JP7575702B2 - Station location design support method and station location design support device - Google Patents

Description

The present invention relates to a station placement design support method and a station placement design support device.

With the spread of various wireless communication systems, the scarcity of frequency resources has become an issue. To make effective use of limited frequency resources, system design must take into account radio wave interference between wireless stations. To perform interference evaluation, interference calculations must be performed based on information about the wireless transmission by the interfering station that causes interference, information about the wireless reception by the interfered station that receives the interference, and the propagation loss of the interference wave that is attenuated due to the distance from the interfering station to the interfered station and other environmental conditions.

In addition, wireless communication using multi-hops (hereinafter referred to as "multi-hop wireless communication") can be considered as a means of communication in rural areas. For example, even if the distance between a base station and a terminal station is long and direct wireless communication between the two stations is not possible, at least one relay station relays the transmission of radio waves to establish a wireless link route, making communication between the two stations possible. When using such multi-hop wireless communication, it is necessary to install base stations and relay stations in appropriate locations, taking into consideration radio wave interference, etc. Hereinafter, designing the placement of wireless stations such as base stations and relay stations will be referred to as "station placement design."

Recently, station placement design support technology that supports operators in station placement design has been studied. For example, the station placement design method described in Patent Document 1 applies a directional antenna to an unaccommodated station that cannot perform wireless communication with an aggregate station or an already-accommodated station using an omnidirectional antenna, thereby enabling wireless communication between the two stations. Furthermore, by appropriately selecting the antenna azimuth angle of the directional antenna, it becomes possible to realize more effective multi-hop wireless communication that is highly robust and reliable and has low equipment costs.

Patent No. 6009637 JP 2004-023726 A JP 2002-010340 A JP 2019-169815 A JP 2005-341317 A JP 2010-093703 A

Hidekazu Taoka, Satoshi Nagata, Kazuaki Takeda, Yuichi Kakishima, Xie Xiangming, Katsutoshi Kusume, "MIMO and Inter-cell Cooperative Transmission and Reception Technology in LTE-Advanced", NTT DOCOMO Technical Journal, Vol.18 No.2, pp.22-30, July 2010. Koji Ishibashi, Hideki Ochiai, Ryuji Kono, "Performance Analysis of Coded DAPSK Modulation Using Cyclic Delay Diversity", Proceedings of the Symposium on Information Theory and Its Applications, 29(2), pp.783-786, November 2006. Shigenori Sasaki, Hidekazu Murata, Koji Yamamoto, Susumu Yoshida, "A Study on Delay Time Distributed Control Method for Cooperative Multi-hop Wireless Networks Using CDD", Technical Report of the Institute of Electronics, Information and Communication Engineers, Vol. 108 No. 117, RCS2008-20, pp. 25-30, June 2008. Ryoko Kawachi, Kazuaki Takeda, Fumiyuki Adachi, "Effect of Cyclic Delay Transmit Diversity on DS-CDMA using Frequency Domain Equalization", Technical Report of the Institute of Electronics, Information and Communication Engineers, Vol. 104, No. 680, RCS2004-392, pp. 13-18, March 2005.

In multi-hop wireless communication, for example, when only a single radio frequency channel is used, radio waves to be received at a relay station may be affected by radio wave interference caused by radio waves transmitted from a radio station that is not adjacent to the relay station on the radio link path (for example, the radio station two stations before on the radio link path). This may result in the multi-hop wireless communication not being performed normally. In order to avoid such radio wave interference, in multi-hop wireless communication, a relay station may use different radio frequency channels for receiving radio waves from a relay source radio station (i.e., the radio station one station before on the radio link path) and transmitting radio waves to a relay destination radio station (i.e., the radio station one station after on the radio link path). However, when multiple radio frequency channels are assigned to the radio link path, the number of radio frequency channels that can be assigned to wireless communication between a relay station and a terminal station accommodated by the relay station is reduced. This causes a problem that the number of terminal stations that can be accommodated is limited.

In view of the above circumstances, the present invention aims to provide a station placement design support method and a station placement design support device that can support station placement design that enables multi-hop wireless communication without increasing the number of radio frequency channels used between relay stations.

One aspect of the present invention is a computer-based station placement design support method for supporting station placement design of a communication network in which a plurality of wireless stations are wirelessly connected to form a communication path, the station placement design support method having a station placement design step of placing a non-adjacent wireless station, which is another wireless station that is not adjacent to the wireless station on the communication path, based on the direction of radiation of radio waves from a directional antenna equipped in the wireless station.

Another aspect of the present invention is a station placement design support device that supports station placement design for a communication network in which a plurality of wireless stations are wirelessly connected to form a communication path, the station placement design support device having a station placement design unit that places a non-adjacent wireless station, which is another wireless station that is not adjacent to the wireless station on the communication path, based on the direction of radiation of radio waves from a directional antenna equipped in the wireless station.

The present invention can assist in station placement design that enables multi-hop wireless communication without increasing the number of radio frequency channels used between relay stations.

FIG. 1 is a diagram illustrating an example of the configuration of a wireless communication system 5a that performs multi-hop wireless communication. FIG. 1 is a diagram illustrating an example of the configuration of a wireless communication system 5a that performs multi-hop wireless communication. 1 is a diagram illustrating an example of the configuration of a wireless communication system 5b that is designed by a station placement design assisting device 1 according to a first embodiment of the present invention. 1 is a block diagram showing a functional configuration of a station placement design assistance device 1 according to a first embodiment of the present invention. 4 is a flowchart showing an operation of the station placement design assistance device 1 in the first embodiment of the present invention. 1 is a diagram illustrating an example of the configuration of a wireless communication system 5c for which station placement design is performed by a station placement design assisting device 1 according to a first embodiment of the present invention. FIG. 13 is a diagram showing an example of the results of station placement design for an existing rural area. FIG. 2 is a diagram showing an example of an antenna pattern of a directional antenna used in a relay station according to the first embodiment of the present invention. 4 is a diagram showing an example of an antenna pattern of an omnidirectional antenna used in a relay station according to the first embodiment of the present invention; FIG. FIG. 1 is a diagram illustrating an example of the configuration of a wireless communication system 5e that performs multi-hop wireless communication. FIG. 1 is a diagram illustrating an example of the configuration of a wireless communication system 5e that performs multi-hop wireless communication. 1 is a diagram illustrating a configuration example of a wireless communication system 5f designed by a station placement design assisting device 1 in a first modified example of the first embodiment of the present invention. FIG. FIG. 1 is a diagram illustrating a configuration example of a wireless communication system 5g designed by a station placement design assisting device 1 in a first modified example of the first embodiment of the present invention. FIG. 11 is a diagram showing an example of the results of station placement design for an existing rural area. FIG. 1 is a diagram showing an example of the configuration of a wireless communication system 5i that performs multi-hop wireless communication. FIG. 11 is a diagram illustrating a configuration example of a wireless communication system 5j designed by a station placement design assisting device 1 in a modified example 2 of the first embodiment of the present invention. 13 is a diagram for explaining selection of candidate positions of relay stations by a station placement design assisting device 1 in a second embodiment of the present invention. FIG. 10 is a flowchart showing an operation of a station placement design assisting device 1 in a second embodiment of the present invention. FIG. 11 is a diagram illustrating an example of the configuration of a wireless communication system 5l for which station placement design is performed by a station placement design assisting device 1 according to a second embodiment of the present invention. FIG. 1 is a diagram for explaining wireless communication when transmit/receive diversity is not used. FIG. 1 is a diagram for explaining wireless communication when transmit/receive diversity is used.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
In each embodiment and modified example of each embodiment described below, a method and an apparatus for supporting station placement design for relay stations that enable multi-hop wireless communication with fewer radio frequency channels will be described. Here, as an example, a case will be described in which station placement design support is performed to enable multi-hop wireless communication in a rural area where the development of communication infrastructure is lagging behind. Also, as an example, here, it is assumed that a relay station is installed on a utility pole, and that a terminal station to be accommodated is installed on a wall surface of a building (e.g., a dwelling house, etc.). Therefore, in the station placement design described below, a candidate installation position for the relay station is selected from the position of the utility pole, and a candidate installation position for the terminal station is selected from the position of the wall surface of the building.

In each of the embodiments and modified examples of each embodiment described below, in order to make the drawings easier to understand, the number of relay stations provided in the wireless communication system that realizes multi-hop wireless communication is set to about 3 to 4. However, the number of relay stations can be any number as long as it is two or more.

(First embodiment)
A first embodiment of the present invention will now be described.

1 and 2 are diagrams showing an example of the configuration of a wireless communication system 5a that performs multi-hop wireless communication. Fig. 1 shows the wireless communication system 5a as seen from a direction horizontal to the ground, and Fig. 2 shows the wireless communication system 5a as seen from above.

As shown in Figures 1 and 2, the wireless communication system 5a is composed of relay stations 50a-1, 50a-2, and 50a-3. Furthermore, relay stations 50a-1, 50a-2, and 50a-3 each have a directional antenna. Relay stations 50a-1, 50a-2, and 50a-3 are wireless stations that relay radio waves transmitted in communication between a base station (not shown) and a terminal station (not shown).

In the following, when there is no need to distinguish between relay station 50a-1, relay station 50a-2, and relay station 50a-3, they may simply be referred to as "relay station 50a."

The relay station 50a-1 receives radio waves transmitted from the base station and transmits the radio waves toward the relay station 50a-2, thereby relaying the radio waves transmitted from the base station to the terminal station. The relay station 50a-1 also receives radio waves transmitted from the terminal station accommodated by the relay station 50a-1 or from the relay station 50a-2, and transmits the radio waves toward the base station, thereby relaying the radio waves transmitted from the terminal station to the base station.

Relay station 50a-2 receives radio waves transmitted from relay station 50a-1 and transmits radio waves toward relay station 50a-3, thereby relaying radio waves transmitted from the base station to the terminal station. Relay station 50a-2 also receives radio waves transmitted from the terminal station accommodated by relay station 50a-2 or relay station 50a-3, and transmits radio waves toward relay station 50a-1, thereby relaying radio waves transmitted from the terminal station to the base station.

Relay station 50a-3 receives radio waves transmitted from relay station 50a-2 and transmits the radio waves toward the terminal station, thereby relaying radio waves transmitted from the base station to the terminal station. Relay station 50a-3 also receives radio waves transmitted from the terminal station it accommodates and transmits the radio waves toward relay station 50a-2, thereby relaying radio waves transmitted from the terminal station to the base station.

Therefore, the wireless link path (communication path) in the wireless communication system 5a is a path in the order of base station, relay station 50a-1, relay station 50a-2, relay station 50a-3, or a path in the reverse order.

Here, the same radio frequency channel is used for radio wave ra-1 transmitted and received between relay station 50a-1 and relay station 50a-2, and radio wave ra-2 transmitted and received between relay station 50a-2 and relay station 50a-3. In Figures 1 and 2, this same radio frequency channel is represented by the same thick solid double-headed arrow.

In Figures 1 and 2, only the range of antenna directivity of the transmitting antenna that transmits radio wave ra-1 from relay station 50a-1 to relay station 50a-2 is shown as antenna directivity range da-1. As shown in Figures 1 and 2, not only relay station 50a-2 but also relay station 50a-3 are located within the range of antenna directivity range da-1. Also, as mentioned above, the same radio frequency channel is used for radio waves ra-1 and ra-2. Therefore, when relay station 50a-3 receives radio wave ra-2 transmitted from relay station 50a-2, radio waves ra-2 and ra-1 interfere with each other. This may interfere with communication from relay station 50a-2 to relay station 50a-3.

