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Hybrid Beamforming for 5G Millimeter-Wave Systems Jun Zhang - - PowerPoint PPT Presentation

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Hybrid Beamforming for 5G Millimeter-Wave Systems Jun Zhang Xianghao Yu Slides available at: https://yuxianghao.github.io/slides/ICCC19.pdf 1 ICCC 2019 Tutorial Collaborators Juei-Chin Shen Khaled B. Letaief (MediaT ek)

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Hybrid Beamforming

for

5G Millimeter-Wave Systems

1

Jun Zhang Xianghao Yu

https://yuxianghao.github.io/slides/ICCC19.pdf

Slides available at:

ICCC 2019 Tutorial

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2

Collaborators

Khaled B. Letaief (HKUST) Juei-Chin Shen (MediaT ek)

ICCC 2019 Tutorial

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 Background and Motivation  Preliminaries of Hybrid Beamforming  Hybrid Beamforming Design

  • Improve Spectral Efficiency: Approaching the Fully Digital
  • Boost Computational Efficiency: Convex Relaxation
  • Fight for Hardware Efficiency: How Many Phase Shifters Are

Needed? Conclusions  Potential Research Directions

Outline

ICCC 2019 Tutorial

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 Era of mobile data deluge

7 x

Data growth by 2021

60 %

Video traffic in 2016

8.0 .0 Billio

ion

Mobile devices/connections in 2016

Background and Motivation

Cisco VNI, March 2017

ICCC 2019 Tutorial

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 Requirements of 5G systems

High data rate Massive connections Green communications Security & privacy Uniform coverage

Background and Motivation

ICCC 2019 Tutorial

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 The 1000x Capacity Challenge for 5G

Background and Motivation

ICCC 2019 Tutorial

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 The 1000x Capacity Challenge for 5G

Background and Motivation

ICCC 2019 Tutorial

Required Performance ~ 1,000 x

Current Performance

Capacity = Bandwidth (Hz) x Spectral Efficiency (bps/Hz) x # Links Mm-wave bands 1000 = 10 x 5 x 20 MIMO Cloud-RAN

(Globecom 17 Tutorial)

Network densification

(WiOpt 18 Tutorial)

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 Higher spectral efficiency

Background and Motivation

ICCC 2019 Tutorial

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 Ultra dense networks

Background and Motivation

ICCC 2019 Tutorial

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Background and Motivation

ICCC 2019 Tutorial

TV broadcast 3G/4G LTE cellular Wi-Fi 28 GHz – LMDS (5G cellular) 38 GHz 5G cellular 60 GHz Wi-Fi 77 GHz vehicular radar

[U.S. Frequency Allocation Chart as of October 2011]

 Spectrum crunch: A fundamental bottleneck

Sub-6 GHz

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 New Spectrum: Beyond sub-6 GHz

Background and Motivation

ICCC 2019 Tutorial

5G = Millimeter wave

At least to someone

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Background and Motivation

ICCC 2019 Tutorial

 Latest activities at mm-wave bands

Standardization (IEEE 802.11 ad) Channel models Small cell networks Hardware products mm-Wave trial

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Background and Motivation

ICCC 2019 Tutorial

 Emerging mm-wave applications [T. S. Rappaport et al., 2014]

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Background and Motivation

ICCC 2019 Tutorial

Sub-6 GHz signals Mm-wave signals Huge path loss Sensitivity to blockages

SNR

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Background and Motivation

ICCC 2019 Tutorial

microwave mm-wave

Small wavelength Large-scale antenna arrays

More antennas can be patched in a small area

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Background and Motivation

ICCC 2019 Tutorial

Higher antenna gains and narrower beams

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Background and Motivation

ICCC 2019 Tutorial

Network densification reduces propagation distance

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Background and Motivation

ICCC 2019 Tutorial

 Conventional beamforming

RF Chain RF Chain RF Chain

Digital baseband precoder

  • Performed digitally at the baseband
  • Require an RF chain per antenna element

ADC

ADCs Mixers Power amplifiers Costly and power hungry for large-scale antenna arrays, especially at mm-wave bands!

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Background and Motivation

ICCC 2019 Tutorial

 Existing solution: Analog beamforming

  • One RF chain only

RF Chain

  • Low cost and hardware complexity
  • Beams direction readily controlled by a series of phase shifters

in the RF domain

the decisive variable

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Background and Motivation

ICCC 2019 Tutorial

 Existing solution: Analog beamforming

  • Limitations

RF Chain

Analog beamforming can

  • nly support single-stream

transmissions Benefits of MIMO

  • Spatial multiplexing
  • Support space-division

multiple access (SDMA)

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Background and Motivation

ICCC 2019 Tutorial

 Hybrid beamforming

RF Chain RF Chain Digital baseband Analog RF

  • Multi-stream transmission, ability to support SDMA
  • Multiple RF chains, the number should be very small
  • Combine the benefits of digital and analog beamforming
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Background and Motivation

ICCC 2019 Tutorial

 General references on mm-wave

  • T. S. Rappaport et al., “Millimeter wave mobile communications for 5G Cellular: It Will

Work!,” IEEE Access, vol. 1, pp. 335-349, 2013.

