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SIMULATION OF SOFTWARE DEFINED RADIO FOR OFDM

TRANSCEIVERS IN VHDL

PROJECT REPORT

Submitted

in partial fulfilment for the award of the degreeof

BACHELOR OF TECHNOLOGY

inELECTRONICS AND COMMUNICATION ENGINEERING

by B.HARISH (13505A0402) D.SURESH (12501A0423)K.SUBRAHMANYAM (13505A0412) B.NAVEEN KUMAR (12501A0407)

Under the Guidance ! D . C!. GANGADHAR" M.T#$!" %!.D."

Associate Professor

DE%ARTMENT OF ELECTRONICS & COMMUNICATION ENGINEERING

%RASAD V. %OTLURI SIDDHARTHA INSTITUTE OF TECHNOLOGY(Affiliated to JNTUK: Kakinada, Approved by AICTE(Accredited by N!A " NAAC and I#$ Certified Instit%tion

Kan%r%, &i'aya ada)*+ -.2015-2016

%RASAD V %OTLURI SIDDHARTHA INSTITUTE OF TECHNOLOGY


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CERTIFICATE

T/is is to certify t/at t/is pro'ect report entitled 'SIMULATION OF SOFT ARE DEFINED

RADIO FOR OFDM TRANSCEIVERS IN VHDL is a bonafide ork 'ointly done by

B.HARISH(13505A0402)"D.SURESH(12501A0423)"K.SUBRAHMANYAM(13505A0412)"B

.NAVEEN KUMAR(12501A0407) carried o%t %nder 0y 1%idance and s%pervision and is

s%b0itted in partial f%lfil0ent of t/e re2%ire0ents for t/e a ard of t/e de1ree of !ac/elor of

Tec/nolo1y in E3ECT4$NIC# AN5 C$66UNICATI$N EN7INEE4IN7 by Ja a/arlal

Ne/r% Tec/nolo1ical University Kakinada, d%rin1 t/e acade0ic year2015*201+.

S,- / # !# G , # S,- / # !# HOD

(D .C!.G/ -/ !/ " M.T#$!" %!.D.) (D .%.R/ #6! K / " M.E" %!.D.)

Associate Professor Professor and 8$5

ACKNO LEDGEMENT


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9irst and fore0ost e sincerely sal%te o%r estee0ed instit%tion%RASAD V. %OTLURISIDDHARTHA INSTITUTE OF TECHNOLOGY for 1ivin1 t/is 1olden opport%nity for f%lfillin1 o%r ar0 drea0s of beco0in1 an en1ineer.

e /ereby e;press sincere 1ratit%de to o%r principalD . K.SIVA8I BABU" 6.TEC8,

P/.5. /o /as rendered %s /is constant enco%ra1e0ent and val%able s%11estions in 0akin1 o%r pro'ect ork s%ccessf%l.

e are also t/ankf%l to o%r 8ead of t/e 5epart0entD . %. R/ #6! K / " 6.E, andP/.5. for /is constant enco%ra1e0ent and val%able s%pport t/ro%1/o%t t/e co%rse of o%r pro'ect

ork.

e are 1lad to e;press deep sense of 1ratit%de toM . C!. G/ -/ !/ " 6.Tec/, P/.5.,Associate Professor, o%r 1%ide for /is 1%idance and co)operation in co0pletin1 t/is pro'ectreport s%ccessf%lly.

e t/ank one and all /o /ave rendered /elp directly or indirectly in t/e co0pletion of pro'ect ork s%ccessf%lly.

% #$ A66 $,/ #69

!.8A4I#8 ( +

5.#U4E#8 (


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ABSTRACT

Orth " na# Fre$uenc% Di&i'i n Mu#ti(#e)in" *OFDM+ i' a tran',i''i ntechni$ue -hich en'ure' e.cient uti#i/ati n ! the '(ectru, 0% a## -in" &er#a( ! carrier'1 OFDM i' a c ,0inati n ! , du#ati n and ,u#ti(#e)in" that i' u'ed in the

tran',i''i n ! in! r,ati n and data1 C ,(ared -ith the ther -ire#e''tran',i''i n techni$ue' #i2e Fre$uenc% Di&i'i n Mu#ti(#e Acce'' *FDMA+3 C deDi&i'i n Mu#ti(#e Acce'' *CDMA+3 OFDM ha' nu,er u' ad&anta"e' #i2e hi"h '(ectra#den'it%3 it' r 0u'tne'' t channe# !adin"3 it' a0i#it% t &erc ,e 'e&era# radii,(air,ent !act r' 'uch a' e4ect ! AWGN3 i,(u#'e n i'e3 ,u#ti(ath !adin"3 etc1Due t thi' it 5nd' -ide a((#icati n in Di"ita# Audi 6r adca'tin" *DA6+3 Di"ita#Vide 6r adca'tin" *DV6+3 and Wire#e'' LAN1 M 't ! the -ire#e'' LAN 'tandard' #i2eIEEE 7891::a r IEEE 7891::" u'e the OFDM a' the ,ain ,u#ti(#e)in" 'che,e ! r0etter u'e ! '(ectru,1 In !act in the ;G te#ec ,,unicati n '%'te, OFDMA i' the0ac20 ne ! it1

Thi' (r


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CONTENTSCONTENTS

S.NoS.No TopicTopic Page No.Pa ge No.

1. Chapter – 1

Introduction

……………………………………………………….....................

2

1.1 hat i!

O"#$%....................................................................

& 1.2 #ata on O"#$……………………………………………….....................

'

1.&

O()ecti*e……………………………………………………........................

5

1.' +ac,

ground…………………………………………………......................

5 1.5 $u tip e cce!! Techni/ue!…………………………………...............

1.5.1 "#$ "re/uenc #i*i!ion $u tip e cce!!e!3

……….....

1.5.2 T#$ Ti4e #i*i!ion $u tip e cce!!3

……………….........

1.5.& C#$ Code #i*i!ion $u tip e cce!!3

………………......... 1.5.&.1C#$

7eneration………………………………….......... 10

2. Chapter – 2


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8iterature 9e*ie:…………………………………………..........................

12

&. Chapter – &

&.1 Theor ; 9e!earch Introduction……………………………..............

16

&.2 O"#$

Princip e!………………………………………………....................

