Channel access for simultaneous uplink transmissions by multiple communication devices

1. A method for communicating in a communication channel of a wireless communication network, the method comprising:

receiving, at a client station from an access point, a downlink physical layer (PHY) data unit via the communication channel, wherein the downlink PHY data unit includes a trigger frame that is configured to prompt the client station to transmit an uplink physical layer (PHY) data unit to the access point, wherein the trigger frame indicates a set of one or more subchannels in which the client station is to transmit the uplink PHY data unit, and wherein the trigger frame includes an indication of whether the client station is required to perform a channel sensing procedure to determine if the one or more subchannels are not idle prior to transmitting the uplink PHY data unit; and

in response to the trigger frame indicating that the client station is required to perform the channel sensing procedure to determine if the one or more subchannels are not idle:

measuring, at the client station, the one or more energy levels in the one or more subchannels to determine whether the one or more subchannels are not idle,

transmitting, by the client station, the uplink PHY data unit only after i) measuring the one or more energy levels in the one or more subchannels and ii) determining that the one or more subchannels are idle, and

not transmitting, by the client station, the uplink PHY data unit in response to i) measuring the one or more energy levels in the one or more subchannels and ii) determining that the one or more subchannels are not idle; and

in response to the trigger frame indicating that the client station is not required to perform the channel sensing procedure to determine if the one or more subchannels are not idle, transmitting, by the client station, the uplink PHY data unit without measuring the one or more energy levels in the one or more subchannels.

2. The method of claim 1 , further comprising:

in response to the trigger frame indicating that the client station is required to perform the channel sensing procedure to determine if the one or more subchannels are not idle:

checking, at the client station, whether a network allocation vector (NAV) timer indicates the one or more subchannels are not idle,

transmitting, by the client station, the uplink PHY data unit only after determining that the NAV timer indicates the one or more subchannels are idle, and

not transmitting, by the client station, the uplink PHY data unit in response to determining that the NAV timer indicates the one or more subchannels are not idle.

3. The method of claim 2 , wherein:

in response to the trigger frame indicating that the client station is not required to perform the channel sensing procedure to determine if the one or more subchannels are not idle, the uplink PHY data unit is transmitted without determining that the NAV timer indicates the one or more subchannels are idle.

4. The method of claim 1 , wherein:

measuring the one or more energy levels in the one or more subchannels comprises measuring the one or more energy levels in the one or more subchannels after reception of the trigger frame.

5. The method of claim 4 , wherein:

measuring the one or more energy levels in the one or more subchannels comprises measuring the one or more energy levels in the one or more subchannels after reception of the trigger frame for a time period equal to a short interframe space (SIFS).

6. The method of claim 1 , wherein:

measuring the one or more energy levels in the one or more subchannels comprises measuring the one or more energy levels in the one or more subchannels during a time period prior to reception of the downlink PHY data unit.

7. The method of claim 1 , wherein:

transmitting the uplink PHY data unit comprises beginning transmission of the uplink PHY data unit after a time period that begins when reception of the downlink PHY data unit ends, wherein the time period is equal to a short interframe space (SIFS).

8. The method of claim 1 , wherein:

the uplink PHY data unit is a first uplink PHY data unit; and

in response to i) the trigger frame indicating that the client station is required to perform the channel sensing procedure to determine if the one or more subchannels are not idle, and ii) a) measuring the one or more energy levels in the one or more subchannels, and b) determining that the one or more subchannels are not idle:

transmitting, by the client station, a second uplink PHY data unit in the one or more subchannels, wherein the second uplink PHY data unit has a duration shorter than a duration of the first uplink PHY data unit.

9. The method of claim 8 , wherein the second uplink PHY data unit is a null data packet (NDP).

10. A communication device, comprising:

a network interface device having one or more integrated circuits (ICs) configured to:

receive, from an access point, a downlink physical layer (PHY) data unit via a communication channel, wherein the downlink PHY data unit includes a trigger frame that is configured to prompt the communication device to transmit an uplink PHY data unit to the access point, wherein the trigger frame indicates a set of one or more subchannels in which the communication device is to transmit the uplink PHY data unit, and wherein the trigger frame includes an indication of whether the communication device is required to perform a channel sensing procedure to determine if the one or more subchannels are not idle prior to transmitting the uplink PHY data unit, and

wherein the one or more ICs are further configured to: in response to the trigger frame indicating that the communication device is required to perform the channel sensing procedure to determine if the one or more subchannels are not idle:

measure the one or more energy levels in the one or more subchannels to determine whether the one or more subchannels are not idle,

transmit the uplink PHY data unit only after i) measuring the one or more energy levels in the one or more subchannels and ii) determining that the one or more subchannels are idle, and

not transmit the uplink PHY data unit in response to i) measuring the one or more energy levels in the one or more subchannels and ii) determining that the one or more subchannels are not idle; and

wherein the one or more ICs are further configured to: in response to the trigger frame indicating that the communication device is not required to perform the channel sensing procedure to determine if the one or more subchannels are not idle, transmit the uplink PHY data unit without measuring the one or more energy levels in the one or more subchannels.

11. The communication device of claim 10 , wherein the one or more ICs are further configured to:

in response to the trigger frame indicating that the communication device is required to perform the channel sensing procedure to determine if the one or more subchannels are not idle:

check whether a network allocation vector (NAV) timer indicates the one or more subchannels are not idle,

transmit the uplink PHY data unit only after determining that the NAV timer indicates the one or more subchannels are idle, and

not transmit the uplink PHY data unit in response to determining that the NAV timer indicates the one or more subchannels are not idle.

12. The communication device of claim 11 , wherein the one or more ICs are further configured to:

in response to the trigger frame indicating that the communication device is not required to perform the channel sensing procedure to determine if the one or more subchannels are not idle, transmit the uplink PHY data unit without determining that the NAV timer indicates the one or more subchannels are idle.

13. The communication device of claim 10 , wherein the one or more ICs are further configured to:

measure the one or more energy levels in the one or more subchannels after reception of the trigger frame to determine whether the one or more subchannels are not idle.

14. The communication device of claim 13 , wherein the one or more ICs are further configured to:

measure the one or more energy levels in the one or more subchannels after reception of the trigger frame for a time period equal to a short interframe space (SIFS) to determine whether the one or more subchannels are not idle.

15. The communication device of claim 10 , wherein the one or more ICs are further configured to:

measure the one or more energy levels in the one or more subchannels during a time period prior to reception of the downlink PHY data unit to determine whether the one or more subchannels are not idle.

16. The communication device of claim 10 , wherein the one or more ICs are further configured to:

begin transmission of the uplink PHY data unit after a time period that begins when reception of the downlink PHY data unit ends, wherein the time period is equal to a short interframe space (SIFS).

17. The communication device of claim 10 , wherein:

the uplink PHY data unit is a first uplink PHY data unit; and

the one or more ICs are further configured to: in response to i) the trigger frame indicating that the communication device is required to perform the channel sensing procedure to determine if the one or more subchannels are not idle, and ii) a) measuring the one or more energy levels in the one or more subchannels, and b) determining that the one or more subchannels are not idle:

transmit a second uplink PHY data unit in the one or more subchannels in response to the trigger frame, wherein the second uplink PHY data unit has a duration shorter than a duration of the first uplink PHY data unit.

18. The communication device of claim 17 , wherein the second uplink PHY data unit is a null data packet (NDP).

19. The communication device of claim 10 , wherein the network interface device comprises:

one or more transceivers implemented on the one or more ICs.

20. The communication device of claim 19 , further comprising:

one or more antennas coupled to the one or more transceivers.