JP2011155321A - Radio communication device, radio communication system, program and radio communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio communication device, a radio communication system, a program and a radio communication method. <P>SOLUTION: The radio communication device includes a communication part for performing communication with one or more radio communication devices forming the same radio communication network, a communication control part for causing the communication part to transmit a broadcast frame in a carrier sense type access method, and a calculating part for calculating a radio link quality for each of the one or more radio communication parts on the basis of the amount of transmission of the broadcast frame per part time and the amount of reception of the broadcast frame per part time in each of the one or more radio communication devices. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a wireless communication device, a wireless communication system, a program, and a wireless communication method.

  In many of the general wireless networks represented by IEEE (Institut of Electrical and Electronic Engineers) 802.11b, each node is a DCF (Distributed Coordination Energies Cultivation Census Cultivation Census Cultivation Census). By using the access method, communication is performed by sharing a limited wireless band with surrounding nodes.

  When this CSMA / CA access method is applied to a wireless multi-hop network, communication quality may deteriorate due to a hidden terminal problem and an exposed terminal problem. The hidden terminal problem is a problem in which, when two nodes are in a positional relationship where they cannot receive each other's radio waves, frames transmitted from each other frequently collide with each other and an error occurs. Further, the exposed terminal problem is a problem that when two nodes are in a positional relationship where they can receive each other's radio waves, if a large number of frames are transmitted by one node, the transmission opportunity of the other node is significantly reduced. The wireless multi-hop network is described in, for example, Patent Document 1 below.

  On the other hand, many general wireless networks can use a plurality of wireless channels. For example, in IEEE 802.11b, 14 radio channels can be used in Japan (the maximum number of radio channels that can be used simultaneously is 4). Therefore, in an environment where a plurality of wireless networks coexist, it is desirable to select a wireless channel with a wide available bandwidth that does not overlap with other wireless networks.

  In this connection, as a method for estimating the available bandwidth in the wireless network, there is a method for measuring the throughput between two nodes. For example, there is an infrastructure type wireless network as a form of a wireless network typified by a wireless LAN network that is currently widely used. This infrastructure type wireless network forms a star topology centering on a node that centrally manages a network represented by an access point. For this reason, in an infrastructure type wireless network, the available bandwidth can be estimated by measuring the throughput (link quality) between a node that centrally manages the network and each other node.

JP 2009-239489 A

  However, in the wireless multi-hop network, unlike an infrastructure wireless network in which each node communicates with a node that centrally manages the network, which node (wireless communication device) communicates with is not determined. For this reason, there is a problem that it is difficult to estimate the communication quality of the entire wireless multihop network simply by estimating the link quality between each node and a specific node.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is a novel that can efficiently calculate the link quality between each wireless communication device constituting the network. Another object of the present invention is to provide an improved wireless communication device, wireless communication system, program, and wireless communication method.

  In order to solve the above problems, according to an aspect of the present invention, a communication unit that communicates with one or more wireless communication devices forming the same wireless network, and a broadcast from the communication unit using a carrier sense type access method. Based on a communication control unit that transmits a frame, a transmission amount per unit time of the broadcast frame, and a reception amount per unit time of the broadcast frame in each of the one or more wireless communication devices, the 1 or A wireless communication device is provided that includes a calculation unit that calculates wireless link quality between each of the two or more wireless communication devices.

  The calculation unit includes an available bandwidth ratio that is a ratio of a transmission amount per unit time of the broadcast frame in a real environment to a transmission amount per unit time of the broadcast frame in an ideal environment, and a per unit time of the broadcast frame. The radio link quality may be calculated by weighting and adding a transmission success rate that is a ratio of the reception amount of the broadcast frame per unit time in each of the one or two or more wireless communication apparatuses to the transmission amount.

  The communication control unit causes the communication unit to transmit the broadcast frame at a transmission rate of 1, and the calculation unit weights and adds the available bandwidth rate and the transmission success rate at the transmission rate of 1. The radio link quality may be calculated.

  The communication control unit may cause the communication unit to transmit the broadcast frame at a transmission rate having the highest use frequency among a plurality of transmission rates.

  The communication control unit causes the communication unit to transmit the broadcast frame at a plurality of transmission rates, and weights and adds the integrated value of the available bandwidth rate and the integrated value of the transmission success rate at each of the plurality of transmission rates. By doing so, the radio link quality may be calculated.

  The calculation unit may calculate channel quality in the radio communication device based on at least one of radio link qualities with each of the one or more radio communication devices.

  The calculation unit may calculate the channel quality in the wireless network based on the channel quality calculated in the one or more wireless communication devices and the channel quality calculated in the wireless communication device.

  The communication control unit may cause a broadcast frame to be transmitted from the communication unit using a plurality of radio channels, and the calculation unit may calculate a radio channel quality in the radio network for each of the plurality of radio channels.

  The communication control unit may select a radio channel having the best channel quality in the radio network calculated by the calculation unit as a communication channel.

  In order to solve the above-described problem, according to another aspect of the present invention, a wireless communication system including a plurality of wireless communication devices forming the same wireless network, each of the plurality of wireless communication devices includes: A communication unit that communicates with another wireless communication device, a communication control unit that transmits a broadcast frame from the communication unit using a carrier sense type access method, a transmission amount of the broadcast frame per unit time, and the other wireless There is provided a wireless communication system comprising: a calculation unit that calculates a wireless link quality with each of the other wireless communication devices based on a reception amount of the broadcast frame per unit time in each of the communication devices.

