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EE392W Project Presentation

EE392W Project Presentation. Cooperative MIMO Techniques in Sensor Networks. Yifan Liang yfl@systems.stanford.edu. 03/08/2005. Wireless Systems Lab Stanford University. Target Problem. Receiver node. Transmitter node. Assisting node. OBJECTIVE: ENERGY EFFICIENCY.

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EE392W Project Presentation

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  1. EE392WProject Presentation Cooperative MIMO Techniques in Sensor Networks Yifan Liang yfl@systems.stanford.edu 03/08/2005 Wireless Systems Lab Stanford University

  2. Target Problem Receiver node Transmitter node Assisting node OBJECTIVE: ENERGY EFFICIENCY THE BEST TRANSMISSION STRATEGY?

  3. Outline • Non-cooperative Transmission • Cooperative Transmission • Diversity Gain • Spatial Multiplexing • Conclusion • Cooperative scheme more energy efficient in the long-range transmission

  4. Outline • Non-cooperative Transmission • Cooperative Transmission • Diversity Gain • Spatial Multiplexing • Conclusion • Cooperative scheme more energy efficient in the long-range transmission

  5. Non-Cooperative Transmission

  6. Non-Cooperative Transmission No use of assisting nodes

  7. Non-Cooperative Transmission No use of assisting nodes Transmitter nodes: TDMA Node in active transmission Node in the waiting list

  8. Non-Cooperative Transmission No use of assisting nodes Transmission Completed Transmitter nodes: TDMA Node in active transmission Node in the waiting list

  9. Non-Cooperative Transmission No use of assisting nodes Transmission Completed Transmitter nodes: TDMA Node in active transmission Node in the waiting list

  10. Non-Cooperative Transmission No use of assisting nodes Transmission Completed Transmitter nodes: TDMA Node in active transmission Node in the waiting list

  11. Non-Cooperative Transmission No use of assisting nodes Transmission Completed Transmitter nodes: TDMA Node in active transmission Node in the waiting list

  12. Non-Cooperative Transmission • No use of assisting nodes • Transmitter nodes work in a TDMA manner • Only one node in active transmission at any time • Call it a Single-Input-Single-Output (SISO) scheme • Energy consumption analysis • Transmission energy • Circuit Energy

  13. System Blocks TX SYN BPF DAC LPF Mixer PA Wireless Link BPF LNA ADC IFA BPF Mixer AAF SYN RX

  14. System Blocks TX Circuitry Transmission Energy Ect = Pct * Ton PA Wireless Link Ec = (Mt * Pct + Mr * Pcr) * Ton Ecr = Pcr * Ton RX Circuitry

  15. Transmission Energy Block Rayleigh Fading + Tx Rx Square-Law Path loss Et Es ~ Et/d2 BER Transmit energy With fading & noise Average over distribution of SNR Average receive energy; Only considers path loss

  16. Outline • Non-cooperative Transmission • Cooperative Transmission • Diversity Gain • Spatial Multiplexing • Conclusion • Cooperative scheme more energy efficient in the long-range transmission

  17. Cooperative Transmission h11 • Channel Model • Similar to SISO • Vector input/output • Channel gain matrix • Assume a simple case • Two transmit nodes • One receive node • One assisting node • Multiple-Input-Multiple-Output (MIMO) y1 x1 h12 h21 y2 x2 h22

  18. Compare MIMO with SISO • Pros • Reduced transmission energy due to higher SNR • Cons • Increased circuit energy consumption • Local data exchange: overhead

  19. Outline • Non-cooperative Transmission • Cooperative Transmission • Diversity Gain • Spatial Multiplexing • Conclusion • Cooperative scheme more energy efficient in the long-range transmission

  20. Cooperation for Diversity Gain • Basic idea • Tx side: The same symbol is sent through each node • Rx side: Combine multiple copies of the same symbol • Motivation for diversity • It is unlikely all links experience deep fading at the same time

  21. Cooperation for Diversity Gain • Alamouti Scheme • Local data exchange necessary at Tx • Data rate R = 1 Transmission Sequence …… x1 (1) -x2* (1) x1 (2) -x2* (2) …… x1* (1) x1* (2) x2 (1) x2 (2)

  22. Cooperation for Diversity Gain • Transmission Timeline Transmission Sequence N1 data y1 data N2 data y1/y2 joint DEC Tx Local Data Exchange Long Haul Transmission Rx Local Data Exchange

  23. Compare MIMO with SISO • Increased circuit energy consumption • Local data exchange: overhead • Reduced long-haul transmission energy • Higher SNR

  24. Transmission Energy Block Rayleigh Fading + Tx Rx Square-Law Path loss Et Es ~ Et/d2 BER Transmit energy With fading & noise Average over distribution of SNR Average receive energy; Only considers path loss

  25. Long-haul Received SNR • Received SNR • Es: signal power • No: noise power • Mt: number of Tx nodes • Chi-squared r.v, degrees of freedom 2MtMr

  26. Compare SISO with MIMO Long haul Transmission Energy BER = 1e-3 Long haul Circuit Energy

  27. Compare SISO with MIMO Long-haul total energy BER = 1e-3 Total energy include local overhead BER = 1e-3

  28. Outline • Non-cooperative Transmission • Cooperative Transmission • Diversity Gain • Spatial Multiplexing • Conclusion • Cooperative scheme more energy efficient in the long-range transmission

  29. Cooperation for Diversity Gain • Alamouti Scheme • Local data exchange necessary at Tx • Data rate R = 1 Transmission Sequence …… x1 (1) -x2* (1) x1 (2) -x2* (2) …… x1* (1) x1* (2) x2 (1) x2 (2)

  30. Cooperation for Spatial Multiplexing • No local data exchange at Tx • Increased data rate R = 2 • Reduced transmission time Transmission Sequence …… x1 (1) x1 (2) x1 (3) x1 (4) …… x2 (1) x2 (2) x2 (3) x2 (4)

  31. Cooperation for Spatial Multiplexing • Transmission Timeline Transmission Sequence y1 data y1/y2 joint DEC NO Tx Local Data Exchange Long Haul Transmission Rx Local Data Exchange

  32. Long-haul Received SNR • ZF receiver • Requires Mr >= Mt • Received SNR • Es: signal power • No: noise power • Mt: number of Tx nodes • Mr: number of Rx nodes

  33. Compare SISO with MIMO Total energy consumption Mt = Mr = 2 Total energy consumption Mt = 2 Mr = 3

  34. Compare SISO with MIMO

  35. Conclusions • Cooperative vs. non-cooperative scheme • Saves transmission energy • Consumes more circuit energy • Local data exchange an overhead • Preferable in the long-range transmission • Spatial Diversity vs. Multiplexing • Multiplexing scheme only beats SISO when Mr>Mt • For fixed (Mt, Mr), diversity scheme edges out • More energy saving not guaranteed with more collaborative nodes

  36. A big THANK YOUto Prof. Aghajan, Sumanth Jagannathan and all fellow 392W students!

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