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August 2004
John Ketchum, et al, QUALCOMM
Slide 1
doc.: IEEE 802.11-04/0873r2
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
John Ketchum, et al, QUALCOMM
Slide 2
doc.: IEEE 802.11-04/0873r2
Submission
Guide to Qualcomm’s Proposal
Four proposal documents:• 11-04-870 High Throughput System Description and
Operating Principles. • 11-04-871 High Throughput Proposal Compliance
Statement (this document.) • 11-04-872 Link Level and System Performance Results for
High Throughput Enhancements.• 11-04-873 High Throughput Enhancements for 802.11:
Features and Performance.
August 2004
John Ketchum, et al, QUALCOMM
Slide 3
doc.: IEEE 802.11-04/0873r2
Submission
Agenda• Introductory remarks• MAC Features• System Performance• PHY Features• Link Performance
August 2004
John Ketchum, et al, QUALCOMM
Slide 4
doc.: IEEE 802.11-04/0873r2
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
John Ketchum, et al, QUALCOMM
Slide 5
doc.: IEEE 802.11-04/0873r2
Submission
Main Points• 20 MHz operation• Maximum PHY data rates:
– 202 Mbps for 2 Tx; 404 Mbps for 4 Tx• 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
John Ketchum, et al, QUALCOMM
Slide 6
doc.: IEEE 802.11-04/0873r2
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
John Ketchum, et al, QUALCOMM
Slide 7
doc.: IEEE 802.11-04/0873r2
Submission
MAC Feature Summary• Low overhead Rate Feedback• Frame aggregation• Eliminate Immediate ACK for MIMO transmissions• PPDU Aggregation from AP to multiple STAs using SCHED and
SCAP– Reduced IFS
• Managed Peer-to-Peer• Adaptive Coordination Function (ACF)• Compressed Block Ack• QoS-capable IBSS with round-robin scheduling
August 2004
John Ketchum, et al, QUALCOMM
Slide 8
doc.: IEEE 802.11-04/0873r2
Submission
Extended Backward Compatible PLCP Header
• Set legacy RATE field to one of eight unused values. – Legacy STAs revert to CCA on seeing unrecognized RATE field.
• PPDU Size (number OFDM symbols). HT STAs can determine medium time occupied by the PPDU.
• Rate vector (DRV) and Training Type included in SIGNAL2 field.• Rate and mode feedback (DRVF) included in FEEDBACK field (extension of
SERVICE field).• MIMO OFDM Training symbols inserted as necessary.
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 PSDU
Tail6 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
John Ketchum, et al, QUALCOMM
Slide 9
doc.: IEEE 802.11-04/0873r2
Submission
Flexible Frame Aggregation
• Frame aggregation– Length field per encapsulated frame– Maximum aggregate size can be negotiated per
flow– Second and subsequent MAC headers in the
aggregated frame can be compressed• Compressed Header Formats: Eliminate, TA,
RA, Duration/ID fields– Aggregation Header is always included when a
frame is transmitted in a MIMO OFDM PPDU.
