Further Discussion on EDCA Power Saving Mechanisms

1. Further Discussion on EDCA Power Saving Mechanisms Authors: Chris Ware, chris.ware@motorola.com Stephen Wang Stephen.H.Wang@motorola.com Motorola, Inc. Date: September 16, 2003

2. QSTA has to initiate a complete frame exchange sequence to put itself to sleep QAP set “more data” to 0 Legacy using power save bit QAP ACK DL data Response frame Non-AP QSTA UL data ACK UL frame Non-AP QSTA set power mode “sleep” Non-AP QSTA set power-mode “Active” Legacy Power Management • Remains in standard, and may be applied to QoS frame types • Essentially a complete and correct frame exchange sequence to provide three way handshake • separates state change signaling from data frame exchanges • May require fix in draft to allow use of More Data bit

3. QAP set “more data” to 0 QAP ACK DL data Non-AP QSTA UL data ACK QSTA put itself to sleep based on APSD sleep rule Motorola Proposal (03/698) • TSPEC signals intention to use this method • Removes ambiguity. • Is simply a method to initiate an unscheduled SP • Follows normal APSD sleep rules once unscheduled SP is triggered • Uplink ACK is protected by DL Data NAV and sent at basic rate • Is an optional optimization that can be used to reduce power drain

4. Pros and Cons • Pros: • Channel contention only required twice • Removes additional frame overhead – 33% efficiency improvement • Is an optional mechanism, can decide not to use it • Significantly reduces power drain over legacy • Minimal implementation complexity for both STA and QAP • Cons: • Suffers from ‘lost uplink ACK Problem’ • not unique, so does legacy PS-Poll • Worst case in lost ACK scenario: • QAP retransmits up to retry limit then drops frame • QAP waits for next unscheduled SP to retransmit • Additional bit required in TPSEC

5. QAP set “more data” to 0 QAP ACK DL data ACK Non-AP QSTA UL data QoSNull + CF-ACK QSTA put itself to sleep based on APSD sleep rule Non-AP QSTA power-mode “Active” QoSNull +CF-ACK Proposal (03/663) • TPSEC signals intention to use the method • STA responds to DL Data (indicating MD=0) with a QoSNull+CF-ACK frame signaling intention to sleep • QAP then responds with ACK and STA returns to sleep • Need to define new double acknowledgement policy for eDCA • DL Data NAV would need to cover double ACK • SP would need to include additional ACK

6. Pros and Cons • Pros • Seems a competent solution to solve lost ACK problem • Improves efficiency over legacy • Cons • Additional frame overhead compared with Motorola proposal • A new frame exchange sequence must be defined, requiring significant changes to the draft (e.g. channel access transfer rules, double ACK procedure, retransmit procedures, etc.) • Improvement over legacy is less significant comparing to the Motorola approach (03/698)

7. Summary • Motorola proposal provides most efficient power management scheme for admitted EDCA flows • Optional mechanism, revert to legacy if you don’t want to use it • Legacy power save provides most robust mechanism at expense of efficiency and power consumption • QoSNull Piggyback proposal requires careful assessment to determine potential impact on current draft. • There may be other solutions available.