JP2019068374A - Radio communication device and control method of the radio communication device - Google Patents

Abstract

To suppress transmission of an unnecessary re-transmission frame.SOLUTION: A base station 10 comprises: a radio communication part 22 that transmits a frame to a mating device on the basis of a back-off control using a contention window defined in accordance with the number of re-transmission by a prescribed back-off algorithm, and receives an ACK frame from the mating device in response to the transmitted frame; a time acquisition part 24 that acquires a reciprocation time before the reception of the ACK frame after the transmission of the frame by the radio communication part 22; and a control part 26 that makes it to re-transmit on the basis of the back-off control after a standby time defined in accordance with the reciprocation time acquired by the time acquisition part 24 from a time that the re-transmission at a (N-1)th is terminated when performing the re-transmitting of the frame by the radio communication part 22 at a Nth (where, N≥1).SELECTED DRAWING: Figure 2

Description

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

  In wireless communication, an access method called Carrier Sense Multiple Access / Collision Avoidance (CSMA / CA) is employed, which avoids collisions between communication frames (also referred to simply as frames) transmitted by a wireless communication apparatus.

  In CSMA / CA, a communication apparatus that intends to transmit a frame performs carrier sensing before transmitting a frame, and transmits a frame when the other communication apparatus has not detected a carrier. More specifically, carrier sensing of IFS (Inter Frame Space) time defined in the communication standard is performed, and then carrier sensing of backoff time determined by a predetermined backoff algorithm is performed. The IFS time and the backoff time are each on the order of several tens of microseconds to several milliseconds.

  Patent Document 1 discloses a technique for obtaining a backoff time that can reduce collisions of frames after retransmission.

Unexamined-Japanese-Patent No. 2015-103849

  However, the communication device may not be able to communicate with the destination device to which the communication device transmits a frame, which may occur for several seconds. For example, when the partner apparatus can move, the partner apparatus may move to a position where radio waves from the communication apparatus can not reach. Also, there are cases where communication becomes impossible due to scanning of the wireless channel performed by the other device.

  Even when the partner apparatus can not communicate for several seconds, the communication apparatus repeats the retransmission with an interval of IFS time and backoff time of about several tens of microseconds to several milliseconds. As a result, there is a problem that an unnecessary retransmission frame is transmitted.

  The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a wireless communication apparatus and the like which suppress unnecessary transmission of retransmission frames.

  In order to solve the above problem, a wireless communication apparatus according to an aspect of the present invention uses a predetermined backoff algorithm to send a frame to the other apparatus based on backoff control using a contention window determined according to the number of retransmissions. A wireless communication unit that transmits and receives an ACK (Acknowledgement) frame for the transmitted frame from the partner apparatus, and a round-trip time that is a time from the wireless communication unit transmitting the frame to receiving the ACK frame A time acquisition unit for acquiring the frame, and the N-th (where N.gtoreq.1) retransmission of the frame by the wireless communication unit, the round trip acquired by the time acquisition unit from the time when the N-1th retransmission is completed A control unit that causes retransmission based on backoff control after a waiting time determined according to the time has elapsed Provided.

  According to this, the wireless communication apparatus stands by for the standby time in the middle of retransmission which is repeated at intervals of the IFS time and the backoff time determined by the predetermined backoff algorithm. Thus, the wireless communication apparatus retransmits the frame at a time longer than the interval between the IFS time and the backoff time. In this way, the wireless communication device suppresses unnecessary transmission of retransmission frames.

  Further, the time acquisition unit acquires a plurality of the reciprocation times, and the control unit uses the time shorter than the plurality of the reciprocation times acquired by the time acquisition unit as the standby time to perform the Nth retransmission. You may

  According to this, the wireless communication apparatus may successfully transmit a frame by retransmission when a time shorter than the average value of the round trip time has elapsed. As a result, the wireless communication apparatus can shorten the round trip time to be calculated thereafter, and can shorten the future standby time when suppressing transmission of useless retransmission frames.

  Further, the time acquisition unit acquires a plurality of the reciprocation times, and the control unit subtracts a standard deviation of the plurality of the reciprocation times from an average value of the plurality of the reciprocation times acquired by the time acquisition unit. A value may be used as the waiting time to cause the Nth retransmission.

