An Efficient Selective Receiver for Multiple-Input Multiple-Output Scheme

Transcription

1 > REPLACE I LINE WI YOUR PAPER IDENIFICAION NUMBER (DOUBLE-CLICK ERE O EDI) < A Effcet electve Recever for Multple-Iput Multple-Output ceme Lu Lu, tudet Member, IEEE, ad Myoug-eob Lm, Member, IEEE Abstract I ts paper, a effcet selectve recever for multple-put multple-output (MIMO) system wc explot beamformg ad space-tme block code (BC) s proposed. I te proposed sceme, we dvde te receved sgals to two groups. By ts way, we ca almost elmate te terferece from te egborg sgals a same symbol almost by alf. e smulato results demostrate tat te proposed sceme ca provde mproved performace. Especally uder mperfect cael estmato, t ca provde more ta 0dB gas at bt error rate (BER). Idex erms Beamformg, MIMO systems, spatal dversty, BC I. INRODUCION E creasg demad of ger data rates, especally wreless systems, as motvated terest Multple-Iput Multple-output (MIMO) system, wc provdes te beeft of spatal dversty wt more cael capacty but o crease of te requred badwdt or trasmtted power []. Beamformg s a well kow complemetary tecque commucato system by provdes array ga. MIMO systems wc explot beamformg ad space-tme block codg (BC) ave recetly attracted eormous terest due to ts potetal to eace performace ad crease te capacty of moble commucato system. arok frstly proposed a BC sceme usg a ortogoal code matrx, so called ortogoal BC (O-BC) []. Later, quas-ortogoal BC (QO-BC) as bee proposed [-5], wc provdes full code rate te trasmt atea case, at te expese of a loss dversty. e dea of combg BC ad beamformg s proposed order to maxmze dversty order as well as beamformg ga [6]. ce array ga wll strogly affect system detecto performace, [7] aoter sceme wc use same umber of ateas but separate tem to dfferet arrays s proposed. e ew sceme s sow to ave a stable performace depedet of DOA ad agular spread. I [8],[9], ts dea s exteded to four trasmtter case. Ad t also could be exteded to MIMO systems. owever, f we crease te umber of trasmtters, ts ca crease te dversty ga, but at te same tme ts may also crease te terferece from te egborg sgals. g terferece from te egborg sgals ot oly curs g decodg complexty but also may reduce te performace. I order to solve ts problem, we propose a ovel sceme, wc are called selectve recevg atea structure. s ca mprove te performace for MIMO systems wc combe beamformg ad BC. I ts paper, we use a four trasmtter case as a example. wo ateas are used at te recevg ed, were te trasmtted sgals are grouped ad amed at eac atea usg beamformer at te trasmtter. e receved sgal at eac atea s grouped te way to elmate te terferece from te sgals te oter group. Because of te reduced terferece, ot oly te processg complexty at te decoder ca be reduced but also te performace ca be gly mproved. I te followg sectos we explore more detal te relatve merts of te proposed recever sceme to usg te BC combg beamformg sceme. I secto II, we troduce te system model ad detecto performace aalyses for te covetoal sceme. I secto III, we preset te detal descrpto of our proposed sceme about te system model ad detecto performace aalyses. Arbtrary umbers of trasmtter cases of covetoal ad proposed scemes ave bee aalyzed secto IV ad V. Ad secto VI, te smulato results ad a dscusso of tese results are sow. Fally, a cocluso s preseted secto VII. Lu Lu s wt te Dvso of Electrocs & Iformato Egeerg, Cobuk Natoal Uversty, Jeou , Korea (correspodg autor to provde poe: ; fax: ; e-mal: lulu@slab.cobuk.ac.kr). Myoug-eob Lm, te Dvso of Electrocs & Iformato Egeerg, Cobuk Natoal Uversty, Jeou , Korea (e-mal: mslm@cobuk.ac.kr). II. E CONVENIAL CEME For smplcty of exposto, a smple example of MI O systems wt four-trasmtter system as bee used as te covetoal sceme. It ca be exteded to ay geeral MIMO system case.

