JP2019009602A - Wireless communication device and wireless communication method - Google Patents

Abstract

To suppress lowering of transmission throughput by making it possible to appropriately receive acknowledgment of receipt for transmission data while data retransmission is suppressed.SOLUTION: The wireless communication device (STA) includes: detection means for detecting information on a frequency of data retransmission to another wireless communication device (AP); setting means for setting to limit a reception rate of its own device and not to limit the transmission rate of the own device, if it is determined that the retransmission frequency increases, on the basis of the information on the retransmission frequency detected by the detection means; and notifying means for notifying another wireless communication device of a setting for limiting the reception rate by the setting means.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a wireless communication apparatus and a wireless communication method.

  As an access control technique in a wireless LAN or the like, a technique using a distributed control access method and a centralized control access method is known. The distributed control access method is a method represented by CSMA / CA (Carrier Cense Multiple Access with Collision Avoidance). In the distributed control type access method, each wireless communication device autonomously determines the data transmission timing and transmission rate. That is, the transmission rate of the own device is determined by the own device, and the reception rate of the own device is determined by the opposite device. In a centralized control access method represented by 3GPP (3rd Generation Partnership Project), the base station determines the data transmission timing and transmission rate in each terminal. As described above, in any method, the reception rate of the own device is determined by the opposite device.

  On the other hand, in order to reduce useless retransmission processing from a base station to a specific mobile station, Patent Literature 1 discloses that the mobile station processes packet data received from the base station according to the processing capability. A technique for limiting the upper limit value of the downlink transmission rate is disclosed. In this technology, the mobile station sets the upper limit of the downlink transmission rate based on the BER (Block Error Rate) value of the received packet data and the ratio value of the packet data discarded in the received packet data, This is notified to the base station.

International Publication No. 2007/058178

However, the technique described in Patent Document 1 is based on the premise that the mobile station can measure the BER of the received packet data. When data is transmitted, that is, when there is no data reception, the BER of the received packet data cannot be measured. Not considered.
When the own device transmits data in the wireless LAN, the own device receives an ACK (Acknowledgment) frame that is a reception confirmation response to the data transmission from the opposite device. At this time, the own device can measure a FER (Frame Error Rate) based on the ratio of whether or not an ACK frame is received. On the other hand, the opposite device transmits an ACK frame after receiving the data, but since the response signal is not received for the ACK frame transmission, the opposite device cannot measure the FER. That is, it is impossible to detect a situation in which reception of an ACK frame in the own device has failed even though data reception in the opposite device is successful.

Therefore, in a wireless LAN, when the reception sensitivity is reduced due to the internal noise of the own device and the ACK frame cannot be received, the own device erroneously determines that the other device has failed to receive data and retransmits the data frame. . At this time, the own device can retransmit the data frame at a lower transmission rate. This data retransmission process is repeated while gradually decreasing the transmission rate until the own apparatus can receive an ACK frame or until a predetermined number of retransmissions is reached.
Thus, the deterioration of the reception sensitivity in the radio communication device on the transmission side causes data retransmission and a decrease in the transmission rate, thereby significantly reducing the transmission throughput.
In view of this, an object of the present invention is to suppress a data retransmission and suppress a decrease in transmission throughput by appropriately receiving a reception confirmation response to data transmission.

  In order to solve the above-described problem, an aspect of a wireless communication device according to the present invention includes a detection unit that detects information related to a data retransmission frequency for another wireless communication device, and information related to a retransmission frequency detected by the detection unit. Based on the setting means, the setting means for limiting the reception rate of the own apparatus and not limiting the transmission rate of the own apparatus, and the setting for limiting the reception rate by the setting means Notification means for notifying the other wireless communication device.

  According to the present invention, it is possible to appropriately receive a reception confirmation response to data transmission, thereby suppressing data retransmission and suppressing a decrease in transmission throughput.

It is a structural example of a communication system provided with the radio | wireless communication apparatus which concerns on this embodiment. It is a figure which shows HT Capabilities element format. It is an example of the hardware block diagram of a radio | wireless communication apparatus (STA). It is an example of the functional block diagram of the radio | wireless communication apparatus (STA) of 1st embodiment. It is a flowchart which shows the operation | movement in 1st embodiment. It is an example of the functional block diagram of the radio | wireless communication apparatus (STA) of 2nd embodiment. It is a flowchart which shows the operation | movement in 2nd embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. The embodiment described below is an example as means for realizing the present invention, and should be appropriately modified or changed depending on the configuration and various conditions of the apparatus to which the present invention is applied. It is not limited to the embodiment.

(First embodiment)
FIG. 1 is a configuration example of a communication system 10 in the present embodiment. In the present embodiment, a case will be described in which the communication system 10 is a wireless LAN system compliant with, for example, the IEEE 802.11n standard. Moreover, in this communication system 10, the case where each radio | wireless communication apparatus autonomously performs radio | wireless communication using a CSMA / CA system is demonstrated.
The communication system 10 includes an STA (Station) 20 that is a wireless communication device that is a wireless LAN slave device, and an AP (Access Point) 30 that is a wireless communication device that is a wireless LAN master device. The STA 20 includes an antenna 21, and the AP 30 includes an antenna 31.

