JP6417376B2 - Wireless communication apparatus, wireless communication method, wireless communication system, and processing apparatus - Google Patents

Description

  The present invention relates to wireless communication technology.

In the IEEE802.11 standard, access control is performed so that a plurality of terminals can share the same frequency. As an example of the access control, CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) is adopted. CSMA / CA avoids collision of transmission data called random backoff control after each wireless terminal station that wants to transmit a frame performs carrier sense (confirmation of wireless channel usage) in advance. This is a method of starting transmission using the control to perform. Random back-off control is defined by the wireless terminal station after the wireless terminal station holding the transmission data performs carrier sense and the channel used for data transmission is in the idle state for DIFS (Distributed Coordination Function Inter Frame Space). This is a control that generates a random number within the CW (Contention Window) range and determines a random backoff time based on the random number.

In addition, when the transmission timing of each wireless terminal station collides, the CW range is further widened to avoid transmission timing collision by performing retransmission. In the IEEE802.11a standard, the CW size can be increased from 15 to 1023 through six stages. When the CW size reaches the maximum value, the CW range is not expanded to a predetermined maximum number of retransmissions, and the maximum value is maintained. If it fails even after the maximum number of retransmissions, the transmission frame is discarded.

The model assumed by the conventional IEEE802.11 standard is that one node repeatedly transmits to an AP (Access Point) in order in uplink communication. Therefore, in the IEEE802.11 standard, a technique called DCF (Distributed Coordination Function) using the CSMA / CA is employed so that a plurality of terminals transmit to the AP at the same time and no collision occurs. With DCF technology, the wireless terminal station that holds the transmission data sends RTS (Request to Send) to the AP, and the AP sends CTS (Clear to Send) to the wireless terminal station. The transmission data collision caused by is avoided. This series of flows is called RTS / CTS exchange, and RTS / CTS exchange is performed based on dot11RTSThreshold. When a frame shorter than dot11RTSThreshold is transmitted, RTS / CTS exchange is not performed.

As described above, in the IEEE802.11 standard, DCF technology is employed so that transmission timings between wireless terminals do not collide as much as possible.
In recent years, in uplink communication, MU-MIMO (Multi User-Multi Input Multi Output) technology in which a plurality of terminals simultaneously transmit data using the same channel has been studied. In MU-MIMO technology, it is important that the data transmission timings of a plurality of terminals are the same, and the frequency band to be used is the same.

In the technique described in Patent Document 1 below, MU-MIMO is realized by extending DCF (additional RTS / CTS exchange).
In the technique described in Patent Document 2 below, simultaneous transmission is realized by controlling the back-off value.

JP 2010-130625 A JP 2011-217234 A

In Patent Document 1, there is a problem that the throughput decreases because the RTS / CTS exchange is performed even when the transmission packet length is short. In addition, the base station needs to specify the transmission timing.
Further, in Patent Document 2, since a back-off value is assigned to all combinations of terminals that transmit simultaneously, there is a problem that the back-off value becomes long depending on the combination. In addition, it is necessary for the transmitting terminal to maintain a table of back-off values for all combinations.

  When implementing the MU-MIMO technology in uplink communication, if the current DCF is adopted, there is a problem that multiple terminals do not transmit simultaneously.

  An object of the present invention is to realize MU-MIMO with almost no change in the mechanism of DCF. It is another object of the present invention to allow transmission timing to be specified on the terminal side.

  According to one aspect of the present invention, there is provided a wireless terminal station device used in a wireless communication system including one wireless base station and a plurality of wireless terminal stations, the wireless terminal station device being one of a plurality of groups. The back-off value when performing random back-off of the wireless terminal station devices belonging to at least one group and belonging to at least one group is a set of values composed of a predetermined limited number. There is provided a wireless terminal station device including a back-off control unit that performs control so as to be selected from a set of off-value candidates.

  In this way, by controlling the set of back-off value candidates, it is possible to perform communication with a plurality of wireless terminal stations at the same time with less protocol change from the conventional method.

  The set of back-off value candidates is configured by the predetermined limited number selected from continuous values from a back-off value candidate range to 0 based on the number of retransmissions of transmission data held by the wireless terminal station A set of values may be used, and as the set of back-off value candidates, a set of integers continuous from 0 configured by the predetermined limited number may be used. Further, as the set of backoff value candidates, it is possible to use a set that is configured by the predetermined limited number and uses a predetermined value as an expected value of the set, or as the set of backoff value candidates, A set determined using the control variable notified from the radio base station or a set notified from the radio base station may be used.

  The set of backoff value candidates may be determined based on a frame length of transmission data held by the wireless terminal station device to which the wireless terminal station device belongs.

  In addition, when the back-off value countdown is stopped halfway, if the back-off value in the stopped state is a value that is not included in the set of back-off value candidates, the back-off value is changed to the back-off value. It is preferable to correct to a value included in the set of value candidates.

  The present invention is also a radio base station apparatus used in a radio communication system composed of one radio base station and a plurality of radio terminal stations, wherein the radio terminal stations belong to any of a plurality of groups. Control variable for controlling the number of values included in a set of backoff value candidates that are candidates for backoff values selected by the wireless terminal station devices belonging to at least one group, which are allocated to A radio base station apparatus having a random back-off control variable determination unit that determines

  The random backoff control variable determining unit is configured to determine the control variable based on at least one of a number of radio terminal station devices accommodated by a radio base station device and a number of antennas included in the radio base station device. Can be determined.

  Further, a set of backoff value candidates obtained by selecting the number of values included in the backoff value from values from 0 to a backoff value candidate range based on the number of retransmissions of transmission data held by the wireless terminal station. A random backoff value candidate set generation unit may be further included.

  The random back-off value set generation unit, when generating a set of back-off value candidates for a plurality of groups, controls so that the values included in each set of back-off value candidates are different. Also good.

  The backoff value candidate set generation unit may set an expected value of a value included in the random backoff value candidate set to a predetermined value.

  At least one of the control variable and the set of backoff value candidates may be notified to the wireless terminal station device for each update.

  According to another aspect of the present invention, there is provided a radio communication method in a radio terminal station apparatus used in a radio communication system including one radio base station and a plurality of radio terminal stations, wherein the radio terminal station apparatus includes: A value configured by a predetermined limited number of backoff values when performing random backoff of the wireless terminal station devices that are assigned to belong to any of a plurality of groups and belong to at least one group There is provided a wireless communication method comprising a step of performing control to select from a set of back-off value candidates that is a set of

  In addition, the present invention is a processing device that causes a wireless terminal station device used in a wireless communication system composed of one wireless base station and a plurality of wireless terminal stations to perform a predetermined function, the wireless terminal station device Are assigned to belong to one of a plurality of groups, and the back-off value when performing random back-off of the wireless terminal station device belonging to at least one group is configured by a predetermined limited number A processing apparatus that exhibits a control function of selecting from a set of back-off value candidates that is a set of values.

