a symmetric matrix, and its diagonal elements are all zeros.

Note that if there is an inconsistency in the proximity information sent by the mobile nodes, for example, if the proximity information sent by mobile node 1 includes the identifier of mobile node 3, but the proximity information sent by mobile node 3 does not include the identifier of mobile node 1, mobile node 1 and mobile node 3 do not satisfy the definition of a "neighboring node pair" above. In such a case, the edge between mobile node 1 and mobile node 3 in Figure 8A no longer exists, and the elements (1, 3) and (3, 1) of the matrix in Figure 8B both become 0. Alternatively, for example, the identifier of mobile node 1 can be added to the proximity information received from mobile node 3, thereby correcting the relationship so that mobile node 1 and mobile node 3 satisfy the definition of a "neighboring node pair." With this correction, an edge between mobile node 1 and mobile node 3 in Figure 8A now exists, and the elements (1, 3) and (3, 1) of the matrix in Figure 8B both become 1.

In step S203, the hop count calculation unit 24a of the location estimation server 20 calculates the number of hops between each node included in the undirected graph of Figure 8A and creates a hop count distance matrix as shown in Figure 9.

In the distance matrix of Figure 9, for example, the number of hops between mobile node 1 and mobile node 3 is 1. Also, the number of hops between mobile node 1 and anchor node A is 4. This means that even in the actual monitoring area S, the actual distance (spatial distance or physical distance) between mobile node 1 and mobile node 3 is likely to be shorter than the actual distance between mobile node 1 and fixed node A. In other words, from the perspective of mobile node 1, mobile node 3 is likely to be located closer than fixed node A.

The specific method for calculating the number of hops between each node included in the undirected graph of Figure 8A is not particularly limited, but well-known algorithms such as breadth-first search and Dijkstra's algorithm can be used. As is clear from the method for creating the distance matrix, the distance matrix of Figure 9 is a symmetric matrix, and all of its diagonal elements are 0.

In step S204, the distance estimation unit 24b of the location estimation server 20 calculates the average distance per hop in the undirected graph of Figure 8A. In detail, the distance estimation unit 24b of the location estimation server 20 calculates the average distance per hop based on the positions of anchor nodes A to C stored in the position memory unit 24c.

Specifically, consider a situation where N nodes exist on a two-dimensional plane corresponding to the floor surface of the monitoring area S. Of the N nodes, the first n (1st to nth) are mobile nodes whose positions are unknown, and the remaining N-n (n+1st to Nth) are anchor nodes whose positions are known. In this first embodiment, there are mobile nodes 1 to 6 and anchor nodes A to C, so N=9 and n=6.

In this case, the average distance Hd per hop in the undirected graph of Figure 8A is calculated according to the following formula (1) from the known positions r _i (i = n + 1, ..., N) of the anchor nodes and the number of hops h _ij (i, j = n + 1, ..., N) between each anchor node.

10, the number of hops between anchor node A and anchor node B is 2, the number of hops between anchor node B and anchor node C is 3, and the number of hops between anchor node C and anchor node A is 4. Also, for example, assume that the distance between anchor node A and anchor node B |r _A - r _B |=8 m, the distance between anchor node B and anchor node C |r _B - r _C |=10 m, and the distance between anchor node C and anchor node A |r _C - r _A |=18 m. In this case, the average distance Hd per hop is Hd=(8+10+18)/(2+3+4)=4.0 m.

In step S205, the distance estimation unit 24b of the location estimation server 20 estimates the actual distance between each node. In detail, the distance estimation unit 24b of the location estimation server 20 multiplies each element of the distance matrix of the number of hops in FIG. 9 by the average distance per hop Hd calculated in step S204 above to create an estimated distance matrix containing estimated distances as elements, as shown in FIG. 11. Each element of the estimated distance matrix in FIG. 11 represents an estimate of the actual distance between each node (estimated distance). However, in the estimated distance matrix in FIG. 11, estimated distances corresponding to elements with a hop count of 3 or more are replaced with a predetermined large value N, for example, 100. Although not present in FIG. 11, estimated distances between nodes for which a proximity relationship cannot be determined are also replaced with a predetermined large value N.

