Efficient Pathloss Model for determining Mobile Radio Link Design

Transcription

1 15 IJSRSET Volume 1 Issue 3 rin ISSN : Online ISSN : Theme Secion: Engineering an Technology Efficien ahloss Moel for eermining Mobile Raio Link Design Alor M.O Deparmen of Elecrical/Elecronic Engineering, Enugu Sae Universiy of Science an Technology, ESUT, Nigeria ABSTRACT The focus of his paper is on efficien pahloss moel for eermining mobile raio link esign. A fixe 3G BTS ransmier was also use o generae he aa. Log-normal shaowing moel was use o analyse he aa. The calculae aa were compare using pah loss exponen an sanar eviaion. They were foun o be wihin he specifie range for urban area cellular raio environmen like Enugu urban. The resul is a provision of a link esign nework wih an aequae coverage an qualiy of service. Keywors: Efficien ahloss Moel, Raio ropagaion Mechanisms, ropagaion ah Loss Moels, Free Space ropagaion Moel, Two-Ray Moel, Mobile Raio I. INTRODUCTION Raio wave is a ype of elecromagneic raiaion (hese are nohing bu oscillaions which propagae wih he velociy of ligh. Approx. =3 18m/s) in free space.[1] Oher forms of elecromagneic waves inclue infrare, visible ligh, ulra-viole, X-rays an gamma rays []. Mobile raio communicaion sysems such as corless elephone, han hel walkie alkie, cellular an pager elephones rely on he propagaion of raio waves hrough air an space for heir operaion. These raio waves ravel along ransmission line an waveguies o an from anennas. The mobile raio link places funamenal limiaions on he performance of wireless communicaion sysem accoring o wireless communicaion [3] The anenna a a mobile erminal is very small, so obsacles an reflecing surfaces in viciniy an pah of anenna have a subsanial influence on he characerisics of he propagaion pah beween he base saion ransmiing anenna an he mobile anenna. The ransmission pah beween he ransmier an he receiver may vary from irec line-of-sigh (LOS) o one ha is heavily obsruce by builings an opology. This is because obsacles an reflecing objecs in a mobile raio environmen grealy reuce he average signal srengh receive by a mobile sysem. II. METHODS AND MATERIAL. The raio propagaion mechanisms The raio propagaion mechanisms which impac propagaion in a mobile communicaion sysem are: i. Reflecion ii. Diffracion iii. Scaering Mobile communicaion coniions operaion is qui severe; he reason is ha mos cellular raio sysems which operae in urban area operae wih no irec Lineof-sigh (LOS) pah beween he ransmier an he receiver. The presence of high builing creaes severe iffracion loss. The pah loss is generally he mos imporan parameer preice by propagaion moels base on he physics of reflecion, iffracion an scaering. Reflecion occurs when elecromagneic waves impinges on obsacles wih larger wavelengh. Diffracion occurs when he raio pah beween he ransmier an receiver is obsruce by a surface ha has sharp eges. The seconary waves resuling from he obsrucing surface are presen hroughou he space an even behin he obsacle given rise o bening of waves aroun he obsacle, even in he absence of line-of-sigh pah beween he ransmier an receiver. IJSRSET15135 Receive: 8 June 15 Accepe: 16 June 15 May-June 15 [(1)3: 7-76] 7

2 Diffracion herefore, remains an imporan phenomenon where signal ransmission hrough builings is virually impossible. r A e GGr 4 Scaering occurs when objecs are of imensions ha are in he orer of a wavelengh or less of he elecromagneic waves. Scaere waves are prouce by irregular objecs such as walls wih rough surface, furniure, foliage ec..1 ropagaion pah loss moels ah loss is efine as he ifference in ecibel beween he effecive ransmie power an he receive power an perhaps inclues he effec of anenna gains. I represens signal aenuaion as a posiive quaniy measure in B [4]. Some of hese moels are iscusse in his secion. A. Free Space ropagaion Moel Free space propagaion environmen is a region ha is free of all obsacles an objecs ha migh absorb or reflec raio frequency energy. Free space propagaion moel assumes an ieal propagaion wih an isoropic anenna raiaing is energy equally in all irecions o an infinie isance. If he raiaing elemen is generaing a fixe power o an ever expaning sphere, he power ensiy on his hypoheical sphere a a isance from he source is given by equaion 1 below: G 1) 4 Where : is he ransmie power G is he ransmiing anenna gain is isance from he source. If a receiving anenna wih gain G r is place a his isance,, he power exrace by he anenna can be calculae using equaions () r = () A e () Where, r is he receive power The free space ransmission loss or propagaion loss equaions for Omni irecional ransmi an receive uniy gain anennas separae by meers is obaine as: r GG 4 For Omni irecional an uniy gain anenna, free space pah loss is given in equaion (6) which is also known as Friis equaion. r r 4 c 4f In erms of pahloss in B, l[ B] 1log r Where, L is ah loss in [B] is he ransmie power r is he receive power The free space pah loss equaion is now: L [B] = 3.44 log f [MHz] log [km] (8) B. Two-Ray Moel The wo-ray moel is use when a single groun reflecion ominaes he mulipah effec, as illusrae in Figure1. The receive signal consiss of wo componens: he LOS componen or ray, which is jus he ransmie signal propagaing hrough free space, an a reflece componen or ray, which is he ransmie signal reflece off he groun. A e is he effecive area of an isoropic anenna A e 4 (3) Figure 1: Two-Ray Moel. 71

