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1 Project Title Date Subitted Source(s) Re: Abstract Purpose otice Release Patet Policy ad Procedures IEEE Broadbad Wireless Access Worig Group < Recoedatio o Tie Varyig Radio Propagatio Chael Models ad Study of Syste Perforace for LMDS (Revisio 1: ) Soa Pitchaiah Voice: LMDS Physical Layer Desig group Fax: Cetre for Wireless Couicatios Eail: soa@cwc.us.edu.sg The atioal Uiversity of Sigapore 0 Sciece Par Road, #0-34/37 TeleTech Par Sigapore Sciece Par-II, Sigapore Additioal Cotributors: Y W M Chia ad L C Og CWC Supporters: 3Co Corporatio, USA atioal Sciece ad Techology Board (STB), Sigapore This cotributio is subitted i respose to call for cotributios fro the IEEE chair for subissios of PHY proposals for BWA, Sessio #7. We recoed ovel flexible propagatio chael odels for urba, suburba ad rural eviroets developed based o easureets coducted i Sigapore applicable to Local Multipoit Distributio Service (LMDS). The followig assuptios were ade i the odelig: (1) Lie of sight (LOS) coditio exists betwee trasitter hub ad receiver atea outed o rooftop; () Coplete blocage of receiver ad heavy rai coditios were ot cosidered; (3) ultipath copoets below 30dB copared to direct LOS sigal were excluded. A geeralised tapped delay lie odel was developed to represet the tie varyig two-sided coplex chael ipulse respose. The syste perforace was studied i ters of various first-order ad secod-order statistical characteristics such as cuulative distributio fuctio, level crossig rate, average fade duratio, ea delay, rs delay spread ad correlatio badwidth of the wide-bad chael. Fially the chael ultipath-fadig behavior was odeled by Ricia K-factor. To provide a iput to the physical layer tas group specific criterio called robustess to chael ipairets ultipath fadig This docuet has bee prepared to assist IEEE It is offered as a basis for discussio ad is ot bidig o the cotributig idividual(s) or orgaizatio(s). The aterial i this docuet is subject to chage i for ad cotet after further study. The cotributor(s) reserve(s) the right to add, aed or withdraw aterial cotaied herei. The cotributor grats a free, irrevocable licese to the IEEE to icorporate text cotaied i this cotributio, ad ay odificatios thereof, i the creatio of a IEEE Stadards publicatio; to copyright i the IEEE's ae ay IEEE Stadards publicatio eve though it ay iclude portios of this cotributio; ad at the IEEE's sole discretio to perit others to reproduce i whole or i part the resultig IEEE Stadards publicatio. The cotributor also acowledges ad accepts that this cotributio ay be ade public by IEEE The cotributor is failiar with the IEEE Patet Policy ad Procedures (Versio 1.0) < icludig the stateet IEEE stadards ay iclude the ow use of patet(s), icludig patet applicatios, if there is techical justificatio i the opiio of the stadards-developig coittee ad provided the IEEE receives assurace fro the patet holder that it will licese applicats uder reasoable ters ad coditios for the purpose of ipleetig the stadard. 1

