Multi-User MIMO Wireless System-From Theory to Chip DesignHiroshi Ochi
ochi@cse.kyutech.ac.jp
Dept. of Computer Science and Electronics
Kyushu Institute of Technology, JAPAN1

Background
Smart PhoneAccess
PointStation
Portable GameMIMO System

Wireless LAN:
IEEE802.11ac
IEEE802.11n
IEEE802.11a

PC

 IEEE 802.11a Maximum transmission rate: 54[Mbps]
 OFDM (Orthogonal Frequency Division Multiplexing) IEEE 802.11n Maximum transmission rate: 600[Mbps]
 MIMO (Multiple Input Multiple Output)
 Transmission method with multi-user CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance)

Overall system throughput is reduced by a higher number of users.

 IEEE 802.11ac Maximum transmission rate: more than 1[Gbps]
 Simultaneous communication with multiple users (MU-MIMO).
Copyrights 2012 Ochi Laboratory . All Rights Reserved.

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IEEE802.11ͼͼͼIEEE 802.11
SISO - DSSS
Data Rate: 2Mbps

5th Generation

3rd Generation

1st Generation
ͼͼͼͼ IEEE 802.11ac
ͼ MU-MIMO - OFDM
ͼ Data Rate: 6.9+ Gbps
→ Designing: 1.3 Gbps

IEEE 802.11g/a
SISO - OFDM
Data Rate: 54 Mbps

2st Generation
ͼͼͼIEEE 802.11b
SISO - DSSS
Data Rate: 11 Mbps

4th GenerationͼͼͼIEEE 802.11n
MIMO - OFDM
Data Rate: 600 Mbps

DSSS: Direct Sequence Spread Spectrum
OFDM : Orthogonal Frequency Division Multiplexing
SISO: Single Input Single Output
MIMO : Multi Input Multi Output
MU-MIMO: Multi-User MIMO

Multiple Access in Single User MIMO

AP

t1

User 1t2

User 2

Spatial
DomainTimeDomain

t3

User 3
t4

User 4 Frequency
DomainUser 1

User 2User 3User 4

t1

t2

t3

t4

TDMA (Time Division Multiple Access)
f1

User 1

f2

User 2
APSpatial
Domainf1
f2 User 1
User 2
f3 User3
f4 User 4

f3

User 3f4Frequency
DomainUser 4

FDMA (Frequency Division Multiple Access)

TimeDomain

Multiple Access in Multi User MIMO
SpatialDomain

H1H2User 1 H
4User 2AP

H3H3User 4

User 3User 3
H4H2User 2TimeDomain

User 4

H1

User 1Frequency
DomainSDMA (Spatial Division Multiple Access)MU-MIMO in LTE・LTE Advanced
3GPP E-UTRA
LTE
Release 8
Down
Link

SU-MIMO Up to 4 streams

UpLinkSU-MIMO 1 stream

MUMIMOUp to 2 users(unitary precoding)

LTE Advanced
Release 9Release 10

Up to 4 streams

Up to 8 streams

Up to 4 users(non-unitary precoding)*Under Development

1 stream

Up to 4 streams

MUUp to 8 streams
Up to 8 streams
Under Development
MIMO*Release 8 unitary precoding for up to 2 users is still supported in Release 9 and 10.

ReferenceQinghua Li et al., “MIMO Techniques in WiMAX and LTE:A Feature Overview” IEEE Communication Magazine, May 2010

MU-MIMO in WiMax2(IEEE802.16m)

Sponsor LAN/MAN Standards Committee of the IEEE Computer Society andthe IEEE Microwave Theory and Techniques Society, “Part16: Air Interface
for Broadband Wireless Access Systems”, 6th May 2011.

IEEE 802.11ac Specification

Copyrights 2012 Ochi Laboratory . All Rights Reserved.

