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Abstract— Thhen subjected gma (ΔΣ) upc

ven-quantisatiomprovement indd-quantisationhannel power (Ahe smaller firsoise for small sgnal is frequen

the spectrumontributor folletter noise perot improve thhen frequency

Currently, the evice plays aeveloping tech

WLAN, mobilequire more po

nd high bandwave high efficsing a pulse tulse position ffective for linivision Multipata rate commFDM suffers fat will limit th

onnectivity, inwards maintai

nd wide bandwAll nonlinear put waveform

uture generatiomethod towardower amplifiermportant technhich can be us

nd phase. PWmplitude and gnals are conte switched mgnals are gengnals must bWM/PPM sign

OFD

2Telecom3Sch

his paper studto OFDM in

converter. Theon method of [n performancen scheme haACP) comparest quantisationsignals, leadingncy offset, a num. The third hlowed by the rformance of the distortion s

offsetting is av

I. INTROcommunicatio

an essential rhnology of w

e 3G & 4G, anower efficienc

width. Switch ciency but thetrain for drivinmodulation (earity requiremplexing (OFD

munications in from high-peahe energy efficn order to obining spectral

width become vPA classes c

m (e.g. class Don of wireless ds high efficirs (RF-PAs) wnique in SMsed to generate

WM/PPM signaphase. The a

trolled by the mode output rnerated in Cabe convertednals.

DM Pe

Sirmaya1School of

mmunication hool of Innov

dies the odd-qunput signals ine results will [9] to establishe. The overall as about 5dBed to the even-

n step results ing to a lower n

umber of distorharmonic is th

image. Interethe odd-quantspectra. Best voided.

ODUCTION on connectivityrole in daily

wireless transmnd public digitcy, good lineamode power ae linearity is ng SMPAs w

(PWM/PPM) ment [3,4]. Or

DM) nowadayn multi-carrier ak-to-average pciency [5]. Thbtain higher efficiency, pe

very critical. can be operateD and E), resul

base stationsiency linear rwhich has been

MPA architecte an RF signalals are usuallyamplitude andpulse width a

respectively. Nartesian formad to Polar f

erformin Car

anti Sirmayanf EngineeringEngineeringvative Techn

E-mail:

uantisation techn a Cartesianbe compared

h whether therperformance

B reduced adquantisation scn lower quant

noise floor. Whrtions become he biggest distestingly, the otisation schemperformance

y through a wy life. The rmitters such tal broadcastinarity, high datamplifiers (SMvery critical

with pulse widin Cartesian

rthogonal Freqys can suppor

systems. Howpower ratio (P

herefore, for wdata rates, dierformance lin

ed with a swilting in SMPA. This is a poradio frequenn proposed [2ture is PWMl with any ampy quantized ind phase of th

and pulse positNormally, basat. Therefore, format to ge

mance wrtesiannti1,2, Vandang and Scienc

g Study Progrnologies and {sirmayanti

hnique

n Delta to the e is an of the

djacent cheme. tisation hen the

visible tortion overall

me does occurs

wireless rapidly as for

ng will ta rate

MPAs) [1,2].

dth and ΔΣ is

quency rt high wever, PAPR)

wireless irected nearity

itching A for a otential ncy of 2]. The M/PPM plitude n both he RF tion of seband

these enerate

Thgenpulsshapby subsFig.to comsign

Fig. phas

A

gensystevenformclocare twoquanthe

ThquanOddpulspha…) valurefesepa

In quanshoulargAccdistr

with On ΔΣ Una Bassoo3, He, Victoria Uram, the StateEngineering,.sirmayanti}

he authors in erate a binaryse position forpe the noise asubtracting thsequent sampl.1 was used toPWM/PPM’

mponents whenal is offset fro

1. Cartesian ΔΣse in odd-quantisa

novel all digierate a pulse ttem was propn-quantisationming the outpuck periods. Thcalculated by

o clock periodntisation at loweven-quantisa

his paper offntisation of [9d-quantisation sewidths by onse reference. Tfor the odd-q

ues for the eerence does narate quantiser

the followintisation will uld be noted t

ge signal dynacess (CDMA) ribution. Th

Odd-EUpconHorace King

University, Me Polytechnic, University o @live.vu.ed

[3,6] developy signal with r driving an SMaway from thehe current qule [7]. The Ca

o suppress the block can

en the carrierom its nominal

Σ Upconverters. Qation scheme.

