Nanang IsmailUIN SGD

Transmission medium and physical layer

Classes of transmission media

Guided transmission media◦ Kabel tembaga Open Wires Coaxial Twisted Pair◦ Kabel serat optik

Unguided transmission media◦ infra merah◦ gelombang radio◦ microwave: terrestrial maupun satellite

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Provides a means for transmitting electro-magnetic signals through the air but do not guide them (wireless transmission)

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Figure Electromagnetic spectrum for wireless communication

Figure Propagation methods

Sinyal berjalan melalui tiga rute◦ Gelombang tanah (Ground wave) Mengikuti contour bumi Sd 2MHz Radio AM◦ Gelombang langit (Sky wave) Amateur radio, BBC world service, Voice of America Sinyal dipantulkan dari lapisan ionosphere dari bagian

atas atmosphere (Persisnya refracted)◦ Line of sight Di atas 30Mhz Mungkin lebih dari optical line of sight krn refraction

Kecepatan glb elektromagnetik adalah fungsi dari densitas material◦ ~3 x 108 m/s dlm vakum, lebih kecil dlm materi lainnya

Glb yg bergerak dari satu medium ke medium lainnya, kecepatannya berubah◦ Menyebabkan pembelokan arah gelombang pd perbatasan◦ Mengarah ke medium yg densitasnya lebih tinggi

Index of refraction (refractive index) adalah◦ Sin(sdt kedatangan)/sin(sdt refraction)◦ Berubah dg panjang gelombang

Menyebabkan perubahan arah mendadak pd transisi antar media

Menyebabkan pembelokan gradual jika densitas medium berubah bervariasi◦ Densitas atmosphere berkurang dg ketinggian◦ Menghasilkan pembelokan ke arah bumi dari glb radio

Redaman ruang bebas (free space loss)◦ Signal menghambur dg jarak◦ Lebih besar utk frek. lebih rendah

Penyerapan atmosphere (atmospheric absorption)◦ Uap air dan oksigen menyerap sinyal radio◦ Lebih besar utk air pd 22GHz, kurang di bawah 15GHz◦ Lebih besar utk oksigen pd 60GHz, kurang di bawah 30GHz◦ Hujan dan kabut menyebarkan glb radio

Multipath◦ Lebih baik utk mendpkan line of sight jika mungkin◦ Sinyal dp dipantulkan menyebabkan sejumlah copy (duplikasi)

pd penerima◦ Mungkin tdk ada sinyal langsung sama sekali◦ Mungkin memperkuat atau menghilangkan sinyal langsung

Refraction◦ Mungkin menghasilkan partial atau total loss dari sinyal pd

penerima

Table 7.4 Bands

Band Range Propagation Application

VLF 3–30 KHz Ground Long-range radio navigation

LF 30–300 KHz Ground Radio beacons andnavigational locators

MF 300 KHz–3 MHz Sky AM radio

HF 3–30 MHz Sky Citizens band (CB),ship/aircraft communication

VHF 30–300 MHz Sky andline-of-sight

VHF TV, FM radio

UHF 300 MHz–3 GHz Line-of-sight UHF TV, cellular phones, paging, satellite

SHF 3–30 GHz Line-of-sight Satellite communication

EHF 30–300 GHz Line-of-sight Long-range radio navigation

Figure 7.19 Wireless transmission waves

Konduktor elektrik digunakan utk meradiasikan energi elektromagnetik atau mengumpulkan energi elektromagnetik

Transmission and reception are achieved by means of antennas◦ For transmission, an antenna radiates

electromagnetic radiation in the air◦ For reception, the antenna picks up

electromagnetic waves from the surrounding medium◦ Antena yg sama biasa digunakan utk kedua sisi◦ The antenna plays a key role

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the transmitting antenna puts out a focused electromagnetic beam

the transmitting and receiving antennas must be aligned

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Dr. Yagi and his Yagi antenna(example of directional antenna)

the transmitted signal spreads out in all directions and can be received by many antennas

In general, the higher the frequency of a signal, the more it is possible to focus it into a directional beam

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Figure Unidirectional antennas

Daya diradiasikan pada semua arah Performansi tdk sama pada semua arah Isotropic antenna adalah (secara teoritis) titik

dalam ruang◦ Radiasi ke semua arah secara merata◦ Memberikan pola radiasi spherical

Digunakan utk microwave terrestrial dan satelit Sumber yg ditempatkan pd focus akan

menghasilkan gelombang-gelombang pantuk paralel sumbu axis◦ Menghasilkan (secara teoritis) beam paralel dari

cahaya/suara/radio Pd penerimaan, sinyal dikonsentrasikan pada

focus, dimana detektor ditempatkan

Mengukur directionality dari antena Daya output pada arah tertentu dibandingkan

dengan yg dihasilkan oleh isotropic antenna Diukur dalam decibels (dB) Kehilangan (loss) daya pada arah lain Effective area berhubungan dengan ukuran

dan bentuk◦ Kaitan dengan gain

Frequencies in the range of about 30 MHz to 40 GHz are referred to as microwave frequencies

2 GHz to 40 GHz◦ wavelength in air is 0.75cm to 15cm wavelength = velocity / frequency◦ highly directional beams are possible◦ suitable for point-to-point transmission

30 MHz to 1 GHz◦ suitable for omnidirectional applications

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Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs.

