V-BLAST type MIMO schemes for UTRA LTE

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1 Pocia Eath an Pantay Scinc 1 ( Pocia Eath an Pantay Scinc h 6 th Intnationa Confnc on Mining Scinc & chnoogy V-BLAS typ MIMO schms fo UA LE Zijian Bai a Chistoph Spig a Guio. Buck a Chistian Dws b Jns Bkmann b Btam Gunzmann b obias Schoan c Pt Jung a a Univsität Duisbug-Essn Lhstuh fü Kommunikationschnik 4748 Duisbug Gmany b Infinon chnoogis AG Am Campon Nubibg Gmany c Infinon chnoogis AG Düssof Lanstaß Duisbug Gmany Abstact OFDM (othogona fquncy ivision mutipxing with MIMO (mutip-input mutip-output schm ca MIMO- OFDM has bn viw as a viab mans to achiv high us infomation ats an was poy in th ownink of th UA LE (UMS stia aio Accss Long m Evoution. h potntia maximization of tansmitt ata ats sha b stiv fo by spatia mutipxing. In paticua high ata ats in th ownink hav bn consi siab. Aso in viw of an fficint impmntation th ownink quis a thoough assssmnt. hfo th authos wi thooughy consi th thotica pfomanc of ata tction tchniqus fo spatia mutipxing in th UA LE ownink in this communication. Stting out fom a isct-tim systm mo a gnaiz mo fo th vauation of th signa-to-nois atio (SN at th ata tcto output wi b intouc an appi to th pfomanc vauation of both ina as w as V-BLAS (Vtica B Labs Lay Spac im ata tction tchniqus. Futhmo thi pfomanc wi b compa with thotica bouns of th match fit an th maximum-ikihoo (ML civs. It wi show that th pfomanc of succssiv intfnc cancation ( bas ata tction tchniqus fo MIMO-OFDM is bnficia. Kywos: MIMO; OFDM (Othogona Fquncy Division Mutipxing; spatia mutipxing; succssiv intfnc cancation; UMS; UA LE; V-BLAS 1. Intouction Owing to its inhnt fxibiity an its attactiv impmntation potntia OFDM (othogona fquncy ivision mutipxing bcoms a pf caniat fo th ownink of th vov UMS [1] []. In o to faciitat high us ata ats which a qui fo th aization of wiss mutimia th combination of OFDM with MIMO (mutip-input mutip-output antnna schms has bn consi as a pf way fowa. In paticua th Aamouti [7] at x ivsity (xd MIMO schm an th V-BLAS (Vtica B Labs Lay Spac im [] tchniqu at spatia mutipxing schm (SM a sn as intsting concpts fo this pupos an both poy in UA LE (UMS stia aio Accss Long m Evoution systm. xd MIMO schm usuay pomiss high aibiity of th ata tansmission whas SM Cosponing autho..: E-mai ass: zijian.bai@kommunikationschnik.og Pubish by Esvi B.V. Opn accss un CC BY-NC-ND icns. oi:1.116/j.pops.9.9.

