MIMO Eigen Beamforming for HSUPA of TD- SCDMA

Transcription

1 25 Asa-Paf Conferene on Communatons, Perth, Western Australa, 3-5 Otober 25. IO Egen Beamformng for SUPA of TD- SCDA LIU Guangy, LIU Xantao, ZANG Janhua, ZANG Png WTI Lab, Bejng Unversty of Posts&Teleommunatons, P.O. Box 92, No., XTuCheng Road, adan Dstrt, Bejng, P.R.Chna,876 Abstrat As the evoluton of the 3G standards, ultple Input and ultple Output (IO) has been adopted to enhane the performane of 3G systems for the potental of beamformng, spatal multplexng or spatal dversty. So far, no IO sheme has been adopted for Tme Dvson- Synhronous Code Dvson ultple Aess(TD-SCDA). In ths paper, 2x8 IO Egen beamformng s proposed to mprove the performane of TD-SCDA. As sze lmted, the antennas at the UE or Node B are orrelated, only one Egen mode of the spatal orrelaton matrx s found to be useful, and only the beamformng gan and spatal dversty gan an be obtaned effently. The smulaton results of gh Speed Upln Paet Aess (SUPA) n the fxed referene hannel show that, ompared to Sngle Input and utple Output (SIO) x8, 3dB performane gan an be obtaned by IO 2x8 Egen beamformng; Whle ompared to that of Sngle Input and Sngle Output (SISO), the performane gan s 8~3dB. Key Words: IO, AC, TD-SCDA, Egen beamformng I. INTRODUCTION Tme Dvson-Synhronous Code Dvson ultple Aess (TD-SCDA) [] s one of the nternatonal 3G standards, proposed by Chnese Aademy of Teleommunaton Tehnology (CATT) and aepted by Internatonal Teleommunaton Unon (ITU) and 3G Partner Projet (3GPP) as a member of Tme Dvson Duplex (TDD) ode. For many advaned tehnques are adopted, suh as smart antenna, jont deteton, synhronous upln, dynamal hannel alloaton, software defned Rado, et., TD-SCDA s a very advaned system and has very hgh theoretal spetrum effeny. owever, ompared to Wdeband Code Dvson ultple Aess (WCDA), few publ researhes on ultple Input and ultple Output (IO) of TD- SCDA an be found. So far, no IO sheme has been adopted for TD-SCDA n 3GPP. As the IO an mprove the system performane by beamformng, spatal multplexng or spatal dversty [3] [4], and the IO Egen beamformng [5] an explot the multplexng gan and the dversty gan optmally [6], n ths paper, IO Egen beamformng s proposed for gh Speed Upln Paet Aess (SUPA) of TD- SCDA frstly by onfgurng 8 antennas at the Node B and 2 antennas at the oble. As a TDD system, the hannel reproty an be exploted to mplement the Egen beamformng easly. By adoptng Adaptve odulaton and odng (AC) and waterfllng power alloaton on the Egen mode sub-hannels, the near IO apaty s obtaned [6]. Besdes IO, ybrd Ths wor s funded by Chnese 863 under grant No. 24AA238. Automat Repeat request (ARQ) s also smulated n ths paper. As the SUPA standard s stll n dsusson, the bt mappng of gh Speed Downln Paet Aess (SDPA) [7] s used nstead for performane evaluaton. The smulaton results show that the throughput and the paet performane of SUPA s mproved by 8~3 db, ompared to that of Sngle Input and Sngle Output (SISO). Ths paper s organzed as follows. The IO Egen beamformng s ntrodued n seton II; the SUPA smulaton parameters are presented n seton III; the smulaton results are gven n seton IV and the onlusons are drawn n seton V. II. IO EIGEN BEAFORING IN TD-SCDA For the lmted sze of the termnal, 2 antennas are onfgured at the general User Equpment (UE). Consderng the pratal applaton and the ba forwards ompatblty for the released verson of TD- SCDA, the spatal nterval between the antennas of the Unform Lnear Arrays (ULA) s half wavelength. So the antennas of the ULAs at both ends of the IO hannel are orrelated. From Fgure., only one Egen value of the spatal orrelaton matrx for 2x8 IO hannel s qute large, and no spatal multplexng gan an be obtaned. In ths paper, IO Egen beamformng s proposed and only the best Egen mode of the IO hannel s used to transmt the data egen value egen values of TD-SCDA IO2X8 Spatal Correlaton atrx PA3Km egen egen Burst Sample Fgure. Egen Values of IO 2x8 spatal orrelaton atrx As a TDD system, TD-SCDA an explot the hannel reproty to mplement the Egen beamformng easly. In ths paper, the hannel mpulse response (CIR) of the IO hannel s assumed to be nown to Node B by subframe delay, whh an be obtaned by upln /5/$2. 25 IEEE. 67

