All CHAPTER_mod_ Phase2.Doc (Modified) (1)

8/12/2019 All CHAPTER_mod_ Phase2.Doc (Modified) (1)

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CHAPTER-1

INTRODUCTION

Wireless technologies have evolved remarkably since Guglielmo

Marconi first demonstrated radio's ability to provide continuous contact with

ships sailing in the English Channel in 18!" #ew theories and applications of

wireless technologies have been developed by hundreds and thousands of

scientists and engineers through the world ever since" Wireless

communications can be regarded as the most important development that has

an e$tremely wide range of applications from %& remote control and cordless

phones to cellular phones and satellitebased %& systems" (t changed people's

life style in every aspect" Especially during the last decade) the mobile radio

communications industry has grown by an e$ponentially increasing rate)

fueled by the digital and *+ ,radio fre-uency. circuits design) fabrication and

integration techni-ues and more computing power in chips" %his trend will

continue with an even greater pace in the near future"

1.1.WIRELESS COMMUNICATION SYSTEMS:

/ wide variety of different wireless data technologies now e$ist) some

in direct competition with one another) others designed to be optimal for

specific applications" Wireless technologies can be evaluated by a variety of

different metrics" 0f the standards evaluated) these can be grouped as

1"Wireless ersonnel /rea #etwork ,W/#. systems 2"Wireless 3ocal /rea

#etwork ,W3/#. systems 4"Wireless Metropolitan /rea #etworks ,WM/#."

1.2. OFDM SYSTEMS:

0rthogonal +re-uency 5ivision Multiple$ing ,0+5M. has grown to be

the most popular communications systems in high speed communications"

0+5M technology is the future of wireless communications" 0+5M is a


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multicarrier transmission techni-ue) which divides the bandwidth into many

carriers each one is modulated by a low rate data stream" (n term of multiple

access techni-ue) 0+5M is similar to +5M/ in that the multiple user access isachieved by subdividing the available bandwidth into multiple channels that

are then allocated to users" 6owever) 0+5M uses the spectrum much more

efficiently by spacing the channels much closer together" %his is achieved by

making all the carriers orthogonal to one another) preventing interference

between the closely spaced carriers" %he difference between +5M and 0+5M

is as shown in the figure 1"1"

Figure 1.1 Frequen! "#e$ru% &' FDM "ign() (n* OFDM "ign()

0+5M is simply defined as a form of multicarrier modulation where

the carrier spacing is carefully selected so that each sub carrier is orthogonal to

the other sub carriers" %wo signals are orthogonal if their dot product is 7ero"

%hat is) if you take two signals multiply them together and if their integral over

an interval is 7ero) then two signals are orthogonal in that interval"

0rthogonality can be achieved by carefully selecting carrier spacing) such as

letting the carrier spacing be e-ual to the reciprocal of the useful symbol


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period" /s the sub carriers are orthogonal) the spectrum of each carrier has a

null at the centre fre-uency of each of the other carriers in the system" %his

results in no interference between the carriers) allowing them to be spaced asclose as theoretically possible" Mathematically) suppose we have a set of

signals then)

,1"1.

%he signals are orthogonal if the integral value is 7ero over the intervala a9%:) where % is the symbol period" ;ince the carriers are orthogonal to

each other the nulls of one carrier coincides with the peak of another sub

carrier" /s a result it is possible to e$tract the sub carrier of interest"

Figure 1.2 Ti%e (n* Frequen! *&%(in +ie, &' OFDM "ign()


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1.2.1. OFDM ener($i&n (n* Ree#$i&n

+igure 1"4 shows the block diagram of a typical 0+5M transceiver"

%he transmitter section converts digital data to be transmitted) into a mappingof subcarrier amplitude and phase" (t then transforms this spectral

representation of the data into the time domain using an (nverse 5iscrete

+ourier %ransform ,(5+%." %he (nverse +ast +ourier %ransform ,(++%.

