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Fair Sharing in Ad Hoc Wireless Networks

Fair Sharing in Ad Hoc Wireless Networks. Jerry Cheng Israel Hsu Zachary Bell. Introduction. MAC 802.11 Starvation Results in Poor Fairness Develop a Decentralized Fair Queuing Algorithm Fairness of Medium Aggregate Throughput. Topics of Discussion. Hidden/Exposed Terminal Problem

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Fair Sharing in Ad Hoc Wireless Networks

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  1. Fair Sharing in Ad Hoc Wireless Networks Jerry Cheng Israel Hsu Zachary Bell CS215 Winter 2001

  2. Introduction • MAC 802.11 • Starvation Results in Poor Fairness • Develop a Decentralized Fair Queuing Algorithm • Fairness of Medium • Aggregate Throughput CS215 Winter 2001

  3. Topics of Discussion • Hidden/Exposed Terminal Problem • Distributed Fair Queuing Approach • Increasing Spatial Reuse • Simulation Results • Conclusion CS215 Winter 2001

  4. Hidden/Exposed Terminal Problem • Node 0 is a Hidden Sender to Node 2 • Node 1 is an Exposed Receiver to Node 2 • Node 1 is a Hidden Receiver to Node 3 CS215 Winter 2001

  5. Distributed Fair Queuing Approach • Model Assumption • Transmission Range is Commutative • Collision Occurs When a Node is Within Range of 2 or More Flows • The Capture Effect is Not Considered • Noise is Not Considered • Sending Nodes are Always Backlogged • All Data Transmissions are Single-Hop CS215 Winter 2001

  6. Distributed Fair Queuing Approach • Start Tag Fair Queuing • A Good Centralized Algorithm • A Decentralized Algorithm: • Each Flow is Associated With a Tag Locally • Tags are Stored in Tables • Exchanged with Neighboring Nodes Through Passive Listening • Transmission Decisions are Based on Local Tag Tables CS215 Winter 2001

  7. Distributed Fair Queuing Algorithm • Algorithm Implementation • Use RTS-CTS-DS-DATA-ACK sequence • As Opposed to RTS-CTS-DATA-ACK in MAC 802.11 • New Tag = Old Tag + Packet Size • Piggyback Tag in Control Packets • Old Tags are Piggybacked Only on RTS and CTS • New Tags are Piggybacked Only on DS and ACK • Overhearing Nodes Update Tag Tables CS215 Winter 2001

  8. Distributed Fair Queuing Algorithm • Sender’s Decision to Transmit • Operate as MAC 802.11, but Before Transmission Wait According to: Wait = TC × (FlowTag – min(sMin, rMin)/ADJ) • TC = Time Constant • ADJ = Adjustment Factor (avg. packet size) • sMin = Minimum Tag of Sender’s Table • rMin = Minimum Tag of Receiver’s Table • If Channel Idle after Wait then Transmit CS215 Winter 2001

  9. Distributed Fair Queuing Algorithm • Receiver’s Decision to Accept Transmission • If RTS Contains Minimum Tag in Receiver’s Table, Reply With CTS • If Not, Use “Drop Once” Scheme: • Reject first RTS • Accept Subsequent RTSs • After Transmission, Piggyback rMin on ACK CS215 Winter 2001

  10. Distributed Fair Queuing Algorithm • Algorithm Behavior Details • No Guarantee of Collision-Free Transmission • Some Nodes’ Tables May be Temporarily Inconsistent Due to Collisions • Future Transmissions Will Correct These Inconsistencies CS215 Winter 2001

  11. Increasing Spatial Reuse • Nodes in Different Spatial Domains can Transmit Simultaneously • Use Flow Contention Graph F1 F1 F2 F6 F2 A B F6 F3 F F5 F3 C F4 E D F5 F4 CS215 Winter 2001

  12. Increasing Spatial Reuse • Fairness and Throughput are Conflicting Goals • Use an Heuristic to Enhance the Algorithm: • Flow with Smallest Flow Degree Receives a Higher Share of the Channel NewTag = FlowDegree × PacketSize + OldTag CS215 Winter 2001

  13. Results: Three Topologies • Simulated in NS-2 • 30.0 seconds • Three Topologies 1. 6 Nodes, 5 Flows, Linear 2. 14 Nodes, 10 Flows, Irregular 3. 21 Nodes, 32 Flows, Grid CS215 Winter 2001

  14. Results: Linear Topology CS215 Winter 2001

  15. Results: Irregular Topology CS215 Winter 2001

  16. Results: Irregular Topology CS215 Winter 2001

  17. 5 16 F0 F8 F17 4 15 27 32 F1 F18 3 14 21 26 31 F2 F9 F12 2 13 20 30 F19 F4 F6 F13 1 7 12 19 25 29 F3 F20 F5 F7 F14 0 11 18 24 28 F11 F15 10 17 23 F16 9 22 F10 8 6 5 16 F 0 F8 Results: Grid Topology F17 4 15 27 32 F1 F18 3 14 21 26 31 F2 F9 F12 2 13 20 30 F19 F4 F6 F13 1 7 12 19 25 29 F3 F20 F5 F7 F14 0 6 11 18 24 28 F11 F15 10 17 23 F16 9 22 F10 8 CS215 Winter 2001

  18. Results: Grid Topology CS215 Winter 2001

  19. Results: Total Throughput CS215 Winter 2001

  20. Conclusions • Proposed Distributed Fair Queuing Algorithm • Provided Fairness • Enhanced Algorithm to Increase Spatial Reuse • Increased Throughput • Comparisons with MAC 802.11 • Future Work • Test More Topologies • Rigorously Define How ADJ and TC Affect Fairness and Throughput CS215 Winter 2001

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