WWiSE IEEE 802.11n Proposal August 13, 2004 Airgo Networks, Bermai, Broadcom, Conexant, STMicroelectronics, Texas Instruments WWiSE group

Contributors and contact information Airgo Networks: VK Jones, vkjones@airgonetworks.com Bermai: Neil Hamady, nhamady@bermai.com Broadcom: Jason Trachewsky, jat@broadcom.com Conexant: Michael Seals, michael.seals@conexant.com STMicroelectronics: George Vlantis, George.Vlantis@st.com Texas Instruments: Sean Coffey, coffey@ti.com WWiSE group

Contents WWiSE approach Overview of key features Proposal description Physical layer design MAC features Discussion Summary WWiSE group

The 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 WWiSE group

Overview 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 WWiSE group

Overview 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 WWiSE group

Physical layer design Data modes Preambles Transmitter structure PHY rates MIMO interleaving Preambles Short sequences Long sequences SIGNAL fields WWiSE group

Transmitter block diagram FEC encoder, puncturer MIMO interleaver Symbol mapper D/A Interpol., filtering, limiter Upconverter, amplifier IFFT Add cyclic extension (guard) Add pilots Insert training WWiSE group

Mandatory 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 WWiSE group

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 3/4 108 Mbps 2/3 64-QAM 121.5 Mbps 135 Mbps 5/6 WWiSE group

2x1 modes, 20 MHz (mandatory) PHY rate Data carriers Pilots Code rate Cyclic prefix, ns Code Constellation 6.75 Mbps 54 2 1/2 800 BCC BPSK 10.125 Mbps 3/4 13.5 Mbps QPSK 20.25 Mbps 27 Mbps 16-QAM 40.5 Mbps 54 Mbps 2/3 64-QAM 60.75 Mbps WWiSE group

Optional data modes 20 MHz: 40 MHz: (all 40 MHz modes optional) 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 2x1, 3x2, 4x2, 4x3 space-time transmit diversity LDPC code option An option in all proposed MIMO configurations and channel bandwidths WWiSE group

Optional modes, common format Code rate Cyclic prefix, ns Code Constellation 1/2 800 BCC, LDPC 16-QAM 3/4 2/3 64-QAM 5/6 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 WWiSE group

Optional mode data rates 20 MHz: 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 108 216 243 270 40 MHz: 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 162 216 243 270 3 Tx, 40 MHz 324 364.5 405 4 Tx, 40 MHz 364 432 486 540 WWiSE group

Interpol., filtering, limiter MIMO interleaver Symbol mapper Add pilots Insert training FEC encoder, puncturer Interpol., filtering, limiter MIMO interleaver Symbol mapper Upconverter, amplifier IFFT D/A Add cyclic extension (guard) WWiSE group

Preambles Mixed-mode preambles: Green-field 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 WWiSE group

Short training sequence 2 Transmitters 3 Transmitters 4 Transmitters STRN 400 ns cs 200 ns cs STRN 400 ns cs 200 ns cs 600 ns cs 20 MHz: STRN = 802.11ag short training sequence 40 MHz mixed mode: STRN = Pair of 802.11ag short sequences separated in frequency by 20 MHz 40 MHz green field: STRN = Newly defined sequence cs = Cyclic shift WWiSE group

Long training sequence and SIGNAL-N, green-field, 2 transmitters GI21 STRN 400 ns cs LTRN 1600 ns cs GI2 SIGNAL-N 20 MHz: LTRN = 802.11ag long training sequence with four extra tones, 6.4 usec 40 MHz: LTRN = Newly defined sequence, 6.4 usec GI21 = GI2 for LTRN with 1600 ns cyclic shift SIGNAL-N = 54 bits, 4 usec WWiSE group

Long training sequence and SIGNAL-N, green-field, 3 and 4 transmitters STRN 400 ns cs 200 ns cs 600 ns cs GI21 LTRN 1600 ns cs GI2 GI23 100 ns cs 1700 ns cs GI22 -GI23 -LTRN -GI22 SIGNAL-N For 3 transmitters, the first three rows are used WWiSE group

Long training and SIGNAL fields, mixed mode, 2 transmitters GI24 STRN 400 ns cs LTRN 3100 ns cs GI2 SIGNAL 2 transmitter green-field long training and SIGNAL-N; plus short sequence if 40 MHz WWiSE group

