JP2015119300A - System and method for applying access control based on allowable transmission time length to wireless lan - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a system and method for executing access control so as not to reduce throughput of the whole wireless LAN, even in the case that a terminal having a low transmission rate exists when seeing from an access point.SOLUTION: An access point transmits a control packet including an allowable transmission time length for a data frame to be transmitted, to a terminal. On the other hand, the terminal adjusts the size of a data frame to be transmitted by the terminal so that transmission time for the data frame is equal to or shorter than the allowable transmission time length. The control packet is a beacon signal whose frame body includes the allowable transmission time length. The access point is executed in a PCF mode. The control packet includes a non-collision time length for a wireless resource. The terminal transmits a data frame having the adjusted size to the access point, when receiving polling.

Description

  The present invention relates to a MAC (Media Access Control) technique in a wireless local area network (LAN).

  The wireless LAN can communicate using a frequency band that does not require a radio station license. Due to its convenience, many access points are installed in various places, and terminals (notebook computers, smartphones, tablets, etc.) possessed by users are also equipped with a wireless LAN communication function as standard. The access point is connected from the user terminal via the wireless LAN, and on the other hand, connected to the access network and the Internet. As a result, the terminal can access a server connected to the Internet via the access point.

According to IEEE802.11 of a wireless LAN, a MAC technique for controlling the timing at which an access point or terminal transmits a data frame is defined (for example, see Non-Patent Document 1). Specifically, there are the following two modes.
DCF (Distributed Coordination Function) mode PCF (Point Coordination Function) mode

(DCF mode)
According to the DCF mode, each terminal performs control in an autonomous and distributed manner by CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) on the premise of data frame collision.

  FIG. 1 is a sequence diagram based on the DCF mode of the wireless LAN.

  According to FIG. 1, the access point 1 and the terminals 2a and 2b communicate via a wireless LAN. The access point 1 and the terminal 2 first confirm that the radio channel is not busy (in use) by carrier sense. When the wireless channel is busy, the process waits until the transmission of the data frame from the terminal in use ends and becomes idle (unused).

When the radio channel is in an idle state, the terminal 2 holding the data frame to be transmitted waits for an IFS (Inter Frame Space) time. Thereafter, the terminal 2 further performs carrier sense only for the “back-off time”, and confirms whether or not the idle state continues. Here, the back-off time avoids frame collision due to simultaneous transmission, and is based on a random number generated by each terminal within a specified range. Specifically, the back-off time based on the random number is determined by the following equation.
Backoff time = slot time × random number There is no bias in the probability of random number generation, and a transmission opportunity is given fairly to the access point 1 and all terminals 2.

(PCF mode)
According to the PCF mode, the access point 1 sets a “non-collision time” called CFP (Contention Free Period). The access point 1 transmits polling (transmission right) in order to call each connected terminal in order during the CFP period. Since only the terminal 2 designated by the access point 1 can transmit a data frame, a data frame collision does not occur in the wireless LAN. During this CFP period, the access point 1 can give a fair communication opportunity to each connected terminal 2.

  In addition, there is a technique that defines a retransmission procedure when delivery confirmation to the counterpart terminal or access point cannot be performed during the CFP period set by the access point (see, for example, Patent Document 1).

JP 2012-015899 A

IEEE Std 802.11-2012, [online], [Search December 8, 2013], Internet <URL: http://en.wikipedia.org/wiki/IEEE_802.11>

  According to Non-Patent Document 1 (IEEE802.11n wireless standard), when MIMO (Multi-Input Multi-Output) spatial multiplexing is not used, a transmission rate of a wireless link of up to 65 Mbps can be achieved for a channel bandwidth of 20 MHz.

Here, it is assumed that the access point 1 having 65 Mbps providing capability communicates with two terminals 2.
Terminal 2a: Close to the access point and the wireless link transmission rate is 65Mbps
Terminal 2b: Distance from the access point, wireless link transmission rate is 1Mbps

Here, fair transmission opportunities are given to both the terminal 2a and the terminal 2b, and data frames of the same size are transmitted with the maximum capability of the radio link. At this time, the transmission time of the terminal 2b takes a transmission time that is 65 times the transmission time of the terminal 2a.
Terminal 2b transmission time = terminal 2a transmission time × 65

That is, the terminal 2a can use only 1/66 in terms of time for the radio resource of the access point 1 having 65 Mbps providing capability. As a result, the transmission rate is as follows, and the performance degradation at the terminal 2a cannot be ignored.
Terminal 2a: 65Mbps / 66 = about 1Mbps
Terminal 2b: 1Mbps x 65/66 = about 1Mbps
Here, in order to simplify the calculation, loss due to radio frame header, IFS time, overhead such as backoff, frame collision, retransmission, etc. is not considered.

