WO2015034304A1 - Communication method using interference alignment in wireless lan - Google Patents

Abstract

A communication method using interference alignment in a wireless LAN is disclosed. An access point according to one embodiment of the present invention receives first channel information between the access point and a station associated with the access point and second channel information between the station associated with the access point and a neighboring access point performing the interference alignment in cooperation with the access point, from the station associated with the access point, and performs the interference alignment on the basis of the first channel information and the second channel information.

Description

Communication method using interference alignment in WLAN

Embodiments relate to a communication method using interference alignment in a WLAN.

Due to the spread of smart phones, the use of wireless LAN is exploding. As a result, an overlapped basic service set (OBSS) environment may be generated.

1 illustrates an interference situation occurring in an overlapped basic service set (OBSS) environment. WLAN communication due to interference in the OBSS environment due to the characteristics of the WLAN technology that the frequency band used for the WLAN is saturated and there is no centralized coordination between access points (APs). Performance degradation can be serious.

Embodiments provide a technique for removing interference between APs in an OBSS environment of a WLAN.

According to an aspect, an operating method of an access point may include determining at least one neighboring access point to perform interference alignment in cooperation with the access point; First channel information between the at least one station and the access point and second channel information between the at least one station and the at least one neighboring access point, from at least one station associated with the access point Receiving; Acquiring information for interference alignment based on the first channel information and the second channel information; And transmitting data based on the information for the interference alignment.

The determining may include transmitting an IA-RTS frame including a candidate AP list to the at least one neighboring access point; Transmitting a CTS-Poll frame to a first neighboring access point included in the candidate AP list; And if an IA-CTS frame is received from the first neighboring access point, determining the first neighboring access point as an interference alignment participating node.

The receiving may include transmitting an IA NDP Announcement frame including an AP list and a STA Info list to the at least one neighboring access point and the at least one station; Transmitting a null data packet (NDP) to the at least one station; And transmitting a AP-Poll frame of a predetermined type to a neighboring access point corresponding to the next order of the AP list.

The neighboring access point corresponding to the address of the RA field included in the AP-Poll frame of the predetermined type resets the NAV, transmits the IA NDP Announcement frame to its associated stations, and transmits the NDP to the stations. Can be.

The receiving may include transmitting an IA BF Report Poll frame to the at least one station; Receiving a BF Report frame including the first channel information and the second channel information from the at least one station; And transmitting a predetermined type of AP-Poll frame to a neighboring access point corresponding to the next order of the AP list.

The BF Report Poll frame may include a Segment Retransmission Bitmap field for the access point and at least one Segment Retransmission Bitmap field for the at least one neighboring access point.

The neighboring access point corresponding to the address of the RA field included in the AP-Poll frame of the predetermined type resets the NAV, transmits the IA BF Report Poll frame to its associated stations, and sends a BF Report from the stations. A frame can be received.

The receiving may include determining a neighbor access point requiring further reception of a BF Report frame; And transmitting the predetermined type of AP-Poll frame to the determined neighboring access point.

The acquiring may include generating interference alignment calculation information for the access point based on the first channel information and the second channel information; Transmitting interference alignment calculation information for the access point to the at least one neighboring access point; And receiving interference alignment calculation information for the at least one neighboring access point from the at least one neighboring access point.

When the interference alignment calculation information for the at least one neighboring access point is received by wire, an expected data transmission period of the at least one neighboring access point may be further received.

The transmitting may include transmitting a multicast RTS frame to the at least one neighboring access point; And receiving a multicast CTS frame from the at least one neighboring access point.

The transmitting may include transmitting an IA Synch frame to the at least one neighboring access point; And transmitting downlink data simultaneously with the at least one neighboring access point during the transmission period included in the IA Synch frame.

The neighboring access point corresponding to the address of the AP BSSID field included in the IA Synch frame may reset the NAV and transmit downlink data by using interference alignment after SIFS.

The transmitting may include transmitting a BAR frame to the at least one station; Receiving a BA frame from the at least one station; And transmitting the AP-Poll frame of a predetermined type to the neighboring access point corresponding to the next order based on the order information of the access points included in the IA Synch frame.

The neighboring access point corresponding to the address of the RA field included in the predetermined type of AP-Poll frame resets the NAV, transmits the BAR frame to stations associated with it, and receives a BA frame from the stations. Can be.

The transmitting may include receiving an AP-Poll frame of a predetermined type from the at least one neighboring access point; Determining neighboring access points requiring further transmission of data based on more data bits included in the predetermined type of AP-Poll frame; And transmitting an IA Synch frame to the determined neighboring access points.

The first channel information is channel information estimated from an NDP received from the access point to which the at least one station is directly associated, and the second channel information belongs to the same IA transmission group although the at least one station is not associated. It may be channel information estimated from the NDP received from the at least one neighboring access point.

1 is a diagram illustrating an interference situation occurring in OBSS.

2 illustrates a concept of interference alignment in accordance with an embodiment.

3 illustrates an interference alignment processing procedure according to an embodiment.

4A-4F illustrate an interference alignment protocol procedure according to one embodiment.

5A illustrates an IA-RTS frame, according to an embodiment.

5B illustrates an IA-RTS Info field, according to one embodiment.

FIG. 6A illustrates an IA-CTS frame according to an embodiment. FIG.

6B illustrates an IA-CTS Info field, according to one embodiment.

6C illustrates the STA Info field, according to an embodiment.

7 illustrates a CTS-Poll frame according to an embodiment.

8A illustrates an IA-NDP Announcement frame according to an embodiment.

8B illustrates a Group Member Indication Bitmap field, according to one embodiment.

8C illustrates a STA Info field according to an embodiment.

8D illustrates a Sounding Dialog Token field, according to an embodiment.

9 illustrates an AP-Poll frame according to an embodiment.

FIG. 10 illustrates an IA Beamforming Report Poll frame according to an embodiment. FIG.

11 illustrates a VHT Compressed Beamforming frame according to an embodiment.

12A illustrates an mRTS frame, according to an embodiment.

12B illustrates an mRTS Info field, according to one embodiment.

13A illustrates an mCTS frame, according to one embodiment.

FIG. 13B illustrates an mCTS Info field, according to an embodiment. FIG.

14 illustrates an IA Synch frame according to an embodiment.

Hereinafter, exemplary embodiments will be described in detail with reference to the accompanying drawings.

2 is a diagram illustrating a concept of interference alignment according to an embodiment. Interference Alignment (IA) is a technique for solving a problem in which transmission performance is degraded due to interference between APs in a wireless channel environment where access points (APs) using the same frequency are overlapped. For example, this technology improves transmission efficiency by controlling interference between APs during wireless transmission.

In order to perform interference alignment in a WLAN, AP group selection, sounding / channel state feedback, basic service set (BSS) exchange of channel information, and transmission obtained by other APs are performed. There is a need for an interference alignment MAC protocol for sharing opportunity (Transmit Opportunity, TXOP), channel protection between different APs, and synchronization for simultaneous transmission of different APs on the same channel.

Embodiments may provide MAC protocol technology for interference alignment in a WLAN. The WLAN interference alignment method according to the embodiments can greatly improve the transmission efficiency in the OBSS by controlling the interference between the APs through cooperation between the APs.

Method of cooperation between APs according to embodiments, for example, selecting an AP group to cooperate, information exchange between BSS, sharing transmission opportunities acquired by other APs, channel protection between different APs, simultaneous transmission between different APs on the same channel The synchronization method for the above may be applied to cooperative communication based on coordination between multiple APs as well as interference alignment. The cooperative method between APs according to embodiments may be variously applied to improve transmission efficiency in an overlapped basic service set (OBSS) environment.

