JP2011035600A - Wireless communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wireless communication system capable of improving the efficiency of transmission by reducing a probability of data frame collisions, also shortening a transmission waiting time when the number of nodes is small. <P>SOLUTION: In the wireless communication system wherein nodes 1a, 1b, 1c, ... existing in the periphery communicate with each other to generate a communication path, each of the nodes 1a, 1b, 1c, ... detects the number of nodes with which the node can communicate, on the basis of communication between nodes and sets a range of a back-off time on the basis of the detected number of nodes. Then, each of the nodes 1a, 1b, 1c, ... detects the presence of wireless transmission from another node and, in the case of detection of the absence of wireless transmission from another node, starts wireless transmission after at least a back-off time selected at random from the set range of the back-off time. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a wireless communication system that performs wireless communication with an arbitrary partner that is a component of a wireless LAN, and more particularly to a wireless communication system in which the configuration of a wireless network changes with time.

The wireless LAN has two types of connection forms, “ad hoc mode” and “infrastructure mode”.
Ad hoc mode communication is a method in which nodes (wireless communication terminals) communicate directly with each other without using a wireless LAN access point.
Further, the communication in the infrastructure mode is a method for performing communication via an access point of a wireless LAN, and it is possible to perform communication with all nodes existing in a range where the access point can communicate.

  In the ad hoc mode and infrastructure mode wireless LAN systems, even when multiple nodes transmit at the same time, CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) is used to prevent data collision as much as possible. / Collision avoidance) method is adopted. In this CSMA / CA system, a node that wants to transmit data monitors the communication status of the communication path (carrier sense), and starts transmission when the communication path is free. At this time, if a plurality of nodes start transmission at the same time, data collides in the communication path and breaks. Therefore, transmission is performed after waiting for a random time, that is, a back-off time.

  In such a CSMA / CA wireless LAN system, a back-off time and a DIFS (Distributed Inter Frame Space), which is a mechanism for avoiding data collision, occur every time data is transmitted, and the overhead of using the radio wave band is increased. Become. The DIFS indicates a time for adjusting the transmission interval between frames, and is used for priority control, but generally has a fixed value.

The back-off time is calculated by the following formula.
Backoff time = random number value × slot time The random number value is a random integer generated from a range of 0 to CW (Contention Window).
By making the back-off time random as described above, measures are taken so that a plurality of nodes do not transmit radio waves simultaneously.

However, if the random number values acquired by each node are the same, the data frames will collide. The range of the random number is “1 to 15” in “IEEE802.11a” which is one standard of wireless LAN.
Therefore, the probability that the data frames of a plurality of nodes collide, for example, when the number of nodes is 5, the probability that the random number values are the same (the probability that the data frames collide) is obtained by each of the 5 different random values. Since we only need to subtract the probability from “1”,
1- (15/15 × 14/15 × 13/15 × 12/15 × 11/15) = 0.525
And the probability of collision is about 52.5%.

In addition, the probability that the random number value is the same when the number of nodes is two (the probability that the data frames collide) is
1- (15/15 × 14/15) = 0.066
The probability of collision is about 6.6%.
As described above, the probability of collision of data frames varies greatly depending on the number of nodes present in the communication area, and the probability of collision of data frames increases as the number of nodes increases.

  In addition, as a known technique related to the present invention, in a wireless communication system that realizes collision avoidance of wireless packets by the CSMA / CA method, how many nodes perform transmission while the own device is waiting for transmission. A technique is known in which transmission efficiency is improved by setting a back-off based on the situation, that is, according to the communication congestion state (see, for example, Patent Document 1). However, when the back-off is set according to the communication congestion state as described above, the back-off becomes large when data with high priority is continuously transmitted from another node. Sending may take time.

JP 2005-12275 A

  As described above, wireless communication systems based on ad hoc and infrastructure have various adjustment times set to avoid collision of data transmitted from a plurality of nodes, and therefore, even in an ideal environment where collision does not occur. The adjustment time has an effect, and there is a problem that an ideal throughput cannot be realized by occupying the radio wave band.

In addition, the probability that data frames collide varies greatly depending on the number of nodes existing in the communication area, and the probability that data frames collide increases as the number of nodes increases.
The present invention has been made to solve the above problem, and when a random back-off time range adapted to the number of nodes existing in the communication area is set and no wireless transmission other than the own device is detected. By starting wireless transmission after waiting at least a backoff time randomly selected from the set backoff time range, the data frame collision probability is reduced and the transmission waiting time is reduced when the number of nodes is small. An object of the present invention is to provide a wireless communication system that can reduce the occupation time of the radio wave band, improve the throughput as a whole, and efficiently transmit data.

