CSE5345_Lecture10 - Performance of DCF 6 Discussion on NAV...

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1 CSE 5345 – Fundamentals of Wireless Networks Yonghe Liu Yonghe@cse.uta.edu 2/16/12 Last Class WLAN MAC Inter-frame Space: DIFS/SIFS One Page Project Proposal Group members Objective Milestones Approach to address challenges, if any SunSPOT tutorial coming soon 3 Distributed Coordination Function (DCF) Distributed random access Carrier sense and virtual carrier sense • NAV Exponential backoff for collision avoidance • Double Contention Window if retransmission • Fallback to CWmin if success • CWmin (e.g. 31 )<= CW <= Cwmax (e.g. 1023) Ack to increase reliability • Local retransmission • Short retry (e.g.4) and long retry (e.g., 7) Today Continue on MAC
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2 5 Discussion Uplink and downlink traffic How to support downlink traffic better Quality of service How to provide QoS guarantee? Power saving Any techniques we can employ?
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Unformatted text preview: Performance of DCF 6 Discussion on NAV What can a station do during NAV? 7 Multi-rate Support Multiple transmission rates at PHY E.g., .11b: 1/2/5.5/11 Can switch rate at transmitter for data No explicit specification Poor decision support Compared to cellular networks 8 Simple Implementation Attempt at highest rate For several times Success -&gt; continue Failure Reduce rate, attempt again 3 9 Complicate Implementation Probe channel quality first Via probe frame, e.g, RTS Receiver measures channel quality Piggyback the info via response frame to sender E.g, CTS Transmitter determines proper rate for TX 10 Discussion Advantages and disadvantages What if RTS/CTS not used?...
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This note was uploaded on 03/22/2012 for the course CSE 5345 taught by Professor Youngheliu during the Spring '12 term at UT Arlington.

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CSE5345_Lecture10 - Performance of DCF 6 Discussion on NAV...

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