2 > REPLACE I LINE WI YOUR PAPER IDENIFICAION NUMBER (DOUBLE-CLICK ERE O EDI) < A. ystem Model A full rate quas-ortogoal desg ca be expressed as [5]: s s s s s s s s = = s s s s s s s s were deotes complex cougate operato., () A covetoal sceme for MIMO system, wc combes beamformg wt QO-BC, s depcted Fg.. I ts sceme, te sgal s ecoded by te QO BC of matrx (), were te sgals colums of matrx () are putted to four trasmtters. Eac trasmtter as multple ateas for beamformg. e beamformg wegt vector may be set as w at te t beamformer. e sgals correspodg to eac row are trasmtted at te same tme slot. We assume a flat fadg cael wc cossts of L spatally separated pats. I our example of (), L equals to te umber of trasmtters of. e fadg coeffcets ad drecto-of- arrvals (DOA) at te lt pat are deoted as, l adθ l, respectvely. e receved sgals over four tme slots ca be expressed as: r s s s s w a ) r w a, () r = = r w a s s s s ( ) θ s s s s ) s s s s ) r w a were r s te receved sgal at te t tme slot. a l ) s te dowlk steerg vector at θ l, ad s a addtve Gaussa ose at te t tme slot. B. Detecto uder Perfect Cael Estmato uppose tat we ave te best estmated cael formato ad perfect kowledge of te cael at te recever. erefore, te beamformg wegt vector w may be set usg te steerg vector k a ), were k s a costat wc ca be assumed as: k = w a = w a = () ) ), (,..., ) were deotes matrx traspose operato. deotes matrx cougate traspose operato. At te recever, based o covetoal BC detecto metod [0], we ca do te detecto for s : = r r r r = k α s k( ) s = C. Detecto uder Imperfect Cael Estmato. () I practcal stuatos, t s mpossble for te recever to obta perfectly estmated cael formato, ad tus we ave te addtoal terferece due to cael estmato error. By cosderg te cael estmato errors, te estmated complex gas ca be expressed as [], ^ = z, ( =,..., ), (5) were z represets te estmato error at te t pat. Usg te same process as te above process, detecto of s ca be foud: = ˆ r ˆ r ˆ r ˆ r were pat. = k[ α s ( ) s = = z s z ( s s s s ) z ( s s s s ) z ( s s s s )] ˆ ˆ ˆ ˆ, (6) α s te magtude respose of cael ga t As preseted () ad (6), tere are terferece terms caused by te oter sgals, suc as s, s, s. III. E PROPOED ELECIVE RECEIVER CEME Fg.. Covetoal recever sceme for MIMO system explot beamformg ad BC ( trasmtters) A. ystem Model From matrx (), eac four tme slots, t ca be foud tat sgals s ad s are trasmtted va atea groups of ad

3 > REPLACE I LINE WI YOUR PAPER IDENIFICAION NUMBER (DOUBLE-CLICK ERE O EDI) < at te frst two tme slots of ad symbol durato uts. I te oter two tme slots, tese two sgals are trasmtted va atea groups of ad. By usg ts property, we propose a ew metod for te BC combed wt beamformg. Fg. llustrates te proposed sceme, were two ateas are used to receve te sgals. Before passg te beamformers at te trasmtter, te sgal at te proposed sceme s as same as te oe te covetoal sceme. e sgals after beamformers wc are trasmtted eac symbol ca be expressed as followg: x s s s s w x s s s s x = w = s x s s s w s x s s s w, (7) were x represets te sgals wc are trasmtted from t atea group. ese sgals are trasmtted separately by amg two dfferet recevg ateas. e trasmttg ateas groups of ad wll am to recevg atea, ad te oter two atea groups wll am to recevg atea. I ts case, te receved sgal at recever atea are correspodg to x ad x correspodg to te oters:, te receved sgal at recever atea are r = r = x x a) ) a x x a) ) a, (8) were r s te receved sgal wc s receved by receve atea. At recevg atea, te receved sgals at tme slots ad are set to te decoder for sgals s ad s, ad tose at te oter two tme slots are swtced to te decoder for te sgals s ad s. Wle, at recevg atea, ts wll go te oter way aroud. e at te recever te proposed sceme, comg sgals to eac atea are