KR20080083085A - Communication method in a wireless network, communication method of a station in a wireless network, and a station - Google Patents

Abstract

A communication method in a wireless network, a communication method of a station in the wireless network, and the station thereof are provided to use a block ACK policy to improve reliability of a multicast data frame. One station transmits an MRTS(Multicast Request to Send) message including a throughput of a multicast traffic to another station belonging to a multicast group. Another station receives the MRTS message, and transmits an MCTS(Multicast Clear to Send) message including a throughput of desired multicast traffic, or does not transmit the MCTS message. A predetermined station of another station belonging to the multicast group transmits the MCTS message to the station.

Description

COMMUNICATION METHOD IN A WIRELESS NETWORK, COMMUNICATION METHOD OF A STATION IN A WIRELESS NETWORK, AND A STATION}

1A and 1B are conceptual diagrams of wireless network systems according to embodiments of the present invention;

2 illustrates a format of a multicast RTS frame according to an embodiment of the present invention;

3 illustrates a format of a multicast CTS frame according to an embodiment of the present invention;

4 is a diagram illustrating a format of a block ACK request frame according to an embodiment of the present invention;

5 is a diagram illustrating a format of a block ACK frame according to an embodiment of the present invention.

The present invention relates to a communication method in a wireless network, a communication method of a station in a wireless network, and a station.

In the case of unicast frame, the transmission can be guaranteed by receiving the ACK frame after receiving the unicast frame.If the ACK frame is not received, the unicast frame can be retransmitted through the binary exponential backoff technique to ensure fairness. fairness). In addition, according to whether the data transmission is successful, it is possible to raise or lower the data transmission rate, thereby providing a rate adaptation function adaptively.

However, for broadcast / multicast no consideration was given if the transmission failed.

Accordingly, an aspect of the present invention is to provide a communication method in a wireless network, a communication method of a station in a wireless network, and a station capable of improving the performance of broadcast or multicast traffic in a wireless network.

Hereinafter, with reference to the accompanying drawings illustrating an embodiment of the present invention.

In a wireless network according to an embodiment of the present invention, a communication method includes transmitting, by one station, a multicast request to send (MRTS) including a transmission rate of multicast traffic to another station belonging to a multicast group. The other station receives the MRTS, and transmits or does not transmit a multicast clear to send (MCTS) including a transmission rate of multicast traffic desired by the other station to the one station.

In a wireless network according to another embodiment of the present invention, a communication method includes transmitting, by one station, a block ACK request to another station belonging to a multicast group. And after the other station receives the block ACK request, transmitting or not transmitting a block ACK including information on its channel state to the one station.

Hereinafter, with reference to the drawings will be described embodiments of the present invention; Hereinafter, embodiments of the present invention will be described using a wireless LAN system as an example of a wireless network system. However, embodiments of the present invention will be substantially the same in the same or allowable range as the WLAN system in the range allowed or supported in various wireless network systems other than the WLAN system. In addition, the terms or words used in the embodiments of the present invention may be used as other terms or words in various wireless network systems, but the present invention may be used when the actual meaning is the same or similar despite the differences between the terms or words. It is included in the scope of the invention.

1A and 1B are conceptual diagrams of wireless network systems according to embodiments of the present invention. Identical components in FIGS. 1A and 1B use the same reference numerals.

Referring to FIG. 1A, a wireless network system, for example, a wireless LAN system 10 may include a plurality of stations or terminals 12, an access point or a wireless base station 14, a backbone network or a distribution system ( 16).

The plurality of stations 14 may be equipped with a network interface card for a wireless LAN to perform operations of a physical layer and a MAC layer based on the IEEE 802.11 standard. In the WLAN system 10 shown in FIG. 1A, a plurality of stations 12 are coupled to an access point 14 to transmit data frames.

The access point 14 performs a wired / wireless interworking bridge function of relaying a frame transmitted from one station to another station. This access point 14 performs the same function as the bridge or switch of Ethernet.

In addition, since the access point includes basically the same physical layer and MAC layer as the station 12 described above, the access point 14 may basically perform the same operation as the station 12. Thus, the access point 14 may be considered the same as the station 12 as needed.

The distribution system 16 is a backbone network connecting several access points 14. The distribution system 16 generally uses Ethernet, but can also wirelessly connect multiple access points. Broadly speaking, the distribution system 16 may include routers or switches connected to Ethernet and servers connected to wired and wireless Internet networks.

