모바일와이맥스시스템에서주변셀의신호세기정보를이용한인접셀간섭감소기법. Mitigation of inter-cell interference using geometrical information in mobile WiMAX system

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1 모바일와이맥스시스템에서주변셀의신호세기정보를이용한인접셀간섭감소기법 염재흥 O 이용환서울대학교전기컴퓨터공학부 Mgaon of ne-ell nefeene usng geomeal nfomaon n moble WMAX sysem Jae-Heung Yeom O Yong-Hwan Lee Shool of Eleal Engneeng INMC Seoul Naonal Unvesy hyeom@l.snu.a.k Absa The Moble-Woldwde Ineopeably fo Mowave Aess (m-wmax an povde weless seves a hgh aes even n hgh mobly. Howeve he pefomane of m-wmax an seously be degaded nea he ell bounday due o ne-ell nefeene (ICI. To mgae he ICI poblem n he downlnk of m- WMAX we onsde ombned use of ICI mgaon ehnques wh mao beamfomng o maxme he use apay n esponse o he hange of nefeene envonmen. The poposed sheme opmally deemnes he onfguaon of ICI mgaon ehnques usng he geomeal nfomaon (e.g. he longem eeved sgnal sengh of neghbong ells. Smulaon esuls show ha he poposed sheme an auaely esmae he use apay hus mpove he apay of uses nea he ell bounday.. Inoduon The Moble-Woldwde Ineopeably fo Mowave Aess (m-wmax o IEEE 8e has been poposed o suppo weless daa seves a hgh aes ompaable o we-lne shemes suh as he dgal subsbe lne (DSL s beng onsdeed as a mgaon pah owad nex geneaon weless sysems []. Reenly a veson of M-WMAX alled WBo has been deployed n Koea. The m-wmax onsdes he use of unvesal fequeny euse yeldng ne-ell nefeene (ICI fo he seve of uses nea he ell bounday. In fa he speal effeny n he wos hannel ondon an be edued o one h of ha n he bes hannel ondon. As a onsequene o suppo eal-me aff a a ae of 5 kbps nea he ell bounday he m-wmax may need o alloae he whole downlnk esoue o a sngle use whh s unaepable o seve povdes. Unless he m- WMAX an sgnfanly mpove he speal effeny paulaly nea he ell bounday may no lam ehnologal advanages ove he numben 3G sysems. Ths wok was n pa suppoed by he KT eseah poe. Thus he mgaon of ICI s one of he mos mpendng poblems n he m-wmax sysem. A numbe of ICI mgaon ehnques have been poposed fo pake-based ohogonal fequeny dvson mulple aess (ODMA sysems nludng he use of nefeene avodane (IA nefeene omaon nefeene anellaon mao dvesy []. IA shemes dynamally alloae he esoue o avod he ICI by exhangng he ne-ell nfomaon [3]. aonal fequeny euse (R ehnques an avod he ICI by pevenng he age ell fom usng fequeny esoues used by adaen ells [4]. Howeve hey may lm he peak ansmsson ae due o he use of a edued euse fao. On he ohe h by anellng ou he ICI wh he use of ne-ell hannel sae nfomaon (CSI nefeene anellaon shemes an nease he aeo-nefeene powe ao (CIR even n full loadng envonmens [5]. Mao dvesy ognaed fom sof hoff n CDMA sysems an povde a dvesy gan [6]. Alhough he above onvenonal ICI mgaon ehnques have he own pos ons he shoomngs an be allevaed wh pope ombned use of hese ehnques. evous woks onsdeed he mgaon of ICI n he WMAX sysem bu hey dd no onsde ombned use of hese ICI mgaon ehnques

2 o ge somewha synegy effe [7]. In hs pape we onsde ombned use of ICI mgaon ehnques o maxme he use apay of he downlnk nea he ell bounday by smply usng he geomeal nfomaon on he eeved sgnal sengh (RSS of neghbo ells. We also onsde esoue alloaon aodng o he fequeny euse fo IA n he paal usage of subhannels (USC mode. Sne he nfomaon beween he seos n a ell an be exhanged n eal-me we onsde he use of na-ell mao dvesy. By makng wo seos ansm he same sgnal he eeve an oban a R ombnng o sof ombnng dvesy gan [6]. Howeve edues he speum effeny o one half due o eseved esoues by he neghbo