FIG. 2 is a diagram showing a format of the HT Capabilities element defined by the IEEE 802.11n standard. The STA 20 adds the elements shown in FIG. 2 to a management frame such as an association request or a probe request and transmits the management frame to the AP 30. In FIG. 2, Element ID has a length of 1 octet and is assigned 45. Length is the field length following the element, and is fixed at 26.
Among the fields following Length, Supported MCS Set is 16 octets long and specifies an MCS (Modulation Coding Scheme) index. Here, the MCS index is a numerical value from 0 to 76 associated with the modulation scheme, the number of used antennas, the communication rate, etc. on a one-to-one basis. That is, the Supported MCS Set is a field for notifying supported rate information indicating information on a transmission rate that can be used by the STA 20 that transmits an element including the field.

The first 77 bits (B0 to B76) of the Supported MCS Set indicate the Rx MCS Bitmask. In the Rx MCS Bitmask, bit 0 (B0) corresponds to MCS0, and bit 76 (B76) corresponds to MCS76. In this Rx MCS Bitmask, a receivable MCS index is specified by setting a bit.
For example, when not using MIMO (Multiple Input Multiple Output) and accepting communication with only one antenna as in this embodiment, it is only necessary to support 0 to 7 of the MCS index. In this case, the corresponding bit is set to 1 and the remaining bits are set to 0. That is, when receiving from MCS0 to MCS7 is possible, bits 0 to 7 are 1, and bits 8 to 76 are 0.

In the present embodiment, the STA 20 detects the retransmission frequency of data in the own device, sets the reception rate of the own device based on the detected retransmission frequency, and notifies the AP 30 of this. More specifically, when the STA 20 determines that the frequency of data retransmission increases, the STA 20 sets a limit on the reception rate and notifies the AP 30 of this. At this time, the transmission rate is not limited.
Upon notification of the reception rate, the STA 20 temporarily disconnects the connection state with the AP 30 and connects again. At the time of this reconnection, the STA 20 notifies the setting for limiting the reception rate by transmitting a connection frame to which information related to the set reception rate is added to the AP 30. In the present embodiment, a case where the connection frame is an association request will be described.

FIG. 3 is a block diagram illustrating an example of a hardware configuration of the STA 20.
The STA 20 includes a control unit 22, a storage unit 23, a radio unit 24, and an antenna switch 25 in addition to the antenna 21 described above.
The control unit 22 controls the overall operation of the STA 20. The control unit 22 can be configured by one or a plurality of CPUs. The storage unit 23 is a memory that stores a control program and the like necessary for the control unit 22 to execute processing, and includes a ROM, a RAM, and the like. The wireless unit 24 performs wireless communication conforming to the IEEE 802.11n standard series. The wireless unit 24 can be configured by a chip that performs wireless communication. The antenna switch 25 is an RF (Radio Frequency) switch, and switches between a reception path from the antenna 21 to the radio unit 24 and a transmission path from the radio unit 24 to the antenna 21. The antenna switch 25 selects a reception path except during transmission.

  Note that the hardware configuration shown in FIG. 3 is an example, and the STA 20 may have other hardware configurations. For example, when the STA 20 is a printer, it may have a printing unit in addition to the configuration shown in FIG. When the STA 20 is a camera, it may have an imaging unit in addition to the configuration shown in FIG. The STA 20 includes various devices such as a camera, a smartphone, a printer, a mobile phone, a PC, a video camera, a smart watch, and a PDA.

FIG. 4 is an example of software function blocks of the STA 20. The functions of the units shown in FIG. 4 can be realized by the CPU of the control unit 22 or the radio unit 24 executing a program.
In the present embodiment, each functional block shown below is described as a function realized as a software program, but a part or all of the functional block included in the functional block may be realized by hardware. When realized by hardware, for example, a dedicated circuit may be automatically generated on the FPGA from a program for realizing each step by using a predetermined compiler. FPGA is an abbreviation for Field Programmable Gate Array. Further, a Gate Array circuit may be formed in the same manner as an FPGA and realized as hardware. Further, it may be realized by an ASIC (Application Specific Integrated Circuit). Note that the functional block diagram shown in FIG. 4 is an example, and a plurality of functional modules may constitute one functional module, or one of the functional modules may be divided into modules that perform a plurality of functions. Good.

The STA 20 includes a communication control unit 201, a frame reception unit 202, an ACK detection unit 203, a retransmission counter setting unit 204, a retransmission counter determination unit 205, a rate limit determination unit 206, a rate limit control unit 207, and a disconnection. / Connection frame generation unit 208. Further, the STA 20 includes a frame transmission unit 209, a timer management unit 210, and a data frame generation unit 211.
The communication control unit 201 controls switching between a reception path for outputting the RF signal received by the antenna 21 to the frame reception unit 202 and a transmission path for outputting the RF signal generated by the frame transmission unit 209 to the antenna 21.