2 149 Z. Bai t a. / Pocia Eath an Pantay Scinc 1 ( schm tagts th maximization of th us ata at by mutpxing iffnt mosty inpnnt ata stams into wiss communication channs simutanousy. SM schm is usuay poy in th physica ownink sha chann (PDSC [8]. Accoing to th attactiv fatu givn by spatia mutipxing ata tction mthos in spatia mutipxing in UA LE ownink tansmission schm a focus in this communication an th potntia systm pfomanc a vauat. In o to imit aitiona impmntation compxity a maximum of two tansmit an two civ antnnas a takn into account. h ata tction in MIMO-OFDM with SM schm can b on in vaious ways. h MIMO tcto with highst compxity is th Maximum-Likihoo squnc tcto (MLSD which aso svs as th thotica boun fo iffnt spatia mutipxing civs. Bock ina quaiz (BLE zo-focing (ZF an minimum man squa o (MMSE giv ow compxity tction soution with a pfomanc oss in tm of tction o pobabiity. W-known tchniqu such as th V-BLAS povi an attactiv o atio pfomanc with a combination of ZF quaization with succssiv intfnc cancation ( mo of opation []. Impovmnts can b achiv whn using minimum man squa o (MMSE quaization insta of ZF quaization in th V-BLAS co. In this communication th suting civ tm -MMSE civ wi b popos by th authos. In what foows compx bas ban notation wi b us poying matix-vcto cacuus to stup systm mo an signa pocssing pocu in ata tctos an futhmo to compa th thi pfomanc. Disct-tim vaiabs wi b not by vctos which a givn as ow cas chaacts in bo fac itaics. Matics wi b not by upp cas chaacts in bo fac itaics. Compx vaus wi b unin. Futhmo ( nots vcto o matix tansposition ( nots mitian of a vcto o a matix. E { } nots th xpctation opation on th givn anom vaiab. An I υ psnts th υ υ intity matix. h main of this communication is oganiz as foows: Sct. wi psnt th systm mo unying th anaysis. Diffnt spatia mutipxing tction tchniqus wi b iustat an anays in Sct.. Simuation suts wi b psnt in Sct.. Sct. wi concu th manuscipt.. Systm mo It has bn known that MIMO schms faciitat th maximization of ata ats by poying antnna aays at both sis of communication systms. Fo this ason K K tansmitt (X antnnas a poy fo communication with at ast K K K K civ (X antnnas. In SM th ova achivab ata at at th X is K tims th ata at of a sing X antnna tansmitt. In what foows a gna systm concpt sha b psnt. W wi consi a sing sot i.. a sing OFDM symbo pio in a tim tansmission intva (I. Each ata symbo is assum to b takn fom an M -ay symbo aphabt. Each X antnna sha tansmit th ata symbos contain in th K ata vctos ( ( k ( k ( k ( k 1 L L k 1L K (1 which contain L ata symbos ach. h compt ata vcto compising ( 1 ( k ( K ( KL mnts is hnc givn by L L. ( Pio to th tansmission an L point IDF (Invs Disct Foui ansfom is appi to ach ata vcto ( k k 1L K of (1. With th IDF matix D cf..g. [4] pp. 78ff. th OFDM symbo vctos ( k ( k k 1 K with L mnts ach a fom. With ( th compt SM-OFDM X vcto with b D L ( ( 1 ( k ( K ( KL mnts is givn by b b L b L b. (4 Assuming cycic pfixs bing mov at th X input th fquncy omain civ samp associat with subcai 1L L is givn by

3 Z. Bai t a. / Pocia Eath an Pantay Scinc 1 ( In (5 ( k k K ( k ( k k ( k ( k k 1 + n 1L L. (5 is th th iagona mnt of th iagona chann matix ( k k ( k k which conncts X antnna k with X antnna k. Owing to this stuctu of th subcais o not intf i.. int-cai intfnc (ICI is absnt. With th subcai spcific ata vcto with th subcai spcific chann matix an with th subcai spcific nois vcto th civ vcto associat with th th subcai is givn by ( 1 ( k ( K ( L L 1L L (6 1L L (7 M M O M ( K 1 ( K ( K K L ( 1 1 ( 1 ( 1 K L ( 1 ( ( K L ( 1 ( k ( K ( n n L n L n 1L L (8 ( 1 ( k ( K ( L L 1L L (9 n L. (1 + 1 L Not that accoing to (7 is not a iagona matix an hnc intsymbo intfnc (ISI is immannt in th OFDM-MIMO tansmission. owv it is a w motivat assumption that th ata symbos contain in of (6 a mutuay uncoat at th tim of tansmission. h ata covaianc matix is givn by { } X K E E I 1L L (11 with E X noting th avag ngy of a tansmitt ata symbo. Futhmo w assum that n psnts thma nois which is whit an Gaussian istibut. Wth th sing-si pow spcta nsity N th nois covaianc matix bcoms { } K n E n n N I 1L L (1. Data tctos.1. Sing us match fit boun (SU-MFB h match fit (MF civ in matix notation was iv in.g. [6]. In this sction w wi aapt th notation of [6] to th cas of MIMO-OFDM. With (1 th K K MF fit matix M MF is givn by

