networking with massive mu-mimo
DESCRIPTION
Networking with massive MU-MIMO. Lin Zhong http:// recg.org. Guiding Principles. Spectrum is scarce Hardware is cheap, and getting cheaper. Antennas. Omni-directional base station. Data 1. Poor spatial reuse; poor power efficiency; high inter-cell interference. Sectored base station. - PowerPoint PPT PresentationTRANSCRIPT
Networking with massive MU-MIMO
Lin Zhonghttp://recg.org
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Guiding Principles
• Spectrum is scarce
• Hardware is cheap, and getting cheaper
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Antennas
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Data 1
Omni-directional base station
Poor spatial reuse; poor power efficiency; high inter-cell interference
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Data 1Data 2
Data 3
Sectored base station
Better spatial reuse; better power efficiency; high inter-cell interference
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Data 2
Data 1Data 3
Data 5
Single-user beamforming base station
Better spatial reuse; best power efficiency; reduced inter-cell interference
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Data 2
Data 1
Data 6
Data 3
Data 4Data 5
Multi-user MIMO base station
M: # of BS antennasK: # of clients (K ≤ M)
Best spatial reuse; best power efficiency; reduced inter-cell interference
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Key benefits of MU-MIMO• High spectral efficiency
• High energy efficiency
• Low inter-cell interference
• Orthogonal to Small Cell solutions– Centralized vs. distributed antennas
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Why massive?
• More antennas Higher spectral efficiency
• More antennas Higher energy efficiency
• Simple baseband technique becomes effective
T.L. Marzetta. Noncooperative cellular wireless with unlimited numbers of base station antennas. IEEE Trans. on Wireless Comm., 2010.
Background: Beamforming
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Background: Beamforming
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=
Constructive Interference
Background: Beamforming
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=
Constructive Interference
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Destructive Interference
Background: Beamforming
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=
Destructive Interference
=
Constructive Interference
Background: Beamforming
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?
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Due to environment and terminal mobility estimation has to occur quickly and periodically
BS
The CSI is then calculated at the terminal and sent back to the BSA pilot is sent from each BS antenna
Background: Channel Estimation
+
+
Align the phases at the receiver to ensure constructive interferenceFor uplink, send a pilot from theterminal then calculate CSI at BS
Path Effects (Walls)Uplink?
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Background: Multi-user MIMO
BS
M: # of BS antennas K: # of clients
K ≤ M
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Multi-user MIMO: Precoding
BS
(M x 1 matrix)(Kx1 matrix)
M: # of BS antennas K: # of clients
K ≤ M
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Linear Precoding
BS
(M x 1 matrix)(Kx1 matrix)
M: # of BS antennas K: # of clients
K ≤ M
sWs
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Background: Zeroforcing Beamforming
Data 1
Null
Null
NullNullNull
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Background: Zeroforcing Beamforming
Data 2
Null
NullNull
Null
Null
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Background: Zeroforcing Beamforming
Data 2
Data 1
Data 6
Data 3
Data 4Data 5
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Background: Conjugate Beamforming
Data 1
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With more antennas
Data 1
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With even more antennas
Data 1
Data 3
Data 5
Conjugate Multi-user Beamforming
Data 1
Data 6
Data 2
Data 4
Conjugate approaches Zeroforcing as M/K∞
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Conjugate vs. Zeroforcing
• Trivial computation
• Suboptimal capacity
• Scalable
• Nontrivial computation
• Close to capacity achieving
• Not scalable
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Recap
1) Estimate channels
2) Calculate weights
3) Apply linear precoding
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Scalability Challenges
1) Estimate channels– M+K pilots, then M•K feedback
2) Calculate weights– O(M•K2), non-parallelizable, centralized
data
3) Apply linear precoding– O(M•K), then O(M) data transport
Argos’ Solutions
1) Estimate channels– New reciprocal calibration method
2) Calculate weights– Novel distributed beamforming method
3) Apply linear precoding– Carefully designed scalable architecture
O(M•K) → O(K)
O(M•K2) → O(K)
O(M•K) → O(K)
C. Shepard et al. Argos: Practical many-antenna base stations. ACM MobiCom, 2012.
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Solution: Argos ArchitectureCentral
Controller
Argos Hub
Argos Hub
Argos Hub
Module
Module
Module
Module
Module
…
…
…
Data Backhaul
ModuleRadio Radio Radio…
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Argos ImplementationCentral
Controller
Argos Hub
Module
Module
Module
…Central
Controller(PC with MATLAB)
Sync Pulse
Ethernet
Clock Distribution
Argos Hub Argos
Interconnect
WARP ModuleFPGA
Power PC
FPGA FabricHardware
ModelPeripherals and Other
I/O
Clock Board
Daughter
Cards
Radio 4
Radio 3
Radio 2
Radio 1
WARP ModuleFPGA
Power PC
FPGA FabricHardware
ModelPeripherals and Other
I/O
Clock Board
Daughter
Cards
Radio 4
Radio 3
Radio 2
Radio 1
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………
Ethe
rne
t
WARP ModuleFPGA
Power PC
FPGA FabricHardware
ModelPeripherals and Other
I/O
Clock Board
Daughter
Cards
Radio 4
Radio 3
Radio 2
Radio 1
ArgosInterconne
ct
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WARP Module
s
Central Controll
er
Argos Hub
Clock Distributio
nEtherne
t Switch
SyncDistributio
n
Argos Interconnects
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Experimental Setup• Time Division Duplex (TDD)
– Uplink and Downlink use the same band
• DownlinkListen to pilot
Calculate BF weights
Send data
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Conjugate vs. Zeroforcing
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Without considering computation
Listen to pilot
Calculate BF weights
Send data
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Linear gains as # of BS antennas increases
Capacity vs. M, with K = 15
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Linear gains as # of users increasesCapacity vs. K, with M = 64
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Considering computation
Listen to pilot
Calculate BF weights
Send data
40Zeroforcing with various hardware configurations
M = 64 K = 15
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Conclusion• First many-antenna beamforming platform– Demonstration of manyfold capacity increase
• Devised novel techniques and architecture– Unlimited Scalability
• Simplistic conjugate beamforming works
• Need adaptive solutions
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Ongoing work
A network of massive MU-MIMO base stations
• Inter-cell interference management
• Pilot contamination• Client grouping & scheduling
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~$2,000 per antenna
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Acknowledgments
http://argos.rice.edu
More BS antennas + MU-MIMO Higher efficiency & lower interference
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More BS antennas + MU-MIMO Higher efficiency & lower interference