Location estimation device, location estimation system and mobile node

Abstract

To provide a position estimation device, a position estimation system and a mobile node having high accuracy in estimating the position and low in cost.SOLUTION: A position estimation device of the present disclosure is a position estimation device for estimating the position of a mobile node. Each node of the mobile node and a fixed node includes an identifier assigned to the node in a radio signal and broadcasts it. The position estimation device includes: a receiving part for receiving proximity information from each node of the mobile node and the fixed node, including identifiers of other nodes included in the radio signal received by the node with a received signal intensity equal to or greater than a predetermined threshold; a proximity relation specifying part for specifying the proximity relation between the nodes based on the proximity information; and a position estimating part for estimating the position of the mobile node based on the proximity relation between the nodes and the position of the fixed node.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a position estimation device, a position estimation system, and a mobile node. [Background technology]

[0002] As a method for estimating location indoors where GPS signals are difficult to reach, various methods using wireless communication technologies such as Wi-Fi, Bluetooth, and BLE (Bluetooth Low Energy) have been proposed.

[0003] 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 (RSSI: Received Signal Strength Indicator) of the wireless signals, and the estimated distance is used to estimate the location.

[0004] However, the relationship between RSSI and distance from a signal source varies depending on the radio wave propagation environment. Therefore, in reality, it is difficult to accurately estimate the distance from a 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, to improve the accuracy of location estimation, a large number of signal sources must be densely installed, which is expensive.

[0005] Furthermore, Non-Patent Document 1 describes a method (fingerprinting) for estimating location by dividing an indoor area into multiple sections, measuring RSSI in advance for each section, and selecting the RSSI closest to the current RSSI from the pre-measured RSSIs. However, even with the fingerprinting method, in order to improve the accuracy of location estimation, a large number of signal sources must be installed, which is similarly costly. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] F. Zafari, A. Gkelias, KK Leung, "A Survey of Indoor Localization Systems and Technologies," IEEE Communications Surveys & Tutorials, Vol. 21, No. 3, pp. 2568-2599, 2019. Summary of the Invention [Problem to be solved by the invention]

[0007] The present disclosure is intended to solve the above-mentioned problems, and aims to provide a position estimation device, a position estimation system, and a mobile node that perform position estimation with high accuracy. [Means for solving the problem]

[0008] In order to solve the above problems, the position estimation device of the present disclosure is a position estimation device that estimates the position of a mobile node, wherein each of the mobile nodes and fixed nodes broadcasts an identifier assigned to that node in a radio signal, and the position estimation device includes: a receiving unit that receives proximity information from each of the mobile nodes and fixed nodes, the proximity information including identifiers of other nodes contained in the radio signal received by that node with a received signal strength equal to or greater than a predetermined threshold; a proximity relationship determination unit that determines the proximity relationship between each node 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 node and the position of the fixed node.

[0009] In addition, a 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, wherein 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, and 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 each node 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 node and the position of the fixed node.

[0010] In addition, 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 contained 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 the other nodes, a proximity relationship identifying unit that identifies proximity relationships between each node based on the proximity information, and a position estimating unit that estimates the position of the mobile node based on the proximity relationships between each node and the positions of fixed nodes.

[0011] 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. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a diagram showing a configuration of a position estimation system according to a first embodiment. [Figure 2] FIG. 2 illustrates an example of proximity information transmitted by a mobile node. [Figure 3] FIG. 2 is a block diagram showing the functional configuration of a mobile node. [Figure 4] FIG. 2 is a block diagram showing the functional configuration of a location estimation server. [Figure 5] 10 is a flowchart detailing the processing performed by the mobile node and the anchor node; [Figure 6] 10A and 10B are diagrams illustrating examples of proximity information created by a mobile node and an anchor node. [Figure 7] 10 is a flowchart illustrating details of a process executed by a location estimation server. [Figure 8A] FIG. 1 is a diagram illustrating an example of an undirected graph representing the proximity relationships of each node. [Figure 8B] FIG. 8B illustrates a matrix representation of the undirected graph of FIG. 8A. [Figure 9]FIG. 10 is a diagram illustrating an example of a distance matrix of the number of hops. [Figure 10] FIG. 10 is a diagram illustrating a method for calculating an average distance per hop. [Figure 11] FIG. 10 is a diagram illustrating an example of an estimated distance matrix. [Figure 12] FIG. 10 is a diagram illustrating a configuration of a position estimation system according to a second embodiment. [Figure 13] 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. [Figure 14] FIG. 2 is a block diagram showing the functional configuration of a mobile node. [Figure 15] 10 is a flowchart illustrating in detail the processing executed by the mobile node. [Figure 16] FIG. 1 illustrates the steps of a process performed by a mobile node. [Figure 17] FIG. 1 illustrates the steps of a process performed by a mobile node. [Figure 18] FIG. 1 illustrates the steps of a process performed by a mobile node. [Figure 19] FIG. 1 illustrates the steps of a process performed by a mobile node. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the drawings, identical or corresponding elements are designated by the same reference numerals, and detailed descriptions thereof will be omitted as appropriate.

