JP7082879B2 - Interference power estimation device and interference power estimation method - Google Patents

Description

The present invention relates to an apparatus and a method for estimating interference power in a wireless network.

In the design of a wireless LAN, the coverage area of each access point (that is, the area that can communicate with the access point) is measured or estimated. For example, the signal strength (RSSI: Received Signal Strength Indicator) received from each access point is measured or estimated, and a reception strength distribution map (RSSI heat map) is created based on the result. Then, the number and arrangement of access points are determined so that interference does not occur between the access points and the non-communication area is as small as possible.

As a related technique, a method of reducing the interference power received by the access point has been proposed (for example, Patent Document 1). Further, a method of calculating the estimated interference power in the base station apparatus has been proposed (for example, Patent Document 2).

Japanese Unexamined Patent Publication No. 2016-225902 Japanese Unexamined Patent Publication No. 2012-74818

However, in the design of the wireless LAN by the conventional technique, the interference between the terminals is not sufficiently considered. Specifically, in the prior art, the influence of the hidden terminal is not taken into consideration. Therefore, even if the coverage area of each access point is appropriately designed, the performance of the wireless LAN may deteriorate due to the hidden terminal depending on the arrangement or operating condition of the terminal. For example, a state in which it is difficult to connect to a wireless LAN may occur. Alternatively, the connection with the wireless LAN may be cut off.

An object of one aspect of the present invention is to provide a device and a method for accurately estimating the interference power caused by a hidden terminal.

The interference power estimation device of one aspect of the present invention estimates interference power in a wireless communication system in which a plurality of wireless communication devices are used in a target area. This interference power estimation device is a propagation loss model that represents the relationship between the propagation distance and the loss of a radio signal in the target area based on a plurality of received power values measured at a plurality of measurement points in the target area. For each wireless communication device and the propagation loss model creation unit that creates the Was extracted by the hidden terminal extraction unit that extracts a wireless communication device that can be a hidden terminal from the plurality of wireless communication devices, the power estimation point set in the target area, and the hidden terminal extraction unit. It includes an interference power estimation unit that estimates the interference power caused by the hidden terminal at the power estimation point based on the distance to the wireless communication device and the propagation loss model.

According to the above aspect, the interference power caused by the hidden terminal can be estimated accurately.

It is a figure which shows an example of the wireless communication system which concerns on embodiment of this invention. It is a figure which shows an example of the interference power estimation apparatus which concerns on embodiment of this invention. It is a figure which shows an example of the interference power estimation method which concerns on embodiment of this invention. It is a figure which shows the example of the measured value of the propagation loss obtained from the measurement data. It is a flowchart which shows an example of the process of creating a propagation loss model. It is a figure which shows an example of the process which creates the propagation loss model. It is a figure which shows an example of a hidden terminal determination. It is a figure which shows an example of the arrangement of a wireless terminal and the setting of a mesh. It is a flowchart (the 1) which shows an example of the method of estimating the interference power caused by a hidden terminal. It is a flowchart (2) which shows an example of the method of estimating the interference power caused by a hidden terminal.

FIG. 1 shows an example of a wireless communication system according to an embodiment of the present invention. The wireless communication system 1 of the embodiment is constructed in a predetermined destination area designated in advance. The destination area corresponds to the area where wireless communication should be carried out. For example, the destination area corresponds to a factory building, an office building, or the like.

As shown in FIG. 1, the wireless communication system 1 includes a plurality of routers 2 (2a to 2d) in a destination area. The router 2 can accommodate one or more wireless terminals and can operate as a wireless access point. That is, the router 2 receives the uplink signal output from the wireless terminal and transmits the downlink signal to the wireless terminal. Further, the router 2 can transmit and receive a radio signal to and from another router 2. That is, the router 2 can operate as a multi-hop router. Note that one of the plurality of routers 2 may operate as a gateway router for connecting to another network.

The interference power estimation device according to the embodiment of the present invention estimates the interference power in the target area shown in FIG. Specifically, the interference power estimation device estimates the interference power caused by the hidden terminal in the case where a plurality of wireless terminals are arranged in the target area. Then, the interference power estimation device creates a heat map in the target area based on the estimation result of the interference power. In this specification, the heat map represents the distribution of received power (for example, interference power caused by a hidden terminal).

