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Gigabit Wireless LAN:
Enhancements in 802.11ac
Eldad Perahia, Ph.D., Intel Corporation,
Robert Stacey, Apple, [email protected]
Dec 2012
Outline• Introduction– History
– Usage models
– PAR
– Enhancements
– Channelization
• PHY– Waveform design
– Packet structure
– PHY Transmitter flow
– Downlink multi-user MIMO
– Very High Throughput (VHT) waveform Preamble
• MAC– Coexistence in wider channels
– Channel access in wider channels
– Dynamic bandwidth operation
– Aggregation
• DL MU-MIMO
2
Early History
• Very High Throughput Study Group (VHTSG)
– Began in May 2007 as a precursor to starting task
group, in which purpose and scope of task group were
defined
– Started initially to address Very High Throughput for <
6 GHz IMT-Advanced operation
– IMT-Advanced objective was dropped
– Focus for < 6 GHz shifted to enhancing 802.11n in 5
GHz band
– <6 GHz PAR approved in Sept 2008
3
Wi-Fi Alliance VHT Usage
Models [6]Category # Usage Model
1. Wireless Display 1a Desktop Storage & Display
1b Projection to TV or Projector in Conf Rom
1c In room Gaming
1d Streaming from Camcorder to Display
1e Broadcast TV Field Pick Up
1f Medical Imaging Surgical Procedure Support
2. Distribution of HDTV 2a Lightly compressed video streaming around home
2b Compr. video streaming in a room / t.o. home
2c Intra Large Vehicle (e.g. airplane) Applications
2d Wireless Networking for Small Office
2e Remote medical assistance
3. Rapid Upload / Download 3a Rapid Sync-n-Go file transfer
3b Picture by Picture viewing
3c Airplane docking
3d Movie Content Download to car
3e Police / Surveillance Car Upload
4. Backhaul 4a Multi-Media Mesh backhaul
4b Point to Point backhaul
5. Outdoor Campus / Auditorium 5a Video demos / telepresence in Auditorium
5b Public Safety Mesh
6. Manufacturing Floor 6a Manufacturing floor automation
4
Compressed Video Streaming
around a House
• Pre-Conditions:
• User has operational WLAN
network which includes a TV with
wireless capabilities, a DVR with
wireless capabilities, and an AP
associated with the WLAN that is
not in the same room as the game
machine and TV.
• Application:
• User can display the output of the
DVR wirelessly on the TV using a
video codec like Motion 2000 JPEG
that compresses video.
5
Rapid Sync-and-Go
• Pre-Conditions:
• User has WLAN connectivity
between a PC, PDA, cell phone, a
camcorder, and a camera.
• Application:
• User can sync movies to/from the
camcorder and transfer the picture
files. An MPEG4 video file of 1
GByte takes 8 seconds over a
single hop 1Gbps link. 200 jpeg
(picture) files of 10 Mbyte takes less
than 30 seconds over a 1Gbps
single hop link . Jitter and delay are
not critical. Instead, the key metric is
the user’s time spent to do a
transfer. Less than 1 minute is
acceptable. 1-5 minutes may be
acceptable. More than 5 minutes is
not acceptable.
6
Wireless I/O
• Pre-Conditions:
• User has operational WLAN network
for Internet access and general data
networking. The wireless network used
for storage and display may or may not
be part of the other operational WLAN
network.
E-Net
E-Net
Wireless Dock
Application:
User can wirelessly display the output of the
computer to monitor or TV using
uncompressed video.
User can wirelessly store data from a
computer to a harddrive. The data being
stored transfers at ~1Gbps, jitter is <
200msec, delay is <200msec, 10E-5 PER.
7
802.11ac Project Authorization
Request (PAR)• PAR requires that the amendment support
single link throughput of at least 500 Mbps
• 802.11ac must support multi-station throughput of at least 1 Gbps
• Operation in 2.4 GHz is excluded
• Must have backward compatibility and coexistence with legacy IEEE802.11 devices in the 5 GHz unlicensed band
8
Recent History• Task group started Nov 2008
• Task group documents
– Specification Framework
– Functional Requirements & Evaluation Methodology
– Amendment to 11n Channel Model
– Usage Models
• Draft 3.0 approved June 2012, will probably be the version
used for WFA certification
• Timeline going forward
– Initial Sponsor Ballot: planned for March 2013
– Recirculation Sponsor Ballot: planned for May 2013
– Final Working Group Approval: planned for November 2013
– RevCom & Standards Board Final Approval: planned for February
2014
9
Different Physical Layers
802.11, a, b, g, n, ac
802.11
802.11b
802.11a 802.11g 802.11n 802.11ac
Access Technology
DSSS DSSS/
CCK
OFDM OFDM SDM / OFDM
MU+SDM / OFDM
Data Rate(Mbps)
1, 2 Up to 11
Up to 54
Up to 54
Up to 600
Up to 6933
Frequency Band (GHz)
2.4 2.4 5 2.4 2.4 and 5 5
Channel Bandwidth (MHz)
22 22 20 22 20 and 40
20, 40, 80, 160
10
PHY Data Rate Improvement in
802.11
1
10
100
1000
10000
dot11 (2.4 GHz)
11b (2.4 GHz)
11a (5 GHz )/
11g (2.4
GHz)
11n (2.4/5 GHz)
11ac; 4ss (5 GHz)
11ac; 8ss (5 GHz)
20/25 MHz
40 MHz
80 MHz
160 MHz
11
New Features and Enhancements
Proposed for IEEE 802.11ac
• Wider bandwidth
– 80 MHz channel width
– 160 MHz channel width
– Non-contiguous 160 MHz (80 MHz + 80 MHz)
• Modulation, coding, and spatial streams
– 256 QAM, rate = 3/4
– 256 QAM, rate = 5/6
– Up to 8 streams
• Downlink Multi-User MIMO (DL MU-MIMO)
• Increased aggregate size limits
• Enhancement to coexistence mechanisms
12
Mandatory vs. Optional 802.11n
PHY Features
Basic MIMO/SDM
20 MHz; 64 QAM
rate 5/6; 56 tones
1, 2* spatial streams 2*, 3, 4 spatial streams
40 MHz, 114 tones
Transmit Beamforming
Convolutional Code Low Density Parity Check
Mandatory Optional
Space Time Block Code
½ Guard Interval
Mixed Format Preamble Green Field Preamble
Throughput
Enhancement
Interoperability
w/ Legacy
Robustness
Enhancement
*2 spatial streams mandatory for AP only
13
Modifications in 802.11ac to
802.11n Features• STBC
– only for 2x1, 4x2, 6x3, 8x4
– No 3x2 or 4x3 as in 11n
• LDPC
– Added block-interleaving of constellation symbols per stream, per
OFDM symbol
• Transmit Beamforming
– Only Explicit feedback, no implicit feedback
– Only Compressed-V feedback, no Uncompressed-V, no CSI
– Only NDP sounding, no staggered sounding
– No unequal modulation
14
Mandatory vs. Optional 802.11ac
PHY Features
Basic MIMO/SDM
20, 40, 80 MHz
1 spatial stream 2 - 8 spatial streams
160 MHz, 80+80 MHz
Transmit Beamforming
Convolutional Code Low Density Parity Check
Mandatory Optional
Space Time Block Code
½ GI, 256 QAM
VHT Preamble
Th
rou
gh
pu
t E
nh
an
cem
en
t
Interoperability
w/ Legacy
Robustness
Enhancement
DL MU-MIMO
15
Channelization for 20/40/80 MHz
• 40/80 MHz channelization
– Consists of two adjacent IEEE 20/40 MHz