  According to this, the wireless communication apparatus suppresses transmission of useless retransmission frames based on a more specific configuration by using the average value of the round trip time and its standard deviation.

  Further, the time acquisition unit acquires a plurality of the reciprocation times, and the control unit uses, as the standby time, a half of an average value of the plurality of the reciprocation times acquired by the time acquisition unit. The Nth retransmission may be performed.

  According to this, the wireless communication apparatus suppresses transmission of useless retransmission frames based on a more specific configuration by using the average value of the round trip time.

  The N-th retransmission may be the second retransmission among the retransmissions in which the value of the contention window matches the maximum value of the contention window in the predetermined backoff algorithm.

  According to this, when the value of the contention window increases at each retransmission according to the backoff algorithm, the wireless communication apparatus performs the next retransmission of the retransmission when the value of the contention window reaches the maximum value, Wait for the waiting time. If transmission of a frame from the wireless communication apparatus to the destination apparatus is not successful until the value of the contention window reaches the maximum value, there is a high probability that the destination apparatus can not communicate. In this case, it is assumed that the frame does not reach the other device even if retransmission is repeated with an interval of IFS time and backoff time according to the backoff algorithm. Therefore, the wireless communication apparatus suppresses unnecessary transmission of retransmission frames by performing standby for the standby time.

  In addition, the control unit may set the value of the contention window in each of the Nth and subsequent retransmissions by the wireless communication unit to the value of the contention window in each of the first transmission and the first and subsequent retransmissions in the predetermined backoff algorithm. May be set to a value.

  According to this, in the retransmission after waiting for the waiting time, the wireless communication apparatus determines the backoff time using the value of the contention window used for the first transmission in the backoff algorithm. Thus, there is an advantage that, when the other device is in a communicable state after the standby time, the other device can receive the frame more quickly, and the ACK frame from the other device can be received more quickly.

  Further, the wireless communication unit may communicate with each of a plurality of the counterpart devices, and the control unit may retransmit the frame using the standby time for each of the plurality of the counterpart devices.

  According to this, since the wireless communication apparatus calculates the standby time for each of the plurality of other devices, even when communicating with the plurality of other devices simultaneously and in parallel, unnecessary transmission of retransmission frames is suppressed.

  Further, in the control method of a wireless communication apparatus according to an aspect of the present invention, a frame is transmitted to the opposite apparatus based on backoff control using a contention window determined according to the number of retransmissions by a predetermined backoff algorithm, The wireless communication step of receiving an ACK (Acknowledgement) frame for the transmitted frame from the counterpart apparatus, and the round trip time which is the time from the transmission of the frame to the reception of the ACK frame in the wireless communication step is acquired. At the time acquisition step and the Nth (where N か ら 1) retransmission of the frame in the wireless communication step, according to the round trip time acquired in the time acquisition step from the time when the N-1th retransmission is completed After the waiting time defined by Causes and a control step.

  Thereby, the same effect as that of the above-described wireless communication device is obtained.

  The present invention can be realized not only as an apparatus, but also as a method in which processing means constituting the apparatus are steps, or a program which causes the computer to execute the steps, or a computer reading the program It can be realized as a recording medium such as a possible CD-ROM, or as information, data or signals indicating the program. And these programs, information, data, and signals may be distributed via a communication network such as the Internet.

  According to the present invention, it is possible to suppress unnecessary transmission of retransmission frames.

FIG. 1 is a schematic view showing a configuration of a communication system including a base station according to the embodiment. FIG. 2 is a block diagram showing a functional block of a base station according to the embodiment. FIG. 3 is an explanatory diagram of a backoff algorithm. FIG. 4 is an explanatory diagram of a first example of the standby time set by the control unit according to the embodiment. FIG. 5 is an explanatory diagram of a second example of the standby time set by the control unit according to the embodiment. FIG. 6 is a flowchart showing the process of calculating the waiting time according to the embodiment. FIG. 7 is a flowchart showing the retransmission process according to the embodiment. FIG. 8 is an explanatory view showing the retransmission timing of the base station according to the related art. FIG. 9 is an explanatory diagram of retransmission timing of the base station according to the embodiment.

