ITS323/CSS331 Transmission Media Media and Spectrum Transmission Media Guided Media Wireless Transmission Antennas ITS323: Introduction to Data Communications Propagation CSS331: Fundamentals of Data Communications Wireless Examples Sirindhorn International Institute of Technology Thammasat University Prepared by Steven Gordon on 3 August 2015 ITS323Y15S1L03, Steve/Courses/2015/s1/its323/lectures/transmission-media.tex, r3920
ITS323/CSS331 Contents Transmission Media Media and Transmission Media and Spectrum Spectrum Guided Media Wireless Guided Media Transmission Antennas Propagation Wireless Transmission Wireless Examples Antennas and Antenna Gain Propagation and Path Loss Wireless Examples
ITS323/CSS331 Transmission Media Transmission Media “the thing between the transmitter and receiver” Media and ◮ Signal propagates from transmitter to receiver via some Spectrum medium Guided Media ◮ Which medium should be used? Wireless Transmission ◮ Maximise data rate Antennas ◮ Maximise distance Propagation ◮ Minimise bandwidth Wireless Examples ◮ Minimise transmission impairments ◮ Minimize cost ◮ Guided (wired) vs unguided (wireless)
ITS323/CSS331 Signals and Spectrum Transmission Media ◮ Communication signals contain components with different frequencies, spectrum of signal Media and Spectrum ◮ Often refer to center frequency and bandwidth of signal Guided Media Wireless Transmission S(f) Antennas 70% Propagation Wireless Examples bandwidth f low centre high cutoff cutoff ◮ Electromagnetic spectrum is used by many applications ◮ International and national authorities regulate usage of spectrum ◮ Aim: minimize interference between applications/users, while allowing many applications/users
ITS323/CSS331 Electromagnetic Spectrum for Communications Transmission Media Frequency [Hz] Media and 10 0 10 3 10 6 10 9 10 12 10 15 10 18 10 21 Visible Spectrum Guided Media Radio Microwave THz Infrared X−ray Gamma Ultraviolet 3kHz 300MHz 300GHz 3THz 30PHz 30EHz Wireless Transmission 10 5 10 0 10 −3 10 −4 10 −8 10 −11 Wavelength [m] Antennas Twisted Pair Remote WiFi ADSL Optical Propagation FM 3G Fibre AM Satellite TV Coaxial Cable Wireless Examples ITU and IEEE bands: VLF LF MF HF UHF VHF SHF EHF THF 3kHz 30kHz 300kHz 3MHz 30MHz 300MHz 3GHz 30GHz 300GHz 3THz ITU L S C X K K K a u 1 2 4 8 12 18 27 40GHz IEEE
ITS323/CSS331 Contents Transmission Media Media and Transmission Media and Spectrum Spectrum Guided Media Wireless Guided Media Transmission Antennas Propagation Wireless Transmission Wireless Examples Antennas and Antenna Gain Propagation and Path Loss Wireless Examples
ITS323/CSS331 Electrical Cables Transmission Media ◮ Transmit electrical signals on a conductor, e.g. copper ◮ Cable carrying electrical current radiates energy, and Media and Spectrum can pick-up energy from other sources Guided Media ◮ Can cause interference on other cables Wireless ◮ Other sources can cause interference on the cable Transmission ◮ Interference results in poor quality signals being received Antennas ◮ To minimise interference: Propagation Wireless Examples ◮ Keep the cable lengths short ◮ Keep the cables away from other sources ◮ Design the cables to minimise radiation and pick-up ◮ Use materials to shield from interference ◮ Organise multiple wires so they dont interfere with each other
ITS323/CSS331 Twisted Pair Transmission Media ◮ Two insulated copper wires arranged in spiral pattern ◮ Most commonly used and least expensive medium Media and Spectrum ◮ Used in telephone networks and in-building Guided Media communications Wireless ◮ Telephone networks designed for analog signalling (but Transmission supporting digital data) Antennas ◮ Also used for digital signalling Propagation ◮ Two varieties of twisted pair: shielded (STP) and Wireless Examples unshielded (UTP); also multiple categories (CAT5)
ITS323/CSS331 Coaxial Cable Transmission Media ◮ Two conductors, one inside the other ◮ Provide much more shielding from interference than Media and Spectrum twisted pair: Higher data rates; More devices on a Guided Media shared line; Longer distances Wireless ◮ Widely used for cable TV, as well as other audio/video Transmission Antennas cabling Propagation ◮ Used in long-distance telecommunications, although Wireless Examples optical fibre is more relevant now