16

&.& "ourier

Tran!


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&. ""T ;

I""T…………………………………………………….........................

2&

&.10 dding a 7uard Period o<

O"#$……………………………............. 2'

4. C!/: # ; 4

'.1 I4p e4entation o< O"#$

S !te4……………………………............ 2

'.2 O"#$ $ode

@!ed…………………………………………….................. 2 '.2.1 Serie! To Para e

con*er!ion…………………………….......... 2

'.2.2 $odu ation o<

#ata………………………………………............. 2

'.2.& In*er!e "ourier

Tran!


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'.'.2

S nchroniBation…………………………………………................

&0

'.'.& Co-channe

inter


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+i( iograph ……………………………………………………………..............................


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LIST OF FIGURES

FIG.NO. NAME OF THE FIGURE %AGE.NO

1.1 T / , , /< =,#> #$#,=, - 6,- /, # @ +1.5 FDMA 6! >, - !/ !# #/$! / > / ,6 /!# # #/$! 6# ,6 /!,$! ,6

!/< / $?$


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3.1 %SK 6? < / 6 ,66, / 6 $$#66,=# :!/6# 6!, 23'.1 C


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C!/: #

1 INTRODUCTION

4ecently, a orld ide conver1ence /as occ%rred for t/e %se ofOrthogonal Frequency Division Multiplexing ($956 as an e0er1in1 tec/nolo1y for /i1/ data rates. In partic%lar, 0any irelessstandards ( i)6a;, IEEE@ +.


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1.1 !/ ,6 OFDM

$956 is a for0 of 0%lticarrier 0od%lation. An $956 si1nal consists of a n%0ber of closelyspaced 0od%lated carriers. /en 0od%lation of any for0 ) voice, data, etc. is applied to a carrier, t/ensidebands spread o%t eit/er side. It is necessary for a receiver to be able to receive t/e /ole si1nal to be

able to s%ccessf%lly de0od%late t/e data. As a res%lt /en si1nals are trans0itted close to one anot/er t/ey 0%st be spaced so t/at t/e receiver can separate t/e0 %sin1 a filter and t/ere 0%st be a 1%ard band bet een t/e0. T/is is not t/e case it/ $956. Alt/o%1/ t/e sidebands fro0 eac/ carrier overlap, t/eycan still be received it/o%t t/e interference t/at 0i1/t be e;pected beca%se t/ey are ort/o1onal to eac/anot/er. T/is is ac/ieved by /avin1 t/e carrier spacin1 e2%al to t/e reciprocal of t/e sy0bol period.

Fig1.1: Traditional view of receiving signals carrying modulationTo see /o $956 orks, it is necessary to look at t/e receiver. T/is acts as a bank of

de0od%lators, translatin1 eac/ carrier do n to 5C. T/e res%ltin1 si1nal is inte1rated over t/e sy0bol period to re1enerate t/e data fro0 t/at carrier. T/e sa0e de0od%lator also de0od%lates t/e ot/er carriers.As t/e carrier spacin1 e2%al to t/e reciprocal of t/e sy0bol period 0eans t/at t/ey ill /ave a /olen%0ber of cycles in t/e sy0bol period and t/eir contrib%tion ill s%0 to ero ) in ot/er ords t/ere is nointerference contrib%tion.

Figure1.2: OFDM Spectrum$ne re2%ire0ent of t/e $956 trans0ittin1 and receivin1 syste0s is t/at t/ey 0%st be linear.

Any non)linearity ill ca%se interference bet een t/e carriers as a res%lt of inter)0od%lation distortion.

T/is ill introd%ce %n anted si1nals t/at o%ld ca%se interference and i0pair t/e ort/o1onality of t/etrans0ission.

In ter0s of t/e e2%ip0ent to be %sed t/e /i1/ peak to avera1e ratio of 0%lti)carrier syste0s s%c/as $956 re2%ires t/e 49 final a0plifier on t/e o%tp%t of t/e trans0itter to be able to /andle t/e peaks

/ilst t/e avera1e po er is 0%c/ lo er and t/is leads to inefficiency. In so0e syste0s t/e peaks areli0ited. Alt/o%1/ t/is introd%ces distortion t/at res%lts in a /i1/er level of data errors, t/e syste0 can relyon t/e error correction to re0ove t/e0.

>


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1.2 D/ / OFDM

T/e data to be trans0itted on an $956 si1nal is spread across t/e carriers of t/e si1nal, eac/carrier takin1 part of t/e payload. T/is red%ces t/e data rate taken by eac/ carrier. T/e lo er data rate /ast/e advanta1e t/at interference fro0 reflections is 0%c/ less critical. T/is is ac/ieved by addin1 a 1%ard

band ti0e or 1%ard interval into t/e syste0. T/is ens%res t/at t/e data is only sa0pled /en t/e si1nal isstable and no ne delayed si1nals arrive t/at o%ld alter t/e ti0in1 and p/ase of t/e si1nal.

Figure1.3: uard !ntervalT/e distrib%tion of t/e data across a lar1e n%0ber of carriers in t/e $956 si1nal /as so0e

f%rt/er advanta1es. N%lls ca%sed by 0%lti)pat/ effects or interference on a 1iven fre2%ency only affect as0all n%0ber of t/e carriers, t/e re0ainin1 ones bein1 received correctly. !y %sin1 error)codin1tec/ni2%es, /ic/ does 0ean addin1 f%rt/er data to t/e trans0itted si1nal, it enables 0any or all of t/ecorr%pted data to be reconstr%cted it/in t/e receiver. T/is can be done beca%se t/e error correction codeis trans0itted in a different part of t/e si1nal.

Initial proposals for $956 ere 0ade in t/e B s and t/e - s. It /as taken 0ore t/an a 2%arter of a cent%ry for t/is tec/nolo1y to 0ove fro0 t/e researc/ do0ain to t/e ind%stry. T/e concept of $956 is2%ite si0ple b%t t/e practicality of i0ple0entin1 it /as 0any co0ple;ities. #o, it is a f%lly soft are pro'ect.

