Doc.: IEEE 802.11-04/0873r1 Submission August 2004 John Ketchum, et al, QUALCOMMSlide 1...

August 2004

John Ketchum, et al, QUALCOMM

Slide 1

doc.: IEEE 802.11-04/0873r1

Submission

High-Throughput Enhancements for 802.11: Features and Performance of QUALCOMM’s

Proposal

John Ketchum, Sanjiv Nanda, Rod Walton, Steve Howard, Mark Wallace, Bjorn Bjerke, Irina Medvedev, Santosh Abraham, Arnaud Meylan, Shravan

Surineni

QUALCOMM, Incorporated9 Damonmill Square, Suite 2A

Concord, MA 01742Phone: 781-276-0915Fax: [email protected]

August 2004


Slide 2

doc.: IEEE 802.11-04/0873r1

Submission

Agenda

• Introductory remarks

• MAC Features

• System Performance

• PHY Features

• Link Performance

August 2004


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doc.: IEEE 802.11-04/0873r1

Submission

Qualcomm’s Status Assessment

• Submitted proposals contain the basis for an excellent solution to HT requirements

• Substantial commonality in proposed approaches– MIMO OFDM– Advanced coding– Frame aggregation– Elimination of IFS

• Qualcomm is committed to working with TGn to establish rapid convergence to a draft standard– Future proof– Optimized performance/complexity tradeoff

• Critical Issues– Informed transmitter operation

• Low-overhead feedback

– Flexible rates– Minimal feature set for support of low-latency operation

August 2004


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doc.: IEEE 802.11-04/0873r1

Submission

Main Points

• 20 MHz operation• Maximum PHY data rates:

– 202 Mbps for stations with two antennas– 404 Mbps for stations with four antennas

• Backward compatible modulation, coding and interleaving• Highly reliable, high-performance operation with existing 802.11

convolutional codes used in combination with Eigenvector Steering spatial multiplexing techniques

• Fall-back to robust Spatial Spreading waveform for uninformed transmitter

• Backward compatible preamble and PLCP with extended SIGNAL field.

• Adaptation of rates and spatial multiplexing mode through low overhead asynchronous feedback. Works with TXOPs obtained through EDCA, HCF or ACF.

• PHY techniques proven in FPGA-based prototype

August 2004


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doc.: IEEE 802.11-04/0873r1

Submission

MAC Design Objectives

• Objectives– Preserve the simplicity and robustness of distributed coordination

– Backward compatible

– Enhancements for high throughput, low latency operation

– Build on 802.11e, 802.11h feature set: • TXOPs,

• Block Ack, Delayed Block Ack,

• Direct Link Protocol

• Dynamic Frequency Selection

• Transmit Power Control

August 2004


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doc.: IEEE 802.11-04/0873r1

Submission

MAC Feature Summary

• Frame aggregation– Length field per encapsulated frame

– Max aggregate size is negotiated per flow.

• Eliminate immediate ACK– No Immediate ACK for Aggregate Frames in Scheduled or Polled TXOPs

– Block Ack Request (BAR) frame does not require Immediate ACK, except in EDCA TXOPs.

• Aggregation for multiple STAs– Only AP is permitted to transmit SCHED and establish SCAP

– PPDU Aggregation

– SCHED: Message indicates Tx and Rx STA, start offset and duration for scheduled TXOPs. Complete information for optimum sleep mode.

• Reduced IFS– No IFS for consecutive scheduled transmissions from AP

– BIFS (10 us) for consecutive scheduled transmissions from STA

– GIFS (800 ns): Guard Period for consecutive scheduled transmissions from multiple STAs.

August 2004


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doc.: IEEE 802.11-04/0873r1

Submission

MAC Feature Summary

• Backward compatible SIGNAL– RATE/Type Field. Overload the legacy RATE field– Legacy STAs will abandon further decoding of the PPDU on seeing unrecognized

RATE field

• Protection mechanisms– Long NAV– RTS/CTS

• Rate Feedback– Extension of SERVICE field– MIMO Training Request and MIMO Rate Feedback Request is implicit. Always

included in PPDU

• MAC header compression– Compressed Header Formats: Eliminate, TA, RA, Duration/ID fields

• Compressed block ACK– Three formats defined– Transmitter option

• RRBSS– QoS-capable IBSS with round-robin scheduling

August 2004


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doc.: IEEE 802.11-04/0873r1

Submission

System Simulation Methodology

• The simulator is based on ns2• Includes physical layer features

– TGn Channel Models– PHY Abstraction determines frame loss events

• MAC features– EDCA– Adaptive Coordination Function (ACF): SCHED and SCAP– Frame Aggregation– ARQ with Block Ack– Closed Loop Rate Control (DRVF and DRV)– MIMO Modes (ES and SS)

• Transport– File Transfer mapped to TCP– QoS Flows mapped to UDP

August 2004


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doc.: IEEE 802.11-04/0873r1

Submission

Simulation Conditions – Fixed

• The following parameters are fixed for all system simulation results.– Bandwidth: 20 MHz.

– Frame Aggregation

– Fragmentation Threshold: 100 kB

– Delayed Block Ack

– Adaptive Rate Control

– Adaptive Mode Control between ES and SS

AC CW min CW max AIFS

0 127 1023 2 BlockAck/VoIP

1 127 1023 4 Video HDTV

2 127 1023 8 Other QoS

3 127 1023 10 Best effort

August 2004


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doc.: IEEE 802.11-04/0873r1

Submission

Simulation Conditions – Varied

The following parameters are varied. Results are provided for different combinations of these parameters.

• Bands: – 2.4 GHz – 5.25 GHz

• MIMO: – 2x2: All STAs with 2 antennas– 4x4: All STAs with 4 antennas– Mixed:

• Scenario 1: the AP and the HDTV/SDTV displays are assumed to have 4 antennas; all other STAs have 2 antennas.

• Scenario 6: AP and all STAs, except VoIP terminals have 4 antennas; VoIP terminals have 2 antennas.

• OFDM symbols– Standard: 0.8 μs Guard Interval, 48 data subcarriers– SGI-EXP: 0.4 μs Shortened Guard Interval, 52 data subcarriers

• Access Mechanisms– ACF (SCHED)– HCF (Poll)– EDCA with additional AC for Block Ack

August 2004


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doc.: IEEE 802.11-04/0873r1

Submission

Additional Scenarios

• Scenario 1 HT is an extension of Scenario 1:– Additonal FTP flow of up to 130 Mbps at 15.6 m from the AP for 2×2.

• Scenario 1 EXT is an extension of Scenario 1:– Additonal FTP flow of up to 130 Mbps at 15.6 m from the AP for 2×2.

– Maximum delay requirement for all video/audio streaming flows is decreased from 100/200 ms to 50 ms.

– Two HDTV flows are moved from 5 m from the AP, to 25 m from the AP.

• Scenario 6 EXT is an extension of Scenario 6:– One FTP flow of 2 Mbps at 31.1 m from the AP is increased up to 80

Mbps for 4x4.