3 is a diagram illustrating an interference alignment processing procedure according to an embodiment, and more specifically, FIG. 3 illustrates a simplified processing procedure of an interference alignment protocol according to embodiments.

Referring to FIG. 3, in step 310, an AP that attempts to perform IA transmission by first accessing a channel may operate as a master AP. The master AP may control the entire protocol sequence.

In step 320, the master AP performs a frame exchange to protect the channel or protocol sequence. The master AP performs interference alignment to determine whether to participate in interference alignment with candidate APs that want to simultaneously transmit data, and then selects an AP to participate in interference alignment. Hereinafter, the candidate AP may refer to at least one AP selected by the master AP among neighboring APs of the master AP.

After determining the APs (hereinafter referred to as participating APs) to participate in the transmission using the interference alignment in step 330, each participating AP performs sounding in each BSS and receives feedback of channel information. At this time, STAs belonging to each AP feed back channel state information of not only the AP of the BSS to which they belong, but also other APs participating in interference alignment together with the AP of the BSS to which they belong.

In step 340, the APs perform an interference alignment algorithm, and the APs exchange interference alignment information with each other.

In step 350, the master AP transmits a sync frame to allow each AP to transmit data at the same time, and the participating APs receiving the sync frame align the interference based on the exchanged interference alignment information to simultaneously transmit data. Send it. Each AP may simultaneously transmit data to a plurality of STAs associated with each AP using a multi-user multiple-input-multiple-output (MU-MIMO), and a single-user multiple (SU-MIMO). You can also send data using -Input-Multiple-Output.

In step 360, each AP is associated with itself and performs a block Ack response process with STAs that transmit data.

If there is additional data to send, the interference alignment participating APs transmit information indicating that there is additional data to be sent to the master AP. The master AP sends sync frames only to APs with more data to send, and performs data transmission and block access. In this case, the process of selecting a participating AP may be omitted. In addition, when there are APs that are removed from the interference alignment group but there are no newly added APs, and the time for channel sounding / feedback has not elapsed much, interference alignment algorithm calculation and interference alignment information exchange may be omitted. In addition, only the sync frame transmission, data transmission, and block charge response processes may be performed.

At this time, if the transmission opportunity (Transmit Opportunity, TXOP) is terminated or insufficient in the previous transmission, the master AP can obtain a TXOP by a new channel access. In this case, the channel must be protected through RTS / CTS (Request to Send / Clear to Send) exchange before sync frame transmission and data transmission.

If there is no new AP added to the interference alignment group, even if the interference-aligned data transmission (hereinafter, IA data transmission) is continued, the channel state changes after a certain coherence time. The interference alignment participating APs may perform channel sounding and feedback, calculation of interference alignment algorithm, and exchange of interference alignment information between APs.

If the interference alignment group is changed, such as a new AP is added, the process may be restarted from the interference alignment participation AP selection process.

4A through 4F are diagrams illustrating an interference alignment protocol procedure according to an embodiment. The detailed procedure of FIGS. 4A-4F can be modified in various forms.

The interference alignment is required when the transmission areas overlap with each other because the distance between APs is close to each other. In this case, the AP participating in the interference alignment may hear the beacons and transmission frames of the other AP. However, some of the STAs in the BSS generated by each AP may be hidden to other APs participating in interference alignment. The interference alignment protocol procedure according to an embodiment is a protocol procedure designed to be robust even when some of the STAs in the BSS generated by each AP are hidden to other APs participating in the interference alignment. It is not algorithm dependent.

Hereinafter, for convenience of description, for example, each AP transmits to STAs in MU-MIMO. For example, SU-MIMO transmission may be performed using the same protocol. For example, in the case of SU-MIMO, only one STA to be transmitted of each AP is different, and the entire protocol procedure may be the same as in the case of MU-MIMO.

Hereinafter, an overall flow of a protocol procedure according to an embodiment will be described with reference to FIGS. 4A to 4F. An example of a detailed protocol procedure will be described later in a frame format description.

[1] Interference Alignment (IA) Participating Node Determination Step 410

Referring to FIG. 4B, an AP for first establishing a channel and performing IA transmission operates as a master AP. In the following, an AP to grab an initial channel and perform IA transmission may be referred to as 1st AP or AP1. The master AP transmits a list of candidate APs to participate in the IA transmission group in an IA-RTS frame (Interference Alignment-Request to Send, IA-RTS frame). The master AP sequentially transmits a CTS-Poll frame (Clear to Send-Poll frame) to the APs specified in the IA-RTS frame, and receives an IA-CTS frame (Interference Alignment-Clear to Send frame) in response. The candidate AP responds with an IA-CTS frame only when it wants to participate in the interference alignment transmission. Candidate APs are polled in the order in the AP list. If there is no response from the AP during the Short Inter Frame Space (SIFS) after polling, after the PCF Inter Frame Space (PIFS) after the CTS-Poll, the master AP sends a CTS-Poll frame back to the AP to request a response, or the AP The CTS-Poll frame is transmitted to the next AP in the list.

[2] NDP (Null Data Packet) Transmission Process During Channel State Information (CSI) Feedback and Sharing Steps 420

Referring to FIG. 4C, after the master AP receives the IA-CTS frame, the master AP selects a specific number, for example, 4 or less IA participating APs (or sounding participating APs). The master AP may select to receive only IA-CTS frames as much as the maximum number of participating APs or to receive some IA-CTS frames in excess of the maximum number, and then only some APs may participate in interference alignment.

The master AP generates an IA NDP Announcement frame including a list of APs of the group to be sounded (or IA transmission group) and a STA Info list of MU-MIMO (or SU-MIMO) STAs to which the AP belongs. send. At this time, the master AP may obtain the STA Info list of the MU-MIMO (or SU-MIMO) STA to which IA transmission belongs to each AP using the IA-CTS frame received from each AP.

Each STA that is the target of MU-MIMO (or SU-MIMO) transmission of each participating AP is able to know that it is a sounding target for IA MU-MIMO (or SU-MIMO) transmission by looking at the IA NDP Announcement frame. In addition to the AP with which it is associated, it may know other IA transport group AP lists (BSSIDs). Each STA that is an MU-MIMO (or SU-MIMO) transmission target of each IA transmission participating AP may listen to and feedback NDP transmitted from the specified AP based on the information obtained from the IA NDP Announcement frame.

APs included in other IA transmission groups such as AP2 and AP3 can listen to the IA NDP Announcement frame sent by the master AP and confirm that they are sounding targets for IA MU-MIMO (or SU-MIMO) transmission. In addition, an AP included in another IA transmission group such as AP2 and AP3 transmits the same IA NDP Announcement frame and NDP as the AP listed in the IA NDP Announcement frame in order to consider a STA that is hidden to the other AP. . Here, AP2 and AP3 are APs included in the IA transmission group.

Each AP transmits NDP after transmitting the IA NDP Announcement frame according to its own order in the order listed in the IA NDP Announcement frame. The AP that transmits the NDP transmits an AP-Poll frame (Type = 0: NDP Announcement) to the next AP in the list to explicitly designate an AP to transmit the next IA NDP Announcement frame.

Upon receiving the AP-Poll frame (Type = 0), the AP may determine whether a RA (Receiver Address) field of the AP-Poll frame (Type = 0) indicates itself. Receiving the AP-Poll frame (Type = 0) indicated by the RA field, the AP resets the set Network Allocation Vector (NAV), transmits its own IA NDP Announcement frame, and transmits the NDP. do. The AP that receives the AP-Poll frame (Type = 0) transmits the AP-Poll frame (Type = 0) to the corresponding AP when there is an AP in the following order.