$956 depends on $rt/o1onality principle. $rt/o1onality 0eans, it allo s t/e s%b carriers,/ic/ are ort/o1onal to eac/ ot/er, 0eanin1 t/at cross talk bet een co)c/annels is eli0inated and inter)

carrier 1%ard bands are not re2%ired. T/is 1reatly si0plifies t/e desi1n of bot/ t/e trans0itter andreceiver, %nlike conventional 956 a separate filter for eac/ s%b c/annel is not re2%ired.

$rt/o1onal 9re2%ency 5ivision 6%ltiple;in1 ($956 is a di1ital 0%lti carrier 0od%lationsc/e0e, /ic/ %ses a lar1e n%0ber of closely spaced ort/o1onal s%b)carriers. A sin1le strea0 of data is

split into parallel strea0s eac/ of /ic/ is coded and 0od%lated on to a s%bcarrier, a ter0 co00only %sedin $956 syste0s.

Eac/ s%b)carrier is 0od%lated it/ a conventional 0od%lation sc/e0e (s%c/ as 2%adrat%rea0plit%de 0od%lation at a lo sy0bol rate, 0aintainin1 data rates si0ilar to conventional sin1le carrier 0od%lation sc/e0es in t/e sa0e band idt/. T/%s t/e /i1/ bit rates seen before on a sin1le carrier isred%ced to lo er bit rates on t/e s%bcarrier.

;


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In practice, $956 si1nals are 1enerated and detected %sin1 t/e 9ast 9o%rier Transfor0al1orit/0. $956 /as developed into a pop%lar sc/e0e for ideband di1ital co00%nication, ireless as

ell as copper ires.

Act%ally, 956 syste0s /ave been co00on for 0any decades. 8o ever, in 956, t/e carriers areall independent of eac/ ot/er. T/ere is a 1%ard period in bet een t/e0 and no overlap /atsoever. T/is

orks ell beca%se in 956 syste0 eac/ carrier carries data 0eant for a different %ser or application. 96radio is an 956 syste0. 956 syste0s are not ideal for /at e ant for ideband syste0s. Usin1 956

o%ld aste too 0%c/ band idt/. T/is is /ere $956 0akes sense.

In $956, s%bcarriers overlap. T/ey are ort/o1onal beca%se t/e peak of one s%bcarrier occ%rs/en ot/er s%bcarriers are at ero. T/is is ac/ieved by reali in1 all t/e s%bcarriers to1et/er %sin1 Inverse

9ast 9o%rier Transfor0 (I99T . T/e de0od%lator at t/e receiver parallel c/annels fro0 an 99T block. Note t/at eac/ s%bcarrier can still be 0od%lated independently.

#ince ort/o1onality is i0portant for $956 syste0s, sync/roni ation in fre2%ency and ti0e 0%st be e;tre0ely 1ood. $nce ort/o1onality is lost e e;perience , # *$/ ,# , # # # $# (ICI . T/is is t/einterference fro0 one s%bcarrier to anot/er. T/ere is anot/er reason for ICI. Addin1 t/e 1%ard ti0e it/no trans0ission ca%ses proble0s for I99T and 99T, /ic/ res%lts in ICI. A delayed version of ones%bcarrier can interfere it/ anot/er s%bcarrier in t/e ne;t sy0bol period. T/is is avoided by e;tendin1t/e sy0bol into t/e 1%ard period t/at precedes it. T/is is kno n as a$?$


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T/e teleco00%nications ind%stry faces t/e proble0 of providin1 telep/one services to r%ralareas, /ere t/e c%sto0er base is s0all, b%t t/e cost of installin1 a ired p/one net ork is very /i1/. $ne0et/od of red%cin1 t/e /i1/ infrastr%ct%re cost of a ired syste0 is to %se a fi;ed ireless radio net ork.T/e proble0 it/ t/is is t/at for r%ral and %rban areas, lar1e cell si es are re2%ired to 1et s%fficientcovera1e.

F,-.1.1 s/o s t/e evol%tion of c%rrent services and net orks to t/e ai0 of co0binin1 t/e0 into a%nified t/ird 1eneration net ork. 6any c%rrently separate syste0s and services s%c/ as radio pa1in1,cordless telep/ony, satellite p/ones and private radio syste0s for co0panies etc, ill be co0bined so t/atall t/ese services ill be provided by t/ird 1eneration teleco00%nications syste0s.

F,-. 1.49 E= < , $ # # > @6 !# # -# # / , >, # @6.C%rrently 7lobal #yste0 for 6obile teleco00%nications (7#6 tec/nolo1y is bein1 applied to

fi;ed ireless p/one syste0s in r%ral areas. 8o ever, 7#6 %ses ti0e division 0%ltiple access (T56A ,/ic/ /as a /i1/ sy0bol rate leadin1 to proble0s it/ 0%ltipat/ ca%sin1 inter)sy0bol interference.

#everal tec/ni2%es are %nder consideration for t/e ne;t 1eneration of di1ital p/one syste0s, it/ t/e ai0of i0provin1 cell capacity, 0%ltipat/ i00%nity, and fle;ibility. T/ese incl%de C56A and $956. !ot/t/ese tec/ni2%es co%ld be applied to providin1 a fi;ed ireless syste0 for r%ral areas. 8o ever, eac/tec/ni2%e as different properties, 0akin1 it 0ore s%ited for specific applications.

$956 is c%rrently bein1 %sed in several ne radio broadcast syste0s incl%din1 t/e proposal for

/i1/ definition di1ital television (85T& and di1ital a%dio broadcastin1 (5A! . 8o ever, little researc//as been done into t/e %se of $956 as a trans0ission 0et/od for 0obile teleco00%nications syste0s.In C56A, all %sers trans0it in t/e sa0e broad fre2%ency band %sin1 speciali ed codes as a basis of c/anneli ation. !ot/ t/e base station and t/e 0obile station kno t/ese codes, /ic/ are %sed to0od%late t/e data sent. $956FC$956 allo s 0any %sers to trans0it in an allocated band, bys%bdividin1 t/e available band idt/ into 0any narro band idt/ carriers. Eac/ %ser is allocated severalcarriers in /ic/ to trans0it t/eir data.

@


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T/e trans0ission is 1enerated in s%c/ a ay t/at t/e carriers %sed are ort/o1onal to one anot/er,t/%s allo in1 t/e0 to be packed to1et/er 0%c/ closer t/an standard fre2%ency division 0%ltiple;in1(956 . T/is leads to $956FC$956 providin1 a /i1/ spectral efficiency.

