Coexistence between WiMAX and Existing FWA Systems in the Band 3500 MHz

Transcription

1 Procdings of th Intrnational MultiConfrnc of Enginrs and Computr Scintists 28 Vol II IMECS 28, March, 28, Hong Kong Coxistnc btwn WiMAX and Existing FWA Systms in th Band 35 MHz Zaid A. Shamsan, Mmbr, IAENG, and Thark Abd Rahman Abstract In this papr, th coxistnc of WiMAX systm and xisting fixd wirlss accss (FWA) systms is studid. Spctral mission mask is usd as wll as intrfrnc to nois ratio () of as on of standard sharing critrion valu at FWA systms rcommndd by intrnational tlcommunication union radio sctor ITU-R. Thr channl bandwidths of (3.5, 7, and 1 MHz) of WiMAX systm ar slctd to b studid with 7 MHz FWA channl in dns urban ara. All paramtrs of th two systms ar prsntd and mthodology is xplaind. It is wll known that frquncy distanc ruls ar an important of frquncy coordination procss in most radio srvics, so frquncy and distanc sparations ar dtrmind and analyzd for both trms cochannl intrfrnc and adjacnt channl intrfrnc in th diffrnt intrfrnc scnarios which ar supposd. Indx Trms Coxistnc and sharing, fixd wirlss accss (FWA) systms, intrfrnc-to-nois ratio, spctral mission mask, WiMAX systms. I. INTRODUCTION Th radio spctrum is a limitd and valuabl rsourc, and as a rsult of th drastic growth dmand for wirlss communication applications, radio spctrum rgulation and managmnt hav bcom incrasingly significant [1]. Du to scarcity of th frquncy spctrum, many bands ar allocatd for mor than on radio srvic and thrfor th sharing is ncssity. Th incrasd sharing of spctrum translats into a highr liklihood of usrs intrfring with on anothr [2]. WiMAX (worldwid introprability for microwav accss) is basd on IEEE standard [3] rcntly considrd as th 3rd gnration broadband wirlss accss (BWA) systm dsignd mainly for wirlss mtropolitan ara ntworks (WMAN) [4]. WiMAX addrsss th last-mil BWA problm in mtropolitan aras and undrsrvd rural aras for th advantags of fast and cost-ffctiv dploymnt, it uss th band 35 MHz which is currntly allocatd to Fixd Wirlss Accss (FWA) systms. Thrfor, th impact of th intrfrnc of WiMAX as a nw tchnology on FWA systms and vic vrsa nds to b studid. Th intrst for th us of 35 Manuscript submittd Dcmbr 1, 27. This work was supportd in part by th Malaysian Communication and Multimdia Commission (MCMC). Z. A. Shamsan is with th Wirlss Communication Cntr, Elctrical Enginring Faculty, Univrsiti Tknologi Malaysia, 8131 UTM Skudai, Johor Bahru, Malaysia (phon: ; -mail: shamsan22@yahoo.com). T. A. Rahman is with th Wirlss Communication Cntr (WCC), Elctrical Enginring Faculty, Univrsiti Tknologi Malaysia, 8131 UTM Skudai, Johor Bahru, Malaysia. (phon: ; fax: ; -mail: thark@fk.utm.my). MHz band (34-38) for FWA/BWA applications has incrasd bcaus its larg siz, high dgr of rliability and wid covrag, particularly in gographical aras with svr rain. A diffrnt compatibility studis in th band 35 MHz btwn broadband FWA and othr srvics (point-to-point fixd links, lctronic nws gathring/outsid broadcasting systms, fixd satllit systms and radiolocation) wr rportd in [5], also impact from Ultra Wid Band (UWB) systms on BWA has bn studid in [6]. Han-shin Jo t al. [7] studid th coxistnc of orthogonal frquncy division multiplxing (OFDM)-basd systms byond 3G (B3G) and point-to-point fixd srvics in th band 35 MHz. Th rmindr of this papr is organizd as follows. In sction II, paramtrs of WiMAX (82.16) and FWA systms ar prsntd in dtail. Sction III is dvotd to discuss sharing critrion. Th mthod and procdur to do this work and th usd propagation modl as wll as spctral missions mask