22

DASAR TELEKOMUNIKASI

2-2

Transmission media

I. Guided media / wireline metalik atau optis

karakteristik yang jelas sangat berbeda

II. Unguided media / wireless

2-3

I. Guided media 1. Transmisi metal (metallic transmission)

a. Twisted pair

1. Kategori 3 ( 4 pairs unshielded telephone wiring – dgn pjg kabel bisa beberapa mil utk transmisi 3000 Hz, utk DSL standarnya lebih kecil

2. Kategori 5 ( 4 pairs shielded LAN wiring, utk ethernet 10 Mbps diatas 100 m)3. Kategori 5E (4 pairs shielded LAN wiring, dispesifikasikan utk full duplex 10

Mbps Ethernet, tp juga bisa utk ethernet 100 Mbps diatas 100 m)4. Kategori 6 (4 pairs shielded LAN wiring, utk 100 Mbps 100 m menggunakan 1

pair utk masing2 arah dikomersialkan utk ethernet 1 Gbps dengan 2 pairs utk masing2 arah.

Keuntungan utama twisted pair Minimal skill Simpel tool Star wiring topologies

2-4

b. Coaxial Cable

RG-58 (3/8 inch diameter luar kabel digunakan utk jarak dekat utk frekuensi radio dan ethernet LAN 10 Mbps

RG-75 (1/2 inch OD cable utk kabel TV diatas 500+ MHz)

Tujuan khusus lainnya digunakan utk jarak jauh seperti LAN atau aplikasi komunikasi data frekuensi radio (RF).

Kabel metalik mempunyai faktor propagasi antara 0,80 dan 0,95 yang bervariasi berdasarkan tipe, fabrikasi, material

karakteristik impedansi saluran transmisi metal (kabel) harus “matched”, sehingga energi maksimum dapat ditransfer dari sumber (source) ke kabel dan dari kabel ke beban (load) utk menghindari refleksi. Terminasi “mismatched” akan menyebabkan data hilang (loss).

2-5

Fiber optik

2. non-metallic transmission

Fiber optik menggunakan gel. Elektromagnetik (gelas/kaca atau kadang-kadang plastik) untuk menghantarkan informasi/pesan.

Panjang gel yang digunakan adalah cahaya tampak (500 nm) atau mendekati spektrum infrared (790 nm, 850 nm, 1310 nm, atau 1550 nm) dengan panjang gelombang yang lebih luas akan dapat mencapai jarak yang lebih panjang dengan loss yang kecil sekitar 3 dB per km atau malah lebih kurang.

2-6

Keuntungan fiber optik

2-7

Fiber optik

2-8

Beberapa fakta penting Fiber optikTeknik Dense Wavelength Division

Multiplex (DWDM) dapat meningkatkan bit rate 100 x melalui single fiber akan tetapi dengan biaya terminal yang cukup tinggi

Peralatan yang digunakan oleh transmisi FO adalah light emitting diode (LED) dan laser dengan tradeoff antara biaya versus jarak dan bandwidth.

Aplikasi telekomunikasi pada umumnya menggunakan single mode fiber dan laser, kenapa? tugas …..!!!!!!

2-9

FO

•Loss pada FO chromatic dispersion (ketika menggunakan LED), intermodal dispersion (biasanya pada multi-mode fiber), dan Rayleigh Scattering (penyerapan karena ketidak murnian kaca)

•Tidak ada radiasi loss atau gangguan dari luar Total Internal Reflection.

•Tapping tanpa physical access ke fiber sangat sulit

•Cross-talk hampir tidak memungkinkan terjadi dan distances-bandwidth product sangat tinggi, 100s kali (atau lebih) baik dari metallic transmission.

2-10

OPTICAL FIBER LINKS

Undersea cables Terrestrial long haul telecommunications

transmission Inter-building computer communications

2-11

2-12

Infrared

Data Communications Infrared through the air systems have been around for many years. We all have used one in our homes daily for many years now. (Think TV)

2-13

Laser

"unguided" transmission but usually considered point-to-point through the use of lasers and lens systems to constrain the optical path to a very narrow beam.

2-14

The beams are often so narrow that mounting of transmitters and receivers on roofs is discouraged due to tilting of the roof surface because of heating of the side of the building in sunlight.

2-15

Unguided media – masih lanjutan lho…!!