FIG. 2 shows an example of an interference power estimation device according to an embodiment of the present invention. The interference power estimation device 10 acquires measurement data from the measurement tool 20. Further, the interference power estimation device 10 can also acquire measurement data from each router 2 (2a to 2d). Then, the interference power estimation device 10 estimates the interference power based on the acquired measurement data, and creates a heat map based on the estimation result.

The interference power estimation device 10 includes interfaces (IF) 11, 12, a memory 13, a propagation loss model creation unit 14, an estimation unit 15, and a heat map creation unit 18. The estimation unit 15 includes a hidden terminal extraction unit 16 and an interference power estimation unit 17. The interference power estimation device 10 may have other functions not shown in FIG. Further, the estimation unit 15 may also have other functions not shown in FIG.

The interface 11 receives the measurement data generated by the measurement tool 20. The interface 12 receives the measurement data generated by each router 2. The measurement data received from the measurement tool 20 and the router 2 is stored in the memory 13. The measurement data received by the interfaces 11 and 12 corresponds to a plurality of received power values measured at each of the plurality of measurement points in the target area. Further, the memory 13 also stores router information indicating the position (or coordinates) of each router 2.

The propagation loss model creation unit 14 creates a propagation loss model representing the propagation loss in the target area based on the measurement data received by the interfaces 11 and 12. The propagation loss model represents the relationship between the propagation distance of a radio signal and the loss. The estimation unit 15 estimates the received power / interference power for the power estimation point set in the target area by using the propagation loss model created by the propagation loss model creation unit 14. At this time, the estimation unit 15 may estimate the received power / interference power for each of the plurality of power estimation points set in the target area. In this case, the plurality of power estimation points correspond to, for example, each intersection of the mesh set for the destination area.

The hidden terminal extraction unit 16 extracts a wireless communication device that can be a hidden terminal from a plurality of wireless communication devices arranged in the target area. "Wireless communication equipment" shall include routers and wireless terminals. The interference power estimation unit 17 is used as a hidden terminal at the power estimation point based on the distance between the power estimation point and the wireless communication device that can be a hidden terminal, and the propagation loss model created by the propagation loss model creation unit 14. Estimate the resulting interference power.

The heat map creation unit 18 creates a heat map in the target area based on the estimated power data calculated by the estimation unit 15. When the interference power estimation unit 17 estimates the interference power caused by the hidden terminal for each of the plurality of power estimation points, the heat map creation unit 18 determines the heat map of the interference power caused by the hidden terminal based on the estimation result. To create.

FIG. 3 shows an example of the interference power estimation method according to the embodiment of the present invention. The interference power estimation method shown in FIG. 3 is executed, for example, with the router 2 installed in the target area. At this time, the wireless terminal may or may not exist in the target area.

The measurement tool 20 has a function of measuring the position and the received power. Further, the measurement tool 20 is mounted on a mobile terminal, for example. Then, the network administrator or the user measures the received power by using the measurement tool 20 at a desired measurement point in the target area.

The measurement tool 20 receives a radio signal output from each router 2, measures its received power (RSSI: Received Signal Strength Indicator), and identifies its source. At this time, the measurement tool 20 measures, for example, the RSSI of a signal whose transmission power is known. The measuring tool 20 may also measure the center frequency of the received signal. Then, the measurement tool 20 notifies the interference power estimation device 10 of the measurement data representing the measurement result. Here, the measurement data includes the following information.
(1) Position of measurement point (2) RSSI
(3) Center frequency of the received signal (4) Identification information that identifies the source router of the received signal

When the measurement tool 20 receives a radio signal from a plurality of routers 2 at one measurement point, the measurement tool 20 generates measurement data for each router 2 and notifies the interference power estimation device 10. Further, the network administrator or the user measures RSSI at a plurality of measurement points in the target area by using the measurement tool 20. That is, the measurement data obtained at each of the plurality of measurement points in the target area is notified from the measurement tool 20 to the interference power estimation device 10.

The measurement data is represented in, for example, a CSV (comma-separated values) format. Then, the measurement data is given to the interference power estimation device 10 after the format is converted by the conversion tool 21. The conversion tool 21 converts the format of the measurement data into a format that can be processed by the interference power estimation device 10 or a format that simplifies the processing of the interference power estimation device 10. However, the conversion tool 21 is not always necessary, and the measurement tool 20 may directly notify the interference power estimation device 10 of the measurement data.

