JP2008252565A - Wireless terminal and communication control method of wireless terminal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wireless terminal and a communication control method of the wireless terminal which can avoid an unnecessary collision/retransmission, even if transmission timings between terminals with high priority are coincident with each other by accident between terminals. <P>SOLUTION: A wireless terminal has a load state information acquiring portion 21 acquiring load state information of a bandwidth, a retransmission history information acquiring portion 22 acquiring data retransmission history information which the wireless terminal has required to transmit data, a determining portion 23 comparing the load state information with the data retransmission history information and determining whether or not a collision/retransmission is easy to occur in a wireless bandwidth channel, and a CWmin updating portion 24 increasing a minimum value (hereinafter, referred to as CWmin) of a contention window to be updated, when the determining portion 23 determines the collision/retransmission is easy to occur in the wireless bandwidth channel. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a wireless terminal adopting wireless LAN QoS defined in IEEE802.11e as a wireless access method and a communication control method for the wireless terminal.

  2. Description of the Related Art In recent years, wireless LAN (Local Area Network) technology that does not require a communication cable has spread due to the spread of the Internet. Wireless LAN technology is widely used not only for information terminals such as personal computers but also in the field of mobile phone terminals, and in the same wireless LAN environment, voice and data are often transmitted and received at the same time.

In order to efficiently transmit and receive various categories of packets such as voice and video, a QoS (Quality of Service) function in a wireless LAN environment is very important.
There is IEEE 802.11e as a standard technology for QoS guarantee in a wireless LAN environment. In a wireless LAN, terminals accessing the same base station share a common wireless channel. Therefore, when the number of terminals accessing the same base station increases, quality degradation such as voice interruption and data delay occurs. May cause.

  In wireless LAN QoS specified by IEEE802.11e, data is defined as four categories, AC_VO (voice), AC_VI (video), AC_BK (background), and AC_BE (best effort), and is defined for each category. The QoS function can be realized based on an EDCA (Enhanced Distributed Coordination Access) method using QoS Parameters.

AC_VO and AC_VI categories are prepared for audio packets and image packets for which transmission delay is to be kept small. These two categories AC_VO and AC_VI are set to a small value as an initial random number at the time of generating the back-off period, as compared with the other categories AC_BK and AC_BE. Specifically, for the back-off period, an integer from 0 to the contention window size (hereinafter referred to as CW) is randomly selected, and the slot time determined by a constant value is multiplied by the selected integer. Calculated as time. Each terminal starts transmission after waiting for a back-off period. If a packet collides and transmission fails, and a category that has not been transmitted due to competition between categories, the CW value is doubled and the transmission procedure is performed again. At this time, the initial value of CW is given by the minimum value of CW (hereinafter referred to as CWmin), and does not exceed the maximum value of CW (hereinafter referred to as CWmax).
As a result, the right of transmission can be acquired preferentially for the categories of audio packets and image packets, and quality degradation such as audio interruption and image data delay can be prevented.

  CWmin is included in QoS Parameter, and a base station (hereinafter referred to as AP (Access Point)) uses a beacon frame that is broadcast information distributed by AP to set a set of QoS Parameters for four categories. Deliver to all terminals. All terminals under the AP use a common value for the QoS Parameter for each category.

  For example, Patent Document 1 discloses a base station having a function of changing CWmax and / or CWmin used when calculating a backoff period. Thereby, an increase in the collision rate of packets can be improved, and performance can be improved.

Patent Document 2 discloses a QoS providing method for changing CWmin for calculating a backoff period based on a smoothed probability of failure or collision.
JP 2006-246030 A Special Table 2006-520140

However, the base station described in Patent Document 1 has the same access category because the QoS parameters are the same in all terminals, although the priority control based on the above-described category functions effectively between different access categories for the QoS function. Priority control does not work in between. In addition, in a terminal in which the initial random number is set small, there is a problem that the collision avoidance function characteristics due to back-off deteriorate when the number of terminals increases.
Furthermore, with respect to the QoS providing method described in Patent Document 2, although the CW can be changed for each terminal, if the transmission timing between the above-described high-priority terminals coincides between the terminals, There is a problem in that collision / retransmission higher than usual occurs as compared with the bandwidth load status information.