Long training and SIGNAL fields, mixed mode, 3 and 4 transmitters STRN LTRN 400 ns cs GI24 3100 ns cs GI2 SIGNAL 3 or 4 transmitter green-field long training and SIGNAL-N; plus short training if 40 MHz 600 ns cs 200 ns cs GI26 100 ns cs GI25 For 3 transmitters, the first three rows are used WWiSE group

Preamble lengths (20 & 40 MHz) 8 Second long 28 4 4x4 3x3 20 2x2 1x1 Total SIGNAL First long Short Configuration Green-field All space-time block codes follow the pattern with the same number of transmit antennas WWiSE group

Preamble lengths (20 & 40 MHz), contd. Mixed mode 0/8 -/8 Second short 8 Third long 4 Second SIGNAL Second long 40/48 4x4 3x3 32/40 2x2 -/40 1x1 Total SIGNAL First long Short Configuration All space-time block codes follow the pattern with the same number of transmit antennas WWiSE group

Interpol., filtering, limiter MIMO interleaver Symbol mapper Add pilots Insert training FEC encoder, puncturer Interpol., filtering, limiter MIMO interleaver Symbol mapper Upconverter, amplifier IFFT D/A Add cyclic extension (guard) WWiSE group

Multiplexing across two encoders Parallel 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 To MIMO interleaver Data payload WWiSE group

Advanced 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 Rate Information bits Block length 1/2 972 1944 2/3 1296 1944 3/4 1458 1944 5/6 1620 1944 WWiSE group

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 WWiSE group

Interpol., filtering, limiter MIMO interleaver Symbol mapper Add pilots Insert training FEC encoder, puncturer Interpol., filtering, limiter MIMO interleaver Symbol mapper Upconverter, amplifier IFFT D/A Add cyclic extension (guard) WWiSE group

MIMO interleaving . Parameterized 802.11a-style interleaver Bit-cycling across NTX transmitters Parameterized 802.11a-style interleaver 5 subcarrier shift, same interleaver . TX 0 interleaved bits Coded bits TX 1 interleaved bits Configuration Idepth 108 tones, 1 Tx, 2x1 12 All others 6 Shift of 5 additional subcarriers for each additional antenna WWiSE group

Interpol., filtering, limiter MIMO interleaver Symbol mapper Add pilots Insert training FEC encoder, puncturer Interpol., filtering, limiter MIMO interleaver Symbol mapper Upconverter, amplifier IFFT D/A Add cyclic extension (guard) WWiSE group

Space-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 WWiSE group

Space-time block codes 2x1: 3x2: 4x2: 4x3: s1* -s2* Tx 2 s2 s1 Tx 1 t2 t1 s1* -s2* Tx 2 s4 s3 Tx 3 s3* -s4* Tx 4 s2 s1 Tx 1 t2 t1 s1* -s2* Tx 2 s4 s3 Tx 3 s2 s1 Tx 1 t2 t1 s1* -s2* Tx 2 s4 s3 Tx 3 s6 s5 Tx 4 s2 s1 Tx 1 t2 t1 The STBC is applied independently to each OFDM subcarrier WWiSE group

Interpol., filtering, limiter MIMO interleaver Symbol mapper Add pilots Insert training FEC encoder, puncturer Interpol., filtering, limiter MIMO interleaver Symbol mapper Upconverter, amplifier IFFT D/A Add cyclic extension (guard) WWiSE group

Power spectral density, 20 MHz WWiSE group

Power spectral density, 40 MHz WWiSE group

MAC features WWiSE group

New 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) WWiSE group

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 WWiSE group

Discussion WWiSE group

100 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 WWiSE group

100 Mbps throughput, contd. Example scenario: 4000 byte packets HTP burst transmission, 3 packets Block ack 10%+ for assorted other users, beacons, etc. Data payload Block ack request/ack BSS share, etc. 20 240 4 240 4 240 24 16 32 34 106 Preamble SIGNAL-N SIFS DIFS 960 usec WWiSE group

Robustness 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 WWiSE group

Capacity 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 WWiSE group

Optionality 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 WWiSE group

References IEEE 802.11/04-0886-00-000n, “WWiSE group PHY and MAC specification,” M. Singh, B. Edwards et al. IEEE 802.11/04-0877-00-000n, “WWiSE proposal response to functional requirements and comparison criteria,” C. Hansen et al. WWiSE group