Tecniche avanzate di Tecniche avanzate di coco simulazionesimulazioneTecniche avanzate di Tecniche avanzate di coco--simulazionesimulazionenonlinearenonlineare--elettromagneticaelettromagnetica di sistemi di sistemi MIMO e sistemi per il riuso di energia MIMO e sistemi per il riuso di energia MIMO e sistemi per il riuso di energia MIMO e sistemi per il riuso di energia

a radiofrequenza.a radiofrequenza.

Dottorando Francesco DonzelliDottorando Francesco Donzelli

Tutor: Chiar.mo Prof. Ing. Vittorio RizzoliTutor: Chiar.mo Prof. Ing. Vittorio RizzoliProf. Ing. Alessandra CostanzoProf. Ing. Alessandra Costanzo

DEIS

U i i à di B lU i i à di B lUniversità di BolognaUniversità di Bologna

MOTIVATION

Even the most simple link Even the most simple link should be characterized more should be characterized more

The world of The world of Telecommunications is Telecommunications is should be characterized more should be characterized more

and more accurately!and more accurately!growing in complexity growing in complexity as well as sizeas well as size

Electromagnetic couplings among components on an IC or between often not taken

into account!antenna array elements, impedance mismatches, port reflections…

into account!

Nonlinear/EM co-simulation: generalitiesA general view – N Tx – N Rx case

The aim is to include all these features into a system-level approach, by means f d h l l l d f l l l d

Multiple Transmitters Multiple Receivers

of a in-depth circuit-level simulation and a final results validation

I1

NLO

TX

TX

1RX

RX

1

2

Ir

NLOS or

TX

TXTX

2

34

RX

RX

3

2

INR

LOS channelTX 5

4 RX

RX

4

5RX5

Realistic channel description

Nonlinear circuit techniques

descr pt on +

Broadband EM analysis of the antenna array

Nonlinear circuit techniques

I. Nonlinear simulation

Device portsDevice ports••The whole frontThe whole front--end can be divided end can be divided into a linea and a nonlinear into a linea and a nonlinear Device portsDevice portssubnetworks, internally connected by a subnetworks, internally connected by a discrete number of device portsdiscrete number of device ports

••External ports are responsible for External ports are responsible for

Nonlinear Nonlinear subnetworksubnetwork

External ports are responsible for External ports are responsible for external excitations, device external excitations, device polarizations and loadspolarizations and loads••The entire system can be solved by The entire system can be solved by subnetworksubnetwork

vD1ID1 IDN vDN

The entire system can be solved by The entire system can be solved by applying the kirchoff current law (in applying the kirchoff current law (in ωω--domain) domain) at each common device at each common device port The dependent variables can be port The dependent variables can be Linear Linear

subnetworksubnetwork

port. The dependent variables can be port. The dependent variables can be found into a discrete number of state found into a discrete number of state variables.variables.

vE1IE1

IEN vE2External portsExternal portsE(X) = 0E(X) = 0E(X) = 0E(X) = 0F l l F l l F l l F l l Final solving systemFinal solving systemFinal solving systemFinal solving system

Time saving techniquesE(X) E(Xn) + J(Xn) (X – Xn)E(X) E(Xn) + J(Xn) (X – Xn)

X X X X

XXi nn--th approximation of X,th approximation of X,ssnn solution updatesolution update

Xn+1 = Xn + snXn+1 = Xn + snJ(XJ(Xn) jacobian matrix for E(X) jacobian matrix for E(Xi)

Exact NewtonExact Newton--Raphson iteration (HB)Raphson iteration (HB)

sn = - [J(Xn)]-1 E(Xn) sn = - [J(Xn)]-1 E(Xn)

r = E(X ) + J(X ) s ≤ f E(X )r = E(X ) + J(X ) s ≤ f E(X )rrn = n= n--th residual th residual ff f in t m f in t m

Inexact NewtonInexact Newton--Raphson iteration (INHB)Raphson iteration (INHB)

Final solution found by means of Krylov subspaces Final solution found by means of Krylov subspaces remarkable improvement in terms of overall timeremarkable improvement in terms of overall time

rn= E(Xn) + J(Xn) sn ≤ fn E(Xn)rn= E(Xn) + J(Xn) sn ≤ fn E(Xn) ffn = forcing term= forcing term(0 ≤ f(0 ≤ fn < 1)< 1)

Modulated HB Modulated HB –– stationary states periodic seriesstationary states periodic series

t)(jΩt)(Vv(t) kk

k exp~ VVkk(t) = complex time(t) = complex time--varying envelope varying envelope ΩΩkk = k= k--th IM productth IM product

