1. 1 Effectiveness of Physical and Virtual Carrier Sensing in IEEE 802.11 Wireless Ad Hoc Networks Fu-Yi Hung and Ivan Marsic WCNC 2007

2. 2 Outline Introduction Interference model Spatial-temporal analysis Simulation Conclusion

3. 3 Introduction IEEE 802.11 MAC protocol, in order to resolve the hidden station problem  Four-way handshake RTS/CTS mechanism is designed to support wireless LANs and not multi-hop wireless ad hoc networks

4. 4 Introduction The network performance depends on  the hidden and exposed stations  vulnerable period relative to the hidden stations  the period of blocking the exposed stations To analysis the network performance with the spatial and temporal viewpoints

5. 5 Interference model P r is the received power. P t is the transmitted power. G t and G r are the antenna gains of the transmitter and receiver. h t and h r are the antenna heights of the transmitter and receiver. d is the transmitter-receiver distance. L is the system loss.

6. 6 Interference model Transmission Range (Rt)  The range within which frames can be reliably transmitted between transmitter and receiver if there is no interference. A

7. 7 Interference model Carrier sensing range (Rc)  The range within which the other stations can sense transmitted power. A

8. 8 Interference model P i (k) is the signal power of interference source k. N is the power of the ambient noise.

9. 9 Interference model Interference Range (Ri) The range within which any other transmission can interfere with the frame receiving on the receiver. AB

10. 10 Spatial-temporal analysis Based on the transmitter-receiver distance, it can be classify into three categories. Case 1: d < R t / (1 + X i ) Case 2: R t / (1 + X i ) < d < R t / X i Case 3: d > R t / X i X i = R i / d =10 (SINR / 40)

11. 11 Spatial-temporal analysis

12. 12 Spatial-temporal analysis

13. 13 Spatial-temporal analysis The physical carrier sensing mechanism  used to detect the presence of any coded signal on the channel. If it senses any energy above the energy detection (ED) threshold  report the channel is busy A

14. 14 Spatial-temporal analysis

15. 15 Simulation Simulator: NS-2 Simulation topology: a ring with 20 evenly distributed stations. Each station sends frame to its right neighbor.

16. 16 Simulation

17. 17 Simulation

18. 18 Conclusion Combining the spatial and temporal to analyze the virtual and physical carrier sensing mechanisms.  The RTS/CTS method has low effectiveness  Combining the virtual and a physical carrier sensing mechanism does not improve the effectiveness

19. 19 Conclusion  An adaptive physical carrier sensing will improve the performance of the basic method depends on the topology, traffic, and channel conditions

20. 20 Thank you!!