$rt/o1onal 9re2%ency 5ivision 6%ltiple;in1 is a sc/e0e %sed in t/e area of /i1/)data)rate0obile ireless co00%nications s%c/ as cell%lar p/ones, satellite co00%nications and di1ital a%dio broadcastin1. T/is tec/ni2%e is 0ainly %tili ed to co0bat inter)sy0bol interference.

1.5 M < ,:


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F,-. 1.+ 9

FDMA 6:#$ " >!# # !# /=/, / $!/ #


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F,-. 1. TDMA FDMA !? , " 6! >, - !/ !# / >, ! ,6 6:


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band idt/. Part (c s/o s t/e received si1nal. T/is consists of t/e re2%ired si1nal, pl%s back1ro%nd noise,and any interference fro0 ot/er C56A %sers or radio so%rces.

T/e received si1nal is recovered by 0%ltiplyin1 t/e si1nal by t/e ori1inal spreadin1 code. T/is process ca%ses t/e anted received si1nal to be dispread back to t/e ori1inal trans0itted data. 8o ever,all ot/er si1nals, /ic/ are %ncorrelated to t/e PN spreadin1 code %sed, beco0e 0ore spread. T/e antedsi1nal in (d is t/en filtered re0ovin1 t/e ide spread interference and noise si1nals.

F,-. 1.109 B/6,$ CDMA G# # / , .

1.5.3.1 CDMA G# # / , 91.5.3.1 CDMA G# # / , 9

C56A is ac/ieved by 0od%latin1 t/e data si1nal by a pse%do rando0 noise se2%ence (PN code ,/ic/ /as a c/ip rate /i1/er t/an t/e bit rate of t/e data. T/e PN code se2%ence is a se2%ence of ones anderos (called c/ips , /ic/ alternate in a rando0 fas/ion. T/e data is 0od%lated by 0od%lar)+ addin1 t/e

data it/ t/e PN code se2%ence. T/is can also be done by 0%ltiplyin1 t/e si1nals, provided t/e data andPN code is represented by < and )< instead of < and .F,-. 1.11 s/o s a basic C56A trans0itter.

F,-. 1.11 S, :


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:9

CHA%TER T O

LITERATURE REVIE


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C!/: #

2 LITERATURE REVIE

J< Jan)Jaap van de !eek , 6a1n%s #andell , Per $la !Hor'esson ,$n #ync/roni ation in $956 #yste0s

Usin1 t/e Cyclic Prefi;, IEEE + B

In t/is paper, e present a data)based 0et/od for si0%ltaneo%s 6a;i0%0 3ikeli/ood (63

sy0bol ti0in1 and carrier)fre2%ency offset esti0ation in ort/o1onal fre2%ency)division 0%ltiple;in1

($956 syste0s. T/e cyclic e;tension, a 1%ard space precedin1 $956 fra0es, is of decisive i0portance

for t/is 0et/od. It is s/o n t/at t/e red%ndancy introd%ced by t/is cyclic e;tension allo s t/e esti0ation

to be perfor0ed it/o%t additional pilots. #i0%lations s/o t/at t/e perfor0ance of t/e fre2%ency

esti0ator is %sable in a trackin1 0ode /ile t/e ti0in1 esti0ation can be %sed in an ac2%isition 0ode.

In t/is paper e /ave presented a si0%ltaneo%s esti0ator of ti0in1 and fre2%ency offset in

$956 syste0s, /ic/ doesn t need pilots b%t %ses t/e red%ndancy introd%ced by t/e cyclic e;tension. It

is derived %nder t/e ass%0ption t/at t/e c/annel only consists of additive noise. #i0%lations s/o t/at in

a dispersive fadin1 environ0ent t/e ti0in1 esti0ator can be %sed in an ac2%isition 0ode and t/e

fre2%ency esti0ator 0ay perfor0 ell in a trackin1 0ode. In a ireless syste0, pilots are needed for

c/annel esti0ation. T/ese kno n sy0bols can be %sed by t/e esti0ator and /ence f%rt/er increase t/e

perfor0ance. 4es%ltin1 sync/roni ers 0ay be /ybrid str%ct%res %sin1 bot/ pilots and cyclic prefi;. 8o

to incorporate pilot sy0bols in s%c/ ti0in1 and fre2%ency esti0ators is not strai1/tfor ard and needs

f%rt/er researc/.

+ 8inda i P%blis/in1 Corporation

EU4A#IP Jo%rnal on ireless Co00%nications and Net orkin1, C. illia0s, #. 6c3a%1/lin, and 6. A.!eac/ , 4ob%st $956 Ti0in1 #ync/roni ation in 6%ltipat/ C/annels , +< April + @

T/is paper addresses pre)99T sync/roni ation for ort/o1onal fre2%ency division 0%ltiple; ($956%nder varyin1 0%ltipat/ conditions. To ens%re t/e 0ost efficient data trans0ission possible, t/ere s/o%ld be no constraints on /o 0%c/ of t/e cyclic prefi; (CP is occ%pied by inter sy0bol interference (I#I .8ere a sol%tion for ti0in1 sync/roni ation is proposed, t/at is, rob%st even /en t/e stron1est 0%ltipat/

co0ponents are delayed relative to t/e first arrivin1 pat/s. In t/is sit%ation, e;istin1 0et/ods perfor0 poorly, /ereas t/e sol%tion proposed %ses t/e derivative of t/e correlation f%nction and is less sensitiveto t/e c/annel i0p%lse response. In t/is paper, sync/roni ation of a 5&! sin1le)fre2%ency net ork isinvesti1ated. A refine0ent is proposed t/at %ses /e%ristic r%les based on t/e 0a;i0a of t/e correlation andderivative f%nctions to f%rt/er red%ce t/e esti0ate variance.

