sob propagasi pd seluler

Propagasi Selular

Pendekatan Analitik dan Empirik

• Mobile Radio Channel Characterisation

• Theoretical approach

– Free space loss

– Plane earth path loss

– Diffraction loss

• Empirical/prediction approach

– Okumura-Hatta - Blomquist-Ladel

– Lee - Alsebrook

– Egli - Ibrahim Parson

• Measurement of large scale and application in coverage prediction

• Some examples

MODEL PROPAGASI SISTEM SELULAR

Model untuk memperkirakan redaman :

• Model teoretis

• Model empiris

• Model Lee

• Persamaan Umum Redaman Propagasi

• Perkiraan Titik demi Titik

• Model Okumura-Hatta

• Faktor Koreksi Undulasi

• Faktor Koreksi Kemiringan

Model Teoretis Sederhana

h1

h2

d = d1 - d0

Karakterisasi Propagasi

Mobile Radio Propagasi

Large-scale propagation Small-scale propagation

Mean signal Signal Variation

Time spreading of signal

Time variation of channel

•Theoretical approach

•Empirical/prediction approach

•Statistical modelling (lognormal for large scale path loss)


Daya yang diterima melalui gelombang langsung :

Pt = Daya pancar

Gt = Gain antena pemacar (BS)

Gt = Gain antena penerima (MS)

d = Jarak pemancar - penerima

= Panjang gelombang yang dipakai

Daya yang diterima melalui gelombang langsung dan gelombang pantul:

2

rttor/d4

1GGPP

2

2

rttr sinjcos1/d4

1GGPP


Dengan menurunkan persamaan dalam tanda mutlak, maka diperoleh

persamaan sederhana sebagai berikut :

Persamaan tersebut menghasilkan dua kondisi yang sesuai dg percobaan, yaitu :

• Path loss sebesar 40 dB / dekade (sebanding dengan d-4) atau 12 dB /

oktaf.

Penambahan path loss dari jarak d1 ke d2 = 40 log d2/d1

• Pertambahan gain sebesar 12 dB/dekade atau 6 dB/oktaf untuk setiap

penambahan ketinggian antena BS.

Penambahan gain antena dari h1 ke h2 = 20 log h2/h1

Sedangkan hasil yang tidak sesuai dg percobaan dan perlu faktor koreksi , yaitu:

• Tidak terdapat faktor interferensi (pjg gel.)

Rumus empiris : Pr = f-n dengan 2 < n < 3

• Teoretis : penambahan tinggi antena pada MS : 6 dB/oktaf

empiris : pengurangan tinggi antena 1/2 - nya : gain berkurang 3 dB.

2

221

rttrd

hhGGPP

Theoretical approach

Free space formula

• Received power density at distance d when Tx antena gain Gt is

• Received power when Rx antenna gain Gt is

• Ratio of Rx/Tx power is

• Free space path loss is Lp(FS) [dB] = 32.45 + 20 log f + 20 log d

2

tt

rd4

GWP

4

G

d4

GWW r

2

2

tt

r

2

rt

2

rt

t

r

df4

cGG

d4 GG

W

W

Plane earth propagation

Ratio of Rx/Tx power is

• Path loss model plane earth is Lp(PE) = 120 + 40 log d –20 log ht – 20 log hr

TxRx

ht hr

d

2

2

rt

rt

t

r2j

2

rt

t

r

d

hhGG

W

We-1

d4GG

W

W

Diffraction Loss

• The difference of path length between direct and diffracted ray is

TxRxd1 d2

h (positif)

Tx Rx

d1 d2

h (negatif)

21

21

2

dd

dd

2

h d

Fresnel zone (path clearance)

• The phase difference when h << d1 and h << d2 is

with v is diffraction parameter which can be expressed as

• The n-th Fresnel zone is area between Tx and Rx inside the

ellipsoide with radius of its cross section of rn where

2

21

21

2

v2dd

dd

2

h2d2

21

21

dd

dd2hv

21

21

ndd

ddnhr

Diffraction Loss

Diffraction loss can be computed from

When v=0 (h=0) diffraction

loss is 6 dB above free space loss

When v=-0.8 diffraction

loss is negligible (56 % of

The 1st Fresnel zone is clear)

v

0

4

8

12

16

20

24-3 -2 -1 10 2 3

Empirical Prediction Approach

• Based on signal measurement

– Okumura - Blomquist-Ladel

– Lee - Alsebrook

– Egli - Ibrahim-Peterson

• Mathematical Formulation based on signal measurement

– Hatta (Japan)

– COST-231 (Europe)

Okumura Model

• Okumura develop propagation model based on extensive signal

measurements in Kanto (near Tokyo) areas.

