JP2009177481A - Radio communication apparatus, radio communication system, and, radio communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio communication apparatus capable of selecting an optimal modulation system regardless of the effect of a hidden terminal problem in a wireless ad-hoc network. <P>SOLUTION: A radio communication apparatus 111, which connects a link mutually to perform direct communication, comprises: a radio communication unit 201 for periodically receiving from a neighboring radio communication apparatus information about the neighboring radio communication apparatus; a storage unit 202 for holding information corresponding to the neighboring radio communication apparatus that is a transmission source of the information; and a collision rate determination unit 203 for determining a radio communication apparatus in a hidden terminal relation based on the held information in the storage unit 202 and the information received by the radio communication unit 201, and estimating a probability of occurrence of a collision due to the hidden terminal, to obtain an index of a communication property of the link based on the estimated collision occurrence probability. The radio communication apparatus 111 further includes a modulation system selection unit 204 for selecting a modulation system on the basis of the obtained index, and determines the modulation system. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

As is well known, in wireless communication, communication quality such as a signal error rate, a large amount of noise, a signal transmission speed, and the like varies depending on a radio wave propagation distance and interference.
Accordingly, in wireless communication (wireless network), a plurality of modulation schemes are prepared, and a suitable one can be selected according to the situation.
That is, BPSK (Binary Phase Shift Keying), QPSK (Quadrature Phase Shift Keying), 16QAM (16-position Quadrature Amplitude Modulation), etc. are selectively used. Applied.

In general, a modulation scheme with a lower transmission speed has better noise resistance and minimum reception sensitivity, and conversely, a modulation scheme with a higher transmission speed tends to have lower noise tolerance and minimum reception sensitivity.
For this reason, when a wireless communication link is established, an optimum modulation method is selected in consideration of communication quality.
That is, a modulation method with a relatively high transmission speed is applied under conditions where communication quality is easily maintained, and conversely, transmission conditions are relatively low under conditions where communication quality is difficult to maintain due to the influence of obstacles. Communication quality is maintained by applying a slow modulation method.
As described above, a technique for maintaining communication quality by adopting adaptive modulation that selects an optimal modulation scheme according to conditions has been proposed (Non-Patent Document 1).

  The technique disclosed in Non-Patent Document 1 takes statistics regarding whether communication has succeeded or failed, compares the number of successes or failures with a certain threshold, and if the number of successes is relatively small, Switch to a modulation method with a slow one-step speed. Conversely, if the number of successes is relatively high, try to switch the modulation method to a modulation method with a fast one-step speed, and select the optimal modulation method. is there.

On the other hand, in wireless communication such as a wireless LAN that can be used without being restricted by the Radio Law, a technique called carrier sense is employed to avoid interference.
Carrier sense refers to autonomously performing mutual carrier sense (detection of the presence or absence of carrier wave radiation) between wireless communication devices that plan to communicate with each other prior to the transmission of data that is the original purpose of communication. This is a technique for maintaining communication quality in wireless communication such as wireless packet communication by avoiding occurrence of wireless communication collision by determining whether or not transmission is possible.

This method is defined in the IEEE 802.11 standard as an access control method called CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) in which a plurality of wireless communication apparatuses transmit data while performing carrier sense so that packet collision does not occur. Has been.
However, in wireless communication (wireless network), carrier sense may not function due to the propagation distance of radio waves or the presence of obstacles, and communication quality may not be maintained (or communication may not be possible).
That is, peripheral devices other than the mutual wireless communication devices perform data transmission by carrier sense performed before transmission / reception of data (packet data) originally intended for communication between wireless communication devices to which CSMA / CA is applied. However, there is a possibility that carrier sense cannot be performed due to the propagation distance of the radio wave or the presence of an obstacle.

  Referring to FIG. 1 showing the wireless communication system of the present invention, this phenomenon will be described. For example, for the four wireless communication devices 111, 112, 113, and 114 in the arrangement shown in FIG. When the possible areas are circles 131, 132, 133, and 134 shown by broken lines, the wireless communication apparatus 111 and the wireless communication apparatus 112 can communicate with each other, while the wireless communication apparatus 111 and the wireless communication apparatus communicate with each other. There may be a situation where carrier sense cannot be performed with the device 113.

In such a case, the mutual wireless communication devices 111 determine that the wireless channel is free even when the wireless communication device 113 is communicating with the wireless communication device 112, and transmit data. Therefore, there arises a problem that communication quality is significantly lowered due to communication collision.
Here, such a problem is referred to as a hidden terminal problem, and a terminal (wireless communication apparatus) that causes the hidden terminal problem is referred to as a hidden terminal.

When applying adaptive modulation as disclosed in Non-Patent Document 1 under conditions where the hidden terminal problem is likely to occur, communication failure due to the hidden terminal problem, or general radio wave propagation distance and obstacles It is not possible to determine whether the communication has failed due to signal deterioration caused by the presence of an object.
For this reason, in the case of the adaptive modulation disclosed in Non-Patent Document 1, communication failure is uniformly treated as communication failure due to signal degradation, and switching to a modulation method with a low communication speed is repeated.