The predetermined large value N has almost no effect on the calculation results when estimating the positions of mobile nodes 1-6 in steps S206 and S207, which will be described below. In other words, replacing the estimated distance corresponding to an element with three or more hops with the predetermined large value N means that when estimating the positions of mobile nodes 1-6, only the estimated distances between nodes with one or two hops, i.e., nodes located relatively close to each other, are used, and the estimated distances between nodes with three or more hops, i.e., nodes located relatively far away, are not used. In other words, the positions of mobile nodes 1-6 are estimated based only on the estimated distances between nearby nodes, which are expected to be highly accurate and are less susceptible to the effects of RSSI errors, which increase in proportion to the distance from the signal source, and the radio wave propagation environment.

The threshold for the number of hops is not limited to 3, and may be adjusted as appropriate depending on the number or density of mobile nodes within the monitoring area S. For example, if there are many mobile nodes within the monitoring area S and the distances between the mobile nodes are short, the threshold for the number of hops may be set to a value smaller than 3. Conversely, if there are few mobile nodes within the monitoring area S and the distances between the mobile nodes are long, the threshold for the number of hops may be set to a value larger than 3.

In step S206, the individual position estimation unit 24d of the position estimation server 20 individually estimates the position of each of the mobile nodes 1-6 based on a multilateration technique. As is well known, multilateration requires three or more signal sources with known positions. Therefore, in this first embodiment, three or more anchor nodes are also required. In multilateration, the position of each of the mobile nodes 1-6 is individually estimated based on the estimated distance between the mobile node and anchor nodes A-C, whose positions are known.

In detail, the individual position estimation unit 24d of the position estimation server 20 estimates the position r i of the mobile node i by performing an appropriate number of repeated calculations according to the following equation (2) from the estimated distance d _ij (i = 1, ..., n; j = n + 1, ..., N) between the mobile node i and the anchor node _j included in the estimated distance matrix of Figure 11.

In the above equation, r _i ^{(1, k)} is the k-th solution, and N _i is the number of anchor nodes j that can be reached by tracing the edges on the undirected graph from mobile node i, the location of which is to be estimated, on the undirected graph that represents the proximity relationships between each node in Figure 8A. Also, A _ij is a variable that indicates whether the estimated distance between mobile node i and anchor node j is known, and if the estimated distance is known, A _ij = 1, and if the estimated distance is unknown, A _ij = 0. Note that the second term in the above equation can be used for r _i ^{(1, 1)} .

In step S207, cooperative position estimation unit 24e of position estimation server 20 simultaneously estimates the positions of mobile nodes 1 to 6 by solving an optimization problem that includes the positions of mobile nodes 1 to 6 as variables. At this time, the positions of mobile nodes 1 to 6 estimated in step S206 above are used as the initial estimated positions of mobile nodes 1 to 6. However, if the number of anchor nodes reachable from the node whose position is to be estimated by tracing edges on the undirected graph is 1, the position of that anchor node is set to r _i ⁽¹⁾ . Also, if the number of anchor nodes reachable from the node whose position is to be estimated by tracing edges on the undirected graph is 0, the center of monitoring area S is set to r _i ⁽¹⁾ .

Specifically, the cooperative location estimation unit 24e of the location estimation server 20 simultaneously obtains the location r _i of the mobile node i by solving a nonlinear optimization problem defined by the following equation (3).

In the above equation, the objective function f(x ₁ , . . . , x _n ) is defined by the following equation (4).

As an example of a method for solving the above optimization problem, stress majorization (E. R. Gansner, Y. Koren, and S. North, "Graph drawing by stress majorization," in Graph Drawing, ser. Lecture Notes in Computer Science, Heidelberg, Germany: Springer, 2005, pp. 239-250) can be used. Furthermore, instead of formulating the optimization problem using equations (3) and (4) above, a formulation based on multidimensional scaling, for example, may be used.

In step S208, the display unit 25 of the location estimation server 20 displays the locations of mobile nodes 1 to 6 estimated in step S207 above. The display format is not particularly limited, but for example, the locations of mobile nodes 1 to 6 may be plotted on a two-dimensional diagram representing the monitoring area S. Once the display is complete, the processing of the flowchart in Figure 7 returns to step S201.

By performing the above process, the positions of mobile nodes 1 to 6 are repeatedly estimated and sequentially displayed on the display unit 25.