  Embodiments will be specifically described below with reference to the drawings.

  Each of the embodiments described below shows a preferable specific example of the present invention. Numerical values, shapes, materials, components, arrangement positions and connection forms of components, steps, order of steps, and the like shown in the following embodiments are merely examples, and the present invention is not limited thereto. Further, among the components in the following embodiments, components not described in the independent claim indicating the highest concept of the present invention will be described as optional components constituting a more preferable embodiment. In addition, the same code | symbol may be attached | subjected to the same component and description may be abbreviate | omitted.

Embodiment
A description will be given of a wireless communication apparatus that suppresses unnecessary retransmission frame transmission in the present embodiment. Although the present embodiment shows an example in which the wireless communication apparatus is realized as a base station, the present invention is not limited to this.

  FIG. 1 is a schematic view showing a configuration of a communication system 1 including a base station 10 according to the present embodiment.

  As shown in FIG. 1, the communication system 1 includes a base station 10 and a terminal 30. The communication system 1 is communicably connected to an external network 50 via the LAN 40.

  The base station 10 is a base station apparatus (generally referred to as an access point) that performs wireless communication with the terminal 30. The base station 10 establishes a wireless communication link with the terminal 30, and performs wireless communication through the wireless communication link. The base station 10 is also connected to an external network 50 via the LAN 40, and transfers frames between the terminal 30 and the external network 50. In addition, although the standard of wireless communication may be what, it may employ | adopt IEEE802.11a, b, g, n etc., for example. The LAN 40 may be a wired LAN, a wireless LAN, or a network in which these are mixed.

  The terminal 30 is a wireless communication terminal (generally referred to as a station) that performs wireless communication with the base station 10. The terminal 30 establishes a wireless communication link with the base station 10 and performs wireless communication through the wireless communication link. The terminal 30 communicates with the external network 50 via the base station 10 and the LAN 40.

  FIG. 2 is a block diagram showing functional blocks of base station 10 according to the present embodiment.

  As shown in FIG. 2, the base station 10 includes a wireless communication unit 22, a time acquisition unit 24, and a control unit 26.

  The wireless communication unit 22 is a wireless communication module that acquires data to be transmitted to the terminal 30, and transmits the acquired data as a frame to the terminal 30 by radio waves. When the transmitted frame does not reach the terminal 30, the wireless communication unit 22 retransmits up to the number of times set as the upper limit. The wireless communication unit 22 includes an antenna, a radio wave transmission / reception circuit, a modulation / demodulation unit, a MAC (Media Access Control) protocol processing unit, and the like.

  When the frame is to be retransmitted, the wireless communication unit 22 transmits the frame to the terminal 30 based on backoff control using a contention window that is determined according to the number of retransmissions by a predetermined backoff algorithm. Also, the wireless communication unit 22 receives an ACK (Acknowledgement) frame for the transmitted frame from the terminal 30. The backoff algorithm and the backoff control using the contention window will be described later.

  The radio communication unit 22 basically determines the timing of retransmission of the frame by backoff control using the contention window, but in addition, according to the control by the control unit 26, only the waiting time is sufficient for retransmission of the frame. stand by.

  The time acquisition unit 24 is a processing unit that acquires a round trip time which is a time from when the wireless communication unit 22 transmits a frame to when an ACK frame is received. The time acquisition unit 24 can be realized by the processor executing a program.

  For example, the time acquisition unit 24 acquires the time when the wireless communication unit 22 ends the transmission of the frame and the time when the reception of the ACK frame for the transmitted frame starts, and calculates the difference between them to calculate the round trip time. get. Here, although the method of calculating the round trip time as described above will be described, instead of the “time when transmission of a frame is ended”, “time when transmission of a frame is started” may be used instead, or Instead of the "time when reception of an ACK frame is started" in the above, "time when reception of an ACK frame is ended" may be used.

  Here, the time acquisition unit 24 may acquire the round trip time for each of the plurality of frames transmitted by the wireless communication unit 22. More specifically, the number of round-trip times may be obtained such that statistical discussions about the distribution of round-trip times for each of a plurality of acquired frames are possible. Specifically, for example, 100 to 1000 The round trip time may be acquired for a predetermined number of or more predetermined frames.