  FIG. 2 is a sequence diagram illustrating that a terminal with a low transmission rate of a radio link occupies a long transmission time of a data frame.

When the terminal 2 having a low transmission rate such as the terminal 2b obtains a transmission opportunity, the transmission time of the transmission frame becomes long, and the radio channel is occupied for a relatively long time. The transmission frame occupation time is calculated as follows.
Occupied time of transmission frame =
Frame header length / transmission rate (fixed) + data length / transmission rate

  As a result, when there is a terminal 2b having a low radio link transmission rate as viewed from the access point 1, a problem arises in that radio resources are consumed greatly. As a result, even if the terminal 2a has a high transmission rate of the wireless link, it is necessary to wait for a long time until a transmission opportunity is obtained, and the throughput of the entire wireless LAN is reduced. This problem becomes more prominent in an environment where a large number of terminals 2 are connected to one access point 1 via a wireless LAN. Although FIG. 2 describes the DCF mode, this problem is the same even in the PCF mode.

  Therefore, the present invention provides a system and method for performing access control so as not to reduce the throughput of the entire wireless LAN even when there is a terminal having a low transmission rate when viewed from the access point. Objective.

According to the present invention, in a system in which an access point and a plurality of terminals communicate via a wireless LAN,
The access point transmits a control packet including an allowable transmission time length for a data frame to be transmitted to the terminal,
The terminal is characterized by adjusting the size of the data frame so that the transmission time for the data frame to be transmitted by itself is equal to or less than the allowable transmission time length.

According to another embodiment of the system of the present invention, for the access point:
The control packet is a beacon signal,
The allowable transmission time length is also preferably included in the frame body of the beacon signal.

According to another embodiment of the system of the present invention, for the access point:
Running in PCF mode,
The control packet includes the non-collision time length of the radio resource,
During that non-collision time length, polling is sent sequentially to each connected terminal,
About the device
When a control packet is received, it shifts to access control to suppress the transmission of data frames during the non-collision time length,
When polling is received, it is also preferable to transmit a data frame having a size adjusted to be equal to or less than the allowable transmission time length to the access point.

According to another embodiment of the system of the present invention,
The terminal includes, in the data frame transmitted to the access point, the remaining non-collision time length obtained by subtracting the time difference from the reception time of the control packet to the current time from the non-collision time length,
It is also preferable that the terminal that has received the data frame shifts to access control to suppress transmission of the data frame for the remaining non-collision time length included in the data frame.

According to another embodiment of the system of the present invention, for the access point:
It is also preferable to variably set the non-collision time length as the radio resource utilization rate increases.

According to another embodiment of the system of the present invention, for the access point:
It is also preferable to variably set the allowable transmission time length as the number of currently connected terminals increases.

According to another embodiment of the system of the present invention, for the access point:
It is also preferable to variably set the allowable transmission time length as the ratio of the data amount in the uplink direction (terminal-> access point) to the data amount in the downlink direction (access point-> terminal) increases. .

According to another embodiment of the system of the present invention,
When the transmission rate calculated from the allowable transmission time length received from the access point and the current wireless modulation rate is equal to or lower than a preset desired transmission rate, the terminal disconnects the wireless link with the access point. It is also preferable.

According to another embodiment of the system of the present invention,
The access point has a function of imparting directivity to the transmission direction of a radio signal using a plurality of antennas, and transmits different control signals to a group of a plurality of terminals at the same time, and has different allowable transmission time length values. It is also preferable to poll each terminal for each directivity at the same time.

According to the present invention, in a data frame transmission method in a system in which an access point and a plurality of terminals communicate via a wireless LAN,
The access point transmits a control packet including an allowable transmission time length for a data frame to be transmitted to the terminal,
The terminal is characterized by adjusting the size of the data frame so that the transmission time for the data frame to be transmitted by itself is equal to or less than the allowable transmission time length.