seo. To mpove he speum effeny we popose he use of mao beamfomng wh oheen ansmsson va wo seos. ollowng Inoduon Seon desbes he sysem model n onsdeaon Seon 3 desbes he poposed mao beamfomng based on uplnk soundng whh s effeve n he na-ell hoff bounday. New saeges o mgae he ICI n he m-wmax sysem ae desbed n Seon 4 he pefomane s vefed by ompue smulaon n Seon 5. nally onlusons ae gven n Seon 6.. Sysem model Consde an m-wmax sysem ompsng N hexagonal ells eah of whh has hee seos. We assume ha eah seo uses wo ansm anennas ( n MS uses wo eeve anennas ( n [8]. When he age use s seved by seo m of ell n he eeved sgnal a subae k an be epesened by y( k H ( k x ( k + H ( k x ( k n n m + H ( k x ( k + n( k n whee x s he ( n sgnal veo of seo of ell n s ( n addve whe Gaussan nose (AWGN wh powe speal densy N H denoes he ( n n hannel max whose elemens ae assumed o have eo mean vaane gven by { } { }. A ( θ L ( d σ E ae ( k ( k. n H H ( Hee E{} denoes he expeaon he supesp denoes onugae anspose ( L d epesens he pah loss fom seo of ell o he age use n debel A( θ denoes he 3-seo anenna paen spefed by θ A( θ mn (db (3 θ 3dB whee θ s defned as he angle beween he deon of ( nees he boesgh of he anenna θ 3dB denoes he 3dB beamwdh n degee. We onsde he esoue alloaon fo IA n a subae pemuaon mode as llusaed n g.. Assumng he whole fequeny esoue s dvded no hee logal bs he fequeny euse se (RS an be defned as ϕ m m m ϕ m m ϕ m m ϕ m (4 { } { } { } { } 3 4 whee m m m denoe he b ndex oespondng o m ( m + %3 ( m + %3 espevely. Hee a% b denoes a modulo b (e.g. when m ϕ { } ϕ { } e.. o example he euse se ϕ ndaes he use of b m m m (.e. oespondng fequeny euse ao (RR s he euse se ϕ ndaes he use of b m m (.e. RR s /3. The dvded fequeny esoues an be alloaed o uses aodng o he ICI ondon. o example when he MS n seo eeves song nefeene fom seo he fequeny esoue n euse se ϕ an be alloaed o uses n seo no o uses n seo. If he MS n seo eeves song nefeene fom seo he fequeny esoue n euse se ϕ 4 (.e. RR s /3 an be alloaed o uses n seo no o uses n seo. 3. Mao Beamfomng Mao dvesy an double he ansm powe dvesy gan bu no povde any ansm aay gan. In hs seo we onsde he use of mao beamfomng o enhane he pefomane of uses n he na-ell hoff bounday egon whh exends he anenna onfguaon fom ( n n o ( n n. The uplnk soundng sgnal ansmed nea he seo bounday an be eeved a leas by wo seos enablng he use of mul-seo beamfomng. The eeved sgnal by mao beamfomng fom seo m m an be epesened by [4] ( y( k H ( k w ( k + H ( k w ( k x+ nm nm nm nm k wnm ( k H ( k H ( k x+ k (5 ( k w H w + whee n( m m n( m m n( m m k H denoes he ( n n k s he ( hannel max n oloed nose veo epesened by H ( k x + H ( k x + n ( k wh E{ } k n n m m n k K NIn n( m m beamfomng wegh veo gven by (6 w s he ( n

3 me ϕ ϕ ( ( ( ( w h h h h. (7 ae he ( ( Hee h h ( n CSI veo of seo m seo m espevely of ell n obaned fom he uplnk soundng of he fs anenna n he MS. Mao beamfomng has a ansm powe onsan gven by { w ( ( w ( } E ae n m mxn m n m mx n m (8 whh an nease he ae-o-nefeene--nose powe ao (CINR. Sne he mao beamfomng needs o eseve he oespondng esoue of he neghbong seo edues he speum effeny by one half. These pos ons of mao beamfomng ae smla o hose of mao dvesy. The dffeene beween he wo shemes s a degee of aay gan. The CINR of mao beamfomng wh pos maxmal ao ombnng an be epesened by [] ( ( ( ( γ n( mm + n( mm N h h w h h w. (9 ( Sne h ( h s a ulaly symme Gaussan om veo wh eo mean vaane σ σ ( σ espevely an be seen ha ( ( h h wn( mm ( ( h h w n( mm an be