In the example shown in FIG. 3, the measurement tool 20 notifies the interference power estimation device 10 of the measurement data, but each router 2 can also notify the interference power estimation device 10 of the measurement data. In this case, the router 2 measures the RSSI of the beacon signal transmitted from the other router 2 by using the peripheral environment measurement unit 22. The measurement data notified from each router 2 to the interference power estimation device 10 includes the following information.
(1) Identification information that identifies the router that performed the measurement (2) RSSI
(3) Center frequency of the received signal (4) Identification information that identifies the source router of the received signal

The interference power estimation device 10 stores the measurement data acquired from the measurement tool 20 and the router 2 in the memory 13. However, the interference power estimation device 10 may acquire measurement data from only one of the measurement tool 20 and the router 2. For example, the interference power estimation device 10 may acquire measurement data only from the measurement tool 20.

The interference power estimation device 10 may calculate the measured value of the propagation loss from the acquired measurement data and store the calculation result in the memory 13. For example, when a set of measurement data (position of measurement point, RSSI, identification information for identifying the source router of the received signal) is received from the measurement tool 20, the interference power estimation device 10 uses the measurement point and the source router. The distance d between can be calculated and the measured propagation loss can be obtained from the distance d and the RSSI measurements. It is assumed that the position of each router 2 and the transmission power of each router 2 are known.

FIG. 4 shows an example of a measured value of propagation loss obtained from the measured data. The measured value of the propagation loss is stored in the memory 13 in association with the distance d between the measurement point and the signal source.

The interference power estimation device 10 creates a propagation loss model based on the measurement data acquired from the measurement tool 20 and / or the router 2, and estimates the interference power caused by the hidden terminal by using the propagation loss model. In the example shown in FIG. 3, the interference power is estimated by the following procedure.

In S1, the propagation loss model creating unit 14 creates a propagation loss model representing the relationship between the propagation distance and the loss of the radio signal in the target area. The propagation loss model will be described in detail later.

In S2, the interference power estimation device 10 arranges a plurality of wireless terminals in the target area on the data representing the wireless communication system 1. The number of wireless terminals and the position of each wireless terminal are represented by terminal arrangement information. The terminal arrangement information is given to the interference power estimation device 10 by the network administrator or the user. For example, the network administrator or the user may specify the position of each wireless terminal by using the GUI displaying the wireless communication system 1.

In S3, the hidden terminal extraction unit 16 extracts a wireless communication device that can be a hidden terminal from a plurality of wireless communication devices arranged in the target area. The "wireless communication device" includes the router 2 and a wireless terminal arranged on the data.

In S4, the interference power estimation unit 17 estimates the interference power caused by the hidden terminal for each power estimation point set in the target area. At this time, the interference power estimation unit 17 is caused by the hidden terminal based on the distance between the power estimation point and the wireless communication device that can be a hidden terminal, and the propagation loss model created by the propagation loss model creation unit 14. Estimate the interference power. The interference power estimation unit 17 estimates the interference power caused by the hidden terminal for each of the plurality of power estimation points set in the target area.

In S5, the heat map creation unit 18 creates a heat map of the interference power caused by the hidden terminal based on the estimation results of the plurality of power estimation points by the interference power estimation unit 17. This heat map is output as image data and displayed on a display device (not shown).

<Creation of propagation loss model>
The propagation loss model creation unit 14 calculates the path loss based on the measurement data obtained at each measurement point. At this time, the propagation loss model creating unit 14 may calculate the path loss based on the measured value of the propagation loss shown in FIG. The propagation loss model is expressed by Eq. (1).

In equation (1), d represents the distance between the measurement point and the signal source, and f _c represents the center frequency of the radio signal. Therefore, by obtaining the coefficients α and β, the propagation loss corresponding to the distance d can be obtained.

In this embodiment, the coefficients α and β are calculated by using the least squares method represented by the equation (2). That is, the coefficients α and β are determined so that the sum of squares of the difference between the approximate value obtained by the propagation loss model and the measured value obtained based on the measured data is minimized.

In equation (2), N represents the number of measured values of propagation loss. n is a variable that identifies each of the N measured values, and corresponds to the measurement number in the example shown in FIG. PL _meas (n) represents a measured value of propagation loss obtained from the nth measurement data. The measured value of the propagation loss is stored in, for example, the memory 13 shown in FIG. PL _calc (d _n ) represents an approximation of the propagation loss calculated by the propagation loss model for the nth measurement data.

