1. Osama Aboul-Magd Huawei Technologies, Canada
IEEE ax – An Overview
Osama Aboul-Magd
Huawei Technologies, Canada

2. Background
In mid 2012 discussions in IEEE WG focused on the evolution of Wi- Fi to meet new use cases other than those related to consumers and enterprises.
The discussion was initiated by network providers motivated by the increased volumes of data offloading
cellular-offload.ppt
wlan-celllular-offload.pptx
Additionally IEEE ac was in sponsor ballot and close to be published.
Work on IEEE ac started in May 2007 just on time for iPhone announcement.

3. Evolution of Use Cases
IEEE ac was designed for the traditional Wi-Fi application.
Consumer market with emphasize on Internet access.
Enterprise application, e.g. an office building or a university with focus on connectivity.
IEEE ac design focus was on achieving higher aggregate throughput
Wider Channels (80 and 160 MHz)
DL MU MIMO
Higher order MCS (256 QAM)

4. New Use Cases
The Wi-Fi landscape has been rapidly changing – more devices and bandwidth demanding applications
Video Traffic is becoming Dominate
Hotspots and Data offloading
Multiple Interfering Devices
(dense deployment)

5. The IEEE ax Scope
This amendment defines standardized modifications to both the IEEE physical layers (PHY) and the IEEE Medium Access Control layer (MAC) that enable at least one mode of operation capable of supporting at least four times improvement in the average throughput per station (measured at the MAC data service access point) in a dense deployment scenario, while maintaining or improving the power efficiency per station.
This amendment defines operations in frequency bands between 1 GHz and 6 GHz. The new amendment shall enable backward compatibility and coexistence with legacy IEEE devices operating in the same band.

6. The IEEE ax Scope
This amendment defines standardized modifications to both the IEEE physical layers (PHY) and the IEEE Medium Access Control layer (MAC) that enable at least one mode of operation capable of supporting at least four times improvement in the average throughput per station (measured at the MAC data service access point) in a dense deployment scenario, while maintaining or improving the power efficiency per station.
This amendment defines operations in frequency bands between 1 GHz and GHz. The new amendment shall enable backward compatibility and coexistence with legacy IEEE devices operating in the same band.
In December 2017 the IEEE-SA NesCom approved ax PAR Modification to include operation in the 6 GHz band

7. Implications
Scenarios with dense deployments are the main focus of the new amendment.
Simulation Scenarios are developed to support dense environment: scenarios.docx
Focus is on per-station performance improvement rather than aggregate throughput.
The new amendment focuses on 2.4 GHz, 5 GHz, and 6 GHz bands
Improving user experience in traditional WLAN bands.
Backward compatibility is still a strong requirement.
Operation in the 6 GHz band added with focus on discovery

8. Timeline RevCom SG Draft & Formation Draft Draft D1.0 Publication D3.0
1/13
1/14
1/15
1/16
1/17
1/18
1/19
1/20
Sponsor
Ballot
Draft
D2.0
Draft
D4.0 TG
Formation

9. IEEE 802.11ax Main Features – A Quick Summary
The use of Orthogonal Frequency Division Multiple Access (OFDMA)
Allows the multiplexing of multiple users in the frequency domain.
A departure from the use of the OFDM where all resources are assigned to a single user as in previous IEEE amendments.
Support of OFDMA is both for the Uplink (UL) and the Downlink (DL)
Supporting Triggered UL MU MIMO
DL MU MIMO support is already in IEEE ac.
Allows multiplexing of multiple users in the spatial domain
The use of 256 FFT (20 MHz Channel) for the data portion of the ax PPDU.
A departure from the 64 FFT used in previous IEEE amendments.
Pre-defined resource unit (RU) sizes
Four frame formats
Allows Spatial Reuse
MCS 10 and MCS 11 introducing 1024 QAM

10. A Quick Summary of Previous Amendments (A/N/AC) – Frame Formats
STF: Short Training Field
LTF: Long Training Field
SIG: Signal Field
Legacy Preamble
“A”
STF
STF
LTF
LTF
SIG
Data
L-Preamble is included for backward compatibility
SU-MIMO: As many LTF fields as number of Antennas
Auto-Detection is achieved by changing the polarity of the signal
“N”
L-Preamble
LTF-1
LTF-2
LTF-n
Data
SIG 1
SIG 2
L-Preamble is included for backward compatibility
SU-MIMO and DL MU-MIMO
SIG-B includes per user signal parameters
Auto-Auto-Detection is achieved by changing the polarity of the signal
“AC”
L-Preamble
Data
SIG-A 1
SIG-A 2
LTF-1
LTF-n
SIG-B