The present invention is also a radio communication method in a radio base station apparatus used in a radio communication system composed of one radio base station and a plurality of radio terminal stations, wherein the radio terminal station is one of a plurality of groups. The number of values included in a set of backoff value candidates that are candidates for backoff values selected by the wireless terminal station device belonging to at least one group used in the system is controlled. A wireless communication method comprising a step of determining a control variable for the purpose.

  In addition, the present invention is a processing device that causes a radio base station apparatus used in a radio communication system composed of one radio base station and a plurality of radio terminal stations to perform a predetermined function. Values included in a set of back-off value candidates that are assigned to belong to any one of a plurality of groups and are used in the system and that are back-off value candidates selected by the wireless terminal station device belonging to at least one group It is a processing device characterized by exhibiting a function of determining a control variable for controlling the number of

  Further, the present invention is a radio communication system including one radio base station and a plurality of radio terminal stations, wherein the radio terminal station devices are distributed so as to belong to any of a plurality of groups, and at least 1 The wireless terminal station devices belonging to one group are controlled to select a back-off value when performing random back-off from a set of back-off value candidates, which is a set of values composed of a predetermined limited number. And a random backoff for determining a control variable for controlling the number of values included in the set of backoff value candidates to be used in the system. A radio communication system having a radio base station apparatus having a control variable determination unit may be used.

  By controlling the set of backoff value candidates, it is possible to perform communication with a plurality of wireless terminal stations at the same time with less protocol change from the conventional method. In addition, the transmission timing can be determined on the wireless terminal station side.

It is a functional block diagram which shows the example of schematic structure of the radio | wireless communications system by embodiment of this invention. It is a functional block diagram which shows the example of 1 structure of the wireless base station 1 by the 1st Embodiment of this invention. FIG. 10 is a flowchart showing a flow of association establishment processing from when a wireless base station receives a connection request until notification of an AID (Association ID) and a preamble transmission resource. It is a figure explaining the transmission resource allocation process of the preamble of a terminal. FIG. 3 is a flowchart showing a flow of operation of each element in FIG. 2. It is a functional block diagram which shows the example of 1 structure of the radio | wireless terminal station 2 by the 1st Embodiment of this invention. It is a flowchart figure which shows the flow of a process until a wireless terminal station makes a connection request | requirement to a wireless base station, and an association is established. It is a flowchart figure which shows the flow of the process which transmits data from a wireless terminal station to a wireless base station. FIG. 6 is a timing chart when MU-MIMO transmission is performed when transmission timings of wireless transmission terminal stations overlap when a wireless terminal station attempts to transmit to a wireless base station. It is a figure which shows the expected value of the collision station number of a transmission timing with respect to the number of accommodation terminal stations in the case of using the random backoff control variable shown by Formula (5), and the case of the conventional IEEE802.11a standard. It is a functional block diagram which shows the example of 1 structure of the wireless base station 1 by 2nd Embodiment. FIG. 10 is a flowchart showing a processing flow until a radio base station determines a random backoff random value candidate set used by a terminal to be subjected to MU-MIMO and finishes receiving a signal from the radio terminal station. FIG. 7 is a diagram in which a random back-off random number holding unit is inserted instead of the CW size changing unit in FIG. 6. It is a flowchart figure which shows the flow of a process after transmitting the transmission frame after receiving the set of the random backoff value candidates for the terminal station which wants to perform MU-MIMO of the wireless terminal station. The functional block diagram which shows the example of 1 structure of a radio | wireless terminal station is shown. It is a flowchart figure which shows the flow of a process of a radio | wireless terminal station. It is a timing diagram of this embodiment. It is a figure which shows an example of a random backoff value candidate when CW size is 15. It is a functional block diagram which shows the example of 1 structure of the wireless base station by the 3rd Embodiment of this invention. FIG. 10 is a flowchart from when a radio base station notifies a set of random backoff value candidates for each group until data is received from a certain radio terminal station. It is a functional block diagram which shows the example of 1 structure of the terminal station of the radio | wireless communication in this embodiment. It is a flowchart figure which shows the flow of a process of the radio | wireless terminal station shown in FIG. It is a timing diagram in communication of this embodiment. It is a figure which shows the example of the set of the random backoff value candidates of the terminal which wants to carry out MU-MIMO of this embodiment, and the set of the random backoff value candidates of the terminal of the conventional system.

(First embodiment)
Hereinafter, a wireless communication technique according to an embodiment of the present invention will be described in detail with reference to the drawings. In the following, it is assumed that it is basically based on the IEEE802.11 standard and the IEEE802.11a standard unless otherwise specified.

FIG. 1 is a functional block diagram illustrating a schematic configuration example of a wireless communication system according to an embodiment of the present invention.
As shown in FIG. 1, the wireless communication system A according to this embodiment includes a wireless base station 1 and wireless terminal stations 2 to 5. It is assumed that each communication station 1 to 5 accommodates all communication stations within the communication range. The radio communication system A shown in FIG. 1 includes, for example, a radio base station 1 that is an access point (AP) and radio terminal stations 2 to 5 having the same transmission frequency. The radio base station 1 has a plurality of antennas, and each of the radio terminal stations 2 to 5 has one antenna. In all the embodiments of the present invention, the number of antennas of the wireless terminal stations 2 to 5 is set to 1 for simplicity of explanation, but a plurality of antennas may be provided. Similarly, the number of antennas possessed by the wireless base station 1 can be changed. In the present embodiment, unless otherwise specified, the transmission frame length is shorter than dot11RTSThreshold in IEEE802.11, and RTS / CTS exchange is not performed.

FIG. 2 is a functional block diagram showing a configuration example of the radio base station 1 according to the first embodiment of the present invention. The radio base station 1 shown in FIG. 2 includes two antennas 100a and 100b, two first radio communication units 101a and second radio communication stations 101b corresponding to each antenna, a switch (SW) 102, a transmission unit 104, and frame generation. Unit 116, control unit 111, preamble transmission resource allocation determination unit 110, random backoff control variable determination unit 115, preamble reception unit 105, channel estimation unit 106, MIMO demodulation unit 107, demodulation unit 108, and error check unit 109. . The control unit 111 controls transmission frame generation, random backoff control variable setting, and preamble transmission resource allocation from the received signal. Here, an example of a method for determining the preamble transmission resource allocation is shown below.
In the present embodiment, it is assumed that a preamble transmission resource is allocated to each number of terminals accommodated by the radio base station 1.

FIG. 3 is a flowchart showing a flow of association establishment processing from when the radio base station 1 receives a connection request until notification of an AID (Association ID) and a preamble transmission resource. In the IEEE 802.11 standard, when establishing an association between a wireless terminal station and a wireless base station, the wireless base station uses a method of assigning an AID to each wireless terminal station based on the MAC address as one of the parameters. ing. AID is assigned in the range of 1 to 2007. In the flowchart shown in FIG. 3, first, the radio base station 1 stands by until a connection request is received by the antenna 100a or the antenna 100b (step S1). When the connection request is received by the antenna 100a or the antenna 100b (YES), the connection request signal including the transmitted MAC address of the terminal is transmitted to the control unit 111 via the wireless communication unit 101a or 101b, the switch 102, and the reception unit 103. Is input. It is assumed that the control unit 111 cannot connect to the radio base station when all hash values are used (step S15). If there is an unused hash value, the control unit 111 assigns the AID of the terminal that transmitted the connection request (step S2). In the present embodiment, the subsequent processing is different from the conventional one. The AID set by the control unit 111 is mapped with a hash function (step S3). This hash value is assigned from 1 to the limit number. In the present embodiment, this limit number is set to 4 and mapped to values of 1 to 4. An example of the hash function is shown below.