August 2004


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doc.: IEEE 802.11-04/0873r1

Submission

Summary of Total Throughput Results

Metric 1 Metric 2 Metric 3 Metric 1 Metric 2 Metric 3 Metric 1 Metric 2 Metric 3Scenario 1 - 2.4GHz standard symbols 84.029 84.029 84.029 84.035 84.035 84.035 NA NA NAScenario 1 - 2.4GHz SGI-EXP symbols 84.029 84.029 84.029 84.036 84.036 84.036 NA NA NAScenario 1 - 2.4GHz SGI-EXP HCF 58.885 58.138 53.201 NA NA NA NA NA NAScenario 1 - 2.4GHz SGI-EXP EDCA 54.532 54.389 51.673 NA NA NA NA NA NAScenario 1 - 5.25GHz SGI-EXP HCF 58.813 57.904 53.003 83.136 83.133 81.657 NA NA NAScenario 1 - 5.25GHz SGI-EXP EDCA 53.007 52.891 50.112 53.941 53.879 51.208 NA NA NAScenario 1 - 5.25GHz standard symbols 77.449 77.442 75.947 84.007 84.007 84.007 NA NA NAScenario 1 - 5.25GHz SGI-EXP symbols 84.018 84.018 84.018 84.032 84.032 84.032 NA NA NAScenario 1 HT - 2.4GHz SGI-EXP symbols 103.111 103.111 103.111 185.841 185.841 185.841 NA NA NAScenario 1 HT - 5.25GHz SGI-EXP symbol 95.069 95.069 95.069 164.750 164.750 164.750 NA NA NAScenario 1 EXT - 2.4GHz SGI-EXP symbols 86.152 86.152 82.165 164.706 164.705 164.705 121.204 121.204 121.204Scenario 1 EXT - 5.25GHz SGI-EXP symbols 68.137 68.087 64.211 130.365 130.363 130.363 105.213 105.213 104.716

Scenario 4 - 2.4GHz SGI-EXP symbols 104.980 104.980 104.980 199.995 199.995 199.995 NA NA NAScenario 4 - 5.25GHz SGI-EXP symbols 100.296 100.296 100.296 191.566 191.566 191.566 NA NA NA

Scenario 6 - 5.25GHz standard symbols 60.228 60.228 60.138 66.138 66.137 66.137 66.119 66.119 66.029Scenario 6 - 5.25GHz standard symbols HCF 44.825 44.689 32.967 NA NA NA NA NA NAScenario 6 - 5.25GHz standard symbols EDCA 45.608 45.167 7.029 NA NA NA NA NA NAScenario 6 EXT- 5.25GHz standard symbols 67.434 67.434 67.256 100.308 100.308 100.308 105.174 105.174 105.085

2x2 4x4 Mixed

• Over 100 Mbps BSS throughput in realistic scenarios

August 2004


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doc.: IEEE 802.11-04/0873r1

Submission

Observations on Total Throughput

• ACF provides highest total throughput compared to HCF and EDCA.• ACF satisfies all QoS flows for all Sceanrios when SGI-EXP symbols are

used. – Only in the case standard symbols are used (giving reduced throughput) at 5.25

GHz (giving reduced range), the PLR requirement of gaming flows is not satisfied.

• No increase in throughput for EDCA with 4x4 compared to 2x2.• Scenario 1 EXT imposes stringent delay (less than 50 ms for streaming) and

range (HDTV flows at 25 m) requirements on QoS flows. – When 2x2 is used, one or two QoS flows are not satisfied. – In the Mixed case, by equipping the AP and the HDTV and SDTV displays with 4

antennas, all QoS flows except the gaming flow are satisfied with an almost 50% increase in total throughput compared to 2x2.

• In Scenario 4, throughput achieved is over 100 Mbps with 2x2 and almost 200 Mbps with 4x4.

• Scenario 6 EXT Mixed case (mixture of 4-antenna and 2-antenna STAs) gives higher TCP throughput than the 4x4 case.

– This is because there is more time available for TCP flows due to the reduced training sequence overhead for VoIP STAs with 2 antennas compared to VoIP STAs with 4 antennas. Sceanrio 6 EXT has 30 VoIP flows.

August 2004


Slide 14

doc.: IEEE 802.11-04/0873r1

Submission

Summary of MAC Efficiency Results2x2 4x4 Mixed

Scenario 1 - 2.4GHz standard symbols 0.650 0.354 NAScenario 1 - 2.4GHz SGI-EXP symbols 0.574 0.295 NAScenario 1 - 2.4GHz SGI-EXP HCF 0.509 NA NAScenario 1 - 2.4GHz SGI-EXP EDCA 0.470 NA NAScenario 1 - 5.25GHz SGI-EXP HCF 0.509 0.415 NAScenario 1 - 5.25GHz SGI-EXP EDCA 0.450 0.231 NAScenario 1 - 5.25GHz standard symbols 0.694 0.406 NAScenario 1 - 5.25GHz SGI-EXP symbols 0.639 0.336 NAScenario 1 HT - 2.4GHz SGI-EXP symbols 0.685 0.634 NAScenario 1 HT - 5.25GHz SGI-EXP symbol 0.673 0.649 NAScenario 1 EXT - 2.4GHz SGI-EXP symbols 0.605 0.610 0.611Scenario 1 EXT - 5.25GHz SGI-EXP symbols 0.599 0.599 0.607

Scenario 4 - 2.4GHz SGI-EXP symbols 0.658 0.659 NAScenario 4 - 5.25GHz SGI-EXP symbols 0.652 0.655 NA

Scenario 6 - 5.25GHz standard symbols 0.614 0.343 0.335Scenario 6 - 5.25GHz standard symbols HCF 0.486 NA NAScenario 6 - 5.25GHz standard symbols EDCA 0.511 NA NAScenario 6 EXT- 5.25GHz standard symbols 0.616 0.578 0.598

• As defined, MAC Efficiency is meaningful only when the offered load for a scenario exceeds the carried load and there is always backlogged traffic at some flow. In the above table, the MAC Efficiency numbers are shown in red for the cases where the medium is forced idle due to no backlog. These numbers are not meaningful.

August 2004


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doc.: IEEE 802.11-04/0873r1

Submission

Observations on MAC Efficiency

• For 2x2, the MAC Efficiency for ACF is between 0.65-0.7.

• For 2x2, the MAC Efficiency for HCF and EDCA is around 0.5.

• For 4x4, the MAC Efficiency for HCF and EDCA reduces to 0.4 and 0.2, respectively. ACF manages to sustain a MAC Efficiency around 0.6, even with 4x4.