2 feedba or upln hannel estmaton on the assoated hannel. The system blo of SUPA s gven n Fg 8. The Channel Impulse Response (CIR) of the IO hannel an be expressed as:,,2 = () 8, 8,2 8 2 Where mn, s the CIR between antenna n of UE and the antenna m of Node B, whh has L m multpath. As [4], the Egen beamformng an be mplemented as two steps. Frst, the transmtted data symbols are preoded wth the onjunton of untary vetor V, whh s orrespondng to the maxmum Egen value of the spatal orrelaton matrx at the transmtter, and then oded sgnals are transmtted on dfferent antennas respetvely. Seond, at the reever, the reeved sgnal vetor s ombned after weghted by the untary vetor U orrespondng to the maxmum Egen value of the spatal orrelaton matrx at the reever. Frst, let s alulate the preodng vetor of the Egen beamformng. The spatal orrelaton matrx at the transmtter s: R T T = = (2) Where T, the number of the transmtter antenna, s equal to 2, and means the onjugatve transpose of a matrx. Then alulate the Sngular Value Deomposton (SVD) of the spatal orrelaton matrx: T T = R VSV, S = V R V (3) T T Where S s a dagonal matrx wth the sngular values ordered on the dagonal poston. V s the untary sngular matrx orrespondng to the sngular value of R T T. Then T V = ( w,,..,.., ) w2 w j w T orrespondng to the maxmum sngular value of R T T, s the preodng vetor of the Egen beamformng, and the operator T means the transpose. As spefed, every data feld n a burst of TD- SCDA s omposed of N data symbol, the n th data symbol on the ode s d n, Q s the spreadng fator, and ode after sramblng s expressed as: = [, 2,..., Q ], =,..., K (4) The sgnal after the spreadng and sramblng s: N n ( n ) Q n= s = d, =,..., QN, =,..., K And, [, Q] =, others (5) (6) s After of all K odes for one user has been summed together, the sgnal s weghted by w j of V and transmtted on dfferent antennas respetvely. The reeved sgnal on the data feld of a burst from the antenna Ka s: T K W Ka w = j Ka, j w+ + j= = w= T K W N w = wh j Ka, jdn ( n ) Q w+ + n j= = w= n= e w h s n For Egen beamformng, the IO Channel Status Informaton (CSI) must be nown aurately at the reever, besdes at the transmtter. To estmate the CSI of IO, dfferent mdamble odes must be transmtted on dfferent antennas wthout preodng of Egen beamformng. As the good autoorrelaton property of the bas mdamble odes n TD-SCDA, the dfferent shfted versons of the same bas mdamble odes an be used to estmate the CSI of the dfferent transmtter antenna smultaneously. The mdamble odes for dfferent transmtter antennas are produed as Fgure 2.. Assume that m = ( m.. m + W.. m + 2W.. m + 3W.. ml) s the bas mdamble ode used for hannel estmaton of the user. L s the total length of the mdamble ode. Then the j mdamble ode m for the antenna j s produed by shftng the bas mdamble ode byw j ylally from rght to left. W s the sze of the hannel estmaton wndow. Fgure 2. damble ode seleton for IO hannel estmaton At the reever, the reeved sgnal of the mdamble part from antenna s: T = [, 2,..., L+ W ] = (, j j) K j= r r r r m T (8) Where the operator * means lnear onvoluton, K s K the ode number per user, and s used to T balane the power of the data part and the mdamble part. As the mdamble s ylal, only the frst 28 samples are used for hannel estmaton: 2 28 (7) rˆ = [ r, r,..., r ] (9) The Fast Furrer Transform (FFT) result of rˆ s expressed as: 68