2 Recoedatio o Tie Varyig Radio Propagatio Chael Models ad Study of Syste Perforace for LMDS P Soa *, Y W M Chia ad L C Og The atioal Uiversity of Sigapore, Cetre for Wireless Couicatios, 0 Sciece Par Road, #0-34/37, TeleTech Par, Sigapore Sciece Par-II, Republic of Sigapore Eail: soa{chiaichael, ogichael}@cwc.us.edu.sg Abstract - Local Multipoit Distributio Service (LMDS) has bee recogised as a effective last ile solutio to provide broadbad wireless access to fixed etwors providig services ragig fro oe-way video distributio ad telephoy to fully iteractive switched broadbad ultiedia applicatios for residetial ad busiess custoers. I this paper, we recoed the realistic ad accurate LMDS chael odels based o the easureets coducted i urba, suburba ad rural eviroets of Sigapore at 7.4 GHz. A geeralised tapped delay lie odel was developed to represet the tie varyig coplex chael ipulse respose. The propagatio characteristics obtaied iclude received sigal short-ter fluctuatios ad delay characteristics. Also the syste perforace was studied usig various first-order ad secod-order statistical characteristics such as cuulative distributio fuctio, level crossig rate ad average fade duratio of the fadig sigal. These characteristics provide valuable iforatio o the coverage liitatios, choice of suitable data rates, word legths ad odulatio ad codig schees i a operatioal LMDS syste. I. Itroductio Local ultipoit distributio service (LMDS) has bee widely recogized as a effective last ile solutio to provide broadbad wireless access to fixed etwors via illieter wave radio trasissio at 7 GHz. It uses cellular-lie etwor architecture to deliver services ragig fro oe-way video distributio ad telephoy to fully iteractive switched broadbad ultiedia applicatios such as iteractive video, video-o-dead, video coferecig real-tie ultiedia file trasfer with high speed iteret access to residetial ad busiess custoers. Large badwidth, lower istallatio cost ad ease of deployet coupled with recet advaceets i MMICs ae LMDS a attractive solutio for broadbad service delivery. The propagatio chael is the ai cotributor for ay probles that beset the perforace of ay digital radio syste. The LMDS syste perforace is liited by the fast sigal atteuatio i this frequecy rage ad excess loss due to rai. I additio, the frequecy selective fadig behaviour becoes sigificat at these higher data rates. However due to the static ature of propagatio sceario, the chael coditios ca be expected to be ore favourable. Thus it is ecessary ad iportat to have thorough uderstadig ad accurate chael odels for optiu syste desig. I the literature, Scott Siedal et al reported propagatio experiets at 8 GHz ad path loss odels with differet types of blocage [1]. Papazia et al reported about area coverage, sigal depolarisatio issue, delay spread values ad K-factors of Ricia distributio []. I aother study Zhag et al reported about chael classificatio ad ipulse respose paraeters [3]. But to the owledge of the author there is o attept to obtai LMDS chael ipulse respose odels siilar to the existig GSM stadard chael odels. I our earlier paper [4], we have reported propagatio easureets coducted i Sigapore, excess pathloss, delay characteristics ad the preliiary tie varyig LMDS chael ipulse respose odels. This paper suarises the easureet ethodology ad reports about a ovel geeralised tapped delay lie odel to represet the tie varyig two-sided coplex chael ipulse respose for urba, suburba ad rural eviroets. Siulatio was carried out to obtai the total received sigal ad the fast fadig behavior was studied usig various first-order ad secod-order statistical characteristics. Also the wide-bad dispersive chael behavior was studied usig delay characteristics. II. Site Descriptio ad Measureets The trasitter was fixed o the rooftop of a buildig located o a hill so as it ca be see by ost of the receiver locatios ragig fro 00-. Measureets were carried out o the rooftops of various 13- storied residetial blocs located i urba, sub-urba ad rural areas. The receiver sites were usually surrouded by several residetial blocs, busiess cetres, foliaged sport grouds ad by a hilly terrai. Factors that affect the service quality iclude atteuatio by vegetatio, blocage by adjacet buildigs. The sigal receptio was cosidered uder various coditios such as clear LOS availability, partial blocage ad coplete blocage by two or ore buildigs. The easureet syste is based o Swept Tie Delay Cross-Correlatio (STDCC) techique to easure the chael ipulse respose. The trasitter odulates a IF carrier at GHz usig BPSK with a 11 bit -sequece at the chip rate of 0 Mb/s ad the up coverted to 7.4GHz. The odulator output was aplified to +30dB ad trasitted through a vertically polarized oidirectioal atea with 11dB gai. The receiver is a flat pael atea with a gai of 31dB ad a 3dB beawidth of 4 o i both aziuth ad elevatio plaes. The received sigal was first dow coverted to GHz IF ad despreaded i a slidig correlator, whose cloc frequecy was slightly offset fro the trasitted code rate. The I ad Q sigals were digitized usig a A/D coverter i a PCMCIA acquisitio card ad stored i a Laptop coputer for further processig.

III. Chael Ipulse Respose Modelig The ipulse respose of the radio chael is very iportat i the desig, developet ad plaig of radio systes as it copletely describes the radio propagatio chael [].

