Submission August 2004 doc.: IEEE 802.11-04/0935r1 S. Coffey, et al., WWiSE group Slide 1 WWiSE IEEE...

S. Coffey, et al., WWiSE groupSlide 1Submission

August 2004 doc.: IEEE 802.11-04/0935r1

WWiSE IEEE 802.11n ProposalWWiSE IEEE 802.11n Proposal

August 13, 2004

Airgo Networks, Bermai, Broadcom, Conexant, STMicroelectronics, Texas Instruments


August 2004 doc.: IEEE 802.11-04/0935r1

Contributors and contact informationContributors and contact information

• Airgo Networks: VK Jones, [email protected]• Bermai: Neil Hamady, [email protected]• Broadcom: Jason Trachewsky, [email protected]• Conexant: Michael Seals, [email protected] • STMicroelectronics: George Vlantis,

[email protected]• Texas Instruments: Sean Coffey, [email protected]


August 2004 doc.: IEEE 802.11-04/0935r1

ContentsContents

• WWiSE approach• Overview of key features• Proposal description

– Physical layer design– MAC features

• Discussion• Summary


August 2004 doc.: IEEE 802.11-04/0935r1

The WWiSE approachThe WWiSE approach

• WWiSE = World Wide Spectrum Efficiency

• The partnership was formed to develop a specification for next generation WLAN technology suitable for worldwide deployment

• Mandatory modes of the WWiSE proposal comply with current requirements in all major regulatory domains: Europe, Asia, Americas

• Proposal design emphasizes compatibility with existing installed base, building on experience with interoperability in 802.11g and previous 802.11 amendments

• All modes are compatible with QoS and 802.11e• Maximal spectral efficiency translates to highest

performance and throughput in all modes


August 2004 doc.: IEEE 802.11-04/0935r1

Overview of key mandatory featuresOverview of key mandatory features

• The WWiSE proposal’s mandatory modes are:– 2 transmit antennas– 20 MHz operation– 135 Mbps maximum PHY rate– 2x1 transmit diversity modes– Mixed mode preambles enabling on-the-air legacy compatibility– Efficient greenfield preambles – no increase in length over legacy– Enhanced efficiency MAC mechanisms– All components based on enhancement of existing COFDM PHY

2x2 MIMO operation in a 20 MHz channel: Goal is a robust, efficient, small-form-factor, universally compliant 100 Mbps mode that fits naturally with the existing installed base


August 2004 doc.: IEEE 802.11-04/0935r1

Overview of key optional featuresOverview of key optional features

• The WWiSE proposal’s optional modes are:– 3 and 4 transmit antennas– 40 MHz operation– Up to 540 Mbps PHY rate– 3x2, 4x2, 4x3 transmit diversity modes– Advanced coding: Rate-compatible LDPC code

• All modes are open-loop


August 2004 doc.: IEEE 802.11-04/0935r1

Physical layer designPhysical layer design

• Data modes– Transmitter structure– PHY rates– MIMO interleaving

• Preambles– Short sequences– Long sequences– SIGNAL fields


August 2004 doc.: IEEE 802.11-04/0935r1

Transmitter block diagramTransmitter block diagram

FEC encoder, puncturer

MIMO interleaver

Symbol mapper D/A

Interpol., filtering, limiter

Upconverter, amplifierIFFT

Add cyclic extension (guard)

Add pilots Insert training


August 2004 doc.: IEEE 802.11-04/0935r1

Mandatory data modesMandatory data modes

• 2 transmitter space-division multiplexing, 20 MHz• 2 transmitter space-time transmit diversity, 20 MHz• 802.11a/g (OFDM) modes• 64-state BCC


August 2004 doc.: IEEE 802.11-04/0935r1

2 transmitter SDM, 20 MHz (mandatory)2 transmitter SDM, 20 MHz (mandatory)