ital approach wtrain for drivinosed in [9]. T

n technique wut is based onhe quantised ay changing thds. However, w signal level

ation scheme isfers an altern9] using a ne

was propone clock perioThe acceptablequantisation ceven-quantisatnot change wrs for amplituding, Cartesian

be considerethat most of toamics. OFDMare often mod

he signals mu

Even Qnverter

1, Mike FaulkMelbourne, Au

c of Ujung Pof Technolog

du.au

ped a Cartesian appropriat

MPA. ΔΣ techne band of inteuantised errorartesian ΔΣ tequantisation n

generate ur frequency ol frequency [8

QR and Q quant

with a quantisng an SMPA inThe proposed where the thren pulses with aamplitudes, e pulsewidthsthis leads to ls as the minims two clock penative approaew scheme ofosed to reduod while maine pulsewidths

compared to thtion. In both with the pulsde and phase. n ΔΣ upconved when apploday’s modulaM and Code deled with a Rust be backed

Quantirs kner1 ustralia

Pandang, Indogy, Mauritius

ian ΔΣ systeme pulse widthniques was use

erest. They opr signal fromechnique shownoise but the ‘Punwanted speof the transm,9].

tise the amplitud

sation techniqun the Cartesianquantiser use

ee-level-wavean even numb of the RF si

s in incremena potential co

mum pulsewideriods. ach to the ef odd-quantisauce the posntaining a conbecome (0, 1,he (0, 2, 4, 6

cases the psewidth, allow

verter with lied to OFDM

ation schemes Division Mul

Rayleigh amplid off so that

sation

onesia s

m to h and ed to erate

m the wn in Polar ectral

mitted

de and

ue to n ΔΣ

ed an form er of ignal

nts of oarse dth in

even-ation. ssible nstant , 3, 5 6 …) phase wing

odd-M. It have ltiple itude t the

n

978-1-4673-2393-2/12/$31.00 ©2012 IEEE

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modulator. Ideaso be concentrThe contributiohannel interferΣ architecture.uantisation schcrease with frput signal is bduced with theThe paper istroduction. Se

uantisation scmulation setupven-quantisatioraw a conclusio

II. ΔΣ filtering versampling aoise power spver a wider baBB) oversamoise proportioaseband is give

here is theampling frequhaped using function (NTF)

g. 2. Mod-2 Lowp

The comparisdd-quantisationuantisation scWM generatioThe PWM/PPversample theutput (fc) by a

The phase is tcrements over

etermined by tom the middulsewidths. Hven by

handle the pead probability ally, thereforerated at the lowon of this paperence caused b. We show thahemes producefrequency offsbacked-off (poe odd-quantisas organized ection II prescheme. Sectiop and results oon and odd-quon in section V

ODD QUANis achieve

and noise shaectral density

andwidth. As empling rate (Oonal to [7en by

e maximum uency. The qfeedback in thfor a lowpass

pass ΔΣ.

on between en schemes heme affects

on block ‘PolaPM process ree nominal RFfactor of OSR

therefore unifor the range 0 the pulse positdle of the puHowever the r

ak powers. Thof low signa

e, the quantisw signal levelser is the evaluby the quantisat both even-que the same distset. On the otower control), tation.

as follows. ents the detai

on III and seof the OFDMuantisation scV.

