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MODUL 2 SISKOMBER
SISTEM TELEPON
WIRELESS KONVENSIONAL
VS
SISTEM TELEPON
SELULER
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
Reinitiating call
F1
F2
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
Konvensional
Sel Sistem
Selular
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 - Low Power
- Large Cell - Frekuensi Re-Use
- Reinitial panggilan - hand-off System
- Kapasitas terbatas - Kapasitas besar
- FDMA - TDMA/CDMA
- Omni Antena - Sectored /Omni Cell
- STKB - 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 Segiempat
Sel lingkaran
Sel segienam
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.
10
3
4
5
11
12
9
4
8
7
6
10
cell
no
12
9
2
1
5
11
6
10
3
4
8
5
11
12
9
8
7
6
K = 12
10
1
5
6
3
4
2
1
5
7
6
10
3
4
2
1
5
11
7
6
3
4
2
1
5
7
6
4
2
1
K = 7
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
D 3NR
10
1
5
6
3
4
2
1
5
7
6
10
3
4
2
1
5
11
7
6
3
4
2
1
5
7
6
4
2
1
K = 7
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
A
E
C
D
G
F
B
A
E
C
D
G
F
B
A
E
C
D
G
F
Assume S = 490 total channels,
k = 70 channels/cell
Clusters are replicated M=3
times
C = 3x490 = 1470 total channels
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
Freq
groups
A1 B1 C1 A2 B2 C2 A3 B3 C3
1 2 3 4 5 6 7 8 9
CH 10 11 12 13 14 15 16 17 18
19 20 21 22 23 24
Misal I : 24 Frekuensi dalam 3/9 Cell Pattern
Misal II : 24 Frekuensi dalam 4/12 Cell Pattern
Freq
groups A1 B1 C1 D1 A2 B2 C2 D2 A3 B3 C3 D3
CH 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)