Note that while the case of transmitting radio waves has been described here, the same applies to reception. For example, if the range of antenna directivity of the receiving antenna of relay station 50a-1 is the antenna directivity range da-1 shown in Figures 1 and 2, when relay station 50a-1 receives radio waves ra-1 transmitted from relay station 50a-2, radio waves ra-1 and ra-2 will interfere with each other. This may prevent communication from relay station 50a-2 to relay station 50a-1.

In this way, when there are other relay stations 50a (non-adjacent wireless stations) that are not adjacent on the wireless link path (for example, the relay station 50a next to the other relay station 50a on the wireless link path) within the range of the antenna directivity of the antenna equipped with the relay station 50a, if radio waves of a single radio frequency channel are used, radio interference may occur, which may disrupt communication between the base station and the terminal station.

The station placement design support device 1 in the first embodiment described below supports the station placement design of the relay station 50a so as to create a wireless communication system in which no radio wave interference occurs or which is minimally affected by radio wave interference.

Figure 3 is a diagram showing an example of the configuration of a wireless communication system 5b designed by the station placement design support device 1 in the first embodiment of the present invention. Figure 3 shows the wireless communication system 5b as seen from above.

As shown in Fig. 3, wireless communication system 5b includes relay station 50b-1, relay station 50b-2, and relay station 50b-3. Furthermore, relay station 50b-1, relay station 50b-2, and relay station 50b-3 each have a directional antenna. Relay station 50b-1, relay station 50b-2, and relay station 50b-3 are wireless stations that relay radio waves transmitted in communication between a base station (not shown) and a terminal station (not shown).

In the following, when there is no need to distinguish between relay station 50b-1, relay station 50b-2, and relay station 50b-3, they may simply be referred to as "relay station 50b."

The wireless link path in the wireless communication system 5b is a path in the order of base station, relay station 50b-1, relay station 50b-2, relay station 50b-3, or a path in the reverse order.

Here, the same radio frequency channel is used for radio waves rb-1 transmitted and received between relay stations 50b-1 and 50b-2, and radio waves rb-2 transmitted and received between relay stations 50b-2 and 50b-3. In Figure 3, this same radio frequency channel is represented by the same thick solid double-headed arrow.

In FIG. 3, only the range of antenna directivity (radiation direction of radio wave rb-1) of the transmitting antenna that transmits radio wave rb-1 from relay station 50b-1 to relay station 50b-2 is shown as antenna directivity range db-1. As shown in FIG. 3, relay station 50b-2 is located within the range of antenna directivity range db-1, but relay station 50b-3 is located outside the range of antenna directivity range db-1. Therefore, although the same radio frequency channel is used for radio waves rb-1 and rb-2, when relay station 50b-3 receives radio wave rb-2 transmitted from relay station 50b-2, there is no radio interference between radio waves rb-2 and rb-1. This allows communication from relay station 50b-2 to relay station 50b-3 to be performed normally.

Note that while the case of transmitting radio waves has been described here, the same applies to reception. For example, if the range of antenna directivity of the receiving antenna of relay station 50b-1 is the antenna directivity range db-1 shown in FIG. 3, when relay station 50b-1 receives radio waves rb-1 transmitted from relay station 50b-2, there is no radio interference between radio waves rb-1 and rb-2. This allows communication from relay station 50b-2 to relay station 50b-1 to be performed normally.

In this way, the station placement design support device 1 in the first embodiment performs station placement design so that there are no other relay stations 50b (e.g., the relay station 50b next to the other relay station 50b on the wireless link path) that are not adjacent on the wireless link path within the range of the antenna directivity of the antenna equipped in the relay station 50b. As a result, even if radio waves of a single radio frequency channel are used on the wireless link path, radio wave interference does not occur and communication between the base station and the terminal station is performed normally.

[Functional configuration of a station placement design assistance device]
4 is a block diagram showing a functional configuration of a station placement design assistance device 1 in the first embodiment of the present invention. The station placement design assistance device 1 is an information processing device such as a general-purpose computer.

As shown in FIG. 4, the station placement design support device 1 is configured to include a control unit 100, a memory unit 101, an operation input unit 102, an output unit 103, a design range designation unit 104, a terminal station position identification unit 105, an equipment information acquisition unit 106, a relay station position selection unit 107, and a radio wave interference evaluation unit 108.

The control unit 100 controls the operation of each of the above-mentioned functional units of the station placement design support device 1. The control unit 100, for example, reads and executes a program stored in the memory unit 101, thereby causing the station placement design support device 1 to function as a device equipped with each of the above-mentioned functional units. The control unit 100 is configured to include a processor, for example a CPU (Central Processing Unit).

The memory unit 101 stores various data and programs. The memory unit 101 stores, for example, map data, station placement design result data, and temporary data used in the station placement design process. The memory unit 101 also stores, for example, information indicating the performance of the antennas provided in the base station, relay station, and terminal station. The antenna performance here refers to antenna characteristics such as output, communication distance, directivity, and reception performance. The memory unit 101 also stores, for example, information indicating the position of the base station. The memory unit 101 may also store information indicating the position of the terminal station.

The memory unit 101 is configured to include storage media such as RAM (Random Access Memory), flash memory, EEPROM (Electrically Erasable Programmable Read Only Memory), and HDD (Hard Disk Drive), or any combination of these storage media.

The operation input unit 102 accepts operation input by a user. The operation input unit 102 includes, for example, an input button, a keyboard, a mouse, etc.

The output unit 103 outputs various information. The output unit 103 displays, for example, station placement design result data. The station placement design result data is, for example, data indicating the selected wireless link route and candidate installation positions of relay stations. The output unit 103 is configured to include an image display device, for example, an LCD (Liquid Crystal Display) or an organic EL (Electro Luminescence) display. The output unit 103 may be a communication interface that outputs various information to an external device.

In addition, the operation input unit 102 and the output unit 103 may be components that integrate input and output functions, such as a touch panel.

The design range designation unit 104 reads out map data, for example, from the storage unit 101. The design range designation unit 104 selects, for example, a rectangular range from the read out map data, for example, based on information indicating the design range output by the operation input unit 102 in response to an operation by the user of the station placement design support device 1. The design range designation unit 104 designates the selected range as the design target area.

The terminal station position identification unit 105 extracts information indicating the position and contours (or walls) of the building for each building from map data within the design area. Based on the extracted information, the terminal station position identification unit 105 identifies, for example, the position of the building's wall (i.e., the candidate installation position of the terminal station). The station placement design support device 1 regards the identified wall position as the installation position of the terminal station and performs subsequent processing. Note that if information indicating the installation position of the terminal station is available, the terminal station position identification unit 105 may use the information to identify the installation position of the terminal station.

The equipment information acquisition unit 106 acquires equipment information, for example, from an external device. The equipment information here refers to information including information indicating the location of equipment (e.g., a utility pole) that is a candidate installation location for the relay station 50b.

The relay station position selection unit 107 selects a candidate installation location for the relay station 50b to be evaluated as a wireless link path from among all candidate installation locations for the relay station 50b. For example, the relay station position selection unit 107 selects at least one utility pole for installing the relay station 50b based on the installation location of the terminal station, the location of the utility pole, and the communication distance between the terminal station and the relay station 50b. For example, the relay station position selection unit 107 selects a utility pole for installing the relay station 50b so that the installation locations of all terminal stations within the design target area can be covered by a smaller number of relay stations 50b.

The radio interference evaluation unit 108 identifies a radio link path based on the location of the base station and the candidate installation location of the relay station 50b selected by the relay station location selection unit 107. The radio interference evaluation unit 108 determines whether the identified radio link path satisfies a predetermined condition. The predetermined condition here is a condition that the installation location of another relay station 50b that is not adjacent on the radio link path is not included within the range of the antenna directivity of the antenna equipped in each relay station 50b.

When the radio interference evaluation unit 108 determines that the specified conditions are met, the control unit 100 controls the output unit 103 to output information indicating the installation location of the relay station 50b, which is the wireless link path.

On the other hand, when the radio interference evaluation unit 108 determines that the predetermined condition is not met, the control unit 100 controls the relay station position selection unit 107 to reselect a candidate installation position for the relay station 50b. When there are no other selectable candidate installation positions for the relay station 50b, the control unit 100 controls the output unit 103 to output, for example, information indicating a location in the wireless link route that does not satisfy the predetermined condition. The control unit 100 may also control the output unit 103 to output information indicating that there is no wireless link route that satisfies the predetermined condition.

[Operation of the channel placement design assistance device]
An example of the operation of the station placement design assistance device 1 will now be described.
5 is a flowchart showing the operation of the station placement design support device 1 in the first embodiment of the present invention. The operation of the station placement design support device 1 shown in this flowchart is started, for example, when a user of the station placement design support device 1 operates the station placement design support device 1 and an instruction to start station placement design is output from the operation input unit 102.

The design range designation unit 104 reads the map data and selects, for example, a rectangular range based on the information indicating the design range output from the operation input unit 102. The design range designation unit 104 designates the selected range as the design target area (step S101).

The terminal station position identification unit 105 extracts information indicating the position and contour (or wall) of the building for each building from map data within the design area. The terminal station position identification unit 105 identifies the position of the building's wall based on the extracted information and identifies the installation position of the terminal station (step S102). Note that identifying the installation position of the terminal station here may also mean determining the position to be regarded as the installation position of the terminal station.

The equipment information acquisition unit 106 acquires equipment information for selecting candidate installation locations for the relay station 50b, for example from an external device (step S103).

The relay station position selection unit 107 selects at least one candidate installation position for the relay station 50b based on the installation position of the terminal station, the equipment information, the communication distance between the terminal station and the relay station 50b, etc. (step S104).

The radio interference evaluation unit 108 identifies a radio link path based on the location of the base station and the candidate installation location of the relay station 50b selected by the relay station location selection unit 107. The radio interference evaluation unit 108 sequentially determines whether each relay station 50b included in the identified radio link path satisfies a predetermined condition (step S105). As described above, the predetermined condition is a condition that the range of the antenna directivity of the antenna provided in each relay station 50b does not include a candidate installation location of another relay station 50b that is not adjacent on the radio link path.

If the relay station 50b included in the wireless link route satisfies the specified condition (step S106, Yes), the radio interference evaluation unit 108 determines whether the next relay station 50b included in the wireless link route satisfies the specified condition (step S106).

On the other hand, if the relay station 50b included in the wireless link route does not satisfy the specified condition (step S106: No), the relay station position selection unit 107 checks whether there are any other candidate installation locations for the relay station 50b that can be selected (step S107).

If there is another candidate installation location for the relay station 50b that can be selected (step S107: Yes), the relay station location selection unit 107 reselects another candidate installation location for the relay station 50b (step S108). The radio interference evaluation unit 108 determines whether the relay station 50b whose installation location has been reselected satisfies a predetermined condition (step S106).

On the other hand, if there are no other selectable candidate installation locations for relay station 50b (step S107: No), the control unit 100 controls the output unit 103 to output information indicating locations in the wireless link route that do not satisfy the specified conditions (step S109).

On the other hand, if all relay stations 50b in the wireless link route satisfy the predetermined condition (step S105, Yes), the control unit 100 controls the output unit 103 to output information indicating candidate installation positions of relay stations 50b in the wireless link route (step S110). This completes the operation of the station placement design support device 1 shown in the flowchart of FIG.

When the station placement design support device 1 performs station placement design as described above, multiple wireless link routes that satisfy the above-mentioned predetermined conditions may be derived for all relay stations. In this case, the station placement design support device 1 may further select a wireless link route that maximizes throughput from the multiple derived wireless link routes. Alternatively, the station placement design support device 1 may further select a wireless link route that minimizes communication delay from the multiple derived wireless link routes. In this way, the station placement design support device 1 can identify a wireless link route that maximizes throughput or minimizes communication delay while avoiding radio interference. Note that any conventional technology can be used as a method for estimating the throughput or communication delay in the derived wireless link route.