T/e tec/ni2%e /as relevance to broadcast, $956A, and 3AN applications, and si0%lations are presented /ic/ co0pare t/e 0et/od it/ e;istin1 approac/es. A ne 0%ltipat/)rob%st $956 ti0in1

:>


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esti0ation tec/ni2%e based on t/e derivative of t/e s%00ed correlation f%nction /as been proposed andt/e perfor0ance e;a0ined for t/e 5&!)T syste0. Even in t/e orst case considered of very s/ort CPs,t/e 0et/od /as s/o n to be s%perior to t/e peak detection 0et/od. In considerin1 co0ple;ity, t/esync/roni ation al1orit/0s are do0inated by t/e correlation calc%lation, and t/e additional n%0ber of 0%ltiplications of t/e derivative and 3# fittin1 are less t/an Jo%rnal of #i1nal and Infor0ation Processin1, + , +=BF'sip.+ =! +>, P%blis/ed $nline A%1%st +


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%sin1 C se2%ence as prea0ble. #i0%lations in t/e 6AT3A! for an A 7N c/annel s/o t/at t/e proposed 0et/od ac/ieves s%perior perfor0ance to e;istin1 tec/ni2%es in ter0s of fre2%ency acc%racyand ran1e.

T/e 0et/od %sin1 C se2%ence as prea0ble for 9re2%ency $ffset Esti0ator enlar1es t/e ran1e of

esti0ation to O= of s%bcarrier spacin1 for $956 based 3AN syste0. T/e acc%racy of esti0ation /asi0proved /en co0pared to ot/er 0et/ods. Co0pared to ot/er data aided tec/ni2%es si0%lated in t/is

paper like #c/0idl, 6inn, 4en for C9$ esti0ation, t/is 0et/od 1ives better acc%racy in t/e esti0ation of

fre2%ency offset.

* #%n et al. EU4A#IP Jo%rnal on ireless Co00%nications and Net orkin1 +


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:@

CHA%TER THREE

THEORY & REASEARCH


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c/annel trans0ission. #ince t/is proved to be diffic%lt to acco0plis/ d%rin1 t/at ti0e period, t/e sc/e0eas dee0ed as not feasible.

8o ever, t/e advent of t/e 9o%rier Transfor0 eli0inated t/e initial co0ple;ity of t/e $956sc/e0e /ere t/e /ar0onically related fre2%encies 1enerated by 9o%rier and Inverse 9o%rier transfor0sare %sed to i0ple0ent $956 syste0s. T/e 9o%rier transfor0 is %sed in linear syste0s analysis, antennast%dies, etc., T/e Fourier transform , in essence, deco0poses or separates a avefor0 or f%nction intosin%soids of different fre2%encies /ic/ s%0 to t/e ori1inal avefor0. It identifies or distin1%is/es t/edifferent fre2%ency sin%soids and t/eir respective a0plit%des.

T/e 9o%rier transfor0 of f(x) is defined as:

dxe x f F x jω ω −∞

∞−∫ ⋅= ((

and its inverse is denoted by:

∫ ∞

∞−

⋅= ω ω π

ω d e F x f x j(+<

(

8o ever, t/e di1ital a1e forced a c/an1e %pon t/e traditional for0 of t/e 9o%rier transfor0 to enco0passt/e discrete val%es t/at e;ist is all di1ital syste0s. T/e 0odified series as called t/e 5iscrete 9o%rier Transfor0 (59T . T/e 59T of a discrete)ti0e syste0, x(n) is defined as:

∑−

=

−⋅= Χ< +

(( N

n

n N jen x π

< ≤ ≤ N

and its associated inverse is denoted by:

∑−

=⋅ Χ=

< +

(<

( N

n

n N

je

N n x

π

< ≤ n ≤ N

8o ever, in $956, anot/er for0 of t/e 59T is %sed, called t/e 9ast 9o%rier Transfor0 (99T ,/ic/ is a 59T al1orit/0 developed in +

*;+

*?+


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3.4 O ! - /


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$rt/o1onal 9re2%ency 5ivision 6%ltiple;in1 ($956 is a 0%lticarrier trans0ission tec/ni2%e, /ic/divides t/e available spectr%0 into 0any carriers, eac/ one bein1 0od%lated by a lo rate data strea0.$956 is si0ilar to 956A in t/at t/e 0%ltiple %ser access is ac/ieved by s%bdividin1 t/e available band idt/ into 0%ltiple c/annels t/at are t/en allocated to %sers.

8o ever, $956 %ses t/e spectr%0 0%c/ 0ore efficiently by spacin1 t/e c/annels 0%c/ closer to1et/er. T/is is ac/ieved by 0akin1 all t/e carriers ort/o1onal to one anot/er, preventin1 interference bet een t/e closely spaced carriers.

Coded $rt/o1onal 9re2%ency 5ivision 6%ltiple;in1 (C$956 is t/e sa0e as $956 e;cept t/atfor ard error correction is applied to t/e si1nal before trans0ission.

T/is is to overco0e errors in t/e trans0ission d%e to lost carriers fro0 fre2%ency selective fadin1,c/annel noise and ot/er propa1ation effects. 9or t/is disc%ssion t/e ter0s $956 and C$956 are %sedinterc/an1eably, as t/e 0ain foc%s of t/is t/esis is on $956, b%t it is ass%0ed t/at any practical syste0

ill %se for ard error correction, t/%s o%ld be C$956.

In 956A eac/ %ser is typically allocated a sin1le c/annel, /ic/ is %sed to trans0it all t/e %ser infor0ation. T/e band idt/ of eac/ c/annel is typically < k8 )= k8 for voice co00%nications.8o ever, t/e 0ini0%0 re2%ired band idt/ for speec/ is only = k8 . T/e allocated band idt/ is 0ade

ider t/an t/e 0ini0%0 a0o%nt re2%ired preventin1 c/annels fro0 interferin1 it/ one anot/er. T/ise;tra band idt/ is to allo for si1nals fro0 nei1/borin1 c/annels to be filtered o%t, and to allo for anydrift in t/e center fre2%ency of t/e trans0itter or receiver. In a typical syste0 %p to * L of t/e totalspectr%0 is asted d%e to t/e e;tra spacin1 bet een c/annels.

T/is proble0 beco0es orse as t/e c/annel band idt/ beco0es narro er, and t/e fre2%ency band increases. 6ost di1ital p/one syste0s %se vocoders to co0press t/e di1iti ed speec/. T/is allo sfor an increased syste0 capacity d%e to a red%ction in t/e band idt/ re2%ired for eac/ %ser. C%rrentvocoders re2%ire a data rate so0e /ere bet een >)


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in t/e 956A e;a0ple. !eca%se of t/is t/ere is no 1reat need for %sers to be ti0e 0%ltiple; as in T56A,t/%s t/ere is no over/ead associated it/ s itc/in1 bet een %sers. T/e ort/o1onality of t/e carriers0eans t/at eac/ carrier /as an inte1er n%0ber of cycles over a sy0bol period.