  In order to solve the above problems, according to another aspect of the present invention, a communication unit that communicates a computer with one or more wireless communication devices forming the same wireless network, and a carrier sense type access method A communication control unit for transmitting a broadcast frame from the communication unit, a transmission amount of the broadcast frame per unit time, and a reception amount of the broadcast frame per unit time in each of the one or more wireless communication devices Based on the above, a program for functioning as a calculation unit that calculates the radio link quality with each of the one or more radio communication apparatuses is provided.

  In order to solve the above problem, according to another aspect of the present invention, a step of transmitting a broadcast frame by a carrier sense type access method, a transmission amount of the broadcast frame per unit time, and surroundings Calculating a wireless link quality with the surrounding wireless communication devices based on the received amount of the broadcast frame per unit time in each of the wireless communication devices.

  As described above, according to the present invention, it is possible to efficiently calculate the link quality between the wireless communication devices constituting the network.

It is explanatory drawing which showed the structural example of several radio | wireless network. It is explanatory drawing which showed the hidden terminal problem. It is explanatory drawing which showed the exposed terminal problem. It is explanatory drawing which showed the specific example of the infrastructure type | mold radio network. It is the functional block diagram which showed the structure of the node 20 by one Embodiment of this invention. It is explanatory drawing which showed the specific example of the maximum transmission amount in each transmission speed in an ideal environment. It is explanatory drawing which showed the specific example of the usage frequency of each transmission rate in a real environment. It is explanatory drawing which showed the specific example of the maximum transmission amount in each transmission speed in a real environment. It is explanatory drawing which showed the mode of transmission of a broadcast frame and the feedback of a receiving condition. It is explanatory drawing which showed the specific example of the reception condition. It is explanatory drawing which showed an example of the network traffic. It is explanatory drawing which showed an example of the network traffic. 3 is a flowchart illustrating an operation of a node 20 according to an embodiment of the present invention.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

  In the present specification and drawings, a plurality of constituent elements having substantially the same functional configuration may be distinguished by attaching # and a different alphabet after the same reference numeral. For example, a plurality of configurations having substantially the same functional configuration are distinguished as nodes 20 # A, 20 # B, and 20 # C as necessary. However, when it is not necessary to particularly distinguish each of a plurality of constituent elements having substantially the same functional configuration, only the same reference numerals are given. For example, the clients 20 # A, 20 # B, and 20 # C are simply referred to as the node 20 when it is not necessary to distinguish between them.

Further, the “DETAILED DESCRIPTION OF THE INVENTION” will be described according to the following item order.
1. 1. Purpose of one embodiment of the present invention 2. Node configuration Node operation Summary

<1. Purpose of one embodiment of the present invention>
First, the gist of one embodiment of the present invention will be described with reference to FIGS.

  When a new wireless multi-hop network is formed by arranging a plurality of nodes, there is a concern that the communication quality of the new wireless multi-hop network may deteriorate due to communication in the existing network. In particular, the degradation of communication quality occurs when the radio channel used by the new radio multi-hop network and the radio channel used by the existing network are the same. Hereinafter, the case where the communication quality is deteriorated will be described in detail with reference to FIGS.

  FIG. 1 is an explanatory diagram showing a configuration example of a plurality of wireless networks. In FIG. 1, network # 2 and network # 3 are shown as existing networks, and network # 1 is shown as a newly formed network.

  Further, as shown in FIG. 1, the network # 2 is formed by the node 22 # L and the node 22 # M, and uses the wireless channel 2 as a communication channel. The network # 3 is formed by the node 22 # O, the node 22 # P, and the node 22 # Q, and uses the wireless channel 3 as a communication channel.

  The network # 1 is formed by the nodes 20 # A to 20 # E according to an embodiment of the present invention. Also, the nodes 20 # A to 20 # E communicate with each other by a carrier sense type access method typified by the CSMA / CA method, for example.

  Here, when the wireless channel 2 is selected as the communication channel of the network # 1, the communication quality deteriorates due to, for example, a hidden terminal problem, and when the wireless channel 3 is selected, the communication quality deteriorates due to, for example, an exposed terminal problem. Hereinafter, the hidden terminal problem and the exposed terminal problem will be described with reference to FIGS. 2 and 3.

  FIG. 2 is an explanatory diagram showing the hidden terminal problem. As shown in FIG. 2, when the node 20 # B and the node 22 # L are in a positional relationship where each radio wave cannot be received, the node 20 # B and the node 22 # L transmit the frame regardless of the other frame transmission. Send.

  For this reason, as shown in FIG. 2, the frames transmitted by the node 20 # B and the node 22 # L collide at the node 20 # A due to the simultaneous transmission of the frames by the node 20 # B and the node 22 # L. Will occur. In the example shown in FIG. 2, the node 22 # L corresponds to the hidden terminal when viewed from the node 20 # B, and the node 22 # B corresponds to the hidden terminal when viewed from the node 20 # L.

  FIG. 3 is an explanatory diagram showing the exposed terminal problem. As shown in FIG. 3, when the node 20 # B and the node 22 # O are in a positional relationship where each radio wave can be received, when the node 20 # B senses the frame transmission by the node 22 # O, the frame transmission is performed. stand by.

  For this reason, as shown in FIG. 3, when a large number of frames are transmitted from the node 22 # O, the transmission opportunity of the node 20 # B is significantly reduced. Thus, the problem that the transmission opportunity decreases due to frame transmission by another node is called an exposed terminal problem.

  As described above, the communication quality of the newly formed network # 1 is adversely affected by the hidden terminal problem and the exposed terminal problem depending on the radio channel selected as the communication channel. For this reason, when a new network # 1 is formed, it is desired to select a radio channel with a wide usable bandwidth and a good channel quality, which is less affected by the hidden terminal problem and the exposed terminal problem.

