Abstract:
In the construction of a wireless network in a building, structure conditions such as the floor plan of the building and the shape of the floor, material conditions such as materials for structures, and the like have a great effect on radio wave propagation characteristics. This causes a problem that unless these pieces of information are taken into consideration, an accurate layout design of wireless base stations cannot be made. In the construction of a new wireless network in a building, a wireless network similar to structure conditions of a newly constructed building is extracted from structure conditions of past buildings in which a wireless network is constructed. The layout positions of wireless base stations used in the extracted wireless network are regarded as the layout positions of wireless base stations in the new wireless network.

Description:
TECHNICAL FIELD 
     The present invention relates to an apparatus for supporting the layout of wireless base stations in a building. More specifically, the invention relates to an apparatus for supporting the layout design of wireless base stations for use in a wireless network system in a building. 
     BACKGROUND ART 
     The multi-hop wireless network communication technology is a technology by which a wireless station exchanges data with the desired wireless station via multiple wireless stations installed as relay stations between the wireless stations by multi-hop communication. 
     In multi-hop communication, a wireless station does not directly wirelessly communicate with the desired window station but wirelessly communicates therewith via relay stations. Accordingly, multi-hop communication is a communication technology that is effective, for example, when an obstacle to radio waves is present. 
     Particularly in recent years, the cost of wireless communication devices for wireless LAN (local area network) or the like has been reduced, and sensor network technologies such as Bluetooth®, which is a short-range wireless communication standard mainly for digital devices, and ZigBee, which is a short-range wireless communication standard mainly for household electrical appliances, have been standardized. Accordingly, expectation for application of wireless technologies to the industry field has been increased, increasing application cases. 
     The multi-hop wireless network technology is expected to contribute to reductions in the number of monitoring/control cables by applying it to the industry field, for example, social infrastructure business, such as electric power or transportation, and monitoring/control networks for the manufacturing industry, such as factory automation (FA) systems and process automation (PA) systems. 
     Further, making wired cables wireless can result in reductions in the cost of cable installation or maintenance cost for a routine check. 
     Furthermore, use of wireless technologies allows business entities to more flexibly deal with changes in operation, such as addition of equipment or a change in the configuration of equipment. 
     As seen, wireless network systems have many advantages. On the other hand, application of wireless real-time communication to the industry field requires high reliability, and a failure that occurs in a wireless network must be dealt with rapidly. 
     For example, assume that a wireless network that meets a requirement by obtaining multiple channels, for example, two communication paths by multi-hop communication is constructed. In this case, at the point in time when one communication path fails, the reliability of the other communication path will decrease. For this reason, in the construction of a communication path, it is necessary to design favorable communication paths that are insusceptible to a failure to the extent possible. 
     In the field of industry, it is particularly important to construct or design communication paths of a wireless network in a building. 
     A wireless environment in a building is significantly susceptible to the floor plan of the building, the height of the ceiling, material characteristics of the wall, ceiling, and floor, the size of an opening such as the door or window, furniture or equipment inside the building, and the like. The wireless environment also shows characteristics that are different among sites over which a wireless network is to be constructed. Accordingly, a wireless network must be constructed or designed considering these factors. 
     For this reason, it is desired to actually measure the propagation state of a radio wave at locations where a wireless base station can be installed, of the sites over which a wireless network is to be constructed and to design the layout of wireless base stations on the basis of the measurement results. 
     However, it is difficult to actually measure the propagation state of a radio wave in all parts of space in the building in terms of cost and time. For this reason, it is practical and effective to design the layout of wireless base stations in a building into which wireless base stations are to be introduced newly, on the basis of the layout design of wireless base stations in a building in which a wireless network is already constructed, instead of measuring the propagation state of a radio wave thoroughly as described above. 
     The present invention relates to a technology of constructing a wireless network in a new building using an already constructed wireless network as described above. 
     Methods for estimating the propagation of a radio wave include a method of using a statistical model based on values which are actually measured at various locations. In addition, Japanese Unexamined Patent Application Publication No. 2009-296572 (Patent Literature 1) and the like have proposed methods for estimating radio wave propagation characteristics. These technologies are configured to, in the installation of wireless base stations into a wide area, estimate the installment locations of wireless base stations using existing radio wave propagation characteristics. 
