Personal Broadband Networks, PBN (CE )

Transcription

1 Faculty of Computing, Engineering & Technology Introduction to Radio Systems Personal Broadband Networks, PBN (CE ) Alison L Griffiths C203 [email protected]

2 2 Objectives Introduction Development of Radio Frequency Communications Reference Block Diagram

3 3 Introduction James Maxwell predicted the existence of electromagnetic radiation 1864 Developed the theory which identified many of their properties including their velocity. Electromagnetic waves, which became known as radio waves, were first transmitted & received by Heinrich Hertz in Consisted of an induction coil, which produced a high voltage from a low voltage battery, that produced sparks across an air gap (rather like a spark plug). The receiver was a coil, located close to the transmitter, in which a voltage was induced which caused a spark to jump across an air gap in the receiver. Marconi developed systems In 1901 made a famous transmission from Cornwall to Newfoundland, a distance of 2500 km. This equipment used Morse code and the process was described as Wireless Telegraphy.

4 4 Morse code, developed by Samuel for telegraphy via landlines, Significant landmark in the development of communications & information theory In early radio systems, the transmitter was turned on & off, to send bursts of radio waves. The on time was long for a dash and short for a dot. The dot/dash code was based on the probability or frequency of occurrence of characters in English text

5 5 Introduction The invention of the battery and the discovery of the magnetic effect of an electric current development of telegraphy Telegraphy required the use of special coders and decoders. The use of Morse code is the most famous example of the kind. telephone systems speech relayed directly without the use of any coding system. Discovery of the electromagnetic radiation wireless communication enabling the development of radio and later television systems. Satellite communication and optical fibres were to follow.

6 6 Electronic Telecommunication Systems Information source converted an electrical signal (transducer) and then encoded into a form suitable for transmission (modulation) Many systems need a transmitter for getting a signal to the transmission path and a receiver to extract it from the path. The path can be of coaxial cable, air or optical fibre. Amplifiers are used (may even be used in the path) to increase the magnitude of the signal. A transmitted signal suffers from (a) attenuation (b) noise which make the signal lose power and produce distortion, when the signal is demodulated. Noise is a random signal that is added to the signal being transmitted.

7 7 Development of Radio Frequency Communications (1) DATE EVENT 1826 Ohms law, relating voltage, current and resistance 1838 Samuel Morse demonstrated Telegraph, a system using wires and the Morse Code to represent characters 1858 First transatlantic cable 1864 James Clerk Maxwell developed electromagnetic theory of light, which led to the discovery of radio waves and the invention of radio. Radio-comes from the Latin word radius, meaning spoke or ray 1876 Alexander Graham Bell, a Scottish immigrant to Boston, USA, patents telephone 1888 Heinrich Hertz produced electromagnetic waves, using a generator, spark gap & a receiver comprising a coil and spark gap

8 8 Development of Radio Frequency Communications (2) 1897 Guglielmo Marconi developed wireless telegraph system and in 1897 sent signals from the Isle of Wight to Bournmouth, 27 miles. In 1899 sent signals across the English Channel a distance of 80 miles Guglielmo Marconi made a famous transmission from Cornwall to Newfoundland, a distance of 2500 km 1904 Flemming invented the Diode 1906 De Forest invents the triode valve. De Forest introduced a control grid in the vacuum diode and amplifiers were developed. For the first few years of radio, no means of amplification were possible. Now radio telephony was possible & significant developments were made during the Great War Armstrong develops super heterodyne rec BBC transmissions started on 14th November 1922, using amplitude modulation.

9 9 Development of Radio Frequency Communications (3) 1926 J. L. Baird (UK) & C. F. Jenkins (USA) demonstrate television 1927 Long wave transmitter at Rugby, Post Office communications with a station in New Jersey 1933 Armstrong invents frequency modulation BBC opens first TV broadcasting system on 2nd November Reeves conceives pulse code modulation (PCM), an important development in digital communications Developments at UHF, SHF, radar and microwave frequencies Shockley, Bardeen and Bratttain invent transistor, at Bell Telephone Labs Shannon s Information Theory published, a significant development for coding and digital communication systems s Development of integrated circuits 1962 Telstar relays first live TV between USA and Europe.

10 10 Development of Radio Frequency Communications (4) 1966 First optical fibre demonstrated 1970 s Large scale integrated and microprocessors developed 1980 s & 1990 s Rapid developments in computer technology, digital signal processing, radio technology and networks has propelled the growth of mobile cellular radio ( and others such as TV, video, music ) systems

11 11 Reference Block Diagram Tx/Rx Speech Data Communications Network To better understand such a system A knowledge of the principles and functions of various elements which make up the system is required. Knowledge of the principles requires an understanding of some of the parameters Speech Data Tx/Rx

12 12 Radio System Schematic Diagram message Encoder Speech & Data encoding Speech & Data decoding Decoder Modulator Analogue: Ampltidue & Frequency Mod/Demod Digital: Frequency & Phase Shift Keying Multiplexing: Frequency, Time & Code Division Mux/Demux Demodulator Mixers Oscillators Frequency Synthesizers Intermediate Frequency Amplifiers Filters Upconversion Downconversion RF Driver Amplifiers Filters Antenna RF Amp message