The “embedded” radiation pattern of the pt-th array element

With the assumption of free space propagation With the assumption of free-space propagation, the total radiated field associated with the t-th array

element in the presence of the other ones at ωRF is:

(t)sT,RF

(t)TφRF

(t)TθRF

(t)T );(Aφ);(Aθ

r)jβexp();(E Vωωrω ,,,r, ˆˆ

r

Due to linearity )(Aθ RFωφ;θ,

The radiated field is a linear functional of the complex phasors

of the voltages excitations (t)sTV(1 x NT) complex

)(Aφ RFωφ;θ,

of the voltages excitations sT,Vprow matrices

the j-th entries of the A’s matrices (1 ≤ t ≤ NT) are found by f i EM l i ith ll t t h t performing an EM analysis with all antenna ports short

circuited except for the t-th one that is excited by a unit voltage source.

Channel description by a t i hray tracing approach

NARROWBAND ARRAY: unique multipath pattern for a given q p p genvironment and TX-RX phase center positions

RFDDDt)(q,

T ω;φ,θ,rE RFAAAr ω;φ,θ,rE ),( tq

h θD

RFDDDT ;φ,,

θA

RXTX

q-th ray

Nq scattering

φD φ

RXTX Points

r

qdj

RFDDDt)(q,

TqN

ql

11

t)(q,RFAA

t)(q,r eω;φ,θ,rEAs,..,s,..,sΓ)ω;φ,θ(r,E

φD φA

N

Effects of ray interactionsSpreading factor, s =length of the -th of the q-th path

Phase shift at the r-th receiving element

q p

Excitation of the receiving array associated with the q-th raywith the q th ray

q-th ray incident I. Antenna in receiving modeScattering q th ray nc nt

from the t-th transmitter

receiving modeθA

Scattering Point

)( ω;φθrt)(q,E

R di i f h R di i f h φA

)( RFAA ω;φ,θr,rE

θA’

II. Antenna in transmitting mode

Radiation pattern of the r-th receiving element

ω;'φ'θrE

Radiation pattern of the r-th receiving element

ω;'φ'θrE

By the Reciprocity

A RFAA ω;φ,θRNE RFAA ω;φ,θRNE

2

y p yTheorem:

r-th

φA’

RRFAARF'

A'

At)(q,

sr, Nr1ω;φ,θr,ω;φ,θJ )()(2 t)(q,r

rRNrr EEY

jelement

excitation

Computation of the Channel transfer t imatrix

RXNR NRSuperposition of the

RX1

RXI1

NRAD NNORADray contributions

RXrNonlinear

subnetworkIr

Y ( )AR T

tRAYN

1t

N

1q

t)(q,sr,sr, JJ

RXr subnetwork

IN

1t 1q

• r-th connection port• Nt

RAY : n° of raysN ° f t itt

sR,sR,RFARsR, JVYI ωRXNR

INR• NT : n° of transmitters

sTRFsR VωHJ computation of the

(NR x NT) sT,RFsR, VωHJ(NR x NT) channel transfer matrix

T-domain simulation: a validation procedure

SolutionSolution: : piecewise linear piecewise linear

•Problem:HB and MHB techniques only deal with circuits and systems in piecewise linear piecewise linear

approximationapproximationcircuits and systems in stationary regime condition

NO INFORMATION

I1(t)V (t)

Y(ω) (EM simulation)•Need for a transient analysis

ABOUT TRANSITORY STATES!

V1(t) (EM simulation)Need for a transient analysis validationExtremely challenging for

highly dispersive linear

Unit ramp responses generated by n-port

highly dispersive linear microwave components (filters,

antennas, etc,)

0N N n

ttRtVtVtVYtI

networkRegime state

,01 1 2

11 pnijj j p

pjpjjijni ttRtVtVtVYtI

Convolution process implemented by a module described in SpectreHdl or Verilog-A language (Cadence Systems)

Y(ω) (EM simulation) Behavioural cellview(EM simulation)

A HB l i b lid t d d mpl t d!Any HB analysis can be validated and completed!