  Incidentally, there is an infrastructure type wireless network shown in FIG. 4 as a form of a wireless network typified by a wireless LAN network that is currently widely used.

  FIG. 4 is an explanatory diagram showing a specific example of an infrastructure type wireless network. As shown in FIG. 4, the infrastructure type wireless network forms a star topology centering on the access point 26 that centrally manages the network. That is, each node 24 uses a link with the access point 26 even when communicating with any node. Therefore, in the infrastructure type wireless network, each node 24 can estimate the available bandwidth by measuring the throughput with the access point 26.

  However, in the wireless multi-hop network, as shown in FIG. 1, it is not determined which node each node 20 communicates with. For this reason, there is a problem that it is difficult to estimate the communication quality (available bandwidth) of the entire wireless multi-hop network simply by estimating the link quality between each node 20 and a specific node 20. .

  In view of the above circumstances, the node 20 according to an embodiment of the present invention has been created. According to the node 20 according to an embodiment of the present invention, for each radio channel, the link quality with other nodes constituting the same network can be efficiently calculated in consideration of hidden terminals and exposed terminals. Can do. Hereinafter, the configuration and operation of the node 20 will be described in detail.

<2. Node configuration>
(Organization of terms)
First, prior to the description of the node configuration, some of the terms used in this specification will be described. The following explanation is an example of the meaning of each term, and the meaning of each term is not limited to the following explanation.
-Ideal environment An environment where there is no frame transmission by another node and there is no transmission frame failure as seen from a certain node.
-Available bandwidth ratio AB
This is the ratio of the transmission amount per unit time of the broadcast frame in the real environment to the transmission amount per unit time of the broadcast frame in the ideal environment. For this reason, in a wireless network using the CSMA / CA access scheme, the closer the available bandwidth ratio is to 1, the more frame transmission opportunities that can be acquired.
・ Communication bandwidth ratio CB
This is the ratio of the amount of successful reception per unit time of the broadcast frame in the real environment to the amount of transmission per unit time of the broadcast frame in the ideal environment.
・ Transmission success rate FS
This is the ratio of the amount of received frames to the amount of transmitted frames. It is equivalent to (communication bandwidth ratio CB) / (available bandwidth ratio AB) and 1-FER (Frame Error Ratio). The transmission success rate FS means that the closer the value is to 1, the closer the number of received frames is to the number of transmitted frames. In other words, the transmission success rate FS means that the closer the value is to 1, the better the communication state is.
・ Radio link quality (#X)
This is the quality of a radio link for a node 20 # X at a certain node 20.

  FIG. 5 is a functional block diagram showing the configuration of the node 20 according to an embodiment of the present invention. As illustrated in FIG. 5, the node 20 includes an antenna 216, a communication unit 220, a communication control unit 224, a calculation unit 230, and a reception status acquisition unit 236. Further, the calculation unit 230 includes a transmission amount measurement unit 232, an availability rate calculation unit 234, a communication rate calculation unit 238, a transmission success rate calculation unit 240, a link quality calculation unit 242, and a channel quality calculation unit 244.

  The antenna 216 receives a radio signal from the surrounding node 20, acquires an electrical high-frequency signal, and supplies the high-frequency signal to the communication unit 220. Further, the antenna 216 transmits a radio signal to the surrounding nodes 20 based on the high frequency signal supplied from the communication unit 220. 5 illustrates an example in which the node 20 includes one antenna 216, the node 20 may include a plurality of antennas and may support MIMO (Multiple Input Multiple Output) communication and diversity communication. .

  The communication unit 220 acquires a received frame by performing demodulation and decoding of the high-frequency signal supplied from the antenna 216. The communication unit 220 also encodes and modulates the transmission frame, converts the transmission frame into a high frequency signal, and supplies the high frequency signal to the antenna 216. Note that the communication unit 220 performs reception processing and transmission processing so that wireless signals are transmitted and received through the wireless channel instructed by the communication control unit 224.

  The communication control unit 224 controls overall communication by the communication unit 220, such as selection of a communication channel and generation of a transmission frame.

  The calculation unit 230 and the reception status acquisition unit 236 are based on the frame length L (Bytes) of the broadcast frame acquired in advance and the maximum transmission amount Tx_real per unit time of the broadcast frame (frame length L) in the ideal environment. The radio link quality and channel quality of the node 20 are calculated.

(Determining the frame length)
The frame length L (Byte) of the broadcast frame may be determined depending on the characteristics of the application using the wireless multi-hop network. For example, when it is assumed that an average L_avg (Bytes) frame transmission / reception occurs in the entire network by the application, the frame length L may be L = L_avg.

(Measurement of maximum transmission amount Tx_real in ideal environment)
In addition, the maximum transmission amount Tx_real per unit time of a broadcast frame in an ideal environment can be measured using, for example, an anechoic chamber. Further, examples of the maximum transmission amount Tx_real include the number of transmission frames per unit time and throughput. In the following description, it is assumed that the maximum transmission amount Tx_real is the number of transmission frames. The maximum transmission amount Tx_real greatly depends on the transmission rate of the physical layer. Therefore, the maximum transmission amount Tx_real is measured for each transmission rate of the broadcast frame used for calculating the radio link quality and the channel quality.

  In the present specification, first to third examples will be described as examples for calculating radio link quality and channel quality. In the first to third examples, as described below, the maximum transmission amount Tx_real that should be measured in advance is different.

