Introduction TSGR1#5(99)623. TSG-RAN Working Group 1 (Radio) meeting #5 Cheju, South Korea, June 1~4 th, Agenda Item: Smart Antenna Technology

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1 TSG-RA Workng Group 1 (Rado) meetng #5 Cheu, South Korea, June 1~4 th, 1999 TSGR1#5(99)623 Agenda Item: Source: Ttle: CWTS WG1 Smart Antenna Technology Document for: Consderaton Introducton Followng the harmonzaton of TD-SCDMA and UTRA-TDD, ths document ntroduces the prncple of smart antenna, whch s one of the most mportant parts of the CWTS RTT proposal. The harmonzaton process was agreed among ARIB, CATT, DoCoMo, Ercsson, oka, Panasonc, RITT and Semens (RP-99248). A smart antenna system s composed of an array of multple antenna elements and coherent transcevers wth advanced dgtal sgnal processng algorthms. Instead of a sngle fxed beam pattern from a tradtonal antenna, the smart antenna can dynamcally generate multple beam patterns, each of them s ponted to a partcular UE, and such beam patterns can adapt to follow any UE ntellgently. On the Rx sde of ode B, such a feature,.e., spatally selectve Rx (uplnk) beamformng, can greatly mnmze co-channel nterference from the co-channel UEs at dfferent locatons, thus ncrease the Rx senstvty and lead to hgher capacty. It can also effectvely coherently add multpath components to combat multpath fadng. On the Tx sde of ode B, ntellgent spatally selectve Tx (downlnk) beamformng can also greatly reduce the nterference to other co-channel UEs, then dramatcally save the output power requrement and lead to hgher capacty. The rest of ths document presents the prncples and some theoretcal background about the use of Smart Antenna. Its applcaton s part of the TD-SCDMA (UTRA-TDD low chprate mode). 1. The basc structure of smart antenna based ode B n the TD-SCDMA (UTRA-TDD low chprate mode) system 1.1. References 1. CWTS WG1 TS C1.24, Physcal layer procedures (TDD) Revson 1.3 1/

2 2. CWTS WG1 xxx, Method and Prncple of Uplnk Synchronzaton 1.2. Smart antenna structure The proposed TD-SCDMA RTT s manly based on the smart antenna technology as descrbed. Generally speakng, a smart antenna based ode B should be that shown n Fgure 1. The smart antenna array s composed of antenna elements, related feed cables and coherent RF transcevers n RF part. By use of the A/D converters or D/A converters n analog baseband (ABB), the Rx and Tx analog sgnals are nterfaced to the dgtal baseband (DBB) part over the hgh-speed data bus. In ths model, all antenna elements, related feed cables and coherent RF transcevers wll be calbrated before operatng Basc operaton prncple Reference to Fgure 1, the ode B s equpped wth smart antenna array and DBB DSP. When a sgnal comes from one UE wthn the coverage of the ode B, each antenna element and coherent RF recever wll get t. Because of the dfferent locaton of the dfferent antenna element, the phase of the Rx sgnal wll be dfferent. In case of multpath propagaton, each path wll come from dfferent drectons wth dfferent ampltude and delay. Then the Rx sgnal at each antenna element wll show dfferent phase and ampltude. After the front-end processng n RF part and A/D converters processng n ABB, dgtzed Rx sgnal wth the phase and ampltude nformaton wll be sent to DSP n DBB part. In a CDMA cellular system, there are many UEs workng smultaneously. The Rx sgnals wll be the sum of the sgnals (ncludng man path and multpath) comng from all the actve UEs wthn the cell and the nterference comng from nearby cells. Let the output of the -th recever be s at the tme n. After despreadng, one may obtan the Rx data of each code channel as x for the l -th symbol, where means the -th code channel. The purpose of smart antenna n uplnk s to fnd the best E b I after the combnaton, 0 The sgnal of the l -th symbol n the -th code channel s denoted as X, then X ( l) = x ( l) w ( l) (1) where W s the uplnk beamformng matrx wth element = 1 w. Many beamformng algorthms can be found n publshed papers. Theoretcally, the uplnk beamformng can add up all useful sgnals whle cancelng all multpath nterference. ext step n smart antenna s to realze downlnk beamformng. The Tx sgnal of the -th code channel s denoted as Y for the l -th symbol. Let the UE obtan the best E b I 0 obtaned that where y = 1, then t can be y ( l) = Y ( l) u ( l) (2) s the Tx sgnal on the -th antenna for the l -th symbol n the -th code channel; U s the downlnk beamformng matrx wth element u TDD and FDD It s well known that there are two duplexng modes n IMT2000 RTTs: TDD and FDD. The wave propagaton envronment s very complex, and t s closely related to workng frequency and tme when the UE s n movng. Reference to secton 1.3, the downlnk beamformng s always followed by uplnk beamformng. And t s always very mportant to reach fast beamformng to catch the tme varaton n moble network. Antenna element TRx TRx TRx s ( ) s ( ) s ( ) 1 n 2 n 3 n s Frequency Revson 1.3 2/9 & Tmng Base TRx

