Closed versus Open Loop Comparisons January 2005 doc.: IEEE 802.11-05/xxxxr0 January 2005 Closed versus Open Loop Comparisons Date: 2005-01-14 Authors: Notice: This document has been prepared to assist IEEE 802.11. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.11. Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures <http:// ieee802.org/guides/bylaws/sb-bylaws.pdf>, including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair <stuart.kerry@philips.com> as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.11 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at <patcom@ieee.org>. John Ketchum, Qualcomm John Ketchum, Qualcomm

Closed vs. Open Loop Quantify the benefits of closed loop January 2005 Closed vs. Open Loop Quantify the benefits of closed loop Feedback on Eigenvector steering (SS) or spatial spreading (SS) Number of streams Rates per stream Throughput and Latency comparisons Eigenvector Steering (ES) with feedback Spatial Spreading (SS) with feedback Spatial Spreading (SS) with no feedback John Ketchum, Qualcomm

Simulation Conditions January 2005 Simulation Conditions Obtained Rate versus Range curves for ES with feedback (ES) SS with feedback (SS closed loop) SS with no feedback (SS open loop) Simulation conditions Qualcomm rate set 2x2. Up to 2 spatial streams 5 GHz SGI-52 (shortened guard interval, 52 data tones) Offered traffic: 1 UDP flow from AP-STA. Packet size = 1500 B HCF, i.e., AP polls STA for Block Ack. Block Ack. No Immediate Ack for BA or BAR. Two cases: Target PHY PER = 2% and 10% Open Loop Rate Control Transmitter decreases “SNR Estimate” by D for each frame that is NAK-ed, and increases by d for each frame that is ACK-ed. D and d are chosen to obtain the desired PHY packet error rate (PER). John Ketchum, Qualcomm

January 2005 Throughput versus SNR John Ketchum, Qualcomm

MAC Throughput Comparisons January 2005 MAC Throughput Comparisons Closed Loop (ES or SS) Little throughput benefit by increasing the PHY PER from 2%-10% Open Loop Significant throughput benefit by increasing the PHY PER from 2%-10% However, high PER results in unacceptable latency tails as shown next. At 23 dB SS open loop (PHY PER = 2%): 50 Mbps SS open loop (PHY PER = 10%): 61 Mbps. But, note increased latency. SS closed loop: 66-69 Mbps ES: 103-105 Mbps At 100 Mbps Closed loop SS gains over open loop SS. 2.5 dB at 10% PHY PER 9 dB at 2% PHY PER ES offers 8 dB gain over SS (closed or open loop) John Ketchum, Qualcomm

January 2005 MSDU Latency Set offered load = 90% of achievable throughput at SNR=27 dB (corresponding to 20 m) At PHY PER = 2% offered UDP load ES: 107.2 Mbps SS closed loop: 68.0 Mbps SS open loop : 55.4 Mbps At PHY PER = 10% offered UDP load ES : 112.4 Mbps SS closed loop : 71.2 Mbps SS open loop : 64.8 Mbps John Ketchum, Qualcomm

MSDU Delay CDF Target PHY PER = 2% January 2005 MSDU Delay CDF Target PHY PER = 2% John Ketchum, Qualcomm

MSDU Delay CDF Target PHY PER = 10% January 2005 MSDU Delay CDF Target PHY PER = 10% John Ketchum, Qualcomm

Latency Comparisons January 2005 Long delay tails with open loop. By setting PHY PER = 2% (instead of 10%) 25-30% loss in throughput. We can pull in the 90th percentile MSDU latency from 45 ms to less than 20 ms. But, the 95th and 99th percentile exceed 50 ms even at PHY PER = 2%. Reason for long tail. Open loop rate selection: the Tx Rate is dropped because of frame errors. The queue service rate is decreased at the time of increased offered load due to retransmissions. This results in significantly higher tails of the delay distribution. We have demonstrated Significant throughput and latency benefit of closed loop. Significant throughput and latency benefit of ES. John Ketchum, Qualcomm

January 2005 Conclusions We have demonstrated throughput and latency benefits of closed loop feedback. MIMO Mode feedback: Eigenmode steering versus spatial spreading Stream feedback: number of spatial streams Rate feedback: rates per spatial stream Significant benefits with very little overhead. 16 bits at Data Rate John Ketchum, Qualcomm