1. Performance analysis of 802.11 DCF in presence of hidden nodes and collision prevention mechanism. - Ruchir Bhanushali. - Sagar. Shah.

2. Outline (What ?) RTS/CTS vs. Basic access mechanism using OPNET Modeler: Case 1:Netwok nodes are hidden (0 – 5). Case 2: Additions of hidden nodes ( 0 – 4). Performance parameters: – Global Statistics: Throughput, MAC delay, Retransmission Attempts. – Node Statistics: Control traffic sent/received.

3. Assumptions (What ? contd.) Physical Characteristics: – 802.11b @ 11Mbps. – Channel 1: center Frequency 2.412Ghz ; BW: 22Mhz. P T: 5mW, Receiver Sensitivity: -95dbm, Coverage: 1200m. – Path loss: L p = L 0 + 10α log10d ; L 0 : 40.04dB for 802.11b.

4. Assumptions (What ? contd.) Data & Control traffic: – Generation: Throughout the simulation with an inter-arrival time of 0.05sec. Min Outcome :256 bytes & Max. Outcome: 2000bytes. – RTS threshold : 512 Bytes. Simulation time: 20 minutes.

5. Typical node settings

6. Case 1 Network Nodes become hidden.

7. Case 1: Assumptions Configuration: Adhoc, Star Topology. Number of periphery nodes: 16. Destination for every periphery node: Center node.

8. Configuration

9. Hidden node creation (HOW ?)

10. Scenarios (How ?) Scenario No.Basic mechanism RTS/CTS mechanism Maximum Distance (R) m. No. of hidden nodes 1 5000 2 5000 3 6101 4 6101 5 6503 6 6503 7 7005 8 7005 9 8007 10 8007 11 9009 12 9009

11. Observations:Traffic Sent(bits/sec)

12. Throughput(bits/sec) Basic RTS/CTS

13. Retransmission Attempts(packets)

14. MAC delay (sec)

15. Data Dropped(bits/sec)

16. Control traffic Sent by Central Node (bits/sec)

17. Throughput Vs. No. of hidden nodes

18. Case 1: Conclusions (So What ?) Robustness of RTS/CTS access mechanism. Weakness of basic access mechanism. Overhead of RTS/CTS frames degrades the performance.

19. Case 2 Introduction of hidden nodes.

20. Assumptions Existing WLAN: Basic Service Set. – Star topology: periphery nodes – 16. Random destinations for Center node. Periphery nodes do not transmit.

21. Assumptions (contd.) Data & Control traffic: – Generation: Uniform distribution: Min Outcome :256 bytes & Max. Outcome: 2000bytes. – RTS threshold : 512 Bytes. Simulation time: 20 minutes.

22. Scenario 2

23. Scenario 3 & 4

24. Scenario 5

25. Configuration

26. Hidden node Configuration

27. Graphs Throughput: – Basic Mechanism:

28. Graphs Throughput: – RTS/CTS Mechanism:

29. Retransmission Attempts (packets)

30. End to End Delay (sec)

31. Data dropped (bits/sec)

32. Conclusion Whether its basic or RTS/CTS mechanism, hidden node effect is more prominent when network nodes are hidden. Overall performance of the basic access method strongly depends on the number of stations in the WLAN and gets degraded with increasing number of nodes in both the cases. On the other hand, the RTS/CTS access method is very robust to hidden station effect in a WLAN environment. Accounting the capability of the RTS/CTS scheme to cope with hidden terminals, we conclude that this access method should be used in the majority of the practical cases.

33. References Performance Modeling and Analysis of the IEEE 802.11 Distribution Coordination Function in Presence of Hidden Stations; Fu-Yi Hung; Pai, S.; Marsic, I.;Oct. 2006. Analyzing the Throughput of IEEE 802.11 DCF Scheme with Hidden Nodes; Ting-Chao Hou, Ling-Fan Tsao, and Hsin-Chiao Liu Performance analysis of the IEEE 802.11 distributed coordination function; Bianchi, G.; Volume 18, Issue 3, March 2000. Performance evaluation of distributed co-ordination function for IEEE 802.11 wireless LAN protocol in presence of mobile and hidden terminals; Khurana, S.; Kahol, A.; Gupta, S.K.S.; Srimani, P.K.;24-28 Oct. 1999.

34. References (contd.) Evaluation Analysis of the Performance of IEEE 802.11b and IEEE 802.11g Standards; Athanasopoulos, A.; Topalis, E.; Antonopoulos, C.; Koubias, S.;23-29 April 2006. Wireless Information networks; Kaveh Pahlavan, Allen h. Levesque; Wiley publication; second edition. IEEE Std 802.11, 1999 edition. OPNET Modeler v 12.0 model documentation.