a study on improved algorithm for mimo antenna measurement

SRANT Lab., Korea Maritime University

A Study on Improved Algorithm for MIMO Antenna Measurement

Thanh-Ngon Tran

Supervisor: Professor Kyeong-Sik Min

SRANT Laboratory, Korea Maritime University

November, 2006

Master Thesis

2SRANT Lab., Korea Maritime University

Contents

Chapter 1: Introduction Chapter 2: Algorithm of antenna measurement

software with noise reduction Chapter 3: Measurement of key parameters of

MIMO antenna Chapter 4: Design of multi-band MIMO test-bed Chapter 5: Conclusion


Introduction (1)

Cordless phone

Voice

Wireless LANHigh Data rate

Home/office systems

Multi-media

Channel capacity increase

Voice/DataMobile phone

Single Antenna

Single Antenna

Single/Multiple Antenna

Multiple Antenna

Antenna development vs. Antenna measurement system

Chapter 1


Introduction (2) – The goal and limitation

The goal: Develop measurement software & system for MIMO antenna & channel measurement.

Apply the improved mea.

software for MIMO ant. mea.

Improve single antenna measurement

software

Design 22 MIMO testbed

for MIMO measurement

Future works

Diversities, Correlation,

Mutual Coupling

Gain, 2D/3D pattern,

Polarization, w/ Filter algorithm

Direct up/down converters,

Software structure and algorithm

MIMO antenna and

channel characterizat

ion

(1) (2) (3) (…)Steps:

Chapter 1


Single antenna measurement system

EL-AZ Positioner

Positioner Controller

Microwave Receiver

CW Signal Generator

Directional Coupler

Frequency Converter

Polarization Positioner

Computer

Linear Polarization

Antenna

Antenna Under Test

GPIB GPIBMicrowave Amplifier

Chapter 2


Previous Software vs. New Software

There are two independent programs Gain Radiation Pattern

This program is not divided in specific functions Simple structure When there are

changes, whole program have to be changed

Chapter 2

Ref.: Young-Hwan Park, “A study on construction of antenna measurement environment,” Master Thesis, Korea Maritime University, Feb. 2005

The program can be modified easily when equipment is changed. 4 measurement functions: gain, 2D and 3D pattern, polarization. New algorithm for noise reduction


Software algorithmChapter 2

Layer 4Graphic user

interface

Layer 3Data processing

Layer 2Equipment interface

Layer 1GPIB interface of computer (DLL)

Layer 1GPIB interface of

Equipment

Equipment processor

GPIB

Equipment CommandsCommand sets

in text file

Software structure

Enter measurement parameters (layer 4)

Start measurement

Process input parameters (layer 3)

Send commands to equipments and receive

data (layer 2&1)

Process measurement data (layer 3)

Display data (layer 4)

End

Software flowchart


TX-RX Antenna in anechoic chamber

TX Ant

AUT

4m

Chapter 2

For experimental measurement:

TX Ant.: Horn antenna, 1-18 GHz

RX Ant.: Helical antenna, ~ 3 GHz

Distance: ~4 meter


Measurement Results with filter algorithm

Original Signal (pattern)

Measured by conventional measurement system

Filtered Signal (pattern)

Measured and processed real-time by noise reduction algorithm

Chapter 2

-100-95-90-85-80-75-70-65-60-55-50

0 50 100 150 200 250 300 350Angle (degree)

Pow

er L

evel

(dB

)

Time 1

Time 2

-100-95-90-85-80-75-70-65-60-55-50

0 50 100 150 200 250 300 350Angle (degree)

Pow

er L

evel

(dB

)

Signal processing algorithm


Noise Reduction Algorithm Combination of time and space mean filter Noise in measurement system is Additive White

Gaussian Noise (AWGN) Mean filter is suitable for removing AWGN

d[j-1]d[j-W/2]

d[j] d[j+1]d[j+W/2]

Angle[degree]

Power[dB]

Space Mean FilterTime Mean Filter

2

2

][1

][

Wi

Wij

jdW

iD

N

jjtid

NiD

1

],[1

][

d[i-1]d[i, tj]

d[i+1]

Angle[degree]

Power[dB]

d[i, tj+1]

Time[ms]

d[i, tj+1]

d[i, tj+N]

],[],[],[ jjj tintiDtid

Measured Power

Expected Power

Noise

Chapter 2


MIMO antenna measurement

Metal box, PDA-size with 4 IFA antennas(PDA: Personal Data Assistant)

(a) Front view (b) Inside view

Measure and evaluate: Diversities: pattern, polarization. Pattern correlation. Mutual coupling.

