IEEE
Wireless LANs
Draft Text D.1 CC9 Resolution of CID 201and 202	
Date:  2013-08-08	
Author(s):	
Name	Affiliation	Address	Phone	email	
James Wang	MediaTek		+1 408 526 1899-88109	james.wang@mediatek.com	
George Calcev	Huawei			George.calcev@huawei.com	
Minho Cheong	ETRI			Minho@etri.re.kr	
Hong Yuan Zhang	Marvell			Hongyuan@marvell.com	

Abstract
This document provides resolution for CID 201 and 202. 

 
Table of Contents
0 Revision Notes

0 Revision Notes

R0:	First draft

201	9.32m	For apple to apple comparison, the training frames for different sectors need to maintain same power levels--this is similar to the requirement of antenna selection in 802.11n.	In the descriptions of Fig 9-44e, and 9-44k, add requirement that the TXVECTOR TXPWR_LEVEL should be identical across different training frames--copy similar sentences from 11n.	
202	9.32m	We'v seen in 802.11n how things were broken down when defining multiple flavors for the same feature. Better not repeat the same story in 11ah by defining multiple sectorization protocols.	Merge the two types of sectorization, or remove one of them.	

CID201

Discussion:

Commenter was correct in pointing out that the sector training NDPs should have the same transmit power as specified by the TXPWR_LEVL in TXVECTOR.

Proposed Resolution:

Accept

Proposed changes:

P157L46
Instruct the editor to insert the following text

When transmitting the consecutive sounding NDPs in transmit and receive ASEL exchanges (illustrated in
Figure 9-44k), the transmitter shall not change the TXPWR_LEVEL parameter of the TXVECTOR.

CID202

Discussion:
As commenter pointed out, merging the two types of sectorization operation simplifies the operation. In the resolution of CID335, Type 0 is renamed group sectorization operation and Type 1 is renamed for TXOP-based sectorization operation. Most of the burden of the sectorization operation rests on the (Sectorized Beam-Capable) AP. Sectorized Beam-Capable APs can optionally operate one type of sectorization operation or both types while Sectorized Beam-Capable STAs support both types of sectorization operation. This would ensure Sectorized Beam-Capable STAs to interoperate with all Sectorized Beam-Capable APs.
Proposed Resolution:
Counter.
Proposed changes:
Instruct editor to change the text in clauses 8.4.2.170f, 8.4.2.170k.2, 8.4.2.170l, 9.32m as below and also replace Figures 9.44f, 9-44g, 9-44h, 9-44i with the updated drawings provided in the resolution of CID694 in “11-13-xxxx-00-00ah-CC9-Resolution-CID 685, 688-694r3 and also reference to the resolution of CID260 and CID694 for the deletion of some drawings and text. 
8.4.2.170f 	Sector Operation element
The Sector Operation element includes the information necessary for a receiving STA to determine the type of sector operation, if it is allowed to transmit during a specified sector time interval and if it can perform sector training. The Sector Operation element can be provided in Probe Response, Beacon or Association Response. 
The format of the Sector Operation element is presented in Figure 8-401cv (Sector Operation element (Sectorization Type is set to 1 for group sectorization)).
												
	Element 
ID	Length	Sectorization 
Type	Period	Omni	Sector 
ID	Number of Groups	GrpID	...	GrpID	Sector Duration	Reserved	
Bits:	8	8	1	6	1	3	4	6		6	6	<8	
Figure 8-401cv—	Sector Operation element (Sectorization Type is group sectorization)	