  According to the system and method of the present invention, even when there is a terminal having a low transmission rate as viewed from the access point, access control is performed so as not to reduce the throughput of the entire wireless LAN. The access point restricts the size of the data frame transmitted from the terminal so that it does not exceed the predetermined allowable transmission time, so that the data frame from the terminal with a low transmission rate occupies radio resources for a relatively long time. To prevent it.

It is a sequence diagram based on DCF of wireless LAN. It is a sequence diagram showing that the terminal with a low transmission rate of a radio link occupies the transmission time of a data frame long. It is a sequence diagram in the present invention. It is a frame block diagram in this invention. It is a function block diagram of the access point in this invention. It is a function block diagram of the terminal in this invention.

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

  According to the present invention, the PCF mode in the MAC is used, and the access point includes “allowable transmission time length” for the data frame to be transmitted in the control packet transmitted to the terminal. On the other hand, when the terminal receives polling during the CFP period (non-collision period), the terminal sets the size of the data frame so that the transmission time for the data frame to be transmitted is less than the allowable transmission time length. adjust. As a result, it is possible to prevent a terminal having a low wireless LAN transmission rate from occupying a data frame transmission time for a relatively long time. That is, it is possible to provide an optimal use environment as a whole for the wireless resources of the wireless LAN.

FIG. 3 is a sequence diagram in the present invention.
FIG. 4 is a frame configuration diagram in the present invention.

(S1) The access point 1 broadcasts a “beacon signal” at regular intervals based on the IEEE 802.11 standard. The beacon signal notifies each terminal 2 of the existence of the connectable access point 1.

  According to the frame of the beacon signal in FIG. 4A, the CFP is set in the duration portion of the MAC header. The CFP represents that the terminal is “non-collision period length” during the duration value (μ seconds). The peripheral terminals 2 that have received this beacon signal shift to PCF mode access control, and suppress the transmission of data frames spontaneously.

  According to the present invention, the frame body of the beacon signal further includes an “access management information element (Controlled Access IE)” and an “allowed transmission time length (Allowed TX Time)” as its information field. The allowable transmission time length means the maximum transmission time that all the terminals 2 can occupy with the data frame to be transmitted by themselves. The CFP set including Controlled Access IE is referred to as “MCFP (Managed Contention Free Period)”.

  Further, the access point 1 is not limited to including the allowable transmission time length in the beacon signal, and may be a “probe response” that is returned when the access point 1 receives a probe request from the terminal 2.

  According to FIG. 4B, the “control packet” separately defined in advance includes the allowable transmission time length. Here, an allowable transmission time length of a data frame transmitted by the terminal is specified as an MCF (Managed Contention Function) data frame. Thus, the present invention is not limited to the frame configuration of the beacon signal or the probe response, and may be configured as a separately defined control packet.

  In the above embodiment, the beacon signal is described as including the allowable transmission time length. However, after authentication between the access point 1 and the terminal 2, an association request (Association Request) transmitted from the terminal 2 is used. On the other hand, the allowable transmission time length can also be included in the frame body of the association response transmitted from the access point 1. That is, it suffices if the allowable transmission time length can be notified from the access point 1 to the terminal 2 at the stage of establishing the wireless link between the access point 1 and the terminal 2.

  According to S1, each terminal 2 knows the start of access control from the access point 1 and the non-collision time length (MCFP) of the radio resource by receiving the MCFP beacon signal. Thereafter, during the non-collision time, the terminal 2 shifts to access control in order to suppress transmission of the data frame, and waits for polling (transmission right) from the access point 1.

  As another embodiment, the access point may preferably set the “non-collision time length” variably so that the non-collision time length becomes longer as the radio resource utilization rate increases. The utilization rate of radio resources may simply be a time ratio during which radio resources are used.

(S2) Since the access point 1 and the terminal 2 are executed in the PCF mode, “SIFS (Short Inter Frame Space)” shorter than DIFS (Distributed Inter Frame Space) is used as the transmission interval between the frames. Can do. In addition, since the PCF mode is used, it is not necessary to take a back-off time for preventing frame collision. As a result, for example, even if a beacon signal in which MCFP is set is not received by a terminal being controlled in the DCF mode, there is room for the terminals to interrupt the PCF mode access point and the terminal and transmit a data frame. Absent.

  The access point 1 sequentially transmits polling (transmission right) to each connected terminal during the non-collision time length. According to FIG. 3, the access point 1 first transmits polling to the terminal 2a after SIFS has elapsed. Each terminal 2 can transmit a data frame only when it receives polling for its own terminal from the access point 1.