  The first example is an example when it is assumed that a fixed transmission rate R_fix (Bytes / s) is used by the node 20 in the network # 1. For this reason, in the first example, the maximum transmission amount Tx_real of the broadcast frame at the transmission rate R_fix in the ideal environment is measured in advance.

  The second example is an example when it is assumed that a plurality of transmission rates are appropriately changed and used by the node 20 in the network # 1. For this reason, in the second example, the maximum transmission amount Tx_real of the broadcast frame in the ideal environment is measured in advance for each of a plurality of transmission rates. According to the second example, the maximum transmission amount Tx_real at the most frequently used transmission rate among the maximum transmission amount Tx_real for each transmission rate measured in advance is used to calculate the usable bandwidth rate. Hereinafter, the maximum transmission amount per unit time at the transmission rate R is expressed as Tx_real [R].

  The third example is an example when it is assumed that a plurality of transmission rates are appropriately changed and used by the node 20 in the network # 1. For this reason, in the third example, as in the second example, the maximum transmission amount Tx_real of the broadcast frame in the ideal environment is measured in advance for each of a plurality of transmission rates. The difference from the second example is that the available bandwidth ratio is calculated by using the maximum transmission amount Tx_real for each transmission rate measured in advance.

  Below, the structure of the calculation part 230 and the reception condition acquisition part 236 is demonstrated as what obtained the maximum transmission amount Tx_real shown in FIG. 6 by said prior measurement.

(Measurement of maximum transmission amount Tx in real environment)
The communication control unit 224 selects one radio channel, causes the communication unit 220 to transmit a broadcast frame at the transmission rate R, and the transmission amount measurement unit 232 determines the maximum transmission amount per unit time at the transmission rate R of the broadcast frame. Tx [R] is measured.

  Specifically, in the first example, a fixed transmission rate R_fix is used as the transmission rate R of the broadcast frame, and the maximum transmission amount Tx [R_fix] in the real environment is measured.

  In the second example, the maximum transmission amount Tx at the transmission rate with the highest use frequency among the plurality of transmission rates is measured. As shown in FIG. 7, the usage rate of the transmission rate R1 is 10%, the usage rate of the transmission rate R2 is 30%, the usage rate of the transmission rate R3 is 40%, and the usage rate of the transmission rate R1. Is 20%, the maximum transmission amount Tx [R3] at the transmission rate R3 with the highest use frequency is measured. In addition, when the node 20 has recorded the usage history of each transmission rate, you may acquire the usage frequency of each transmission rate from the said usage history.

  In the third example, the maximum transmission amounts Tx [R1], Tx [R2], Tx [R3], and Tx [R4] at each of the transmission rates R1 to R4 are measured. Hereinafter, the description will be made assuming that the measurement result shown in FIG. 8 is obtained.

(Calculation of available bandwidth ratio AB)
The available rate calculation unit 234 calculates an available bandwidth rate AB (0 ≦ AB ≦ 1) from the maximum transmission amount Tx_real in the ideal environment and the maximum transmission amount Tx in the real environment. Specifically, in each of the first to third examples, the available bandwidth ratio AB is calculated as follows. U (R) means the frequency of use of the transmission rate R.

First example AB = Tx [R_fix] / Tx_real [R_fix]

Second example AB = Tx [R] / Tx_real [R] (R that maximizes U [R])
= Tx [R3] / Tx_real [R3]

・ Third example

AB = Σ ((Tx [R] / Tx_real [R]) × U [R]) (ΣU [R] = 1)
= (Tx [R1] / Tx_real [R1]) × U [R1]
+ (Tx [R2] / Tx_real [R2]) × U [R2]
+ (Tx [R3] / Tx_real [R3]) × U [R3]
+ (Tx [R4] / Tx_real [R4]) × U [R4]

  Therefore, when the measurement results shown in FIGS. 6 to 8 are used, the following available bandwidth ratio AB is calculated in each of the first to third examples.

First example AB = Tx [R1] / Tx_real [R1]
= 135/160
≒ 0.84 (when R_fix = R1)
AB = Tx [R2] / Tx_real [R2]
= 65/80
≒ 0.81 (when R_fix = R2)
AB = Tx [R3] / Tx_real [R3]
= 25/40
≈ 0.63 (when R_fix = R3)
AB = Tx [R4] / Tx_real [R4]
= 15/20
= 0.75 (when R_fix = R4)

Second example AB = Tx [R3] / Tx_real [R3]
≒ 0.63

Third example AB = (Tx [R1] / Tx_real [R1]) × U [R1]
+ (Tx [R2] / Tx_real [R2]) × U [R2]
+ (Tx [R3] / Tx_real [R3]) × U [R3]
+ (Tx [R4] / Tx_real [R4]) × U [R4]
= (135/160) x 0.1
+ (65/80) x 0.3
+ (25/40) x 0.4
+ (15/20) x 0.2
≒ 0.73

As described above, the node 20 can calculate the available bandwidth ratio AB by transmitting a broadcast frame. Here, by using a broadcast frame instead of a unicast frame, for example, the following remarkable effects can be obtained.
(1) When a broadcast frame is used, the available bandwidth ratio AB can be calculated by the node 20 alone without preparing a communication partner.
(2) When a unicast frame is used, it is assumed that transmission is stopped unless an ACK is received from a communication partner. In this case, the maximum transmission amount Tx cannot be accurately calculated.

(Calculation of communicable bandwidth ratio CB)
The available bandwidth ratio AB calculated as described above is useful as a material for determining the status of the radio channel. However, in a real environment, the frame transmitted by the node 20 may not be normally received at the counterpart node. In particular, when the communication medium is wireless, there are many cases where a frame cannot be normally received at the counterpart node as compared to the wired case.