PHY rate Data carriers

Pilots

Code rate

Cyclic prefix, ns

Code Constellation

54 Mbps 54 2 1/2 800 BCC 16-QAM

81 Mbps 54 2 3/4 800 BCC 16-QAM

108 Mbps 54 2 2/3 800 BCC 64-QAM

121.5 Mbps

54 2 3/4 800 BCC 64-QAM

135 Mbps 54 2 5/6 800 BCC 64-QAM


August 2004 doc.: IEEE 802.11-04/0935r1

2x1 modes, 20 MHz (mandatory)2x1 modes, 20 MHz (mandatory)

PHY rate Data carrier

s

Pilots Code rate

Cyclic prefix, ns

Code Constellation

6.75 Mbps 54 2 1/2 800 BCC BPSK

10.125 Mbps

54 2 3/4 800 BCC BPSK

13.5 Mbps 54 2 1/2 800 BCC QPSK

20.25 Mbps

54 2 3/4 800 BCC QPSK

27 Mbps 54 2 1/2 800 BCC 16-QAM

40.5 Mbps 54 2 3/4 800 BCC 16-QAM

54 Mbps 54 2 2/3 800 BCC 64-QAM

60.75 Mbps

54 2 3/4 800 BCC 64-QAM


August 2004 doc.: IEEE 802.11-04/0935r1

Optional data modesOptional data modes

• 20 MHz:– 3 Tx space-division multiplexing– 4 Tx space division multiplexing– 3x2, 4x2, 4x3 space-time transmit diversity

• 40 MHz: (all 40 MHz modes optional)– 1 Tx antenna– 2 Tx space division multiplexing– 3 Tx space division multiplexing– 4 Tx space division multiplexing– 2x1, 3x2, 4x2, 4x3 space-time transmit diversity

• LDPC code option– An option in all proposed MIMO configurations and channel

bandwidths


August 2004 doc.: IEEE 802.11-04/0935r1

Optional modes, common format Optional modes, common format

Code rate

Cyclic prefix, ns

Code Constellation

1/2 800 BCC, LDPC 16-QAM





All combinations of 2, 3, 4 transmit antennas and 20/40 MHz offer exactly these 5 modes

All 20 MHz modes have 54 data subcarriers, 2 pilots. All 40 MHz modes have 108 data subcarriers, 4 pilots


August 2004 doc.: IEEE 802.11-04/0935r1

Optional mode data ratesOptional mode data rates

Configuration

Rate ½, 16-QAM

Rate ¾, 16-QAM

Rate 2/3, 64-QAM

Rate ¾, 64-QAM

Rate 5/6, 64-QAM

3 Tx, 20 MHz

81 121.5 162 182.25 202.5

4 Tx, 20 MHz

108 162 216 243 270

Configuration

Rate ½, 16-QAM

Rate ¾, 16-QAM

Rate 2/3, 64-QAM

Rate ¾, 64-QAM

Rate 5/6, 64-QAM

1 Tx, 40 MHz

54 81 108 121.5 135

2 Tx, 40 MHz

108 162 216 243 270

3 Tx, 40 MHz

162 243 324 364.5 405

4 Tx, 40 MHz

216 364 432 486 540

40 MHz:40 MHz:

20 MHz:20 MHz:


August 2004 doc.: IEEE 802.11-04/0935r1


MIMO interleaver

Symbol mapper D/A






August 2004 doc.: IEEE 802.11-04/0935r1

PreamblesPreambles

• Mixed-mode preambles:– Capable of operation in

presence of legacy 11a/g devices

– Ensure correct deferral behavior by devices compliant to legacy spec

• Green-field preambles:– Operate in environment

or time interval with only 11n devices on the air

– Applicable in combination with protection mechanisms, as in 11g, or in 11n-only BSSs

– Greater efficiency than mixed-mode preambles

Both preamble types are derived from a common basic structure, providing reuse in algorithms