  The control unit 26 is a processing unit that calculates a standby time used for retransmission by the wireless communication unit 22 and controls the timing of retransmission by the wireless communication unit 22. During the N-th (where N is an integer satisfying N 取得 1) retransmission by the wireless communication unit 22, the control unit 26 reciprocates the time acquisition unit 24 from the time when the N−1-th retransmission is completed. After the waiting time determined in accordance with the time has elapsed, retransmission is performed based on the backoff control. That is, the control unit 26 controls the timing of retransmission of the frame that the wireless communication unit 22 is about to transmit at the present time, based on the round trip time for the frame transmitted by the wireless communication unit 22 in the past. The control unit 26 can be realized by the processor executing a program.

  The standby time calculated by the control unit 26 may be shorter than the average value of the round trip time. If a waiting time shorter than the average value of the round trip time is used, frame transmission may be successful by retransmission at a time point shorter than the average value of the round trip time. Thereby, the subsequent round trip time is calculated to be short, and as a result, there is an advantage that the future waiting time can be shortened.

  Note that the user sets the integer N (i.e., at which re-transmission time is used for the re-transmission control using the waiting time) for the re-transmission control to be performed by the control unit 26 in advance as a fixed value in the control unit 26. It may be dynamic or may be dynamic. In addition, when saying "the 0th retransmission", it shall mean the first transmission which is not retransmission about a flame | frame.

  The control unit 26 may control the timing of retransmission by the wireless communication unit 22 only when the time acquisition unit 24 can acquire the round trip time for the predetermined number or more of frames. This has the advantage that the timing of the retransmission can be controlled only if a statistical discussion of the distribution of waiting time is possible.

  FIG. 3 is an explanatory diagram of a backoff algorithm. The backoff control using the contention window will be described with reference to FIG.

  In the backoff control based on the backoff algorithm, when the carrier is not detected by carrier sense in IFS time, the base station attempting to transmit the frame generates a random number within a predetermined contention window, and the back based on the random number The off time is decided.

  As the IFS time, DIFS (Distributed Inter Frame Space) time, AIFS (Arbitration Inter Frame Space) time or the like is used according to the communication standard. DIFS time is a frame interval used for normal distributed control. The AIFS time is a frame interval for each frame priority, and is expressed as “AIFSN × slot time” using an AIFSN (AIFS Number) indicating the frame priority.

  The backoff time is expressed as “R (0, CW) × slot time” using random number values R (0, CW) within the range of contention window [0, CW].

  Here, the value CW of the contention window is a value that increases with each retransmission within the range from the minimum value CWmin of the contention window to the maximum value CWmax of the contention window. The value CW of the contention window in the n-th retransmission is expressed as (Expression 1).

CW = (CWmin + 1) × 2 ⁿ −1 (when (CWmin + 1) × 2 ⁿ −1 <CWmax)
CW = CWmax (when (CWmin + 1) × 2 ⁿ −1 ≧ CWmax)
(Formula 1)

  By such control, the value CW of the contention window increases at each retransmission from the minimum value CWmin of the contention window to the maximum value CWmax of the contention window, and after reaching the maximum value CWmax, the maximum value CWmax is maintained Do.

  FIG. 3 shows a contention window at the time of transmission of a frame when CWmin = 15 and CWmax = 63, and at the time of retransmission of the frame. Here, the value of the contention window at the time of the first transmission of the frame is 15, and the value of the contention window at the time of the first to fourth retransmission is 31, 63, 63, 63, respectively. .

  FIG. 4 is an explanatory diagram of a first example of the standby time set by the control unit 26 according to the present embodiment. More specifically, FIG. 4 is an explanatory view of the waiting time obtained by subtracting the standard deviation of the round trip time from the average value of the round trip time.