  • Z. Pi and F. Khan, “An introduction to millimeter-wave mobile broadband systems,” IEEE
  • Commun. Mag., vol. 49, no. 6, pp. 101-107, June 2011.
  • E. Torkildson, U. Madhow, and M. Rodwell, “Indoor millimeter wave MIMO: Feasibility and

performance,” IEEE Trans. Wireless Commun., vol. 10, no. 12, pp. 4150–4160, Dec. 2011.

  • M. R. Akdeniz et al., “Millimeter wave channel modeling and cellular capacity evaluation,”

IEEE J. Sel. Areas Commun., vol. 32, no. 6, pp. 1164–1179, Jun. 2014.

  • T. S. Rappaport, R. W. Heath, R. C. Daniels, and J. N. Murdock, Millimeter Wave Wireless
  • Communications. New York, NY, USA: Pearson Education, 2014.
  • P. Wang, Y. Li, L. Song, and B. Vucetic, “Multi-gigabit millimeter wave wireless

communications for 5G: From fixed access to cellular networks,” IEEE Commun. Mag., vol. 53, no. 1, pp. 168–178, Jan. 2015.

  • S. Rangan, T. S. Rappaport, and E. Erkip, “Millimeter-wave cellular wireless networks:

Potentials and challenges,” Proc. IEEE, vol. 102, no. 3, pp. 366–385, Feb. 2014.

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23 ICCC 2019 Tutorial

 Recognitions on hybrid beamforming

  • O. E. Ayach, S. Rajagopal, S. Abu-Surra, Z. Pi, and R. W. Heath, Jr., “Spatially sparse

precoding in millimeter wave MIMO systems,” IEEE Trans. Wireless Commun., vol. 13, no. 3,

  • pp. 1499-1513, Mar. 2014.
  • The 2017 Marconi Prize Paper Award in Wireless Communications
  • F. Sohrabi and W. Yu, “Hybrid digital and analog beamforming design for large-scale

antenna arrays,” IEEE J. Sel. Topics Signal Process., vol. 10, no. 3, pp. 501-513, Apr. 2016.

  • The 2017 IEEE Signal Processing Society Best Paper Award
  • A. Alkhateeb, O. El Ayach, G. Leus, and R. W. Heath, Jr., “Channel estimation and hybrid

precoding for millimeter wave cellular systems,” IEEE J. Sel. Topics Signal Process., vol. 8, no. 5, pp. 831-846, Oct. 2014.

  • The 2016 Signal Processing Society Young Author Best Paper Award
  • X. Yu, J.-C. Shen, J. Zhang, and K. B. Letaief, “Alternating minimization algorithms for

hybrid precoding in millimeter wave MIMO systems,” IEEE J. Sel. Topics Signal Process., vol. 10, no. 3, pp. 485-500, Apr. 2016.

  • The 2018 Signal Processing Society Young Author Best Paper Award

Background and Motivation

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Preliminaries of Hybrid Beamforming

ICCC 2019 Tutorial

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Preliminaries of Hybrid Beamforming

 Hybrid beamforming

ICCC 2019 Tutorial

  • Also called Hybrid precoding; Analog/digital precoding

RF Chain RF Chain

Digital baseband precoder Analog RF precoder

  • Notations in hybrid beamforming
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Preliminaries of Hybrid Beamforming

ICCC 2019 Tutorial

 Fully digital precoding vs. Hybrid precoding

RF Chain RF Chain

Digital baseband precoder Analog RF precoder

  • Main differentiating part: Analog RF precoder
  • Mapping from low-dimensional RF chains to high-dimensional

antennas, typically implemented by phase shifters

RF Chain RF Chain RF Chain

Digital baseband precoder

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Preliminaries of Hybrid Beamforming

ICCC 2019 Tutorial

 Hybrid precoder structure

(I) Mapping strategy:

Which antennas should be connected to each RF chain?

(II) Hardware implementation:

What kind of hardware should be used to realize each connection?

