29 th NATIONAL RADIO SCIENCE CONFERENCE (NRSC 2012) April 10-12, 2012, Faculty of Engineering/Cairo University, Egypt

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1 Apr 10-1, 01, Facuty of Engneerng/Caro Unversty, Egypt Combned Coaboratve and Precoded MIMO for Upnk of the LTE-Advanced Karm A. Banawan 1, Essam A. Sourour 1 Facuty of Engneerng, Unversty of Aexandra, Aexandra, Egypt, karmbanawan@yahoo.com Facuty of Engneerng, Unversty of Aexandra, Aexandra, Egypt, sourour@eee.org ABSTRACT In ths paper, we w focus on the coaboratve MIMO n combnaton wth the LTE-advanced system. In ths system, two or more users each usng mutpe antennas are transmttng ther data wthn the same frequency/tme grd. In ths paper, we nvestgate the MIMO enhancements ntroduced to the LTE upnk of the LTE-advanced system. User equpment here s equpped by -4 antennas whch can be used aong the coaboratve MIMO system to ncrease data rate, enhance system performance and match channe condtons accordng to the channe knowedge at transmtter. We propose a space frequency bock codes (SFBC) precodng for the upnk to acheve space dversty n accompany wth spata mutpexng gan acheved before usng the coaboratve system. Then, we propose a combnaton between the coaboratve system and the precoded MIMO whether deay (SVD precodng) or suboptmay usng codebook precodng. The resuts show dramatc enhancement n performance and acheves the peak spectra effcency of the upnk mode of the LTE-advanced. Keywords: LTE-advanced, Coaboratve MIMO, SC-FDMA, SFBC, SVD-precodng, Codebook precodng, ML. I. INTRODUCTION The LTE-advanced defned n reease 10 of the thrd generaton partnershp project (3GPP) ams to acheve upnk (UL) peak spectrum effcency of 15bts/s/Hz [1]. LTE s the evouton of 3GPP s Unversa Mobe Teecommuncaton System (UMTS) towards an a-ip network []. The mutpe access scheme n LTE downnk s the Orthogona Frequency Dvson Mutpe Access (OFDMA) and upnk uses Snge Carrer Frequency Dvson Mutpe Access (SC-FDMA). SC-FDMA has been adopted for upnk transmsson to aow effcent termna power ampfer desgn, whch s reevant to the termna battery fe [3]. Coaboratve MIMO (known aso as Vrtua MIMO or coaboratve spata mutpexng (CSM)) s ntroduced to the upnk of the LTEadvanced to ncrease the whoe throughput of the upnk and to acheve vrtua MIMO wthout ncreasng the compexty of the user equpment (UE) [4]. CSM works as two or more users havng UEs equpped wth snge or mutpe antennas, each one of them transmts ndependent data stream from the others. Those users are coaboratvey transmttng on the same resource bocks (RBs),.e., same frequency/tme grd resource bock. The above transmsson technque creates vrtua MIMO nk n a sense that the coaboratve users are just antennas for a vrtua arger UE. The Evoved Node B (enodeb) receves combned data from a coaboratve users. enodeb w then separate the data of each user usng mutuser equazaton technques [5]. In ths paper, we dscuss the mutpe antennas enhancements ntroduced to the LTE upnk of the LTEadvanced [1]. In LTE-advanced, the LTE upnk mode s equpped by -4 antennas whch can be used n accompany wth the coaboratve MIMO system to ncrease data rate, enhance system performance and match channe condtons to acheve the channe capacty assumng fu or parta channe knowedge at the transmtter end. Three precodng schemes are presented n the context of ths paper. In the frst scheme, we propose combnng the spata mutpexng advantages of the CSM wth the dversty advantages of the space frequency bock codes (SFBC) [6],[7], ths w enhance the whoe performance of coaboratve system wthout any need of channe knowedge at the transmtter. In the second scheme, we propose expotng the mutpe antennas at the transmtter by apror precodng the spata substreams usng snguar vaue decomposton (SVD) of the channe matrx [8] and fterng the resutant sgnas at enodeb. Ths w maxmze the