multi user detection in cdma project report

7/23/2019 multi user detection in cdma project report

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A SEMINAR REPORT ON

MULTI-USER DETECTION IN CDMA

Submitted in partial fulfillment of the requirements

for the award of the degree of

Bachelor of Technology

In

Electronics & Communication Engineering

Guide Submitted b!

Mrs" PIN#I NA$A# TAR%N #%MAR

Roll No" &'''&()*&+

Amity School of Engineering & Technology

Guru Gobind Singh Indraprastha University GGSI!U"# $elhi

%'(%)"


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CE*TI+ICATE

This is to ,ertif! that the seminar report entitled -M%.TI/%SER 0ETE1TION IN 10MA2

submitted b! TAR%N #%MAR 3Enrollment number &'''&()*&+45"TE16

3E1E74ASET4)&&+7 has been a,,omplished under m! guidan,e.

This report is submitted in partial fulfillment of the award of degree of 5A16E.OR O8

TE16NO.OG$ in (th!ear at AMIT$ S16OO. O8 ENGG" AN0 TE16" affiliated to G%R%

GO5IN0 SING6 IN0RAPRAST6A %NI9ERSIT$: 0E.6I"

0ATE:

P.A1E:NE;0E.6I

Mrs" PIN#I NA$A# 0r" RE#6A AGGAR;A.

SEMINAR G%I0E 6O0 3E1E7

ii


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AC,-./0E$GE1E-T

I am than


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ABST*ACT

iv


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One of the ma?or issues in present wireless ,ommuni,ations is how users share the resour,es and

parti,ularl!: how the! a,,ess to a ,ommon frequen,! band" 1ode 0i=ision Multiple A,,ess 310MA7 is

one of the te,hniques e@ploited in third generation ,ommuni,ations s!stems and is to be emplo!ed in the

ne@t generation" In 10MA ea,h user uses dire,t sequen,e spread spe,trum 30S/SS7 to modulate its bits

with an assigned ,ode: spreading them o=er the entire frequen,! band" ;hile t!pi,al re,ei=ers deal onl!

with interferen,es and noise intrinsi, to the ,hannel 3i"e" Inter/S!mboli, Interferen,e: intermodulation

produ,ts: spurious frequen,ies: and thermal noise7: in 10MA we also ha=e interferen,e produ,ed b! other

users a,,essing the ,hannel at the same time" Interferen,e limitation due to the simultaneous a,,ess of

multiple users s!stems has been the stimulus to the de=elopment of a powerful famil! of Signal

Pro,essing te,hniques: namel! Multi/user 0ete,tion 3M%07"

These te,hniques ha=e been e@tensi=el! applied to 10MA s!stems" Thus: most of last generation digital

,ommuni,ation s!stems su,h as Global Positioning S!stem 3GPS7: wireless *&)"''b: %ni=ersal Mobile

Tele,ommuni,ation S!stem 3%MTS7: et,: ma! ta


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se=eral users: %MTS in,orporates 1ode 0i=ision Multiple A,,ess 310MA7" 5esides a lot of pra,ti,al

ad=antages: 10MA suffers from multi/ user interferen,e limiting spe,tral effi,ien,! dramati,all!"

6owe=er: bandwidth is a =er! =aluable resour,e and should be used as effi,ientl! as possible" One

appropriate mean to in,rease spe,tral effi,ien,! of 10MA s!stems is multi/ user dete,tion"

This report gi=es an o=er=iew of different multi/ user dete,tion te,hniques" Their performan,e is

,ompared with the ,on=entional single/user dete,tion in,luding ,hannel ,oding" Spe,ifi,all!: linear as

well as nonlinear multi/ user dete,tors are ,onsidered" Effi,ient reali>ations of linear dete,tors are gi=en

leading to impro=ed nonlinear te,hniques" It is shown that nonlinear M%0 in,luding ,hannel de,oding

,an a,hie=e a spe,tral effi,ien,! twi,e as high as that of the well/


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AC,-./0E$GE1E-T iii

ABST*ACT iv

0IST .+ +IGU*ES

23 I-T.$UCTI.-

1.1 Synchronous CDMA 9

1.2 Asynchronous CDMA 10

%3 !*ACTICA0 C$1A *ECIE4E*

2.1. Description 11

2.2 Perfect power control 12

2.3 Near far effect in CDMA 13

53 C$1A C.11U-ICATI.- S6STE1 1.$E0 A-$ 1U$

3.1 Multiple access interference (MA! 1"

3.2 MA #ersus ntersy$%ol interference (S! 1"

73 1A8I1U1 0I,E0I9..$ SE:UE-CE $ETECTI.-

&.3 'asic concept 1

&.& )or$ulation 1

3


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'3 C.-4E-TI.-A0 $ETECTI.- +.* 1U0TI!0E ACCESSES

