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Harnessing Mobile Multiple Harnessing Mobile Multiple Access Efficiency with Location Access Efficiency with Location InputInput
Wan Du* and Mo Li
School of Computer Engineering
Nanyang Technological University, Singapore
Main access to WLAN
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“Smart phones overtake client pcs in 2011,” 2012. www.canalys.com/newsroom/smart-phones-overtake-client-pcs-2011
Pervasive Location Information• Outdoors
– GPS (meters)• Indoor Localization
– Sound (centimeter)– WiFi (meter) – Camera (meter)
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Key Observation
• Improving the communication efficiency using location input–Hidden terminal and exposed terminal problems in mobile WLAN
• In two campus WLAN of CENTAUR, 40% links of exposed terminals and 10% links with 70% throughput reduction due to hidden terminals.
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Location error of
localization
Indoor: <1m
Outdoor: <13.7m
<< Communication range of
WiFi
Indoor: >50m
Outdoor: >200m
outline• Problem review and State-of-the-Art• Design of CO-MAP• Implementation and Evaluation• Conclusions
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State-of-the-Art• Extra coordination channel
– DC-MAC (TPDS 2012)• New hardware or USRP implementation
• Conflict map based scheduling– RXIP (INFOCOM’ 12)
• Overhead of map learning • Centralized control for downlinks
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Exposed Terminal
• Detect this relation• Enable concurrent transmissions• Multiple exposed terminal problem
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Collision!
State-of-the-Art• Extra coordination channel
– Attached-RTS (TPDS 2012)• New hardware or USRP implementation
• Conflict map based scheduling– CMAP (NSDI’ 08) and CENTAUR (MobiCom’ 09)
• Overhead of map learning • Multiple exposed terminal problems• Centralized control for downlinks
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Co-Occurrence MAP - Overview
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Co-Occurrence MAP
log normal shadowing
propagation model
Exposed Terminals Hidden Terminals
Minimize collisionMaximize spatial reuse
Dynamic
packet size
Enchanced
CSMA
Fast
Uniform
Distributed
Dynamic Packet Length for Hidden Terminals
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Probability of node i transmiting in slot s
Packet size
Number of hidden terminalNumber of
contending nodes
Implementation• Testbed of six laptops
– Intel Wireless 4965AGN network adapter – MAC80211 and iwlegacy wireless drivers.
• Three Components– CO-MAP– Header and concurrent ET transmission– Packet length adaptation
• Data rate adaptation – Minstrel (Default)
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Large Scale Network on NS-2
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• Network layout– Three APs separated about 60m– Nine clients.– Thirty topological configurations
• 48% exposed links and 19% hidden terminals
Tolerance to Position Inaccuracy
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Location Error Range
Misclassification percentage
Wrong ET Missing ET Wrong HT Missing HT
1m 0.2% 0.3% 0.2% 0.2%
5m 1.2% 1.4% 1.1% 0.8%
10m 2.1% 2.3% 2.4% 1.4%
Conclusion• A practical work leveraging pervasive
location information to improve spatial reuse and reduce hidden collisions in mobile WLAN
• Distributed design with rapid construction of conflict map
• Successful practice using sensor hints in protocol design
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