Referring to FIG. 1B, a wireless network system, for example, a wireless LAN system 10 includes a plurality of stations or stations 12. The WLAN system 10 is directly connected point-to-point between a plurality of stations 12. Thus, unlike FIG. 1A, in the WLAN system 10 illustrated in FIG. 1B, a separate access point 14 or a distribution system 16 does not exist, and a plurality of stations 12 may replace their roles, Some roles or functions may be omitted.

Although the WLAN system 10 has been described with reference to FIGS. 1A and 1B, a wireless network system including a WLAN system 10 according to an exemplary embodiment of the present invention is not limited thereto, and a combination or a completely different one thereof. It can be implemented as a system. In addition, the wireless network system according to an embodiment of the present invention may exist alone, but may interwork with another wireless network system, a mobile communication network, or a wired / wireless internet network.

For example, the WLAN system may provide roaming service by interworking with a mobile communication network. Specifically, when the WLAN system provides a voice service, a dual band dual mode (DBDM) terminal supporting both WLAN and WCDMA performs a voice call using a mobile communication network, and then supports the WLAN system. In the wireless LAN system can be automatically roaming seamlessly.

Whether the wireless LAN system 10 shown in FIG. 1A or the wireless LAN system 10 shown in FIG. 1B is required to pass data between stations 12 or through a coupling process between the station 12 and the access point 14 Can transmit

In FIG. 1A, the access point 14 may know the stations 12 belonging to the multicast group. In order to join a multicast group, stations 12 send an Internet Group Management Protocol (IGMP) join packet to a router (not shown), where access point 14 is a Generic Attribute Registration Protocol (GARP) or GARP Multicast (GMRP). Registration protocol) is used to overhear an IGMP join packet. The IGMP join packet includes the address of each station belonging to the multicast group and the address of the multicast group so that the access point 14 can know the stations belonging to the multicast group.

In addition, the access point 14 can know the channel status of the stations belonging to the multicast group by the multicast diagnostic function defined in IEEE 802.11v.

In the multicast diagnostic function, if the stations belonging to a multicast group have not received a multicast frame for a period of time, the highest multi that they can currently support by sending a multicast diagnostic report The access point may be informed of the multicast PHY rate.

When the access point 14 receives the multicast dynamic report from stations belonging to the multicast group, the access point 14 selects the station having the worst channel condition as the leader. However, the criteria by which an access point selects a leader is outside the scope of the present invention.

Multimedia multicasting

Multimedia multicasting uses a relatively high amount of bandwidth and requires a certain level of quality of service (QoS). The Enhanced Distribution Channel Access (EDCA) scheme of IEEE 802.11e may provide priority QoS (QoS) for voice, video, and best-effort traffic. However, multicast does not effectively use the preferential QoS provided by EDCA.

Assume that a broadcast frame or a multicast frame collides with a unicast frame. In this case, if the priority of multicast traffic is increased, it is necessary to use a voice or video access category. In this case, the collision probability is further increased.

When a collision occurs, the QoS of multimedia traffic is rather degraded because broadcast or multicast frames do not attempt to retransmit.

Multimedia traffic uses relatively high bandwidth. Therefore, there is a need to efficiently use the bandwidth provided by the physical layer. IEEE 802.11a / b will provide up to 54Mbps and 11Mbps, and IEEE 802.11n will support data rates above 100Mbps.

In order to efficiently use the bandwidth provided by the physical layer, it is important to select an appropriate modulation code for the channel state in the MAC layer. However, in the case of broadcast / multicast frames, only fixed modulation code is used in the basic rate set, and multicast receivers also do not give feedback on channel status. Accordingly, PHY rate adaptation in the physical layer for broadcast / multicast frames is not provided, and the high bandwidth provided by the physical layer cannot be effectively used.

The IEEE 802.11 WLAN system introduces a Request To Send (RTS) / Clear To Send (CTS) exchange scheme to prevent collisions between unicast frames caused by the presence of hidden stations before transmitting unicast frames. Since the RTS / CTS exchange scheme is not applied to broadcast / multicast frames, there is no way to prevent collision.

In an embodiment of the present invention, a multicast RTS / CTS exchange prevents collision between multicast frames caused by the presence of a hidden station and adaptively adjusts the transmission rate of multicast traffic according to the channel state of the multicast receivers. Suggest a method.