performs the same operations as an (5+%) e$cept that it is much more

computationally efficiency) and so is used in all practical systems" (n order to

transmit the 0+5M signal the calculated time domain signal is then mi$ed up

to the re-uired fre-uency" %he receiver performs the reverse operation of the

transmitter) mi$ing the *+ signal to base band for processing) then using a +ast

+ourier %ransform ,++%. to analy7e the signal in the fre-uency domain" %he

amplitude and phase of the subcarriers is then picked out and converted back

to digital data" %he (++% and the ++% are complementary function and the

most appropriate term depends on whether the signal is being received or

generated" (n cases where the signal is independent of this distinction then the

term ++% and (++% is used interchange

"

Figure 1. /)&0 *i(gr(% &' OFDM $r(n"%i$$er (n* reei+er


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%he high data rate serial input bit stream is fed into serial to parallel

converter to get low data rate output parallel bit stream" (nput bit stream is

taken as binary data" %he low data rate parallel bit stream is modulated in;ignal mapper" Modulation can be ;=) and >/M etc" %he

modulated data are served as input to inverse fast +ourier transform so that

each subcarrier is assigned with a specific fre-uency" %he fre-uencies selected

are orthogonal fre-uencies" (n this block) orthogonality in subcarriers is

introduced" (n (++%) the fre-uency domain 0+5M symbols are converted into

time domain 0+5M symbols" Guard interval is introduced in each 0+5M

symbol to eliminate inter symbol interference ,(;(." /ll the 0+5M symbols

are taken as input to parallel to serial data" %hese 0+5M symbols constitute a

frame" / number of frames can be regarded as one 0+5M signal" %his 0+5M

signal is allowed to pass through digital to analog converter ,5/C." (n 5/C

the 0+5M signal is fed to *+ power amplifier for transmission" %hen the

signal is allowed to pass through additive white Gaussian noise channel

,/WG# channel."

/t the receiver part) the received 0+5M signal is fed to analog to digital

converter ,/5C. and is taken as input to serial to parallel converter" (n these

parallel 0+5M symbols) Guard interval is removed and it is allowed to pass

through +ast +ourier transform" 6ere the time domain 0+5M symbols are

converted into fre-uency domain" /fter this it is fed into ;ignal demapper fordemodulation purpose" /nd finally the low data rate parallel bit stream is

converted into high data rate serial bit stream which is in form of binary"

1.2.2. OFDM SYSTEM:

%he following block diagram shows 0rthogonal +re-uency 5ivision

Multiple$ing ,0+5M. system consists of various blocks as in figure 1"?"%he

input data bits are mapped by the modulation >;= where the bits are


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grouped as symbols and (nverse +ast +ourier transform is taken" #ow the

training se-uences and cyclic prefi$ are inserted which is passed through the

/WG# and +ading channel" With the help of synchroni7ation) the 0+5Msymbols are mapped to the original position if any offset occurs due to the

channel behavior" /fter that removal of cyclic prefi$) training se-uences and

++% is taken for the 0+5M symbols" #ow the symbols are decoded into bits"

Figure 1. /)&0 *i(gr(% &' OFDM S!"$e% ,i$ S!nr&ni3($i&n

1.. ISSUES ASSOCIATED WITH THE RECEI4ER SU/-SYSTEM:

0+5M systems are very sensitive to timing synchroni7ation) fre-uency

offset synchroni7ation and fre-uencyselective fading channels" Carrier

fre-uency offset ,C+0. estimation and compensation are critical in 0+5M

communications) since the orthogonality of subcarriers makes a simple 0+5M

receiver feasible" 6owever) C+0 destroys the orthogonality between active

users) and causes intercarrier interference ,(C(. and multipleaccess

interference ,M/(." %ime synchroni7ation is another issue involves finding the

DATA /ITS

SYNCHRONI5ATION

6PS7

MAPPIN

IFFT CYCLIC

PREFI8

AWN 9

FADIN

CHANNEL

REMO4ECYCLIC

PREFI8TR

AININ

SE6UENCE

FFTE6UAILI5ATION

SYM/OLDETECTIO

N

TRAININ

SE6UENCE


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best possible time instant for the start of received 0+5M frame" ;o it is

necessary to mitigate the above two issues associated with the receiver sub

system"