11. IEEE 802.11ax Main PHY FeaturesRU
General Frame
Format
L-Preamble
RL-SIG
HE-SIG-A
HE-SIG-B …
HE-Data
HE-STF
HE-LTF
HE-LTF
As in IEEE n/ac, HEW PPDU starts with a legacy preamble for backward compatibility. Legacy preamble is duplicated on every 20 MHz channel.
L-Preamble consists of L-STF, L-LTF, and L-SIG.
Repeated L-SIG (RL-SIG) is included for auto-detection.
HE-SIG-A is two-symbol long and is duplicated on every 20 MHz channel. HE-SIG-A is available in every PPDU.
HE-SIG-B is of variable length. It includes resource allocation information. HE-SIG-B is only present in the MU PPDU.
HE-Data uses DFT period of 12.8 msec and subcarrier spacing of KHz.
Tone plan allowing 26-tone, 52-tone, 106-tone, 242-tone for OFDMA. 484-tone and 996-tone for non-OFDMA cases.
Mandatory support for LDPC coding in HE PPDU Data field for allocation sizes of 484 tones, 996 tones and 996*2 tones.
1024-QAM is an optional feature for SU and MU using resource units equal to or larger than 242 tones in 11ax.
Dual sub-carrier modulation (DCM) is an optional modulation scheme for the HE-SIG-B and Data fields. DCM is only applied to BPSK, QPSK and 16-QAM modulations

12. 802.11ax: A Quick Score Card 802.11ax 802.11ac 802.11n
Channel Bandwidth
20, 40, 80, and 160 MHz
20, 40 MHz
Same Channel Bandwidth as in Wi-Fi 5
Waveform
OFDMA
OFDM
Achieve multiplexing gain and per User focus
Band
2.4, 5, and 6 GHz
5 GHz
2.4 and 5 GHz
Make use of the large spectrum available in the 6 GHz band
Number of Antennas 8 4
Same as in Wi-Fi 5
Advanced Power Save
Target Wake up Time (TWT) No
Efficient support of devices with power constraints
Aggregate Data Rate
9.6 Gbps
6.9 Gbps
600 Mbps
Modest rate increase compared to Wi-Fi 5
User Experience
4x improvement ?
Focus is on user experience and per user throughput.
20 MHz-only operation
Yes
Allows support of IoT applications and eventual replacement of Wi-Fi 4
Spatial Reuse
Efficient use of available spectrum
MU MIMO
DL MU MIMO and Triggered UL MIMO
DL MU MIMO
Access point schedules users based on their traffic requirements, e.g. buffer size and delay requirements.
Outdoor
Improved support
Improved outdoor performance for open stadiums and hot spots.
QAM
1024 QAM
256 QAM
64 QAM
Improved throughput by packing more signals in the same space.

13. Frame Format (I) – Single User (SU) Frame Format
L-LTF
SIG-A 1
SIG-A 2
L-STF
L-STF
L-LTF
L-SIG
R-SIG
STF
LTF
LTF
Data
Bit
Field Name B0
Frame format (SU PPDU or Trigger-based PPDU)
B19-B20
Bandwidth
B11-B12
Pre-FEC padding Factor B1
Beam Change
B21-B22
GI+LTF Size
B13
BE Disambiguaty B2
UL/DL
B23-B25
Nsts
B14
Reserved
B3-B6
MCS
B0-B6
TXOP Duration
B15
Doppler B7
DCM
Coding
B16-B19
CRC
B8-B13
BSS Color B8
LDPC Extra Symbol
B20-B25
Tail
reserved B9
STBC
B15-B18
Spatial Reuse
B10
TxBF
SIG-A 1
And
SIG-A2

14. Frame Format (II) – SU Extended Range
L-LTF
SIG-A 1
SIG-A 2
SIG-A 2
L-STF
L-STF
L-LTF
L-SIG
R-SIG
SIG-A 1
STF
LTF
LTF
Data
Repeated SIG-A
Originally designed for out-door environment to increase SIG-A reliability
Results have shown a gain of 6 dbs allowing the signal to reach further
The SIG-A contents are the same as the SU Frame format

15. Frame Format (III)- Multi-User (MU) Frame Format
L-LTF
L-LTF
L-SIG
SIG-A 1
SIG-A 2
L-STF
R-SIG
SIG-B
STF
LTF
LTF
Data
Bit
Field Name B0
UL/DL
B22
SIG-B Compression
B15
PE Disambiguity
B1-B3
SIG-B MCS
B23-B24
GI+LTF Size
B16-B19
CRC B4
SIG-B DCM
B25
Doppler
B20-B25
Tail
B5-B10
BSS Color
B0-B6
TXOP Duration B7
DCM
B8-B10
Number of LTF Symbols
B11-B14
Spatial Reuse
B11
LDPC Extra Symbol
B15-B17
Bandwidth
B12
STBC
B18-B21
Number of Sig-B symbols or MU-MIMO Users
B13-B14
Pre-FEC padding Factor
SIG-A 1
And
SIG-A2