     In a building, however, there are large differences in structure among sites. Accordingly, to construct a wireless network system which is required to have high reliability, it is important to design a wireless network considering a propagation environment specific to each site. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2009-296572 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     A radio wave propagation characteristic estimation support system disclosed in the above-mentioned Patent Literature 1 stores attribute information of an area and reference information which is useful in estimating radio wave propagation characteristics of this area in such a manner that the attribute information and the reference information are associated with each other. An attribute information input unit of the system receives attribute information of an area whose radio wave propagation characteristics are desired to estimate. 
     An output unit thereof searches information stored in a storage unit, identifies an area having attributes matching the attribute information received by the attribute information input unit, and outputs reference information associated with the identified area. 
     As seen, the technology described in Patent Literature 1 is a large wireless communication system for performing mobile communications in an extremely wide area and is a method for estimating radio wave propagation characteristics related to open, large space. 
     However, space through which radio waves propagate in a building is not open, large space in a wide area described above but narrow, closed space. Further, there are many accessory structure conditions. Accordingly, there is a limit to the above-mentioned technology, and the technology is not applicable in practice. 
     The accessory structure conditions include structure conditions, such as the floor plan of the building and the shapes of the wall and floor, and material conditions, such as the materials for the accessory structures. These accessory structure conditions have a great effect on radio wave propagation characteristics. Accordingly, there is a problem that unless these pieces of information are taken into consideration, an accurate layout design of wireless base stations cannot not be made. 
     An object of the present invention is to provide an apparatus for supporting the layout of wireless base stations in order to construct a reliable wireless network in newly constructing a wireless network in a building. 
     Solution to Problem 
     The present invention is characterized in that an apparatus for supporting layout of wireless base stations in a building includes: storage means configured to store at least a floor plan of a existing building, an attribute of a structure of the existing building, a layout position of a wireless base station in the existing building, or the like; graph generation means configured to, based on a floor plan of a new building or an attribute of a structure of the new building, define part of space included in the new building as a node and define, as an edge (link), a propagation path which is located between the node and another node adjacent to the node and through which a radio wave propagates, and to generate a graph by adding information indicating a link between the node and the edge (link); graph detection means configured to evaluate correlation between a subgraph serving as part of a graph related to the new building generated by the graph generation means and a subgraph serving as part of a graph related to the existing building, the graph related to the existing building being generated by the graph generation means and stored in the storage means, and to extract an existing subgraph having a high degree of correlation; and display means configured to display the floor plan of the new building as well as to extract the layout position of the wireless base station from the subgraph of the existing building extracted by the graph detection means and display the layout position. 
     As used herein, a new building refers to a building in which a wireless network is to be newly constructed. Even if a building is an existing building, the building means a new building as long as a wireless network is to be newly constructed in the building. 
     Advantageous Effects of Invention 
     According to the present invention, in the construction of a new wireless network in a building, it is possible to extract a wireless network similar to structure conditions of the building, in which a wireless network is to be newly constructed, from structure conditions of past buildings in which a wireless network is constructed and to use layout information of wireless base stations used in the extracted past wireless network as the layout of wireless base stations in a new wireless network. Thus, a reliable wireless network can be constructed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram showing a configuration of an apparatus for supporting layout of wireless base stations according to an embodiment of the present invention. 
         FIG. 2  is an example floor plan of a particular floor of a building. 
         FIG. 3  is a diagram where attributes corresponding to structures on the particular floor of the building are described. 
         FIG. 4  is a diagram where attributes of wireless base stations on the particular floor of the building are described. 
         FIG. 5  is a diagram where attributes of receiving antennas on the particular floor of the building are described. 
         FIG. 6  shows an example floor plan of the particular floor of the building. 
         FIG. 7  is a floor plan showing the existence state of nodes in the floor plan shown in  FIG. 6 . 
         FIG. 8  is a diagram where attributes of the nodes shown in  FIG. 6  are described. 
         FIG. 9  is a floor plan showing the existence state of edges (links) linking the nodes shown in  FIG. 6 . 
         FIG. 10  is a diagram where attributes of the edges (links) shown in  FIG. 9  are described. 
         FIG. 11  is a flowchart showing a method for generating a graph for obtaining nodes and edges (links) on the particular floor of the building. 
         FIG. 12  is a diagram showing an example topology representing the relationships between the nodes and edges (links) obtained from the flowchart shown in  FIG. 11 . 
