WE CLAIM:
1. An apparatus, comprising:
a transceiver operable as an access point and capable of communicating in a wireless network, said transceiver adapted to perform a down link multi user -multiple input multiple output (DL MU-MIMO) transmission and further adapted to transmit a null data packet (NDP) (110) to sound channels between intended recipient wireless stations (STAs) (120, 140, 160);
wherein following a DL MU-MIMO transmission of said NDP, said transceiver is to separately poll each of multiple ones of said STAs for channel state information (CSI) with a polling frame (200) and receive a feedback frame from at least one of said STAs in response to at least one of the polling frames;
wherein the feedback frame (130, 150, 170) is to include a token to verify that said feedback frame is associated with a correct NDP.
2. The apparatus of claim 1, wherein said polling frame (200) comprises a duration field, a receive address (RA) field (230), and a transmit address field.
3. The apparatus of claim 1, wherein a format of said polling frame (200) is to include the address of a STA performing a sounding in the transmit address (TA) (240).
4. The apparatus of claim 1, wherein a format of said polling frame (200) is to include a duration value (220) that will set a NAV of 3rd party STAs in order to protect a solicited feedback frame (130, 150, 170) from collision by possible transmissions from said STAs.
5. The apparatus of claim 1, wherein a format of said polling frame (200) is to include that said polling frame (200) is short and can thus be

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efficiently transported using a low MCS and thus be received by all STAs in a vicinity of said AP.
6. A method, comprising:
operating a transceiver as an access point (AP) and communicating in a wireless network, said transceiver adapted to perform a down link multi user -multiple input multiple output (DL MU-MIMO) transmission said communicating including:
transmitting a null data packet (NDP) (110) to sound channels between intended recipient wireless stations (STAs) (120, 140, 160); and
separately polling each of multiple ones of said STAs for channel state information with a polling frame (200) and receiving a feedback frame (130, 150, 170) from at least one of said STAs in response to at least one of the polling frames;
wherein the feedback frame (130, 150, 170) is to include a token to verify that said feedback frame (130, 150, 170) is associated with a correct NDP.
7. The method of claim 6, wherein said polling frame (200) comprises a duration field, a receive address field, and a transmit address field.
8. The method of claim 6, wherein a format of said polling frame (200) includes an address of an intended recipient in a receive address (RA) field (230).
9. The method of claim 6, wherein a format of said polling frame (200) includes the address of a STA performing a sounding in the transmit address (TA) (240).

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10. The method of claim 6, wherein a format of said polling frame (200) includes a duration value (220) that will set a NAV of 3rd party STAs in order to protect a solicited feedback frame (130, 150, 170) from collision by possible transmissions from said STAs.
11. The method of claim 6, wherein a format of said polling frame (200) includes that said polling frame (200) is short and can thus be efficiently transported using a low MCS and thus be received by all STAs in a vicinity of said AP.
12. A machine-readable medium encoded with computer executable instructions, which when accessed, cause a machine to perform operations comprising:
controlling a transceiver as an access point (AP) in a wireless network, said transceiver adapted to perform a down link multi user - multiple input multiple output (DL MU-MIMO) transmission;
transmitting a null data packet (NDP) (110) to sound channels between intended recipient wireless stations (STAs) (120, 140, 160); and
separately transmitting a polling frame, subsequent to said transmitting the NDP, to each of multiple ones of said STAs for channel state information and receiving a feedback frame from at least one of said STAs in response to at least one of the polling frames;
wherein the feedback frame is to include a token to verify that said feedback frame is associated with a correct NDP.
13. The machine-readable medium encoded with computer executable
instructions of claim 12, wherein a format of said polling frame (200) includes
an address of an intended recipient in a receive address (RA) field (230).

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14. The machine-readable medium encoded with computer executable instructions of claim 12, wherein a format of said polling frame (200) includes the address of a STA performing a sounding in the transmit address (TA) (240).
15. The machine-readable medium encoded with computer executable instructions of claim 18, wherein a format of said polling frame (200) includes a duration value (220) that will set a NAV of 3rd party STAs in order to protect a solicited feedback frame (130, 150, 170) from collision by possible transmissions from said STAs.
16. The machine-readable medium encoded with computer executable instructions of claim 18, wherein a format of said polling frame (200) includes that said polling frame (200) is short and can thus be efficiently transported using a low MCS and thus be received by all STAs in a vicinity of said AP.
17. An apparatus, comprising:
a transceiver capable of operating as a mobile device in a wireless communications network capable of multiuser-multiple input multiple output (MU-MIMO) communications, the transceiver adapted to:
receive a null data packet (NDP) (110) from an access point (AP) for sounding channels between the transceiver and the access point;
receive, subsequent to said receiving the NDP, a polling frame (200) from the AP; and
transmit channel state information in response to said receiving the polling frame (200) and receive a feedback frame (130, 150, 170) from at least one of said STAs in response to at least one of the polling frames;
wherein the feedback frame (130, 150, 170) is to include a token to verify that said feedback frame (130, 150, 170) is associated with a correct NDP.

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18. The apparatus of claim 17, wherein the transceiver is further
adapted to:
derive the channel state information from the received NDP; and include that derived channel state information in the response.
19. A method, comprising:
operating as a mobile device in a wireless communications network capable of multiuser-multiple input multiple output (MU-MIMO) communications;
receiving a null data packet (NDP) from an access point (AP) for sounding channels between the access point and the mobile device;
receiving, subsequent to said receiving the NDP, a polling frame (200) from the AP; and
transmitting channel state information in response to said receiving the polling frame (200) and receiving a feedback frame (130, 150, 170) from at least one of said STAs in response to at least one of the polling frames;
wherein the feedback frame is to include a token to verify that said feedback frame is associated with a correct NDP.
20. The method of claim 19, further comprising:
deriving the channel state information from the received NDP; and including that derived channel state information in the response.
21. A computer readable non-transitory medium encoded with
computer executable instructions, which when accessed, cause a machine to
perform operations comprising:
operating as a mobile device in a wireless communications network capable of multiuser-multiple input multiple output (MU-MIMO) communications;

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receiving a null data packet (NDP) (110) from an access point (AP) for sounding channels between the access point and the mobile device;
receiving, subsequent to said receiving the NDP, a polling frame (200) from the AP; and
transmitting channel state information in response to said receiving the polling frame (200) and receiving a feedback frame (130, 150, 170) from at least one of said STAs in response to at least one of the polling frames;
wherein the feedback frame is to include a token to verify that said feedback frame (130, 150, 170) is associated with a correct NDP.
22. The medium of claim 21, wherein the operations further comprise: deriving the channel state information from the received NDP; and including that derived channel state information in the response.