[3] Beamforming Report Transmission Process During Channel State Information (CSI) Feedback and Sharing Step 420

Referring to FIG. 4C, after all IA NDP Announcement / NDP transmission processes are completed, the master AP transmits an IA Beamforming Report Poll frame to its MU-MIMO (or SU-MIMO) STAs to form a Beamforming Report. Receive

Here, the IA Beamforming Report Poll frame transmission and the Beamforming Report frame feedback process may be performed according to the IEEE 802.11ac standard. At this time, according to one embodiment, the maximum number of APs to be sounded by one STA is one or more (for example, four), and thus, one or more segment retransmission bitmap fields defined in the IEEE 802.11ac standard. (For example, four).

In addition, for feedback of the Beamforming Report frame, a VHT (Very High Throughput) Compressed Beamforming frame defined in the IEEE 802.11ac standard may be used. At this time, according to an embodiment, the AP Index may be indicated using 2 bits reserved in the VHT MIMO Control field. For example, the AP index may be used to indicate which one of the plurality of APs is a feedback to. Hereinafter, the beamforming report frame may be a very high throughput (VHT) compressed beamforming frame.

When an AP completes a BF report poll / feedback exchange for a MU STA (Multi-User Station) belonging to the AP, the AP-Poll frame (Type: 1, IA) -Feedback). The AP designated as RA in the AP-Poll frame (Type: 1) resets the NAV and performs IA Beamforming Report Poll / Feedback Exchange. Hereinafter, BF refers to beamforming.

If the BF report frame is not received within the TXOP from STAs associated with a specific AP in the IA group, the master AP catches the next TXOP, and then sends IA-Poll (Type: 1) to the AP to perform the BF report poll / feedback. Receive the rest of the feedback frame.

The AP, which is the last order, sends an IA-Poll (Type: 1) to the master AP when the feedback is completed, indicating that the feedback process is completed.

[4] IA calculation information exchange step (430)

Referring to FIG. 4D, after the BF feedback process is completed, the IA participating APs exchange IA calculation information by wire (or wireless).

[5] IA data transmission stage

The master AP enters a step for transmitting IA data after catching TXOP. The step for transmitting the IA data may include a protection step 440 and an IA data transmission step 450 for the IA data transmission.

Referring to FIG. 4E, for protection of IA data transmission, the master AP may secure a channel by capturing a channel and exchanging mRTS / mCTS between multiple APs according to an embodiment. Alternatively, the master AP may exchange existing RTS / CTS between multiple APs.

Referring to FIG. 4F, the master AP sends an IA Synch frame to instruct the STAs in the IA group to transmit IA. Each AP belonging to the IA transmission group transmits by padding the frame according to a transmission duration specified by the master AP through the IA Synch frame.

APs receiving the IA Synch frame reset their NAVs and transmit data to their MU STAs simultaneously using interference alignment after SIFS when they are specified in the Basic Service Set ID (BSSID) of the IA Synch frame. .

[6] Block Ack Step

IA data transmission step 450 may include a Block Ack step. Referring to FIG. 4F, Block Ack Request (BAR) / Block Ack (BA) exchange is performed in the order of AP specified in the IA-Synch frame. When an AP completes the BAR / BA exchange for the MU STA belonging to the AP, the AP sends an AP-Poll frame (Type: 2, BA) to the AP in the next order.

The AP-Poll frame (Type: 2) explicitly notifies that the BAR / BA exchange process of a specific AP is completed, and then allows the next AP to start the BAR / BA. For example, the AP designated as RA in the AP-Poll frame (Type: 2) resets the NAV and performs a BAR / BA exchange.

Data to be transmitted simultaneously to the IA when AP-Poll frame (Type: 2) is transmitted by using more data bits in the Frame Control field of the MAC header of the AP-Poll frame (Type: 2). Is indicated whether there is more. The AP, which is the last order on the AP list, sends an AP-Poll frame (Type: 2) to the master AP after completing the BAR / BA exchange process.

When there is an AP that sends an AP-Poll frame (Type: 2) in which the more data bit of the MAC header is set to 1, or when the master AP itself also has data to transmit to the IA, the master AP uses the remaining TXOP. IA transmission can proceed. If the remaining TXOP is insufficient, the master AP collects a new TXOP and transmits an IA-Synch frame including only the AP that sent the AP-Poll frame (Type: 2) with data bit 1 to the list. It may be.

Frame Format and Detailed Protocol Procedures

The frame format used in the interference alignment protocol and related protocol procedures are as follows. The frame format is one example and the detail fields and order may be changed or variously combined. The detailed protocol procedure is also an embodiment, and details can be changed and combined. In addition, the length of the field is also an example, and the length may vary as necessary.

(A) IA-RTS frame

5A illustrates an IA-RTS frame according to an embodiment, and FIG. 5B illustrates an IA-RTS Info field according to an embodiment.

The AP that initially acquires the channel and initiates IA transmission serves as the master AP. The master AP determines an IA transmission participating AP by transmitting an IA-RTS frame including a list of candidate APs participating in interference alignment. Hereinafter, the master AP may be referred to as 1 ^st AP or AP1.

The IA-RTS frame includes the Frame Control field 511, Duration field 512, RA field 513, TA field 514, IA-RTS Info field 515, Expected Transmission duration field 516, candidate AP list. 517, and at least one of the FCS field 518.

The TA field indicates the address (BSSID) of the AP sending the IA-RTS frame (eg, the master AP). The Duration field indicates the duration until the process of determining the IA participating node and receiving CSI feedback. Protect IA protocol sequence from 3rd party AP / STA through Duration field.

If the feedback is long, the master AP may set the duration field to a maximum TXOP (max TXOP). The master AP acquires a new channel after the maximum TXOP and sends the AP-Poll to the AP that has not completed the feedback, so that the feedback sequence can continue.

In the case where it is possible to set one TXOP not exceeding the maximum TXOP from the determination of the IA participating node to the transmission of the IA data by omitting the sounding process, the master AP sets the duration field to the interval from the determination of the IA participating node to the transmission of the IA data It can be set as the period of. In this case, the mRTS / mCTS exchange immediately before the IA-Synch frame transmission may be omitted.

The RA field may be set to the address of the corresponding AP when there is one candidate AP, and set to the broadcast address when there are several candidate APs. In the case of broadcast, the IA transmission candidate AP address list may be further included in the IA-RTS frame.

An AP transmitting an IA-RTS frame sets an expected transmission duration field of data to be transmitted using IA in this data transmission TXOP (TXOP (b) of FIG. 4) (eg, in microseconds). The other participating AP may determine whether to participate in IA transmission by referring to the expected transmission duration field. For example, since it is preferable to transmit APs having similar transmission data durations together, participation can be determined based on whether the transmission data periods have similar lengths.

The IA-RTS Info field includes a Number of Candidate AP field 521, a Number of AP Antenna field 522, and a BW field 523. The Number of Candidate AP field specifies the number (eg, number n) of APs included in the Candidate AP list. The Number of AP Antenna field specifies the number of antennas of the master AP (for example, values 0 to 7 mean 1 to 8 antennas). The BW field specifies the bandwidth (Bandwidth, BW) that the master AP intends to use for transmission (for example, 0 to 3 means 20, 40, 80, and 160 or 80 + 80, respectively). For protection, the master AP transmits IA-RTS frames as non-HT duplicate frames by the bandwidth specified in the BW field.

