1. RSS-based Carrier Sensing and Interference Estimation in 802.11 Wireless Networks Jeongkeun Lee*, Sung-Ju Lee +, Wonho Kim*, Daehyung Jo*, Taekyoung Kwon* and Yanghee Choi* IEEE SECON 2007

2. Outline Introduction Carrier sense and Interference relation RSS based prediction Evaluation Conclusion

3. Introduction Estimate the carrier sensing and Predict interference  Before: Symmetric CS relation  This paper: Asymmetric CS relation Based on 802.11a mesh network testbeds  Two links

4. Carrier sensing and Interference relation In 802.11a systems  Energy-detection carrier sensing threshold 20dB (6 Mbps) CS range ≦ Communication range  RSS: receiver signal strength

5. Carrier sensing and Interference relation C1 : Y (L2 can be sensed by L1) F1: Y (L1 suffers interference form L2)

6. Two Link Topologies Mutual CS No interference (INT)Mutually hidden INT Mutual INT One-way hidden INT

7. Normalized link throughput/goodput UDP packets: 1000bytes PHY rate: 6Mbps Broadcast/unicast transmission period: 30s TX throughput (traffic rate) RX goodput (traffic rate successfully delivered)

9. RSS based prediction RSS Measurement Methodology Carrier Sensing and TX Throughput Prediction Interference and RX Goodput Prediction

10. RSS Measurement Methodology Broadcast hello messages  6 Mbps  High power and normal power HP = NP + Y dB

11. Carrier Sensing and TX Throughput Prediction RSS low RSS high

12. Carrier Sensing and TX Throughput Prediction S1 R1 S2 R2 r 1 = S 1 estimates by the RSS of hellos form S2 TX 1 =1- C*TX def,1 ^^

13. Interference and RX Goodput Prediction SIR at R 1 : sir 1 = r 11 –r 21 (dB) SIR : signal-to-interference-ratio

14. Evaluation Testbed in HP labs(HPL) 11 nodes 200 hello packet for each node 9hrs

15. Evaluation

16. Conclusion RSS based prediction  Physical layer capture  Hidden interference In experiments  O(n) measurement overhead Future work  Different chipsets  Many interferers

17. Thank for your listening

18. Occurrence Frequency 10-node testbed in HP labs(HPL) 11-node testbed in Seoul National University (SNU)