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Communication Systems (0331411) First semester 2008/2009 Dr. Ali Jamoos Email: email@example.com 1/17
Historical Background 1844 – The Telegraph was invented by Samuel Morse 1864 – James Clerk Maxwell formulated the electromagnetic theory 1875 – The Telephone was invented by Alexander Graham Bell 1887 – Heinrich Hertz confirmed the existence of radio waves 1901 – Marconi received a radio signal, 1700 miles across the Atlantic 1904 – John Ambrose Fleming invented the vacuum-tube diode 1906 – John Ambrose Fleming invented the vacuum-tube triode 1918 – Edwin Armstrong invented the superheterodyne radio receiver 1928 – The Television system was demonstrated by Philo Farnsworth 1933 – Edwin Armstrong demonstrated the Frequency Modulation (FM) 2/17
Historical Background 1946 – The first computer, ENIAC, was built at Pennsylvania university 1948 – The transistor was invented at Bell Laboratories 1958 – The first Integrated Circuit (IC) was produced by Robert Noyce 1962 – The Telstar satellite, built by Bell Laboratories, was lunched 1971 – The first computer network, called the ARPANET, was built 1985 – The ARPANET was renamed the Internet 1983 - Advanced Mobile Phone System (AMPS) was lunched in US 1991 - Global System for Mobile (GSM) was lunched in Europe 3/17
A communication Model • Source - generates data to be transmitted, examples are telephones and computers • Transmitter - converts data into transmittable signals • Transmission System - carries data from source to destination • Receiver - converts received signal into data • Destination - takes incoming data 4/17
Communications Tasks 5/17
Data Communication Model user keys in message m comprising bits g buffered in source PC memory input data is transferred to I/O device (transmitter) as sequence of bits g(t) using voltage shifts transmitter converts these into a signal s(t) suitable for transmission media being used whilst transiting media signal may be impaired so received signal r(t) may differ from s(t) receiver decodes signal recovering g’(t) as estimate of original g(t) which is buffered in destination PC memory as bits g’ being the received message m’ 6/17
Elements of digital communication systems Source of Information Source encoder Channel encoder Modulator Noise and interference (Unwanted signals) Channel User of information Source decoder Channel decoder Demodulator The information source generate a message signal The source encoder removes redundant information from the message signal and produce a source code word The channel encoder add some bits for the purpose of error detection and correction and produce the channel code word The modulator represent each symbol of the channel code word by a corresponding analog symbols (resulting in signal waveform) suitable for the transmission through the channel Noise and interfering signals corrupt the transmitted signal in the channel Channel types: guided media (twisted pair, coaxial, fiber optic), unguided (wireless) At the receiver, the received signal is processed in reverse order to that in the transmitter so as to recover the message signal 7/17
Cellular telephone system • The cellular mobile telephone system consists of: • Mobile Stations (MS), Base Stations (BS) and Mobile Switching Center (MSC), connected to the Public Switching Telephone Network (PSTN) 8/17
Satellite Communication system The information-bearing signal is transmitted from the earth terminal to the satellite via the uplink, amplified by the transponder (electronic circuitry on board the satellite), and then retransmitted from the satellite via the downlink to the other earth terminal 9/17
OSI Network Model 11/17
Electromagnetic Spectrum 4/44 12/17
Electromagnetic wavelength, frequency and photon energy • The electromagnetic wave at a particular wavelength λ has an associated frequency f and photon energy E : • where • is the light speed • Planck’s constant 13/17
Operating frequency of various guided and unguided transmission techniques 14/17
Electromagnetic Spectrum 16/17
Electromagnetic Spectrum 17/17