Lect 3 Wireless Network Charactristics.pdf

University of Science & Technology Faculty of Computer Science & Information Technology Department of information for communication and technology Mobile communications & wireless technology_ it 709 4year/sem 7 Tawffeeg Mohammed Tawfeeg Outline...

University of Science & Technology Faculty of Computer Science & Information Technology Department of information for communication and technology Mobile communications & wireless technology_ it 709 4year/sem 7 Tawffeeg Mohammed Tawfeeg Outline  Review of data communication  Wireless and Mobile Networks  Hidden Terminal and Fading Problems  Bit Error  Elements of a wireless network.  Infrastructure mode and Infrastructure less mode 2  Data Communication Information can be transmitted on wires by varying some physical property such as voltage and current. By representing the value of this voltage or current as a single-valued function of time, f(t), we can model the behavior of the signal and analyze it mathematically. computer 1 computer 2 bits bits transmission medium transmitter receiver electric current light electromagnetic waves 3  Electromagnetic Fields Any moving electric charge is surrounded by an electric field and a magnetic field. 4 Electromagnetic Fields Cont. A changing magnetic field creates a changing electric field. One example of this is a transformer which transfers electric – In the main coil changing electric current produces a changing magnetic field – Which then creates a changing electric field in another coil producing an electric current – The reverse is also true. 5  Making Electromagnetic Waves The magnetic and electric fields create each other again and again. 6 Making Electromagnetic Waves They travel as vibrations in electrical and magnetic fields. –Have some magnetic and some electrical properties to them. 7  Wavelength & Frequency The number of oscillation per second of a wave is called its frequency, f, and is measured in Hertz (Hz). Frequency= number of wavelengths that pass a given point in 1 s. As frequency increases, wavelength becomes smaller. 8  Wave Length Wavelength= distance from crest to crest. The distance between two consecutive maxima (or minima) is called the wavelength, which is universally designated by the Greek letter λ (lambda) 9 Different Frequencies 10 Different Frequencies 11 Can a wave be a particle? In 1887, Heinrich Hertz discovered that shining light on a metal caused electrons to be ejected. Whether or not electrons were ejected depended upon frequency not the amplitude of the light! Remember energy depends on amplitude. 12 Can a wave be a particle? Years later, Albert Einstein explained Hertz’s discovery: EM waves can behave as a particle called a photon whose energy depends on the frequency of the waves. 13 Can a particle be a wave? Electrons fired at two slits actually form an interference pattern similar to patterns made by waves 14  What is the speed of EM waves? All EM waves travel Material Speed 300,000 km/sec in space. (speed of (km/s) light-nature’s limit!) Vacuum 300,000 EM waves usually Air