1.. LITERATURE SUR4EY:

(n 1:) the authors discussed about synchroni7ation using training

se-uences" Estimation of timing offset) fre-uency offset are done in this

report"

(n 2:) symbol detection using one training se-uence for two symbols"

%he algorithm use Cram@erA*ao lower bound for fre-uency offset"

(n 4:) describes about Ma$imum 3ikelihood Estimation ,M3E. of

symbol and carrier fre-uency offset with the help of Cyclic prefi$"

(n ?:) describes optimal M3 estimator of time and fre-uency offsetusing window" %he correlation residing in cyclic prefi$ samples and

useful data samples"

1.;. SCOPE OF THE WOR7:

(t is aimed to study the receiver synchroni7ation algorithm of 0+5M

systems which is shown in figure 1"? by simulating a transceiver model" With

the help of design specification chosen) the algorithm in 1: was carried out

with the help of M/%3/< simulation considering the effects of multipath

channel impairments) Carrier +re-uency 0ffset ,C+0. and synchroni7ation of

0+5M symbol"


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+ollowing to this introduction) Chapter 2 describes various multipath

channel and provides generation of training se-uence" Chapter 4 e$plains the

techni-ues involved in synchroni7ation of 0+5M receiver over time) carrierfre-uency and phase offsets" %he simulation specifications and observed

results are discussed in Chapter ?" Chapter B concludes the work carried out in

phase(( proect work"


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CHAPTER-2

MULTIPATH CHANNELS AND ENERATION OF

TRAININ SE6UENCE

(n this chapter we will first describe fading and multipath) the

performancelimiting phenomena that occur in wireless atmospheric radio

channels) and then turn our attention to modeling and simulation of these

channels" +ading and Multipath occur in many radio communication systems"

%hese effects were first observed and analy7ed in troposcatter systems in the

1BDs and early 1Ds" (n any wireless communication system there could be

more than one path over which the signal can travel between the transmitter

and receiver antennas" %he presence of multiple paths is due to atmospheric

scattering and refraction) or reflections from buildings and other obects" (n a

multipath situation) the signals arriving along different paths will have

different attenuations and delays and they might add at the receiving antenna

either constructively or destructively" (f the path lengths andFor the geometry

change due to changes in the transmission medium or due to relative motion of

the antennas) as in the mobile case) the signal level might be subected to wild

fluctuations" Multipath fading affects the signal in two ways dispersion ,time

spreading or fre-uency selectivity. and timevariant behavior"

Mobile communication is affected) in addition to multipath ,or small-

scale fading.) to another type of fading which is referred to as shadowor large

scale fading" ;hadow fading reveals itself as an attenuation of the average

signal power" ;hadow fading is induced by prominent terrain contours ,hills)

buildings) etc". between transmitter and receiver" %he receiver is said to be

shadowedby these obects"


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2.1. WIRELESS CHANNELS:

Wireless channels operate through electromagnetic radiation from the

transmitter to the receiver" (n principle) one could solve the electromagneticfield e-uations) in conunction with the transmitted signal) to find the

electromagnetic field impinging on the receiver antenna" %his would have to

be done taking into account the obstructions caused by ground) buildings)

vehicles) etc" in the vicinity of this electromagnetic wave"

/ good understanding of the wireless channel) its key physical

parameters and the modeling issues) lays the foundation for simulating a

wireless channel" %he defining characteristic of the mobile wireless channel is

the variations of the channel strength over time and over fre-uency" %he

variations can be roughly divided into two types

Large-scale fading) due to path loss of signal as a function of

distance and shadowing by large obects such as buildings and

hills" %his occurs as the mobile moves through a distance of the

order of the cell si7e) and is typically fre-uency independent"

