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
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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