ar laboratd and dscribd in dtails in th sctions IV, V, and VI. Sharing and coxistnc scnarios and analyss as wll as th compatibility btwn WiMAX and FWA in co-channl and adjacnt channl ar xcutd in sctions VII and VIII. Finally, th conclusion is prsntd in sction IX. II. WIMAX AND FIXED SYSTEMS PARAMETERS DESCRIPTION In ordr to xamin coxisting and sharing issus, it is ncssary to clarify th paramtrs of WiMAX and FWA that will affct th intrfrnc lvl and critrion. A. Paramtrs of WiMAX WiMAX movs toward highr data rats through widr modulation bandwidths from 1.25 to 2 MHz for point-topoint and point-to-multipoint fixd applications. IEEE BWA working group [8] dfind th radio frquncy paramtrs and charactristics of WiMAX (fixd and mobil), this study will only focus on fixd WiMAX, and ths paramtrs ar shown in Tabl I for both transmittr and rcivr. As th systm can occupy a bandwidth up to 2 MHz w chos thr diffrnt channl bandwidths 3.5, 7, and 1 MHz (in ordr comparison with currnt FWA systm) ach with cntr frquncy of 35 MHz. Th spctral mission mask rquirmnts follow ETSI-EN (EqC-PET=O, EqC- EMO=6) or Typ-G mask ETSI-EN3121 [9], [1] spcifications and according to [11]. Not- EqC-PET mans Equipmnt Classification- Primary Equipmnt Typ and EqC-EMO mans Equipmnt Classification- Equivalnt Modulation Ordr. ISBN: IMECS 28

2 Procdings of th Intrnational MultiConfrnc of Enginrs and Computr Scintists 28 Vol II IMECS 28, March, 28, Hong Kong Tabl I: WiMAX systm paramtrs Tabl II: Existing FWA systm paramtrs Paramtr Valu Cntr frquncy of opration 35 Bandwidth 3.5, 7, 1 Bas station transmittd powr (m) 36 Trminal station transmittd powr (m) 24 Spctral missions mask rquirmnts Typ-G ETSI- EN3121 Bas station antnna gain (i) 16 Rcivr antnna gain (i) 8 Bas station antnna hight (m) 3 Rcivr antnna hight (m) 2 Nois figur of Bas station () 4 Nois figur of rcivr () 7 Paramtr Valu Cntr frquncy of opration 35 Bandwidth 7 Bas station transmittd powr (m) 35 Trminal station transmittd powr (m) 22 Spctral missions mask rquirmnts Typ-F ETSI EN3121 Bas station antnna gain (i) 17 Trminal station antnna gain (i) 2 Bas station antnna hight (m) 2 Trminal station antnna hight (m) Nois figur of bas station () 5 Nois figur of trminal station () 7 B. Paramtrs of th Currnt FWA In Malaysia th frquncy rang GHz is allocatd for FWA systms, it is dividd into sub-bands for duplx us (non duplx systms can still b usd in this band), MHz paird with MHz as wll as MHz paird with MHz. Ths FWA bands ar to b usd for dirct radio connction in th last mil btwn a fixd radio cntral station and subscribr trminal stations in a point-to-point and/or point-to-multipoint configuration. Countris hav various frquncy channl spacing within th 3.5 GHz bands 1.25, 1.75, 3.5, 7, 8.75, 1, 14, and 28 MHz can b usd according to capacity nds. Th spctral mission mask (is discussing in a nxt sction) rquirmnts follow ETSI-EN (EqC- PET=O, EqC-EMO=4) [9] or Typ-F mask ETSI- EN3121 [1] spcifications according to [5]. W will focus on th paramtrs listd in Tabl II. III. SHARING CRITERION For discussion of various sharing scnarios, it is ncssary to dvlop appropriat ruls for sharing. Intrsystm intrfrnc can b dscribd as short trm or long-trm, th short- trm intrfrnc is rarly valuatd in th coordination litratur as it is vry much statistical in natur and not found for many srvics and will b spcific to th cass considrd [12], [13]. In this papr w considr long trm intrfrnc only. Th intrfrnc protction critria can b dfind as an absolut intrfrnc powr lvl I, intrfrnc-to-nois powr ratio, or carrir-to-intrfring signal powr ratio C/I as shown in Fig. 1 [13]. ITU-R