Harnessing Mobile Multiple Access Efficiency with Location Input

1. Harnessing Mobile Multiple Access Efficiency with Location Input • Wan Du* and Mo Li • School of Computer Engineering • Nanyang Technological University, Singapore

2. Main access to WLAN “Smart phones overtake client pcs in 2011,” 2012. www.canalys.com/newsroom/smart-phones-overtake-client-pcs-2011

3. Pervasive Location Information • Outdoors • GPS (meters) • Indoor Localization • Sound (centimeter) • WiFi (meter) • Camera (meter)

4. Location Based Applications • Navigation • Augmented reality • Fine-grained location in supermarkets

5. Key Observation Location error of localization Indoor: <1m Outdoor: <13.7m Communication range of WiFi Indoor: >50m Outdoor: >200m << • 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.

6. outline • Problem review and State-of-the-Art • Design of CO-MAP • Implementation and Evaluation • Conclusions

7. Hidden Terminal Collision! • Detect this relation • Prevent concurrent transmissions

8. 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

9. Exposed Terminal • Detect this relation • Enable concurrent transmissions • Multiple exposed terminal problem Collision!

10. 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

11. Co-Occurrence MAP - Overview log normal shadowing propagation model Fast Uniform Co-Occurrence MAP Exposed Terminals Hidden Terminals Distributed Dynamic packet size Enchanced CSMA Maximize spatial reuse Minimize collision

12. Exposed Terminal

13. Exposed Terminal

14. Concurrent Transmissions

15. Concurrent Transmissions 15

16. Concurrent Transmissions Multiple Exposed Terminals  Enhanced CSMA 

17. Concurrent Transmissions

18. Concurrent Transmissions ACK Lost Problem  Windowed ACK 

19. Hidden Terminal

20. Hidden Terminal

21. Hidden Terminal Important Parameters: Number of HTs Packet Size

22. Dynamic Packet Length for Hidden Terminals Packet size Number of hidden terminal Probability of node i transmiting in slot s Number of contending nodes

23. Implementation • Testbed of six laptops • Intel Wireless 4965AGN network adapter • MAC80211 and iwlegacywireless drivers. • Three Components • CO-MAP • Header and concurrentETtransmission • Packetlengthadaptation • Data rate adaptation – Minstrel (Default)

24. Implementation • Header in data packets • Thirteen bytes (address and CRC) in PHY header

25. Evaluation – Exposed Terminal 78%

26. Evaluation – Hidden Terminal 39%

27. Large Scale Network on NS-2 • Network layout • Three APs separated about 60m • Nine clients. • Thirty topological configurations • 48% exposed links and 19% hidden terminals

28. Large Scale Network on NS-2 39%

29. Large Scale Network on NS-2 39% 19%

30. Tolerance to Position Inaccuracy

31. Conclusion • A practical work leveraging pervasive location information to improve spatial reuseand reduce hidden collisions in mobile WLAN • Distributed design with rapid construction of conflict map • Successful practice using sensor hints inprotocol design

32. Thanks. Questions? Wan DU, duwan@ntu.edu.sg Research Fellow @ NTU, Singapore