capacty of the MIMO channe n expense of fu channe state nformaton (CSI). In practce, the feedback messages cannot provde fu CSI at UE, aso the seecton of precoder n LTE-advanced s sgnaed va enodeb, so a mted number of codebookbased precoders shoud be avaabe. So, we propose a suboptma combnaton between codebook precoded MIMO and coaboratve MIMO system as a thrd scheme wth dfferent seecton methods [9]. Varous smuaton resuts are examned n dfferent channe condtons and dfferent mutuser equazaton technques. The paper s organzed as foows: secton (II) ntroduces the used system mode, secton (III) gves a bref terature revew about SVD and codebook precodng, then secton (IV) presents the proposed precodng technques. Secton (V) enumerates the performance of these schemes va computer smuatons. Note that bod face etters denote matrces, (. ) H,. T,. are Hermtan, transpose and Eucdean norm. 1

2 Apr 10-1, 01, Facuty of Engneerng/Caro Unversty, Egypt II. SYSTEM MODEL UE 1 Channe codng Channe codng UE K x ρ x 1 Symbo (base band moduaton) Symbo (base band moduaton) y 1 DFT Y 1 Y 1 "M" and DRS y ρ DFT Y ρ Y ρ and DRS "M" IFFT "N" IFFT "N" s 1 CP s 1 Frequency doman precodng V s ρ CP s NT r 1 CP extracton FFT R 1 Y 1 Frequency Doman Mutuser equazer de IDFT Symbo Demoduaton Channe Decodng Channe codng Channe codng x 1 x ρ Symbo (base band moduaton) Symbo (base band moduaton) y 1 DFT Y 1 Y 1 "M" and DRS y ρ DFT Y ρ Y ρ and DRS "M" IFFT "N" IFFT "N" s 1 CP s 1 Frequency doman precodng V s ρ CP s NT r p CP extracton FFT R p Y p de IDFT Symbo Demoduaton Channe Decodng Fg.1 system mode (a) UEs transmtter bock dagram (b) enodeb recever The CSM system shown n Fg.(1) has K users each has a UE equpped wth mutpe antennas N T. The data of the k th user s ndependenty processed, frst each user w have ρ ndependent data streams (caed rank of transmsson), ρ N T, these data streams are symbo mapped to have the moduated symbos n th ayer y k. The moduaton symbos are then transformed to the frequency representaton va the untary Dscrete Fourer transform (DFT) of sze M to have Y k Y k m = 1 M y k n exp j π (1) M M n 1 m 1 n=1 where m s the subcarrer ndex and n s the symbo ndex, m, n ε 1,,, M. The output of the DFT s then mapped usng the subcarrer [3], whch has two versons: the dstrbuted and the ocazed, the ater s adopted n Reease 8, where the user's symbos are mapped nto consecutve subcarrers. Ths w acheve the mutuser dversty and frequency dversty when assgnng each user to subcarrers wth favorabe transmsson characterstcs. So, ocazed subcarrer s apped to have Y k. In ths work, we assume fu RB usage so Y k () = Y k εγ k 0 otherwse where Γ k s the N eement set of the k th user Γ k ε N M+,, N+M and N s the FFT sze. The output of the subcarrer s then precoded n the frequency doman to map the ρ streams to N T streams by one of the precodng schemes that w be presented n secton (IV). The output of the precodng stage s fed to a conventona OFDM transmtter whch conssts of Inverse Fourer transform stage (IFFT) (N > M), m, nε 1,,, N s k n = 1 N N n=1 Y k m exp j π N () n 1 m 1 (3) Fnay, the cycc prefx (CP) s nserted wth ength arger than the maxmum deay spread of the mutpath channe, to mtgate ntersymbo nterference (ISI) and enabe smpe frequency doman equazaton (FDE). The above steps w resut n a SC-FDMA sgna. Now, each user's data streams have been transmtted through mutpath Rayegh channe whch s modeed as normazed baseband equvaent sampe spaced channe mpuse response h kp (m, ) where m s the tme nstant, s the path number of L taps and p s the recevng antenna ndex wth unform power deay profe. Each path s assumed to be Wde Sense Statonary Uncorreated Scatterng (WSSUS) ftered by Dopper PSD modeed n Jakes [10]. In ths paper, we assume perfect channe knowedge at the transmtter. So, the resut of mutpath fterng of the k th user to p th recevng antenna channe can be modeed as

