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Reverse Polling for Non-Automatic Power Saving Delivery

This research discusses the use of reverse polling to enhance power saving delivery in 802.11e networks. It outlines the process and advantages of reverse polling compared to other proposals. The paper also emphasizes the importance of considering contention reduction and improved power saving when using Enhanced Distributed Channel Access (EDCA) with Automatic Power Saving Delivery (APSD) as an option.

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Reverse Polling for Non-Automatic Power Saving Delivery

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

  2. Reverse Polling • Reverse polling can be done with the legacy power management mechanism enhanced with existing 802.11e features M. Benveniste, Avaya Labs - Research

  3. Reverse Polling Contention time (not drawn to scale) Downlink Frames ------------- Uplink Frames 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. 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, orthe 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, orthe 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. 5. 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

  5. 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

  6. Reverse Polling vs Proposal 03/661 Reverse Polling Downlink Frames ------------- Uplink Frames More Data field = 1 More Data field = 0 ACK D data D data ACK time 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 Data PM field=0 ACK Null+ACK PM field=1 Also provides protection for a lost Ack 03/661 Proposal Downlink Frames ------------- Uplink Frames More Data field = 1 More Data field = 0 ACK D data D data time Data ACK ACK M. Benveniste, Avaya Labs - Research

  7. 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

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