reduced alf because we use two selectve ateas. For example, we detectg s, we oly eed to cosder te receved sgals cludg te formato of s durg te etre tme slots as equato (9): r = a ) s w a ) s w r = a ) s w a ) s w r = a ) s w a ) s w r = a ) s w a ) s w, (9) Fg.. Proposed selectve recever sceme for MIMO systems l were r represets te receved sgal wc s receved by te l t recever atea at te t tme slot. B. Detecto uder Perfect Cael Estmato Usg te same detecto process as te covetoal sceme, e detecto for s at te proposed recever structure uder perfect cael estmato ca be expressed as: = r r r r = k( α α α α ) s. (0) Compare (0) wt (), t could be obta tat, after sgal detectg, our ew sceme ave o terferece terms wc from egborg sgals a same symbol left uder te perfect cael estmato. C. Detecto uder Imperfect Cael Estmato e decoded sgal for s at te proposed recever structure uder mperfect cael estmato wll be descrbed as: = ˆ r ˆ r ˆ r ˆ r = k[ α s z ( s s ) z ( s s ) = z ( s s ) z ( s s )] ˆ ˆ ˆ ˆ. () It s otable tat te result as muc less terferece terms ta equato (6). I equato (), we do ot ave ay terms for s ad s, wc are te oter group. Our ew sceme results reduced terferece ta te covetoal system uder mperfect cael estmato. Our metod applcable to ay MIMO system wc explot space tme code, were te sgals at te recever are separated usg a best way accordg to te ecoded matrx, ad tus we ca reduce terferece from te egborg sgals ad eace te performace.

4 > REPLACE I LINE WI YOUR PAPER IDENIFICAION NUMBER (DOUBLE-CLICK ERE O EDI) < IV. E CONVENIAL CEME WI ARBIRARY NUMBER OF RANMIER Let us cosder square trasmsso matrxes. uc matrxes are full rate, sce te matrx s square, ad also full trasmt dversty. Fg. gves te covetoal recever sceme model for geeral -by- trasmt matrx. As sow Fg., te sgals trasmtter are ecoded by a BC ecoder. Assumg te umber of trasmt ateas as, at eac symbol, a block of bts formato deoted by = ( s, s,..., s ). () For eac symbol, te BC trasmsso matrxes ca be gve by s s = =. () s s e coded sgals correspodg to t colums s te set to t beamformer ad wegted by te wegtg vector w. Depedg o te ecodg matrx, te cael coeffcet matrx ca be expressed te geeralzed form. =. () ere, eac of te matrx elemets ca ave postve or egatve sg ad te cougated trasform of te fadg coeffcet wc s correspodg to sgal s s trasmsso. uppose tat we ave te best estmated cael formato ad perfect kowledge of te cael at te recever. I ts case, te beamformg wegted vector w may be set usg te steerg vector k a ), were k s a costat wc ca be assumed as k = w a = w a =. (5) ) ), (,..., ) Fg.. Covetoal recever sceme for geeral trasmsso matrx e receved sgals ca be represeted as r s k = r s, (6) s = k s Were r ca be cougate trasform of te receved sgal at t tme slot, ad ca be cougate trasform of addtve Gaussa ose at t tme slot. erefore, te estmato of sgals ca be obtaed by followg equato, r =. (7) r Based o te equato above, we ca detect te t sgal of eac symbol as, = = k ( s s... s ), ( =,,..., ) =. (8) It s wort to meto tat depedg o dfferet BC ecodg matrx, some terms ca be zero. I equato (8), tere are totally terms cludg te formato of sgals. owever, ust terms, wc ca be expressed as s, are related wt sgal s. erefore, tere are egborg sgals. terferece terms form V. E PROPOED CEME WI ARBIRARY NUMBER OF RANMIER Fg.. sows te proposed selcetve recever sceme for geeral trasmsso matrx. e sgal s ecoded usg te same -by- matrx (). Before passg te beamformer, te sgals s same as te oes te covetoal sceme. e beamformg wegted vector w may be also set usg te steerg vector k a ). Accordg to te ecoded matrx, te sgals are dvded equally to two groups to be trasmtted by amg two dfferet recevg ateas. At te recever, te sgals two groups are decoded separately dfferet BC decoders.