5%e to t/is, t/e spectr%0 of eac/ carrier /as a n%ll at t/e center fre2%ency of eac/ of t/e ot/er carriers in t/e syste0. T/is res%lts in no interference bet een t/e carriers, allo in1 t/en to be spaced asclose as t/eoretically possible. T/is overco0es t/e proble0 of over/ead carrier spacin1 re2%ired in956A. Eac/ carrier in an $956 si1nal /as a very narro band idt/ (i.e. < k8 , t/%s t/e res%ltin1sy0bol rate is lo . T/is res%lts in t/e si1nal /avin1 a /i1/ tolerance to 0%ltipat/ delay spread, as t/edelay spread 0%st be very lon1 to ca%se si1nificant I#I (e.1. * %sec .

3.7 OFDM -# # / , 93.7 OFDM -# # / , 9

To 1enerate $956 s%ccessf%lly t/e relations/ip bet een all t/e carriers 0%st be caref%lly

controlled to 0aintain t/e ort/o1onality of t/e carriers. 9or t/is reason, $956 is 1enerated by firstlyc/oosin1 t/e spectr%0 re2%ired, based on t/e inp%t data, and 0od%lation sc/e0e %sed. Eac/ carrier to be

prod%ced is assi1ned so0e data to trans0it. T/e re2%ired a0plit%de and p/ase of t/e carrier is t/en

calc%lated based on t/e 0od%lation sc/e0e (typically differential !P#K, P#K, or A6 .

T/e re2%ired spectr%0 is t/en converted back to its ti0e do0ain si1nal %sin1 an Inverse 9o%rier Transfor0. In 0ost applications, an Inverse 9ast 9o%rier Transfor0 (I99T is %sed. T/e I99T perfor0st/e transfor0ation very efficiently, and provides a si0ple ay of ens%rin1 t/e carrier si1nals prod%ced areort/o1onal. T/e 9ast 9o%rier Transfor0 (99T transfor0s a cyclic ti0e do0ain si1nal into its e2%ivalentfre2%ency spectr%0. T/is is done by findin1 t/e e2%ivalent avefor0, 1enerated by a s%0 of ort/o1onalsin%soidal co0ponents. T/e a0plit%de and p/ase of t/e sin%soidal co0ponents represent t/e fre2%encyspectr%0 of t/e ti0e do0ain si1nal.

. T/e I99T perfor0s t/e reverse process, transfor0in1 a spectr%0 (a0plit%de and p/ase of eac/co0ponent into a ti0e do0ain si1nal. An I99T converts a n%0ber of co0ple; data points, of len1t/,

/ic/ is a po er of +, into t/e ti0e do0ain si1nal of t/e sa0e n%0ber of points. Eac/ data point infre2%ency spectr%0 %sed for an 99T or I99T is called a bin. T/e ort/o1onal carriers re2%ired for t/e$956 si1nal can be easily 1enerated by settin1 t/e a0plit%de and p/ase of eac/ bin, t/en perfor0in1 t/eI99T. #ince eac/ bin of an I99T corresponds to t/e a0plit%de and p/ase of a set of ort/o1onal sin%soids,

9:


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t/e reverse process 1%arantees t/at t/e carriers 1enerated are ort/o1onal.

F,-. 3.2 OFDM B< $@ D,/- /

F,-. 3.2 s/o s t/e set%p for a basic $956 trans0itter and receiver. T/e si1nal 1enerated is a base band, t/%s t/e si1nal is filtered, t/en stepped %p in fre2%ency before trans0ittin1 t/e si1nal. $956ti0e do0ain avefor0s are c/osen s%c/ t/at 0%t%al ort/o1onality is ens%red even t/o%1/ s%b)carrier spectra 0ay overlap. Typically A6 or 5ifferential %adrat%re P/ase #/ift Keyin1 (5 P#K0od%lation sc/e0es are applied to t/e individ%al s%b carriers. To prevent I#I, t/e individ%al blocks areseparated by 1%ard intervals /erein t/e blocks are periodically e;tended.

3. M


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by D °. T/e oFp of t/e t o balanced 0od%lators are added in t/e adder and trans0itted.

F,-. 3.3 AM S?6 #T/e trans0itted si1nal is t/%s 1iven by

# (t V M< (t A cos (+Π9c t W M+ (t A sin (+Π9c t

8ence, t/e 0%ltiple;ed si1nal consists of t/e in)p/ase co0ponent XA M< (t and t/e 2%adrat%re p/aseco0ponent XYA M+ (t .

B/


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If t o or 0ore bits are co0bined in so0e sy0bols, t/en t/e si1nallin1 rate ill be red%ced. T/%s, t/efre2%ency of t/e carrier needed is also red%ced. T/is red%ces t/e trans0ission c/annel !. . 8ence, beca%se of 1ro%pin1 of bits in sy0bols t/e trans0ission c/annel !. can be red%ced. In P#K t os%ccessive bits in t/e data se2%ence are 1ro%ped to1et/er. T/is red%ces t/e bits rate or si1nallin1 rate andt/%s red%ces t/e !. of t/e c/annel. In case of !P#K, e kno t/at /en sy0. C/an1es t/e level, t/e

p/ase of t/e carrier is c/an1ed by distinct sy0bols. /en t/e sy0 is c/an1ed to ne;t sy0, t/en t/e p/ase of t/e carrier is c/an1ed by >*de1rees.

#.N$ IFP #%ccessive bits #y0bol P/ase s/ift in carrier

IV<


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$ne of t/e 0ost i0portant properties of $956 trans0issions is t/e rob%stness a1ainst 0%ltipat/delay spread. T/is is ac/ieved by /avin1 a lon1 sy0bol period, /ic/ 0ini0i es t/e I#I. T/e level of rob%stness, can in fact is increased even 0ore by t/e addition of a 1%ard period bF trans0itted sy0bols.T/e 1%ard period allo s ti0e for 0%ltipat/ si1 s fro0 t/e previo%s sy0bol to die a ay before t/einfor0ation fro0 t/e c%rrent sy0bol is 1at/ered.