It is confirmed whether the set hash value is already set in another accommodated terminal (step S4). If it is not set in the other terminal (YES), AID and preamble transmission resources Is transmitted to the terminal that has requested connection (step S5). If the same hash has already been used for the accommodating terminal in step S4 (NO), 1 is added to the current hash value, or 1 if the current hash value is the maximum value (step S16))
Confirm again in step S4. In step S15, if all hash values are used, connection is not allowed, so that the terminal performing step S4 can assign any hash value from 1 to 4.

FIG. 4 is a diagram for explaining transmission resource allocation processing of a preamble of a terminal.
In this embodiment, the preamble transmission resources are allocated by assigning every four OFDM subcarrier numbers to each hash value as shown in FIG. By shifting the assigned number by one for each hash value, it is possible to prevent the preamble transmission resources of the terminals having the respective hash values from overlapping. In IEEE802.11a, OFDM subcarriers are as shown in FIG. 4B, so that there are 52 subcarriers in total. In the present embodiment, the subcarriers are allocated to four hash values mapped. The channel estimation method is shown in the following equation. First, a predetermined preamble A is expressed by the following equation.

Similarly, the signal Ri received from the wireless terminal station i is expressed by the following equation.

  When channel estimation is performed from the preamble, the frequency to which no transmission resource is allocated is interpolated using a sinc function or the like.

FIG. 5 is a flowchart showing an operation flow of each element of FIG.
The radio base station 1 periodically checks the number of accommodated terminals and the number of antennas possessed by the radio base station and obtains a random backoff control variable (step S6). The determined back-off control variable is input to the frame generation unit 116, and the radio terminal station that is the accommodating terminal of the radio base station 1 via the transmission unit 104, the switch 102, the radio communication unit 101a or 101b, and the antenna 100a or 100b. 2 to 5 are transmitted (step S7).

  The radio base station 1 waits for reception of a preamble (step S8). When the preamble is received, the preamble is input to the preamble receiving unit 105 from the two antennas 100a and 100b via the wireless communication units 101a and 101b, the switch 102, and the receiving unit 103, respectively. The channel estimation unit 106 estimates a channel from the received preamble (step S9).

Further, preamble reception section 105 confirms the transmission resource of the received signal. The number of terminals that transmitted the preamble can be obtained by confirming the actually transmitted resource with respect to the allocated transmission resource. The preamble receiver 105 checks whether the received signal has been received from a plurality of terminals (step S10). When receiving signals from a plurality of terminals, the MIMO separation unit 107 performs MIMO separation on the signals from the respective terminals using the channel estimation value (
In step S11), the demodulator 108 performs demodulation (step S12). Step S10
If the signals are not transmitted from a plurality of terminals, the demodulation processing unit 108 performs demodulation (step S1).
2).

An error check is performed on the signal demodulated by the demodulation unit 108 by the error check unit 109 (step S13), and the presence / absence of an error is input to the frame generation unit 116.
The frame generation unit 116 generates an ACK (Acknowledge) frame based on the result of the error check, and transmits the transmission unit 104, the switch 102, one wireless communication unit 101b,
An ACK frame is transmitted via one antenna 100b (step S14).

After transmitting the ACK frame, the radio base station 1 starts waiting for reception of the next frame.
FIG. 6 is a functional block diagram showing a configuration example of the wireless terminal station 2 according to the first embodiment of the present invention. As shown in FIG. 6, the wireless terminal station 2 includes an antenna 200, a wireless communication unit 201, a switch 202, a reception unit 203, a transmission unit 204, a demodulation unit 205, a frame generation unit 206, an error check unit 207, a control unit 208, A data holding unit 209, a CW size changing unit 210, and a random back-off setting unit 211 are provided. Further, in the figure, the control unit 208, the CW size changing unit 210, and the random backoff setting unit 211 are collectively referred to as a backoff control unit 212.

  In the conventional random back-off setting, a uniform random number (integer) of [0, CW size] is set, and transmission is started at the timing obtained by multiplying the integer selected from the uniform random number by the slot time.

In the conventional method, the CW size is determined by a predetermined method. However, in this embodiment, the number of terminals accommodated by the radio base station 1 and the number of terminals accommodated by the CW size determined by the conventional method are as follows. Change to narrow based on at least one of the number of antennas. As an example of the change, there is a method in which a random back-off control variable (≦ 1) is multiplied by a CW size determined by a conventional method to obtain a CW size for a terminal that is desired to be MU-MIMO. This reduces the CW size shared between terminals that want to be MU-MIMO. As an example, an example of how to obtain the random backoff control variable X based on the number of terminals accommodated by the radio base station 1 is shown by the following mathematical formula.

Here, N is the number of accommodated terminals, and CWmin is the smallest size among the CW sizes determined by the conventional method. The new CW size CWMU-MIMO of the terminal to be MU-MIMOed at this time is shown in Equation 6.

Here, CW is a CW size determined by a conventional method. In the IEEE802.11a standard, the CW size is in the range of 15 to 1023 and is increased each time retransmission is performed. Formula 7 shows how to obtain the CW size in the conventional IEE802.11a. However, n = number of retransmissions.

The effect of the random back-off control variable X obtained by Equation 5 will be described with reference to FIG.
This will be described later with reference to 0.

The operation of each element in FIG. 6 will be described using the flowcharts of the wireless terminal stations in FIGS.
FIG. 7 is a flowchart showing the flow of processing from when the wireless terminal station 2 makes a connection request to the wireless base station 1 until the association is established. The wireless terminal station 2 transmits a connection request to the wireless base station 1 (step S100), and the wireless base station 1 sends a connection permission frame (connection permission notification,
It waits for reception of a preamble transmission resource and AID (step S101). When the connection permission frame is received by the antenna 200, the error check unit 207 performs an error check via the wireless communication unit 201, the switch 202, the reception unit 203, and the demodulation unit 205 (step S102). If there is no error in step S102, the connection is successful,
The process ends. If an error occurs in step S102, a connection request frame is generated by the frame generation unit 206, and the connection request is transmitted again from the antenna 200 via the transmission unit 204, the switch 202, and the wireless communication 201.

FIG. 8 is a flowchart showing a flow of processing for transmitting data from the wireless terminal station 2 to the wireless base station 1. The radio terminal station 2 in FIG. 6 receives a signal (a limited signal) including a random backoff control variable transmitted from the radio base station 1 by the antenna 200 (step S10).
3). The received signal includes a wireless communication unit 201, a switch 202, a reception unit 203, and a demodulation unit 20.
5 to the error check unit 207. The signal (limit signal) including the random back-off control variable input to the error check unit 207 is subjected to an error check by the error check unit 207 and input to the back-off control unit 212. The signal input to the back-off control unit 212 is input to the CW size changing unit 210 via the control unit 208. The CW size changing unit 210 performs control to change the CW size of the wireless terminal station 2 based on the notified random backoff control variable (step S130).