8Wide bandwidth

80MHz
TGac規格
20MHz
11a規格

40MHz
11n規格
frequency

20MHz40MHz

40MHz80MHz

PHY Specification
PARAMETER

11ac draft
Mandatory

11ac draft
Optional

Number of Antenna

1-2 (non AP/AP)

5-8

MCS

0-7

8-9 (256-QAM)

Packet Mode

Legacy mode
(V)HT Mixed mode

Legacy mode
(V)HT Mixed mode

Number of subcarrier

52 /56/114/242

52 /56 /114/242/484

Bandwidth

20/40/80 [MHz]20/40/80/160/80+80 [MHz]-Short G.I.
TX Beamforming
MU-MIMO
LDPC, STBC

6.0 – 292.5 [Mbps]

6.0 – 6933.3 [Mbps]

Other

Transmission RateCopyrights 2012 Ochi Laboratory . All Rights Reserved.

10

IEEE802.11TGac International Standardization
 Sameer Vermani, Lin Yang, Richard van Nee, Thet Htun Khine, Leonardo Lanante,Yuhei Nagao, Vinko Erceg, Eldad Perahia, Youhan Kim, Hongyuan Zhang, Sudhir
Srinivasa, “Phase Rotations for 80 MHz”, IEEE802.11-10/1083r0, Sep., 2010.



In 80MHz transmission, the phase rotations to be used in each 20 MHz sub-band.
Phase rotation pattern should achieve low PAPR and backward compatibility with 11a/n.

-128
2012/2/22

20MHz20MHz20MHz20MHzr-r-r-r-640
Subcarriers #64127

Copyrights 2012 Ochi Lab., Kurosaki Lab, Miyazaki Lab., Kuroki Lab. All Rights Reserved.

11 Jun Zheng, Vinko Erceg, Sameer Vermani, Hongyuan Zhang, Eldad Perahia, YouhanKim, Uikun Kwon, Yongho Seok, Brian Hart, Sean Coffey, Vish Ponnampalam, George
Vlantis, Thet Htun Khine, Leonardo Lanante, “Legacy CSD Table for 11ac”,
IEEE802.11-10/1301r0, Nov., 2010.
CSD is a simple way to avoid unintentional beamforming that causes large variations inreceive power.

2012/2/22

Copyrights 2012 Ochi Lab., Kurosaki Lab, Miyazaki Lab., Kuroki Lab. All Rights Reserved.

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MU-MIMO Key TechnologyPre-Coding

BackgroundAP

Spatial Division Multiplexing Access (SDMA)

User 1

Advantage

User 2

 AP can transmits data simultaneously to multiple users inthe same frequency band.

PrecodingUser 3

Disadvantage
 An Inter User Interference (IUI) occurs.

Precoding techniques cancel IUI.

IUIUser 4(Inter User Interference)Linear precoding - Low complexity, Low data rate (capacity) Channel Inversion
 Block Diagonalization]Non-linear precoding - High complexity, High data rate (capacity)
 Tomlinson Harashima Precoding Vector Perturbation

Research ThemeImproving transmission performance by using new precoding algorithm
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Copyrights 2011 Ochi Laboratory . All Rights Reserved.

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Linear Precoding

Channel Inversion
APPrecoding

Normalize

H −1u

γ CI

1Hxy

User 2sTransmitter
Transmit symbol
Precoded symbol
Transmit signal(Normalizedprecoded symbol)

Receiveru

Receive signal−1

y = Hx + n =1

AWGN noise

s=H u
x==

Normalization Gain

User 1γ CI
1γ CIγ CI = ss=−1H u
21γ CI1γ CIHH −1u + nu+n

Decoding Process Noise Enhancement Gainyˆ = γ CI y = u + γ CI n

Copyrights 2011 Ochi Laboratory . All Rights Reserved.

16

Multi User MIMO model
Normalization in TX
 Why should we normalize transmit power?
Transmit signal power is limited by Wireless LAN standards

Block Diagonalization
uPowerNormalized

x11

y11

x12

y12

x21

y21

x22

y22

User 1
u: Transmitted Signal
y : Received Signal

User 2In
Inmulti-user
multi-usercommunication,communication,timetimeand
andfrequency
frequencyare
areusedusedsimultaneouslysimultaneouslyby
bysomesomeusers.
users.
Received symbol
IUI (Inter-User Interference)y = Hx y11   h11
  y 1   y12  h21
y  =  y  = h2131
 2 y 22  h41

h12

h13

h22
h32

h23
h33

h42

h43

h14   x11 user 1
h24   x12 h34   x 21    user 2
h44   x 22 

Copyrights 2012 Ochi Laboratory . All Rights Reserved.