3 rˆ = [ rˆ, rˆ,..., rˆ ] (), FFT, FFT, FFT, FFT 2 28 And the FFT of the frst 28 sample of the bas mdamble ode s expressed as: = [, 2,..., 28] () Then the hannel CIR between reevng antenna and all the transmtter antennas an be estmated by Stener s algorthm [] as followng:, FFT ˆ ˆ rˆ T [,,,2,...] ( = IDFT ) (2) K After all the hannel mpulse responses between the transmtter and reever antenna has been estmated, the CIR of the IO hannel an be onstruted as Ĥ : ˆ ˆ,,2 ˆ = (3) ˆ ˆ 8, 8,2 8 2 Based on Ĥ, the nterferene sgnal, whh s reated by the mdamble passed through the tme dsperse IO hannel, an be reonstruted and elmnated from the reeved sgnal on the data feld. For the sgnal from the antenna Ka at the reever, the nterferene reonstruted s: ( m ˆ Ka, j ) 2 Ka j K I = (4) T j= The reeved sgnal after the nterferene elmnated s: Ka Ka Ka Ka Ka [ eˆ,..., eˆ ] = [ e,..., e ] I NQ+ NQ+ L+ W NQ+ NQ+ L+ W (3) As [4], the post beamformng vetor should be alulated for the deteton. The spatal orrelaton matrx at the transmtter and reever an be estmated respetvely as: T T = Rˆ = ˆ ˆ, Rˆ ˆ ˆ R R = = (5) Where ˆ s the th multpath of the IO CIR Ĥ, L m s the number of the multpath. Then the sngular Value deomposton (SVD) of spatal orrelaton matrx at the transmtter and reever are respetvely as followng [4]: ˆ ˆ ˆ ˆ R VSV, ˆ ˆ S = V R ˆ V ˆ (6) T T = T T ˆ ˆ ˆ ' ˆ RR R = USU, ˆ ' ˆ S = U Rˆ ˆ R R U (7) Where the untary vetor ˆV s orrespondng to the maxmum Egen value of the spatal orrelaton matrx of the transmt antenna array. The untary vetor Û s orrespondng to the maxmum Egen value of the spatal orrelaton matrx of the reepton antenna array. Then the reeved sgnal on the Egen mode hannel an be expressed as: ˆ 2 eˆ = U ( eˆ, eˆ ) (8) Whle the vrtual hannel mpulse response on the IO Egen mode hannel seleted an be expressed as: ˆ ˆ h= U V ˆ ˆ (9) ĥ and ê after the Egen beamformng and mdamble nterferene aneled are sent to jont deteton, then data symbols on the best Egen mode hannel are deteted out and the nter-symbol nterferene and multple aess nterferene s elmnated. After the demodulaton, denterleavng and deodng, the data stream s reovered. Egen beamformng above an be appled n both Sngle Input and ultple Output (SIO) and IO system. For SIO, the preodng vetor s. III. SUPA SIULATION PARAETERS FOR FIXED REFERENCE CANNEL For the SUPA standards are stll not avalable, n ths paper, the bt mappng and ARQ sheme of gh Speed Downln Paet Aess (SDPA) from the ategory (.4bps) s smulated for fxed referene hannel [7]. The bt mappng of referred SDPA s adopted as TABLE I.. The nformaton data rate s ept onstant, the modulaton type fxed, the UE hannel qualty ndator (CQI) error and the sgnalng error s not smulated and therefore Anowledge/Non-Anowledge (ACK/NACK) reports are onsdered error free. The system model of the SUPA ln s as Fgure 8.. In every TTI, only one user s sheduled to transmt n the upln. A. Tme slot alloaton The tme slot alloaton sheme adopted for SUPA s as Fgure 3.. TS of every subframe must be used for downln broadastng nformaton and TS must be used as UL TS to aess the users, report the CQI and transmt other sgnalng. TS2~TS5 an be ombned together for data transmsson n UL, and TS6 s used for downln ontrol nformaton. In every data TS, odes wth length 6 are used for QPSK transmsson, or 9 odes wth length 6 are used for 6QA transmsson. S-SCCs SUPA data S-SIC ms Subframe n Subframe n+ TS TS TS2 TS3 TS4 TS5 TS6 TS TS TS2 TS3 TS4 TS5 TS6 Fgure 3. tmeslot alloaton for SUPA smulaton TABLE I. S-DSC FIXED REFERENCE CANNEL CATEGORY Parameter Unt Value odulaton QPSK 6QA axmum nformaton bt rate Kbps Number of ARQ Proesses 4 4 N Informaton Bt Payload ( INF ) Bts Number Code Blos Blos Total Avalable of Soft Channel bts Bts

4 n UE Number of Soft Channel bt per Bts ARQ Pro. Number of oded bts per TTI Bts Codng Rate Number of S-USC Tmeslots Slots 4 4 Number of S-USC odes per TS Codes 9 Spreadng fator SF 6 6 B. ARQ ARQ sheme of SDPA s adopted here to guarantee the relable data transmsson, whh s spefed n [9]. If the retransmsson exeeds 4, the data blo s dropped. C. Performane metr The performane metr s the nformaton bt throughput at the Node B. In the smulaton, parameter I ˆ or / I o s used to get throughput plots. I ˆ / or I o s ntrodued by the 3GPP n [], where I ˆor s the posthannel transmtted power densty by a transmtter,.e. UE here. I o s the sum of nterferene from