The master AP polls the candidate APs in the order of the candidate AP list listed in the IA-RTS frame and receives the IA-CTS frame. If there is one target candidate AP, the AP list is omitted, and the master AP transmits a CTS-Poll frame to the AP specified in the RA field. If there are several target candidate APs, the master AP transmits CTS-Poll frames sequentially from the first AP in the AP candidate list.

The candidate AP responds with an IA-CTS frame only when it wants to participate in the interference alignment transmission. The candidate AP responds with the IA-CTS frame ignoring the previous NAV setting if the RA field of the CTS-Poll frame is the same as its own address.

The master AP may receive only IA-CTS frames as many as the maximum number of participating APs, or may select some APs participating in interference alignment after receiving IA-CTS frames exceeding the maximum number. In this case, sounding may be performed only for the selected AP.

If there is no IA-CTS frame response in SIFS after sending a CTS-Poll frame, the master AP sends a previous CTS-Poll frame to an unresponsive AP and sends a CTS-Poll frame after PIFS to request a response again, or a candidate The IA-CTS frame is requested by sending a CTS-Poll frame to the next AP in the BSSID list. If no IA-CTS frame is received, the master AP transmits only the master AP in the TXOP or sends a CF-End (Contention Free-End) frame to terminate the TXOP. By sending a CTS-Poll frame directly to a master AP (or one target AP) without receiving an IA-CTS frame, even if the first candidate AP does not send an IA-CTS frame due to its intention to participate May not lose TXOP.

(B) IA-CTS frame

6A illustrates an IA-CTS frame according to an embodiment, FIG. 6B illustrates an IA-CTS Info field according to an embodiment, and FIG. 6C illustrates an STA Info field according to an embodiment. It is a figure.

The IA-CTS frame includes a Frame Control field 611, a Duration field 612, an RA field 613, a TA field 614, an IA-CTS Info field 615, and a plurality of IAs (e.g., four). -At least one of the STA Info fields 616, and the FCS field 617.

The Duration field may specify the remaining TXOP transmission period based on the duration specified in the duration field of the IA-RTS frame or the duration field of the CTS-Poll frame. The Duration field can be used for protection.

The IA-CTS Info field includes a Number of MU STA field 621, a Number of AP Antenna field 622, and a BW field 623. The Number of MU STA field specifies the number of STAs (eg, up to four) that the CTS transmitting AP wants to transmit to a multiple-user (MU). The Number of AP Antenna field specifies the number of antennas of the responding AP (eg, values 0 to 7 mean 1 to 8 antennas). The BW field specifies the bandwidth (BW) that the responding AP intends to use for transmission (eg, 0 to 3 means 20, 40, 80, and 160 or 80 + 80, respectively).

Each of the plurality of IA-STA Info fields may be the same as the STA Info field defined in the IEEE 802.11ac standard. For example, each IA-STA Info field may include an AID field 631, a Feedback Type field 632, and an Nc Index field 633.

The responding AP may transmit the IA-CTS frame as a non-HT duplicate frame by the bandwidth specified in the BW field. For protection, the bandwidth specified in the BW field may be less than or equal to the bandwidth specified in the BW field of the IA-RTS frame.

(C) CTS-Poll Frame

7 illustrates a CTS-Poll frame according to an embodiment. The CTS-Poll frame includes at least one of a Frame Control field 711, a Duration field 712, an RA field 713, a TA field 714, and an FCS field 715. The CTS-Poll frame is used to specify the AP to which the next IA-CTS frame should respond. The RA field is set to the BSSID of the AP to which the next responds. The Duration field specifies the remaining TXOP transmission period. The Duration field is used for protection.

(D) IA NDP Announcement Frame

FIG. 8A illustrates an IA-NDP Announcement frame according to an embodiment, FIG. 8B illustrates a Group Member Indication Bitmap field according to an embodiment, and FIG. 8C illustrates an STA Info field according to an embodiment. It is a figure explaining.

The IA NDP Announcement frame includes the Frame Control field (811), Duration field (812), RA field (813), TA field (814), Sounding Dialog Token field (815), Group Member Indication Bitmap field (816), and candidate AP list. 817, the STA Info list 818 of each AP, and the FCS field 819.

After the master AP has received the IA-CTS frame, including the AP list of the group to be sounded (or IA transmission group) and the STA Info list of STAs for each AP (using information received from each AP to IA-CTS). Transmit IA NDP Announcement frame.

The MU transmission target STA of the AP participating in the IA transmission may recognize that the STA is a sounding target for the IA MU transmission by looking at the IA NDP Announcement frame. In addition, the MU transmission target STA of the AP participating in the IA transmission may use the IA NDP Announcement frame to know another AP list (BSSID) in the IA transmission group in addition to the AP to which it is associated. The MU transmission target STA of the AP participating in the IA transmission listens to the NDP transmitted from the AP to which it is associated and other APs in the IA transmission group based on the information obtained from the IA NDP Announcement frame and provides feedback.

The AP included in the IA transmission group such as AP2 and AP3 may receive the IA NDP Announcement frame sent by the master AP and determine whether they are sounding targets for IA MU transmission based on the IA NDP Announcement frame. In addition, in order to consider STAs hidden to other APs included in the IA transmission group, APs included in the IA transmission group such as AP2 and AP3 may have the same IA NDP Announcement frame and NDP as the master AP sent in the IA NDP Announcement frame. Transmit in order of AP.

The master AP always enters the front of the AP list. The maximum number of participating APs may be four, for example, including four master APs in this embodiment. The RA field is set to the broadcast address.

8D illustrates a Sounding Dialog Token field, according to an embodiment. Referring to FIG. 8D, the Sounding Dialog Token field includes a Sounding Dialog Token Number field 841. The Sounding Dialog Token Number field is set to a value for the Beamformer to identify the IA NDP Announcement frame. The Sounding Dialog Token Number field may be set according to the Sounding Dialog Token Number field defined in the IEEE 802.11ac standard.

Referring back to FIG. 8A, the Duration field is set to a value obtained by subtracting the IA NDP Announcement transmission period from the period specified in the duration field of the immediately preceding transmission frame. Because of this, the rest of the TXOP can be protected.

The Group Member Indication Bitmap field designates the BSSID of an AP belonging to an IA transmission group (or sounding group) or the number of MU STAs of the AP.

As an example, the Group Member Indication Bitmap field may include a Number of MU STA (AP1) field 821, a Number of MU STA (AP2) field 822, a Number of MU STA (AP4) field 824, and a Number of MU STA (AP4) field 824 may be included. Here, a bit of a predetermined length may be allocated to each AP. For example, in this embodiment, 3 bits may be allocated to each AP. In this case, when the Group Member Indication Bitmap field is 000, this may mean that the STA is in the zero range. In this case, the AP itself may not be included in the IA NDP Announcement frame. When the Group Member Indication Bitmap field is 001, this may mean that there is one STA. In this case, only one STA Info field may exist after the corresponding AP BSSID. In addition, when the Group Member Indication Bitmap field is 100, this may mean that there are four STAs. 101-111 may be reserved.

For example, if the Group Member Indication Bitmap field is 011 010 001 000, the list included in the IA NDP Announcement frame may include three STAs associated with AP1, two STAs associated with AP2, and one STA associated with AP3. Includes STA Info fields. The IA group includes three APs and AP4 is not included in the group.

More specifically, the list included in the IA NDP Announcement frame may include AP1 BSSID, STA Info 1 of AP1, STA Info 2 of AP1, and STA Info 3 of AP1; AP2 BSSID, STA Info 1 of AP2, STA Info 2 of AP2; And STA Info 1 of AP3. Since the AP4 has zero STAs, neither the BSSID nor the STA Info of the AP4 is included in the list included in the IA NDP Announcement frame.