NTISATION Sed through aping. Oversamy (PSD) when expected, incr

OSRBB) will de7].The oversam

signal bandwquantisation ehe ΔΣ filter. 2nd order ΔΣ

ven-quantisatiare now disthe QR and

r to PWM/PPMequires the digF carrier frequ

RF. The OSRRF

ormly quantiseto 2 . The qution. The phasulse and is 0reference for

he result is thaal levels in thsation levels ss. ation of the ad

sation process uantisation antortion produc

ther hand, whthe noise prob

Section I iils of the newection IV giv

M test signal fochemes. Finall

SCHEME the processempling reducthe noise is

easing the basecrease the inmpling ratio

width and error is also

The noise tr(Fig. 2) is giv

ion [9] and thscussed. TheQ blocks an

M’ of Fig.1. gital clock (fcuency of the F is given by

ed into NP (=Ouantised phasese reference is0 degrees for

odd pulsewid

at there he ΔΣ should

djacent in the

nd odd-cts that hen the blem is

is the w odd-ve the or both ly, we

es of ces the spread seband n-band of the

(1)

is the noise

ransfer ven by:

(2)

he new e new nd the

lock) to signal

(3)

OSRRF) e, , is s taken r even dths is

(4)

Thas ampclocbantracof todd

Fig. OSR

If

pulsampone ampoddcan Phaand dimqua

Fiin thradipoinquacroscorrdashand ampmeashow

Thshow

The

Thfund

he quantised ashown in Fiplitude conditick periods. T

ndpass filteringce shows a redthree clock ped pulsewidth co

Phase referencpoint of odd num

of clock period

c

Q

EVEN

Q

ODD

3. Calculation fRRF=8.

f the quantisedsewidths, thenplitude quantis dimensionalplitudes are cod and even pu

cause a chanase Modulatiod phase quanmensional opeantiser complexig. 4 shows thhe Polar planial lines shownts of QE[

antised points sses. and responding tohed circles be

d black is for plitude quantisasured midwawn as dashed he quantised wn in Fig. 4 (b

e threshold for

he amplitudedamental spec

, with

amplitude, , g. 3. The toion for OSRRFThe output isg produces theduced amplitueriods. The phonditions is cl

Phase referencpoint of even num

of clock period

ce mber ds

ref

Tc

co Tclk

cE Tclk

for with the e

d amplitudes n the phase resation and phal operations; onfined to all tlsewidths are

nge in phase (Aon (PM) convntisation musteration and lxity.

he even-quantine. The radius w the quantised

] are illust of QO[ ]

are theo the I and Qetween each o

odd-Polar) aser ( ). The pay between twlines. phase is bas

below), given

r the quantised

e levels are ctral componeamplitudes 1,

is determined op trace showF=8 and has a ps a full squaree sinusoidal oude sinewave hase referencelearly shown.

ce mber ds

Tc

un(4Tclk,0)

un(3Tclk,0)

even-odd number

are confineference does nase quantisatio

similarly, if the odd pulsewallowed a ch

Amplitude Moversion) and st be applied.leads to a g

isation and the of the circlesd phase, . Ttrated by red] are illustrate quantised Q output of thof circles (red are the threshphase threshowo phase inc

ed on the odby

d phase is calcu

calculated bent of the thre, 0, and -1. po

by the pulsewws the maximpulsewidth of e wave, and

output. The bowith a pulsew

e for the even

RF Signal

r of clock period

ed to all the not change anon are indepenf the quantisawidths. When

hange in ampliodulation (AMso joint ampli. This is a great increas

e odd-quantisas is set by .

The even-quand dots. The ted by the bvalues of [R

he ΔΣ filters. is for even-P

hold levels forld levels, ( )crements, and

dd-Polar plane

ulated by equa

by evaluating e-level wavef

o is the pulsew

width mum f four after

ottom width n and

l

ds for

even nd so ndent ation both itude

M) to itude two-e in

ation The

ntised odd-

black R,�] The

Polar, r the ), are d are

e, as

(5) ation (6)

the form, width

cocytimPP

Figpla

SthusveFo whamfir

orresponding tycles (cE is for me delay or aPM delay in cl

g. 4. The even-qane scale for OSR

Since e spectral com

sing the Fouriersion of ourier transfor

here K is thmplitude of thrst frequency b

to the cO clockr even). pp is thadvance. pp = lock periods.

quantisation (top)RRF=8.

is a repeamponent can bier series. Her

to getrm (DFT).

he fast Fourhe fundamentabin, k=1

k cycles (cO is he pulse positi(0, … (NP-1))

) and the odd-qu

ating waveformbe generated frre, we use a ht the same res

rier transformal of the pulse

for odd) or cEion and refers) and represen

uantisation (below

m, the ampliturom one periohighly oversasult from a di

m (FFT) size

wave occurs

E clock s to the nts the

w) Polar

ude of d only

ampled iscrete

(7) e. The

in the

to thTh

two

wheA

usedreprlocadetefromwheThePW

G

Fig.

