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WWiSE IEEE 802.11n Proposal

WWiSE IEEE 802.11n Proposal. August 13, 2004 Airgo Networks, Bermai, Broadcom, Conexant, STMicroelectronics, Texas Instruments. Contributors and contact information. Airgo Networks: VK Jones, vkjones@airgonetworks.com Bermai: Neil Hamady, nhamady@bermai.com

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WWiSE IEEE 802.11n Proposal

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  1. WWiSE IEEE 802.11n Proposal August 13, 2004 Airgo Networks, Bermai, Broadcom, Conexant, STMicroelectronics, Texas Instruments S. Coffey, et al., WWiSE group

  2. 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 S. Coffey, et al., WWiSE group

  3. Contents • WWiSE approach • Overview of key features • Proposal description • Physical layer design • MAC features • Discussion • Summary S. Coffey, et al., WWiSE group

  4. 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 S. Coffey, et al., WWiSE group

  5. 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 S. Coffey, et al., WWiSE group

  6. 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 S. Coffey, et al., WWiSE group

  7. Physical layer design • Data modes • Transmitter structure • PHY rates • MIMO interleaving • Preambles • Short sequences • Long sequences • SIGNAL fields S. Coffey, et al., WWiSE group

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

  9. 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 S. Coffey, et al., WWiSE group

  10. 2 transmitter SDM, 20 MHz (mandatory) S. Coffey, et al., WWiSE group

  11. 2x1 modes, 20 MHz (mandatory) S. Coffey, et al., WWiSE group

  12. Optional 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 S. Coffey, et al., WWiSE group

  13. Optional modes, common format 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 S. Coffey, et al., WWiSE group

  14. Optional mode data rates 20 MHz: 40 MHz: S. Coffey, et al., WWiSE group

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

  16. 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 Preambles Both preamble types are derived from a common basic structure, providing reuse in algorithms S. Coffey, et al., WWiSE group

  17. STRN STRN STRN STRN 400 ns cs STRN 400 ns cs STRN 400 ns cs STRN 200 ns cs STRN 200 ns cs STRN 600 ns cs Short training sequence 4 Transmitters 3 Transmitters 2 Transmitters 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 S. Coffey, et al., WWiSE group

  18. GI2 STRN SIGNAL-N LTRN STRN 400 ns cs GI21 LTRN 1600 ns cs SIGNAL-N 1600 ns cs Long training sequence and SIGNAL-N, green-field, 2 transmitters 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 S. Coffey, et al., WWiSE group

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

  20. 2 transmitter green-field long training and SIGNAL-N; plus short sequence if 40 MHz GI2 STRN SIGNAL LTRN GI24 LTRN 3100 ns cs SIGNAL 3100 ns cs STRN 400 ns cs Long training and SIGNAL fields, mixed mode, 2 transmitters S. Coffey, et al., WWiSE group

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

  22. Configuration Short First long SIGNAL Second long Total Green-field 1x1 8 8 4 0 20 2x2 8 8 4 0 20 3x3 8 8 4 8 28 4x4 8 8 4 8 28 Preamble lengths (20 & 40 MHz) All space-time block codes follow the pattern with the same number of transmit antennas S. Coffey, et al., WWiSE group

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

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

  25. BCC encoder, puncturer To MIMO interleaver BCC encoder, puncturer Multiplexing across two encoders (round robin) Parallel encoders • For 40 MHz modes with more than two spatial streams, two parallel BCC encoders are used: Data payload S. Coffey, et al., WWiSE group

  26. 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 S. Coffey, et al., WWiSE group

  27. 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 S. Coffey, et al., WWiSE group

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

  29. Parameterized 802.11a-style interleaver 5 subcarrier shift, same interleaver Bit-cycling across NTX transmitters . . . MIMO interleaving TX 0 interleaved bits Coded bits TX 1 interleaved bits Shift of 5 additional subcarriers for each additional antenna S. Coffey, et al., WWiSE group

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

  31. AP STA 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 S. Coffey, et al., WWiSE group

  32. 2x1: 3x2: 4x2: 4x3: t1 t2 t1 t2 Tx 1 s1 s2 Tx 1 s1 s2 Tx 2 -s2* s1* Tx 2 -s2* s1* Tx 3 s3 s4 Tx 4 -s4* s3* t1 t2 t1 t2 Tx 1 s1 s2 Tx 1 s1 s2 Tx 2 -s2* s1* Tx 2 -s2* s1* Tx 3 s3 s4 Tx 3 s3 s4 Tx 4 s5 s6 Space-time block codes The STBC is applied independently to each OFDM subcarrier S. Coffey, et al., WWiSE group

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

  34. Power spectral density, 20 MHz S. Coffey, et al., WWiSE group

  35. Power spectral density, 40 MHz S. Coffey, et al., WWiSE group

  36. MAC features S. Coffey, et al., WWiSE group

  37. 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) S. Coffey, et al., WWiSE group

  38. 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 S. Coffey, et al., WWiSE group

  39. Discussion S. Coffey, et al., WWiSE group

  40. 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 S. Coffey, et al., WWiSE group

  41. 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 BSS share, etc. Block ack request/ack 20 240 4 240 106 24 240 4 34 16 32 SIFS DIFS SIGNAL-N Preamble 960 usec S. Coffey, et al., WWiSE group

  42. 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 S. Coffey, et al., WWiSE group

  43. 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 Capacity and operating points, 2x2 Baseline 108 is a 2 Tx system with 802.11a/g 54 Mbps S. Coffey, et al., WWiSE group

  44. 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 S. Coffey, et al., WWiSE group

  45. 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. S. Coffey, et al., WWiSE group

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