So far, we have explained the case where there are three relay stations, but it is possible to avoid radio interference in the same way even if there are four or more relay stations. Below, we will explain the case where there are four relay stations as an example.

Figure 6 is a diagram showing an example of the configuration of a wireless communication system 5c designed by the station placement design support device 1 in the first embodiment of the present invention. Figure 6 shows the wireless communication system 5c as seen from above.

6, the wireless communication system 5c includes relay stations 50c-1, 50c-2, 50c-3, and 50c-4. Each of relay stations 50c-1, 50c-2, 50c-3, and 50c-4 is equipped with a directional antenna. Relay stations 50c-1, 50c-2, 50c-3, and 50c-4 are wireless stations that relay radio waves transmitted in communication between a base station (not shown) and a terminal station (not shown).

In the following, when there is no need to distinguish between relay station 50c-1, relay station 50c-2, relay station 50c-3, and relay station 50c-4, they may simply be referred to as "relay station 50c."

The wireless link path in the wireless communication system 5c is a path in the order of relay station 50c-1, relay station 50c-2, relay station 50c-3, relay station 50c-4, or a path in the reverse order.

Here, the same radio frequency channel is used for radio waves rc-1 transmitted and received between relay stations 50c-1 and 50c-2, radio waves rc-2 transmitted and received between relay stations 50c-2 and 50c-3, and radio waves rc-3 transmitted and received between relay stations 50c-3 and 50c-4. In Figure 6, this same radio frequency channel is represented by the same thick solid double-headed arrow.

In Fig. 6, only the range of antenna directivity of the transmitting antenna that transmits radio waves rc-1 from relay station 50c-1 to relay station 50c-2 is shown as antenna directivity range dc-1. As shown in Fig. 6, relay station 50c-2 is located within the range of antenna directivity range dc-1, but relay station 50c-3 and relay station 50c-4 are located outside the range of antenna directivity range dc-1.

Therefore, although the same radio frequency channel is used for radio waves rc-1 and rc-2, when relay station 50c-3 receives radio waves rc-2 transmitted from relay station 50c-2, radio waves rc-2 and rc-1 do not interfere with each other. This allows normal communication from relay station 50c-2 to relay station 50c-3. Similarly, although the same radio frequency channel is used for radio waves rc-1 and rc-3, when relay station 50c-4 receives radio waves rc-3 transmitted from relay station 50c-3, radio waves rc-3 and rc-1 do not interfere with each other. This allows normal communication from relay station 50c-3 to relay station 50c-4.

In this embodiment, the station placement design support device 1 performs station placement design for each relay station 50c so that the range of antenna directivity of each antenna of the relay station 50c does not include other relay stations 50c that are not adjacent to each other on the wireless link path, as shown in Figure 6. This makes it possible to prevent or reduce the occurrence of radio interference even when a single radio frequency channel is used on the wireless link path.

Note that the arrangement of the four relay stations 50c shown in Figure 6 roughly corresponds to the results of station placement design performed for the actual rural area shown in Figure 7.

Figure 7 is a diagram showing an example of the results of station placement design for an actual rural area. Figure 7 shows a wireless communication system 5d for which station placement has been designed on map data of an actual rural area.

7, the wireless communication system 5d includes a relay station 50d-1, a relay station 50d-2, a relay station 50d-3, and a relay station 50d-4. The relay stations 50d-1, 50d-2, 50d-3, and 50d-4 each include a directional antenna. The relay stations 50d-1, 50d-2, 50d-3, and 50d-4 are wireless stations that relay radio waves transmitted in communication between a base station (not shown) and a terminal station (not shown).
Hereinafter, when there is no need to distinguish between the relay station 50d-1, the relay station 50d-2, the relay station 50d-3, and the relay station 50d-4, they may be simply referred to as "relay station 50d."

In Figure 7, the small solid circles indicate utility poles (i.e., potential installation locations for relay station 50d). The four dashed circles represent the ranges within which each relay station 50d can communicate with the terminal stations. Relay station 50d is installed on the utility pole located at the center of each of the four dashed circles. As shown in the figure, the range consisting of these four circles covers the location of at least one wall of all buildings in the map data shown in Figure 7 (i.e., installation locations of terminal stations). In this way, relay stations 50d are positioned so that all terminal stations in the design area can be accommodated by one of the four relay stations 50d.

In wireless communication system 5d designed as shown in Figure 7, the angle between the direction from relay station 50d-1 to relay station 50d-2 and the direction from relay station 50d-2 to relay station 50d-3 is 66 degrees. Also, the angle between the direction from relay station 50d-2 to relay station 50d-3 and the direction from relay station 50d-3 to relay station 50d-4 is 70 degrees.

The angle between the direction from relay station 50d-1 to relay station 50d-2 and the direction from relay station 50d-1 to relay station 50d-3 is 31 degrees. The angle between the direction from relay station 50d-2 to relay station 50d-3 and the direction from relay station 50d-2 to relay station 50d-4 is 35 degrees. The angle between the direction from relay station 50d-3 to relay station 50d-2 and the direction from relay station 50d-3 to relay station 50d-1 is 34 degrees. The angle between the direction from relay station 50d-4 to relay station 50d-3 and the direction from relay station 50d-4 to relay station 50d-2 is 33 degrees.

If these angles are equal to or larger than the half-width θ _BW of the antenna pattern of the antenna used in each relay station 50d, each relay station 50d can avoid radio wave interference caused by radio waves transmitted from other relay stations 50d that are not adjacent to each other on the wireless link path. The half-width θ _BW will be described in detail later.

The operation of step S101 of the station placement design support device 1 shown in the flowchart in Figure 5 is an operation of specifying a design target area for station placement design, which corresponds to, for example, the operation of specifying the range of the map data shown in Figure 7. The operation of step S103 is an operation of acquiring equipment information, which corresponds to, for example, the operation of acquiring equipment information indicating the position of equipment such as utility poles, and plotting it (with small solid circles) on the map data shown in Figure 7.

As shown in Fig. 7, in reality, many utility poles exist along the road. Therefore, in the operation of step S104 of the station placement design support device 1 shown in the flowchart in Fig. 5, it is desirable to add a constraint condition for narrowing down the candidate installation positions of the relay station 50d.

The constraint condition here means, for example, selecting candidate installation locations for relay station 50d by taking into consideration the location of a settlement where buildings are densely packed. In other words, the constraint condition means selecting candidate installation locations for relay station 50d so that more buildings are included in the coverage area of relay station 50d shown by the dashed circle in Figure 7 (i.e., so that more terminal stations are accommodated). In other words, this is equivalent to selecting a location where more terminal stations can communicate as a candidate installation location for relay station 50d.

The station design support device 1 may select the position of a utility pole located near the center of a circle that satisfies such conditions as a candidate installation location for the relay station 50d. The candidate installation locations for the relay station 50d selected in this manner are generally close to the center of each settlement.

The example result of the station placement design for an actual rural area shown in Figure 7 was created by narrowing down the candidate installation locations for relay station 50d-2 and relay station 50d-3 based on the above constraints.

As described above, the station placement design support device 1 in this embodiment performs station placement design so that there is no other relay station 50d that is not adjacent on the wireless link path within the range of the antenna directivity of the antenna equipped in the relay station 50d. The range of antenna directivity here means, for example, within the angle at which the half-value angle at which the gain drops by 3 [dB] in the antenna pattern of the directional antenna used. For example, in the case of a directional antenna with a half-value angle of 10 degrees, the range of antenna directivity is the range within the direction of 10 degrees, which is the half-value angle, with respect to the direction from the station to the adjacent relay station 50d on the wireless link path.

Below, we will explain an example of a directional antenna used in wireless communication between relay stations in this embodiment.

Figure 8 is a diagram showing an example of an antenna pattern of a directional antenna used in a relay station of the first embodiment of the present invention. Here, as an example of a directional antenna, a 10-degree directional antenna for 4.9 GHz band wireless made by RADWIN is given. Figure 8 shows the antenna pattern of the directional antenna in the horizontal direction.

As shown in Fig. 8, in the horizontal antenna pattern of this directional antenna, the gain difference exceeds 16 [dB] at the boundary of ±20 degrees from the front direction (0 degrees). Also, as shown in Fig. 8, in the horizontal antenna pattern of this directional antenna, the half-width (half-value angle) θ _BW at which the gain is -3 [dB] from the peak gain in the front direction (0 degrees) is ±5 degrees (10 degrees) from the front direction (0 degrees). In Fig. 8, the range within the half-width (half-value angle) θ _BW is the shaded range.

As described above, in the wireless communication system 5d designed as shown in Figure 7, the angle between the direction from relay station 50d-1 to relay station 50d-2 and the direction from relay station 50d-2 to relay station 50d-3 is 66 degrees. Also, the angle between the direction from relay station 50d-2 to relay station 50d-3 and the direction from relay station 50d-3 to relay station 50d-4 is 70 degrees. In the antenna pattern of the directional antenna shown in Figure 8, the gain difference is 26 dB and 34 dB for angles of 66 degrees and 70 degrees from the front direction (0 degrees).

According to the station placement design support device 1 in this embodiment, in station placement design for a wireless communication system that realizes multi-hop wireless communication, a relay station is placed at a position where the gain difference is equal to or greater than a predetermined value when the transmission/reception direction of radio waves changes at the relay station. In other words, each relay station is placed so that the gain difference does not fall below a predetermined value. This prevents or reduces radio interference.

Next, an example of an antenna used on the relay station side in wireless communication between the relay station and the terminal station in this embodiment will be described. In this embodiment, a non-directional antenna (omni-antenna) is used as the relay station side antenna in wireless communication with the terminal station.

Figure 9 is a diagram showing an example of an antenna pattern of an omnidirectional antenna used in a relay station of the first embodiment of the present invention. Here, as an example of an omnidirectional antenna, a 7 [dBi] Omni antenna used in LigoWave's 4.9 [GHz] band outdoor wireless bridge is given. Figure 9 shows the horizontal antenna pattern of the omnidirectional antenna.

When such an omnidirectional antenna is used on the relay station side in wireless communication between the relay station and the terminal station, the terminal station present within a concentric range centered on the relay station is accommodated by the relay station. However, the gain of the omnidirectional antenna is lower than the gain in the front direction in the antenna directivity of a directional antenna as shown in Figure 8. For example, the gain in the front direction of the directional antenna shown in Figure 8 is 23 [dBi], while the gain of the omnidirectional antenna shown in Figure 9 is 7 [dBi].

However, since an omnidirectional antenna has roughly the same gain in all directions, the horizontal shape of the coverage area of a relay station that accommodates terminal stations is circular. Therefore, an omnidirectional antenna is suitable for evenly accommodating terminal stations installed on the walls of multiple buildings surrounding a relay station.

In addition, by using different radio frequency channels for the radio waves used for multi-hop wireless communication between relay stations and the radio frequency channels used for wireless communication between the relay station and the terminal station, it is possible to avoid radio interference between the wireless communications between the two.

As described above, in the first embodiment, the station placement design support device 1 that supports station placement design for a wireless communication system in which a single radio frequency channel is used in a wireless link path has been described. The station placement design support device 1 performs station placement design so that no other relay station that is not adjacent on the wireless link path is present within the range of the antenna directivity of the antenna equipped in the relay station. By having such a configuration, the station placement design support device 1 in the first embodiment can support station placement design that enables multi-hop wireless communication without increasing the number of radio frequency channels used between relay stations.

