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DAC: Distributed Asynchronous Cooperation for Wireless Relay Networks

This paper introduces Distributed Asynchronous Cooperation (DAC) for wireless relay networks, addressing synchronization issues inherent in cooperative relaying. The DAC protocol allows multiple transmitters to send the same packet concurrently, improving throughput through innovative MAC and PHY layer designs like CSMA/CR. It discusses relay selection strategies and analyzes performance using GNURadio and simulation experiments. The results indicate significant throughput gains, particularly in lossy network environments, while maintaining fairness across multiple unicast scenarios. The paper concludes that DAC effectively circumvents synchronization problems in cooperative communication.

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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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