The Element ID has one octet length and specifies the corresponding value of the Sectorization Operation element specified in Table 8-55 (Element IDs). 
The Length field is one octet length specifies the length of Sectorization Operation element in octets
The Sectorization Type is 1 bit length and specifies the type of sectorization. When the Sectorization Type is set to 0, it indicates group sectorization operation. Note that the Sectorization Type can be set to 0 only when the AP Sectorized Beam-Capable setting is either 2 or 3.  
The Period field has 6 bit length and specifies the time interval expressed in time units equal to 10 milliseconds each until the next transmission of the same Sector ID
The Omni bit indicates if the present transmission is sectorized or Omni.
The Sector ID is 3 bit length and identifies the ID of the active sector.
The Number of Groups is 4 bit length and indicates the number of group IDs following this field.
The GrpID has 6 bit length and identifies the group of stations that are allowed to transmit during this sector interval. 
The GrpID 0 stations are allowed to transmit within a beacon interval regardless of whether it is a sectorized beacon interval or not.
The Sector Duration field has 6 bits, it indicates the duration of the current sector transmissions and it is measured in 10 milliseconds time units.
Sector Operation element may be provided in Association Response when dot11S1GSectorization-Activated is true and it indicates the GrpID allocated to that station to be used during for the sectorization purpose, the type of sectorization method,  the value of the Period duration, and the Sector Duration if all the sector durations are equal. If the Sector Duration (the sector time duration) is not equal for all sectors the Sector Duration value provided at the association time has zero value.  The values of Sector ID and Omni are omitted by the station in the Association Response message. By default all the stations consider themselves in GrpID zero unless is specified otherwise via the Association Response. This way all the stations can transmit at any time before their association. It is expected that during the association, stations receive a non-zero GrpID, which will restrict their activity to a particular sector interval or during Omni time interval. The AP may allow some stations to have the group zero even after association, for instance public safety stations or some high priority sensors.
The Sector Operation element in the Beacon will provide information related to the type of sectorization operation, indication if the Beacon is sectorized or not, the Sector ID the GrpID that identifies the group allowed transmitting during the currenct sector duration and respectively the duration of this sector. A station that receives a Beacon frame that includes a Sector Operation element determines if the received beacon is sectorized or Omni. If the received Beacon is Omni the stations are allowed to transmit in all geographical sectors provided that their group ID is group zero or it is listed in Sector Operation element. If the received Beacon is sectorized, the stations with group zero from any sector are allowed to transmit and the stations that receive the sectorized beacon and have the GrpID listed in the Sector Operation element are allowed to transmit during the current sector duration. A beacon that not carries a Sector Operation element does not impose any sectorization restriction on the receiving stations.
When the Sectorization Type is TXOP-based sectorization operation the element is presented in Figure 8-401cw (Sectorization Operation Element (Sectorization Type is set to 1 for  TXOP-based sectorization operation)).

	Element 
ID	Length	Sectorization 
Type	Periodic Training Indicator	Training 
Period	Remaining 
Beacon Interval	Reserved	
Bits:	8	8	1	1	6	6	2	
Figure 8-401cw—	Sector Operation Element (Sectorization Type is TXOP-based sectorization Operation)	

The Sectorization Type field is set to 1 to indicate TXOP-based sectorization operation. Note that the Sectorization Type can be set to 1 only when the AP Sectorized Beam-Capable setting is 1 or 3.  

The Periodic Training Indicator is set to 1 to indicate periodic sector training is conducted by the AP and stations may perform Sector training. The Periodic Training Indicator is set to 0 to indicate periodic sector training is not conducted by the AP.

The Training Period field is set to the number of beacon Intervals in which the AP repeats the Sector Training.

The Remaining Beacon Interval field is set to the remaining beacon intervals before the next Sector Training commences. A value of 0 indicates the sector training is conducted in the current beacon interval.

8.4.2.170k.2 	S1G Capabilities info field
The structure of the S1G Capabilities Info field is defined in Figure 8-401dg (S1G Capabilities Info field).
	B0	B1	B2	B3	B4	B5	B6	B7	
	Uplink 
Synch 
Capable	Dynamic
AID	BAT
Support	TIM ADE
Support	Non-TIM
Support	TWT
Support	STA 
Type
Support	
Bits:	1	1	1	1	1	1	2	

	B0	B1  B2	B3  B7	
	STA Sectorized Beam-Capable	AP Sectorized Beam-Capable	Reserved	
Bits:	1	2	5	
Figure 8-401dg—	S1G Capabilities Info field	

The subfields of the S1G Capabilities Info field are defined in Table 8-191d (Subfields of the S1G Capabilities Info field).