As described above, the position estimation system 100 according to the first embodiment of the present disclosure includes mobile nodes 1-6 whose positions are unknown, anchor nodes A-C whose positions are known, and a position estimation server 20. Mobile nodes 1-6 and anchor nodes A-C constantly broadcast radio signals containing their own node identifiers to their surroundings at a predetermined transmission power. In other words, not only anchor nodes A-C but also mobile nodes 1-6 broadcast radio signals containing their own node identifiers to their surroundings.

Mobile nodes 1-6 and anchor nodes A-C transmit proximity information to location estimation server 20, including the identifiers of other nodes received by the node with an RSSI above a predetermined threshold. In other words, only information about nearby nodes that are relatively close to the node and are unlikely to be affected by RSSI errors, which increase in proportion to the distance from the signal source, or the radio wave propagation environment, and are therefore expected to be highly accurate, is transmitted to location estimation server 20.

When the location estimation server 20 receives proximity information from mobile nodes 1-6 and anchor nodes A-C, it identifies the proximity relationships (undirected graph) between each node based on the proximity information, and estimates the location of each mobile node 1-6 based on the proximity relationships between each node and the locations of anchor nodes A-C. In other words, the location of each mobile node 1-6 is estimated based only on information from nearby nodes, which is expected to be highly accurate and is less susceptible to the effects of RSSI errors, which increase in proportion to the distance from the signal source, and the radio wave propagation environment.

As described above, by estimating the positions of mobile nodes 1-6 based on the proximity relationships between mobile nodes 1-6 and anchor nodes A-C, the accuracy of position estimation is improved compared to conventional techniques that estimate the positions of mobile nodes based on the RSSI of wireless signals transmitted from signal sources. In particular, when there are many mobile nodes within the monitoring area S and the distances between the mobile nodes are short, higher estimation accuracy can be achieved than conventional techniques. Furthermore, by utilizing the proximity relationships between each node, it is possible to estimate the positions of mobile nodes that cannot directly receive wireless signals transmitted from anchor nodes A-C (mobile nodes 3-4 in the example of Figure 8A). This allows the number of anchor nodes to be kept low, resulting in lower costs. Furthermore, there is no need for the time and effort required for advance preparation, as with fingerprinting.

Furthermore, in steps S206 and S207 of FIG. 7, the position estimation problem for mobile nodes 1 to 6 is formulated as a nonlinear optimization problem, and the positions of mobile nodes 1 to 6 are estimated by solving this problem. Therefore, the positions of mobile nodes 1 to 6 estimated in this embodiment 1 are estimated using a mathematically valid method.

In the above-described first embodiment, if the positions of mobile nodes 1 to 6 estimated by individual position estimation unit 24d are not used as the initial estimated positions of cooperative position estimation unit 24e, the processing of individual position estimation unit 24d can be omitted. Alternatively, the processing of cooperative position estimation unit 24e may be omitted, and the positions of mobile nodes 1 to 6 estimated by individual position estimation unit 24d may be displayed on display unit 25.

Also, as a variation of the above-described first embodiment, instead of mobile nodes 1-6 transmitting proximity information to location estimation server 20 in step S105 of FIG. 5, mobile nodes 1-6 may exchange proximity information with each other, and each mobile node 1-6 may individually execute the processing of steps S201-S208 of FIG. 7, which is performed by location estimation server 20.

(Embodiment 2)
In location estimation system 100 according to the first embodiment, location estimation server 20 estimates the location of each of mobile nodes 1 to 6 based on proximity information transmitted from mobile nodes 1 to 6 and anchor nodes A to C. In contrast, location estimation system 200 according to the second embodiment does not have a configuration equivalent to a location estimation server, and each mobile node estimates its own location in an autonomous and decentralized manner, independently of other nodes.

Figure 12 is a diagram showing the configuration of a position estimation system 200 according to a second embodiment of the present disclosure. Three fixed nodes (anchor nodes) D to F capable of transmitting wireless signals are installed in a monitoring area S. The positions (X and Y coordinates) of the anchor nodes D to F on a two-dimensional plane are known. Note that the number of anchor nodes is not limited to three, and may be three or more.

Furthermore, there are four people in the monitored area S, each carrying mobile nodes 201-204 capable of sending and receiving wireless signals. The positions (X and Y coordinates) of the mobile nodes 201-204 on a two-dimensional plane change as the people carrying the mobile nodes 201-204 move around within the monitored area S. Note that the number of mobile nodes is not limited to four, and can be one or more.

