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Qualcomm MAC Supplementary Presentation

Qualcomm MAC Supplementary Presentation. Sanjiv Nanda, John Ketchum QUALCOMM, Inc. List of Topics. Backward Compatibility and Legacy Sharing Scalability Future-proof Highest Performance Permit low complexity implementations for low capability devices

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Qualcomm MAC Supplementary Presentation

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  1. Qualcomm MAC Supplementary Presentation Sanjiv Nanda, John Ketchum QUALCOMM, Inc. Sanjiv Nanda, Qualcomm, Inc.

  2. List of Topics • Backward Compatibility and Legacy Sharing • Scalability • Future-proof Highest Performance • Permit low complexity implementations for low capability devices • Highlights of Throughput and Performance Results • Essential MAC features and quantification of benefits • Block Ack Mechanism • 20/40 MHz Operation Sanjiv Nanda, Qualcomm, Inc.

  3. Backward Compatibility • 802.11a/g Preamble and SIGNAL field is unchanged. • RATE field in 802.11a/g SIGNAL is set to a value “undefined” in 802.11a/g • Legacy STAs will abandon further decoding of the PPDU and go to CCA when they detect an undefined value of RATE field. • This is different from “spoofing” specified in other proposals. Spoofing provides protection but at a cost: • Legacy SIGNAL field is consumed. Benefit has not been quantified. • Power drain at legacy STAs. Sanjiv Nanda, Qualcomm, Inc.

  4. Legacy Sharing: CC15 • CC15 Results are provided for the case of a single 802.11n STA-AP link sharing the medium with: • 802.11g STA-AP link in the 2.4 GHz band • 802.11a STA-AP link in the 5 GHz band • We show that the 802.11n MAC allows the legacy STA to “fairly” share the bandwidth. • Legacy STA only: 24.4 Mbps • Legacy STA in shared network: 11.9 Mbps • The MAC permits other possible sharing policies Sanjiv Nanda, Qualcomm, Inc.

  5. Legacy Sharing: CC15 Sanjiv Nanda, Qualcomm, Inc.

  6. Scalability • Scalable, future-proof, highest performance • High data rates with up to 4 streams • Highest throughputs with Eigenvector Steering • Lowest latency MAC operation with ACF • However, scalable design also permits low complexity implementations for low capability STAs • Low complexity PHY receiver designs to accommodate • Decoding delays • MIMO processing delays • Receiver limit on maximum aggregate frame size • Scheduled operation for lowest power consumption Sanjiv Nanda, Qualcomm, Inc.

  7. Mandatory and Optional Features • PHY Mandatory • Spatial Spreading • Minimum of two antennas and two spatial streams • PLCP header supports rate indication for four streams (ordered rates ) • PLCP header extension supports rate feedback for four streams • PLCP MIMO training supports transmission of steered reference • PHY Optional • Eigenvector steering • Calibration capability mandatory for ES mode • EVD/SVD capability at AP or STA Sanjiv Nanda, Qualcomm, Inc.

  8. Mandatory and Optional Features • MAC Mandatory • Frame aggregation • SCHED and SCAP • Rate feedback per stream • Extensions to Block ACK mechanism • MAC Optional • Compressed Block ACK Sanjiv Nanda, Qualcomm, Inc.

  9. Throughput and Performance Highlights • We have shown in Berlin: • Significantly higher throughput compared to other proposals. • 100 Mbps BSS throughput in realistic scenarios with 20 MHz BW • Significantly higher range compared to other proposals. • Updated results show further improvement. Sanjiv Nanda, Qualcomm, Inc.

  10. Summary of System Simulation Results • Parameters • 5.25 GHz; BW = 20 MHz • SGI-52 OFDM symbols, except for Scenario 6 (Hot Spot) • Significantly higher throughput compared to other proposals. Sanjiv Nanda, Qualcomm, Inc.

  11. Extended Scenarios • Mandatory Scenarios have been extended to demonstrate the capabilities of our design. • 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. More realistic. • Two HDTV flows are moved from 5 m from the AP, to 25 m from the AP. Representative of real deployments. • 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. Sanjiv Nanda, Qualcomm, Inc.

  12. Throughput versus Range for Channel Model B • Throughput above the MAC of 100 Mbps is achieved at: • 29 m (35 m) for 2x2, 5.25 GHz for Channel Model B (D). • 40 m (54 m) for 2x2, 2.4 GHz • 47 m (65 m) for 4x4, 5.25 GHz • 75 m (102 m) for 4x4, 2.4 GHz • Significantly higher range compared to other proposals. Sanjiv Nanda, Qualcomm, Inc.