3 Apr 10-1, 01, Facuty of Engneerng/Caro Unversty, Egypt L rkp m = h kp m, s k (m ) =0 At enodeb, whch s equpped by N r antennas (N r K. ρ), the coaboratve users' sgnas are added together wth contamnaton of AWGN, whch s modeed by IID compex Gaussan nose sampes w(m) wth zero mean and varance σ w = 1/ N. γ s, where γ s s the symbo to nose rato (E s ). Then, the receved sgna r p at the p th antenna s wrtten as K.ρ r p (m) = rkp m + w(m) (5) k=1 The enodeb takes the FFT of each receved stream to transform the nput streams back nto frequency doman and prepares them for the FDE. The receved sgna n the frequency doman at any subcarrer can be wrtten as R = H Y + W() (6) where : s the subcarrer ndex and H : s the channe matrx upon the th subcarrer (4) H = H 11 H 1K H P1 H PK (7) III. EXISTENT PRECODING SCHEMES FOR ORDINARY SPATIAL MULTIPLEXING The man motvaton of precodng the spata substreams s to match channe condtons by ncreasng the receved sgna power n case of perfect or parta CSI, aso decrease the nterstream nterference from other antennas and maxmze the channe capacty of the wreess channe [1]. So, optma communcaton over N R N T MIMO channe uses channe-dependent precoder, whch adopts the roes of both transmt beamformng and power aocaton across the transmtted streams, and a matchng receve beamformng structure [6]. A. Optma Precodng Scheme (SVD Precodng) The we-known optma (capacty-maxmzng) precoder n terature for expotng the channe knowedge at the transmtter s to send data over the strongest egenmodes of the channe. A common way to express the channe matrx n th subcarrer s through ts SVD [8], [9] as H = U Σ V H () (8) where U s N R N R orthonorma matrx, V s N T N T orthonorma matrx and Σ = dag(λ 1, λ,.. ) s egenmodes dagona matrx. The matrx V s used to precode the nput data stream n the frequency doman to have Z() as Z() = V Y() (9) In the enodeb frequency doman equazer, the precodng process eads to orthogona streams f channe s further ftered by U H () (channe matched fter) as Y() = Σ 1 U H ()R (10) or usng the MMSE near equazer for the equvaent channe H eq = H V() Y = (H eq H ()H eq () + 1/γ s I K ) 1 H eq H ()R (11) The SVD precodng aows decomposng channe matrx nto SISO channes, whose gans are λ 1, λ, to ncrease the capacty of the MIMO system, snce the nterstream nterference s apror removed, however the scheme requres perfect CSI and can enhance peak to average power rato (PAPR). 3

4 Apr 10-1, 01, Facuty of Engneerng/Caro Unversty, Egypt B. Codebook Based Precodng For Upnk of LTE-Advanced In practce, the feedback messages cannot provde fu CSI at UE, aso the seecton of precoder n LTEadvanced s sgnaed va enodeb, so a mted number of codebook-based precoders F () shoud be avaabe. A fnte set F of N T ρ precoders s defned n upnk of LTE-advanced.These precoders are chosen to be confned to QPSK aphabet {±1, ±j} as n the tabe 5.3.3A.-1 through tabe 5.3.3A.-5 n reease 10 [11] to ease the precodng process mpementaton, and have constant moduus property for maxmzng power effcency of the power ampfer [1].The UL precoders dffer from the DL ones of havng one nonzero eement n each row whch ensures that no near combnaton between dfferent ayers s aowed to decrease the resutng PAPR whch s consdered a major ssue n UL transmsson. On the other hand, these precodng matrces suffer from degradaton n precodng gan. The precoder s chosen so that t maxmzes the receved sgna power.e. F = argmax = argmax H eq H()F () (1) Ths s equvaent to maxmzng the post-mmse channe power matrx metrc whch corresponds to the sum of the equvaent channe gans for the ρ ayers defned n [9] where m F k = dag(m F ()). M F () = (H H eq ()H eq () + 1/γ s I K ) 1 H H eq ()H eq () (13) F = argmax ρ k=1 m F k. ς w 1 m F (k) (14) IV. PROPOSED PRECODING SCHEMES FOR COLLABORATIVE SPATIAL MULTIPLEXING A. Combned Coaboratve MIMO and Space