sistem komunikasi
Post on 31-Dec-2015
65 Views
Preview:
DESCRIPTION
TRANSCRIPT
Sistem Komunikasi
oleh Warsun Najib
04/19/23 Sistem Komunikasi 2
Pengantar
Telekomunikasi = komunikasi yang dipisahkan oleh jarak
Ada 3 komponen utama : Isyarat Komunikasi Kanal Komunikasi Jaringan Komunikasi
04/19/23 Sistem Komunikasi 3
Isyarat Komunikasi
04/19/23 Sistem Komunikasi 4
Isyarat Komunikasi Sistem Komunikasi harus menyediakan transmisi
yang bagus dengan frekuensi2 di mana spectrum-nya signifikan.
Kanal komunikasi harus bisa melewatkan isyarat dengan range frekuensi 300 Hz s/d 3.4 kHz agar isyarat suara (manusia) dapat terkirim
Sistem telepon menggunakanLPF 4kHz (Low-pass)
Komponen-komponen frekuensi di dalam gelombang isyarat menjadi Lebar Bidang Isyarat
04/19/23 Sistem Komunikasi 5
Isyarat Komunikasi Isyarat Musik mengandung komponen-komponen
frekuensi signifikan dari 20Hz sampai 20kHz. Untuk mengirimkan isyarat musik diperlukan LPF dengan
Bandwidth 15kHz Isyarat data biner, interval terkecil antara 0-1, T,
dinamakan interval pengisyaratan (signaling interval) 1/T dinamakan kecepatan isyarat (signaling rate) dengan
satuan bits per second [bps]. Lebar bidang transmisi pada sistem data biner secara
proporsional mendekati bit rate [High data rate = Wider BW of channel]
04/19/23 Sistem Komunikasi 6
Kanal Komunikasi
Ada 2 kanal komunikasi yang dominan dipakai saat ini
Sistem gelombang terpandu, menggunakan media fisik, seperti kable Twisted Pair Cable [ UTP, STP, 10BaseT] Coaxial Cable [thin-coax, thick-coax] Optical Fibers [OC-3, OC-12, OC-48]
Sistem radio, dengan gelombang elektromagnetis
04/19/23 Sistem Komunikasi 7
Kanal Komunikasi
VLF Very Low Frequency Less than 30kHz
LF Low Frequency 300kHz
MF Medium Frequency 3MHz
HF High Frequency 30MHz
VHF Very High Frequency 300MHz
UHF Ultra High Frequency 3GHz
SHF Super High Frequency 30GHz
EHF Extra High Frequency 300GHz
04/19/23 Sistem Komunikasi 8
Kabel Twisted Pair Total pelemahan (total attenuation) karena kabel
tergantung pada panjangnya Pelemahan (isyarat) juga tgt pada frekuensi, akan
meningkat dengan bertambahnya frekuensi. Untuk mempertahankan agar pelemahan isyarat tetap rendah, maka diperlukan equalizer [LPF: Low Pass Filter]
Untuk single pair cable [telephone cable], induktor-induktor dipakai untuk meningkatkan karakteristik transmisi untuk mendapatkan frekuensi respone yang lebih baik
Pada multi-pair cable, cross-coupling dapat menambah kapasitasi antara 2 konduktor. Hal ini menyebabkan suatu isyarat dapat terganggu karena ada kabel lain.
04/19/23 Sistem Komunikasi 9
Kabel Coaxial Dipakai untuk komunikasi yang memerlukan
Bandwidth yang lebih besar dari padaTwisted pair
Pelemahan (attenuation) meningkat kira-kira mendekati akar kuadrat frekuensi, sehingga untuk jarak yang jauh dibutuhkan penapisan
Efek kulit (“Skin Effect”), yaitu banyak isyarat dgn frekuensi yang tinggi akan hilang di dekat permukaan. Dibutuhkan penambahan ukuran kabel untuk BW yang lebih besar
BW Isyarat bisa mencapai 60MHz [140Mbps digital transmission]
Crosstalk sangat berkurang pada kabel coaxial
04/19/23 Sistem Komunikasi 10
Fiber Optis
Advantages Disadvantages
1. Economic : high BW, lowtransmission loss
2. Dimension : small size, lowweight
3. Chemical/Physicalproperties : resist chemicalcorrosion, high temperaturecapacity
4. Reliability : insensitive toelectromagnetic
5. Raw Material : abundant andcheap [sand]
Optical sources detectors,connector, couplers, andtest equipment are relativelycomplex and expensive atpresent
04/19/23 Sistem Komunikasi 11
Fiber Optis [1] Yang paling sederhana : inti fiber [diameter
sekitar 50 micron] dengan index bias n1, dilapisi fiber dengan index bias yang lebih kecil n2
Cahaya berjalan sepanjang inti
n1 sin1 = n2 sin2
sin1 = n2sin2 n1
04/19/23 Sistem Komunikasi 12
Snell’s Law of Refraction Critical angle = sin-1 n2/n1
n1 sin1 = n2 sin2
sin1 = n2sin2 n1
Where 1 = c and 2 =90
04/19/23 Sistem Komunikasi 13
Total Internal Reflection
04/19/23 Sistem Komunikasi 14
Multimode Step Index The pulse spreading places a limit on the
transmission rate over a fiber of given length Hence, the effective bandwidth of MMS fiber
depends on length and on the index difference [n1-n2] and it is normally used for a short haul systems
04/19/23 Sistem Komunikasi 15
Multimode Graded Index The fiber bandwidth is greatly improved with the
parabolic refractive index profile which gradually reduces from a maximum at the center to the core-cladding interface
The pulse spreading is very much reduced compared with a step index fiber because all rays paths having almost the same propagation delay
04/19/23 Sistem Komunikasi 16
Single Mode Step Index Single mode step index is known as “Monomode” By making a core diameter and index difference
sufficiently small, there will be only one possible mode travel in the fiber.