  Therefore, in the present embodiment, the communicable bandwidth ratio CB is calculated in consideration of the reception status of the counterpart node. Specifically, for example, when a broadcast frame is transmitted from the node 20 # B to calculate the communicable bandwidth ratio CB, as shown in FIG. 9, the reception status acquisition unit 236 of each node 20 Get the reception status of and record it. Each node 20 constituting the network # 1 operates using the same radio channel.

  Thereafter, the communication control unit 224 of each node 20 feeds back the broadcast frame reception status from the communication unit 220 to the node 20 # B. As the reception status, as shown in FIG. 10, the number of received frames per unit time for each transmission rate, average received RSSI (Received Signal Strength Indicator), average received frame length (= broadcast frame length L), etc. Is given.

  Further, the feedback of the reception status may be performed by unicast to the transmission source of the broadcast frame, or may be performed by broadcast describing the transmission source.

  The communicable rate calculation unit 230 calculates the communicable bandwidth rate CB [X] for the node 20 # X (any node forming the same network) from the reception status thus obtained and the maximum transmission amount Tx_real in the ideal environment. calculate. Specifically, in each of the first to third examples, the communicable bandwidth ratio CB is calculated as follows. Rx [#X, R] means the number of received frames per unit time at the node 20 # X at the transmission rate R.

First Example CB [#X] = Rx [#X, R_fix] / Tx_real [R_fix]

Second example CB [#X] = Rx [# X, R] / Tx_real [R]
(R that maximizes U [R])
= Rx [# X, R3] / Tx_real [R3]

Third Example CB [#X] = Σ ((Tx [# X, R] / Tx_real [R]) × U [R])
(ΣU [R] = 1)
= (Rx [# X, R1] / Tx_real [R1]) × U [R1]
+ (Rx [# X, R2] / Tx_real [R2]) × U [R2]
+ (Rx [# X, R3] / Tx_real [R3]) × U [R3]
+ (Rx [# X, R4] / Tx_real [R4]) × U [R4]

  Therefore, when the measurement results shown in FIG. 6 and the reception status shown in FIG. 10 are used, the following communicable bandwidth ratio CB [#X] is calculated in each of the first to third examples. .

First Example CB [#X] = Rx [#X, R1] / Tx_real [R1]
= 130/160
≒ 0.81 (when R_fix = R1)
CB [#X] = Rx [#X, R2] / Tx_real [R2]
= 60/80
= 0.75 (when R_fix = R2)
CB [#X] = Rx [#X, R3] / Tx_real [R3]
= 20/40
= 0.5 (when R_fix = R3)
CB [#X] = Rx [#X, R4] / Tx_real [R4]
= 10/20
= 0.5 (when R_fix = R4)

Second example CB [#X] = Rx [#X, R3] / Tx_real [R3]
= 20/40
= 0.5

Third Example CB [#X] = (Rx [#X, R1] / Tx_real [R1]) × U [R1]
+ (Rx [# X, R2] / Tx_real [R2]) × U [R2]
+ (Rx [# X, R3] / Tx_real [R3]) × U [R3]
+ (Rx [# X, R4] / Tx_real [R4]) × U [R4]
= (130/160) x 0.1
+ (60/80) x 0.3
+ (20/40) x 0.4
+ (10/20) x 0.2
≒ 0.61

  As described above, the node 20 can calculate the communicable bandwidth ratio CB by transmitting a broadcast frame and receiving the reception status from surrounding nodes. According to this quantitative evaluation, even when there are a plurality of surrounding nodes, it is possible to calculate the communicable bandwidth ratio CB for each node by transmitting a broadcast frame once. Is more efficient than sending

  In particular, in a wireless multi-hop network, the communication partner differs depending on which node communicates with, and the communication partner changes from moment to moment according to the movement of the node and the state of the radio channel. Therefore, as in the method of calculating the communicable bandwidth CB according to the present embodiment, it is possible to efficiently obtain the communicable bandwidth CB while suppressing overhead compared to a method using unicast communication. It is extremely effective in the network.

(Calculation of transmission success rate FS)
The transmission success rate calculation unit 240 uses the available bandwidth rate AB calculated by the available rate calculation unit 234 and the communicable bandwidth rate CB calculated by the communication possible rate calculation unit 238 as the received frame amount with respect to the transmission frame amount. A certain transmission success rate FS is calculated. Specifically, in each of the first to third examples, the transmission success rate FS is calculated as follows. Note that FS [#X] means a frame transmission success rate for the node 20 # X.

First example FS [#X] = CB [#X] / AB
= 0.81 / 0.84
≈ 0.96 (when R_fix = R1)
FS [#X] = CB [#X] / AB
= 0.75 / 0.81
= 0.93 (when R_fix = R2)
FS [#X] = CB [#X] / AB
= 0.5 / 0.63
= 0.79 (when R_fix = R3)
FS [#X] = CB [#X] / AB
= 0.5 / 0.75
= 0.67 (when R_fix = R4)

Second example FS [#X] = CB [#X] / AB
= 0.5 / 0.63
= 0.79

Third example FS [#X] = CB [#X] / AB
= 0.61 / 0.73
= 0.84

  In the above description, an example in which the transmission success rate calculation unit 240 calculates the transmission success rate FS from the available bandwidth rate AB and the communicable bandwidth rate CB has been described. However, the method for calculating the transmission success rate is not limited to this example. . For example, the transmission success rate calculation unit 240 may calculate the transmission success rate FS from the maximum transmission amount Tx measured by the transmission amount measurement unit 232 and the reception amount Rx fed back from the node 20 # X.