(Modification 1 of the first embodiment)
A first modified example of the first embodiment of the present invention will be described below.

In the first embodiment described above, a case where a single radio frequency channel is used in a radio link path is described. In the following, a first variant of the first embodiment is described, which supports station placement design for a wireless communication system in which two radio frequency channels are used alternately in a radio link path. Note that, as an example, a configuration in which two radio frequency channels are used is described here, but the present invention is not limited to this, and a configuration in which three or more radio frequency channels are used alternately may also be used.

In addition, since the block diagram showing the functional configuration of the station placement design support device in variant example 1 of the first embodiment is similar to the block diagram showing the functional configuration of the station placement design support device 1 in the first embodiment shown in Figure 4, the following description will be given with the same reference numerals assigned to each functional unit.

Figures 10 and 11 are diagrams showing an example of the configuration of a wireless communication system 5e that performs multi-hop wireless communication. Figure 10 shows the wireless communication system 5e as seen from a direction horizontal to the ground, and Figure 11 shows the wireless communication system 5e as seen from above.

As shown in Figures 10 and 11, the wireless communication system 5e includes relay stations 50e-1, 50e-2, 50e-3, and 50e-4. Furthermore, relay stations 50e-1, 50e-2, 50e-3, and 50e-4 each have a directional antenna. Relay stations 50e-1, 50e-2, 50e-3, and 50e-4 are wireless stations that relay radio waves transmitted in communication between a base station (not shown) and a terminal station (not shown).

In the following, when there is no need to distinguish between relay station 50e-1, relay station 50e-2, relay station 50e-3, and relay station 50e-4, they may simply be referred to as "relay station 50e."

The relay station 50e-1 receives radio waves transmitted from the base station and transmits the radio waves toward the relay station 50e-2, thereby relaying the radio waves transmitted from the base station to the terminal station. The relay station 50e-1 also receives radio waves transmitted from the terminal station accommodated by the relay station 50e-1 or from the relay station 50e-2, and transmits the radio waves toward the base station, thereby relaying the radio waves transmitted from the terminal station to the base station.

Relay station 50e-2 receives radio waves transmitted from relay station 50e-1 and transmits radio waves toward relay station 50e-3, thereby relaying radio waves transmitted from the base station to the terminal station. Relay station 50e-2 also receives radio waves transmitted from the terminal station accommodated by relay station 50e-2 or relay station 50e-3, and transmits radio waves toward relay station 50e-1, thereby relaying radio waves transmitted from the terminal station to the base station.

Relay station 50e-3 receives radio waves transmitted from relay station 50e-2 and transmits radio waves toward relay station 50e-4, thereby relaying radio waves transmitted from the base station to the terminal station. Relay station 50e-3 also relays radio waves transmitted from the terminal station accommodated by relay station 50e-3 or relay station 50e-4, by transmitting radio waves toward relay station 50e-2, thereby relaying radio waves transmitted from the terminal station to the base station.

Relay station 50a-4 receives radio waves transmitted from relay station 50a-3 and transmits the radio waves toward the terminal station, thereby relaying radio waves transmitted from the base station to the terminal station. Relay station 50a-4 also receives radio waves transmitted from the terminal station it accommodates and transmits the radio waves toward relay station 50a-3, thereby relaying radio waves transmitted from the terminal station to the base station.

Therefore, the wireless link path in the wireless communication system 5e is a path in the order of base station, relay station 50e-1, relay station 50e-2, relay station 50e-3, relay station 50e-4, or a path in the reverse order.

As described above, in the wireless communication system 5e in this modified example, two radio frequency channels are alternately used in the wireless link path. That is, the same radio frequency channel is used for the radio wave re-1 transmitted and received between the relay station 50e-1 and the relay station 50e-2, and the radio wave re-3 transmitted and received between the relay station 50e-3 and the relay station 50e-4. In Figs. 10 and 11, this same radio frequency channel (radio wave re-1 and radio wave re-3) is represented by the same thick solid double-headed arrow. On the other hand, a different radio frequency channel is used for the radio wave re-2 transmitted and received between the relay station 50e-2 and the relay station 50e-3, and the radio waves re-1 and re-3. In Figs. 10 and 11, this different radio frequency channel (only the radio wave re-2) is represented by a thick dashed double-headed arrow.

10 and 11, only the range of antenna directivity of the transmitting antenna that transmits radio wave re-1 from relay station 50e-1 to relay station 50e-2 is shown as antenna directivity range de-1. As shown in Fig. 10 and 11, not only relay station 50e-2 but also relay station 50e-3 and relay station 50e-4 are located within the range of antenna directivity range de-1.

As mentioned above, radio waves re-1 and re-2 use different radio frequency channels. Therefore, when relay station 50e-3 receives radio waves re-2 transmitted from relay station 50e-2, radio wave interference does not occur between radio waves re-2 and re-1. This ensures that communication from relay station 50e-2 to relay station 50e-3 is not impeded.

On the other hand, as mentioned above, the radio waves re-1 and re-3 use the same radio frequency channel. Therefore, when relay station 50e-4 receives radio waves re-3 transmitted from relay station 50e-3, radio waves re-3 and re-1 interfere with each other. This may prevent communication from relay station 50e-3 to relay station 50e-4.

Even in a wireless communication system 5e in which two radio frequency channels are alternately used in a wireless link path, as in the example shown in Figures 10 and 11, radio interference may occur if the relay station 50e is positioned such that another relay station 50e (for example, the third adjacent relay station) is present within the antenna directivity range de-1 of an antenna directed to an adjacent relay station 50e on the wireless link path.

Note that while the case of transmitting radio waves has been described here, the same applies to reception. For example, if the range of antenna directivity of the receiving antenna of relay station 50e-1 is the antenna directivity range de-1 shown in Figures 10 and 11, when relay station 50e-1 receives radio waves re-1 transmitted from relay station 50e-2, radio waves re-1 and re-3 will interfere with each other. This may prevent communication from relay station 50e-2 to relay station 50e-1.

In this way, when there are other relay stations 50e that are adjacent to each other on the wireless link path within the range of the antenna directivity of the antenna equipped with the relay station 50e, as well as other relay stations 50e that are not adjacent to each other on the wireless link path (for example, the relay station 50e that is three stations away on the wireless link path), if radio waves of the same radio frequency channel are used, radio interference may occur, and communication between the base station and the terminal station may be hindered.

The station placement design support device 1 in variant 1 of the first embodiment described below supports the station placement design of relay station 50f so as to create a wireless communication system in which no radio wave interference occurs or which is minimally affected by radio wave interference.

Figure 12 is a diagram showing an example of the configuration of a wireless communication system 5f designed by a station placement design support device 1 in variant 1 of the first embodiment of the present invention. Figure 12 shows the wireless communication system 5f as seen from above.

12, the wireless communication system 5f includes a relay station 50f-1, a relay station 50f-2, a relay station 50f-3, and a relay station 50f-4. The relay stations 50f-1, 50f-2, 50f-3, and 50f-4 each include a directional antenna. The relay stations 50f-1, 50f-2, 50f-3, and 50f-4 are wireless stations that relay radio waves transmitted in communication between a base station (not shown) and a terminal station (not shown).
Hereinafter, when there is no need to distinguish between the relay station 50f-1, the relay station 50f-2, the relay station 50f-3, and the relay station 50f-4, they may be simply referred to as "relay station 50f."

The wireless link path in the wireless communication system 5f is a path in the order of base station, relay station 50f-1, relay station 50f-2, relay station 50f-3, relay station 50f-4, or a path in the reverse order.

Here, the same radio frequency channel is used for radio waves rf-1 transmitted and received between relay stations 50f-1 and 50f-2, and radio waves rf-3 transmitted and received between relay stations 50f-3 and 50f-4. In FIG. 12, this same radio frequency channel (radio waves rf-1 and rf-3) is represented by the same thick solid double-headed arrow. On the other hand, a different radio frequency channel is used for radio waves rf-2 transmitted and received between relay stations 50f-2 and 50f-3, and radio waves rf-1 and rf-3. In FIG. 12, this different radio frequency channel (radio waves rf-2 only) is represented by a thick dashed double-headed arrow.

In FIG. 12, only the range of antenna directivity of the transmitting antenna that transmits radio waves rf-1 from relay station 50f-1 to relay station 50f-2 is shown as antenna directivity range df-1. As shown in FIG. 12, relay station 50f-2 and relay station 50f-3 are located within the range of antenna directivity range df-1, but relay station 50f-4 is located outside the range of antenna directivity range df-1. Therefore, although the same radio frequency channel is used for radio waves rf-1 and rf-3, when relay station 50f-4 receives radio waves rf-3 transmitted from relay station 50f-3, there is no radio interference between radio waves rf-3 and rf-1. As a result, communication from relay station 50f-3 to relay station 50f-4 is performed normally.

12, relay station 50f-2 and relay station 50f-3 are both located within antenna directivity range df-1, but radio waves rf-1 and rf-2 use different radio frequency channels, so when relay station 50f-3 receives radio waves rf-2 transmitted from relay station 50f-2, radio waves rf-2 and rf-1 do not interfere with each other. As a result, communication from relay station 50f-2 to relay station 50f-3 is also performed normally.

Note that, although the case of transmitting radio waves has been described here, the same applies to the case of receiving. For example, if the range of antenna directivity of the receiving antenna of relay station 50f-1 is the antenna directivity range df-1 shown in FIG. 12, when relay station 50f-1 receives radio waves rf-1 transmitted from relay station 50f-2, radio waves rf-1 and rf-3 do not interfere with each other. Furthermore, because different radio frequency channels are used for radio waves rf-1 and rf-2, radio waves rf-1 and rf-2 do not interfere with each other either. As a result, communication from relay station 50f-2 to relay station 50f-1 is normally performed.

In this way, the station placement design support device 1 in the first modified example of the first embodiment supports station placement design for a wireless communication system in which two radio frequency channels are used alternately in a wireless link path. The station placement design support device 1 in this modified example performs station placement design so that other relay stations 50f that are three or more neighbors on the wireless link path (for example, other relay stations 50f that are three, five, seven, etc. neighbors on the wireless link path) are not present within the range of the antenna directivity of the antenna equipped in the relay station 50f. As a result, even if radio waves of two radio frequency channels are used alternately in the wireless link path, radio wave interference does not occur, and communication between the base station and the terminal station is normally performed.

In this variant, a case has been described in which two radio frequency channels are used alternately on a wireless link path, but the same applies to a case in which three or more radio frequency channels are used alternately on a wireless link path.

In this way, the station location design support device 1 performs station location design to position each relay station so that multiple other relay stations using the same radio frequency channel are not included within the range of the antenna directivity of the antenna of each relay station.

Next, we will describe another example configuration of a wireless communication system in which two radio frequency channels are used alternately in a wireless link path.

Figure 13 is a diagram showing an example of the configuration of a wireless communication system 5g designed by a station placement design support device 1 in variant 1 of the first embodiment of the present invention. Figure 13 shows the wireless communication system 5g as seen from above.

13, the wireless communication system 5g includes relay stations 50g-1, 50g-2, 50g-3, 50g-4, 50g-5, and 50g-6. Each of relay stations 50g-1, 50g-2, 50g-3, 50g-4, 50g-5, and 50g-6 is equipped with a directional antenna. Each of relay stations 50g-1, 50g-2, 50g-3, 50g-4, 50g-5, and 50g-6 is a wireless station that relays radio waves transmitted in communication between a base station (not shown) and a terminal station (not shown).

Hereinafter, when there is no need to distinguish between relay station 50g-1, relay station 50g-2, relay station 50g-3, relay station 50g-4, relay station 50g-5, and relay station 50g-6, they may simply be referred to as "relay station 50g."