3 III. Chael Ipulse Respose Modelig The ipulse respose of the radio chael is very iportat i the desig, developet ad plaig of radio systes as it copletely describes the radio propagatio chael []. The total received sigal at ay istat of tie ca be obtaied as follows, r ( t) = s( t) h( t, τ ) + ( t) (1) where s(t) is ay trasitted sigal, h(t,τ) is the tie varyig two-sided coplex chael ipulse respose ad (t) is the AWG oise sigal as give i [6]. The chael ipulse respose at ay observatio tie t ca be represeted by tapped delay lie odel, which is give by, 1 = 0 j( ωcτ + φ ) h ( t, τ ) = c ( τ ) δ ( t τ ) e () where is the tap idex, is the axiu uber of taps, ω c is the carrier agular frequecy, τ is the excess delay of each ultipath copoet ad Φ is the rado phase i the rage [0,π). The factor c odels the tie varyig ature of chael ipulse respose ad (τ ) represets a particular ultipath cluster, which provides the distributio of the tap gais of various ultipath copoets. The chael ipulse respose ay cotai oe to five ultipath clusters with differet pea ties depedig o the type of chael eviroet. There are two ajor advatages with our chael odellig copared to others [,3]. The first oe is that the tie variatios as well as distace variatios of the chael ipulse respose withi the sae type of eviroet were cosidered. Secod advatage is that the loger delayed two-sided ultipath clusters were icluded i the odel as they ca cause larger delay spread values eve though they are wea. Fig.1 to Fig.4 shows the oralised averaged power delay profiles obtaied fro the easureets i various chael coditios, approxiated with the developed atheatical equatios. The ai differeces are the axiu excess delay tie ad the presece of various ultipath clusters for various chaels. Fig.1 shows the derived power delay profiles for the worst case ad best case of the urba eviroet. The presece of loger delayed ultipath clusters, aily due the surroudig high rise buildigs, ca cause high delay spread ad hece iter-sybol iterferece. However it ca be oticed that the loger delayed ultipath clusters are db wea copared to the direct LOS sigal. Fig. shows the power delay profiles easured i typical urba eviroet. It ca be observed fro the Fig. that the delay profile varies slightly for differet easureet locatios, which was also tae ito cosideratio i the developet of the chael odels. Fig.3 shows the power delay profiles obtaied i the suburba eviroet, where the receiver is surrouded by residetial blocs of sae height. It ca be see that there are o sigificat loger delayed ultipath clusters preset. Fig.4 shows the easured power delay profiles i rural eviroet, where the receiver was located earer to the trasitter ad o buildigs preset i betwee the. It ca be see fro the plot that there were o secodary ultipath clusters preset i this case. Fig.1. Power delay profiles for dese urba chael with clear LOS. Fig.. Power delay profiles for typical urba chael with clear LOS. Fig.3. Power delay profiles for suburba areas with clear LOS. Fig.4. Power delay profiles for earby rural areas with clear LOS. 3

4 Aog the easureet locatios i Sigapore, it was observed that 80 percet of the were fall i urba area, 1 percet fall i suburba area ad the reaiig percet belogs to rural eviroet. The geeral equatio used to fit a particular ultipath cluster is of the for: τ τ p ( τ = ) α exp β (3) 100 where β cotrols the rate of decay of tap gais, α is the pea aplitude ad τ p is the pea tie of a particular ultipath cluster. The values of these chael ipulse respose paraeters are suarized i Table 1. The decay factor β ad c are rado variables, whose values are give i Table based o easureets for various chael types such as dese urba, typical urba, suburba ad rural eviroets. Table 1. Suary of chael odel paraeters Case (i) Pea tie, τ p (s) Atteuatio factor, α i Decay factor, β i Excess delay τ (s) 1 40 s 40 s β 1 β s 0.1 β s 0.1 β s 1100 s 100 s Table. Classificatio of propagatio chael Paraeter Urba1 Urba Suburba Rural c (db) β β β β τ ax (s) IV. Propagatio Chael Characterisatio The total received sigal was obtaied by covolutig the chael ipulse respose with a uodulated uit step trasitted sigal i the presece of additive white Gaussia oise as give by Eq.(1). Fig. shows the copleetary cuulative distributio (ccdf) curves of the received sigal for various chael coditios. It ca be observed that oly 6 percet of the tie the sigal level lies above local ea. This suggests the provisio of extra li argi of 10dB for the reliable operatio of the receiver over 9 percet of the tie. Level crossig rate (lcr) at ay threshold level is defied as the expected rate at which the sigal evelope crosses that level i positive (or egative) goig directio [6]. Fig.6 shows the variatio of oralised lcr as a fuctio of threshold level, which is foud to be 18 at the local ea. Assuig a relative speed of 1/s betwee the receiver ad propagatio chael, the sigal crosses the local ea for each 40.µs of observatio tie, which is four ties the saplig iterval. Provisio of 10dB extra argi icreases this to 43.3µs, which clarifies the favourable slow fadig behaviour of LMDS chael. The received sigal experiece periods isufficiet sigal stregth or fadig iterval durig which the bit error rate is close to oe half ad the receiver ay ot fuctio reliably. The characteristic average fade duratio (afd) deteries how log the sigal lies below a give threshold level o average. Thus helps to deterie the ost liely uber of sigalig bits that ay be lost durig a fade [6]. At the local ea oralised afd was foud to be 0.0, which correspods to 18.µs for each secod of observatio period. However it reduces to 7.3µs with the provisio of 10dB fade-argi. These two characteristics aed lcr ad afd are called secod-order statistics sice they deped o both observatio tie ad distace. These are useful i predictig the burst of errors without doig the ed-to-ed syste siulatio ad i the desig of the error cotrol codes, iterleaver ad diversity schees [6]. The widebad dispersive ature of the LMDS chael ca be characterized usig average excess delay, rs delay spread, correlatio badwidth. These are useful i the choice of suitable data rates ad codec to avoid itersybol iterferece. The average delay (T D ) is the power weighted average of the excess delays give by the first oet of the ipulse respose. The rs delay spread (S) is the power weighted stadard deviatio of the excess delays give by the secod oet of the ipulse respose ad provides a easure of the variability of ea delay. For a sapled versio of the power delay profile average delay ad rs delay spread ca be calculated as follows []: T S D = = τ = 0 = 0 P (τ ( τ T ) ( τ ) where, P is the total eergy give by, = 0 P D ) (4) () P = ( τ ) (6) Fig.7 shows the ccdf curves of the excess delay for various chael types. It ca be oticed that over 9 percet of tie ea delay lies below 47s, 0s ad s for rural, suburba ad typical urba areas respectively. But i high dese urba area it exceeds 6s over 9 percet of the tie. This characteristic is useful i the desig of equiliser taps. The iiu uber taps ca be evaluated usig the followig siple relatio, τ ax = + 1 (7) T s where, T s is the sybol duratio. Fig.8 shows the ccdf curves of rs delay spread for various chael eviroets. It ca be oticed that over 9 percet of tie delay spread lies below 10s, 0s ad 40s for rural, suburba ad typical urba areas respectively. Where as delay spread exceeds 10s over 9 percet of tie i high dese urba area. This is aily due to the presece of loger delayed ultipath clusters. 4