T/e 0ost effective 1%ard period to %se is a cyclic e;tension of t/e sy0bol. If a 0irror in ti0e, of t/e end of t/e sy0bol avefor0 is p%t at t/e start of t/e sy0bol as t/e 1%ard period, t/is effectivelye;tends t/e len1t/ of t/e sy0bol, /ile 0aintainin1 t/e ort/o1onally of t/e avefor0. Usin1 t/is cyclice;tended sy0bol t/e sa0ples re2%ired for perfor0in1 t/e 99T (to decode t/e sy0 , can be takenany /ere over t/e len1t/ of t/e sy0. T/is provides 0%ltipat/ i00%nity as ell as sy0 ti0esync/roni ation tolerance.

As lon1 as t/e 0%ltipat/ delay ec/oes stay it/in t/e 1%ard period d%ration, t/ere is strictly noli0itation re1ardin1 t/e si1nal level of t/e ec/oes: t/ey 0ay even e;ceed t/e si1nal level of t/e s/orter pat/Z T/e si1nal ener1y fro0 all pat/s '%st adds at t/e inp%t to t/e receiver, and since t/e 99T is ener1y

conservative, t/e /ole available po er feeds t/e decoder. If t/e delay spread is lon1er t/an t/e 1%ardinterval t/en t/ey be1ins to ca%se I#I. 8o ever, provided t/e ec/oes are s%fficiently s0all t/ey do notca%se si1nificant proble0s.

T/is is tr%e 0ost of t/e ti0e as 0%ltipat/ ec/o s delayed lon1er t/an t/e 1%ard period ill /ave been reflected of very distant ob'ects. $t/er variations of 1%ard periods are possible. $ne possiblevariation is to /ave /alf t/e 1%ard period a cyclic e;tension of t/e sy0bol, as above, and t/e ot/er /alf a

ero a0plit%de si1nal. T/is ill res%lt in a si1nal as s/o n inF,-.3.+.

Usin1 t/is 0et/od t/e sy0bols can be easily identified. T/is possibly allo s for sy0bol ti0in1 to berecovered fro0 t/e si1nal, si0ply by applyin1 envelop detection. T/e disadvanta1e of %sin1 t/is 1%ard period 0et/od is t/at t/e ero period does not 1ive any 0%ltipat/ tolerance, t/%s t/e effective active 1%ard period is /alved in len1t/. It is interestin1 to note t/at t/is 1%ard period 0et/od /as not been 0entioned inany of t/e researc/ papers read, and it is still not clear /et/er sy0bol ti0in1 needs to be recovered %sin1t/is 0et/od.

F,-. 3.+ S#$ , / OFDM 6,- /< 6! >, - 5 6?


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9


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97

CHA%TER FOUR

IM%LEMENTATION OF OFDM

SYSTEMS


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C!/: #

4 IM%LEMENTATION OF OFDM SYSTEM

4.1 I :


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4.2.2 M


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4.3 H,-! D/ / R/ #69

An advanta1e of t/e $956 sc/e0e is t/at it nat%rally co0bats inter)sy0bol interference /ilestill allo in1 a /i1/ data rate. In order to f%lly %nderstand t/is, e ill first take a look at a traditional

ireless trans0ission as seen inF,-. 4.2 .

F,-. 4.2. T / , , /< 6? < / 6 ,66,

In a traditional trans0ission, if t/e syste0 as to /ave a /i1/ data rate t/e sy0bol len1t/ o%ld

/ave to be s/ort t/%s 0akin1 t/e rate /i1/ as seen in t/e 9i1.>.+. T/e proble0 it/ t/is tec/ni2%e is t/atin ireless trans0ission, inter sy0bol interference presents a /%1e proble0 /en s/ort sy0bols are %sed.As seen inF,-. 4.3 , even s0all I#I cons%0es 0%c/ of t/e act%al sy0bol. In t/is e;a0ple, I#I cons%0esro%1/ly one t/ird of eac/ sy0bol. T/erefore, a lar1e portion of t/e act%al infor0ation is corr%pted.

F,-. 4.3. Traditional sy0bol trans0ission it/ I#I

No let s take a look at an $956 trans0ission.

F,-. 4.4 $956 sy0bol trans0ission

In an $956 trans0ission, t/e sy0bols do not need to be s/ort to prod%ce a /i1/ data rate. T/is isill%strated inF,- 4.4. 4ecall t/at in an $956 trans0ission, t/e infor0ation is represented in t/efre2%encies of t/e sy0bol and not t/e sy0bol itself.

>:


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T/erefore, t/e sy0bol 0ay be very len1t/y b%t can still can a lar1e a0o%nt of infor0ation in itsco0ponent fre2%encies. A lar1e sy0bol len1t/ is a nat%ral ay to co0bat I#I as seen in 9i1>.*. T/e I#I in9i1. is t/e sa0e len1t/ as in 9i1. b%t only cons%0es ro%1/ly one ei1/t/ of eac/ sy0bol.

T/erefore, a lar1e portion of t/e act%al infor0ation is preserved.

F,-. 4.5. $956 trans0ission it/ I#I

4.4. % , ! OFDM9

4.4.1 %#/@* *M#/ % ># R/ , 9

An $956 si1nal 0ay e;/ibit a /i1/ instantaneo%s peak po er it/ respect to t/e avera1e si1nallevel, seein1 t/at t/e $956 si1nal is t/e s%perposition of a lar1e n%0ber of 0od%lated s%b c/annelsi1nals. In addition, /en a ti0e)do0ain si1nal 0oves fro0 a lo to a /i1/ instantaneo%s po er

avefor0, lar1e a0plit%de s in1s are enco%ntered. In t/e conte;t, t/e peak)to)0ean po er envelopefl%ct%ates considerably, /en traversin1 t/e ori1in %pon s itc/in1 fro0 one p/asor to anot/er.