When transmission data is generated, the frame generation unit 206 generates a transmission frame (step S105). The generated transmission frame is input to the transmission unit 204. Based on the CW size changed by the CW size changing unit 210, the random back-off setting unit 211 determines a back-off value using a set of consecutive integers from 0 to CW size as a uniform random number (step S106). . Next, the wireless terminal station 2 performs carrier sense and determines whether or not the channel is busy (
Step S104). If the channel is busy in step S104, it waits until it becomes idle. If the channel is not busy in step S104, it is confirmed whether the back-off value is 0 (step S107). If the back-off value is not 0 in step S107, the back-off value is decreased by 1 (step S112). When the back-off value is decreased, after waiting for the slot time in IEEE802.11, carrier sense is performed again, and the channel state is confirmed (step S104). In step S107, when the back-off value is 0, the transmission frame generated by the frame generation unit 206 is transmitted from the antenna 200 via the switch 202 and the wireless communication unit 201 in the order of the preamble and transmission data as the transmission timing. Transmit (step S108).

In step S108, after the transmission data of the wireless terminal station 2 is transmitted, it waits until ACK is received (step S113). The above ACK is not known until it is received and demodulated. If ACK is received in step S113, it is confirmed whether the received ACK is for itself (step S109). In step S113, if ACK is not transmitted corresponding to “SIFS (Short Inter Frame Space) time + ACK frame length” in IEEE802.11, it is assumed that the transmission has failed, and the CW size changing unit 210 changes the CW size. (Step S114) The backoff value is set again by the random backoff setting unit 211 (Step S106). The method for changing the CW size conforms to the IEEE802.11 standard. ACK received in step S109
If is directed to you, it ends. If the received ACK was not for you,
Wait until the ACK is received again (step S113).

FIG. 9 shows that when the wireless terminal stations A to C try to transmit to the wireless base station, the wireless transmitting terminal station A
, C transmission timing overlaps, and is a timing diagram when MU-MIMO transmission is performed.

The wireless terminal stations A to C wait for a certain time after the previous frame ends and start backoff. The blank period 300 at this time corresponds to an IEEE802.11 DIFS (DCF Inter Frame Space) time. Blank times 301 to 309 correspond to slot times in IEEE 802.11, respectively. In the example of FIG. 9, since the backoff value selected by the wireless terminal stations A and C is 4 and the backoff value selected by the wireless terminal station B is 5, the wireless terminal station A having a small selected backoff value. , C obtain the transmission right simultaneously. Since there are two terminals that transmit a transmission frame to the radio base station, MU-MIMO of two terminals is realized. In the present embodiment, the CW size is limited by a random backoff control variable in order to increase the probability that each backoff value selected by a plurality of terminals takes the same value. The wireless terminal station A transmits the preamble 310 using transmission resources allocated in advance. Subsequently, the data 311 is transmitted to the radio base station in the occupied band of the radio terminal station A. Similarly, the wireless terminal station C also transmits the preamble 312 and the data 313 to the wireless base station. At this time, the occupied bands of the wireless terminal stations A and C are the same.

The wireless base station that simultaneously receives data from the two terminals transmits ACK (A) 314 for the wireless terminal station A and ACK (C) 315 for the wireless terminal station C to the wireless terminal stations A and C, respectively. The blank time 316 at this time corresponds to SIFS (Short Inter Frame Space) time in the IEEE802.11 standard. In the timing diagram of FIG. 9, the SIFS time interval is provided each time a plurality of ACKs are transmitted. However, since the wireless terminal station performs reception until ACK is received, ACK (A) 314 and ACK (C) 315 are received. May be transmitted continuously without leaving SIFS time. When the wireless terminal stations A and C receive the respective ACKs, data transmission / reception is started again. After the blank time 310 again, the wireless terminal station B starts counting down the back-off 309 for the carry-over. Thereafter, when the preamble 317 and data 318 are transmitted to the radio base station and the ACK (B) 319 for the radio terminal station B is received, the transmission from the radio terminal station B is terminated.

FIG. 10 is a diagram illustrating an expected value of the number of collision stations at the transmission timing with respect to the number of accommodated terminal stations in the case of using the random backoff control variable expressed by the equation (5) and the case of the conventional IEEE802.11a standard. It is. However, in the comparison shown in FIG. 10, since the transmission is the first time, the conventional CW size and CWmin are 15. This is the minimum value of the IEEE802.11a standard. When a uniform random number of [0, CW] is used for random backoff, assuming that the number of accommodated terminals is N, the expected value E of the number of stations with which transmission timing collides in the conventional method is shown below.

  In the proposed method shown in FIG. 10, CW is obtained using (Equation 5) and (Equation 6).

In this example, since CW = CWmin, (Equation 9) is CWMU-MIMO = N / 2. This CWMU-MIMO
Is substituted for CW in (Equation 8) to obtain the expected value E in the proposed method.

As can be seen from FIG. 10, by reducing the CW size, the probability of collision of transmission timings of a plurality of terminals is improved, and MU-MIMO in uplink communication can be realized. The method described in this embodiment is easy to implement because there are few changes to the conventional method. The transmission terminal can determine the transmission timing. In this embodiment, the CW size is limited in order to reduce the number of random backoff value candidates. However, when there are radio base stations that perform similar control in the vicinity, radio terminals that communicate with the respective radio base stations Station transmissions may collide and communication errors may occur. In such a case, as a method of reducing the number of random backoff value candidates, a random value is selected as a random backoff value candidate, and different candidate values are used between neighboring radio base stations. Anyway.

(Second Embodiment)
In the present embodiment, an embodiment in which a terminal that wants to perform MU-MIMO and a conventional terminal transmit to a common AP is shown. Also in this embodiment, unless otherwise specified, it is based on the IEEE 802.11 standard and the IEEE 802.11a standard. Unless otherwise specified, it is assumed that the transmission frame length is shorter than dot11RTSThreshold in IEEE802.11, and RTS / CTS exchange is not performed. As described above, in this embodiment, MU-MIMO can be realized with almost no change in the DCF mechanism.

In FIG. 1, an embodiment assuming a system model of a radio base station 1, radio terminal stations 2 and 4 for which MU-MIMO is desired, and other radio terminal stations 3 and 5 will be described. FIG. 11 is a functional block diagram illustrating a configuration example of the radio base station 1 according to the second embodiment. Here, in the functional block diagram of FIG. 11, a random backoff value candidate set generation unit 250 is added between the random backoff control variable determination unit 115 and the frame generation unit 116 of FIG. To the control unit 111. Further, a CW size holding unit 117 is added between the control unit 111 and the random backoff value candidate set generation unit 250.