  FIG. 4C shows a CF-Poll polling frame. Note that since CF-Poll does not include a payload, it cannot include additional information such as an allowable transmission time length.

(S3) Upon receiving polling from the access point 1, the terminal 2a recognizes that its own terminal has obtained the transmission right and waits for SIFS. Then, the terminal 2a adjusts the size of the data frame to be transmitted to the access point 1 so as to be equal to or less than the allowable transmission time length, and transmits the data frame to the access point 1. Specifically, the data frame length can be calculated by the following equation.
Data frame length = (permitted transmission time x transmission rate-frame header length)
Here, since the terminal 2a is close to the access point 1 and has a relatively high transmission rate, it is assumed that the data frame transmission only takes a time shorter than the allowable transmission time length.
Then, the access point 1 receives a data frame from the terminal 2a.

(S4) Next, after waiting for SIFS, the access point 1 transmits CF-Poll polling to the terminal 2b.

(S5) By receiving polling from the access point 1, the terminal 2b recognizes that its own terminal has obtained the transmission right, and waits for SIFS. Then, the terminal 2 b adjusts the size of the data frame to be transmitted to the access point 1 so as to be equal to or less than the allowable transmission time length, and transmits the data frame to the access point 1.
Here, the terminal 2b is far from the access point 1 and has a relatively low transmission rate. However, data frames can be transmitted only up to the allowable transmission time length. In this case, it is assumed that the terminal 2b takes a full allowable transmission time length to transmit a data frame.
Then, the access point 1 receives a data frame from the terminal 2b.

(S6) Next, after waiting for SIFS, the access point 1 further transmits CF-Poll polling to another terminal 2.

(S7) Finally, the access point 1 waits for PIFS when the MCFP period is reached or when there is no data frame transmission from the terminal 2.
Then, the access point 1 broadcasts CF-End to all the terminals 2 in order to release radio resources from access control. As a result, the access point 1 terminates the non-collision period of the access-controlled MCFP.
After the release of the MCFP, each terminal 2 can also transmit a data frame that has not been transmitted during the MCFP period in the DCF mode.

[Device that cannot receive the access point signal]
(S8) As another embodiment, the operation of the terminal 2c that cannot receive the radio waves of the access point 1 will be described. It is assumed that the terminal 2c is farther away from the access point 1 and has not received a beacon signal. Therefore, the terminal 2c does not recognize that it is the MCFP period. At this time, the terminal 2c may spontaneously transmit a data frame in the DCF mode.

Therefore, each terminal 2 includes the remaining non-collision time length obtained by subtracting the time difference from the reception time of the control packet to the current time from the non-collision time length in the data frame transmitted to the access point.
Remaining non-collision time length = non-collision time length-time difference from the reception time of the control packet to the present time

  Specifically, it is also preferable to include the “remaining non-collision time length” in the duration included in the MAC header of the transmission frame. For example, the terminal 2c detects a data frame transmitted from the terminal 2b toward the access point 1, and recognizes that the duration of the data frame includes the remaining non-collision time length. At this time, the terminal 2c recognizes that the PCF mode is in the non-collision period during the time value, and does not transmit the data frame spontaneously. As a result, the terminal 2c does not transmit a packet that collides with a data frame transmitted between the access point 1 and the terminals 2a and 2b.

[Variable setting of allowable transmission time length]
As another embodiment, it is also preferable to change the allowable transmission time length defined by the access point 1 according to the surrounding environment of the wireless LAN. For example, there are two methods.

(First variable setting)
It is set variably so that the allowable transmission time length becomes shorter as the number of currently connected terminals increases.

(Second variable setting)
According to the Web server-client system, the data amount in the uplink direction (terminal-> access point) is usually smaller than the data amount in the downlink direction (access point-> terminal). Therefore, the allowable transmission time length is variably set as the ratio of the uplink data amount to the downlink data amount increases. On the contrary, the allowable transmission time length is set to be shorter as the ratio of the uplink data amount is lower.

[Disconnection of radio link from terminal when desired transmission rate cannot be obtained]
As another embodiment, the terminal 2 can calculate a trial transmission rate from the allowable transmission time length received from the access point 1 and the current radio modulation rate.
Trial transmission rate = allowable transmission time length × wireless modulation rate currently in use The terminal 2 disconnects the radio link with the access point when the trial transmission rate is equal to or lower than a preset desired transmission rate. Thereafter, reconnection to another access point or mobile phone network can be performed.