Table 8-191d—	Subfields of the S1G Capabilities Info field	
Subfield	Definition	Encoding	
Uplink Synch Capable	If sent by an AP STA, this subfield indicates support for synch frame transmission for uplink.

If sent by a non-AP STA, this subfield indicates request for synch frame transmission for uplink.

(see 9.32h.1 (Synch frame transmission procedure for uplink traffic) 	If sent by an AP STA: 
Set to 0 if not supported.
Set to 1 if supported.

If sent by a non-AP STA:
Set to 0 if not requested.
Set to 1 if requested.
 	
Dynamic AID	The STA sets the Dynamic AID field to 1 when dot11DynamicAIDActivated is true, and sets it to 0 otherwise. See 10.43b (Dynamic AID assignment operation).	Set to 1 if dot11DynamicAIDActivated is true.
Set to 0 otherwise.	
BAT Support	The BAT Support subfield indicates support for the use of the BAT frame in Block Agreements. When dot11BATImplemented is true, this field is set to 1 to indicate support for BAT frames as both originator and recipient.	Set to 1 if dot11BATImplemented is true.
Set to 0 otherwise.	
TIM ADE Support	This bit indicates support of the ADE mode of TIM bitmap encoding as described in 8.4.2.7.1.4 (ADE mode
).	Set to 1 if a STA supports the ADE mode of TIM bitmap encoding as described in 8.4.2.7.1.4 (ADE mode
).
Set to 0 otherwise.	
Non-TIM Support	This bit indicates support of Non-TIM mode.	For a non-AP STA:
Set to 0: the non-AP STA does not support Non-TIM mode, it needs TIM entry as in legacy PS mode
Set to 1: the non-AP STA supports Non-TIM mode and it does not need TIM entry when in Non-TIM mode

For an AP STA:
Set to 0: the AP STA does not support STA's Non-TIM mode
Set to 1: the AP STA supports STA's Non-TIM mode	
TWT Support	This bit indicates support of TWT described in 9.32f (Target Wake Time).	Set to 1 if dot11TWTOptionActive is true.
Set to 0 otherwise.	
STA Type Support	If sent by an AP STA, this subfield indicates STA types that are supported by the AP STA.

If sent by a non-AP STA, this subfield indicates STA types of the non-AP STA.	If sent by an AP STA:
Set to 0 if the AP STA supports both a Sensor type and a non-Sensor type STA.
Set to 1 if the AP STA supports only a Sensor type STA.
Set to 2 if the AP STA supports only a non-Sensor type STA.
3 is reserved.

If sent by a non-AP STA:
Set to 0 if the STA is both Sensor type and non-Sensor type STA.
Set to 1 if the STA is a Sensor type STA.
Set to 2 if the STA is a non-Sensor type STA.
3 is reserved.
	
STA Sectorized Beam Capable	indicate whether the STA supports the sectorized operation	Set to 0 if not supported,
Set to 1 if supported
When set to 1, a STA shall support both group sectorization and TXOP-based sectorization operation	
AP Sectorized Beam-Capable	indicate which type of sectorization operation is supported by AP	Set to 0 if sectorization operation is not supported,
Set to 1 if only TXOP-based sectorization operation is supported,
Set to 2 if only group sectorization operation is supported,
Set to 3 if both group sectorization and TXOP-based sectorization operations are supported,	