AggregationHeader Type LengthReserved
Bits 2 2 12
FrameControl
Duration/ID Address 1 Address 2 Address 3 Sequence QoS
ControlAddress 4 Frame Body
Octets 2 2 2 6 6 6 2 6 2 n 4
FCSAggregationHeader
Aggregate MAC Frame(One or More Encapsulated MAC Frames)
EncapsulatedMAC Frame
(or Fragment)
EncapsulatedMAC Frame
(or Fragment)
EncapsulatedMAC Frame
(or Fragment)
EncapsulatedMAC Frame
(or Fragment)
PSDU
August 2004
John Ketchum, et al, QUALCOMM
Slide 10
doc.: IEEE 802.11-04/0873r2
Submission
Eliminate Immediate ACK, Reduced IFS
• MIMO OFDM transmissions impose greater burden on the receiver– Compared to 802.11a/g– Advanced decoders make matters worse
• Inefficient solution– Longer signal extension
• Efficient solution– Exploit 802.11e Block ACK and Delayed Block ACK mechanisms
• Eliminate Immediate ACK for MIMO OFDM transmissions• Scheduled transmissions permit Reduced IFS
– TXOP Bursting with zero IFS (AP transmissions) – TXOP Bursting with BIFS (STA transmissions)– Consecutive scheduled STA TXOPs separated by GIFS (800 ns Guard IFS)
• Block Ack (Window-based ARQ) offers a simple way to relieve PHY receiver complexity
August 2004
John Ketchum, et al, QUALCOMM
Slide 11
doc.: IEEE 802.11-04/0873r2
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 TXOPs for the SCAP. – Each TXOP assignment element in SCHED message indicates Tx and Rx STA,
start offset and duration. Complete information permits optimum power-save at STAs.
• No CCA required for scheduled STA transmissions during SCAP– Permits reduced IFS
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
John Ketchum, et al, QUALCOMM
Slide 12
doc.: IEEE 802.11-04/0873r2
Submission
Scheduled Operation – Protection and Recovery
• Protection of SCAP– Mandatory DFS to avoid overlapping BSS.– CTS-to-Self to clear out NAV for SCAP. For 802.11n STAs NAV is set through
Duration field in SCHED frame.– Keep SCAP short (< 4 ms) to minimize impact of collisions with legacy STAs
during SCAP.– Can use RTS/CTS within scheduled TXOPs.
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
John Ketchum, et al, QUALCOMM
Slide 13
doc.: IEEE 802.11-04/0873r2
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
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
TrainingType3 bits
SIGNAL21 OFDMSymbol
Tail6 bits
Parity1 bit
Resv’d1 bit
PPDU Control SegmentRate and Format
PPDU Type 0000
August 2004
John Ketchum, et al, QUALCOMM
Slide 14
doc.: IEEE 802.11-04/0873r2
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
Scheduled AccessPeriodSCHEDHCCA
TXOPPoll
CAP
CAP
SCAP SCAP
EDCA
EDCA
EDCA
CAP
SCAP
EDCA
CAP
EDCA
SCAP SCAP SCAPCAP
SCAP SCAP
EDCA
CAP
EDCATXOP
EDCATXOP
EDCATXOP
HCCATXOPPoll
CTSto
Self
SCAP
APTXOP
August 2004
John Ketchum, et al, QUALCOMM
Slide 15
doc.: IEEE 802.11-04/0873r2
Submission
Compressed Block Ack
• Compressed Block Ack offers significant reduction in overhead.– 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 TA BAControl
Block Ack StartingSequence Control
No Fragments BlockAck Bitmap FCS
FrameControl
Octets 2 2 6 6 2 2 m 4
Duration RA TA BAControl
Block Ack StartingSequence Control
Mixed Block AckBitmap FCS
FrameControl
Octets 2 2 6 6 2 2 n 4
Duration RA TA BAControl
Block Ack StartingSequence Control
Shortened BlockAck Bitmap FCS
August 2004
John Ketchum, et al, QUALCOMM
Slide 16
doc.: IEEE 802.11-04/0873r2
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– Robust operation: Explicit token passing, No single STA is designated “master”
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
John Ketchum, et al, QUALCOMM
Slide 17
doc.: IEEE 802.11-04/0873r2
Submission
Low Latency Operation• Low latency operation is critical
– To operate with small buffers. This is critical at high data rates. – For MIMO operation with EDCA, HCCA or ACF
• Rate and Mode Feedback• Eigenvector Steering