A first invention is a wireless communication system comprising an access point and a plurality of nodes wirelessly connected to the access point.
The access point includes node management means for managing the nodes existing in the communication area of the own device, and node number information transmission means for wirelessly transmitting information representing the number of managed nodes to each of the nodes. With
The node includes a setting unit that sets a range of a back-off time based on information transmitted from the access point, a carrier detection unit that detects presence / absence of radio transmission from a device other than the own device, and a wireless signal from a device other than the own device. When no transmission is detected, it comprises transmission means for waiting at least a back-off time randomly selected from the set back-off time range and starting radio transmission.

A second invention is the radio communication system according to the first invention, wherein
The node further comprises a DIFS setting means for setting a DIFS based on information transmitted from the access point,
The transmission means waits for a back-off time randomly selected from the set DIFS and the set back-off time range when radio transmission from other than the own device is not detected, and starts the radio transmission. It is characterized by.

According to a third aspect of the present invention, there is provided a wireless communication system for creating a communication path by performing communication between nodes existing in the vicinity.
The node includes node detection means for detecting the number of nodes that can communicate with each other based on communication between the nodes, and setting means for setting a backoff time range based on the detected number of nodes; A carrier detection means for detecting presence / absence of radio transmission from a device other than the own device, and a backoff randomly selected from at least the range of the set backoff time when no radio transmission from a device other than the own device is detected. Transmission means for waiting for a time and starting wireless transmission.

A fourth invention is the radio communication system according to the third invention, wherein
The node further comprises DIFS setting means for setting DIFS based on the number of detected nodes,
The transmission means waits for a back-off time randomly selected from the set DIFS and the set back-off time range when radio transmission from other than the own device is not detected, and starts the radio transmission. It is characterized by.

  According to the present invention, a wireless communication system based on an infrastructure mode in which a plurality of nodes communicate via an access point, or a wireless communication system based on an ad hoc mode in which a communication path is created by communication between nodes existing in the vicinity. In this case, a random backoff time range is set based on the number of nodes existing in the communication area, and at least when the wireless transmission other than the own device is not detected, it is randomly selected from the set backoff time range. By waiting for the specified backoff time and starting wireless transmission, the data frame collision probability is reduced, and when the number of nodes is small, the transmission waiting time can be reduced to reduce the occupied time of the radio band, and the overall throughput can be reduced. Can improve efficiency and send data efficiently

It is a figure which shows the communication image of the wireless LAN by the ad hoc mode which concerns on Example 1 of this invention. It is a block diagram which shows the structure of the node in the Example 1. FIG. It is a block diagram which shows the structure of the ad hoc routing process part in the Example 1. FIG. 4 is a flowchart illustrating a processing operation at the time of transmission of each node in the first embodiment. It is a schematic block diagram of the wireless LAN system by the infrastructure mode which concerns on Example 2 of this invention. It is a block diagram which shows the structure of the access point in the Example 2. FIG. It is a block diagram which shows the structure of the node in the Example 2. It is a block diagram which shows the structure of the transmission timing control part in the communication control part in FIG. 10 is a timing chart showing the operation of each node of the wireless LAN system according to the second embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

The first embodiment shows an example in which the present invention is applied to a wireless LAN system in an ad hoc mode in which nodes (wireless communication terminals) communicate directly with each other without using an access point.
FIG. 1 is a diagram illustrating a communication image of a wireless LAN in an ad hoc mode according to the first embodiment of the present invention. In a wireless LAN using the ad hoc mode, a plurality of nodes 1a, 1b, 1c,... Existing in a communicable area communicate with each other to create a communication path. The nodes 1a, 1b, 1c,... Are constituted by wireless communication terminals such as personal computers having a communication function.

2 is a block diagram showing the configuration of the nodes 1a, 1b, 1c,..., And FIG. 3 is a block diagram showing the configuration of the ad hoc routing processing unit in FIG.
Since the nodes 1a, 1b, 1c,... Have the same configuration, the configuration of the node 1a will be described. The node 1a includes a communication processing unit 10, a radio unit 20, and an antenna 30 as shown in FIG.

The communication processing unit 10 includes a host application processing unit 11, an ad hoc routing processing unit 12, a communication processing unit 13, and a wireless transmission / reception unit driver 14.
As shown in FIG. 3, the ad hoc routing processing unit 12 includes an ad hoc routing protocol processing unit 121, a route search processing unit 122, a node determination unit 123, and a data transmission / reception unit 124. The ad hoc routing protocol processing unit 121 is shown in FIG. The route search processing unit 122 and the data transmission / reception unit 124 are connected to the communication processing unit 13.