8.4.2.170l 	Sector Capabilities element
An S1G STA may declare that it can support sectorization by transmitting the Sector Capabilities element during the association. 
The Sector Capabilities element contains a number of fields that are used to advertise sector capabilities of an S1G STA including the Sectorized Beam Capable field, the Sectorization Type field, the Sector ID Feedback Capable field, the Total Sector Number field (0 to 7 represents the number of total sectors 1 to  8, respectively) and the Sector Training Capable field. 
Table 8-191e—	Sector Capabilities element format	
Subfield	Bits	Definition	Encoding	
Element ID	8			
Length	8			
Sectorization Beam Capable	1	indicate whether the AP or STA supports the sectorized operation	Set to 0 if not supported,
Set to 1 if supported
When set to 1, a STA shall support both group sectorization and TXOP-based sectorization	
Sectorization Type	2	indicate supports of which type of sectorization scheme	Set to 0 if only Type 0 Sectorization is supported,
Set to 1 if only Type 1 Sectorization is supported,
Set to 2 if both Type 0 Sectorization and Type 1 Sectorization are supported,
Set to 3, else	
Total Sector Number	3	Indicate the total number of sectors AP supports in the BSS	Set to 0 to 7 to represents number of sector 1 to 8, respectively	
Sector ID Feedback Capable	1	indicate whether the STA supports sector ID Feedback	Set to 0 if not supported,
Set to 1 if supported	
Sector Training Capable	1	Indicate whether the AP or STA supports sector training	Set to 0 if not supported,
Set to 1 if supported	
Reserved	TBD			

9.32m 	Sectorized beam operation
9.32m.1 	Introduction
The partition of the coverage area of a BSS into sectors, each containing a subset of stations, is called sectorization. This partitioning is generally achieved by the AP transmitting or receiving through a set of antennas or a set of synthesized antenna beams to cover different sectors of the BSS. The goal of the sectorization is to reduce medium contention or interference by the reduced number of stations within a sector. All stations associated with the BSS shall be covered by at least one sector. Stations are allowed to move from one sector to another sector. The entire BSS is assumed to be covered by the omni-directional beam or the omni-directional antenna of the AP.
9.32m.1.1 	Sector Capabilities Exchange
A sectorized beam-capable STA shall exchange its S1Gector Capabilities element with an AP. After the STA associated with a sectorized beam-capable AP, the AP can transmit through its sectorized beam to a sectorized beam-capable STA.
If dot11S1GSectorImplemented is true, an STA shall set the STA Ssectorized Bbeam-Ccapable field in the S1Gector Capabilities element to 1 in the Association Request Frame. The sectorized beam-capable STA shall support both group sectorization and TXOP-based sectorization operations. If dot11S1GSectorImplemented is false, the STA shall set the STA Ssectorized Bbeam-Ccapable field in the S1Gector Capabilities element to 0. 
If dot11S1GSectorImplemented is true, an AP shall set the AP Ssectorized Bbeam-Ccapable field in the S1Gector Capabilities element to 1 in the Association Response Frame. The AP also sets the Sectorization Type  field in accordance with whether it is supports group and/or TXOP-based sectorization operation in the Association Response Frameand indicates the total number of Sectors in the Sector Capabilities element. If dot11S1GSectorImplemented is false, the AP shall set the AP Ssectorized Bbeam-Ccapable field in the S1Gector Capabilities element to 0. 
An AP is a sectorized beam-capable AP if it sets the AP Ssectorized Bbeam-Ccapable field to 1, 2, or 3.