– To meet low delay guarantees for multimedia applications in all operating regimes
• Different access methods can provide low latency in different operating environments
• EDCA/HCCA with lightly loaded system• RRBSS (with or without AP)• Scheduled operation for heavily loaded system
August 2004
John Ketchum, et al, QUALCOMM
Slide 18
doc.: IEEE 802.11-04/0873r2
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– HCCA– Adaptive Coordination Function (ACF): SCHED and SCAP– Frame Aggregation– ARQ with Block Ack. No compressed Block Ack– Closed Loop Rate Control (DRVF and DRV)– MIMO Modes (ES and SS)
• Scheduler– Based on delay requirement and buffer status of flows. Similar to 802.11e Annex H
• Transport– File Transfer mapped to TCP– QoS Flows mapped to UDP
August 2004
John Ketchum, et al, QUALCOMM
Slide 19
doc.: IEEE 802.11-04/0873r2
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
John Ketchum, et al, QUALCOMM
Slide 20
doc.: IEEE 802.11-04/0873r2
Submission
Simulation Conditions – Varied• 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/SCAP)– HCF (Poll/CAP)– EDCA with additional AC for Block Ack
August 2004
John Ketchum, et al, QUALCOMM
Slide 21
doc.: IEEE 802.11-04/0873r2
Submission
Additional Scenarios• Scenario 1 HT is an extension of Scenario 1:
– Additional FTP flow of up to 130 Mbps at 15.6 m from the AP. • Scenario 1 EXT is an extension of Scenario 1:
– Additional FTP flow of up to 130 Mbps at 15.6 m from the AP. – 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
John Ketchum, et al, QUALCOMM
Slide 22
doc.: IEEE 802.11-04/0873r2
Submission
Summary of Total Throughput Results
• 100 Mbps BSS throughput in realistic scenarios with 20 MHz– Scenario 1 EXT (Residential Extended)
• HDTV flows with 50 ms delay requirement; at 25 m from AP.• AP and HDTV (4 antennas); all other STAs (2 antennas)
– Scenario 4 Enterprise 2x2– Scenario 6 EXT Hot Spot
• VoIP STAs with 2 antennas; all other STAs with 4 antennas
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
August 2004
John Ketchum, et al, QUALCOMM
Slide 23
doc.: IEEE 802.11-04/0873r2
Submission
Summary of Total Throughput ResultsMetric Scenario ACF 2x2 ACF 4x4
CC3 Aggregate goodput (Metric 2) [Mbps]
Scenario 1 HT 95.1 164.8
Scenario 4 100.3 191.6
Scenario 6 EXT 67.4 100.3
CC18 Aggregate non-QoS throughput [Mbps]
Scenario 1 HT 16.0 78.0
Scenario 4 88.9 178.9
Scenario 6 EXT 21.4 52.1
CC19 Number of QoS flows supported
Scenario 1 HT 17 / 17 17 / 17
Scenario 4 18 / 18 18 / 18
Scenario 6 EXT 37 / 39 39 / 39
CC58 HT spectral efficiency [bps/Hz] 5.85
• Parameters– 5.25 GHz– SGI-EXP OFDM symbols, except for Scenario 6
• Significantly higher throughput compared to other proposals.
August 2004
John Ketchum, et al, QUALCOMM
Slide 24
doc.: IEEE 802.11-04/0873r2
Submission
Summary of QoS Flows SatisfiedNumber 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
John Ketchum, et al, QUALCOMM
Slide 25
doc.: IEEE 802.11-04/0873r2
Submission
Throughput versus Range for Channel Model DThroughput vs Range in 20MHz, channel model D
0.0
50.0
100.0
150.0
200.0
250.0
300.0
350.0
0 20 40 60 80 100 120 140 160 180 200
Distance [m]
Thro
ughp
ut [M
bps]
2x2 2.4Ghz
2x2 5.25Ghz
4x4 2.4Ghz
4x4 5.25Ghz
August 2004
John Ketchum, et al, QUALCOMM
Slide 26
doc.: IEEE 802.11-04/0873r2
Submission
Observations• MAC Efficiency with Frame Aggregation
– ACF: between 0.65-0.7 (2x2) reduces to 0.6 (4x4)– HCF: around 0.5 (2x2) reduces to 0.4 (4x4)– EDCA: around 0.45 (2x2) reduces to 0.23 (4x4). No increase in
throughput of EDCA with 4x4.• More QoS flows are satisfied with HCF than with EDCA. However,
ACF is required to address stringent QoS requirements.• Frame Aggregation is not enough, need ACF for a future-proof MAC• Throughput versus Range
– 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• The plots for Channel Model B and Channel Model D are roughly similar.