Signal flow Adopted hardware

RF Chain RF Chain RF Chain

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Preliminaries of Hybrid Beamforming

ICCC 2019 Tutorial

 The state-of-the-art hybrid precoder structure

  • Mainly focus on different mapping strategies

RF Chain RF Chain RF Chain RF Chain

Fully-connected Partially-connected

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Preliminaries of Hybrid Beamforming

ICCC 2019 Tutorial

 The state-of-the-art hybrid precoder structure

  • One prevalent hardware implementation: Single phase shifter (SPS)

RF Chain RF Chain RF Chain RF Chain

SPS Fully-connected SPS Partially-connected

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Preliminaries of Hybrid Beamforming

ICCC 2019 Tutorial

 General multiuser multicarrier (MU-MC) systems

RF Chain RF Chain

Digital baseband precoder Analog RF precoder

  • One single digital precoder for each user on each subcarrier
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Preliminaries of Hybrid Beamforming

ICCC 2019 Tutorial

 General multiuser multicarrier (MU-MC) systems

Digital RF Chain Analog IFFT

Frequency domain Time domain Combines the data streams to all the users

  • Analog precoder FRF is shared by all the users and subcarriers
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Preliminaries of Hybrid Beamforming

ICCC 2019 Tutorial

 Generic hybrid precoder design problem

  • Minimize the Euclidean distance between the hybrid precoders and

the fully digital precoder [O. El Ayach et al., 2014]

Main difficulty

  • varies according to different hybrid precoder structures,

e.g., for the SPS fully-connected structure

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Preliminaries of Hybrid Beamforming

ICCC 2019 Tutorial

 Generic hybrid precoder design problem

  • This formulation applies for an arbitrary digital precoder
  • It is applicable for different hybrid beamformer structures
  • It facilitates beamforming algorithm design
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Preliminaries of Hybrid Beamforming

ICCC 2019 Tutorial

 An early work on hybrid beamforming

  • Nov. 2005
  • Phase shifter based RF beamforming
  • NRF=2 is enough for Ns=1 to achieve the performance of the fully

digital precoder

  • Have not got too much attention before hybrid beamforming was

proposed (cited 75 times before 2014 while 327 times after 2014)

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Preliminaries of Hybrid Beamforming

ICCC 2019 Tutorial

 An extension

  • Sep. 2014
  • Generalization: NRF=2Ns to achieve the performance of the fully

digital precoder

  • The number of RF chains to achieve fully digital will be very large

for MU-MC systems

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Preliminaries of Hybrid Beamforming

ICCC 2019 Tutorial

 Questions to be answered in this tutorial

  • Q1: Can hybrid precoder provide performance close to the fully

digital one with NRF<2Ns?

  • Q5: How to efficiently design hybrid precoding algorithms?
  • Q3: How many phase shifters are needed?
  • Q4: How to connect RF chains with antennas?
  • Q2: How many RF chains are needed?

Spectral efficiency Hardware efficiency Computational efficiency

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Preliminaries of Hybrid Beamforming

ICCC 2019 Tutorial

  • “Scoring triangle”

 Performance metrics

Spectral efficiency Hardware efficiency Computational efficiency

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Improve Spectral Efficiency: Approaching the Fully Digital Beamforming

[Ref] X. Yu, J.-C. Shen, J. Zhang, and K. B. Letaief, “Alternating minimization algorithms for hybrid precoding in millimeter wave MIMO systems,” IEEE J. Sel. Topics Signal Process., Special Issue on Signal Process. for Millimeter Wave Wireless Commun., vol. 10, no. 3, pp. 485-500, Apr. 2016. (The 2018 IEEE Signal Processing Society Young Author Best Paper Award)

ICCC 2019 Tutorial

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Improve Spectral Efficiency

ICCC 2019 Tutorial

 Single phase shifter (SPS) implementation

RF Chain

  • Fully digital achieving condition:

Q: Can we further reduce the number of RF chains?

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40 ICCC 2019 Tutorial

Improve Spectral Efficiency

(I) Fully-Connected Mapping

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 Existing work

  • Mar. 2014
  • Orthogonal matching pursuit (OMP) algorithm
  • The columns of the analog precoding matrix FRF is selected from a

candidate set C (array response vectors)

Citation >1354

Improve Spectral Efficiency

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 Existing work

  • OMP Algorithm

Improve Spectral Efficiency

Find the array response vector along which the optimal precoder has the maximum projection Appends the selected array response vector to the FRF Least squares solution to FBB Calculate “residual precoding matrix”

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Improve Spectral Efficiency

(I) Fully-Connected Mapping

ICCC 2019 Tutorial

 Simulation result

  • Prominent performance

loss especially with a small number of RF chains Q: How to improve spectral efficiency with a few RF chains?

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  • “Scoring triangle”

 Performance metrics

Spectral efficiency Hardware efficiency Computational efficiency Baseline: SPS fully-connected with OMP

2 3 4

Improve Spectral Efficiency

(I) Fully-Connected Mapping

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 Start from single-user systems

  • Digital precoder:
  • Difficulty: Analog precoder design with the unit modulus constraints
  • The vector forms a complex circle manifold
  • Alternating minimization

Improve Spectral Efficiency

(I) Fully-Connected Mapping

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 Manifold optimization

  • What is a manifold?
  • In mathematics, a manifold is a

topological space that locally resembles Euclidean space near each point. More precisely, each point of an n-dimensional manifold has a neighborhood that is homeomorphic to the Euclidean space

  • f dimension n.
  • How to optimize on manifolds?

