Telecommunications and Video Systems

Telecommunications and Video Systems TVS, By Ya Bao

ASSESMENT OF THE UNIT • There will be one 2-hour written examination (70%), and laboratory assessed work (30%). • Deadline of submission 4 May. 2007 . • CORE MATERIALS Schweber, W., Electronic Communication Systems: A Complete Course, 4/e Prentice Hall, 2002, ISBN: 0-13-091621-8 http://eent3.sbu.ac.uk/staff/baoyb/TVS TVS, By Ya Bao

1. Introduction to communication systems 1.1 What is telecommunications • Communication • Telecommunications 1.2 Development of telecommunications • 1837 telegraph S.Morse • 1876 telephone A. Bell • 1894 radio communications G. Marconi • 1915 transcontinental telephone line • 1948 first transistor • 1962 first communication satellite • 1963 first laser • 60’s optical fibres, IC, PCM • 70’s computer net, microprocessor • 80’s cellular telephone, Internet • 90’s GPS, ATM, ISDN, GSM • 21 Century 3G, Broad access, DAB radio, digital and HD TV, WLAN, 4G, ... TVS, By Ya Bao

1.3 The block diagram of a communication system TVS, By Ya Bao

2. The Electromagnetic Spectrum 2.1 Electromagnetic Waves and Energy • wavelength:distance between peaks • velocity:speed at which the energy travels through • frequency: the number of oscillations or cycles per second (hertz, abbreviated Hz) of the waveform • Wavelength: the distance between peaks of the oscillations of the energy wave TVS, By Ya Bao

Wavelength can also be measured as the distance between the negative peaks, zero points, TVS, By Ya Bao

speed of light: • The propagation velocity is less in any medium other than vacuum • In wire, it is anywhere from 60% to 85% of c • a common type of cable used for cable TV has a propagation factor of 75% of c. Example 1 What is the wavelength in vacuum for a frequency of 1 million hertz? Example 2 What is the frequency when the measured wavelength is 6 m? TVS, By Ya Bao

2.2 The Electromagnetic Spectrum TVS, By Ya Bao

TABLE 1‑1 CCIR Band Designations Frequency Range Designations --------------------------------------------------- 30 Hz‑----300 Hz ELF 0.3 kHz‑--3 kHz VF 3 kHz-----‑30 kHz VLF 30 kHz‑---300 kHz LF 0.3 MHz‑-3 MHz MF 3 MHz‑----30 MHz HF 30 MHz---300 MHz VHF 0.3 GHz‑--3 GHz UHF 3 GHz‑----30 GHz SHF 30 GHz‑---300 GHz EHF 0.3 THz‑---3 THz Infrared light 3 THz‑------30 THz Infrared light 30 THz‑----300 THz Infrared light 0.3 PHz‑---3 PHz Visible light 3 PHz‑-----30 PHz Ultraviolet light 30 PHz‑----300 PHz X‑rays 0.3 EHz‑---3 EHz Gamma rays 3 EHz‑------30 EHz Cosmic rays 1 kilohertz (kHz)= 103 Hz, 1 megahertz (MHz)= 1*106 Hz 1 gigahertz (GHz)= 1*109 Hz, 1012 : terahertz (THz); 1015 : petahertz (PHz); 1018 : exahertz (EHz); TVS, By Ya Bao

2.3 BANDWIDTH AND INFORMATION CAPACITY • Bandwidth: Bandwidth is the span of frequencies within the spectrum occupied by a signal and used by the signal for conveying information. • To send more information in a short time requires more bandwidth. Example Suppose that a communications link is using a transmitter of 10 W power, and there is 1 W of noise power in the same link. The available bandwidth is 1 kHz. What is the channel capacity? TVS, By Ya Bao

2.4 SIMPLEX, DUPLEX, AND HALF‑DUPLEX SYSTEMS • SIMPLEX: one direction only • DUPLEX: both directions at a time • HALF‑DUPLEX: either direction, but only one direction at a time TVS, By Ya Bao

2.5 TIME AND FREQUENCY DOMAINS • Description of a signal versus time ---time‑domain representation • Description of a signal versus frequency --frequency‑domain representation TVS, By Ya Bao

Telecommunications and Video Systems