other ells and thermal nose. Aordng to [], throughput s desrbed as equaton (2) wth the assumpton that ARQ s used. FERr R = R ( ) (2) b Where R s throughput measured n term of bts per seond; Rb s the transmtted nformaton bt rate. FERr s the resdual Frame Error Rate beyond the maxmum number of transmssons; N s the average number of transmsson attempts. D. Other General Smulaton parameters The other general smulaton parameter s as TABLE II.. TABLE II. GENERAL SIULATION PARAETERS FOR SUPA SIULATION Parameter Assumpton Carrer Frequeny 2 Gz Chp rate.28 ps Fast fadng model Jaes spetrum Channel ray mappng Shfted to nearest multple of the samplng rate RRC flter Off Reever Jont Deteton (SE-BLE) damble One bas mdamble s used for one user Turbo deodng axlogap 4 teratons Input to turbo deoder Soft ARQ As 3GPP TR Propagaton model Pedestran A at 3m/h IV. SIULATION RESULTS As the lmted sze, 2 antennas are onfgured at the UE, and the antenna spatal nterval s set as half of the wavelength, so the antennas at the both UE and Node B are hghly orrelated, lttle spatal multplexng an be obtaned. Only the best Egen mode s used for data N transmsson. For the referene, the throughput and average paet delay performane of the SISO antenna and SIO x8 Egen beamformng are smulated. From Fgure 4. Fgure 5. Fgure 6. Fgure 7., the performane of SIO and IO Egen beamformng are muh better than that of SISO; the performane gan s about 5dB for SIO ase, and about 3dB more performane gan s obtaned by IO for 2 antennas are onfgured at the UE, dversty gan an be obtaned for the same transmsson power at the Node B. From Fg 6 and Fg 7, the performane gan for SIO s about db, and about 3dB more gan for IO Egen beamformng. Comparng the results of QPSK and 6QA, more gan s obtaned n 6QA, beause 6QA s more senstve to the nose and hannel estmaton error. V. CONCLUSION In ths paper, IO Egen beamformng s proposed to mprove the performane of TD-SCDA SUPA for the hannel reproty an be exploted easly n TDD system. As the lmted sze, 2 antennas are onfgured at the UE. As the antennas at the both UE and Node B are hghly orrelated, lttle spatal multplexng an be obtaned. Only the best Egen mode s used for data transmsson. Compared to SISO, the performane gan of SIO x8 Egen beamformng s about db for 6QA, and 5dB for QPSK; 3dB more gan an be obtaned by IO 2x8 Egen beamformng for reepton dversty at the UE. gher order modulaton, suh as 64QA may be appled for IO Egen beamformng for hgher throughput. REFERENCES [] [2] 3GPP R4-445, SUPA Node B Performane Requrements. [3] G. J. Foshn and. J. Gans, On the lmts of wreless ommunatons n a fadng envronment when usng multple antennas, Wreless Personal Communaton, vol. 6, pp , 998. [4] E. Telatar, Capaty of ult-antenna Gaussan Channels, European Transatons on Teleommunatons, vol., no. 6, pp , November /Deember 999. [5] Brunner, C, Utsh, W and Nosse, J. A. Explotng the shortterm and long-term hannel propertes n spae and tme: egenbeamformng onepts for the BS n WCDA European Transatons on Teleommunatons, vol 2, no. 5, Sept-Ot 2. [6].Foshn, G. J, Lozano, A, Rashd-Farroh, F and Valenzuela, R. A. Spae-tme proessng for multple-nput multple-output wreless ommunaton systems, European Patent applaton EP 7 97 A2, fled 2th Deember 2. [7] R4-228 SDPA smulaton assumpton update for fxed referene hannel for.28 ps TDD opton, TSG-RAN WG4 meetng #24 elsn Fnland, Semens AG. 8/22. [8] TS25.36v5.. UE Rado Aess Capabltes. 3GPP TSG RAN2, 3/22. [9] 3GPP TR v6.., ultplexng and hannel odng (TDD) (Release 6). [] Bernd Stener, Peter Jung, Optmum and Suboptmum Channel Estmaton for upln of CDA moble Rado systems wth Jont deteton, European Transatons on Teleommunatons, Vol. 5, No., Jan, 994. [] 3GPP TR v.6., Physal Layer Aspets of gh speed downln paet aess. 7

5 Fgure 4. Throughput of QPSK n Pedestran A 3m/h Fgure 6. Throughput of 6QA n Pedestran A 3m/h Fgure 5. paet delay of QPSK n Pedestran A at 3m/h Fgure 7. paet delay of6qa n Pedestran A 3m/h Fgure 8. Theoretal Blo of the IO Egen Beamformng 7