appoxmaed as om vaables σ χ4n σ χ espevely. Hee χ n denoes a Ch-squaed om vaable wh n degees of feedom []. Theefoe he aveaged pos CINR s gven by ( σ E E E N n m { γmb } { χ4n } + { χ} n m σ ( n +. N ( Thus he mao beamfomng an maxmally oban an aay gan whh s.5 mes ove he mao dvesy fo downlnk MIMO. ( seo seo seo oal subaes ϕ ϕ oal subaes ϕ ϕ oal subaes g.. Resoue alloaon aodng o he fequeny euse se 4. oposed ICI Mgaon Saegy We onsde a new ICI mgaon saegy ha maxmes he apay of uses nea he ell bounday wh ombned use of IA nefeene anellaon mao beamfomng. Mos of onvenonal ICI mgaon ehnques only onsde he amoun of ICI. If he ICI envonmen (e.g. domnan ne-seo nefeene n s own ell domnan nefeene fom ohe ells an be onsdeed addonally hey may fuhe nease he apay. Le s C be he use apay assoaed wh neseo oopeaon ulng wo seos IA nefeene anellaon defned by [] { log ( } C E υρ + ηγ ( s whee s denoes a ndex elaed wh ne-seo oopeaon (e.g. denoe no feasble mao dvesy mao beamfomng espevely denoes a euse se ndex denoes a ndex ndang whehe nefeene anellaon s feasble o no (.e. denoe no feasble feasble espevely η s a paamee elaed o he mplemenaon loss oespondng o CINR γ ρ denoes he RR gven by ρ 3 3 ( 3 4 υ s denoes he seo euse ao gven by s υs (3 s. The man onen s o maxme he apay of uses nea he ell bounday gven as Cmax max C (4 maxυρ log + ηe γ. The aveage CINR { s } eplaed by geomey G s as ( { } s { γ } IS E γ an appoxmaely be E G g nm s s ( ( IC s Sm n m ( s n m ( s + σ m ϕ (5 whee denoes he RSS of seo m of ell n as he sevng seo S m denoes he nefeene fom seo m of all ells ϕ denoes he euse se of ndex ( IS ( s denoes he RSS of neghbo seo ( IC avoded by ne-seo oopeaon ( s denoes he RSS of seo m ell n o be anelled by he eeve σ s he nose powe level of he MS g s denoes he aay gan of MIMO nludng he powe gan.

4 The nefeene em S S m an be epesened as N m m m m. n m n m n m N n m n ( IS ( s an be epesened as max s m { m m } ( IS s ( s Mn + m s 3 ohewse. (6 (7 ( IC ( s s assoaed wh he nefeene anellaon mehod he ell s seo nefeng a he maxmum level o eah euse se exep he sevng seo he seo oopeang wh mao anenna ehnque. I an be found by nm ( s max n m s n N m { mo m m} ( n m max n m s n N m { m m m} ( n m ( n m max n m s n N m { m m} ( n m max n m s n N m { m m} ( n m ( n m max n m 3 s n N m { m m} ( n m max n m 3 s n N m { m m} ( n m ( n m max n m 4 n N m m ( n m ohewse. (8 Moeove he neessay ondon fo he MS o esmae he CSI of he nefeng seo s gven by ( IC ( s ( s T ( s Sm n m( s + σ m ϕ ohewse (9 whee T es s a heshold of he CINR fo he MS o esmae he CSI. We assume ha he plo paen of he sevng seo s ohogonal o ha of an nefeng seo by usng ell-spef samblng odes. The aay gan g s s assoaed wh he mao anenna ehnques he feasbly of nefeene anellaon fo gven anenna ehnque. When nefeene anellaon s onsdeed he aay gan s edued by one half beause he eeve aay gan an no be aheved []. nally we an maxme he use apay (4 by fndng a se of ICI mgaon ehnques ha maxmes he geomey apay C s gven by ( sˆ ˆ ˆ ag max C ag maxυρ log + ag max C ( ηg s es ( 5. efomane evaluaon We vefy he pefomane of he poposed ICI mgaon sheme n he downlnk of WBo sysem by ompue smulaon. Table I summaes he smulaon paamees. We assume ha he MS an oban he CSI of he songes nefeng ell when s aveage CINR s lage han db as desbed n (9. o ease of vefaon we also assume ha he BS alloaes esoue o he MS a evey fame me he MS s seved by seo. We onsde wo geogaphal egons o nvesgae sevee nefeene envonmens whee uses n he seo bounday expeene song