In this embodiment, the wireless terminal stations that want to MU-MIMO use a set of common random backoff value candidates determined by the AP, thereby improving the transmission timing collision probability. The set of random back-off value candidates here is a set of back-off value candidates selected by a terminal to be subjected to MU-MIMO. A terminal that wants to MU-MIMO selects a back-off value by using all integers included in the set of random back-off value candidates as a uniform random number.

  A series of flows in which the wireless base station 1 receives a connection request from any one of the wireless terminal stations 2 to 5 and transmits a connection permission frame to the wireless terminal station that has transmitted the connection request is described in the first embodiment. Since it is the same as that described with reference to FIGS.

FIG. 12 shows a processing flow until the radio base station 1 determines a set of random backoff random value candidates used by a terminal to be MU-MIMO and completes reception of a signal from the radio terminal station 2. It is a flowchart figure. In addition, about the process equivalent to 1st Embodiment and the process of FIG. 5, it has described using the same number.

The radio base station 1 uses the random backoff control variable determining unit 115 in FIG. 11 to randomly determine the random backoff control variable for the radio terminal station to be MU-MIMO based on the number of accommodated terminals and the number of antennas of the radio base station. Is determined (step S6). Based on the determined random back-off control variable, the random back-off value candidate set generation unit 250 obtains a set of random back-off value candidates of the wireless terminal station to be subjected to MU-MIMO (step S17). That is, in this embodiment, each wireless terminal station that wants to perform MU-MIMO does not determine the CW size, but the wireless base station determines the CW size.

An example of how to determine a set of random backoff value candidates in the present embodiment is shown below.
As an example of a method for determining a set of random backoff value candidates in the present embodiment, it is possible to use a CW size obtained by a method similar to the conventional method. The expected value of the random backoff candidate of the wireless terminal station to be MU-MIMO is 'CW size / 2', and the number of random backoff value candidates is 'floor ((1 + CW size) * random backoff control variable)' Set as follows. Here, 'floor (x)' is set to 'floor (x) = a' when the value of x is 'a ≦ x <a + 1' with respect to the integer a.

By setting the expected value of the random back-off value candidate as described above, the expected value of the back-off value selected by the conventional terminal and the terminal that wants to perform MU-MIMO when the CW size is the same.

As a result, there is no significant difference between the terminal (wireless terminal stations 2 and 4 in the present embodiment) that is desired to be MU-MIMO and the conventional terminal (wireless terminal stations 3 and 5 in the present embodiment). The random back-off control variable (≦ 1) here is the same as that described in the first embodiment. By periodically changing the set of random back-off value candidates of the terminal that wants to be MU-MIMO, there is no difference between the two types of terminals (the terminal that wants to be MU-MIMO and the conventional terminal).

FIG. 24 shows an example of a set of random backoff value candidates of terminals desired to be MU-MIMO according to the present embodiment and a set of random backoff value candidates of conventional terminals. In FIG. 24, blank times 502 to 510 correspond to slot times in the IEEE 802.11 standard. The numbers (1 to 15) written in the spaces are the values of the back-off counter. The example of FIG. 24 shows a case where the CW size of the terminal that is to be MU-MIMO and the CW size of the conventional terminal are equal to 15.

When the random backoff control variable X = 0.25, the expected value of the set of random backoff value candidates is 7.5, and the number of integers included in the set of value candidates is 4. In FIG. 24, {1, 5, 9, 15} is used as an example of a set of random backoff value candidates that satisfy the above relationship.
In FIG. 24, backoff times 502, 506, and 510 are candidates for random backoff values used by a terminal that wants to perform MU-MIMO. In addition, since the conventional terminal can take all backoff values within the CW size, the set of random backoff value candidates of the conventional terminal is [0, 15]. Each is a uniform random number.

The determined set of random backoff value candidates is input to the frame generation unit 116 and transmitted to the radio terminal stations 2 and 4 via the transmission unit 104, the switch 102, the radio communication unit 101a or 101b, and the antenna 100a or 100b. (Step S18). The radio base station 1 waits for reception of the preamble (step S8). The process from the reception of the preamble (step S8) to the demodulation process (step S12) is the same as that of the first embodiment, and is omitted because it has been described with reference to FIG.

The received signal demodulated by the demodulator 108 is checked for errors by the error checker 109 (step S19). If no error occurs in the error check unit 109, the radio base station 1 generates an ACK frame for the terminal of the received signal in the frame generation unit 116, and transmits the transmission unit 104, the switch 102, the radio communication unit 101a or ACK is transmitted to each of the antennas 100a and 100b via 100b (step S14). Step S1
If an error occurs in step 9, the CW size held in the CW size holding unit 117 is changed in order to reset the set of random backoff value candidates of the terminal that is desired to be MU-MIMO (step S12). As an example, the CW size can be changed by using a method similar to the conventional IEEE 802.11 method.

Using the changed CW size and the random backoff control variable, the CW size for the terminal to be subjected to MU-MIMO that has been processed based on (Equation 5) is input to the CW size holding unit 117. after that,
The random backoff value candidate set generation unit 250 determines a set of backoff value candidates, and from the antenna 100a or 100b via the frame generation unit 118, the transmission unit 104, the switch 102, and the wireless communication unit 101a or 101b, A set of new random back-off value candidates is transmitted to the accommodated wireless terminal stations (wireless terminal stations 2 and 4).

FIG. 13 is a functional block diagram illustrating a configuration example of the wireless terminal station 2 that is a terminal that is desired to perform MU-MIMO. In the configuration example shown in FIG. 13, a random back-off random number holding unit 300 is inserted instead of the CW size changing unit 210 of FIG. 6. This random back-off value candidate set holding unit 300 holds a set of random back-off value candidates used by a terminal to be subjected to MU-MIMO notified by the radio base station 1. In the figure, the control unit 208, the random back-off random number holding unit 300, and the random back-off setting unit 211 are collectively referred to as a back-off control unit 213.

Each wireless terminal station holds a set of random backoff value candidates used by the terminals that want to use the common MU-MIMO, which increases the probability that the transmission timing of the terminals that want to use MU-MIMO will collide. Realize. The random backoff value candidate set holding unit 300 continues to hold the current set of backoff value candidates until the notification is received again.

FIG. 14 shows a flow of processing from reception of a set of random backoff value candidates for a terminal station to be subjected to MU-MIMO, until transmission of a transmission frame, in the wireless terminal station 2 in the present embodiment. It is a flowchart figure. However, at this time, the wireless terminal station 2 is a terminal that is desired to be MU-MIMO. The flowchart from the time when the wireless terminal station 2 transmits a connection request to the wireless base station until the establishment of the association may be the same as that described with reference to FIG. In FIG. 14, instead of receiving the random back-off control variable (step S103) and changing the CW size (step S130) in FIG. 8, receiving a random back-off value candidate set (step S150) is inserted, and changing the CW size (step S114). ) In place of the random backoff value candidate set (step S120) and rewriting the random backoff value candidate set (step S120).
Step S151) is inserted.