Here, the same radio frequency channel is used for radio wave rg-1 transmitted and received between relay station 50g-1 and relay station 50g-2, radio wave rg-3 transmitted and received between relay station 50g-3 and relay station 50g-4, and radio wave rg-5 transmitted and received between relay station 50g-5 and relay station 50g-6. In FIG. 13, this same radio frequency channel is represented by the same thick solid double-headed arrow. On the other hand, the same radio frequency channel is used for radio wave rg-2 transmitted and received between relay station 50g-2 and relay station 50g-3, and radio wave rg-6 transmitted and received between relay station 50g-1 and relay station 50g-6. In FIG. 13, this same radio frequency channel is represented by the same thick dashed double-headed arrow. Different radio frequency channels are used for radio wave rg-1, radio wave rg-3, and radio wave rg-5, and radio wave rg-2 and radio wave rg-6.

In FIG. 13, only the range of antenna directivity of the transmitting antenna that transmits radio wave rg-1 from relay station 50g-1 to relay station 50g-2 is shown as antenna directivity range dg-1. As shown in FIG. 13, relay station 50g-2 and relay station 50g-3 are located within the range of antenna directivity range dg-1, but relay station 50g-4 is located outside the range of antenna directivity range dg-1. Therefore, although the same radio frequency channel is used for radio waves rg-1 and rg-3, when relay station 50g-4 receives radio wave rg-3 transmitted from relay station 50g-3, radio waves rg-3 and rg-1 do not interfere with each other. This allows communication from relay station 50g-3 to relay station 50g-4 to be performed normally.

13, relay station 50g-2 and relay station 50g-3 are both located within antenna directivity range dg-1, but radio waves rg-1 and rg-2 use different radio frequency channels, so when relay station 50g-3 receives radio waves rg-2 transmitted from relay station 50g-2, radio waves rg-2 and rg-1 do not interfere with each other. This allows communication from relay station 50g-2 to relay station 50g-3 to be performed normally.

Also, as shown in FIG. 13, when designing a wireless link route connecting relay station 50g-1, relay station 50g-5, and relay station 50g-6, the station placement design support device 1 in this modified example designs the routes to connect relay station 50g-1, relay station 50g-6, and relay station 50g-5 in that order, rather than connecting relay station 50g-1, relay station 50g-5, and relay station 50g-6 in that order, which would be the shortest route.

This is because if the wireless link route is connected in the order of relay station 50g-1, relay station 50g-5, and relay station 50g-6, relay station 50g-5 may be included in the antenna directivity range of relay station 50g-3, and relay station 50g-3 may be included in the antenna directivity range of relay station 50g-5. In this case, the same radio frequency channel is used for radio waves rg-2 transmitted and received between relay station 50g-2 and relay station 50g-3, and radio waves transmitted and received between relay station 50g-1 and relay station 50g-5, causing radio wave interference between the two. This may interfere with communication between relay station 50g-2 and relay station 50g-3, and communication between relay station 50g-1 and relay station 50g-5.

In this manner, the station placement design support device 1 in this modified example performs station placement design, including the connection order of the relay stations 50g on the wireless link path, so that other relay stations 50g (e.g., other relay stations 50g that are three or more neighbors on the wireless link path) are not present within the range of the antenna directivity of the antenna equipped in the relay station 50g. As a result, even if radio waves of two radio frequency channels are used alternately on the wireless link path, radio wave interference does not occur and communication between the base station and the terminal station is normally performed.

Note that the arrangement of the six relay stations 50g shown in Figure 13 roughly coincides with the results of station placement design performed for the actual rural area shown in Figure 14.

Figure 14 is a diagram showing an example of the results of station placement design for an existing rural area. Figure 14 shows a wireless communication system 5h for which station placement has been designed on map data of an existing rural area.

14, the wireless communication system 5h includes relay stations 50h-1, 50h-2, 50h-3, 50h-4, 50h-5, and 50h-6. Each of relay stations 50h-1, 50h-2, 50h-3, 50h-4, 50h-5, and 50h-6 is equipped with a directional antenna. Each of relay stations 50h-1, 50h-2, 50h-3, 50h-4, 50h-5, and 50h-6 is a wireless station that relays wireless radio waves transmitted in communication between a base station (not shown) and a terminal station (not shown).

In the following, when there is no need to distinguish between relay station 50h-1, relay station 50h-2, relay station 50h-3, relay station 50h-4, relay station 50h-5, and relay station 50h-6, they may simply be referred to as "relay station 50h."

As in FIG. 7, in FIG. 14, small solid circles indicate utility poles (i.e., candidate installation locations for relay stations 50h). The six dashed circles represent the ranges within which each relay station 50h can communicate with each terminal station. Each relay station 50h is installed on the utility pole located at the center of each of the six dashed circles. As shown in the figure, the range consisting of the six circles covers the location of at least one wall of all buildings in the map data shown in FIG. 14 (i.e., installation locations of terminal stations). In this way, the relay stations 50h are arranged so that all terminal stations in the design area can be accommodated by one of the six relay stations 50h.

In the wireless communication system 5h designed as shown in FIG. 14, the angle between the direction from relay station 50h-1 to relay station 50h-2 and the direction from relay station 50h-2 to relay station 50h-3 is 15 degrees. For example, if a directional antenna with a 45 degree angle is used, the angle difference of 15 degrees can be considered to be within the range of the antenna directivity. However, in the wireless communication system 5h, two radio frequency channels are alternately used in the wireless link path, so that the radio waves transmitted from relay station 50h-3 and received by relay station 50h-2 do not interfere with the radio waves transmitted from relay station 50h-4. This allows communication from relay station 50b-2 to relay station 50b-3 to be performed normally.

In addition, in the wireless communication system 5h designed as shown in FIG. 14, the angle between the direction from relay station 50h-2 to relay station 50h-3 and the direction from relay station 50h-3 to relay station 50h-4 is 96 degrees. Therefore, relay station 50h-4 is not included in the range of the antenna directivity of the antenna of relay station 50h-2, and relay station 50h-2 is not included in the range of the antenna directivity of the antenna of relay station 50h-4. Furthermore, different radio frequency channels are used for the radio waves transmitted and received between relay station 50h-2 and relay station 50h-3 and the radio waves transmitted and received between relay station 50h-3 and relay station 50h-4, so communication from relay station 50h-3 to relay station 50h-4 and communication from relay station 50h-3 to relay station 50h-2 are normally performed.

The angle between the direction from relay station 50h-1 to relay station 50h-2 and the direction from relay station 50h-1 to relay station 50h-4 is 35 degrees. The angle between the direction from relay station 50h-4 to relay station 50h-3 and the direction from relay station 50h-4 to relay station 50h-1 is 73 degrees. Therefore, relay station 50h-4 is not included within the range of the antenna directivity of the antenna of relay station 50h-1, and relay station 50h-1 is not included within the range of the antenna directivity of the antenna of relay station 50h-4. Therefore, the radio waves transmitted from relay station 50h-2 and received by relay station 50h-1 do not interfere with the radio waves transmitted from relay station 50h-4. Furthermore, the radio waves transmitted from relay station 50h-3 and received by relay station 50h-4 do not interfere with the radio waves transmitted from relay station 50h-1. As a result, communication from the relay station 50h-2 to the relay station 50h-1 and communication from the relay station 50h-3 to the relay station 50h-4 are normally performed.

As in Fig. 13, in the wireless communication system 5h designed as shown in Fig. 14, the wireless link route is designed in the order of relay station 50h-1, relay station 50h-6, and relay station 50h-5, rather than the shortest route of relay station 50h-1, relay station 50h-5, and relay station 50h-6. This prevents radio waves transmitted to relay station 50h-2 by the directional antenna of relay station 50h-3 from interfering with radio waves received by relay station 50h-5.

In addition, in wireless communication system 5h designed as shown in Figure 14, the angle between the direction from relay station 50h-3 to relay station 50h-2 and the direction from relay station 50h-2 to relay station 50h-1 is -15 degrees. The angle between the direction from relay station 50h-2 to relay station 50h-1 and the direction from relay station 50h-1 to relay station 50h-6 is -29 degrees. The angle between the direction from relay station 50h-1 to relay station 50h-6 and the direction from relay station 50h-6 to relay station 50h-5 is 142 degrees.

The angle between the direction from relay station 50h-3 to relay station 50h-2 and the direction from relay station 50h-3 to relay station 50h-6 is 21 degrees. The angle between the direction from relay station 50h-6 to relay station 50h-1 and the direction from relay station 50h-6 to relay station 50h-3 is 23 degrees.

All of these angles are equal to or greater than the half-width θ _BW of the antenna pattern of the antenna used in each relay station 50h shown in Fig. 8. Therefore, each relay station 50h can avoid radio wave interference caused by radio waves transmitted from other relay stations 50h that are not adjacent to each other on the wireless link path.

The operation of step S101 of the station placement design support device 1 shown in the flowchart in Figure 5 is an operation of specifying a design area to be targeted for station placement design, which corresponds to, for example, an operation of specifying the range of the map data shown in Figure 14. The operation of step S103 is an operation of acquiring equipment information, which corresponds to, for example, an operation of acquiring equipment information indicating the position of equipment such as utility poles, and plotting the equipment information (with small solid circles) on the map data shown in Figure 14.

As shown in FIG. 14, in reality, there are many utility poles along the road. Therefore, in the operation of step S104 of the station placement design support device 1 shown in the flowchart shown in FIG. 5, it is desirable to add a constraint condition for narrowing down the candidate installation positions of the relay station. Note that the relay station referred to here is the relay station 50h shown in FIG. 14 in this modified example, and is the relay station corresponding to the relay station 50b shown in FIG. 3 in the first embodiment described above. As described above, the constraint condition is to select the candidate installation positions of the relay station 50h so that more buildings are included in the coverage area of the relay station 50h shown in the dashed circle in FIG. 14 (i.e., so that more terminal stations are accommodated).

The example result of the station placement design for an actual rural area shown in Figure 14 was created by narrowing down the candidate installation locations for relay station 50h-2, relay station 50h-3, relay station 50h-5, and relay station 50h-6 based on the above constraints.

As described above, in the first modification of the first embodiment, the station placement design support device 1 that supports station placement design of a wireless communication system in which two radio frequency channels are alternately used on a wireless link path has been described. The station placement design support device 1 performs station placement design so that no other relay station is located more than three neighbors on the wireless link path (e.g., other relay stations that are three neighbors, five neighbors, seven neighbors, etc. on the wireless link path) within the range of the antenna directivity of the antenna equipped in the relay station 50f.

As a result, even if radio waves of two radio frequency channels are used alternately in the wireless link path, radio wave interference does not occur and communication between the base station and the terminal station is normally performed. By having such a configuration, the station placement design support device 1 in the first modification of the first embodiment can support station placement design that enables multi-hop wireless communication without increasing the number of radio frequency channels used between relay stations.

(Modification 2 of the first embodiment)
A second modification of the first embodiment of the present invention will now be described.

In the above-mentioned first embodiment and variant 1 of the first embodiment, station placement design for a wireless link path that does not include a branch has been described. However, in practice, station placement design for a wireless link path that includes a branch may be performed. In variant 2 of the first embodiment described below, a station placement design support device that supports station placement design for a wireless communication system having a wireless link path that includes a branch will be described.

In addition, since the block diagram showing the functional configuration of the station placement design support device in variant example 2 of the first embodiment is similar to the block diagram showing the functional configuration of the station placement design support device 1 in the first embodiment shown in Figure 4, the following description will be given with the same reference numerals assigned to each functional unit.

