1. Balancing the Hidden and Exposed Node Problems With Power Control In CSMA/CA-Based Wireless Networks Yihong Zhou and Scott M. Nettles Department of Electrical and Computer Engineering The University of Texas at Austin WCNC 2005

2. outline Introduction Related work CSMA/CA-based physical model Power control schemes Simulation result Conclusion

3. Introduction Problems in MACs : The hidden node problem The exposed node problem Three Ranges Transmit range Carrier sense range Interference Range

4. Introduction Enhancing collisions is worse than limiting spatial reuse Main goal balance hidden nodes and exposed nodes

5. Related work Typical scheme Although the reduced transmit power reduces the exposed nodes, it greatly increases the hidden nodes.

6. CSMA/CA-based physical model

7. CSMA/CA-based physical model -- Physical Model When X transmits to Y TRx: Pr > thrd rx CSRx: Pr > thrd cs, defines the potential set of exposed nodes IRy:SIR < SIR cap, defines the potential set of hidden nodes

8. CSMA/CA-based physical model -- Physical Model Use free space propagation model and two-way ground model Transmit range Carrier sense range

9. CSMA/CA-based physical model -- Physical Model Interference Range d ir is determined by both d and Pt

10. CSMA/CA-based physical model -- The Relationship Between the Three Ranges

11. Power control schemes Strong Transmit Power:

12. Power control schemes Weak Transmit Power:

13. Power control schemes The Optimal Transmit Power MAC:

14. Power control schemes The Optimal Transmit Power MAC:

15. Power control schemes The Optimal Transmit Power MAC: Sending a RTS using P max Sending a CTS using P max The sender calculates the distance d by using Pr and P max The sender then calculates the P otp Sending the data packet using P otp An ACK using P otp

16. Simulation result Two Traffic Flows:

17. Simulation result Two Traffic Flows:

18. Simulation result Chain Topologies:

19. Simulation result Chain Topologies:

20. Simulation result Random Topologies:

21. conclusion This paper has better spatial reuse than 802.11 and avoid problems with collisions that occur in other power control-based MACs.