High-Throughput Enhancements for 802.11: Features and Performance

1. High-Throughput Enhancements for 802.11: Features and Performance John Ketchum, Sanjiv Nanda, Rod Walton, Steve Howard, Mark Wallace, Bjorn Bjerke, Irina Medvedev, Santosh Abraham, Arnaud Meylan, Shravan SurineniQUALCOMM, Incorporated9 Damonmill Square, Suite 2AConcord, MA 01742Phone: 781-276-0915Fax: 781-276-0901johnk@qualcomm.com John Ketchum, et al, Qualcomm

2. Qualcomm Proposal Documents • Original submissions (as revised) • 11-04-870r1 High Throughput System Description and Operating Principles. • 11-04-871r2 High Throughput Proposal Compliance Statement (this document.) • 11-04-872r2 Link Level and System Performance Results for High Throughput Enhancements. • 11-04-873r2 High Throughput Enhancements for 802.11: Features and Performance • November Presentations: • 11-04-1404r1 Qualcomm Complete Proposal • 11-04-1449r0 Qualcomm PHY Supplement • 11-04-1452r0 Qualcomm MAC Supplement John Ketchum, et al, Qualcomm

3. Goals • Maximize Throughput, QoS, and Spectral Efficiency • Minimize complexity and assure backward compatibility • Provide balance between TTM needs and 11n design longevity economics John Ketchum, et al, Qualcomm

4. Throughput Comparison 0 dB: 120 m 10 dB: 60 m 20 dB: 30 m 30 dB: 15 m 37.5 dB: 10m SGI-52: 52 data subcarriers with short guard interval • Results given with closed loop rate control, except STBC-OL • SS-STBC can achieve 120Mbps at 30m (20dB) • ES has > 6 dB advantage over other at 150 Mbps PHY throughput • At 30 m (20 dB) ES has >50% PHY t’put advantage over others John Ketchum, et al, Qualcomm

5. Proposal Summary: PHY • Builds on 802.11a waveform • 20 MHz bandwidth with 802.11a/b/g spectral mask • 802.11a modulation, coding, interleaving with expanded rate set • Backward compatibility through legacy STF, LTF and SIG • Supports a maximum of 4 wideband spatial streams • Two forms of spatial processing • Spatial Spreading (SS): modulation and coding per wideband spatial channel • No calibration required • SNR per wideband spatial stream known at Tx • Eigenvector Steering (ES): via wideband spatial modes/SVD per subcarrier • Tx and Rx steering • Over the air calibration procedure required • Rate adaptation enables sustained high rate operation • PHY techniques proven in FPGA-based prototype John Ketchum, et al, Qualcomm

6. Spatial Spreading • Spatial spreading for 2 Tx and 4 Tx uses Hadamard matrix • No multiplies required to execute Matrix-Vector multiply • Flexible number of spatial streams • 1 ≤ Ns≤ Ntx • All transmit antennas used, regardless of stream count John Ketchum, et al, Qualcomm

7. Spatial Spreading: Mandatory & Optional Features • Mandatory • Hadamard matrix-vector multiply at transmitter • Cyclic transmit diversity at transmitter • Receiver must be capable of handling spatially spread signals (zero-forcing, MMSE, etc.) • Support for rate feedback in PLCP/MAC header • Optional • Rate feedback functionality John Ketchum, et al, Qualcomm

8. Eigenvector Steering • Substantial throughput gains over baseline spatial spreading • Full MIMO channel characterization required at Tx • Tx steering using per-bin channel eigenvectors from SVD • Rx steering renders multiple Tx streams orthogonal at receiver, allowing transmission of multiple independent spatial streams • This approach maximizes both data rate and range • Per-stream rate control and rate feedback required for robust high throughput operation John Ketchum, et al, Qualcomm