*.1 +utput of the ,th user 19

*.2 Matri- Notation 19

*.3 Data ter$ an MA ter$ 20

;3 SYNCHRONOUS AND ASYNCHRONOUS CHANNEL

".1 Channel correlation $atri- 21

".2 Decorrelatin/ etector 22

".3 Polyno$ial e-pansion etectors 22

7.1I-I1U1 1EA- S:UA*E E**.* 11SE" $ETECTI.- 24


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0IST .+ +IGU*ES

Chapter ( 2

8ig" '"' As!n,hronous 10MA B

5


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Chapter ( %

8ig" )"' Pra,ti,al 10MA re,ei=ers ''

8ig" )") A;GN =s" %sers graph ')

Chapter ( 5

8ig" C"' 10MA ,ommuni,ation s!stem model '

Chapter = '

8ig +"' 1on=entional dete,tion for multiple a,,esses 'B

Chapter = ;

8ig "' As!n,hronous and S!n,hronous ,hannel ))

Chapter = es near/far effe,t7"

8E1/ and AR/s!stems"

0i=ersit!/s!stems / Spatial / 8requen,! Q Time"

Multi/user dete,tion"

$.) MAI *ersus Inersy+,o# &nerference 'ISI(

Note that there e@ists a strong parallelism between the problem of MAI and that of ISI

6en,e: a number of multi/user dete,tors ha=e their equali>er ,ounter parts as

Ma@imum li


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ero/for,ing"

Minimum mean square"

0e,ision feedba,


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CHAPTER-) MAIMUM LIELIHOOD SEUENCE

DETECTION

).$3%s&c conce!

The Ma@imum .iity/ In e@hausti=e sear,h )N=e,tors to be

,onsidered 3users:Nbits7"

Requires estimation of received amplitudes and phasesthat ta


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CHAPTER -4 CON5ENTIONAL DETECTION 6OR MULTIPLE

ACCESSES

4.1Ou!u of he 7h user

0ete,tion qualit! depends on ,ode ,ross/ and auto,orrelation

.

6en,e we require a large auto,orrelation and small ,ross ,orrelation 3small ISI7"

The output for the th user ,onsist of the signal: MAI and filtered Gaussian noise terms 3as

dis,ussed earlier7"

Re,ei=ed SNR of this was ,onsidered earlier in this report"

4.2 M%r&8 No%&on

Assume a three user s!n,hronous s!stem with a mat,hed filter re,ei=er

19


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That is e@pressed b! the matri@/=e,tor notation as

4.$ D%% er+ %n0 MAI er+

Matri@ *,an be partitioned into two parts b! setting

Note that hen,e:,ontains off/diagonal elements or *3or the ,ross,orrelations7

And therefore M8 outputs ,an be e@pressed as

Therefore the term Ad,ontains the de,oupled data and :Adrepresents the MAI"

.bective of all 1U$ schemes is to cancel out the 1AI(term as effectively as possible 3,onstraints

to hardware4software ,omple@it! and ,omputational effi,ien,!7"

Mat,hed filter outputs

1orrelations between ea,h pair of ,odes

Re,ei=ed amplitudes

0ata

Noise

3 7 y I : Ad C d :AdA C

20


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CHAPTER-9 SYNCHRONOUS AND ASYNCHRONOUS

CHANNEL

In s!n,hronous dete,tion de,isions ,an be made bit/b!/bit" In as!n,hronous dete,tion bits o=erlap and

multi/user dete,tion is based on ta


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Note that the resulting matri@ is sparse be,ause most of the bits do not o=erlap" Sparse matri@ algorithms

,an be utili>ed to redu,e ,omputational diffi,ulties 3memor! si>e U ,omputational time7"

9.2 Decorre#%&n 0eecor

The de,orrelating dete,tor applies the in=erse of the ,orrelation matri@ to suppress MAI:

and the data estimate is therefore

;e note that the de,orrelating dete,tor eliminates the MAI ,ompletel! 6owe=er: ,hannel noise is

filtered b! the in=erse of ,orrelation matri@ / This results in noise enhan,ement0e,orrelating dete,tor is

mathemati,all! similar to >ero for,ing equali>er as applied to ,ompensate ISI"