[0014] (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 stations, airports, and city halls).

[0015] Three fixed nodes (anchor nodes) A ​​to C, which are wireless communication devices capable of transmitting and receiving wireless signals, are installed in the monitoring area S. The positions (X and Y coordinates) of the anchor nodes A to C on a two-dimensional plane are known. There is no particular limitation on the installation method of the anchor nodes A to C, and they may be installed on the floor of the 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 can uniquely identify each anchor node. Note that the number of anchor nodes is not limited to three, and may be three or more. 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.

[0016] The anchor nodes A to C may be dedicated wireless communication devices or IoT (Internet of Things) devices, etc. The wireless communication method of the 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), etc.

[0017] Additionally, there are six people in the monitored area S, each carrying mobile nodes 1 to 6, which are wireless communication devices capable of transmitting and receiving wireless signals. The positions (X and Y coordinates) of the mobile nodes 1 to 6 on a two-dimensional plane change as the people carrying the mobile nodes 1 to 6 move around within the monitored area S. The 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, and may be one or more.

[0018] The mobile nodes 1 to 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 of the mobile nodes 1 to 6 is not particularly limited, and may be, for example, Wi-Fi, Bluetooth, BLE, ZigBee, or UWB.

[0019] 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 that are received by their own nodes with an RSSI equal to or greater than a predetermined threshold, from among the wireless signals broadcast by other nodes.

[0020] Mobile nodes 1 to 6 and anchor nodes A to C transmit "proximity information" including identifiers of other nodes contained in wireless signals received by their own nodes with an RSSI equal to or greater than a predetermined threshold to location estimation server 20 at a predetermined first period. Note that the fact that the proximity information includes only identifiers received by their own nodes with an RSSI equal to or greater than a predetermined threshold means that the information includes only identifiers of other nodes that exist relatively close to their own nodes.

[0021] FIG. 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 mobile node itself. Therefore, in the example of FIG. 2, ID_1, the identifier of mobile node 1, is stored. However, if location estimation server 20 can identify the node that transmitted the proximity information by other means, such as by referring to header information included in the wireless signal, the identifier of the mobile node itself may be omitted. The second and subsequent identifiers in the proximity information are identifiers of other nodes received by the mobile node with an RSSI greater than or equal to a predetermined threshold, i.e., identifiers of other nodes located relatively close to the mobile node itself. In the example of FIG. 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.

[0022] 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 period. Upon receiving proximity information from mobile nodes 1-6 and anchor nodes A-C, location estimation server 20 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.

[0023] Figure 3 is a block diagram showing the functional configuration of mobile node 1. Mobile nodes 2 to 6 and anchor nodes A to C have similar functional configurations. Mobile node 1 includes broadcast unit 11, receiver 12, creator 13, transmitter 14, and wireless communication interface 15. However, the configuration shown in Figure 3 is a functional configuration, and the hardware configuration may be different.

[0024] The broadcasting unit 11 broadcasts a wireless signal including ID_1, which is the identifier of the node itself, to the surrounding area via the wireless communication interface 15 at a predetermined transmission power. The receiving unit 12 receives wireless signals broadcast by other nodes via the wireless communication interface 15. The creating unit 13 acquires the identifier of the other node included in a wireless signal received by the receiving unit 12 with an RSSI equal to or greater than a predetermined threshold, and creates proximity information including the identifier of the other node. The transmitting unit 14 transmits the proximity information created by the creating unit 13 to the location estimation server 20 via the wireless communication interface 15. Note that the anchor nodes A to C may further include a wired communication interface (not shown), and transmit the proximity information created by the creating unit 13 to the location estimation server 20 via wired communication.

[0025] Fig. 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 specifying unit 23, a location estimation unit 24, and a display unit 25. However, the configuration shown in Fig. 4 is a functional configuration, and the hardware configuration may be different. Furthermore, the functions of the location estimation server 20 may be distributed and implemented in multiple physically separated components.

[0026] Receiver 22 receives proximity information from mobile nodes 1-6 and anchor nodes A-C via wireless communication interface 21. As described above, the proximity information includes 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 wired communication interfaces, 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.

[0027] Proximity relationship identification unit 23 creates an undirected graph representing the proximity relationships between each node based on the proximity information. Position estimation unit 24 estimates the positions of 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.

[0028] The position estimation unit 24 includes a hop count calculation unit 24a, a distance estimation unit 24b, a position storage 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 the first embodiment, the distance estimated by the distance estimation unit 24b is referred to as the "estimated distance." The position storage unit 24c stores the positions of anchor nodes A to C in advance. 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. 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 individual position estimation unit 24d as initial estimated positions. Display unit 25 is configured, for example, with a liquid crystal display panel, and displays the positions of mobile nodes 1-6 estimated by cooperative position estimation unit 24e.