  13. Throughput versus Range for Channel Model D • Throughput above the MAC of 100 Mbps is achieved at: • 29 m (35 m) for 2x2, 5.25 GHz for Channel Model B (D). • 40 m (54 m) for 2x2, 2.4 GHz • 47 m (65 m) for 4x4, 5.25 GHz • 75 m (102 m) for 4x4, 2.4 GHz • Significantly higher range compared to other proposals. Sanjiv Nanda, Qualcomm, Inc.

  14. Adaptive Coordination Function • ACF Features • No Immediate ACK • For BlockAckRequest and BlockAck • SCHED • PPDU Aggregation with Reduced and Zero IFS • Multi-Poll • Low latency closed loop operation • Achieve higher PHY rates due to smaller backoff and MIMO Mode Control Sanjiv Nanda, Qualcomm, Inc.

  15. Benefits of ACF • ACF versus HCF with Frame Aggregation • Throughput Gain in Scenario 1: 70% Sanjiv Nanda, Qualcomm, Inc.

  16. Benefits of ACF • ACF Features • No Immediate ACK • For BlockAckRequest and BlockAck • MAC Efficiency Gain over HCF with Frame Aggregation: ~18% • SCHED • PPDU Aggregation with Reduced and Zero IFS • Multi-Poll • MAC Efficiency Gain over HCF with Frame Aggregation : ~7% • Low latency closed loop operation • Achieve higher PHY rates due to smaller backoff and MIMO Mode Control • Mean PHY Rate Gain over HCF: ~35% Sanjiv Nanda, Qualcomm, Inc.

  17. Benefit of 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 • Comparison: • Closed Loop: Rate selection and MIMO mode selection • Open Loop: SS only • Substantial throughput gains: • 2x2, standard symbols • Scenario 1: 50% • 80.4 Mbps versus 53.6 Mbps • Scenario 6: 38% • 81.9 Mbps versus 59.5 Mbps Sanjiv Nanda, Qualcomm, Inc.

  18. Benefit of Eigensteering • Comparison: • Closed Loop: Rate selection and MIMO mode selection • Closed Loop: SS only • Sample Gains: • 2x2, SGI-52 symbols • 30% throughput gain in Scenario 1. • 40% in Scenario 4. Sanjiv Nanda, Qualcomm, Inc.

  19. Reduced Complexity PHY Implementations • MAC design choices must not impose excessive complexity on PHY implementation • Allow low complexity PHY implementations for low capability devices, e.g., VoIP phone, PDA. • Fewer antennas. • MIMO processing delay. • Delayed decoding. • Permit STA designs with reduced PHY complexity • Limit on reception of Aggregate frames, • Limit on reception of Aggregate PPDUs, • Turn-around time for Block Ack. • Turn-around time for estimation of steering vectors. Sanjiv Nanda, Qualcomm, Inc.

  20. Frame Aggregation • On-the-fly frame aggregation at the transmitter • Flexible, without additional complexity. • Maximum aggregate size in Block Ack negotiation. • To permit low receiver complexity. • No frame aggregation across multiple RAs. • Requires reception of the largest Multiple-RA aggregate. Unnecessary burden on receiver complexity. • Use PPDU Aggregation instead. Sanjiv Nanda, Qualcomm, Inc.

  21. PPDU Aggregation • Improved throughput efficiency • Reduced or Zero IFS • No preamble if Tx power is unchanged • SCHED Frame: • Message indicates TA and RA, start offset and duration for scheduled TXOPs. • Advantages of PPDU Aggregation with SCHED: • Inclusion of RA and start offset in SCHED means STA needs to decode only its own PPDU rather than the entire aggregate. • Permits reduced receiver complexity. • Permits optimum sleep mode. • Start offset is with respect to the SCHED frame transmission. No global synchronization issue. • May be used by AP or STA Sanjiv Nanda, Qualcomm, Inc.

  22. PPDU Aggregation • 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 Sanjiv Nanda, Qualcomm, Inc.

  23. Compression • MAC Header Compression • Compressed Header Formats: Eliminate, TA, RA, Duration/ID fields • Gain: unavailable. • Compressed Block Ack • Transmitter option. Receiver mandatory. • Gain: 2% throughput gain. Results for Scenario 1 and Scenario 6. Sanjiv Nanda, Qualcomm, Inc.

  24. Robust Block Ack Operation • The 802.11e Block Ack mechanism offers a flexible Window-Based Selective Reject ARQ engine. • Does not require Immediate Block Ack to maximize throughput. • Keep the “pipe” full; avoid window “stalling.” • Simple corrections/clarifications of 802.11e Block Ack mechanism. • “Synchronized” operation between frame transmissions and Block Acks is not required. • Block Acks need not be acknowledged. • Operates seamlessly if Block Acks are lost. • Operates seamlessly if Block Acks are delayed. • Block Ack Requests can be implicit. Sanjiv Nanda, Qualcomm, Inc.