August 2004 doc.: IEEE 802.11-04/0935r1

Short training sequenceShort training sequence

STRN

STRN400 ns

cs

STRN

STRN400 ns cs

STRN200 ns cs

STRN

STRN400 ns cs

STRN200 ns cs

STRN600 ns cs

2 Transmitters

3 Transmitters

4 Transmitters

20 MHz: STRN = 802.11ag short training sequence40 MHz mixed mode: STRN = Pair of 802.11ag short sequences separated in frequency by 20 MHz40 MHz green field: STRN = Newly defined sequence

cs = Cyclic shift


August 2004 doc.: IEEE 802.11-04/0935r1

Long training sequence and SIGNAL-N, Long training sequence and SIGNAL-N, green-field, 2 transmittersgreen-field, 2 transmitters

20 MHz: LTRN = 802.11ag long training sequence with four extra tones, 6.4 usec40 MHz: LTRN = Newly defined sequence, 6.4 usec

GI21 = GI2 for LTRN with 1600 ns cyclic shift

SIGNAL-N = 54 bits, 4 usec

GI21

STRN

STRN400 ns cs

LTRN

LTRN1600 ns

cs

GI2 SIGNAL-N

SIGNAL-N1600 ns cs


August 2004 doc.: IEEE 802.11-04/0935r1

Long training sequence and SIGNAL-N, Long training sequence and SIGNAL-N, green-field, 3 and 4 transmittersgreen-field, 3 and 4 transmitters

STRN400 ns cs

STRN

STRN200 ns

cs

STRN600 ns cs

GI21

LTRN

LTRN1600 ns

cs

GI2

GI23

LTRN100 ns

cs

LTRN1700 ns

cs

GI22

GI21

LTRN

LTRN1600 ns

cs

GI2

GI23

LTRN100 ns cs

LTRN1700 ns cs

GI22

SIGNAL-N

SIGNAL-N100 ns cs

SIGNAL-N1600 ns cs

SIGNAL-N1700 ns cs

For 3 transmitters, the first three rows are used


August 2004 doc.: IEEE 802.11-04/0935r1

Long training and SIGNAL fields, mixed Long training and SIGNAL fields, mixed mode, 2 transmittersmode, 2 transmitters

GI24

STRN

STRN400 ns cs

LTRN

LTRN100 ns

cs

GI2 SIGNAL

SIGNAL100 ns cs

2 transmitter green-field

long training and SIGNAL-N;

plus short sequence if 40

MHz


August 2004 doc.: IEEE 802.11-04/0935r1

Long training and SIGNAL fields, mixed Long training and SIGNAL fields, mixed mode, 3 and 4 transmittersmode, 3 and 4 transmitters

STRN LTRN

STRN400 ns cs

GI24LTRN

100 ns cs

GI2 SIGNAL

SIGNAL100 ns cs

3 or 4 transmitter green-field

long training and SIGNAL-N;

plus short training if 40

MHzSTRN

600 ns csSIGNAL

200 ns cs GI26

LTRN200 ns cs

STRN200 ns

cs

LTRN100 ns

cs

GI25SIGNAL

100 ns cs

For 3 transmitters, the first three rows are used


August 2004 doc.: IEEE 802.11-04/0935r1

Preamble lengths (20 & 40 MHz)Preamble lengths (20 & 40 MHz)

All space-time block codes follow the pattern with the same number of transmit antennas

8

8

0

0

Second long

284884x4

284883x3

204882x2

204881x1

TotalSIGNAL

First long

Short

Configuration

Green-Green-fieldfield


August 2004 doc.: IEEE 802.11-04/0935r1

Preamble lengths (20 & 40 MHz), contd.Preamble lengths (20 & 40 MHz), contd.

