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MIMO and TCP: A CASE for CROSS LAYER DESIGN

MIMO and TCP: A CASE for CROSS LAYER DESIGN. Soon Y. Oh, Mario Gerla Computer Science Dept. University of California, Los Angeles {soonoh, gerla}@cs.ucla.edu Joon-Sang Park Dept. of Computer Engineering, Hongik University, Seoul Korea jsp@cs.hongik.ac.kr.

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MIMO and TCP: A CASE for CROSS LAYER DESIGN

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  1. MIMO and TCP: A CASE for CROSS LAYER DESIGN Soon Y. Oh, Mario Gerla Computer Science Dept. University of California, Los Angeles {soonoh, gerla}@cs.ucla.edu Joon-Sang Park Dept. of Computer Engineering, Hongik University, Seoul Korea jsp@cs.hongik.ac.kr

  2. TCP performs poorly in wireless networks Mobility leads to path breaks and TCP time outs Radio channel problems (noise, fading, jamming etc) cause pkt loss and throughput degradation TCP and IEEE 802.11 time out interactions cause unfairness and capture In this paper we focus on Capture Introduction

  3. Reception Range Flow 3 Interference range Node C d Node B Flow 2 d Node A Flow 1 Example of TCP Capture • FTP Flows 1, 2, 3 use TCP • The flows “interfere” with each other • Interference causes capture

  4. CAPTURE in the current system

  5. Previous solutions MAC Layer: modify the IEEE 802.11 retransmission mechanism Network layer (NRED): Selective drop of packets in the aggressive flows Problems – both schemes require non trivial changes in protocols Proposed solution - Physical and MAC Layer Use MIMO antenna weights to minimize interference Use SPACE-MAC, a MIMO aware MAC protocol Solutions to the Capture Problem

  6. Targets Beamforming MIMO Enables multiple communications by nullifying interferers Uses RTS/CTS exchange to learn about channel B F A D SPACE-MAC

  7. r(t) = wRTHwTs(t) Where wT = [wT1 wT2 wT3]T: tx weights, wR = [wR1 wR2 wR3]T: rx weights, H: 3x3 channel matrix H Transmitter Receiver wR1 wT1 s(t) r(t) wR2 wT2  wR3 wT3 SPACE-MAC PHY Model

  8. When A wishes to transmit to B B F D A Operation of SPACE-MAC

  9. A sends RTS to B; D and F learn about A B F D A Operation of SPACE-MAC

  10. B F D A Operation of SPACE-MAC • B responds with CTS; D and F learn about B

  11. B F D A Operation of SPACE-MAC • D and F beamform; signals from/to B and A are nulled; • A and B start communicating

  12. B F D A D Operation of SPACE-MAC • While A and B are communicating, D and F also can start talking

  13. Simulation environment Qualnet Rayleigh fading 512 bytes/packet 802.11b; 2Mbps channel data rate;370m radio range 5 antennas for each node TCP experiments with: SPACE-MAC conventional IEEE 802.11 MAC Simulation Settings

  14. 3 parallel FTP/TCP flows d = 350 ~ 400 m Flow 3 Reception Range Node C d Node B Flow 2 d Node A Flow 1 CASE 1: 3 FTP/TCP Flows Topology

  15. Distance between intermediate nodes: d = 400m A and C are out of B’s reception range (no nulling) However, A and C are within B interference range No interference between A and C CASE 1: d = 400m Throughput

  16. Distance between intermediate nodes: d = 350m A and C are within B’s reception range (SPACE MAC can null ) A and C interfere with each other CASE 1: d = 350m Throughput

  17. Distance between intermediate nodes: d = 350m A and C are within B’s reception range (SPACE MAC can null ) A and C interfere with each other CASE 1: d = 350m Total Throughput

  18. 100 nodes uniformly distributed in 750m x 750m area Random 20 FTP/TCP flows Throughput of each flow CASE 2: More General Scenario

  19. 100 nodes uniformly distributed in 750m x 750m area Random 20 FTP/TCP flows Aggregated throughput CASE 2: More Realistic Scenario

  20. “Capture” seriously impacts TCP performance in wireless Ad Hoc networks MIMO and SPACE MAC beamforming prevents capture by “deconflicting” the flows Moreover, MIMO increases total TCP throughput by reducing interference Future work: Testbed experiments using MIMO and Space MAC Conclusions

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