Specifically, the coefficients α and β are calculated by the equation (3).

When the equation (3) is solved, the coefficients α and β are expressed by the equation (4).

FIG. 5 is a flowchart showing an example of a process for creating a propagation loss model. The processing of this flowchart is executed by the propagation loss model creating unit 14 after the measurement data is notified to the interference power estimation device 10. It is assumed that the interference power estimation device 10 obtains the measured value of the propagation loss from each measurement data and stores it in the memory 13.

In S11, the propagation loss model creating unit 14 acquires the measured value of the propagation loss. At this time, the propagation loss model creation unit 14 also acquires the “distance” corresponding to the measured value. The measured value of the propagation loss and the corresponding distance are stored in the memory 13 as described above. Subsequently, in S12, the propagation loss model creating unit 14 calculates the coefficients α and β representing the propagation loss model. The coefficients α and β are calculated by giving the measured values of the propagation loss obtained at each measurement point and the corresponding distances to the above equations (1) to (4).

In S13 to S16, the propagation loss model creation unit 14 executes an outlier determination loop for detecting outliers. The outlier determination loop is executed for each measured value. That is, the propagation loss model creating unit 14 selects the measured values to be determined one by one from all the measured values, and determines whether or not the selected measured values are outliers. The outlier determination loop is as follows.

In S13, the propagation loss model creating unit 14 calculates the propagation loss corresponding to the measured value to be determined by using the coefficients α and β calculated in S12. At this time, the propagation loss is calculated by giving the propagation distance (and the center frequency of the radio signal) corresponding to the measured value of the determination target to the equation (1).

In S14, the propagation loss model creating unit 14 calculates the difference between the measured value of the propagation loss obtained based on the actually measured RSSI and the calculated value of the propagation loss obtained in S13. Then, the propagation loss model creating unit 14 determines whether or not this difference is larger than a predetermined threshold value.

When the difference is larger than the threshold value, the propagation loss model creation unit 14 determines that the measured value to be determined is an outlier. In this case, the propagation loss model creating unit 14 excludes the measured value to be determined in S15 from the measured value for creating the propagation loss model. When the difference is equal to or less than the threshold value, the process of S15 is skipped.

In S16, the propagation loss model creating unit 14 determines whether or not a measured value that has not been selected as a determination target remains. Then, if the unselected measured value remains, the process of the propagation loss model creating unit 14 returns to S13. That is, when the processing of S13 to S16 is completed for all the measured values, the processing of the propagation loss model creating unit 14 proceeds to S17.

In S17, the propagation loss model creation unit 14 determines whether or not an outlier is detected in the outlier determination loop executed immediately before. Then, when one or more outliers are detected, the processing of the propagation loss model creating unit 14 returns to S12. That is, when one or more outliers are detected, the coefficients α and β are recalculated.

The processes S12 to S17 are repeatedly executed until no outliers are detected in the outlier determination loop. Therefore, according to the procedure shown in FIG. 5, the coefficients α and β are calculated while suppressing the influence of outliers (that is, peculiar measured values). Therefore, a highly accurate propagation loss model is created.

If the above threshold value is reduced, the accuracy of the propagation loss model will be improved. However, if the threshold value is set too small, the measured values will be excessively removed, and the number of measured values used to create the propagation loss model will be small, so that the accuracy may be rather low. This problem can be solved by increasing the number of measurement points, but increasing the number of measurement points increases the time and effort required to create a propagation loss model. Therefore, it is preferable to appropriately determine the threshold value in consideration of these factors.

FIG. 6 shows an example of a process for creating a propagation loss model. In FIG. 6, x and Δ represent measured values. However, the Δ mark indicates a peculiar measured value (that is, an outlier). Further, the curve shows an approximate curve (that is, a propagation loss model) calculated based on the measured value.

FIG. 6A shows a propagation loss model M1 calculated in a state including outliers. The propagation loss model M1 (α = 21.0, β = 34.8) is created in S12 to S13. After that, in S14 to S15, the outliers are deleted.

