1. DeepSleep: Power Saving Mode to Support a Large Number of Devices
Month Year
doc.: IEEE /xxxxr0
March 2012
DeepSleep: Power Saving Mode to Support a Large Number of Devices
Date:
Authors:
Hung-Yu Wei, National Taiwan University
John Doe, Some Company

2. March 2012
Abstract
In this contribution, we propose a power saving mechanism that supports low-power STAs in ah.
Hung-Yu Wei, National Taiwan University

3. Motivation To save power, STAs could reduce the time in active state.
March 2012
Motivation
To save power, STAs could reduce the time in active state.
To save power, a STA could spend a long time in power saving mode. Upon waking up, the STA wakes up to communication shortly and then goes back to power save mode as soon as possible.
Hung-Yu Wei, National Taiwan University

4. Spend Less Time in Active State for Energy Efficiency
March 2012
Spend Less Time in Active State for Energy Efficiency
Reducing backoff time and listening time could improve energy efficiency.
A STA with reduced CWmin has shorter contention time and could go back to power saving mode sooner
There are concerns about reducing CWmin
Fairness to contention
Collision probability
To be fair, only STAs that have been stay in sleep mode for a while should be qualified for setting small CWmin value.
Hung-Yu Wei, National Taiwan University

5. Reduce Contention Nodes for Energy Efficiency
March 2012
Reduce Contention Nodes for Energy Efficiency
With large number of devices, reducing channel contention improves energy efficiency
A large percentage of STAs are configured to enter sleep mode to reduce contention and to save energy
Similar solutions to resolve issues caused by large number of STAs have been proposed for 11ah [1][2]
Hung-Yu Wei, National Taiwan University

6. 802.11 Contention and Waste of Energy
March 2012
Contention and Waste of Energy
Energy waste during this time period
Hung-Yu Wei, National Taiwan University

7. March 2012
Proposal Overview
We propose an enhanced mechanism to save power for low-power ah STAs
The low-power STAs (which have been stayed in sleep mode for a long time) has higher priority when it wakes up. These STAs could have shorter idle listening period and going back to power-saving mode sooner
The channel access fairness is also considered.
Only STAs that do not access channel for a while are qualified for high priority access because of fairness
Hung-Yu Wei, National Taiwan University

8. Design Overview STAs go to DeepSleep STAs wake up
March 2012
Design Overview
STAs go to DeepSleep
Enter DeepSleep mode randomly
If (P < Prob_Threshold)
Optional extension: a STA considers its energy status
Stay in DeepSleep for a while (DeepSleep_Duration )
STAs wake up
If the STA has slept for a long enough time
The wake-up STA applies smaller contention window to have high priority to transmit.
Otherwise,
The wake-up STA operates in the original mode
Hung-Yu Wei, National Taiwan University

9. Our proposal Algorithm: March 2012 Randomly Enter DeepSleep Mode
if(P < Threshold)
then{
Enter DeepSleepMode (Stay in sleep for DeepSleep_Duration)
Bool_Sleep = TRUE; }
Wakeup
if (Bool_Sleep)
CWmin = CW_Sleep;
Bool_Sleep = FALSE;
else{
CWmin = CW_Original;
Hung-Yu Wei, National Taiwan University

10. Simulation Settings Use NS-2 simulator Number of devices : 100
March 2012
Simulation Settings
Use NS-2 simulator
Number of devices : 100
traffic interval: 1s
beacon period: 1s
TX power: 550 mW
RX power: 250 mW
Idle power: 200 mW
Sleep power: 40 mW
CWmin_Orignal: 31
CWmin_DeepSleep: 15
DeepSleep_Duration : 10 beacon periods
Case 1: 100 devices use the proposed scheme
Case 2: 100 devices use default scheme
Case 3: 50 devices with the proposed scheme, 50 default scheme
Hung-Yu Wei, National Taiwan University

11. Better Energy Efficiency
March 2012
Better Energy Efficiency
Hung-Yu Wei, National Taiwan University

12. Lower Collision Probability
March 2012
Lower Collision Probability
Hung-Yu Wei, National Taiwan University

13. Stay in Sleep Mode Longer
March 2012
Stay in Sleep Mode Longer
Sleep time rate is defined as the time ratio that a STA is stayed in PSM mode. For example, sleep time rate = 0.95 implies a STA operates in active mode 5% of time and stays in power save mode 95% of time.
Hung-Yu Wei, National Taiwan University

14. Lower Retransmission Count
March 2012
Lower Retransmission Count
To successfully deliver a packet, how many time does a STA needs to transmit (e.g. transmission per packet delivered = 1, if there is no packet loss; transmission per packet delivered = 2, if the average re-transmission count is 1).
Hung-Yu Wei, National Taiwan University

15. The Same Packet Delivery Ratio
March 2012
The Same Packet Delivery Ratio
Hung-Yu Wei, National Taiwan University

16. Conclusions We proposed a power saving mechanism for the STAs.
March 2012
Conclusions
We proposed a power saving mechanism for the STAs.
Reducing the contention level caused by large number of devices.
Reducing the backoff time and channel listening time upon a STA wakes up.
Simulation results show the proposed mechanism effectively improve energy efficiency.
Hung-Yu Wei, National Taiwan University

17. March 2012
References
[1] ah-dcf-enhancements-for-large-number-of-stas
[2] ah-power-saving-possibilities-for-networks-supporting-a-large-number-of-stas
Hung-Yu Wei, National Taiwan University