Wireless Communication Networks and Systems: Chapter 6

CHAPTER 6 THE WIRELESS CHANNEL These slides are made available to faculty in PowerPoint form. Slides can be freely added, modified, and deleted to suit student needs. They represent substantial work on the part of the authors; Wireless Communication therefore, we request the follo...

CHAPTER 6 THE WIRELESS CHANNEL These slides are made available to faculty in PowerPoint form. Slides can be freely added, modified, and deleted to suit student needs. They represent substantial work on the part of the authors; Wireless Communication therefore, we request the following. Networks and Systems If these slides are used in a class setting or posted on an internal or 1st edition, Global edition external www site, please mention the source textbook and note our copyright of this material. Cory Beard, William Stallings All material copyright 2016 © 2016 Pearson Education, Ltd. Cory Beard and William Stallings, All Rights Reserved The Wireless Channel 6-1 antennas An antenna is an electrical conductor or system of conductors Transmission - radiates electromagnetic energy into space Reception - collects electromagnetic energy from space In two-way communication, the same antenna can be used for transmission and reception The Wireless Channel 6-2 Types of Antennas Isotropic antenna (idealized) Radiates power equally in all directions Dipole antennas Half-wave dipole antenna (or Hertz antenna): length of the antenna is one half the wavelength of the wave Quarter-wave vertical antenna (or Marconi antenna): the length of the antenna should be one quarter of the radio signal wavelength. Parabolic Reflective Antenna:A bowl-shaped antenna that reflects and focuses incoming radio waves into a narrow beam directed toward a receiver typically positioned above the center of the unit. Directional Antennas Arrays of antennas In a linear array or other configuration Signal amplitudes and phases to each antenna are adjusted to create a directional pattern Very useful in modern systems The Wireless Channel 6-3 6.2 Simple Antennas The Wireless Channel 6-4  6.4 Parabolic Reflective Antennas ‫ة‬ The Wireless Channel 6-5 Antenna Gain Antenna gain Power output, in a particular direction, compared to that produced in any direction by a perfect omnidirectional antenna (isotropic antenna) Effective area Related to physical size and shape of antenna The Wireless Channel 6-6 Antenna Gain Relationship between antenna gain and effective area G = antenna gain Ae = effective area f = carrier frequency c = speed of light (» 3 ´ 108 m/s) λ = carrier wavelength The Wireless Channel 6-7 Propagation Modes Ground-wave propagation Sky-wave propagation Line-of-sight propagation The Wireless Channel 6-10 6.5 Wireless Propagation Modes knln The Wireless Channel 6-11 Ground Wave Propagation Follows contour of the earth Can propagate considerable distances Frequencies up to 3 MHz Example AM radio The Wireless Channel 6-12 Sky Wave Propagation Signal reflected from ionized layer of atmosphere back down to earth Signal can travel a number of hops, back and forth between ionosphere and earth’s surface Reflection effect caused by refraction Examples Amateur radio CB radio The Wireless Channel 6-13 Line-of-Sight Propagation Transmitting and receiving antennas must be within line of sight Satellite communication – signal above 30 MHz not reflected by ionosphere Ground communication – antennas within effective line of site due to refraction Refraction – bending of microwaves by the atmosphere Velocity of electromagnetic wave is a function of the density of the medium When wave changes medium, speed changes Wave bends at the boundary between mediums The Wireless Channel 6-14 Line-of-Sight Equations Optical line of sight d 3.57 h Effective, or radio, line of sight d 3.57 h d = distance between antenna and horizon (km) h = antenna height (m) K = adjustment factor to account for refraction, rule of thumb K = 4/3 The Wireless Channel 6-15 6.7 Optical and Radio Horizons The Wireless Channel 6-16 Line-of-Sight Equations Maximum distance between two antennas for LOS propagation:  3.57 h1  h2  h1 = height of first antenna h2 = height of second antenna The Wireless Channel 6-17 Exercise The maximum distance between two antenna for LOS transmission if one antenna is 100 m high and the other is at ground level is : Now suppose that the receiving antenna is 10 m high. To achieve the same distance, how high must the transmitting antenna be?