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Interference Alignment By Motion Interference Alignment By Motion

Interference Alignment By Motion - PowerPoint Presentation

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Interference Alignment By Motion - PPT Presentation

Swarun Kumar Fadel Adib Omid Aryan Shyamnath Gollakota and Dina Katabi Major Advances in MIMO Eg Interference Alignment Significant gains in throughput SingleAntenna Devices ID: 630707

antenna interference downlink alignment interference antenna alignment downlink throughput c1c2c3 random direction null interfere signals traffic node 33210 solution

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Slide1

Interference Alignment By Motion

Swarun Kumar

Fadel Adib, Omid Aryan, Shyamnath Gollakota and Dina Katabi Slide2

Major Advances in MIMO

E.g. Interference Alignment Significant gains in throughputSlide3

Single-Antenna Devices

Single Antennas, due to limits on power and size

Largely left out of these MIMO benefitsSlide4

Bring MIMO Benefits to Single Antenna Devices“Interference Alignment”

GoalSlide5

Interference Alignmentantenna 1

C1 C2 C3 antenna 2

AP 1

C1

interfere

interfere

2-antenna node can decode only 2 signals

1

2

C2

C3Slide6

Interference Alignmentantenna 1

C1 C2 C3 antenna 2

AP 1

C1

interfere

interfere

1

2

C2

C3

2-antenna node can decode only 2 signalsSlide7

Interference Alignmentantenna 1

C1 C2 C3 antenna 2

AP 1

C1

interfere

interfere

1

2

C2

C3

“align”

2-antenna node can decode only 2 signalsSlide8

Interference Alignment

antenna 1C1 C2 C3 antenna 2

AP 1C1

interfere

interfere

1

2

C2

C3

“align”

2-antenna node can decode only 2 signalsSlide9

Interference Alignmentantenna 1

C1 antenna 2

C1interfereinterfere1

C2

C3

one unwanted interferer

2

AP 1

“align”

2-antenna node can decode only 2 signalsSlide10

Single-Antenna Devices

C1

interfereinterfere1C2

C3

antenna 1

C1

C2

C3

antenna 2

Can we still perform interference alignment?

Signals from all

clients will change

2

AP 1Slide11

Single-Antenna Devices

C1

interfereinterfere1C2

C3

antenna 1

C1

C2

C3

antenna 2

Signals from all

clients will change

2

AP 1

Perform Interference Alignment purely at the AP

Eliminates feedback/cooperation with clients

Brings benefits of alignment to new devices

Can we still perform interference alignment?Slide12

MoMIMOMoves the AP’s antenna to positions that achieve interference alignment

Needs to only displace antenna by up to 2 inchesAchieves 1.98x gain in throughput over 802.11nSlide13

1

. How do we “find” positions of alignment?2. How does it impact general wireless networks?Slide14

Feasibility of “Alignment by Motion” Record antenna displacement for interference to drop below noise

AP 1

2 inch radius21interferedesired

C1

C2

C3Slide15

Feasibility of “Alignment by Motion” Slide16

Feasibility of “Alignment by Motion”

Why is the required displacement small?

Median:

0.3 inch

90

th

Percentile:

1 inchSlide17

A Simple Example

antenna 1C1 antenna 2

alignReferenceReference

C1

1

2

AP 1Slide18

A Simple Example

antenna 10align

ReferenceReference

C11

2

AP 1

Goal

: Minimize signal from C1 to antenna 2

C1

antenna 2Slide19

Paths combine constructively or destructively based on phase

Indoor Environments Rich in Multipath

High signal @2

(poor alignment)

C1

1

2

AP 1Slide20

Indoor Environments Rich in MultipathPaths

differ by extra 2”Paths combine constructively or destructively based on phaseFor Wi-Fi, 2” ≈ λ/2

λ0°360°

C1

1

2

AP 1Slide21

Indoor Environments Rich in MultipathPaths combine constructively or destructively based on phase

For Wi-Fi, 2” ≈ λ/2In-phase paths now out-of-phase!Low Signal @2 (good alignment)

0°180°λ2

C1

1

2

AP 1

Paths

differ

by extra 2”

Small displacement suffices for alignment

Generalizes to many reflectors, any alignmentSlide22

{

{How Can We Find Good Alignment?We must quantify goodness of alignmentantenna 1C1 C2

antenna 2interference

C1

C2

interference

Poor

Good

C1

C2

interference

≈ 0

Goal:

Find antenna location that minimizes interferenceSlide23

Naïve solution: Random walk

Simulated the spatial profile of interferenceTen reflectors placed in randomly chosen locationsApplied standard multipath modelsDoes not work!Slide24

30

20100-10

Interference (dB)Naïve solution: Random walkHigh interferencex (in)y (in)3120-1

-2-33

2

1

-1

-2

-3

0Slide25

3

120-1

-2-33210-1-2-33020100-10Interference (dB)

Naïve solution

: Random walk

Low interference

Goal

:

Find blue spots

y (in)

x (in)Slide26

3

120-1

-2-33210-1-2-33020100-10

Naïve solution: Random walk

x (in)

y (in)