However, when a modulation method with a low communication speed is applied, the time required to transmit the same amount of data is extended, and as a result, the chances of suffering a hidden terminal problem increase under conditions that are affected by the hidden terminal. For this reason, the probability of occurrence of communication failure due to signal collision as described above tends to increase, resulting in a vicious circle.
Several techniques for dealing with the hidden terminal problem have already been proposed. For example, a communication priority is set for each communication station (wireless communication device), and the difference between the frame interval of the communication station with the higher priority and the frame interval of the lower communication station is determined by RTS (Request To Send: transmission request). ) There is a proposal to set the time to be equal to or longer than the time required to complete reception of a CTS (Clear To Send) packet after the start of packet transmission (for example, Patent Document 1).

According to the disclosure of Patent Document 1, a communication station having a lower priority order can receive a CTS packet in response to a RTS packet transmitted from a communication station that is a hidden terminal for the local station. Since it is possible to receive and set a NAV (Network Allocation Vector) and wait for transmission, it is said that collision can be avoided correctly.
Further, in a wireless communication system in which a communication station (wireless communication apparatus) performs random access in a communication environment in which a plurality of communication channels are prepared, a communication station that transmits a packet assigns a communication channel in units of packets. This allows each communication station to autonomously perform random access operations based on carrier detection or media status monitoring such as CSMA (Carrier Sense Multiple Access) without having a relationship between the control station and the controlled station. There is also a proposal that a wireless network can be suitably constructed by avoiding the hidden terminal problem by performing in a distributed manner (for example, Patent Document 2).

JP 2006-41627 A (Summary, paragraphs 0037 to 0040, etc.) Japanese Patent Laying-Open No. 2006-42076 (Summary, paragraphs 0047 to 0053, etc.) “IEEE 802.11 Rate Adaptation: A Practical Approach,” INRIA Research Report No. 5208, May 2004.

The problem in the case of applying adaptive modulation in Non-Patent Document 1 described above is not treated as a technical problem in the disclosure of this document itself, and the possibility of causing the above-mentioned vicious circle is still unresolved.
On the other hand, the techniques of Patent Document 1 and Patent Document 2 also attempt to identify whether the deterioration of communication quality is due to a hidden terminal problem or due to the existence of a general radio wave propagation distance or an obstacle. There is no viewpoint, and therefore, the above-mentioned unsolved problems in Non-Patent Document 1 are not solved by applying the techniques of Patent Document 1 and Patent Document 2.
The present invention has been made in view of such a situation. A wireless communication apparatus, a wireless communication system, and a wireless communication apparatus that do not have a risk of facilitating deterioration of communication quality due to a hidden terminal problem while applying adaptive modulation. An object of the present invention is to provide a wireless communication method.

In order to solve the above problems, the present application proposes an apparatus and a method as listed below.
That is, one wireless communication device according to the present invention provides address information for identifying each corresponding wireless communication device in communication with another device that establishes a communication link for direct wireless communication with the own device and per unit time in the wireless communication. Wireless communication means for exchanging state announcements including communication state information representing transmission and reception occupancy ratios with other devices;
Storage means for holding state announcement data formed by said state announcement;
Based on the state announcement data stored in the storage means, the presence / absence of another device having a hidden terminal relationship with the own device is determined, and the hidden terminal and the own device are determined according to the determination result. A collision rate calculation means for calculating a collision rate related to communication;
A modulation method selection means for selecting a modulation method to be applied to a communication link between the own device and the other device based on the collision rate calculated by the collision rate calculation means;
It is characterized by having.

According to the wireless communication apparatus as described above, the presence / absence of another apparatus having a hidden terminal relationship with the own apparatus is determined based on the state announcement data stored in the storage unit, and the determination is made. Depending on the result, the collision rate relating to the communication between the hidden terminal and the device itself is calculated by the collision rate calculating means.
Based on the calculated collision rate, the modulation method selection means selects a modulation method to be applied to the communication link between the own device and the other device.
Therefore, even when communication quality deterioration is caused by hidden terminals, adaptive modulation is applied uniformly without distinguishing it from the case of general radio wave propagation distance or the presence of obstacles, thereby increasing communication quality deterioration. This effectively avoids such a problem.

Further, in the wireless communication device as described above, as one aspect thereof, the collision rate calculation means relates to one address information representing the address of each neighboring device related to the own device and one neighboring device related to the own device. Compare with other address information representing the address of each neighboring device based on the state announcement data held in the storage device, and from the comparison result, there is a hidden terminal relationship with the own device It is comprised so that it may have a hidden terminal determination means which determines the presence or absence of another apparatus.
By adopting such a configuration, the hidden terminal determination means has another terminal in a hidden terminal relationship with the own apparatus based on the one and other address information read from the state announcement data. It is possible to determine the presence or absence of the.

  In addition, as another aspect, the wireless communication device as described above may be configured such that the collision rate calculation means includes a value of a reception occupancy rate per unit time in communication of each adjacent device related to the own device and all of the related devices. It is comprised so that it may have a calculating means which calculates the collision rate in communication with the other apparatus which has the relationship of the said hidden terminal based on the total value of the transmission occupation rate per unit time in the communication which concerns on an adjacent apparatus.