E.g. Rectenna transient response -i id l it ti t 2 45GHsinusoidal excitation at 2.45GHz

300

Cadence AWR

-100

0

100

200

Cur

rent

(μA

)

-300

-200

0 0.2 0.4 0.6 0.8 1

Time (ns)

C

Time (ns)

I. 2x2 MIMO link: Near-field couplings…

d 2x2 MIMO link fRF = 2.437 GHz (WLAN band) dfRF 2.437 GHz (WLAN band) Half-wave dipoles Variable d for transmitting

Remarkable pattern deformation due to

antennas

6

8 [V/m]60

90120

deformation due to mutual couplings

5 0

single dipole d=λ/8 d=λ/2d=λ d=4λ

2

4

6

30150

-10-50

(dB

)

-30-20-10

(dB

)

single dipoleand d 4

180 0

25-20-1510

S11

70-60-50-40

S21

d /8d /2d

210

240270

300

330-252.2 2.3 2.4 2.5

Frequency (GHz)

-70

…and influence on transmitter performancesInteractions between transmitting antenna array and nonlinear front end

Strong influence on the gain compression curveg p

single dipole and d=4λ d=λ/8 d=λ/2 d=λ

1 2

1.6

ensi

ty

g p

2

*TT EE MIMO front ends

0.8

1.2po

wer

de

mW

/m2 )

2must always be analysed under the

mpti n f

0.0

0.4

Far-

field

(massumption of

realistic EM behavior

-30 -25 -20 -15 -10

IF power (dBm)

Fbehavior

Optimal antenna spacing: I

NLOS channel (60m) AWGN link analysis with enhanced number of symbols by AWGN link analysis with enhanced number of symbols by

ANN model 1.600000 total samples PIN = -27dBm

1.E-01

1.E+00750,000 bit Optimal

distance:

1 E 04

1.E-03

1.E-02

BE

R

distance: λ/4

1.E-06

1.E-05

1.E-04

0 0.5 1 1.5 2Distanza fra le antenne (in frazioni di λ)

Optimal antenna spacing: IIChannel transfer matrix

Distance between receiving Variable dipole spacing

gantennas = λ /2 (fixed)

Scenario: NLOS (more than 3000 rays)

d=λ/4 d=λOptimal

4.E-06 |H | |H | |H | |H |11 21 12 22 4.E-06 |H | |H | |H | |H |11 21 12 22

2.E-06

3.E-06

2.E-06

3.E-06

0 E+00

1.E-06

0 E+00

1.E-06

0.E+00-1.28 -0.64 0.00 0.64 1.28

Frequency offset (MHz)

0.E+00-1.28 -0.64 0.00 0.64 1.28

Frequency offset (MHz)

Optimal antenna spacing: III

NLOS i i SISO

Input vs Output Power Spectrum Modulation format: 16-QAM

NLOS scenario in SISO case – starting point

Q Signal bit rate = 1.25Mb/sec Envelope oriented Harmonic

Balance TechniqueBalance Technique Equal Gain Combining Technique

-20

0

pect

rum

Input

Output

Remarkable Asimmetrical

-60

-40

d po

wer

sp(d

B) Spectral

Regrowth

-100

-80

Nor

mal

ized

g

-2.5 -1.5 -0.5 0.5 1.5 2.5Frequency offset (MHz)

N

SISO-20

0

ectr

um

Input

OutputBy varying the

-60

-40

zed

pow

er sp

(dB

)

pBy varying the antenna spacing d: MIMO

Worst case…

d=λ -100

-80

-2.5 -1.5 -0.5 0.5 1.5 2.5F ff t (MH )

Nor

mal

iz

-20

0

er sp

ectr

um

Input

Output

Frequency offset (MHz)

-80

-60

-40

mal

ized

pow

e(d

B)

0m

d=λ/4

-100-2.5 -1.5 -0.5 0.5 1.5 2.5

Frequency offset (MHz)

Nor

m

-40

-20

0

wer

spec

trum

B)

Input

Output

100

-80

-60

rmal

ized

pow

(dB

MIMOoptimal case

-100-2.5 -1.5 -0.5 0.5 1.5 2.5

Frequency offset (MHz)

Nor

p

II. RF ENERGY HARVESTING

Growing integration of electronics into human lives and environmentsand environments Paradigm of pervasivity

Micro-/Nano-electronics Micro /Nano electronicsallow for ultra-low powerdesignsdesigns

Sustainability andenergy autonomyenergy autonomy Longer-lifes Avoid bulky batteries Avoid bulky batteries Unprecedented applications

RF harvesting from ambient source has great RF harvesting from ambient source has great potential to inpact on portable device as a whole.

Energy scavenging from common RF SourcesM l d d Many common wireless standards to

be exploited (GSM-900, GSM-1800, UMTS, 802.11,…)

How to proceed?

Rectenna conceptual scheme

CLow-barrier

2. Charge pump circuit1. Patch antenna

Cp

CpSchottky diode SMS7630-001

• full-wave mechanism• easy to realize and integrate full wave mechan sm• best trade off between

complexity and performances

easy to realize and integrate• many different project

strategies!