[0029] Next, a description will be given of the process of estimating the position of each of mobile nodes 1 to 6 in position estimation system 100 according to Embodiment 1. The process of estimating the position of each of mobile nodes 1 to 6 is divided into a process executed by mobile nodes 1 to 6 and anchor nodes A to C, and a process executed by position estimation server 20 in response to these processes.

[0030] FIG. 5 is a flowchart illustrating the details of the processing executed by mobile nodes 1 to 6 and anchor nodes A to C.

[0031] In step S101, broadcasting units 11 of mobile nodes 1 to 6 and anchor nodes A to C each start broadcasting a wireless signal including the identifier of the node via wireless communication interface 15. The transmission power at this time is the same for all mobile nodes 1 to 6 and anchor nodes A to C, and is, for example, 2.5 mW.

[0032] In step S102, the receivers 12 of the mobile nodes 1-6 and anchor nodes A-C receive all wireless signals with an RSSI equal to or greater than a predetermined threshold via the wireless communication interface 15 and acquire 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 receivers 12 may acquire identifiers of other nodes contained in wireless signals received with an RSSI equal to or greater than the predetermined threshold at least once within a predetermined period, for example, 100 ms.

[0033] For example, suppose that receiver 12 of mobile node 1 can receive the wireless signal broadcast by mobile node 3, the wireless signal broadcast by mobile node 5, and the wireless signal broadcast by anchor node C at least once within a predetermined time period with an RSSI equal to or greater than a predetermined 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, which is the identifier of mobile node 3, ID_5, which is the identifier of mobile node 5, and ID_C, which is the identifier of anchor node C. The same applies to mobile nodes 2 to 6 and anchor nodes A to C.

[0034] In step S103, creation unit 13 of each of mobile nodes 1 to 6 and anchor nodes A to C creates proximity information based on the identifiers of other nodes acquired in step S102. As described above, the proximity information includes the identifier of the own node (optional) and the identifiers of other nodes existing in the vicinity of the own node. Figure 6 shows an example of a list of each piece of proximity information created by creation unit 13 of each of mobile nodes 1 to 6 and anchor nodes A to C.

[0035] In step S104, transmitter 14 of each of mobile nodes 1 to 6 and anchor nodes A to C transmits the proximity information created in step S103 to location estimation server 20 via wireless communication interface 15. In particular, transmitter 14 of each of mobile nodes 1 to 6 and anchor nodes A to C transmits the proximity information to location estimation server 20 via wireless communication interface 15. If wired communication is possible between anchor nodes A to C and location estimation server 20, transmitter 14 of anchor nodes A to C may transmit the proximity information to location estimation server 20 via wired communication.

[0036] In step S105, mobile nodes 1 to 6 and anchor nodes A to C wait for a predetermined time, for example, 100 ms. This wait time corresponds to the above-mentioned predetermined first cycle in which mobile nodes 1 to 6 and anchor nodes A to C transmit proximity information to location estimation server 20. When the predetermined wait time expires, the process of the flowchart in FIG. 5 returns to step S102.

[0037] By performing the above process, mobile nodes 1 to 6 and anchor nodes A to C can repeatedly transmit proximity information including identifiers of other nodes present in the vicinity of the own node to position estimation server 20 at a predetermined first period.

[0038] FIG. 7 is a flowchart illustrating in detail the processing executed by location estimation server 20, corresponding to the processing executed by mobile nodes 1 to 6 and anchor nodes A to C in FIG.

[0039] In step S201, receiver 22 of location estimation server 20 receives, via wireless communication interface 21, the proximity information transmitted by mobile nodes 1 to 6 and anchor nodes A to C in step S104 of FIG. 5 for a predetermined period of time, for example, one second. That is, receiver 22 of location estimation server 20 receives all of the proximity information of 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 to C and location estimation server 20, receiver 22 of location estimation server 20 may receive the proximity information from anchor nodes A to C via wired communication.

[0040] In step S202, the proximity relationship identification unit 23 of the location estimation server 20 creates an undirected graph as shown in FIG. 8A that represents the proximity relationships of each node based on the proximity information of the mobile nodes 1 to 6 and the anchor nodes A to C received in step S201 above.

[0041] In detail, in the first embodiment, a pair of nodes that can receive each other's identifier with an RSSI equal to or greater than a predetermined threshold is defined as a "pair of neighboring nodes." For example, when mobile node 1 can receive the identifier of mobile node 3 with an RSSI equal to or greater than a predetermined threshold, and mobile node 3 can receive the identifier of mobile node 1 with an RSSI equal to or greater than a predetermined threshold, mobile node 1 and mobile node 3 become a "pair of neighboring nodes." By linking these pairs of neighboring nodes, an undirected graph such as that shown in FIG. 8A is created. FIG. 8B is a matrix representation of the undirected graph of FIG. 8A. As is well known, a matrix that represents an undirected graph with a finite number of vertices is a symmetric matrix, and all of its diagonal elements are zero.