Without MU-MIMO Precoding,each user will receive interference
from all other users

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Block Diagonalizationuu

Wt

Power
Power
Normalized
Normalizedx11

y11x12y12x21

y21

x22

y22

User 1
Wt : Precoding Matrix

User 2In
Inmulti-user
multi-usercommunication,communication,time
timeandandfrequency
frequencyare
areusedusedsimultaneously
simultaneouslyby
bysomesomeusers.
users.

x = Wt uIEEE 802.11ac System

Received symbol

y = Hx = (HWt ) u IUI is removed

 y11   h11
  y 1   y12  h21
y  =  y  =  021
 2 y22  0h12h2200

IUI can be removed by precoding matrix0   u11 00   u12  Precoding Matrix Generation Method
1. Obtaining Channel Information
h33 h34  u 21  
2. Calculating Precoding Matrix
h43 h44  u 22 
• Channel Inversion
Copyrights 2012 Ochi Laboratory . All Rights •Reserved.
Block Diagonalization 19190

Nonlinear Precoding

Tomlinson Harashima Precoding (THP) QR Decomposition (QRD)

H H = QR
(H = Q(R ) )−1(We assume that M = K ) Q1,1 L Q1, K Q= MOM QK ,1 L QK , K H −1 R1,1 L R1, K R=OM 
 0RK , K 

 D1,10   R1,10  
D=OO
= 0
DK , K   0RK , K 

A decomposition of the matrix into an unitary matrix and an upper triangular matrix.
Q Modulo Operation
 z +τ / 2 fτ (z ) = z − τ τ 

The modulo operation lets I-ch andQ-ch of signals go into the range oforiginal symbol mapping. [- τ /2, τ /2)

uRestrain transmission power

H −1QRDτI(τ is a symbol mapping width) Tomlinson Harashima Precoding
AP−τ

ModuloSymbol mapping (QPSK)

ModuloNormalize
ModuloCopyrights 2011 Ochi Laboratory . All Rights Reserved.

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Vector Perturbation
Vector Perturbed symbol
Precoded symbol
Thus, vector perturbation techniqueminimizes the signal power andhence has higher capacity
Transmit symbol

Choose l such thatthe norm of s is
minimized

Vector Perturbationl = arg min γl′= arg min H (u + τl′)−12l′QExampleNumber of transmit antenna : 4
Number of Constellation set : 9
Needed iteration forfinding optimal
perturbation vector

49 = 6561

ISimulation Results
Nm/Nc are the tradeoff
parameters of theproposed algorithm andQRDME respectively

The proposed algorithm has
roughly the same performancecompared to QRDMEThe complexity
comparisons are seen on thenext slide11ac System RTL Design

Copyrights 2012 Ochi Laboratory . All Rights Reserved.

25

4x[2 2] MU-MIMO System for 11ac

Copyrights 2012 Ochi Laboratory . All Rights Reserved.

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4x[2 2] MU-MIMO System for 11ac

27

4x[2 2] MU-MIMO System for 11ac28Synthesis Target
4x[2 2] MU-MIMO System Synthesis Target
FPGAVirtex 5XC5VSX240T
149760 LUTs andregisters

画像：http://www.inrevium.jp/data/board/TD-BD-SPP3000-090402.pdf
Copyrights 2012 Ochi Laboratory . All Rights Reserved.

29

SoC Architecture for 11n

30

Synphony HLS

31

Synthesis Result
TransmitterRegister

LUTs

RAM

PSDU

248

6320

Scrambler

32320

Encoder Parser

12300

Convolutional Encoder

58700

Spatial Stream Parser

688

5506

0Interleaver

2690

3532

32M=312Constellation Mapper

1528680Pilot Inserter

642780Spatial Mapper

1225

26448

1IFFT (4 parallel)

10710

34795

36B=17

GI Inserter

50

402

36B=10Windowing

3262

11665

0Total

19192

84258

Copyrights 2012 Ochi Laboratory . All Rights Reserved.

