Download - Performance analysis of 802.11 DCF in presence of hidden nodes and collision prevention mechanism
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Performance analysis of 802.11 DCF in presence of hidden nodes and collision prevention mechanism.
- Ruchir Bhanushali. - Sagar. Shah.
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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.
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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.
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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.
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Typical node settings
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Case 1
Network Nodes become hidden.
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Case 1: Assumptions
• Configuration: Adhoc, Star Topology.• Number of periphery nodes: 16.• Destination for every periphery node: Center node.
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Configuration
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Hidden node creation (HOW ?)
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Scenarios (How ?)Scenario No. Basic
mechanismRTS/CTS
mechanismMaximum
Distance (R) m.No. of hidden
nodes
1 500 0
2 500 0
3 610 1
4 610 1
5 650 3
6 650 3
7 700 5
8 700 5
9 800 7
10 800 7
11 900 9
12 900 9
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Observations:Traffic Sent(bits/sec)
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Throughput(bits/sec)• Basic RTS/CTS
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Retransmission Attempts(packets)
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MAC delay (sec)
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Data Dropped(bits/sec)
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Control traffic Sent by Central Node (bits/sec)
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Throughput Vs. No. of hidden nodes
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Case 1: Conclusions (So What ?)
• Robustness of RTS/CTS access mechanism. • Weakness of basic access mechanism.• Overhead of RTS/CTS frames degrades the
performance.
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Case 2
• Introduction of hidden nodes.
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Assumptions
• Existing WLAN: Basic Service Set.– Star topology: periphery nodes – 16.
• Random destinations for Center node.• Periphery nodes do not transmit.
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Assumptions (contd.)
• Data & Control traffic:– Generation: • Uniform distribution: Min Outcome :256 bytes & Max.
Outcome: 2000bytes.
– RTS threshold : 512 Bytes.
• Simulation time: 20 minutes.
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Scenario 2
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Scenario 3 & 4
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Scenario 5
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Configuration
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Hidden node Configuration
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Graphs
• Throughput: – Basic Mechanism:
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Graphs
• Throughput: – RTS/CTS
Mechanism:
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Retransmission Attempts (packets)
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End to End Delay (sec)
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Data dropped (bits/sec)
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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.
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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.
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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.