Reducing power consumption in a wireless communication system

1. A method, comprising:

transitioning a network interface of a first wireless communication device from a low power state to an active state, wherein

when the network interface is in the low power state, the network interface is unable to at least one of (i) transmit signals via a wireless communication medium and (ii) receive signals via the wireless communication medium, and

when the network interface is in the active state, the network interface is capable of both (i) transmitting signals via the wireless communication medium and (ii) receiving signals via the wireless communication medium;

after transitioning the network interface to the active state, determining whether a communication channel is available;

generating a first data unit that includes a request for a second wireless communication device to transmit to the first wireless communication device data for the first wireless communication device that is buffered at the second wireless communication device;

in response to determining that the communication channel is available, transmitting to the second wireless communication device, via the communication channel, the first data unit that includes the request;

receiving from the second wireless communication device, via the communication channel, a second data unit that includes

i) only a subset of non-zero bits of a traffic indication map (TIM), the subset having multiple bits including a bit corresponding to the first wireless communication device, wherein the bit corresponding to the first wireless communication device serves as an indication that there is data for the first wireless communication device buffered at the second wireless communication device, and

ii) timing information to facilitate the first wireless communication device to determine a subsequent time at which the second wireless communication device will transmit data for the first wireless communication device that is buffered at the second wireless communication device,

wherein the second data unit is responsive to the first data unit;

determining, based on the timing information in the second data unit, a wakeup time at which the network interface of the first wireless communication device is to subsequently transition from the low power state to the active state in order to receive a subsequent transmission from the second wireless communication device;

transitioning the network interface of the first wireless communication device from the active state to the low power state after receiving the second data unit;

at the determined wakeup time, transitioning the network interface of the first wireless communication device from the low power state to the active state;

receiving, from the second wireless communication device and after the determined wakeup time, a beacon data unit;

processing the beacon data unit to determine the subsequent time at which the second wireless communication device will transmit data for the first wireless communication device that was buffered at the second wireless communication device;

transitioning the network interface of the first wireless communication device from the active state to the low power state after receiving the beacon data unit;

at the determined subsequent time, transitioning the network interface of the first wireless communication device from the low power state to the active state; and

receiving, from the second wireless communication device and after the determined subsequent time, data for the first wireless communication device that was buffered at the second wireless communication device.

2. The method of claim 1 , wherein generating the first data unit that includes the request comprises generating the first data unit to include data for transmission to the second wireless communication device.

3. The method of claim 1 , wherein the second data unit is an acknowledgment data unit that acknowledges receipt of the first data unit that includes the request.

4. The method of claim 3 , wherein the acknowledgment data unit includes data for the first wireless communication device buffered at the second wireless communication device.

5. The method to of claim 1 , wherein between (i) transitioning the network interface from the low power state to the active state and (ii) transmitting to the second wireless communication device the first data unit that includes the request, the second wireless communication device does not transmit the beacon data unit.

6. The method to of claim 1 , wherein:

the timing information in the second data unit includes a timestamp; and

the method further comprises adjusting a clock of the network interface of the first wireless communication device using the timestamp to adjust for clock drift between i) the clock of the network interface of the first wireless communication device and ii) a clock of a network interface of the second wireless communication device.

7. The method to of claim 1 , wherein the second data unit further includes information regarding changes to parameters for communication within a basis service set (BSS).

8. A first wireless communication device for use in a wireless communication network, the first wireless communication device comprising:

a network interface configured to

transition the network interface from a low power state to an active state, wherein

when the network interface is in the low power state, the network interface is unable to at least one of (i) transmit signals via a wireless communication medium and (ii) receive signals via the wireless communication medium, and

when the network interface is in the active state, the network interface is capable of both (i) transmitting signals via the wireless communication medium and (ii) receiving signals via the wireless communication medium;

after transitioning the network interface to the active state, determine whether a communication channel is available;

generate a first data unit that includes a request for a second wireless communication device to transmit to the first wireless communication device data for the first wireless communication device that is buffered at the second wireless communication device;

in response to determining that the communication channel is available, transmit to the second wireless communication device, via the communication channel, the first data unit that includes the request;

receive from the second wireless communication device, via the communication channel, a second data unit that includes

i) only a subset of non-zero bits of a traffic indication map (TIM), the subset having multiple bits including a bit corresponding to the first wireless communication device, wherein the bit corresponding to the first wireless communication device serves as an indication that there is data for the first wireless communication device buffered at the second wireless communication device, and

ii) timing information to facilitate the first wireless communication device to determine a subsequent time at which the second wireless communication device will transmit data for the first wireless communication device that is buffered at the second wireless communication device,

wherein the second data unit is responsive to the first data unit;

receive, from the second wireless communication device and after the determined wakeup time, a beacon data unit;

process the beacon data unit to determine the subsequent time at which the second wireless communication device will transmit data for the first wireless communication device that was buffered at the second wireless communication device;

transition the network interface from the active state to the low power state after receiving the beacon data unit;

at the determined subsequent time, transition the network interface from the low power state to the active state; and

receive, from the second wireless communication device and after the determined subsequent time, data for the first wireless communication device that was buffered at the second wireless communication device.

9. The first wireless communication device of claim 8 , wherein the network interface is configured to generate the first data unit that includes the request to also include data for transmission to the second wireless communication device.

10. The first wireless communication device of claim 8 , wherein the second data unit is an acknowledgment data unit that acknowledges receipt of the first data unit that includes the request, wherein the acknowledgement data unit is received from the second wireless communication device, via the communication channel.

11. The first wireless communication device of claim 8 , wherein between (i) transitioning the network interface from the low power state to the active state and (ii) transmitting to the second wireless communication device the first data unit that includes the request, the second wireless communication device does not transmit the beacon data unit.

12. The first wireless communication device of claim 8 , wherein:

the timing information in the second data unit includes a timestamp; and

the network interface of the first communication device is configured to adjust a clock of the network interface of the first communication device using the timestamp to adjust for clock drift between i) the clock of the network interface of the first wireless communication device and ii) a clock of a network interface of the second wireless communication device.

13. The first wireless communication device of claim 8 , wherein the second data unit further includes information regarding changes to parameters for communication within a basis service set (BSS).