Note:

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Parabolic dish Focused beam Line of sight Telekomunikasi jarak jauh Frekuensi lebih tinggi laju data lebih tinggi

Limited to line-of-sight (LOS) transmission◦ This means that microwaves

must be transmitted in a straight line and that no obstructions can exists, such as buildings or mountains, between microwave stations.

To avoid possible obstructions, microwave antennas often are positioned on the tops of buildings, towers, or mountains

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With no intervening obstacles, the maximum distance between antennas is

◦ d is the distance between antennas in kilometers,◦ h is the antenna height in meters◦ k is an adjustment factor to account for the fact that

microwaves are bent or refracted with the curvature of the earth k ~ 4/3

Example◦ Two antennas at a height of 100m may be as far as

82km apart

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khd 14.7=

Long-distance telecommunication service◦ requires fewer amplifiers or repeaters than

coaxial cable◦ requires line-of-sight transmission◦ Example telephone system TV distribution

Short point-to-point links◦ Data link between local area network ◦ closed-circuit TV

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Another apps: cellular communication, and LANs

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Freq. Band Use Range Data Rate824 - 894 MHz Analog cell phones (AMPS) 20 km per cell 13 kbps/channel902-928 MHz License free in North America1.7 - 2.3 GHz PCS digital cell phones < 1 km per cell1.8 GHz GSM digital cell phones 16 kbps/channel2.400-2.484 GHz global license free band2.4 GHz 802.11, Lucent WaveLAN 100 m - 25 km 2 - 11 Mbps2.45 GHz Bluetooth about 10 m 1 Mbps4 - 6 GHz commercial (telecomm.) 40 - 80 km 100 MbpsInfrared short distance line of sight 5 - 100 m 1 Mbps

The higher the frequency used, the higher the potential bandwidth and therefore the higher the potential data rate

Band (GHz) | Bandwidth (MHz) | Data rate (Mbps)

2 7 126 30 9011 40 9018 220 274

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◦ d is the distance◦ λ is the wavelength

repeaters or amplifiers may be placed farther apart for microwave systems - 10 to 100 km is typical

Attenuation increases with rainfall, especially above 10 GHz

The assignment of frequency bands is strictly regulated (http://www.postel.go.id/utama.aspx?MenuID=3&MenuItem=3)

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24log10

=λπdL

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Satelit adalah suatu station relay Satelit menerima pada satu frekuensi,

memperkuat atau mengulang sinyal dan transmit pd frekuensi lain

Memerlukan orbit geo-stationary◦ Tinggi 35,784km

Aplikasi◦ Televisi◦ Telepon jarak jauh◦ Private business networks

a satellite is a microwave relay station◦ link two or more ground-

based microwave transmitter/receivers (known as earth stations or ground stations)

The satellite receives transmissions on one frequency band (uplink), amplifies or repeats the signal, and transmits it on another frequency (downlink)◦ An orbiting satellite operate

on a number of frequency bands, called transponder channels

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It is launched into an orbit above the equator at 35786 km◦ This orbit distance means that the

satellite is orbiting the earth as fast as the earth is rotating.

◦ It appears to earth stations that the satellite is stationary, thus making communications more reliable and predictable

◦ Earth stations is less expensive because they can use fixed antennas

Delay is 250 -500ms for geostationary satellites

Apps: television broadcasting and weather forecasting, and have a number of important defense and intelligence applications, VSAT

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A Very Small Aperture Terminal (VSAT), is a two-way satellite ground station with a dish antenna that is smaller than 3 meters.

Most VSAT antennas range from 75 cm to 1.2 m.

Data rates typically range from 56 Kbit/s up to 4 Mbit/s

VSATs access satellites in geosynchronous (geostationary) orbit (to relay data from small remote earth stations (terminals) to other terminals (in mesh configurations) or master earth station "hubs" (in star configurations).