         FIG. 13  is a flowchart showing a method for obtaining the correlation between new and existing buildings and extracting a graph of an existing building having a high degree of correlation. 
         FIG. 14  is a diagram showing an example where graphs having a high degree of correlation obtained in  FIG. 13  are laid out and displayed on the floor plan of the new building. 
         FIG. 15  is a diagram showing an example where the graphs having a high degree of correlation obtained in  FIG. 13  are laid out on the floor plan of the new building to display wireless base stations. 
         FIG. 16  is a diagram showing the configuration of an apparatus for supporting layout of wireless base stations according to another embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     Hereafter, an embodiment of the present invention will be described in detail with reference to the drawings.  FIG. 1  is a diagram showing an example configuration of a wireless environment detection apparatus  100  according to a first embodiment of the present invention. 
     The wireless environment detection apparatus  100  includes an input unit  101 , a graph generation unit  102 , a storage unit  103 , a graph detection unit  104 , and a display unit  105 . These components are coupled together via a signal line  106  so as to exchange signals with one another. 
     The input unit  101  receives various inputs such as an input of three-dimensional structures in a new building in which a wireless network is to be constructed, an input of three-dimensional structures in a building in which a wireless network is already installed and whose wireless propagation environment is known, and inputs of antenna installation of radio base stations and transmission power distribution of radio waves from the radio base stations. 
       FIG. 2  shows an example of three-dimensional structures in a typical building. The example of  FIG. 2  shows the floor structure of a particular floor of a building. A wireless network is to be constructed in the floor structure of the particular floor. To construct a wireless network, coordinates are assigned to structures in the floor structure. 
     For example, this floor structure includes accessory structures, such as walls W 1  to W 4 , a floor F, a ceiling (not shown), a window (not shown), and pillars P 1  to Pn. The floor structure also includes accessory structures such as pieces of equipment M and furniture (not shown) installed in rooms partitioned by walls or partitions. 
     The layout positions of fundamental structures, such as the walls W, the window, and pillars P, forming the floor structure of the particular floor, in which a wireless network is to be constructed, and optionally the layout positions of the equipment M and furniture, antennas AP 1 , AP 2 , receiving stations ST 1  to STn, or the like are represented by predefined, three-dimensional coordinate systems (x, y, z). 
     An x component represents a coordinate in the length direction of the floor; a y component a coordinate in the width direction thereof; and a z component a coordinate in the height direction thereof. 
     The coordinate positions of the structures, such as the walls W, the floor F, the ceiling, the window, the pillars P, the equipment M and furniture installed in the room, and the base station antennas AP and the receiving antennas ST, are predefined, for example, using the lower-left corner as the origin of the three-dimensional coordinate system (x, y, z). 
       FIG. 3  shows an example of three-dimensional structure information where the structures and the like shown in  FIG. 2  are represented by coordinates. The three-dimensional information includes, for example, (1) type of structure, (2) name of structure, (3) three-dimensional coordinate system (x, y, z), and (4) shape. These pieces of information are stored in the storage unit  103  of the wireless environment detection apparatus  100 . 
     For the structures having a rectangular parallelepiped shape, such as the walls and pillars, three-dimensional structure information thereof is represented in such a manner that the coordinate positions of two diagonal points thereof are specified. For example,  FIG. 3  shows that the wall W 1  located in an lower portion of  FIG. 2  is a rectangular parallelepiped-shaped structure having a starting point at coordinates (0 0 0) and an end point at coordinates (16 0.5 3) and thus having a length of 16 m, a thickness (width) of 0.5 m, and a height of 3 m. Similarly, the wall W 2  in a right portion of  FIG. 2 , the wall W 3  in an upper portion thereof, and the wall W 4  in a left portion thereof are defined. 
       FIG. 3  also shows that the pillar P 1  located at the origin of the floor structure is a rectangular parallelepiped-shaped structure having a starting point at coordinates (0 0 0) and an end point at coordinates (1 1 3) and thus having a length of 1 m, a thickness (width) of 1 m, and a height of 3 m. 
     Similarly, the pillar P 2  adjacent to the pillar P 1  is a rectangular parallelepiped-shaped structure having a starting point at coordinates (3 0 0) and an end point at coordinates (4 1 3) and thus having a length of 1 m, a thickness of 1 m, and a height of 3 m. Other pillars Pn are defined as well. 