ITS323/CSS331 Optical Fibre Transmission Media ◮ Light (optical rays) is guided within glass or plastic fibres Media and Spectrum ◮ Used in long-distance telecommunications, as well as Guided Media telephone systems, LANs, and city-wide networks Wireless ◮ Advantages of optical fibre over electrical cables: Transmission 1. Lower loss: can transfer larger distances Antennas 2. Higher bandwidth: a single fibre is equivalent to 10’s or Propagation 100’s of electrical cables Wireless Examples 3. Small size, light weight: lowers cost of installation 4. Electromagnetic isolation
ITS323/CSS331 Comparison of Guided Media Transmission Media Electrical Cables Media and Spectrum ◮ Moderate data rates: 1Gb/s Guided Media ◮ Maximum distance: 2km (twisted pair); 10km (coaxial) Wireless Transmission ◮ Cheapest for low data rates Antennas ◮ UTP: easy to install, susceptible to interference Propagation ◮ STP, Coaxial Cable: rigid, protection against Wireless Examples interference Optical Cables ◮ Very high data rates: 100Gb/s+ ◮ Maximum distance: 40km ◮ Expensive equipment, but cost effective for high data rates ◮ Difficult to install
ITS323/CSS331 Contents Transmission Media Media and Transmission Media and Spectrum Spectrum Guided Media Wireless Guided Media Transmission Antennas Propagation Wireless Transmission Wireless Examples Antennas and Antenna Gain Propagation and Path Loss Wireless Examples
ITS323/CSS331 Wireless Transmission Model Transmission Media Common wireless systems for communications include: Media and ◮ Terrestrial microwave, e.g. television transmission Spectrum ◮ Satellite microwave, e.g. IPstar Guided Media Wireless ◮ Broadcast radio, e.g. IEEE 802.11 WiFi (wireless LAN) Transmission ◮ Infrared, e.g. in-home communications Antennas Propagation Wireless Examples Transmit Receive Antenna Antenna Signal Transmitter Receiver
ITS323/CSS331 Wireless Transmission Model Transmission Media G t G r Media and Spectrum Guided Media P t L P r Wireless Transmission Antennas Propagation Wireless Examples ◮ Transmit electrical signal with power P t ◮ Tx antenna converts to electromagentic wave; introduces a gain G t ◮ Signal loses strength as it propagates; loss L ◮ Rx antenna converts back to electrical signal, gain G r ◮ Receive signal with power P r
ITS323/CSS331 Wireless Transmission Issues Transmission Media ◮ What is the role of an antenna? Media and ◮ What is antenna gain? Spectrum ◮ How does the signal propagate in different Guided Media environments? Wireless Transmission ◮ How much power is lost when it propagates? Antennas Propagation Wireless Examples
ITS323/CSS331 Contents Transmission Media Media and Transmission Media and Spectrum Spectrum Guided Media Wireless Guided Media Transmission Antennas Propagation Wireless Transmission Wireless Examples Antennas and Antenna Gain Propagation and Path Loss Wireless Examples
ITS323/CSS331 Antennas Transmission Media ◮ Antenna converts between electrical current and electromagnetic waves Media and Spectrum ◮ Waves are within the Radio and Microwave bands of 3 Guided Media kHz to 300 GHz Wireless Transmission ◮ Antenna characteristics are same for sending or receiving Antennas ◮ Direction and propagation of a wave depends on Propagation antenna shape Wireless Examples ◮ Isotropic antenna: power propagates in all directions equally (spherical pattern, ideal) ◮ Omni-directional antenna: power propagates in all directions on one plane (donut) ◮ Directional antenna: power concentrated in particular direction ◮ Power output in particular direction compared to power produced by isotropic antenna is antenna gain [dBi]
ITS323/CSS331 Example: Isotropic Antenna (2D) Transmission Media Pr Media and Spectrum Guided Media Wireless Transmission 1m Antennas Pt Propagation Wireless Examples ◮ Transmit with power P t ◮ Measure received power 1m away to be P r ◮ Received power is same at any point equidistant from transmitter (black circle)
ITS323/CSS331 Example: Directional Antenna (2D) Transmission Media Pr Media and Spectrum Guided Media Pr Wireless Transmission 1m Antennas Px Pt Propagation Wireless Examples Gain = Px Pr ◮ Transmit with same power P t ◮ Blue shape: at each point, received power is P r ◮ Measure received power 1m away to be P x ◮ Gain of antenna (compared to isotropic) is P x / P r
ITS323/CSS331 Antenna Patterns Transmission Media Media and Spectrum Guided Media Wireless Transmission Antennas Propagation Wireless Examples Isotropic Dipole Horn Dipole Sector
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