9. Support for Eigenvector Steering • Base standard mandatory features are required to support optional ES mode • Independent rates per stream for up to four streams • Modulation/coding/interleaving must support independent rates per stream • Rate feedback • Fields in PLCP header extension or MAC header • MIMO training waveform design • Must support steered reference • Allows implicit channel state feedback in all PPDUs • Tone interleaving (TGnSync) or Walsh cover (Qualcomm) • Related elements such as signaling for mode control John Ketchum, et al, Qualcomm

10. Eigenvector Steering • Some features are mandatory for devices supporting optional ES mode • Messaging and sounding waveforms to support over-the-air calibration • Transmit steering and computation of Tx steering vectors • Real-time matrix-vector multiply capability • Determine steering vectors from unsteered training sequence • Steered training sequence • Other optional Eigenvector Steering features • Bi-directional steering: Both STAs in a corresponding pair use Eigenvector steering • Uni-directional steering: Only one STA in corresponding pair (e.g. AP) use Eigenvector Steering John Ketchum, et al, Qualcomm

11. Another Approach • Space-Time Block Coding with Spatial Spreading • Additional Tx diversity benefit of STBC with flexibility of SS • Number of STBC streams decoupled from number of Tx antennas • Can adjust power allocations in unequal diversity cases • Possible compromise approach – best of both worlds John Ketchum, et al, Qualcomm

12. Throughput Comparison 0 dB: 120 m 10 dB: 60 m 20 dB: 30 m 30 dB: 15 m 37.5 dB: 10m SGI-52: 52 data subcarriers with short guard interval • Results given with closed loop rate control, except STBC-OL • SS-STBC can achieve 120Mbps at 30m (20dB) • ES has > 6 dB advantage over other at 150 Mbps PHY throughput • At 30 m (20 dB) ES has >50% PHY t’put advantage over others John Ketchum, et al, Qualcomm

13. 802.11n PLCP Preamble/Header • Legacy portion 100% backward compatible • HT portion supports up to four wideband spatial channels using Spatial Spreading (SS) or Eigenvector Steering (ES) • PLCP header extension carries scrambler init and rate feedback John Ketchum, et al, Qualcomm

14. Preamble Legacy Portion • Legacy portion of preamble transmitted using cyclic transmit diversity (no spatial multiplexing or eigenvector steering) • Legacy SIGNAL field used to indicate HT • Rate field set to unused value indicates HT • Size/Request field indicates HT PPDU length. John Ketchum, et al, Qualcomm

15. HT Portion • HT-SIG conveys rates, MIMO training type and length • MIMO training can be either steered training or direct training • Uses Walsh functions to establish orthogonality among eigenmodes or Tx antennas • Uses unique training sequence on each mode or Tx antenna to ensure equal levels at Rx • Used by Rx STA to calculate Rx steering • Used by Rx STA to calculate Tx steering when using ES John Ketchum, et al, Qualcomm

16. Legacy and MIMO Training for 2, 3, and 4 Tx • STS: 802.11a STS • LTS: 802.11a LTS • L_SIG: 802.11a SIGNAL • HT-SIG: Extended SIGNAL • MTSn: MIMO training symbol for Tx antenna n • CDx: x ns cyclic delay • Shows unsteered MIMO training John Ketchum, et al, Qualcomm

17. Modulation/Coding/Interleaving • Proposal specifies parallel coding/decoding to support multiple rates in parallel • Legacy BCC with extended rates/puncturing patterns to provide expanded MCS set • Tail per stream per PPDU– requires parallel decoding for best performance • Alternative is tail per stream per OFDM symbol • Small increase in overhead, allows single-decoder architecture John Ketchum, et al, Qualcomm

18. Alternative Modulation/Coding/Interleaving • Simplified single-decoder architecture • Parse/demux must be coordinated with puncture patterns John Ketchum, et al, Qualcomm

19. Advanced Coding • No advanced coding included in proposal • Advanced coding must support independent rates per stream for eigenvector steering. • Single coder/decoder architectures are more feasible with advanced coding such as Turbo codes. John Ketchum, et al, Qualcomm