Each storage unit of mobile nodes 201-204 stores the "node's hop count," which indicates the number of hops from the anchor node to the node itself, and the "anchor node's position." However, in the initial state, nothing is stored as the node's hop count or the anchor node's position. The definition and calculation method of the hop count are the same as in embodiment 1. As mobile nodes 201-204 repeatedly execute the autonomous distributed processing described below, information about the node's hop count and anchor node's position is added to the storage unit of each mobile node 210-204.

Figure 13 shows an example of the number of hops of the mobile node 201 and the location of the anchor node stored in the memory unit of the mobile node 201. In the example of Figure 13, 1 hop from D, 2 hops from F, and 4 hops from E are stored as the number of hops of the mobile node 201. This information indicates that the distance of the mobile node 201 from anchor node D is 1 hop, the distance from anchor node F is 2 hops, and the distance from anchor node E is 4 hops. In addition, the locations of anchor nodes D, F, and E are stored as the locations of the anchor nodes.

Anchor nodes D-F constantly broadcast their own locations to the surrounding area. When mobile nodes 201-204 can receive a wireless signal broadcast by an anchor node with an RSSI above a predetermined threshold, they determine that they are in close proximity to that anchor node, and add information about their own node's hop count and the anchor node's location to their own device's memory based on the anchor node's location contained in the wireless signal.

Mobile nodes 201-204 broadcast their own hop count and anchor node location stored in their own device's memory to their surroundings at a predetermined second cycle. Furthermore, if a mobile node 201-204 can receive a wireless signal broadcast by another mobile node with an RSSI above a predetermined threshold, it determines that it is in close proximity to that other mobile node, and adds information about its own hop count and anchor node location to its own device's memory based on the other node's hop count and anchor node location contained in the wireless signal.

However, when adding information to the device's memory, if identical information has already been added, the information will not be added again. Also, when adding new information about the number of hops for the device, if the starting anchor node is the same and only the number of hops differs, the information with the fewer number of hops will be added and the other will be discarded.

By repeatedly executing the above autonomous distributed processing, information about the number of hops of the local node and the location of the anchor node is added to the memory unit of each of the mobile nodes 201-204. After a sufficient number of repetitions, the number of hops of the local node and the location of the anchor node stored in the memory unit of each of the mobile nodes 201-204 will converge to the correct value based on the same principle as the Bellman-Ford algorithm used in Internet routing protocols.

Mobile nodes 201-204 can estimate their own positions on a two-dimensional plane using a multilateration technique based on the number of hops of their own node and the position of the anchor node stored in their own memory.

Figure 14 is a block diagram showing the functional configuration of mobile node 201. Mobile nodes 202 to 204 also have a similar functional configuration. Mobile node 201 comprises a broadcast unit 211, a receiving unit 212, an adding unit 213, a storage unit 214, a position estimation unit 215, a wireless communication interface 216, and a display unit 217. However, the configuration shown in Figure 14 is a functional configuration, and the hardware configuration may differ.

The broadcast unit 211 broadcasts a wireless signal containing the hop count of the local node and the location of the anchor node stored in the memory unit 214 to the surrounding area via the wireless communication interface 216 at a predetermined transmission power. The receiver 212 receives wireless signals broadcast by other mobile nodes or anchor nodes via the wireless communication interface 216. The adder 213 acquires either or both of the hop count of the other node and the location of the anchor node contained in wireless signals received by the receiver 212 that are received with an RSSI equal to or greater than a predetermined threshold. In particular, in the case of a wireless signal broadcast by another mobile node, both the hop count of the other node and the location of the anchor node are acquired, and in the case of a wireless signal broadcast by an anchor node, only the location of the anchor node is acquired. The adder 213 adds the hop count of the local node and the location of the anchor node to the memory unit 214 based on either or both of the acquired hop count of the other node and the location of the anchor node.

The position estimation unit 215 includes a distance estimation unit 215a and an individual position estimation unit 215b. The distance estimation unit 215a estimates the actual distance from anchor nodes D to F to the own node based on the number of hops from anchor nodes D to F to the own node and the positions of anchor nodes D to F. In this second embodiment, the distance estimated by the distance estimation unit 215a is referred to as the "estimated distance." The individual position estimation unit 215b estimates the position of the own node using a multilateration technique based on the estimated distance from anchor nodes D to F to the own node and the positions of anchor nodes D to F. The display unit 217 displays the position of the own node estimated by the individual position estimation unit 215b of the position estimation unit 215.

