Communication Systems ( ) First semester 2008/2009 Dr. Ali Jamoos 1/17

2/17 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)

3/17 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 Advanced Mobile Phone System (AMPS) was lunched in US Global System for Mobile (GSM) was lunched in Europe

4/17 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

5/17 Communications Tasks Transmission system utilizationAddressing InterfacingRouting Signal generationRecovery SynchronizationMessage formatting Exchange managementSecurity Error detection and correctionNetwork management Flow control

6/17 Data Communication Model 1.user keys in message m comprising bits g buffered in source PC memory 2.input data is transferred to I/O device (transmitter) as sequence of bits g(t) using voltage shifts 3.transmitter converts these into a signal s(t) suitable for transmission media being used 4.whilst transiting media signal may be impaired so received signal r(t) may differ from s(t) 5.receiver decodes signal recovering g(t) as estimate of original g(t) 6.which is buffered in destination PC memory as bits g being the received message m

7/17 Elements of digital communication systems Source of Information Source encoder Channel encoder Modulator Channel User of information Source decoder Channel decoder Demodulator Noise and interference (Unwanted signals) 1.The information source generate a message signal 2.The source encoder removes redundant information from the message signal and produce a source code word 3.The channel encoder add some bits for the purpose of error detection and correction and produce the channel code word 4.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 5.Noise and interfering signals corrupt the transmitted signal in the channel 6.Channel types: guided media (twisted pair, coaxial, fiber optic), unguided (wireless) 7.At the receiver, the received signal is processed in reverse order to that in the transmitter so as to recover the message signal

8/17 Cellular telephone system The cellular mobile telephone system consists of: 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) Mobile Stations (MS), Base Stations (BS) and Mobile Switching Center (MSC), connected to the Public Switching Telephone Network (PSTN)

9/17 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

10/17 Computer Networks and the Internet

11/17 OSI Network Model

4/44 Electromagnetic Spectrum 12/17

13/17 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 Plancks constant

14/17 Operating frequency of various guided and unguided transmission techniques

15/17 Atmospheric Transparency for Electromagnetic waves

16/17 Electromagnetic Spectrum Band Frequency range Propagation characteristics Typical use ELF (extremely low frequency)30 to 300 Hz Ground Wave (GW) propagation Power line frequencies VF (voice frequency)300 to 3000 Hz GW propagation Used by the telephone system for analog subscriber lines VLF (very low frequency)3 to 30 kHz GW propagation Long-range navigation; submarine communication LF (low frequency)30 to 300 kHz GW propagation Long-range navigation; marine communication MF (medium frequency)300 to 3000 kHzSky-Wave (SW) ionospheric propagation AM broadcasting HF (high frequency)3 to 30 MHzSW ionospheric propagationinternational broadcasting, military communication; long- distance aircraft and ship communication

17/17 Electromagnetic Spectrum Band Frequency range Propagation characteristics Typical use VHF (very high frequency)30 to 300 MHzSW ionospheric and tropospheric propagation; Line-Of-Sight (LOS) Propagation VHF television; FM broadcast AM aircraft communication; Aircraft navigational aids UHF (ultra high frequency)300 to 3000 MHzLOS Propagation UHF television; cellular telephone; radar; microwave links; personal communications systems SHF (super high frequency)3 to 30 GHz LOS Propagation Satellite communication; radar; terrestrial microwave links; wireless local loop EHF (extremely high frequency)30 to 300 GHz LOS Propagation Experimental; wireless local loop Infrared300 GHz to 400 THz LOS Propagation Infrared LANs; consumer electronic applications Visible light 400 THz to 900 THz LOS Propagation Optical communication