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DAC: Distributed Asynchronous Cooperation for Wireless Relay Networks

DAC: Distributed Asynchronous Cooperation for Wireless Relay Networks. Xinyu Zhang, Kang G. Shin. University of Michigan. PHY layer. MAC layer. Outline. Implementation & evaluation. Design. Introduction. Conclusion. CSMA/CR. DAC (routing). GNURadio /USRP. simulation. analysis.

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DAC: Distributed Asynchronous Cooperation for Wireless Relay Networks

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  1. DAC: Distributed Asynchronous Cooperation for Wireless Relay Networks Xinyu Zhang, Kang G. Shin University of Michigan

  2. PHY layer • MAC layer Outline • Implementation & evaluation • Design • Introduction • Conclusion CSMA/CR • DAC(routing) GNURadio/USRP simulation analysis

  3. Motivation: sync problem in cooperative relaying A B C S Non-orthogonal cooperative relaying Multiple transmitters sending the same packet (V-MISO) In theory, realized via STBC or beamforming Major obstacle towards practical use: Sync among distributed relays

  4. DAC: asynchronous non-orthogonal relaying A B C S A B C S (b) DAC, asynchronous non-orthogonal relaying (a) Synchronous non-orthogonal relaying protocol DAC: Circumvent the sync problem Preserve transmit diversity Via a new MAC/PHY: CSMA/CR (CSMA with collision resolution)

  5. PHY • MAC The DAC network stack DAC Asynchronous, non-orthogonal relaying protocol • Cooperative relaying CSMA/CR Encourage resolvable collisions via intelligent sensing and scheduling Resolve collisions via signal processing

  6. CSMA/CR: PHY layer Resolve the collided packet by iterative decoding A C D Y B E Z A C C' D' E' A' B' Z' Y' B S=A' + C P1 S --- the received symbol. A’ --- estimated based on A C = S – A’ P1 Key problem: how to reconstruct A’ based on A?

  7. A C D Y B E Z C' D' E' A' B' Z' Y' S=A' + C Challenges and solutions: Identify exact start time of packets: sample level correlation Channel estimation (phase and amplitude): correlation Frequency offset estimation: Costas loop Symbol and sample level timing offset: MM circuit Transmitter distortion: reverse engineering tx filter

  8. Implementation on GNURadio and verification on an SDR network: A D B A, B transmit the same packets to D PER performance of forward-direction collision resolution

  9. CSMA/CR: MAC layer Sensing and scheduling: Key rule: If the channel is busy, and the packet on the air is the one to transmit, then start the transmission. --- encourage resolvable collision A C P1 B P1 P1 P1 Otherwise, degenerate to CSMA/CA

  10. DAC: CSMA/CR-based cooperative relaying DAC (Distributed Asynchronous Cooperation) Objective: Improve throughput performance of cooperative relaying using collision resolution 11 10 9 6 S 8 3 1 2 D 7 4 Basic idea: 5 Establish a primary path Add secondary relays to primary relays How to select relays?

  11. DAC: relay selection Select secondary relays: secondary relay primary relay Optimal relay selection: Select resulting in minimum delay from to A model-driven approach, based on average link quality

  12. DAC: Diversity-multiplexing tradeoff Secondary relay provides diversity gain for the primary path, but may reduce the multiplexing opportunity of other flows. Throughput −− Throughput ++ Interference range Q: Does DAC improve total network throughput?

  13. Analytical results: Network model: Homogeneous erasure network with reception probability throughput of DAC throughput of the single-path routing protocol Sufficient conditions for : Grid network: Arbitrary network topology: Wireless LAN: A: DAC improves the throughput of lossy networks (e.g. Roofnet)

  14. DAC: Simulation experiments Implement DAC in ns-2 Benchmark protocol: ETX routing * D. Couto, D. Aguayo, J. Bicket and R. Morris, A High-throughput Path Metric for Multi-hop Wireless Routing, In Proc. of ACM MobiCom, 2003 • Routing metric: expected transmission count

  15. Single-unicast scenario: DAC throughput gain ranges from 1.1 to 2.9, avg 1.7 Throughput gain is higher for low-throughput paths

  16. Multiple-unicast scenario: DAC results in higher network throughput DAC shows a higher level of fairness

  17. Multiple-unicast scenario, non-lossy networks: DAC may have lower network throughput DAC still maintains a higher level of fairness

  18. Related work: Cooperative relaying: * R. Mudumbai, et al. On the Feasibility of Distributed Beamforming in Wireless Networks, in IEEE Trans. On Wireless Communications. Vol. 6, No. 5, May 2007. * J. Zhang, J. Jia, Q. Zhang and E. M. K. Lo, Implementation and Evaluation of Cooperative Communication Schemes in Software-Defined Radio Testbed. In Proc. of IEEE INFOCOM, 2010 Iterative cancellation: * S. Gollakotam, D. Katabi. ZigZag Decoding: Combating Hidden Terminals in Wireless Networks, in Proc. of ACM SIGCOMM, 2008.

  19. Conclusion DAC (Distributed Asynchronous Cooperation): Circumvent sync problem in cooperative relaying via PHY layer signal processing Collision tolerant scheduling & relay selection Diversity-multiplexing tradeoff DAC: asynchronous cooperative relaying, based on a SDR PHY

  20. Thank you!

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