[Setting of allowable transmission time length for different directivity for spatial multiplexing]
In recent years, spatial multiplexing has been put into practical use by using multiple antennas to provide directivity in the data transmission direction, thereby suppressing interference between multiple wireless links and enabling simultaneous communication of multiple wireless links. I am trying to do.
Therefore, as another embodiment, the access point 1 is directed in the radio signal transmission direction using a plurality of antennas based on the spatial multiplexing technology (MIMO (multiple-input and multiple-output), IEEE 802.11n) technology. It may be provided with a function of imparting properties. As a result, the access point 1 can simultaneously transmit different control signals to a group of a plurality of terminals, set different allowable transmission time length values, and simultaneously poll each terminal for each directivity.

  FIG. 5 is a functional configuration diagram of the access point in the present invention.

[Transmission side functional component]
The Ethernet communication unit 101 outputs the IP packet received from the Ethernet (registered trademark) to the transmission buffer unit 111.
The transmission buffer unit 111 temporarily accumulates data for each connected terminal 2 and outputs the data frame to the transmission MAC unit 112.
The transmission MAC unit 112 converts the data frame input from the transmission buffer unit 111 into a wireless LAN MAC frame format. Specifically, a MAC header is added. Then, transmission MAC section 112 outputs the MAC frame to transmission PHY (Physical Layer) section 113 at the timing instructed by the scheduling section. The transmission MAC unit 112 generates a management MAC frame and a control MAC frame necessary for controlling the wireless LAN, in addition to the IP packet received by the Ethernet communication unit 101.
The transmission PHY unit 113 digitally modulates the MAC frame to convert it into an analog signal, and outputs the analog signal to an RF (Radio Frequency) unit 102.
The RF unit 102 up-converts the analog signal from the baseband band to the transmission frequency band and outputs it to the antenna.
The radio signal transmitted from the antenna is transmitted to the peripheral terminal 2.

[Receiving side function component]
The antenna outputs the received radio signal to the RF unit 102.
The RF unit 102 down-converts the radio signal from the reception frequency band to the baseband band, and outputs the radio signal to the reception PHY unit 123.
The reception PHY unit 123 digitally demodulates the analog signal and converts it into a MAC frame. The MAC frame is output to reception MAC section 122. Further, when the reception PHY unit 123 detects the reception power, the reception PHY unit 123 notifies the scheduling unit 131 to that effect.
When the destination address of the input MAC frame is addressed to the own terminal, the reception MAC unit 122 converts the MAC frame into the IP packet format. The IP packet is output to the reception buffer unit 121. If the received MAC frame is a management MAC frame, the process is executed based on the IEEE 802.11 standard without being converted into an IP packet. Further, when the reception MAC unit 122 identifies the MAC frame, the reception MAC unit 122 notifies the scheduling unit 131 to that effect.
The reception buffer unit 121 sequentially outputs the input IP packets to the Ethernet communication unit 101.
The Ethernet communication unit 101 sequentially transmits the IP packets to the Ethernet.

[Scheduling unit 131]
The scheduling unit 131 instructs the transmission MAC unit 112 on the transmission timing of the data frame in the PCF mode (or DCF mode) (see the transmission timing on the access point side in S2 to S7 in FIG. 3). The scheduling unit 131 sequentially transmits polling to each connected terminal and executes access control.

  The scheduling unit 131 determines “busy state” and “idle state” in the radio resource based on notifications from the reception PHY unit 123 and the reception MAC unit 122. If it is busy, the scheduling unit 131 causes the transmission MAC unit 112 to suspend transmission of the MAC frame. On the other hand, if it is in the idle state, the scheduling unit 131 instructs the transmission MAC unit 112 to transmit the MAC frame when the continuation of the idle state is still confirmed after the SIFS (or DIFS, backoff time, PIFS, etc.) has elapsed. To do.

[Control Packet Transmitter 132]
The control packet transmission unit 132 transmits a control packet including the allowable transmission time length for the data frame to be transmitted to the terminal (see S1 in FIG. 3). The control packet is, for example, a beacon signal, and the allowable transmission time length may be included in the frame body of the beacon signal. It is also preferable that the control packet includes a non-collision time length (MCFP) of the radio resource and notifies the start of access control in the PCF mode.

  FIG. 6 is a functional configuration diagram of a terminal according to the present invention.