Frequency Bock Codes (SFBC) for the Upnk of the LTE-Advanced To acheve spata dversty and spata mutpexng jonty wthout a need of any feedback sgnang, a nove combned scheme of SFBC and coaboratve spata mutpexng s proposed. In ths scheme, each user equpped by antennas w precode ts sgna by the we known frequency doman verson of the orthogona Aamout s matrx [7],[1].Ths w resut n encodng each two successve subcarrers for the k th user as Ant 1 Ant Y k ()/ Y k ( + 1)/ Y k ( + 1)/ Y k ()/ (15) The resut of SFBC precodng of each user w acheve transmt spata dversty and orthogona substream transmsson. The resut of SFBC w be transmtted coaboratvey across same tme and frequency resource bock, whch corresponds to spata mutpexng. Consderng the case of users x recevng antennas, then the receved sgna at the th subcarrer woud be R = H 11 H 1 H 13 H 14 H 1 H H 3 H 4 H Y 1 () Y 1 ( + 1) Y () Y ( + 1) + W() (16) where H s x4 MIMO channe whch s assumed to be quas statc over every two successve subcarrers. Smary the receved sgna at the ( + 1) th woud be Y 1 ( + 1) R + 1 = H Y 1 () Y ( + 1) + W( + 1) (17) Y () Then, the recever utzng the nherent orthogonaty of the SFBC encodng, the recever w do the foowng mutpcaton, conjugate and Hermtan processes to have X 4

5 Apr 10-1, 01, Facuty of Engneerng/Caro Unversty, Egypt X = H 11 H H 14 R 1 H 1 H H 4 R H 11 H 14 R H 1 H 4 R + 1 (18) where R 1, R are the receved sgnas aong the th subcarrer on antenna 1 and antenna respectvey. Apparenty we can expot the fu dversty of the coaboratve system per user and aso excude the nterstream nterference as we make a specfc near combnaton of the rows of X. To maxmze the dversty of Y 1, the rows are added n the foowng order θ 1 = X 1 + X 5 + X 10 + X 14 = H 11 + H 1 + H 1 + H Y 1 + H 11 H13 + H 11 H14 + H 1 + H 1 H4 H 1 H 13 H H 3 Y + 1 H3 + H 1 H 14 + H H 4 Y = α 1 Y 1 + βy + γy + 1 (19) Equaton (19) shows the excuson of nterstream nterference Y 1 ( + 1) and expotng a the spata channes experenced by Y 1.Smary, to maxmze Y 1 + 1, Y, Y ( + 1) to have θ, θ 3, θ 4 respectvey as θ = X + X 6 X 9 X 13 θ 3 = X 3 + X 7 + X 1 + X 16 θ 4 = X 4 + X 8 X 11 X 15 (0) Then the equvaent transmsson scheme can be wrtten as quas-orthogona system of equatons as α 1 0 β γ Y 1 () θ 1 0 α 1 γ β Y 1 ( + 1) θ β = γ α 0 Y () θ 3 γ β 0 α Y ( + 1) θ 4 where α = H 13 + H 14 + H 3 + H 4 H eq () Θ() (1) The estmate of the receved subcarrers can be ready obtaned as Y = H eq 1 () Θ() () The scheme makes use of nherent spata dversty shown n α 1, α, doubes the spectra effcency (4 symbos x subcarrers) wth no CSI at the transmttng end. Note that the seectve nature of the channe s a man ssue n ths scheme because the channe gans are assumed to be quas statc over two successve subcarrers, so hghy seectve channe w degrade the whoe performance of the scheme. It s worth sayng that extendng the scheme for users x 4 recevng antennas at enodeb to acheve hgher dversty order s qute smpe wth ony extensons of X, Θ, α 1, α, α, β to acqure the extra channes. B. Combned Coaboratve and SVD-Precoded MIMO for the Upnk of the LTE- Advanced To optmay expot the extra antennas ntroduced to the upnk of the LTE-advanced n the context of coaboratve MIMO system, the precodng of a streams of the coaboratve users seems to be attractve. However, the optma SVD-precodng requres the knowedge of other user s data to use the precodng matrx resuted from SVD decomposton of channe matrx H as equatons (8), (9). A suboptma SVD-precodng whch don t requre knowng other user s data s ntroduced n ths secton. Consder the channe matrx at the th subcarrer assumng perfect CSI at UE 5