     Similarly, the pieces of equipment M and furniture (not shown) are represented by three-dimensional coordinates and shapes. 
     While an example of three-dimensional information is shown in  FIG. 3 , (5) at least one of permittivity, permeability, and conductivity, which are electrical properties, is stored along with three-dimensional information for each of the structures. Unlike in a case where the target space is wide as in Patent Literature 1, these parameters are important in estimating radio signal propagation characteristics inside a building. 
     Specifically, when a structure is the wall W, permittivity, permeability, or conductivity, which is an electrical property of the material for the wall, is stored. Of course, when another structure is a pillar, an electrical property of the material for the pillar is stored as well. 
     AP 1  and AP 2  shown in  FIG. 2  represent the layout positions of the base station antennas. A wireless network is constructed in the floor structure of the particular floor via radio waves emitted by the base station antennas AP 1  and AP 2 . 
     For example, as shown in  FIG. 4 , three-dimensional information of the base station antennas AP 1  and AP 2  includes the following information with respect to a dipole antenna, a planar antenna, or the like: (1) type of antenna, (2) name of antenna, (3) transmission power, (4) three-dimensional coordinate values (x, y, z), (5) tilt angle, and (6) azimuth angle. 
     For example,  FIG. 4  shows that the base station antenna AP 1  located in an upper right portion of  FIG. 2  uses a dipole antenna, has transmission power of 13 dBm, and is installed with a tilt angle of 0° and an azimuth angle of 0° at a coordinate position (10 15 2.7). 
     Similarly,  FIG. 4  shows that the base station antenna AP 2  located in a lower left portion of  FIG. 2  uses a planar antenna, has transmission power of 13 dBm, and is installed with a tilt angle of 0° and an azimuth angle of 90° at a coordinate position (1 3 2.7). 
     White circles shown in  FIG. 2  represent the positions of receiving antennas ST and represents points at which the receiving antennas ST 1  to STn receive power from the base station antennas AP 1  and AP 2  and measure the power. 
       FIG. 5  shows an example of radio wave propagation characteristic values measured by the receiving antennas ST and specifically shows the following information with respect to each receiving antenna ST: (1) name, (2) three-dimensional coordinate value (x, y, z), and (3) values of power received from the base station antennas AP 1  and AP 2 . 
     These pieces of information are stored in the storage unit  103  of the wireless environment detection apparatus  100 , as described above. 
     Three-dimensional information of the accessory structures, the base station antennas AP, the receiving antennas ST, and the like as shown in  FIGS. 3 to 5  is inputted using the input unit  101 . 
     The input unit  101  may be an input unit with which an operator inputs information manually, such as a keyboard, an input unit configured to receive data transmitted from another medium (DVD, CD, flash memory, etc.), or an input unit configured to automatically obtain these pieces of information when coupled to another apparatus. 
     For example, the input unit  101  may be coupled to a computer aided design (CAD) apparatus to use a CAD drawing as three-dimensional information. Further, the input unit  101  may be used as an apparatus for inputting space information by coupling it to a laser range scanner, three-dimensional recognition camera, or the like. 
     The graph generation unit  102  has a function of generating graph information by defining pieces of space formed by three-dimensional structures as nodes and defining edges (links) for linking the defined nodes. 
     The function of the graph generation unit  102  will be described based on a floor plan of the building shown in  FIG. 6 .  FIG. 6  shows a floor plan obtained by viewing three-dimensional structures received by the input unit  101  and stored in the storage unit  103  from above. Although these three-dimensional structures are shown two-dimensionally, they correspond to three-dimensional structures. (Note that this embodiment is not limited to three-dimensional data, and the effectiveness of the present invention does not change even when the data is two-dimensional data. 
     In  FIG. 6 , reference numerals  201 ,  202  represent walls; a pillar  203  is disposed along the walls  201 ,  202 ; and a pillar  204  which is different from the pillar  203  is disposed on the floor. While many walls and pillars other than the walls  201 ,  202  and the pillars  203 ,  204  are disposed, reference numerals thereof are omitted in the drawing. These walls and pillars are typified by the walls  201 ,  202  and the pillars  203 ,  204 . 
     Partitions  205 ,  206 ,  207  for partitioning the room are disposed on the floor. Pieces of furniture, desks  208 ,  209 , are disposed in the partitioned room. While many partitions and furniture pieces other than those described above are disposed, reference numerals thereof are omitted in the drawing. 
