05 Tm2106euo1_eg0001 CDMA System Aspects(Abeer)

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CDMA System Aspects Siemens

CDMA System Aspects

Contents

1

1.1.1

1.1.2

1.2

1.2.1

1.2.2

1.2.3

1.2.4

2

2.1

3

3.1

3.2

3.2.13.3

4

Power Control in CDMA

Effect of No Power Control

The NEAR !AR Pro"lem

Cl#ssific#tion of Power Control Techni$%es

Accor&in' to wh#t is me#s%re& to &etermine power control comm#n&

Accor&in' to %pte str#te'ies

Accor&in' to &irection of tr#nsmission

Accor&in' to techni$%es

Rake Receiver

R#(e Recei)er Theory #n& Str%ct%re

Handoff Versus Handover

Handoff Versus Handover

Soft *#n&o)er

The +mport#nce ,f Soft *#n&offSofter *#n&o)er

Multiuser Detection

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4

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SiemensCDMA System Aspects

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1 Power Control in CDMA

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1.1 Introduction

Power control is one of the most import#nt system re$%irement #n& it is #n#lye& for

cell%l#r networ(s "#se& on !DMA #n& TDMA #n& for DS5CDMA cell%l#r networ(s +n mostmo&ern systems "oth "#se st#tions #n& mo"iles h#)e the c#p#"ility of re#l5time 6&yn#mic7#&8%stment of their tr#nsmit powers.

1.1.1 Effect of NO Power Control:

+n c#se of no power control if # mo"ile st#tion si'n#l is recei)e& #t the "#se st#tion with# too low le)el of recei)e& power 9MS is f#r from the cell site or in #n %n%s%#l hi'h#tten%#tion ch#nnel: *i'h le)el of interference is e;perience& "y this mo"ile #n& itsperform#nce 6NEAR-AR? pro"lem.

1.1.2 !e "NEA# $ %A#& Pro'lem

+n i&e#l c#ses the power recei)e& #t the


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1.2 Cl(ssific(tion of Power Control ec!ni)ues

Accordin# to w$at is %easured to deter%ine &ower control co%%and' &ower

control tec$ni(ues can )e classified into*1. Stren'th5"#se&.

2. S+R5"#se&.

3.


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1+2+2 Accordin# to direction of trans%ission' &ower control can )eclassified into*

1. !orw#r& lin( 6from mo"iles to "#se st#tions7.

2. Re)erse lin( 6from "#se st#tions to mo"iles7.

1+ orward link &ower control*

!orw#r& lin( 6"#se st#tion to mo"ile7 power control is # one step process .The "#sest#tion controls its tr#nsmittin' power so th#t # 'i)en mo"ile recei)es e;tr# power too)ercome f#&in' interference


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1+2+3 Accordin# to tec$ni(ues' &ower control can )e classified as follows*

1. ,pen5loop power control.

2. Close&5loop power control.

3. ,%ter loop power control

1+ 6&en-loo& &ower control

Re)erse lin( 6mo"ile to "#se st#tion7 open loop power control is #ccomplishe& "y#&8%stin' the mo"ile tr#nsmit power so th#t the recei)e& si'n#l #t the "#se st#tion isconst#nt irrespecti)e of the mo"ile &ist#nceG where e#ch mo"ile comp%tes the rel#ti)e p#thloss #n& compens#tes the loss "y #&8%stin' its tr#nsmittin' power. The tot#l recei)e& power#t the cell site is the s%m of #ll powers which &etermines the system c#p#city.

2+ Closed-loo& &ower control

Close&5loop power control is #ccomplishe& "y me#ns of power %p or power &owncomm#n& ori'in#tin' from the cell site. A sin'le power control "it is inserte& into the forw#r&enco&e& t# stre#m the mo"ile respon&s "y #&8%stin' the power. +n or&er to lowerprocessin' &el#y #n& to s#)e "#n&wi&th in the forw#r& lin( comm#n& "its for power controlfrom the "#se to the mo"ile st#tion #re not co&e& #n& they #re s%scepti"le to errors.

