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 [email protected] in third generation ,ommuni,ations s!stems and is to be emplo!ed in the

    [email protected] 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 [email protected]=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 [email protected] 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

    [email protected] 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 [email protected] .iity/ In [email protected]=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 [email protected] b! the [email protected]/=e,tor notation as

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

    [email protected] *,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 [email protected] 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 ,[email protected]! 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 [email protected] is sparse be,ause most of the bits do not o=erlap" Sparse [email protected] 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 [email protected] 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 [email protected] / 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 */' [email protected],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 res