  FIG. 4A shows the distribution of the round trip time obtained by the wireless communication unit 22. However, in (a) of FIG. 4, the round trip time when the terminal 30 receives the frame by the relatively small number of retransmits without retransmitting the frame or about once or twice of the round trip time is excluded. It is shown. In other words, (a) of FIG. 4 shows only the round trip time larger than the predetermined threshold Th among the round trip time acquired by the wireless communication unit 22. The predetermined threshold value Th is a round trip time having a probability density sufficiently smaller than the probability density in the average value of the round trip time shown in FIG. 4A, for example, from the average value of the round trip time, the round trip time (Eq. 2) can be calculated by subtracting three times the standard deviation s of.

   Th = Av-3 × s (Equation 2)

  Further, (b) of FIG. 4 is an explanatory diagram of the standby time calculated by the control unit 26. The waiting time shown in (b) of FIG. 4 is a waiting time obtained by subtracting the standard deviation of the round trip time from the average value of the round trip time.

  The control unit 26 determines the waiting time W at the time of transmission of the Nth retransmission frame according to the round trip time acquired by the time acquiring unit 24. Specifically, the control unit 26 calculates the standby time W by subtracting the standard deviation s of the round trip time from the average value Av of the round trip time.

   W = Av-s (Equation 3)

  The control unit 26 causes frame transmission to stand by for the waiting time W calculated as shown in (Expression 3) immediately before the Nth retransmission of the wireless communication unit 22. In other words, the control unit 26 inserts the standby time W calculated by (Expression 3) immediately before the backoff time of the Nth retransmission of the wireless communication unit 22.

  When the waiting time W has elapsed from the end time of the (N-1) th retransmission, the wireless communication unit 22 transmits a frame relating to the Nth retransmission based on the backoff control using the contention window.

  FIG. 5 is an explanatory diagram of a second example of the standby time set by the control unit 26 according to the present embodiment. More specifically, FIG. 5 is an explanatory view of the waiting time which is 1/2 of the average value of the round trip time.

  Similarly to (a) of FIG. 4, (a) of FIG. 5 illustrates the distribution of the round trip time acquired by the wireless communication unit 22.

  (B) of FIG. 5 is an explanatory diagram of the standby time calculated by the control unit 26. The waiting time shown in (b) of FIG. 5 is a waiting time that is 1/2 of the average value of the round trip time.

  The control unit 26 determines the waiting time W at the time of transmission of the Nth retransmission frame according to the round trip time acquired by the time acquiring unit 24. Specifically, the control unit 26 calculates the standby time W by (Equation 4) by halving the average value Av of the round trip time.

  W = Av / 2 (Equation 4)

  As in the case of using (Equation 3), the control unit 26 inserts the waiting time W calculated by (Equation 4) immediately before the Nth retransmission of the wireless communication unit 22, and when the waiting time W elapses, Based on the backoff control using the tension window, the transmission of the frame relating to the Nth retransmission is performed.

  The process of the base station 10 configured as described above will be described below.

  FIG. 6 is a flowchart showing the process of calculating the waiting time according to the present embodiment.

  In step S101, the time acquisition unit 24 acquires the round trip time. The time acquisition unit 24 acquires, for example, the time when the wireless communication unit 22 completes the transmission of the frame and the time when the wireless communication unit 22 starts the reception of the ACK frame, and calculates the difference between them. To get

  In step S102, the control unit 26 calculates the standby time. The calculation of the waiting time is performed, for example, by the above (Equation 3) or (Equation 4).

  The control unit 26 calculates the standby time by the above series of processes.

  FIG. 7 is a flow chart showing retransmission processing according to the present embodiment.

  In step S201, the wireless communication unit 22 transmits a frame. This is the first transmission of a frame to be transmitted to the terminal 30, not retransmission.

  In step S202, the wireless communication unit 22 determines whether an ACK frame for the frame transmitted in step S201 has been received from the terminal 30. If an ACK frame is received, the series of processing shown in FIG. 7 is ended on the assumption that the transmission of the frame is successful. On the other hand, if the ACK frame is not received even after the short interframe space (SIFS) time after the transmission of the frame, the process proceeds to step S203.

  In step S203, the wireless communication unit 22 adds one to the number of retransmissions R. Then, the wireless communication unit 22 determines whether the number of retransmissions R exceeds the upper limit. If the number of times of retransmission R exceeds the upper limit, it is determined that transmission of the frame has failed, and the series of processes shown in FIG. 7 is ended. On the other hand, when the number of retransmissions R does not exceed the upper limit, the process proceeds to step S204.

