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Life-Add: A novel WiFi design with battery life, throughput and fairness improvement

WiOpt 2013. 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. Background.

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Life-Add: A novel WiFi design with battery life, throughput and fairness improvement

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  1. WiOpt 2013 Life-Add: A novel WiFi design with battery life, throughput and fairness improvement Shengbo Chen*, TarunBansal*, Yin Sun*, PrasunSinha and Ness B. Shroff Dept. ECE & CSE, The Ohio State University

  2. Background • Battery life is a serious problem for most smartphone users • WiFi, 4G LTE, GPS, Bluetooth, screen, CPU, ... • Web browsing via WiFi • Test 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 802.11ac

  3. Existing Solutions toProlong Lifetime • Mobile Charging Additional equipment • Solar charger portable battery wireless charger • Reduce power when sensing • Lower hardware clock-rate [E-MiLi, Mobicom 11] • Broadcom SoC Solution • 802.11 ac • Used in HTC One and Samsung Galaxy S 4 • Test: 7.8 hours by • Trade bandwidth/throughput for power reduction • Cannot have both benefits

  4. IEEE 802.11 Standard Evolution • Physical layer • Significant evolutions towards high throughput • MAC • CSMA/CA and its enhancements • QoS, security, frame aggregation, block ACK WLAN 802.11- 1997 2 Mbps, DSSS, FHSS 802.11b 11 Mbps, CCK, DSSS 802.11n 600 Mbps with 4x4 MIMO, 20/40 MHz BW, 2.4 or 5 GHz 802.11a 54 Mbps, OFDM, 5 GHz 802.11p 27 Mbps,10 MHz BW, 5.9 GHz 802.11af TVWS TV White Spaces Wireless Access for Vehicular Environment 802.11g 54 Mbps, OFDM, 2.4 GHz 802.11ac 256QAM 160MHz Wireless Gigabit, <6 GHz 802.11ad Wireless Gigabit, 60 GHz

  5. Can we do better? • Life-Add: An innovative MAC design • Battery Lifetime • Avoid unnecessary sensing • Throughput • Reduce collisions and starvations • Fairness • Near-far effect B L E T I F E I M E N R F A I N E E S S F I U G H P U T T R O T H

  6. Contents • Background • Life-Add: An innovative MAC design • Simulation Results • Summary

  7. Life-Add: Smartphone energy model • Power source: • Strong: Wall power, portable battery • Weak: Solar charger • Other components • 4G LTE, CPU, screen, … • WiFi chip • ON: Transmit/receive/sensing • High power consumption • OFF: Sleep • Very low power consumption • Too much sensing means a significant waste of energy • Sleep/wake (asynchronous)

  8. Life-Add: Sleep/Wake + Channel Contention • Uplink Device 1 Device 1 Device 2 Device 2 ACK AP AP

  9. Life-Add: Sleep/Wake + Channel Contention • Uplink Device 1 wakes up earlier and senses the channel Device 1 Device 1 Device 2 Device 2 ACK AP AP

  10. Life-Add: Sleep/Wake + Channel Contention • Uplink Device 1 transmits, Device 2 goes back to sleep Data Device 1 Device 1 Device 2 Device 2 ACK AP AP

  11. Life-Add: Sleep/Wake + Channel Contention • Uplink AP replies an ACK to Device 1. Cycle 1 completes. Data Device 1 Device 1 Device 2 Device 2 ACK ACK AP AP Cycle 1

  12. Life-Add: Sleep/Wake + Channel Contention • Uplink Devices 1 and 2 wake up at almost the same time Data Device 1 Device 1 Device 2 Device 2 ACK ACK AP AP Cycle 1

  13. Life-Add: Sleep/Wake + Channel Contention • Uplink A collision occurs, followed by a timeout. Cycle 2 completes. Data Data Device 1 Device 1 Data Device 2 Device 2 ACK ACK AP AP Cycle 2 Cycle 1

  14. Life-Add: Sleep/Wake + Channel Contention • Uplink • A new renewal process model: each cycle is an i.i.d. period • Requires 2 assumptions: • Exponential distributed sleep period: Memoryless (independent from last cycle) • Tdata+ TACK≈ Tcollision + Ttimeout(only assumed in analysis, not in simulations) Data Data Device 1 Device 1 Data Data Device 2 Device 2 ACK ACK AP AP Cycle 2 Cycle 1

  15. Life-Add vs IEEE 802.11 • Life-Add • IEEE 802.11 • Sleep backoff vs sensing backoff (save energy) • Renewal process vs 2D Markov chain [Bianchi 2000] (simplify optimization) Data Data Device 1 Data Data Device 2 ACK ACK AP Cycle 2 Cycle 1 Data Data Device 1 Data Data Device 2 ACK ACK AP