After the exchange of the S1Gector Capabilities element during the Association, a sectorized beam-capable AP supporting group sectorization operation shall transmit  Sector Operation element, with the Sectorization Type field sets to 0 to advertise its sectorization rotation cycle, omni-directional indicator, current sector ID, and allowable group IDs, and the sub-period for the current sector ID in the Sector Operation element in a sectorized beacon to start a beacon interval. A  sectorized beam-capable AP supporting of TXOP-based sectorization operation may transmit  Sector Operation element with the Sectorization Type field sets to 1 to advertise if periodic sector training is on or off, its training period, and the remaining beacon interval to periodic training in the Sector Operation element in a beacon.
A sectorized beam-capable AP may (re)assign a specific Sector ID to a sectorized beam-capable STA after the Association. A sectorized beam-capable STA may optionally send Sector ID feedback to its associated sectorized beam-capable AP. A sectorized beam-capable STA may optionally request Sector Training from its associated sectorized beam-capable AP. A sectorized beam-capable AP has at least two sectors.
Group Sectorization Operation
Group sectorization operation is based on the AP transmitting a sectorized beacon through a sectorized beam. A sectorized beacon is a beacon transmitted through a sectorized beam which covers a specific sector of the BSS. A BSS that employing a sectorization scheme is called a Sectorized BSS. The sectorization scheme of operation in a BSS is signaled by the presence of a Sector Operation element in beacon, probe response, and association response frames. In a Sectorized BSS, the AP may alternate the sectorized beacons and the non-sectorized (omni) beacons, for instance as showed in Figure 9-44e. Stations in different sectors may be allowed to transmit at the same time, that is more than one sector may be active at one moment. During the omni time interval all the stations may transmit regardless their geographical location. Sectorized beacons are transmitted to selected geographical areas to inform groups of stations that they are allowed to transmit during the sector intervals specified in the Sector Operation element. The AP with group sectorization operation receives transmissions from all sectors continuously. All beacons in a sectorized BSS carry the Sector Operation element. The one-bit omni field indicator within the Sector Operation element distinguishes between the sectorized beacon and the omni beacon transmission.  The Sector Operation element further specifies the type of sectorization scheme, the type of beacon (sectorized or omni), the complete rotation period of all (sectorized and omni) beacons, the sub-period for the current beacon, and the list of groups of stations that are allowed to transmit during the current beacon interval. In a Sectorized BSS with group sectorization operation, each station is allocated a group ID related to the sectorization operation. Stations that have group ID zero are allowed to transmit in all beacon intervals. During a beacon interval, the stations which are Sectorized beam capable and with its group ID (GrpID) contained in the list of group IDs carried in the Sector Operation element are allowed to transmit within that beacon interval.  By default all stations have GrpID zero unless otherwise specified at the association. Because by default all stations belong to GrpID zero before association, all the stations can transmit at any time before their association. It is expected that during the association, stations receive a non-zero GrpID, which will restrict their activity to a particular sector interval and  Omni time interval. The AP may allow some stations to have the group zero even after association, for instance public safety stations or some high priority sensors. A station that receives a beacon in a Sectorized BSS shall verify if its group ID is contained in the group ID list of the Sector Operation element in the beacon if it intends to transmit within the beacon interval. A station that has a non-zero group ID, which is not listed in the Sector Operation element of the beacon it is not allowed to transmit during that sector duration. In a BSS with group sectorization operation, a station maintains its allowable transmission periods as provided in last received Sector Operation.
	
