6610-l9- - 1 Wireless Scheduling Puzzle Man in a boat...

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Unformatted text preview: 1 Wireless Scheduling Puzzle Man in a boat floating in a swimming pool He has a large solid iron ball If he drops the ball into the water, what happens to the level of water in the swimming pool? (increases, decreases, stays the same?) 3 Wireless Fair Queuing Wireless channel capacities are scarce Fair sharing of bandwidth becomes critical Both short-term and long-term fairness important 4 Wireless FQ & Wireless Environment Location dependent and bursty errors For the same wireless channel, a mobile station might experience a clean channel while another might experience high error rates. Why? In wireline fair queuing, the channel is either usable by all flows or unusable by any of the flows 5 Wireless Channel Model Base station performs arbitration Schedules both uplink and downlink traffic Neighboring cells use different channels Every mobile host has access to base- station 6 Wireless Channel Characteristics Dynamically varying capacity Location dependent channel errors and bursty errors Contention No global state Scarce resources (battery & processing power) 7 Service Model Short term fairness Long term fairness Short term throughput bounds Long term throughput bounds Delay bounds for packets 8 Some terminology Error free service Leading flows Lagging flows In sync flows 9 Impact of Location Dependent Errors Example 1 3 flows f1, f2, f3 Period 1: f3 experiences lossy channel Flows f1 and f2 receive of channel Period 2: f3 experiences clear channel Wireline fair queuing would give a net service of 5/6 to f1 and f2, and 1/3 to f3 UNFAIR! Wireline fair queuing does not distinguish between flows that are not backlogged and flows that are backlogged but cannot transmit! 10 Impact (Contd.) Example 2 Same scenario Flow f1 has only 1/3 offered service Hence, for period 1 f2 receives 2/3 service If some compensation is given to f3 during period 2, should f1 be penalized for compensating f3? 11 Issues addressed by Wireless Fair Scheduling Is it acceptable to compromise on separation for f1?...
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This note was uploaded on 12/14/2009 for the course ECE 6610 taught by Professor Staff during the Fall '08 term at Georgia Institute of Technology.

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6610-l9- - 1 Wireless Scheduling Puzzle Man in a boat...

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