Thus, pulse spreading due to mode velocity difference cannot exist
Single mode step index is the fastest mode in optical communications
Due to the complexity of manufacturing, a single mode fiber optic cable is therefore the most expensive one
04/19/23 Sistem Komunikasi 17
Radio Systems An Electromagnetic wave is launched from an
antenna at the transmitter, propagates through the atmosphere an on arrival at the receiver is picked up by a receiving antenna
There are five major of Radio Propagation1. Line of Sight2. Surface wave or ground wave3. Ionospheric propagation4. Tropospheric scattering5. Free space propagation
04/19/23 Sistem Komunikasi 18
Radio Propagation Line of Sight
Omidirectional : is used for radio broadcasting Directional : is used for point-to-point radio communication
link Surface wave or ground wave
A radio wave travels along the curvature of the earth as a result of currents flowing in the ground
Ionospheric propagation Radio wave can refracted by the ionosphere and returned to
the surface some considerable distance from the transmitter This is because the gradual reduction with height of the
refractive index in the ionosphere
04/19/23 Sistem Komunikasi 19
Radio Propagation[1]
Tropospheric scattering Radio wave can be scattered by small particles in the
lower atmosphere to provide over-the-horizon radio communication
Free space propagation Wave can propagate without the aid of a physical
medium and this is how light from the Sun and other stars reaches the Earth
04/19/23 Sistem Komunikasi 20
Communication Network The communication cannot takes place in
isolation Each source and destination needs to have at
least one connection to make communication happen
The classic example of communication network are : Switched Network
Data NetworkIntegrated Services Digital Network
04/19/23 Sistem Komunikasi 21
Switched Network Switching center can produce all possible connections
required but not all at once The statistical properties of the communication requirements
of large user groups are relied upon to effect an economy The idea of a star connection can be extended to form a star
of star hierarchical network the central switching center must provide a sufficient
communication capacity to allow several message to be transferred simultaneously
This is achieved by combining several message waveforms to form a single composite message and it is known as “multiplexing” [TDM,FDM]
04/19/23 Sistem Komunikasi 22
Data Network A protocol is a well-defined procedure to enable
terminals/nodes to communicate effectively over a network
Ring topology allows any nodes to communicate to any other nodes by simply applying signals to the ring
This is essence of a form of Local Area Network [LAN] used for computer/data communications
Data circulate around the ring in packets, a packet being a sequence of binary digits
Protocol layering of OSI reference model provide the standard for data network
04/19/23 Sistem Komunikasi 23
Protocol Layering (OSI layer)
Layer1 Physical [Please]Layer2 Data link [Do]Layer3 Network [Not]Layer4 Transport [Throw]Layer5 Session [Sausage]Layer6 Presentation [Pizza]Layer7 Application [Away]
04/19/23 Sistem Komunikasi 24
ISDN Increasingly, both signal transmission and switching
are implemented using digital data technique and the telephone systems are rapidly moving to a digital network
In addition, there is an increasing need for the wide range of telecommunication services ; data transmission, E-mail, Video conference, etc.
In combining a various services and make these available on a single network with the continued expansion of digital transmission and switching
It gives rise to form an Integrated Services Digital Network [ISDN]
04/19/23 Sistem Komunikasi 25
Satuan ukuran
Common Unit of measurement : Gain & Loss
Current Gain [Ai] = Io/IiVoltage Gain [Av] = Vo/ViPower Gain [G] = Po/PiPower Loss [L] = Pi/Po
Note: G = 1/L or L = 1/G
04/19/23 Sistem Komunikasi 26
Satuan Decibels [dB] Power Gain expressed in dB : G[dB] = 10 log G
Gain G = Po/Pi G [dB]
100 +20 dB
1 0 dB
0.1 -10 dB
04/19/23 Sistem Komunikasi 27
Satuan dBw dan dBm dBw dan dBm digunakan untuk menyatakan
daya absolute dengan referensi 1 Watt (untuk dBw) dan 1milliwatt (untuk dBm)
Contoh, daya P=100W Dinyatakan dlm dBw = 10 log P/P[ref]
= 10 log 100W/1W= 20 dBw
Dinyatakan dlm dBm = 10 log P/P[ref]= 10 log 100W/1mW= 10 log 105mW/1mW= 50 dBm
Catatan : dBm = dBw + 30
top related