Next, we will explain the process by which mobile nodes 201-204 estimate their own positions in the position estimation system 200 according to the second embodiment.

Figure 15 is a flowchart explaining the details of the processing executed by mobile nodes 201-204. Note that anchor nodes D-F simply constantly broadcast their own locations to the surrounding area and do not execute the processing shown in Figure 15.

In step S301, the broadcast unit 211 of each mobile node 201-204 broadcasts, via the wireless communication interface 216, a wireless signal containing the node's hop count and the anchor node's position, which are stored in the node's memory unit 214. However, as mentioned above, in the initial state, nothing is stored in the memory unit 214 of each mobile node 201-204. Therefore, the wireless signal broadcast when step S301 is executed for the first time contains nothing.

In step S302, the receiver 212 of each of the mobile nodes 201-204 receives all wireless signals with an RSSI above a predetermined threshold via the wireless communication interface 216, and obtains either or both of the number of hops of other nodes and the location of the anchor node contained in each received signal.

Specifically, when step S302 is executed for the first time, as shown in FIG. 16(A), mobile node 201 receives a wireless signal broadcast by anchor node D and obtains the position of anchor node D contained in the wireless signal. Similarly, mobile node 202 receives a wireless signal broadcast by anchor node F and obtains the position of anchor node F contained in the wireless signal. Similarly, mobile node 204 receives a wireless signal broadcast by anchor node E and obtains the position of anchor node E contained in the wireless signal. However, in FIG. 16(A), mobile node 201 is represented by "1", mobile node 202 by "2", mobile node 203 by "3", and mobile node 204 by "4". The same applies to FIGS. 17 to 19.

In step S303, the adding unit 213 of each mobile node 201-204 adds the number of hops of its own node and the location of the anchor node to its own storage unit 214 based on either or both of the number of hops of the other node and the location of the anchor node obtained in step 302 above.

Specifically, when step S303 is executed for the first time, as shown in FIG. 16 (B), mobile node 201 adds one hop from D to the number of hops of its own node. Mobile node 201 also adds the location of anchor node D to the location of the anchor node. Similarly, mobile node 202 adds one hop from F to the number of hops of its own node, and also adds the location of anchor node F. Similarly, mobile node 204 adds one hop from E to the number of hops of its own node, and also adds the location of anchor node E.

In step S304, the position estimation unit 215 of each mobile node 201-204 determines whether its own node's position can be estimated. Specifically, if the number of hops for the own node and the position of the anchor node stored in its own device's memory unit 214 are each three or more, i.e., the minimum number required for multilateration (described below), it is determined that position estimation is possible. In this case, processing for the mobile nodes 201-204 proceeds to step S305. On the other hand, if the number of hops for the own node and the position of the anchor node stored in its own device's memory unit 214 are each less than three, it is determined that position estimation is impossible. In this case, processing for the mobile nodes 201-204 skips steps S305-S307 and proceeds to step S308.

In step S308, the mobile nodes 201-204 wait for a predetermined time. This wait time is set to, for example, 100 ms. This wait time corresponds to the predetermined second period mentioned above, during which the mobile nodes 201-204 broadcast to the surrounding area the number of hops of their own node and the location of the anchor node stored in their own memory unit 214. When the predetermined wait time expires, the processing of the mobile nodes 201-204 returns to step S301.

When step S301 is executed for the second time, as shown in FIG. 17(A), mobile node 201 broadcasts to its surroundings the number of hops (one hop from D) of its own node and the location of anchor node D. Similarly, mobile node 202 broadcasts to its surroundings the number of hops (one hop from F) of its own node and the location of anchor node F. Similarly, mobile node 204 broadcasts to its surroundings the number of hops (one hop from E) of its own node and the location of anchor node E.

When step S302 is executed for the second time, as shown in FIG. 17(A), mobile node 201 obtains the mobile node 202's hop count (one hop from F) and the location of anchor node F from the wireless signal broadcast by mobile node 202. Similarly, mobile node 202 obtains the mobile node 201's hop count (one hop from D) and the location of anchor node D from the wireless signal broadcast by mobile node 201. Similarly, mobile node 203 obtains the mobile node 202's hop count (one hop from F) and the location of anchor node F from the wireless signal broadcast by mobile node 202. Furthermore, mobile node 203 obtains the mobile node 204's hop count (one hop from E) and the location of anchor node E from the wireless signal broadcast by mobile node 204.