Each of the STA Info fields included in the STA Info list may be identical to the STA Info field defined in the IEEE 802.11ac standard. For example, each STA Info field may include an AID field 831, a Feedback Type field 832, and an Nc Index field 833.

Each AP transmits NDP immediately after sending an IA NDP Announcement frame in its own order (for example, the order listed in the IA NDP Announcement frame). If a range of BSSs overlaps with each other such that the MU STAs to which the interference AP participating in each interference alignment group can hear all the IA NDP Announcement frames of other APs belonging to the interference alignment group, only the master AP sends an IA NDP Announcement frame. Can be. In this case, the other AP may transmit only the NDP and AP-Poll frames without sending the IA NDP Announcement frame.

The AP that transmits NDP explicitly specifies AP to transmit next IA NDP Announcement frame by sending AP-Poll frame (Type = 0: Poll for NDP Announcement) to next AP in list. The AP that receives the AP-Poll frame (Type = 0) (the AP whose RA field is the AP-Poll frame) resets the set NAV, transmits its own IA NDP Announcement frame, and transmits the NDP. do. If there is an AP in the following order, AP-Poll frame (Type = 0) is transmitted to the AP.

If an AP does not transmit an IA NDP Announcement frame from an AP that receives the AP-Poll after SIFS after transmitting the AP-Poll frame, the AP that transmitted the AP-Poll frame is the same AP as the AP-Poll frame again after PIFS. Poll or transmit an AP-Poll frame to the next AP. The AP of the last order transmits the AP-Poll frame in which the RA field is designated as the BSSID of AP1 to the master AP after NDP transmission. When the master AP receives the AP-Poll frame, the master AP recognizes that the NDP transmission process is completed, and also resets the configured NAV and starts poll transmission to receive the beamforming report.

The AP which finally failed the IA NDP Announcement frame / NDP transmission is excluded from the transmission group in the IA data transmission step.

(E) AP-Poll Frame

9 illustrates an AP-Poll frame according to an embodiment. Referring to FIG. 9, the AP-Poll frame includes a frame control field 911, a duration field 912, an RA field 913, a TA field 914, a poll type field 915, and an FCS field 916. At least one.

After completing the frame exchange sequence (for example, IA NDP Announcement / NDP, IA Beamforming Report Poll / IA Beamforming Report, BAR / BA, etc.), the AP transmits an AP-Poll frame to indicate that the frame exchange sequence is terminated in its BSS. Explain explicitly. In addition, the AP that has completed the frame exchange sequence explicitly specifies an AP to perform the frame exchange sequence in its next order.

After receiving the AP-Poll frame, the AP (for example, an AP whose RA of the AP-Poll frame matches its BSSID) resets its NAV and performs a frame exchange process (IA NDP Announcement / NDP, Beamforming Report Poll). / IA Beamforming Report, BAR / BA).

If the designated APs complete the frame exchange sequence in sequence, the AP that performed the last frame exchange sends an AP-Poll frame to the master AP. After receiving the AP-Poll frame, the master AP transmits a frame for the next step. Or, the master AP terminates TXOP when there is no more data to send. When the AP-Poll frame is received, the master AP resets its NAV.

If the Poll Type field is 0, the AP-Poll frame is a frame for IA NDP Announcement; if the Poll Type field is 1, the AP-Poll frame is a frame for IA-feedback; if the Poll Type is 2, the AP-Poll frame Indicates a frame for BA. The remaining values that can be specified in the Poll Type field are reserved.

In Poll Type 2, each AP uses the More Data bit in the Frame Control field of the MAC header included in the AP-Poll frame to send the AP-Poll (for example, immediately after Data Transfer-BA). Indicate whether there is more data to be transmitted simultaneously to the IA.

If there is an AP sending an AP-Poll frame with the more data bit set to 1, and / or if the master AP itself has data to send to the IA, the master AP may use the remaining TXOP immediately after BAR / BA, or the remaining TXOP is insufficient. If a new TXOP is acquired, the IA transmission is continued by transmitting an IA-Synch frame including only the AP having the data bit of 1 in the previous transmission.

In case of catching a new TXOP, after protection is performed through mRTS / mCTS transmission or multiple RTS / CTS transmission between APs remaining in the IA transmission group, the IA-Synch frame transmission / data transmission / BA process may proceed. have.

(F) IA Beamforming Report Poll Frame

10 illustrates an IA Beamforming Report Poll frame according to an embodiment. The IA Beamforming Report Poll frame corresponds to the frame described as Poll in FIG. 4C.

The IA Beamforming Report Poll frame includes one of a Frame Control field 1011, a Duration field 1012, an RA field 1013, a TA field 1014, a plurality of Feedback Segment Retransmission bitmap fields 1015, and an FCS field 1016. At least one.

After all of the IA NDP Announcement / NDP transmission process is completed, the master AP transmits an IA Beamforming Report Poll frame to its MU STAs to receive a Beamforming Report frame.

Here, the IA Beamforming Report Poll frame transmission and the Beamforming Report frame reception (feedback) process may be performed according to the IEEE 802.11ac standard. At this time, according to an embodiment, since the maximum number of APs to be sounded by one STA is plural (for example, four in this embodiment), a segment retransmission bitmap field defined in the IEEE 802.11ac standard. Can be extended to multiple (eg, four).

When the Beamforming Report frames for each AP are not divided into segments, a plurality of VHT Compressed Beamforming frames may be transmitted per STA (for example, up to four in this embodiment). If the Beamforming Report frame for each AP is segmented, the number of VHT Compressed Beamforming frames transmitted per STA may be further increased. Here, the VHT Compressed Beamforming frame corresponds to a Beamforming Report frame.

For example, compared to the case of conforming to the IEEE 802.11ac standard, the number of VHT Compressed Beamforming frames transmitted per STA may be increased up to four times. Because, according to the IEEE 802.11ac standard, the STA transmits only the Beamforming Report frame for the BSS to which it belongs, but according to embodiments, the STA must also transmit the Beamforming Report frame for the other AP belonging to the interference alignment group to the AP to which it belongs. Because.

To this end, the STA according to the embodiments transmits one VHT Compressed Beamforming frame modified in the IEEE 802.11ac standard, one per AP. Alternatively, when the VHT Compressed Beamforming frame is long, segmentation may be performed according to the IEEE 802.11ac standard. In this case, several VHT Compressed Beamforming frames may be transmitted for one AP.

The beamforming report frame is aggregated into one A-MPDU at every poll and fed back within a range not exceeding the maximum PPDU length. For example, if all Beamforming Report frames for all AP groups belonging to the IA group can be aggregated to an Aggregated MAC Protocol Data Unit (A-MPDU) within a maximum PPDU size, feedback is completed in one Poll.

According to embodiments, since there is a large feedback size, it may be difficult to aggregate all Beamforming Report frames for all AP groups belonging to the IA group to one A-MPDU within a maximum PPDU size.

In this case, the beamforming report frames are transmitted in response to multiple polls. At this time, a segment for another AP may be simultaneously included in one transmitted A-MPDU. For example, the last segment of AP1 and the first segment of AP2 may be aggregated into one A-MPDU. By including the AP index field in the VHT Compressed Beamforming frame, it is possible to distinguish which AP segment the VHT Compressed Beamforming frame is. In the AP index field, 0, 1, 2, and 3 may be allocated in the order of APs listed in the IA NDP Announcement frame. Because of this, feedback can be included including as many segments as possible at one time.

The order in which the bitmap appears is in accordance with the order of the AP list specified in the IA NDP Announcement frame. For example, bitmap 1 may correspond to a retransmitted bit map for the master AP (retransmission bitmap), and the like bitmap 2 is a bit map for the 2 ^nd AP.