Figure 15 is a diagram showing an example of the configuration of a wireless communication system 5i that performs multi-hop wireless communication. Figure 15 shows the wireless communication system 5i as seen from above.

15, the wireless communication system 5i includes relay stations 50i-1, 50i-2, 50i-3, 50i-4, and 50i-5. Each of relay stations 50i-1, 50i-2, 50i-3, 50i-4, and 50i-5 is equipped with a directional antenna. Each of relay stations 50i-1, 50i-2, 50i-3, 50i-4, and 50i-5 is a wireless station that relays wireless radio waves transmitted in communication between a base station (not shown) and a terminal station (not shown).

Hereinafter, when there is no need to distinguish between relay station 50i-1, relay station 50i-2, relay station 50i-3, relay station 50i-4, and relay station 50i-5, they may simply be referred to as "relay station 50i."

15, the wireless link route in wireless communication system 5i is a route that starts from base station, relay station 50i-1, relay station 50i-2, and relay station 50i-3, and then branches to relay station 50i-4 and relay station 50i-5, or a route that follows the reverse order. In other words, a route that follows the reverse order is a route in which the route from relay station 50i-4 to relay station 50i-3 and the route from relay station 50i-5 to relay station 50i-3 merge at relay station 50i-3, and then the route follows relay station 50i-2 and relay station 50i-1.

Here, the same radio frequency channel is used for radio wave ri-1 transmitted and received between relay station 50i-1 and relay station 50i-2, and radio wave ri-5 transmitted and received between relay station 50i-3 and relay station 50i-5. In FIG. 15, this same radio frequency channel is represented by the same thick solid double-headed arrow. On the other hand, the same radio frequency channel is used for radio wave ri-2 transmitted and received between relay station 50i-2 and relay station 50i-3, and radio wave ri-3 transmitted and received between relay station 50i-3 and relay station 50i-4. In FIG. 15, this same radio frequency channel is represented by the same thick dashed double-headed arrow. Different radio frequency channels are used for radio wave ri-1 and radio wave ri-5, and radio wave ri-2 and radio wave ri-3.

The wireless communication system 5i shown in FIG. 15 basically has a wireless link path in which two wireless frequency channels are used alternately. However, as shown in FIG. 15, in a wireless link path that includes a branch, the same wireless frequency channel is used continuously in at least one of the multiple branched paths. For example, in FIG. 15, the same wireless frequency channel is used continuously in the section between relay station 50i-2 and relay station 50i-3 and the section between relay station 50i-3 and relay station 50i-4, which are consecutive sections on the wireless link path.

In FIG. 15, only the range of antenna directivity of the transmitting antenna that transmits radio wave ri-1 from relay station 50i-1 to relay station 50i-2 is shown as antenna directivity range di-1. As shown in FIG. 15, relay station 50i-2, relay station 50i-3, and relay station 50i-5 are located within the range of antenna directivity range di-1, but relay station 50i-4 is located outside the range of antenna directivity range di-1. Therefore, although the same radio frequency channel is used for radio waves ri-2 and ri-3, when relay station 50i-4 receives radio wave ri-3 transmitted from relay station 50i-3, radio waves ri-3 and ri-2 do not interfere with each other. This allows communication from relay station 50i-3 to relay station 50i-4 to be performed normally.

15, relay station 50i-2 and relay station 50i-3 are both located within antenna directivity range di-1, but radio waves ri-1 and ri-2 use different radio frequency channels, so when relay station 50i-3 receives radio wave ri-2 transmitted from relay station 50i-2, radio waves ri-2 and ri-1 do not interfere with each other. As a result, communication from relay station 50i-2 to relay station 50i3 is also performed normally.

On the other hand, as mentioned above, both relay station 50i-2 and relay station 50i-5 are located within antenna directivity range di-1, and radio waves ri-1 and ri-5 use the same radio frequency channel. Therefore, when relay station 50i-5 receives radio waves ri-5 transmitted from relay station 50i-3, radio waves ri-5 and ri-1 interfere with each other. This may prevent communication from relay station 50i-3 to relay station 50i-5.

In this way, when there are other relay stations 50i that are not adjacent on the wireless link path (for example, the third relay station 50i on the wireless link path) within the range of the antenna directivity of the antenna equipped to the relay station 50i, if radio waves of the same radio frequency channel are used, radio interference may occur, and communication between the base station and the terminal station may be hindered.

The station placement design support device 1 in variant example 2 of the first embodiment described below supports the station placement design of relay station 50j so as to create a wireless communication system in which no radio wave interference occurs or which is minimally affected by radio wave interference.

Figure 16 is a diagram showing an example of the configuration of a wireless communication system 5j designed by a station placement design support device 1 in variant example 2 of the first embodiment of the present invention. Figure 16 shows the wireless communication system 5j as seen from above.

16, wireless communication system 5j includes relay station 50j-1, relay station 50j-2, relay station 50j-3, relay station 50j-4, and relay station 50j-5. Relay station 50j-1, relay station 50j-2, relay station 50j-3, relay station 50j-4, and relay station 50j-5 each have a directional antenna. Relay station 50j-1, relay station 50j-2, relay station 50j-3, relay station 50j-4, and relay station 50j-5 are wireless stations that relay radio waves transmitted in communication between a base station (not shown) and a terminal station (not shown).

Hereinafter, when there is no need to distinguish between relay station 50j-1, relay station 50j-2, relay station 50j-3, relay station 50j-4, and relay station 50j-5, they may simply be referred to as "relay station 50j."

16, the wireless link route in wireless communication system 5j is a route that goes in the order of base station, relay station 50j-1, relay station 50j-2, and relay station 50j-3, and then branches to relay station 50j-4 and relay station 50j-5, or a route in the reverse order. In other words, a route in the reverse order is a route in which the route from relay station 50j-4 to relay station 50j-3 and the route from relay station 50j-5 to relay station 50j-3 merge at relay station 50j-3, and then the route goes in the order of relay station 50j-2 and relay station 50j-1.

Here, the same radio frequency channel is used for radio waves rj-1 transmitted and received between relay stations 50j-1 and 50j-2, and radio waves rj-5 transmitted and received between relay stations 50j-3 and 50j-5. In FIG. 16, this same radio frequency channel is represented by the same thick solid double-headed arrow. On the other hand, the same radio frequency channel is used for radio waves rj-2 transmitted and received between relay stations 50j-2 and 50j-3, and radio waves rj-3 transmitted and received between relay stations 50j-3 and 50j-4. In FIG. 15, this same radio frequency channel is represented by the same thick dashed double-headed arrow. Different radio frequency channels are used for radio waves rj-1 and rj-5, and radio waves rj-2 and rj-3.

The wireless link path of the wireless communication system 5j shown in FIG. 16 differs from the wireless link path of the wireless communication system 5i shown in FIG. 15 described above in that, whereas in FIG. 15 the relay station 50i-5 is located within the antenna directivity range di-1, in FIG. 16 the relay station 50j-5 is located outside the antenna directivity range dj-1.

As mentioned above, the radio waves rj-1 and rj-5 use the same radio frequency channel, but relay station 50j-5 does not exist within antenna directivity range dj-1. Therefore, when relay station 50j-5 receives radio waves rj-5 transmitted from relay station 50j-3, there is no radio interference between radio waves rj-5 and rj-1. This allows communication from relay station 50j-3 to relay station 50j-5 to be carried out normally.

Note that, although the case of transmitting radio waves has been described here, the same applies to the case of receiving. For example, if the range of antenna directivity of the receiving antenna of relay station 50j-1 is the antenna directivity range dj-1 shown in FIG. 16, when relay station 50j-1 receives radio waves rj-1 transmitted from relay station 50j-2, there is no radio interference between radio waves rj-1 and rb-5. This allows communication from relay station 50j-2 to relay station 50j-1 to be performed normally.

As described above, in the second modification of the first embodiment, the station placement design support device 1 has been described, which supports station placement design for a wireless communication system having a wireless link path including a branch and in which two wireless frequency channels are used alternately. The station placement design support device 1 performs station placement design so that no other relay station is located more than three neighbors on the wireless link path (e.g., other relay stations that are three, five, seven, etc. neighbors on the wireless link path) within the range of the antenna directivity of the antenna equipped in the relay station 50j.

As a result, even in a wireless link route that includes a branch, radio interference does not occur, and communication between the base station and the terminal station is normally performed. With such a configuration, the station placement design support device 1 in the second modification of the first embodiment can support station placement design that enables multi-hop wireless communication without increasing the number of radio frequency channels used between relay stations.

Second Embodiment
A second embodiment of the present invention will now be described.

The station placement design support device 1 in the above-mentioned first embodiment, variant 1 of the first embodiment, and variant 2 of the first embodiment is configured to prevent or reduce the occurrence of radio wave interference by arranging each relay station so that other relay stations that are not adjacent to the relay station on the wireless path are not included within the range of the antenna directivity of the relay station antenna. However, in reality, for example, there are cases where the options for candidate installation positions of relay stations are limited, and cases may arise where other relay stations that are not adjacent to the relay station on the wireless path must be arranged even if they are within the range of the antenna directivity of the relay station antenna.

The station placement design support device in the second embodiment described below calculates interference between an interfered station and an interfering station when another relay station that is not adjacent to the relay station on the wireless path is included within the range of the antenna directivity of the relay station's antenna. Here, the interfered station is a wireless station that is within the range of the antenna directivity of the interfering station's antenna but is not adjacent to the interfering station on the wireless link path.

In the present embodiment, the station placement design support device selects the position of the interfered station as a candidate position for the relay station if the result of the interference calculation shows that the difference between the received power and the interference power in the original wireless link path is sufficiently large. Note that the station placement design support device may select the position of the interfered station as a candidate position for the relay station if the result of the interference calculation shows that the interference power is sufficiently small.

In addition, since the block diagram showing the functional configuration of the station placement design support device in the second embodiment is similar to the block diagram showing the functional configuration of the station placement design support device 1 in the first embodiment shown in Figure 4, the following explanation will be given by assigning the same reference numerals to each functional unit.

Figure 17 is a diagram for explaining the selection of candidate relay station positions by the station placement design support device 1 in the second embodiment of the present invention.

Figure 17 shows relay station 50k-1, relay station 50k-2, and relay station 50k-3. Relay station 50k-1, relay station 50k-2, and relay station 50k-3 are each equipped with a directional antenna. As shown in the figure, relay station 50k-1, relay station 50k-2, and relay station 50k-3 are arranged approximately on a straight line, and relay station 50k-2 and relay station 50k-3 are arranged in front of the antenna directivity of the antenna of relay station 50k-1.

In the following, when there is no need to distinguish between relay station 50k-1, relay station 50k-2, and relay station 50k-3, they may simply be referred to as "relay station 50k."

When relay station 50k-1, relay station 50k-2, and relay station 50k-3 are arranged in this manner, if the radio frequency channel of the radio waves transmitted from relay station 50k-1 to relay station 50k-2 is the same as the radio frequency channel of the radio waves transmitted from relay station 50k-2 to relay station 50k-3, radio interference due to the radio waves transmitted from relay station 50k-1 may occur when relay station 50k-3 receives the radio waves transmitted from relay station 50k-2. Therefore, in the station placement design support device 1 in the first embodiment, the first modified example of the first embodiment, and the second modified example of the first embodiment described above, station placement design is performed so that relay station 50k is not arranged in this manner.

However, if the distance between relay station 50k-1 and relay station 50k-3 is sufficient, the radio waves transmitted from relay station 50k-1 will be attenuated to some extent before reaching relay station 50k-3. In the second embodiment, station placement design support device 1 performs interference calculation to compare the received power of the radio waves transmitted from relay station 50k-2 at relay station 50k-3 with the interference power of the radio waves transmitted from relay station 50k-1.