By adopting such a configuration, the calculation means causes the value of the reception occupancy rate per unit time in communication of each adjacent device related to the own device and the unit time in communication related to all the adjacent devices related to the adjacent device. It is possible to calculate the collision rate in communication with other devices in the relationship of the hidden terminal based on the total value of the transmission occupancy rate per hit.
Therefore, the calculated collision rate can be applied as a selection criterion factor when selecting a modulation method to be applied to a communication link between the own device and the other device, and an appropriate modulation method can be selected. Is possible.

In addition, as another aspect, the wireless communication device as described above, the modulation method selection means, the collision rate data calculated by the collision rate calculation means and the corresponding communication for each other device is successful. A modulation scheme to be applied to the communication link is selected based on at least one of statistical data and failure statistical data.
By taking such a configuration, based on the collision rate data calculated by the collision rate calculation means and at least one of the statistical data of success and the statistical data of failure related to the communication for each other device concerned, Since the modulation method selection means selects a modulation method to be applied to the communication link, even when communication quality is deteriorated due to a hidden terminal, deterioration due to uniform application of the applied modulation method Will be avoided.

On the other hand, the wireless communication system of the present invention is configured to include a plurality of wireless communication devices that connect communication links for direct wireless communication, and the plurality of wireless communication devices include:
Corresponds to a state announcement including address information that identifies each of its own device and the wireless communication device that connects the device and the communication link, and communication state information that represents the occupancy rate of transmission and reception per unit time in the wireless communication Wireless communication means for sending and receiving with the wireless communication device;
Storage means for holding state announcement data formed by said state announcement;
Based on the state announcement data stored in the storage means, the presence / absence of another device having a hidden terminal relationship with the own device is determined, and the hidden terminal and the own device are determined according to the determination result. A collision rate calculation means for calculating a collision rate related to communication;
A modulation method selection means for selecting a modulation method to be applied to a communication link between the own device and the other device based on the collision rate calculated by the collision rate calculation means;
It is characterized by having each.

In the wireless communication system as described above, the presence / absence of another device having a hidden terminal relationship with the own device is determined based on the state announcement data stored in the storage unit of the wireless communication device. According to the determination result, the collision rate related to the communication between the hidden terminal and the own device is calculated by the collision rate calculating means.
Based on the calculated collision rate, the modulation method selection means selects a modulation method to be applied to the communication link between the own device and the other device.
Therefore, even when communication quality deterioration is caused by hidden terminals, adaptive modulation is applied uniformly without distinguishing it from the case of general radio wave propagation distance or the presence of obstacles, thereby increasing communication quality deterioration. This effectively avoids such a problem.

Further, the wireless communication system of the present invention includes a discriminating unit that discriminates whether the cause of the communication failure is due to the hidden terminal or the signal deterioration, and a selection unit that selects an optimum modulation method according to the discrimination result, It is comprised including.
In the wireless communication system, the determination unit determines whether the cause of the communication failure is caused by a hidden terminal or signal degradation, and the selection unit selects an optimal modulation method according to the determination result. .
For this reason, even when communication quality degradation is caused by a hidden terminal, adaptive modulation is applied uniformly without distinguishing it from the case of general radio wave propagation distance or the presence of an obstacle to reduce communication quality degradation. The problem of increasing the length is effectively avoided.

On the other hand, the wireless communication method of the present invention is the self-device, the self-device, and the self-device between each wireless communication device of a wireless communication system configured to include a plurality of wireless communication devices that connect communication links for direct wireless communication. Sending and receiving state announcements including address information for identifying other devices linking communication links and communication state information indicating the occupation rate of transmission and reception per unit time in the wireless communication,
Holding state announcement data formed by the state announcements received and received;
Based on the held state announcement data, the presence / absence of another device having a hidden terminal relationship with the own device is determined, and communication between the hidden terminal and the own device is performed according to the determination result. Calculate the collision rate,
The wireless communication method selects a modulation scheme to be applied to a communication link between the own device and the other device based on the calculated collision rate. In the wireless communication method, the own device is based on the state announcement data. The presence / absence of another device having a hidden terminal relationship is determined, the collision rate related to the communication between the hidden terminal and the own device is calculated according to the determination result, and the own rate is determined based on the calculated collision rate. A modulation scheme to be applied to a communication link between the device and the other device is selected.

Therefore, even when communication quality deterioration is caused by hidden terminals, adaptive modulation is applied uniformly without distinguishing it from the case of general radio wave propagation distance or the presence of obstacles, thereby increasing communication quality deterioration. This effectively avoids such a problem.
The wireless communication method of the present invention is characterized in that it is determined whether the cause of communication failure is due to a hidden terminal or signal deterioration, and an optimal modulation method is selected according to the determination result. And
In the above wireless communication method, it is determined whether the cause of the communication failure is due to the hidden terminal or the signal deterioration, and an optimum modulation method is selected according to the determination result.
For this reason, even when communication quality degradation is caused by a hidden terminal, adaptive modulation is applied uniformly without distinguishing it from the case of general radio wave propagation distance or the presence of an obstacle to reduce communication quality degradation. The problem of increasing the length is effectively avoided.

