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

Outline

Introduction Carrier sense and Interference relation RSS based prediction Evaluation Conclusion

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

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

Carrier sensing and Interference relation

C1 : Y (L2 can be sensed by L1)F1: Y (L1 suffers interference form L2)

Two Link Topologies

Mutual CS

No interference (INT)Mutually hidden INT

Mutual INT

One-way hidden INT

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

d)

RSS based prediction

RSS Measurement Methodology Carrier Sensing and TX Throughput Predict

ion Interference and RX Goodput Prediction

RSS Measurement Methodology

Broadcast hello messages 6 Mbps High power and normal power

HP = NP + Y dB

Carrier Sensing and TX Throughput Prediction

RSSlow

RSShigh

Carrier Sensing and TX Throughput Prediction

S1

R1

S2

R2

r1= S1 estimates by the RSS of hellos form S2

TX1 =1- C*TXdef,1^ ^

Interference and RX Goodput Prediction

SIR at R1 : sir1 = r11 –r21 (dB)SIR : signal-to-interference-ratio

Evaluation

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

Evaluation

Conclusion

RSS based prediction Physical layer capture Hidden interference

In experiments O(n) measurement overhead

Future work Different chipsets Many interferers

Thank for your listening

Occurrence Frequency

10-node testbed in HP labs(HPL) 11-node testbed in Seoul National Uni

versity (SNU)