5 > REPLACE I LINE WI YOUR PAPER IDENIFICAION NUMBER (DOUBLE-CLICK ERE O EDI) < 5 Comparg () wt (8), we ca easly fd tat our proposed sceme ca decrease at least alf terferece terms from egborg sgals. If te o-ortogoal sgals are separated perfectly, tere wll be o terferece terms wc from egborg sgals left, suc as te - trasmtter example gve before. It s wort to ote tat te ardware of decodg processg wll be decreased almost alf. After comparg (7) ad (), we ca foud tat te multplcato wll decreased from to /. Ad te adder wll decreased from to /. Fg.. Proposed seletctve recever sceme for geeral trasmsso matrx I order to avod te terferece from egborg sgals, two o-ortogoal sgal streams are dvded to dfferet groups. Cosderg te receved sgal at recevg atea oe symbol, t ca be expressed as, were r s k = ' (9) r / s / / / ' =. (0) / By usg (0), we ca detect te sgals wc receved by recevg atea as(), r =. () / r / / VI. IMULAION REUL We evaluate te performace of te proposed sceme, wt te leged selectve recever structure, ad compare t to te covetoal recever for MIMO systems wc explot beamformg ad BC, wt te leged MIMO wt BF-BC (x-rx), uder perfect cael estmato as well as mperfect cael estmato. I order to sow te superorty of te proposed sceme, we also compared te BER wt te system wc as te same ardware equpmet as te proposed sceme wt te leged MIMO wt BF-BC (x-rx). I all smulatos, we assume four uform lear array (ULA) ateas wt 8 elemets per array. e total emtted power from all te trasmt ateas s kept detcal. We use a flat Rayleg fadg cael, ad set te agle spread (A) to 0 ad 50 degrees. e performace comparso of te bt-error-rato (BER) versus te sgal- to-ose-rato (NR) uder bot perfect cael estmato ad mperfect cael estmato are plotted Fg.5 ad Fg. 6, wc tus sow tose results tat te better performace ca be aceved by te proposed selectve recever scemes. e detecto of te t sgal at te proposed recever structure ca be rewrte as, = / / = k ( s s... s ), ( =,,..., / ) =. () ere are totally / terms cludg te formato of sgals, equato (). owever, ust / terms, wc ca be expressed as s, are related wt sgal s. erefore, tere are ( egborg sgals. )/ terferece terms from Fg. 5. Comparso of BER vs. NR uder perfect cael estmato

6 > REPLACE I LINE WI YOUR PAPER IDENIFICAION NUMBER (DOUBLE-CLICK ERE O EDI) < 6 ACKNOWLEDGMEN s researc was supported by te MIC (Mstry of Iformato ad Commucato), Korea, uder te IRC (Iformato ecology Researc Ceter) support program supervsed by te IIA (Isttute of Iformato ecology Assessmet). Fg. 6. Comparso of BER vs. NR uder mperfect cael estmato e smulato results demostrate tat, uder a flat Rayleg fadg cael, te performace of our proposed selectve recever sceme ca aceve db mprovemets, we compared wt te covetoal recever for four-trasmtter oe-recever MIMO system, some mprovemets compared wt te covetoal four-trasmtter two-recever MIMO system, wt te perfect cael estmato. Ad uder a flat Rayleg fadg cael, te performace of our proposed selectve recever sceme ca aceve 0 db mprovemets, we compared wt te covetoal four-trasmtter oe-recever MIMO system, ad 5dB mprovemets compared wt te covetoal four-trasmtter two-recever MIMO system, wt te mperfect cael estmato. It s also mportat to