Based on the comparison result, the station location design support device 1 can determine whether the radio waves transmitted from relay station 50k-1 have reached a level that interferes with the reception of radio waves transmitted from relay station 50k-2. As a result, even if relay station 50k-3 is included within the antenna directivity range Ra of the antenna of relay station 50k-1, the station location design support device 1 can select a candidate installation location for relay station 50k-3 within communication range Rb based on the distance relationship between relay station 50k-1 and relay station 50k-2 and relay station 50k-3.

17 shows an example in which the antenna directivity of the antenna of relay station 50k-1 is directed toward relay station 50k-2, the antenna directivity of the antenna of relay station 50k-2 is directed toward relay station 50k-3, and the antenna directivity of the antenna of relay station 50k-3 is directed toward relay station 50k-2. However, if the antenna directivity of the antenna of relay station 50k-3 is not directed toward relay station 50k-2 and relay station 50k-2, the interference power of the radio waves transmitted from relay station 50k-1 at relay station 50k-3 will be smaller, and the effect of radio wave interference may be eliminated.

[Operation of the channel placement design assistance device]
An example of the operation of the station placement design assistance device 1 will now be described.
18 is a flowchart showing the operation of the station placement design support device 1 in the second embodiment of the present invention. The operation of the station placement design support device 1 shown in this flowchart is started, for example, when a user of the station placement design support device 1 operates the station placement design support device 1 and an instruction to start station placement design is output from the operation input unit 102.

The design range designation unit 104 reads the map data and selects, for example, a rectangular range based on the information indicating the design range output from the operation input unit 102. The design range designation unit 104 designates the selected range as the design target area (step S201).

The terminal station position identification unit 105 extracts information indicating the position and contour (or wall) of the building for each building from map data within the design area. The terminal station position identification unit 105 identifies the position of the building's wall based on the extracted information, and identifies the installation position of the terminal station.

The equipment information acquisition unit 106 acquires equipment information for selecting candidate installation locations for the relay station 50k, for example from an external device.

The relay station position selection unit 107 selects at least one candidate installation position for the relay station 50k based on the installation position of the terminal station, the equipment information, the communication distance between the terminal station and the relay station 50k, etc. (step S202).

The radio interference evaluation unit 108 identifies a radio link path based on the location of the base station and the candidate installation location of the relay station 50k selected by the relay station location selection unit 107. The radio interference evaluation unit 108 sequentially determines whether each relay station 50k in the identified radio link path satisfies a predetermined condition (step S203). The predetermined condition here is a condition based on the result of an interference calculation described later.

The relay station position selection unit 107 sets candidate installation positions for relay stations to be evaluated for interference calculation (step S205). If the determination has been made for all relay stations involved in the multi-hop (step S206, Yes), the process returns to step S203. On the other hand, if the determination has not been made for all relay stations involved in the multi-hop (step S206, No), the radio interference evaluation unit 108 re-sets the interfered station and the interfering station from among the candidate installation positions for relay stations set by the relay station position selection unit 107 (step S207).

The radio interference evaluation unit 108 performs an interference calculation, and if the interference power of the interfering station is sufficiently small compared to the received power in the wireless link path (step S208, Yes), the process returns to step S206. On the other hand, if the radio interference evaluation unit 108 determines that the interference power of the interfering station is not sufficiently small compared to the received power in the wireless link path (step S208, No), the relay station position selection unit 107 checks whether there is a candidate installation position for the relay station that can be selected (step S209).

If there are other candidate locations for the relay station that can be selected (step S209: Yes), the relay station location selection unit 107 reselects another candidate location for the relay station (step S210). The radio interference evaluation unit 108 performs interference evaluation again (step S208).

On the other hand, if there are no other candidate installation locations for the relay station 50k that can be selected (step S209, No), the control unit 100 controls the output unit 103 to output information indicating locations in the wireless link route that do not satisfy the specified conditions (step S211).

On the other hand, if it is determined whether or not the predetermined condition is satisfied for all relay stations in the wireless link route (step S203, Yes), the control unit 100 controls the output unit 103 to display the wireless link route that satisfies the predetermined condition (step S204). This ends the operation of the station placement design support device 1 shown in the flowchart of FIG. 18.

In the interference calculation mentioned above, the interference power at the interfered station is calculated based on, for example, the frequency of the radio waves transmitted by the interfering station, the transmission power, the directivity (horizontal plane pattern) of the antennas used by the interfering and interfered stations, the direction of the antennas (azimuth angle), and the distance between the interfering and interfered stations. Furthermore, for the directivity of a directional antenna, the elevation angle pattern, the height at which the antenna is installed, and the elevation and depression angles of the antenna are used to perform the interference calculation, enabling more precise calculation of interference. In addition, more precise calculation of interference is possible by taking into account the surrounding environment, such as the terrain between the interfering and interfered stations and the presence of obstacles such as buildings between the two stations.

In addition, any method can be used as the method of specifying conditions in calculating interference between two wireless stations (here, between an interfering station and an interfered station) and the method of calculating interference based on the specified conditions, but for example, the method described in Patent Document 4 can be used.

Figure 19 is a diagram showing an example configuration of a wireless communication system 5l designed by the station placement design support device 1 in the first embodiment of the present invention.

As shown in FIG. 19, the wireless communication system 5l includes relay stations 50l-1, 50l-2, 50l-3, 50l-4, 50l-5, and 50l-6. Each of relay stations 50l-1, 50l-2, 50l-3, 50l-4, 50l-5, and 50l-6 is equipped with a directional antenna. Each of relay stations 50l-1, 50l-2, 50l-3, 50l-4, 50l-5, and 50l-6 is a wireless station that relays radio waves transmitted in communication between a base station (not shown) and a terminal station (not shown).

Hereinafter, when there is no need to distinguish between relay station 50l-1, relay station 50l-2, relay station 50l-3, relay station 50l-4, relay station 50l-5, and relay station 50l-6, they may simply be referred to as "relay station 50l."

The wireless link path in the wireless communication system 5l is a path in the order of relay station 50l-1, relay station 50l-2, relay station 50l-3, relay station 50l-4, relay station 50l-5, relay station 50l-6, or a path in the reverse order.

Here, the same radio frequency channel is used for radio waves rl-1 transmitted and received between relay station 50l-1 and relay station 50l-2, radio waves rl-2 transmitted and received between relay station 50l-2 and relay station 50l-3, radio waves rl-3 transmitted and received between relay station 50l-3 and relay station 50l-4, radio waves rl-4 transmitted and received between relay station 50l-4 and relay station 50l-5, and radio waves rl-5 transmitted and received between relay station 50l-5 and relay station 50l-6. In FIG. 19, this same radio frequency channel is represented by the same thick solid double-headed arrow.

In Figure 19, only the antenna directivity range of the transmitting antenna that transmits radio waves rl-1 from relay station 50l-1 to relay station 50l-2 is shown as antenna directivity range dl-1.

As shown in FIG. 19, relay station 50l-2, which is adjacent to relay station 50l-1 on the wireless link path and communicates with it, is located within the antenna directivity range dl-1.

In addition, among the relay stations 50l that are not adjacent to relay station 50l-1 in the wireless link path, relay station 50l-3 and relay station 50l-4 are not within antenna directivity range dl-1, but are outside antenna directivity range dl-1. Therefore, when relay station 50l-3 receives radio waves rl-2 transmitted from relay station 50l-2, radio wave interference due to radio waves rl-1 transmitted from relay station 50l-1 is unlikely to occur. In addition, when relay station 50l-4 receives radio waves rl-3 transmitted from relay station 50l-3, radio wave interference due to radio waves rl-1 transmitted from relay station 50l-1 is unlikely to occur.

Furthermore, among the relay stations 50l that are not adjacent to relay station 50l-1 on the wireless link path, relay station 50l-5 and relay station 50l-6 are present within the antenna directivity range dl-1 (radiation direction of radio wave rl-1). However, relay station 50l-5 points its directional antenna in the direction of relay station 50l-4 and relay station 50l-6, both of which are different from the direction in which relay station 50l-1 is located. Therefore, when relay station 50l-5 receives radio wave rl-4 transmitted from relay station 50l-4 and radio wave rl-5 transmitted from relay station 50l-6, it can be said that radio wave interference due to radio wave rl-1 transmitted from relay station 50l-1 is unlikely to occur.

On the other hand, relay station 50l-6 has its directional antenna facing the direction of relay station 50l-5, which is also the direction in which relay station 50l-1 is located. Therefore, when relay station 50l-6 receives radio waves rl-5 transmitted from relay station 50l-5, there is a possibility that radio wave interference will occur due to radio waves rl-1 transmitted from relay station 50l-1. Therefore, with the station placement design support device 1 in the above-mentioned first embodiment, variant 1 of the first embodiment, and variant 2 of the first embodiment, station placement design is performed so as to avoid such a placement of relay station 50l.

In contrast, in the second embodiment, the station location design support device 1 performs interference calculation to compare the received power of radio waves rl-5 transmitted from relay station 50l-5 at relay station 50l-6 with the interference power of radio waves rl-1 transmitted from relay station 50l-1.

Based on the comparison result, the station placement design support device 1 determines whether the radio waves rl-1 transmitted from relay station 50l-1 have reached a level that interferes with the reception of radio waves rl-5 transmitted from relay station 50l-5. Specifically, for example, the determination is made based on whether the difference between the received power and the interference power is equal to or greater than a predetermined value. If the difference between the received power and the interference power is equal to or greater than a predetermined value, the station placement design support device 1 selects the position of this relay station 50l-6 as a candidate installation position.

As a result, even if relay station 50l-6 is included within the antenna directivity range dl-1 of the antenna of relay station 50l-1, the station location design support device 1 can select a candidate installation location for relay station 50l-6 within the antenna directivity range dl-1 depending on the strength of the interfering radio waves that attenuate based on factors such as the distance between relay station 50l-1 and relay station 50l-5 and relay station 50l-6.

As described above, in the second embodiment, the station location design support device 1 performs an interference calculation when another relay station that is not adjacent on the wireless link path is present within the range of the antenna directivity of the antenna equipped in the relay station. If the result of the interference calculation at the other relay station shows that the interference power is sufficiently small compared to the received power, the station location design support device 1 allows the other relay station to be a candidate installation location even if it is within the range of the antenna directivity of the relay station.

By providing such a configuration, the station placement design support device 1 in the second embodiment may be able to select a candidate installation location for another relay station that is not adjacent to the relay station in the wireless link path, even if it is within the range of the antenna directivity of the antenna provided in the relay station, thereby further expanding the selection possibilities for the candidate installation location of the other relay station. Also, by providing such a configuration, the station placement design support device 1 in the second embodiment can support station placement design that enables multi-hop wireless communication without increasing the number of wireless frequency channels used between relay stations.

Third Embodiment
A third embodiment of the present invention will now be described.

In the above-mentioned first embodiment, variant 1 of the first embodiment, variant 2 of the first embodiment, and second embodiment, it is assumed that the communication between relay stations in the wireless communication system designed by the station placement design support device 1 is one-to-one wireless communication using one antenna on each side. On the other hand, in the third embodiment described below, it is assumed that the communication between relay stations in the wireless communication system designed by the station placement design support device 1 is two-to-two wireless communication using two antennas on each side.

Here, the two antennas of the relay station perform transmit/receive diversity, which simultaneously transmits and receives radio waves using the same radio frequency channel. In this case, cyclic delay diversity (CDD) may be used. Cyclic delay diversity is a type of transmit diversity technology that applies different cyclic delay amounts to the same data signal between the transmit antennas and transmits the data signal (see, for example, Patent Documents 5 and 6, and Non-Patent Documents 1 to 4). By applying such delay amounts, it is possible to obtain frequency diversity while avoiding inter-symbol interference.

