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Linear MMSE detec t ion technique for MC-C O M A

J.-F. I khrd . J.-Y. ni ida is ai i t l J. Citernc

ELECTRONICSLETTERS 30th March 2 Vol. 36

iicl Dascri 011 tliesc :issiiiiiptioris iind considcriiig frcqLicncy inter-Icaving, l h c cciiiiplcx chiinncl Ihding cocflicicnts are intlcpeidcntt'or CICII subc:irricrand can hc cstimiiterl 101 hc subcwrierk b y 11.- p P ~ ~ ~ ~lrc signal rcceivecl artcr tlic inverse O1:DM opxition(seriul to p ~ i r d l e laiivcrsioii arid dii.ect PFT) ; inti rlei~i(crlciiving,caii lx cnprcssed i t s

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111 hc full lond casc (x, LJ (aiitl only in this cnsc), lhc quantityC . A . V is c q u d to the identity matrix and llic cqunlisntion cocffi-cieiits matrix G is a diagonal matrix with the ktli s ub ci rr ic r c y d -i s a h cocfficicnt equd to eqn. 3.

Simihrion I .L:FL~ ~s :Fig. 2 sliows the pertbrinance or vniioiis dctcc-lion syslcms with L,. = T , = 64, aking into accounl the nuinbcrN,, f active users against llic ncccssnry E VU to achieve n HER =

W3. A rull-load systcm is obtaincd for N,, = L, = N p = 64. ' l h closs due to the guard interval, synchrouisalioiiancl chatincl csti-mation is not taken into account. Tn any ciisc, IIGC und MRCpe rh nn poorly.Tbe performanceo f the MMSE per carricr syslcinwith the equalisation cocficiciits optiiniscd indepeiideiitlyMI eachsubcarrier according to eqii. 3 is compared to tlic performance orllic MMSE pcr user systetn with the equalisation cocffcicntmatrix C. equal to c c p . 8. For fdl-la:~cl ystems iV,, = M , the per-formance of the two MMSE appruwlics iirc tlic same, while fornon-full-load syslnns thc M MS pcr user criterion achievesa gainof > 2 d B with 4 = 32 or 16.

, -20

i o 2

10 '

EdNo=8dS

1o 2

a

k4

10

To firrtlier improve rhereceiver's perfoiinancc,multi-uscr detec-tion (MD) techniques wch as iiikrfcrcncc c:inccllatiot~CM heiinplemantcd. Pirrallcl interference cancellalion O IC) dctcctorsestimate the iulorfmnco duc to the other siniultuieous users inorder tn remove this mulliple iiscr intcrfcrcnce component rromthc rcccived signal. Interference ciiiiccllation ciin h arried oiitilerativcly in iniiltiplc detcction stages.A p e r k w w comparison

of two-stage parallel interference cancellation systcinswith the twoMMSE techniques against the nuinbei. or active I I S C ~ S with /Nu= 8dD) is prescntcd in Fig. 3 with Lr = N = 4 he new MMSCper user detection schcineoutperforms theMMSE per carrier sys-tem. For example, wirh X,,/No = SdB and for a BER = I O - ,lhcbase slation can supply iy = 21 users with PIC-MMSEpcr ctrrricrant1 itp to N I ,= 3 uscrs with PIC-MMSE per iiscr dctcctioii.

Concltwkm:Taking advwntagc of the despmiding process, novelapproach has been presented based on tlic MMSE criterionaplil id pcr iiscr and no more per. carrier which offers veiy goodresults Tor non-full-load systetiis with linear deleclionand ulso formulti-user PIC detcctioii schcmcs.

Hcfercnccs

1

2

iinitn. s. and P R . ~ S A D , .: Ovcrvicw or indticrrrriei CDMA , IEL 1:

D ~ S I LVA .v hI , and W U S A . w.: Muli iwrricr orthogon;il signals forrliiari-syncliroiiou~coinmunications sy sk m a ' , I E E J. Se . Areirs

3 SOIIROIJK. A, ntid N A K A G AWA , M.: 'Pcrforinancc o f orthogonalinolticurricr CDMA in a irmltipath lhtling chiuiincl', IEEL 1Yiin.T.f'~)+lvf?iw.. 9'16, 44, (3), ]>I>.356-367K A I S C K , s.: Annlyrical pcrfotmancc evnlutilion u l OFDM-CDMAmobile radio Fystcnis'. I'roc. First European Personiil and Mobilc(:onlmtinicalioos Coni. (EPMCC'95), I3oIoglia, Ilnly, November1995, pp. 215-220

COIiIRtutI ,+[OX., 1997, pp. 126--133

C, OOItriErri, 1994, 12, 5 ) , l>p, 842-852

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Neoter ic signal: method for l inear is ingnarrowband amplifiers or signal paths up t otheir peak power s

H.E. SchernclA coiislii i i t~nipli~utlclirricr is phnw inorlulaicd in spccial wilyso that thc slxctrutn conlailis n r q k i of the signol to lwainplifieil. The w r i c r drivcs itti ampliticr to ai~hirlition. ilrcquircd) nnrl the replica, which can cqllal tl~c erk ani1)lilierpnwcr, is sclcctctl by n simplelillcr. I11 principlc, thcir ix nbsolutc1inc:iriry. I 'hc satnc tcwtinique ea11linearise i igriel p;itli withairiplihtdc rlidoiLion.

Liiiearisalion tcchniq ucs For narrow-band ai1qNiei.scurrcntl y i iscpwdislu r t inn [ I ] fed-forward [I], Cartesian feedback [I], LING121 and pulsc tmdulatiori [3 The last two achicvc lincarityby theuse or coiislantamplittidc drive signals bnt a t thc cxpcnsc of band-width cxpansidri. l lie iicotcric signal [4] falls into this latter catgory but is otherwise belicved 10 bc novel. Fig. shows twopossibblc methods of generntioii using hard limitcr and a he-queiicy doubler. A narrow-hand signa[ at fi'crltici1cy.L is arlrlcd to:in idlc freqi1ency .I; a1a diffcrciiccx,, such that,h =

c s =: T cos(w,t + 8) =e ; = I . C O S ( 5 J i l ) . n J J t i

- .,A1 ..et

where 0 = 2nf, s i i l l i c c s .