channels
– Non-overlapping channelization
14
0
13
6
13
2
12
8
12
4
12
0
11
6
11
2
10
8
10
4
10
0
16
5
16
1
15
7
15
3
14
9
64
60
56
52
48
44
40
36IEEE channel #
20 MHz
40 MHz
80 MHz
5170
MHz
5330
MHz
5490
MHz
5710
MHz
5735
MHz
5835
MHz
14
416
Channelization for Contiguous
160 MHz• Apply the same rule as in 40 and 80 MHz channel
construction
– Consists of two adjacent IEEE 80 MHz channels
– Non-overlapping channelization
• Not necessary to come up with coexistence rules for partially overlapping channels
14
0
13
6
13
2
12
8
12
4
12
0
11
6
11
2
10
8
10
4
10
0
16
5
16
1
15
7
15
3
14
9
64
60
56
52
48
44
40
36IEEE channel #
20 MHz
40 MHz
80 MHz
5170
MHz
5330
MHz
5490
MHz
5710
MHz
5735
MHz
5835
MHz
160 MHz
14
417
Noncontiguous 160 MHz
(VHT80+80) BSS• Any two nonadjacent 80 MHz channels may be used in
setting up a noncontiguous 160 MHz (VHT80+80) BSS– Allows VHT80 STA to associate with the VHT80+80 BSS
– Allows contiguous-only devices to associate with the VHT80+80 BSS as a VHT80 STA
14
0
13
6
13
2
12
8
12
4
12
0
11
6
11
2
10
8
10
4
10
0
16
5
16
1
15
7
15
3
14
9
64
60
56
52
48
44
40
36IEEE channel #
20 MHz
40 MHz
80 MHz
5170
MHz
5330
MHz
5490
MHz
5710
MHz
5735
MHz
5835
MHz
Examples of
VHT80+80 BSS
Setup
14
418
80 MHz Sub-Carrier Design
• 14 Null tones: {-128, … -123, -1, 0, 1, 123, …
127}
• 242 Populated tones: {-122, … -2, 2, … 122}
– 8 Pilot tones: {-103, -75, -39, -11, 11, 39, 75, 103}
– 234 Data tones: {Populated tones} – {Pilot tones}
-128 127-122
-103 -39 -11
-2 2
11 39 75
122OFDM sub carrier number
103-75
19
PHY Transmitter Flow Overview:
Single User, 20-80 MHz
• Scrambler same as 11a/n
• BCC encoder /
puncturing same as 11a/n
• LDPC fully optional
• Spatial Mapping same as
11n
Interleaver
(for BCC)
Insert GI
and
Window
Analog
and RF
CSD
CSD
Str
ea
m P
ars
er
Constellation
mapper
ST
BC
Interleaver
(for BCC)
Constellation
mapper
IDFT
Sp
atia
l M
ap
pin
g
Insert GI
and
Window
Analog
and RFIDFT
Scra
mb
ler
En
co
de
r P
ars
er
append tail (for BCC),
encoding,
puncturing (for BCC)
append tail (for BCC),
encoding,
puncturing (for BCC)
A-MPDUAppend MAC
padding
Append PHY Padding:
0-7 bits
Prepend Service Field:
Scrambler seed, Reserved,
VHT-SIG-B CRC
20
160 MHz Sub-Carrier Design
28 Null tones: {-256, … -251,-129,-128, -127, -5,…-1,0,1… 5, 127, 128,129,251, … 255}
484 Populated tones: {-250, … -6, 6, … 250}
• 16 Pilot tones: {+/-231, +/-203, +/-167, +/-139, +/-117, +/-89, +/-53, +/-25}
• 468 Data tones: {Populated tones} – {Pilot tones}
-256 -250
-231 -167 -139
-130 -126
-117 -89 -53
-6
OFDM sub carrier number
-25-203
2556
25 89 117
126 130
139 167 203
250
23153
21
PHY Transmitter Flow Overview:
Single User, 160 MHz contiguous
– Code across 160 MHz, BCC interleaver per 80 MHz
– There may be 1 or more FEC encoders when BCC encoding is used
– When using LDPC, BCC interleavers not used
– When using BCC, the LDPC tone mappers not used
Interleaver
CSD
ST
BC
BCC
Interleaver
Sp
atia
l M
ap
pin
g
Constellation
mapper
Constellation
mapper
PH
Y P
ad
din
g
Scra
mb
ler
FE
C E
nco
de
r
Insert GI
and
Window
Analog
and RF
FE
C E
nco
de
r
En
co
de
r P
ars
er
Str
ea
m P
ars
er
FE
C E
nco
de
r
Se
gm
en
t
Pa
rse
r
IDFT
Se
gm
en
t
Pa
rse
r
LDPC tone
mapper
BCC
Interleaver
CSD
ST
BC
BCC
Interleaver
Sp
atia
l M
ap
pin
g
Constellation
mapper
Constellation
mapperIDFT
Insert GI
and
Window
Analog
and RF
LDPC tone
mapper
LDPC tone
mappter
512 pt
IDFT
234
subcarriers
22
PHY Transmitter Flow Overview:
Single User, 80+80 MHz non-contiguous
Interleaver
CSD
ST
BC
BCC
Interleaver
Sp
atia
l M
ap
pin
g
Constellation
mapper
Constellation
mapper
PH
Y P
ad
din
g
Scra
mb
ler
FE
C E
nco
de
rF
EC
En
co
de
r
En
co
de
r P
ars
er
Str
ea
m P
ars
er
FE
C E
nco
de
r
Se
gm
en
t
Pa
rse
r
Se
gm
en
t
Pa
rse
r
LDPC tone
mappter
BCC
Interleaver
CSD
ST
BC
BCC
Interleaver
Sp
atia
l M
ap
pin
g
Constellation
mapper
Constellation
mapper
LDPC tone
mappter
LDPC tone
mappter
Insert GI and
Window
Analog
and RFIDFT
Insert GI and
Window
Analog
and RFIDFT
Insert GI and
Window
Analog
and RFIDFT
Insert GI and
Window
Analog
and RFIDFT
256 pt
IDFT
234
subcarriers
For 80+80 MHz sub-carrier design, each frequency segment follows the 80 MHz
format
23
PPDU overview (SU)
• Illustrating 80 MHz bandwidth
• Parallel L-TFs, L-SIG, VHT-SIG-A, VHT-STF represents 20 MHz waveform replicated on each sub-channel
• MAC provides an A-MPDU that fills the frame to the last byte for each user
• L-SIG length and rate indicate PPDU duration (number of symbols)
• PHY Padding (0 – 7 bits)
• Tail after pad (in 11n, tail before pad)
L-TFs L-SIG VHT-SIG A
Service
Last Symbol
VHT A-MPDUPHY
PadTail
PPDU Duration (# of symbols)
MAC PadL-TFs L-SIG VHT-SIG A
L-TFs L-SIG VHT-SIG A
L-TFs L-SIG VHT-SIG A
VHT-
SIG B
VHT-STF
VHT-STF
VHT-STF
VHT-STF
VHT-LTFs
Freq
24
Preamble Overview
• Legacy format the same as 11a/n
• VHT-SIG-A replaces HT-SIG
• VHT-STF and VHT-LTF similar to HT-STF and HT-LTF
• New VHT-SIG-B
L-STF L-LTFL-
SIGVHT-SIG-A
VHT-
STF
VHT-
LTFData
VHT format PPDU
VHT-
LTF
8μs 8μs 8μs4μs 4μsVHT-LTFs
4μs per LTF
VHT-
SIG-B
4μs
L-STF L-LTFL-
SIGHT-SIG
HT-
STF
HT-
LTFData
HT mixed format PPDU
HT-
LTF
8μs 8μs 8μs4μs 4μsHT-LTFs
4μs per LTF
25
L-SIG
• Same number of subcarriers (data
and pilot) as 11n for 20 MHz and
40 MHz
• For 80MHz and 160MHz: same
number of subcarriers and
positions as 11a/n L-SIG in each
20 MHz subchannel
• Same rate, length, reserve, parity
and tail format
• As in 11n, 20 MHz waveform
replicated in each 20 MHz sub-
channel for 40, 80, and 160 MHz
• Major difference from 11n:
– Length field in L-SIG used to
convey number of symbols in
VHT packet
– No length field in VHT-SIG-A
– See next slides
26
L-SIG
Length Conveys Number of Symbols (1/2)
• Similar to 11n, use L-SIG spoof rate of 6 Mbps for 11ac packets
– 3 bytes / symbol
• Long GI packet
– 4 us / symbol
– Legacy spoof symbols = L-SIG length / 3 bytes per symbol
– VHT payload symbols = Legacy spoof symbols – VHT preamble symbols
VHT Payload
legacy spoof symbols = L-SIG length / 3 bytes per symbol
L
preamble
VHT
preamble
L-SIG spoof rate is fixed at 6 Mbps (3 bytes / symbol)
20 usec
VHT payload symbols = legacy spoof symbols VHT preamble symbols
27
L-SIG
Length Conveys Number of Symbols (2/2)
• Short GI packet
– 3.6 us / VHT symbol
– End of frame may not be aligned to a 4 us boundary
– Legacy devices using L-SIG may find the end of the
packet to occur up to 3.6 usec after the energy on the air
has disappeared
VHT Payload
3.6 * VHT symbols
Legacy spoof time = 4 usec per symbol * legacy spoof symbols
Legacy spoof symbols = L-SIG length / 3