When step S303 is executed for the second time, as shown in FIG. 17(B), mobile node 201 adds two hops from F to the number of hops of its own node and adds the location of anchor node F. Similarly, mobile node 202 adds two hops from D to the number of hops of its own node and adds the location of anchor node D. Similarly, mobile node 203 adds two hops from E to the number of hops of its own node and adds the location of anchor node E. Furthermore, mobile node 203 adds two hops from F to the number of hops of its own node and adds the location of anchor node F.

When the determination in step S304 is made the second time, the processing of the mobile nodes 201-204 skips steps S305-S307 and proceeds to step S308. When step S308 is executed the second time, the mobile nodes 201-204 wait for a predetermined time and then return to step S301.

When step S301 is executed for the third time, as shown in FIG. 18(A), mobile node 202 broadcasts to its surroundings the number of hops (two hops from D) of its own node and the location of anchor node D. Similarly, mobile node 203 broadcasts the number of hops (two hops from E and two hops from F) of its own node, as well as the locations of anchor node E and anchor node F.

When step S302 is executed for the third time, as shown in FIG. 18(A), mobile node 202 obtains the number of hops (two hops from E) of mobile node 203 and the location of anchor node E from the wireless signal broadcast by mobile node 203. Similarly, mobile node 203 obtains the number of hops (two hops from D) of mobile node 202 and the location of anchor node D from the wireless signal broadcast by mobile node 202. Similarly, mobile node 204 obtains the number of hops (two hops from F) of mobile node 203 and the location of anchor node F from the wireless signal broadcast by mobile node 203.

When step S303 is executed for the third time, as shown in FIG. 18(B), mobile node 202 adds three hops from E to its own node's hop count and adds the location of anchor node E. Similarly, mobile node 203 adds three hops from D to its own node's hop count and adds the location of anchor node D. Similarly, mobile node 204 adds three hops from F to its own node's hop count and adds the location of anchor node F.

When the determination in step S304 is made for the third time, the processing of mobile nodes 202 and 203 proceeds to step S305. On the other hand, the processing of mobile nodes 201 and 204 skips steps S305 to S307 and proceeds to step S308.

In step S305, the distance estimation unit 215a of the mobile node 202 estimates the actual distance from anchor nodes D to F to the mobile node itself using a method similar to steps S204 to S205 in embodiment 1. Similarly, the distance estimation unit 215a of the mobile node 203 estimates the actual distance from anchor nodes D to F to the mobile node itself.

In step S306, the individual position estimation unit 215b of the mobile node 202 estimates the position of the mobile node 202 using a multilateration technique based on the estimated distance from anchor nodes D to F to the mobile node and the positions of anchor nodes D to F, in a manner similar to step S206 in embodiment 1. Similarly, the individual position estimation unit 215b of the mobile node 203 estimates the position of the mobile node 202 using a multilateration technique based on the estimated distance from anchor nodes D to F to the mobile node and the positions of anchor nodes D to F.

In step S307, the display unit 217 of the mobile node 202 displays the position of the mobile node estimated by the individual position estimation unit 215b. Similarly, the display unit 217 of the mobile node 203 displays the position of the mobile node estimated by the individual position estimation unit 215b.

When step S308 is executed for the third time, the mobile nodes 201-204 wait for a predetermined time and then return to step S301.

When step S301 is executed for the fourth time, as shown in FIG. 19(A), mobile node 202 broadcasts to its surroundings the number of hops (3 hops from E) of its own node's distance and the location of anchor node E. Similarly, mobile node 203 broadcasts to its surroundings the number of hops (3 hops from D) of its own node's distance and the location of anchor node D.

When step S302 is executed for the fourth time, as shown in FIG. 19(A), mobile node 201 obtains the number of hops (3 hops from E) of mobile node 202 and the location of anchor node E from the wireless signal broadcast by mobile node 202. Similarly, mobile node 204 obtains the number of hops (3 hops from D) of mobile node 203 and the location of anchor node D from the wireless signal broadcast by mobile node 203.