• Propagation environments are classified into:

• Urban areas (highly dense populated areas)

• Suburban areas (moderate population)

• Open/rural areas (few population, rare building/structure)

• Okumura develop propagation loss (mean and variance) in the form of

curves of propagation loss vs distance for different parameters, such as

frequencies, antenna heights, ground curvature/undulation, etc).

• Okumura curves often used by others to construct mathematical models.

• Masaharu Hatta makes use of Okumura model and transform Okumura curves into Hatta mathematical formulas, therefore the name of Okumura-Hatta model.

• Project COST - 231 in Europe further develop mathematical formula of Hatta model for use in DCS/PCS frequencies (1800 MHz).

• Hatta model is valid for urban area, and corrections factors are provided for suburban and open areas.

• Hatta dan COST-231 models are the most common models used in cellular system due to their simple use with reasonable accuracy.

Hatta and COST-231 Models

Okumura –Hatta Model

Lp(open) = Lp(urban) –4.78(logf)2 + 18.33 log f – 40.94

For urban area:

Lpu [dB] = 69.55 + 26.16 log f – 13.82 log hb – a(hm) + (44.9 – 6.55 log hb) log d

Model Okumura - Hatta• Okumura melakukan percobaan di daerah Tokyo dg menggunakan :

• Tinggi antena BS : 200 m

• Tinggi antena Ms : 3 m

• Hatta menyatakan hasil percobaan Okumura dalam bentuk persamaan :

KLASIFIKASI

DAERAH

PELAYANAN

RUMUS REDAMAN PERAMBATAN

Urban Area

Lu = 69,55 +26,16 log fc – 13,82 log hb – a (hm) + (44,9

– 6,55 log hb) log R……………..(dB)

Faktor koreksi untuk tinggi antena stasiun mobil

yang bergantung kepada tipe daerah urban yang

dibagi sebagai berikut :

Medium – small city :

a (hm) = (1,1 log fc – 0,7) hm – (1,56 log fc – 0,8) ….(dB)

Large City

a (hm) = 8,29 (log fc 1,54 hm)2 – 1,1 , fc < 200 MHz

a (hm) = 3,2 (log fc 11,75 hm)2 – 4,97 , fc > 400 MHz

Sub Urban Area Lsu = Lu (urban area) – 2 [log (fc/28)]2 – 5,4 ….(dB)

Open Area Lo = Lu (urban area) – 4,78 (log fc)2 + 18,33 log fc –

40,94 ….(dB)

Keterangan :

fc = frekuensi kerja yang berharga : 150 MHz – 1500 MHz

hb = tinggi antena stasiun tetap (RBS) : 30 m – 200 m

hm = tinggi antena stasiun mobil (MS) : 1 m – 3 m

R = jarak pemancar penerima : 1 km – 20 km

Model Lee...

Dua pendekatan umum untuk menentukan 2 parameter tsb. :

• Jika tipe daerah atau struktur bangunan tidak sama dengan hasil

pengukuran yang telah ditabelkan di atas, maka harus dilakukan

pengukuran.

r = jarak dari BS ke MS dlm km

ro = jarak dari BS ke MS 1,6 km.

= konstanta propagasi dalam dB/dekade

o = faktor koreksi parameter terhadap keadaan sebenarnya, antara lain

parameter : tinggi antena BS ( 1), tinggi antena MS ( 2), daya pancar BS

( 3), gain antena BS ( 4), gain antena MS ( 5).

)dB(f

flogn

r

rlogP

)linier(f

f

r

rPP

o

oo

ro

o

n

oo

ror

Model Lee...

Kondisi standar yang digunakan Lee, dalam mencari konstanta propagasi :

• Frekuensi fo : 900 MHz

• Tinggi BS : 30,48 m (100 ft)

• Daya pada antena BS : 10 Watt (40 dBm)

• Gain antena BS : 6 dB terhadap dipole

• Tinggi antena MS : 3 m (6 ft)

• Gain antena MS : 0 dB terhapadap dipole

Dengan menggunakan data tersebut, Lee melakukan percobaan di berbagai

daerah dengan hasil seperti digambarkan pada gambar di halaman berikut.

Model Lee(Persamaan Umum)

Perkiraan area ke area menurut Model Lee membutuhkan 2 parameter :

• Daya pada jarak tertentu biasanya 1,6 km / mil (Pro)

• Kemiringan redaman atau path loss slope ( ).

