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

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1 Wireless Scheduling
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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?)
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3 Wireless Fair Queuing Wireless channel capacities are scarce Fair sharing of bandwidth becomes critical Both short-term and long-term fairness important
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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 …
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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
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6 Wireless Channel Characteristics Dynamically varying capacity Location dependent channel errors and bursty errors Contention No global state Scarce resources (battery & processing power)
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7 Service Model Short term fairness Long term fairness Short term throughput bounds Long term throughput bounds Delay bounds for packets
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8 Some terminology … Error free service Leading flows Lagging flows In sync flows
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9 Impact of Location Dependent Errors Example 1 3 flows f1, f2, f3 Period 1: f3 experiences lossy channel Flows f1 and f2 receive ½ 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!
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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?
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11 Issues addressed by Wireless Fair Scheduling Is it acceptable to compromise on separation for f1?
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