(Calculation of radio link quality)
Here, the relationship between the usable bandwidth rate AB and the transmission success rate FS described above, and the exposed terminal problem and the hidden terminal problem will be examined.

  As shown in FIG. 3, when the node 20 # B corresponds to the exposed terminal of the node 22 # O, the frame transmission from the node 20 # B to the node 20 # A is the same as the frame transmission from the node 22 # O. Access competition due to CSMA / CA occurs. For this reason, it is expected that the transmission opportunity of the node 20 # B decreases and the usable bandwidth AB of the node 20 # B also decreases. That is, the available bandwidth ratio AB is a value that depends on the influence of the exposed terminal, and can also be regarded as a parameter indicating the degree of the influence of the exposed terminal.

  On the other hand, as illustrated in FIG. 2, when the node 22 # L exists as a hidden terminal of the node 20 # B, the frame transmission success rate FS from the node 20 # B to the node 20 # A is the node 22 # L. It is expected to decrease due to a collision with a frame transmitted from. That is, the transmission success rate FS is a value that depends on the influence of the hidden terminal, and can also be regarded as a parameter indicating the degree of the influence of the hidden terminal.

  Therefore, in this embodiment, by using both the available bandwidth rate AB and the transmission success rate FS, the radio link quality LQ [#X] and the radio channel quality considering the degree of influence of the hidden terminal and the exposed terminal are set. calculate. Specifically, the link quality calculation unit 242 calculates the radio link quality LQ [#X] by weighting and adding the available bandwidth rate AB and the transmission success rate FS according to the following formula.

    LQ [#X] = AB × α + FS [#X] × (1−α) (0 ≦ α ≦ 1)

  In the above equation, α is a weighting factor that determines the dependence of the radio link quality LQ on the influence of hidden terminals and the influence of exposed terminals. For example, if the weighting factor α is increased, the influence of the terminal is greatly reflected on the radio link quality LQ, and if the weighting factor α is decreased, the influence of the hidden terminal is greatly reflected on the radio link quality LQ. It becomes like this. Moreover, the setting method of this weighting coefficient (alpha) is not specifically limited. For example, the operator may set the weighting factor α according to the purpose, or the node 20 may dynamically set the weighting factor α based on the network topology or the like.

  Therefore, when weighting factor α = 0.5, the following radio link quality LQ [#X] is calculated in each of the first to third examples.

First example LQ [#X] = 0.84 × 0.5 + 0.96 × 0.5
≈ 0.9 (when R_fix = R1)
LQ [#X] = 0.81 × 0.5 + 0.93 × 0.5
= 0.87 (when R_fix = R2)
LQ [#X] = 0.63 × 0.5 + 0.79 × 0.5
= 0.71 (when R_fix = R3)
LQ [#X] = 0.75 × 0.5 + 0.67 × 0.5
= 0.71 (when R_fix = R4)

Second example LQ [#X] = 0.63 × 0.5 + 0.79 × 0.5
= 0.71

Third example LQ [#X] = 0.73 × 0.5 + 0.84 × 0.5
= 0.79

  As described above, the link quality calculation unit 242 calculates the radio link quality LQ between adjacent nodes in a form that takes into account the effects of hidden terminals and exposed terminals. For example, the link quality calculation unit 242 of the node 20 # B illustrated in FIG. 1 performs the radio link quality LQ with the nodes 20 # A, 20 # C, 20 # D, and 20 # E that form the same network. Is calculated.

(Calculation of radio channel quality CQ)
The channel quality calculation unit 244 of the node 20 # X first calculates the radio channel quality CQ [#X] at the node 20 # X based on the radio link quality LQ between adjacent nodes calculated by the link quality calculation unit 242. calculate. Then, channel quality calculation section 244 acquires radio channel quality CQ [#] at adjacent nodes forming the same radio network, radio channel quality CQ [#] at adjacent nodes, and radio channel quality CQ at node 20 # X. The final radio channel quality CQ is calculated based on [#X].

  Furthermore, the wireless channel quality CQ can be calculated for each wireless channel by each node 20 configuring the network sequentially changing the wireless channel and performing the processing described above. As a result, based on the radio channel quality CQ for each radio channel, it is possible to select a radio channel having the widest available bandwidth and good communication quality as a communication channel. Hereinafter, the calculation method of the radio channel quality CQ [#X] and the final radio channel quality CQ in the node 20 # X will be specifically described.

  First, channel quality calculation section 244 calculates radio channel quality CQ [#X] at node 20 # X as follows. Note that LQ [#X, #Y] means the radio link quality for the node #Y in the node 20 # X.

CQ [#X] = Σ (LQ [# X, m]) / number of nodes adjacent to node 20 # X
(Node m is all nodes adjacent to node 20 # X)

  That is, the channel quality calculation unit 244 of the node 20 # X calculates the radio channel quality CQ [#X] at the node 20 # X by averaging the radio link quality LQ for all the nodes adjacent to the node 20 # X. To do. Therefore, for example, the channel quality calculation unit 244 of the node 20 # B illustrated in FIG. 1 calculates the radio channel quality CQ [#B] as follows.

CQ [#B] = (LQ [#B, #A] + LQ [#B, #C]
+ LQ [#B, #D] + LQ [#B, #E]) / 4

  All the nodes 20 constituting the same wireless network can transmit the wireless channel quality CQ [#] in each node 20 calculated by the channel quality calculation unit 244 as described above by unicast, broadcast, or flooding to a specific node. Send. Thereby, each node 20 or a specific node can acquire the radio channel quality CQ [#] in all the nodes 20 configuring the same radio network.