VHT Compressed Beamforming Frame

11 illustrates a VHT Compressed Beamforming frame according to an embodiment. Referring to FIG. 11, the VHT Compressed Beamforming frame includes an Nc Index field 1111, an Nr Index field 1112, a Channel Width field 1113, a Grouping field 1114, a Codebook Information field 1115, and a Feedback Type field 1116. ), A Remaining Feedback Segments field 1117, a First Feedback Segments field 1118, an AP index field 1119, and a Sounding Dialog Token Number field 1120.

For feedback, the VHT Compressed Beamforming frame defined in the IEEE 802.11ac standard may be used. For example, a frame composed of a Category field, a VHT Action field, a VHT MIMO Control field, a VHT Compressed Beamforming Report field, and a MU Exclusive Beamforming Report field may be used. In this case, reserved 2 bits of the VHT MIMO Control field defined in the IEEE 802.11ac standard may be used to indicate the AP index.

Feedback for each NDP consists of each VHT Compressed Beamforming frame, and is aggregated and transmitted to the A-MPDU within the maximum PPDU range. For example, if the feedback size for each AP (eg, four) does not exceed the maximum PPDU size, four VHT Compressed Beamforming frames are aggregated and transmitted in the A-MPDU. If the maximum PPDU size is exceeded, it is divided into separate polls / feedbacks within the range not exceeded and transmitted. The VHT Compressed Beamforming frame for one AP may be transmitted in Poll / Feedback by dividing into segments as specified in the VHT specification.

The AP Index is indicated using a reserved 2 bit of the VHT MIMO Control field. The AP Index is used to specify which AP feedback is. For example, AP index 0 is indicated that the feedback to the master AP specified in the IA NDP Announcement frame, the AP index 1, AP index 2, AP index 3 is feedback for each of the 2 ^nd AP, 3 ^rd AP, 4 ^th AP Indicates that

The STA may inform the AP whether it is a feedback for which AP and / or a number of segments of the feedback by using the AP index and segment information (eg, Remaining Feedback Segments and First Feedback Segments).

If the STA does not hear the NDP from a specific AP belonging to the IA sounding group, the STA transmits null feedback. Here, the null feedback may be feedback except for the VHT compressed beamforming report and the MU exclusive beamforming report among the VHT compressed beamforming frames.

When an AP completes a BF report poll / feedback exchange for an MU STA belonging to the AP, the AP accesses the AP-Poll frame (Type: 1, IA-Feedback) to the AP in the next order on the AP list of the IA NDP Announcement frame. Send it.

The AP-Poll frame (Type: 1) may explicitly notify that the BF report poll / feedback exchange process of a specific AP is completed. In addition, the AP-Poll frame (Type: 1) may cause the next AP to start BF report poll / feedback exchange. For example, the AP designated as RA in the AP-Poll frame (Type: 1) may reset the NAV and perform IA Beamforming Report Poll / Feedback Exchange.

When the AP, the last order on the AP list of the IA NDP Announcement frame, completes the BF report poll / feedback exchange process, the AP sends an AP-Poll frame (Type: 1) to the master AP. The master AP resets its NAV after receiving the AP-Poll. When exchanging IA calculation information over the wire, the master AP transmits a CF-End to terminate the remaining TXOP when the remaining TXOP remains. If the IA calculation information is exchanged over the air, the IA calculation information exchange process may be performed wirelessly using the remaining TXOP.

In the CSI feedback and sharing step, a specific AP in the IA group may not receive all the BF report frames in the TXOP from STAs. In this case, after acquiring the next TXOP, the master AP transmits an IA-Poll frame (Type: 1) to the AP to perform BF report poll / feedback to receive the remaining feedback frame (for example, the remaining BF report frame). Can be. After receiving the IA-Poll frame (Type: 1) from the master AP, the AP resets the NAV, performs the remaining BF report poll / feedback, and then transmits the IA-Poll frame (Type: 1) to the next AP in the list. In this case, after the channel acquisition of the master AP before the transmission of the IA-Poll frame (Type: 1), the protection is performed through a plurality of RTS / CTS transmission or mRTS / mCTS transmission between the AP and the master AP that did not complete the feedback process Can be.

(A) IA Calculation Information Exchange

IA calculation information can be exchanged by wire or wirelessly.

(a) Example of exchanging by wire

After all beamforming feedback exchanges are completed, each IA participating AP exchanges IA calculation information with each other by wire. When each AP exists in the same subnet, IA calculation information is broadcasted over the wire. When each AP exists in a different subnet, IA calculation information can be transmitted to each other AP. In this case, each AP may transmit its IA calculation information to another AP and notify the master AP of the completion of transmission. Each AP may inform the master AP of the expected data duration to be transmitted in the IA transmission phase when exchanging IA calculation information.

The master AP may acquire a new TXOP for IA data transmission after completing the exchange of IA calculation information. MRTS / mCTS may be performed after the master AP establishes a channel for protection of IA data transmission. If the number of participating APs is two, the APs may be protected by exchanging existing RTS / CTS. MRTS / mCTS or RTS / CTS exchange process may be skipped if there is already protection for IA transport group APs through RTS / CTS, CTS-Poll / IA-CTS, or other data frame exchange in the same TXOP. have.

(b) Example of exchanging by wireless

After all beamforming feedback exchanges are completed, each IA participating AP exchanges IA calculation information with each other wirelessly. In this case, each IA participating AP may transmit its IA calculation information to other APs in a broadcast or unicast order in the order of APs listed in the IA NDP Announcement frame. In the case of broadcast transmission, since the number of transmission frames is reduced but no response is received, an AP that cannot receive IA calculation information may be generated. On the other hand, unicast transmission allows a reliable transmission because ack is received, but the number of transmission frames increases.

In case of broadcast, each AP broadcasts its IA Calculation information when its order specified in IA NDP Announcement frame arrives, and then transmits AP-Poll frame to AP in the next order. Upon receiving the AP-Poll frame, the AP resets its NAV and broadcasts its IA calculation information. After the last AP broadcasts IA calculation information, it sends an AP-Poll frame to the master AP. After receiving this, the master AP resets the NAV and transmits an IA-Synch frame to enter the IA data transmission step. If TXOP is insufficient after exchanging IA calculation information, the master AP catches a new TXOP and transmits IA-Synch frame. When a new TXOP is caught, the transmission interval may be protected through mRTS / mCTS or RTS / CTS between the master AP and the IA transmission group AP.

To compensate for the reliability of the broadcast process, each AP sends a poll to each AP immediately after broadcasting its own IA Calculation information, and receives a response from the AP receiving the poll. Can check whether IA calculation information is properly received. The target AP may transmit a response to the poll only when the IA calculation information is received.

In the case of unicast, each AP sequentially transmits its IA Calculation information to other APs in the IA group when its order specified in the IA NDP Announcement frame arrives. For example, if AP1 sends IA calculation information, AP1 first sends IA calculation information to AP2 and receives an ack for IA calculation information. Subsequently, AP1 sends IA calculation information to AP3 and receives an ack for IA calculation information. AP1 then transmits the AP-Poll frame to the next AP2 in the order specified in the NDP Announcement frame. When AP2 receives AP-Poll frame, it resets NAV and sends IA calculation information to AP1 and AP3 sequentially and receives ack.