  Various methods are considered as an ad hoc routing protocol in the ad hoc routing processing unit 12, a reactive type that creates a routing table at the start of communication, a proactive type that creates a routing table by periodically exchanging information, and these It can be classified into a combined hybrid type. In the first embodiment, a proactive type is adopted as an ad hoc routing protocol so that the number of nodes is always grasped and appropriate control is possible. That is, the ad hoc routing processing unit 12 periodically acquires node information using a routing protocol, and creates a route table of nodes when performing ad hoc communication. This information acquisition is periodically executed in each of the nodes 1a, 1b, 1c,..., And the latest route table at that time is created. When each node 1a, 1b, 1c,... Starts data transmission, it calculates the number of nodes existing in its own communication area (in the area where its own radio wave reaches) based on this route table. A node coefficient is calculated from the number of nodes.

  The node coefficient is a coefficient defined for weighting according to the number of nodes existing in an area where radio waves reach. This node coefficient is set to “1” at the maximum, decreases when the number of nodes is small (for example, “0.1” in one-to-one communication), and increases when the number of nodes is large. When the number of nodes is large, the possibility of data collision increases, so the node coefficient is assumed to be the same as the original wireless LAN setting time.

Next, processing operations at the time of transmission of the nodes 1a, 1b, 1c,... (Routing protocol processing executed by the ad hoc routing processing unit 12) will be described with reference to the flowchart shown in FIG.
Each of the nodes 1a, 1b, 1c,... Periodically acquires information of other nodes by the ad hoc routing protocol processing executed by the ad hoc routing protocol processing unit 121, and performs a route search by the route search processing unit 122. The routing table is updated (step A1).

  Then, the presence / absence of data transmission in the own device is determined (step A2). If data transmission is to be executed, carrier sense is performed in order to investigate the band usage status (step A3), and it is determined whether transmission is possible. (Step A4). At this time, if another node is transmitting, it is determined that transmission is not possible (NG), and the process returns to step A3 to perform carrier sense. If it is confirmed by this carrier sense that no other node is transmitting, the process proceeds to the following transmission process.

  First, a transmission frame is generated from transmission data (step A5), and the node determination unit 123 determines the number of nodes existing in the communicable area from the route table updated in step A1 (step A6). Then, a node coefficient is calculated based on the number of nodes determined in step A6 (step A7).

Next, “DIFS (Distributed Inter Frame Space)” is multiplied by the “node coefficient” to set a transmission waiting time (step A8).
The DIFS is a time for adjusting the transmission interval between frames. The processing time and propagation delay of the node, the transmission timing of ACK (SIFS: short interframe space, waiting time when transmitting ACK at the shortest frame transmission interval) ) And is determined as follows.

DIFS = slot time × 2 + SIFS
DIFS is the time used for priority control, and is set to cooperate with other nodes (ie, to transmit ACK with priority so that it does not collide with ACK). The possibility of collision is also reduced. Therefore, not only the back-off depending on the number of nodes but also a generally fixed DIFS is changed. In this case, the value of “slot time × 2” is a fixed value because it reflects the processing time and propagation delay. To shorten the DIFS, the “SIFS” portion is adjusted by multiplying by the node coefficient.

Also, a transmission waiting time is set by multiplying the random back-off time by the node coefficient (step A9). Therefore, if the node coefficient is small, the back-off time is shortened as a whole.
The back-off time multiplied by the node coefficient is calculated by the following equation.
Backoff time = random value × slot time After the waiting time set in steps A8 and A9 has elapsed, data is transmitted (step A10), and the ad hoc mode routing protocol processing is terminated.

If it is determined in step A2 that data is not to be transmitted, the ad hoc mode routing protocol processing is terminated.
Calculate the node coefficient based on the number of nodes present in the communication area as described above, set a random back-off time range according to this node coefficient, when no wireless transmission other than its own device is detected, By waiting for at least a backoff time randomly selected from the set backoff time range and starting wireless transmission, the data frame collision probability is reduced and the transmission waiting time is reduced when the number of nodes is small. Thus, the occupation time of the radio wave band can be reduced, and the throughput can be improved as a whole and data can be transmitted efficiently.