3+ 6uter oo& PC

Si'n#l to interference r#tio is )#rie& to '%#r#ntee oS 6


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2 #A*E #ecei+er

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2.1 #A*E #ecei+er !eory (nd Structure

A spre#&5spectr%m si'n#l w#)eform is well m#tche& to the m%ltip#th ch#nnel. +n #

m%ltip#th ch#nnel the ori'in#l tr#nsmitte& si'n#l reflects from o"st#cles s%ch #s "%il&in's#n& mo%nt#ins #n& the recei)er recei)es se)er#l copies of the si'n#l with &ifferent &el#ys.+f the si'n#ls #rri)e more th#n one chip #p#rt from e#ch other the recei)er c#n resol)ethem. Act%#lly from e#ch m%ltip#th si'n#lHs point of )iew other m%ltip#th si'n#ls c#n "ere'#r&e& #s interference #n& they #re s%ppresse& "y the processin' '#in. *owe)er #f%rther "enefit is o"t#ine& if the resol)e& m%ltip#th si'n#ls #re com"ine& %sin' RAIErecei)er. Th%s the si'n#l w#)eform of CDMA si'n#ls f#cilit#tes %tili#tion of m%ltip#th&i)ersity. E;pressin' the s#me phenomenon in the fre$%ency &om#in me#ns th#t the"#n&wi&th of the tr#nsmitte& si'n#l is l#r'er th#n the coherence "#n&wi&th of the ch#nnel#n& the ch#nnel is fre$%ency selecti)e 6i.e. only p#rt of the si'n#l is #ffecte& "y the f#&in'7.

RAIE recei)er consists of correl#tors e#ch recei)in' # m%ltip#th si'n#l. After&espre#&in' "y correl#tors the si'n#ls #re com"ine& %sin' for e;#mple m#;im#l r#tiocom"inin'. Since the recei)e& m%ltip#th si'n#ls #re f#&in' in&epen&ently &i)ersity or&er#n& th%s perform#nce #re impro)e&.

After spre#&in' #n& mo&%l#tion the si'n#l is tr#nsmitte& #n& it p#sses thro%'h #m%ltip#th ch#nnel which c#n "e mo&ele& "y # t#ppe& &el#y line 6i.e. the reflecte& si'n#ls#re &el#ye& #n& #tten%#te& in the ch#nnel7.

+t is necess#ry to me#s%re the t#ppe& &el#y line profile #n& to re#lloc#te RAIE fin'erswhene)er there is nee&. Sm#ll5sc#le ch#n'es less th#n one chip #re t#(en c#re of "y #co&e5tr#c(in' loop which tr#c(s the time &el#y of e#ch m%ltip#th si'n#l.

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, -(ndoff ersus -(ndo+er

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,.1 -(ndoff +ersus -(ndo+er

The #ct of tr#nsferrin' s%pport of # mo"ile from one "#se st#tion to #nother is terme&

h#n&o)er or *#n&off. +t occ%rs when # c#ll h#s to "e h#n&e& o)er or off from one cell to#nother #s the %ser mo)es "etween cells. +n SM system it is terme& h#r& h#n&off or*#n&o)er where the connection to the c%rrent cell is "ro(en #n& then the connection to thenew cell is m#&e. This is (nown #s # J"re#(5"efore5m#(eJ h#n&off.


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,., Softer -(ndo+er

+s # soft h#n&o)er "etween two sectors of # cell. As (nown th#t in # cell%l#r system

there is sp#ti#l sep#r#tion "etween cells %sin' the s#me fre$%encies7. This is c#lle& thefre$%ency re%se concept.


