1. How Physical Carrier Sense Affects System Throughput in IEEE 802.11 Wireless Networks Zheng Zeng, Yong Yang and Jennifer C. Hou Department of Computer Science, University of Illinois at Urbana- Champaign IEEE INFOCOM 2008

2. Outline Introduction Background Material Analytical Model Simulation Conclusion

3. Introduction IEEE 802.11 DCF ▫CSMA  Detecting ongoing transmission and Mitigating interference  Physical and Virtual carrier sense ▫Back-off  Resolving contention

4. Introduction (cont.) IEEE 802.11 DCF ▫CS th is a tunable parameter  Spatial reuse  Transmission quality ▫CS th Interference Spatial reuse Network Throughput

5. Background Material p-persistent Model that Characterizes IEEE 802.11 DCF in WLANs Interference Model

6. p-persistent Model that Characterizes IEEE 802.11 DCF in WLANs

7. Interference Model

8. Analytical Model Assumption ▫ ▫Max transmission range : R tx ▫SINR : β ▫Accumulative interference contributed by nodes that are outside R CS ▫

9. Analytical Model Multi-hop wireless network

10. Analytical Model – E(I)

11. Analytical Model – E(N c ) and E(T c )

12. Tpye-1 Collision Simultaneous transmission within the interference range

13. Tpye-2 Collision

14. Tpye-3 Collision

15. Modification of t v

16. Simulation setup J-sim (http://www.j-sim.org/)http://www.j-sim.org/ 480 nodes (240 senders) 900m* 900m D SR = 80m Data rate = 2Mbps and 6Mbps CW size = 8 ~ 256 R CS = 140m~220m CBR packets of size = 512 KB

17. Simulation result

21. Conclusion New analytical model ▫Physical carrier sense ▫SINR ▫Collision caused by accumulative interference and hidden terminals Future research ▫The effect of CW ▫The effect of routing and MAC and intra-flow interference