Shengbo Chen Tarun Bansal Yin Sun Prasun Sinha and Ness B Shroff Dept ECE amp CSE The Ohio State University WiOpt 2013 Background Battery life is a serious problem for most smartphone users ID: 745954
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Life-Add: A novel WiFi design with battery life, throughput and fairness improvement
Shengbo Chen*, Tarun Bansal*, Yin Sun*,Prasun Sinha and Ness B. Shroff Dept. ECE & CSE, The Ohio State University
WiOpt 2013
Slide2
Background
Battery life is a serious problem for most smartphone usersWiFi, 4G LTE, GPS, Bluetooth, screen, CPU, ...Web browsing via WiFiTest results in April 2013 by Battery life < 11 hours for most popular smartphones
iPhone 5
802.11n
Samsung Galaxy S 4
802.11ac
HTC One
802.11acSlide3
Existing Solutions to Prolong Lifetime
Mobile Charging Additional equipmentSolar charger portable battery wireless chargerReduce power when sensingLower hardware clock-rate [E-MiLi, Mobicom 11]Broadcom SoC Solution802.11 acUsed in HTC One and Samsung Galaxy S 4Test: 7.8 hours by Trade bandwidth/throughput for power reduction Cannot have both benefitsSlide4
Physical layer
Significant evolutions towards high throughputMACCSMA/CA and its enhancementsQoS, security, frame aggregation, block ACKIEEE 802.11 Standard EvolutionWLAN802.11-19972 Mbps, DSSS, FHSS802.11b11 Mbps, CCK, DSSS802.11a
54 Mbps, OFDM, 5 GHz
802.11n
600 Mbps with 4x4 MIMO, 20/40 MHz BW, 2.4 or 5 GHz802.11p27 Mbps,10 MHz BW, 5.9 GHz
802.11af
TVWS
802.11g
54 Mbps,
OFDM, 2.4 GHz
802.11ac
256QAM
160MHz
802.11ad
Wireless Access
for Vehicular
Environment
TV White
Spaces
Wireless Gigabit, <6 GHz
Wireless Gigabit, 60 GHzSlide5
Life-Add: An innovative MAC designBattery Lifetime
Avoid unnecessary sensing ThroughputReduce collisions and starvationsFairnessNear-far effectCan we do better? THLROUGIH
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Contents
BackgroundLife-Add: An innovative MAC designSimulation ResultsSummarySlide7
Life-Add: Smartphone energy model
Power source:Strong: Wall power, portable batteryWeak: Solar charger Other components4G LTE, CPU, screen, …WiFi chipON: Transmit/receive/sensingHigh power consumptionOFF: SleepVery low power consumptionToo much sensing means a significant waste of energySleep/wake (asynchronous)Slide8
Life-Add: Sleep/Wake + Channel Contention
UplinkDevice 2
Device 1
AP
ACK
Device 2
Device 1
APSlide9
Life-Add: Sleep/Wake + Channel Contention
UplinkDevice 2
Device 1
AP
ACK
Device 2
Device 1
AP
Device 1 wakes up earlier and senses the channelSlide10
Life-Add: Sleep/Wake + Channel Contention
UplinkDevice 2
Device 1
AP
ACK
Data
Device 2
Device 1
AP
Device 1 transmits, Device 2 goes back to sleepSlide11
Life-Add: Sleep/Wake + Channel Contention
UplinkDevice 2
Device 1
AP
ACK
Data
ACK
Cycle 1
Device 2
Device 1
AP
AP replies an ACK to Device 1. Cycle 1 completes.Slide12
Life-Add: Sleep/Wake + Channel Contention
UplinkDevice 2
Device 1
AP
ACK
Data
ACK
Cycle 1
Device 2
Device 1
AP
Devices 1 and 2 wake up at almost the same timeSlide13
Life-Add: Sleep/Wake + Channel Contention
UplinkDevice 2
Device 1
AP
ACK
Data
ACK
Data
Data
Cycle 1
Cycle 2
Device 2
Device 1
AP
A collision occurs, followed by a timeout. Cycle 2 completes.Slide14
Life-Add: Sleep/Wake + Channel Contention
UplinkA new renewal process model: each cycle is an i.i.d. periodRequires 2 assumptions:Exponential distributed sleep period: Memoryless (independent from last cycle)Tdata + TACK≈ Tcollision + Ttimeout (only assumed in analysis, not in simulations)
Device 2
Device 1
AP
ACK
Data
ACK
Data
Data
Data
Cycle 1
Cycle 2
Device 2
Device 1
APSlide15
Life-Add
IEEE 802.11Sleep backoff vs sensing backoff (save energy)Renewal process vs 2D Markov chain [Bianchi 2000] (simplify optimization)Life-Add vs IEEE 802.11Device 2
Device 1
AP
ACK
Data
ACK
Data
Data
Data
Cycle 1
Cycle 2
Device 2
Device 1
AP
ACK
Data
ACK
Data
Data
DataSlide16
Life-Add: Downlink
Still a renewal processUplink: sleep + data + overhead (ACK/collision/timeout)Downlink: sleep + data + overhead (ACK/Ps-poll/collision/timeout)Additional Ps-poll packet as part of overheadCan be modeled togetherDevice 2
Device 1
AP
Data
Cycle 1
Cycle 2
Beacon
Ps-poll
Data
ACK
Ps-poll
ACK
Ps-poll
A short Ps-poll packet is used to contend for the channelSlide17