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/ Multiuser Detection

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The c%rrent CDMA recei)ers #re "#se& on the RAIE recei)er principle which consi&ersother %sersH si'n#ls #s interference. *owe)er in #n optim%m recei)er #ll si'n#ls wo%l& "e&etecte& 8ointly or interference from other si'n#ls wo%l& "e remo)e& "y s%"tr#ctin' themfrom the &esire& si'n#l. This is possi"le "ec#%se the correl#tion properties "etween si'n#ls#re (nown 6i.e. the interference is &eterministic not r#n&om7.

The c#p#city of # &irect se$%ence CDMA system %sin' RAIE recei)er is interferencelimite&. +n pr#ctice this me#ns th#t when # new %ser or interferer enters the networ( other%sersH ser)ice $%#lity will 'o "elow the #ccept#"le le)el. The more the networ( c#n resistinterference the more %sers c#n "e ser)e&. M%ltiple #ccess interference th#t &ist%r"s #"#se or mo"ile st#tion is # s%m of "oth intr#5 #n& inter5cell interference. M%lti%ser &etection6M0D7 #lso c#lle& 8oint &etection #n& interference c#ncell#tion 6+C7 pro)i&es # me#ns ofre&%cin' the effect of m%ltiple #ccess interference #n& hence incre#ses the systemc#p#city.

+n the first pl#ce M0D is consi&ere& to c#ncel only the intr#5cell interference me#nin'th#t in # pr#ctic#l system the c#p#city will "e limite& "y the efficiency of the #l'orithm #n&the inter5cell interference. +n #&&ition to c#p#city impro)ement M0D #lle)i#tes the ne#rBf#rpro"lem typic#l to DS5CDMA systems. A mo"ile st#tion close to # "#se st#tion m#y "loc(the whole cell tr#ffic "y %sin' too hi'h # tr#nsmission power. +f this %ser is &etecte& first #n&s%"tr#cte& from the inp%t si'n#l the other %sers &o not see the interference. Since optim#lm%lti%ser &etection is )ery comple; #n& in pr#ctice impossi"le to implement for #nyre#son#"le n%m"er of %sers # n%m"er of s%"optim%m m%lti%ser #n& interferencec#ncell#tion recei)ers h#)e "een &e)elope&. The s%"optim%m recei)ers c#n "e &i)i&e& intotwo m#in c#te'ories line#r &etectors #n& interference c#ncell#tion. @ine#r &etectors #pply# line#r tr#nsform into the o%tp%ts of the m#tche& filters th#t #re tryin' to remo)e the

m%ltiple #ccess interference %sin' too hi'h # tr#nsmission power. +f this %ser is &etecte&first #n& s%"tr#cte& from the inp%t si'n#l the other %sers &o not see the interference. Sinceoptim#l m%lti%ser &etection is )ery comple; #n& in pr#ctice impossi"le to implement for #nyre#son#"le n%m"er of %sers # n%m"er of s%"optim%m m%lti%ser #n& interferencec#ncell#tion recei)ers h#)e "een &e)elope&. The s%"optim%m recei)ers c#n "e &i)i&e& intotwo m#in c#te'ories line#r &etectors #n& interference c#ncell#tion. @ine#r &etectors #pply# line#r tr#nsform into the o%tp%ts of the m#tche& filters th#t #re tryin' to remo)e them%ltiple #ccess interference 6i.e. the interference &%e to correl#tions "etween %ser co&es7.E;#mples of line#r &etectors #re &ecorrel#tor #n& line#r minim%m me#n s$%#re error6@MMSE7 &etectors. +n interference c#ncell#tion m%ltiple #ccess interference is firstestim#te& #n& then s%"tr#cte& from the recei)e& si'n#l. P#r#llel interference c#ncell#tion

6P+C7 #n& s%ccessi)e 6seri#l7 interference c#ncell#tion 6S+C7 #re e;#mples of interferencec#ncell#tion.

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05 Tm2106euo1_eg0001 CDMA System Aspects(Abeer)

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