Rcommndation F dtails two gnrally accptd valus for th intrfrnc to thrmal-nois ratio () for long-trm intrfrnc into fixd srvic rcivrs. Whn considring intrfrnc from othr srvics, it idntifis an valu of 6 or 1 matchd to spcific rquirmnts of individual systms. This approach provids a mthod for dfining a tolrabl limit that is indpndnt of most charactristics of th victim rcivr, apart from nois figur. Each fixd srvic accpts a 1 dgradation (i.., th diffrnc in dcibls btwn carrir-to-nois ratio (C/N) and carrir to nois plus intrfrnc ratio C/(N + I) in rcivr snsitivity. In som rgard, an of 6 bcoms th fundamntal critrion for coxistnc [14], so it should b that [15]: I Figur 1: Intrfrnc protction critrions I N α (1) Whr I is th intrfrnc lvl in m, N is th thrmal nois floor of rcivr in m and α is th protction ratio in and hr has valu of which mans that th intrfrnc must b approximatly 6 blow thrmal nois as Fig. 1 shows. IV. METHOD AND PROCEDURE Th mthod consists in calculating th ratio and thn comparing it with th ncssary ( ) at th victim rcivr. Stp 1: Calculat th intrfrnc lvl I (m) at th victim rcivr by assssing th lvl of missions from th intrfrr falling within th victim rcivr bandwidth for both co-channl frquncy and adjacnt frquncy situations according to [7]: I C/I C/N ( Δ f ) = Pt + Gt + Gr + Mask( Δf ) + corr _ band Att Whr Pt: transmittd powr of th intrfrr in m, Gt: gain of th intrfrr transmittr in i Gr gain of th victim rcivr antnna in i Mask( f): attnuation of adjacnt frquncy du to mask whr ( f) is th diffrnc btwn th carrirs of intrfrr and th victim. corr_band: corrction factor of band ratio, whr corr_band= if BW intrfrnc < BW victim or corr_band=-1log(bw intrfrnc /BW victim ), if not. C N (2) ISBN: IMECS 28

3 Procdings of th Intrnational MultiConfrnc of Enginrs and Computr Scintists 28 Vol II IMECS 28, March, 28, Hong Kong Att: attnuation du to th propagation (modl in ITU-R P.452 is usd). Stp 2: Dtrmin th thrmal nois floor of victim rcivr as th following: ( ) N = NF +1log1 BW victim (3) Tabl III: Nominal cluttr hights and distancs Cluttr catgory Cluttr hight ha Nominal distanc d k Rural 4.1 Suburban 9.25 Urban 2.2 Dns urban 25.2 Whr NF is nois figur of rcivr in and BW victim rprsnt victim rcivr bandwidth in MHz. Stp 3: Substitut I and N of stps 2 and 3 abov into (1) to dtrmin th sharing and coxistnc fasibility btwn th two systms and driv th rlationship btwn: a). frquncy sparation f and ratio b). distanc sparation and ratio. V. PROPAGATION MODEL s o r l u t C l Rural Suburban Dns urban Urban In particular, thr is no singl propagation modl usd for diffrnt sharing studis bcaus th particular dploymnt of th systms rquirs using spcific propagation modl rlvant to th spcific systm. WiMAX has a spcific usag as it may b fixd or mobil and to oprat in lin or non-lin of sight nvironmnt. Th standard modl agrd upon in CEPT and ITU for a trrstrial intrfrnc assssmnt at microwav frquncis is clarly markd in ITU-R P [16]. This is modl which is usd for this coxistnc study includs th attnuation du to cluttr in diffrnt nvironmnts. L ( d) = log d + 2log f + Ah (4) Whr d is th distanc btwn intrfrr and victim rcivr in kilomtrs, f is th carrir frquncy in GHz, and Ah is loss du to protction from local cluttr or calld cluttr loss, it is givn by th xprssion: d h k Ah = tanh (5) ha Whr d k is th distanc (km) from nominal cluttr point to th antnna, h is th antnna hight (m) abov local ground lvl, and ha is th nominal cluttr hight (m) abov local ground lvl. In [16], cluttr losss ar valuatd for diffrnt catgoris: trs, rural, suburban, urban, and dns urban, tc. Th most gographical