Chapter 3

#1

#2#3

#4

75 mm

110

mm

7 m

m

z

y

x

This EUT is chosen because it is: One of MIMO appli-cation. Elements have differ-ent polarization, pattern, gain, coupling …


Pattern (gain) diversityChapter 3

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Element #1Element #2 Element #3Element #4

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Gain of antenna elements on x-y plane

Gain of antenna elements on x-z plane

Gain of antenna elements on y-z plane

x

yz

x

z

y

#4 is the best choice#3 is the best choice #1 is the best choice

#2 is thebest choice

Maximum gain of EUT antenna elements on three planes is about 6 dBi (y-z plane). In any direction, there is at least one element with high gain. Difference between the

highest and lowest gain is higher than 3 dB at any direction. Conclusion: This difference of gain pattern shows good gain diversity.


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E-theta E-phi

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E-theta E-phi

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E-theta E-phi

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E-theta E-phi

Polarization diversityChapter 3

Element #1 and #4: linear horizontal polarization. Element #2 and #3: linear vertical polarization. Conclusion: Good the polarization diversity.

Element #1, x-z planeXPD = 22dB @ 178o

Element #4, x-z planeXPD = 20dB @ 183o

Element #2, x-y planeXPD = 20dB @ 89o

Element #3, x-y planeXPD = 20dB @ 268o

dBcrossdBcocross

co EEE

EXPD log20 Eco and Ecross are

co-polarization and cross-polarization components of E-field, respectively.

x

yz

x x

y z

x


Pattern Correlation

Elements

x-y plane x-z plane y-z plane x-y plane x-z plane y-z plane

#1 and #2 0.103 0.426 0.022 0.331 0.222 0.175

#1 and #3 0.152 0.481 0.260 0.071 0.131 0.269

#1 and #4 0.100 0.616 0.352 0.382 0.607 0.073

#2 and #3 0.486 0.822 0.198 0.107 0.847 0.027

#2 and #4 0.196 0.616 0.085 0.186 0.118 0.244

#3 and #4 0.147 0.543 0.270 0.110 0.343 0.139

E E

Chapter 3

359

0

359

0

222

211

359

02211

)][()][(

)][)(][(

i i

ic

EiEEiE

EiEEiE

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E-theta E-phi

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330

E-theta E-phi

x

y

x

y

Element #2, x-y plane Element #3, x-y plane


Mutual Coupling Measurement

Frequency (GHz)

5.0 5.1 5.2 5.3 5.4 5.5

Mu

tual

cou

pli

ng

(dB

)

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-15

-10C12

C13

C14

C23

Chapter 3

MW Receiver & Freq. converter

EUT


MIMO TestbedChapter 4

Block diagram of 22 MIMO testbed FPGA:

APEX-20K600

Output

CPU: SH-4 (SH7750)

OS: NetSBD

Analog (RF)

DACI/O

DAC: DAC904

FPGA: APEX-20K600

Input

Direct Up-converter

1

Direct Up-converter

2

TX Ant. 1

TX Ant. 2

I1

I2

Q1

Q2

T C P / I P

N e t w o r k

FPGA: APEX-20K600

Output

CPU: SH-4 (SH7750)

OS: NetSBD

Analog (RF)

ADCI/O

ADC: SPT7938

FPGA: APEX-20K600

Input

Direct Down

converter 1

Direct Down

converter 2

RX Ant. 1

RX Ant. 2

I1

I2

Q1

Q2

Windows PC

Brains Co. - DA System

Brains Co. - AD System

• Freq.: 1.8 – 5.8 GHz

• Use direct-conversion technique for analog RF circuits

• RF analog circuits are coupled with DSP algorithm


RX - Design of Down-converter

FPGA: APEX-20K600

Output

CPU: SH-4 (SH7750)

OS: NetSBD

Analog (RF)

DACI/O

DAC: DAC904

FPGA: APEX-20K600

Input

Direct Up-converter

1

Direct Up-converter

2

TX Ant. 1

TX Ant. 2

I1

I2

Q1

Q2

T C P / I P

N e t w o r k

FPGA: APEX-20K600

Output

CPU: SH-4 (SH7750)

OS: NetSBD

Analog (RF)

ADCI/O

ADC: SPT7938

FPGA: APEX-20K600

Input

Direct Down

converter 1

Direct Down

converter 2

RX Ant. 1

RX Ant. 2

I1

I2

Q1

Q2

Windows PC



Design the wide bandwidth direct down-conversion receivers by:

Combine the analog front-end circuit with base-band DSP

Freq.: 1.8 – 5.8 GHz

Analog front-end

Baseband DSP

Bandwidth is Wider

RF LNA

I

Q

Quadrature down-converter

90° LO

A

B

LPF

LPF

A/D

A/D

DSP

xLO,I (t) = cos(2p fC t)

xLO,Q (t) = – gsin(2p fC t + )

xI (t)

xQ (t)

Analog front end circuit is simpler

LORF

Q

12

3

Phase shifterMixer

Baseband Amp.