Small-scale fading) due to the constructive and destructive

interference of the multiple signal paths between the transmitter

and receiver" %his occurs at the spatial scale of the order of the

carrier wavelength) and is fre-uency dependent"

2.1.1. R(!)eig (nne):

*ayleigh channel is also a kind of slow fading channel" (n a radio link)

the *+ signal from the transmitter may be reflected from obects such as hills)

buildings) or vehicles" %his gives rise to multiple transmission paths at the

receiver" %he relative phase of multiple reflected signals can causeconstructive or destructive interference at the receiver" %his is e$perience over


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very short distances ,typically at half wavelength distances.) thus is given the

termfast fading" %he *ayleigh distribution is commonly used to describe the

statistical time varying nature of the received signal power"

2.1.2. Di"re$e %u)$i#($ (nne) %&*e):

(f a multipath channel is composed of a set of discrete resolvable

components that originate as reflections or scattering from smaller structures)

e"g") houses) small hills) etc") it is called a discrete multipath channel" %he

model in its most general form has) in addition to variable tap gains) variable

delays and a variable number of taps" %his model is applicable mostly to

rapidly changing environments" %he low passe-uivalent impulse response of a

discrete multipath channel is given in the following e-uation 2"1)

H ,2"1.

With the corresponding output is given by)

H ,2"2.

+or many channels it can be assumed as a reasonable appro$imation that

the number of discrete components is constant and the delay values vary very

slowly and can also be assumed constant" %he model then simplify

H ,2"4.

%his multipath channel model can be reali7ed by means of multi tap +(*

filter) where the number of taps depends on number of reflected paths"


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2.2. INTRODUCTION OF SYNCHRONI5ATION:

;ynchroni7ation is the method which synchroni7es the transmitter and

receiver of the 0+5M symbols" %here are two categories of synchroni7ation

in general

D($(-Ai*e* %e$&*":/ known data se-uences is to be transmitted and

which has to be known to both transmitter and receiver" %he drawback

of the dataaided scheme is the leakage of the bandwidth efficiency due

to redundancy overhead"

%wo methods are used namely)

ilot based

%raining se-uence based

(n #i)&$


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Tenique" in S!nr&ni3($i&n:

Correlation based

(n &rre)($i&n


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Figure 2.1 T!#e" &' "!nr&ni3($i&n err&r

2.. ENERATION OF TRAININ SE6UENCE:

/ seudorandom #oise ,#. se-uence is a se-uence of binary

numbers) e"g" I1) which appears to be randomJ but is in fact perfectly

deterministic" %he se-uence appears to be random in the sense that the binary

values and groups or runs of the same binary value occur in the se-uence in

the same proportion they would if the se-uence were being generated based on

a fair Kcoin tossingK e$periment" (n the e$periment) each head could result in

one binary value and a tail the other value"

/ # se-uence is generated and used as a training se-uence" 6ere

assumed order H ) the generator polynomial used is $ 9$ ?9 1" (n the

simulation we used training se-uenceH2B) so it will produce B11 symbols"

0ut of that the first 2B symbols are used as training se-uence" # se-uence isconstructed by linear shift back registers and e$clusive 0* gate as shown in

figure 2"2"

Figure 2.2 ener($i&n &' PN "equene

We consider the effects of ;ymbol timing and *+ mismatch oscillator which

leads to timing offset and fre-uency offset respectively are e$plained in the

future chapters


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CHAPTER-

OFDM RECEI4ER DESIN CONSIDERATIONS

(n digital radio communication systems information symbols are

transmitted by means of suitably chosen waveforms that modulate a carrier

signal with a suitably chosen fre-uency" 5ue to the radio environment)

imperfections generate fluctuations in these waveforms actually are received"


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;econd it has to estimate and correct for the carrier fre-uency offset of the

received signal because any offset which introduces (C(" (n this chapter we

discuss timing synchroni7ation techni-ues) fre-uency offset estimationtechni-ues and phase offset estimation techni-ues in detail in order to nullify

the effects of (C(" %he baseband modulated signals(n)) after parallel to serial

conversion and (++% is e$pressed as)

,4"1.