  According to the present invention, a wireless communication device, a wireless communication system, and a wireless communication method that realize adaptive communication while not causing deterioration in communication quality due to the hidden terminal problem are realized.

Hereinafter, the present invention will be clarified by describing embodiments of the present invention in detail with reference to the drawings. In the drawings to be referred to below, for the sake of convenience, the main part that is the subject of the description is exaggerated as appropriate, and other than the main part is appropriately simplified or omitted.
(Radio communication system of the present invention)
FIG. 1 is a conceptual diagram showing the configuration of a wireless communication system as an embodiment of the present invention.

This wireless communication system is configured to include a plurality (four here for convenience of explanation) of wireless communication devices 111, 112, 113, and 114, and the wireless communication devices 111 to 114 are connected by wireless communication links. ing.
That is, the wireless communication devices 111 and 112 are connected by a wireless communication link 121. Similarly, the wireless communication devices 112 and 113 are connected by a wireless communication link 122, and the wireless communication devices 112 and 114 are connected by a wireless communication link 123. The wireless communication devices 114 and 111 are connected by a wireless communication link 124, respectively.

Each wireless communication link described above is assigned communication resources in order to avoid interference, but this wireless communication system does not include a control station such as a base station in a mobile phone, and each wireless communication device 111, 112, 113 and 114 do not have a relationship of a control station and a controlled station, and autonomously determine whether or not transmission is possible.
Each of the wireless communication devices 111, 112, 113, and 114 does not need to be the same type of wireless communication device having the same specifications, and as long as the functions described later with reference to FIG. 2 are satisfied. Various communication devices.
Further, in the following description, regarding the wireless communication devices 111, 112, 113, and 114, for wireless communication devices that perform direct communication, a relationship in which one of the wireless communication devices is viewed from the other as appropriate. This is called an adjacent wireless communication device. Further, a wireless communication link applied by one wireless communication device to communication with an adjacent wireless communication device is appropriately referred to as an adjacent wireless link.

(Wireless communication apparatus of the present invention)
FIG. 2 is a functional block diagram showing the wireless communication apparatus of the present invention, which is suitable for configuring the wireless communication system of FIG.
In FIG. 2, the configuration that each wireless communication device 111, 112, 113, and 114 in FIG. 1 should generally satisfy is shown as a functional block diagram. The wireless communication devices 111, 112, 113, and 114 do not need to be devices of the same type and the same specifications.

In FIG. 2, these wireless communication devices are typically shown with reference numerals 200.
The wireless communication apparatus 200 includes the following units having a relationship described later. That is, a wireless communication unit 201, a storage unit 202, a collision rate determination unit 203, and a modulation method selection unit 204 are provided.
The wireless communication unit 201 includes address information for identifying each corresponding wireless communication device (adjacent wireless communication device) in communication with another device that connects a communication link (adjacent wireless link) that directly performs wireless communication with the own device, and the above-described address information. A state announcement including communication state information indicating transmission and reception occupancy per unit time in wireless communication is exchanged with the above-described other apparatus.

Note that the state announcement will be described in more detail later with reference to the drawings. In this embodiment, the communication related to the exchange of the state announcement in the wireless communication unit 201 is repeatedly executed at a predetermined cycle. Is done.
In addition, the wireless communication unit 201 monitors the communication state, and records communication state history information indicating the state (for example, statistical information regarding communication quality including information indicating whether the communication has succeeded or failed). Form.

The storage unit 202 holds state announcement data formed by the state announcement acquired through the wireless communication unit 201. Note that the communication state history information formed by the wireless communication unit 201 is also held as part of the state announcement data.
In the present embodiment, the state announcement data is held in a table format as will be described later with reference to the drawings.

The collision rate determination unit 203 uses the hidden terminal determination unit 203a to determine whether there is another device having a hidden terminal relationship with the own device based on the state announcement data stored in the storage unit 202. Then, in accordance with the determination result, the own calculation unit 203b calculates the collision rate related to the communication between the hidden terminal and the own device.
The modulation method selection unit 204 selects a modulation method to be applied to the communication link between the own device and the other device based on the collision rate calculated by the collision rate calculation unit 203 (using this collision rate as a selection criterion factor). .

(State announcement)
FIG. 3 is a conceptual diagram for explaining the state announcement.
FIG. 3 shows a part of a frame format of packet data exchanged through the wireless communication unit 201 of FIG. 2 as a state announcement.
In this type of actual communication, information elements such as a frame ID and a packet length are exchanged, but the description thereof is omitted for the sake of brevity.
The frame format shown in FIG. 3 includes address information (denoted as “transmission node information” in FIG. 3) indicating the wireless communication device that is the transmission source of the state announcement.