The second embodiment shows an example in which the present invention is implemented in a wireless LAN system in an infrastructure mode in which a plurality of nodes communicate via an access point.
FIG. 5 is a schematic configuration diagram of a wireless LAN system in infrastructure mode according to the second embodiment of the present invention. In FIG. 5, reference numeral 41 denotes a server that manages the entire system, and at least one or more access points (AP) 43 are connected to the server 41 via, for example, a wired line 42. A plurality of nodes 45a, 45b, 45c,... Existing in the communication area 44 of the own device are wirelessly connected to the access point 43.

  The access point 43 includes an antenna 431, a radio unit 432, and a communication processing unit 433 that communicate with nodes 45a, 45b, 45c,... Existing in the communication area 44 of the own device as shown in FIG. The node management unit 434 that manages the nodes 45a, 45b, 45c,... Existing in the 44, the random value range determination unit 435 that determines the range of the random value based on the number of nodes managed by the node management unit 434, and the above A DIFS determination unit 436 that determines DIFS based on the number of nodes is provided.

  The access point 43 configured as described above uses the range of the random value determined by the random value range determination unit 435 as node number information in the communication area 44 from the communication processing unit 433 via the radio unit 432 and the antenna 431. To the nodes 45a, 45b, 45c,.

7 is a block diagram showing the configuration of the nodes 45a, 45b, 45c,..., And FIG. 8 is a block diagram showing the configuration of the transmission timing control unit in FIG.
Since the nodes 45a, 45b, 45c,... Have the same configuration, the configuration of the node 45a will be described. As shown in FIG. 7, the node 45a includes a communication processing unit 10a, a radio unit 20a, and an antenna 30a.

The communication processing unit 10a includes a host application processing unit 11a, a transmission timing control unit 15, a communication processing unit 13a, and a wireless transmission / reception unit driver 14a.
The transmission timing control unit 15 includes a data transmission / reception unit 151 that transmits / receives data to / from the access point 43 as shown in FIG. 8, and a carrier detection unit 152 that detects presence / absence of wireless transmission from other than the own device, as shown in FIG. A back-off time range setting unit 153 that sets a range of back-off time based on the number of nodes transmitted from the access point 43, and a DIFS setting unit 154 that sets DIFS based on the number of nodes transmitted from the access point 43. It has.

  The transmission timing control unit 15 is randomly selected from at least the back-off time range set by the back-off time range setting unit 153 when the carrier detection unit 152 does not detect wireless transmission from other than the own device. The data transmission / reception unit 151 waits for the back-off time or waits for a back-off time randomly selected from the range of the DIFS set by the DIFS setting unit 154 and the back-off time range set by the back-off time range setting unit 153. Start wireless transmission.

Next, the operation of the wireless LAN system according to the second embodiment will be described with reference to the timing chart shown in FIG.
In the infrastructure mode, communication is always performed via the access point 43. Therefore, the access point 43 knows how many nodes exist in its communication area 44 by the node management unit 434, and the collision probability is determined in advance. A random value range that is constant for each number of nodes is obtained and held by the random value range determination unit 435. For example, if the collision probability of a data frame is 30% or less, the range of random values for each number of nodes is
When the number of nodes = 2, random numbers = 1-4
When the number of nodes = 3, random numbers = 1-9
When the number of nodes = 4, random number values = 1-20
When the number of nodes = 5, random numbers = 1-30
・
・
・
It becomes.

  The access point 43 periodically notifies each of the nodes 45a, 45b, 45c,... Using a beacon frame as a node number information using a beacon frame. The nodes 45a, 45b, 45c,... That have received the beacon frame set the back-off range using the range of random values included in the frame.

The back-off time is calculated by the following equation as in the case of the first embodiment.
Backoff time = random value × slot time FIG. 9 assumes that nodes 45a, 45b, and 45c exist in the communication area 44 of the access point 43, and that the nodes 45a and 45c have data to be transmitted. When executing data transmission, the nodes 45a and 45b perform carrier detection processing to detect the presence / absence of wireless transmission from a device other than its own (step B1). A transmission frame is generated from this to wait for the DIFS time (step B2).

The DIFS is a time for adjusting the transmission interval between frames, and is determined in consideration of the node processing time, propagation delay, and ACK transmission timing (SIFS) as described in the first embodiment. Expression DIFS = slot time × 2 + SIFS
Is required.

  After the DIFS time has elapsed, the nodes 45a and 45c set a back-off range using the range of random values sent from the access point 43, and the back-off time is determined from the back-off range according to the random value. A random selection is made, waiting for the back-off time (step B3), and then wireless transmission is started. In this case, in the example of FIG. 9, the back-off time of the node 45a is shorter than the back-off time of the node 45c, and the node 45a first acquires the radio channel and transmits the data frame 51 to the node 45b (step B4). The node 45c becomes busy while the node 45a transmits the data frame 51 (step B5).