ne-seo nefeene fom he same ell uses n he ell bounday expeene song ICI fom ohe ells. g. (a deps he esmaed geomey apay oespondng o vaous ses ombned wh ICI mgaon ehnques whh s obaned by usng he RSS of neghbo ells. RS RS RS3 RS4 denoe esoue alloaon oespondng o eah euse se as llusaed n Seon. I an be seen ha se MB_ RS whh ombnes mao beamfomng fo seo of s own ell IA (.e. RS fo seo oupefoms ohe ses. g. (b deps he use apay when he lnk adapaon s pefomed a evey fame wh ombned use of ICI mgaon ehnques. I an be seen ha he poposed sheme ha maxmes he esmaed apay oupefoms he use of pue IA pue IC sheme [5]. g. 3 (a deps he esmaed apay when ICI mgaon ehnques ae only employed n he ell bounday egon a an aveage CINR of -5dB. TABLE I. Smulaon paamees. aamees Values Numbe of 3-seo Cells 9 Cae fequeny.3 GH T Se 4 Channel bwdh 8.75 MH Samplng fequeny MH Cell adus km Anenna sheme Beamfomng (B Subae alloaon USC ah loss model COST 3-Haa Sububan BS anenna paen 65 (-3dB Cell loadng fao Channel model ITU-R edesan A 3km/h Channel esmaon efe Reeve algohm Lnea MMSE I an be seen ha ombned use of IA (.e. RS RS 3 nefeene anellaon yelds he bes pefomane n deon of he use of IA yelds he bes pefomane n deon of 3 ombned use of mao beamfomng IA (.e. yelds he bes pefomane n deon of 6. I an be seen fom g. 3 (b ha he poposed sheme oupefoms he onvenonal shemes pue IC pue IA.

5 6. Conlusons We have poposed a new ICI mgaon saegy ha maxmes he apay of uses nea he ell bounday. The poposed saegy opmally ombnes ICI mgaon ehnques based on he geomeal nfomaon. We have onsdeed addonal use of mao beamfomng o avod song ne-seo nefeene whle obanng he ansm aay gan. The smulaon esuls show ha he poposed saegy an enhane he use apay by adapvely employng ICI mgaon ehnques. Refeenes [] G. Lawon Wha les ahead fo ellula ehnology IEEE Compue vol. 38 pp. 4-7 June 5. [] 3G TR 5.84 hysal laye aspes fo evolved UTRA seon 7..6 V7.. Sep. 6. [3] I. Kaela M. Naghshneh Channel assgnmen shemes fo ellula moble eleommunaon sysems: a ompehensve suvey IEEE Weless Commun. vol. 3 no. 3 pp. -3 June 996. [4] 3G TSG-RAN R-5896 Despon smulaons of nefeene managemen ehnque fo ODMA based E-UTRA downlnk evaluaon Qualomm Euope Sep. 5. [5] 3G TSG-RAN R-633 efomane evaluaon of STTD yl shf dvesy n he pesene of ne-ell/seo nefeene n downlnk MIMO sysem fo LTE Noel May 6. [6] 3G TSG-RAN R-565 Invesgaons on neseo dvesy n evolved UTRA downlnk NTT DoCoMo June 5. [7] A. Ghosh D. R. Wole Boadb weless aess wh WIMAX/8: uen pefomane benhmaks fuue poenal IEEE Comm. Magan. vol. 43 ssue pp eb. 5. [8] WMAX oum WMAX oum Moble Sysem ofle v.. May 6. [9] IEEE Sd 8e a 6: A Inefae fo xed Moble Boadb Weless Aess Sysems De. 5. [] J. G. oaks Dgal Communaons ouh Edon MGaw-Hll Hghe Eduaon. [] D. Tse. Vswanah undamenals of Weless Communaon Cambdge Unvesy ess 5. [] A. aula R. Naba D. Goe Inoduon o Spae-Tme Weless Communaons Cambdge Unvese ess 3. Esmaed apy (bs/subae Use apay (bs/subae.9.8. B-RS B-RS B-RS3 B-RS4 MD-RS MD-RS MB-RS MB-RS long-em CINR (db pe anenna fo RR of.9.8. (a Esmaed apay B-RS (pue IC B-RS4 (pue IA MD-RS poposed sheme long-em CINR (db pe anenna fo RR of (b Use apay g.. Capay n he bounday beween seo. Use apay (bs/subae Esmaed apay (bs/subae. B-RS B-RS B-RS3 B-RS4 MB-RS MB-RS 3 6 Angle of depaue beween BS MS wh espe o he boadsde of BS aay (a Esmaed apay B-RS (pue IC B-RS4 (pue IA poposed sheme. 3 6 Angle of depaue beween BS MS wh espe o he boadsde of BS aay (b Use apay g. 3. Capay n he ell bounday egon wh an aveage CINR of -5dB.