  According to FIG. 6, the RF unit 202, the transmission buffer unit 211, the transmission MAC unit 212, the transmission PHY unit 213, the reception buffer unit 221, the reception MAC unit 222, and the reception PHY unit 223 function in the same manner as in FIG. And only the difference between the transmitting side and the receiving side. In addition, the transmission buffer unit 211 and the reception buffer unit 221 input and output data with the application unit via the memory 201.

[Scheduling unit 231]
The scheduling unit 231 instructs the transmission MAC unit 212 about the transmission timing of the data frame in the PCF mode (or DCF mode) (see the transmission timing on the terminal side in S2 to S7 in FIG. 3). The scheduling unit 231 acquires the polling received from the access point 1 from the reception MAC unit 222 and determines the transmission timing of the data frame for the access point 1.

  Further, the scheduling unit 231 determines “busy state” and “idle state” in the radio resource based on notifications from the reception PHY unit 223 and the reception MAC unit 222. If it is busy, the scheduling unit 231 causes the transmission MAC unit 112 to suspend transmission of the MAC frame. On the other hand, if it is in the idle state, the scheduling unit 231 instructs the transmission MAC unit 212 to transmit the MAC frame when the continuation of the idle state is still confirmed after the SIFS (or DIFS, backoff time, PIFS, etc.) has elapsed. To do.

  Furthermore, when receiving a control packet (for example, a beacon signal) from the reception MAC unit 222, the scheduling unit 231 shifts to access control to suppress transmission of a data frame for a non-collision time length (S1 in FIG. 3). (See the transmission timing on the terminal side in).

[Transmission rate management unit 232]
The transmission rate management unit 232 manages the transmission rate notified from the reception MAC unit 122. The transmission rate in communication with the access point 1 is determined by the device of the wireless LAN chip or the device manufacturer. Generally, a lower transmission rate is set as the reception power of the wireless LAN is lower, or a lower transmission rate is set as transmission errors and retransmissions increase. As a result, communication quality is maintained. The transmission rate is output to the data length adjustment unit 233.

[Data length adjustment unit 233]
The data length adjustment unit 233 acquires the allowable transmission time length included in the control packet from the reception MAC unit 222. Also, the current transmission rate is acquired from the transmission rate management unit 232. Then, based on the transmission rate, the data length adjusting unit 233 sets the size of the data frame to the transmission buffer unit 211 so that the transmission time for the data frame to be transmitted is equal to or less than the allowable transmission time length. Adjust (split / reassemble). Specifically, the data length is adjusted as in the following equation.
Allowable transmission time <(PHY header length / basic transmission rate + MAC frame length / transmission rate)
Here, the basic transmission rate is the lowest transmission rate supported by the access point in order to be compatible with the existing IEEE802.11 standard. The 2.4 GHz band is 1 Mbps or 2 Mbps, and the 5 GHz band is 6 Mbps.

  As described above in detail, according to the system and method of the present invention, even when there is a terminal having a low transmission rate when viewed from the access point, the throughput of the entire wireless LAN is not reduced. Perform access control. The access point restricts the size of the data frame transmitted from the terminal so that it does not exceed the predetermined allowable transmission time, so that the data frame from the terminal with a low transmission rate occupies radio resources for a relatively long time. To prevent it.

  According to the present invention, a TDMA (Time Division Multiple Access) access control system is applied to a wireless LAN system using a CDMA / CA access control system. As a result, even if there are many terminals having a low transmission rate around the access point, communication of terminals having a high transmission rate is not affected. Since the transmission time from a terminal having a low transmission rate is limited to the “allowable transmission time length”, the throughput of the entire system can be increased.

  Finally, the effect of applying the present invention will be described with respect to the example described above as the subject of the present invention.

Assume that the access point 1 having the provision capability of 65 Mbps communicates with two terminals 2.
Terminal 2a: Close to the access point and the wireless link transmission rate is 65Mbps
Terminal 2b: Distance from the access point, wireless link transmission rate is 1Mbps

When the CFP period = 0.5 seconds, each terminal can transmit the following data amount.
Terminal 2a alone: 65Mbps x 0.5 = 32.5Mbit during CFP period Terminal 2b alone: 1Mbps x 0.5 = 0.5Mbit during CFP period

Here, when the two terminals 2a and 2b coexist in the CFP period, the data frame of the terminal 2b occupies 65 times as long as the terminal 2a. Therefore, only the following data amount can be transmitted even in the PCF mode.
Terminal 2a: 65 × 0.5 / 66 = about 0.5 Mbits Terminal 2b: 1 × 0.5 × 65/66 = about 0.5 Mbits The terminal 2a and 2b can transmit only a data amount of about 1 Mbit during the CFP period.