Improve Spectral Efficiency

(I) Fully-Connected Mapping

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 Manifold optimization (cont.)

  • Euclidean space: gradient descent
  • Similar approaches on manifolds?

Q: For any given point xk

  • n the manifold, where to

go to further decrease the

  • bjective?

Improve Spectral Efficiency

(I) Fully-Connected Mapping

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 Manifold optimization (cont.)

Improve Spectral Efficiency

(I) Fully-Connected Mapping

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 Manifold optimization (cont.)

Improve Spectral Efficiency

(I) Fully-Connected Mapping

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 Manifold optimization (cont.)

Improve Spectral Efficiency

(I) Fully-Connected Mapping

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 Manifold optimization (cont.)

Improve Spectral Efficiency

(I) Fully-Connected Mapping

https://www.manopt.org/ ORBEL Wolsey Award 2014

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 MO-AltMin Algorithm

Improve Spectral Efficiency

(I) Fully-Connected Mapping

Manifold optimization for analog precoder

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 SPS fully-connected (cont.)

  • A low-complexity algorithm
  • Enforce a semi-orthogonal constraint on
  • Digital precoder design
  • Semi-orthogonal Procrustes solution

Improve Spectral Efficiency

(I) Fully-Connected Mapping

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 SPS fully-connected (cont.)

  • Analog precoder design
  • Phase extraction (PE-AltMin)
  • When NRF=Ns, the upper bound is tight, the only approximation is

the additional semi-orthogonal constraint

Improve Spectral Efficiency

(I) Fully-Connected Mapping

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Improve Spectral Efficiency

(II) Partially-Connected Mapping

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 Existing work

Improve Spectral Efficiency

(II) Partially-Connected Mapping

  • Apr. 2016

Citation > 350

  • SPS partially-connected structure: Energy efficiency
  • Concept of successive interference cancellation (SIC) was

transplanted to design the precoding algorithm

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 Existing work

Improve Spectral Efficiency

(II) Partially-Connected Mapping

  • Apr. 2016
  • Q: How to directly design hybrid beamforming with the

partially-connected mapping?

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 SPS partially-connected

phase shifters connected to the i-th RF chain

  • Problem decoupled for each RF chain
  • Closed-form solution for
  • : Block diagonal with unit modulus non-zero elements

Improve Spectral Efficiency

(II) Partially-Connected Mapping

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 SPS partially-connected (cont.)

  • Optimization of
  • Reformulate as a non-convex problem
  • Semidefinite relaxation (SDR) is tight for this case so globally
  • ptimal solution is obtained [Z.-Q. Luo et al., 2010]

convex

Improve Spectral Efficiency

(II) Partially-Connected Mapping

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 Simulation results

  • Effectiveness of the proposed

AltMin algorithms

  • The fully-connected mapping

can easily approach the performance of the fully digital precoding

Improve Spectral Efficiency

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Improve Spectral Efficiency

ICCC 2019 Tutorial

 Simulation results

  • ~Ns RF chains are enough for

the fully-connected mapping

  • Employing fewer PSs, the

partially-connected mapping needs more RF chains

Limitation: Computational efficiency of the MO-AltMin is not good, thus difficult to extend to MU-MC settings

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 Simulation results

  • PE-AltMin algorithm serves as

an excellent low-complexity algorithm for hybrid beamforming when NRF=Ns

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 Conclusions

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 Other approaches

Improve Spectral Efficiency

  • Apr. 2016
  • Directly maximize the spectral efficiency with the semi-orthogonal

constraint on the digital precoding matrix FBB

  • Element-wise alternating minimization for the matrix FRF

Citation > 366

  • Mainly focus on the special case NRF=Ns
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 Other approaches

Improve Spectral Efficiency

  • Apr. 2016
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Boost Computational Efficiency: Convex Relaxation

ICCC 2019 Tutorial

[Ref] X. Yu, J. Zhang, and K. B. Letaief, “Alternating minimization for hybrid precoding in multiuser OFDM mmWave Systems,” in Proc. Asilomar Conf. on Signals, Systems, and Computers, Pacific Grove, CA, Nov. 2016. (Invited Paper) [Ref] X. Yu, J. Zhang, and K. B. Letaief, “Doubling phase shifters for efficient hybrid precoding in millimeter- wave multiuser OFDM systems,” J. Commun. Inf. Netw., vol. 4, no. 2, pp. 51-67, Jul. 2019.