ote tat tere s o reducto te trasmsso rates. Altoug we sould employ a addtoal atea at te recever, te decodg complexty of te proposed sceme s cosderably smaller, because of te reduced terferece terms. VII. CONCLUION I ts paper, we proposed a ovel sceme to eace te performace of a MIMO system combed wt beamformg ad BC. Because te proposed selectve recever separates te receved BC sgals, we ca mmze te terferece te decodg process. e smulato results ts paper reveal tat te proposed sceme aceves gly mproved BER performace ta te covetoal MIMO recever sceme uder perfect cael estmato as well as mperfect cael estmato. REFERENCE [] L zog Zeg, se, D.N.C., Dversty ad Multplexg: A Fudametal radeoff Multple-Atea Caels, IEEE ras. Iform. eory, Vol. 9, Issue 5, pp , May 00 [] V. arok,. Jafarka, ad A.R. Calderbak, pace-tme block codes from ortogoal desgs, IEEE ras. Iform. eory, Vol. 5, No. 5, pp.56-56, July 999. []. Jafarka, A quas-ortogoal space-tme block code, IEEE ras. Comm. Vol. 9, No., pp.- Ja. 00. [] C. B. Papadas, G. J. Fosc, A space-tme codg approac for system employg four trasmt ateas, IEEE ZCAP, Vol., pp.8-8, 00. [5] Ja ou, Moo o Lee, Ju Yog Park, Matrces aalyss of quasortogoal space-tme block codes, IEEE Comm. Letters, Vol. 7, Issue 8, pp , Aug. 00. [6] Zogdg Le, C F. P.., Yg- Cag Lag, Combed beamformg wt space-tme block codg for wreless dowlk trasmsso, IEEE 56t, Cof. o Vecular ecology Proceedgs, Vol., pp. -8, ept. 00. [7] Zu F., Lm M.., Combed beamformg wt space-tme block codg usg double atea array group, IEE Electrocs Letters, Vol. 0, Issue, pp. 8-8, Ju. 00. [8] G. Jogre, M. koglud, ad B. Otterste, Combg beamformg ad ortogoal space-tme block codg, IEEE ras. o Iform. eory, Vol. 8, pp , Mar. 00. [9]. Zou ad G. B. Gaaks, Optmal trasmtter ege- beamformg ad space-tme block codg based o cael mea feedback, IEEE ras. gal Processg, Vol. 50, No. 0, pp , Oct. 00. [0] A.M. Alamout, A smple trasmt dversty tecques for wreless commucatos, IEEE J. AC, Vol. 6, No. 8, pp.5-58, Oct [] X. Feg ad C. Leug, Performace sestvty comparso of two dversty scemes, IEE Electrocs Letters, Vol. 6, No.9, pp.88-89, Apr [] Dakdouk, A.., Baket, V.L., Mykaylov, N.K. ad kopa, A.A., Dowlk processg algortms for mult-atea wreless commucatos, IEEE Commucatos Magaze, Vol., No., pp.-7, Ja Lu Lu was bor ube, Ca 98. e receved a B.. degree Computer cece departmet from out-cetral Uversty for Natoalty, Ca, 00, ad receved M.. degree form te departmet of Electroc Egeerg from Cobuk Natoal Uversty, Korea, 006. e s curretly workg towards a P.D. degree at te Dvso of Electrocs & Iformato Egeerg at Cobuk Natoal Uversty, Korea. er researc terests focus o MIMO, OFDM ad mart atea. Myoug-eob Lm receved a B.. degree, a M.. degree ad a P.D. from te departmet of Electroc Egeerg from Yose Uversty, Korea 980, 98 ad 990, respectvely. e as worked for te Electrocs ad elecommucatos Researc Isttute (ERI) form e developed te commercal CDMA system uder te ot developmet proect betwee ERI ad Qualcomm from e as oed te departmet of Iformato ad Commucato, Cobuk Uversty 996. s researc areas clude te modulato/demodulato, sycrozato, error correcto codg for te advaced CDMA system, MIMO system, OFDM system, UWB ad Vecular Ifortocs.