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)