  A radio terminal according to the present invention includes a load status information acquisition unit that acquires load status information of a band, a retransmission history information acquisition unit that acquires data retransmission history information required for the radio terminal to retransmit data, and a load status Information and data retransmission history information are compared to determine whether collision / retransmission is likely to occur in the radio band channel, and the determination unit is likely to cause collision / retransmission in the radio band channel. And a CWmin updating unit that updates the contention window by increasing a minimum value (hereinafter referred to as CWmin).

With such a configuration, in a situation where collision / retransmission is likely to occur, the back-off period can be started from a longer period, and data can be transmitted at a timing different from that of other terminals.
For this reason, even when the transmission timing between terminals with high priority coincides accidentally between terminals, unnecessary collision / retransmission can be avoided.

  The wireless terminal communication control method according to the present invention includes a step of acquiring bandwidth load status information, a step of acquiring data retransmission history information required for the wireless terminal to retransmit data, a load status information, and Comparing with data retransmission history information to determine whether collision / retransmission is likely to occur in the radio band channel, and when it is determined that collision / retransmission is likely to occur in the radio band channel And a step of increasing and updating the minimum value of the contention window (hereinafter referred to as CWmin).

  By such a method, in a situation where collision / retransmission is likely to occur, unnecessary collision / retransmission can be avoided even if the transmission timing between terminals with high priority coincides accidentally between terminals.

  According to the present invention, it is possible to provide a wireless terminal and a wireless terminal communication control method capable of avoiding unnecessary collision / retransmission even when the transmission timing between terminals with high priority coincides accidentally between terminals. can do.

Embodiment 1 of the Invention
Hereinafter, a specific first embodiment to which the present invention is applied will be described in detail with reference to the drawings. FIG. 1 is a diagram showing a configuration of a wireless LAN system including a wireless terminal according to Embodiment 1 of the present invention. As shown in FIG. 1, in the wireless LAN system, a plurality of VoIP (Voice over Internet Protocol) terminals 12 to 14 as wireless LAN terminals are connected to an AP (access point) 11 as a wireless LAN base station.
Here, the AP 11 and the VoIP terminals 12 to 14 are devices compliant with IEEE 802.11e. Although not shown in FIG. 1, a plurality of VoIP terminals can exist in addition to the VoIP terminals 12 to 14.

FIG. 2 is a diagram illustrating an internal configuration of the VoIP terminals 12 to 14.
As shown in FIG. 2, the VoIP terminal includes a load status information acquisition unit 21 that acquires bandwidth load status information from a beacon frame, a retransmission history information acquisition unit 22 that acquires the number of data retransmissions as data retransmission history information, A determination unit 23 that determines whether or not collision / retransmission is likely to occur in the wireless band channel, and a CWmin update unit 34 that increases and updates CWmin are provided. Although not shown in FIG. 2, it is assumed that the VoIP terminal also has other necessary functions based on IEEE 802.11e.

Next, in the wireless LAN system shown in FIG. 1, a specific operation by the VoIP terminal according to Embodiment 1 of the present invention will be described. In the first embodiment described below, it is assumed that all VoIP terminals 12 to 14 transmit data in a 20 ms cycle.
FIG. 3 is a flowchart showing processing by the VoIP terminal according to Embodiment 1 of the present invention.

  As shown in FIG. 3, the load status information acquisition unit 21 first receives a beacon frame from the AP 11, and acquires the load status information of the band based on the QBSS load information included in the beacon frame (S301).

The beacon frame is transmitted by broadcast so that the AP 11 periodically notifies the broadcast information. As shown in FIG. 4, the beacon frame 41 is a parameterized quality of service (QoS) of IEEE802.11e. It includes a QBSS (QoS Basic Service Set) Load element 42 as a service set (BSS), and further includes Channel Utilization 43 information indicating the load status information of the band.
Thereby, the VoIP terminal can grasp | ascertain the load condition of a zone | band.
The means for acquiring the load status of the band is not limited to the channel utilization 43 information. For example, the VoIP terminal transmits a probe request to the AP 11 and acquires the load status of the band based on the response status from the AP 11. You may comprise as follows.

Next, the retransmission history information acquisition unit 22 acquires the number of data retransmissions as data retransmission history information required for the VoIP terminal to retransmit one piece of data (S302).
The data retransmission history information is not limited to the number of data retransmissions, and may be calculated based on, for example, the data transmission time required for data transmission.