[0042] Note that if there is a contradiction 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 "neighbor node pair" above. In such a case, the edge between mobile node 1 and mobile node 3 in FIG. 8A no longer exists, and the elements (1,3) and (3,1) of the matrix in FIG. 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 "neighbor node pair." With this correction, an edge between mobile node 1 and mobile node 3 in FIG. 8A exists, and the elements (1,3) and (3,1) of the matrix in FIG. 8B both become 1.

[0043] In step S203, the hop count calculation unit 24a of the position estimation server 20 calculates the number of hops between each node included in the undirected graph of FIG. 8A, and creates a distance matrix of the number of hops as shown in FIG.

[0044] In the distance matrix of FIG. 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.

[0045] The specific method for calculating the number of hops between each node included in the undirected graph of Fig. 8A is not particularly limited, and well-known algorithms such as breadth-first search, Dijkstra's algorithm, etc., can be used. Furthermore, as is clear from the method for creating the distance matrix, the distance matrix of Fig. 9 is a symmetric matrix, and all of its diagonal elements are 0.

[0046] In step S204, distance estimation unit 24b of position estimation server 20 calculates the average distance per hop in the undirected graph of Fig. 8A. In detail, distance estimation unit 24b of position estimation server 20 calculates the average distance per hop based on the positions of anchor nodes A to C stored in position storage unit 24c.

[0047] Specifically, consider a situation in which 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 Nn (n+1th 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.

[0048] In this case, the average distance per hop Hd in the undirected graph in Figure 8A is calculated by dividing the known position r of the anchor node by the i (i=n+1, ,N) and the number of hops between each anchor node h ij (i, j=n+1, , N) according to the following formula (1).

[0049]

number

[0050] 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. In addition, for example, the distance |r A -r B |=8m, the distance between anchor node B and anchor node C |r B -r C |=10m, the distance between anchor node C and anchor node A |r C -r AIn this case, the average distance Hd per hop is Hd = (8 + 10 + 18) / (2 + 3 + 4) = 4.0 m.

[0051] 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, thereby creating an estimated distance matrix including 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 shown in FIG. 11, estimated distances between nodes for which a proximity relationship cannot be determined are also replaced with a predetermined large value N.

[0052] 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 from each other, 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.

[0053] The threshold value 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 the number of mobile nodes within the monitoring area S is large and the distances between the mobile nodes are short, the threshold value for the number of hops may be set to a value smaller than 3. Conversely, if the number of mobile nodes within the monitoring area S is small and the distances between the mobile nodes are long, the threshold value for the number of hops may be set to a value larger than 3.

[0054] In step S206, individual position estimation unit 24d of position estimation server 20 individually estimates the position of each of mobile nodes 1-6 based on a multilateration technique. As is well known, multilateration requires three or more signal sources whose positions are known. Therefore, in this first embodiment, three or more anchor nodes are also required. In multilateration, the position of each of 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.

[0055] In detail, the individual position estimation unit 24d of the position estimation server 20 calculates the estimated distance d between the mobile node i and the anchor node j included in the estimated distance matrix of FIG. ij (i=1,...,n; j=n+1,...,N) and perform an appropriate number of iterations according to the following formula (2) to obtain the position r i Estimate.

[0056]

number

[0057] However, in the above formula, r i (1,k) is the kth solution, and N i is the number of anchor nodes j that can be reached by tracing edges on the undirected graph from the mobile node i whose position is to be estimated, on the undirected graph that represents the proximity relationships between each node in Figure 8A. ij is a variable that indicates whether the estimated distance between mobile node i and anchor node j is known. If the estimated distance is known, A ij= 1, and if the estimated distance is unknown, A ij =0. Note that r i (1,1) The second term in the above equation can be used to

[0058] In step S207, cooperative location estimation unit 24e of location estimation server 20 simultaneously estimates the locations of mobile nodes 1 to 6 by solving an optimization problem that includes the locations of mobile nodes 1 to 6 as variables. At this time, the locations of mobile nodes 1 to 6 estimated in step S206 are used as the initial estimated locations of mobile nodes 1 to 6. However, if the number of anchor nodes reachable by tracing edges on the undirected graph from the node whose location is to be estimated is 1, the location of that anchor node is set to r i (1) In addition, if the number of anchor nodes that can be reached by tracing edges on the undirected graph from the node whose position is to be estimated is 0, the center of the monitoring area S is set to r i (1) Let's say.

