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Designing Multi-User MIMO for Energy Efficiency Emil Björnson ‡* Joint work with: Luca Sanguinetti ‡§, Jakob Hoydis †, and Mérouane Debbah ‡ ‡ Alcatel-Lucent.

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Presentation on theme: "Designing Multi-User MIMO for Energy Efficiency Emil Björnson ‡* Joint work with: Luca Sanguinetti ‡§, Jakob Hoydis †, and Mérouane Debbah ‡ ‡ Alcatel-Lucent."— Presentation transcript:

1 Designing Multi-User MIMO for Energy Efficiency Emil Björnson ‡* Joint work with: Luca Sanguinetti ‡§, Jakob Hoydis †, and Mérouane Debbah ‡ ‡ Alcatel-Lucent Chair on Flexible Radio, Supélec, France * Dept. Signal Processing, KTH Royal Institute of Technology, Sweden § Dip. Ingegneria dell’Informazione, University of Pisa, Pisa, Italy † Bell Laboratories, Alcatel-Lucent, Stuttgart, Germany Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH)1 When is Massive MIMO the Answer?

2 Outline Presentation is based on E. Björnson, L. Sanguinetti, J. Hoydis, M. Debbah, “Designing Multi-User MIMO for Energy Efficiency: When is Massive MIMO the Answer?,” Submitted IEEE WCNC 2014 Preprint available on arXiv: Main Question -How should a single-cell downlink system be designed to maximize energy efficiency? -Optimization variables: Number of base station antennas Number of active user equipments Data rate guaranteed per user Conclusions -Result depends strongly on physical layer precoding scheme -Unconventionally many users and antennas can be optimal! Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH)2

3 Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH)3 Introduction

4 What are the Expectations? Tons of Plenary Talks and Overview Articles -Fulfilling dream of ubiquitous wireless connectivity Expectation: Many Metrics Should Be Improved in 5G -Higher user data rates -Higher area throughput -Great scalability in number of connected devices -Higher reliability and lower latency -Better coverage with more uniform user rates -Improved energy efficiency These are Conflicting Metrics! -Impossible to maximize all metrics simultaneously -Our goal: High energy efficiency (EE) with uniform user rates Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH)4

5 Multi-User MIMO System Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH)5 Space-division multiple access (SDMA)

6 Multi-User MIMO System (2) Cell: Area with user location and pathloss distribution Scheduling: Pick users randomly, with random location Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH)6 Some UE Distribution

7 How to Measure Energy Efficiency? Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH)7

8 Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH)8 System Model: Average Sum Throughput

9 Time-Division Duplex (TDD) Protocol Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH)9 Assumption: Perfect estimation

10 Average Sum Throughput Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH)10 Cost of estimation Average over channels and user selection Signal-to-interference+noise ratio (SINR)

11 Impact of Precoding Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH)11 Maximize signal Minimize interference Balance signal and interference

12 Uniform User Performance Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH)12

13 Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH)13 System Model: Power Consumption

14 Reasonable Power Consumption Model Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH)14

15 Reasonable Power Consumption Model (2) Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH)15

16 Reasonable Power Consumption Model (3) Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH)16

17 Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH)17 Optimize System Parameters for Energy Efficiency

18 Preliminaries Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH)18

19 Optimal Number of BS Antennas Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH)19

20 Optimal Transmit Power Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH)20 Theorem 2 (Optimal )

21 Optimal Number of Active UEs Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH)21

22 Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH)22 Numerical Illustrations

23 Simulation Scenario Main Characteristics -Circular cell with radius 250 m -Uniform user distribution with 35 m minimum distance -Uncorrelated Rayleigh fading, typical 3GPP pathloss model Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH)23

24 Optimal System Design: ZF Precoding Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH)24

25 Optimal System Design: MRT Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH)25 Single-user transmission! Only exploit precoding gain

26 Why This Huge Difference? Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH)26 Only 2x difference in EE 100x difference in throughput

27 Energy Efficient to Use More Power? Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH)27 Essentially linear growth

28 Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH)28 Conclusions

29 What if a Single-Cell System Designed for High EE? -Need: Reasonable throughput model -Need: Reasonable power consumption model Contributions -General power consumption model -Closed-form results for ZF: Optimal number of antennas Optimal number of active UEs Optimal transmit power -Observations: More circuit power  Use more transmit power Numerical Example -ZF/RZF precoding: Massive MIMO system is optimal -MRT precoding: Single-user transmission is optimal -Small difference in EE, but huge difference in throughput! Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH)29

30 Greentouch Open Forum, Designing Multi-User MIMO for Energy Efficiency, E. Björnson (Supélec & KTH) Thank You for Listening! Questions? Main reference: E. Björnson, L. Sanguinetti, J. Hoydis, M. Debbah, “Designing Multi-User MIMO for Energy Efficiency: When is Massive MIMO the Answer?” Submitted IEEE WCNC 2014 Preprint available on arXiv:


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