Next, the determination unit 23 compares the load status and the number of data retransmissions to determine whether or not collision / retransmission is likely to occur due to accidental coincidence of transmission timings between VoIP terminals with high priority in the radio band channel. Is determined (S303).
Here, for comparison of the load status and the number of data retransmissions, for example, compare the number of data retransmissions is small despite the high load status, or the number of data retransmissions is large despite the low load status, In such a case, the number of data retransmissions according to the channel usage status is not reached, and it is determined that collision / retransmission is likely to occur.

When the determination unit 23 determines that a collision / retransmission is likely to occur due to accidental coincidence of transmission timings between VoIP terminals with high priority in the wireless band channel, the CWmin update unit 24 selects the VoIP terminal. The CWmin of the category AC_VO set in is increased and updated as will be described later (S304).
Thereby, the VoIP terminal can start the back-off period from a longer period. For this reason, data can be transmitted at a different timing from other terminals, and collision can be avoided.

Next, an initial setting value of CWmin and an updating method thereof will be described.
First, CWmin that is the minimum value of the contention window for category AC_VO will be described.
When the CWmin of the category AC_BE is set to aCWmin, the initial setting value of the CWmin of the category AC_VO is calculated based on the following Equation 1.
AC_VO CWmin = ((aCWmin + 1) / 4) −1 (Expression 1)
When the initial setting value of CWmin of the category AC_VO calculated by the above equation 1 is increased and updated, it is increased based on the following equation 2 and updated by changing the constant n.
AC_VO CWmin = ((aCWmin + 1) / 4) + n (Expression 2)

Also, CWmax, which is the maximum value of the contention window for category AC_VO, is calculated based on the following Equation 3.
AC_VO CWmax = ((aCWmin + 1) / 2) −1 (Expression 3)
On the other hand, CWmin for category AC_VI is calculated based on Equation 4 below.
AC_VI CWmin = ((aCWmin + 1) / 2) −1 (Expression 4)

Here, when the category AC_VO CWmin calculated by the above equation 2 is larger than the category AC_VI CWmin calculated by the above equation 4, for example, VI data is transmitted by the category AC_VI to the wireless LAN system shown in FIG. The priority of the VoIP terminal may fall when there is a terminal to do.
For this reason, the CWmin of the category AC_VO needs to satisfy CWmin <CWmax and satisfy AC_VO CWmin <AC_VI CWmin with respect to the AC_VI CWmin of the category AC_VI having a lower priority. That is, the CWmin of the category AC_VO needs to satisfy the following formula 5 based on the above formula 2, formula 3, and formula 4.
AC_VO CWmin: ((aCWmin + 1) / 4) −n <((aCWmin + 1) / 2) −1 (Equation 5)
Therefore, from Equation 1, Equation 2, and Equation 5, the constant n satisfies the following Equation 6.
−１-1 <n <((aCWmin + 1) / 4) -1 (Expression 6)

  In the above example, the method of updating the CWmin of the category AC_VO set in the VoIP terminal has been described, but the present invention is not limited to this. For example, the CWmin of the category AC_VI may be configured to start from the initial setting value and increase so as not to exceed the CWmax of the category AC_VI and the CWmin of the category AC_BK.

Embodiment 2 of the Invention
Next, a wireless terminal according to Embodiment 2 of the present invention will be described with reference to the drawings. The overall configuration of the wireless system including the wireless terminal according to Embodiment 2 of the present invention is the same as the configuration shown in FIG.

FIG. 5 is a diagram showing an internal configuration of the VoIP terminals 12 to 14 as wireless LAN terminals according to the second embodiment of the present invention.
As shown in FIG. 5, the VoIP terminal includes a load status information acquisition unit 51 that acquires bandwidth status information from a beacon frame, and a retransmission status change that detects a tendency for the number of data retransmissions to increase as a change in the data retransmission status. A detection unit 52, a determination unit 53 that determines whether or not a collision / retransmission is likely to occur in a radio band channel, and a CWmin update unit 54 that increases and updates CWmin are provided. Although not shown in FIG. 5, it is assumed that the VoIP terminal also has other necessary functions based on IEEE802.11e.

