INDOOR CHANNEL MODELING AT 60 GHZ FOR WIRELESS LAN APPLICATIONS

Transcription

1 IDOOR CHAEL MODELIG AT 60 GHZ FOR WIRELESS LA APPLICATIOS ekaos Moas, Plp Consannou aonal Tecncal Unesy of Aens, Moble RadoCommuncons Laboaoy 9 Heoon Polyecnou Zogafou, Aens, Geece, moa@moble.nua.g Absac - Ts pape epos naowband and wdeband esuls deed by popagaon modelng a 60 GHz fo ndoo WLA applcaons. A mul-ay model s poposed and efed oug a smulaon pocess. Te popagaon n e se-specfc enonmen can be descbed usng 4-5 ays wou educng e accuacy of e esuls. RMS delay spead aes w dsance fom 0.57 ns up o 2.32 ns. Coeence bandwd fo 0.9 coelaon was found 65 MHz, 116 MHz and 87 MHz fo soopc, omn-omn and on-on anenna confguaons especely. Keywods weless LA, wdeband cannel, delay spead. I. ITRODUCTIO Mulmeda and compue communcaons ae playng a mao ole n oday s socey, ceang new callenges fo e deelopmen of elecommuncaons sysems. Te pessue fo weless sysems o cope w nceasng daa aes s enomous and Weless Boadband Sysems (WBSs), wc ae sysems w aes geae an 2 Mbps, ae emegng apdly [1]. We can menon enoug sysem cases a may modfy e WBSs pespeces, bu wo man appoaces ae come o lg. Te Weless Local Aea ewoks (WLAs), wc ae focused on compue communcaons and Moble Boadband Sysems (MBSs) [2] focusng on cellula sysems podng full mobly o B-ISD uses. Fo e deelopmen of e menoned boadband sysems, wde fequency segmens ae been allocaed n e mllmee egon of e specum and especally aound 60 GHz. In mllmee wae fequences, e popagaon modelng, apa fom e known empcal models, can be ealzed based on geomecal opcs usng ay-acng eoy. In e 60 GHz egon e dffacon penomenon can be negleced, and e sum of e dec ay and e efleced ays s enoug o descbe e beao of e popagaon cannel w gea accuacy [1,3]. Te modelng n exemely g fequences poses e poblem of e accuae descpon of e popagaon scenaos a e waeleng scale (5 mm a 60 GHz). Hence e man age s o descbe e man obsucons and e sufaces a affec e sgnal popagaon. Te descpon s no only n ems of e geomec caacescs of e popagaon enonmen bu also n ems of e suface elecomagnec paamees (elae delecc consan, losses ec) n ode o exac e suface eflecon coeffcens. In s pape we pesen a mul-ay model n ode o descbe e sgnal popagaon a 60 GHz n an ndoo enonmen. Te model s aldy s efed oug a smulaon pocess fom e naowband and wdeband pon of ew of e cannel especely. Te popagaon mecansms ae explaned analycally weeas cannel paamees suc as RMS delay spead and coeence bandwd ae calculaed. Ts pape s oganzed as follows. Secon II deals w e popagaon modelng descbng analycally e geomey of e enonmen unde consdeaon, e poposed mulay model and e smulaon pocedue. In Secon III, LoS popagaon esuls ae pesened fom e naowband pon of ew, explanng e mecansms and e beao of e sgnal popagaon. Secon IV, deals w esuls fom e wdeband pon of ew n ode o ealuae e wdeband cannel paamees. Fnally, Secon V s deoed o dscusson and conclusons deed by e ene smulaon pocedue. II. PROPAGATIO MODELIG A. Descpon of e Enonmen Geomey Te smulaon enonmen s a long codo w dmensons 44 x 2.20 x 2.75 m 3 as sown n Fg. 1. Te Lef Wall suface s made of bck and plaseboad w wooden doos eey 3 m bu n ode o smplfy e smulaon pocedue we assume e suface as a unfom wall made of bck and plaseboad w s delecc caacescs gen n Fg. 1. Fuemoe, all e maeal caacescs ae poded as well as e popagaon geomey and e emnal posons. Te begnnng and e end of e codo ae open aeas (ey lage spaces) and ae no aken no accoun. B. Mul-Ray Model Te mul-ay model s a geneal case of e wo-ay model [4,5] fo moe an wo efleced componens. Te efleced componens may exb sngle o double eflecon fom a plane suface. Td o fou ode eflecons, especally a 60 GHz, ae neglgble conbuos o e aeage powe and ae no aken no accoun /02/$ IEEE PIMRC 2002