Power div. I

Chapter 4


0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

2.00

1.6 2.0 2.4 2.8 3.2 3.6 4.0 4.4 4.8 5.2 5.6 6.0

Frequency (GHz)

Am

plit

ude

Imba

lanc

e

Simulation

Measurement

5% amplitude imbalance

Imbalance parameters

-90.00

-70.00

-50.00

-30.00

-10.00

10.00

30.00

50.00

70.00

90.00

1.6 2.0 2.4 2.8 3.2 3.6 4.0 4.4 4.8 5.2 5.6 6.0

Frequency (GHz)

Pha

se I

mba

lanc

e (d

egre

e) Simulation

Measurement

Conventional bandwidth: 0.25 GHz

(5o imbalance)

Chapter 4


RX - I/Q signalsChapter 4

Lissajuos graph of the I and Q signal at 1.8 GHz

V_Q (Volts)

Measured sig.Processed sig.Reference sig.

V_I

(V

olts

)

Frequency: 1.8 GHz

Amp. imbalance: 0.898

Phase imbalance: -75.74 degree


V_Q (Volts)


V_I

(V

olts

)

Frequency: 4.0 GHz


Phase imbalance: -13.25 degree


V_Q (Volts)


V_I

(V

olts

)

Frequency: 5.6 GHz


Phase imbalance: 44.50 degree

I

Q

A/D

A/D

xI (t)

xQ (t)+

cos

1

g

cos

sin

DSP

'Iz

'Qz


TX - Design of Up-converter

FPGA: APEX-20K600

Output

CPU: SH-4 (SH7750)

OS: NetSBD

Analog (RF)

DACI/O

DAC: DAC904

FPGA: APEX-20K600

Input

Direct Up-converter

1

Direct Up-converter

2

TX Ant. 1

TX Ant. 2

I1

I2

Q1

Q2

T C P / I P

N e t w o r k

FPGA: APEX-20K600

Output

CPU: SH-4 (SH7750)

OS: NetSBD

Analog (RF)

ADCI/O

ADC: SPT7938

FPGA: APEX-20K600

Input

Direct Down

converter 1

Direct Down

converter 2

RX Ant. 1

RX Ant. 2

I1

I2

Q1

Q2

Windows PC



RF AMP

I

Q

Quadrature up-converter

90°LO

A

B

LPF

LPF

D/A

D/A

DSP

xLO,I (t) = cos(2p fLO t)

xLO,Q (t) = – gsin(2p fLO t + )

xI (t)

xQ (t)

LPF

Analog front-end circuit is coupled with DSP algorithm to compensate the imbalance characteristics of analog circuit (as in down converter).

LO leaky is controlled by bias voltage on MIXER chips.Measurement setup

Up converter circuit

LORF

QPhase shifterMixer

Power combiner

I

Chapter 4


Leaky signal suppression

RF AMP

I

Q


90°LO

A

B

LPF

LPF

D/A

D/A

DSP



xI (t)

xQ (t)

LPF

fLO + f0fLO – f0 fLO fLO + f0fLO – f0 fLO

Desired signal

Desired signal

Sideband leakage

Carieer leakage

Carieer leakage

Sideband leakage

Spectrum of output signal before and after imbalance compensation

Suppressed by

controlling amplitude and phase coefficient

Suppressed by

controlling bias voltage on MIXER

chips

Chapter 4


Measurement results of output spectrum

RF AMP

I

Q


90°LO

A

B

LPF

LPF

D/A

D/A

DSP



xI (t)

xQ (t)

LPF

Spectrum of output signal without I/Q imbalance compensation at 3.0 GHz

Spectrum of output signal with I/Q imbalance compensation at 3.0 GHz

I-Channel: 0.402VDC + 0.142Vac, phase = 0o

Q-Channel: 0.308VDC + 0.150Vac, phase = 112.3o

Spectrum of output signal without I/Q imbalance compensation at 5.0 GHz

Spectrum of output signal with I/Q imbalance compensation at 5.0 GHz

I-Channel: 0.239VDC + 0.120Vac, phase = 0o

Q-Channel: 0.638VDC + 0.122Vac, phase = 73.9o

Chapter 4


Conclusion and future study

Development of measurement software & system for MIMO antenna & channel measurement is divided into 3 steps with the good experiments results: Improve single antenna measurement software:

Gain, 2D/3D pattern, polarization with noise reduction. Apply the improved measurement software for MIMO

antenna measurement: Diversities, Correlation, Mutual Coupling.

Design 22 MIMO testbed for MIMO measurement. Direct up/down converter, system design.

Future study: Develop algorithm for MIMO antenna and channel characterization.


THANK YOU FOR YOUR ATTENTION!

a study on improved algorithm for mimo antenna measurement

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