[0059] Specifically, the cooperative location estimation unit 24e of the location estimation server 20 estimates the location r of the mobile node i. i are simultaneously obtained by solving the nonlinear optimization problem defined by the following equation (3).

[0060]

number

[0061] In the above equation, the objective function f(x1, ,x n ) is defined by the following equation (4):

[0062]

number

[0063] As an example of a method for solving the above optimization problem, stress majorization (ER 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 the above equations (3) and (4), a formulation based on multidimensional scaling, for example, may be used.

[0064] In step S208, display unit 25 of location estimation server 20 displays the locations of mobile nodes 1-6 estimated in step S207 above. The display format is not particularly limited, but for example, the locations of mobile nodes 1-6 may be plotted on a two-dimensional diagram representing monitoring area S. When the display is complete, the process of the flowchart in FIG. 7 returns to step S201.

[0065] By executing the above process, the positions of the mobile nodes 1 to 6 are repeatedly estimated and displayed on the display unit 25 one after another.

[0066] As described above, location estimation system 100 according to the first embodiment of the present disclosure includes mobile nodes 1-6 whose locations are unknown, anchor nodes A-C whose locations are known, and location estimation server 20. Mobile nodes 1-6 and anchor nodes A-C constantly broadcast wireless signals containing their own node identifiers to their surroundings at a predetermined transmission power. That is, not only anchor nodes A-C but also mobile nodes 1-6 broadcast wireless signals containing their own node identifiers to their surroundings.

[0067] Mobile nodes 1 to 6 and anchor nodes A to C transmit proximity information including identifiers of other nodes received by their own nodes with RSSIs equal to or greater than a predetermined threshold to location estimation server 20. In other words, they transmit to location estimation server 20 only information on nearby nodes that are relatively close to their own nodes, are less susceptible to the effects of RSSI errors that increase in proportion to the distance from the signal source, the radio wave propagation environment, and the like, and are therefore expected to provide high accuracy.

[0068] When 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 of mobile nodes 1-6 based on the proximity relationships between each node and the locations of anchor nodes A-C. That is, the location of each of mobile nodes 1-6 is estimated only based 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.

[0069] 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 in 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 the nodes, 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 FIG. 8A). This allows the number of anchor nodes to be kept small, resulting in lower costs. Furthermore, there is no need for the time and effort required for advance preparation, as with fingerprinting.

[0070] 7, the problem of estimating the positions of 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 first embodiment are estimated using a mathematically correct method.

[0071] 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.

[0072] Furthermore, as a variation of the above-described first embodiment, instead of the mobile nodes 1 to 6 transmitting proximity information to the location estimation server 20 in step S105 of FIG. 5, the mobile nodes 1 to 6 may exchange proximity information with each other, and each of the mobile nodes 1 to 6 may individually execute the processing of steps S201 to S208 of FIG. 7 performed by the location estimation server 20.

[0073] (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.

[0074] 12 is a diagram illustrating a 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 coordinate and Y coordinate) 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.

[0075] Additionally, there are four people in the monitored area S, each carrying mobile nodes 201-204 that are capable of transmitting 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 may be one or more.

[0076] The storage unit of each of mobile nodes 201-204 stores the "number of hops of the own node," which indicates the number of hops from the anchor node to the own node, and the "position of the anchor node." However, in the initial state, nothing is stored as the number of hops of the own node or the position of the anchor node. The definition and calculation method of the number of hops are the same as in embodiment 1. As mobile nodes 201-204 repeatedly execute the autonomous distributed processing described below, information on the number of hops of the own node and the position of the anchor node is added to the storage unit of each of mobile nodes 210-204.

[0077] Figure 13 is a diagram showing an example of the number of hops of the local node and the position of an anchor node stored in the storage unit of 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 local node. This information indicates that mobile node 201 is 1 hop away from anchor node D, 2 hops away from anchor node F, and 4 hops away from anchor node E. In addition, the positions of anchor nodes D, F, and E are stored as the positions of the anchor nodes.

[0078] Anchor nodes D to F constantly broadcast their own locations to the surrounding area. When mobile nodes 201 to 204 can receive a wireless signal broadcast by an anchor node with an RSSI equal to or greater than a predetermined threshold, they determine that they are in a proximity relationship with the anchor node, and add information about the number of hops of their own node and the location of the anchor node to their own memory based on the location of the anchor node contained in the wireless signal.

[0079] Mobile nodes 201-204 broadcast their own hop count and anchor node location stored in their own storage unit to the surrounding area at a predetermined second cycle. Furthermore, when mobile nodes 201-204 can receive a wireless signal broadcast by another mobile node with an RSSI equal to or greater than a predetermined threshold, they determine that they are in a proximity relationship with the other mobile node, and add information about their own hop count and anchor node location to their own storage unit based on the other node's hop count and anchor node location contained in the wireless signal.