FIG. 6 (b) shows the propagation loss model M2 obtained after the outliers are deleted from the state shown in FIG. 6 (a). Since the propagation loss model M2 (α = 19.5, β = 36.6) is calculated without using a peculiar measured value, it is considered that the propagation loss is represented more accurately than the propagation loss model M1.

As described above, according to the embodiment of the present invention, since the propagation estimation model is created based on the actually measured power value, its accuracy or reliability is high. In addition, outliers are excluded from the measurements when creating the propagation estimation model, further increasing its accuracy or reliability.

<Judgment of hidden terminal>
In a wireless LAN where CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) is adopted, the transmitting terminal confirms whether or not the wireless resource is used by another terminal before starting data transmission. At this time, if the received power (for example, RSSI) detected by the carrier sense exceeds a predetermined threshold value, the transmitting terminal can determine that the radio resource is being used by another terminal, and thus starts data transmission. do not do. That is, collisions are avoided. In the following description, this threshold value may be referred to as a "busy detection threshold value".

When the wireless communication device performs carrier sense, if the power of the signal received from a certain signal source exceeds the busy detection threshold value, the wireless communication device determines that the signal source is an "adjacent node". That is, the signal source is not determined to be a "hidden terminal". On the other hand, when the power of the signal received from a certain signal source is smaller than a predetermined threshold value (hereinafter, may be referred to as "reception detection threshold value") which is sufficiently smaller than the busy detection threshold value, another signal. It is considered that there is virtually no interference with. That is, in the case where the power of the received signal is smaller than the reception detection threshold value, it is not necessary to consider the signal source as a hidden terminal. Therefore, in this embodiment, in consideration of these factors, when the power of the signal received from a certain signal source is equal to or more than the reception detection threshold value and smaller than the busy detection threshold value, the hidden terminal extraction unit 16 sets the hidden terminal extraction unit 16. The signal source is determined to be a "wireless communication device that can be a hidden terminal".

FIG. 7 shows an example of the hidden terminal determination. In the embodiment shown in FIG. 7, M3 and M4 represent a propagation loss model in a wireless LAN using carriers in the 5 GHz band and the 2.4 GHz band, respectively.

In this embodiment, it is assumed that the transmission power of each wireless communication device is constant and known. Then, if the distance between the transmitting node and the receiving node is given to the propagation loss model, the propagation loss between the transmitting node and the receiving node is calculated, and the received power at the receiving node is uniquely calculated. Then, if the calculated reception power is checked "whether or not it is equal to or more than the reception detection threshold value and smaller than the busy detection threshold value", it is possible to determine whether or not the pair of nodes can be "hidden terminals" for each other. It is judged. That is, assuming that the transmission power of the signal is known, the propagation loss and the reception power correspond uniquely. Therefore, if the distance between the transmission node and the reception node is obtained, the pair of nodes are "hidden" from each other. It is determined whether or not it can be a "terminal". For example, in the 2.4 GHz band wireless LAN shown in FIG. 7, when the distance between the nodes is about 15 m or more and smaller than about 40 m, it is determined that the pair of nodes are "hidden terminals" with each other. Will be done.

<Estimation of interference power>
In the estimation of the interference power caused by the hidden terminal, a plurality of wireless terminals are arranged in the target area on the data representing the wireless communication system 1. The position of each wireless terminal is specified by, for example, the terminal arrangement information given to the interference power estimation unit 17 by the network administrator or the user. It is assumed that the positions of the routers 2 actually mounted on the wireless communication system 1 are registered in advance.

Further, the interference power estimation unit 17 sets a mesh for designating a position for estimating the interference power over the entire target area on the data representing the wireless communication system 1. The position for estimating the interference power corresponds to the above-mentioned "power estimation point".

FIG. 8 shows an example of the arrangement of wireless terminals and the setting of mesh. R represents the position of the router 2 actually mounted on the wireless communication system 1. S represents the position of the wireless terminal arranged by the terminal arrangement information. In the example shown in FIG. 8, eight wireless terminals 3a to 3h are arranged in the target area. The dashed line represents the mesh. The mesh spacing is specified, for example, by the network administrator or user. The intersection of these meshes corresponds to the power estimation point at which the interference power is estimated. In the example shown in FIG. 8, m × k power estimation points are set by this mesh. Then, the interference power estimation unit 17 estimates the interference power caused by the hidden terminal at each of the m × k power estimation points by the method described later.