Short GI symbol time= 3.6 usec
L-SIG symbol time = 4.0 usec
Remainder <= 3.6 usec
L
preamble
VHT
preamble
28
L-SIG
Ambiguous End of Short GI Packets
• L-SIG can only indicate time in units of 4 us
• Two 3.6 us short GI boundaries may map to the same 4 us
normal GI boundary used by L-SIG
• Addressed with extra short GI bit in VHT-SIG-A
– LSB set to 1 for short GI
– MSB set to 1 for short GI AND Nsym%10 == 9
3.6
3.6
3.6
3.6 3.63.6
3.6
444
Short GI packet with N symbols
Short GI packet with N+1 symbols
L-SIG spoof with M symbols
29
Length & Duration at Tx
• Tx MAC computes the number of
OFDM symbols and padding,
which includes
– A-MPDU (L)
– Service
– MAC Padding (to last byte
boundary)
– PHY Padding (0-7 bits)
– PHY BCC tail (6 bits / encoder)
• TXTIME
– Covers entire PLCP packet
– Short or long GI
• L_LENGTH
– Similar to 11n
8 service tail ESSYM STBC
STBC DBPS
L N N NN m
m N
8PAD SYM DBPS service tail ESN N N L N N N
_ _TXTIME for SGI LEG PREAMBLE L SIG VHT SIG A VHT PREAMBLE
SYMS SYMVHT SIG B SYM
SYM
T T T T
T NT T
T
334
20TXTIMEL_LENGTH
30
Length & Duration at Rx
• Compute RXTIME from
L_LENGTH
• Compute Nsym from RXTIME,
NVHT-LFT , short GI
• Correction factor for SGI
– If SGI bits = 11 and STBC=0,
then subtract one from N_sym
– If SGI bits = 11 and STBC=1,
then subtract two from N_sym
• Full Length in Octets
L_LENGTH 3RXTIME *4 20
3
_
RXTIME
for SGI floor
L STF L LTF L SIG VHT SIG A
VHT STF VHT LTF LTF VHT SIG B
SYM
SYMS
T T T T
T T N TN
T
PSDU_LENGTH floor8
SYM DBPS service tail ESN N N N N
31
Example of Short GI Correction
– 20 MHz, single stream, 64-QAM, r=5/6, ½ GI
PSDU Length (bytes)
# of 11ac symbols
TXTIME (usec) LSIG Length (bytes)
# of 11ac symbols computed from LSIG without correction
1232 38 180 117 38
1233 39 184 120 40
1264 39 184 120 40
1265 40 184 120 40
1297 40 184 120 40
1298 41 188 123 41
32
VHT-LTF:
Phase tracking during LTFs
• Carrier frequency offset causes EVM degradation at RX– Carrier frequency offset estimation error due to phase noise
– Carrier frequency drift
• 11a/n has pilot tones in data symbols to track phase per symbol
– Compensate residual frequency offset error and phase noise
– But no pilot tones in HT-LTF
• No phase tracking during HT-LTF
• 11ac supports max. 8 spatial streams (compared to 4 in 11n)
– Much longer VHT-LTF (e.g. 8 VHT-LTF symbols)
• More susceptible to phase rotations
– Simulation results show significant channel estimation performance degradation w/o phase tracking during VHT-LTF
• 11ac requires higher channel estimation quality and EVM– Higher order MIMO, 256-QAM, DL MU-MIMO
33
VHT-LTF:
PER Performance with Frequency Drift
• 40MHz, NLOS B
• 2000 bytes / packet
• Phase noise added at both TX and
RX (IEEE phase noise model)
• Initial carrier frequency offset
estimation using L-LTF
• ML MIMO receiver
• Phase tracking always enabled for
data symbols
• 4x4, 4 streams, 64-QAM 5/6
• IPN = -36 dBc
• Freq. drift = 50 Hz/us
0.0100
0.1000
1.0000
-59 -57 -55 -53 -51 -49
PE
R
RSSI (dBm)
w/o tracking
10/771r0, “Phase Tracking During VHT-LTF”
34
VHT-LTF:
P-Matrix for Pilot Subcarriers• Identical pilot values for all space-time streams
– All tones in VHT-LTF symbols, except pilot tones, are multiplied by the
PVHTLTF matrix (VHT-LTF mapping matrix) as in 11n
– Pilot tones are multiplied by a row-repetition matrix RVHTLTF instead
• Dimension of RVHTLTF = Dimension of PVHTLTF (NSTS x NLTF)
• All rows in RVHTLTF is the same as the 1st row of PVHTLTF
– Avoid spectral line
• Allows phase tracking during VHT-LTF w/o MIMO channel
estimation
– Simple digital solution to mitigate carrier frequency offset and drift
CSD
xkVHTLTF
x
1,
k
VHTLTF nA
STS
k NQ
IFFT
IFFT
,STS
k
VHTLTF N nA
, if is a pilot tone
, otherwise
VHTLTFk
VHTLTF
VHTLTF
R kA
P
XnmX nm matrix of column and rowin element ,
35
VHT-LTF:
Receiver Processing for Pilot Subcarriers
• Possible approach
– Estimate channel on pilot tones from first
VHT-LTF
– Used pilot tones on subsequent VHT-LTFs for
phase tracking
– Phase tracking during the VHT-LTFs is not
required
36
VHT-SIG-A Waveform Design
• Two symbols (VHT-SIG-A1 and VHT-SIG-A2)
• Same number of subcarriers (data and pilot) and
positions as legacy format
• For 80MHz and 160MHz: same number of
subcarriers and positions and values as legacy in
each 20 MHz subchannel
• CSD and phase rotations same as legacy
• Extend 80 MHz preamble to 160 MHz preamble
by simple repetition
37
Auto-detection
VHT
11n MF
11a Data (BPSK… 64-QAM)
4us 4us 4us
38
VHT-SIG-A1 Fields and OrderBit Index
Field MU bit allocation
SU bit allocation
Description
0-1 BW 3 3 B0-B1: Set to 0 for 20 MHz, 1 for 40 MHz, 2 for 80 MHz, 3 for 160 MHz or 80+80 MHz mode
2 Reserved
Reserved for possible expansion of BW field. Set to 1.
3 STBC 1 1 Set to 1 for STBC, 0 otherwise
4-9 Group ID
6 6 Set to all ones indicating:-A single user transmission-A transmission where the group membership has not yet been established-A transmission that needs to bypass a group (e.g. broadcast)For MU: used to identify users
Integer fields are transmitted in unsigned binary format, LSB first
39
Bit Index
Field MU bit allocation
SU bit allocation
Description
10-21 NSTS 12 12 For SU: • first 3 bits contain stream allocation, set to
0 for one space time stream, set to 1 for two space time streams, … 7 for eight space time streams
• Remaining 9 bits contain partial AID: being the 9 LSB bits of AID. For Broadcast and multicast, these 9 bits are set to 0.
For MU: 3 bits/user with maximum of 4 users• Set to 0 for 0 space time streams• Set to 1 for 1 space time stream• Set to 2 for 2 space time streams• Set to 3 for 3 space time streams• Set to 4 for 4 space time streams
22 No TXOP PS
1 1 Set to 0 by VHT AP if it allows non-AP VHT STAs in
TXOP power save mode to enter Doze state during a
TXOP.
Set to 1 otherwise.
The bit is reserved and set to 1 in VHT PPDUs transmitted
by a non-AP VHT STA.
23 Reserved 1 1 Set to 1
Total 24 24
40
VHT-SIG-A2 Fields and OrderBit Index
Field MU bit allocation
SU bit allocation
Description
0-1 Short GI 2 2 •B0 set to 1 for short GI•B1 set to 1 for short GI AND Nsym%10 == 9
2-3 Coding 2 2 B2:•SU: set to 0 for BCC or 1 for LDPC•MU: if the NSTS field for user 1 is non-zero, then B2 indicates the coding used for user 1; set to 0 for BCC and 1 for LDPC. If the NSTS field for user 1 is set to 0, then this field is reserved and set to 1.
B3: set to 1 if LDPC PPDU encoding process (or at least one LPDC user’s PPDU encoding process) results in an extra OFDM symbol (or symbols). Set to 0 otherwise.