4 149 Z. Bai t a. / Pocia Eath an Pantay Scinc 1 ( With (1 an with th tct ata vcto th MF output is givn by 1 M 1L L. (1 MF N ( 1 ( k ( K ( $ $ L $ L $ 1L L (14 $ n + N N N 1L In o to vauat th signa-to-nois atio (SN at th MF output an consqunty th o atio ( k ( k pfomanc th usfu ngy at th MF output E sha b tmin fisty. E can b cacuat whn MF ( k assuming that ony a sing ata symbo is tansmitt whas a oth ata symbos as w as any nois a absnt. With th unit vcto k L 1 { L 1L L (16 kth position th tansmitt ata vcto is givn by ( k ( k k k MF (15 1L L. (17 With (17 th usfu ngy at th output of th match fit is givn by ( k MF E $ k { $ } k ( E k k E 1L X N N (18 k Scony th istubanc ngy at th MF output N MFB sha b tmin. h bst possib pfomanc can b obtain whn th tansmitt ata vcto is qua to th a-zo vcto an th nois vcto is non-zo vcto. h cosponing situation yis th sing us match fit boun (MFB. W yi Sinc th SN at th MF output is ( k { } ( NMFB E $ $ 1L L. (19 k k k k N K ( k k k k k 1 1L L ( γ E 1L L. (1 K ( k X ( k k MFB N k 1 Accoing to (1 th sing us MFB is govn by th th avag ngy of a tansmitt ata symbo th sing-si pow spcta nsity N an th chann cofficints associat with th ink btwn th k th

5 Z. Bai t a. / Pocia Eath an Pantay Scinc 1 ( tansmit antnna an ach on of th K civ antnnas. (1 fcts th absnc of ISI an psnts an ia ivsity civ with cohnt cption... Maximum-ikihoo squnc tcto (MLSD h optimum civ fo th tansmission of th ata vcto squnc tcto (MLSD $ ag max % % 1L L { } ² givn in (6 is th maximum ikihoo K h MLSD of ( quis th vauation of M hypothss. In th cas of K qua to two tansmit antnnas an QPSK (Quaatu Phas Shift Kying 16-QAM (Quaatu Ampitu Mouation o 64-QAM which a fosn fo UA LE an 496 hypothss spctivy a qui... Bock ina quaizs (BLEs Bock ina quaizs (BLEs [5] hav th ow pocssing ffots compa with MLSD fo MIMO-OFDM systm. wo vaiants of BLEs zo-focing (ZF an minimum man squa o (MMSE a psnt h yiing th two quaiz typs ZF-BLE an MMSE-BLE. h gna stuctu of th chaactistic civ quation fo BLEs is givn by 1L ( $ C ( ( h K K matix C of ( has th foowing poptis: In (4 w us th Win fit IK C W 1L ZF-BLE MMSE-BLE (4 N W IK + ( 1L L. (5 E X Whn tmining th usfu ngy E ( k BE of a BLE w st out fom (17 an yi E ( k BE E { $ $ } k k h istubanc ngy N ( k BE E X C 1L k k at th output of a bock quaiz is givn by (6