%he received comple$ signal that is transmitted over a multipath channel

with impulse response h,n)l.) $,n. is the output signal which is e$pressed as

$,n.H ,4"2.

%he received signal is corrupted by /WG# noise and fading by

channel" %he offsets between the transmitter and receiver is modeled in

received signal with schematic shown in figure 4"1" %he received is modeled

with e-uation ,4"4."

9w,n. ,4"4.

Where)

nknown arrival time of the received symbol

+re-uency offset"

/WG# channel


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Figure .1 /)&0 *i(gr(% &' $i%e 'requen! #("e &''"e$ in"er$i&n in

$r(n"%i$$e* "ign() ,i$ AWN (nne)

%he estimated offsets are used to correct the received signal beforepassing the same to the detector" %he process carrier out in the course is

depicted in figure 4"2"

Figure .2 In$ern()


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6ence) 0+5M needs to employ time and fre-uency synchroni7ation"

%ime synchroni7ation is to decide for the symbol boundaries" Commonly) a

se-uence of known symbols preamble ,training se-uence. is used to detect thesymbol boundaries" (t has less sensitivity to timing offset as compared with

singlecarrier systems) since timing offset does not violate the orthogonality of

subcarriers in 0+5M system) but causes (;( in singlecarrier systems"

%he 0+5M symbol is added with training se-uences and cyclically

e$tended and transmitted over the air" (f the channel is static during the

duration of one 0+5M symbol and if the receiver is perfectly synchroni7ed)

the subcarriers orthogonality is maintained at the receiver" %herefore) the data

transmitted on each subcarrier can be recovered by means of a 5+%"

6owever) the receiver has to be synchroni7ed with the transmitter both in

fre-uency and time domain"

%he method uses the training se-uence to detect the beginning of the

0+5M symbol" %he frame structure of the 0+5M structure is shown in

figure4"4"+or every 1DD 0+5M symbols) one training se-uence is used"

%raining se-uence of length of B12 is used"

%raining

se-uence

;ym1 ;ym2 N" N" ;ym

1DD

%raining

se-uence

;ym1 ;ym2 N ;ym

1DD

Figure . S$ru$ure &' OFDM "!%


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se-uence is correlated with the received signal to achieve timing

synchroni7ation" (n a buffer having a length of one subframe containing the

received signal) the samples over training se-uences length are collected fromtheir reference locations in the transmitted se-uence and correlated with the

local copy of training se-uence" %he algorithm is described by e-uation ,4"?.)

arg min O ,4"?.

Where)

HEstimated %iming point

#H 3ength of training se-uence

.2. CARRIER FRE6UENCY OFFSET:

0ne of the principal disadvantages of 0+5M is sensitivity to fre-uency

offset in the channel" %here are two deleterious effects caused by fre-uency

offsetJ one is the reduction of signal amplitude in the output of the filtersmatched to each of the carriers and the second is introduction of (C( from the

other carriers which are now no longer orthogonal to the filter"


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/ fre-uency offset estimate may be generated at the receiver with the

aid of known training se-uences to the receiver" /n algorithm based on

correlating the cyclic prefi$ is presented to estimate fre-uency offset from thedemodulated data signals in the receiver" %he techni-ue involves repetition of

a data symbol and comparison of the phases of each of the carriers between the

successive symbols" ;ince the modulation phase values are not changed) the

phase shift of each of the carriers between successive repeated symbols is due

to the fre-uency offset" %he fre-uency offset is estimated using a ma$imum

likelihood estimate ,M3E. algorithm as in e-uation ,4"B."

Figure . C(rrier Frequen! O''"e$ in OFDM "#e$ru%

%he procedure for obtaining fre-uency offset is obtained by leaving the

training se-uences) considers only the 0+5M symbols which include C" %he

correlation of cyclic prefi$ with the tail of the 0+5M symbols yields the

estimated value of fre-uency offset) provided by e-uation ,4"B. and this

method is called as ma$imum likelihood estimate ,M3E. "

,4"B.