Integer fields are transmitted in unsigned binary format, LSB first
41
Bit Index
Field MU bit allocation
SU bit allocation
Description
4-7 MCS 0 4 For SU:•MCS indexFor MU:•B4: Indicates coding for user 2 if the NSTS field for user 2 is non-zero: set to 0 for BCC, 1 for LDPC. If NSTS for user 2 is set to 0, then reserved and set to 1.•B5: Indicates coding for user 3 if the NSTS field for user 2 is non-zero: set to 0 for BCC, 1 for LDPC. If NSTS for user 3 is set to 0, then reserved and set to 1.•B6: Indicates coding for user 4 if the NSTS field for user 2 is non-zero: set to 0 for BCC, 1 for LDPC. If NSTS for user 4 is set to 0, then reserved and set to 1.•B7 is reserved and set to 1
8 SU-Beamformed
0 1 Set to 1 when packet is a SU-beamformed packet, 0 otherwise
For MU: reserved and set to 1
42
Bit Index Field MU bit allocation
SU bit allocation
Description
9 Reserved 6 1 Set to 1
10-17 CRC 8 8 CRC calculated as in 11n Section 20.3.9.4.4 with C7 in B10
18-23 Tail 6 6 All zeros
Total 24 24
43
MCS Exclusions• For the TGac Tx data flow, the number of data bits per
OFDM symbol (N_dbps) and number of coded bits per
OFDM symbol (N_cbps) must be an integer value for each
BCC encoder
– also true for 11a and 11n, but this was always the case for all rates
and MCSs
• New conditions in TGac lead to fractional N_dbps and
N_cbps per encoder:
– 80 MHz with 234 data subcarriers
– 256-QAM
– More than two encoders
• Even thought MSC exclusions do not apply to LDPC, for
simplicity same MCSs for LDPC
44
20 MHz MCSs
1 & 2 SS
• 1 SS, MCS 9 excluded due to BCC fractional bit issue
• 2 SS, MCS 9 excluded due to BCC fractional bit issue
1 SS
MCS
Inde
x
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI
400ns
GI
0 BPSK 1/2 1 6.5 7.2
1 QPSK 1/2 1 13.0 14.4
2 QPSK 3/4 1 19.5 21.7
3 16-QAM 1/2 1 26.0 28.9
4 16-QAM 3/4 1 39.0 43.3
5 64-QAM 2/3 1 52.0 57.8
6 64-QAM 3/4 1 58.5 65.0
7 64-QAM 5/6 1 65.0 72.2
8 256-QAM 3/4 1 78.0 86.7
9
2 SS
MCS
Inde
x
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI
400ns
GI
0 BPSK 1/2 1 13.0 14.4
1 QPSK 1/2 1 26.0 28.9
2 QPSK 3/4 1 39.0 43.3
3 16-QAM 1/2 1 52.0 57.8
4 16-QAM 3/4 1 78.0 86.7
5 64-QAM 2/3 1 104.0 115.6
6 64-QAM 3/4 1 117.0 130.0
7 64-QAM 5/6 1 130.0 144.4
8 256-QAM 3/4 1 156.0 173.3
9
45
20 MHz MCSs
3 & 4 SS3 SS
MCS
Inde
x
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI
400ns
GI
0 BPSK 1/2 1 19.5 21.7
1 QPSK 1/2 1 39.0 43.3
2 QPSK 3/4 1 58.5 65.0
3 16-QAM 1/2 1 78.0 86.7
4 16-QAM 3/4 1 117.0 130.0
5 64-QAM 2/3 1 156.0 173.3
6 64-QAM 3/4 1 175.5 195.0
7 64-QAM 5/6 1 195.0 216.7
8 256-QAM 3/4 1 234.0 260.0
9 256-QAM 5/6 1 260.0 288.9
• 4 SS, MCS 9 excluded due to BCC fractional bit issue
4 SS
MCS
Inde
x
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI
400ns
GI
0 BPSK 1/2 1 26.0 28.9
1 QPSK 1/2 1 52.0 57.8
2 QPSK 3/4 1 78.0 86.7
3 16-QAM 1/2 1 104.0 115.6
4 16-QAM 3/4 1 156.0 173.3
5 64-QAM 2/3 1 208.0 231.1
6 64-QAM 3/4 1 234.0 260.0
7 64-QAM 5/6 1 260.0 288.9
8 256-QAM 3/4 1 312.0 346.7
9
46
20 MHz MCSs
5 & 6 SS5 SS
MCS
Inde
x
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI
400ns
GI
0 BPSK 1/2 1 32.5 36.1
1 QPSK 1/2 1 65.0 72.2
2 QPSK 3/4 1 97.5 108.3
3 16-QAM 1/2 1 130.0 144.4
4 16-QAM 3/4 1 195.0 216.7
5 64-QAM 2/3 1 260.0 288.9
6 64-QAM 3/4 1 292.5 325.0
7 64-QAM 5/6 1 325.0 361.1
8 256-QAM 3/4 1 390.0 433.3
9
6 SS
MCS
Inde
x
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI
400ns
GI
0 BPSK 1/2 1 39.0 43.3
1 QPSK 1/2 1 78.0 86.7
2 QPSK 3/4 1 117.0 130.0
3 16-QAM 1/2 1 156.0 173.3
4 16-QAM 3/4 1 234.0 260.0
5 64-QAM 2/3 1 312.0 346.7
6 64-QAM 3/4 1 351.0 390.0
7 64-QAM 5/6 1 390.0 433.3
8 256-QAM 3/4 1 468.0 520.0
9 256-QAM 5/6 1 520.0 577.8
• 5 SS, MCS 9 excluded due to BCC fractional bit issue
47
20 MHz MCSs
7 & 8 SS
7 SS
MC
S
Inde
x
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI400ns GI
0 BPSK 1/2 1 45.5 50.6
1 QPSK 1/2 1 91.0 101.1
2 QPSK 3/4 1 136.5 151.7
3 16-QAM 1/2 1 182.0 202.2
4 16-QAM 3/4 1 273.0 303.3
5 64-QAM 2/3 1 364.0 404.4
6 64-QAM 3/4 1 409.5 455.0
7 64-QAM 5/6 1 455.0 505.6
8 256-QAM 3/4 2 546.0 606.7
9
8 SS
MCS
Inde
x
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI
400ns
GI
0 BPSK 1/2 1 52.0 57.8
1 QPSK 1/2 1 104.0 115.6
2 QPSK 3/4 1 156.0 173.3
3 16-QAM 1/2 1 208.0 231.1
4 16-QAM 3/4 1 312.0 346.7
5 64-QAM 2/3 1 416.0 462.2
6 64-QAM 3/4 1 468.0 520.0
7 64-QAM 5/6 1 520.0 577.8
8 256-QAM 3/4 2 624.0 693.3
9
• 7 SS, MCS 9 excluded due to BCC fractional bit issue
• 8 SS, MCS 9 excluded due to BCC fractional bit issue
48
40 MHz MCSs
1 & 2 SS1 SS
MCS
Inde
x
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI
400ns
GI
0 BPSK 1/2 1 13.5 15.0
1 QPSK 1/2 1 27.0 30.0
2 QPSK 3/4 1 40.5 45.0
3 16-QAM 1/2 1 54.0 60.0
4 16-QAM 3/4 1 81.0 90.0
5 64-QAM 2/3 1 108.0 120.0
6 64-QAM 3/4 1 121.5 135.0
7 64-QAM 5/6 1 135.0 150.0
8 256-QAM 3/4 1 162.0 180.0
9 256-QAM 5/6 1 180.0 200.0
2 SS
MCS
Inde
x
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI
400ns
GI
0 BPSK 1/2 1 27.0 30.0
1 QPSK 1/2 1 54.0 60.0
2 QPSK 3/4 1 81.0 90.0
3 16-QAM 1/2 1 108.0 120.0
4 16-QAM 3/4 1 162.0 180.0
5 64-QAM 2/3 1 216.0 240.0
6 64-QAM 3/4 1 243.0 270.0
7 64-QAM 5/6 1 270.0 300.0
8 256-QAM 3/4 1 324.0 360.0
9 256-QAM 5/6 1 360.0 400.0
49
40 MHz MCSs
3 & 4 SS3 SS
MCS
Inde
x
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI
400ns
GI
0 BPSK 1/2 1 40.5 45.0
1 QPSK 1/2 1 81.0 90.0
2 QPSK 3/4 1 121.5 135.0
3 16-QAM 1/2 1 162.0 180.0
4 16-QAM 3/4 1 243.0 270.0
5 64-QAM 2/3 1 324.0 360.0
6 64-QAM 3/4 1 364.5 405.0
7 64-QAM 5/6 1 405.0 450.0
8 256-QAM 3/4 1 486.0 540.0
9 256-QAM 5/6 1 540.0 600.0
4 SS
MCS
Inde
x
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI
400ns
GI
0 BPSK 1/2 1 54.0 60.0
1 QPSK 1/2 1 108.0 120.0
2 QPSK 3/4 1 162.0 180.0
3 16-QAM 1/2 1 216.0 240.0
4 16-QAM 3/4 1 324.0 360.0
5 64-QAM 2/3 1 432.0 480.0
6 64-QAM 3/4 1 486.0 540.0
7 64-QAM 5/6 1 540.0 600.0
8 256-QAM 3/4 2 648.0 720.0
9 256-QAM 5/6 2 720.0 800.0
50
40 MHz MCSs
5 & 6 SS5 SS
MCS
Index
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI400ns GI
0 BPSK 1/2 1 67.5 75.0