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Boost Computational Efficiency

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 Existing works

  • Jan. 2015

Citation > 93

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Boost Computational Efficiency

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 Existing works

  • Dec. 2014
  • Low-complexity algorithm based on channel phase extraction

Citation > 342

  • Enables asymptotic performance analysis with Rayleigh fading
  • Can only deal with single-antenna multiuser MIMO and NRF=K
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 Existing works

  • Jun. 2019
  • Phase extraction operations for different implementations
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Boost Computational Efficiency

ICCC 2019 Tutorial

 Main approaches to handle the unit modulus constraints

  • Candidate set/codebook based, with unit modulus elements
  • E.g., OMP
  • Manifold optimization – directly tackle unit modulus constraints
  • E.g., MO-AltMin
  • Phase extraction
  • E.g., Liang et al., WCL 14.
  • Convex relaxation
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(I) Fully-Connected Mapping

ICCC 2019 Tutorial

 Main difficulty in designing the SPS implementation

  • Analog precoder with the unit modulus constraints
  • An intuitive way to boost computational efficiency is to relax this

highly non-convex constraint as a convex one

  • The value of γ does not affect the hybrid beamformer design
  • We shall choose γ=2 instead of keeping it as 1. Why?
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 Double phase shifter (DPS) implementation

  • The relaxed solution with γ=2 can be realized by a hardware

implementation

  • Sum of two phase shifters
  • Unit modulus constraint is

eliminated

RF Chain

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(I) Fully-Connected Mapping

ICCC 2019 Tutorial

 Fully-connected mapping

  • RF-only precoding

LASSO

  • Closed-form solution for semi-unitary codebooks
  • Hybrid precoding

Redundant

Matrix factorization

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 Fully-connected mapping (cont.)

  • Optimality in single-carrier systems
  • Multi-carrier systems
  • Low-rank matrix approximation: SVD, globally optimal solution
  • It reduces the required number of RF chains by half for achieving

the fully digital precoding Minimum number of RF chains

Boost Computational Efficiency

(I) Fully-Connected Mapping

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 Fully-connected mapping (cont.)

Boost Computational Efficiency

(I) Fully-Connected Mapping

  • Q: How to use this relaxed result for SPS implementation?
  • Phase extraction

unit modulus constraint

  • Some clues: The unitary matrix U1 fully extracts the information
  • f the column space of FRFFBB, whose basis are the orthonormal

columns in FRF

  • Optimal solution:

Convex relaxation-enabled (CR-enabled) SPS

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 Partially-connected mapping

  • Decoupled for each RF chain
  • Eigenvalue problem
  • Block diagonal structure

Boost Computational Efficiency

(II) Partially-Connected Mapping

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(II) Partially-Connected Mapping

ICCC 2019 Tutorial

 DPS partially-connected mapping (cont.)

  • Not much performance gain obtained by simply adopting the

DPS implementation

  • Modified K-means algorithm

 Centroid:  Clustering:

  • Convergence guarantee

Adaptively separate all antennas into groups

  • Dynamic mapping:
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 MU-MC systems: Inter-user interference

  • Approximating the fully digital precoder leads to near-optimal

performance in single-user single-carrier, single-user multicarrier, and multiuser single-carrier mm-wave MIMO systems

  • Inter-user interference will be more prominent in multiuser

multicarrier systems as the analog precoder is shared by a large number of subcarriers

  • Additional care is needed
  • Cascade an additional block diagonalization (BD) precoder

 Effective channel:  BD:

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 Simulation results (Fully-connected)

  • Achieve near-optimal spectral

efficiency and optimal multiplexing gain with low- complexity algorithms

  • Effectiveness of the proposed

CR-enabled SPS method

[Ref] F. Sohrabi and W. Yu, “Hybrid Analog and Digital Beamforming for mmWave OFDM Large-Scale Antenna Arrays,” IEEE J. Sel. Areas Commun., vol. 35, no. 7, pp. 1432-1443, July 2017.

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 Simulation results (Partially-connected)

  • Simply doubling PSs in the

partially-connected mapping is far from satisfactory

  • Superiority of the modified

K-means algorithm with lower computational complexity than the greedy algorithm

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 Conclusions

1 2 3 4

Spectral efficiency Hardware efficiency Computational efficiency DPS fully-connected Spectral efficiency Hardware efficiency Computational efficiency DPS partially-connected

6 6

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 Discussions

  • Comparison of computational complexity
  • The proposed DPS implementation enables low complexity

design for hybrid beamforming

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 Discussions

  • The number of RF chains has been reduced to the minimum
  • A large number of high-precision phase shifters are still needed
  • Need to adapt the phases to channel states

 Practical phase shifters are typically with coarsely quantized phases

Fully-connected Partially-connected SPS NtNRF Nt DPS 2NtNRF 2Nt How to reduce # phase shifters?

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[Ref] X. Yu, J. Zhang, and K. B. Letaief, “Hybrid precoding in millimeter wave systems: How many phase shifters are needed?” in Proc. IEEE Global Commun. Conf. (Globecom), Singapore, Dec. 2017. (Best Paper Award) [Ref] X. Yu, J. Zhang, and K. B. Letaief, “A hardware-efficient analog network structure for hybrid precoding in millimeter wave systems,” IEEE J. Sel. Topics Signal Process., Special Issue on Hybrid Analog-Digital Signal Processing for Hardware-Efficient Large Scale Antenna Arrays, vol. 12, no. 2, pp. 282-297, May 2018.