  Then, the node 20 # X that has acquired the radio channel quality CQ [#] in all the nodes 20 configuring the same radio network averages the radio channel quality CQ [#] in all the nodes 20 as shown below. Thus, the final radio channel quality CQ is calculated.

CQ = Σ (CQ [n]) / total number of nodes present in the network
(Node n is all nodes existing in the network)

  Alternatively, when the traffic quality of each node 20 can be predicted, the channel quality calculation unit 244 of the node 20 # X can determine the radio channel quality CQ in each node 20 according to the traffic volume of each node 20 as shown below. The radio channel quality CQ may be calculated by weighting [#].

CQ = Σ (β [n] × CQ [n]) / total number of nodes existing in the network
(Β [n] = T [n] / Σ (T [p]))

  Here, β [n] is a value obtained by normalizing the traffic amount T [n] of the node n by the total traffic amount Σ (T [p]). Therefore, Σβ [n] = 1 is satisfied.

(Modification)
The radio channel quality CQ calculated by the method described above is a value depending on the radio link quality of all radio links (bidirectional) constituting the network. Therefore, when it is expected that all wireless links constituting the network will be used during actual network operation as shown in FIG. 11, it is effective to calculate the wireless channel quality CQ by the above method.

  On the other hand, as shown in FIG. 12, when traffic is concentrated on some radio links and it is expected that some radio links will not be used during actual network operation, the radio link quality of the radio links that are not used is It is not always preferable to be reflected in the radio channel quality CQ.

  Therefore, the channel quality calculation unit 244 of the node 20 # X calculates the radio channel quality CQ [#X] at the node 20 # X by a method according to the traffic flow when the traffic during network operation can be predicted. Also good. Specifically, the channel quality calculation unit 244 of the node 20 # X, as shown below, performs the radio link quality [#X for the node #N expected as the frame transmission destination from the node 20 # X during network operation. , #N], radio channel quality CQ [#X] may be calculated.

    CQ [#X] = LQ [#X, #N]

  Therefore, for example, as shown in FIG. 12, when traffic is expected to concentrate on the radio link between the node 20 # B and the node 20 # E, the channel quality calculation unit 244 of the node 20 # B Quality CQ [#B] is calculated as follows.

    CQ [#B] = LQ [#B, #E]

  With this configuration, it is possible to calculate the radio channel quality CQ reflecting the radio link quality of the radio link used during actual network operation, so it is possible to select a radio channel more appropriately. Note that traffic during network operation may be predicted by operating the network on any one of the radio channels on a trial basis.

(Selection of radio channel and use as communication channel)
Based on the radio channel quality CQ for each radio channel calculated by the channel quality calculation unit 244, the node 20 selects the radio channel with the best quality as the communication channel. Then, the communication channel is changed to the selected radio channel together with other nodes 20 constituting the same network.

  Note that the node 20 may transmit information indicating the radio channel selected as the communication channel and the change timing to the radio channel to other nodes 20 configuring the same network. For example, the node 20 may transmit the information by unicast, may be transmitted by broadcast, or may be transmitted by flooding.

  Thereby, the plurality of nodes 20 constituting the same network can grasp the new radio channel and the change timing to the new radio channel, and can simultaneously change the communication channel to the new radio channel.

<3. Node operation>
The configuration of the node 20 according to the present embodiment has been described above. Next, the operation of the node 20 according to the present embodiment will be described with reference to FIG.

  FIG. 13 is a flowchart showing the operation of the node 20 according to the present embodiment. As shown in FIG. 13, first, the node 20 determines the frame length L of the broadcast frame (S304). Subsequently, the node 20 measures the maximum transmission amount Tx_real of the broadcast frame in the ideal environment (S308). The measurement of the maximum transmission amount Tx_real may be performed at each node 20 or may be performed at one node 20. In the latter case, each node 20 calculates each parameter using the maximum transmission amount Tx_real measured in one node 20.

  Then, the node 20 selects one radio channel from among a plurality of available radio channels, and sets the selected radio channel as a communication channel together with other nodes 20 configuring the same network (S312). Thereafter, each node 20 sequentially transmits a broadcast frame (S316), and measures the maximum transmission amount Tx in the real environment (S320). Further, the available rate calculation unit 234 of each node 20 calculates the available bandwidth rate AB from the maximum transmission amount Tx_real and the maximum transmission amount Tx (S324).

  Each node 20 acquires the received frame amount Rx from each of the broadcast frame recipients (S328). Then, the communicable rate calculator 238 of each node 20 calculates the communicable bandwidth CB from the maximum transmission amount Tx_real and the received frame amount Rx (S332). Further, the transmission success rate calculation unit 240 of each node 20 calculates the transmission success rate FS from the available bandwidth rate AB and the communicable bandwidth rate CB (S336).

  Thereafter, the link quality calculation unit 242 of each node 20 calculates the radio link quality LQ of each link from the available bandwidth rate AB and the transmission success rate FS (S340). Then, the channel quality calculation unit 244 of each node 20 calculates the radio channel quality CQ [#] in each node 20 based on the radio link quality LQ of each link calculated by the link quality calculation unit 242, and Based on the radio channel quality CQ [#] at the node 20, the radio channel quality CQ in the network is calculated (S344).

  Subsequently, when all the radio channels have been selected and the radio channel quality CQ of all the radio channels is obtained, the radio channel having the best radio channel quality is selected as the communication channel (S356). On the other hand, when there is an unselected radio channel, the unselected radio channel is selected as a communication channel, and the processing from S316 is repeated (S352).