1 QPSK 1/2 1 135.0 150.0
2 QPSK 3/4 1 202.5 225.0
3 16-QAM 1/2 1 270.0 300.0
4 16-QAM 3/4 1 405.0 450.0
5 64-QAM 2/3 1 540.0 600.0
6 64-QAM 3/4 2 607.5 675.0
7 64-QAM 5/6 2 675.0 750.0
8 256-QAM 3/4 2 810.0 900.0
9 256-QAM 5/6 2 900.0 1000.0
6 SS
MC
S
Inde
x
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI
400ns
GI
0 BPSK 1/2 1 81.0 90.0
1 QPSK 1/2 1 162.0 180.0
2 QPSK 3/4 1 243.0 270.0
3 16-QAM 1/2 1 324.0 360.0
4 16-QAM 3/4 1 486.0 540.0
5 64-QAM 2/3 2 648.0 720.0
6 64-QAM 3/4 2 729.0 810.0
7 64-QAM 5/6 2 810.0 900.0
8 256-QAM 3/4 2 972.0 1080.0
9 256-QAM 5/6 2 1080.0 1200.0
51
40 MHz MCSs
7 & 8 SS8 SS
MCS
Inde
x
Modulatio
nR
N
ES
Data rate (Mb/s)
800ns GI 400ns GI
0 BPSK 1/2 1 108.0 120.0
1 QPSK 1/2 1 216.0 240.0
2 QPSK 3/4 1 324.0 360.0
3 16-QAM 1/2 1 432.0 480.0
4 16-QAM 3/4 2 648.0 720.0
5 64-QAM 2/3 2 864.0 960.0
6 64-QAM 3/4 2 972.0 1080.0
7 64-QAM 5/6 2 1080.0 1200.0
8 256-QAM 3/4 3 1296.0 1440.0
9 256-QAM 5/6 3 1440.0 1600.0
7 SS
MCS
Index
Modulatio
nR
NE
S
Data rate (Mb/s)
800ns
GI
400ns
GI
0 BPSK 1/2 1 94.5 105.0
1 QPSK 1/2 1 189.0 210.0
2 QPSK 3/4 1 283.5 315.0
3 16-QAM 1/2 1 378.0 420.0
4 16-QAM 3/4 2 567.0 630.0
5 64-QAM 2/3 2 756.0 840.0
6 64-QAM 3/4 2 850.5 945.0
7 64-QAM 5/6 2 945.0 1050.0
8 256-QAM 3/4 3 1134.0 1260.0
9 256-QAM 5/6 3 1260.0 1400.0
52
80 MHz MCSs
1 & 2 SS1 SS
MCS
Inde
x
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI
400ns
GI
0 BPSK 1/2 1 29.3 32.5
1 QPSK 1/2 1 58.5 65.0
2 QPSK 3/4 1 87.8 97.5
3 16-QAM 1/2 1 117.0 130.0
4 16-QAM 3/4 1 175.5 195.0
5 64-QAM 2/3 1 234.0 260.0
6 64-QAM 3/4 1 263.3 292.5
7 64-QAM 5/6 1 292.5 325.0
8 256-QAM 3/4 1 351.0 390.0
9 256-QAM 5/6 1 390.0 433.3
2 SS
MCS
Inde
x
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI
400ns
GI
0 BPSK 1/2 1 58.5 65.0
1 QPSK 1/2 1 117.0 130.0
2 QPSK 3/4 1 175.5 195.0
3 16-QAM 1/2 1 234.0 260.0
4 16-QAM 3/4 1 351.0 390.0
5 64-QAM 2/3 1 468.0 520.0
6 64-QAM 3/4 1 526.5 585.0
7 64-QAM 5/6 2 585.0 650.0
8 256-QAM 3/4 2 702.0 780.0
9 256-QAM 5/6 2 780.0 866.7
53
80 MHz BCC MCSs
3 & 4 SS
• 3SS, MCS 6 excluded due to BCC fractional bit issue
3 SS
MCS
Inde
x
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI
400ns
GI
0 BPSK 1/2 1 87.8 97.5
1 QPSK 1/2 1 175.5 195.0
2 QPSK 3/4 1 263.3 292.5
3 16-QAM 1/2 1 351.0 390.0
4 16-QAM 3/4 1 526.5 585.0
5 64-QAM 2/3 2 702.0 780.0
6
7 64-QAM 5/6 2 877.5 975.0
8 256-QAM 3/4 2 1053.0 1170.0
9 256-QAM 5/6 3 1170.0 1300.0
4 SS
MCS
Inde
x
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI
400ns
GI
0 BPSK ½ 1 117.0 130.0
1 QPSK 1/2 1 234.0 260.0
2 QPSK 3/4 1 351.0 390.0
3 16-QAM 1/2 1 468.0 520.0
4 16-QAM 3/4 2 702.0 780.0
5 64-QAM 2/3 2 936.0 1040.0
6 64-QAM 3/4 2 1053.0 1170.0
7 64-QAM 5/6 3 1170.0 1300.0
8 256-QAM 3/4 3 1404.0 1560.0
9 256-QAM 5/6 3 1560.0 1733.3
54
80 MHz BCC MCSs
5 & 6 SS5 SS
MCS
Inde
x
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI
400ns
GI
0 BPSK 1/2 1 146.3 162.5
1 QPSK 1/2 1 292.5 325.0
2 QPSK 3/4 1 438.8 487.5
3 16-QAM 1/2 2 585.0 650.0
4 16-QAM 3/4 2 877.5 975.0
5 64-QAM 2/3 3 1170.0 1300.0
6 64-QAM 3/4 3 1316.3 1462.5
7 64-QAM 5/6 3 1462.5 1625.0
8 256-QAM 3/4 4 1755.0 1950.0
9 256-QAM 5/6 4 1950.0 2166.7
6 SS
MCS
Index
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI
400ns
GI
0 BPSK 1/2 1 175.5 195.0
1 QPSK 1/2 1 351.0 390.0
2 QPSK 3/4 1 526.5 585.0
3 16-QAM 1/2 2 702.0 780.0
4 16-QAM 3/4 2 1053.0 1170.0
5 64-QAM 2/3 3 1404.0 1560.0
6 64-QAM 3/4 3 1579.5 1755.0
7 64-QAM 5/6 4 1755.0 1950.0
8 256-QAM 3/4 4 2106.0 2340.0
9
• 6SS, MCS 9 excluded due to BCC fractional bit issue
55
80 MHz BCC MCSs
7 & 8 SS
• 7 SS, MCS 6 excluded due to BCC fractional bit issue
7 SS
MCS
Inde
x
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI
400ns
GI
0 BPSK ½ 1 204.8 227.5
1 QPSK ½ 1 409.5 455.0
2 QPSK 3/4 3 614.3 682.5
3 16-QAM ½ 2 819.0 910.0
4 16-QAM 3/4 3 1228.5 1365.0
5 64-QAM 2/3 4 1638.0 1820.0
6
7 64-QAM 5/6 6 2047.5 2275.0
8 256-QAM 3/4 6 2457.0 2730.0
9 256-QAM 5/6 6 2730 3033.3
8 SS
MCS
Inde
x
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI
400ns
GI
0 BPSK 1/2 1 234.0 260.0
1 QPSK 1/2 1 468.0 520.0
2 QPSK 3/4 2 702.0 780.0
3 16-QAM 1/2 2 936.0 1040.0
4 16-QAM 3/4 3 1404.0 1560.0
5 64-QAM 2/3 4 1872.0 2080.0
6 64-QAM 3/4 4 2106.0 2340.0
7 64-QAM 5/6 6 2340.0 2600.0
8 256-QAM 3/4 6 2808.0 3120.0
9 256-QAM 5/6 6 3120.0 3466.7
56
160 MHz MCSs
1 & 2 SS1 SS
MCS
Inde
x
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI
400ns
GI
0 BPSK 1/2 1 58.5 65.0
1 QPSK 1/2 1 117.0 130.0
2 QPSK 3/4 1 175.5 195.0
3 16-QAM 1/2 1 234.0 260.0
4 16-QAM 3/4 1 351.0 390.0
5 64-QAM 2/3 1 468.0 520.0
6 64-QAM 3/4 1 526.5 585.0
7 64-QAM 5/6 2 585.0 650.0
8 256-QAM 3/4 2 702.0 780.0
9 256-QAM 5/6 2 780.0 866.7
2 SS
MCS
Inde
x
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI
400ns
GI
0 BPSK 1/2 1 117.0 130.0
1 QPSK 1/2 1 234.0 260.0
2 QPSK 3/4 1 351.0 390.0
3 16-QAM 1/2 1 468.0 520.0
4 16-QAM 3/4 2 702.0 780.0
5 64-QAM 2/3 2 936.0 1040.0
6 64-QAM 3/4 2 1053.0 1170.0
7 64-QAM 5/6 3 1170.0 1300.0
8 256-QAM 3/4 3 1404.0 1560.0
9 256-QAM 5/6 3 1560.0 1733.3
57
160 MHz BCC MCSs
3 & 4 SS3 SS
MCS
Inde
x
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI
400ns
GI
0 BPSK 1/2 1 175.5 195.0
1 QPSK 1/2 1 351.0 390.0
2 QPSK 3/4 1 526.5 585.0
3 16-QAM 1/2 2 702.0 780.0
4 16-QAM 3/4 2 1053.0 1170.0
5 64-QAM 2/3 3 1404.0 1560.0
6 64-QAM 3/4 3 1579.5 1755.0
7 64-QAM 5/6 4 1755.0 1950.0
8 256-QAM 3/4 4 2106.0 2340.0
9
4 SS
MCS
Inde
x
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI
400ns
GI
0 BPSK 1/2 1 234.0 260.0
1 QPSK 1/2 1 468.0 520.0
2 QPSK 3/4 2 702.0 780.0
3 16-QAM 1/2 2 936.0 1040.0
4 16-QAM 3/4 3 1404.0 1560.0
5 64-QAM 2/3 4 1872.0 2080.0
6 64-QAM 3/4 4 2106.0 2340.0
7 64-QAM 5/6 6 2340.0 2600.0
8 256-QAM 3/4 6 2808.0 3120.0
9 256-QAM 5/6 6 3120.0 3466.7
• 3 SS, MCS 9 excluded due to BCC fractional bit issue
58
160 MHz MCSs
5 & 6 SS6 SS
MCS
Inde
x
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI
400ns
GI
0 BPSK 1/2 1 351.0 390.0
1 QPSK 1/2 2 702.0 780.0
2 QPSK 3/4 2 1053.0 1170.0
3 16-QAM 1/2 3 1404.0 1560.0