20. Summary of MAC Objectives • Enhanced efficiency built on 802.11e • Ensure high QoS and high throughput • Support MIMO operation with limited overhead • Limit introduction of new features • Minimize burden on transmit and receive processing John Ketchum, et al, Qualcomm

21. MAC Throughput vs Range • Throughput above the MAC of 100 Mbps is achieved at: • 5.25 GHz : 2x2 – 29m, 4x4 – 47m • 2.4 GHz: 2x2 - 40m, 4x4 -75 m. • Highest throughput of all proposals. John Ketchum, et al, Qualcomm

22. MAC Elements Summary • Mandatory Enhancements to 802.11e • Aggregation • Frame Aggregation to a single RA. • PPDU Aggregation: Reduced or zero IFS • Adaptive Coordination Function (ACF) • Multi-poll enhancement to HCCA • Low latency • Data rate feedback from Rx to Tx • Enhanced rate adaptation • Very low overhead John Ketchum, et al, Qualcomm

23. Aggregation • Significant performance gains at higher date rates: • 25-60% greater throughput for PHY rates of 50-100 Mbps • Key Attributes: • Frame Aggregation to a single RA. • PPDU Aggregation: Reduced or zero IFS John Ketchum, et al, Qualcomm

24. Adaptive Coordination Function • SCAP (Scheduled Access Period) initiated by SCHED message • Acts as consolidated multi-STA poll • Indicate TA, RA, start offset and duration of TXOP. • Permits effective PPDU Aggregation • Eliminate Immediate ACK for Block Ack frames • MIMO training in SCHED message functions as broadcast sounding waveform for channel estimation and SVD calculation John Ketchum, et al, Qualcomm

25. Adaptive Coordination Function • Benefits • ACF offers 50% to 100% throughput gain over EDCA & HCCA depending on traffic model • ACF meets and exceeds QoS requirements with greater efficiency John Ketchum, et al, Qualcomm

26. Data Rate Feedback John Ketchum, et al, Qualcomm

27. Data Rate Feedback • 16-bit field in PLCP header extension specifies up to four preferred rates • Tx PHY rate is maximized after single ACK received • Accurate PHY rate tracking for time varying channels • Substantial throughput gains • Scenario 1: 50% • Scenario 6: 38% John Ketchum, et al, Qualcomm

28. Goals • Maximize Throughput, QoS, and Spectral Efficiency • Eigenvector Steering (ES) and rate feedback provide the highest throughput and QoS performance. • ES should be an Optional Feature that can provide significant longevity to the 11n standard. • Provision for optional ES in 802.11n requires a few mandatory and some specified optional features. John Ketchum, et al, Qualcomm

29. Goals • Minimize complexity and assure backward compatibility • Builds on 802.11a waveform • 20 MHz bandwidth with 802.11a/b/g spectral mask • 802.11a modulation, coding, interleaving with expanded rate set • Backward compatibility through legacy STF, LTF and SIG • Provision for optional ES in 802.11n requires a few mandatory and some specified optional features. John Ketchum, et al, Qualcomm

30. Goals • Provide balance between TTM needs and 11n design longevity economics • Both Spatial Spreading and Spatial Spreading with Space Time Block Coding are good mandatory alternatives that meet TTM objectives • ES should be an Optional Feature that can provide significant longevity to the 11n standard. John Ketchum, et al, Qualcomm

31. Summary • Qualcomm proposal builds on existing 802.11a,g,e design • 802.11n can enable new markets & applications: • Multimedia distribution in the home • Enhanced enterprise applications (e.g. VoD, Video Conf.) • These applications require: • High throughput  SS/ES, ACF, rate feedback • High QoS  SS/ES, ACF, rate feedback • Maximized range  ES • Maximum spectral efficiency  ES • SS/ES + rate feedback + ACF meet the requirements associated with these new markets & applications: • Highest network capacity: greater than 100 mbps above the MAC inside 30 m (20 MHz, 2x2, 5 GHz) • Reliable coverage • QoS: Less than 50 ms latency with “ZERO packet loss” John Ketchum, et al, Qualcomm