1. Power saving mechanism consideration for 802.11ah framework
July 2011
doc.: IEEE /xxxxr0
Sept 2011
Power saving mechanism consideration for ah framework
Date:
Authors:
ZTE Corporation
ZTE Corporation

2. July 2011
doc.: IEEE /xxxxr0
Sept 2011
Abstract
This presentation is target to provide consideration on power saving for ah framework.
ZTE Corporation
ZTE Corporation

3. Several PS mechanisms in 802.11 (1)
July 2011
doc.: IEEE /xxxxr0
Sept 2011
Several PS mechanisms in (1)
Basic power management mechanism in infrastructure network
AP is aware of power management state of STA and buffer traffic for Doze STA, with periodic announcement of buffer status in TIM/DTIM of Beacon frames.
STA achieves power saving with entering into Doze state, and wakes up to listen for Beacon to receive the TIM. By examining the TIM/DTIM, STA determines if AP has buffered traffic on its behalf.
To retrieve buffered frames, PS-Poll Control frames is used by STA. And all STAs must use the random backoff algorithm before transmitting the PS-Poll frames when multiple STA have buffered frames.
Basic mechanism for system
Could be reused in ah. However STA with buffered data is required to remain in active mode in the beacon interval until getting its own data successfully from AP, which means more power consumption in STA has late channel access opportunities.
ZTE Corporation
ZTE Corporation

4. Several PS mechanisms in 802.11 (2)
July 2011
doc.: IEEE /xxxxr0
Sept 2011
Several PS mechanisms in (2)
APSD in e
For Qos STA in basic PS mode
unscheduled APSD (U-APSD)
Qos STA sets an AC to be trigger-enabled or delivery-enabled. The MSDUs from delivery-enabled AC will be buffered. Qos STA wakes up and transmits a trigger frame to the Qos AP to retrieve the buffered MSDUs or management frames during unscheduled service period.
scheduled APSD (S-APSD)
A non-AP Qos STA using scheduled service period shall wake up at a fixed time interval equal to the Service Interval. The STA shall first wake up to receive downlink unicast frames buffered and/or polls from the AP/Hybrid Coordinator.
Could be reused, however power saving effort depending on channel competition efficiency
ZTE Corporation
ZTE Corporation

5. Several PS mechanisms in 802.11 (3)
Sept 2011
Several PS mechanisms in (3)
PSMP Power Saving mechanisms in n
providing a time schedule that is used by an access point (AP) and its stations (STAs) to access the wireless medium. The mechanism is controlled using the PSMP Action frame.
could be considered in 11ah PS, but for 11ah, the number of STA will be several hundreds to even 6000 (Smart Grid application).
Group concept could be introduced to improve PSMP mechanism to be repeated based on group, then STA may wake up in corresponding group PSMP period and sleep in the other PSMP period
ZTE Corporation

6. Several PS mechanisms in 802.11 (4)
July 2011
doc.: IEEE /xxxxr0
Several PS mechanisms in (4)
Sept 2011
Power Saving mechanisms in v (1)
Proxy ARP
AP indicates that it can proxy ARP frames for STAs.
Fit for 11ah use case 2 and 3, when ARP running in the devices
BSS Max Idle Period
AP advertises a time period during which the AP does not disassociate a STA due to non-receipt of frames from the STA.
The current Max Idle Period field is 17.8h( 16bit in units of 1000TU (1.024s) ).For 11ah meter and sensor applications, the idle period may be longer such as several weeks or several months. =
ZTE Corporation
ZTE Corporation

7. Several PS mechanisms in 802.11 (5)
July 2011
doc.: IEEE /xxxxr0
Several PS mechanisms in (5)
Sept 2011
Power Saving mechanisms in v (2)
Traffic Filtering Service
AP/STA negotiate TCLAS patterns for filtering processing, including UP of MSDUs and frame classifier parameters. AP reduce the number of frames sent to the STA by discarding frames that do not match the traffic filters.
WNM-Sleep Mode
STA does not need to listen for every DTIM Beacon frame, and does not perform GTK/IGTK updates. Sleep interval (2 octets, numbers of DTIMs) is less than BSS max idle period.
TIM Broadcast
Allows STA to receive a TIM element without receiving a Beacon frame. TIM frames have shorter duration and transmitted at a higher data rate than Beacon frames. The Interval is the number of beacon period, and the rate unit is 0.5Mbps. TIM transmits at the TTTT plus a offset value (+/- 4ms) of TBTT.
ZTE Corporation
ZTE Corporation

8. Several PS mechanisms in 802.11 (6)
July 2011
doc.: IEEE /xxxxr0
Several PS mechanisms in (6)
Sept 2011
Power Saving mechanisms in v (3)
BSS Termination Notification
AP requests STAs to transition to a specific AP or indicate a set of preferred APs, due to BSS Termination.
For AP power save, not essential for 11ah.
Flexible Multicast Service
STA request an alternate DTIM delivery interval for one or more sets of received group addressed streams. AP support from one to eight different FMS Stream delivery intervals for any number of FMS streams.
Directed Multicast Service
AP transmit the requested group addressed (multicast) traffic as the individual addressed (unicast) traffic to the requesting STA in an A- MSDU frame format.
Although DMS may further save the power of STA and make the traffic more reliable, it will increase the airtime frames of AP.
ZTE Corporation
ZTE Corporation

9. Sept 2011
Summary
Most of power management/saving mechanisms could be reused, as analyzed
Some mechanisms may need extensions to fit for ah scenario
BSS Max Idle Period in v, time period designed in original field may be extended.
Introducing group concept in PSMP mechanism to enhance the power saving affection.
ZTE Corporation