Figure 9-44e—	Sectorized BSS operation	

9.32m.3 	TXOP-based Sectorization Operation
TXOP-based sectorization operation is based on the AP transmitting or receiving through the sectorized beam within a TXOP. At the beginning of a frame exchange, AP may start with the omni-directional beam transmission to establish a link with a station and to set up protection duration within a TXOP before switching to the sectorized beam transmission and reception. In different TXOPs, the AP may use different sectorized beams to communicate with different stations. A Sectorized beam capable AP supporting TXOP-based sectorization operation shall be able to transmit or receive through both the omni-direcitonal beam or the sectorized beams. In a BSS with TXOP-based sectorization operation, the AP shall signal the operation in beacons, probe response, association response, or other frames using the Sector Operation element. The operation of TXOP-based sectorization is defined by the following rules:
•		The switching between the omni-direcctional beam and the sectorization beam occurs during the interframe spacing between two consecutive packets or in-between the omni preamble and the beamformed preamble of a long preamble. 
•		When an AP is aware of the sector in which a station is in, AP may transmit to or receive from the station using the sectorized beam either during the scheduled transmission such as RAW or within a TXOP. Otherwise, AP transmits or receives through omni directional beam to a station. 
•		Once AP transmits to a station through a sectorized beam, it shall use the same sectorized beam to receive from the station within the same TXOP.
•		Once the AP switches to the sectorized beam transmission during an exchange, it shall continue with sectorized beam transmission with the same sectorized beam and the TXOP truncation is not allowed for the remainder of the protected duration. 
The forming of the sectorized beam(s) is beyond the scope of the standard.
In TXOP-based sectorization operation, during a frame exchange between the AP employing sectorized beam and a station, spatial re-use by OBSS APs or stations sharing the same wireless medium is allowed under the following rules: 
When the protection is set up by the AP's omni-directional beam transmission for a duration within a TXOP and if the spatially orthogonal (SO) condition is confirmed by an OBSS station or AP, the OBSS station or AP can reset its NAV to initiate a new spatially orthogonal exchange starting with a non-beamformed RTS/CTS.
The spatially orthogonal (SO) condition is satisfied if an OBSS station or AP which receives the omni-directional transmission but not the subsequent the sectorized beam transmission from the AP and not the transmission from the station involving in the frame exchange.
Four types of frame exchange sequences which can lead to the SO conditions by OBSS stations or APs are described.
a)		SO frame exchange sequence 1: The AP starts a frame exchange with the omni-directional beam to establish a link with a station and then uses the omni-preamble of a long preamble to set up the protection for the duration of the sectorized beam transmission and the switches to the sectorized beam transmission starting with the beamformed preamble of the long preamble. The AP continues with the sectorized beam transmission for the remainder of the protected duration. SO condition is confirmed by an OBSS station or AP which observes the omni-transmission of the AP but not the beamformed preamble of the AP and not the station's transmission. Note that an OBSS station or OBSS AP infers its spatial orthogonality with the AP by observing the first omni-beam packet and the omni-preamble of the long preamble but not observing the subsequent sectorized beam transmission and with the station by observing a gap of no transmission between the first omni-beam packet and the omni-preamble of the long preamble.
	
Figure 9-44f—	SO frame exchange sequence 1	

b)		SO frame exchange sequence 2: The AP starts a frame exchange with the omni-transmission of a packet to establish a link with a station and then uses the omni-transmission of a subsequent packet to set up the protection for the duration of the sectorized beam transmission and the switches to the sectorized beam transmission for the remainder of the protected duration. SO condition is confirmed by an OBSS station or AP which observes the omni-transmission of the AP but not the beamformed transmission of the AP and not the station's transmission. Note that an OBSS station or OBSS AP infers its spatial orthogonality with the AP by observing the omni-beam transmission but not observing the sectorized beam transmission and with the station by observing a gap of no transmission between the first two omni-beam packets by the AP.
	
Figure 9-44g—	SO frame exchange sequence 2	
b)		
c)		SO frame exchange sequence 3: The AP starts a frame exchange with an omni-RTS to solicit a CTS response from a station and then uses the omni-transmission to set up the protection for the duration of the sectorized beam transmission and the switches to the sectorized beam transmission for the remainder of the protected duration. SO condition is confirmed by an OBSS station or AP which observes the omni-transmission of the AP but not the beamformed transmission of the AP and not the station's transmission. Note that in the first diagram in Figure 9-44h (SO frame exchange sequence 3), an OBSS station or OBSS AP infers its spatial orthogonality with the AP by observing the omni RTS and omni-preamble of the long preamble but not the subsequent sectorized beam transmission and with the station by observing a gap of no transmission between the omni RTS and the omni-preamble of the long preamble. Note that in the second diagram in Figure 9-44h (SO frame exchange sequence 3), an OBSS station or OBSS AP infers its spatial orthogonality with the AP by observing the omni-RTS and the omni-beam short packet transmission but not observing the subsequent sectorized beam transmission and with the station by observing a gap of no transmission between the omni-RTS and the omni-beam short packets by the AP.
	