2 Celng: fued celng made of alumnum Tx Rx 2.75 m Tx - Rx Hozonal Sepaaon (codo 0-44 m) Floo: concee coeed w mable Lef Wall : lg wall made of bck and plaseboad Maeal Delecc Caacescs Lef Wall : e = 4.44, σ = Rg Wall : e = 5, σ = Floo : e = 3, σ = Celng : e = 1, σ = 2e6 Tx x Rx y 2.2 m Rg Wall : exenal wall made of bck and concee Dec Componen Sngle Reflecon Double Reflecon x : Tx dsance fom e g ecal suface (0.8 m) y : Rx dsance fom e g ecal suface (1.4 m) : Tx eg (2 m) : Rx eg (1.5 m) Fg. 1. Smulaon enonmen, popagaon geomey and maeal delecc caacescs. Te eflecon geomey can be descbed n e ozonal as well as n e ecal plane as sown n Fg. 1. Hence, f we know e geomey of e enonmen wee e sgnal popagaes (leng, wd, eg) and e suface eflecon coeffcens, one may calculae e popagaon losses. Te popagaon losses ae calculaed by e summaon of sngle efleced and M double efleced ays gen by: L p ( d ) M 1 R R R φ a = log + + e = = d 1 d d 0 1 b e φ (1) wee d s e ozonal sepaaon beween Tx and Rx, d 0 s e pa leng of e dec componen and d, d ae e pa lengs eac of e sngle efleced and double efleced ays. Moeoe, R s e eflecon coeffcen of sngle efleced ay wls R, R ae e a b eflecon coeffcens of e double efleced ays on a 2π and b eflecng sufaces especely. Fnally φ = l λ 2π and φ = l ae e pase dffeenals beween e λ dec and e efleced ays w l and l e dffeenal pa lengs beween e dec and e sngle and double efleced ays, and λ s e waeleng (5 mm). C. Smulaon Pocedue Fo e smulaon of e sgnal popagaon a 60 GHz e mul-ay model gen by (1) wll be used fo e specfc enonmen sown n Fg. 1. Te eceed sgnal (n dbm), s gen by: P ( d ) = P + G + G L ( d ) (2) p wee L p ( d ) s gen by (1). We use 4 sngle efleced ( = 4), plus 4 double efleced ( M = 4 ) ays and e dec componen. Te dffacon s no aken no accoun snce a 60 GHz e penomenon s almos neglgble and e dffaced powe does no conbue o e oal eceed powe. Te non-unfomes of e suface maeals n ndoo enonmens ae suc a e poduced scaeng as no a subsanal conbuon o e eceed powe. Te mos sgnfcan conbuon s fom e 9 ays peously epoed. Fue efleced ays ae no aken no accoun snce e conbuon o e oal eceed powe s nsgnfcan. I wll be sown a 9 ays n oal can descbe w gea accuacy e sgnal popagaon n e specfc enonmen. Up o second ode eflecons ae aken no accoun snce d o fou ode eflecons, especally a 60 GHz, ae neglgble conbuos o e aeage powe. Amospec popagaon losses ae no aken no accoun snce n ndoo enonmens e aenuaon s ey small ( db/m). Te anenna adaon paens ae aken no accoun n ecal and ozonal plane especely fo bo ansme and ecee, deemnng e ncdence angle of eac ay G θ. Te ays a ae wn e 3 db beam- G ( θ ), ( )

3 wd of e anenna s man lobe ae assumed o ae a consan gan. Rays ousde e man lobe ae negleced. In oe wods we do no ake no accoun e sde lobes of e anenna adaon paen snce a 60 GHz e ays a emegng fom e anenna s sde lobes do no conbue o e oal eceed powe. Te mos sgnfcan sde lobes ae a leas 15 db below e man lobe. Dung e ene smulaon pocedue ecal polazaon s assumed. Hence, fo e ays efleced fom ecal walls we use e pependcula eflecon coeffcen ( R ), weeas fo e ays fom floo and celng sufaces we use e paallel eflecon coeffcen ( R s ). Bo eflecon coeffcens ae gen n [4] equaons (3.24) and (3.25). In e eflecon coeffcen equaons e complex delecc consan [4] s gen by: s ε = ε 60σλ (3) wee ε s e elae delecc consan of e eflecng suface, σ s e conducy of e suface n Semens/m and λ s e waeleng. Te alues of ε and σ ae gen n Fg. 1 [6,7]. We assume ee dffeen ansmsson sysems w dffeen anenna caacescs and ansmed powe. Ts s done so as o examne ow e anenna adaon paens affec e sgnal popagaon n e ndoo enonmen. Te sysems ae: Sysem 1: Isoopc anennas on bo ansme and ecee and 20 dbm oupu powe. Sysem 2: P = 20 dbm, G = G = 8.5 db omn-deconal anennas w θ = 8 o. (a) (b) Sysem 3: P = 10 dbm, G = G = 20.8 db on anennas w θ = 15 o and