6 Apr 10-1, 01, Facuty of Engneerng/Caro Unversty, Egypt H = H 11 H 1 H 1 H H N R 1 1 H N R 1 H N R 1 H N R H 1 KNT 1 H KNT 1 H N R 1 KN T 1 H N R KN T 1 H 1 KNT H KNT H N R 1 KN T H NR KN T (3) where H s N R KN T channe matrx. To tacke the probem of jont precodng, we w suboptmay precode the data streams of each user ndvduay.e., we w precode each N R N T submatrx ndependenty as H user 1 = H 11 H 1 H 1 H H N R 1 1 H N R 1 H N R 1 H N R H 1 NT H NT H N R 1 N T H NR N T Ths submatrx w be SVD decomposed as (8),(9) as H user 1 = U 1 Σ 1 V H 1 () (5) The process w contnue to the remanng K 1 users to have K precodng matrces.then the transmtted sgnas of a users w be Z = V 1 Y 1 V Y V K Y K () and the equvaent channe matrx w be H eq = [H user 1 V 1 H user K V K ] (7) Then the equazaton methods dscussed n equatons (11),(1) can be used. Note that ths scheme s suboptma n a sense that t ensures remova of a nterstream nterference for each user aone, whe the mutuser nterference st exsts, however ths comes n expense for not needng the knowedge of other users data. The performance of ths scheme w be the mdde way between perfecty precoded scheme whch corresponds to KN T orthogona streams at the recever and unprecoded one whch suffers from nterstream and mutuser nterferences. C. Combned Coaboratve and Codebook-Precoded MIMO for the Upnk of the LTE- Advanced To make use of the new spata dmenson ntroduced n LTE-advanced wth mted feedback sgnang n case of coaboratve MIMO system, codebook-based precodng shoud be taken nto consderaton. Three dfferent precoder seecton technques are presented n comparson 1) Submatrx Precodng : Ths seecton method s the same as the prevous scheme, the channe matrx s dvded nto K submatrces and each one of them s precoded ndependenty by metrc dentfed n equatons (1),(13),(14) thus precodng matrx of k th user s F userk = argmax H user k ()F () (8) where H user k () s the channe coumns corresponds to the k th user. The equvaent channe woud be H eq = [H user 1 F user1 H user K F userk ] (9) ) Jont Maxmzaton Precodng: In ths seecton method, the MIMO channe s dvded nto KxK submatrces, For exampe for rank 1, users equpped by transmttng antennas and 4 recevng antennas, we w have 4 submatrces x each H = H 1 1 user 1() H user () (30) H user 1 () H user () 1 where H user 1 () s x MIMO channe between user 1 and recevng antennas 1,. Here we w choose the precoder so as to jonty maxmze the norm of these subchannes as (4) (6) 6

7 BER BER BER 9 th NATIONAL RADIO SCIENCE CONFERENCE Apr 10-1, 01, Facuty of Engneerng/Caro Unversty, Egypt 1 F userk = argmax ( H user 1 F 34 + H user 1 F ) (31) and the equvaent channe woud be as equaton (9) 3) Lnear Combnaton Precodng: In ths seecton crtera, the precoder s chosen as a near 1 34 combnaton of the precoders whch maxmze the metrc of H user 1 (), H user 1 () ndependenty as F userk = argmax 1 H user 1 F + argmax 34 H user 1 F (3) The chosen precoder must be normazed. The drawback of ths seecton method s that the resutant precoder doesn t have a constant moduus and can probaby enhance PAPR. V. SIMULATION RESULTS For nk eve smuatons, the smuaton parameters of most of smuaton cases are shown n tabe 1, other smuaton parameters are mentoned expcty Comparson between presented precodng schemes reference curve fat fadng wthout precodng x4 antennas 10-7 SFBC precodng users x 4 receve antennas Codebook precodng user x 4 ant. rank 1 SVD precodng users x 4 ant. rank 10-8 unprecoded rank and codebook precoded rank Fg. comparson between presented precodng technques Tabe 1: common smuaton parameters Smuaton Vaues Parameters Channe codng None (defaut) Moduaton schemes 16QAM Frame duraton 10ms Frame structure Type 1 FDD FFT sze 56 subcarrers Number of RBs 15, fuy utzed Bandwdth.7 MHz SC-FDMA symbos 6 Cycc prefx choce extended separaton 15KHz Carrer frequency GHz Sampng frequency 3.84MHz Deay spread 5μs (defaut) Deay- power profe Unform/0 km/hr Channe estmaton Perfect CSI at transmtter 10 0 Effect of seectvty aong presented precodng schemes 10 0 codebook precodng Vs. ordnary CSM precodng x4 rank 1 unprecoded x4rank 1 precodng x4rank (asunprecodng) precodng x8 rank 1 unprecoded usersx8 ant. precodng x 8 rank unprecoded usersx8ant. rank precodng usersx8 ant. rank 3 unprecoded users x 8 ant. rank 3 precodng x8 rank4 (asunprecoded) SVD precodng rank 4 codebook fat fadng channe codebook deay spread=us codebook deay spread=5us codebook deay spread=15us SFBC fat fadng 10-7 SFBC deay spread 1uS SFBC deay spread=3.5us SFBC deay spread=us SFBC deay spread=5us Fg.4 seectvty effects on the presented precodng schemes Fg.3 Codebook and SVD precodng Vs. ordnary CSM 7