5 V. Coclusio I this paper, we suerised the propagatio easureet capaig coducted at 7.4GHZ i Sigapore ad reported the ew tapped delay lie LMDS chael ipulse respose odels for urba, suburba ad rural ultipath propagatio eviroets. The variatios of chael ipulse respose w.r.t both observatio tie ad distace withi a particular chael type were also cosidered. The LMDS syste perforace was studied usig various first-order ad secod-order statistical characteristics such as ccdf, lcr ad afd as well as delay characteristics. The results show that the excess path loss due to blocage coditios ad rs delay spread are the ost serious propagatio ipairets for LMDS syste. Ricia K-factor values were foud to be i the rage of 10-1dB for various eviroets. The suary of these characteristics is listed i Table 3. Fig.. Copariso of sigal ccdf curves for various eviroets. Table 3. Suary of propagatio characteristics Characteristic Urba1 Urba Suburba Rural lcr -10dB afd -10dB Mea Delay (s) Delay Spread (s) CorrBW (MHz) K-Factor (db) VI. Acowledgeets The authors would lie to tha the 3Co Corporatio, USA for sposorig the easureet capaig through a co-operative research ad developet wor. Also the authors are grateful to atioal Sciece ad Techology Board, Sigapore for their cotiuous support. The cotributios of K V Ravi, R..S. Ruwa, T.B. Chua, C.L. Chia ad W. Myit to the success of easureet capaig are highly appreciated. Refereces [1] S.Y. Siedel ad H.W. Arold, Propagatio easureets at 8 GHz to ivestigate the perforace of local ultipoit distributio service, IEEE Globeco'9, vol.1, pp 74-77, 199. [] P.B. Papazie, G.A. Hufford, R.J. Achatz ad R. Hoffa, Study of the Local Multipoit Distributio Service Radio Chael, IEEE Tras. o Broadcastig, Vol.43, o., pp , Jue [3] W. Zhag ad. Moayeri, Recoedatio o Chael Propagatio Model for Local Multipoit Distributio Service, Docuet uber IEEE pc-00/16, preseted at Sessio #6 IEEE eetig, Albuquerque, ew Mexico, 6-9 March, 000. [4] K.V. Ravi ad P. Soa, Aalysis ad odellig of local ultipoit distributio service (LMDS) chael, Proceedigs of the 1999 IEEE Globeco, pp [] J.D. Parsos, The Mobile Radio Propagatio Chael, Petech Press, Lodo, [6] T.S. Rappaport, Wireless Couicatios: Priciples ad Practice, Pretice Hall PTR, ew Jersey, Fig.6. Copariso of oralised lcr curves for various eviroets. Fig.7. Copariso of ea delay ccdf curves for various eviroets. Fig.8. Copariso of delay spread ccdf curves for various eviroets.

Solution 2 Discussion:

Solution 2 Discussion: Mobile Couicatios Solutio 2 Discussio: 4..2007 Solutio 2.: Multiplexig For ultiplexig, SDMA, TDMA, FDMA, ad CDMA were preseted i the lecture. a.) What liits the uber of siultaeous users i a TDM/FDM syste