Blue spots of low interference are small

 Hard to stumble upon in a

random walk

Goal

:

Find blue spots

Interference

(dB)Slide27

3

1

20-1-2-33210-1-2-3302010

0-10Key Observation

: Interference

is smooth

Wireless channels are continuous and smooth functions

over space

x (in)

y (in)

Interference

(dB)Slide28

3

1

20-1-2-33210-1-2-3302010

0-10Solution: A Hill Climbing Algorithm

M

ove in random direction and track

interference

x (in)

y (in)

Interference

(dB)Slide29

3

120

-1-2-33210-1-2-33020100-10

Solution: A Hill Climbing AlgorithmMove in random direction and track interference

If interference

: continue in that direction

x (in)

y (in)

Interference

(dB)Slide30

3

120

-1-2-33210-1-2-33020100-10

Solution: A Hill Climbing AlgorithmMove in random direction and track

interference

If interference

: continue in that direction

x (in)

y (in)

Interference

(dB)Slide31

3

120

-1-2-33210-1-2-33020100-10

Solution: A Hill Climbing AlgorithmMove in random direction and track interference

If interference

: continue in that direction

If

interference

: continue in opposite direction

x (in)

y (in)

Interference

(dB)

Algorithm converges to spot of minimum interference

Guides antenna to find positions of alignmentSlide32

1. How do we “find” positions of alignment?

2. How does it impact general wireless networks?Slide33

Interference Alignment

AP 1

C1C2C3

AP 2

AP 3

A

lign

C2 and C3Slide34

Interference Alignment

AP 1

C1C2C3

AP 3

A

lign

C1 and C3

AP 2Slide35

Interference Alignment

AP 1

C1C2C3

A

lign

C1 and C2

AP 2

AP 3Slide36

Interference Alignment

AP 1

C1C2C3

AP 2

AP 3

3 concurrent streams

 Gain in throughput!

N antenna APs enable

N+1 concurrent uplink streamsSlide37

What about downlink traffic?

AP 1

C1C2C3

AP 2

AP 3Slide38

What about downlink traffic?

AP 1

C2C3Slide39

AP 1 has 2 antennas

null??2 antenna node can null interference at up to 1 antennaNothing!C2 & C3 alignedat AP 1

AP 1C2C3Slide40

AP 1 has 2 antennas

null2 antenna node can null interference at up to 1 antennaC2 & C3 alignedat AP 1

AP 1C2C3

null for free!Slide41

Uplink Wireless Channels

AP 1

C2C3

h

1

h

2

h

3

h

4

antenna 1

antenna 2

(h

1

,

h

2

)

(h

3

, h

4

)

h

1

h

2

h

3

h

4

=Slide42

Downlink Wireless Channels

AP 1

C2C3

h

1

h

2

h

3

h

4

Channel Reciprocity

x

h

1

x + h

2

α

x

null

α

xSlide43

Downlink Wireless Channels

AP 1

C2C3

h1

h

2

h

3

h

4

Channel Reciprocity

x

α

x

h

1

x + h

2

α

x

= 0

nullSlide44

Downlink Wireless Channels

AP 1

C2C3

h1

h

2

h

3

h

4

Channel Reciprocity

x

α

x

α

=

null

-h

1

h

2

α

=

-h

3

h

4

h

1

h

2

h

3

h

4

=

null

Alignment on the uplink enables nulling on the downlink, with no extra movementSlide45

Downlink Traffic

AP 1

C1C2C3

AP 2

AP 3Slide46

Downlink Traffic

AP 1

C1C2C3

AP 2

AP 3Slide47

Downlink Traffic

AP 1

C1C2C3

AP 2

AP 3Slide48

Downlink Traffic

AP 1

C1C2C3

AP 2

AP 3

3 concurrent streams on the downlink

MoMIMO

provides gains to uplink & downlink trafficSlide49

Experimental ResultsSlide50

MoMIMO ImplementationImplemented on USRP N210

Mounted antenna on Roomba to emulate sliding antennasCompare MoMIMO with 802.11n, n+Slide51

TestbedRandomly assign nodes to red locations

Class RoomOffice SpaceSlide52

Can Alignment Reduce Interference?

CDF

Interference (dB)Slide53

Can Alignment Reduce Interference?CDF

802.11n

MoMIMO

Downlink

Median:

-2.5dB

Interference

(dB)Slide54

Throughput

Heterogeneous mix of 1 & 2-antenna nodes

CDF

Network Throughput

(Mbps)Slide55

Throughput

Heterogeneous mix of 1 & 2-antenna nodes

1.98x

CDF

Network Throughput

(Mbps)

802.11n

MoMIMOSlide56

Throughput

Heterogeneous mix of 1 & 2-antenna nodes

1.31x

CDF

Network Throughput

(Mbps)

802.11n

n+

MoMIMOSlide57

ConclusionPerforms Interference Alignment purely by moving an antenna of the AP

Displaces antenna by up to 2 inchesNew applications at intersection of networkingand robotics