  The frame reception unit 202 converts the RF signal output from the communication control unit 201 into an IEEE802.11n MAC frame and outputs the MAC frame to the ACK detection unit 203. Based on the MAC frame output from the frame reception unit 202, the ACK detection unit 203 detects whether or not an ACK frame (hereinafter simply referred to as “ACK”) has been received at a predetermined time. Here, the ACK detection timing is specified by the timer management unit 210 described later. When the retransmission counter setting unit 204 determines that ACK has not been received at the specified time based on the detection result of the ACK detection unit 203, the retransmission counter setting unit 204 counts the number of retransmissions as a frame transmission failure. Add 1 to the value.

  The retransmission counter determination unit 205 determines whether or not the retransmission counter set by the retransmission counter setting unit 204 is greater than or equal to the first threshold or less than or equal to the second threshold. Here, the first threshold TH11 is the number of retransmissions that can be determined to increase the retransmission frequency of the data frame in the own device, and is, for example, TH11 = 5. The second threshold TH12 is the number of retransmissions at which it can be determined that the frequency of retransmission of data frames in the own apparatus has decreased. For example, TH12 = 1.

The rate limit determination unit 206 determines whether or not the setting for limiting the reception rate is made. Specifically, the rate limit determination unit 206 transmits a connection frame including an Rx MCS Bitmask indicating that all eight reception rates from MCS0 to MCS7 are supported when the connection state with the AP 30 is established. It is determined whether or not. Rate limit control section 207 determines whether or not to perform limit setting or limit setting cancellation on the basis of the determination result in retransmission counter determination section 205 and the determination result in rate limit determination section 206.
The disconnection / connection frame generation unit 208 generates a disconnection frame (Disassociation) and a connection frame (Association Request) in accordance with an instruction from the rate limit control unit 207. Then, the disconnect / connect frame generation unit 208 outputs the generated disconnect frame and connection frame to the frame transmission unit 209.

The frame transmission unit 209 converts the MAC frame (disconnection frame, connection frame) generated by the disconnection / connection frame generation unit 208 into an RF signal, outputs the RF signal to the communication control unit 201, and instructs frame transmission. Also, the frame transmission unit 209 converts the MAC frame (data frame) generated by the data frame generation unit 211 into an RF signal and outputs the RF signal to the communication control unit 201 to instruct frame transmission. At this time, the frame transmission unit 209 notifies the timer management unit 210 that the data frame has been transmitted.
In response to the notification from the frame transmission unit 209, the timer management unit 210 measures SIFS (Short Inter Frame Space) time from the transmission of the data frame. When the timer management unit 210 determines that the SIFS time has elapsed since the data frame transmission, the timer management unit 210 notifies the ACK detection unit 203 that it is time to detect whether or not ACK has been received. The data frame generation unit 211 generates a data frame including retransmission and outputs it to the frame transmission unit 209.

Next, the operation of the STA 20 will be described.
FIG. 5 is a flowchart for explaining the operation of the STA 20. The processing of FIG. 5 is started at the timing when the STA 20 and the AP 30 are connected and the STA 20 transmits a data frame, for example. However, the execution timing of the process is not limited to the above. Hereinafter, the alphabet S means a step in the flowchart.
The processing shown in FIG. 5 is realized by the CPU constituting the control unit 22 or the radio unit 24 of FIG. 3 reading and executing a necessary program. However, the processing of FIG. 5 may be realized by operating at least a part of each functional module shown in FIG. 4 as dedicated hardware. In this case, the dedicated hardware operates based on the control of the CPU.

  First, in S <b> 1, the frame transmission unit 209 transmits the data frame generated by the data frame generation unit 211 to the AP 30 via the communication control unit 201. After the transmission is completed, the timer management unit 210 starts SIFS time measurement. When the SIFS time has elapsed, in S2, the ACK detection unit 203 performs an ACK detection process and determines whether or not an ACK has been received from the AP 30. Then, the ACK detection unit 203 proceeds to S3 when determining that the ACK has not been received, and proceeds to S9 when determining that the ACK has been received.

  In S3, the retransmission counter setting unit 204 adds 1 to the value of the retransmission counter, and proceeds to S4. Here, the initial value of the retransmission counter is zero. In S4, the retransmission counter determination unit 205 determines whether or not the retransmission counter is greater than or equal to the first threshold value. Here, the first threshold value TH11 can be set to 5, for example. The retransmission counter determination unit 205 returns to S1 when determining that the retransmission counter is less than the first threshold value TH11, and proceeds to S5 when determining that the retransmission counter is equal to or greater than the first threshold value TH11.