     The graph generation unit  102  extracts, from the floor plan, pieces of space which do not block radio waves or pieces of space which transmit radio waves while blocking them less effectively. The expression “do not block radio waves” means that there is no structure. Note that an object having a size of about 2 to 5 times the wavelength of the target radio frequency is negligible. 
       FIG. 7  shows an example of pieces of space that do not block radio waves or pieces of space that transmit radio waves while blocking them less effectively, obtained by the graph generation unit  102 . 
     In  FIG. 7 , the above-mentioned pieces of space are represented by regions enclosed by dotted lines and typified by pieces of space having reference numerals  210  to  217 . Methods for extracting these pieces of space include voxel division, by which space is divided uniformly and finely, a method of dividing space while noting the boundaries among sides forming a structure, and k-d tree division. Use of these methods allows features of space to be identified. Reference numeral  210  represents space outside the building. 
     The graph generation unit  102  defines these pieces of space as nodes. Attributes of the nodes are shown in  FIG. 8 .  FIG. 8  shows (1) three-dimensional space coordinate values (m) of starting point and (2) lengths (m) in axis directions (three-dimensional directions) of space corresponding to each node. 
     A value represented by (3) furniture, etc. represents the volume of furniture or the like contained in space corresponding to each node; (4) weight refers to, for example, a value obtained by subtracting the volume of furniture or the like from the volume of space corresponding to each node and represents the ease of propagation of radio waves through the space. The weight, that is, the ease of propagation of radio waves also varies according to such as the material for the furniture. Depending on the material, a modification to the weight is considered. 
     The graph generation unit  102  also has a function of calculating an edge (link) for linking nodes. Specifically, it identifies a structure present between nodes with respect to each of boundary surface directions of each node and calculates and generates an edge (link) with respect to nodes interposing the identified structure. Such an edge (link) is calculated using attributes of the structures described in  FIG. 3  or the like. 
     Note that all the attributes shown in  FIG. 3  need not necessarily be used in this calculation, in other words, any attributes may be used as long as an edge (link) is obtained appropriately. 
     If part of a boundary surface between nodes is covered by a structure, the area of the remaining part of the boundary surface, which is not covered by the structure, is regarded as the area of an opening. An edge (link) is generated with respect to the nodes interposing the opening so as to link the nodes. 
     For example, note a node  212  of  FIG. 7 . Edges (links) can be established between the node  212  and a node  211 , between the node  212  and a node  213 , between the node  212  and a node  214 , between the node  212  and a node  215 , between the node  212  and a node  216 , and between the node  212  and a node  217 . 
     Specifically, in  FIGS. 7 and 9 , the upper boundary surface of node  212  is adjacent to a node  210  with a portion of the wall  202  therebetween and adjacent to the node  210  with a portion of the pillar  203  therebetween. Accordingly, edges (links)  220  and  221  are generated between the nodes  212  and  210 . 
     Similarly, the right boundary surface of node  212  is adjacent to nodes  211 ,  214 , and  215  with the partition  205  therebetween. Accordingly, edges (links)  222 ,  223 , and  224  are generated between the nodes  212  and  211 , between the nodes  212  and  214 , and between the nodes  212  and  215 , respectively. 
     Further, since the partition  207  is present between the lower boundary surface of the node  212  and a node  216 , an edge (link)  225  is generated between the nodes  212  and  216 . 
     On the other hand, the lower boundary surface of node  212  is linked to node  217  without the entire lower boundary surface being covered by the area of the partition  207 . Accordingly, an edge (link)  226  is generated between the nodes  212  and  217  as an opening directly adjacent to the node  212 . If a window, for example, is disposed on the wall  202  or if a door, for example, is disposed on the partition  206 , an edge (link) is also generated with respect to this portion. 
     Similarly, edges (links)  227  to  229  are generated between the nodes  212  and  213 . 
       FIG. 10  shows descriptions of the edges shown in  FIG. 9 . In  FIG. 10 , the following items are defined for each edge: (1) name, (2) starting point node and endpoint node, (3) boundary surface direction of starting point, (4) blocking category, (5) category of blocking structure, (6) weight of edge, and the like. 
     Next, a process for generating such edges (links) will be described based on a flowchart shown in  FIG. 11 . In step S 230  of  FIG. 11 , in order to generate a graph, a floor plan as shown in  FIG. 6  is read from the storage unit  103  and loaded into the graph generation unit  102 . 
