STA Antenna Indication in VHT Capabilities Month Year Month Year doc.: IEEE 802.11-yy/xxxxr0 doc.: IEEE 802.11-yy/xxxxr0 STA Antenna Indication in VHT Capabilities Date: 2011-11-09 Slide 1 Brian Hart, Cisco Systems Page 1 John Doe, Some Company John Doe, Some Company

Executive Summary Situation Via VHT Capabilities element, an AP can find out the minimum number of RX and TX antennas of a STA A client might silently have additional antennas and use them for proprietary PHY processing Problem AP cannot make optimal decisions with silent antennas E.g. a client switches antennas after sounding and AP sees unexpectedly lower BFing performance, and could lead AP to sound a channel more often than needed Solution We propose to redefine two reserved bits in “VHT Capabilities Info field” to provide indication of the possibility of antenna pattern change.

Situation: A STA advertizes min capabilities only RX/TX MCS Map in VHT Supported MCS Set field in VHT Capabilities element lists the number of spatial streams and supported MCSs per SS So AP can infer the minimum number of RX and TX antennas Yet, there are many devices with more antennas than they indicate in their RX/TX MCS Map The additional antennas are usually used for various PHY processing to enhance PHY layer robustness by antenna diversity techniques 802.11ac forces a STA to remain silent about its additional antennas

Problem: AP lacks info to make better decisions There are devices with more RX antennas that perform antenna switching Antenna switching causes the already sounded channel to be mostly useless for subsequent transmissions without AP knowing it, particularly for MU transmission Frequent antenna switching could appear as channel change due to mobility, leading AP to interpret the associated client as a mobile STA and to sound the channel more frequently than it’s needed Some STAs might switch RX antennas often, even per frame A STA after antenna switching usually stays on the selected antenna(s), causing its TX antenna pattern to change without AP knowing it This causes problem for the AP that performs advanced signal processing

Solution: Allow STA to clarify its antenna capabilities 1 bit: “RX Antenna Pattern Consistency” in VHT Capabilities element Set to 0 if RX antenna pattern can change during association Set to 1 if RX antenna pattern remains fixed during association 1 bit: “TX Antenna Pattern Consistency” in VHT Capabilities element Set to 0 if TX antenna pattern can change during association Set to 1 if TX antenna pattern remains fixed during association B13 B15 B16 B18 B19 B20 B21 B22 B23 B25 B26 B27 B28 B29 B29-B31 Compressed Steering Number of BF Antennas Supported Number of Sounding Dimensions MU BFer Capable MU BFee Capable VHT TXOP PS +HTC-VHT Capable Max A-MPDU Length Exponent VHT Link Adaptation Capable RX Antenna Pattern Consistency TX Antenna Reserved Bits: 3 3 1 2