[0080] However, when adding information to the storage unit of the own device, if information of the same content has already been added, the information will not be added redundantly. Also, when adding new information on the number of hops of the own node, if the anchor node of the starting point is the same and only the number of hops is different, the information with the fewer number of hops will be added and the other will be discarded.

[0081] By repeatedly executing the above autonomous distributed processing, information on the number of hops of the local node and the location of the anchor node is added to the storage unit of each of 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 storage unit of each of mobile nodes 201-204 converge to the correct value based on the same principle as the Bellman-Ford algorithm used in Internet routing protocols.

[0082] Mobile nodes 201 to 204 can estimate their own positions on a two-dimensional plane using a multilateration technique based on the number of hops of their own nodes and the positions of anchor nodes stored in their own memory units.

[0083] Figure 14 is a block diagram showing the functional configuration of mobile node 201. Mobile nodes 202 to 204 have similar functional configurations. Mobile node 201 includes broadcast unit 211, receiving unit 212, adding unit 213, storage unit 214, position estimating unit 215, wireless communication interface 216, and display unit 217. However, the configuration shown in Figure 14 is a functional configuration, and the hardware configuration may be different.

[0084] Broadcast unit 211 broadcasts a wireless signal containing the hop count of its own node and the location of the anchor node stored in storage unit 214 to the surrounding area via wireless communication interface 216 at a predetermined transmission power. Receiving unit 212 receives wireless signals broadcast by other mobile nodes or anchor nodes via wireless communication interface 216. Adding unit 213 acquires one or both of the hop count of other nodes and the location of the anchor node contained in wireless signals received by receiving unit 212 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 other nodes 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. Adding unit 213 adds the hop count of its own node and the location of the anchor node to storage unit 214 based on one or both of the acquired hop count of other nodes and the location of the anchor node.

[0085] Position estimation unit 215 includes distance estimation unit 215a and individual position estimation unit 215b. Distance estimation unit 215a estimates the actual distance from anchor nodes D to F to its own node based on the number of hops from anchor nodes D to F to its own node and the positions of anchor nodes D to F. In the second embodiment, the distance estimated by distance estimation unit 215a is referred to as the "estimated distance." Individual position estimation unit 215b estimates the position of its own node by a multilateration technique based on the estimated distance from anchor nodes D to F to its own node and the positions of anchor nodes D to F. Display unit 217 displays the position of its own node estimated by individual position estimation unit 215b of position estimation unit 215.

[0086] Next, a process in which mobile nodes 201 to 204 estimate their own positions in position estimation system 200 according to the second embodiment will be described.

[0087] Figure 15 is a flowchart illustrating in detail the processing executed by mobile nodes 201 to 204. Note that anchor nodes D to F simply constantly broadcast their own positions to the surrounding area, and do not execute the processing in Figure 15.

[0088] In step S301, broadcast unit 211 of each of mobile nodes 201-204 broadcasts, via wireless communication interface 216, a wireless signal including the number of hops of the node and the position of the anchor node stored in memory unit 214 of the mobile node. However, as described above, in the initial state, nothing is stored in memory unit 214 of each of mobile nodes 201-204. Therefore, the wireless signal broadcast when step S301 is executed for the first time contains nothing.

[0089] In step S302, the receiver 212 of each of the mobile nodes 201 to 204 receives all wireless signals with an RSSI greater than or equal to a predetermined threshold via the wireless communication interface 216, and acquires either or both of the number of hops of other nodes and the position of the anchor node contained in each received signal.

[0090] Specifically, when step S302 is executed for the first time, as shown in Figure 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 Figure 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 Figures 17 to 19.

[0091] In step S303, the adding unit 213 of each of the mobile nodes 201 to 204 adds the number of hops of its own node and the position of the anchor node to its own memory unit 214 based on either or both of the number of hops of the other node and the position of the anchor node obtained in step 302 above.

[0092] Specifically, when step S303 is executed for the first time, as shown in Figure 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.

[0093] In step S304, position estimation unit 215 of each of mobile nodes 201-204 determines whether or not the position of the own node can be estimated. Specifically, if the number of hops of the own node and the position of the anchor node stored in memory unit 214 of the own node are each three or more, that is, the minimum number required for performing multilateration, as described below, it is determined that position estimation is possible. In this case, processing for mobile nodes 201-204 proceeds to step S305. On the other hand, if the number of hops of the own node and the position of the anchor node stored in memory unit 214 of the own node are each less than three, it is determined that position estimation is impossible. In this case, processing for mobile nodes 201-204 skips steps S305-S307 and proceeds to step S308.

[0094] In step S308, 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 mobile nodes 201-204 broadcast to the surrounding area their own hop counts and anchor node positions, which are stored in their own storage unit 214. When the predetermined wait time expires, the processing of mobile nodes 201-204 returns to step S301.

