sistem konvensional

Karakteristik khusus :
•Cakupan (coverage) sebuah sel sangat luas
•Daya pancar antena Base Station (BS) besar
•Antena BS ditempatkan cukup tinggi
•Satu frekuensi digunakan oleh satu sel
F1
F2
Reinitiating call
Kelemahan
Kapasitas kanal kecil
• Interferensi adjacent channel
• Daya pancar tidak efisien (boros)
• Mobile station (MS) yang pindah sel harus memulai
panggilan baru (reinitiating call)
Keuntungan
• Desain sistem dan infrastruktur sederhana
• Biaya awal cukup murah
SISTEM SELULAR
Karakteristik utama :
• Coverage sebuah sel kecil
• Daya pancar antena BS kecil
• Terjadi pengulangan frekuensi (frequency reuse)
• Pemecahan sel (cell splitting)
• Hand-off dan pengontrolan
terpusat
Sel Sistem
Selular
Sel Sistem
Konvensional
KONSEP AWAL WIRELESS
• Menggunakan Transmitter (Base Station) dengan
tower yang tinggi dan daya pancar yang tinggi
untuk coverage yang luas.
Pemancar ditempatkan
pada posisi yang tinggi
dengan jangkauan sampai
50 km lebih, seperti halnya
Broadcast Televisi dan
radio pemancar AM/FM.
Ilustrasi Jangkauan :
Pemancar dengan daya pancar 1 kilowatt pada frekuensi 450 MHz,
antenna gain 10 dBi pada ketinggian tower 70 meter.
Asumsi mendekati free space loss:
Redaman Lp
= 32.45 + 20 log d [km] + 20 log f [MHz]
= 32.45 + 20 log d [km] + 53
= 85.45 + 20 log d [km]
Bila sensitivitas penerima disyaratkan – 80 dBm untuk batas coverage dengan
gain antena penerima 3 dBi, maka:
- 80 dBm = 30 dBm + Gt – Lp + Gr
- 80 dBm = 30 + 10 – 85.45 - 20 log d [km] + 3
d [km] = 1037.55/20= 75.4 km
 Menggunakan beberapa transmitter (Base Station) daya dan
ketinggian yang rendah untuk memberikan coverage yang
terbatas.
 Menggunakan sekelompok sel (Cluster) untuk membagi
spektrum frekuensi ke dalam kanal yang berbeda.
 Radio pada BTS merupakan node network yang
langsung interface ke customer.
Konsep Konvensional
Konsep Selular
- High Power
- Large Cell
- Reinitial panggilan
- Kapasitas terbatas
- FDMA
- Omni Antena
- STKB
- Low Power
- Frekuensi Re-Use
- hand-off System
- Kapasitas besar
- TDMA/CDMA
- Sectored /Omni Cell
- GSM, CDMA
Cara mendisain Sel
 Definition of service area
 Depends on market, demographics, investment capital
Definition of traffic profile
 Forecast of potential subscribers and demand within
service area
Choice of reuse pattern
 Given traffic distribution and interference
requirements
Cara Mendisain Sel
 Location of base stations
 Chosen close to center of target regions, constrained by land,
available infrastructure, local regulations
 Cell radius depends on traffic distribution - smaller in denser
populations
 Radio coverage prediction
 Given topography and terrain, signal strength is predicted on
computer and/or measured in field
 Design checkup, field measurements, and system re-evaluation
Bentuk Sel
Secara teoretis terdapat beberapa bentuk sel, yaitu sel segi tiga, segi empat,
lingkaran, dan sel heksagonal (segienam).
Ingat cerita Madu lebah  Bentuk hexagonal merupakan yang paling efisien
dalam penggunaan ruang
Sel Segitiga
Sel lingkaran
Sel segienam
Sel Segiempat
Sel keadaan sebenarnya
Kelompok Sel
Seluruh daerah pelayanan dicakup oleh beberapa kelompok sel yang disebut
Cluster.
• Satu cluster terdiri dari beberapa sel (K sel).
• K bisa berharga 3, 4, 7, 9, 12, dst.
3
1
6
10
7
4
5
3
1
6
2
7
4
5
3
6
10
2
3
5
7
6
2
4
5
10
2
12
1
6
9
8
11
7
4
10
5
4
5
1
2
4
1
cell
no
12
11
3
1
6
9
8
7
12
4
5
10
6
9
8
11
11
K=7
K = 12
Pola Pengulangan Frekuensi
 Let S = total number of duplex channels
 k = number of channels per cell
 N cells = size of cell cluster (typically 4, 7, or 12)
 then S = kN and frequency reuse factor = 1/N
 If clusters are replicated M times, then total number of
channels (system capacity) = C = MkN = MS
 Choice of N determines distance between co-channel
cells and depends on how much interference can be
tolerated by mobile stations
Cell Design - Reuse Pattern ...
 Due to hexagonal geometry, choices of N must satisfy N = i2 + ij +
j2 where i and j are non-negative integers
 Given R = cell radius, distance D between neighboring co-channel
cells is
3
1
6
10
7
4
5
3
1
6
2
7
4
5
1
5
3
1
6
2
4
2
7
4
5
10
1
6
2
11
K=7
D  3NR
Cell Design - Reuse Pattern ...
 Example: Cell cluster size = 7, frequency reuse factor =
1/7, assume S = 490 total channels, k = 70 channels per
cell
B
G
C
Assume S = 490 total channels,
k = 70 channels/cell
A
F
B
G
D
E
C
A
F
G
D
E
C
Clusters are replicated M=3
times
D
C = 3x490 = 1470 total channels
B
A
F
E
 Frekuensi atau grup frekuensi bisa dipergunakan pada sel
yang terpisahkan dengan jarak pengulangan yang cukup.
 Sel-sel yang padat populasi dipecah (Cell Splitting) menjadi
beberapa sel baru (cluster baru) yang lebih kecil untuk menambah
kapasitas.