8 BER spectra effcency b/s/hz 9 th NATIONAL RADIO SCIENCE CONFERENCE Apr 10-1, 01, Facuty of Engneerng/Caro Unversty, Egypt Fg.() shows a comparson between the presented precodng schemes. Smuaton resuts revea that for rank 1 transmsson n fat fadng channe, SFBC precodng and codebook precodng are amost dentca, and outperforms the unprecoded system by more than 3dB at a target BER=, so SFBC n ths case s preferred due to the no CSI need at the transmtter. For rank, the SVD precodng outperforms the codebook precodng by.5db. Fg (3) shows codebook precodng versus ordnary coaboratve spata mutpexng for dfferent ranks as ncreasng the rank of the transmsson, ncreases the spectra effcency n expense of enhanced nterstream nterferences and hence hgher BER. Fg.(4) shows the seectvty effect on the precodng schemes, SFBC precodng fas for hgh seectvty due to the assumpton of fat channe gans over each successve subcarrers. So, ncreasng the deay spread to μs w enhance the performance of SFBC. An error foor w appear f the deay spread μs. On the contrary, codebook precodng expots the hgh seectvty of the channe as nherent frequency dversty. Fg.(5) shows a comparson between the codebook seecton methods. The fgure reveas that the submatrx precodng expots the fu channe knowedge and hence better nterstream and nteruser nterference canceaton. For the jont maxmzaton method, the performance s degraded by 1dB because the scheme searches for the precoder whch jonty maxmzes the channe metrc of the sub MIMO channes, so more nterstream nterference w exst. Choosng to maxmze the best sub MIMO channe ony w degrade the performance by another 0.5dB. Fg.(6) and Fg.(7) show the spectra effcency of the resutant CSM system for and 4 transmttng antennas n case of 16QAM moduaton. The resuts show that the threshods of usng the adaptve rank codebook precodng for the CSM system. These threshods can be summarzed n tabe. Note that the acheved spectra effcency exceeds the target spectra effcency of the LTE-advanced. Fg.(8) shows the effect of precodng the coaboratve streams on other equazaton technques. Smpfed nta guess (IGML) soutons presented n [5] w be n the order of O(KρM). Smpfed IGML s a user by user separaton by means of QR-decomposton of the equvaent channe matrx H eq obtaned n (7). SIC based system w be the same as presented n [5], but the nterference w be regenerated assumng the channe matrx s the equvaent channe matrx presented aso n (7). Fg.(8) shows that SIC-based equazer concdes wth the MMSase equazer. Because the SIC performance s dependent on the SINR, and for precoded system most of the nterference components are excuded and hence sght enhancement n performance can be expected. The QR based IGML recever outperforms the MMSE equazer by 1dB n expense of the ncreased compexty of checkng the error metrc of a possbe consteaton ponts. Tabe : SINR threshods of the adaptve rank precodng for CSM system of users x 8 recevng ant. CSM Confguraton Rank 1 Rank Rank 3 Rank 4 Transmttng antennas= <.5dB(8b/s/Hz).5 db(16b/s/hz) - - Transmttng antennas=4 <7.8dB(8b/s/Hz) dB(16b/s/Hz) dB (4b/s/Hz) 5.5dB (3b/s/Hz) 10 - Comparson between seecton methods of precoders forusersx8 receve ant. rank 1 Submatrx precodng jont maxmzaton near combnaton best channe metrc precodng Spectra effcency of codebook precoded usersxrecevng antennas and UE havng transmttng antennas rank 1 rank Fg.5 Seecton methods for the codebook precodng methods Fg.6 Spectra effcency of users CSM system each UE havng transmttng antennas, 16QAM moduaton 8