considrd whr WiMAX tchnology will b opratd and dploymnts can b profitabl [17] ar dns urban and rural (th availability of othr altrnativs is limitd) as wll as low profitabl in suburban and urban (mdium population dnsitis and high availability of othr accss ntwork altrnativs). Incrasing of antnna hight up to th cluttr hight lads to dcras th cluttr loss, as shown in Tabl III and Fig. 2 which contain th four catgoris. In our cas, dns urban catgory will b considrd Antnna hight (m) Fig. 2: Cluttr loss for rural, suburban, urban, and dns urban aras VI. SPECTRAL EMISSIONS MASKS Th spctral mission mask is a graphical rprsntation of a st of ruls that apply to th spctral missions of radio transmittrs. Such ruls ar st forward by rgulatory bodis such as FCC and ETSI. It is dfind as th spctral powr dnsity mask, within ± 25 % of th rlvant channl sparation (ChS), which is not xcdd undr any combination of srvic typs and any loading. Th masks vary with th typ of radio quipmnt, thir frquncy band of opration and th channl spacing for which thy ar to b authorizd. WiMAX and FWA masks according to [9] and [1] ar dpictd and tabulatd, whr spctrum masks for WiMAX is dclard in Tabl IV for thr channl bandwidths and 7 MHz channl spacing is only dpictd in Fig. 3 in ordr to compar that with FWA mask for 7 MHz which is shown in Fig. 4 and Tabl V. Th spctral mission mask is considrd in this study bcaus it may b usd to gnrat a worst cas powr spctral dnsity for worst cas intrfrnc analysis purposs, whr th coxistnc study can b applid by spctrum mission mask as an ssntial paramtr for adjacnt frquncy sharing analysis to valuat th attnuation of intrfrnc signal powr in th band of th victim rcivr. To carry out this study th spctral missions mask in th Fig. 3 is applid for coming intrfrnc from WiMAX systms and Fig. 4 is applid for coming intrfrnc from FWA systms as th following sction dtails. ISBN: IMECS 28

4 Procdings of th Intrnational MultiConfrnc of Enginrs and Computr Scintists 28 Vol II IMECS 28, March, 28, Hong Kong Tabl IV: Rfrnc frquncis for spctrum masks of Typ-G ETSI- EN3121 (WiMAX) Frq./Ch. Sparation (Normalizd) Ch. Spacing Tabl V: Rfrnc frquncis for spctrum masks of Typ-F ETSI- EN3121 (FWA) Frq./Ch. Sparation (Normalizd) Ch. Spacing n sity D w r o P tra l S pc t iv R la Frquncy/Channl Sparation Figur 3: WiMAX spctral mission mask for 7 MHz y n si t D w r o P tra l S pc t R l a iv Frquncy/Channl Sparation Figur 4: FWA spctral mission mask for 7 MHz VII. SHARING, COEXISTENCE SCENARIOS AND ANALYSIS A. Intrfrnc from WiMAX into FWA BS in dns urban ara As sn from Figs. 5, 6, and 7 th intrfrnc from WiMAX bas station (BS) systms into 7 MHz FWA BS as a victim rcivr is applid, whr th minimum sparation distanc and frquncy sparation for th minimum ratio of ar analyzd according to th thr slctd bandwidth of WiMAX channls in th dns urban ara. It can b obsrvd that th minimum sparation distanc btwn th two bas stations must b gratr than 14 m and 11 m for frquncy sparation of 3.5 and 7 MHz, rspctivly. For frquncy sparation of 1 MHZ a.9 km must b takn into account for adjacnt channl coxistnc. For dploying th two systms with a null guard band th sparation distancs must b gratr than 29 m, 48 m, and 54 m for WiMAX bandwidth of 3.5, 7, and 1 MHz, rspctivly. Th frquncy sparation quals to: Zro _ Guard _ Band =.5( BW WiMAX + BW ) (6) FWA Whr BW WiMAX and BW FWA ar bandwidth of WiMAX and FWA, rspctivly. Zro guard band is rprsntd by a vrtical lin in th graphs. Sharing th sam channl (co-channl) is fasibl btwn two systms only in cas of sparation distancs ar of th ordr of 3.5 km for 3.5 and 7 