The AP in the last sequence transmits the AP-Poll frame to the master AP after completing the unicast of the IA calculation information. After receiving the AP-Poll frame, the master AP resets the NAV and transmits an IA-Synch frame to enter the IA data transmission step. If TXOP is insufficient after exchanging IA calculation information, the master AP catches a new TXOP and transmits IA-Synch frame. When a new TXOP is caught, the transmission interval may be protected through mRTS / mCTS or RTS / CTS between the master AP and the IA transmission group AP.

When IA calculation information is exchanged over the air, the IA calculation frame may be large and may not be sent in one TXOP. In this case, the master AP may hold a new TXOP, protect the channel by using mRTS / mCTS or RTS / CTS, and then transmit an AP-Poll frame to the next transmission target AP. As a result, the IA calculation information exchange process may continue.

MRTS frame

12A illustrates an mRTS frame according to an embodiment. Referring to FIG. 12A, an mRTS frame includes a Frame Control field 1211, a Duration field 1212, an RA field 1213, a TA field 1214, an mRTS Info field 1215, and a plurality of STA MAC address fields 1216. ), And at least one of the FCS fields 1217.

The mRTS frame is used for transmission protection between multiple APs / STAs. By using the mRTS frame, the overhead of exchanging RTS / CTS multiple times can be reduced. The RA field of the mRTS frame is set to a broadcast address.

12B illustrates an mRTS Info field, according to an embodiment. 12B, the mRTS Info field includes at least one of a Number of STAs field 1221, a BW field 1222, and a Dynamic BW operation field 1223.

The Number of STAs field indicates the number of STAs to which a response CTS is to be sent. As many STA addresses as specified in the Number of STAs field are included in the mRTS frame.

The BW field indicates the bandwidth (BW) to be used for transmission. For example, 0 to 3 represent 20, 40, 80, and 160 or 80 + 80, respectively. As many mRTS frames as BW specified in the BW field are transmitted as non-HT duplicate frames. If the Dynamic BW Operation field is 0, this indicates a static bandwidth operation, and if the Dynamic BW Operation field is 1, this indicates a dynamic bandwidth operation.

STAs included in the mRTS frame transmit the mCTS at SIFS intervals in the order listed.

(Car) mCTS frame

FIG. 13A illustrates an mCTS frame according to an embodiment. FIG. Referring to FIG. 13A, an mCTS frame includes at least one of a Frame Control field 1311, a Duration field 1312, an RA field 1313, an mCTS Info field 1314, and an FCS field 1315. STAs included in the mRTS frame transmit the mCTS frame at SIFS intervals in the order shown in the list.

FIG. 13B illustrates an mCTS Info field according to an embodiment. FIG. Referring to FIG. 13B, the mCTS Info field includes a BW field 1321. The BW field specifies the bandwidth (BW) used by the responding STA. For example, 0 to 3 represent 20, 40, 80, and 160 or 80 + 80, respectively. According to the Dynamic BW Operation field of the mRTS frame, bandwidth (BW) negotiation is performed by a dynamic bandwidth operation or a static bandwidth operation.

The responding STA may transmit the mCTS frame as a non-HT duplicate frame by the bandwidth specified in the BW field. For protection, the bandwidth specified in the BW field may be less than or equal to the bandwidth specified in the BW field of the mRTS frame.

The final determined bandwidth (BW) is a bandwidth corresponding to the BW intersection of the mRTS / mCTS participating STAs. If the mCTS frame to be sent in the corresponding order after SIFS is not transmitted, the master AP backs off and acquires a channel. When the number of APs (or STAs) to be protected is three or less, the RTS / CTS may be exchanged twice to be protected.

(Ka) IA Synch frame

14 illustrates an IA Synch frame according to an embodiment. The master AP sends an IA Synch frame after channel acquisition and protection to instruct the STAs in the IA group to transmit the IA.

The IA Synch frame includes a Frame Control field 1411, a Duration field 1412, an RA field 1413, a TA field 1414, a Transmission duration field 1415, a plurality of AP BSSID fields 1416, and an FCS field ( 1417).

The master AP designates the value of the Transmission duration field, and each AP belonging to the IA transmission group transmits by padding the frame according to the value of the Transmission duration field. The master AP determines the duration of data to be sent to the IA. For example, the master AP defaults to a transmission duration based on a period of data to be transmitted by the master AP, and may inform the determined transmission time through an IA Synch frame. When IA calculation information is exchanged by wire, the master AP may receive an expected data transmission period from another participating AP in advance, and may set a transmission duration based on the expected data transmission period.

The IA Synch frame contains a list of AP BSSIDs to participate in the transmission to the IA.

If there are two APs to participate in the IA transmission (eg, master AP and AP2), the RA field is set to the address of AP2, the TA field is set to the address of the master AP, and the BSSID list is included in the IA Synch frame. It doesn't work. If there are three or more APs to participate in the IA transmission, the RA field is set to a broadcast address and is included in the AP BSSID list from AP2. Since the BSSID of the master AP transmitting the IA Synch frame is identified by the TA field of the IA Synch frame, it is not separately included in the AP BSSID list.

APs receiving an IA Synch frame, if they are specified in the BSSID field of the IA Synch frame, reset their NAV and, after SIFS, simultaneously transmit data to their MU-MIMO (or SU-MIMO) STA using interference alignment. Send it.

(A) Block Ack Detailed Course

BAR / BA exchange is performed in the order of AP appearing in IA-Synch frame. The master AP always performs the BAR / BA exchange first.

The block Ack of the first MU STA belonging to the master AP may be transmitted immediately without the BAR. For example, the block response of the first MU STA belonging to the master AP may be transmitted after SIFS after data transmission. The STA then sends a BAR to receive the BA. Here, BAR / BA exchange may be performed according to the scheme described in the IEEE 802.11ac standard and / or the BAR / BA format defined in the IEEE 802.11ac standard.

When an AP completes the BAR / BA exchange for the MU STA belonging to the AP, the AP sends an AP-Poll frame (Type: 2, BA) to the AP in the next order. The AP-Poll frame (Type: 2) may explicitly notify that the BAR / BA exchange process of a specific AP is completed. In addition, the AP-Poll frame (Type: 2) may cause the next AP to start BAR / BA. For example, an AP designated as an RA in an AP-Poll frame (Type: 2) may reset the NAV and perform a BAR / BA exchange.

In addition, when the AP-Poll is transmitted using a more data bit of the Frame Control field of the MAC header included in the AP-Poll frame (Type: 2) (for example, immediately after the data transmission-BA). It is indicated whether there is more data that the AP wants to transmit simultaneously to the IA.

The AP, which is the last order on the AP list, sends an AP-Poll frame (Type: 2) to the master AP after completing the BAR / BA exchange process. The master AP resets its NAV after receiving the AP-Poll frame (Type: 2). If there is an AP that sends an AP-Poll frame (Type: 2) with the More Data bit in the MAC Header set to 1, and / or if the Master AP itself has more data to send to the IA as well, the Master AP uses the remaining TXOP or If the remaining TXOP is insufficient, the new TXOP is collected and the IA transmission is continued by transmitting an IA-Synch frame including only the AP that sent the AP-Poll frame (Type: 2) having a data bit of 1 to the list. In case of catching a new TXOP, after protection is performed through mRTS / mCTS transmission or multiple RTS / CTS transmission between APs remaining in the IA transmission group, the IA-Synch frame transmission / data transmission / BA process may proceed. have.

In the BAR / BA exchange phase, if all the BAR / BA exchanges are not received within a TXOP from a specific AP in the IA group, the master AP catches the next TXOP and then sends an IA-Poll frame (Type: 2) to the AP to perform the BAR / BA. You can also send a) to complete the BAR / BA. After receiving IA-Poll frame (Type: 2) from master AP, AP resets NAV and proceeds with remaining BAR / BA.After completion of BAR / BA, AP receives IA-Poll frame (Type: 2) Send it. In this case, for protection, the master AP may perform a plurality of RTS / CTS or mRTS / mCTS with APs that have not completed the BAR / BA process before transmission of the IA-Poll frame (Type: 2) after channel acquisition.

