1 / 30

### High-Throughput Enhancements for 802.11: Features, Performance, and Future Directions ###

This document outlines significant advancements in the 802.11 wireless communication standard, focusing on high-throughput solutions designed by Qualcomm. Key goals include maximizing throughput, enhancing Quality of Service (QoS), and maintaining backward compatibility. The paper discusses innovative approaches such as Spatial Spreading and Eigenvector Steering, demonstrating their effectiveness in achieving over 150 Mbps PHY throughput under specific conditions. It also emphasizes the importance of rate adaptation and the balance between time-to-market needs and design longevity. ###

tevy
Télécharger la présentation

### High-Throughput Enhancements for 802.11: Features, Performance, and Future Directions ###

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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

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

  18. 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

  19. 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

  20. 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

  21. 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

  22. 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

  23. 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

  24. 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

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

  26. 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

  27. 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

  28. 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

  29. 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

  30. 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

More Related