Evaluate IEEE 802.11e EDCA Performance
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Transcript of Evaluate IEEE 802.11e EDCA Performance
Evaluate IEEE 802.11e EDCA Performance
Tyler Ngo
CMPE 257
EDCA vs. DCF
EDCA classifies traffic flows in different access categories (AC). Modifiable MAC parameters include:
– Arbitration Interframe Space (AIFS) replaces the DIFS in IEEE 802.11.– Minimum Contention Window (CWmin).– Maximum Contention Window (CWmax).– Transmission Opportunity (TXOP).
Shorter CW and AIFS for higher-priority traffic.
AC CWmin CWmax AIFSN Max TXOP Background (AC_BK) 31 1023 7 0 Best Effort (AC_BE) 31 1023 3 0
Video (AC_VI) 15 31 2 3.008ms Voice (AC_VO) 7 15 2 1.504ms
Legacy DCF 15 1023 2 0
Analytical Modeling Transmission Probability
Let W = CWmin, then CWmax = W * 2m, where m is the maximum backoff stage.
Let ρc be the probability that a packet of class c encounters a collision on the channel. Let τc be the probability that a station of class c transmit in a random
chosen slot. Then:
Analytical Modeling Throughput
Let ρtr be the probability that there is at least one transmission in the considered slot time. Then:
Let ρs,i be the probability that a transmission of a packet of node i occurring on the channel is successful. Let τj be the probability that a node j transmit data (j ≠ i, j = [1, n]). Then:
Analytical Modeling Throughput, Cont.
Let Ts,c be the average time that a node of class c senses the channel busy because of a successful transmission, TC,c be the average time that a node of class c senses the channel busy during a collision. Let E[P] be the expected packet length, H = PHYhdr + MAChdr be the packet header, δ be the propagation delay, and α be the length of a slot time. Then:
The throughput of node i, Si is then:
Simulation Modeling
Controlled Parameters:– Loss Model: Log Distance
Exponent = 3 Reference Distance = 1 Reference Loss: 46.67
– Delay Model: Random, Uniform variable; Constant speed.– Nist Error Rate Model– Transmission Range
Energy Detection Threshold: -96.0 CCA Mode1 Threshold: -99.0 Tx Power End/Start: 16.0206
– Routing Protocol: OLSR– TCP Protocol: New Reno– Data Rate: 5MB/s– Run time = ~100s– TCP Packet Size = 1024– UDP Packet Size = 120
Topology 1
Traffic: 6 7; 9 1; 3 8; 5 2 Total run duration: 100s
Topology 1
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X
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Topology 1: N6to7 TCP/BE; Others UDP/BE or AC_VO
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Packet ID
Del
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Stationary:BE
Stationary:BE/AC_VO
Mobility:BE
Mobility:BE/AC_VO
Topology 1: N6to7 TCP/AC_VO; Others UDP/BE
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0.025
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Packet ID
Del
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s)
Mobility
Stationary
Topology 2
Traffic:– 6 7; – 9 1; – 3 8; – 5 2;
Total run duration: 100s
Topology 2
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X-Pos
Y-Po
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Topology 2: N6to7 TCP/BE; Others UDP/BE or AC_VO
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Packet ID
Del
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s)
Stationary: BE
Mobile: BE
Stationary: BE/AC_VO
Mobility: BE/AC_VO
Topology 2: N6to7 TCP/AC_VO; Others UDP/BE
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Packet ID
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Stationary
Mobility
Topology 3
Traffic: – 6 7; – 9 1; – 3 8; – 5 2;
Total run duration: 100s Mobile environment only
– Gaussian Markov Mobility Model
Topology 3: N6to7 TCP/BE or AC_VO; Others UDP/BE or AC_VO
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Packet ID
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BE
TCP: BE; UDP: AC_VO
TCP: AC_VO; UDP: BE
Conclusion
Higher-priority tagging improves throughputs. But…
What are the rules for tagging? TCP starvation is the main issue.