9 spectra effcency b/s/hz BER 9 th NATIONAL RADIO SCIENCE CONFERENCE Apr 10-1, 01, Facuty of Engneerng/Caro Unversty, Egypt Codebook precoded coaboratve spata mutpexng for 4 transmttng antennas rank 1 usersx8ant. rank usersx8ant. rank 3 users x8ant. rank 4 userx8ant Effect of dfferent equazaton technques accompanyng codebook precodng users, 4Tx ant., rank 1, 8 recevng antennas SIC equazaton smpfed IGML equazaton MMSE equazaton Fg.7 Spectra effcency of users CSM system each UE havng 4 transmttng antennas, 16QAM moduaton Fg.8 Dfferent mutuser equazaton technques accompanyng the codebook precodng VI. CONCLUSION In ths paper, we expot the mutpe transmttng antennas n the upnk of the LTE-advanced. We have ntroduced a bnd SFBC-based precodng whch doesn t need any channe knowedge at the transmtter and derved a sutabe recever for t. We concuded that SFBC precodng performance amost concdes wth codebook precodng for fat fadng channe, but the man dfference that the performance of the SFBC precodng degrades n case of moderate and hgh seectve channes because of the assumpton of fat channe gans over each two successve subcarrers. On the contrary, we compared between three seecton methods for sutabe precoders and we found that the submatrx precodng technque outperforms the others because t expots the fu dversty of the MIMO channe. The performance of the codebook precodng s enhanced n case of hgh seectve channe because an extra dversty source (frequency) exsts. Aso we ntroduce suboptma SVD precodng for each of the coaboratve users. Aso the resutant spectra effcences are shown to exceed the target spectra effcency of the LTE-advanced (15bts/s/Hz). The resuts nstruct usng adaptve precodng scheme that uses SFBC based precodng for ow and medum seectve channe. As seectvty ncreases, use the adaptve rank codebook transmsson usng the submatrx seecton method. Fnay as SNR s suffcenty hgh to use the fu rank of the MIMO channe you can use the SVD-based precodng. REFERENCES [1] C.S. Park, Y.-P.E.Wang,G.Jo ngren,d.hammarwa, Evouton of upnk MIMO for LTE-advanced IEEE Communcatons Magazne, Voume: 49 Issue:,pp , Feb. 011 [] Davd Astéy, Erk Dahman, Anders Furuskär, Yva Jadng, Magnus Lndström, and Stefan Parkva, Ercsson Research LTE: The evouton of mobe broadband," IEEE Communcatons Magazne, vo. 47, no. 4, pp , Apr 009. [3] H. G. Myung, J. Lm, and D. J. Goodman, Snge Carrer FDMA for Upnk Wreess Transmsson, IEEE Vehcuar Technoogy Mag., vo. 1, no. 3, pp , Sep [4] V. Jungncke, M. Schemann, A. Forck, H. Gber, S. Wahs, A. Ibng, K. Manoaks, T. Hausten, W. Zrwas, J. Echnger, E. Schuz, C. Juchems, F. Luhn, and R. Zavrtak, Demonstraton of Vrtua MIMO n the Upnk, n IET Smart Antennas and Cooperatve Communcatons Semnar, London, UK, Oct. 007, nvted. [5] Karm A. Banawan, Essam Sourour Enhanced SIC and Inta guess ML recevers for coaboratve MIMO of the LTE Upnk, Vehcuar Technoogy Conference (VTC011-Fa), Sept [6] S. Sesa, I. Toufk, and M. Baker, Eds., LTE: The UMTS Long Term Evouton. John Wey and Sons, 009 [7] J. Lee, J.-K. Han, and J. Zhang, MIMO Technooges n 3GPP LTE and LTE-Advanced, EURASIP Journa on Wreess Communcatons and Networkng, vo. 009, May 009. [8] A. Godsmth, Wreess Communcatons. Cambrdge, U.K.: Cambrdge Unv. Press, 004. [9] G.Berardne, T.B.Sørensen, P.Mogensen, K.Pajukosk SVD-based vs. Reease 8 codebooks for Snge User MIMO LTE-A Upnk Vehcuar Technoogy Conference (VTC 010-Sprng),May 010. [10] W. Jakes and D. Cox, Mcrowave Mobe Communcatons. Wey-IEEE Press, [11] 3GPP TS V (011-04). [1] Aamout, S.M. (1998) A smpe transmt dversty technque for wreess communcatons. IEEE Journa on Seected Areas n Communcatons, 16(8),