θ = 28 o. Fnally, e smulaon s conduced w MaLab scp, usng 9 ays n oal. Te nal ansme poson s a e begnnng of e codo and e ecee s mong away fom Tx w 1 m nal sepaaon. We assume a e ecee s mong a almos consan speed of 0.2 m/sec and we collec a sgnal sample as a funcon of dsance eey m ( λ /4). Te oal numbe of samples fo e ene codo (44 m) s III. LIE-OF-SIGHT PROPAGATIO RESULTS In Fg. 2 ae depced e eceed powe as a funcon of dsance as well as e eceed sgnal seng of e aous efleced ays n espec o e LoS componen as a funcon of dsance. Te specfc plos wll ge us nfomaon concenng e pecenage of e sngle and double efleced ay conbuon o e oal eceed sgnal. Te poded esuls concen e d ansmsson sysem (on-on anennas). (c) Fg. 2. (a) Receed powe as a funcon of dsance, (b) omalzed eceed feld of e sngle efleced ays as a funcon of dsance, (c) omalzed eceed feld of e double efleced ays as a funcon of dsance. I s obseed n Fg. 2(a), a e eceed powe decays n w dsance a a ae of 1 / d. Ts ae depends on e numbe of e eflecons a conbue o e oal sgnal,

4 as well as e e amplude w espec o e LoS componen. Usng fng n a mnmum mean squae eo sense we found n=1.75 suggesng wae gudng effecs along e codo, as s expeced. Te elecc feld of e efleced ays w espec o e LoS componen s calculaed as a funcon of dsance along e codo. Te cues n some cases exb dsconnues snce e popagaon pas fade due o e enonmen geomey. Fom Fg. 2 we obsee a a e fs 8 m, only e dec componen conbues o e oal sgnal, wls e celng sngle eflecon sas o conbue (100% o equally w e dec ay) afe 8 m unl e end of e codo. Te celng eflecon conbues sgnfcanly because e ansme s close o e celng. Moeoe, e maeal of e celng (alumnum) s a pefec eflecng suface ( R 1). Te gound sngle efleced ay conbues afe 26 m w 70%, eacng 80% a e end of e codo. Te sngle eflecons fom e lef and g walls sa o conbue afe 6 m eacng 60% a e end of e codo. Te conbuon s almos equalen and e ny dffeences ae due o e dffeen maeal caacescs. Te double efleced ays conbue o e oal eceed powe bu n a smalle amoun n compason w e sngle eflecons. Fom Fg. 2(c) we obsee a e double eflecons fom e g-lef (.e. fs and second eflecon) and lef-g wall sa o conbue afe 15 m and 20 m especely, snce e ozonal plane beamwd ( θ = 28 o ) ncludes ese componens afe e specfc dsances. Te conbuon oug, eaces only 10% and 18%. Te double eflecon fom gound-celng s zeo due o e naow beamwd of e anenna a e ecal plane ( θ = 15 o ) and e fac a e ansme s close o e celng. Te same effec occus fo e celng-gound double eflecon, wc conbues only a e las 6 m of e codo, oug w a sgnfcan pecenage (72%). I s wowle o menon a n ode o smulae e popagaon n e specfc enonmen we may educe e numbe of ays, usng 4-5 ays nsead, wou affecng e accuacy of e esuls. Hence we may use ays a conbue w 50% o moe o e oal eceed powe. Apa fom e dec componen one can use e 4 sngle eflecons and only one double eflecon. I s clea fom e esuls a d o geae ode eflecons would no ae sgnfcan effec o e sgnal popagaon. Fo e ndoo popagaon enonmen wee e me ayng facos of e mpulse esponse ypcally ae uman moemen, s appopae o ea e cannel as quassaonay. Assumng a e pase aaons n e CIR ae a unfom dsbuon we may consde only e amplude and e delay componens. Te mos sgnfcan paamee deed fom e pocedue s e eceed powe as a funcon of e me delay known also as e powe delay pofle (PDP). Te powe delay pofle can be expessed as: ( ) = P ( d ) δ ( τ τ ) P τ (5) = 1 wee P ( d ) s e eceed sgnal of e ay and s e oal numbe of e ays used n e smulaon pocedue. Te me esoluon s assumed 1 ns. Dung e daa bnnng pocess we assgned eac eco o e neaes alue of delay equal o a mulple of 1 ns. Te aeage eceed powe n eey bn s nomalzed o e maxmum eceed powe. A sgnfcan paamee o be ealuaed s e RMS Delay Spead ( τ RMS ), wc caacezes e fequency selece beao of e cannel [4]. Te Foue ansfom of