August 2004


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doc.: IEEE 802.11-04/0873r1

Submission

Summary of QoS Flows Satisfied

Number of Qos Flows

2x2 4x4 MixedScenario 1 - 2.4GHz standard symbols 17 17 17 NAScenario 1 - 2.4GHz SGI-EXP symbols 17 17 17 NAScenario 1 - 2.4GHz SGI-EXP HCF 17 13 NA NAScenario 1 - 2.4GHz SGI-EXP EDCA 17 7 NA NAScenario 1 - 5.25GHz SGI-EXP HCF 17 13 15 NAScenario 1 - 5.25GHz SGI-EXP EDCA 17 7 10 NAScenario 1 - 5.25GHz standard symbols 17 15 17 NAScenario 1 - 5.25GHz SGI-EXP symbols 17 17 17 NAScenario 1 HT - 2.4GHz SGI-EXP symbols 17 17 17 NAScenario 1 HT - 5.25GHz SGI-EXP symbol 17 17 17 NAScenario 1 EXT - 2.4GHz SGI-EXP symbols 17 16 17 17Scenario 1 EXT - 5.25GHz SGI-EXP symbols 17 15 17 16

Scenario 4 - 2.4GHz SGI-EXP symbols 18 18 18 NAScenario 4 - 5.25GHz SGI-EXP symbols 18 18 18 NA

Scenario 6 - 5.25GHz standard symbols 39 38 39 38Scenario 6 - 5.25GHz standard symbols HCF 39 36 NA NAScenario 6 - 5.25GHz standard symbols EDCA 39 13 NA NAScenario 6 EXT- 5.25GHz standard symbols 39 37 39 38

Number of flows that meet their QoS requrement

August 2004


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doc.: IEEE 802.11-04/0873r1

Submission

Observations on QoS Flows

• Scenario 1 EXT imposes stringent delay (less than 50 ms for streaming) and range (HDTV flows at 25 m) requirements on QoS flows. – When 2x2 is used, one or two QoS flows are not satisfied.

– In the Mixed case, by equipping the AP and the HDTV and SDTV displays with 4 antennas, all QoS flows except the gaming flow are satisfied with an almost 50% increase in total throughput compared to 2x2.

• More QoS flows are satisfied with HCF than with EDCA. However, ACF is required to address stringent QoS requirements.

• QoS for uplink EDCA VoIP flows is not satisfied.

• All QoS Flows are satisfied for Scenario 4.

August 2004


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doc.: IEEE 802.11-04/0873r1

Submission

Summary of non-QoS Flow Throughput

• Scenario 6 EXT Mixed case (mixture of 4-antenna and 2-antenna STAs) gives higher TCP throughput than the 4x4 case.

– This is because there is more time available for TCP flows due to the reduced training sequence overhead for VoIP STAs with 2 antennas compared to VoIP STAs with 4 antennas. Sceanrio 6 EXT has 30 VoIP flows.

All figures except ratio are in Mbps

Non-QoS offered load

Aggregate non-QoS

throughputRatio

Aggregate non-QoS

throughputRatio

Aggregate non-QoS

throughputRatio

Scenario 1 - 2.4GHz standard symbols 31.00 31.66 1.02 31.66 1.02 NA NAScenario 1 - 2.4GHz SGI-EXP symbols 31.00 31.66 1.02 31.66 1.02 NA NAScenario 1 - 2.4GHz SGI-EXP HCF 31.00 6.88 0.22 NA NA NA NAScenario 1 - 2.4GHz SGI-EXP EDCA 31.00 2.33 0.08 NA NA NA NAScenario 1 - 5.25GHz SGI-EXP HCF 31.00 6.67 0.22 31.33 1.01 NA NAScenario 1 - 5.25GHz SGI-EXP EDCA 31.00 0.98 0.03 3.44 0.11 NA NAScenario 1 - 5.25GHz standard symbols 31.00 25.08 0.81 31.71 1.02 NA NAScenario 1 - 5.25GHz SGI-EXP symbols 31.00 31.66 1.02 31.66 1.02 NA NAScenario 1 HT - 2.4GHz SGI-EXP symbols Extra TCP 50.74 x 133.47 x NA NAScenario 1 HT - 5.25GHz SGI-EXP symbol Extra TCP 42.55 x 112.45 x NA NAScenario 1 EXT - 2.4GHz SGI-EXP symbols Extra TCP 33.78 x 112.33 x 68.84 xScenario 1 EXT - 5.25GHz SGI-EXP symbols Extra TCP 16.04 x 77.99 x 52.92 x

Scenario 4 - 2.4GHz SGI-EXP symbols 451.02 93.48 0.21 187.24 0.42 NA NAScenario 4 - 5.25GHz SGI-EXP symbols 451.02 88.86 0.20 178.93 0.40 NA NA

Scenario 6 - 5.25GHz standard symbols 20.00 15.58 0.78 20.09 1.00 20.14 1.01Scenario 6 - 5.25GHz standard symbols HCF 20.00 0.259 0.01 NA NA NA NAScenario 6 - 5.25GHz standard symbols EDCA 20.00 0.87 0.04 NA NA NA NAScenario 6 EXT- 5.25GHz standard symbols Extra TCP 21.37 x 52.13 x 56.76 x

HT Usage Models Supported (non QoS)

2x2 4x4 Mix

August 2004


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doc.: IEEE 802.11-04/0873r1

Submission

Throughput versus Range for Channel Model B

Throughput vs Range in 20Mhz, channel model B

0.0

50.0

100.0

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300.0

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0 20 40 60 80 100 120 140 160 180 200

Distance [m]

Th

rou

gh

pu

t [M

bp

s]

2x2 2.4Ghz

2x2 5.25Ghz

4x4 2.4Ghz

4x4 5.25Ghz

August 2004


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doc.: IEEE 802.11-04/0873r1

Submission

Throughput versus Range for Channel Model D

Throughput vs Range in 20MHz, channel model D

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50.0

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0 20 40 60 80 100 120 140 160 180 200

Distance [m]

Th

rou

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bp

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2x2 2.4Ghz

2x2 5.25Ghz

4x4 2.4Ghz

4x4 5.25Ghz

August 2004


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doc.: IEEE 802.11-04/0873r1

Submission

Observations on Throughput versus Range

• The plots for Channel Model B and Channel Model D are roughly similar.

• Throughput above the MAC of 100 Mbps is achieved at:– 29 m for 2x2, 5.25 GHz

– 40 m for 2x2, 2.4 GHz

– 47 m for 4x4, 5.25 GHz

– 75 m for 4x4, 2.4 GHz

August 2004


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doc.: IEEE 802.11-04/0873r1

Submission

Qualcomm 802.11n PHY Design• Fully backward compatible with 802.11a/b/g

– 20 MHz bandwidth with 802.11a/b/g spectral mask – OFDM based on 802.11a waveform

• Optional expanded OFDM symbol (4 add’l data subcarriers) and shortened guard interval

• Modulation, coding, interleaving based on 802.11a– Expanded rate set

• Scalable MIMO architecture – Supports a maximum of 4 wideband spatial streams

• Two forms of spatial processing– Eigenvector Steering (ES): via wideband spatial modes/SVD per subcarrier

• Tx and Rx steering• Over the air calibration procedure required

– Spatial Spreading (SS): modulation and coding per wideband spatial channel• No calibration required• SNR per wideband spatial stream known at Tx

• Use of Eigenvector steering extends the life of low-complexity 802.11 BCC• Sustained high rate operation possible via rate adaptation

– low overhead asynchronous feedback.• PHY techniques proven in FPGA-based prototype

August 2004


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doc.: IEEE 802.11-04/0873r1

Submission

Code Rates and ModulationBits/subcarrier Bit/s/spatial chan1 Bit/s/spatial chan2 Code Rate Modulation