Proportional-fair Utility Maximization max ∑ log E{Throughput of Device i}
s.t.E{Battery Life of Device i} ≥ Tmin,iLife-Add: Single APSlide18
Proportional-fair Utility Maximization max ∑ log E{Throughput of Device i}
s.t. Maximal device-ON probability: biVariables: average sleep period 1/RiLife-Add: Single APPr{Device i’s RF is ON}≤ biSlide19
Proportional-fair Utility Maximization max ∑ log E{Throughput of Device i}
s.t. Maximal device-ON probability: biVariables: average sleep period 1/RiNon-convexAsynchronous network with collisionsChannel access probabilities of the devices are coupledWe propose a solution: Life-AddTheorem: Asymptotically optimal, as Tsensing /(Tdata + TACK)0E.g., 802.11b: Tsensing= 4us, Tdata + TACK=511us~1573usLife-Add: Single AP
Pr{Device i’s RF is ON}≤ b
iSlide20
Problem formulation
where , is a scaling constant is the transmission success probability is the device-ON probabilityProof idea: Problem structure, KKT necessary conditions Upper and lower bounds converge to the same valueSlide21
Life-Add: Single AP
Implementation procedure:Each device reports bi to the APThe AP computes , and broadcast them to the devicesIf ,If , Device n uses and to computeUse to generate the sleeping periodLow complexity, easy to implement
Pr{Device i’s RF is ON}≤ b
iSlide22
NS-3 simulation for a homogeneous scenario
Red curve: simulated performance with no approximationBlue point: closed form solution of Life-AddObservation: Life-Add is near optimal The renewal process model is reasonably accurateLife-Add: Single APSlide23
Life-Add: general multiple APs
Too complicated interference modelGlobal optimization is very difficultNear-far effectDevice 1 can access the channel all the timeDevice 2 is in starvationHidden terminal problemTwo devices cannot sense each other and cause collisionsSlide24
Life-Add: general multiple APs
Near-far effectNode collaboration Device 1 computes the two values of average sleep period suggested by AP 1 and AP 2Device 1 chooses the longest average sleep period to reduce collisions with Device 2, which is vulnerableTo care for the vulnerableSlide25
Life-Add: general multiple APs
Hidden terminal problemIncrease average sleep period after a collisionReset average sleep period after a successful transmissionSimilar idea to 802.11 MACSlide26
Life-Add: general multiple APs
Implementation procedure:Each device reports bi to nearby APsEach AP computes and broadcasts andIf ,If , Device n uses and to compute suggested by nearby APsChoose to use the smallest value Reduce at collision, reset after receiving ACK Use to generate the sleeping periodSlide27
NS-3 simulation results:
Uplink: 4 APs, 30 smartphones, randomly located in a 500×500 m field, UDP saturation bi = 1 no lifetime (power-ON prob.) constraints1/3 with battery, 1/3 with battery + solar panel, 1/3 to wall powerBattery level: uniform distribution within 200~1000 mAhLifetime and throughput benefitsLife-Add: general multiple APsSlide28
Life-Add: general multiple APs
NS-3 simulation results:Per-device performance:Battery life improvement for all 5 devicesSignificant throughput increase for the low-rate deviceSlide29
Life-Add: general multiple APs
Average performance gainBattery Life: Sleep/Wake Throughput:Node collaboration (reduce collisions and starvations)Parameter optimizationFairness:Node collaboration (to care for the vulnerable)Proportional-fair utilitySlide30
Life-Add: general multiple APs
Coexisting with IEEE 802.11AP 1,2 and their users upgrade from IEEE 802.11 to Life-AddBattery lifeLonger if you use Life-AddThroughputHigher no matter you use Life-Add or not, due to less collisionsSlide31
Summary
A novel renewal process model for energy efficient WiFi designProportional-fair utility maximization problemNon-convexLife-Add MAC designNear optimal for single AP casesAlleviate “near-far effect” and “hidden terminal problem” in general casesEasy to implementNs-3 simulationsBattery life, throughput, and fairness improvementCoexists harmoniously with IEEE 802.11Not just WiFi: Last-hop decentralized accessInternet of Things, Military,… US patent filedSlide32
Tasks to do…More simulations for joint uplink and downlink
Practical trafficsWeb browsing, video streaming, email, searchingHardware testingSlide33
Thank you
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