3 DBB DSP Spreadng Tx (downlnk) beamformng Data Bus QPSK MODEM Sync & Despreadng Rx (uplnk) beamformng MCU Data and Sgnalng Fgure 1. Smart antenna based ode B structure In TDD system, the uplnk and downlnk are operated at the same frequency but n dfferent tme slots. Ths make t possble to drectly use the uplnk beamformng results (W n equaton (1)) to downlnk beamformng (U n equaton (2)) because of the symmetrcal performance n wave propagaton. The recprocal prncple n electro-magnetc theory provdes the theoretcal foundaton. In FDD mode, the dfferent carrer frequences between downlnk and uplnk results n dfferent wave propagaton envronments. Theoretcally, for FDD system, there s no practcal model can be used to foresee the downlnk propagaton n a real envronment. What one can do s only to provde a pencl beam for downlnk focusng on the drecton of the UE. 2. Beamformng 2.1. The maxmum energy combnaton As shown n Fgure 2, the most practcal array used n smart antenna s crcular array or lnear array. The crcular array s sutable for omndrectonal cell desgn whle the lnear one s sutable for sectoral (180 o or 120 o ) cell desgn. Let the array be composed of antenna elements, where the frst (reference) antenna element s located at the poston of (R, 0), and the k -th element s located at the locaton of ( R cos 2kπ, Rsn2kπ ) n crcular array. And the frst (reference) antenna element s located at the poston of (0, 0), and the k -th element s located at the locaton of ( kd, 0) n lnear array respectvely. ( R cos 2kπ, R sn 2kπ ) α A k δ k R An ncomng wave wth ncdent angle α A 0 ( R,0) α a) Crcular array An ncomng wave wth ncdent angle α α (0,0) (kd,0) d b) Lnear array Fgure 2. The geometrc llustraton for antenna array Revson 1.3 3/