2 illustrates a format of a multicast RTS frame according to an embodiment of the present invention.

Referring to FIG. 2, the multicast RTS frame includes frame control, duration, receiver address (RA), transmitter address (TA), group address (GA), Multicast PHY rate, and FCS.

The type of frame control is set to '01' indicating a control frame, and the subtype uses reserved bits to indicate a multicast RTS frame.

The duration sets the time required for a station transmitting a multicast RTS frame for the entire frame exchange sequence that occurs after the transmission of the multicast RTS frame.

The receiver address includes the MAC address of the leader of the multicast group. In general, the leader of a multicast group is selected as the station with the worst channel condition.

The transmitter address includes the address of the station transmitting the multicast RTS frame. The group address includes the address of the multicast group.

The multicast PHY rate includes the transmission rate of multicast traffic for transmission of multicast traffic.

3 illustrates a format of a multicast CTS frame according to an embodiment of the present invention.

Referring to FIG. 3, the multicast CTS frame includes frame control, duration, receiver address (RA), transmitter address (TA), and multicast PHY rate. , And FCS.

The type of frame control is set to '01' indicating a control frame, and the subtype uses one bit of reserved bits to indicate a multicast CTS frame.

The duration includes the time required for transmitting the multicast CTS frame from the duration value set in the multicast RTS frame and a value obtained by subtracting the short interframe space (SIFS) before transmitting the multicast CTS.

The receiver address includes the address of the station that transmitted the multicast RTS frame. That is, the MAC layer copies the transmitter address of the multicast RTS frame to the receiver address of the multicast CTS frame.

The transmitter address includes the address of the station sending the multicast CTS frame. The new transmitter address is added to allow more than one station to send a multicast CTS, so that it can determine which station sent the multicast CTS.

The transmission rate of multicast traffic includes the transmission rate of multicast traffic desired by the station transmitting the multicast CTS frame.

Hereinafter, a method for exchanging a multicast RTS frame and a multicast CTS frame newly proposed by the present invention will be described.

Multicast RTS Of CTS  exchange

In this embodiment, the station transmitting the multicast RTS frame and receiving the multicast CTS frame is described as being an access point 14. In addition, as described above, the access point 14 may know the stations belonging to the multicast group and the channel state of each station, and select the station having the worst channel state as a leader of the multicast group. Assume that

First, the access point 14 sets the receiver address (RA) of the multicast RTS frame as the MAC address of the reader, and sets the reader in the Multicast PHY rate field of the multicast RTS frame. After setting the transmission rate of the multicast traffic suitable for the (leader), the multicast RTS frame is transmitted to the stations belonging to the multicast group in a multicast manner.

A leader receiving a multicast RTS frame from the access point 14 always responds with a multicast CTS frame. At this time, the leader transmits the transmission rate of its desired multicast traffic in the multicast PHY rate of the multicast CTS frame.

When the access point 14 receives the multicast CTS response frame from the leader, it transmits the multicast data to stations belonging to the multicast group according to the transmission rate of the multicast traffic included in the multicast CTS frame.

If a station other than the reader cannot support the transmission rate of the multicast traffic included in the multicast RTS frame, the station includes the desired transmission rate of the multicast traffic in the multicast PHY rate of the multicast CTS frame. send. In this case, collision with the multicast CTS frame transmitted by the leader will occur.

Accordingly, if the access point 14 does not receive the multicast CTS, the access point 14 determines that there is a collision of the multicast CTS frame, and retransmits the multicast RTS frame. The access point 14 multicasts the multicast RTS frame upon retransmission. The transmission rate of traffic can be reduced.

If the access point 14 does not receive the multicast CTS frame twice in a row, the access point 14 again reduces the transmission rate of the multicast traffic and newly elects a leader.

To newly elect a leader, the access point 14 repeatedly transmits a multicast RTS frame while sequentially changing the receiver address of the multicast RTS frame. At this time, the station that wants the lowest multicast traffic rate is elected as the leader.

In another embodiment of the present invention, a block ACK policy is used to improve the reliability of the multicast data frame.

4 illustrates a format of a Block Ack Request frame according to an embodiment of the present invention.

Referring to FIG. 4, the block ACK request frame includes frame control, duration, receiver address, transmitter address, BAR control, block ACK starting sequence control, and FCS.

In the block ACK request frame proposed by the present invention, the BAR control includes a 4-bit reserve bit, a 4-bit target PER (Target Packet Error Rate), and a 4-bit TID (Traffic Identifier). The target PER is a threshold set by the station sending the block ACK request.

