1 Yue Qiao Computer Science and Engineering Sep AirExpress: Enabling Seamless In-band Wireless Multi-hop Transmission Joint work with Bo Chen, Ouyang Zhang, and Kannan Srinivasan

2 Wired Ethernet Cut-through Routing Source Router A Router B Router C Client

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

4 Wireless In-band Cut-through Routing? AirExpress

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

6 Received Signal Forwarder Interference ABCD Self Interference SI FI time

7 Received Signal Forwarder Interference ABCD Self Interference SI FI time

8 Received Signal Forwarder Interference ABCD Self Interference SI FI Measure the Superposed Channel? time

9 Forwarding Channel DACADC DACADC Node C Node B Forwarding Channel No frequency offset for the forwarding channel!Measure the Superposed Channel is Possible!

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

11 Cross-Hop Interference Challenge: Various cross-hop channels (1) ABCDE ABCDE ABCDEABCDE (2) (3) Causal Non-causal

12 Unified Cancellation Module Design Philosophy Causal: cancel out (SI, FI and CHI) Non-causal: multipath components Method: Hierarchical Cancellation Structure ABCDE Training Transmitting Receiving Inactive Forwarding

13 Unified Cancellation Module Design Philosophy Causal: cancel out (SI, FI and CHI) Non-causal: multipath components Method: Hierarchical Cancellation Structure ABCDE Training Transmitting Receiving Inactive Forwarding

14 Unified Cancellation Module Design Philosophy Causal: cancel out (SI, FI and CHI) Non-causal: multipath components Method: Hierarchical Cancellation Structure ABCDE Training Transmitting Receiving Inactive Forwarding

15 Unified Cancellation Module Design Philosophy Causal: cancel out (SI, FI and CHI) Non-causal: multipath components Method: Hierarchical Cancellation Structure ABCDE Training Transmitting Receiving Inactive Forwarding

16 Have Successfully Dealt with Interference Simultaneous Transmission Possible

17 Noise accumulation Error propagation Packet Discarded due to high Error rate Drawback

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

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 GHz center frequency and 20MHz bandwidth Unified cancellation block

21 Implementation Indoor: 20 locations, single flow

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

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

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

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

27 Throughput performance of AirExpress under different routing algorithm Network Performance

28 Throughput gain of AirExpress, TDMA and Perfect D&F Network Performance

29 Delay performance of AirExpress, TDMA and perfect D&F Network Performance

30 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

31 Q&A Thanks