  FIG. 6 is a flowchart showing processing by the VoIP terminal according to Embodiment 2 of the present invention. In the second embodiment described below, it is assumed that VoIP terminals that transmit data at a cycle of 20 ms and VoIP terminals that transmit data at a cycle of 40 ms are mixed.

  As shown in FIG. 6, first, the load status information acquisition unit 21 receives a beacon frame from the AP 11, and acquires the load status information of the band based on the QBSS load information included in the beacon frame (S601).

Next, the retransmission status change detection unit 52 detects a tendency for the number of data retransmissions to increase as a change in the data retransmission status based on at least a plurality of pieces of history information included in the stored data retransmission history information (S602). Here, the number of data retransmissions as data retransmission history information acquired by the retransmission history information acquisition unit 22 is stored in a memory (not shown) over a certain period.
The data retransmission history information is not limited to the number of data retransmissions, and may be calculated based on, for example, the data transmission time required for data transmission.
Thereby, it is possible to detect a phenomenon in which the number of data retransmissions increases or decreases over a certain period.

Next, the determination unit 53 compares the load status detected in S601 and the number of data retransmissions in the cycle in which the number of data retransmissions increases, thereby periodically matching the transmission timing between terminals with high priority. It is determined whether or not a collision / retransmission is likely to occur (S603).
Here, for comparison of the load status information and the number of data retransmissions, for example, a comparison is made such that the number of data retransmissions is small even though the load status is high, or the number of data retransmissions is large even though the load status is low. In such a case, it is determined that the number of times of data retransmission according to the channel usage status is not reached and collision / retransmission is likely to occur.

When the determination unit 53 determines that a situation in which collision / retransmission is likely to occur due to the coincidence of transmission timings between terminals having high priority, the CWmin update unit 54 increases the number of data retransmissions. The CWmin of the category AC_VO set in the VoIP terminal is increased and updated according to the period to be performed (S604).
Thereby, the VoIP terminal can start the back-off period from a longer period in accordance with the cycle in which the number of times of data retransmission increases. For this reason, data can be transmitted at a different timing from other terminals, and collision can be avoided.

Embodiment 3 of the Invention
Next, a wireless terminal according to Embodiment 3 of the present invention will be described with reference to the drawings. The overall configuration of the wireless system including the wireless terminal according to Embodiment 3 of the present invention is the same as the configuration shown in FIG.

FIG. 7 is a diagram showing an internal configuration of the VoIP terminals 12 to 14 as wireless LAN terminals according to the third embodiment of the present invention.
As shown in FIG. 7, the VoIP terminal includes a TIM information extraction unit 71 that extracts TIM information from a beacon frame, a determination unit 72 that determines whether collision / retransmission is likely to occur in a radio band channel, A CWmin updating unit 73 that updates the CWmin by increasing it is provided. Although not shown in FIG. 7, it is assumed that the VoIP terminal also has other necessary functions based on IEEE 802.11e.

  FIG. 8 is a flowchart showing processing by the VoIP terminal according to Embodiment 3 of the present invention. In the third embodiment described below, it is assumed that the VoIP terminals 12 to 14 are expected to collide immediately after the beacon frame.

As shown in FIG. 8, first, the TIM information extraction unit 71 extracts TIM (Traffic Indication Map) information indicating whether or not the AP 11 has data addressed to the wireless terminal from the beacon frame, and the packet addressed to the terminal itself. It is confirmed whether or not is buffered (S801).
Further, the TIM information extraction unit 71 checks whether or not there are a plurality of TIMs addressed to other terminals other than the terminal itself (S802).

  Here, as shown in FIG. 9, the beacon frame 91 includes TIM information 92 including information indicating the presence / absence of transmission data to the wireless terminal in the power save mode.

  Next, when the determination unit 72 indicates that, based on the TIM information, the AP 11 has the data addressed to its own terminal and the data addressed to a plurality of other terminals, It is determined whether or not collision / retransmission is likely to occur (S803).

When the determination unit 72 determines that collision / retransmission is likely to occur in the radio band channel, the CWmin update unit 73 is set in the VoIP terminal because a collision due to PS-Poll / QoS Null is expected. The CWmin of the category AC_VO to be updated is temporarily increased (S804).
Note that the temporarily increased CWmin may be configured to return to a value before the increase when, for example, a TIM addressed to the terminal itself is not set.
Thus, by temporarily increasing CWmin, it is possible to avoid a collision due to PS-Poll / QoS Null.