5 illustrates a format of a block ACK frame according to an embodiment of the present invention.

Referring to FIG. 5, a block ACK frame includes a frame control, a duration, a receiver address, a transmitter address, a BA control, a block ACK starting sequence control, a block ACK bitmap, and an FCS.

In the block ACK frame proposed by the present invention, the BA control includes 8 bits of SINR and 4 bits of TID (Traffic Identifier).

Hereinafter, a block ACK exchange will be described using a block ACK request frame and a block ACK frame newly proposed by the present invention.

block ACK

The Block Ack mechanism improves channel effiency by aggregating several acknowledgments into one frame. There are two types of block ACK mechanisms: immediate block ACK and delayed block ACK. There are two types of Block Ack mechanism: immediate and delayed.

Immediate Block ACK is suitable for traffic with high bandwidth and low response rate, and Delayed Block ACK is suitable for applications that allow moderate response speed (Immediate Block Ack is suitable). for high-bandwidth, low-latency traffic while the delayed Block Ack is suitabl for applications that tolerate moderate latency).

The Block Ack mechanism is initialized by an exhange of ADDBA Request / Response frames. After initialization, blocks of QoS data frames can be transmitted from the originator to recipient.

A block may be started within a transmission opportunity (TXOP) or by winning an Enhanced Distributed Channel Access (EDCA) competition (A block may be started within a polled TXOP or by winning EDCA contention). The number of frames in the block is limited, and the amount of state that is to be kept by the recipient is bounded. The MPDUs within the block of frames are acknowledged by a BlockAck control frame, which is requested by a BlockAckReq control frame (BRU).

A QSTA attempting to use the block ACK mechanism to send QoS data frames to another QSTA checks for the Delayed Block Ack and Immediate Block Ack capability bits, so that the other QSTA blocks ACK. A QSTA that intends to use the Block Ack mechanism for the transmission of QoS data frames to a peer should first check whether the intended peer QSTA is capable of participating in Block Ack mechanism by discovering and examining is Delayed Block Ack and Immediate Block Ack capability bits).

If the intended peer QSTA is capable of participating, the originator sends an ADDBA request frame indicating the TID for the sender sends a ADDBA request frame indicating the TID for establishing a block ACK. which the Block Ack is being set up). The Block Ack Policy and Buffer Size fields in the ADDBA Request frame are advisory and may be changed by the recipient. The receiving QSTA shall respond by an ADDBA Response frame. The receiving QSTA, which is the intended peer, has the option of accepting or rejecting the request. When the QSTA accepts, then a Block Ack agreement exists between the originator and recipient. When the QSTA accepts, it indicates the type of Block Ack and number of buffers, the receiving QSTA indicates the type of block ACK and the number of buffers allocated to support this block. that it shall allocate for the support of this block). If the receiving QSTA rejects the requests, then the originator shall not use the Block Ack mechanism.

Once the Block Ack exchange has been set up, data and ACK frames are transffered. The originator may transmit a block of QoS data frames separated by a Short Interframe Space (SIFS) interval, so long as the total number of frames does not exceed the buffer size subfield value in the ADDBA request frame. data frmaes separated by SIFS period, with the total number of frames not exceeding the Buffer Size subfield value in the associated ADDBA Response frame). Each of the frames shall have an Ack Policy subfield in the QoS Control field for setting the Block ACK. (Each of the frames shall have the Ack Policy subfield value in the QoS Control field set to Block Ack). The RA field of the frames shall be the recipient's unicast address. The originator will request acknowledgment of QoS data frames by sending a BAR frame (the originator requests acknowledgement of outstanding QoS data frmaes by sending a BlockAckReq frame). The recipient shall maintain a Block Ack record for the block.

If the immediate Block Ack policy is used, the recipient shall respond to a BlockAckReq frmae with a BlockAck frame . If the recipient sends a block ACK frame, the sender updates its record, and attempts to retransmit the unacknowledged frame in the block ACK frame, either individually or individually (If the recipient sends the BlockAck frame, the originator updates its own) record and retries any frames that are not acknowledged in the BlockAck frame, either in another block or individually).

If the delayed Block Ack policy is used, the recipient shall respond to a BlockAckReq frame with an ACK frame. The recipient shall then send its Block Ack response in a subsequently obtained TXOP. Upon receipt of a block ACK frame, the originator shall respond with an ACK frame upon receipt of the BlockAck frame.

