An Adaptive “Sleep” Algorithm for Efficient Power Management in WLANs
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An Adaptive “Sleep” Algorithm for Efficient Power Management in An Adaptive “Sleep” Algorithm for Efficient Power Management in WLANs WLANs Mahasweta Sarkar and Rene L Cruz CAL(IT)2 Student Spectrum October 25 th , 2004 • Time divided into equal unit length slots •Bernoulli Packet Arrival at the beginning of a slot with rate = p •Deterministic service rate [1 packet/slot] •Cut-through service policy •Perfect channel condition •Downlink traffic only • P a >> P s Tx Rx2 Rx1 Sleep Rx3 Awake The System Model The System Model Buffer P sa P a P s The Problem The Problem •Sleeping increases delay •Sleeping decreases power consumption •Hence, the obvious question is: What is the optimal “sleep duration” for a given delay constraint, that maximizes power saving ? RR scheme -At time t=0 RR scheme -At time t=0 A C B AP 1 2 3 Allocate random sleep durations to each node (say…Sa, Sb, Sc ) Buffers are empty At time t=Sa..Calculate At time t=Sa..Calculate Next Sleep Duration Next Sleep Duration Calculate Da –(CD)a = Da –(CD)a = a a which can take the following which can take the following values: values: a a =0, a a >0, a a <0 Early On time but 0 pkts On time + pkts a>0 Lengthe n sleep Lengthe n sleep Lengthe n sleep a<0 Lengthe n sleep Lengthe n sleep Shorte n sleep P sa At time At time t=Sa…..Service Policy t=Sa…..Service Policy • Gated Time limited Service Gated Time limited Service Policy Policy • Occasionally Exhaustive Occasionally Exhaustive Policy Policy • What if B doesn’t wake up? What if B doesn’t wake up? Another Service Order Another Service Order Besides RR Besides RR Nodes are served as and when they Nodes are served as and when they wake up. wake up. At every slot, sleep durations are At every slot, sleep durations are arranged in ascending order. arranged in ascending order. Service policy is the same Service policy is the same Calculate NextSleepDuration Calculate NextSleepDuration similarly, similarly, except definition of waking up except definition of waking up “early” changes. “early” changes. D elay vs Pow e rC om parison 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 A vg. P ktD elay A vg.Pow er/slo P ow er_R R P ow er_D P P w er_N R
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An Adaptive “Sleep” Algorithm for Efficient Power Management in WLANs Mahasweta Sarkar and Rene L Cruz CAL(IT)2 Student Spectrum October 25 th , 2004. The System Model. The Problem Sleeping increases delay Sleeping decreases power consumption Hence, the obvious question is: - PowerPoint PPT Presentation
Transcript of An Adaptive “Sleep” Algorithm for Efficient Power Management in WLANs
An Adaptive “Sleep” Algorithm for Efficient Power Management in WLANsAn Adaptive “Sleep” Algorithm for Efficient Power Management in WLANsMahasweta Sarkar and Rene L Cruz
CAL(IT)2 Student SpectrumOctober 25th, 2004
•Time divided into equal unit
length slots
•Bernoulli Packet Arrival at the
beginning of a slot with rate = p
•Deterministic service rate
[1 packet/slot]
•Cut-through service policy
•Perfect channel condition
•Downlink traffic only
•Pa >> Ps
Tx
Rx2Rx1
Sleep
Rx3
Awake
The System ModelThe System Model
Buffer
Psa
PaPs
The ProblemThe Problem
•Sleeping increases delay
•Sleeping decreases power consumption
•Hence, the obvious question is:
What is the optimal “sleep duration” for a given delay constraint, that maximizes power saving ?
RR scheme -At time t=0RR scheme -At time t=0
A
C
B AP
1
2
3
Allocate random sleep durationsto each node (say…Sa, Sb, Sc )Buffers are empty
At time t=Sa..Calculate Next Sleep At time t=Sa..Calculate Next Sleep DurationDuration
Calculate Da –(CD)a = Da –(CD)a = a which a which can take the following values:can take the following values:aa =0, aa >0, aa <0
Early On time but 0 pkts
On time + pkts
a>0 Lengthen sleep
Lengthen sleep
Lengthen sleep
a<0 Lengthen sleep
Lengthen sleep
Shorten
sleep
Psa
At time t=Sa…..Service PolicyAt time t=Sa…..Service Policy•Gated Time limited Service PolicyGated Time limited Service Policy•Occasionally Exhaustive PolicyOccasionally Exhaustive Policy•What if B doesn’t wake up?What if B doesn’t wake up?•What if C wakes up? What if C wakes up?
Another Service Order Besides RRAnother Service Order Besides RR
Nodes are served as and when they wake up.Nodes are served as and when they wake up.
At every slot, sleep durations are arranged in At every slot, sleep durations are arranged in ascending order.ascending order.
Service policy is the sameService policy is the same
Calculate NextSleepDuration similarly, Calculate NextSleepDuration similarly, except definition of waking up “early” changes.except definition of waking up “early” changes.
Delay vs Power Comparison
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
Avg. Pkt Delay
Av
g.P
ow
er/
slo
t
Power_RR
Power_DP
Pwer_NR
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