SOB-Propagasi pd Seluler

36 Pages·2014·0.41 MB·English

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
d = d - d
1 0
h
1
h2
Karakterisasi Propagasi
Mobile Radio Propagasi
Large-scale propagation Small-scale propagation
Signal Variation
Mean signal
•Theoretical approach
Time Time
•Empirical/prediction approach
spreading of variation of
•Statistical modelling
signal channel
(lognormal for large scale path
loss)
Model Teoretis Sederhana
Daya yang diterima melalui gelombang langsung :
2
1
P P G G
or t t r
4 d/
P = Daya pancar
t
G = Gain antena pemacar (BS)
t
G = Gain antena penerima (MS)
t
d = Jarak pemancar - penerima
= Panjang gelombang yang dipakai
Daya yang diterima melalui gelombang langsung dan gelombang pantul:
2
1
2
P P G G 1 cos jsin
r t t r
4 d/
Model Teoretis Sederhana
Dengan menurunkan persamaan dalam tanda mutlak, maka diperoleh
persamaan sederhana sebagai berikut :
2
h h
P P G G 1 2
r t t r d2
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 : P = f-n dengan 2 < n < 3
r
• Teoretis : penambahan tinggi antena pada MS : 6 dB/oktaf
empiris : pengurangan tinggi antena 1/2 - nya : gain berkurang 3 dB.
Theoretical approach
Free space formula
• Received power density at distance d when Tx antena gain G is
t
W G
P t t
r 4 d2
W G 2G
• Received power when Rx antenna gain G is W t t r
t r 4 d2 4
2 2
W c
• Ratio of Rx/Tx power is r G G G G
W t r 4 d t r 4 df
t
• Free space path loss is L [dB] = 32.45 + 20 log f + 20 log d
p(FS)
Plane earth propagation
Rx
Tx
d
h h
t r
Ratio of Rx/Tx power is
2 2
W W h h
2
r G G 1- ej r G G t r
W t r 4 d W t r d2
t t
• Path loss model plane earth is L = 120 + 40 log d –
p(PE)
20 log h – 20 log h
t r
Diffraction Loss
h (positif)
R
T d d x
x 1
2
d d
1 2
T R
x x
h (negatif)
• The difference of path length between direct and diffracted ray is
h2 d d
d 1 2
2 d d
1 2
Fresnel zone (path clearance)
• The phase difference when h << d and h << d is
1 2
2 d 2 h2 d d
1 2 v2
2 d d 2
1 2
with v is diffraction parameter which can be expressed as
2 d d
v h 1 2
d d
1 2
• The n-th Fresnel zone is area between Tx and Rx inside the
ellipsoide with radius of its cross section of r where
n
n d d
r h 1 2
n d d
1 2