All space-time block codes follow the pattern with the same number of transmit antennas

Mixed modeMixed mode

0/8

0/8

0/8

/8

Second short

8

8

0

0

Third long

4

4

4

4

Second SIGNAL

8

8

8

8

Second long

40/484884x4

40/484883x3

32/404882x2

/404881x1

TotalSIGNAL

First long

ShortConfiguration


August 2004 doc.: IEEE 802.11-04/0935r1


MIMO interleaver

Symbol mapper D/A






August 2004 doc.: IEEE 802.11-04/0935r1

Parallel encodersParallel encoders

• For 40 MHz modes with more than two spatial streams, two parallel BCC encoders are used:

Multiplexing across two encoders

(round robin)

BCC encoder, puncturer

BCC encoder, puncturer

To MIMOinterleaver

Data payload


August 2004 doc.: IEEE 802.11-04/0935r1

Advanced coding optionAdvanced coding option

• Rate-compatible LDPC code with the following parameters:

• Transmitter block diagram as for BCC modes, except symbol interleaver, rate-compatible puncturing, and tail bits are not used

194416205/6

194414583/4

194412962/3

19449721/2

Block lengthInformation bitsRate


August 2004 doc.: IEEE 802.11-04/0935r1

LDPC code, contd.LDPC code, contd.

• There is no change required to SIFS or to any other system timing parameters when the advanced coding option is used

• The block size of 1944 reduces or eliminates the need for pad bits at the end of a packet– Pad bits are eliminated for 2 transmitter operation in 20 MHz

channels, and 2x1 and 1x1 in 40 MHz channels

• The four parity check matrices are derived from the rate-1/2 matrix via row combining

• The parity check matrices are structured and based on square-shaped building blocks of size 27x27

• The parity check matrices are structured to enable efficient encoding


August 2004 doc.: IEEE 802.11-04/0935r1


MIMO interleaver

Symbol mapper D/A






August 2004 doc.: IEEE 802.11-04/0935r1

MIMO interleavingMIMO interleaving

Coded bits

TX 0 interleaved bits

TX 1 interleaved bits

Configuration Idepth

108 tones, 1 Tx, 2x1 12

All others 6

Bit-cycling across NTX transmitters

Parameterized 802.11a-

style interleaver

5 subcarrier shift, same interleaver

...Shift of 5 additional subcarriers for each additional antenna


August 2004 doc.: IEEE 802.11-04/0935r1


MIMO interleaver

Symbol mapper D/A






August 2004 doc.: IEEE 802.11-04/0935r1

Space-time block codes and asymmetrySpace-time block codes and asymmetry

• Simple space-time block codes (STBCs) are used to handle asymmetric antenna configurations– STBC rate always is an integer

No new PHY rates result from STBC encoding of streams

– Block size is always two OFDM symbols– STBC encoding follows the stream encoding

AP STA


August 2004 doc.: IEEE 802.11-04/0935r1

Space-time block codesSpace-time block codes

• 2x1:

• 3x2:

• 4x2:

• 4x3:

s1*s2*Tx 2

s2s1Tx 1

t2t1

s1*s2*Tx 2

s4s3Tx 3

s2s1Tx 1

t2t1

s1*s2*Tx 2

s4s3Tx 3

s3*s4*Tx 4

s2s1Tx 1

t2t1

s1*s2*Tx 2

s4s3Tx 3

ssTx 4

s2s1Tx 1

t2t1

The STBC is applied independently to each OFDM subcarrier


August 2004 doc.: IEEE 802.11-04/0935r1


MIMO interleaver

Symbol mapper D/A






August 2004 doc.: IEEE 802.11-04/0935r1

Power spectral density, 20 MHzPower spectral density, 20 MHz


August 2004 doc.: IEEE 802.11-04/0935r1

Power spectral density, 40 MHzPower spectral density, 40 MHz


August 2004 doc.: IEEE 802.11-04/0935r1

MAC featuresMAC features


August 2004 doc.: IEEE 802.11-04/0935r1

New MAC featuresNew MAC features

• The WWiSE proposal builds on 802.11e functionality as much as possible, in particular EDCA, HCCA, and Block Ack– Goal is backward compatibility and simplicity– Block Ack is mandatory in the proposal

• Bursting and Aggregation:– MSDU aggregation– PSDU aggregation– Increased maximum PSDU length, to 8191 octets– HTP burst: sequence of MPDUs from same transmitter,

separated by zero interframe spacing (if at same Tx power level and PHY configuration) or 2 usec (otherwise)


August 2004 doc.: IEEE 802.11-04/0935r1

New MAC features, contd.New MAC features, contd.