9 to 10 are flowcharts showing an example of a method of estimating the interference power caused by the hidden terminal. The processing of this flowchart corresponds to S3 to S4 shown in FIG. Therefore, the processing of this flowchart is executed after the propagation loss model is created and the wireless terminal is further arranged. In the following description, for the sake of simplicity, it is assumed that the transmission power of each wireless communication device is constant and known.

In S21, the estimation unit 15 sets a mesh over the entire target area on the data representing the wireless communication system 1. That is, a plurality of power estimation points are set in the target area. After that, the hidden terminal extraction unit 16 executes a process of extracting the hidden terminal in S22 to S29.

In S22, the hidden terminal extraction unit 16 identifies the position of the wireless communication device mounted or arranged in the target area. The "wireless communication device" includes routers 2a to 2d actually mounted on the wireless communication system 1 and wireless terminals 3a to 3h arranged on data representing the wireless communication system 1.

In S23, the hidden terminal extraction unit 16 selects one of all the wireless communication devices as the transmission node. In S24, the hidden terminal extraction unit 16 selects one of all wireless communication devices as the receiving node. However, the transmitting node and the receiving node shall be different from each other.

In S25, the hidden terminal extraction unit 16 calculates the distance between the transmission node selected in S23 and the reception node selected in S24. In S26, the hidden terminal extraction unit 16 calculates the propagation loss between the two nodes by giving the distance calculated in S25 to the propagation loss model. Then, in S28, the hidden terminal extraction unit 16 uses the propagation loss calculated in S26 to estimate the RSSI detected by the receiving node when the signal is transmitted from the transmitting node with a predetermined power.

In S29, the hidden terminal extraction unit 16 determines whether or not the RSSI calculated in S28 is equal to or greater than the reception detection threshold value and smaller than the busy detection threshold value. Then, when the RSSI is within this range, the hidden terminal extraction unit 16 determines that the transmitting node and the receiving node can be hidden terminals to each other. In this case, in S31 to S37, the interference power estimation unit 17 executes a process of estimating the interference power caused by the hidden terminal. On the other hand, when RSSI is out of the above range (S29: No), S31 to S37 are skipped.

In this embodiment, it is assumed that the transmission power of each wireless communication device is constant and known, but the estimation unit 15 may estimate the transmission power of each wireless communication device. For example, when the transmitting node selected in S23 is the router 2, the estimation unit 15 may estimate the transmission power of the router 2. For example, the estimation unit 15 can back-calculate the transmission power of the router 2 from the measurement data stored in the memory 13 by using the propagation loss model created earlier. This transmission power may be used when calculating RSSI in S34.

In S31, the interference power estimation unit 17 selects one of a plurality of power estimation points set in the destination area. In S32, the interference power estimation unit 17 calculates the distance between the power estimation point selected in S31 and the transmission node selected by the hidden terminal extraction unit 16 in S23. In S33, the interference power estimation unit 17 calculates the propagation loss between the transmission node and the power estimation point by giving the distance calculated in S32 to the propagation loss model. Then, in S34, the interference power estimation unit 17 estimates RSSI detected at the power estimation point when a signal is transmitted from the transmission node with a predetermined power by using the propagation loss calculated in S33. When the transmitting node is the router 2, the interference power estimation unit 17 may estimate RSSI by using the transmission power estimated in S27 and the propagation loss calculated in S33.

In S35, the interference power estimation unit 17 determines whether or not the RSSI calculated in S34 is equal to or greater than the reception detection threshold value and smaller than the busy detection threshold value. Then, when the RSSI is within this range, the interference power estimation unit 17 determines that the signal transmitted from the transmission node causes interference. In this case, the interference power estimation unit 17 updates the interference parameter in S36. Specifically, the interference power estimation unit 17 adds the RSSI newly calculated in S34 to the interference parameter previously calculated for the power estimation point selected in S31. As a result, the cumulative value of the interference parameter is obtained for the power estimation point selected in S31. However, the interference parameter is RSSI (or a predetermined index generated based on RSSI) in this embodiment. The initial value of the interference parameter is zero. When RSSI is out of the above range (S35: No), S36 is skipped.

In S37, the interference power estimation unit 17 determines whether or not there are remaining power estimation points for which the processes S32 to S36 have not been executed. When such a power estimation point remains, the processing of the interference power estimation unit 17 returns to S31. In this case, the processes S32 to S36 are executed for the next power estimation point. Then, when the processes of S32 to S36 are executed for all the power estimation points, the process of the estimation unit 15 proceeds to S38.