16. Frame Format (VI) – Trigger-Based Frame Format
Bit
Field Name B0
Frame format (SU PPDU or Trigger-based PPDU)
B0-B6
TXOP Duration
B1-B6
BSS Color
B7-B15
Reserved
B7-B10
Spatial Reuse 1
B16-B19
CRC
B11-B14
Spatial Reuse 2
B20-B25
Tail
B15-B18
Spatial Reuse 3
B19-B22
Spatial Reuse 4
B23
reserved
B24-B25
Bandwidth
SIG-A 1
And
SIG-A2

17. OFDMA Tone Plan – 20 MHz, 40 MHz, and 80 MHz Channel7
D C 26 52 DC
102+4 pilots 1 13
5 Edge
5 Edge
6 Edge
6 Edge
HE20 with 7DC for OFDMA
12 Edge
242 26
102+4 52 1 2 5 DC
242 26
102+4 52 1 2
11 Edge 5
D C
12 Edge
11 Edge
12 Edge 5 DC
11 Edge
12 Edge 5
D C
11 Edge
12 Edge
484 usable tones +5 DC
11 Edge
20 MHz Tone Plan
40 MHz Tone Plan
12 Edge
242 26 52
102+4 2 1 13 7 DC 13
242 26 52
102+4 2 1
11 Edge
12 Edge 13 7 DC 13
11 Edge
12 Edge 13 7 DC 13
11 Edge
12 Edge 13 7 DC 13
11 Edge
12 Edge
996 usable tones +5 DC
11 Edge
80 MHz Tone Plan

18. Downlink (DL) Procedure
STA-1
STA-2 H
STA-3 AP
STA-4
BA STA-1
STA
BA STA-2
Time
BA STA-3
BA STA-4
ACKs from different stations are transmitted using trigger-based PPDU format
Unlike DL MU MIMO in ac where different stations are polled to transmit their ACKs to the AP.
ACK resources are indicated in either a Trigger frame or Resource Allocation A-Control (Aggregate Control) field.

19. Uplink (UL) Procedure
BA STA-1
BA STA-2
BA STA-3 AP
Trigger
BA STA-4
STA-1
Time
STA
STA-2 H
STA-3
STA-4
AP initiates UL transmissions by mean of a trigger frame
Trigger frame includes information related to each STA participating in the UL transmissions.
Stations responds with a triggered-based PPDU SIFS time units after the reception of the trigger frame.
The AP may use the multi-STA block ACK to acknowledge UL transmissions from multiple stations.
The AP may send the
Padding

20. Uplink (UL) Procedure AP
Trigger
Multi-STA BA
STA-1
Time
STA
STA-2 H
STA-3
STA-4
AP initiates UL transmissions by mean of a trigger frame
Trigger frame includes information related to each STA participating in the UL transmissions.
Stations responds with a triggered-based PPDU SIFS time units after the reception of the trigger frame.
The AP may use the multi-STA block ACK to acknowledge UL transmissions from multiple stations.
The AP may send the
Padding

21. Scheduled Trigger Frames
The main power save mechanism in ax
Makes use of the Target Wake Time (TWT) to establish trigger frame schedule with the AP
TWT was introduced in ah amendment to address requirements of low-power devices, e.g. sensors
Two TWT flavors are introduced:
Individual TWT
Broadcast TWT

22. Trigger Frame Variants
Trigger Dependent Common Info
Trigger Dependent User Info
Basic Trigger
Not present
Beamforming Report Poll
Not Present
MU-BAR Variant
MU-RTS Variant
BSRP Variant
GCR MU-BAR Variant
BQRP Variant
MPDU MU
Spacing
TID Aggregation
Limit
AC Preference
Level
Preferred AC
Feedback Segment
Retransmission Bitmap
BAR Control
BAR Information
BAR Control
BAR Information

23. Spatial Reuse: The Concept
OBSS
OBSS
CCA idle A
CCA busy
Intra-BSS
CCA busy->idle;
duration decoding correctly
OBSS B
CCA busy->idle;
duration decoding error
Pre NAV rule: A station updates its NAV based on the Duration field in any valid frame.
Setting OBSS PD level to -72dBm, an intra-BSS device A located in the OBSS yellow ring with receiving OBSS signal strength from (-82, -72)dBm can change from CCA busy to idle.
However, if device A decodes the duration field correctly from OBSS signal, device A can’t transmit for spatial reuse due to the higher NAV value, following 11ac NAV rule.
When a STA uses its OBSS PD level(e.g. -72dBm) for OBSS signal, it should not update its NAV when receiving a valid duration field from OBSS signal, if the measured RSSI of OBSS signal is less than the OBSS PD level.
A station will need to maintain two NAV timers.