  The wireless terminal station 2 receives the set of random back-off value candidates notified from the wireless base station 1 (step S150). A signal from the radio base station 1 including a set of random backoff value candidates is input to the error check unit 207 via the radio communication unit 201, the switch 202, and the reception unit 203. The signal including the set of random backoff value candidates subjected to the error check by the error check unit 207 is input to and held in the random backoff value candidate set holding unit 300.

When transmission data is generated, the frame generation unit 206 generates a transmission frame (step S105). The generated transmission frame is input to the transmission unit 204. The random backoff setting unit 211 randomly determines the backoff value so that each number included in the set held by the random backoff value candidate set holding unit 300 is selected with the same probability (step S106). ). When the back-off value is determined, carrier sense is performed to check whether the channel is not busy (step S104). If the channel is busy in step S104, it waits until it becomes idle. If the channel is not busy, it is checked whether the back-off value is 0 (step S107). If the back-off value is 0 in step S107, it is regarded as the transmission timing. If the back-off value is not 0, the transmission unit 204 decrements the current back-off value count by one (step S112).

When the back-off counter is decreased, the process returns to the step immediately after the random back-off setting (step S106) after waiting for the slot time. When the transmission timing is regarded as the transmission timing in step S107, the transmission frame generated by the frame generation unit 206 is transmitted from the antenna 200 via the switch 202 and the wireless communication unit 201 in the order of the preamble and the transmission data (step S108). However, the preamble is transmitted using the transmission resource assigned by the radio base station, and the transmission data is transmitted in the occupied band of the radio terminal station 2.

After the transmission data of the wireless terminal station 2 is transmitted, it waits until ACK is received for a predetermined time (step S113). To which terminal the ACK is the ACK is not known until reception and demodulation. Further, the predetermined time here is “SIFS time + ACK frame length” in the IEEE802.11 standard. When ACK is received within the time in step S113, the ACK received by the demodulation unit 205 via the wireless communication unit 201, the switch 202, and the reception unit 203 is demodulated,
It is confirmed whether the received ACK is for itself (step S109). Step S1
If no ACK is received at step 13, it is confirmed again whether a set of random backoff value candidates is received (step S120). When a set of random backoff value candidates is received, the received signal including the set of random backoff value candidates is transmitted to the error check unit 207 via the wireless communication unit 201, the switch unit 202, the reception unit 203, and the demodulation unit 205. Is input. The signal subjected to the error check by the error check unit 207 is input to the back-off control unit 213. The signal input to the back-off control unit 213 rewrites the random back-off value candidate set held in the random back-off value candidate set holding unit 300 via the control unit 208 (step S151). The setting is resumed from the setting of the random back-off value by the off setting unit 211 (step S106). When a set of random backoff value candidates is not received in step S120, rewriting is not performed, and the random backoff setting unit 211 resumes from the random backoff setting (step S106). If the ACK received in step S109 is directed to the user, the process ends. If the received ACK is not intended for itself, it waits for the ACK to be received again (step S113).
Conventional wireless terminal stations 3 and 5 perform data transmission based on the conventional IEEE802.11 standard.

  FIG. 15 is a functional block diagram illustrating a configuration example of the wireless terminal station 3. FIG. 15 shows the wireless terminal station 3 in FIG. However, since the CW size changing unit 210 in FIG. 6 and the CW size changing unit 260 in FIG. 15 are different in operation, they are given different numbers. Unlike the first embodiment, the CW size changing unit 260 in the present embodiment does not change the CW size using a random backoff control variable. However, the method for increasing the CW size when transmission fails is the same as in the first embodiment, and an example conforming to the IEEE 802.11 method is taken as an example.

  FIG. 16 is a flowchart showing a process flow of the wireless terminal station 3. The process shown in FIG. 16 is obtained by eliminating the random back-off control variable reception process (step S103) and the CW size change process (step S130) in FIG.

  When the transmission data is generated, the wireless terminal station 3 generates a transmission frame by the frame generation unit 206 (step S105). The generated transmission frame is input to the transmission unit 204. The random back-off setting unit 211 determines a back-off value as a uniform random number of [0, CW size] based on the CW size of the terminal (step S106).

The back-off setting (step S106) to end is assumed to be the same as that of the first embodiment and has been described above with reference to FIG. However, the CW size changing unit 210 in the first embodiment is the CW size changing unit 260 in the present embodiment.

FIG. 17 is a timing chart of this embodiment. The wireless terminal stations A and C are terminals that want to perform MU-MIMO, and the wireless terminal station B is a conventional terminal. The radio base station has two antennas. FIG. 17 shows a case where the back-off values selected by the wireless terminal stations A, B, and CC for the first time are all combined. After the transmission of the previous frame is completed, after waiting for the DIFS time (blank time 400) in IEEE802.11, the countdown of the back-off value of each wireless terminal station is started. Here, the blank time 401 is a slot time in the IEEE802.11 standard. Since the wireless terminal stations A, B, and C all have a back-off value of 3, the transmission frames 402, 403, and 404 of the three terminals are transmitted simultaneously. Here, the transmission frame 402 is a transmission frame of the wireless terminal station A. The contents of the transmission frame 402 are a preamble signal to be transmitted using the specified resource and transmission data to be transmitted in the occupied band of the wireless terminal station A. Similarly, the transmission frame 403 is a transmission frame of the wireless terminal station B, and the transmission frame 404 is a transmission frame of the wireless terminal station C.

  Since the radio base station received transmission frames from three terminals simultaneously, MIMO cannot be separated and an error occurs. Therefore, a new random back-off value candidate set 405 is transmitted to the accommodating wireless terminal station. The blank time 410 here corresponds to the SIFS time in the IEEE802.11 standard.

  From the set of new random back-off value candidates, the wireless terminal stations A and C set back-off values again. A wireless terminal station, which is a conventional terminal, widens the CW size and sets the backoff value again. After waiting for DIFS time, each terminal starts counting down the backoff value. Here, since the wireless terminal stations A and C have selected 2 for the backoff value set again and the wireless terminal station B has selected 4 for the backoff value set again, the transmission frames of the wireless terminal stations A and C are transmitted first. Is done. Therefore, the wireless terminal station B uses the 2-count slot time 421 held by the wireless terminal station B in the next transmission.

  When the backoff value becomes 0, the wireless terminal stations A and C transmit the transmission frames 406 and 407, respectively. The transmission frames 406 and 407 are frames having the same contents as the transmission frames 402 and 404 generated to be transmitted last time. This is because the wireless terminal stations A and C were retransmitted because they could not receive the ACK directed to themselves last time.

Since the radio base station has received from two terminals, it transmits ACK (A) 408 and ACK (B) 409 to each terminal. When wireless terminal stations A and B each receive an ACK for itself, transmission is terminated.

In this embodiment, a method for selecting a terminal that is desired to be MU-MIMO is not specified, but a method for selecting a terminal according to the size of a transmission frame is given as an example. When the selection threshold for this transmission frame is the dot11RTSThreshold of the IEEE802.11 standard, the wireless terminal station that does not perform RTS / CTS exchange performs MU-MIMO, and the terminal that performs RTS / CTS exchange is one terminal. Therefore, the probability that an RTS signal transmitted from a certain terminal and a data frame transmitted from a certain terminal collide with each other is reduced.