The node represented by the address information in this case corresponds to the wireless communication device 111 (FIG. 1), for example.
Furthermore, in the state announcement of this example, an index indicating the amount of transmission data (in this example, the occupancy rate of the data transmission time with respect to the unit time in the communication period is used and expressed as “transmission time ratio” in FIG. 3), In addition, an index indicating the amount of received data (in this example, the occupancy ratio of the time in the data reception state with respect to the unit time in the communication period is used and expressed as “reception time ratio” in FIG. 3).

In addition, the occupation rate in the “reception time ratio” is not limited to the time related to the reception of data transmitted from the adjacent wireless communication device to the own device (wireless communication device 111) but also to other devices. It is assumed that this is the occupancy rate of the time including the current time.
In addition, an address (“adjacent node address # 1” in FIG. 3, “ The state announcement includes “adjacent node address # 2”... Expressed as “adjacent node address #n”).

(State announcement data table)
FIG. 4 is a diagram illustrating an example of a table based on state announcement data (state announcement data table). This table is held in the storage unit 202 as described above.
The state announcement data table in FIG. 4 includes information on n + 1 wireless communication devices (the own device and the above-described adjacent wireless communication devices).
In FIG. 4, “adjacent wireless communication device address” is an address representing the own device and each wireless communication device (adjacent wireless communication device) that communicates directly with the own device. Incidentally, NODE_0 is its own device, and NODE_1 is one adjacent wireless communication device.
For each of these wireless communication devices described as NODE_0 to NODE_n, data as shown in the figure is shown in each column to the right of the notation of “adjacent wireless communication device address” (NODE_0 to NODE_n) in each row. Each data is defined as follows.

“Transmission rate per unit time” is an occupation rate of data transmission time with respect to unit time in communication time.
“Reception rate per unit time” is the occupancy rate of the time in the data reception state with respect to the unit time in the communication time, and not only the time related to reception of data transmitted to the own device but also transmission to other devices This is the occupancy rate of the time in the data reception state including the time during which the data is performed.
The “adjacent node address” is an address representing an adjacent wireless communication device viewed from each wireless communication device described in the leftmost column.

The “estimated collision rate” is a collision rate related to communication between the hidden terminal and the own device calculated by the collision rate determination unit 203 described with reference to FIG.
The “number of successful transmissions” is a history of the number of successful communications in communications after a predetermined reference time (for example, statistical data such as a calculation value).
The “number of transmission failures” is a history of the number of communication failures in communication after the reference time (for example, statistical data such as a calculation value).
The “adopted modulation scheme” is a modulation scheme selected by the modulation scheme determination unit 204 described with reference to FIG.

As described above, the “estimated collision rate” is calculated as the collision rate related to the communication between the hidden terminal and the own apparatus by the collision rate determination unit 203 and is stored as data as a result thereof.
The collision rate determination unit 203 constitutes a collision rate calculation means as an element of the wireless communication apparatus of the present invention, and the calculation of the “estimated collision rate” in the collision rate determination unit 203 is executed as follows. .

  That is, the collision rate determination unit 203 includes a hidden terminal determination unit 203a. The hidden terminal determination unit 203a includes the “adjacent node address” of each adjacent wireless communication device and the one wireless device related to the wireless communication device that is the own device. Compare the “adjacent node address” of each adjacent wireless communication device related to the adjacent wireless communication device of the communication device, and hide the wireless communication device registered only as the “adjacent node address” of the latter adjacent wireless communication device It is determined that there is a relationship. This determination will be described later in detail by way of example.

  Further, the collision rate determination unit 203 includes a calculation unit 203b, and the calculation unit 203b is provided for each wireless communication device (adjacent wireless communication device) indicated as “adjacent wireless communication device address” in the table illustrated in FIG. In addition, the “reception rate per unit time” of the corresponding wireless communication device, the value of NODE — 0, that is, the “transmission rate per unit time” regarding the own device, and the adjacent wireless of other known wireless communication devices (other than hidden terminals) Based on the comparison with the sum of the “transmission rate per unit time” regarding the communication device, the collision rate generated by the node determined to be a hidden terminal by the hidden terminal determination unit 203a is calculated. This calculation will be described in detail later by way of example.

On the other hand, as described above, the “adopted modulation method” is selected by the modulation method determination unit 204.
In other words, the modulation scheme determination unit 204 constitutes a modulation scheme selection means as an element of the wireless communication apparatus of the present invention, and the collision rate data calculated by the above-described collision rate calculation means and the communication for each corresponding device. A modulation scheme to be applied to the communication link is selected based on at least one of the success statistical data and the failure statistical data.

More specifically, based on the statistical information regarding the transmission error rate obtained by dividing the “transmission failure number” by the sum of the “transmission success number” and the “transmission failure number”, the collision rate determination unit 203 obtains “ If the “estimated collision rate” is higher than the current transmission error rate, the modulation method is not changed. If the estimated collision rate is lower than the current transmission error rate, the modulation method is selected so that the rate is lower and the error is stronger. Select the modulation method to apply.
In the above description, the state announcement described with reference to FIG. 3 includes the own wireless communication device address, the transmission rate per unit time, and the reception per unit time included in the first row of the adjacent information table. It is generated by an operation of copying information of the rate and the adjacent wireless communication device addresses (NODE_1 to NODE_n) in the second and lower rows.