WIRELESS, RADIO, PCS, atau CORDLESS TELEPHONY

Akan dibahas dalam suatu mata kuliah khusus !!!!!

2-16

WIRELESS/RADIO POINTS - 1

Electromagnetic radiation--as we learned from Maxwell's Equations--happens for all alternating currents in wires. All metallic transmission media are antennas!

Efficiently built and installed antennas transmit radio signals when built to be an appreciable fraction of the operating wavelength or larger. 

Propagation is characteristic of the wavelength due to terrestrial factors and possible antenna construction at various sizes.

Radio signals are made and used practically as low at KHz frequencies (imagine the wavelength and antenna sizes needed) up to 100 GHz or where practical transmitting and receiving electronics is not available.

2-17

WIRELESS/RADIO POINTS - 2

Various modulation techniques are used depending on application. 

Impairments depend on wavelength, modulation system employed, and atmospheric absorption, multipath distortion and other reflection caused problems, and even refraction causing phenomena. 

Co-channel and adjacent channel interference can limit cause problems in channelized systems. Unlicensed (but legal) services are increasingly greatly, and spread spectrum techniques (especially in unlicensed bands) are exploding in use. Full characterization is not known.

2-18

The Electromagnetic Spectrum

Above "light" frequencies used by optical communications comes ultra-violet, X-rays, and eventually cosmic rays. They're all electromagnet radiation, mathematically the same. Thank Maxwell for showing this.

2-19

Lower frequencies/longer wavelengths require large antennas, propagate via ionosphere reflections (e.g. worldwide short wave radio); higher frequencies such as microwave have highly directional antennas, require "line of sight" transmission, and are used for point to point and satellite transmission.

2-20

Satelit1. GEOSYNCHRONOUS SATELLITES (GSO)

23.300 mil diatas bumi (3x diameter bumi dan 1/10 jarak ke bulan). Periode orbital rotasi bumi (diatas equator "stationary“

Low Earth satellites spt Space Station mengelilingi buni dalam 90 minute (bulan 28 hari ), dan satelit GPS pada ketinggian 11,000 mil merotasi bumi 2x sehari actually exactly twice per sidereal day.

Geosynchronous satellites world wide data communications link (alternatif fiber optik).

Waktu propagasi cukup tinggi dibandingkan media transmisi lainnya “mengganggu" protokol very low effective data rates transmisi satelit tidak sesuai utk aplikasi/sistem komunikasi tertentu.

2-21

This ring of allowable locations (i.e. 23,000 miles above the equator) for geosynchronous satellites is known as, "The Clarke Belt", in honor of science fiction author Sir Arthur C. Clarke, who is said to  have devised the concept.

Clarke is now in his 80s and lives in Sri Lanka, the only non-native with permanent residency status there. He is ailing but still actively publishing--his new book just came out--and participates in a weekly web cast. He also hosts a science program on public television.

2-22

2-23

GEOSYNCHRONOUS SATELLITE COVERAGE & BANDWIDTH

• Coverage for each satellite can be for about 1/3 to 1/4 the Earth's surface from each satellite, but footprints can be constrained much smaller by directional antenna techniques as well as longitude at which a given satellite is assigned.

•Very northern and southern locations are problematical but possible with large ground antennas mounted high enough to have a distant horizon to "see" the satellite.

•Each satellite has a number of 6 MHz channels, each called a "transponder", that relays ground transmissions received on one frequency called an "uplink" to a paired "downlink" frequency.

•A number of frequency bands are allocated internationally for geosynchronous satellites but frequency reuse limit satellite spacing to 1 degree at best. There are a lot of geosynchronous satellites in the Clarke Belt, mostly filling up all the usable longitudes.

2-24

Geosynchronous Orbit

Geosynchronous (adj.): geo-, earth and synchronous, going on at the same rate and exactly together.

A satellite in geosynchronous orbit circles the earth once each day. The time it takes for a satellite to orbit the earth is called its period. For a satellite's orbit period to be one day, it must be approximately 35,786 kilometers (19,323 nautical miles or 22,241 statute miles) above the earth's surface. That is a lot higher than the Shuttle ever goes (usually about 300 kilometers).

To stay over the same spot on earth, a geostationary satellite also has to be directly above the equator.

2-25

Tugas

Makalah sekitar 2500 kata mengenai :

WIRELESS, RADIO, PCS, CORDLESS TELEPHONY,Atau MEO & LEO