In S5, the rate limit determination unit 206 determines whether the reception rate is limited. The rate limit determination unit 206 determines that there is a rate limit when the current support rate is not from MCS0 to MCS7, and determines that there is no rate limit when the current support rate is from MCS0 to MCS7. to decide. If the rate limit determining unit 206 determines that there is a rate limit, the rate limit control unit 207 determines to maintain the rate limit as it is and returns to S1. On the other hand, if the rate limit determination unit 206 determines that there is no rate limit, the rate limit control unit 207 determines that the rate limit is to be performed, and proceeds to S6.
In S6, the disconnection / connection frame generation unit 208 generates a disconnection frame for disconnecting the connection with the AP 30, and the frame transmission unit 209 transmits the disconnection frame to the AP 30 via the communication control unit 201. Thereby, STA20 and AP30 will be in a cutting | disconnection state.

In S7, the rate limit control unit 207 performs rate limit setting. The rate limit control unit 207 instructs the disconnection / connection frame generation unit 208 to generate a connection frame for limiting the support rate from, for example, MCS0 to MCS4. At this time, the disconnection / connection frame generation unit 208 generates a connection frame including an Rx MCS Bitmask in which bits 0 to 4 are 1 and bits 5 to 76 are 0.
In S8, the frame transmission unit 209 transmits the connection frame generated in S7 or S14 described later to the AP 30 via the communication control unit 201. Thereby, STA20 and AP30 will be in a connection state.

  In S9, the retransmission counter determination unit 205 determines whether or not the retransmission counter is equal to or smaller than the second threshold value. Here, the second threshold value TH12 can be set to 1, for example. If the retransmission counter determination unit 205 determines that the retransmission counter is greater than the second threshold value TH12, the process proceeds to S10. The retransmission counter setting unit 204 clears the retransmission counter to 0 and then returns to S1. On the other hand, if the retransmission counter determination unit 205 determines in S9 that the retransmission counter is equal to or smaller than the second threshold value TH12, the retransmission counter determination unit 205 proceeds to S11.

  In S11, the retransmission counter setting unit 204 clears the retransmission counter to 0 and proceeds to S12. In S12, the rate limit determination unit 206 determines whether the reception rate is limited. If the rate limit determination unit 206 determines that there is no rate limit, the rate limit control unit 207 determines to maintain the state without the rate limit as it is, and returns to S1. On the other hand, if the rate limit determination unit 206 determines that there is a rate limit, the rate limit control unit 207 determines to cancel the rate limit and proceeds to S13.

In S13, the disconnection / connection frame generation unit 208 generates a disconnection frame for disconnecting the connection with the AP 30, and the frame transmission unit 209 transmits the disconnection frame to the AP 30 via the communication control unit 201. Thereby, STA20 and AP30 will be in a cutting | disconnection state.
In S14, the rate limit control unit 207 cancels the rate limit. The rate limiting control unit 207 instructs the disconnection / connection frame generation unit 208 to generate a connection frame for setting the support rate from MCS0 to MCS7. At this time, the disconnection / connection frame generation unit 208 generates a connection frame including an Rx MCS Bitmask in which bits 0 to 7 are 1, and bits 8 to 76 are 0, and the process proceeds to S8.

Next, the operation when data frames are continuously transmitted from the STA 20 to the AP 30 will be specifically described.
Here, it is assumed that the STA 20 is connected to the AP 30. Further, it is assumed that the STA 20 has already transmitted a connection frame (Association Request) including an Rx MCS Bitmask in which bits 0 to 7 are 1 and bits 8 to 76 are 0 when connected to the AP 30. That is, it is assumed that the STA 20 has already transmitted the support rate information that enables reception of MCS0 to MCS7 to the AP 30. Further, it is assumed that the AP 30 can receive the MCS7 frame, which is the highest transmission rate.

In this case, when the STA 20 transmits an MCS7 data frame to the AP 30 (S1 in FIG. 5), the AP 30 receives the data frame and transmits an ACK to the STA 20 in the MCS 7. However, at this time, when the reception sensitivity of the STA 20 is reduced and the STA 20 can only receive frames of MCS0 to MCS4 having a low transmission rate, the STA 20 cannot receive the ACK transmitted by the AP 30 (in S2). No).
For this reason, the STA 20 determines that data transmission to the AP 30 has failed, and retransmits the data frame of the MCS 7. First, the STA 20 counts the number of retransmissions using a data frame retransmission counter (S3). At this time, since the retransmission counter is 1, and the number of retransmissions has not reached the first threshold value TH11 (for example, 5 times) (No in S4), the STA 20 retransmits the data frame while maintaining the reception rate setting. (S1). Here, a case will be described where the STA 20 retransmits a data frame while maintaining the transmission rate setting. That is, the STA 20 repeats the retransmission of the data frame of the MCS 7 while the state where no ACK is received continues.