MHz and 2.9 km for 1 MHz channl bandwidth, bcaus at ths distancs th intrfrnc is always 6 or mor blow th thrmal nois floor as th figurs show. Ths ntir rquirmnts ar summarizd in Tabl VI km.29km 3.5km Figur 5: Intrfrnc from WiMAX BS (3.5 MHz) into FWA BS (7MHz) B. Intrfrnc from FWA BS into WiMAX in dns urban ara This scnario is applid using 7 MHz channl FWA mission mask as intrfrr on WiMAX BS. Hr, intrfrr is FWA systm assumd has fixd channl bandwidth and thus fixd spctrum mission mask whras WiMAX BS is th victim rcivr with thr slctd bandwidths Figs. 8-1 dpict th rquird minimum sparation distanc and frquncy sparation vrsus th standard intrfrnc to nois ratio ( ) for 3.5, 7, and 1 MHz bandwidth of WiMAX channls. In th thr plots, it is clarly obsrvd that th co-channl coxistnc can b satisfid as distanc btwn bas stations of two systms incras, whr th minimum sparation distanc is 4.4 km for both 3.5 and 7 MHz, and it quals to 3.7 km for 1 MHz. In ordr to dploy th two systms in adjacnt band, th minimum frquncy sparation is 14 MHz and th minimum sparation distanc must b gratr than.14 km for 3.5 and 7 MHz, and.12 km for 1 MHz. ISBN: IMECS 28

5 Procdings of th Intrnational MultiConfrnc of Enginrs and Computr Scintists 28 Vol II IMECS 28, March, 28, Hong Kong Tabl VI: Minimum rquird sparation distanc and frquncy sparation for diffrnt channl bandwidths and intrfrnc cass in dns urban ara (intrfrnc from WiMAX into 7 MHz FWA) Minimum rquird sparation distanc (km) and WiMAX frquncy carrirs sparation bandwidth ( MHz) Co-channl sharing Adjacnt channl sharing Zro guard band km MHz km MHz km MHz km.175 km km Figur 8: Intrfrnc from FWA (7MHz) into WiMAX (3.5 MHz) 2.11 km km km Figur 6: Intrfrnc from WiMAX (7 MHz) into FWA (7MHz) km.12 km km Figur 9: Intrfrnc from FWA (7MHz) into WiMAX (7 MHz) km.54 km km Figur 7: Intrfrnc from WiMAX (1 MHz) into FWA (7MHz) 2.12 km Dploying FWA BS and WiMAX BS with zro guard band sparation is also can b satisfid providd both of sparation distanc and frquncy sparation ar takn into account as shown in th Tabl VII. VIII. COMPATIBILITY BETWEEN WIMAX AND FWA According to prvious rsults and by comparing Tabl VI and Tabl VII, it is can b statd that WiMAX systm and FWA systm abl to shar and coxist in th co-channl frquncy and adjacnt channl by considring th sparation distanc and frquncy sparation as wll as typ of spctral mission mask and charactristics of two systms paramtrs. It should b notd that th rsults ar mor favourabl for compatibility whn using 1 MHz bandwidth channl for WiMAX which mans highr data rats. Th rsults ar also indicat that intrfrnc impacts form FWA km 3.7 km Figur 1: Intrfrnc from FWA (7MHz) into WiMAX (1 MHz) Tabl VII: Minimum rquird sparation distanc and frquncy sparation for diffrnt channl bandwidths and intrfrnc cass in dns urban ara (intrfrnc from 7 MHz FWA into WiMAX) Minimum rquird sparation distanc (km) and WiMAX frquncy carrirs sparation bandwidth ( MHz) Co-channl sharing Adjacnt channl sharing Zro guard band km MHz km MHz km MHz ISBN: IMECS 28

6 Procdings of th Intrnational MultiConfrnc of Enginrs and Computr Scintists 28 Vol II IMECS 28, March, 28, Hong Kong on WiMAX is mor worst than th intrfrnc form WiMAX into FWA, this is bcaus of th wid mask rquirmnts of FWA, highr antnna hight of WiMAX, and highr antnna gain of FWA. Thrfor, th minimum sparation distanc and frquncy sparation in Tabl VII should b takn into account for dploying th two systms bcaus it rprsnts th worst cas scnario btwn thm. Intrfrnc-to nois ratio dgrads as sparation distanc incrass, and th sam bhavior occurs whn frquncy sparation btwn carrirs