Cochannel Interference:
Cochannel interference is interference from a cochannel cell using
the same frequency
Results from frequency reuse scheme
Can be minimized by careful design (Accurate reuse distance)
Keep frequency separation between each site/sector in a cluster as to
avoid possible direct interference.
Adjacent Channel Interference :
Adjacent channel interference is interference from a nearby cell
using a frequency adjacent to one in use
Results from imperfect receiver filters
Can be minimized by careful filtering and channel assignments
Keep frequency separation between each channel in a cell as large as
possible
Misal I : 24 Frekuensi dalam 3/9 Cell Pattern
Freq
groups
A1
CH
B1
C1
A2
B2
C2
A3
B3
C3
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Misal II : 24 Frekuensi dalam 4/12 Cell Pattern
Freq
groups
CH
A1
B1
C1
D1
A2
B2
C2
D2
A3
B3
C3
D3
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Mekanisme panggilan
Base station
Mobile station
FOCC (forward
control channel)
Lock on strongest
channel for cont.
control data
RECC (reverse
control channel)
Send control data
to network
FVC (forward
voice channel)
Tune to assigned
frequency
RVC (reverse
voice channel)
Tune to assigned
frequency
Mekanisme panggilan
 Identification numbers:
 Mobile station’s 32-bit binary ESN (electronic serial
number) stored in ROM at time of manufacture

8-bit manufacturer code + 6-bit reserved (unused) + 18-bit
manufacturer assigned serial number
 Service provider’s 15-bit binary SID (system
identification number)

Transmitted by mobile station to identify system
 Mobile station’s 34-bit MIN (mobile identification
number) = 10-digit telephone number
Types of calls
Calls are defined by their point of origin and point of
destination. There are three basic types of calls:
•Mobile to Land (MTL)
•Land to Mobile (LTM)
•Mobile to Mobile (MTM)