  In the above description, an example in which the node 20 performs each process illustrated in the flowchart of FIG. 13 has been described. However, a part of the process illustrated in the flowchart of FIG. 13 may be performed manually. For example, the determination of the frame length of the broadcast frame shown in S304, the selection of the radio channel shown in S312, S352, S356, etc. may be performed manually by the operator.

<4. Summary>
As described above, according to an embodiment of the present invention, by using both the available bandwidth rate AB and the transmission success rate FS, the radio link quality LQ considering the degree of influence of hidden and exposed terminals, and Radio channel quality can be calculated.

  Further, according to an embodiment of the present invention, the node 20 can calculate the available bandwidth ratio AB by transmitting a broadcast frame. When a broadcast frame is used, it is effective in that the available bandwidth ratio AB can be calculated by the node 20 alone without preparing a communication partner.

  Furthermore, according to an embodiment of the present invention, the communicable bandwidth ratio CB can be calculated by transmitting a broadcast frame and receiving the reception status from surrounding nodes. According to this quantitative evaluation, even when there are a plurality of surrounding nodes, it is possible to calculate the communicable bandwidth ratio CB for each node by transmitting a broadcast frame, so a unicast frame is transmitted to each node. This is more efficient than

  Although the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

  For example, each step in the processing of the node 20 in this specification does not necessarily have to be processed in time series in the order described in the flowchart. For example, each step in the processing of the node 20 may be processed in an order different from the order described as the flowchart, or may be processed in parallel.

  In addition, it is possible to create a computer program for causing hardware such as a CPU, a ROM, and a RAM built in the node 20 to perform the same functions as the components of the node 20 described above. A storage medium storing the computer program is also provided.

216 antenna 220 communication unit 224 communication control unit 230 calculation unit 232 transmission amount measurement unit 234 availability rate calculation unit 236 reception status acquisition unit 238 communication rate calculation unit 240 transmission success rate calculation unit 242 link quality calculation unit 244 channel quality calculation unit

Claims (12)

A communication unit that communicates with one or more wireless communication devices forming the same wireless network;
A communication control unit for transmitting a broadcast frame from the communication unit in a carrier sense type access method;
Based on the transmission amount of the broadcast frame per unit time and the reception amount of the broadcast frame per unit time in each of the one or more wireless communication devices, and each of the one or more wireless communication devices A calculation unit for calculating the radio link quality between
A wireless communication device.   The calculation unit includes an available bandwidth ratio that is a ratio of a transmission amount per unit time of the broadcast frame in a real environment to a transmission amount per unit time of the broadcast frame in an ideal environment, and a per unit time of the broadcast frame. The radio link quality is calculated by weighting and adding a transmission success rate that is a ratio of a reception amount per unit time of the broadcast frame in each of the one or two or more wireless communication apparatuses to a transmission amount. A wireless communication device according to 1. The communication control unit transmits the broadcast frame at a transmission rate of 1 from the communication unit,
The radio communication apparatus according to claim 2, wherein the calculation unit calculates the radio link quality by weighted addition of the available bandwidth rate and the transmission success rate at the transmission rate of 1.   The wireless communication apparatus according to claim 3, wherein the communication control unit causes the communication unit to transmit the broadcast frame at a transmission rate having the highest use frequency among a plurality of transmission rates. The communication control unit causes the broadcast unit to transmit the broadcast frame at a plurality of transmission rates,
The radio communication apparatus according to claim 2, wherein the radio link quality is calculated by weighted addition of the integrated value of the available bandwidth ratio and the integrated value of the transmission success rate at each of the plurality of transmission rates.   The said calculation part calculates the channel quality in the said radio | wireless communication apparatus based on at least any one of the radio link quality between each of the said 1 or 2 or more radio | wireless communication apparatuses. The wireless communication device described.   The calculation unit calculates channel quality in the wireless network based on the channel quality calculated in the one or more wireless communication devices and the channel quality calculated in the wireless communication device. A wireless communication device according to 1. The communication control unit transmits a broadcast frame from the communication unit through a plurality of radio channels,
The wireless communication device according to claim 7, wherein the calculation unit calculates channel quality in the wireless network in each of the plurality of wireless channels.   The radio communication apparatus according to claim 8, wherein the communication control unit selects a radio channel having the best channel quality in the radio network calculated by the calculation unit as a use channel. A wireless communication system comprising a plurality of wireless communication devices forming the same wireless network, wherein:
Each of the plurality of wireless communication devices is
A communication unit that communicates with other wireless communication devices;
A communication control unit for transmitting a broadcast frame from the communication unit in a carrier sense type access method;
Radio link quality with each of the other wireless communication devices based on the transmission amount of the broadcast frame per unit time and the reception amount of the broadcast frame per unit time in each of the other wireless communication devices A calculating unit for calculating
A wireless communication system. Computer
A communication unit that communicates with one or more wireless communication devices forming the same wireless network;
A communication control unit for transmitting a broadcast frame from the communication unit in a carrier sense type access method;
Based on the transmission amount of the broadcast frame per unit time and the reception amount of the broadcast frame per unit time in each of the one or more wireless communication devices, and each of the one or more wireless communication devices A calculation unit for calculating the radio link quality between
Program to function as Transmitting a broadcast frame by a carrier sense type access method;
Based on the transmission amount of the broadcast frame per unit time and the reception amount of the broadcast frame per unit time in each of the surrounding wireless communication devices, the wireless link quality with the surrounding wireless communication device is calculated. Steps and;
A wireless communication method.

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