I prototype: 2x2 patch arrayExtremely performing antenna

Matching section

Extremely performing antenna array (Gain ~ 12 dB) designed for

UMTS uplink band (1.92÷1.98 GHz)

RectifierS11

A common watch has

BUT:• Strictly linearly polarized

radiated farfield, not suitable been switched on by a simple

phone call!

for unpredictable sources• Too large to be converted into

a wearable implementation

II prototype: coplanar rectenna arrayPout1Pout1

Pout ≈ N*Pouti1

2

NPoutN

• Designed for GSM-1800 uplink band• Individually less performing (Gain≈5dB)• Modularity principle exploitedy p p p• Good axial ratio and band• More flexible project!

Main advantage: circular polarizationcircular polarization

Tag antennaEinc RF source

zψ

EINC

ΘΦg

θz

yr

ΦEREIRR

O

xφ

y

Measurements: Pout-DC vs Pinc-RFI prototype II prototype

MEASUREMENTS (3 ELEMENTS)

160180200

ched

1.35 GHz1.36 GHz

MEASUREMENTS (2x2 PATCH ARRAY)

250300 1.73 GHz

1.74 GHz

I prototype II prototype

B t li t

6080

100120140160

out_

DC

on

mat

cL

oad

(uW

) 1.37 GHz1.38 GHz1.39 GHz1.4 GHz

100150200250

out_

DC

(uW

) 1.74 GHz1.75 GHz1.76 GHz1.77 GHz1.78 GHz

Best alignmentbetween source

and tag…

02040

0 1 2 3 4 5 6Pinc (uW/cm^2)

Po

050

10 20 30 40Pinc (uW/cm^2)

P

MEASUREMENTS (3 ELEMENTS)

160180200

ed L

oad

1.35 GHz1.36 GHz1 37 GHz

MEASUREMENTS (2x2 PATCH ARRAY)

250

300

W)

1.73 GHz1.74 GHz1 75 GH

406080

100120140160

ut_D

C o

n m

atch

e(u

W)

1.37 GHz1.38 GHz1.39 GHz1.4 GHz

50

100

150

200

Pout

_DC

(uW 1.75 GHz

1.76 GHz1.77 GHz1.78 GHz

…and worst one

02040

0 1 2 3 4 5 6Pinc (uW/cm^2)

Pou

0

50

10 20 30 40Pinc (uW/cm^2)

The second prototype shows much more versatility towards unknown sources! The second prototype shows much more versatility towards unknown sources!

III prototype: multiresonator aperture coupled antenna

A multiresonator approach is exploited:H1 = 4 mm

0 635 mm

III.

II.

I. Feed lineII. Resonant apertures

0.635 mm I.

III.Patches

• Possibility to scavenge energy from most common wireless standards (GSM900 GSM common wireless standards (GSM900, GSM 1800, 802.11)

• Circular polarization obtained along a huge bandwidthbandwidth

• Compact layout, suitable for wearable implementations

0.9 GHz

1.75 GHz

2.4 GHz

Working principle Isolated antenna

R di i Radiating antenna

Gap-coupled multiband resonator

Performances are up to the most advanced research studies, all

over the bandwidth!400

600

Vdc

[mV

] 0.9GHz

VDC vs RF over the bandwidth!

0

200

-35 -30 -25 -20 -15 -10 -5 0Pav [dBm]

VVDC vs RF Input power

single-frequency

[ ]

600

200

400

Vdc

[mV

]

2.45GHz

R. Vullers,“Energy harvesting for Autonomous Sensor systems”,

Holst center 2009

0-35 -30 -25 -20 -15 -10 -5 0

Pav [dBm]

Rectifier layer

Antenna layer

-50

dB)

numerical modelling measurements

-20-15-10

-5

urn

Loss

(d

14 cm

-30-25

0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3

Ret

u

Frequency (GHz)

600V)

200

400

600

tpu

t (m

V

Measured900-MHz i id t

0

200

0 0 4 0 8 1 2 1 6 2

DC

out Measured

Predictedincident wave

@ 1 t0 0.4 0.8 1.2 1.6 2

Incident power density (uW/cm^2)@ 1-meter

TEXTILE IMPLEMENTATION

A challenging technology conversion, which implies:

II A detailed

I. An overview of

II.A detailed investigation about

antenna performances when bent on curved I. An overview of

suitable electrotextile materials

when bent on curved surfaces with human body characteristics

Electro-textiles: generally created by incorporating created by incorporating

conductive threads into fabrics by means of weaving and knitting

FUTURE DEVELOPMENTS

• A complete t-domain MIMO link characterization pis under progress as we speak

bl T f RF i i • A wearable Tag for RF energy scavenging is about to be fabricated and tested

• The collaboration with VTT Technical Research Centre of Finland will hopefully result in an all-p yembracing integration of our CAD techniques into an MMID sensor project by the next six months.