Fisignof pulsof triantwofromsym

IFi

Carat (appof th

wheeach

is the index

he odd pulsewhe amplitude t

o amplitude qu

ere the index ofter quantisatid to convertresentation toation of the ermined usingm Q block. Aere the pulse e output of Q

WM process.

Odd PWM Generation

5. Odd PWM gen

ig. 5 illustratnals using a st

quantised asewidths, PW1the line ngular wavefo

o sample increm the phase

mmetry about i

III. TEST SIGig. 6 shows thertesian ΔΣ upc

with fc=1024plicable bandwhe ΔΣ is relate

ere the index h output samp

x for the diffe

width threshold leve

uantised levels

of is selecteion, then the t the quanti

o RF using Ppulse posit

g the quantisedA change in po

edges must oQR block, d

0

P

P

Middthe odd q

7

5

3

neration.

tes the PWMtepped triangl

amplitudes: 1 and PW2, ar

and orm signal. Thements to deresponse. Th

its midpoint.

GNAL CHARAe simulation m

converters. Th4 MHz which width to WLAed to the nomi m is the num

ple of the ΔΣ, (

,

erent pulsewid

els are given bs,

,

ed in ascendin‘Polar to PWsed signals,

PWM and PPtion of the d phase, , w

osition dependsccur on the ddetermines th

0

W1

PW2

dle line of quantisation

1

3

5

M generation e wave. It sho

andre defined by t

respectively he pulsewidth couple the amhe pulsewidt

ACTERISTICmodel for test e OFDM bandequivalent to

AN). The sampinal carrier fre

mber of carrier(m=n/2, where

,

dths correspon

. by the midpoi

ng order. WM/PPM’ bloc

[ ], in PPM schemes.

PPM proceswhich is the ou

s on a change digital timing he duration of

7

9

of odd quanows two exam

. The outhe crossing p

and the stepmust change

mplitude resph then main

CS OF OFDMsignal OFDMdwidth (B) waa Bofdm of 16 M

pling frequencyequency fc. r periods betwe n is an intege

(8)

nding

nt of

(9)

ck is Polar

The ss is utput of grid. f the

ntised mples utput oints pped with

ponse ntains

M into as set MHz y (fs)

(10) ween er).

Figoff WevraIf ofnoinbesu

AOSto upnofachhanofroar

g. 6. OFDM as infset carrier.

When n=1 and very half perioate. In this wo

is the bin f subcarriers, ominal numbecluding the

etween adjaceummarized in T

Para

Modulat

Frequenc

OS

Oversampling

Offset f

IA spectrum pSRRF of 16 an urms= 1) ob

pconverter is sominal positiocilitate the un

hannel 1. The armonic is situoise is lowest om fc and maxround that regi

nput the I and Q s

m=1/2, the puod of the carrork we use m=frequency spatherefore Bof

er of subcarrnull sub-car

ent channels. Table I.

TSIMULATIO

ameter

ted Signal

y carrier, fc

SRBB

g ratio (OSRRF)

N

A

f

frequency

IV. SIMULATplot of a pulsnd an input sigbtained at thshown in Fig. on of the carnderstanding o image is preuated in chann

in channel 0ximum attenuaion (ΔΣ-filters

signal to Cartesian

ulse width andrier, which is

=1 (n=2) and uacing betweenfdm is equal toriers in the crriers forming

The simulat

TABLE I ON PARAMETERS

Q

20 MHz,

TION RESULse waveform gnal level, u= he output of

7. The adjacerrier are drawf the plot. The

esent in channnel 3 with the

0 as the NTF ation of quants with MOD2)

n ΔΣ upconverter

d position is ups the highest uupdate every pn the active tono . Nchannel bandg the guard tion paramete

Value

PSK, OFDM

1024 MHz

64

16

20

16

1 MHz

guard band 0.2

TS with an RF -7 dB (with rthe Cartesia

ent channels awn on the fige signal is presnel -1 and thee highest noisof the ΔΣ op

tisation noise o).