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 Commonly-used hardware in hybrid beamforming

Phase shifter ~ unit modulus Adaptive Quantized with fixed phases Butler matrix ~ FFT matrix Switch ~ binary Generate fixed phase difference between antenna elements

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 Different implementations

  • How to reduce the overall hardware complexity while maintaining

good performance?

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Fight for Hardware Efficiency

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 Existing works with switches

  • Switches with a lower dimension

analog precoder:Antenna selection

  • Performance loss
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 Existing works with switches

  • Switches only with a higher

dimension analog precoder

  • Sub-matrix structure
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(I) Fixed phase shifter implementation

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 Fixed phase shifter (FPS) implementation

Q: How to design these adaptive switches?

RF Chain RF Chain RF Chain

switch network

  • multi-channel fixed PSs [Z. Feng et al., 2014]
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 Problem formulation

  • FPS matrix
  • Binary switch matrix

 An objective upper bound enables a low-complexity algorithm

  • Enforce a semi-orthogonal constraint on [X.

Yu et al., 2016]

NP-hard Phases are fixed

Fight for Hardware Efficiency

(I) Fixed phase shifter implementation

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 Alternating minimization

  • Digital precoder
  • Semi-orthogonal Procrustes solution
  • Switch matrix optimization
  • Once

is optimized, the optimal is determined correspondingly

Fight for Hardware Efficiency

(I) Fixed phase shifter implementation

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 Alternating minimization (cont.)

  • Search dimension:
  • Search dimension
  • Optimization of
  • Acceleration: Optimal point can only be obtained at
  • Convergence guarantee

Fight for Hardware Efficiency

(I) Fixed phase shifter implementation

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 Two common mapping strategies

RF Chain RF Chain RF Chain RF Chain

Fully-connected Partially-connected

Fight for Hardware Efficiency

(II) Flexible hardware-performance tradeoff Performance Hardware efficiency

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 A mapping strategy for flexible hardware-performance tradeoff

  • Group-connected mapping
  • : Fully-connected
  • : Partially-connected

Directly migrate the design for the fully-connected mapping

RF Chain RF Chain

RF Chain RF Chain

Group Group

Save hardware by times

Fight for Hardware Efficiency

(II) Flexible hardware-performance tradeoff

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 Simulation results: MU-MC systems

  • Slightly inferior to the DPS

fully-connected mapping with much fewer PSs

  • Significant improvement over

the OMP algorithm

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 Simulation results: How many PSs are needed?

  • Only ~10 fixed phase shifters

are sufficient!

  • 200 times reduction

compared with the DPS implementation

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 Simulation results: How much power can be saved?

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 Simulation results

  • A flexible approach to

balance the achievable performance and hardware efficiency

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 Conclusions

4 5 6

Spectral efficiency Hardware efficiency Computational efficiency FPS group-connected

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Conclusions

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 Questions answered

YES

Alternating minimization provides the basic principle Manifold optimization provides good benchmark Convex relaxation enables low-complexity algorithms

  • Q1: Can hybrid precoder provide performance close to the fully

digital one?

  • Q5: How to efficiently design hybrid precoding algorithms?
  • Q4: How to connect the RF chains and antennas?
  • Q3: How many phase shifters are needed?
  • Q2: How many RF chains are needed?

Group-connected ~10 FPSs

Conclusions

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Conclusions

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Conclusions

 Comparisons between different hybrid precoder structures

  • SPS: May not be a good

choice

  • DPS: An excellent

candidate for low- complexity algorithms

  • FPS: A trade-off between

the hardware and computational complexity, with satisfactory performance

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Potential research directions

  • Joint design with CSI acquisition and uncertainty

Beam design for the training stage with the hybrid structures Hybrid precoding with partial CSI or covariance info. only

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  • Comparison between different antenna configurations

Hybrid beamforming and channel estimation with lens antenna arrays

Potential research directions

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  • Hybrid beamforming for THz communications

How to use antennas efficiently?

Potential research directions

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  • Performance evaluation

Performance characterization of hybrid precoding Comparison between MU-MIMO and single user spatial multiplexing

Potential research directions

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  • Further reduction in computational complexity

Potential research directions

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  • Hardware implementation and testing

Potential research directions

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  • Hybrid precoding with low-precision ADCs

High-precision ADCs at mm-wave frequencies are extremely expensive Performance evaluation with tractable quantization models

Potential research directions

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Conclusions

 Our own results

  • X. Yu, J.-C. Shen, J. Zhang, and K. B. Letaief, “Alternating minimization algorithms for

hybrid precoding in millimeter wave MIMO systems,” IEEE J. Sel. Topics Signal Process., Special Issue on Signal Process. for Millimeter Wave Wireless Commun., vol. 10, no. 3, pp. 485- 500, Apr. 2016. (The 2018 SPS Young Author Best Paper Award)

  • X. Yu, J. Zhang, and K. B. Letaief, “Alternating minimization for hybrid precoding in

multiuser OFDM mmWave Systems,” in Proc. Asilomar Conf. on Signals, Systems, and Computers, Pacific Grove, CA, Nov. 2016. (Invited Paper)

  • X. Yu, J. Zhang, and K. B. Letaief, “Doubling phase shifters for efficient hybrid precoding

in millimeter-wave multiuser OFDM systems,” J. Commun. Inf. Netw., vol. 4, no. 2, pp. 51- 67, Jul. 2019.