[0095] 17(A), when step S301 is executed for the second time, mobile node 201 broadcasts to its surroundings the number of hops of its own node, one hop from D, and the location of anchor node D. Similarly, mobile node 202 broadcasts to its surroundings the number of hops of its own node, one hop from F, and the location of anchor node F. Similarly, mobile node 204 broadcasts to its surroundings the number of hops of its own node, one hop from E, and the location of anchor node E.

[0096] 17(A), when step S302 is executed for the second time, mobile node 201 acquires, from the wireless signal broadcast by mobile node 202, one hop from F, which is the number of hops of mobile node 202, and the location of anchor node F. Similarly, mobile node 202 acquires, from the wireless signal broadcast by mobile node 201, one hop from D, which is the number of hops of mobile node 201, and the location of anchor node D. Similarly, mobile node 203 acquires, from the wireless signal broadcast by mobile node 202, one hop from F, which is the number of hops of mobile node 202, and the location of anchor node F. Furthermore, mobile node 203 acquires, from the wireless signal broadcast by mobile node 204, one hop from E, which is the number of hops of mobile node 204, and the location of anchor node E.

[0097] When step S303 is executed for the second time, as shown in Figure 17(B), mobile node 201 adds two hops from F to its own node's hop count and also adds the location of anchor node F. Similarly, mobile node 202 adds two hops from D to its own node's hop count and also adds the location of anchor node D. Similarly, mobile node 203 adds two hops from E to its own node's hop count and also adds the location of anchor node E. Furthermore, mobile node 203 adds two hops from F to its own node's hop count and also adds the location of anchor node F.

[0098] When making the determination in step S304 the second time, the processing of mobile nodes 201 to 204 skips steps S305 to S307 and proceeds to step S308. When executing step S308 the second time, mobile nodes 201 to 204 wait for a predetermined time and then return to step S301.

[0099] 18(A), when step S301 is executed for the third time, mobile node 202 broadcasts to its surroundings the number of hops of its own node (two hops from D) and the location of anchor node D. Similarly, mobile node 203 broadcasts the number of hops of its own node (two hops from E and two hops from F), as well as the locations of anchor node E and anchor node F.

[0100] 18(A), when step S302 is executed for the third time, mobile node 202 acquires, from the wireless signal broadcast by mobile node 203, the number of hops of mobile node 203 (two hops from E) and the location of anchor node E. Similarly, mobile node 203 acquires, from the wireless signal broadcast by mobile node 202, the number of hops of mobile node 202 (two hops from D) and the location of anchor node D. Similarly, mobile node 204 acquires, from the wireless signal broadcast by mobile node 203, the number of hops of mobile node 203 (two hops from F) and the location of anchor node F.

[0101] When step S303 is executed for the third time, as shown in Figure 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.

[0102] When the determination in step S304 is made 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.

[0103] In step S305, distance estimation unit 215a of mobile node 202 estimates the actual distance from anchor nodes D to F to the local node in the same manner as in steps S204 to S205 in embodiment 1. Similarly, distance estimation unit 215a of mobile node 203 estimates the actual distance from anchor nodes D to F to the local node.

[0104] In step S306, individual position estimation unit 215b of mobile node 202 estimates the position of its own node by multilateration, using the same method as in step S206 in embodiment 1, based on the estimated distances from anchor nodes D to F to its own node and the positions of anchor nodes D to F. Similarly, individual position estimation unit 215b of mobile node 203 estimates the position of its own node by multilateration, based on the estimated distances from anchor nodes D to F to its own node and the positions of anchor nodes D to F.

[0105] In step S307, display unit 217 of mobile node 202 displays the position of the mobile node estimated by individual position estimation unit 215b. Similarly, display unit 217 of mobile node 203 displays the position of the mobile node estimated by individual position estimation unit 215b.

[0106] When step S308 is executed for the third time, mobile nodes 201 to 204 wait for a predetermined time and then return to step S301.

[0107] 19(A), when step S301 is executed for the fourth time, mobile node 202 broadcasts to its surroundings the number of hops from E (three hops) that is its own node's distance, and the location of anchor node E. Similarly, mobile node 203 broadcasts to its surroundings the number of hops from D (three hops) that is its own node's distance, and the location of anchor node D.

[0108] 19(A), when step S302 is executed for the fourth time, mobile node 201 acquires, from the wireless signal broadcast by mobile node 202, the number of hops of mobile node 202 (three hops from E) and the location of anchor node E. Similarly, mobile node 204 acquires, from the wireless signal broadcast by mobile node 203, the number of hops of mobile node 203 (three hops from D) and the location of anchor node D.

[0109] 19(B), when step S303 is executed for the fourth time, 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.

[0110] 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, 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 the first embodiment.