3 C. Mobile Raio Link Communicaion engineers are generally concerne wih he applicaion of wo main raio channel links. These channel links are he mobile raio link parameers an ime ispersion naure of he channel. The mobile raio link parameers consis of he pah loss exponens (n) or pah loss rae an he sanar eviaion ( ) abou is mean value. The pah loss exponen inicaes he rae a which propagaion (pah) loss increases wih isance, while he sanar eviaion accouns for he ranom shaowing effecs which occur over a large number of measuremen locaions which have same ransmier-receiver separaion, bu have ifferen levels of cluer on he propagaion pah [5]. The emphasis of his research is on he eerminaion of mobile raio link esign for a given propagaion environmen using pah loss moel. These parameers are use in link buge esign o eermine funamenal quaniies such as ransmi power requiremens, coverage areas, baery life an he analysis of pah losses in any mobile raio environmen. The ime ispersive parameers of a mulipah channel are he mean excess elay, rms elay sprea an he maximum excess elay sprea [6]. The ime ispersive naure of he channel eermines he maximum aa rae ha can be ransmie wihou equalizaion.. racical link buge eerminaion using he pah loss moels Mos raio propagaion moels are erive using a combinaion of analyical an empirical mehos. The empirical approach is base on fiing curves or analyical expressions ha recreae a se of measure aa. This has he avanage of implicily aking ino accoun all propagaion facors, boh known an unknown, hrough acual fiel measuremens. However, he valiiy of empirical moels a ransmission frequencies or environmens oher han hose use o erive he moel can only be esablishe by aiional measure aa in he new environmen a he require frequency. Over ime, some classical empirical moels have emerge, which are now use o preic boh largescale an meium-scale coverage for mobile communicaion sysem esign. The wo pracical mobile raio link esign echniques are: i. The log-isance pah loss moel. ii. The log-normal pah loss moel. (i) The log-isance pah loss moel Boh heoreical an measuremen base propagaion moels inicae ha he coverage receive signal power ecreases logarihmically wih isance, wheher in ouoor or inoor raio channels. The average largescale pah loss for an arbirary ransmi-receiver (T-R) separaion is expresse as a funcion of isance by using pah loss exponen (n) as I( ) ( / o ) n Or L( B) L( ) 1nlog( / ) Where n is he pah loss exponen, is he close-in reference isance which is eermine from measuremens close o ransmier an is he T-R separaion isance. The value of n epens on he specific propagaion environmen. For example if free space is an when obsrucions are presen, n will have a larger value as shown in able 1 [7] I is imporan o selec a close in reference isance ha is appropriae for he propagaion environmen. In large coverage cellular sysems, 1km reference isance is commonly use, whereas in microcellular sysems smaller isance such as 1m is commonly use. The reference isance shoul always be in he far fiel of he anenna so ha near fiel effec oes no aler he reference pah loss. The reference pah loss L( o ) is calculae using free space pah loss formula given equaion (1) or hrough fiel measuremen a isance ( o ). Table 1 lis pah loss exponens obaine in mobile raio environmen Table 1: ah loss exponens for ifferen environmens Environmen ah loss Exponen, n Free space 7

4 Urban cellular/cs.7 o 4. Shaowe urban 3 o 5 cellular/cs Inoor LoS 1.6 o 1.8 Obsruce Inoor 4 o 6 Obsruce in facories o 3 having a specific T-R separaion an his moel may be use in compuer simulaion o provie receive power levels for ranom locaions in communicaion sysem esign an analysis [8] (ii) The log-normal shaowing moel III. RESULTS AND DISCUSSION The log-isance pah moel oes no consier he fac ha he surrouning environmenal cluer may be vasly ifferen a wo ifferen locaions having he same T-R separaion. This leas o measure signals, which are vasly ifferen from he average value preice by (1). The log-normal isribuion escribes he ranom shaowing effecs which occur over a large number of measuremen locaions which have he same T-R separaion, bu have ifferen levels of cluer on he propagaion pah. This phenomenon is referre o as lognormal shaowing. Log-normal shaowing implies ha measure signal level a a specific T-R separaion have a Gaussian (normal) isribuion abou he isanceepenen mean of equaion 1 where he mean signal levels have values in B. The sanar eviaion of he Gaussian isribuion ha escribes he shaowing also in B. Measuremens have shown ha a any value of, he pah loss L() a a paricular locaion is ranom an isribue log-normally (normal in B) abou he mean isance epenen value. i.e. L( )[ B] L( B) x The real ime measuremens were conuce using CDMA 1x BTS locae a Heaquarer opposie Teachers House Enugu as he es ransmier locaion. The eigh raial fiel measuremens were carrie along specific separaion isances for Norh, Wes an Eas roues. The fiel measuremen were carrie ou using 3G CDMA echnology raher han he GSM because of is avanages such as higher banwih capaciy, highspee packe aa an mulipah faing reucion. (A) Daa Gahering The fiel measuremen were carrie ou using a raio propagaion simulaor calle ebug access equipmen global posiioning sysem (GS) an simulaion of free space moel equaion. The GS inicaes he T-R separaion isances while he ebug access equipmen measure receive power levels a various isances away from a CDMA 1xBTS. The simulaion was also one o compare he receive signal levels a (11) he eigh raial isances. L( )[ B] L( An, ) 1nlog 4. Sysem Specificaion x (1) The sysem esign for he 3G CDMA BTS a various separaion isances an he receive power are specifie as follows: r( )[ Bm] [ Bm] L( )[ B] Where x is a zero-mean Gaussian isribue ranom variable (B) wih sanar eviaion also in B. The close in reference isance ( ), he pah loss exponen (n), an he sanar eviaion ( ) saically escribe he pah loss moel for an arbirary locaion (13) A. Base Transceiver Saion BTS ransmi power = 1w BTS anenna gain = B BTS ransmier frequency = 881.5MHz Heigh of BTS anenna = 45m 73