6 1494 Z. Bai t a. / Pocia Eath an Pantay Scinc 1 ( ( ( ( ( k ( k k NBE k E $ $ k k k 1L (7 With (6 (7 an C bing qua to Win fit W th SN at th MMSE-BLE output is xpss as γ ( ( k EX W k k MMSE-BLE N E X ( W k k W k k 1L N ( + W W k k (8 h SN at th ZF-BLE output can b iv fom (8 by substituting γ ( k ZF-BLE In th cas of EX N appoaching zo both ( MMSE-BLE E 1 X N ( ZF-BLE ( ( k MMSE-BLE k k appoaching infinity both γ an γ appoach infinity..4. V-BLAS an -MMSE civs k k I K fo W as 1L (9 ( ZF-BLE k γ an γ appoach zo. In th cas of EX N A viab appoach of ucing th compxity of th ML civ is ca th V-BLAS (Vtica B Labs Lay Spac im []. h V-BLAS schm is bas on succssiv intfnc cancation (. h oigina V-BLAS sts out fom a ZF appoach somtims tm -ZF. A futh impovmnt of th obustnss can b obtain by poying an MMSE appoach yiing th -MMSE. In what foows th civs sha b scib using th sam cacuus as abov. h civs a itativ having K itation stps. h fist stp i 1 is tm th initiaization which wi b iscuss in th nxt paagaph. ( i In th initiaization w st out fom th civ vcto with i 1 which is intica with of (1. With ( i ( i th systm matix bing qua to in th cas of i 1 an with th ata vcto bing intica with in th fist itation stp i 1 w thfo fin ( i ( i ( i + n 1L L i 1. ( Fisty w choos th quaiz typ by fining th fit matix to b ith ( ( ( i ( i ( i ( i i -ZF M M 1L L i 1 (1 in th cas of th V-BLAS (-ZF o

7 Z. Bai t a. / Pocia Eath an Pantay Scinc 1 ( ( ( ( i ( i ( i ( i ( i i -MMSE M M W 1L L i 1 ( in th cas of th -MMSE. Scony w tmin th SN p ata symbo i.. w comput ith (8 o (9 pning on th choic ( i of M. hiy w ank th comput SN vaus accoing to thi magnitu an sct that paticua ata symbo inx ν ( i { 1L K } which cospons to th gatst SN vau. ( ( i Fouthy w tmin th tct ata symbo ν ( i ( i ν i th mnt of M accoing $ by quantizing th ( to th chosn ata symbo aphabt. Lt Q { } b th quantization opato; thn w hav ( ν ( i ( i ( i { M ν ( i } $ Q 1 L L i 1. ( In th nxt itation stp i w fist cay out th intfnc cancation: ( i ( i 1 ( i 1 ( ν ( i $ 1L L i. (4 k ( ( i In th cas of pfct cision fback i.. in th cas of $ ν bing qua to th tu tansmitt ata symbo ( ( i ν which can b psnt as ( ν ( i 1L L i (5 k (4 bcoms ( i ( i ( I n K k k + 1L L i. (6 Fig. 1. Unco BE fo QPSK mouation x-mimo GPP SCM-A chann mo [1]

8 1496 Z. Bai t a. / Pocia Eath an Pantay Scinc 1 ( Whn appying ( IK k k ( i ( IK k k contains ony to ( i as in (6 th ( ( i 1 K zos. his mans that ν th coumn of th suting matix ( ( i ν os not hav any ffct on Sinc th infunc of th fist ata symbo has bn mov th moifi civ vcto ( 1 ( ( i of (6. 1L L contains ss intfnc than 1L L. nc th tction of th maining symbos can b impov. h ( ( ( tction pocu as th fou stps givn abov is thn pat with th nw vcto tcting $ ν. his pocu is pat unti a ata symbos hav bn tct. In th at tction itation th maining symbos wi hav ss intfnc mo ivsity gain thfo yi btt tction suts. 4. Simuation suts Pfomanc vauation an compaison btwn pvious iscuss iffnt MIMO-OFDM compiant ata tctos within th UA LE compiant simuating nvionmnt a psnt in this sction. Foowing th paamts fo UA LE systm [1][] ach OFDM subcai xpincs fat ayigh faing. hfo tction of symbos wi b cai out in th subcai spcifi Sub-MIMO systm inpnnty. Unco tansmission suts a ass h to intify th ffcts of th vaious tctos mo asiy than in th cas of co tansmission. Fig. 1 an Fig. shows th obtain simuation suts in th fom of unco bit o atio (BE P cuvs vsus th ova signa to nois atio 1og1 ( Eb N. In Fig. 1 th suts fo QPSK a shown whas Fig. shows th pfomanc obtain in th cas of 16-QAM. h consi civ schms a th BLE tctos tctos MLSD an th sing-us MFB iscuss in Sct.. Fig.. Unco BE fo 16QAM mouation x-mimo GPP SCM-A chann mo [1] In th cas of tctos both th aistic cision fback (DFE i.. th fback of th tct ata symbos an th pfct cision fback (PDFE i.. th fback of th tansmitt ata symbos ma known by a magic gni vic a consi. As xpct th MMSE tctos pfom btt than th ZF vsions in vaious tcto typs. Accoing to Fig. 1 th sing us MFB inicats th owst boun within UA LE compiant MIMO- OFDM systm an SN of 1. B fo P qua to 1. As iscuss abov this boun can ony b ach with ia ivsity civ with cohnt cption. h MLSD quis an SN of 15.8 B fo P qua to 1. h