Dua pendekatan umum untuk menentukan 2 parameter tsb. :

• Membandingkan tipe daerah / struktur bangunan

Lee Model

Lee formulated the path loss of being

Lp[dB] = L0 + log d ; with L0 is path loss at d = 1 km and is the

path loss slope.

Area L0 [dB] (dB/decade]

Free space 91.2 20

Open/rural area 90.4 43.5

Suburban area 104.3 38.4

New Ark 105.5 43.1

Philadelphia 112.8 36.8

New York City 117.5 48

Tokyo 128.1 30.5

Egli Model

Based on Plane Earth Theoretical model with correction factors

Lp [dB] = 120 + 40 log d – 20 log ht – 20 log hr +

• Where ht and hr is Tx and Rx antenna height respectively, d is path length

and = 20 log (f/40) in dB for correction of carrier frequency.

• Egli model is derived from propagation measurement using the carrier

frequencies of between 90 and 1000 MHz.

• Egli model is therefore has a limited application for such an area which can

be considered as a plane earth situation.

Blomquist-Laded Model

• This model considers the combination of free space, plane earth,

and diffraction loss models together.

• The model is expressed as

Lp [dB] = Lfree space +{(Liplane earth – Lfree space)2 + (Ldiffraction)2}1/2

• For more than one diffraction mechanisms, diffraction loss is

computed using multiple diffraction loss from Bullington, Epstein

Peterson, and Deygout models.

• For situation with no diffraction, this model become the plane earth

model

Alsebrook Model

• Based on measurement in British cities areas (Birmingham and Bath at frequencies

of between 75 and 450 MHz.

• For flat areas Lp [dB] = Lplane earth +LB + , where LB is correction for building and is

correction for UHF frequencies.

• For hilly areas Lp [dB] = Lfree space +{(Liplane earth – Lfree space)2 + (Ldiffraction)2}1/2 + LB

+

• Correction for building is

– Where ho is average height of building, hm is mobile antenna height, effective

width of street, and f is carrier frequency

• Correction of carrier frequency is increasing linearly from 0 to 15 dB as frequency

increases from 200 to 500 MZ

1610Wfx548

hhlog20]dB[L

3

m0

B

Ibrahim-Peterson Model

• Based on measurement in London areas at freq 168 – 900 MHz with Base

antenna height 46 m.

• Semi empirical formula based on regression analysis from signal

measurement, which is then correlated with plane earth model for

corrections.

• Path loss model is Lp [dB] = 40 log d – 20 log(hbhm) +

= 20 + f/40 +0.18 L – 0.34 H +K

Where

L = land use factor (percentage of area covered by building)

H = terrain factor (different of average ground height between Tx and Rx)

K = urbanisation factor (K = 0.094 U – 5.9 [dB]), U is the percentage of building

having 4 or more floors)

Path Loss Measurement

The received signal looks like this

• The proper measurement distance is L = 2 because if measurement

distance is too short may not give the mean value (signal still

varying) and if too long may average out large scale (large scale

variation is smoothed out).

• The number of measurement samples n >36 for 90 % confidence

interval.

2 wavelength

Regression from Measurement Data

Select several locations at d1

And perform measurement

For the mean path loss

Repeat for d2 and d3, etc

Plot the mean value of

Path loss as a function of

Distance

See next page

Cell site (Tx)

d1 d2

d3

Obtain the Mean and Std Deviation

Measurement for urban, suburban,

and open areas

At a constant radius,

path loss can be difference

From regression we can

obtain the best fit for the mean

as well as the std deviation

around the mean

Example for urban : path loss

Slope = 33.2 dB/decade and

Std dev. = 7 dBDistance d [km]

Path

loss [d

B]

urban

suburban

open

x x

x

x x

x x x

x x

x x

x x

x x

o o o

o o o

o o

o o

o o

o o

o

o o

# #

# #

# #

#

3 4 6

79

85

75

Application in Coverage prediction

• Example at distance d2 = 4 km (see previous page for urban area)

• Path loss at 4 km is 79 dB.