  After receiving the data frame 51 from the node 45a, the node 45b waits for SIFS time (step B6) and responds with an ACK frame 52 (step B7). Further, after the node 45a transmits the data frame 51 in step B4, the node 45c waits for the DIFS time (step B8) and transmits the data frame. In this case, since the SIFS time is set shorter than the DIFS time, the ACK frame 52 transmitted by the node 45b and the data frame transmitted by the node 45c do not collide.

  As described above, the access point 43 notifies each of the nodes 45a, 45b, 45c,... Of the random value range corresponding to the number of nodes existing in the communication area 44, and the nodes 45a, 45b, 45c,. By setting a back-off range according to the range of the random number values that have been set and selecting a back-off time at random from the back-off range, a data frame can be obtained without depending on the number of nodes existing in the communication area 44. Can be reduced to a certain value or less, and when the number of nodes is small, the overall throughput can be improved and data can be transmitted efficiently.

In the first embodiment, when each node 1a, 1b, 1c,... Calculates the node coefficient, a random number value in which the collision probability of the data frame is constant for each number of nodes existing in the communication area as in the second embodiment. May be obtained, a node coefficient is determined based on the range of the random value, and the range of the back-off time may be set.
In the second embodiment, the DIFS determination unit 436 of the access point 43 holds a plurality of DIFS values as values corresponding to the number of nodes, and uses the beacon frame to set the DIFS values to the nodes 45a, 45b, 45c, .., And each node may use the notified DIFS. In this case, the DIFS is set to be shorter as the number of nodes is smaller. The adjustment of DIFS is performed within the SIFS range as in the first embodiment.

  Further, the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying constituent elements without departing from the scope of the invention in the implementation stage.

  1a, 1b, 1c ... node, 10, 10a ... communication processing unit, 11, 11a ... upper application processing unit, 12 ... ad hoc routing processing unit, 121 ... ad hoc routing protocol processing unit, 122 ... route search processing unit, 123 ... node Judgment unit 124 ... Data transmission / reception unit 13, 13a ... Communication processing unit 14, 14a ... Radio transmission / reception unit driver 15 ... Transmission timing control unit 151 ... Data transmission / reception unit 152 ... Carrier detection unit 153 ... Back-off time Range setting unit, 154... DIFS setting unit, 20, 20a... Radio unit, 30, 30a .. antenna, 41 .. server, 42 .. line, 43 .. access point, 431 ... antenna, 432 ... radio unit, 433 ... communication processing unit 434 ... Node management unit, 435 ... Random value range determination unit, 436 ... DIFS determination unit, 44 Communication area, 45a, 45b, 45 c ... node 51 ... data frame, 52 ... ACK frame.

Claims (4)

In a wireless communication system comprising an access point and a plurality of nodes wirelessly connected to the access point,
The access point is
Node management means for managing the node existing in the communication area of the own device;
Node number information transmitting means for wirelessly transmitting information representing the number of managed nodes to each of the nodes;
With
The node is
Setting means for setting a range of a back-off time based on information transmitted from the access point;
Carrier detection means for detecting presence / absence of wireless transmission from other than the own device;
When wireless transmission from a device other than the own device is not detected, at least a transmission unit that waits for a backoff time randomly selected from the set backoff time range and starts wireless transmission;
A wireless communication system comprising: The node further comprises:
A DIFS setting means for setting a DIFS based on the information transmitted from the access point;
The transmission means waits for a back-off time randomly selected from the set DIFS and the set back-off time range when radio transmission from a device other than the own device is not detected, and starts radio transmission. The wireless communication system according to claim 1. In a wireless communication system that creates a communication path by communicating between nodes existing in the vicinity,
The node is
Node detection means for detecting the number of nodes that can communicate with each other based on communication between the nodes;
Setting means for setting a backoff time range based on the number of detected nodes;
Carrier detection means for detecting presence / absence of wireless transmission from other than the own device;
When wireless transmission from a device other than the own device is not detected, at least a transmission unit that waits for a backoff time randomly selected from the set backoff time range and starts wireless transmission;
A wireless communication system comprising: The node further comprises:
A DIFS setting means for setting a DIFS based on the number of detected nodes;
The transmission means waits for a back-off time randomly selected from the set DIFS and the set back-off time range when radio transmission from a device other than the own device is not detected, and starts radio transmission. The wireless communication system according to claim 3.

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