9.$ !o#yno+&%# e8!%ns&on 0eecors

Man! M%0 te,hniques require in=ersion of *" This ,an be obtained effi,ientl! b! PE

22


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& '

& '

&

M """S

S

S

NNi

P8 i N

i

w y w y w y w y

d * * * *

8or finite length message a finite length PE series ,an s!nthesi>e */' e@a,tl!" 6owe=er: in pra,ti,e a

trun,ated series must be used for ,ontinuous signaling

23


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CHAPTER-: MINIMUM MEAN SUARE ERROR 'MMSE(

DETECTION

5ased on sol=ing MMSE optimi>ation problem with

that should be minimi>ed"

This leads into the solution

One notes that under high SNR this solution is the same as de,orrelating re,ei=er" This multi/user

te,hnique is equal to MMSE linear equali>er used to ,ombat ISI"

!*.S Pro=ides impro=ed noise beha=ior with respe,t of de,orrelating dete,tor"

C.-S

Require estimation of received amplitudes and noise level3

Performan,e depends also on powers of interfering users"

24


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CHAPTER-; SUCCESSI5E INTER6ERENCE

CANCELLATION 'SIC(

Ea,h stage dete,ts: regenerates and ,an,els out a user

8irst the strongest user is ,an,elled be,ause

It is easiest to s!n,hroni>e and demodulate"

This gi=es the highest benefit for ,an,eling out the other users"

Note that the strongest user has therefore no use for this MAI ,an,eling s,heme

PROS Small 6; requirements and large performan,e impro=ement when ,ompared to

,on=entional dete,tor"

1ONS Pro,essing dela!: signal reorderedif their powers ,hanges: in low SNR performan,e

suddenl! drops"

25


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CHAPTER-< PARALLEL INTER6ERENCE CANCELLATION

'PIC(


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Simplifies s!stem anal!sis"

0oing a partial MAI ,an,ellation at ea,h stage with the amount of ,an,ellation in,reasing for

ea,h su,,essi=e stage"

Tentati=e de,isions of the earlier stages are less reliable / hen,e the! should ha=e a lower

weight"

9er! large performan,e impro=ements ha=e a,hie=ed b! this method"

Probabl! the most promising suboptimal M%0"

27


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CHAPTER-1= 3ENE6ITS AND LIMITATION O6 MULTIUSER

DETECTION 'MUD(

Signifi,ant capacity improvement/ usuall! signals of the own ,ell are in,luded "

More efficient uplin spectrum utiliation/ hen,e for downlin< a wider spe,trum ma! be

allo,ated"

*educed 1AI and near(far effect / redu,ed pre,ision requirements for power ,ontrol"

More efficient po?er utiliationbe,ause near/far effe,t is redu,ed"

If the neighboring cellsare not in,luded interferen,e ,an,ellation effi,ien,! is greatl! redu,ed"

Interferen,e ,an,ellation is =er! diffi,ult to implement indo?nlinre,eption where: howe=er:

larger ,apa,it! requirements e@ist 30. traffi, tends to be larger7"

!*.SD

C.-SD

28


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CONCLUSION AND 6UTURE >OR

It has been shown that 10MA s!stems suffer from se=ere multi/ user interferen,e" Although strong error

,ontrol ,oding is able to ensure reliable transmissions for medium s!stem loads: it is benefi,ial to appl!

multi/ user dete,tion espe,iall! for high s!stem loads" 5ased on the uplin< of an O80M/10MA

en=ironment: the performan,es of =arious multi/user dete,tors ha=e been demonstrated" 1on,erning

linear approa,hes: the MMSE dete,tor ,an be effi,ientl! appro@imated b! iterati=e strategies li


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RE6ERENCES

1.Mu#& user 0eec&on us&n CDMA%y Ser/io ;eru.

2.L&cen&%e Course on S&n%# Process&n &n Co++un&c%&ons(CDMA +#er#iew! %y Mi,a 4aitola of

No,ia 4esearch Center 4aio Co$$unications 6a%oratory.

3.I+!#e+en%&on Issues of Mu#&-user Deec&on &n CDMA Co++un&c%&on Syse+s%y hn? 4onal '@hn,e an

Prof. Dr. n/ arl an Dir, a$$eyer.

.Mu#&-User Deec&on forCDMA Syse+s ,yAle-aner Duel Ballen an oran #onar.

.O!&+%# Mu#&user Deec&on for CDMA Syse+s ,yDr M Motani.

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multi user detection in cdma project report