On the other hand, according to the present invention, for example, MCFP period = 0.5 seconds and “allowable transmission time = 0.25 seconds” for each terminal 2a, 2b. In this case, the following data amount can be transmitted.
Terminal 2a: 65 × 0.25 = 16.25M bit Terminal 2b: 1 × 0.25 = 0.25M bit This reduces the amount of transmission data of the terminal 2b, but a total of 16.5M bit data can be transmitted in the MCFP period. . Thus, according to the present invention, the throughput of the entire system can be increased.

  Various changes, modifications, and omissions of the above-described various embodiments of the present invention can be easily made by those skilled in the art. The above description is merely an example, and is not intended to be restrictive. The invention is limited only as defined in the following claims and the equivalents thereto.

DESCRIPTION OF SYMBOLS 1 Access point 101 Ethernet communication part 102 RF part 111 Transmission buffer part 112 Transmission MAC part 113 Transmission PHY part 121 Reception buffer part 122 Reception MAC part 123 Reception PHY part 131 Scheduling part 132 Control packet transmission part 2 Terminal 201 Memory 202 RF part 211 Transmission buffer unit 212 Transmission MAC unit 213 Transmission PHY unit 221 Reception buffer unit 222 Reception MAC unit 223 Reception PHY unit 231 Scheduling unit 232 Transmission rate management unit 233 Data length adjustment unit

Claims (10)

In a system in which an access point and a plurality of terminals communicate via a wireless LAN (Local Area Network),
The access point transmits a control packet including an allowable transmission time length for a data frame to be transmitted to the terminal,
The system, wherein the terminal adjusts the size of the data frame so that the transmission time for the data frame to be transmitted is equal to or less than the allowable transmission time length. About the access point
The control packet is a beacon signal;
The system according to claim 1, wherein the allowable transmission time length is included in a frame body of the beacon signal. About the access point
It is executed in PCF (Point Coordination Function) mode,
The control packet includes a non-collision time length of radio resources,
During that non-collision time length, polling is sent sequentially to each connected terminal,
About the terminal
When receiving the control packet, during the non-collision time length, shift to access control to suppress the transmission of the data frame,
3. The system according to claim 1, wherein when the polling is received, a data frame having a size adjusted to be equal to or less than the allowable transmission time length is transmitted to the access point. 4. The terminal includes, in the data frame transmitted to the access point, a remaining non-collision time length obtained by subtracting a time difference from the reception time of the control packet to the current time from the non-collision time length,
The system according to claim 3, wherein the terminal that has received the data frame shifts to access control to suppress transmission of the data frame for a remaining non-collision time length included in the data frame. About the access point
5. The system according to claim 3, wherein the system is variably set so that the non-collision time length becomes longer as the utilization rate of radio resources is higher. About the access point
The system according to any one of claims 1 to 5, wherein the system is variably set so that the allowable transmission time length becomes shorter as the number of currently connected terminals increases. About the access point
The allowable transmission time length is variably set longer as the ratio of the data amount in the upstream direction (terminal-> access point) to the data amount in the downstream direction (access point-> terminal) is higher. 6. The system according to any one of claims 1 to 5, characterized in that When the transmission rate calculated from the allowable transmission time length received from the access point and the current wireless modulation rate is equal to or lower than a preset desired transmission rate, the terminal establishes a wireless link with the access point. The system according to claim 1, wherein the system is cut.   The access point has a function of imparting directivity to the transmission direction of a radio signal using a plurality of antennas, and transmits different control signals to a group of a plurality of terminals at the same time, and has different allowable transmission time lengths. The system according to claim 1, wherein a value is set and polling is simultaneously performed for each terminal for each directivity. In a data frame transmission method in a system in which an access point and a plurality of terminals communicate via a wireless LAN,
The access point transmits a control packet including an allowable transmission time length for a data frame to be transmitted to the terminal,
The data frame transmission method, wherein the terminal adjusts the size of the data frame so that a transmission time for the data frame to be transmitted by itself is equal to or less than the allowable transmission time length.

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