  • X. Yu, J. Zhang, and K. B. Letaief, “Hybrid precoding in millimeter wave systems: How

many phase shifters are needed?” in Proc. IEEE Global Commun. Conf. (Globecom), Singapore,

  • Dec. 2017. (Best Paper Award)
  • X. Yu, J. Zhang, and K. B. Letaief, “A hardware-efficient analog network structure for

hybrid precoding in millimeter wave systems,” IEEE J. Sel. Topics Signal Process., Special Issue

  • n Hybrid Analog-Digital Signal Processing for Hardware-Efficient Large Scale Antenna Arrays, vol.

12, no. 2, pp. 282-297, May 2018.

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Conclusions

 References in this tutorial

  • X. Zhang, A. F. Molisch, and S.-Y. Kung, “Variable-phase-shift-based RF-baseband codesign

for MIMO antenna selection,” IEEE Trans. Signal Process., vol. 53, no. 11, pp. 4091-4103,

  • Nov. 2005.
  • E. Zhang and C. Huang, “On achieving optimal rate of digital precoder by RF-baseband

codesign for MIMO systems,” in Proc. IEEE 80th Veh. Technol. Conf. (VTC2014-Fall), Vancouver, BC, Sep. 2014, pp. 1-5.

  • O. E. Ayach, S. Rajagopal, S. Abu-Surra, Z. Pi, and R. W. Heath, Jr., “Spatially sparse

precoding in millimeter wave MIMO systems,” IEEE Trans. Wireless Commun., vol. 13, no. 3,

  • pp. 1499-1513, Mar. 2014.
  • N. Boumal, B. Mishra, P. A. Absil, R. Sepulchre, “Manopt, a Matlab toolbox for
  • ptimization on manifolds,” The Journal of Machine Learning Research vol. 15, no, 1, pp.

1455-1459, 2014.

  • X. Gao, L. Dai, S. Han, C.-L. I, and R. W. Heath, Jr., “Energy-efficient hybrid analog and

digital precoding for mmWave MIMO systems with large antenna arrays,” IEEE J. Sel. Areas in Commun., vol. 34, no. 4, pp. 998-1009, Apr. 2016.

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Conclusions

 References in this tutorial

  • F. Sohrabi and W. Yu, “Hybrid digital and analog beamforming design for large-scale

antenna arrays,” IEEE J. Sel. Topics Signal Process., vol. 10, no. 3, pp. 501-513, Apr. 2016.

  • Y. Lee, C.-H. Wang, and Y.-H. Huang, “A hybrid RF/baseband precoding processor based
  • n parallel-index-selection matrix-inversion-bypass simultaneous orthogonal matching

pursuit for millimeter wave MIMO systems,” IEEE Trans. Signal Process., vol. 63, no. 2, pp. 305–317, Jan. 2015.

  • L. Liang, W. Xu, and X. Dong, “Low-complexity hybrid precoding in massive multiuser

MIMO systems,” IEEE Wireless Commun. Lett., vol. 3, no. 6, pp. 653–656, Dec. 2014.

  • F. Sohrabi and W. Yu, “Hybrid Analog and Digital Beamforming for mmWave OFDM

Large-Scale Antenna Arrays,” IEEE J. Sel. Areas Commun., vol. 35, no. 7, pp. 1432-1443, July 2017.

  • Z. Feng, S. Fu, T. Ming, and D. Liu, “Multichannel continuously tunable microwave phase

shifter with capability of frequency doubling,” IEEE Photon. J., vol. 6, no. 1, pp. 1–8, Feb. 2014.

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Conclusions

 References in this tutorial

  • A. Alkhateeb, O. El Ayach, G. Leus, and R. W. Heath, Jr., “Channel estimation and hybrid

precoding for millimeter wave cellular systems,” IEEE J. Sel. Topics Signal Process., vol. 8, no. 5, pp. 831-846, Oct. 2014.

  • Z. Gao, C. Hu, L. Dai, and Z. Wang, “Channel estimation for millimeter-wave massive

MIMO with hybrid precoding over frequency-selective fading channels,” IEEE Commun. Lett.,

  • vol. 20, no. 6, pp. 1259-1262, June 2016.
  • A. Alkhateeb, O. El Ayach, G. Leus, and R. W. Heath, Jr., “Hybrid precoding for millimeter

wave cellular systems with partial channel knowledge,” in Proc. Inf. Theory Applications Workshop (ITA), San Diego, CA, 2013, pp. 1-5.

