Ultra Massive MIMOVision and different embodiments

Emil Björnson

Visiting professor, KTH Royal Institute of Technology, Sweden

Associate professor, Linköping University, Sweden

Massive MIMO versus Ultra Massive MIMO

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5G in 3.5 GHz band64 antenna-integrated radios

1 m x 0.5 m

Beamforming gainSpatial multiplexing gain

Massive MIMO arrayMany antennasElectrically small

Ultra Massive MIMOEven more antennas

Electrically large

Ways to Increase the Capacity Towards 1 Terabit/s

• Capacity of a communication system:

• Three ways to increase it:

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Multiplexed layers . Bandwidth . log! 1 +Signal power . Beamforming gain . Pathloss

𝑁" . Bandwidth

Multiplexed more layersTo one or multiple users

Use more bandwidthMust be associated with higher

power or beamforming gain

Reduce rangeImprove pathloss

Scoring the Terabit/s Goal in Different Bands

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50 MHz bandwidth, 3 GHz band 1 GHz bandwidth, 60 GHz band

Low bandsMultiplex 10000 signals per site

Good channel coherence

High bandsMultiplex fewer signalsUse more bandwidth

E. Björnson, L. Van der Perre, S. Buzzi, E. G. Larsson, “Massive MIMO in Sub-6 GHz and mmWave: Physical, Practical,

and Use-Case Differences,” IEEE Wireless Communications, 2019

Fundamental Limit: Spatial Degrees-of-Freedom

• Determines how many signals an array can separate• Like sampling of a band-limited signal, but we have a space-limited signal

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Definition:Number of layers 𝜂 that can spatially multiplexed, while controlling the interference

Ultra Massive MIMO𝐿 = 10 m, 𝐻 = 30 m𝜂 ≈

𝜋𝜆! 𝐿𝐻 ≈ 100000

Planar array (length 𝐿, height 𝐻):

𝜂 ≈𝜋𝜆!𝐿𝐻

We are very far from the limits!The richness of the channels is key

Three Potential Embodiments of 6G MIMO Technology

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2) Intelligent reflecting surface

1) Cell-free Massive MIMO

3) Ultra MassiveMIMO

Holographic Radio: A New Paradigm in Array Design

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Passive patch

Diod to varyimpedance

Radio unit

Arrays with ultra many elementsRadio units at the same order asdesired spatial degree-of-freedom

MetasurfaceWhy “holographic”?

Phase-shift pattern is the hologramRecord it from uplink pilots

What about Orbital Angular Momentum (OAM)?Generate wavefronts that spin in different ways Special case of MIMO: No extra degrees-of-freedom

E-karimi, Wikimedia Commons

FOR MORE INFORMATION

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Blog: https://ma-mimo.ellintech.se