  16. Life-Add: Downlink • Still a renewal process • Uplink: sleep + data + overhead (ACK/collision/timeout) • Downlink: sleep + data + overhead (ACK/Ps-poll/collision/timeout) • Additional Ps-poll packet as part of overhead • Can be modeled together A short Ps-poll packet is used to contend for the channel Ps-poll Ps-poll ACK Device 1 ACK Device 2 Ps-poll Data Data AP Beacon Cycle 2 Cycle 1

  17. Life-Add: Single AP • Proportional-fair Utility Maximization max ∑ log E{Throughput of Device i} s.t. E{Battery Life of Device i} ≥ Tmin,i

  18. Life-Add: Single AP • Proportional-fair Utility Maximization max ∑ log E{Throughput of Device i} s.t. • Maximal device-ON probability: bi • Variables: average sleep period 1/Ri • Pr{Device i’s RF is ON}≤ bi

  19. Life-Add: Single AP • Proportional-fair Utility Maximization max ∑ log E{Throughput of Device i} s.t. • Maximal device-ON probability: bi • Variables: average sleep period 1/Ri • Non-convex • Asynchronous network with collisions • Channel access probabilities of the devices are coupled • We propose a solution: Life-Add • Theorem: Asymptotically optimal, as Tsensing /(Tdata+ TACK)0 • E.g., 802.11b: Tsensing= 4us, Tdata+ TACK=511us~1573us • Pr{Device i’s RF is ON}≤ bi

  20. Problem formulation • where , is a scaling constant • is the transmission success probability • is the device-ON probability • Proof idea: Problem structure, KKT necessary conditions Upper and lower bounds converge to the same value

  21. Life-Add: Single AP • Pr{Device i’s RF is ON}≤ bi • Implementation procedure: • Each device reports bi to the AP • The AP computes , and broadcast them to the devices • If , • If , • Device n uses and to compute • Use togenerate the sleeping period • Low complexity, easy to implement

  22. Life-Add: Single AP • NS-3 simulation for a homogeneous scenario • Redcurve: simulated performance with no approximation • Bluepoint: closed form solution of Life-Add • Observation: Life-Add is near optimal The renewal process model is reasonably accurate

  23. Life-Add: general multiple APs • Too complicated interference model • Global optimization is very difficult • Near-far effect • Device 1 can access the channel all the time • Device 2 is in starvation • Hidden terminal problem • Two devices cannot sense each other and cause collisions

  24. Life-Add: general multiple APs • Near-far effect • Node collaboration • Device 1 computes the two values of average sleep period suggested by AP 1 and AP 2 • Device 1 chooses the longest average sleep period to reduce collisions with Device 2, which is vulnerable • To care for the vulnerable

  25. Life-Add: general multiple APs • Hidden terminal problem • Increase average sleep period after a collision • Reset average sleep period after a successful transmission • Similar idea to 802.11 MAC

  26. Life-Add: general multiple APs • Implementation procedure: • Each device reports bi to nearby APs • Each AP computes and broadcasts and • If , • If , • Device n uses and to compute suggested by nearby APs • Choose to use the smallest value • Reduceat collision, reset after receiving ACK • Use to generate the sleeping period

  27. Life-Add: general multiple APs • 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.) constraints • 1/3 with battery, 1/3 with battery + solar panel, 1/3 to wall power • Battery level: uniform distribution within 200~1000 mAh • Lifetime and throughput benefits

  28. Life-Add: general multiple APs • NS-3 simulation results: • Per-device performance: • Battery life improvement for all 5 devices • Significant throughput increase for the low-rate device

  29. Life-Add: general multiple APs • Average performance gain • Battery Life: • Sleep/Wake • Throughput: • Node collaboration (reduce collisions and starvations) • Parameter optimization • Fairness: • Node collaboration (to care for the vulnerable) • Proportional-fair utility

  30. Life-Add: general multiple APs • Coexisting with IEEE 802.11 • AP 1,2 and their users upgrade from IEEE 802.11 to Life-Add • Battery life • Longer if you use Life-Add • Throughput • Higher no matter you use Life-Add or not, due to less collisions

  31. Summary • A novel renewal process model for energy efficient WiFi design • Proportional-fair utility maximization problem • Non-convex • Life-Add MAC design • Near optimal for single AP cases • Alleviate “near-far effect” and “hidden terminal problem” in general cases • Easy to implement • Ns-3 simulations • Battery life, throughput, and fairness improvement • Coexists harmoniously with IEEE 802.11 • Not just WiFi: Last-hop decentralized access • Internet of Things, Military,… • US patent filed

  32. Tasks to do… • More simulations for joint uplink and downlink • Practical traffics • Web browsing, video streaming, email, searching • Hardware testing

  33. Thank you B E T L I F I M E E N R F A I N E E S S F I U P T G H U T T H R O

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