Transcript Performance analysis of 802.11 DCF in presence of hidden

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