24. Spatial Reuse – BSS Color and 2 NAV Timers
BSS color in SIG-A field allows devices to differentiate between Intra- BSS frames and Inter-BSS frames.
An IEEE ax station maintains two NAV timers (Network Access Vector): Basic NAV and Intra-BSS NAV
Pre IEEE devices maintain a single NAV. The value of the NAV is updated according to the Duration/ID field in the Frame Control.
The medium is idle when the two NAV timers are zero.
Two types of Spatial Reuse are defined:
OBSS PD-based Spatial Reuse
Spatial Reuse Parameters

25. OBSS_PD Adjustment
If using OBSS PD-based spatial reuse, an HE STA shall maintain an OBSS PD level and may adjust this OBSS PD level in conjunction with its transmit power and this adjustment shall be made in accordance with Equation: 

26. CCA Sensitivity
The ax hasn’t changed the CCA levels on the primary 20 MHz

27. CCA Sensitivity
The ax accounts for the introduction of the new parameter OBSS_Pdlevel
Any signal within the any 20 MHz subchannel of secondary 20 MHz, secondary 40 MHz or second-ary 80 MHz at or above a threshold of –62 dBm within a period of aCCATime after the signal arrives at the receiver's antenna(s); then the PHY shall not issue PHY-CCA.indication(IDLE) primitive while the threshold continues to be exceeded.
An 80 MHz non-HT duplicate, VHT PPDU or HE PPDU detected in the secondary 80 MHz channel at or above max(–69 dBm, OBSS_PDlevel + 6 dB) with > 90% probability within a period aCCAMidTime (see (HE PHY)).
A 40 MHz non-HT duplicate, HT_MF, HT_GF, VHT or HE PPDU detected in any 40 MHz sub-channel of the secondary 40 MHz or the secondary 80 MHz channel at or above max(–72 dBm, OBSS_PDlevel + 3 dB) with > 90% probability within a period aCCAMidTime.
A 20 MHz NON_HT, HT_MF, HT_GF, VHT, or HE PPDU detected in the any 20 MHz subchannel of secondary 20 MHz, secondary 40 MHz or secondary 80 MHz channel at or above max(–72 dBm, OBSS_PDlevel) with >90% probability within a period aCCAMidTime (see (HE PHY)). 

28. Operation in the 6 GHz Band- Channelization
U-NII-5
U-NII-6
U-NII-7
U-NII-8
5945
5965
5985
6005
6025
6045
6065
6085
6105
6125
6145
6165
6185
6205
6225
6245
6285
6305
6325
6345
6365
6385
6405
6425
6445
6465
6485
6505
6525
6545
6565
6585
6605
6625
6645
6665
6685
6705
6725
6745
6765
6785
6805
6825
6845
6865
6885
6905
6925
6945
6965
6985
7005
7025
7045
7065
7085
7105
7125
189
193
197
201
205
209
213
217
221
225
229
233
237
241
245
249
257
261
265
269
273
277
281
285
289
293
297
301
305
309
313
317
321
325
329
333
337
341
345
349
353
357
361
365
369
373
377
381
385
389
393
397
401
405
409
413
417
421
191
199
207
215
223
231
239
247
263
271
279
287
295
303
311
319
327
335
343
351
359
367
375
383
391
399
407
415
195
211
227
243
259
275
291
307
323
339
355
371
387
403
203
235
267
299
331
363
395
Starting frequency of 5940 MHz
Only 10 MHz of Guard band for U-NII-5
Challenging filter design
Channels can cross U-NII boundaries
In case U-NII-5 and 6 work under different regulatory rules
No 80 MHz channel in U-NII-6
Only one 40 MHz channel in U-NII-6
Center Frequency [MHz]
20 MHz Channels
40 MHz Channels
80 MHz Channels
160 MHz Channels

29. Operation in the 6 GHz
An HE STA indicated its capability to operate in the 6 GHz band
An HE AP operating in the 6 GHz band shall indicate support for at least 80 MHz channel width 
A STA shall not transmit an HT PPDU (802.11n) in the 6 GHz band. A STA shall not transmit a VHT PPDU (802.11ac) in the 6 GHz band. A STA shall not transmit a DSSS, HR/DSSS (802.11b), or ERP-OFDM (802.11g) PPDU in the 6 GHz band. 
An HE AP may transmit an HE SU beacon in the 6 GHz band. 
Rules are defined for passive and active scanning and out-of-band discovery (for APs in the 2.4 and 5 Ghz and collocated with AP in the 6 GHz).

30. Closing Notes
IEEE ax is the next PHY layer after the successful n and ac.
It is the first amendment to introduce OFDMA to wireless LAN.
IEEE ax adds UL MU MIMO
Allows power save based on scheduled trigger frames