0 0 0 0 N/A

0.50 6 Mbit/s 7.2 Mbit/s r=1/2 BPSK

0.75 9 10.8 r=3/4 BPSK

1.00 12 14.4 r=1/2 QPSK

1.50 18 21.7 r=3/4 QPSK

2.00 24 28.9 r=1/2 16 QAM

2.50 30 36.1 r=5/8 16 QAM

3.00 36 43.3 r=3/4 16 QAM

3.50 42 50.6 r=7/12 64QAM

4.00 48 57.8 r=2/3 64QAM

4.50 54 65 r=3/4 64QAM

5.00 60 72.2 r=5/6 64QAM

5.00 60 72.2 r=5/8 256 QAM

6.00 72 86.7 r=3/4 256 QAM

7.00 84 101.1 r=7/8 256 QAMNotes: 1) short OFDM symbols; 2) expanded OFDM symbols with short guard interval

August 2004


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doc.: IEEE 802.11-04/0873r1

Submission

Spatial Processing• Two forms of Spatial Processing for data transmission

– Eigenvector Steering (ES): Tx attempts to steer optimally to intended Rx– Spatial Spreading (SS): Tx does not attempt to steer optimally to specific Rx

• ES operating modes take advantage of channel reciprocity inherent in TDD systems– Full MIMO channel characterization required at Tx– Calibration procedure required– 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 data rate and range

• SS Operation for partially informed transmitter– No explicit knowledge of channel or channel eigenvectors at Tx– Tx has only data rate per wideband spatial channel– Transmit full power regardless of the number of streams Tx’d

• Requirement for robust CSMA operation– Maximize diversity per transmitted data stream

• Minimize outage probability maximize throughput– Backwards compatible operation– Spatial spreading of data with simple unitary matrices– Cyclic diversity transmission per Tx antenna to introduce additional diversity

August 2004


Slide 25

doc.: IEEE 802.11-04/0873r1

Submission

Spatial Channels and Spatial Streams

• ES and SS approaches result in synthesis of spatial channels, or wideband spatial channels.– Also referred to as eigenmodes, or wideband eigenmodes

• On MIMO channel between a transmitting STA with NTx antennas and a receiving STA with NRx antennas, maximum of

wideband spatial channels available.

• Each resulting spatial channel may carry a payload, referred to as a spatial stream.

• Number of spatial streams, NS, may not be greater than the Nm

min ,m Tx RxN N N

August 2004


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Submission

Over-the-Air Calibration

• ES approach requires over-the-air calibration procedure – Compensates for amplitude and phase differences in Tx

and Rx chains

– Calibration required infrequently– typically on association only

– Simple exchange of calibration symbols and measurement information requires little overhead and background processing• Total of ~1000 bytes of calibration data exchanged for 2x2 link

• ~2800 bytes for 4x4 link

August 2004


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doc.: IEEE 802.11-04/0873r1

Submission

Preamble and Training Sequences

• Use Standard 802.11a preamble with enhancements– Time and Frequency acquisition and AGC

– Last short preamble symbol is inverted to provide improved timing reference

– Cyclic delay is applied across Tx antennas• Cyclic delay applied to entire 8 µs short preamble

• Cyclic delay applied to entire 8 µs long preamble

• Delay increment Tcd=50 ns

• Extended SIGNAL field

• MIMO training sequence– Orthonormal (in time) cover sequence

• Walsh for 2 Tx and 4 Tx

• Fourier for 3 Tx

– Cyclic shift k*50 ns on Tx antenna k

– Combination of orthonormal cover and cyclic shift ensures equal Rx power on all preamble symbols

– Number of OFDM symbols = Number of Tx antennas

• Supports steered MIMO training for Eigensteered operation

August 2004


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Submission

Feedback for ES and SS Modes• Rate adaptation

– Receiving STA determines preferred rates on each of up to four wideband spatial channels

• One rate per wideband spatial channel – NO adaptive bit loading– Sends one 4-bit value per spatial channel, differentially encoded, (13 bits

total) to inform corresponding STA/AP of rate selections• Corresponding STA/AP uses this info to select Tx rates• Piggy-backed on out-going PPDUs

– SS Mode can use single rate across all spatial streams• Channel state information

– For ES operation, Tx must have full channel state information– This is obtained through exchange of transmitted training sequences that

are part of PLCP header• Very low overhead.

– Distributed computation of steering vectors (SVD calculation)• STAs do SVD, send resulting training sequence to AP

– For SS operation, unsteered training sequences transmitted in PLCP header to support channel estimation at receiver

• Feedback operates with asynchronous MAC transmissions

August 2004


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doc.: IEEE 802.11-04/0873r1

Submission

Wideband Eigenmodes and OFDM

• OFDM chosen so that subcarrier spacing << coherence bandwidth

• Find ranked eigenmodes/eigenvalues in each OFDM subcarrier:

• Ensemble of eigenmodes of a given rank across OFDM symbol comprise a wideband eigenmode

• Highest ranked wideband eigenmodes exhibit very little frequency selectivity

• Smallest ranked wideband eigenmode exhibits frequency selectivity of underlying channel

1 2( ) ( ) ( )Nk k k

August 2004


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doc.: IEEE 802.11-04/0873r1

Submission

Wideband Eigenmodes TGn Channel B

Power is relative to average total receive power at a single antenna

August 2004


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doc.: IEEE 802.11-04/0873r1

Submission

Use of Reference for Eigensteering• STAs must be calibrated to use Tx steering• MIMO training sequence part of PLCP preamble for all PPDUs• STA can compute Tx and Rx steering vectors from either steered

MIMO training sequence or direct MIMO training sequence– If unsteered MIMO training sequence is used, SVD or similar is required

to compute steering vectors from direct channel estimate– One STA in a corresponding pair must compute SVD from direct channel

estimate– STA that does SVD sends steered MIMO training sequence in PLCP

preamble of PPDU with steered data. Receiving STA uses steered MIMO training sequence to compute Rx and Tx steering

– STA not computing SVD must send direct MIMO training sequence to STA computing SVD

• Can be part of broadcast message such as SCHED at AP• Can be MIMO training sequence in PLCP preamble

• Support of bi-directional steering with SVD calculation distributed to client STAs

– Off-loads SVD from AP– Minimal complexity hit to STA

August 2004


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doc.: IEEE 802.11-04/0873r1

Submission

Simulation of Spatial Multiplexing Using Tx & Rx Eigensteering

• Common MIMO Training Sequence broadcast by AP once every SCAP (Scheduled Access Period) (…,t0,t3,…). Forward link (FL) channel coefficients estimated by STA receiver

• FL Dedicated MIMO Training Sequence (steered) transmitted by AP at t1=0.5 ms, immediately followed by FL data PPDU

• Reverse link (RL) Dedicated MIMO Training Sequence transmitted by STA at t2=1.5 ms, immediately followed by RL data PPDU

• Transmit and receive steering vectors derived from most recent channel estimates

• Closed-loop rate adaptation: FL and RL data rates determined based on receive SNRs observed in previous frames