32Synthesis Result
ReceiverRegister

LUTs

RAM

GI Remover

111

268

32X1D=16,16B=1

FFT (2 parallel)

5362

17420

36B=9

Channel Estimator

687

2783

36B=8

MU-MIMO Decoder

2169

32131

0

Demapper92

1518

0DeInterleaver

1150

2290

32M=156,
36B=2

Spatial Stream Deparser

237

463

0Encoder Deparser

15150

Scrambler

28

190Total

9761

56907

Copyrights 2012 Ochi Laboratory . All Rights Reserved.

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Synthesis Results
ReceiverRegister

LUTs

Max Frequency

SVD

2641

28552

81.7 MHzV Compression

1035

8591

74.3 MHz

Block Diagonalization

931

18904

109 MHz

Final goal of this project is the ASIC implementation running at
240 MHz. SVD and V compression might need further
modification to meet this timing.

Copyrights 2012 Ochi Laboratory . All Rights Reserved.

34

Demonstration EnvironmentWe use the four boards for IEEE802.11n 2x2 WLAN implementation

35

RF Experiments

Constellation Comparisons
受信機

FFT

ADC

DAC

ストリーム1

送信機

FFT

ADCDAC

ストリーム2

信号点配置

MIMO復号器

送信信号時間波形

64QAM

Spectrum Mask
 Satisfy IEEE802.11n Spectrum Mask
 fc=5.24GHz，BW=20MHz
IEEE802.11n transmit spectral mask

-20dB
-8dB

-45dB

Center freq. 5.2400GHz
10MHz/div

IEEE802.11n 2x3MIMO Chipby Radrix co.ltd

Conclusion & Future work Conclusion
We have presented our hardware design of a 1.3Gbps
802.11ac MU-MIMO system its synthesis result on FPGA.
Some blocks such as the viterbi decoder, and MU-MIMO
related blocks are still work in progress either to reducecomplexity or meet timing.

 Future work
FPGA prototype
MU-MIMO Experimental validation

Copyrights 2012 Ochi Laboratory . All Rights Reserved.

40

Reference[1] T.H. Tran, A. Ardiansyah, N. Surantha, Y. Nagao, M. Kurosaki, H.
Ochi,”Design and ASIC Implementation of 600Mbps IEEE 802.11n 4x4
MIMO OFDM System,” IEICE Society Conference 2011, Hokkaido, Japan,
Sept.2011[2] IEEE 802.11ac, specification framework document. IEEE 802.1109/0992r21, January 2011.
[3] IEEE 802.11n-2009 part 11: Wireless LAN medium access control (MAC)and physical layer (PHY) specifications.
[4] Q.H., Spencer, ”An introduction to the multi-user MIMO downlink”, IEEECommunications Magazine, Vol. 42, Issue 10, 2004
[5] E. Perahia, R.Stacey, Next Generation Wireless LANs: Throughput,Robustness, and Reliability in 802.11n, Cambridge University Press, 2008.
[6] Q. H. Spencer, A. L. Swindlehurst, and M. Haardt, ”Zero-Forcing Methods
for Downlink Spatial Multiplexing in Multi-User MIMO Channels”, IEEE
Trans. Sig. Proc., vol. 52, 2004
Copyrights 2012 Ochi Laboratory . All Rights Reserved.