S38 is provided for the hidden terminal extraction unit 16 to sequentially select all the wireless communication devices as receiving nodes one by one. Further, S39 is provided for the hidden terminal extraction unit 16 to sequentially select all the wireless communication devices as transmission nodes one by one. That is, the hidden terminal extraction unit 16 determines whether or not each of the combinations (transmission node and reception node) selected from the wireless communication devices mounted or arranged in the target area is a hidden terminal. Is determined. Then, when the hidden terminal is extracted, the interference power estimation unit 17 updates the interference parameter by the signal transmitted from the transmission node.

Next, the processing of the flowcharts shown in FIGS. 9 to 10 will be described with reference to FIG. Here, it is assumed that the interference power at the power estimation point Z shown in FIG. 8 is estimated.

For example, in S23 to S24, when the terminal 3a is selected as the transmitting node and the terminal 3g is selected as the receiving node, in S25 to S28, RSSI is estimated based on the distance between the terminals 3a and 3g. Here, it is assumed that this RSSI is equal to or higher than the reception detection threshold and smaller than the busy detection threshold (S29: Yes). Then, the terminals 3a and 3g are determined to be hidden terminals from each other. When the terminals 3a and 3g are hidden terminals, arbitration by carrier sense is not performed between the terminals 3a and 3g, so that the terminals 3a and 3g may transmit data signals at the same time. Therefore, in order to estimate the interference power caused by the signal transmitted from the terminal 3a, the processes S32 to S36 are executed for each power estimation point.

When the power estimation point Z shown in FIG. 8 is selected in S31, RSSI (3a_Z) is estimated based on the distance between the terminal 3a and the power estimation point Z. Here, it is assumed that RSSI (3a_Z) is equal to or higher than the reception detection threshold and smaller than the busy detection threshold (S35: Yes). In this case, the signal transmitted from the terminal 3a within the busy period acts as an interference signal at the power estimation point Z. Therefore, the interference power estimation unit 17 saves "RSSI (3a_Z)" as an interference parameter.

When RSSI (3a_Z) is smaller than the reception detection threshold value, it is considered that the power of the signal reaching the power estimation point Z from the terminal 3a is sufficiently small and the influence of interference is sufficiently small. Further, when RSSI (3a_Z) is equal to or higher than the busy detection threshold value, assuming that the wireless communication device Z is mounted at the power estimation point Z, the wireless communication device Z can recognize the terminal 3a by carrier sense. That is, since the terminal 3a and the wireless communication device Z do not transmit data signals at the same time, it is not necessary to consider the influence of interference. Therefore, in this embodiment, the interference parameter is updated only when the RSSI calculated in S34 is equal to or greater than the reception detection threshold value and smaller than the busy detection threshold value.

When terminal 3c is selected as the transmitting node and terminal 3h is selected as the receiving node, RSSI is estimated based on the distance between terminals 3c and 3h. Here, it is assumed that this RSSI is equal to or higher than the reception detection threshold and smaller than the busy detection threshold. In this case, the terminals 3c and 3h are determined to be hidden terminals.

Then, RSSI (3c_Z) is estimated based on the distance between the terminal 3c and the power estimation point Z. Here, it is assumed that RSSI (3c_Z) is also equal to or higher than the reception detection threshold and smaller than the busy detection threshold. In this case, the signal transmitted from the terminal 3c also acts as an interference signal at the power estimation point Z. Therefore, the interference power estimation unit 17 updates the interference parameter by adding the newly obtained "RSSI (3c_Z)" to the previously calculated and stored interference parameter "RSSI (3a_Z)". ..

By performing the above processing for all combinations (transmitting node and receiving node), the cumulative value of the interference parameter is obtained for the selected power estimation point. That is, the interference power caused by the hidden terminal is estimated for the selected power estimation point. Further, the estimation unit 15 estimates the interference power caused by the hidden terminal for all the power estimation points in the target area.

<Creating a heat map>
The heat map creation unit 18 creates a heat map showing the estimation result of the interference power for each power estimation point. On the heat map, for example, a region having a large interference power is displayed in a dark color, and an region having a small interference power is displayed in a light color. Then, the heat map creation unit 18 converts the created heat map into image data in a predetermined format and outputs it. This image data is displayed on the display device. As described above, according to the embodiment of the present invention, the distribution of the interference power caused by the hidden terminal is visualized.