As described above, in this embodiment, by limiting the set of back-off value candidates of terminals that are desired to be MU-MIMO, both terminals that are desired to be MU-MIMO and conventional terminals can be simultaneously connected to the AP.

(Third embodiment)
In this embodiment, the accommodated wireless terminal stations are divided into two groups according to the size of the transmission frame, and the random back-off value candidates that can be taken by each group are distributed so as not to overlap, thereby transmitting between the groups. A case where data collision is avoided will be described. In this embodiment, the wireless base station 1 of FIG. 1 and wireless terminal stations 2 to 5 accommodated in the wireless base station 1 are used.
1 shows an embodiment of a system model composed of

  FIG. 19 is a functional block diagram illustrating a configuration example of the radio base station 1 according to the third embodiment. 19 eliminates the random backoff control variable determination unit 115 and the random backoff value candidate set generation unit 250 in FIG. 11, and replaces the random backoff value candidate distribution unit 501 with the control unit 111 and the frame generation unit 116. Inserted in between.

  FIG. 20 is a flowchart from when the radio base station 1 notifies a set of random backoff value candidates of each group until data is received from a certain radio terminal station. Note that the process from receiving a connection request from a wireless terminal station to establishing an association is the same as in the first embodiment, and has been described with reference to FIGS.

The random backoff value candidate distribution unit 501 in FIG. 19 periodically distributes a set of random backoff value candidates for each group from a set of [0, CW size] (step S2
00). An example of the distribution method at this time is shown below.

The expected value of the set of random value candidates in each group is set to CW size / 2, and the number of random backoff value candidates is set to floor ((CW size + 1) / 2). At this time, the random backoff value candidates of the two groups are not set to the same value. FIG. 18 is a diagram illustrating an example of random backoff value candidates when the CW size is 15. As illustrated in FIG. However, the time 500 in FIG. 18 corresponds to the slot time in the IEEE802.11 standard.

  When the random back-off value candidates are assigned to each group, a frame including the set of random back-off value candidates is generated by the frame generation unit 116, via the transmission unit 104, the switch 102, and the wireless communication unit 101. Then, it transmits from the antenna 100 to the accommodation terminal of the radio base station (step S18). When transmission to each terminal is completed, it waits for reception of a preamble (step S8). The steps from the preamble reception (step S8) to the demodulation process (step S12) are the same as those in the first embodiment and have been described with reference to FIG.

The demodulated signal is checked for errors by the error check unit 109 (step S1).
9). If there is no error, an ACK is returned to each terminal that sent the data. If an error has occurred in step S19, the CW size holding unit 117 widens the size of the CW to be held (step S202). The CW size to be widened is determined by (Equation 7), assuming that it is the same as the conventional IEEE802.11 standard. FIG. 21 is a functional block diagram showing a configuration example of the terminal station 2 for wireless communication in the present embodiment. FIG. 21 is a diagram in which the control unit 208 and the data holding unit 209 in FIG. 13 are connected bidirectionally. FIG. 22 is a flowchart showing a flow of processing relating to FIG.

  The wireless terminal station 2 receives a signal including a set of random back-off value candidates for each group from the wireless base station via the antenna 200 (step S150). The received signal is input to the error check unit 207 via the wireless communication unit 201, the switch 202, the reception unit 203, and the demodulation unit 205. The signal that has been confirmed by the error check unit 207 that there is no error starts processing by the control unit and is input to the random backoff value candidate set holding unit 300. The random back-off value candidate set holding unit 300 holds a set of back-off value candidates that each group can take. The random backoff value candidate set holding unit 300 is the same as that described in the second embodiment until the current backoff value candidate set is received from the radio base station 1 again until the random backoff value candidate set is notified. Keep holding.

Data in the data holding unit 209 is input to the frame generation unit 206, and a transmission frame is generated (step S105). Grouping is performed based on the generated frame (step S201). An example of grouping will be described below.

  In this embodiment, the length of the transmission frame length is used for grouping. By using a certain threshold for the frame length of transmission data, it is divided into two groups. In the present embodiment, this threshold value is referred to as a “grouping threshold value”. If “transmission frame length ≦ grouping threshold value”, group 1 is set, and if “transmission frame length> grouping threshold value”, group 2 is set.

As an example, when this grouping threshold is set to dot11RTSThreshold of the IEEE802.11 standard, the possibility that the transmission timing of the wireless terminal station that does not perform RTS / CTS exchange and the terminal that performs RTS / CTS exchange collides decreases. .

  After grouping by the above method, from the set of random backoff value candidates held in the random backoff value candidate set holding unit 300, random backoff of the group to which the wireless terminal station 2 is assigned Using the set of value candidates, the random backoff setting unit 211 sets a backoff value (step S106).

When the setting of the back-off value is completed, carrier sense is performed to check whether the channel is not busy (step S104). If the channel is busy, backoff value correction is performed (step S152). In the backoff value correction, the current backoff value is corrected to a value included in a set of random backoff value candidates to which one's group is assigned. Therefore, there is no need for correction immediately after the back-off setting (step S106). Step S152 will be described after the back-off value is reduced (step S112). If the channel is not busy in step S104, it is confirmed whether the back-off value is 0 (step S107). If the back-off counter is not 0, carrier sense is performed again to check whether the channel is busy. If the channel is busy, it is determined that another terminal has already started transmission. In the first and second embodiments, when another wireless terminal station starts transmission during the count-down of the back-off value, the current back-off value after the count-down is held and transmission is attempted again. Is used as the current back-off value, but in this embodiment, the back-off value that can be taken for each group is divided, so that the remaining count is distributed to the own group. It may not be the backoff value.

  Therefore, before returning to the step immediately after the random back-off setting (step S106), the back-off value is corrected to a value included in the set of random back-off value candidates to which the own group is assigned (step S152). Examples of this correction method include: “Adjust back to the value closest to the current count among the back-off values assigned to my group” or “Value lower than the remaining count in my group, Further, it is possible to use “correction to a value closest to the remaining count”, or “if within the same group, it is highly likely that the current back-off value stopped is equal and no correction is performed”.

  When the channel is in an idle state, after waiting for the DIFS time in IEEE802.11, the backoff value corrected in step S152 is used to start the countdown of the backoff value again. If the back-off value is 0 in step S110, the transmission data is regarded as transmission timing (step S108).

After data transmission (step S108), it waits for ACK to be received (step S113). If ACK is received, it is confirmed whether the ACK is for itself (step S109). If ACK is not received in step S113, it is confirmed whether or not a signal including a set of random backoff value candidates is received again (step S120). When the set of random back-off value candidates is received again, the back-off value is set again using the candidate values (step S10).
6). When the set of random backoff value candidates is not received in step S120, the set of random backoff value candidates and the group are not changed, and the backoff value is determined again (step S106).

If the ACK received in step S109 is directed to the user, the process ends. If the received ACK is not for you, wait for the ACK to be received again.

