Presentation on 802.11ac

Gigabit Wireless LAN:

Enhancements in 802.11ac

Eldad Perahia, Ph.D., Intel Corporation,

[email protected]

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

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 users 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

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

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


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


Convolutional Code Low Density Parity Check

Mandatory Optional

Space Time Block Code

GI, 256 QAM

VHT Preamble

Thro

ughput E

nhance

ment

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


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

ati

al

Ma

pp

ing

Constellation

mapper

Constellation

mapper

PH

Y P

ad

din

g

Sc

ram

ble

r

FE

C E

nc

od

er

Insert GI

and

Window

Analog

and RF

FE

C E

nc

od

er

En

co

de

r P

ars

er

Str

ea

m P

ars

er

FE

C E

nc

od

er

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

ati

al

Ma

pp

ing

Constellation

mapper

Constellation

mapperIDFT

Insert GI

and

Window

Analog

and RF

LDPC tone

mapper

LDPC tone

mappter

512 pt

IDFT

234

subcarriers

22


Single User, 80+80 MHz non-contiguous

Interleaver

CSD

ST

BC

BCC

Interleaver

Sp

ati

al

Ma

pp

ing

Constellation

mapper

Constellation

mapper

PH

Y P

ad

din

g

Sc

ram

ble

r

FE

C E

nc

od

er

FE

C E

nc

od

er

En

co

de

r P

ars

er

Str

ea

m P

ars

er

FE

C E

nc

od

er

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

ati

al

Ma

pp

ing

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



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

8s 8s 8s4s 4sVHT-LTFs

4s per LTF

VHT-

SIG-B

4s

L-STF L-LTFL-

SIGHT-SIG

HT-

STF

HT-

LTFData

HT mixed format PPDU

HT-

LTF

8s 8s 8s4s 4sHT-LTFs

4s 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

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, 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


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


SU bit allocation

Description

0-1 Short GI 2 2 B0 set to 1 for short GIB1 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 LDPCMU: 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 users 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


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


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

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


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



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 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

Inde

x

Modulatio

nR NES

Data rate (Mb/s)

800ns

GI

400ns

GI

0 BPSK 1 204.8 227.5

1 QPSK 1 409.5 455.0

2 QPSK 3/4 3 614.3 682.5

3 16-QAM 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


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


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


Secondary

channel

Energy detect only:

-62 dBm

Valid signal: -72dBm


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 11ns 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


Multi User

......

Sp

ati

al

Ma

pp

ing

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

Sc

ram

ble

r BC

C

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

Sc

ram

ble

r

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


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


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

Documents

Presentation on 802.11ac