Figure 9-44h—	SO frame exchange sequence 3	
c)		
d)		SO frame exchange sequence 4: A station starts with the omni-directional beam to establish a link with the AP. AP uses omni-transmission to set up the protection for the duration of the sectorized beam transmission and the switches to the sectorized beam transmission. The AP continues with the sectorized beam transmission for the remainder of the protected duration. SO condition is confirmed by an OBSS station or AP which observes the omni-transmission of the AP but not the beamformed transmission of the AP and not the station's transmission. Note that in the first diagram in Figure 9-44i (SO frame exchange sequence 4), an OBSS station or OBSS AP infers its spatial orthogonality with the AP by observing the omni-preamble of the long preamble but not the subsequent sectorized beam transmission and with the station by observing a gap of no transmission before the AP response to PS-Poll or trigger frame from the station. Note that in the second diagram in Figure 9-44i (SO frame exchange sequence 4), an OBSS station or OBSS AP infers its spatial orthogonality with the AP by observing the first omni-beam short packet but not observing the subsequent sectorized beam transmission and with the station by observing a gap of no transmission before the first omni-beam short packets by the AP.
	
Figure 9-44i—	SO frame exchange sequence 4	
d)		
To facilitate the detection of the spatially orthogonal conditions by OBSS stations or OBSS APs, the short CTS NDP may be transmitted preceding the SO frame exchange. If the Early Sector Indicator in the CTS frame is set to 1, it indicates that the NDP CTS frame is followed by the sectorized beam frame exchange.  Setting the early sector indicator to 1 also indicates to the OBSS STAs that it can cancel its NAV setting if the Spatially Orthogonal conditions are subsequently met. Hence, if the early sector indicator is set to 0, OBSS STA need not check for spatially orthogonal conditions. Figure 9-44j (CTS-to-self preceding SO frame exchange sequence) illustrates the frame exchange preceded by CTS-to-self using CTS NDP.
	
Figure 9-44j—	CTS-to-self preceding SO frame exchange sequence 	

9.32m.4 	Sector training operation
9.32m.4.1 	Introduction
The sector training is one way to help the stations to determine the best sectors to communicate with the AP. Sector training requires the AP to transmit training NDPs over all sectors. The best sector might be chosen by a station based on instantaneous or averaged CSI. The specific method of choosing the sector is beyond the scope of this standard. The results of the sector training may be fed-back by the stations to the AP using Sector ID feedback frame. These training NDPs shall be transmitted consecutively and should be sent within a single TXOP. The training information is exchanged using the HT variant Control field. The sector training supports up to eight sectors. The AP may use other methods to determine the station's best sector.
9.32m.4.2 	Procedure
In the sector training, the AP sends a sector training announcement followed by a series of NDP sector training frames separated by SIFS. 
In TXOP-based sectorization operation, the sector training may occur periodically with the training period and the beacon interval in which the training occurs as indicated in Sector Operation element (TXOP-based), in response to a request from a STA, or initiated by the AP. The stations may perform the sector training by receiving the training NDPs from AP. In the case that the AP receives the sector training request from a station, the AP shall initiate a sector training. AP supporting TXOP-based Sectorization shall support sector training and sector training request. In the Sector Operation element (TXOP-based) (see 8.4.2.170l), which is transmitted in beacon, probe response, or association response, the AP indicates in which beacon interval and in how many beacon intervals a periodic sector training occurs. The total number of sectors is signalled during the AP capability exchange.
In group sectorization operation, a STA can basically find its best sector ID by listening to all the sectorized beacons. The Sector Operation element (group) carried in the sectorized beacon provides the sectorized beacons rotation period, sector ID, the sub-period of the current sector and the group IDs of the groups of STAs which are allowed to transmit within the current beacon interval. The sector training may also be used for STAs which support Sector Training Capable to reduce time for sector discovery and allow STAs which don't listen to all the sectorized beacons for its power saving. 
When a station joins a BSS with sectorization, it shall indicate whether it supports Sector ID Feedback Capable and Sector Training Capable during the Sector Capabilities exchange (see 8.4.2.170l (S1Gector Capabilities element)). The station may use the Sector ID feedback frame (see 8.5.23.4a (VHT Sector ID Feedback frame format)) to signal to the AP which sector is the best sector found. 
The station may request Sector Training from AP by using the HT Variant Control field if it is capable of sector training request. By setting the MAI=14 in the Link Adaptation Control subfield of the HT Variant Control field, the station indicates HT variant control field is used for signaling Sector Training (or Antenna Selection) information. The Sector training (or sector training resumption) is requested by a station when the ASELC subfield is set to 1 and the ASEL Data subfield with values in the range of 1 to 15, being the number of the first NDP training frames to be transmitted when the command is Sector Training Resumption, where 0 corresponds to the first training frame in the Sector Training Request. When the NDP Announcement field is also set to 1, it indicates training NDP frames to follow with two consecutive training NDP frames separated by SIFS.
The frame exchange sequence for sector training is shown in Figure 9-44k (Sector training), where the AP transmits training NDP frames, and the STA provides Sector ID feedback. The frame exchange comprises the following steps:
a)			(Optional) A station may initiate the sector training by sending a +HTC frame with the ASELC set to 1 for sector training request.
b)			The AP sends out consecutive training NDPs separated by SIFS in a TXOP of which it is the TXOP holder with no ACK over different sectorized beams. NDP CTS frames (8.3.4a.1.1), with NDP MAC Frame Type=3, are used in sector training. Each training NDP is transmitted over one sector beam. The first training NDP frame shall be preceded by a +HTC frame with NDP announcement subfield set to 1. The positions of the training NDP frames correspond to the sector IDs of the sectorized beams, in ascending order starting with Sector ID =0. 
c)			The station(s) may perform training by estimating the received signal quality corresponding to each training NDP.
d)			The station(s) engages in the training by receiving the sector training frames may respond with a selected sector ID using the sector ID feedback frame in a subsequent TXOP or during Sector Report RAW which may be indicated by beacon for fast sector discovery of multiple STAs (see 9.32m.4.4 (Fast Sector Discovery)).
	