(Operation sequence)
FIG. 5 is a sequence diagram showing the operation of the wireless communication system of the present invention. In FIG. 5, it is assumed that the arrangement of each wireless communication device in the wireless communication system is in the state shown in FIG.
At the present time, as schematically shown by the thin arrows, the wireless communication device 111 is performing data communication with the wireless communication device 112, and the wireless communication devices 113 and 114 are wirelessly communicating. 112 Assume that data communication is performed with the wireless communication device 112.
In this case, a state announcement is transmitted from the wireless communication device 111 to the wireless communication devices 112 and 114 as schematically indicated by thick arrows, and further, the wireless communication devices 113 and 114 transmit the wireless communication device. The state announcement is transmitted to 112, and the wireless communication device 112 transmits the state announcement to the wireless communication devices 111 and 113.

The above-described transfer of the state announcement will be described in detail later with reference to FIG.
In the example of FIG. 5, the wireless communication device 111 performs the collision rate calculation and the modulation method selection after the transmission / reception of the state announcement.
As described above, the wireless communication unit 201 (FIG. 2) of the wireless communication device 111 holds communication state history information in the storage unit 201 in a predetermined table format.

(Example of table held in storage unit)
FIG. 6 is a diagram illustrating an example of a table formed in the wireless communication device 111 and held in the storage unit 202 of the wireless communication device 111 in the course of the operation of FIG.
Each data item in the table of FIG. 6 is the same as that described above with reference to FIG.
As shown in the figure, in the first row of the data registration area, the address 101a representing the wireless communication device 111 as the own device is registered in the leftmost column, and each corresponding data is registered in the sequential column on the right. Is done.
That is, the data in the first row of the table includes each of “transmission rate per unit time” TX_a and “reception rate per unit time” RX_a described above with reference to FIG. Data is registered.

In the second and third rows of the table, “number of successful transmissions” (SUCC_b; SUCC_c) and “number of transmission failures” (FAIL_b; FAIL_c) and “adopted modulation method” (MOD_b) of the wireless communication devices 112 and 113 are displayed. MOD_c) are registered respectively.
As a method for discovering adjacent wireless communication devices, broadcast information or an adjacent node discovery protocol generally used in wireless LANs defined in IEEE 802.11 may be applied. A method that relies on state announcements may be applied.

FIG. 7 is a conceptual diagram showing the contents of each state announcement in the transmission / reception of the state announcements indicated by the thick arrows in FIG.
FIG. 7A shows a state announcement transmitted from the wireless communication device 111.
FIG. 7B shows a state announcement received by the wireless communication apparatus 111 from the wireless communication apparatus 112.
FIG. 7C shows a state announcement received by the wireless communication device 111 from the wireless communication device 114.
As described above with reference to FIG. 5, wireless communication device 112 exchanges state announcements with wireless communication devices 113 and 114 corresponding to the adjacent wireless communication device of its own device.
Here, when a state announcement is received from a wireless communication device on a new road, the table is updated to add a new entry to the table held in the storage unit 202.

FIG. 8 is a conceptual diagram illustrating an example of an updated state announcement (table).
In the table of FIG. 8, for example, based on the state announcement of FIG. 7B received from the wireless communication device 112, the “transmission rate per unit time” and the “reception rate per unit time” regarding the wireless communication device 112. ", TX_b and RX_b are respectively subscribed.
Further, as the “adjacent node address” of the wireless communication device 112, addresses 101a, 101c, and 101d representing the wireless communication devices 111, 113, and 114 are respectively subscribed.
Further, the state announcement of FIG. 7C received from the wireless communication apparatus 114 is also reflected in the table of FIG.
The wireless communication device 111 periodically or as needed, for example, at the timing of receiving the state announcement, the collision rate determination unit 203 (FIG. 2) performs a collision rate for each corresponding adjacent wireless communication device. Is estimated.

(Example of collision rate calculation process)
FIG. 9 is a flowchart illustrating a process related to estimation of a collision rate when the wireless communication apparatus 111 performs communication.
The calculation of the collision rate in the flowchart of FIG. 9 relates to the collision rate when the wireless communication apparatus 111 transmits to the wireless communication apparatus 112.
First, “neighboring node address” in the state announcement data in the table of FIG. 8 is referred to (step S901), and the presence of a hidden terminal is determined (step S902).

  The determination of the hidden terminal in step S902 is performed as follows. That is, the adjacent node addresses of the entry of the wireless communication device 112 are the wireless communication devices 111, 113, and 114, and the adjacent wireless communication devices in the entry of 111 that is the own wireless communication device are 112 and 114. Therefore, it is determined that the wireless communication device 113 is a wireless communication device unknown to the wireless communication device 111, that is, a hidden terminal.

The processing result in step S <b> 902 means that a collision occurs when the wireless communication device 113 transmits data to the wireless communication device 112 when the wireless communication device 111 transmits data to the wireless communication device 112.
Next, an adjacent wireless communication device common to the wireless communication devices 111 and 112 is determined (step S903). In step S903, the adjacent wireless communication device 114 is determined to be an adjacent wireless communication device common to the wireless communication devices 111 and 112 by referring to the table of FIG.