FLdata

SCAP (2.048 ms)

FL data RL data

t1=0.5 mst0=0 ms t2=1.5 ms t3=2.048 ms

August 2004


Slide 33

doc.: IEEE 802.11-04/0873r1

Submission

Simulation Parameters• 2x2, 4x2, and 4x4 system configurations• IEEE 802.11n channel models B, D and E• IEEE 802.11n impairment models:

– Time-domain channel simulator with 5x oversampling rate (Ts=10 ns)– Rapp nonlinear power amplifier model (IM1):

• Total Tx power = 17 dBm; Psat = 25 dBm• 2x2 backoff = 11 dB per PA; 4x4 backoff = 14 dB per PA

– Carrier frequency offset : -13.675 PPM (IM2)– Sampling clock frequency offset: -13.675 PPM (IM2)– Phase noise at both transmitter and receiver (IM4)

• 100 channel realizations generated for each SNR point • In each channel realization the Doppler process evolves over three

SCAPs to allow simulation of channel estimation, closed-loop rate adaptation and FL/RL data transmission in fading conditions

• Stopping criterion: 10 packet errors or 400 packets transmitted per channel realization

• Targeted packet error rate performance: mean PER <= 1%

August 2004


Slide 34

doc.: IEEE 802.11-04/0873r1

Submission

PHY Simulation Results

• What we simulated– Standard OFDM symbols

• Eigenvector Steering• Spatial Spreading

– Expanded OFDM symbols (52 data tones/400ns guard interval: SGI-52)• Eigenvector Steering• Spatial Spreading

• PER vs SNR for Fourier channel 1×1, 2×2, 3×3, and 4×4 (CC59) – All above cases

• PHY throughput and PER vs SNR; CDFs of throughput and PER – Standard OFDM symbols, ES & SS

• 2×2, 4×4, and 4×2• Channels B, D, and E

– SGI-52 OFDM symbols, ES & SS• 2×2, 4×4, and 4×2• Channel B

August 2004


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doc.: IEEE 802.11-04/0873r1

Submission

PHY Simulation Results (2)

• Average PER vs SNR– Standard OFDM symbols, ES & SS

• 2×2, 4×4, and 4×2

• Channels B, D, and E

August 2004


Slide 36

doc.: IEEE 802.11-04/0873r1

Submission

Highlights of PHY Simulation Results

• Highest PHY throughputs achieved in Eigenvector Steering mode– Eigenvector steering is very effective in combination with 802.11

convolutional codes

– 256-QAM contributes substantially to throughput in ES mode. ES array gain overcomes effects of receiver impairments in these cases

• Convolutional codes not as effective in Spatial Spreading mode– High SNR variance across subcarriers within an OFDM symbol on an SS

spatial channel degrades the performance of convolutional codes

– This is particularly pronounced on channel B and on link with 4 Tx and 2 Rx.

– Reducing number of streams (NS < min(NTx,NRx)) reduces variance and improves overall performance.

• Rate adaptation has clearly demonstrated benefits– Many cases where a given fixed rate has poor performance, but using rate

adaptation, higher overall throughput is achieved with lower PER

– Part of rate adaptation is controlling the number of streams used

August 2004


Slide 37

doc.: IEEE 802.11-04/0873r1

Submission

Highlights of PHY Simulation Results

• Use of shortened guard interval and extra data subcarriers contributes to increased throughput– Increased vulnerability to delay spread and ACI.

– Improved receiver design should help with this

– Optional mode can be turned off in the presence of too much delay spread

– Many environments where high rates will be required, such as residential media distribution, have naturally low delay spread.

August 2004


Slide 38

doc.: IEEE 802.11-04/0873r1

Submission

PHY Throughput and PER Ch. B, 2×2: Eigenvector Steering

0 5 10 15 20 25 30 35 40 45 500

20

40

60

80

100

120

140

160

ES, 802.11n Ch. B, 2x2

Es/N

0 (dB)

Av

era

ge

Th

rou

gh

pu

t (M

bp

s)

FLRL

0 5 10 15 20 25 30 35 40 45 50

10-3

10-2

10-1

Av

era

ge

PE

R

August 2004


Slide 39

doc.: IEEE 802.11-04/0873r1

Submission

Average PER w/fixed rates Ch. B, 2×2 : Eigenvector Steering

-10 0 10 20 30 40 50 60 7010

-3

10-2

10-1

100

802.11n ch. B, 2x2, ES

Es/N

0 (dB)

PE

R

1 stream (6 Mbps)2 streams (102 Mbps)2 streams (132 Mbps)2 streams (168 Mbps)

August 2004


Slide 40

doc.: IEEE 802.11-04/0873r1

Submission

PHY Throughput and PER Ch. B, 2×2: Spatial Spreading

0 5 10 15 20 25 30 35 40 45 500

20

40

60

80

100

120

140

160

SS, 802.11n Ch. B, 2x2

Es/N

0 (dB)

Av

era

ge

Th

rou

gh

pu

t (M

bp

s)

FLRL

0 5 10 15 20 25 30 35 40 45 50

10-2

10-1

Av

era

ge

PE

R

August 2004


Slide 41

doc.: IEEE 802.11-04/0873r1

Submission

PHY Throughput and PER Ch. B, 2×2: Eigenvector Steering, SGI-52

0 5 10 15 20 25 30 35 40 45 500

20

40

60

80

100

120

140

160

180

200

ES, 802.11n Ch. B, 2x2

Es/N

0 (dB)

Av

era

ge

Th

rou

gh

pu

t (M

bp

s)

FLRL

0 5 10 15 20 25 30 35 40 45 50

10-3

10-2

10-1

Av

era

ge

PE

R

August 2004


Slide 42

doc.: IEEE 802.11-04/0873r1

Submission

PHY Throughput and PER Ch. B, 4×4 : Eigenvector Steering

0 5 10 15 20 25 30 35 40 45 500

40

80

120

160

200

240

280

320

ES, 802.11n Ch. B, 4x4

Es/N

0 (dB)

Av

era

ge

Th

rou

gh

pu

t (M

bp

s)

FLRL

0 5 10 15 20 25 30 35 40 45 50

10-4

10-3

10-2

10-1

Av

era

ge

PE

R

August 2004


Slide 43

doc.: IEEE 802.11-04/0873r1

Submission

Average PER w/fixed rates Ch. B, 4×4 : Eigenvector Steering

-10 0 10 20 30 40 50 60 7010

-3

10-2

10-1

100

802.11n ch. B, 4x4, ES

Es/N

0 (dB)

PE

R

1 stream (6 Mbps)2 streams (54 Mbps)3 streams (162 Mbps)4 streams (180 Mbps)4 streams (276 Mbps)4 streams (336 Mbps)

August 2004


Slide 44

doc.: IEEE 802.11-04/0873r1

Submission

PHY Throughput and PER Ch. B, 4×4: Eigenvector Steering, SGI-52

0 5 10 15 20 25 30 35 40 45 500

40

80

120

160

200

240

280

320

360

400

ES, 802.11n Ch. B, 4x4

Es/N

0 (dB)

Av

era

ge

Th

rou

gh

pu

t (M

bp

s)