9 Z. Bai t a. / Pocia Eath an Pantay Scinc 1 ( scon bst pfomanc sut is obtain with th -MMSE which quis 19.6 B at P qua to 1 in th DFE vsion. h -MMSE DFE quis a.5 B high SN at P qua to 1 whn compa with th -MMSE PDFE. h -ZF psntation of V-BLAS in th gn of figu ns.8 B fo P qua to 1 quiing. B mo at P qua to 1 than th PDFE vsion. h MMSE-BLE ns 6 B high SN at P qua to 1 than th -MMSE DFE. h ZF-BLE quis a.6 B high SN at P qua to 1 than th -ZF. Stting out fom Fig. th sing-us MFB inicat owst boun is an SN of 16.6 B fo P qua to 1. h MLSD quis.4 B fo P qua to 1. h scon bst pfomanc sut is obtain with th - MMSE which quis 6.7 B an B SN at P qua to 1 in th DFE an PDFE vsions spctivy. h -ZF ns 7.5 B an 4.5 B fo P qua to 1 in th DFE an PDFE vsions spctivy. h MMSE-BLE ns a.6 B high SN at P qua to 1 than th -MMSE DFE. h ZF-BLE ns a. B high SN at P qua to 1 than th -ZF DFE. A of th givn suts in Fig. 1 an Fig. with tctos incu th optima tction oing. 5. Concusions In this manuscipt th authos iscuss spatia mutipxing as a mans to incas th ata at. Futhmo iffnt SM civ stuctus w iustat an thi pfomanc w anayz in simuations fo UA LE systm. It was foun that th -MMSE outpfoms th V-BLAS schm an th two BLE tctos. Athough th -MMSE cannot povi cption as obust as in th cas of spatia ML civs it aows a bnficiay ow impmntation compxity an thfo is a viab caniat fo tminas using MIMO tchniqus. Acknowgmnt h authos wish to gatfuy acknowg th suppot of thi coagus at Infinon chnoogis an at th Lhstuh fü Kommunikationschnik of th Univsität Duisbug-Essn. Pats of this wok a cai out within th scop of th EUEKA MEDEA+ pojct MIMOWA which is paty fun by th Gman Fa Ministy of Eucation an sach. fncs [1] hi Gnation Patnship Pojct chnica Spcification Goup aio Accss Ntwok: Physica Lay Aspcts fo Evov UA ; GPP [] hi Gnation Patnship Pojct chnica Spcification Goup aio Accss Ntwok: quimnts fo Evov UA (E- UA an Evov UAN (E-UAN; (as 7 ; GPP 5.91 V7... [] P.W. Woniansky G.J. Foschini G.D. Gon an.a. Vanzua Pocings of th USI Intnationa Symposium on Signas Systms an Ectonics. Nw Yok [4] J. Map Digita Spcta Anaysis with Appications. Engwoo Ciffs: Pntic a [5] X. Lasn C. Baoux an K.G. Kawas Joint cption of muti-us ata fo synchonous co-ivision mutip-accss. COS 1 D(9185 sinki 199. [6] P. Jung Anays un Entwuf igita Mobifunksystm. Stuttgat: B.G. ubn [7] S. Aamouti A simp tansmit ivsity tchniqu fo wiss communica-tions. IEEE Jouna on Sct Aas in Communications. 16 ( [8] hi Gnation Patnship Pojct chnica Spcification Goup aio Accss Ntwok: LE Physica Lay-Gna Dsciption ; GPP S 6.1.