  The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention.

1 is a configuration diagram of a wireless LAN system according to an embodiment of the present invention. It is a block diagram of the radio | wireless terminal concerning embodiment of this invention. It is a flowchart which shows the process of the radio | wireless terminal concerning embodiment of this invention. It is a figure which shows the beacon frame concerning embodiment of this invention. It is a block diagram of the radio | wireless terminal concerning embodiment of this invention. It is a flowchart which shows the process of the radio | wireless terminal concerning embodiment of this invention. It is a block diagram of the radio | wireless terminal concerning embodiment of this invention. It is a flowchart which shows the process of the radio | wireless terminal concerning embodiment of this invention. It is a figure which shows the beacon frame concerning embodiment of this invention.

Explanation of symbols

11 AP
12-14 VoIP terminal 21 Load status information acquisition unit 22 Retransmission history information acquisition unit 23 Determination unit 24 CWmin update unit 41 Beacon frame 42 QBSS Load
43 Channel Utility
51 Load Status Information Acquisition Unit 52 Retransmission Status Change Detection Unit 53 Determination Unit 54 CWmin Update Unit 71 TIM Information Extraction Unit 72 Determination Unit 73 CWmin Update Unit 91 Beacon Frame 92 TIM Information

Claims (8)

A load status information acquisition unit for acquiring bandwidth status information;
A retransmission history information acquisition unit for acquiring data retransmission history information required for the wireless terminal to retransmit data;
A determination unit that compares the load status information and the data retransmission history information and determines whether collision / retransmission is likely to occur in a radio band channel; and
A CWmin update unit that increases and updates a minimum contention window value (hereinafter referred to as CWmin) when the determination unit determines that collision / retransmission is likely to occur in the wireless band channel; Wireless terminal. The wireless terminal is
Based on at least a plurality of history information included in the data retransmission history information, further comprises a retransmission status change detection unit for detecting a cycle in which the data retransmission status changes,
The determination unit compares the load status information and the data retransmission history information in a period in which the data retransmission status changes, and determines whether or not collision / retransmission is likely to occur in a radio band channel,
The radio terminal according to claim 1, wherein the CWmin update unit updates the CWmin by increasing the CWmin in accordance with a cycle in which the data retransmission status changes. A TIM information extraction unit that extracts TIM (Traffic Indication Map) information included in the beacon frame;
When the TIM information indicates that the base station has data addressed to itself and a plurality of data addressed to other terminals, collision / retransmission is likely to occur in a radio band channel. A determination unit for determining whether or not a situation is present;
And a CWmin update unit that increases and updates a minimum contention window value (hereinafter referred to as CWmin) when the determination unit determines that collision / retransmission is likely to occur in a radio band channel. Wireless terminal. The wireless terminal according to claim 4, wherein the CWmin updating unit updates the CWmin by temporarily increasing the CWmin. Obtaining bandwidth load status information;
Obtaining data retransmission history information required for the wireless terminal to retransmit the data;
Comparing the load status information and the data retransmission history information, determining whether or not collision / retransmission is likely to occur in a radio band channel; and
Communication control of a wireless terminal comprising a step of increasing and updating a minimum contention window (hereinafter referred to as CWmin) when it is determined that collision / retransmission is likely to occur in the wireless band channel Method. The communication control method includes:
Further comprising detecting a change in data retransmission status based on at least a plurality of history information included in the data retransmission history information;
Compare the load status information and the data retransmission history information in a cycle in which the data retransmission status changes, determine whether or not a collision / retransmission is likely to occur in the radio band channel,
6. The communication control method for a radio terminal according to claim 5, wherein CWmin is increased and updated according to a cycle in which the data retransmission status changes. Extracting TIM (Traffic Indication Map) information included in the beacon frame;
When the TIM information indicates that the base station has data addressed to itself and a plurality of data addressed to other terminals, collision / retransmission is likely to occur in a radio band channel. Determining whether a situation is present;
A communication control method for a wireless terminal, comprising: a step of increasing and updating a minimum contention window value (hereinafter referred to as CWmin) when it is determined that collision / retransmission is likely to occur in a wireless band channel. The wireless terminal communication control method according to claim 7, wherein the CWmin is temporarily increased and updated.

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