FLRL

0 5 10 15 20 25 30 35 40 45 5010

-3

10-2

10-1

Av

era

ge

PE

R

August 2004


Slide 45

doc.: IEEE 802.11-04/0873r1

Submission

PHY Throughput and PER Ch. B, 4×2 : Eigenvector Steering

0 5 10 15 20 25 30 35 40 45 500

20

40

60

80

100

120

140

160

ES, 802.11n Ch. B, 4x2

Es/N

0 (dB)

Av

era

ge

Th

rou

gh

pu

t (M

bp

s)

FLRL

0 5 10 15 20 25 30 35 40 45 50

10-4

10-3

10-2

10-1

Av

era

ge

PE

R

August 2004


Slide 46

doc.: IEEE 802.11-04/0873r1

Submission

PHY Throughput and PER Ch. B, 4×2: Spatial Spreading

0 5 10 15 20 25 30 35 40 45 500

20

40

60

80

100

120

140

160

SS, 802.11n Ch. B, 4x2

Es/N

0 (dB)

Av

era

ge

Th

rou

gh

pu

t (M

bp

s)

FLRL

0 5 10 15 20 25 30 35 40 45 50

10-3

10-2

10-1

Av

era

ge

PE

R

August 2004


Slide 47

doc.: IEEE 802.11-04/0873r1

Submission

Effect of increased latency on Eigensteering: Average Throughput, 2x2, Channel B

0 5 10 15 20 25 30 35 40 45 500

20

40

60

80

100

120

140

160

ES, 802.11n Ch. B, 2x2, FL

Es/N

0 (dB)

Ave

rage

Thr

ough

put (

Mbp

s)

1x5x10x20x

August 2004


Slide 48

doc.: IEEE 802.11-04/0873r1

Submission

Summary

• MIMO PHY design builds on existing 802.11a,g PHY design

• Two operating modes provide highly robust operation under a wide range of conditions– Eigenvector Steering provides best rate/range performance

– Spatial Spreading

• Adaptive rate control through low-overhead rate feedback supports sustained high throughput operation

• Low-overhead training sequence exchange supports high-capacity Eigenvector Steered operation for best rate/range performance

• Spatial Spreading operation provides robust high throughput operation when Tx does not have sufficiently accurate channel state information

• MAC enhancements are required to take full advantage of HT PHY– Required for 100 Mbps throughput in realistic operating environments

– QoS-sensitive applications are not satisfied with EDCA

August 2004


Slide 49

doc.: IEEE 802.11-04/0873r1

Submission

APPENDIX: MAC Details

August 2004


Slide 50

doc.: IEEE 802.11-04/0873r1

Submission

Critical Features for High Throughput Operation

• Critical Features for High Data Rates– Adaptation of PHY rates and MIMO transmission mode

• Low overhead feedback

• Compatible with EDCA or HCCA

– Low latency• To support PHY adaptation

• To satisfy end-to-end delay requirements of multimedia/interactive applications

– High MAC Efficiency, reduced contention overhead• Frame aggregation, Compressed Block ACK

• Enhanced Polling

– Simplify QoS handling compared to 802.11e• Exploit high data rates of 802.11n

August 2004


Slide 51

doc.: IEEE 802.11-04/0873r1

Submission

Different Operating Environments

• Application to different operating regimes– Evolution of current deployments

• Solution: Simple enhancements: frame aggregation, closed loop rate control

• Low loads: EDCA

• High loads: HCCA

– Large enterprise networks• Solution: Enhancements to HCCA for deployments with large

numbers of STAs

• Optimized scheduled operation

• Implemented in Enterprise-class AP

• Flexible operation modes. See examples.

– Small networks with significant QoS traffic• Solution: IBSS with distributed round-robin scheduling

August 2004


Slide 52

doc.: IEEE 802.11-04/0873r1

Submission

Flexible Frame Aggregation

• Eliminate MAC throughput bottleneck– Throughput saturates at ~70 Mbps

even with 802.11e features– Permits aggregation of encrypted or

unencrypted frames– MAC headers in the aggregated

frame can be compressed

AggregationHeader Type

LengthReserved

Bits 2 2 12

FrameControl

Duration/ID

Address 1 Address 2 Address 3 SequenceQoS

ControlAddress 4 Frame Body

Octets 2 2 2 6 6 6 2 6 2 n 4

FCSAggregation

Header

Aggregate MAC Frame(One or More Encapsulated MAC Frames)

EncapsulatedMAC Frame

(or Fragment)


(or Fragment)


(or Fragment)


(or Fragment)

PSDU

August 2004


Slide 53

doc.: IEEE 802.11-04/0873r1

Submission

Eliminate Immediate ACK for MIMO Transmissions

• Receiver delay for demodulation and decoding of (coded) OFDM transmissions– 802.11a SIFS is 16 us.– 802.11g provides a 6 us OFDM signal extension

• MIMO OFDM transmissions impose even greater burden on the receiver– Aggregated frames make matters worse

• Inefficient solution– Larger SIFS or longer signal extension

• Efficient solution– Eliminate Immediate ACK for MIMO OFDM transmissions

• Use 802.11e Block ACK and Delayed Block ACK mechanisms

– Reduced IFS for scheduled transmissions• TXOP Bursting with zero IFS (AP transmissions) • Consecutive scheduled STA TXOPs separated by GIFS (800 ns Guard IFS)• TXOP Bursting with BIFS (STA transmissions)

August 2004


Slide 54

doc.: IEEE 802.11-04/0873r1

Submission

Backward Compatible PLCP Header

• Compatible Preamble– Changes described in PHY section

• Extended Backward Compatible SIGNAL Field– Set Rate field in current SIGNAL1 field to one of eight unused values.

– Indicates presence of SIGNAL2.

PLCP Preamble16 us

(if present)

SIGNAL11 OFDMSymbol

0/2/3/4 TrainingSymbols

DATAVariable Number of OFDM Symbols

RATE/Type4 bits

Resv’d1 bit

DRV13 bits

PPDU Size/Request12 bits

Tail6 bits

Parity1 bit

PPDU Control SegmentRate and Format

SERVICE16 bits

PSDUTail

6 bits/Mode

PadVariable

PPDU Data Segment Rate andFormat

FEEDBACK16 bits

TrainingType3 bits

SIGNAL21 OFDMSymbol

Tail6 bits

Parity1 bit

Resv’d1 bit

PPDU Control SegmentRate and Format PPDU Type 0000

August 2004


Slide 55

doc.: IEEE 802.11-04/0873r1

Submission

PPDU Size and LENGTH Fields

• LENGTH Field in Legacy SIGNAL field is used by the Receiving STA to parse the received octet stream– To determine location of FCS, length of PAD.

• For aggregated frame, need length per encapsulated MAC frame. – Aggregation Header contains LENGTH field for each encapsulated

MAC frame.

• PPDU Size Field included in Extended SIGNAL– Indicates PPDU Size in number of standard or SGI OFDM symbols.

– SIGNAL at 6 Mbps can be decoded by all 802.11n STAs to determine medium time occupied by the PPDU.