  25. Operation with Lost BlockAck Frame • Frame Transmissions can continue even if Block Acks are lost. • Frames EFGH can be transmitted even though BlockAck is lost. • Up to size of window. • Immediate ACK of BlockAck or BlockAckRequest Frame is not required Sanjiv Nanda, Qualcomm, Inc.

  26. Operation with Decoding Delay • Frame Transmissions can continue even with Decoding Delay • Frames EFGH can be transmitted even if Frames ABCD are still being decoded at the receiver • BAR Request Count is “echoed” back to the transmitter • Indicates last received BAR Request Count • Frames EFGH should not be retransmitted. Sanjiv Nanda, Qualcomm, Inc.

  27. Robust 40/20 MHz Operation • 40 MHz channels are defined as (2n, 2n+1) carrier pairs. (2n+1, 2n+2) pair is not allowed. • Primary and Secondary Carriers • Ensures that overlapping 40 MHz BSS always have the same primary carrier. • Medium Access (CSMA/CA) is managed on the Primary carrier. • CCA must be done on Secondary carrier also. • Secondary Carrier Interference Events (SCIE) are tracked by AP and STAs. • Excessive SCIE Count implies overlap with a 20 MHz BSS on secondary. • Procedures are defined to eliminate overlapping 20 MHz BSS on Secondary. Sanjiv Nanda, Qualcomm, Inc.

  28. 40 MHz Channel Pairs • 40 MHz channels are defined as (2n, 2n+1) carrier pairs. (2n+1, 2n+2) pair is not allowed. • Carrier 2n: Primary carrier • Carrier 2n+1: Secondary carrier • Ensures that overlapping 40 MHz BSS always have the same primary carrier. Sanjiv Nanda, Qualcomm, Inc.

  29. Overlapping 40 MHz BSS • Medium Access (CSMA/CA) is managed on the Primary carrier. • Overlapping 40 MHz BSS have the same primary carrier. Sanjiv Nanda, Qualcomm, Inc.

  30. Overlapping 40/20 MHz BSS • Medium Access (CSMA/CA) is managed on the Primary carrier. • Overlapping 20 MHz BSS on the primary carrier is permitted. • Procedures are defined to eliminate overlapping 20 MHz BSS on secondary. Sanjiv Nanda, Qualcomm, Inc.

  31. Overlapping 20 MHz BSS on Secondary • Clear Channel Assessment must be done on Secondary carrier also. • During CCA, if there is a transmission on the secondary. Transmit only on primary. • Secondary Carrier Interference Events (SCIE) are tracked by AP and STAs. Sanjiv Nanda, Qualcomm, Inc.

  32. Secondary Carrier Interference Events • Secondary Carrier Interference Events (SCIE) are tracked by AP and STAs. • During reception of a 20 MHz transmission on the primary if there is energy on the secondary. • During CCA, if there is a transmission on the secondary. • During reception of a 40 MHz transmission if there is lower SNR on the secondary. Sanjiv Nanda, Qualcomm, Inc.

  33. Fall-Back to 20 MHz • Excessive SCIE Counts imply overlap with a 20 MHz BSS on secondary. • Mandatory fall-back to 20 MHz operation. • Can move to another 40 MHz FA. Sanjiv Nanda, Qualcomm, Inc.

  34. Robust 40/20 MHz Operation: Summary • 40 MHz channels are defined as (2n, 2n+1) carrier pairs. (2n+1, 2n+2) pair is not allowed. • Carrier 2n: Primary carrier • Carrier 2n+1: Secondary carrier • Ensures that overlapping 40 MHz BSS always have the same primary carrier. • Medium Access (CSMA/CA) is managed on the Primary carrier. • Overlapping 40 MHz BSS have the same primary carrier. • Overlapping 20 MHz BSS on the primary carrier is permitted. • Procedures are defined to eliminate overlapping 20 MHz BSS on secondary. • CCA must be done on Secondary carrier also. • During CCA, if there is a transmission on the secondary. Transmit only on primary. • Secondary Carrier Interference Events (SCIE) are tracked by AP and STAs. • During CCA, if there is a transmission on the secondary. • During reception of a 40 MHz transmission if there is lower SNR on the secondary. • During reception of a 20 MHz transmission on the primary if there is energy on the secondary. • Excessive SCIE Count implies overlap with a 20 MHz BSS on secondary. • Mandatory fall-back to 20 MHz operation. • Can move to another 40 MHz FA. Sanjiv Nanda, Qualcomm, Inc.

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