4 16-QAM 3/4 4 2106.0 2340.0
5 64-QAM 2/3 6 2808.0 3120.0
6 64-QAM 3/4 6 3159.0 3510.0
7 64-QAM 5/6 8 3510.0 3900.0
8 256-QAM 3/4 8 4212.0 4680.0
9 256-QAM 5/6 9 4680.0 5200.0
5 SS
MCS
Inde
x
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI
400ns
GI
0 BPSK 1/2 1 292.5 325.0
1 QPSK 1/2 2 585.0 650.0
2 QPSK 3/4 2 877.5 975.0
3 16-QAM 1/2 3 1170.0 1300.0
4 16-QAM 3/4 4 1755.0 1950.0
5 64-QAM 2/3 5 2340.0 2600.0
6 64-QAM 3/4 5 2632.5 2925.0
7 64-QAM 5/6 6 2925.0 3250.0
8 256-QAM 3/4 8 3510.0 3900.0
9 256-QAM 5/6 8 3900.0 4333.3
59
160 MHz MCSs
7 & 8 SS7 SS
MCS
Inde
x
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI
400ns
GI
0 BPSK 1/2 1 409.5 455.0
1 QPSK 1/2 2 819.0 910.0
2 QPSK 3/4 3 1228.5 1365.0
3 16-QAM 1/2 4 1638.0 1820.0
4 16-QAM 3/4 6 2457.0 2730.0
5 64-QAM 2/3 7 3276.0 3640.0
6 64-QAM 3/4 7 3685.5 4095.0
7 64-QAM 5/6 9 4095.0 4550.0
8 256-QAM 3/4 12 4914.0 5460.0
9 256-QAM 5/6 12 5460.0 6066.7
8 SS
MCS
Inde
x
Modulatio
nR NES
Data rate (Mb/s)
800ns
GI
400ns
GI
0 BPSK 1/2 1 468.0 520.0
1 QPSK 1/2 2 936.0 1040.0
2 QPSK 3/4 3 1404.0 1560.0
3 16-QAM 1/2 4 1872.0 2080.0
4 16-QAM 3/4 6 2808.0 3120.0
5 64-QAM 2/3 8 3744.0 4160.0
6 64-QAM 3/4 8 4212.0 4680.0
7 64-QAM 5/6 9 4680.0 5200.0
8 256-QAM 3/4 12 5616.0 6240.0
9 256-QAM 5/6 12 6240.0 6933.3
60
VHT-SIG-B:
Bit encoding• Single stream Data field OFDM symbol format per user w/ BPSK, R=1/2 modulation
• In 20 MHz mode, 26 bits are available
• For 40/80/160 MHz, repeat bits including tail bits
– No frequency repetition of 20 MHz sub-channels into other sub-channels
– Provides easy way for receiver to get processing gain by averaging repeated soft values at the decoder
input
• For higher BWs, additional bits are available due to extra tones
– In 40 MHz, we get 27 bits
– In 80/160 MHz, we get 29 bits
20 bits6 tail
bits
21 bits6 tail
bits21 bits
6 tail
bits
23 bits6 tail
bits23 bits
6 tail
bits23 bits
6 tail
bits23 bits
6 tail
bits
23 bits6 tail
bits
1 Pad
bit
23 bits6 tail
bits23 bits
6 tail
bits23 bits
6 tail
bits
1 Pad
bit23 bits
6 tail
bits23 bits
6 tail
bits23 bits
6 tail
bits23 bits
6 tail
bits
1 Pad
bit
20 MHz
40 MHz
80 MHz
160 MHz
80+80 MHz
Repeated
Repeated
Repeated
Repeated
61
VHT-SIG-B:
Bit Allocation
• VHT-SIGB Allocation (20/40/80 MHz):
– * Additional bits to accommodate large packet sizes in 5.46ms (max packet duration in LSIG)
– 160 MHz repeats the 80 MHz VHT-SIG-B twice in frequency
SIGB Fields MU – Bit allocation SU – Bit allocation
20 MHz 40 MHz 80 MHz 20 MHz 40 MHz 80 MHz
Length (in units of 4 octets) 16 17* 19* 17 19 21
MCS 4 4 4 - - -
RSVD 0 0 0 3 2 2
Tail 6 6 6 6 6 6
Total # bits 26 27 29 26 27 29
62
VHT-SIG-B:
Length
• Length in VHT-SIG-B is provided to indicate useful data
in PSDU, which allows receivers to shut-off PHY
processing after receiving useful data thereby saving some
power
L-TFs L-SIG
VHT A-MPDU
VHT-SIG A
PHY
PadTailService
Last Symbol
VHT A-MPDU
VHT A-MPDU
Service
Service
PHY
PadTail
PHY
PadTail
PPDU Duration (# of symbols)
A-MPDU
subframe 1
A-MPDU
subframe 2
Null
subframe
Null
subframe
A-MPDU
subframe n
Last byte
boundary
Less than
8-bitMPDU
Length = 0
MPDU
Length = 0
Final
MAC
Pad
0-3
octets
VHT-TFsVHT-
SIG B
Dword
MAC
Pad
0-3
octets
User
VHT-SIGB Length
63
VHT-SIG-B:
CRC in SERVICE Field • Transmitter shall include VHT-SIG-B CRC in SERVICE field
• Transmitter shall compute 8-bit CRC based on SIG B "not including
tail" and insert 8-bit CRC in 8 MSBs of the SERVICE field
– Transmitter will not include scrambler seed in computation of CRC bits
– CRC defined in 802.11n-2009 section 20.3.9.4.4. C7 of the CRC is
mapped to B8 of the SERVICE field, C6 to B7, …, C0 to B15
• The resulting SERVICE field and PSDU shall be scrambled, as in 11n
• CRC achieves protection of the scrambler init field
– Any error in the scrambler init field will result in a corrupted CRC field
after descrambling
– Check of the CRC field against the contents of SIG-B will then fail
20 bits in 20MHz
*21 (40MHz) / 23(80MHz) bits
Tail
(6bit)
Scrambler
Seed (7bit)
Rsvd
(1bit)
CRC
(8bit)
VHT-SIG-B Service Field
64
VHT-SIG-B:
Requirements for Single User
• Tx
– Required to compute and populate DWORD
length, tail, and reserved bits
– Required to compute and populate VHT-SIG-B
CRC in SERVICE field
• Rx
– Optional to process VHT-SIG-B
65
PHY Transmitter Flow:
256 QAM– Normalization factor
00001000 00011000 00111000 00101000 01101000 01111000 01011000 01001000 11001000 11011000 11111000 11101000 10101000 10111000 10011000 10001000
00001001 00011001 00111001 00101001 01101001 01111001 01011001 01001001 11001001 11011001 11111001 11101001 10101001 10111001 10011001 10001001
00001011 00011011 00111011 00101011 01101011 01111011 01011011 01001011 11001011 11011011 11111011 11101011 10101011 10111011 10011011 10001011
00001010 00011010 00111010 00101010 01101010 01111010 01011010 01001010 11001010 11011010 11111010 11101010 10101010 10111010 10011010 10001010
00001110 00011110 00111110 00101110 01101110 01111110 01011110 01001110 11001110 11011110 11111110 11101110 10101110 10111110 10011110 10001110
00001111 00011111 00111111 00101111 01101111 01111111 01011111 01001111 11001111 11011111 11111111 11101111 10101111 10111111 10011111 10001111
00001101 00011101 00111101 00101101 01101101 01111101 01011101 01001101 11001101 11011101 11111101 11101101 10101101 10111101 10011101 10001101
00001100 00011100 00111100 00101100 01101100 01111100 01011100 01001100 11001100 11011100 11111100 11101100 10101100 10111100 10011100 10001100
00000100 00010100 00110100 00100100 01100100 01110100 01010100 01000100 11000100 11010100 11110100 11100100 10100100 10110100 10010100 10000100
00000101 00010101 00110101 00100101 01100101 01110101 01010101 01000101 11000101 11010101 11110101 11100101 10100101 10110101 10010101 10000101
00000111 00010111 00110111 00100111 01100111 01110111 01010111 01000111 11000111 11010111 11110111 11100111 10100111 10110111 10010111 10000111
00000110 00010110 00110110 00100110 01100110 01110110 01010110 01000110 11000110 11010110 11110110 11100110 10100110 10110110 10010110 10000110