• Solution:– Replace LENGTH by PPDU Size in Extended SIGNAL.

– Include Aggregation Header whenever MIMO PPDU is used.

August 2004


Slide 56

doc.: IEEE 802.11-04/0873r1

Submission

Rate and Mode Adaptation

• Rate vector (DRV) included in Extended SIGNAL field.• Rate and mode feedback (DRVF) included in FEEDBACK field• MIMO OFDM Training symbols inserted as necessary• Fast ramp up to exploit high PHY rates for bursty traffic• Enormous throughput benefit with low overhead• Robustness to interference, shadowing, channel and receiver impairments

PLCP Preamble16 us

(if present)

SIGNAL11 OFDMSymbol



RATE/Type4 bits

Resv’d1 bit

DRV13 bits


Tail6 bits

Parity1 bit


SERVICE16 bits

PSDUTail

6 bits/Mode

PadVariable

PPDU Data Segment Rate andFormat

FEEDBACK16 bits

TrainingType3 bits

SIGNAL21 OFDMSymbol

Tail6 bits

Parity1 bit

Resv’d1 bit


PPDU Type 0000

August 2004


Slide 57

doc.: IEEE 802.11-04/0873r1

Submission

Compressed Block Ack

• Compressed format 1: Do not indicate status of fragments. Shrink BlockAck Frame from 152 to 32 octets.

• Compressed format 2: Indicate status of fragments only if there are missing fragments• Compressed format 3: Remove trailing zeroes from Bitmap.

FrameControl

Octets 2 2 6 6 2 2 8 4

Duration RA TABA

ControlBlock Ack StartingSequence Control

No Fragments BlockAck Bitmap

FCS

FrameControl

Octets 2 2 6 6 2 2 m 4

Duration RA TABA


Mixed Block AckBitmap

FCS

FrameControl

Octets 2 2 6 6 2 2 n 4

Duration RA TABA


Shortened BlockAck Bitmap

FCS

August 2004


Slide 58

doc.: IEEE 802.11-04/0873r1

Submission

Scheduled Operation – SCHED Message

• SCHED message and Scheduled Access Period (SCAP) are enhancements of HCCA CAP– 802.11n AP acquires the medium after PIFS (as in the HCCA CAP) and transmits a SCHED

message (instead of Poll). – The SCHED message defines the schedule of transmissions for the SCAP. Default values of

SCAP: 1.024ms, 2.048 ms, 4 ms.

• SCHED is a Multiple Poll Message– Lower overhead, more efficient– Indicates Tx STA and Rx STA for TXOPs => Improved power saving

Scheduled AccessPeriod

Scheduled Transmissions(AP-STA, STA-AP, STA-STA)

MIMO OFDMEDCA

FRACHPeriod

APto STA B

STA C toAP

STA Eto STA F

SCHED

APto STA D

APto STA G

STA Gto AP

STA Eto AP

CTSto

Self

August 2004


Slide 59

doc.: IEEE 802.11-04/0873r1

Submission

Scheduled Operation – Protection and Recovery

• Protection of SCAP– High level procedures to avoid overlapping BSS: Mandatory DFS

– CTS-to-Self to clear out NAV for SCAP. For 802.11n STAs set NAV through Duration field in SCHED frame.

– Keep SCAP short (< 4 ms) to minimize impact of collisions with legacy STAs during SCAP

• No CCA required for transmissions during SCAP



MIMO OFDMEDCA

FRACHPeriod

APto STA B

STA C toAP

STA Eto STA F

SCHED

APto STA D

APto STA G

STA Gto AP

STA Eto AP

CTSto

Self

August 2004


Slide 60

doc.: IEEE 802.11-04/0873r1

Submission

Scheduled Operation – Reduced IFS

• Reduced IFS– Since, no CCA required for transmissions during SCAP

– PPDU Aggregation: IFS and preambles may be eliminated between consecutive Scheduled AP transmissions.

– Consecutive Scheduled TXOPs from STAs may be transmitted with GIFS (800 ns)

• Optionally, FRACH and Protected EDCA may be scheduled during a SCAP



MIMO OFDMEDCA

FRACHPeriod

APto STA B

STA C toAP

STA Eto STA F

SCHED

APto STA D

APto STA G

STA Gto AP

STA Eto AP

CTSto

Self

August 2004


Slide 61

doc.: IEEE 802.11-04/0873r1

Submission

Scheduled Operation – Managed Peer-to-Peer

• Managed Peer-to-Peer Operation is an enhancement of DLP• In Scheduled STA-STA TXOPs

– PPDU Size in SIGNAL1 is replaced by Request– AP promiscuously decodes Request field in STA-STA transmissions. – STAs indicate SCHED Rate, QoS and requested length for subsequent TXOP.

• STAs do closed loop rate control• AP does scheduling

PLCP Preamble16 us

(if present)

SIGNAL11 OFDMSymbol



RATE/Type4 bits

Resv’d1 bit

DRV13 bits


Tail6 bits

Parity1 bit


TrainingType3 bits

SIGNAL21 OFDMSymbol

Tail6 bits

Parity1 bit

Resv’d1 bit


PPDU Type 0000

August 2004


Slide 62

doc.: IEEE 802.11-04/0873r1

Submission

SCHED Frame Format and Fields

• SCHED Frame Fields– CTRL0, CTRL1, CTRL2, CTRL3 fields are separately coded and transmitted at

6, 12, 18, 24 Mbps, respectively

– Multiple Assignment Elements are included in each CTRLJ• Each Assignment Element specifies: Tx STA (may be AP), Rx STA (may be AP), Start

Time, TXOP Duration

– MAP field identifies start of FRACH and Protected EDCA within SCAP

CTRL0 CTRL1 CTRL2 CTRL3ORG

Octets 20 m0 m1 m2 m3

FrameControl

PowerManagement

MAP FCSBSSID Reserved

Octets 2 6 3 6 1 2

August 2004


Slide 63

doc.: IEEE 802.11-04/0873r1

Submission

Summary of HCF Enhancements

• Advantages of SCHED over HCF Poll– Reduced overhead: single message instead of multiple Polls, multiple IFS

– Efficient encoding of TXOP/RXOP assignments

– Improved Power Saving: After decoding the SCHED message, STAs not scheduled for Tx or Rx can sleep for the remaining SCAP

– Efficient feedback for ES operation: MIMO OFDM Training symbols attached to SCHED frame permit STAs to estimate the AP-STA channel and achievable rate.

– Improved QoS handling: Optimized low-latency operation for 802.11n STAs

• Managed peer-to-peer operation – STAs do closed loop rate control. AP does scheduling

• Protected Contention Periods to complement scheduling– FRACH

– Protected EDCA

August 2004


Slide 64

doc.: IEEE 802.11-04/0873r1

Submission

Operation of Adaptive Coordination Function (ACF)

• SCAP is an enhancement of the HCCA CAP

• Setting NAV– The Duration field in the SIGNAL field of the SCHED frame sets the NAV for the SCAP at

all 802.11n STAs.– To set the NAV for the SCAP at legacy STAs, the AP may transmit a CTS-to-Self prior to the

transmission of the SCHED frame.