Further, the state announcement data according to the table of FIG. 8 is obtained by calculating the sum of the “transmission rates per unit time” of the adjacent wireless communication devices of the wireless communication device 112 known to the wireless communication device 111, that is, the wireless communication devices 111 and 114. (Step S904).
The calculation in step S904 will be described next.
The “reception rate per unit time” RX_b of the wireless communication device 112 is the “transmission rate per unit time” TX_a, TX_c of the wireless communication devices 111, 113, and 114 respectively corresponding to the adjacent wireless communication of the wireless communication device 112. And equal to the sum of TX_d (RX_b = TX_a + TX_c + TX_d).

This is because the “reception rate per unit time” includes not only the ratio used by each adjacent wireless communication device described above to receive data sent to the own wireless communication device 112 but also each adjacent wireless communication device itself. This is because it also includes the ratio of the time for sending data to another wireless communication device that is a third party other than the wireless communication device 112.
From the above, in the calculation of step S904, the total transmission rate per unit time of each adjacent wireless communication device of the wireless communication device 112 known to the wireless communication device 111 is calculated based on the table data of FIG. In this example, it is the total value of “transmission rate per unit time” Tx_d of the wireless communication device 114 and “transmission rate per unit time” TX_a of the own wireless communication device 111.

Next, the “transmission rate per unit time” of the wireless communication device 113 determined to be a hidden terminal in step S902 is calculated (step S905).
In this step S 905, the total value (the value calculated in step S 904) of the “transmission rate per unit time” of each adjacent wireless communication device of the wireless communication device 112 known to the wireless communication device 111 is calculated by the wireless communication device 112. The above-described “transmission rate per unit time” is calculated by subtracting from “reception rate per unit time” RX_b.

In this case, if there are a plurality of hidden terminals, the traffic volume in transmission per unit time by these hidden terminals is calculated.
The “transmission rate per unit time” of the hidden terminal is a probability of collision with transmission from the hidden terminal, that is, an estimated collision rate (RX_b-TX_a-TX_d).
In this example, it is an estimated collision rate when the wireless communication apparatus 111 transmits to the wireless communication apparatus 112. The estimated collision rate when the wireless communication device 111 transmits to the wireless communication device 114 is not unknown to the wireless communication device 111 adjacent to the wireless communication device 114, and therefore the hidden terminal is not present. It does not exist, and the estimated collision rate is zero.
As described above, the results determined or calculated up to step S905 are reflected in the table of FIG. 8 (step S906).
FIG. 10 is a diagram showing a state announcement data table reflecting the processing result in the flowchart of FIG.

(Modulation method selection example)
FIG. 11 is a flowchart showing a process of selecting a modulation scheme executed by modulation scheme selection section 204 of the wireless communication apparatus.
Next, processing for selecting a modulation method will be described with reference to FIG. 10 as appropriate and along the flowchart of FIG.
First, the transmission failure rate under the condition that the hidden terminal can exist is calculated from the statistical value of communication (historical information of data related to communication), that is, the state announcement data in the table of FIG. 10 (step S1101).
In step S1101 in this example, when transmitting from the wireless communication apparatus 111 to the wireless communication apparatus 112, a statistical transmission failure rate = number of transmission failures / (number of successful transmissions + number of transmission failures) is calculated.

Next, the transmission failure rate is compared with the estimated collision rate (step S1102).
A modulation scheme is selected according to the comparison result of step S1102 (step S1103).
When the transmission failure rate is lower than the estimated collision rate in the selection in step S1103, it is determined that the communication failure is caused by the collision by the hidden terminal, and the modulation scheme is not changed. Conversely, the transmission failure rate is higher than the estimated collision rate. Is executed by changing the modulation scheme to one having a lower rate and higher noise resistance than the scheme that is currently applied because it is determined that the communication quality is deteriorated due to a change in surrounding conditions.

Alternatively, the error rate due to propagation may be calculated by subtracting the estimated collision rate from the transmission failure rate, and the modulation method as described in Non-Patent Document 1 may be determined based on the error rate due to propagation.
As described above, according to the conventional technique disclosed in Non-Patent Document 1, statistics on communication success and failure are taken, and based on this statistic, when the number of failures exceeds a predetermined threshold, the rate is low and the noise is low. An algorithm that changes to a more robust one is applied.

In this case, it is not identified whether or not the communication failure is caused by the hidden terminal, and it is treated as a failure due to a change in the surrounding situation. The probability of failure will tend to increase, leading to a vicious circle.
On the other hand, according to the present invention, even when a communication failure is caused by a hidden terminal, since it is not gradually switched to a modulation method having a low transmission rate (rate) uniformly, a vicious circle as in the prior art is avoided. The danger of being invited is wiped out.

  The present invention can be applied to multi-hop communication such as a wireless ad hoc network, a wireless mesh network, and a multi-cellular network in addition to a general communication network, and is particularly applied under a condition that may cause a hidden terminal problem. Therefore, it is effective for ensuring the data transmission efficiency.