  In step S204, the wireless communication unit 22 determines whether the number of retransmissions R is equal to an integer N, that is, whether or not to perform the N-th retransmission. If the number of retransmissions R is equal to the integer N, the process proceeds to step S205, and if not, the process proceeds to step S206.

  In step S205, the control unit 26 controls the wireless communication unit 22 to wait until the waiting time W elapses from the time when the N−1th retransmission is completed.

  In step S206, the wireless communication unit 22 retransmits the frame based on the backoff control. When step S206 is completed, the process proceeds to step S202.

  By the above series of processes, the waiting time W can be inserted before the Nth retransmission.

  Next, an example of retransmission timing by the base station will be described while comparing an example in the related art of the related art with an example in the present embodiment.

  FIG. 8 is an explanatory view showing the retransmission timing of the base station according to the related art.

  Here, the average value of the round trip time is 50 ms, the standard deviation of the round trip time is 10 ms, the frame transmission time is 200 μsec, CWmin = 1, CWmax = 63, one slot time is 10 μsec, and the SIFS time is 10 μsec. The case where AIFSN is 3 will be described as an example. Further, it is assumed that the standby time is calculated to be 50 milliseconds by the control unit 26.

  Further, FIG. 8 illustrates frame transmission and retransmission with the relative time with the time when the wireless communication unit 22 starts initial transmission of the frame as zero.

  As shown in FIG. 8, it is assumed that the start times of the first to fifth retransmissions are 250, 500, 770, 1020, and 1400 μ seconds, respectively. Further, it is assumed that the backoff times of the first to fifth retransmissions are 50, 50, 70, 50, and 180 μ seconds, respectively.

  The AIFS time is calculated as 40 μsec by “AIFSN × slot time + SIFS time”. Therefore, it is understood that the backoff time by the contention window for the first to fifth retransmissions in this case is 10, 10, 30, 10, and 140 μ seconds, respectively.

  In this case, the start time of the sixth retransmission of the frame by the wireless communication unit 22 is calculated as follows. The backoff time B6 of the sixth retransmission is in the range of 40 μs to 660 μs according to (Equation 5).

  B6 = AIFSN x slot time + R (0, CW) x slot time (Equation 5)

  Therefore, the start time of the sixth retransmission is in the range of 1640 μs to 2260 μs as the time when the backoff time B6 has elapsed from 1600 μs which is the end time of the fifth retransmission.

  If the ACK frame from the terminal 30 can not be received even after the sixth retransmission, the seventh time using the backoff time selected from the range of 40 μs to 660 μs after the sixth retransmission. Subsequent retransmissions are made. When the terminal 30 can not communicate for several seconds, even if retransmission of frames is repeated at the above intervals, the retransmitted frame is not received by the terminal 30, and an ACK frame is not sent back. That is, the retransmitted frame in the above corresponds to a useless retransmission frame.

  On the other hand, FIG. 9 is an explanatory view showing retransmission timing of the base station 10 according to the present embodiment. Here, the case where N = 6, that is, the case where the control unit 26 inserts a waiting time before the backoff time of the sixth retransmission of the frame will be described.

  The timing of transmission of the frame shown in FIG. 9 and the timing of the first to fifth retransmissions are the same as the timing of the retransmission in FIG.

  According to the base station 10 of the present embodiment, the waiting time is inserted before the backoff time of the sixth retransmission.

  When the waiting time is calculated using the above (Equation 3), the waiting time W is calculated to be 40 ms, where Av = 50 milliseconds and s = 10 milliseconds in (Equation 3). In this case, the start time of the sixth retransmission is in the range of 41640 μs to 42260 μs.

  When the standby time is calculated using the above (Equation 4), the standby time W is calculated to be 25 ms, assuming that Av = 50 ms in (Equation 4). In this case, the sixth retransmission is performed in the range of 26640 μs to 27260 μs.

  By doing this, when the terminal 30 becomes incapable of communication for several seconds, the base station 10 does not repeat useless retransmission frame transmission as in the case of FIG. Wait for progress. Then, the base station 10 can suppress unnecessary transmission of the retransmission frame by transmitting the retransmission frame after the standby time has elapsed.