  Thereafter, when the number of retransmissions of the data frame reaches the first threshold value TH11 (Yes in S4), the STA 20 determines to limit the reception rate (No in S5), and temporarily disconnects the connection between the STA 20 and the AP 30 (S6). ). Then, the STA 20 generates a connection frame indicating that the support rate is limited to MCS0 to MCS4 (S7), and transmits the connection frame to establish a connection state again (S8). At this time, the AP 30 is set to transmit a transmission frame addressed to the STA 20 at a rate of MCS0 to MCS4 based on the Rx MCS Bitmask information in the connection frame received from the STA20.

  After the above reconnection, the STA 20 transmits the MCS7 data frame to the AP 30 again (S1). Then, the AP 30 that has received the data frame transmits ACK to the STA 20 at the rate of MCS4. For this reason, the STA 20 succeeds in receiving the ACK transmitted from the AP 30, and determines that the data transmission to the AP 30 is successful (Yes in S2). At this point, since the retransmission counter is 5 (No in S9), the STA 20 only clears the retransmission counter (S10) and maintains the reception rate limit setting as it is.

Subsequently, the STA 20 creates the next data frame and transmits it to the AP 30 (S1). Then, the AP 30 receives the data frame transmitted from the STA 20 and transmits an ACK of the MCS 4 to the STA 20. Then, the STA 20 receives the ACK transmitted from the AP 30 (S2). The retransmission counter at this time is cleared to 0 (Yes in S9). Therefore, after clearing the retransmission counter (S11), the STA 20 determines to release the restriction on the reception rate (Yes in S12).
That is, the STA 20 once disconnects the connection between the STA 20 and the AP 30 (S13). Then, the STA 20 generates a connection frame indicating that the support rate is from MCS0 to MCS7 (S14), and transmits the connection frame to establish a connection state again (S8). At this time, the AP 30 is set to transmit a transmission frame addressed to the STA 20 at a rate of MCS0 to MCS7 based on the Rx MCS Bitmask information in the connection frame received from the STA20.

  As described above, the wireless communication apparatus (STA) 20 in the present embodiment detects the number of data retransmissions as information regarding the frequency of data retransmission to another wireless communication apparatus (AP) 30. Specifically, the STA 20 counts the number of data retransmissions based on whether or not a reception confirmation response (ACK) is received for data transmission from the AP 30. When the STA 20 determines that the data retransmission frequency is increased based on the number of data retransmissions, the STA 20 performs a setting for limiting the reception rate of the own apparatus and notifies the AP 30 of the setting. At this time, the STA 20 does not limit the transmission rate of the own device.

  Thereby, even when the reception sensitivity of the STA 20 is reduced due to internal noise of the STA 20 on the data transmission side, it is possible to receive ACK in the STA 20. Therefore, the STA 20 can suppress the erroneous determination that the data reception at the AP 30 has failed even though the data reception at the AP 30 has succeeded, and the data retransmission to the AP 30 being repeated. As a result, a decrease in transmission throughput can be suppressed. If the STA 20 determines that the frequency of data retransmission increases, the STA 20 limits only the reception rate of the device itself, and does not limit the transmission rate. Therefore, it is possible to suppress transmission at a rate lower than the rate at which communication is actually possible, and to suppress a decrease in transmission throughput.

  Furthermore, when the number of data retransmissions is equal to or greater than the first threshold, the STA 20 determines that the retransmission frequency is increased, and sets a reception rate limit. Thus, by comparing the number of data retransmissions with a predetermined threshold, it is possible to detect the failure frequency of ACK reception and appropriately detect the situation where the reception sensitivity of the STA 20 is reduced. Therefore, it is possible to limit the reception rate at an appropriate timing.

  In addition, after limiting the reception rate, the STA 20 determines that the retransmission frequency has decreased when the number of data retransmissions is equal to or smaller than the second threshold value, which is smaller than the first threshold value, and releases the restriction on the reception rate. The setting is performed and the setting is notified to the AP 30. In this way, by comparing the number of data retransmissions with a predetermined threshold, it is possible to appropriately detect that the reception sensitivity of the STA 20 has been recovered. Therefore, it is possible to remove the restriction on the reception rate at an appropriate timing. Further, by setting the second threshold value TH12 for determining a decrease in retransmission frequency to be smaller than the first threshold value TH11 for determining an increase in retransmission frequency, reception rate restriction setting and restriction setting release are frequently repeated. Can be prevented.

  Further, the STA 20 transmits a connection frame to which the support rate information is added to the AP 30 when the connection state with the AP 30 is once disconnected and the connection state is again connected upon notification of reception rate restriction setting and restriction setting release. . Here, the connection frame includes an association request frame and a probe request frame. Thus, since the notification is performed using the connection frame, the AP 30 can appropriately grasp the support rate of the STA 20 and can appropriately set the transmission rate for the STA 20.

