| CPC H04B 7/0643 (2013.01) [H04B 7/0626 (2013.01)] | 22 Claims |

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1. An apparatus comprising:
at least one processor and at least one machine-readable medium storing executable instructions which when executed by the at least one processor configure the apparatus for:
sending, to one or more stations (STAs), a request for channel state information (CSI), the request comprising both a null data packet announcement (NDPA) frame and a null data packet (NDP), the NDPA frame including a first field and a second field, the first field comprising one or more bits set to indicate presence of the second field, the second field being separate from the first field and indicating a variant of the NDPA frame; and
receiving, from the one or more STAs, a CSI feedback response based on the request.
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