In order to solve t/ese proble0s, t o t/in1s can be done:

• R# $# !# :#/@* * #/ : ># / , . Usin1 a different encodin1 or 0appin1 sc/e0e before0od%lation can ac/ieve t/is.• I : =# !# / :9


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;1;1> C channe# Inter!erence;1;1> C channe# Inter!erence

Co c/annel interference in cell%lar co00%nications syste0s are co0bated by co0binin1 adaptiveantenna tec/ni2%es it/ $956 trans0issions. it/ t/e aid of bea0 steerin1, it is possible to foc%s t/ereceiver s antenna bean on t/e served %ser, /ile atten%atin1 t/e co c/annel interferers. T/is is si1nificant

since $956 is sensitive to co c/annel interferences.

4.5ALGORITHMS USED IN THE OFDM TRANSCEIVER S DESIGN

4.5.1 FAST*FOURIER TRANSFORM

4.5.1.1 ALTERNATIVE SOLUTIONS AND DESIGN CHOICE

As a specification reference for 0y $956 transceiver s para0eters I %sed @ +.


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As can be seen fro0 t/e final e;pression for Cooley)T%key al1orit/0, by %sin1 a tec/ni2%e of ti0e and fre2%ency indices re)0appin1 B>)point 99T is split into t o @)point 99Ts:

• T/e inner @)point 99T it/ n< ti0e inde; calc%lated for a specific val%e of n+.T/ro%1/ t/e dependence on n+ val%e t/e inner @)point 99T is e0bedded in t/e o%ter @) point 99T.

• T/e o%ter @)point 99T it/ n+ ti0e inde;.

4.5.1.4 M < ,:, )point 9ast 9o%rier Transfor0 re2%ires >D nontrivial co0ple; 0%ltiplications. 8o ever, t/ereare only ei1/t %ni2%e sets of co0ple; constants /ic/ allo to co0p%te all >D 0%ltiplications it/

conditional interc/an1e and ne1ation operations. T/is i0portant observation co0bined it/ t/erepresentation of eac/ constant in Canonical #i1ned)5i1it representation (binary ei1/tsϵ [)


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• 6akes efficient %se of t/e spectr%0 by allo in1 overlap.• !y dividin1 t/e c/annel into narro band flat fadin1 s%b c/annels, $956 is 0ore resistant to

fre2%ency selective fadin1s t/an sin1le carrier syste0s are.• Eli0inates I#I and I9I t/ro%1/ %se of a cyclic prefi;.• Usin1 ade2%ate c/annel codin1 and interleavin1 one can recover sy0bols lost d%e to t/e

fre2%ency selectivity of t/e c/annel.• C/annel e2%ali ation beco0es si0pler t/an by %sin1 adaptive e2%ali ation tec/ni2%es it/ sin1lecarrier syste0s.

• It is possible to %se 0a;i0%0 likeli/ood decodin1 it/ reasonable co0ple;ity.

• $956 is co0p%tationally efficient by %sin1 99T tec/ni2%es to i0ple0ent t/e 0od%lation

and de0od%lation f%nctions. Also, for 0%ltiple co00%nication c/annels, as is t/e case in di1ital

a%dio broadcastin1 (5A! syste0s, partial 99T al1orit/0s can be %sed in order to i0ple0ent

pro1ra0 selection and deci0ation.

• In con'%nction it/ differential 0od%lation t/ere is no need to i0ple0ent a c/annel esti0ator.• Is less sensitive to sa0ple ti0in1 offsets t/an sin1le carrier syste0s.

• Provides 1ood protection a1ainst co c/annel interference and i0p%lsive parasitic noise.

• Preservation of ort/o1onality in severe 0%ltipat/.

• Used for /i1/est speed applications.

• #%pports dyna0ic packet access.

• #%pport for TM and 4M diversity.

• #%pport for:i. adaptive antenna arrays

ii. 6IN$Fspace ti0e codin1iii. adaptive 0od%lation and toneFpo er allocation

4.7 D,6/ =/ /-#6 OFDM9

T/e $956 si1nal /as a noise like a0plit%de it/ a very lar1e dyna0ic ran1e, t/erefore it re2%ires

49 po er a0plifiers it/ a /i1/ peak to avera1e po er ratio.• It is 0ore sensitive to carrier fre2%ency offset and drift t/an sin1le carrier syste0s are d%e to

leaka1e of t/e 59T.

>?


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4. OFDM A::


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>

CHA%TER FIVE RESULT & DISCUSSION


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Chapter

5 RESULT & DISCUSSION

SIMULATION RESULTS

>7


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"I7@9ED 5.1 >uadrature 4p itude $odu ation > $3

"I7@9ED 5.2 INFE9SE " ST "O@9IE9 T9 NS"O9$ POINT I""T3

>B


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;8


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"I7@9ED 5.& " ST "O@9IE9 T9 NS"O9$ POINT ""T3

Figure: 5.4 Demodulation of QAM

Figure: 5.5 RTL Schematic of OFDM

;:


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Figure: 5.6 Simulation of OFDM

;9


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;>

CHA%TER SI

CONCLUSION AND SCO%E OF ORK


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C!/: #

+ CONCLUSION AND SCO%E OF ORK

T/e p%rpose of t/is doc%0ent as to 1ive so0e insi1/t into t/e po er of t/e $956 trans0issionsc/e0e. It /as disc%ssed not only t/e trans0ission sc/e0e itself, b%t also so0e of t/e proble0s t/at are presented in 0obile co00%nications as ell as t/e tec/ni2%es to correct t/e0.

5i1ital Co00%nications is a rapidly 1ro in1 ind%stry and $rt/o1onal 9re2%ency 5ivision 6%ltiple;in1is on t/e forefront of t/is tec/nolo1y. $956 ill prove to revol%tioni e 0obile co00%nications byallo in1 it to be 0ore reliable and rob%st /ile 0aintainin1 t/e /i1/ data rate t/at di1italco00%nications de0ands.

T/e n%0ber of clock cycles re2%ired is red%ced and bot/ blocks 1ives t/e final o%tp%ts as desired. 8ere,

t/e real val%e inp%ts are 1iven to t/e 99T blocks /ile all t/e i0a1inary inp%t val%es are ero.e /ave s%ccessf%lly i0ple0ented t/e @)point I99T " 99T al1orit/0s %sin1 &853 to be %sed in t/e

@ +.


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REFRENCES• !a/ai, A., and !. #alt ber1. 6%lticarrier 5i1ital Co00%nications: T/eory and Applications of

$956. Ne ?ork: Kl% er Acade0icFPlen%0 P%blis/ers,

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