incrass. IX. CONCLUSION In th abov discussion th rquird frquncy and distanc sparation btwn WiMAX and FWA systms hav bn drivd. A coxistnc analysis is thoroughly prformd in this papr basd on spctral mission mask and intrfrnc to nois ratio to dtrmin mutual intrfrnc btwn BSs of both systms in th dns urban ara. Th coxistnc problm is dividd into two altrnating trms, co-channl frquncy sharing and adjacnt channl coxistnc, also a coxistnc with zro guard band btwn th two systms is introducd. Th frquncy sparation rquird to protct both systms will b quit important whn WiMAX and FWA ar supposd to b clos vicinity istanc around.14 km) for adjacnt channl sharing and dcrass significantly to dploy co-channl frquncy sharing whr th sparation distanc is largr than (4.4 km) for both 3.5 MHz and 7 MHz and (3.7 km) for 1 MHz WiMAX channl bandwidth. W ar looking furthr for studying coxistnc btwn IMT-Advancd and currnt broadband FWA, mor studis ar rquird in diffrnt catgoris aras and using othr mitigation tchniqus. [9] ETSI EN (V1.2.2), Fixd radio systms; multipoint quipmnt and antnnas; part 2: harmonizd EN covring th ssntial rquirmnts of articl 3.2 of th R&TTE dirctiv for digital multipoint radio quipmnt, 27. [1] ETSI EN (V1.6.1), Fixd radio systms; point-tomultipoint quipmnt; tim division multipl accss (TDMA); pointto-multipoint digital radio systms in frquncy bands in th rang 3 GHz to 11 GHz, 23. [11] WiMAX GHz mini-pci rfrnc dsign sris, Availabl: uct_brif_jan7.pdf [12] Ptr Gardnnir, Mansoor Shafi, Robrt B. Vrnall, and Murray Milnr, Sharing issus btwn FPLMTS and fixd srvics, IEEE Comm. Mag., vol. 32, no. 6, pp , Jun [13] NTIA Rport 5-432, Intrfrnc Protction Critria Phas 1 - compilation from xisting sourcs, Oct. 25. Availabl: [14] IEEE Std , IEEE rcommndd practic for local and mtropolitan ara ntworks coxistnc of fixd broadband wirlss accss systms, March 24. [15] ITU-R Rcommndation F.142, Frquncy sharing critria btwn a land mobil wirlss accss systm and a fixd wirlss accss systm using th sam quipmnt typ as th mobil wirlss accss systm, [16] ITU-R Rcommndation P , Prdiction procdur for th valuation of microwav intrfrnc btwn stations on th surfac of th arth at frquncis abov about.7 GHz, Mar. 25. [17] T. Smura, Comptitiv potntial of WiMAX in th broadband accss markt: a tchno-conomic analysis, in Procdings of ITS 25, 25. Availabl: REFERENCES [1] B. Gabrys, R.J. Howltt, and L.C. Jain (Eds), A novl spctrum sharing schm using rlay station with intllignt rcption, KES 26, Part III, LNAI 4253, pp , Springr-Vrlag Brlin Hidlbrg, 26. [2] J. D. Lastr and J. H. Rd, Intrfrnc rjction in wirlss communications, IEEE Commun. Mag., vol. 14, pp. 372, May [3] Arunabha Ghosh and David R. Woltr, Jffry G. Andrws and Runhua Chn,, "broadband wirlss accss with WiMax/8O2.16: currnt prformanc bnchmarks and Futur potntial, IEEE Comm. Mag., vol. 43,no. 2, Fb. 25, pp [4] Fangmin Xu, Luyong Zhang, and Zhng Zhou, Intrworking of Wimax and 3GPP ntworks basd on IMS, IEEE Comm. Mag. vol. 45,no.3, Mar. 27, pp [5] CEPT ECC Rport 1, Compatibility studis in th band MHz btwn broadband wirlss accss (BWA) systms and othr srvics, Brn, Fb. 27. [6] CEPT ECC Rport 64, Th protction rquirmnts of radiocommunications systms blow 1.6 GHz from gnric UWB applications, Fb. 25. [7] Han-Shin Jo, Hyun-Goo Yoon, Jawoo Lim, Woo-Gh Chung, Jong- Gwan Yook, and Han-Kyu Park, Th coxistnc of OFDM-basd systms byond 3G with fixd srvic microwav systms, Journal of Communications. and Ntworks, Vol. 8, No. 2, pp , Jun. 26. [8] Rza Arfi, Margart LaBrcqu, IEEE and RF Charactristics, Intl Corporation, IEEE C /3, 25. Availabl : ISBN: IMECS 28