00000010 00010010 00110010 00100010 01100010 01110010 01010010 01000010 11000010 11010010 11110010 11100010 10100010 10110010 10010010 10000010
00000011 00010011 00110011 00100011 01100011 01110011 01010011 01000011 11000011 11010011 11110011 11100011 10100011 10110011 10010011 10000011
00000001 00010001 00110001 00100001 01100001 01110001 01010001 01000001 11000001 11010001 11110001 11100001 10100001 10110001 10010001 10000001
00000000 00010000 00110000 00100000 01100000 01110000 01010000 01000000 11000000 11010000 11110000 11100000 10100000 10110000 10010000 10000000
1701MODK
66
MAC
67
Coexistence in Wider Channels
• With 11n it is relatively easy to handle overlapping networks:
• Easy to avoid overlap by choosing different channel
• Choose primary channel that matches neighbor if overlap unavoidable
• With 11ac it becomes much harder
• More channels used means greater probability of co-channel operation
• Harder to choose primary channel common to all overlapping networks
Channels:36, 40
Channel:36
Channels:36, 40, 44, 48
Channels:36, 40
Channels:44, 48
802.11n 802.11ac
68
Enhancements to Coexistence
Mechanisms
• 802.11ac extends the medium access protocol developed in
11n to wider channels
• 802.11ac improves co-channel operation with the
following:
• Enhanced secondary channel CCA
• Improved dynamic channel width operation
• Operating Mode Notification frame
69
Channel access in wider channels
• Basic 11n channel access mechanism is extended to wider bandwidth
• Random backoff (AIFS+CW) is based on primary channel activity
• Secondary channels must be sensed idle PIFS before transmission
• If some of the subchannels are busy, a narrower transmission is permitted
– A transmission always includes primary channel
• Note that mid-packet signal detect is needed on secondary channel since
packet may start while primary channel transmission is in progress
Secondary channels
Primary channel AIFS CW
80 MHz PPDUPIFS
PIFS
PIFS40 MHz PPDU
40 MHz PPDU
AIFS CWPIFS
40 MHz PPDU
40 MHz PPDU 40 MHz PPDU
Secondary channels
Primary channel
70
Enhanced CCA
802.11n 802.11ac
Primary
channel
Valid signal: -82 dBm
Energy detect: -62 dBm
Valid signal: -82 dBm
Energy detect: -62 dBm
Secondary
channel
Energy detect only:
-62 dBm
Valid signal: -72dBm
Energy detect: -62 dBm
• Detecting a valid signal in secondary channel is harder than in primary
channel
• Because the STA always transmits in the primary channel, it only needs to
detect start of packet in primary channel
• Because a secondary transmission may begin while a primary channel
transmission is in progress, a STA must be able to detect signal in middle
of a packet on secondary channel
71
Improved Dynamic Channel Width Operation
• E.g. STA1 receives interference from STA2, but transmission
is not detected by AP1
• BW signaling is added to RTS and CTS frames
• AP1 sends RTS with BW of intended transmission
• STA1 sends CTS response with BW of clear channels
• AP1 only sends data on clear channels
AP1:36,40,44,48
AP2:44,48
InterferenceBA
BA
RTS
RTS
RTS
RTS
CTS
CTS
Interference
Data
Data
STA2STA1
72
Operating Mode Notification Frame
• If the interference in the previous example is strong or
frequent, then STA1 can send a Operating Mode
Notification frame
• Operating Mode Notification frame tells AP that the STA
is changing the BW on which it operates
• E.g. 80 MHz 40 MHz
• AP will then only send data frames occupying the reduced
BW
• Operating Mode Notification frame can also be used to
reduce the number of spatial streams that a STA can receive
(enhancement of 11n’s SM power save mechanism)
73
Aggregation in 11n
• 802.11n added two forms of
aggregation:
• A-MSDU
– Performed at the top of the MAC
– Easily done in software
– Limited by max A-MSDU size
(approx 8kB)
• A-MPDU
– Performed at the bottom of the MAC
– Done in hardware
– Limited by PPDU length field of 64kB
• Most 11n implementations only did A-
MPDU
• Doing both A-MSDU and A-
MPDU, while permitted, had little
benefit
MSDU MSDU MSDUMAC
Header FCS
A-MSDU
A-M
PD
UD
elim
iter
MPDU
A-M
PD
UD
elim
iter
MPDU
A-M
PD
UD
elim
iter
MPDU
A-MPDU
74
Aggregation in 11ac
• With 11ac, both A-MSDU and A-MPDU aggregation are required to achieve good efficiency at higher data rates
• Also, in 11ac all packets required to be A-MPDU
– PHY no longer conveys the number of octets in the packet, just number of OFDM symbols
– MPDU only contains duration, not length
– Delimiter in A-MPDU contains MPDU length
MSDU MSDU
MSDU MSDU MSDUMAC
Header FCS
A-M
PD
UD
elim
iter
MPDU
A-M
PD
UD
elim
iter
MPDU
MSDU
A-M
PD
UD
elim
iter
MPDU
MSDUs typically ≤1500B in size
A-MSDU
A-MSDU encapsulated in MPDU(length limit increased to 11,454B)
Aggregated to form A-MSDU
MPDUs aggregated to form A-MPDU(length limit increased to 1MB,BA window limit of 64 remains
unchanged)
75
Aggregation in 11ac
A-MPDU only vs A-MSDU+A-MPDU
Throughput simulation, 1 and 2 spatial streams, 160 MHz
0.00%
10.00%
20.00%
30.00%
40.00%
50.00%
60.00%
70.00%
80.00%
0
200
400
600
800
1,000
1,200
1,400
0 500 1,000 1,500
MA
C E
ffic
ien
cy
Thro
ugh
pu
t (M
bp
s)
PHY Data Rate (Mbps)
Throughput with 10% PER
11,414B A-MSDU Limit
7,935B A-MSDU Limit
3,839B A-MSDU Limit
No A-MSDU
11,414B A-MSDU Limit
7,935B A-MSDU Limit
3,839B A-MSDU Limit
No A-MSDUWithout A-MSDU,only reach 660 Mbps
With A-MSDU,reach 1.16 Gbps
At 11n rates, no benefit from
A-MSDU+A-MPDU
76
Downlink Multi User MIMO
(DL MU-MIMO)• In 11n MIMO, the access point
transmits multiple data streams to a
single station at a time
• In 11ac DL MU-MIMO, the access
point simultaneously transmits data
streams to multiple stations
• Example:
– Access point with 6 antenna
– One hand-held client device with
one antenna (STA1)
– One laptop client device (STA2)
with two antennas
– One TV set top box client device
with two antennas (STA3)
– Access point simultaneously
transmits one stream to STA1, two
streams to STA2, and two streams
to STA3
STA1STA2
STA3
77
PHY Transmitter Flow Overview:
Multi User
......