By implementing transmit/receive diversity in communications between relay stations, the wireless link path is made redundant (duplicated), improving resistance to failures, etc. For example, even if one of the antennas of the relay station stops functioning due to some kind of failure, wireless communications can be maintained. In addition, by implementing transmit/receive diversity in communications between relay stations, the transmission power of radio waves per antenna can be suppressed, thereby preventing or reducing the effects of radio wave interference.

In addition, by implementing transmit/receive diversity in communication between relay stations, antenna directivity can be improved compared to the case where a directional antenna is used. In addition, by implementing transmit/receive diversity in communication between relay stations, the range covered by the relay station to accommodate terminal stations can be shared by two antennas, so the range covered by one antenna can be made smaller, and the transmission power used by the relay station to communicate with the terminal station can be suppressed. This also suppresses the effects of radio interference in communication between the relay station and the terminal station.

Figure 20 is a diagram for explaining wireless communication when transmit/receive diversity is not used. As shown in Figure 20, the configuration of wireless communication system 5m corresponds to the configuration of the wireless system in the first embodiment, variant 1 of the first embodiment, variant 2 of the first embodiment, and second embodiment described above.

As shown in FIG. 20, the wireless communication system 5m includes relay station 50m-1, relay station 50m-2, and relay station 50m-3. Relay station 50m-1 is equipped with an antenna 51m-11. Relay station 50m-1 performs wireless communication with relay station 50m-2 using antenna 51m-11. Relay station 50m-2 is equipped with antennas 51m-21 and 51m-22. Relay station 50m-2 performs wireless communication with relay station 50m-1 using antenna 51m-21, and performs wireless communication with relay station 50m-3 using antenna 51m-22. Relay station 50m-3 is equipped with an antenna 51m-31. Relay station 50m-3 performs wireless communication with relay station 50m-2 using antenna 51m-31.

As shown in Fig. 20, the angle between the direction from relay station 50m-1 to relay station 50m-2 and the direction from relay station 50m-1 to relay station 50m-3 is θ. As described above, when relay station 50m-3 receives radio waves transmitted from relay station 50m-2, in order to avoid radio wave interference caused by radio waves transmitted from relay station 50m-1, it is necessary to satisfy θ ≥ θ _BW . As described above, θ _BW is the half-width of the antenna pattern of the antenna used at the relay station.

Figure 21 is a diagram for explaining wireless communication when transmit/receive diversity is used. The configuration of the wireless communication system 5n shown in Figure 21 is the configuration of the wireless system in the third embodiment.

As shown in FIG. 21, the wireless communication system 5n includes a relay station 50n-1, a relay station 50n-2, and a relay station 50n-3. The relay station 50n-1 includes an antenna 51n-11, an antenna 51n-13, and a cyclic shifter 52n-11. The relay station 50n-2 includes an antenna 51n-21, an antenna 51n-22, an antenna 51n-23, an antenna 51n-24, a cyclic shifter 52n-21, and a cyclic shifter 52n-22. The relay station 50n-3 includes an antenna 51n-31, an antenna 51n-33, and a cyclic shifter 52n-31.

Cyclic shifter 52n-11, cyclic shifter 52n-21, cyclic shifter 52n-22, and cyclic shifter 52n-31 impart a cyclic delay to the transmitted data signal.

Relay station 50n-1 wirelessly communicates with relay station 50n-2 using transmit/receive diversity technology with antennas 51n-11 and 51n-13. Relay station 50n-2 wirelessly communicates with relay station 50n-1 using transmit/receive diversity technology with antennas 51n-21 and 51n-23, and wirelessly communicates with relay station 50n-3 using transmit/receive diversity technology with antennas 51n-22 and 51n-24. Relay station 50n-3 wirelessly communicates with relay station 50n-2 using transmit/receive diversity technology with antennas 51n-31 and 51n-33.

Here, the angle between the direction from the midpoint between antennas 51n-11 and 51n-13 of relay station 50n-1 to the midpoint between antennas 51n-21 and 51n-23 of relay station 50n-2 and the direction from the midpoint between antennas 51n-11 and 51n-13 of relay station 50n-1 to the midpoint between antennas 51n-31 and 51n-33 of relay station 50n-3 is θ _d degrees.

In such a configuration using transmit/receive diversity, when the relay station 50n-3 receives the radio waves transmitted from the relay station 50n-2, the angle _θd required to avoid radio interference caused by the radio waves transmitted from the relay station 50n-1 is _θd < θ. That is, in a configuration using transmit/receive diversity, radio interference can be avoided at an angle _θd smaller than the angle θ required to avoid radio interference in a configuration not using transmit/receive diversity. Therefore, by using transmit/receive diversity, it is possible to further increase the antenna directivity at the relay station.

Furthermore, as mentioned above, a wireless communication system having such redundant (duplicated) radio links can reduce the effects of radio interference, making it an effective system not only in rural areas but also when installed in urban areas where there are more factors of radio interference.

As described above, in the third embodiment, the station placement design support device 1 supports station placement design in a wireless communication system 5n in which two directional antennas are used on each side for communication between relay stations. The two directional antennas of each relay station perform transmission and reception diversity, thereby increasing directivity compared to the case where only one directional antenna is used.

By being provided with the above-mentioned configuration, the station placement design support device 1 in the third embodiment can perform station placement design taking into consideration the fact that the antenna directivity has been improved by the transmission and reception diversity. This can further expand the selection possibilities for candidate installation locations for relay stations. In addition, by being provided with the above-mentioned configuration, the station placement design support device 1 in the third embodiment can support station placement design that enables multi-hop wireless communication without increasing the number of radio frequency channels used between relay stations.

According to the above-mentioned embodiments and modifications, the station placement design support device supports station placement design of a communication network that wirelessly connects a plurality of wireless stations to form a communication path. For example, the wireless stations are relay stations 50a to 50n in the embodiment, the communication path is a wireless link path in the embodiment, and the communication network is wireless communication systems 5a to 5n in the embodiment. The station placement design support device includes a station placement design unit that places a non-adjacent wireless station, which is another wireless station that is not adjacent to the wireless station on the communication path, based on the radiation direction of the radio wave by the directional antenna equipped in the wireless station. For example, the station placement design unit is the radio wave interference evaluation unit 108 and the relay station position selection unit 107 in the embodiment, the radiation direction of the radio wave is the direction of the antenna directivity range in the embodiment (for example, the range of the half-value angle θ _BW ), and the non-adjacent wireless station is another relay station that is three or more ahead on the wireless link path in the embodiment.

In addition, the station placement design unit may place multiple radio stations so that no non-adjacent radio stations exist in the radiation direction.

The station placement design unit may place multiple radio stations so that there are no non-adjacent radio stations in the radiation direction that communicate using radio waves of the same frequency as the radio waves.

When a branch radio station, which is a radio station that branches a communication path, is included in the communication network, the station placement design unit may place non-adjacent radio stations that are arranged on either side of the branch radio station in the communication path in a direction different from the radiation direction, or may set the non-adjacent radio stations to radio stations that communicate using radio waves with a frequency different from that of the radio waves. For example, the branch radio stations are relay stations 50i-3 and 50j-3 in the embodiment.

In addition, the station placement design unit may place a non-adjacent radio station in the radiation direction if the difference between the received power of the radio waves received by the non-adjacent radio station and the interference power of the radio waves interfering with the received radio waves is less than a predetermined value when the non-adjacent radio station is placed in the radiation direction.

The radiation direction may be within the range of the half-value angle of the radio wave.

The wireless station may transmit and receive radio waves using multiple directional antennas, and perform cyclic delay diversity, which imparts different cyclic delay amounts to data signals transmitted by radio waves from each directional antenna. For example, the multiple directional antennas are antennas 51n-11 and 51n-13, antennas 51n-21 and 51n-23, antennas 51n-22 and 51n-24, and antennas 51n-31 and 51n-33 in the embodiment.

A part or all of the station placement design support device 1 in each of the above-mentioned embodiments may be realized by a computer. In that case, a program for realizing this function may be recorded on a computer-readable recording medium, and the program recorded on the recording medium may be read into a computer system and executed to realize the function. Note that the "computer system" here includes hardware such as an OS and peripheral devices. Furthermore, the "computer-readable recording medium" refers to a portable medium such as a flexible disk, an optical magnetic disk, a ROM, a CD-ROM, and a storage device such as a hard disk built into a computer system. Furthermore, the "computer-readable recording medium" may include a medium that dynamically holds a program for a short period of time, such as a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line, and a medium that holds a program for a certain period of time, such as a volatile memory inside a computer system that is a server or client in that case. Furthermore, the above-mentioned program may be a program for realizing a part of the above-mentioned function, or may be a program that can realize the above-mentioned function in combination with a program already recorded in the computer system, or may be a program that is realized using a programmable logic device such as an FPGA (Field Programmable Gate Array).

The above describes in detail an embodiment of the present invention with reference to the drawings, but the specific configuration is not limited to this embodiment and also includes designs that do not deviate from the gist of the present invention.

1...station placement design support device, 5...wireless communication system, 50...relay station, 51...antenna, 52...cyclic shifter, 100...control unit, 101...memory unit, 102...operation input unit, 103...output unit, 104...design range designation unit, 105...terminal station position identification unit, 106...facility information acquisition unit, 107...relay station position selection unit, 108...radio interference evaluation unit

Claims (5)

A station placement design support method by a computer that supports station placement design of a communication network in which a plurality of wireless stations are wirelessly connected to form a communication path, comprising:
a station placement design step of placing a non-adjacent radio station, which is another radio station that is not adjacent to the radio station on the communication path, based on a radiation direction of radio waves from a directional antenna provided in the radio station;
the station placement design support method, in which, in the station placement design step, when the non-adjacent radio station is placed in the radiation direction, if a difference between a received power of a radio wave received by the non-adjacent radio station and an interference power of the radio wave interfering with the received radio wave is less than a predetermined value, the non-adjacent radio station is not placed in the radiation direction, and if the difference is equal to or greater than the predetermined value, the non-adjacent radio station is placed in the radiation direction. 2. The station placement design support method according to claim 1, wherein, in the station placement design step, when a branch radio station that is a radio station that branches off the communication path is included in the communication network, the non-adjacent radio stations that are arranged on either side of the branch radio station with respect to the radio station on the communication path are placed in a direction different from the radiation direction, or are made to be radio stations that communicate using radio waves of a frequency different from that of the radio waves. The station location design support method according to claim 1 or 2 , wherein the radiation direction is a direction within a range of a half-value angle of the radio wave. The radio station transmits and receives the radio waves using a plurality of the directional antennas, and performs cyclic delay diversity in which a different cyclic delay amount is applied to a data signal transmitted by the radio waves from each directional antenna. The station placement design support method according to any one of claims 1 to 3 . A station placement design support device that supports station placement design of a communication network in which a plurality of wireless stations are wirelessly connected to form a communication path,
a station placement design unit that places a non-adjacent radio station, which is another radio station that is not adjacent to the radio station on the communication path, based on a radiation direction of radio waves from a directional antenna included in the radio station;
the station placement design unit, when the non-adjacent wireless station is placed in the radiation direction, does not place the non-adjacent wireless station in the radiation direction if a difference between a received power of a radio wave received by the non-adjacent wireless station and an interference power of the radio wave interfering with the received radio wave is less than a predetermined value, and places the non-adjacent wireless station in the radiation direction if the difference is equal to or greater than the predetermined value.

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