• Block Ack frames ACK policy– Reduce Block Ack overhead

• Legacy remediation– N-STA detection/advertisement

Identification of TGn and non-TGn devices and BSSs– Legacy Protection mechanisms

Additions to existing protection mechanisms– 40/20 MHz channel switching

Equitable sharing of resources with legacy


August 2004 doc.: IEEE 802.11-04/0935r1

DiscussionDiscussion


August 2004 doc.: IEEE 802.11-04/0935r1

100 Mbps throughput100 Mbps throughput

• See response to CC 27 in 11/04-0877-00-000n• Efficiency upgrades in 802.11e and further enhancements in 11n mean that the 45-50% system

efficiencies of old 802.11 systems have evolved to 75-85% in contemporary systems– Many such enhancements are commercially available in firmware upgrades from multiple vendors

• 100 Mbps throughput is achieved from 135 Mbps PHY rate in a variety of setups– Both EDCA and HCCA allow this efficiency

• 100 Mbps throughput may even be achieved from 121.5 Mbps PHY rate– This requires HCCA; EDCA does not suffice


August 2004 doc.: IEEE 802.11-04/0935r1

100 Mbps throughput, contd.100 Mbps throughput, contd.

• Example scenario:– 4000 byte packets– HTP burst transmission, 3 packets– Block ack– 10%+ for assorted other users, beacons, etc.

BSS share, etc.

Preamble SIGNAL-N SIFS DIFS

960 usec

Data payload

Block ack request/ack

20 240 240

2404 4 24 16

32 34

106


August 2004 doc.: IEEE 802.11-04/0935r1

Robustness of modesRobustness of modes

• 2x2 operation achieving 100 Mbps throughput in a 20 MHz channel is feasible– Requires high-performance signal processing– At highest rates, high performance MIMO detection and/or

advanced coding are required

• 2x3 operation achieving 100 Mbps throughput in a 20 MHz channel is very feasible– Achieves throughput targets with MMSE processing and BCC

• Balance and approach are up to the implementer and beyond the scope of the standard


August 2004 doc.: IEEE 802.11-04/0935r1

Capacity and operating points, 2x2Capacity and operating points, 2x2

• Channel model D,

NLOS, half-wavelength spacing

• Curves are envelopes of curves for the 5 rates

• For each constituent curve, capacity is reduced by outage

Baseline 108 is a 2 Tx system with 802.11a/g 54 Mbps


August 2004 doc.: IEEE 802.11-04/0935r1

Optionality of 40 MHzOptionality of 40 MHz Reasons why 40 MHz channels are not proposed as

mandatory:

• Limited worldwide applicability– Europe: clause 4.4.2.2 of ETSI EN 301 893 V1.2.3– Japan: ARIB STD-T71

• The repackaging effect: – Halving the number of channels to provide each twice the data

rate is of questionable value as an enhancement• System and contention overhead:

– Double the number of users in a single BSS results in increased contention losses; two separate 20 MHz channels generally provide better network capacity, especially with coordinated management

• Backward compatibility and interoperability:– In dense legacy network deployments, contiguous 40 MHz

transmission bandwidth may not be available or performance may be impaired


August 2004 doc.: IEEE 802.11-04/0935r1

ReferencesReferences

1. IEEE 802.11/04-0886-00-000n, “WWiSE group PHY and MAC specification,” M. Singh, B. Edwards et al.

2. IEEE 802.11/04-0877-00-000n, “WWiSE proposal response to functional requirements and comparison criteria,” C. Hansen et al.

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