  • M. N. Kulkarni, A. Ghosh, and J. G. Andrews, “A comparison of MIMO techniques in

downlink millimeter wave cellular networks with hybrid beamforming,” IEEE Trans. Commun., vol. 64, no. 5, pp. 1952-1967, May 2016.

  • X. Gao, L. Dai, Y. Sun, S. Han, and C.-L. I, “Machine learning inspired energy-efficient

hybrid precoding for mmWave massive MIMO systems,” in Proc. IEEE Int. Conf. Commun. (ICC), Paris, France, May, 2017, pp. 1-6.

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Conclusions

 References in this tutorial

  • A. Alkhateeb, S. Alex, P. Varkey, Y. Li, Q. Qu, and D. Tujkovic, “Deep learning

coordinated beamforming for highly-mobile millimeter wave systems,” IEEE Access, vol. 6,

  • pp. 37328-37348, 2018.
  • W. Roh et al., “Millimeter-wave beamforming as an enabling technology for 5G cellular

communications: theoretical feasibility and prototype results,” IEEE Commun. Mag., vol. 52,

  • no. 2, pp. 106-113, Feb. 2014.
  • J. Mo, A. Alkhateeb, S. Abu-Surra and R. W. Heath, “Hybrid architectures with few-bit

ADC receivers: Achievable rates and energy-rate tradeoffs,” IEEE Trans. Wireless Commun.,

  • vol. 16, no. 4, pp. 2274-2287, Apr. 2017.
  • Y. Zeng and R. Zhang, “Millimeter Wave MIMO With Lens Antenna Array: A New Path

Division Multiplexing Paradigm,” IEEE Trans. Commun., vol. 64, no. 4, pp. 1557-1571, Apr. 2016.

  • X. Gao, L. Dai, S. Han, C.-L. I, and X. Wang, “Reliable beamspace channel estimation for

millimeter-wave massive MIMO systems with lens antenna array,” IEEE Trans. Wireless Commun., vol. 16, no. 9, pp. 6010-6021, Sep. 2017.

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Conclusions

 Other references

  • A. F. Molisch, V. V. Ratnam, S. Han, Z. Li, S. L. H. Nguyen, L. Li, and K. Haneda, “Hybrid

beamforming for massive MIMO: A survey,” IEEE Commun. Mag., vol. 55, no. 9, pp. 134– 141, Sep. 2017.

  • J. Brady, N. Behdad, and A. M. Sayeed, “Beamspace MIMO for millimeter-wave

communications: System architecture, modeling, analysis, and measurements,” IEEE Trans. Antennas Propag., vol. 61, no. 7, pp. 3814–3827, Jul. 2013.

  • J. Singh and S. Ramakrishna, “On the feasibility of codebook-based beamforming in

millimeter wave systems with multiple antenna arrays,” IEEE Trans. Wireless Commun., vol. 14, no. 5, pp. 2670–2683, May 2015.

  • S. Park, A. Alkhateeb, and R.W. Heath, Jr., “Dynamic subarrays for hybrid precoding in

wideband mmWave MIMO systems,” IEEE Trans. Wireless Commun., vol. 16, no. 5, pp. 2907–2920, May 2017.

  • T. E. Bogale, L. B. Le, A.Haghighat, and L.Vandendorpe, “On the number of RF chains and

phase shifters, and scheduling design with hybrid analog digital beamforming,” IEEE Trans. Wireless Commun., vol. 15, no. 5, pp. 3311–3326, May 2016.

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Conclusions

  • A. Alkhateeb and R.W. Heath, Jr., “Frequency selective hybrid precoding for limited

feedback millimeter wave systems,” IEEE Trans. Commun., vol. 64, no. 5, pp. 1801–1818, May 2016.

  • R. Mendez-Rial, C. Rusu, N. Gonzalez-Prelcic, A. Alkhateeb, and R. W. Heath, Jr., “Hybrid

MIMO architectures for millimeter wave communications: Phase shifters or switches?” IEEE Access, vol. 4, pp. 247–267, Jan. 2016.

  • W. Ni and X. Dong, “Hybrid block diagonalization for massive multiuser MIMO systems,”

IEEE Trans. Commun., vol. 64, no. 1, pp. 201–211, Jan. 2016.

  • T. E. Bogale and L. B. Le, “Beamforming for multiuser massive MIMO systems: Digital

versus hybrid analog-digital,” in Proc. IEEE Global Commun. Conf., Austin, TX, USA, Dec. 2014, pp. 4066–4071.

 Other references

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Thanks

ICCC 2019 Tutorial

For more information and Matlab codes: http://www.eie.polyu.edu.hk/~jeiezhang