In the present embodiment, the case where the STA 20 retransmits the data frame without changing the transmission rate when the ACK from the AP 30 cannot be received has been described. However, if ACK reception for data transmission is not performed, the STA 20 can also perform so-called multi-rate control in which a data frame is retransmitted while gradually decreasing the transmission rate.
In this case, when the STA 20 fails to receive the ACK for the data frame transmission of the MCS 7, the STA 20 retransmits the data frame at the MCS 6 whose rate is lowered. If the STA 20 also fails to receive an ACK for the data frame transmission of the MCS 6, the STA 20 retransmits the data frame at the MCS 5 whose rate is further lowered. This data retransmission process is repeated until the STA 20 receives an ACK or until a predetermined number of retransmissions is reached. Thereby, it is possible to prevent repeated data retransmission at a high rate at which communication is impossible.

  However, if ACK cannot be received due to a decrease in reception sensitivity in STA 20, no matter how much the transmission rate is lowered, ACK cannot be received unless the reception rate is limited. Therefore, in this case, although the AP 30 normally receives data, the STA 20 performs unnecessary data retransmission while gradually reducing the transmission rate. As described above, the deterioration of the transmission side reception sensitivity causes an undesirably significant decrease in transmission speed. Since communication at a low rate requires a longer transmission time than communication at a high rate, the line usage rate is higher than communication at a high rate. In other words, a decrease in transmission speed leads to a decrease in use efficiency of the wireless communication line.

In the present embodiment, when the STA 20 detects an increase in the frequency of data retransmission, the STA 20 can limit the reception rate and enable ACK reception. Therefore, transmission at a rate lower than the rate at which communication can be performed frequently occurs. Can be suppressed. Therefore, the bandwidth of the wireless communication line can be used efficiently.
Further, in this embodiment, when an increase in data retransmission frequency is detected, only the reception rate is limited, and the transmission rate is not limited. That is, even if the transmission rate is limited by multi-rate control before the reception rate is limited, the limitation on the transmission rate is canceled when the reception rate limitation is started. Therefore, it is possible to appropriately suppress a decrease in transmission throughput.

  Note that the multi-rate control method is not limited to the above. When ACK reception for data transmission is not performed, first, a data frame may be retransmitted at the same transmission rate, and after the number of retransmissions exceeds a specified number, the transmission rate may be gradually decreased. In this embodiment, the data frame is retransmitted at the same transmission rate until the reception rate is limited, and if no ACK is received even when the reception rate is limited, the transmission rate may be limited by multirate control. Good.

(Second embodiment)
Next, a second embodiment of the present invention will be described.
In the first embodiment described above, the case where the retransmission frequency is detected based on the number of data retransmissions has been described. In the second embodiment, a case will be described in which a retransmission frequency is detected based on a signal-to-noise ratio (SNR) of a received signal.
The configuration of the communication system in the second embodiment is the same as that shown in FIG. The hardware configuration example of the STA 20 is the same as that in FIG.

FIG. 6 is an example of software function blocks of the STA 20 in the second embodiment. In FIG. 6, parts having the same functions as those in FIG. 4 are denoted by the same reference numerals as those in FIG.
The SNR detector 221 detects the SNR of the received signal received by the frame receiver 202. In the present embodiment, a beacon that is a notification signal for the AP 30 to notify network information is used as the reception signal. The SNR determination unit 222 determines whether or not the SNR detected by the SNR detection unit 221 is less than or equal to the first threshold value or greater than or equal to the second threshold value. Here, the first threshold value TH21 is an SNR value that can be determined as frequent data retransmission, and can be set to, for example, 15 dB. The second threshold TH22 is a value of SNR that can be determined that data retransmission does not occur, and can be set to, for example, 25 dB. In this way, by setting the relationship TH21 <TH22, it is possible to prevent frequent reception rate limitation / cancellation.

FIG. 7 is a flowchart for explaining the operation of the STA 20. The process of FIG. 7 is repeatedly executed while the STA 20 and the AP 30 are in a connected state, for example. However, the execution timing of the process is not limited to the above.
The processing shown in FIG. 7 is realized by the CPU configuring the control unit 22 or the wireless unit 24 of FIG. 3 reading and executing a necessary program. However, the processing of FIG. 7 may be realized by operating at least a part of each functional module shown in FIG. 4 as dedicated hardware. In this case, the dedicated hardware operates based on the control of the CPU.

First, in S21, the frame reception unit 202 determines whether or not a beacon that the AP 30 periodically transmits has been received. If the frame receiving unit 202 has not received a beacon, the frame receiving unit 202 waits until a beacon is received. In S22, the SNR detector 221 calculates the difference in dB between the noise intensity immediately before frame reception and the signal intensity of the beacon frame.
In S23, the rate limit determination unit 206 determines whether the reception rate is limited. If the rate limit determination unit 206 determines that there is no rate limit, the process proceeds to S24. If the rate limit determination unit 206 determines that there is a rate limit, the rate limit determination unit 206 proceeds to S28.