  Note that the integer N used when the control unit 26 controls retransmission may be set in advance by the user as a fixed value in the control unit 26 or may be dynamically varied. For example, even if the Nth retransmission is determined as the second retransmission among the retransmissions in which the value of the contention window matches the maximum value of the contention window in a predetermined backoff algorithm, the integer N is determined. Good. For example, in the case of the example shown in FIG. 3, the value of the contention window in the retransmission after the “second retransmission” is 63, which matches the maximum value. Therefore, since the second retransmission "3rd retransmission" corresponds to the above, the integer N may be set to 3. When transmission of a frame from the wireless communication unit 22 to the terminal 30 does not succeed until the value of the contention window reaches the maximum value, retransmission is repeated with an interval of IFS time and backoff time according to the backoff algorithm. Also, it is assumed that the frame does not reach the other device. Therefore, by causing the wireless communication unit 22 to wait for the standby time, unnecessary transmission of retransmission frames is suppressed.

  The control unit 26 sets the value of the contention window in each of the Nth and subsequent retransmissions by the wireless communication unit 22 to the value of the contention window in each of the first transmission and the first and subsequent retransmissions in a predetermined backoff algorithm. It may be set to That is, in the Nth retransmission by the wireless communication unit 22, the control unit 26 sets the CW in the backoff algorithm to CWmin, which is the value of the contention window in the first retransmission, and calculates the backoff time. In subsequent retransmissions, the value of the contention window for the first and subsequent retransmissions in the backoff algorithm may be set. By doing this, there is an advantage that the ACK frame from the terminal 30 can be received more quickly when the terminal 30 is in the communicable state after the waiting time has elapsed.

  On the other hand, the control unit 26 may change the value of the contention window in each of the Nth and subsequent retransmissions by the wireless communication unit 22 while maintaining the change of the contention window so far. This is because, when the terminal 30 is in the communication disconnection state even after the waiting time has elapsed, repeating the retransmission using a relatively long backoff time can reduce the number of frames to be retransmitted.

  When the wireless communication unit 22 communicates with each of the plurality of terminals 30, the control unit 26 calculates the standby time for each of the plurality of terminals 30, and retransmits the frame using the calculated standby time. It is also good. By doing so, even when the base station 10 communicates with a plurality of terminals 30 simultaneously and in parallel, it is possible to suppress unnecessary transmission of retransmission frames.

  In the present embodiment, an example is shown in which the wireless communication apparatus according to the present invention is realized as the base station 10, but the wireless communication apparatus according to the present invention may be realized as the terminal 30. When the terminal 30 is movable, the movement may make it impossible to communicate with the base station 10. In that case, according to a predetermined backoff algorithm, unnecessary retransmission frame transmission may be repeated. Therefore, as in the above, by inserting the waiting time before the N-th retransmission, it is possible to suppress useless retransmission frame transmission.

  As described above, the wireless communication apparatus according to the present embodiment waits for the waiting time in the middle of retransmission which is repeated at intervals of the IFS time and the backoff time determined by a predetermined backoff algorithm. Thus, the wireless communication apparatus retransmits the frame at a time longer than the interval between the IFS time and the backoff time. In this way, the wireless communication device suppresses unnecessary transmission of retransmission frames.

  Also, the wireless communication apparatus may successfully transmit a frame by retransmission when a time shorter than the average value of the round trip time has elapsed. As a result, the wireless communication apparatus can shorten the round trip time to be calculated thereafter, and can shorten the future standby time when suppressing transmission of useless retransmission frames.

  Also, the wireless communication apparatus suppresses unnecessary transmission of retransmission frames based on a more specific configuration by using the average value of the round trip time and the standard deviation thereof.

  Also, the wireless communication apparatus suppresses unnecessary transmission of retransmission frames based on a more specific configuration by using the average value of the round trip time.