It is a conceptual diagram showing the structure of the radio | wireless communications system as one embodiment of this invention. It is a functional block diagram showing the radio | wireless communication apparatus of this invention adapted to comprise the radio | wireless communications system of FIG. It is a conceptual diagram for demonstrating a state announcement. It is a figure showing the example of the table (state announcement data table) by state announcement data. It is a sequence diagram showing operation | movement of the radio | wireless communications system of this invention. FIG. 6 is a diagram illustrating an example of a table formed in the wireless communication device in the course of the operation of FIG. 5 and held in the storage unit of the wireless communication device. It is a conceptual diagram showing the content of each state announcement in transmission / reception of the state announcement illustrated with the thick arrow line in FIG. It is a conceptual diagram showing the example of the updated state announcement (table). It is a flowchart showing the process which concerns on estimation of the collision rate in case a wireless communication apparatus communicates. It is a figure showing the state announcement data table reflecting the processing result in the flowchart of FIG. It is a flowchart showing the process which selects the modulation system performed in the modulation system selection part of a radio | wireless communication apparatus.

Explanation of symbols

111, 112, 113, 114 ... wireless communication devices 121, 122, 123, 124 ... wireless communication links 131, 132, 133, 134 ... communicable area 200 ... wireless communication device 201 ... wireless communication unit 202 ... storage unit 203 ... Collision rate determination unit 204 ... modulation method selection unit

Claims (8)

Address information for identifying each corresponding wireless communication device in communication with another device that establishes a communication link for direct wireless communication with its own device, and communication status information indicating the occupancy rate of transmission and reception per unit time in the wireless communication Wireless communication means for exchanging a state announcement including
Storage means for holding state announcement data formed by said state announcement;
Based on the state announcement data stored in the storage means, the presence / absence of another device having a hidden terminal relationship with the own device is determined, and the hidden terminal and the own device are determined according to the determination result. A collision rate calculation means for calculating a collision rate related to communication;
A modulation method selection means for selecting a modulation method to be applied to a communication link between the own device and the other device based on the collision rate calculated by the collision rate calculation means;
A wireless communication apparatus comprising:   The collision rate calculation means stores the one address information representing the address of each neighboring device related to the own device and the other address information representing the address of each neighboring device related to one neighboring device of the own device. Hidden terminal determination means for comparing on the basis of the state announcement data held in a device and determining the presence / absence of another device having a hidden terminal relationship to the own device from the comparison result The wireless communication apparatus according to claim 1.   The collision rate calculation means includes a value of a reception occupancy rate per unit time in communication of each adjacent device related to the own device and a value of a transmission occupancy rate per unit time in communication related to all the adjacent devices related to the adjacent device. The wireless communication apparatus according to claim 1, further comprising: a calculation unit that calculates a collision rate in communication with another apparatus having the hidden terminal relationship based on   The modulation scheme selection means is based on the communication rate data calculated by the collision rate calculation means and the communication link based on at least one of the statistical data of success and the statistical data of failure related to communication for each other device concerned. The radio communication apparatus according to any one of claims 1 to 3, wherein a modulation scheme to be applied to is selected. A wireless communication system configured to include a plurality of wireless communication devices that connect communication links for direct wireless communication, the plurality of wireless communication devices,
Corresponds to a state announcement including address information that identifies each of its own device and the wireless communication device that connects the device and the communication link, and communication state information that represents the occupancy rate of transmission and reception per unit time in the wireless communication Wireless communication means for sending and receiving with the wireless communication device;
Storage means for holding state announcement data formed by said state announcement;
Based on the state announcement data stored in the storage means, the presence / absence of another device having a hidden terminal relationship with the own device is determined, and the hidden terminal and the own device are determined according to the determination result. A collision rate calculation means for calculating a collision rate related to communication;
A modulation method selection means for selecting a modulation method to be applied to a communication link between the own device and the other device based on the collision rate calculated by the collision rate calculation means;
A wireless communication system comprising:   It is characterized in that it comprises a judging means for judging whether the cause of the communication failure is caused by a hidden terminal or a signal deterioration, and a selecting means for selecting an optimum modulation method according to the judgment result. Wireless communication system. An address for specifying each of the own device and other devices that connect the communication link with the own device among the individual wireless communication devices of the wireless communication system configured to include a plurality of wireless communication devices that directly connect the wireless communication link. Sending and receiving state announcements including information and communication state information representing the occupancy rate of transmission and reception per unit time in the wireless communication;
Holding state announcement data formed by the state announcements received and received;
Based on the held state announcement data, the presence / absence of another device having a hidden terminal relationship with the own device is determined, and communication between the hidden terminal and the own device is performed according to the determination result. Calculate the collision rate,
A radio communication method, comprising: selecting a modulation scheme to be applied to a communication link between the device itself and the other device based on the calculated collision rate.   A wireless communication method characterized in that it is determined whether a cause of communication failure is caused by a hidden terminal or signal deterioration, and an optimum modulation method is selected according to the determination result.

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