• SCAP Timing– 802.11n STAs respect the SCAP interval so that their transmissions terminate when the SCAP

expires. – The AP may schedule back-to-back SCAPs.

Beacon

SCAP

Beacon

Beacon


SCHEDHCCATXOP

Poll

CAP

CAP

SCAP SCAP

EDCA

EDCA

EDCA

CAP

SCAP

EDCA

CAP

EDCA

SCAP SCAP SCAPCAP

SCAP SCAP

EDCA

CAP

EDCATXOP

EDCATXOP

EDCATXOP

HCCATXOP

PollCTSto

Self

SCAP

APTXOP

August 2004


Slide 65

doc.: IEEE 802.11-04/0873r1

Submission

ACF – Example Operating Mode

• Case: No CAP– Legacy STAs, if present, can satisfy their QoS using EDCA

• Setting NAV– The Duration field in the SIGNAL field of the SCHED PPDU sets the NAV for the

SCAP at all 802.11n STAs.– If only 802.11n STAs are present, there is no need for CTS-to-Self.

• Beacon announces CFP to protect most of the Beacon interval to avoid interference from arriving legacy STAs

– If medium is shared with legacy STAs, use CTS-to-Self at start of SCAP

• Interspersed SCAP and EDCA periods permit “fair” sharing of the medium– 802.11n QoS Flows are served during SCAP– 802.11n non-QoS flows use EDCA periods along with legacy STAs.

Beacon

SCAP

EDCA

EDCA

SCAP SCAP

EDCA

Beacon

Beacon

SCAP

EDCA

SCAP

EDCA

EDCA

SCAP SCAP

EDCA

August 2004


Slide 66

doc.: IEEE 802.11-04/0873r1

Submission

ACF – Optimized Scheduled Operation

• Setting NAV– Beacon sets NAV at legacy STA for CFP.

– The Duration field in the SIGNAL field of the SCHED frame sets the NAV for the SCAP at all 802.11n STAs.

– Protected EDCA periods for 802.11n STAs included in Scheduled Access Period

Beacon

SCAP

Beacon

Beacon



802.11nEDCA

FRACHPeriod

SCHED

SCAP

EDCA

SCAP

EDCATXOP

EDCATXOP

EDCATXOP

SCAPSCAP SCAP SCAP

Beacon

SCAP

EDCA

SCAP SCAPSCAP SCAP SCAP SCAP SCAP

SCAPCFP CP

• Case: Limited resource required for legacy STAs. – Legacy STAs with non-QoS flows that may be

satisfied with only occasional allocations of EDCA periods (CP)

August 2004


Slide 67

doc.: IEEE 802.11-04/0873r1

Submission

RRBSS – QoS capable IBSS operation

• Provide QoS capability without AP– May also be used by low-end AP

– Applicable to usage scenarios with CE devices with high throughput, high QoS needs

– Exploit the large PHY data rates of MIMO OFDM to simplify scheduling and QoS management.

– Designed for up to 15 STAs

– Distributed admission control

– Self identification of QoS flows

– Distributed Round-Robin Scheduling

– Short Beacon Period for low latency

Beacon Beacon

TBTT

RR TXOPRRID = X

RR TXOPRRID = Y

RR TXOPRRID = Z

RRP CP

Frame Frame

RR Schedule for Beacon Period: RRID X, RRID Y, RRID Z

ATIMWindow

August 2004


Slide 68

doc.: IEEE 802.11-04/0873r1

Submission

RRBSS – Long Token PPDU

• Round Robin order for current Beacon period included in Complete RR List– Up to 15 RRIDs

• RR Seq indicates changes in RR List– Long Token must be transmitted by each STA if RR Seq changes

• Connectivity Vector indicates RRIDs that the STA can hear– Permits clustering of contiguous STAs on RR List

• RR Bandwidth Management field permits distributed sharing– Simple standardized rules

PLCP Preamble16 us

SIGNAL11 OFDMSymbol

RATE/Type4 bits

Resv’d1 bit

Tail6 bits

Parity1 bit


SIGNAL24 OFDMSymbol

Tail6 bits

FCS8 bit

Resv’d3 bit


RRSeq

4 bits

RR BandwidthManagement

8 bits

CompleteRR List64 bits

ConnectivityVector15 bits

NextRRID4 bits

RR List60 bits

TBTTLength2 bits

RRPFraction

4 bits

MaxIncrement

2 bits

Long Token PPDUPPDU Type 1010

August 2004


Slide 69

doc.: IEEE 802.11-04/0873r1

Submission

RRBSS – Short Token PPDU

• STA must transmit Long or Short Token PPDU if no data to send. – Explicit Token Passing using Long or Short Token

– Implicit Acknowledgment by Next STA

• Compact RR List contains – RRID of STA

– RRID of Next STA for Token Passing

– RRID of Last STA on RR List

Short Token PPDUPPDU Type 1000

PLCP Preamble16 us

SIGNAL11 OFDMSymbol

RATE/Type4 bits

Resv’d1 bit

Tail6 bits

Parity1 bit


SIGNAL21 OFDMSymbol

Tail6 bits

FCS4 bits

Resv’d2 bits


RRID4 bits

RRSeq

4 bits

NextRRID4 bits

LastRRID4 bits

TBTTLength2 bits

RR BandwidthManagement

8 bits

CompactRR List12 bits

RRPFraction

4 bits

MaxIncrement

2 bits

August 2004


Slide 70

doc.: IEEE 802.11-04/0873r1

Submission

RRBSS – Robust Operation

• Explicit token passing. – Implicit acknowledgment of token passing by Next STA on RR List. – Otherwise STA must pass token to the following STA.

• RR List rotates at each Beacon period– No single STA is “designated master”– Last STA in Beacon period n, becomes First STA in Beacon period n+1.

• Transmits Beacon and Long Token in Beacon period n+1.• First STA seizes medium at PIFS. • If medium is idle at DIFS, previous First STA transmits Beacon and Long Token. Last

STA is dropped from RR List.– Changes in RR List indicated through RR Seq– Each STA must transmit Long Token when RR Seq increments

Beacon Beacon

TBTT

RR TXOPRRID = X

RR TXOPRRID = Y

RR TXOPRRID = Z

RRP CP

Frame Frame

RR Schedule for Beacon Period: RRID X, RRID Y, RRID Z

ATIMWindow

August 2004


Slide 71

doc.: IEEE 802.11-04/0873r1

Submission

Simplified QoS Handling

• In all operating regimes– Exploit high data rates to simplify QoS handling

• Simple admission control– Based on simplified TSPEC: Mean data rate, Delay bound– Mean data rate

• Mapped to symbols per second for resource allocation– Delay bound

• Mapped to scheduling period, and• ARQ operation

• Low latency operation is critical– To operate with small buffers. This is critical at high data rates. – To meet low delay guarantees in all operating regimes

• EDCA/HCCA with lightly loaded system• RRBSS (with or without AP)• Scheduled operation for heavily loaded system

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Doc.: IEEE 802.11-04/0873r1 Submission August 2004 John Ketchum, et al, QUALCOMMSlide 1...

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