  Also, when the value of the contention window increases at each retransmission according to the backoff algorithm, the wireless communication apparatus waits for the waiting time after the retransmission following the retransmission when the value of the contention window reaches the maximum value. Wait for If transmission of a frame from the wireless communication apparatus to the destination apparatus is not successful until the value of the contention window reaches the maximum value, there is a high probability that the destination apparatus can not communicate. In this case, it is assumed that the frame does not reach the other device even if retransmission is repeated with an interval of IFS time and backoff time according to the backoff algorithm. Therefore, the wireless communication apparatus suppresses unnecessary transmission of retransmission frames by performing standby for the standby time.

  Also, in the retransmission after waiting for the waiting time, the wireless communication apparatus determines the backoff time using the value of the contention window used for the first transmission in the backoff algorithm. Thus, there is an advantage that, when the other device is in a communicable state after the standby time, the other device can receive the frame more quickly, and the ACK frame from the other device can be received more quickly.

  Further, since the wireless communication device calculates the standby time for each of the plurality of other devices, even in the case of communicating with the plurality of other devices simultaneously in parallel, unnecessary transmission of retransmission frames is suppressed.

  As mentioned above, although the radio | wireless communication apparatus etc. of this invention were demonstrated based on embodiment, this invention is not limited to this embodiment. Without departing from the spirit of the present invention, various modifications that may occur to those skilled in the art may be made to the present embodiment, or a form constructed by combining components in different embodiments is also included in the scope of the present invention. .

  The present invention can be applied to a wireless communication apparatus that suppresses transmission of useless retransmission frames. Specifically, it is applied to a wireless base station and a wireless terminal.

1 communication system 10 base station 22 wireless communication unit 24 time acquisition unit 26 control unit 30 terminal 40 LAN
50 network

Claims (8)

A frame is transmitted to the opposite device based on backoff control using a contention window defined according to the number of retransmissions by a predetermined backoff algorithm, and an acknowledgment (ACK) frame for the transmitted frame is received from the opposite device. Wireless communication unit,
A time acquisition unit for acquiring a round trip time which is a time from the wireless communication unit transmitting the frame to receiving the ACK frame;
A standby time determined according to the round trip time acquired by the time acquisition unit from the time when the N-1th retransmission is completed, at the Nth (where N ≧ 1) retransmission of a frame by the wireless communication unit And a control unit configured to perform retransmission based on backoff control after e. The time acquisition unit acquires a plurality of the round trip times,
The control unit
The wireless communication apparatus according to claim 1, wherein the Nth retransmission is performed using a time shorter than the plurality of round trip times acquired by the time acquisition unit as the standby time. The time acquisition unit acquires a plurality of the round trip times,
The control unit
The N-th retransmission is performed using a value obtained by subtracting a plurality of standard deviations of the round trip time from the average value of the round trip times acquired by the time acquisition unit as the waiting time. A wireless communication device as described. The time acquisition unit acquires a plurality of the round trip times,
The control unit
The wireless communication apparatus according to claim 1, wherein the Nth retransmission is performed using half of an average value of the plurality of round trip times acquired by the time acquisition unit as the standby time. The Nth retransmission is the second retransmission of retransmissions in which the value of the contention window matches the maximum value of the contention window in the predetermined backoff algorithm. The wireless communication device according to claim 1. The control unit sets the value of the contention window in each of the Nth and subsequent retransmissions by the wireless communication unit to the value of the contention window in each of the first transmission and the first and subsequent retransmissions in the predetermined backoff algorithm. The wireless communication apparatus according to any one of claims 1 to 5, wherein the setting is performed. The wireless communication unit communicates with each of the plurality of counterpart devices.
The wireless communication device according to any one of claims 1 to 6, wherein the control unit retransmits the frame using the standby time for each of the plurality of other devices. A frame is transmitted to the opposite device based on backoff control using a contention window defined according to the number of retransmissions by a predetermined backoff algorithm, and an acknowledgment (ACK) frame for the transmitted frame is received from the opposite device. Wireless communication step,
A time acquisition step of acquiring a round trip time which is a time from transmission of the frame to reception of the ACK frame in the wireless communication step;
A standby time determined according to the round trip time acquired in the time acquisition step from the time when the N-1th retransmission is completed, at the time of the Nth (where N た だ し 1) retransmission of the frame in the wireless communication step And D. a control step of causing retransmission based on backoff control after e.

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