1. Enhancement of Low Power Medium Access STAs
February 2008
doc.: IEEE /2376r0
Date: May, 2012
Enhancement of Low Power Medium Access STAs
Date:
Authors:
Liwen Chu Etc.
Liwen Chu, STMicroelectronics

2. Low Power Medium Access [1]
Date: May, 2012
Low Power Medium Access [1]
A low power STA doesn’t need to listen to TIM. It can send PS-Poll any time. The AP receives PS-Poll will respond ACK or buffered data frame to the low power STA.
Beacon
ACK
BU=1
Data
Beacon PS
Poll
Doze
Awake Time
Doze
Example with buffered data frames in AP
Beacon
ACK
BU=0
Beacon PS
Poll
Doze
Awake Time
Doze
Example without buffered data frames in AP 2

3. Optimization 1: STA’s Low Power Capability Indication
Date: May, 2012
Optimization 1: STA’s Low Power Capability Indication
A STA can indicate its low power operation when it associates with the AP.
A Low Power Indication bit can added to STA’s extended Capabilities or other IEs.
The AP can use this information to do some optimization operation when it allocates AIDs, creates TIM etc.
The AIDs of low power STAs are allocated to different beacon interval.
This can decrease collisions.
The AIDs of low power STAs are at the edge of AID set in the beacon interval.
This can decrease TIM length.
The AP will not to send TIM indication for the low power STAs.
AIDs for low power STAs
xxxxxxxxx………..xxxxxxxxxx
AID319
Group 5 AID set
AID256 3

4. Optimization 2: Distributed Low Power Medium Access
Date: May, 2012
Optimization 2: Distributed Low Power Medium Access
In a smart-grid BSS or sensing BSS, almost all STAs are low power STAs.
Low power STAs may wake up at the same time to poll the AP.
This may creates more collisions.
Solution:
the STAs poll the AP in different time:
An AP proposes different offset, period to each STA through association procedure or other management frames.
Each STA requests offset period of its polling. The AP accepts or rejects the request.
The STA should follow the negotiated polling time. It may also poll the AP in other time per its situation (e.g. sensing result ready etc).
The AP may transmit unicast management frame as downlink frame after receiving the trigger frame.
Such management frame can be used as timing, management synchronization. 4

5. Date: May, 2012
Reference
[1] 11-12/127r1, Low Power Medium Access. 5