In the present embodiment, a station transmitting a multicast data frame and a block ACK request and receiving a block ACK is described as an access point 14.

First, the access point 14 transmits a block ACK request to stations belonging to the multicast group in a multicasting manner. At this time, as shown in Figure 4, the target PER is included in the BAR control field of the block ACK request is transmitted.

When using an immediate block acknowledgment policy, the leader immediately sends a block ACK. At this time, the reader includes its current Signal to Interference plus Noise Ratio (SINR) value in the BA control field of the block ACK and transmits it to the access point 14.

In the case of using a delayed block acknowledgment policy, a leader transmits an ACK after receiving a block ACK request from the access point 14, and sends a block ACK after a predetermined time after transmitting the ACK. do. Similarly, the BA control field of the block ACK includes the current SINR value of the reader and is transmitted.

Stations other than the leader may transmit a block ACK before the leader when their packet error rate (PER) is higher than the target PER. The higher the PER, the less backoff time.

When a block ACK is received from a station other than the leader, the access point 14 changes the leader to that station. In addition, when the access point 14 does not receive a block ACK, the access point 14 newly selects a leader.

In the above embodiments, reference has been made to IEEE 801.11 and IEEE 801.11e, but the present invention is not limited to these standards.

In the above embodiments, a station for performing operations of the physical layer and the MAC layer based on the IEEE 802.11 standard by mounting a network interface card for a wireless LAN, and relaying a frame transmitted from one station to another station Although the access point performing the wired / wireless interworking bridge function has been described as an example, the present invention is not limited thereto.

In addition, since the access point basically includes the same physical layer and MAC layer as the station described above, the access point can basically perform the same operation as the station. Thus, the access point may be considered to be the same as the station as needed.

In the above embodiments, the WLAN system has been described as an example, but the present invention includes a wireless network system including a WLAN system, and a combination thereof or a completely different system may be implemented. In addition, although the wireless network system may exist alone, the present invention may interwork with other wireless network systems, mobile communication networks, and wired and wireless Internet networks.

For example, the WLAN system may provide roaming service by interworking with a mobile communication network, for example, Wideband Code Division Multiple Access (WCDMA). Specifically, when the WLAN system provides a voice service, a dual band dual mode (DBDM) terminal supporting both WLAN and WCDMA performs a voice call using a mobile communication network, and then supports the WLAN system. In the wireless LAN system can be automatically roaming seamlessly.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above-described specific embodiment, and the present invention may be used in the art without departing from the gist of the present invention as claimed in the claims. Various modifications can be made by those skilled in the art, and such changes are within the scope of the claims.

As described above, according to an embodiment of the present invention, there is an effect that can improve the performance of multicast traffic transmission in a wireless network.

Claims (39)

