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.
Analytical Modeling Transmission Probability Let W = CW min, then CW max = W * 2 m, where m is the maximum backoff stage. Let ρ c be the probability that a packet of class c encounters a collision on the channel. Let τ c be the probability that a station of class c transmit in a random chosen slot. Then:
Analytical Modeling Throughput Let ρ tr be the probability that there is at least one transmission in the considered slot time. Then: Let ρ s,i be the probability that a transmission of a packet of node i occurring on the channel is successful. Let τ j be the probability that a node j transmit data (j ≠ i, j = [1, n]). Then:
Analytical Modeling Throughput, Cont. Let T s,c be the average time that a node of class c senses the channel busy because of a successful transmission, T C,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 = PHY hdr + MAC hdr be the packet header, δ be the propagation delay, and α be the length of a slot time. Then: The throughput of node i, S i 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