e nomalzed PDP ges e nomalzed fequency coelaon funcon fom wc we calculae e coeence bandwd fo 90% 75% and 50% coelaon. ose-paddng ecnques ae appled, po o DFT, n ode o efne e aceed fequency esoluon. Fg. 3 depcs a nomalzed powe delay pofle deed by smulaon pocedue usng (1), (2) and (5). Dung e pocess e on-on anenna sysem s used, wls e ecee s 30 m away fom e base saon. IV. WIDEBAD RESULTS Te wdeband mulpa cannel s ofen modeled as a me ayng lnea fle w complex mpulse esponse (CIR) [4]: (, ) = a (, τ ) exp( φ (, τ )) δ ( τ τ ( ) ) τ (4) = 1 Fg. 3. omalzed PDP concenng e on-on ansmsson sysem w 30 m Tx-Rx sepaaon. Fom Fg. 2 and 3, s eden a e fs wo aed componens ae e dec and celng eflecon ays w equal powe conbuon as menoned n Secon III. Te eflecons fom e lef and g walls ae ogee a 4

5 ns bu ey appea as one componen due o e bnnng pocedue. Te song peak a aes a 6 ns s e sngle eflecon fom e gound, wc s moe delayed snce sas o conbue afe 27 m as sown n Fg. 2(b). Ts s abued o e naow beamwd a e ecal plane (15 o ) ence e adaon paen ncludes e gound ay afe e specfc dsance, eefoe exbng geae delay. Fnally, n Fg. 3 e RMS delay spead s 1.58 ns and e maxmum delay spead s 7 ns. Fg. 4 depcs e fequency coelaon funcons w 30 m sepaaon beween Tx and Rx compang e ee alenae ansmsson confguaons epoed n Secon II. I s clea a w soopc anennas e coelaon dops fase mplyng lage delays snce all e mulpa componens conbue o e oal eceed sgnal. Ts as o do w e anenna adaon paens; eefoe soopc anennas nclude all e efleced ays n e dagams. On e oe and e on-on confguaon, wc as ey naow anenna beamwds, does no nclude all e ays suppessng some of e mulpa componens a ae o e ecee. Ts educes e RMS delay spead, nceasng e cannel qualy. Ts s esfed on Table 1 wee e cannel paamees ae ndcaed fo e ee anenna confguaons. Fg. 4. omalzed fequency coelaon funcons fo e ee ansmsson confguaons. Te sepaaon s 30 m beween Tx and Rx. Table 1 Cannel paamees fo e ee ansmsson confguaons. τ RMS (ns) B 0.5 B 0.75 B 0.9 Isoopc Omn-Omn Hon-Hon Fom Table 1, s clea a e bes esuls ae poded by e omn-omn confguaon due o s ey naow ecal paen (only 8 o ) educng sgnfcanly e eflecons fom e celng and e gound. Inceasng e anenna decy, RMS delay spead s educed fom 2.31 ns o 1.18 ns and 1.58 ns as sown n Table 1. V. COCLUSIOS aowband and wdeband paamees wee ealuaed oug a smulaon pocess a 60 GHz fo ndoo WLA applcaons. Te sgnal can popagae w 4-5 ays (onon anennas) o conbue o e oal eceed sgnal. Hence less an 9 ays may be enoug o descbe, w gea accuacy, e ndoo sgnal popagaon. Te sgnal n decays w dsance a a ae of 1 / d wee n=1.75 fo e specfc geomey suggesng wae gudng effecs. Te anenna adaon paens affec sgnfcanly e sgnal popagaon, snce dffeen paens may ale e esuls cangng e space and e me conbuon of e efleced ays. Fuemoe, e maeal caacescs affec n gea exen e popagaon ee eflecng pefecly e sgnal (alumnum) o absob sgnfcan amoun of enegy dependng always on e ncdence angle. Inceasng e anenna decy, RMS delay spead alues can be educed suppessng e mulpa componens. REFERECES [1] L.M Coea, and R. Pasad, An oeew of weless boadband communcaons, IEEE Commun. Mag., pp , Jan [2] L. Fenandes, R2067 MBS - Moble Boadband Sysem, 2 nd IEEE ICUPC, Oawa, Oc , 1993, pp [3] R. Pasad, Oeew of weless communcaons: Mcowae pespeces, IEEE Commun. Mag., pp , Ap [4] T.S. Rappapo, Weless Communcaons, Uppe Saddle Re, J: Pence Hall, [5] W. Scäfe, Cannel modelng of so-ange ado lnks a 60 GHz fo moble neecle communcaon, 41 s IEEE Vecula Tecnology Confeence, pp , S. Lous, [6] K. Sao e al, Measuemens of e complex eface ndex of concee a 57.5 GHz, IEEE Tans. Anennas Popaga., ol. 44, no. 1, pp , Jan [7] K. Sao e al., Measuemens of eflecon and ansmsson caacescs of neo sucues of offce buldng n e 60-GHz band, IEEE Tans. Anennas Popaga., ol. 45, no. 12, pp , Dec