EL 675 UHF Propagation for Modern Wireless Systems. Henry L. Bertoni Polytechnic University

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1 EL 675 UHF Propagatio for Moder Wireless Systems Hery L. Bertoi Polytechic Uiversity

2 otext for Discussig Wireless hael haracteristics Frequecies above ~ 300 MHz (λ < m) adio liks i ma-made eviromets At least oe ed is amog the buildigs Lik legths Macrocells (20 km > > km) Microcells (2 km > > 00 m) Picocells/idoor ( < 00 m) Presece of may objects with sizes from 0 cm to 00 m Wave iteractios described by scatterig ad shadowig, rather tha resoaces by H.L. Bertoi 2

3 Need to Bridge Electromagetics (EM) ad ommuicatios (om) Electromagetics Deals with determiistic physical eviromet - seek precise solutio Field quatities are predictio output ommuicatios Deals with radom processes - seek statistical solutios equired iputs that are statistical measures of received sigal properties Must phrase the electromagetic solutios i ways that ca be used by commuicatio commuity Uderstad ad predict chael characteristics by H.L. Bertoi 3

4 omplimetary View Poits Electromagetic view poit Objects cause a rich set of ray paths coectig trasmitter ad receiver (multipath) ommuicatios view poit eceived sigal is the sum of delayed versios of the trasmitted sigal (multipath) Iterpretig the ray descriptio of electromagetic fields provides the chael characteristics EM propagatio govers the chael characteristics, but sigal processig govers what is observed Iterpret ray results to predict observed statistics by H.L. Bertoi 4

5 ommuicatio Systems Drive Descriptios of the adio hael How to characterize chael depeds o the radio system ad lik geometry All require kowledge of the power level Differet measures of multipath iterferece Narrowbad -- pulsed -- multi-frequecy systems Fast fadig -- delay spread -- coherece badwidth oherece distace -- agle spread --? Macrocells, microcells ad idoor picocells Differet cosideratios of multipath iterferece Slow fadig statistics ad rage depedece vs. determiistic variatios power level by H.L. Bertoi 5

6 EM Effects That Need to Be osidered Propagatio of waves through space eflectio, trasmissio ad diffractio Mechaisms by which fields get to locatios ot visible to the trasmitter adiatio ad receptio by ateas ay descriptio of radiatio by H.L. Bertoi 6

7 Basic ocepts Operatio of idividual radio systems is depedet o specific chael parameters -- all systems deped o received power ad iterferece. Frequecy re-use as a basis for icreased system capacity by H.L. Bertoi 7

8 Pre 980 Vehicular Mobile Telephoe System Sigle high base statio served etire metropolita area with N c frequecy chaels Frequecy chaels reused i other metropolita areas Because of physical separatio, desired sigal S much larger tha the iterferig sigal I S I ~00km ~00km by H.L. Bertoi 8

9 ellular Mobile adio: Frequecy e-use Withi a Metropolita Area Advaced Mobile Phoe System (AMPS) has 395 two-way chaels i two 25 MHz bads cetered at 850 MHz e-usig frequecy chaels i N sub-regios allows for 395N simultaeous phoe calls f f 395 chaels f 395 chaels f 395 chaels f f Metropolita egio f f f f by H.L. Bertoi 9 f

10 Dividig Sub-egios Ito N ells Allows Spatial Separatio of ells Usig Same Frequecy To Telephoe Network N = 7 frequecy re-use patter for hexagoal cells i each sub-regio Sub-regio f 5 f 7 f 4 ELL f 3 SITE f 6 f 6 MTSO MTSO assigs chaels to mobile ad coects to telephoe etwork f f 5 f 2 f 4 Sub-regio by H.L. Bertoi 0

11 ell Splittig to Icrease apacity ell have same umber of chaels (N / N ) o matter what size. Small cells accommodate higher subscriber desity by H.L. Bertoi

12 Number of ells Needed i Each Sub egio Determied by: I. Propagatio characteristics of the eviromet Simplest form of propagatio depedece P = P T A / P = eceived power P T = Trasmitted power A, = Amplitude ad rage idex depedet o frequecy, atea height, buildigs II. Miimum sigal to iterferece ratio for adequate receptio by radio system. For AMPS systems P/ I 50 (0log P/ I > 7dB) by H.L. Bertoi 2

13 Example of Liear ells Alog a Highway f f 2 f 3 f f 2 f 3 P I ell ell 2 ell 3 ell ell 2 ell 3 N = 3 euse Factor egio egio 2 Sigal Power for mobile at the cell boudary from base statio of ell, egio : P = P T A / Iterferece from base statio of ell, egio 2: I = P T A / [( 2N - ) ] by H.L. Bertoi 3

14 N for Liear ells for Differet age Idex Accoutig for iterferece oly from the earest co-chael cell or N P I P = I mi [ ] ( 2N ) [ + ( P/ I) mi ] 2 ( ) = 2N For ( P/ I) mi = 50 oditio N Free space 2 4 Flat earth by H.L. Bertoi 4