When step S303 is executed for the fourth time, as shown in FIG. 19(B), mobile node 201 adds four hops from E to its own node's hop count and adds the location of anchor node E. Similarly, mobile node 204 adds four hops from D to its own node's hop count and adds the location of anchor node D.

When the determination in step S304 is made for the fourth time, the processing of all mobile nodes 201-204 proceeds to step S305. In step S305, the distance estimation unit 215a of each mobile node 201-204 estimates the actual distance from anchor nodes D-F to the mobile node itself using a method similar to steps S204-S205 in embodiment 1.

In the fourth step S306, the individual position estimation unit 215b of each mobile node 201-204 estimates its own position using a multilateration technique based on the estimated distance from anchor nodes D-F to the own node and the positions of anchor nodes D-F, in a manner similar to step S206 in embodiment 1.

In the fourth step S307, the display unit 217 of each mobile node 201-204 displays the position of the node estimated by the individual position estimation unit 215b.

When step S308 is executed for the fourth time, the mobile nodes 201-204 wait for a predetermined time and then return to step S301.

By repeatedly executing the above process, information about the number of hops of the mobile node and the location of the anchor node is added to the storage unit 214 of each mobile node 201-204, and eventually converges to the correct value. This allows the mobile nodes 201-204 to correctly estimate their own location.

Furthermore, if it is desired to track changes in the positions of the mobile nodes 201-204 over time, the mobile nodes 201-204 can clear all information stored in their own memory unit 214 at a predetermined third cycle, for example, every second, and restart the process shown in Figure 15.

As described above, mobile nodes 201-204 according to the second embodiment of the present disclosure include a storage unit 214 that stores the number of hops of the mobile node and the location of the anchor node. Mobile nodes 201-204 broadcast the number of hops of the mobile node and the location of the anchor node to the surrounding area at a predetermined transmission power. Mobile nodes 201-204 acquire either or both of the number of hops of other nodes and the location of the anchor node contained in radio signals broadcast by other mobile nodes or anchor nodes that are received with an RSSI equal to or greater than a predetermined threshold.

Mobile nodes 201-204 add their own node's hop count and anchor node location to storage unit 214 based on either or both of the acquired other node's hop count and anchor node location. Mobile nodes 201-204 estimate their own node's location based on their own node's hop count and anchor node information stored in storage unit 214.

Due to the above characteristics, the location estimation system 200 according to the second embodiment does not require a configuration equivalent to the location estimation server of the first embodiment, and each mobile node 201-204 can estimate its own location independently from other nodes in an autonomous and decentralized manner.

Several embodiments of the present disclosure have been described, but these embodiments are presented as examples and are not intended to limit the scope of the disclosure. These embodiments can be embodied in a variety of other forms, and various omissions, substitutions, modifications, etc. can be made without departing from the spirit of the disclosure. These embodiments and their variations are within the scope and spirit of the disclosure, as well as the disclosure and its equivalents as set forth in the claims.

Furthermore, the processing of the present disclosure is not limited to any particular standard, and the illustrated settings may be changed as appropriate. Furthermore, the processing procedures of the present disclosure may be considered as a method having a series of these procedures. Alternatively, the processing procedures of the present disclosure may be considered as a program for causing a computer to execute these series of procedures, or as a recording medium for storing such a program. In such cases, the processing of the present disclosure is executed by a processor such as a CPU of the computer. Furthermore, the type of recording medium is not particularly limited, as it does not affect the embodiments of the present disclosure.

Furthermore, each component shown in Figures 3, 4, and 14 of the present disclosure may be implemented in software or hardware. For example, each component may be a software module implemented in software such as a microprogram, and each component may be implemented by a processor executing the software module. Alternatively, each component may be implemented by a circuit block on a semiconductor chip (die), for example, an integrated circuit such as an ASIC (Application Specific Integrated Circuit) or FPGA (Field Programmable Gate Array). Furthermore, the number of components does not have to match the number of pieces of hardware that implement the components. For example, one processor or circuit may implement multiple components. Conversely, one component may be implemented by multiple processors or circuits.

Furthermore, the processors described in this disclosure are not limited in type. The processor may be, for example, a CPU (Central Processing Unit), an MPU (Micro Processing Unit), or a GPU (Graphics Processing Unit).