     Next, the process proceeds to step S 231  to perform a space analysis process. In this step, pieces of space which do not block radio waves or pieces of space which transmit radio waves while blocking them less effectively are extracted from the floor plan read as described above. 
     After extracting the pieces of space, the process proceeds to step S 232  to generate nodes corresponding to the extracted pieces of spaces. After generating the nodes, the process proceeds to step S 233  to define attributes of the nodes. As shown in  FIG. 8 , these attributes include the position of each node, the sizes of each node, presence of furniture, and the weight of each node. 
     Next, in steps S 232  and S 233 , a node k is generated, and attributes thereof are determined. The process proceeds to step S 234  to determine the boundary surface directions of the node k serving as a reference. The process then proceeds to step S 235  to analyze the existing structures using attributes as described in  FIG. 3 . 
     Based on the analysis result, in step S 236 , a node present in the direction of a structure j with respect to the node serving as a reference is determined. In step S 237 , an edge (link) is generated. 
     If it is determined in step S 238  that an opening such as a window or door is present in any boundary surface direction, an edge (link) is generated between nodes passing through this opening, in step S 239 . 
     In this way, the definition of edges (link) as shown in  FIG. 10  is completed. The process then proceeds to step S 240  to perform a graph storage process. 
       FIG. 12  shows a topology where the relationships between these nodes and edges (links) are shown as a graph. In the case of a three-dimensional structure, each node has one or more edges (links) with respect to a boundary surface thereof in each direction and has information as to whether radio waves are blocked between nodes. 
     As seen above, when three-dimensional (or two-dimensional) structures as shown in  FIG. 6  are provided, the graph generation unit  102  performs space analysis to generate a graph. 
     If the building is a building in which a wireless network is already constructed, the graph generation unit  102  stores the generated graph as a database in the storage unit  103  along with data indicating the layout of base station antennas in the building as shown in  FIG. 4  and the propagation environment measured values of the receiving antennas shown in  FIG. 5 . These are used as graphs known to the graph detection unit  104  to be discussed later. 
     These databases are updated and accumulated each time a wireless network is constructed. Accordingly, more accurate data is accumulated as the database is expanded, and the degree of correlation can be increased in graph detection to be discussed later. 
       FIG. 13  is an example of a flowchart showing a process performed by the graph detection unit  104 . 
     In the construction of a new wireless network, the graph detection unit  104  detects a graph Gs representing a new building. In this case, an edge (link) corresponding to each node is generated in a process as shown in  FIG. 11 . 
     In step S 242 , the graph detection unit  104  performs a process described below with respect to each node k in the graph Gs. 
     Specifically, in step S 243 , the graph detection unit  104  performs a process of extracting a subgraph Gs (k, n) in which up to n number of edges (links) are allowed, with respect to each node k. The subgraph Gs (k, n) is a subgraph of the graph Gs and includes nodes from a node k serving as a center to nodes which are distant from the node k by n number of edges (links). 
     Such a subgraph represents relationships as shown in  FIG. 12 . The number n may be a predetermined value, or the process may be performed repeatedly with respect to numbers from one to the maximum number, N. 
     Step S 244  shows that a process similar to that shown in step S 243  is performed with respect to each graph Gj in the existing database. 
     In step S 245 , the graph detection unit  104  performs a process of, with respect to each node i included in a graph Gj in the database, extracting a subgraph Gj (i, n) having the node as a center. In this process, a subgraph Gj (i,n) similar to the subgraph Gs (k,n) obtained in step  243  is extracted. 
     Accordingly, a more similar subgraph G (i, n) is obtained as the database becomes more sufficient. In this case, a single subgraph Gj (i, n) may be extracted from the database, or in some cases, multiple subgraphs Gj (i, n) may be extracted. 
     After obtaining the subgraph Gs (k, n) of the new building and the similar subgraph Gj (i, n) in the database through the above-mentioned process, the graph detection unit  104  performs a process of calculating a correlation value between both graphs, in step S 246 . A correlation value between both graphs is obtained, for example, by vectorizing the weights of nodes, the weights of edges (links) coupled at equal distances, or the like and calculating the inner product of the vectors. Note that the method for determining a correlation value is not limited to the above-mentioned one, and a method suitable to the building is selected and used. 
