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AirExpress: Enabling Seamless In-band Wireless Multi-hop Transmission

Yue Qiao Computer Science and Engineering Email: qiaoyu@cse.ohio-state.edu Sep. 10 2015. AirExpress: Enabling Seamless In-band Wireless Multi-hop Transmission. Joint work with Bo Chen, Ouyang Zhang, and Kannan Srinivasan. Wired Ethernet. Source. 0001. 1011. 1100. 0101. Router B.

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AirExpress: Enabling Seamless In-band Wireless Multi-hop Transmission

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  1. Yue Qiao Computer Science and Engineering Email: qiaoyu@cse.ohio-state.edu Sep. 10 2015 AirExpress: Enabling Seamless In-band Wireless Multi-hop Transmission Joint work with Bo Chen, Ouyang Zhang, and Kannan Srinivasan

  2. Wired Ethernet Source 0001 1011 1100 0101 Router B Router A Client Router C Cut-through Routing

  3. Problem Increased Throughput Decreased Latency Source Router B Router A Destination Router C

  4. Wireless In-band Cut-through Routing? AirExpress

  5. Challenges Full-Duplex Cross-Hop Interference Source Self Interference Router B Router A Forwarder Interference AirExpress: Estimate Channel Only Once at One Node Measure Each Interfereing Channel? Inefficient and Impractical Router C Destination • Various types of interference

  6. A B C D FI SI Forwarder Interference Received Signal Self Interference Forwarder Interference time

  7. A B C D FI SI Forwarder Interference Received Signal Self Interference Forwarder Interference time

  8. A B C D FI SI Forwarder Interference Received Signal Self Interference Forwarder Interference Measure the Superposed Channel? time

  9. Forwarding Channel ADC DAC ForwardingChannel Node C Node B ADC DAC Measure the Superposed Channel is Possible! No frequency offset for the forwarding channel!

  10. Our Solution Full-Duplex Technique Superposed Channel • Self Interference • Forwarder Interference • Cross-Hop Interference

  11. A A A A B B B B C C C C D D D D E E E E Cross-Hop Interference (1) Causal (2) Non-causal (3) Challenge: Various cross-hop channels

  12. Training Transmitting Receiving Inactive Forwarding A B C D E Unified Cancellation Module Design Philosophy • Causal: cancel out (SI, FI and CHI) • Non-causal: multipath components Method: Hierarchical Cancellation Structure

  13. Training Transmitting Receiving Inactive Forwarding A B C D E Unified Cancellation Module Design Philosophy • Causal: cancel out (SI, FI and CHI) • Non-causal: multipath components Method: Hierarchical Cancellation Structure

  14. Training Transmitting Receiving Inactive Forwarding A B C D E Unified Cancellation Module Design Philosophy • Causal: cancel out (SI, FI and CHI) • Non-causal: multipath components Method: Hierarchical Cancellation Structure

  15. Training Transmitting Receiving Inactive Forwarding A B C D E Unified Cancellation Module Design Philosophy • Causal: cancel out (SI, FI and CHI) • Non-causal: multipath components Method: Hierarchical Cancellation Structure

  16. Have Successfully Dealt with Interference Simultaneous Transmission Possible

  17. 10010010010001 Drawback 11110100001111 Packet Discarded due to high Error rate 10010010010001 10010010010011 10010100010011 11110100010011 11110100001111 Noiseaccumulation Error propagation

  18. Virtual-Hop 1 Virtual-Hop 2 Virtual-Hop Design Long paths are divided into smaller Hops 1 Long paths are divided into smaller Virtual-Hops Other considerations: bottleneck link, latency....

  19. MAC and Routing • Matching MAC and Routing Algorithms are designed for the AirExpress. • Radios in the network can support AirExpress system through distributed coordination. It also includes the Hierarchical Cancellation Structure realization and multi-hop link build and release • Details in paper

  20. Implementation • NI PXIe 1082 • 2.4GHz center frequency and 20MHz bandwidth • Unified cancellation block

  21. Implementation • Indoor: 20 locations, single flow

  22. Throughput Gain over TDMA 1.71 2.39 2.75 Hierachical cancellation structure works nicely! Throughput gain increases as the number of hops increases

  23. Large Network Evaluation • NS3, 100 nodes in a 1000m X 1000m area, multi flows • TDMA vs AirExpress • Virtual hop size: 2~5 • The cancellation residue interference information is based on the real testbed measurements

  24. Network Performance 4-hop AirExpress outperforms TDMA by ~2X on average Throughput performance of AirExpress and TDMA

  25. Network Performance TDMA has a 3X delay over 4-hop AirExpress Delay performance of AirExpress andTDMA

  26. Network Performance Throughput gain of AirExpress with different virtual-hop size >4 did not further increase the performance due to noise accumulation

  27. Conclusion and Looking forward • AirExpress: First fully functional in-band wireless cut-through system • The fundamental description of transmission pattern in wireless ad hoc network is challenged. • A building block of future multi-hop network architecture

  28. Thanks Q&A

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