1 Mobile node 2 Mobile node 3 Mobile node 4 Mobile node 5 Mobile node 6 Mobile node 11 Broadcast unit 12 Receiving unit (first receiving unit)
13 Creation unit 14 Transmission unit 15 Wireless communication interface 20 Position estimation server (position estimation device)
21 wireless communication interface 22 receiving unit (second receiving unit)
23 Proximity relation identification unit 24 Position estimation unit 24a Hop number calculation unit 24b Distance estimation unit 24c Position storage unit 24d Individual position estimation unit 24e Cooperative position estimation unit A Anchor node (fixed node)
B Anchor node (fixed node)
C Anchor node (fixed node)
100 Position estimation system 200 Position estimation system 201 Mobile node 202 Mobile node 203 Mobile node 204 Mobile node 211 Broadcast unit 212 Receiving unit 213 Adding unit 214 Storage unit 215 Position estimation unit 215a Distance estimation unit 215b Individual position estimation unit D Anchor node (fixed node)
E Anchor node (fixed node)
F anchor node (fixed node)

Claims (9)

A location estimation device for estimating a location of a mobile node, comprising:
Each of the mobile nodes and fixed nodes broadcasts an identifier assigned to that node in a radio signal;
the position estimation device,
a receiving unit that receives, from each of the mobile node and the fixed node, proximity information including an identifier of another node contained in a wireless signal received by the node with a received signal strength equal to or greater than a predetermined threshold;
a proximity relationship specification unit that specifies proximity relationships between the nodes based on the proximity information;
a position estimation unit that estimates the position of the mobile node based on the proximity relationships between the nodes and the positions of the fixed nodes. The position estimation device according to claim 1, wherein the proximity relationship determination unit determines the proximity relationship between the nodes by identifying pairs of nodes that can receive each other's identifiers. The position estimation device according to claim 1 or 2, wherein the position estimation unit includes a hop count calculation unit that calculates the number of hops between each node based on the proximity relationship between each node. The position estimation device of claim 3, wherein the position estimation unit includes a distance estimation unit that estimates the actual distance between the nodes based on the number of hops between the nodes and the positions of the fixed nodes. The position estimation device of claim 4, wherein the distance estimation unit calculates the average distance per hop based on the number of hops between each of the nodes and the position of the fixed node, and estimates the actual distance between each of the nodes from the average distance per hop and the number of hops between each of the nodes. 6. The position estimation device according to claim 4, wherein the position estimation unit includes an individual position estimation unit that individually estimates the positions of one or more of the mobile nodes by a multilateration technique based on the estimated actual distances between the mobile nodes and the fixed nodes . The position estimation device according to any one of claims 1 to 6, wherein the position estimation unit includes a cooperative position estimation unit that simultaneously estimates the positions of the multiple mobile nodes by solving an optimization problem that includes the positions of the multiple mobile nodes as variables. a mobile node capable of transmitting and receiving wireless signals;
a fixed node capable of transmitting and receiving wireless signals;
a position estimation device;
Each of the mobile node and the fixed node
a broadcasting unit that broadcasts a wireless signal including an identifier assigned to the node;
a first receiving unit for receiving a radio signal broadcast by another node;
a generating unit that generates proximity information including an identifier of the other node included in a wireless signal received with a received signal strength equal to or greater than a predetermined threshold, among wireless signals received by the first receiving unit;
a transmitter that transmits the proximity information to the position estimation device;
the position estimation device,
a second receiving unit for receiving the proximity information from the mobile node and the fixed node;
a proximity relationship specification unit that specifies proximity relationships between the nodes based on the proximity information;
a position estimation unit that estimates the position of the mobile node based on the proximity relationships between the nodes and the positions of the fixed nodes. A mobile node capable of transmitting and receiving wireless signals,
a broadcasting unit for broadcasting a radio signal including an identifier assigned to the mobile node;
a first receiving unit for receiving a radio signal broadcast by another node;
a generating unit that generates proximity information including an identifier of the other node included in a wireless signal received with a received signal strength equal to or greater than a predetermined threshold, among wireless signals received by the first receiving unit;
a transmitter that transmits the proximity information to the other node;
a second receiving unit configured to receive the proximity information from the other node;
a proximity relationship specification unit that specifies proximity relationships between the nodes based on the proximity information;
a position estimation unit that estimates the position of the mobile node based on the proximity relationships between the nodes and the positions of the fixed nodes.