1 yue qiao computer science and engineering email:...

1

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

2

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

6

Received Signal



A B C D

( )sh x t( )x t

( )fh x t

Self Interference

SI

FI

time

7

Received Signal



A B C D

( )sh x t( )x t

( )fh x t

Self Interference

SI

FI

sh

time

8

Received Signal



A B C D

( )sh x t( )x t

( )fh x t

Self Interference

SI

FI

fsh h

Measure the Superposed Channel?

time

9

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!

10

Our Solution

Self Interference


Cross-Hop Interference

Full-Duplex Technique

Superposed Channel

11

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

12

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

13




A B C D E


14




A B C D E


15




A B C D E


16

Have Successfully Dealt with Interference

Simultaneous Transmission Possible

17

Noise accumulation

Error propagation

10010010010001 1001001001001110010100010011 11110100010011 11110100001111

10010010010001

11110100001111

Packet Discarded due to high Error rate

Drawback

18

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

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

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 andTDMATDMA 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

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

1 yue qiao computer science and engineering email:...

Documents