Figure 9-44k—	Sector training	

If the AP receives a +HTC MPDU with the MAI subfield equal to 14, the ASEL Command subfield equal to Sector Training Request (=1), and the ASEL Data subfield equal to a zero to correspond to the command Sector Training, the station shall assume a total number of training NDPs that corresponds to the total number of sectors. If the AP receives a +HTC MPDU with the MAI subfield equal to 14, the ASEL Command subfield equal to Sector Training Request (=1), and the ASEL Data subfield equal nonzero value to correspond to the command Sector Training Resumption (a Resumption MPDU), the station shall assume the number of training frames that follow the Resumption MPDU is equal to the number of training NDPs from the total number of sectors minus the order number transmitted in the ASEL Data subfield of the Resumption MPDU.
AP may schedule sector sounding for multiple STAs by RAW in a beacon interval using the RAW Parameter Set element with the Sounding RAW Indication set to 1 (see 8.4.2.170b (RPS element)). During the Sounding RAW, non-AP STAs are prohibited to transmit but can elect to listen to the sector training for the entire RAW. This Sounding RAW may be scheduled in a periodic or impromptu way. 
The sector training within the Sounding RAW starts with a frame with NDP announcement indicator set to 1 in the HT control field and is followed in SIFS by a number of NDP CTS frames, each transmitted through different antenna sector starting with Sector ID equal to 0, and separated by SIFS. The Sounding RAW indication sub-field set to 0 indicates no sector sounding is performed within the RAW. 

9.32m.4.3 	Sector ID feedback
A station may optionally use a VHT action frame (see 8.5.23.4a) for (solicited and unsolicited) Sector ID feedback.
9.32m.4.4 	Fast Sector Discovery
When multiple STAs report their Sector ID feedback frames to AP, Sector ID feedback frames may be protected by Sector Report RAW indicated in the beacon (signaling TBD) to avoid contentions with others. The Sector Report RAW may be assigned after the Sounding RAW for fast sector discovery of multiple STAs.