5 B. Mobile Saion (MS) MS ransmi power = 3MW MS Sensiiviy less han = 14B MS anenna gain = B MS ransmier carrier Frequency = 841.5MHz Heigh of MS anenna = 1.6m Average cell raius = 5km The isance beween BTS = 9km The eigh receive power measuremen aken a various isances raially along Norh, Wes an Eas were esigne as follows using (14) an (15) ( G Gr i ) 1log 4 i i( ) 1nlog where, = T-R separaion isance. = close in reference isance x = zero-mean Gaussian (normal) isribue ranom variable (B) wih sanar eviaion, (B). From he parameer, =1w G =B = 1 G r = B = 1 = 1m f = =.34m From equaion 14 i( ) 111(.34) 1log 4 (1) i ( ) = 41.36Bm Then using fiel measuremen a a close in reference isance ( ) of 1m, i ) = -4Bm. ( So, recall equaion (15) an subsiue, i 4 1n log 1 For 1m, 1 4 1n i = -4 For m, (14) 4 4 (15) 1n 1 log 1 4 1n log 1 = 4 3n For 5m, n log 1 3 = 4 7n For 1m, 4 = 4 1n For m, 1 log n log 1 5 = 4 13n For 3m, n log 1 6 = 4 15n For 4m, 7 4 1n 7 = 4 16n For 5m, log n log 1 8 = 4 17n The Table for he evaluaion of MSE is shown in able Base on he fiel measuremen he esimae receive power for he specifie isances were foun using (15). 74

6 Figure : RSSI along Norh 6878 n 194 n = The pah loss exponen for he mobile raio link is 3.1 Table 3 : Receive power measuremen aken a various isances along Norh, Wes an Eas Roues Figure 3: RSSI along Wes Figure 4: RSSI along Eas The plo of he receive signal srengh along he ifferen roues is shown in Figure, Figure 3,Figure 4 an Figure 5 Figure 5: lo of he Receive ower along he specifie roue 75

7 IV. CONCLUSION Mobile raio link esign using pah loss moel can be easily esigne using parameers of base ransceiver saion (BTS), mobile saions (MS) an he Log-normal shaowing pahloss moel. In his paper, he pah loss exponen an he sanar eviaion ue o ranom shaowing in Enugu urban are 3.1 an 5.65B respecively. These Mobile raio link esigns were eermine using he Log-normal shaowing pah loss moel. The pah loss exponen value shows he rae a which he pahloss increases wih isance in a CDMA 1x. This pah loss moel is very goo for preicing isance epenan receive power in obsruce environmen. The accurae qualiaive unersaning of he raio propagaion using pah loss moel as a funcion of isance from where he signal level coul be preice is essenial for reliable wireless sysem esign. V. REFERENCES [1] Michael J. Marin, (6), Raio frequency hysics: he rules are changing, IBM Canaa, January 6. [] Walisch,J. e al,(8)" A heoreical moel of uhf propagaion in urban environmens",ieee Transacions on Anenna an propagaion pp [3] Rappapor T.S.,(6)"Wireless communicaion principles an pracice"earson Eucaion. [4] Gupel V,e al,(8) "Efficien pahloss preicion in mobile wireless communicaion Neworks, proceeing of worl Acaemy of Science, Engineering an Technology, Vol 36. [5] Smih M.S. e al,()"a new mehoology for elivery pahloss moel for cellular rive es aa. [6] Simon Haykins Communicaion Sysems-John Willy & Sons,Fourh eiion [7] Kahryn Oliver, (4), Inroucion o Auomaic Design of Wireless Neworks, Cenre for Inelligen Nework Design, Cariff Universiy, UK, 4. [8] Tansu A., Xingzhe F., Tamer B., Mura A., an Jon T.W, (4), ower Conrol for Mulicell CDMA Wireless Neworks: A Team Opimizaion Approach, Universiy of IIIinois a Urbana-Champaign, 4 76