– Significantly higher range compared to other proposals.
August 2004
John Ketchum, et al, QUALCOMM
Slide 27
doc.: IEEE 802.11-04/0873r2
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
John Ketchum, et al, QUALCOMM
Slide 28
doc.: IEEE 802.11-04/0873r2
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
John Ketchum, et al, QUALCOMM
Slide 29
doc.: IEEE 802.11-04/0873r2
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
John Ketchum, et al, QUALCOMM
Slide 30
doc.: IEEE 802.11-04/0873r2
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
John Ketchum, et al, QUALCOMM
Slide 31
doc.: IEEE 802.11-04/0873r2
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
John Ketchum, et al, QUALCOMM
Slide 32
doc.: IEEE 802.11-04/0873r2
Submission
Legacy and MIMO Training for 2, 3, and 4 Tx
• STS: 802.11a STS• LTS: 802.11a LTS• SIG1: 802.11a SIGNAL• SIG2: Extended SIGNAL• MTSn: MIMO training symbol
for Tx antenna n• CDx: x ns cyclic delay
STS LTS SIG 1 SIG 2 MTS 1 MTS 1
STS CD50 LTS CD50
SIG 1 CD50
SIG 2 CD50
MTS 2 CD50
-MTS 2 CD50
STS LTS SIG 1 SIG 2 MTS 1 MTS 1
STS CD50 LTS CD50
SIG 1 CD50
SIG 2 CD50
MTS 2 CD50
-MTS 2 CD50
STS CD100
LTS CD100
SIG 1 CD100
SIG 2 CD100
MTS 3 CD100
MTS 3 CD100
STS CD150
LTS CD150
SIG 1 CD150
SIG 2 CD150
MTS 4 CD150
-MTS 4 CD150
MTS 1 MTS 1
MTS 2 CD50
-MTS 2 CD50
-MTS 3 CD100
-MTS 3 CD100
-MTS 4 CD150
MTS 4 CD150
Tx 1
Tx 2
Tx 1
Tx 2
Tx 3
Tx 4
STS LTS SIG 1 SIG 2 MTS 1 MTS 1
STS CD50 LTS CD50
SIG 1 CD50
SIG 2 CD50
MTS 2 CD50
W·MTS 2 CD50
STS CD100
LTS CD100
SIG 1 CD100
SIG 2 CD100
MTS 3 CD100
W2·MTS 3 CD100
MTS 1
W2·MTS 2 CD50
W4·MTS 3 CD100
Tx 1
Tx 2
Tx 3
W = exp(j2π/3)
8 µs 8 µs 4 µs 4 µs 4 µs 4 µs 4 µs 4 µs
August 2004
John Ketchum, et al, QUALCOMM
Slide 33
doc.: IEEE 802.11-04/0873r2
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
August 2004
John Ketchum, et al, QUALCOMM
Slide 34
doc.: IEEE 802.11-04/0873r2
Submission
Preamble and Training Sequences• 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• Length of MIMO training sequence is always equal to the number of
transmit antennas– This ensures that the receiver can always track the full channel state, and
thus make fully informed rate decisions– Also ensures stable received power estimate
• Two forms of MIMO Training– Steered MIMO Training Sequence supports Eigensteered operation– Direct MIMO Training Sequence supports direct channel estimation
August 2004
John Ketchum, et al, QUALCOMM
Slide 35
doc.: IEEE 802.11-04/0873r2
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
John Ketchum, et al, QUALCOMM
Slide 36
doc.: IEEE 802.11-04/0873r2
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
John Ketchum, et al, QUALCOMM
Slide 37
doc.: IEEE 802.11-04/0873r2
Submission
Wideband Eigenmodes TGn Channel B
Power is relative to average total receive power at a single antenna
August 2004
John Ketchum, et al, QUALCOMM
