trigger frame是802.11ax中新引入的一种帧格式。它属于control type, subtype是2。其用来实现OFDMA和MU-MIMO的UL。
trigger 本身又分为7种，在payload的最开始用4个bits指定:
Basic
Beamforming Report Poll
MU-BAR
MU-RTS
Buffer Status Report Poll
GCR MU-BAR
Bandwidth Query Report Poll
trigger 的payload分为user-common和user-specific部分。
一个trigger frame的详细格式如下（payload）：
user-common部分
filed: trigger type UL length More Trigger(TF) CS required
length: 4 12 1 1
value:
meaning: - set the value of L-SIG length of HE TB PPDU more triggers following user respond whether check ED/NAV
(continued)
filed: UL BW GI & LTF type MU MIMO LTF mode
length: 2 2 1
value:
meaning: set BW in HE-SIG-A of HE TB PPDU - 0: single stream pilots 1: masked LTF sequence of each spatial stream
(continued)
filed: number of HE LTF symbols and midamble priodicity UL STBC LDPC extra symbol segment
length: 3 1 1
value:
meaning:
(continued)
filed: AP tx power UL packet extension UL spatial reuse
length: 6 3 16
value: (0-60 --> -20-40 dBm w/ 1dBm step)
meaning: per 20MHz Bandwidth first 2 bits: pre-FEC padding factor, the 3rd bit: indicate PE-Disambiguity set Spatial reuse field of HE-SIG-A filed of TB PPDU
(continued)
filed: Doppler UL HE-SIG-A2 reserved reserved
length: 1 9 1
value:
meaning: indicate a higher doppler mode transmission set HE-SIG-A2 resered bits in TB PPDU
(continued)
( present only when GCR MU_BAR)
filed: BA control BA information
length: - -
value: - -
meaning:
user-specific 部分:
filed: ADI12 RU Allocation UL Fec Coding Type
length: 12 8 1
value: 0/1
meaning: 0- BCC 1- LDPC
(continued)
filed: UL MCS UL DCM SS Allocation
length: 4 1 6
value:
meaning: Spatial Stream Allocation(3 bits- starting spatial stream 3bits-spatial stream number)
(continued)
filed: UL Target RSSI Reserved
length: 7 1
value:
meaning: 0-90 -->-110--20dBm w/ 1dBm step, 127 --> max tx power allowed for the assigned MCS
(continued)
(only when basic trigger type)
filed: MPDU MU Spacing Factor TID Aggregation Limit AC Preference Level Preferred AC
length: - -
value:
meaning: the value by which the minimum MPDU start spacing is multiplied maximum number of TIDs that can be aggregated by a STA in a multi-TID A-MPDU in HE TB PPDU w/ Preferred AC? preferred AC or higher priorities recommended within a multi-TID A-MPDU in HE TB PPDU
(continued)
(only when MU-BAR trigger type)
filed: BA control BA information
length: - -
value:
meaning:
(continued)
(only when Beamforming Report Poll trigger type)
filed: Feedback Segment Retransmission Bitmap
length: -
value:
meaning: request feedback segments of an HE Compressed Beamforming report