<Hardware configuration>
The interference power estimation device 10 includes a processor. The propagation loss model creation unit 14, the hidden terminal extraction unit 16, the interference power estimation unit 17, and the heat map creation unit 18 are realized by executing an interference power estimation program using a processor. In this case, the interference power estimation program is stored in a memory area accessible to the processor. Some of the functions of the propagation loss model creation unit 14, the hidden terminal extraction unit 16, the interference power estimation unit 17, and the heat map creation unit 18 may be realized by a hardware circuit.

<Variation>
The interference power estimation device / method according to the embodiment of the present invention can be used as a survey tool before introducing the system. It can also be used as an evaluation tool for existing systems.

1 Wireless communication system 2 (2a to 2d) Routers 3a to 3h Terminal 10 Interference power estimation device 13 Memory 14 Propagation loss model creation unit 15 Estimating unit 16 Hidden terminal extraction unit 17 Interference power estimation unit 18 Heat map creation unit 20 Measurement tool 21 Conversion tool 22 Surrounding environment measurement unit

Claims (6)

An interference power estimation device that estimates interference power in a wireless communication system in which a plurality of wireless communication devices are used in a target area.
Creation of a propagation loss model that represents the relationship between the propagation distance and loss of a radio signal in the target area based on a plurality of received power values measured at a plurality of measurement points in the target area. Department and
For each wireless communication device, the received power of a signal transmitted from another wireless communication device is estimated using the propagation loss model, and based on the estimated received power, it is hidden from the plurality of wireless communication devices. A hidden terminal extraction unit that extracts wireless communication devices that can be terminals,
Interference power caused by the hidden terminal at the power estimation point based on the distance between the power estimation point set in the target area and the wireless communication device extracted by the hidden terminal extraction unit and the propagation loss model. Interference power estimation unit that estimates
Interference power estimation device. The interference power estimation unit is based on the distance from the wireless communication device extracted by the hidden terminal extraction unit and the propagation loss model for each of the plurality of power estimation points set in the target area. The interference power estimation device according to claim 1, wherein the interference power caused by the hidden terminal is estimated. The interference power estimation device according to claim 2, further comprising a heat map creating unit that creates a heat map representing the interference power estimated for each of the plurality of power estimation points by the interference power estimation unit. The hidden terminal extraction unit
The first radio by giving the propagation loss model the distance between the first radio communication device of the plurality of radio communication devices and the second radio communication device of the plurality of radio communication devices. The first propagation loss, which represents the propagation loss between the communication device and the second wireless communication device, is calculated.
Based on the first propagation loss, the first received power representing the power of the signal received from the first wireless communication device in the second wireless communication device is calculated.
The first wireless communication device as a wireless communication device that can be a hidden terminal when the first received power is equal to or higher than the first threshold value and smaller than the second threshold value larger than the first threshold value. The interference power estimation device according to claim 1, further comprising extracting the power. The interference power estimation unit is
A second propagation representing the propagation loss between the first wireless communication device and the power estimation point by giving the distance between the first wireless communication device and the power estimation point to the propagation loss model. Calculate the loss,
Based on the second propagation loss, a second received power representing the power of the signal received from the first wireless communication device at the power estimation point is calculated.
When the second received power is equal to or greater than the first threshold value and smaller than the second threshold value, interference caused by the hidden terminal at the power estimation point is based on the second received power. The interference power estimation device according to claim 4, wherein the power is estimated. It is an interference power estimation method that estimates the interference power in a wireless communication system in which a plurality of wireless communication devices are used in a target area.
Based on a plurality of received power values measured at a plurality of measurement points in the target area, a propagation loss model representing the relationship between the propagation distance and the loss of the radio signal in the target area is created.
For each wireless communication device, the received power of a signal transmitted from another wireless communication device is estimated using the propagation loss model, and based on the estimated received power, it is hidden from the plurality of wireless communication devices. Extract wireless communication devices that can be terminals
To estimate the interference power caused by the hidden terminal at the power estimation point based on the distance between the power estimation point set in the target area and the extracted wireless communication device and the propagation loss model. A characteristic interference power estimation method.

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