• This path loss is designed for the mean

value at 50 % confidence level

• Since std. Dev for urban in

this example is 7 dB,

therefore to obtain

confidence level of 84 % (1 )

need margin of 7 dB and

for confidence of 97.7 % (2 )

need margin of 14 dB

Cell site (Tx)

d1 d2d3

JARAK JANGKAU BTS

• Contoh data :

Frekuensi kerja BS : 800 MHz

Sistem modulasi FM dengan F : 12 KHz

Daya pancar BS : 10 Watt

faktor derau : 7 dB

Tinggi antena BS : 40 m

Tinggi antena MS : 1,5 m

Gain antena BS : 8,5 dB

Gain antena MS : 2 dB

Redaman feeder di BS : 3,2 dB per 40

a. Menghitung nilai ambang penerimaan dg keandalan thd. Fading cepat

• kTB = 10 log (1,38 x 10-23 . 300 . 2 (12+3,4) )

= - 128,9 dBm

• Faktor derau= 7 dB

• FM threshold = 10 dB

Perhitungan Jarak Jangkau RBS

• Cadangan fading cepat = 8,7 dB

(untuk keandalan 90 %)

TOTAL = - 103,2 dBm

b. Nilai ambang penerimaan dengan keandalan terhadap fading lambat

Nilai ambang sesungguhnya (misal keandalan didasarkan pada 90% fading

cepat dan 90% pada fading lambat) dihitung sbb. :

md = nilai rata-rata sinyal penerimaan pada jarak d dari BS (logaritmik, dBm)

dBm36,94mMaka

;dB8,6urbandaerah

m2,10330,1

mrx

30,1x)x(erf19.0

)x(erf1)rr(P

d

ddd

od


c. Redaman di daerah Urban (contoh di daerah urban) :

Nilai fc = 800 MHz,

Tinggi antena BS hb = 40 m

Tinggi antena MS hm = 1,5 m

Redaman dapat dinyatakan sebagai fungsi radius sel sbb. :

L = 69,55 + 26,16 log (800) - 13,82 log 40 - 0 +

(44,9 - 6,55 log (40)) log R

L = 123, 35 + 34,4 log R

d. Jarak jangkau sebuah BS

Power (P) Loss (T) Redaman perambatan (L)

Atx Arx


d. Jarak jangkau sebuah BS

Jarak jangkau dihitung sbb. :

Pr = Pt - T + Atx - L + Arx - a

-94,36 = 40 - 2,5 8,5 - L + 2 - 3,2

L = 139,16

Dari persamaan di halaman sebelumnya (49) diperoleh :

L = 123,35 + 34,4 log R

R = 2,88 km.

Jarak jangkauan BS tersebut dengan contoh data sederhana yang disajikan di

atas menghasilkan radius sel = 2,88 km.

Pada kenyataan tentunya tidak sesederhana seperti contoh perhitungan disini.

Contoh persoalan : Model Lee(Perhitungan Titik Demi Titik)

• Kondisi Dengan Penghalang

Contoh :

Terdapat kontur sbb. :

Frekuensi kerja sistem tersebut = 900 MHz.

Hitung redaman total sistem dengan penghalang tersebut.

5 m

3 m

35 m

25 m

60 m

hp

4 k m 6 k m

Jawaban : Soal Model Lee

(Perhitungan Titik Demi Titik)

• Kondisi Dengan Penghalang

Jawab :

dB18,121dB14dB18,107rambatredamanMaka

dB18,107900log2010log201,28a

dB14adiperoleh04,1VdiperolehgrafikDari

04,16000

1

4000

1

3/1

28,20V

m3/1900

300gelombangPanjang

m8,20dihitunghp

o

z

Example

• A mobile terminal located at the cell’s edge is receiving signal from a BTS in urban area. The minimum signal level (receicer sensitivity) of the MS is – 100 dBm. BTS Tx power is 10 W at 40 m high, feeder loss at BTS is 7 dB, BTS Tx antenna gain is 13 dB, mobile Rx antenna gain is 3 dB, handset body loss is 3 dB. Operating carrier freq is 1.8 GHz.

– Compute cell radius using Okumura-Hatta Model.

– If it were in free space condition, compute the received signal level at the

MS.

• AnswerRx_min = Tx – Lf + Gt – Lu +Gr – LB Lu=40 -7+13 +100+3-3 = 146 dB

Hatta Lpu=69.55+26.16 log(1.8x103)-13.82 log(40) + [44.9-6.55 log(40)] log R

146 = 154.7 – 22.14 + 34.4 log R R = 2.5 km (cell radius).

Lfreespace = 32.45 + 20 log (1.8x103) + 20 log (2.5) = 105.5 dB

Rx = 40 – 7 + 13 – 105.5 + 3 – 3 = - 59.5 dBm (Received signal level if freespace)

Ringkasan

• Propagation path loss (Large scale path loss) is a measure of path loss expressed in terms of the mean value and its variation around the mean.

• Large scale path loss is well known to be lognormally distributed (Normal distribution in dB scale).

• Large scale path loss is useful for prediction of the received signal, coverage prediction, and hand-off control.

• Reliability (confidence level) of the received signal can be computed when path loss slope and the std. dev. of the path loss are known

sob propagasi pd seluler

Documents