In S24, the SNR determination unit 222 determines whether or not the SNR calculated in S22 is equal to or less than a first threshold value TH21 (for example, 15 dB). If the SNR determination unit 222 determines that the SNR is higher than the first threshold value TH21, the SNR determination unit 222 returns to S21. If the SNR determination unit 222 determines that the SNR is equal to or less than the first threshold value TH21, the process proceeds to S25.
In S25, the disconnection / connection frame generation unit 208 generates a disconnection frame for disconnecting the connection with the AP 30, and the frame transmission unit 209 transmits the disconnection frame to the AP 30 via the communication control unit 201. Thereby, STA20 and AP30 will be in a cutting | disconnection state.

In S26, the rate limit control unit 207 performs rate limit setting. The rate limit control unit 207 instructs the disconnection / connection frame generation unit 208 to generate a connection frame for limiting the support rate from, for example, MCS0 to MCS4. At this time, the disconnection / connection frame generation unit 208 generates a connection frame including an Rx MCS Bitmask in which bits 0 to 4 are 1 and bits 5 to 76 are 0.
In S27, the frame transmission unit 209 transmits the connection frame generated in S26 or S30 described later to the AP 30 via the communication control unit 201. Thereby, STA20 and AP30 will be in a connection state.

In S28, the SNR determination unit 222 determines whether or not the SNR calculated in S22 is equal to or greater than a second threshold TH22 (for example, 25 dB). If the SNR determining unit 222 determines that the SNR is less than the second threshold TH22, the SNR determining unit 222 returns to S21. If the SNR determining unit 222 determines that the SNR is greater than or equal to the second threshold TH22, the SNR determining unit 222 proceeds to S29.
In S29, the disconnection / connection frame generation unit 208 generates a disconnection frame for disconnecting the connection with the AP 30, and the frame transmission unit 209 transmits the disconnection frame to the AP 30 via the communication control unit 201. Thereby, STA20 and AP30 will be in a cutting | disconnection state.
In S30, the rate limit control unit 207 cancels the rate limit. The rate limiting control unit 207 instructs the disconnection / connection frame generation unit 208 to generate a connection frame for setting the support rate from MCS0 to MCS7. At this time, the disconnection / connection frame generation unit 208 generates a connection frame including an Rx MCS Bitmask in which bits 0 to 7 are 1 and bits 8 to 76 are 0, and the process proceeds to S27.

Next, the operation for notifying the STA 20 or the AP 30 of the reception rate restriction will be specifically described.
Here, it is assumed that the STA 20 is connected to the AP 30. Further, it is assumed that the STA 20 has already transmitted a connection frame (Association Request) including an Rx MCS Bitmask in which bits 0 to 7 are 1 and bits 8 to 76 are 0 when connected to the AP 30. That is, it is assumed that the STA 20 has already transmitted the support rate information that enables reception of MCS0 to MCS7 to the AP 30.

  The AP 30 periodically transmits a beacon frame for informing network information. When the STA 20 receives the beacon transmitted from the AP 30 (Yes in S21 of FIG. 7), the STA 20 calculates the SNR of the received signal (S22). Since the reception rate is not limited at this point (No in S23), the STA 20 compares the calculated SNR with the first threshold TH21 of 15 dB, and when the SNR exceeds 15 dB (No in S24), The state where the reception rate is not limited is maintained as it is.

  From this state, it is assumed that the SNR has decreased to, for example, 10 dB. In this case, since the SNR is equal to or less than 15 dB, which is the first threshold TH21 (Yes in S24), the STA 20 determines to limit the reception rate, and temporarily disconnects the connection between the STA 20 and the AP 30 (S25). Then, the STA 20 generates a connection frame indicating that the support rate is limited to MCS0 to MCS4 (S26), and transmits the connection frame to establish a connection state again (S27). At this time, the AP 30 is set to transmit a transmission frame addressed to the STA 20 at a rate of MCS0 to MCS4 based on the Rx MCS Bitmask information in the connection frame received from the STA20.

After limiting the reception rate in this way, the STA 20 compares the SNR calculated based on the received beacon with the second threshold TH22, which is 25 dB, and determines whether to cancel the reception rate. If the SNR is less than 25 dB (No in S28), the reception rate restriction state is maintained as it is, and if the SNR recovers to 25 dB or more (Yes in S28), the STA 20 determines to release the restriction on the reception rate. To do.
That is, the STA 20 once disconnects the connection between the STA 20 and the AP 30 (S29). Then, the STA 20 generates a connection frame indicating that the support rate is from MCS0 to MCS7 (S30), and transmits the connection frame to establish a connection state again (S27). At this time, the AP 30 is set to transmit a transmission frame addressed to the STA 20 at a rate of MCS0 to MCS7 based on the Rx MCS Bitmask information in the connection frame received from the STA20.