[0111] In the fourth step S306, each individual position estimation unit 215b of mobile nodes 201 to 204 estimates the position of its own node using a multilateration technique based on the estimated distance from anchor nodes D to F to its own node and the positions of anchor nodes D to F, in a manner similar to step S206 in embodiment 1.

[0112] In step S307 for the fourth time, display unit 217 of each of mobile nodes 201 to 204 displays the position of the node estimated by individual position estimation unit 215b.

[0113] When step S308 is executed for the fourth time, mobile nodes 201 to 204 wait for a predetermined time and then return to step S301.

[0114] By repeatedly executing the above process, information on the number of hops of the own node and the position of the anchor node is added to storage unit 214 of each of mobile nodes 201-204, and eventually converges to the correct value, allowing mobile nodes 201-204 to correctly estimate their own positions.

[0115] Furthermore, if it is desired to track the change in the position of each of the mobile nodes 201 to 204 over time, the mobile nodes 201 to 204 can clear all information stored in their own memory unit 214 at a predetermined third period, for example, at a one-second period, and restart the process of Figure 15.

[0116] As described above, mobile nodes 201-204 according to the second embodiment of the present disclosure include 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 received with an RSSI equal to or greater than a predetermined threshold, from among radio signals broadcast by other mobile nodes or anchor nodes.

[0117] Based on either or both of the acquired number of hops of other nodes and the position of the anchor node, mobile nodes 201-204 add the number of hops of their own node and the position of the anchor node to storage unit 214. Mobile nodes 201-204 estimate their own positions based on the information on the number of hops of their own node and the anchor node stored in storage unit 214.

[0118] Due to the above features, 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 of the mobile nodes 201 to 204 can estimate its own location in an autonomous and decentralized manner independently from other nodes.

[0119] Although several embodiments of the present disclosure have been described, these embodiments are presented as examples and are not intended to limit the scope of the disclosure. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, etc. can be made without departing from the spirit of the disclosure. These embodiments and modifications thereof are included in the scope and spirit of the disclosure, as well as in the disclosure described in the claims and their equivalents.

[0120] Furthermore, the processes of the present disclosure are not limited to a specific standard, and the illustrated settings may be changed as appropriate. Furthermore, the process procedures of the present disclosure may be considered as a method having a series of these procedures. Alternatively, the process procedures of the present disclosure may be considered as a program for causing a computer to execute these procedures, or as a recording medium storing the program. In this case, the processes of the present disclosure are 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.

[0121] 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 an 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.

[0122] The processors described in this disclosure are not limited to specific types, and may be, for example, a central processing unit (CPU), a micro processing unit (MPU), or a graphics processing unit (GPU). [Explanation of symbols]

[0123] 1 Mobile Node 2 Mobile Node 3 Mobile Node 4 Mobile Node 5 Mobile Node 6 Mobile Node 11 Broadcast Section 12 Receiving unit (first receiving unit) 13 Creation Department 14 Transmitter 15 Wireless communication interface 20 Location estimation server (location estimation device) 21 Wireless communication interface 22 Receiving unit (second receiving unit) 23 Proximity relationship identification unit 24 Position estimation part 24a Hop count calculation unit 24b Distance estimation part 24c Position memory section 24d Individual position estimation section 24e Cooperative position estimation unit A anchor node (fixed node) B Anchor node (fixed node) C Anchor node (fixed node) 100 Location Estimation System 200 Location Estimation System 201 Mobile Node 202 Mobile Node 203 Mobile Node 204 Mobile Node 211 Broadcast Department 212 Receiving unit 213 Additional Section 214 Storage section 215 Position estimation part 215a Distance estimation part 215b Individual position estimation unit D Anchor node (fixed node) E Anchor node (fixed node) F anchor node (fixed node)

Claims

1. 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; A position estimation device comprising:

2. The position estimation device according to claim 1 , wherein the proximity relationship specifying unit specifies the proximity relationship between the nodes by specifying a pair of nodes that can receive each other's identifier.

3. The position estimation device according to claim 1 , wherein the position estimation unit includes a hop number calculation unit that calculates the number of hops between each of the nodes based on the proximity relationships between the nodes.

4. The position estimation device according to claim 3 , wherein the position estimation unit includes a distance estimation unit that estimates actual distances between the nodes based on the number of hops between the nodes and the positions of the fixed nodes.

5. 5. The position estimation device according to claim 4, wherein the distance estimation unit calculates an average distance per hop based on the number of hops between each of the nodes and the positions of the fixed nodes, and estimates an actual distance between each of the nodes from the average distance per hop and the number of hops between each of the nodes.

6. 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.

7. 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 plurality of mobile nodes by solving an optimization problem that includes the positions of the plurality of mobile nodes as variables.

8. a mobile node capable of transmitting and receiving wireless signals; a fixed node capable of transmitting and receiving wireless signals; A location estimation device Equipped with 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; Including, 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 location estimation system including:

9. 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; A mobile node comprising:

Images