4 Then, when an ncomng wave from the drecton of dstance ( where D ) between the frst and the k -th antenna element wll be k D α, for crcular array, the dfferental optcal 1 2 k = R cosδ k [2(1 cos 2kπ )] (3) R s the radus of the crcular array; k = 1,2, L, 1; s the total number of antenna element. The ncdent wave comes from the drecton of α as shown n Fgure2, and δ k = α + π ( 1 2 k ) For lnear array, the dfferental optcal dstance wll be: D = k d cosα (4) k Where d s the dstance between adacent antenna elements. S k as the Rx sgnal at the k -th antenna element from the -th path of the -th UE,then S k ( n) = a ( n)exp[ ( ωτ + ϕ k )] for the n -th samplng (5) where, a s the ampltude of the -th path from the -th UE; τ s the tme delay of the -th path from the -th UE; ϕ k s the phase dfferent between the k -th element and the reference element for the - th path from the -th UE: ϕ k and = 2π D k λ D k s the dfferental optcal dstance between the frst and the k -th antenna element for the -th path from the -th UE; ω s the angle frequency and λ s the wavelength. Let s denote S k as the total output from the k -th recever to DBB, then: S k ( n) = S k ( n) for the n -th samplng (6) After despreadng n the DBB processor, the data related to each code channel wll be obtaned as x k at the symbol l. The goal of smart antenna n uplnk s to fnd the best E b I 0 for Rx sgnal at the DBB, Let s denote the X as the output of smart antenna for the l -th symbol from the -th UE, then t can be obtaned that 1 = X ( l) x k wk (7) k = 1 where W s the uplnk beamformng matrx wth ts element w k. Consderng the requrement of real tme operaton and the present level of mcroelectroncs, the maxmum energy combnaton algorthm s used n beamformng as follows: * k x k w = (8) In TDD mode, as mentoned n secton 2 of ths document, we calculate the average of the uplnk beamformng data n 40 symbols and use t as the downlnk beamformng matrx drectly. 3. Features 3.1. Capacty ssue Capacty or spectrum effcency s one of the most mportant ssues n requrements of IMT2000. In most tradtonal CDMA system, the CDMA resources can not be fully used because of the Revson 1.3 4/

5 nterference from the other code channels and multpath. For examples, wthout smart antenna, there are 64 code channels desgned n IS-95 system, but approxmately only 20~30 code channels can be smultaneously put nto traffc servce; n the UTRA-TDD wth Mcps mode, 8~10 code channels may be smultaneously used for traffc servce although the spreadng factor s 16. On the basc prncple n usual antenna array, the beamwdth wll be ψ n the case of maxmum energy combnaton algorthm, where ψ s the beamwdth of one antenna element and s the number of antenna elements n the array. Ths means that the beamformng of smart antenna system wll narrow the beamwdth. In other words, the energy of the receved nterference wll be reduced by the same level as that n the unform dstrbuton model. Lower nterference means hgher capacty n CDMA system. In the TD-SCDMA RTT proposal, the spreadng factor s 16 and the 16 code channels can be smultaneously put nto traffc servce. Ths s the man advantageous feature of smart antenna technology Coverage ssue The smart antenna system wll ncrease both the Rx senstvty and the Tx EIRP of ode B. When the maxmum energy combnaton beamformng algorthm s deployed, both the Rx senstvty and the Tx EIRP wll ncrease 10lg db and 20lg db respectvely. The coverage dstance wll ncrease 80% when =10 and the 4-order propagaton law s used. In other words, one can use low cost LA wth hgher F n Rx and low cost PA wth lower Tx power n Tx n a smart antenna system, but the coverage s stll up to or even better than that of the tradtonal wreless communcaton system Cost ssue It s well known that the most expensve part n ode B s the last-stage lnear HPA. And the cost for lnear HPA s not easy to reduce. For examples, a lnear HPA wth P out of 30W wll cost a few thousand $US, and a lnear HPA wth P out more than 100W wll cost more than 10 thousand $US. When the smart antenna technology s deployed, the cost for PA can be greatly reduced for the lower Tx power PA can be used n system. For example, f one use a 12-element crcular antenna array wth maxmum power combnaton beamformng algorthm, and P of 1W n each PA, the Tx EIRP wll be equal to 20lg(12) + 30dBm = 52dBm or 160W. But the cost for the 12 peces of transcevers ncludng PAs wll be less than a few thousand $US. In the relablty ssue, the multple transcevers and PAs n the smart antenna system wll solve the redundancy problem n ode B. In other words, the relablty of the smart antenna system wll be much hgher than a sngle HPA system. Of course, one may desgn a ode B wth more than one HPA for redundancy, but then the hgh cost wll double. In addton, less power consumpton of low output PA wll reduce the cost for power supply unt. As a concluson, the smart antenna technology s a low cost soluton to ode B n IMT2000, and t meets the man requrements of ITU. 4. Related technologes and parameters 4.1. Chprate and software rado Reference to Fgure 3, an example of the Rx path n a smart antenna based ode B. One may calculate the btrate on the hgh-speed bus under the followng basc condtons: umber of antenna elements: ; QPSK modulaton; 16-bt parallel nput and output bus; Chprate: R; 8-tme oversamplng n both I and Q branches; then the btrate wll be: btrate = 2 8 R = 260Mbps ( R = Mcps) Or 786.4Mbps ( R = 4.096Mcps) where = 12 as an example. Obvously, so hgh rate btstream can not be processed n DSP n real tme. One way s to separate the hgh-rate part (over samplng, for example) n each TRx by DSP or ASIC, then the btrate on the bus wll be reduced by a factor of 8 that: btrate = 32. 5Mbps ( R = Mcps) Or 98.3Mbps ( R = 4.096Mcps) Obvously, lower chprate s easer to process on the bus. out Revson 1.3 5/