The embodiments described above may be implemented as hardware components, software components, and / or combinations of hardware components and software components. For example, the devices, methods, and components described in the embodiments may include, for example, processors, controllers, arithmetic logic units (ALUs), digital signal processors, microcomputers, field programmable gates (FPGAs). It may be implemented using one or more general purpose or special purpose computers, such as an array, a programmable logic unit (PLU), a microprocessor, or any other device capable of executing and responding to instructions. The processing device may execute an operating system (OS) and one or more software applications running on the operating system. The processing device may also access, store, manipulate, process, and generate data in response to the execution of the software. For convenience of explanation, one processing device may be described as being used, but one of ordinary skill in the art will appreciate that the processing device includes a plurality of processing elements and / or a plurality of types of processing elements. It can be seen that it may include. For example, the processing device may include a plurality of processors or one processor and one controller. In addition, other processing configurations are possible, such as parallel processors.

The software may include a computer program, code, instructions, or a combination of one or more of the above, and configure the processing device to operate as desired, or process it independently or collectively. You can command the device. Software and / or data may be any type of machine, component, physical device, virtual equipment, computer storage medium or device in order to be interpreted by or to provide instructions or data to the processing device. Or may be permanently or temporarily embodied in a signal wave to be transmitted. The software may be distributed over networked computer systems so that they may be stored or executed in a distributed manner. Software and data may be stored on one or more computer readable recording media.

The method according to the embodiment may be embodied in the form of program instructions that can be executed by various computer means and recorded in a computer readable medium. The computer readable medium may include program instructions, data files, data structures, etc. alone or in combination. The program instructions recorded on the media may be those specially designed and constructed for the purposes of the embodiments, or they may be of the kind well-known and available to those having skill in the computer software arts. Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks, and magnetic tape, optical media such as CD-ROMs, DVDs, and magnetic disks, such as floppy disks. Magneto-optical media, and hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. Examples of program instructions include not only machine code generated by a compiler, but also high-level language code that can be executed by a computer using an interpreter or the like. The hardware device described above may be configured to operate as one or more software modules to perform the operations of the embodiments, and vice versa.

Although the embodiments have been described with reference to the accompanying drawings as described above, various modifications and variations are possible to those skilled in the art from the above description. For example, the described techniques may be performed in a different order than the described method, and / or components of the described systems, structures, devices, circuits, etc. may be combined or combined in a different form than the described method, or other components. Or even if replaced or substituted by equivalents, an appropriate result can be achieved. Therefore, other implementations, other embodiments, and equivalents to the claims are within the scope of the claims that follow.

Claims (17)

1. In the operation method of the access point,

   Determining at least one neighboring access point to cooperate with the access point to perform interference alignment;

   First channel information between the at least one station and the access point and second channel information between the at least one station and the at least one neighboring access point, from at least one station associated with the access point Receiving;

   Acquiring information for interference alignment based on the first channel information and the second channel information; And

   Transmitting data based on the information for the interference alignment

   Method of operation of the access point comprising a.
2. The method of claim 1,

   The determining step

   Transmitting an IA-RTS frame including a candidate AP list to the at least one neighboring access point;

   Transmitting a CTS-Poll frame to a first neighboring access point included in the candidate AP list; And

   If an IA-CTS frame is received from the first neighboring access point, determining the first neighboring access point as an interference alignment participating node;

   Including, the method of operation of the access point.
3. The method of claim 1,

   The receiving step

   Transmitting an IA NDP Announcement frame including an AP list and a STA Info list to the at least one neighboring access point and the at least one station;

   Transmitting a null data packet (NDP) to the at least one station; And

   Transmitting a predetermined type of AP-Poll frame to a neighboring access point corresponding to the next order of the AP list;

   Including, the method of operation of the access point.
4. The method of claim 3,

   The neighboring access point corresponding to the address of the RA field included in the AP-Poll frame of the predetermined type resets the NAV, transmits the IA NDP Announcement frame to its associated stations, and transmits the NDP to the stations. The operation method of the access point.
5. The method of claim 1,

   The receiving step

   Transmitting an IA BF Report Poll frame to the at least one station;

   Receiving a BF Report frame including the first channel information and the second channel information from the at least one station; And

   Transmitting a predetermined type of AP-Poll frame to a neighboring access point corresponding to the next order in the AP list;

   Including, the method of operation of the access point.
6. The method of claim 5,

   The BF Report Poll frame

   And a segment retransmission bitmap field for the access point and at least one segment retransmission bitmap field for the at least one neighboring access point.
7. The method of claim 5,

   The neighboring access point corresponding to the address of the RA field included in the AP-Poll frame of the predetermined type resets the NAV, transmits the IA BF Report Poll frame to its associated stations, and sends a BF Report from the stations. A method of operation of an access point for receiving a frame.
8. The method of claim 5,

   The receiving step

   Determining a neighbor access point requiring further reception of a BF Report frame; And

   Transmitting the predetermined type of AP-Poll frame to the determined neighboring access point

   Further comprising a method of operation of the access point.
9. The method of claim 1,

   The acquiring step

   Generating interference alignment calculation information for the access point based on the first channel information and the second channel information;

   Transmitting interference alignment calculation information for the access point to the at least one neighboring access point; And

   Receiving interference alignment calculation information for the at least one neighboring access point from the at least one neighboring access point

   Including, the method of operation of the access point.
10. The method of claim 9,

    And when the interference alignment calculation information for the at least one neighboring access point is received by wire, an expected data transmission period of the at least one neighboring access point is further received.
11. The method of claim 1,

    The transmitting step

    Transmitting a multicast RTS frame to the at least one neighboring access point; And

    Receiving a multicast CTS frame from the at least one neighboring access point

    Including, the method of operation of the access point.
12. The method of claim 1,

    The transmitting step

    Transmitting an IA Synch frame to the at least one neighboring access point; And

    Transmitting downlink data simultaneously with the at least one neighboring access point during the transmission period included in the IA Synch frame

    Including, the method of operation of the access point.
13. The method of claim 12,

    The neighboring access point corresponding to the address of the AP BSSID field included in the IA Synch frame resets the NAV and transmits downlink data using interference alignment after SIFS.
14. The method of claim 1,

    The transmitting step

    Transmitting a BAR frame to the at least one station;

    Receiving a BA frame from the at least one station; And

    Transmitting, based on the order information of the access points included in the IA Synch frame, an AP-Poll frame of a predetermined type to a neighboring access point corresponding to the next order;

    Including, the method of operation of the access point.
15. The method of claim 14,

    The neighboring access point corresponding to the address of the RA field included in the AP-Poll frame of the predetermined type resets the NAV, transmits the BAR frame to its associated stations, and receives a BA frame from the stations. , Operation method of access point.
16. The method of claim 1,

    The transmitting step

    Receiving a predetermined type of AP-Poll frame from the at least one neighboring access point;

    Determining neighboring access points requiring further transmission of data based on more data bits included in the predetermined type of AP-Poll frame; And

    Transmitting an IA Synch frame to the determined neighboring access points.

    Including, the method of operation of the access point.
17. The method of claim 1,

    The first channel information is channel information estimated from an NDP received from the access point to which the at least one station is directly associated,

    And the second channel information is channel information estimated from an NDP received from the at least one neighboring access point that is not associated with the at least one station but belongs to the same IA transmission group.

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