Slide 38
doc.: IEEE 802.11-04/0873r2
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
John Ketchum, et al, QUALCOMM
Slide 39
doc.: IEEE 802.11-04/0873r2
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
John Ketchum, et al, QUALCOMM
Slide 40
doc.: IEEE 802.11-04/0873r2
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
John Ketchum, et al, QUALCOMM
Slide 41
doc.: IEEE 802.11-04/0873r2
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
John Ketchum, et al, QUALCOMM
Slide 42
doc.: IEEE 802.11-04/0873r2
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
John Ketchum, et al, QUALCOMM
Slide 43
doc.: IEEE 802.11-04/0873r2
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 average 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
John Ketchum, et al, QUALCOMM
Slide 44
doc.: IEEE 802.11-04/0873r2
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
John Ketchum, et al, QUALCOMM
Slide 45
doc.: IEEE 802.11-04/0873r2
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/N0 (dB)
Ave
rage
Thr
ough
put (
Mbp
s)FLRL
0 5 10 15 20 25 30 35 40 45 5010
-3
10-2
10-1
Ave
rage
PER
August 2004
John Ketchum, et al, QUALCOMM
Slide 46
doc.: IEEE 802.11-04/0873r2
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/N0 (dB)
Ave
rage
Thr
ough
put (
Mbp
s)FLRL
0 5 10 15 20 25 30 35 40 45 50
10-2
10-1
Ave
rage
PER
August 2004
John Ketchum, et al, QUALCOMM
Slide 47
doc.: IEEE 802.11-04/0873r2
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/N0 (dB)
Ave
rage
Thr
ough
put (
Mbp
s)
FLRL
0 5 10 15 20 25 30 35 40 45 50
10-3
10-2
10-1
Ave
rage
PER
August 2004
John Ketchum, et al, QUALCOMM
Slide 48
doc.: IEEE 802.11-04/0873r2
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/N0 (dB)
Ave
rage
Thr
ough
put (
Mbp
s)FLRL
0 5 10 15 20 25 30 35 40 45 50
10-4
10-3
10-2
10-1
Ave
rage
PER
August 2004
John Ketchum, et al, QUALCOMM
Slide 49
doc.: IEEE 802.11-04/0873r2
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/N0 (dB)
Ave
rage
Thr
ough
put (
Mbp
s)
FLRL
0 5 10 15 20 25 30 35 40 45 5010
-3
10-2
10-1
Ave
rage
PER
August 2004
John Ketchum, et al, QUALCOMM
Slide 50
doc.: IEEE 802.11-04/0873r2
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/N0 (dB)
Ave
rage
Thr
ough
put (
Mbp
s)FLRL
0 5 10 15 20 25 30 35 40 45 50
10-4
10-3
10-2
10-1
Ave
rage
PER
August 2004
John Ketchum, et al, QUALCOMM
Slide 51
doc.: IEEE 802.11-04/0873r2
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/N0 (dB)
Ave
rage
Thr
ough
put (
Mbp
s)FLRL
0 5 10 15 20 25 30 35 40 45 50
10-3
10-2
10-1
Ave
rage
PER
August 2004
John Ketchum, et al, QUALCOMM
Slide 52
doc.: IEEE 802.11-04/0873r2
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/N0 (dB)
Aver
age
Thro
ughp
ut (M
bps)
1x5x10x20x
August 2004
John Ketchum, et al, QUALCOMM
Slide 53
doc.: IEEE 802.11-04/0873r2
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