15 Frequecy e-use Patter for overig Area Symmetric patters based o hexagoal cells have all co-chael cells located o circles. There are six cells o the smallest circle of radius D, where D For symmetric reuse patters N = = m 2 3N. + m k + k where m, k are ay itegers. Lowest values are N = 3, 4, 7, 9, 2, 3, 9, 2, 25, 27, 3, D o-chael cells i the first tier by H.L. Bertoi 5

16 Frequecy e-use for S = A/ Sigal Variatio Sigal Power from base statios to mobile at the cell edge P = P T A /( ) Iterferece power from co-chael base statios i the first tier I = PT A + + ( D D ) D+ ( ) D+ D D+ D D D by H.L. Bertoi 6

17 N for Symmetric Patter of Hexagoal ell P I P = mi I D D D+ 05. = ( D) + D D If ( P/ I) 50, ad sice D= 3N, the mi = c + ( ) N 3N 3N + oditio N Free space 2 0 Flat earth by H.L. Bertoi 7

18 Iterferece Limited ellular Systems System desig is depedet o the propagatio characteristics For sigal depedece: S = A/ Free space propagatio: = 2 ad N will be large (N = 0) Propagatio over flat earth: = 4 ad N = 7 For ellular Mobile adio, N ~ 400 haels / cell Base Statio/,000 alls 2 ~ 4 ~250 4 ~ 60 ~ by H.L. Bertoi 8

19 Use Sectored ells to Accout for ealistic Propagatio Laws age idex is betwee 3 ad 4 for elevated base statio atea Additioal radom fadig of the sigal exists Use sectored cells to achieve P/ I > 50 Three sectors per cell is variatio of N = 2 frequecy re-use patter Patters for cell sectorizatio usig directive ateas. Sigle base statio serves three sectors by H.L. Bertoi 9

20 Effect of age Idex o Dow Lik System apacity for DMA System Same frequecy used to commuicate to subscribers i all cells. Differet code used for each subscriber. Sigals to subscribers i other cells act as iterferece. Subscribers i same cells have orthogoal codes, but multipath iterferece results i some iterferece. Subscriber ca receive same sigal from up to three base statios. For adequate receptio, I FP, where the value of F > depeds processig gai, voice activity factor, etc by H.L. Bertoi 20

21 P / I for Subscriber at Juctio of 3 ells for A / Propagatio Depedece Power receiveded from 3 earest base statios : P = 3P A/ Multipath iterferece due sigals set to other subscribers i cells A, B, : ( ) I = 3γ N P A/ 0 I = 3N P A/( 2 ) Iterferece due to sigals to subscribers i cells, 2, L, 6 : I 6N P A/ 7 T S T where 0< γ < Iterferece due to sigals set to subscribers i cells I, II, III : α S T β = S T ( ) 2 I A B 6 III 3 2 N S active subscribers i each cell II by H.L. Bertoi 2

22 Iterferece Power eceived From Base Statios Outside of the losest 2 Smear out base statios over a ifiite disk with a hole of radius to achieve a trasmitted power desity P = N P /(area of a cell). D S T I 3 4 B 7 II Area of cell = so that 2 2 NP S T PD = To fid the radius of the hole, set the area 2 of the hole π equal to the area of the 2 cells. Thus c 2 A III = = π by H.L. Bertoi 22

23 Iterferece eceived From Smeared Out Base Statios o the Ifiite Disk A Iterferece power = ID Tx power desity area elemet For circular symmetry NP A I d N P A S T d D = S T 2 4π ( 2π 2 )= If 2, the ID = If > 2, the 4π A 4π NP S T A ID = NSPT = 2 2 ( 2) 3 3 ( 2) 3 3 ( 2) ( 35. ) = NP A ( 2) S T ( 2)( 3. 5) = ( ) ( ) by H.L. Bertoi 23

24 P/I equiremet ad apacity Ns Total iterferece I = I + I + I + I 3 I F Sigal Power F PA T ( )=. For adequate receptio For 2: I = so that capacity N = 0 For : I P A NS NS > 2 = T N 3γ ( S ) ( 7) eceptio requiremet gives N D o α 2 γ ( 7) β D S N 2 ( 2)( 3. 5) ( ) s To see the role of, recall that F > ad suppose that γ = 0. If = 4: N ( F + 0. ) = 4. 47( F + 0. ) If = 3: N. 70( F + 0. ) ( 2)( 3. 5) S ( 2) S S F + γ by H.L. Bertoi 24

25 oclusios Moder systems employ frequecy re-use to icrease capacity Wireless systems employig frequecy re-use are iterferece limited It is ecessary to balace coverage ad iterferece Desig of Systems to accommodate a give umber of subscribers is depedet o the propagatio characteristics Higher values of rage idex allow for less base statios to cover a give area Other chael characteristics will ifluece system desig adom spatial fadig Doppler spread, time delay spread by H.L. Bertoi 25

V. Propagation Effects Observed Indoors

V. Propagation Effects Observed Indoors V. Propagatio Effects Observed Idoors Multipath fadig for arrowbad sigals Wall loss ad rage depedece Spatial fadig of pulsed sigals Delay spread ad coherece badwidth 1 Multipath Fadig for CW Sigals Fadig