As described above, the radio communication apparatus (STA) 20 in the present embodiment detects the signal-to-noise ratio (SNR) of the received signal as information related to the frequency of data retransmission with respect to the other radio communication apparatus (AP) 30. . Then, when the SNR is equal to or less than the first threshold, the STA 20 determines that the retransmission frequency is increased, sets a limit on the reception rate of the own device, and notifies the AP 30 of this. Here, as the received signal, a beacon that is a notification signal transmitted by the AP 30 can be used.
In this way, by comparing the SNR with a predetermined threshold, it is possible to appropriately detect a situation in which the data retransmission frequency can increase. Therefore, it is possible to limit the reception rate at an appropriate timing. As a result, even when the reception sensitivity of the STA 20 is reduced due to the internal noise of the STA 20 on the data transmission side, ACK reception at the STA 20 is possible, data retransmission to the AP 30 is suppressed, and transmission throughput is reduced. The decrease can be suppressed.

  In addition, after limiting the reception rate, the STA 20 determines that the retransmission frequency is reduced and releases the restriction on the reception rate when the SNR becomes equal to or higher than the second threshold value TH22 which is larger than the first threshold value TH21. To notify the AP 30 of the setting. Thus, by comparing the SNR with the second threshold value TH22, it is possible to appropriately detect that the reception sensitivity of the STA 20 has been recovered. Therefore, it is possible to remove the restriction on the reception rate at an appropriate timing. In addition, by setting the second threshold value TH22 for determining a decrease in retransmission frequency larger than the first threshold value TH21 for determining an increase in retransmission frequency, reception rate restriction setting and restriction setting release are frequently repeated. Can be prevented.

(Other embodiments)
In the above embodiment, the wireless LAN system conforming to the IEEE802.11n standard has been described as an example. However, the present invention is not limited to the IEEE802.11n standard and can be applied to a system using other communication methods. The method of limiting the reception rate in the above embodiment is merely an example, and other methods such as transmitting a rate change request to the partner apparatus without disconnecting the connection with the partner apparatus may be used.
The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a recording medium, and one or more processors in the computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

  DESCRIPTION OF SYMBOLS 10 ... Communication system, 20 ... Wireless communication apparatus (STA), 30 ... Wireless communication apparatus (AP), 201 ... Communication control part, 202 ... Frame receiving part, 203 ... ACK detection part, 204 ... Retransmission counter setting part, 205 ... Retransmission counter determination unit, 206 ... Rate limit determination unit, 207 ... Rate limit control unit, 208 ... Disconnection / connection frame generation unit, 209 ... Frame transmission unit, 210 ... Timer management unit, 211 ... Data frame generation unit

Claims (11)

Detecting means for detecting information relating to the frequency of retransmission of data for other wireless communication devices;
If it is determined that the retransmission frequency is increased based on the information regarding the retransmission frequency detected by the detection unit, a setting unit configured to limit the reception rate of the own device and not limit the transmission rate of the own device;
A wireless communication apparatus comprising: notification means for notifying the other wireless communication apparatus of a setting for limiting the reception rate by the setting means. The detection means detects the number of retransmissions of the data as information on the retransmission frequency,
The wireless communication apparatus according to claim 1, wherein the setting unit determines that the frequency of retransmission increases when the number of retransmissions is equal to or greater than a first threshold. The setting means, when the number of retransmissions is less than or equal to a second threshold value smaller than the first threshold value, determines that the retransmission frequency has decreased and performs a setting to release the restriction on the reception rate,
The wireless communication device according to claim 1, wherein the notification unit notifies the other wireless communication device of a setting for releasing the reception rate restriction by the setting unit. The detection means detects a signal-to-noise ratio of a received signal as information on the retransmission frequency,
4. The wireless communication apparatus according to claim 1, wherein the setting unit determines that the retransmission frequency increases when the signal-to-noise ratio is equal to or less than a first threshold. 5. The setting means, when the signal-to-noise ratio is equal to or greater than a second threshold value greater than the first threshold value, determines that the retransmission frequency has decreased, and performs a setting to release the restriction on the reception rate;
5. The wireless communication device according to claim 4, wherein the notifying unit notifies the other wireless communication device of a setting for releasing the reception rate restriction by the setting unit.   The wireless communication apparatus according to claim 4, wherein the received signal is a notification signal transmitted from another wireless communication apparatus. The notification means includes
The wireless communication apparatus according to claim 1, wherein the setting is notified when the connection with the other wireless communication apparatus is disconnected and reconnected. The notification means includes
When a connection with the other wireless communication device is disconnected and reconnected, a connection frame to which support rate information indicating transmission rate information usable by the device is added is transmitted to the other wireless communication device. The wireless communication apparatus according to claim 7, wherein the setting is notified.   The wireless communication apparatus according to claim 1, wherein wireless communication is performed with the other wireless communication apparatus using a CSMA / CA method. Detecting information relating to the frequency of retransmission of data for other wireless communication devices;
When it is determined that the retransmission frequency is increased based on the detected information regarding the retransmission frequency, the step of limiting the reception rate of the own device and not limiting the transmission rate of the own device;
And notifying the other wireless communication device of a setting for limiting the reception rate.   The program for functioning a computer as each means of the radio | wireless communication apparatus described in any one of Claim 1 to 9.

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