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.. P("e &''"e$ :

+re-uency estimation alone could not complete the carrier

synchroni7ation) additionally it re-uires estimating and correcting the phase

offset also" 3et the C+0 corrected signal is represented is d,k.) then the

resultant fre-uency offset corrected signal r,k.) which is represented as

,4".

/ll the symbols are phase rotated by a constant " %o estimate the

phase) received signal is r,k. is multiplied with conugate of training se-uence)

which is represented as

,4"!.

%he angle of y,k. provides the estimate of the phase" With this) the

phase corrected signal is obtained as 7,k. given by)

,4"8.

%his 7,k. is synchroni7ed signal which is passed through a 0+5M

demodulator for further processing to retrieve the information from the signal"


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CHAPTER

OFDM RECEI4ER SIMULATION

%he block diagram of 0+5M system shown in figure has been carried

out with the following design specifications with anomalies described in the

earlier chapters like %ime offset) Carrier +re-uency offset and phase offset"

.1. DESIN SPECIFICATIONS:

(n this work) the simulation parameters have taken as stated in 1:" %his

used 2B point fast +ourier transform ,++%. with 2?D active subcarriers) 1B

guard subcarriers) 1? cyclic prefi$) sample fre-uency of 1"M67) subcarriers

spacing of "2Bk67) training se-uences of 2B" %hese have been summari7ed

in table ?"1,a.) ,b."

T( De"ign "#ei'i($i&n =I>

PARAMETERS 4ALUE

#fft 2B#sed Carriers 2?D

#umber of lower fre-uency guard sub carriers 8

#umber of higher fre-uency guard sub carriers !

Cyclic prefi$ 1?

T(


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.2. SIMULATION OF OFDM SYSTEM IN RAYLEIH CHANNEL:

%he simulation of 0+5M system is carried out with the help of

following design specification in *ayleigh multipath channel

T(


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5933 5933.2 5933.4 5933.6 5933.8 5934 5934.2 5934.4 5934.6 5934.8 59350

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1PROBABILITY VS ESTIMATED TIMING

estimated timing

probability

Figure .1 Pr&


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0 5 10 15 20 250

0.2

0.4

0.6

0.8

1

1.2x 10

-5

SNR in dB

MSE

forCFO

MSE plot for delw=0.0025

Figure .2. SNR 4" MSE '&r [email protected]

(t is observed that the offset is possible to estimate e$actly while the channel is

/WG#" (f the noise increases or channel becomes highly faded) the error in

the estimate becomes larger beyond the values"

.. PHASE OFFSET ESTIMATION

(n figure ?"4 as ;#* increases) M;E of hase offset estimation,in

radian. decreases"


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Figure . SNR 4" MSE &' #("e &''"e$=B.;2; in

r(*i(n>

%he following table shows estimation of phase for different values of

offset shown in %able ?"?

T(

P("e

&''"e$=in

r(*i(n>

E"$i%($e*

&''"e$=AWN

(nne)>

E"$i%($e*

&''"e$=R(!)eig

(nne)>

D"B24 D"B2?1 D"B4

D"1D D"1D! D"1!D

D"8 D"D D"B4

D"!8B? D"!8BD D"!1

D"8!2! D"8!4D D"88B?D"B D"B D"B8

1"D?!2 1"D?8 1"D4?D

1"14?B 1"14?8 1"1BD4

1"221! 1"2218 1"2!4


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/s in the case of fre-uency estimation) the phase estimate also works

well in the higher ;#* and deviates from the e$pected while the noise

increases as well as fading increases"

CHAPTER- ;

CONCLUSION AND FUTURE WOR7

;.1. CONCLUSION:

%hus in this proect 0+5M system is simulated based on the selected

specifications and receiver algorithm was verified with the help of M/%3/E; (# 0+5M

;X;%EMV) #ational Conference on *ecent %rends in (nformation and

Communication %echnology *%(C%L12)

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