One station transmitting a multicast request to send (MRTS) including a transmission rate of multicast traffic to another station belonging to the multicast group; And Receiving, by the other station, the MRTS, and transmitting or not transmitting a multicast clear to send (MCTS) including a transmission rate of the multicast traffic desired by the other station to the one station; . The method of claim 1, A predetermined station among other stations belonging to the multicast group transmits the MCTS to the one station. The method of claim 2, Stations other than a predetermined station among other stations belonging to the multicast group transmit the MCTS to the one station only when the transmission rate of the multicast traffic included in the MRTS cannot be supported. Way. The method of claim 1, When the one station receives the MCTS from the other station, transmitting the multicast data to the other station according to a transmission rate of the multicast data included in the MCTS. Communication method The method of claim 1, The transmission rate of the multicast traffic is included in the multicast PHY rate field of the MRTS or MCTS. One station transmitting a multicast request to send (MRTS) including a transmission rate of multicast traffic to another station belonging to the multicast group; And Receiving or not receiving a multicast clear to send (MCTS) including a transmission rate of multicast traffic desired by the other station from the other station. The method of claim 6, And the one station receives the MCTS from a predetermined station among other stations belonging to the multicast group. The method of claim 6, And if the MCTS fails to receive the MCTS from the other station, the one station retransmitting an MRTS. The method of claim 6, When the one station receives the MCTS from the other station, transmitting the multicast data to the other station according to the multicast data transmission rate included in the MCTS. Station communication method. The method of claim 6 The transmission rate of the multicast traffic is included in the multicast PHY rate field of the MRTS or MCTS. Receiving a multicast request to send (MRTS) including a transmission rate of multicast traffic from another station; And And transmitting a multicast clear to send (MCTS) including a transmission rate of multicast traffic desired by the user to the other station. The method of claim 11, And said station transmits said MCTS to said other station only if it cannot support the transmission rate of multicast traffic included in said MRTS. The method of claim 11, And receiving, by the station, the multicast data from the other station according to a transmission rate of the multicast data included in the MCTS. The method of claim 11, The transmission rate of the multicast traffic is included in the multicast PHY rate field of the MRTS or MCTS. Multicast Request To Send (MRTS) including transmission rate of multicast traffic to other stations belonging to the multicast group, and Multicast Clear To Send (MCTS) including transmission rate of multicast traffic desired by the other station from the other station Stations that do or do not receive). The method of claim 15, And receive the MCTS from a predetermined station among other stations belonging to the multicast group. The method of claim 15, If the MCTS does not receive the MCTS from the other station, the station retransmits an MRTS. The method of claim 15, And transmit the multicast frame to the other station according to the transmission rate of the multicast traffic included in the MCTS received from the other station. The method of claim 15, The transmission rate of the multicast traffic, characterized in that included in the multicast PHY rate field of the MRTS or MCTS. One station sending a block ACK request to another station belonging to the multicast group; And And after the other station receives the block ACK request, transmitting or not transmitting a block ACK to the one station that includes information on a channel state of the other station. The method of claim 20, A predetermined station among other stations belonging to the multicast group, after receiving the block ACK request, transmits the block ACK to the one station. The method of claim 21, The block ACK request includes a target PER (Target Packet Error Rate), Stations other than a predetermined station among other stations belonging to the multicast group, after receiving the block ACK request, transmit the block ACK to the one station only when their PER is higher than the target PER. A communication method in a wireless network. The method of claim 22, wherein the information about the channel state, SINR (Signal to Interference plus Noise Ratio). One station sending a block ACK request to another station belonging to the multicast group; And Receiving a block ACK from the other station, the block ACK including information about a channel state of the other station. The method of claim 24, And the one station receives the block ACK from a predetermined station among other stations belonging to the multicast group. The method of claim 25, The block ACK request includes a target PER (Target Packet Error Rate), And the one station receives the block ACK from a station having a PER higher than a target PER among stations except for a predetermined station among other stations belonging to the multicast group. The method of claim 24, wherein the information about the channel state, A communication method of a station in a wireless network, characterized in that it is Signal to Interference plus Noise Ratio (SINR). Receiving a block ACK request from another station; And Transmitting or not transmitting a block ACK including information on a channel state of the other station to the other station. The method of claim 28, And when the station corresponds to a predetermined station among stations belonging to the multicast group, the predetermined station transmits a block ACK to the other station. The method of claim 29, The block ACK request includes a target packet error rate (PER), If the station corresponds to a station except a predetermined station among the stations belonging to the multicast group, and has a PER higher than the target PER, And the station transmits a block ACK to the other station before the predetermined station. The method of claim 28, wherein the information about the channel state, A communication method of a station in a wireless network, characterized in that it is Signal to Interference plus Noise Ratio (SINR). A station for transmitting a block ACK request to another station belonging to a multicast group, and receiving a block ACK from the other station, the block ACK including information about the channel state of the other station. 33. The method of claim 32, And receive the block ACK from a predetermined station among other stations belonging to the multicast group. The method of claim 33, wherein The block ACK request includes a target PER (Target Packet Error Rate), And the one station receives the block ACK from another station having a PER higher than the target PER among stations except for a predetermined station among other stations belonging to the multicast group. The method of claim 32, wherein the information about the channel state, Station characterized in that the signal to interference plus noise ratio (SINR). A station that receives a block ACK request from another station and transmits or does not transmit a block ACK to the other station including information about its channel state. The method of claim 36, And when the station corresponds to a predetermined station among stations belonging to the multicast group, the predetermined station transmits a block ACK to the other station. The method of claim 37, The block ACK request includes a target packet error rate (PER), If the station corresponds to a station except a predetermined station among the stations belonging to the multicast group, and has a PER higher than the target PER, Wherein the station transmits a block ACK to the other station before the predetermined station. The method of claim 36, wherein the information about the channel state, Station characterized in that the signal to interference plus noise ratio (SINR).

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