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For small mobile personal communications terminals, a network with significantly reduced transmission and processing delay is required

Such a service could be provided by low earth orbit (LEO) and medium earth orbit (MEO) satellite systems

These systems can provide direct personal-terminal-to-personal-terminal connectivity (satellite phone services)

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A Low Earth Orbit (LEO) typically is a circular orbit about 400 kilometers above the earth’s surface and, correspondingly, a period (time to revolve around the earth) of about 90 minutes

One of apps: to provide satellite phone services, primarily to remote areas

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Medium Earth orbit (MEO), sometimes called intermediate circular orbit (ICO), is the region of space around the Earth above low Earth orbit (altitude of 2,000 kilometers (1,243 mi)) and below geostationary orbit (altitude of 35,786 kilometers (22,236 mi))

The most common use for satellites in this region is for navigation, such as the GPS

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Optimum frequency range for satellite transmission is 1 - 10GHz

Below 1 GHz, there is significant noise from nature sources

About 10 GHz, the signal is severely attenuated by atmosphere

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Typical frequency bands for

uplink/downlink usual terminology6/4 GHz C band8/7 GHz X band14/12 GHz Ku band30/20 GHz Ka band

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Typical frequency bands for

uplink/downlink usual terminology1.6/1.5 GHz L band30/20 GHz Ka band

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Typical frequency bands for

uplink/downlink usual terminology12 GHz Ku band

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Radio waves are used for multicast communications, such as radio and television, and paging systems.

Note:

Omnidirectional Line of sight Rentan thd interferensi multipath◦ Refleksi

Aplikasi◦ Radio FM◦ Televisi UHF dan VHF

Physical description◦ omnidirectional

Applications◦ AM broadcasting Operating frequencies MF (medium frequency): 300 kHz - 3 MHz HF (high frequency): 3 MHz - 30 MHz HF is the most economic means of low information rate

transmission over long distances (e.g. > 300km)

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A HF wave emitted from an antenna is characterized by a groundwave and a skywave components.

The groundwave follows the surface of the earth and can provide useful communication over salt water up to 1000km and over land for some 40km to 160km

The skywave transmission depends on ionosphericrefraction. ◦ Transmitted radio waves hitting the ionosphere are bent or

refracted. ◦ When they are bent sufficiently, the waves are

returned to earth at a distant location. ◦ Skywave links can be from 160km to 12800km.

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FM broadcasting operating frequencies◦ VHF (very high frequency): 30 MHz - 300 MHz

TV broadcasting◦ operating frequencies: VHF UHF (ultra high frequency): 300 MHz - 3000MHz

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Memodulasi cahaya infrared noncoherent Line of sight (atau refleksi) Blocked oleh dinding mis. TV remote control, IRD port

Does not penetrate walls◦ no security or interference problems

no frequency allocation issue◦ no licensing is required

Apps: Infrared Wireless LAN

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Infrared signals can be used for short-range communication in a closed area using line-of-sight propagation.

Note:

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Power loss : penurunan daya sinyal

Power gain : penguatan daya sinyal

Decibel : “satuan” untuk menyatakan power loss/gain◦ Decibel merupakan satuan

ukuran daya yang logaritmis◦ Pertama kali digunakan oleh

Alexander Graham Bell (satuan decibel digunakan untuk menghormati jasanya)

◦ Decibel : dB

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Alexander Graham BellBorn 1847 - Died 1922

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Gaing = Pout/Pin

Gain in dBgdB = 10 log (Pout/Pin)

LossL = Pin/Pout

Loss in dBLdB = 10 log (Pin/Pout)

Overall Gaing = g1*g2

Overall Gain in dBgdB = g1(dB) + g2(dB)

Contoh: - Bila daya output 10 Watt dan daya input 1 Watt,maka Gain = 10 dB

- Bila daya input 10 Watt dan daya output 1 Watt,maka Loss = 10 dB (atau Gain = -10 dB)

Rumus dB menyatakan ukuran daya Jika kita lebih tertarik akan perubahan pada

tegangan maka faktor impedansi harus dimasukkan pada perhitungan dB

ZZ log 10

VV log 20

PP log 10

out

in

in

out

in

out

+

=

=dBg

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Sampai titik ini kita masih melihat penerapan dB untuk menyatakan perbandingan daya

Bagaimana cara menyatakan level daya absolut menggunakan dB?

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Gunakan suatu daya referensi

Daya referensi yang banyak digunakan adalah 1 mW

Satuan dB yang dihasilkan adalah dBm

Contoh: suatu level daya 10 mW bila dinyatakan di dalam dB adalah 10 dBm

Daya referensi lain yang dapat digunakan: 1 Watt (satuan dB yang digunakan dBW)

=

=

WPP

mWPP

dBW

dBm

1 log 10

1 log 10

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Contoh penggunaan dB

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Daya pancar P1 = 1W atau +30 dBmGain antena = 30 dBRedaman link = 110 dBDaya diterima terima P2,dBm = +30 dBm + 30 dB –110 dB +30 dB = –20 dBmBila dinyatakan di dalam Watt P2 = 10 μW.

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Redaman serat optik 0,5 dB/km

Daya pancar P1,dBm = 0 dBmRedaman serat optik = 0,5 dB/km, maka redaman total serat optik = 0,5*40 =20 dB Daya terima P2,dBm = 0 dBm – 20 dB = –20 dBm

Satuan lain yang biasa digunakan untuk menyatakan suatu perbadingan adalah Neper

1 Neper (Np) = 8,685889638 dB

1 dB = 0,115129254 Np

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John Napier or Nepernicknamed Marvellous Merchiston

(1550, 1617) Penemu Logaritma