     After obtaining a correlation value by performing the process of calculating a correlation value between both graphs, the graph detection unit  104 , in step S 247 , extracts a subgraph Gk (k, j, n) having a correlation value not smaller than a predetermined value, for example, a subgraph Gk (k, j, n) having the greatest correlation value from the database, with respect to each node of the graph Gs of the new building. 
     After extracting, for example, a subgraph G (k, j, n) having the greatest correlation value from the database, the graph detection unit  104 , in step S 248 , performs a process of synthesizing a subgraph Gk (k, j, n) corresponding to each node k of the graph Gs of the new building. One of advantageous methods is a method of disposing a subgraph Gk (k, j, n) having a node k as a center and, when there are overlapping nodes, selecting a node and edge (link) included in a subgraph G (k, j, n) having a higher correlation value. 
     By performing the above-mentioned process, the graph detection unit  104  can extract a subgraph having a higher correlation value from among subgraphs contained in the existing database. 
       FIG. 14  is a diagram showing an example where the subgraphs having a higher correlation value are displayed on the display unit  105  in a combined manner. Reference numeral  250  represents a floor plan of a building in which base stations are desired to install newly. The ranges of structure data (for example, three-dimensional structure data) composed of the subgraphs having a higher correlation value extracted from the database and respective correlation values are overlaid on this floor plan. 
     Reference numeral  251  represents a subgraph corresponding to part of a building A stored in the database, and the correlation value of the subgraph is 900. 
     Reference numeral  252  represents a subgraph corresponding to part of a building B stored in the database, and the correlation value of the subgraph is 80%; reference numeral  253  represents a subgraph corresponding to part of the building B stored in the database, and the correlation value of the subgraph is 50%; and reference numeral  254  represents a subgraph corresponding to part of a building C stored in the database, and the correlation value of the subgraph is 50%. 
     A wireless network is constructed while regarding base stations installed in the subgraphs as base stations to be installed in the new building. 
     This is shown in  FIG. 15 .  FIG. 15  is an example where a base station antenna  255  of the building A, a base station antenna  256  of the building B, and a base station antenna  257  of the building C are shown. In  FIG. 15 , a sparsely hatched region and a densely hatched region show degrees of correlation visually, and the densely hatched region represents a higher degree of correlation. Alternatively, degrees of correlation may be shown by hatching the regions with different colors. 
     As seen, according to the first embodiment of the present invention, in the construction of a wireless network system in a building, a condition similar to structure conditions of the building in which it a wireless network system is desired to newly install is retrieved from among the structure conditions of buildings in which a wireless network system was installed in the past. As a result, a layout of base stations in a new building can be easily obtained using past base station layout information. 
     While the single apparatus has been described in this embodiment, the above-mentioned process may be performed by constructing a database in a data center to accumulate data from many vendors and connecting with the database using a network. In this case, many pieces of data are accumulated, allowing a subgraph having higher similarity to be obtained. 
     Second Embodiment 
       FIG. 16  is characterized in that the wireless environment detection apparatus  100  includes a propagation information synthesis unit  107  in addition to the components of the first embodiment shown in  FIG. 1 . The propagation information synthesis unit  107  performs the following process in the registration of a graph related to an existing building and a propagation environment measured value in the database. 
     The propagation information synthesis unit  107  obtains a subgraph having a high correlation value and a propagation environment measured value from among graphs which are already registered in the database. 
     Next, the propagation information synthesis unit  107  compares the subgraph having a high correlation value with a subgraph of the existing building with respect to each node and edge (link). It then extracts nodes or edges (links) which are different by a predetermined value or more. 
     The propagation information synthesis unit  107  then compares the propagation environment measured value obtained from the database with a propagation environment measured value to be registered this time. If the difference is not greater than a predetermined value, the propagation information synthesis unit  107  combines the subgraphs together. Nodes or edges (links) extracted as portions corresponding to the difference are registered as a less effective error factor in the database. 
     In contrast, if the difference between the respective propagation environment measured values is not less than the predetermined value, the different is registered as an effective error factor in the database. 
     By performing the above-mentioned process, robustness against such as an error factor of the database can be increased. 
     LIST OF REFERENCE SIGNS 
     
         
           1  wireless environment detection apparatus 
           101  input unit 
           102  graph generation unit 
           103  storage unit 
           104  graph detection unit 
           105  display unit 
           107  propagation information synthesis unit