6 Revson 1.3 6/

7 1st recever Rx IF I LPF A/D Sync 90 o Dgtal Q LPF A/D Sync Baseband Processor k-th recever -th recever IF Lo n LPF: Low pass flter Data Bus A/D: Analog to Dgtal converter Sync: uplnk synchronzaton processng unt DBB Fgure 3. Example for DBB recever used n synchronous CDMA and smart antenna system As mentoned above, the beamformng wll be processed n DSP by software. The processng capacty of the avalable commercal DSP at present s about 1GIPS, and may be up to 2 to 3 GIPS by end of If the DSP s nterfaced to bus wth a rate of a few hundreds Mbps, t wll have no tme for data processng! Parallel processng may be a soluton, but t wll brng complexty. As a concluson, lower chprate wll be easy to adopt smart antenna technology based on the present and the short future level n software rado technology Uplnk synchronzaton As mentoned before, the DOA estmaton and beamformng of smart antenna s performed n DBB DSP. It s requested that the DBB recevers n each Rx path n ode B should brng the phase and ampltude nformaton of the Rx sgnal to DBB processor for smart antenna processng. The smplest way to desgn the DBB recever s that llustrated n Fgure 3. It s obvous that the recever can only be used n a CDMA system wth uplnk synchronzaton. In other words, synchronous CDMA wll lead to a smplfed soluton to smart antenna system Multpath It s well known that multpath propagaton s the maor nterference source n CDMA system. In smart antenna system, formed beam wll be ponted to the target UE, and the nterference wth DOA out of the man lob of the formed beam wll be pressed down approxmately 10dB. Ths wll greatly enhance the capacty of the system. However, the multpath may arrve n the nearby ncdent angle as man lob, then the nterference can not be canceled by space flter. Ths worst stuaton may appear n the vehcle envronment. Smulaton result shows that, when transmttng 2Mbps hgh-speed data servce, smart antenna can make great beneft because there s only one user n the system n ndoor envronment. But the capacty wll be lmted to 8 users n one tme slot when the number of the antenna elements n the array s 8 and wthout addtonal data processng solutons n outdoor to ndoor envronment. To get the maxmum capacty, one may use an array wth 16 antenna elements or deploy addtonal solutons to combatng multpath such as channel equalzaton after space flterng. 5. Concluson In ths workng document, a basc descrpton for the structure of smart antenna system n ode B s provded, as well as the beamformng prncple and features n TD-SCDMA system. It s shown that the advantageous features such as hgh spectrum effcency, low cost, etc., are manly contrbuted by the smart antenna technology. Smart antenna s one of the most mportant parts n TD-SCDMA (UTRA-TDD low chprate mode) ode B. Revson 1.3 7/