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Sistem Komunikasi

Sistem Komunikasi. oleh Risanuri Hidayat. Pengantar. Telekomunikasi = komunikasi yang dipisahkan oleh jarak Ada 3 komponen utama : Isyarat Komunikasi Kanal Komunikasi Jaringan Komunikasi. Isyarat Komunikasi. Isyarat Komunikasi.

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Sistem Komunikasi

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  1. Sistem Komunikasi oleh Risanuri Hidayat

  2. Pengantar Telekomunikasi = komunikasi yang dipisahkan oleh jarak Ada 3 komponen utama : • Isyarat Komunikasi • Kanal Komunikasi • Jaringan Komunikasi Sistem Komunikasi

  3. Isyarat Komunikasi 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 dapat isyarat suara (manusia) dapat terkirim • Sistem telepon menggunakanLPF 4kHz (Low-pass) • Komponen-komponen frekuensi di dalam gelombang isyarat menjadi Lebar Bidang Isyarat 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 transmisipada sistem data biner secara proporsional mendekati bit rate [High data rate = Wider BW of channel] 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 Sistem Komunikasi

  7. Kanal Komunikasi 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-couplingdapat menambah kapasitasi antara 2 konduktor. Hal ini menyebabkan suatu isyarat dapat terganggu karena ada kabel lain. 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 Sistem Komunikasi

  10. Fiber Optis Sistem Komunikasi

  11. Fiber Optis [1] • Yang paling sederhana : inti fiber [sekitar 50 micron diameter] dengan index bias n1, dilapisi fiber dengan index bias yang lebih kecil n2 • Cahaya berjalan sepanjang inti Sistem Komunikasi

  12. Snell’s Law of Refraction • Critical angle = sin-1 n2/n1 Sistem Komunikasi

  13. Total Internal Reflection 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 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 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 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 Propagation 1. Line of Sight 2. Surface wave or ground wave 3. Ionospheric propagation 4. Tropospheric scattering 5. Free space propagation 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 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 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 Network Integrated Services Digital Network 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] 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 Sistem Komunikasi

  23. Protocol Layering • Layer1 Physical [Please] • Layer2 Data link [Do] • Layer3 Network [Not] • Layer4 Transport [Throw] • Layer5 Session [Sausage] • Layer6 Presentation [Pizza] • Layer7 Application [Away] 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] Sistem Komunikasi

  25. Satuan ukuran Common Unit of measurement : Gain & Loss Current Gain [Ai] = Io/Ii Voltage Gain [Av] = Vo/Vi Power Gain [G] = Po/Pi Power Loss [L] = Pi/Po Note: G = 1/L or L = 1/G Sistem Komunikasi

  26. Satuan Decibels [dB] • Power Gain expressed in dB : G[dB] = 10 log G 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 Sistem Komunikasi

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