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Yue Qiao
Computer Science and EngineeringEmail: [email protected]. 10 2015
AirExpress: Enabling Seamless In-band Wireless Multi-hop Transmission
Joint work with Bo Chen, Ouyang Zhang, and Kannan Srinivasan
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Wired Ethernet
0001101101011100
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 InterferenceSource
Router A
Router B
Router C Destination
Full-Duplex
Measure Each Interfereing Channel?Inefficient and ImpracticalAirExpress: Estimate Channel Only Once at One
Node
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Received Signal
Forwarder Interference
Forwarder Interference
A B C D
( )sh x t( )x t
( )fh x t
Self Interference
SI
FI
time
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Received Signal
Forwarder Interference
Forwarder Interference
A B C D
( )sh x t( )x t
( )fh x t
Self Interference
SI
FI
sh
time
8
Received Signal
Forwarder Interference
Forwarder Interference
A B C D
( )sh x t( )x t
( )fh x t
Self Interference
SI
FI
fsh h
Measure the Superposed Channel?
time
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Forwarding Channel
DACADC
DACADC
Node C
Node B
Forwarding Channel
No frequency offset for the forwarding channel!
B( ) ( )B C t
Bj
Ch te x
( ) ( ) ( )B C C Bj tCB BC
j th xe teh
C
( )x t
BCh
CBh
( )CB BCh h x t
Measure the Superposed Channel is Possible!
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Our Solution
Self Interference
Forwarder Interference
Cross-Hop Interference
Full-Duplex Technique
Superposed Channel
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Cross-Hop Interference
Challenge: Various cross-hop channels
(1)
A B C D E
A B C D E
A B C D E
A B C D E
(2)
(3)
Causal
Non-causal
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Unified Cancellation Module
Design PhilosophyCausal: cancel out (SI, FI and CHI)Non-causal: multipath components
Method: Hierarchical Cancellation Structure
A B C D E
Training TransmittingReceiving InactiveForwarding
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Unified Cancellation Module
Design PhilosophyCausal: cancel out (SI, FI and CHI)Non-causal: multipath components
Method: Hierarchical Cancellation Structure
A B C D E
Training TransmittingReceiving InactiveForwarding
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Unified Cancellation Module
Design PhilosophyCausal: cancel out (SI, FI and CHI)Non-causal: multipath components
Method: Hierarchical Cancellation Structure
A B C D E
Training TransmittingReceiving InactiveForwarding
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Unified Cancellation Module
Design PhilosophyCausal: cancel out (SI, FI and CHI)Non-causal: multipath components
Method: Hierarchical Cancellation Structure
A B C D E
Training TransmittingReceiving InactiveForwarding
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Have Successfully Dealt with Interference
Simultaneous Transmission Possible
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Noise accumulation
Error propagation
10010010010001 1001001001001110010100010011 11110100010011 11110100001111
10010010010001
11110100001111
Packet Discarded due to high Error rate
Drawback
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Virtual-Hop Design
Long paths are divided into smaller Hops 1
Long paths are divided into smaller Virtual-Hops
Other considerations: bottleneck link, latency....
Virtual-Hop 1
Virtual-Hop 2
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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
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Implementation
NI PXIe 1082
2.4GHz center frequency and 20MHz bandwidth
Unified cancellation block
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Implementation
Indoor: 20 locations, single flow
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Throughput Gain over TDMA
1.71 2.39 2.75
Throughput gain increases as the number of hops increases
Hierachical cancellation structure works nicely!
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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
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Throughput performance of AirExpress and TDMA
Network Performance
4-hop AirExpress outperforms TDMA by ~2X on average
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Network Performance
Delay performance of AirExpress andTDMATDMA has a 3X delay over 4-hop AirExpress
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Throughput gain of AirExpress with different virtual-hop size
Network Performance
>4 did not further increase the performance due to noise accumulation
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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
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Q&A
Thanks