rs for an

pdated update period. nes (A) is the

dwidth, band

ers are

5Bofdm

carrier respect an ΔΣ and the gure to sent in e third e. The perates occurs

Fig. ΔΣ u

Thoddadjashifspecpowweras w

Fig. (ACP

Fi

the Caris ththe to esignthe thanquaeven

-7

-6

-5

-4

-3

-2

-1

Spec

trum

relat

ive

to th

e O

FDM

sign

al (d

B)

-7

-6

-5

-4

-3

-2

-1

AC

P no

rmal

ised

to si

gnal

pow

er (d

B)

7. Spectrum plot upconverter with o

he out-of-band-quantisation acent channelfted one chanctral images.

wer in the adjre calculated. well as distorti

8, Cartesian ΔΣP in adjacent chan

ig. 8 shows a psix adjacen

rtesian ΔΣ schhe optimum infigure, the od

even-quantisatnal levels is thodd-quantisat

n the even-quantisation schen-quantisation

95070

60

50

40

30

20

10

0

Ch -3

-40 -3570

60

50

40

30

20

0

0

even

odd

of even-quantisatoffset OFDM sign

nd distortions schemes are

l powers (ACnnel to the rThe ACPs w

jacent channeThe noise pow

ion arising fro

Σ with even-quannnel vs. input lev

plot of input lnt channels oheme. The shanput signal levdd-quantisatiotion for most ihe improvemtion scheme huantisation sceme has at lean scheme. Ag

1000Freque

P

c

Ch -2 Ch -1

-30 -25Input Pow

tion and odd-quannal.

for both evencompared by

CPs). The deright to examwhich are defel divided by wer includes m PPM.

ntisation and odel).

level (dB) agaobtained afte

ape of the curvvel for best SN

on has reducedinput signal leent less obviohas at least 4

cheme. In chaast 5.57 dB lgain, it can

1050ency (MHz)

Positionof

carrier

Ch 0 Ch 1

-20 -15wer-to-noise (dB)

ntisation in Cartes

n-quantisationy calculating esired signal

mine the resufined as the n

the signal poquantisation n

d-quantisation sc

ainst ACP (dBer simulating ves indicates -NR. As showd ACP compevels; only at lous. In chann4.83 dB less Aannel 0, the less ACP thanbe observed

EveOdd

Ch 2 Ch 3

-10 -5

Channel 2 (even)Channel 3 (even)Channel 0 (even)Channel -1 (even)Channel -2 (even)Channel -3 (even)Channel 2 (odd) Channel 3 (odd)Channel 0 (odd)Channel -1 (odd)Channel -2 (odd)Channel -3 (odd)

sian

n and their was

ultant noise ower noise

cheme

B) for the

-7dB wn in pared large

nel 2, ACP odd-

n the that

1100

end

0

channel 3 (Fig.7) which represents the third harmonic has the highest noise. Channel -1 representing the image has the second highest noise. Channel 0 has lower noise than channel 2 as channel 0 is centered at fc. This plot further validates the conclusions drawn from Fig. 7.

V. CONCLUSION

This paper compares even-quantisation and odd-quantisation schemes for Cartesian ΔΣ upconverters. OFDM is used as the input signal. The characteristics of the input test signals and the OSR for both schemes are kept the same. The overall performance of the even-quantisation scheme is worse than the odd-quantisation scheme as the even-quantisation structure has an inherently higher noise floor. It can be observed that the third harmonic is the biggest noise contributor followed by the image. Interestingly, the overall better performances of the odd-quantisation scheme occur at lower input signal levels. These levels benefit from the lower first quantisation step of the odd-quantisation scheme. The benefit is lost when the input signal level rises to within about 7dB of the optimum signal level. The image and third order distortions dominate the performance at large signal levels and make signal tuning by using frequency offsetting at baseband a non-attractive proposition. The type of quantisation does not improve this aspect of the output spectrum. Tuning by changing the sample rate would obviate the need for offsetting and so avoid the problem.

VI. REFERENCES

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[9]

[10]

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