1. Non-Automatic Power Saving Delivery
Mathilde Benveniste
Avaya Labs – Research
August 26, 2003

2. August 2003
Reverse Polling
Reverse polling can be done with the legacy power management mechanism enhanced with existing e features
M. Benveniste, Avaya Labs - Research

3. Station in power save mode
August 2003
Reverse Polling
Contention time (not drawn to scale)
Downlink
Frames
Uplink
More Data field = 1
More Data field = 0
ACK
D data
D data
ACK
time
Data
PM field=0
ACK
Null+ACK
PM field=1
Station wakes up
Station in power save mode
M. Benveniste, Avaya Labs - Research

4. Month 2002
doc.: IEEE /xxxr0
August 2003
Uplink transmissions
1.       The station will signal the AP that it is awake by sending an uplink frame with the Power Management field set to 0 in the frame control field.
2.      The station will stay awake until it has transmitted all its uplink frames and has received notice from the AP that either there are no buffered frames pending transmission, or downlink transmission of buffered frames is postponed. A downlink frame with the More Data field set to 0 in the frame control field, will signal that there are no more downlink frames pending transmission. A downlink frame with the Last field set to 1 in the QoS control field, signals that the AP will not transmit more downlink frames during this wake-up period.
3.       The station will stay awake until it has received a frame with the More Data field set to 0, a QoS frame with a “queue size” value of ‘0’, a beacon with its TIM bit cleared, or the Last bit set to 1.
4. Having received a frame with the More Data field set to 0, a QoS frame with a “queue size” value of ‘0’, a beacon with its TIM bit cleared, or the Last bit set to 1, the station shall indicate in its last frame that it is going back to sleep. The last frame will be either the last uplink MSDU or a (Null+)ACK to the last downlink frame.
A station that goes to sleep having received a downlink frame with the Last field set to 1 and the More Data field set to 1 may subsequently send a null frame with Power Management field set to 0 to receive the remaining buffered frames.
M. Benveniste, Avaya Labs - Research
John Doe, His Company

5. Month 2002
doc.: IEEE /xxxr0
August 2003
AP Operation
1. The AP sends frames buffered for a power saving station as soon as the station wakes up. That is indicated when a frame is received from that station with the Power Management field set to 0 in the frame control field. If there is no frame to send in a cycle, it sends nothing.
2. Receipt of a frame with the Power Management field set to 1 in the frame control field indicates that the station sending the frame is in power save mode.
3. The AP buffers the frames destined to a station in power save mode.
4. The More Data field in the frame control field is 1 for all buffered frames except the last, in which the same is set to 0.
5. The Last bit in the QoS control field is 0 for all downlink frames sent to a station until the AP determines that other downlink transmissions have precedence, in which case the AP sends downlink frames with the Last field set to 1.
M. Benveniste, Avaya Labs - Research
John Doe, His Company

6. Reverse Polling vs Proposal 03/661
August 2003
Reverse Polling
Downlink
Frames
Uplink
More Data field = 1
More Data field = 0
ACK
D data
D data
ACK
time
Data
PM field=0
ACK
Null+ACK
PM field=1
Also provides protection for a lost Ack
03/661 Proposal
Downlink
Frames
Uplink
More Data field = 1
More Data field = 0
ACK
D data
D data
time
Data
ACK
ACK
Reverse polling has an additional Null frame in the last frame exchange sequence
In an error-free channel, the added frame would increases channel use minimally – much better than the 33% that 03/661 suggests for pure legacy (only one more frame is transmitted, and that without contention)
In a noisy channel, reverse polling uses the channel more efficiently than proposal 03/661 because the extra Null frame in reverse polling prevents the repeated retransmission of a downlink frame whose ACK might be lost right before the station goes to sleep
M. Benveniste, Avaya Labs - Research

7. Discussion Reverse polling is possible with present TGe draft standard
August 2003
Discussion
Reverse polling is possible with present TGe draft standard
Any reverse polling mechanism has the problem of repeated retransmissions in case the final downlink ACK is lost
This problem is already addressed by the mechanism described here
A solution is not specified in proposal 03/661
Because of contention reduction and improved power saving achieved by EDCA when using APSD, APSD should remain an option
M. Benveniste, Avaya Labs - Research