Performance analysis of 802.11 DCF in presence of hidden nodes and collision prevention mechanism.

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. • PT: 5mW, Receiver Sensitivity: -95dbm, Coverage: 1200m. • Path loss: Lp = L0 + 10α log10d ; L0: 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 ?)

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.