1 / 20

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

rafael-houston
Télécharger la présentation

Fair Sharing in Ad Hoc Wireless Networks

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related