FIG. 23 is a timing chart of the present embodiment. In the example of FIG. 23, it is assumed that all transmission frame lengths are equal to or less than dot11RTSThreshold of the IEEE802.11 standard. Therefore, RTS / CTS exchange is not performed. In the example of FIG. 23, the grouping threshold is a predetermined value smaller than dot11RTSThreshold of the IEEE802.11 standard.

  The example shown in FIG. 23 includes one wireless base station and wireless terminal stations A to C. In this embodiment, the groups are divided according to the frame length of the transmission data. However, in order to make the explanation easy to understand, FIG. 23 shows the group to which the terminal belongs after the transmission data is generated in advance.

After the transmission of the previous frame is completed, after waiting for the DIFS time (blank time 600) in the IEEE802.11 standard, each terminal starts counting down the back-off value. Here, all blank times 601 correspond to slot times in the IEEE 802.11 standard. Depending on the length of the transmission frame, the back-off value of wireless terminal stations A and C belonging to group 1 is selected as 3, and the back-off value of wireless terminal station B belonging to group 2 is selected as 4. And Therefore, the wireless terminal stations A and C simultaneously transmit the transmission frame 602 and the transmission frame 603 to the wireless base station, thereby realizing MU-MIMO communication. Here, the transmission frame 602 is a transmission frame of the wireless terminal station A, and is a preamble that is transmitted using the specified preamble resource and transmission data that is transmitted in the occupied band of the wireless terminal station A. Similarly, the transmission frame 603 is a transmission frame transmitted by the wireless terminal station C.

  The wireless base station that has received the transmission frames from the two terminals simultaneously waits for the time corresponding to the SIFS time in the IEEE802.11 standard (blank time 604) for each of the wireless terminal stations A and C, and then ACK (A) 605 and SIFS. After waiting for time, ACK (C) 606 is transmitted. ACK (A) 605 is an ACK for the wireless terminal station A, and similarly ACK (C) 606 is an ACK for the wireless terminal station C.

When the transmission of the ACK to the wireless terminal stations A and C is completed, the terminal having the transmission data starts to count down the backoff value using the reset backoff value.

The remaining back-off value of the wireless terminal station B in the middle of the count-down of the back-off value is 1. However, there is no 1 in the set of random backoff value candidates to which group 2 is assigned, and the backoff value of wireless terminal station B is smaller than 1 in the set of random backoff value candidates to which group 2 is assigned. , The value closest to 1 is corrected to 0. Therefore, the wireless terminal station B transmits the transmission frame 607 immediately after waiting for the DIFS time (blank time 600). A transmission frame 607 is a preamble transmitted by the wireless terminal station B using a preamble transmission resource designated as a wireless base station, and transmission data transmitted in the occupied band of the wireless terminal station B.

  The wireless base station that has received the transmission frame 607 from the wireless terminal station B transmits ACK (B) 610 to the wireless terminal station B. As in the second embodiment, this embodiment also describes the case where a blank time is inserted between ACKs when transmitting a plurality of ACKs from the radio base station. However, there is no blank time between ACKs. There is also a possibility.

As described above, also in this embodiment, MU-MIMO communication can be realized with almost no change to the conventional IEE802.11 standard scheme. Further, since the back-off values that can be taken are different for each group, it is possible to avoid a collision of transmission frames between groups.

  In the above-described embodiment, the configuration and the like illustrated in the accompanying drawings are not limited to these, and can be changed as appropriate within the scope of the effects of the present invention. In addition, various modifications can be made without departing from the scope of the object of the present invention.

  Each component of the present invention can be arbitrarily selected, and an invention having a selected configuration is also included in the present invention.

  In addition, a program for realizing the functions described in the present embodiment is recorded on a computer-readable recording medium, and the program recorded on the recording medium is read into a computer system and executed to execute processing of each unit. May be performed. The “computer system” here includes an OS and hardware such as peripheral devices.

  Further, the “computer system” includes a homepage providing environment (or display environment) if a WWW system is used.

  The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Furthermore, the “computer-readable recording medium” dynamically holds a program for a short time like a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line. In this case, a volatile memory in a computer system serving as a server or a client in that case, and a program that holds a program for a certain period of time are also included. The program may be a program for realizing a part of the above-described functions, or may be a program that can realize the above-described functions in combination with a program already recorded in a computer system. At least a part of the functions may be realized by hardware such as an integrated circuit (sometimes referred to as a processing device).

  The present invention is applicable to a communication device.

DESCRIPTION OF SYMBOLS A ... Wireless communication system, 1 ... Wireless base station, 2-5 ... Wireless terminal station, 100a * 100b ... Antenna, 101a ... 1st wireless communication part, 101b ... 2nd wireless communication station, 102 ... Switch (SW), 104 DESCRIPTION OF SYMBOLS Transmission part 116 ... Frame generation part 111 ... Control part 110 ... Preamble transmission resource allocation determination part 115 ... Random backoff control variable determination part 105 ... Preamble reception part 106 ... Channel estimation part 107 ... MIMO demodulation , 108 ... demodulator, 109 ... error checker, 200 ... antenna, 201 ... wireless communication unit, 202 ... switch, 203 ... receiver, 204 ... transmitter, 205 ... demodulator, 206 ... frame generator, 207 ... Error checking unit, 208 ... control unit, 209 ... data holding unit, 210 ... CW size changing unit, 211 ... random backoff Tough.

Claims (4)

A wireless terminal station device included in a plurality of wireless terminal station devices that communicate with a wireless base station device,
The communication method with the radio base station apparatus includes single user transmission in which only the own apparatus communicates with the radio base station apparatus, and the radio base station apparatus simultaneously with at least one of the plurality of radio terminal station apparatuses. Including multi-user transmission to communicate,
A control unit that performs back-off control in which a random back-off value candidate used when performing the single-user transmission and a random back-off value candidate used when performing the multi-user transmission; and
A receiving unit that acquires information indicating a value used for random backoff control used when the control unit performs the multiuser transmission; and
A radio terminal station apparatus that starts the multiuser transmission after setting by a control signal received from the radio base station apparatus.   The information indicating the value used for random backoff control received from the radio base station apparatus is periodically received, and the multiuser transmission is set based on the information indicating the value used for the random backoff control. The wireless terminal station device according to 1. A wireless communication method executed by a wireless terminal station device that communicates with a wireless base station device,
The communication method with the radio base station apparatus includes single user transmission in which only the own apparatus communicates with the radio base station apparatus, and the radio base station apparatus simultaneously with at least one of the plurality of radio terminal station apparatuses. Including multi-user transmission to communicate,
Random back-off value candidates used when performing the single user transmission and random back-off value candidates used when performing the multi-user transmission perform different random back-off control,
Obtaining information indicating a value used for the random back-off control used when performing the multi-user transmission from the base station apparatus,
A wireless communication method, wherein the multi-user transmission is started after setting by a control signal received from the wireless base station device . The information indicating the value used for random backoff control received from the radio base station apparatus is periodically received, and the multiuser transmission is set based on the information indicating the value used for the random backoff control. The wireless communication method described in 1.

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