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Published Paper List
 Leonardo Lanante Jr., Arumjeni Mitayani, Yuhei Nagao, Masayuki Kurosaki, Hiroshi Ochi,"Packet Delayed Lattice Reduction Algorithm for High Performance MIMO Decoder" IEEE
Wireless Communications and Networking Conference (WCNC 2012), Paris France, April
2012, pp 236-240
 Yuya Miyaoka, Yuhei Nagao, Masayuki Kurosaki, and Hiroshi Ochi, "Sorted QR
Decomposition for High-Speed MMSE MIMO Detection Based Wireless Communication
Systems," Proc. 2012 IEEE International Symposium on Circuits and Systems (ISCAS2012),
pp. 2857--2860, Seoul, Korea, May 20-23(23), 2012
 Thi Hong Tran, Leonardo Lanante, Yuhei Nagao, Masayuki Kurosaki, Hiroshi Ochi, “Hardware
Implementation of High Throughput RC4 Algorithm,” 2012 IEEE International Symposium onCircuits and Systems (ISCAS-2012), Korea, May 2012 pp. 77-80.
 Muneaki Matsuo, Masayuki Kurosaki, Akio Miyazaki and Hiroshi Ochi, "JPEG 2000 Image
Transmission using Encryption Domain Authentication by Paillier Cryptosystem," IEEE
International Conference on Communications(ICC) 2012, Ottawa, Canada, June. 14 2012.
 Leonardo Lanante Jr., Shogo Fujita, Yuji Yokota, Yuhei Nagao, Baiko Sai, Masayuki Kurosaki,Hiroshi Ochi, "Hardware Design of 1.3Gbps Multi-User MIMO System for IEEE802.11ac"
IEEE Vehicular Technology Society(VTS) Asia Pacific Wireless Communications
Symposium(APWCS) 2012, Kyoto, Japan, August , 2012
 Thi Hong Tran, Yuhei Nagao, Masayuki Kurosaki, Hiroshi Ochi, Baiko Sai, “Model-based
Design Method for Wireless System VLSI with Synopsys Synphony Tool,” The 2nd Solid-State
Systems Symposium - VLSI & Related Technologies (4S), Vietnam, Aug. 2012, pp. 283-289.
 Shogo Fujita, Leonardo Lanante Jr., Yuhei Nagao, Masayuki Kurosaki, and Hiroshi Ochi,"Modified Tomlinson Harashima Precoding Using Square Root for Multi-User MIMO
Systems", IEEE Vehicular Technology Conference(VTC) 2012-Fall, Quebec, Canada, Sep.
2012.

MU Beamforming Process AP announce MU transmission, then send training frames
 STAs calculate their Compressed V Feedbac and send back to AP. The compressed
V Feedback is computed as follows
 Compute V component of channel matrix using SVD
 V matrix compression using series of Givens rotation
 AP compute beamforming weight by using received CSI from each STAs.
 Decompress Received CV matrix
NDPA : Null Data Packet AnnouncementNDP: Null Data Packet
 Compute Block Diagonalization
SP: Sounding Poll
Weight matrix
MU-MIMO able

AP
STA1
STA2

NDPA

NDP

SP

Beamforming

CVF
Compressed V feedback
CVF
Copyrights 2012 Ochi Laboratory . All Rights Reserved.

43

IEEE802.16m Specifications
IEEE 802.16e

IEEE802.16m
必須

目標

周波数

2.3GHz,2.5GHz,3.3-3.8GHz(1GHz,) 2.3GHz, 2.5GHz, 3.3-3.8GHz

帯域幅

3.5, 5, 7, 8.75, 10MHz5, 10, 20, 40MHz

変調方式

OFDM(256), OFDM(2048), QPSK, 16QAM, 64QAM

最大伝送速度(DL)

64Mbps（2×2、チャネル帯域が10MHzの時）

160Mbps以上（2×2、チャネル帯域が20MHzの時）300Mbps以上（4×4、チャネ
ル帯域が20MHzの時）

最大伝送速度(UL)

28Mbps（2×2、MIMO使用時、チャネル帯域が10MHzの時）

56Mbps（1×2、チャネル帯域が20MHzの時）

112Mbps（2×4、チャネル帯域が20MHzの時）

2×2 MIMO

2×2 MIMO

2×4, 4×2, 4×4, 8×8
MIMO

1×2 MIMO

1×2 MIMO

1×4, 2×2, 2×4 MIMO

MIMO設定(DL)MIMO設定(UL)[1]
2012/11/6

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Reserved.

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