Sp
atia
l M
ap
pin
g
Insert GI
and
Window
Analog
and RFIDFT
Insert GI
and
Window
Analog
and RFIDFT
Insert GI
and
Window
Analog
and RFIDFT
...
PH
Y P
ad
din
g
Scra
mb
ler B
CC
En
co
de
r
CSD
Str
ea
m P
ars
er
Constellation
mapper
ST
BC
Constellation
mapper
...
User Nu (Using BCC)
BCC
Interleaver
BCC
Interleaver
En
co
de
r P
ars
er
BC
C
En
co
de
r
CSD
...
PH
Y P
ad
din
g
Scra
mb
ler
LD
PC
En
co
de
r
CSDStr
ea
m P
ars
er
Constellation
mapper
ST
BC
Constellation
mapper
LDPC
tone
mapper
LDPC
tone
mapper
...
User 1 (Using LDPC)
...
78
DL MU-MIMO Parameters
• Maximum number of users in a
transmission is 4
• Maximum number of spatial streams per
user is 4
• Maximum total number of spatial streams
(summed over users) is 8
79
PPDU overview (MU)
• Illustrating parallel transmissions to multiple users
• Parallel VHT-SIG-B, Service, VHT A-MPDU represents directional transmission to each users
• MAC provides an A-MPDU that fills the frame to the last byte for each user
• Same preamble structure is used for both SU and MU VHT frames
– Require that A-MPDU always be used with both SU and MU VHT frames
– “Aggregation” bit in VHT-SIG is then not needed
• Tail: 6 bits per BCC encoder for each user
ReservedMPDU
length = 0CRC
Delimiter
SignatureEOF
Octets:
MPDU Delimiter
4
When RX MAC detects
the EOF padding
delimiter, it can inform RX
PHY to stop receiving
VHT A-MPDUPHY
PadTail
Last Symbol
VHT A-MPDU
VHT A-MPDU
PHY
PadTail
PHY
PadTail
PPDU Duration (# of symbols)
A-MPDU
subframe 1
A-MPDU
subframe 2
Null
subframe
(EOF)
Null
subframe
(EOF)
A-MPDU
subframe n
Last byte
boundary
Less than
8-bitMPDU
Length = 0
MPDU
Length = 0
Final
MAC
Pad
0-3
octets
Dword
MAC
Pad
MAC Pad
MAC Pad
0-3
octets
Service
Service
Service
VHT-
SIG BVHT-
SIG BVHT-
SIG B
L-TFs L-SIG VHT-SIG A
VHT-
STFVHT-
STFVHT-
STF
VHT-LTF
VHT-LTF
VHT-LTF
User
80
MU Ack Protocol
•Ack protocol is unchanged from 802.11n
•MU PPDU may solicit a response from only one STA
•Remaining STAs are polled for response
•Note: Not to scale; BAR-BA is of much shorter
duration that MU PPDU
RA=STA 1, implicit block ack request
RA=STA 2, block ack
RA=STA 3, block ack
BA
BA
BARRA=STA 2AP
STA 1
STA 2
STA 3
BARRA=STA 3
BA
81
Group ID concept
GroupID
NstsIndex
0 -
1 -
2 0
… …
63 1
Space-time streams 0, 1
Space-time streams 2, 3
Space-time stream 4
Group ID
Nsts Table
2 2 0 2 1
STA 1
GroupID
NstsIndex
0 0
1 1
2 2
… …
63 3
STA 3
GroupID
NstsIndex
0 1
1 2
2 3
… …
63 -
STA 4
GroupID
NstsIndex
0 -
1 0
2 1
… …
63 2
STA 2
VHT-SIG-A
To STA 1
To STA 3
To STA 4
Per STA lookup tables
1. AP transmits MU MIMO PPDU to a group of STAs identified by Group ID
2. STAs use Group ID to index local table to identify its Nsts Index 3. Nsts Index determines
which space-time streams the STA demodulates
82
Sounding and Feedback Protocol
1. Sounding feedback sequence starts with AP sending an NDP Announcement frame
followed by an NDP
– NDP Announcement identifies the first responder after the NDP and may identify other STAs
which will be polled subsequently
2. STA identified as first by the NDP Announcement sends VHT Compressed Beamforming
report frame SIFS time after the NDP
3. AP polls all remaining STAs using the Beamforming Report Poll frame
• Note that in the SU case, the sequence is simply NDP Announcement-NDP-VHT
Compressed Beamforming report frame
83
Acronyms (1/4)
• A-MPDU - aggregate MAC protocol data unit
• A-MSDU – aggregate MAC service data unit
• ACK - acknowledgment
• AID - association identifier
• AIFS - arbitration interframe space
• A-MPDU - aggregate MAC protocol data unit
• AP – access point
• BA - Block Acknowledgment
• BAR - Block Acknowledgment request
• BB – baseband
• BCC - binary convolutional code
• BF - beamforming
• BPSK - binary phase shift keying
• BW – bandwidth
• CCA - clear channel assessment
• CCK - complementary code keying
• CRC - cyclic redundancy code
• CSD - cyclic shift diversity
• CSI - channel state information
• CSMA/CA - carrier sense multiple access with
collision avoidance
• CTS - clear to send
• CW - contention window
• DL - downlink
• DSSS - direct sequence spread spectrum
84
Acronyms (2/4)
• FFT - Fast Fourier Transform
• FEC - forward error correction
• FEM – front-end module
• GI – guard interval
• HT – high throughput
• IBSS – independent basic service set
• ID - identification
• Infra-BSS – infrastructure basic service set
• IMT-Advanced - International Mobile
Telecommunications - Advanced
• ISM - industrial, scientific, and medical
• LDPC - low-density parity check
• L-SIG – legacy signal field
• L-TF, LTF – legacy training field
• MAC - medium access control
• MCS – modulation, coding scheme
• MF – mixed format
• MIB - management information base
• MIMO - multiple input, multiple output
• MPDU - MAC protocol data unit
• MSDU - MAC service data unit
• MU – multi user
• NDP - null data packet
• NDPA – NDP announcement
85
Acronyms (3/4)
• OFDM - orthogonal frequency division
multiplexing
• PAR - Project Authorization Request
• PAPR - Peak-to-Average Power Ratio
• PHY - physical layer
• PIFS - point (coordination function) interframe space
• PLCP - physical layer convergence procedure
• PPDU - PLCP protocol data unit
• PS – power save
• PSDU - PLCP service data unit
• QAM - quadrature amplitude modulation
• QPSK - quadrature phase shift keying
• RFIC – radio frequency integrated circuit
• RX – receive or receiver
• RTS - request to send
• SC – single carrier
• SDM – spatial division multiplexing
• SIFS - short interframe space
• SIG – signal field
• SNR – signal to noise ratio
• STA – station
• STBC - space-time block coding
• STF – short training field
• SU – single user
• TG – task group
• TX – transmit or transmitter
• TXOP - transmission opportunity
86
Acronyms (4/4)
• VHT – very high throughput
• WG – working group
• WLAN – wireless local area networking
87
References1. Perahia, Eldad, and Stacey, Robert, “Next Generation Wireless LANs: Throughput,
Robustness, and Reliability in 802.11n”, Cambridge University Press, 2008
2. Kim, Youhan, “Channelization for 11ac”, 11-10/1064r2,
https://mentor.ieee.org/802.11/dcn/10/11-10-1064-02-00ac-channelization-for-11ac.ppt
3. Stacey, Robert, “Specification Framework for TGac”, 11-09/992r21,
https://mentor.ieee.org/802.11/dcn/09/11-09-0992-21-00ac-proposed-specification-
framework-for-tgac.doc
4. Merlin, Simone, “Protocol for SU and MU Sounding Feedback”, 11-10/1091,
https://mentor.ieee.org/802.11/dcn/10/11-10-1091-00-00ac-protocol-for-su-and-mu-sounding-
feedback.pptx
5. Merlin, Simone, “ACK protocol and backoff procedure for MU-MIMO”, 11-10/1092,
https://mentor.ieee.org/802.11/dcn/10/11-10-1092-00-00ac-ack-protocol-and-backoff-
procedure-for-mu-mimo.pptx
6. P802.11ac Draft 4.0
7. Myles, Andrew, and de Vegt, Rolf, “Wi-Fi Alliance (WFA) VHT Study Group Usage
Models”, 11-07/2988r4, https://mentor.ieee.org/802.11/dcn/07/11-07-2988-04-0000-liaison-
from-wi-fi-alliance-to-802-11-regarding-wfa-vht-study-group-consolidation-of-usage-
models.ppt
88
