Week 02

BJTE 3053 COMMUNICATION TECHNOLOGY Week 2

1.0 Introduction  TELECOMMUNICATION   

TELE in Greek meaning distance COMMUNICATIO meaning connection Telecommunication is the transmission of signals over a distance for the purpose of communication

Copy of the original phone of Alexander Graham Bell at Musee des Arts et Metiers in Paris

1.1 Evolution of human communication  1440  1844  1866  1876  1879  1887  1895

Gutenberg invents the printing press Morse patents the telegraph First successful use of a transatlantic telegraph cable Bell invents and patents the telephone Eastman develops photographic film Hertz discovers radio wave Marconi demonstrates wireless telegraphy

 1923

Television is invented  1948 Transistor is invented  1950s Cable television first appears  1954 Color television broadcasting begins  1959 Integrated circuit is invented  1962 First communication satellite  1969 Internet is invented  1975-81 Personal computer comes into use

 1983  1989  1998

First cellular telephone system becomes operation The World Wide Web is ‘invented’ Digital television takes place

1.1 Element in a communication system

Transmitter (modulator) Information source

Receiver (demodulator) Communication channel

destination

Cont: 1. Information source  

Audio, video, text or data. Are converted into electrical signal

2. Transmitter - Convert the input message or information into electrical signals such as voltage or current or into electromagnetic waves such as radio waves, microwaves or light waves such that it is suitable for transmission and compatible with the channel. - The main process in the transmitter is modulation and encoding. - It may be as simple as a microphone or as complex as a microwave radio transmitter.

 3.

Communication channel there are two main forms of communication 



Free space media –for radio, microwave or satellite communication system Line cable transmission- coaxial or optical fibre cables.

 4.

Receiver 







Receives the electrical signals or electromagnetic waves that are sent by the transmitter through the channel. Primary purpose of the receiver is to separate the information from the received signal or wave and sent the information to the user/ destination. Basically receiver consists of several stages of amplification, frequency conversion and filtering. The main process is demodulation or detection of the received signal.

 5.  

Destination Where the user receives the information It may be loud speaker, printer, computer monitor.

Types of Electronic Communication  There

are three ways in which electronic communication classified:   

__________________ __________________ __________________

Simplex  In

simplex communication , the information travels in one direction only.  Eg:__________________

Duplex  Is

two way communication  Communicate over telephone ( full duplex)

Analog signals  Another

way to categorize electronic communications is by the types of intelligence signals transmitted.  There are 2 types of signal:  

Analog Digital

 Analog

signal is a continuously varying voltage or

current  Eg: sine wave tone or voice

Digital Signals  The

earliest forms of both wire and radio communications used a type of on/off digital code  Telegraph used Morse Code  Radio telegraph used international code of dots and dashes.  Data used in computer used digital where binary codes representing number, letters and symbol

Baseband Signals  Baseband

signal : original information signals whether analog or digital signal  Baseband transmission: Putting the original voice, video or digital signal directly into the medium.

Modulation  Transmit

baseband signal by radio, modulation technique must be used.  Modulation : Is the process of having a baseband voice, video or digital signal modify another , higher frequency signal called the carrier. The information to be sent is said to be impressed upon the carrier.

1.2 Modulation process and its need  What 





is modulation

Modulation is the process in the transmitter, by which two signals are combined, with one signal affecting one another. The resultant signal contains the information of both but with different frequency spectrum The signal that is modulated by the information bearing signal is called the carrier.



In this process, one of the characteristics of the carrier signal (the high frequency signal) is changed according to the variations of the modulating signal (the information/ audio signal).

 Types 

Analog modulation  

Where the parameter of the carrier is changed proportionally with the modulating signal It can be categorized by 3 main techniques   



of modulation

Amplitude modulation Frequency modulation Phase modulation

Pulse modulation 

Where the carrier is a periodic pulse train and one of the parameter( amplitude, width or position) changes according to audio signal.

 Why   



modulation is needed

To generate a modulated signal suited and compatible to the characteristics of the transmission channel. Reduction of noise and interference To increase the transmission speed , reduce the transmission time and increase the distance covered for the transmission. To overcome hardware limitation 

The physical size of some electronic components depend on the range of frequencies that are used in the circuit.

 Let

the antenna size be L,  L ≥ λ /10 ; λ = c/f 

Where   

λ = wavelength (m) c = speed of light = 3×108 m/s f = frequency

1.3 Electromagnetic spectrum

1.4 Various types of communication system  Broadcast  



communication system

It is point-to-multipoint communication system AM radio, FM radio, TV broadcast, shortwave radio

Mobile communication system 



It is type of transmitter- receiver combination that can be easily moved about. Portable communication system, cellular telephone, mobile satellite

 Fixed 



communication systems

It is a radio communication service between specified fixed transmitter and fixed receiver points Public telephone service, telegraph, telex or facsimile

 Data 

 

communication systems

It is a method of transferring of data from a computer terminal to another computer terminal. This system used computer lines for data transmission. Since telephone lines are designed for voice communication , a device called MODEM (MODulator- DEModulator) is needed.

1.5 Limitations in a communication system  Technological    

constraint

Equipment availability Economy and cost factor National and international law Interaction with existing systems

 Physical 

constraint

Bandwidth 





Is defined as the information carrying capacity of a system or the frequency content of a signal. More specifically, BW is the difference between the upper frequency, fH and the lower frequency, fL of the signal. The limitation due to the bandwidth is applied to both signal and system as a measure of speed. 

It means that the short transmission time will result in high speed transmission ,which require large bandwidth and hence increasing the cost of the system.



Noise 



Is defined as any unwanted electrical energy present in the usable passband of a communication system. Noise is relative to an information and is measured in terms of signal-to-noise ratio (SNR). Its limitations may be related as follows. 



High SNR > High transmitted power > high cost

There are basically two type of noise 



External noise  Is generated outside of the communication system Internal noise



This noise is random noise created by the passive or active devices that made up communication system. 

Noise is measured in terms of the following:  Ratio of the signal power to the noise power (SNR)  SNR=(Signal power, S ) / (Noise power, P)  = 10 log 10 (S/N) dB, S and N in watts  = 20 log 10 (Vs / Vn ) where Vs is the signal voltage in volts and Vn is the noise voltage in volts.   

Noise factor, F Ratio of SNR at the input to the SNR at the output F = SNR input / SNR output

 Example 

An input signal of a receiver is 240µV and internal noise at the input is 14µV. After passing through an amplifying circuit, the output signal is 5.2V. If the noise factor is 10 dB, calculate the output noise voltage.

REVISION • Telegraphy – Morse code invented by Samuel Morse in 1837

REVISION  Telegraphy 

in 1875, Emile Baudot developed the Baudot code for telegraphy

– each letter was encoded into fixed-length binary code words of length 5

REVISION  Telephony

– Alexander Graham Bell invented the telephone in 1876 – invention of the amplifier by Lee Deforest in 1906 – automatic switch, developed by Strowger in 1897, was an electromechanical step-by-step switch

REVISION 

Telephony – digital switch was placed in service in 1960 – fiber optic are replacing copper wire and coaxial cables in the telephone system – development of fax machine, modem etc. – computer-telephony integration (CTI)

REVISION  Wireless

Communications – James C. Maxwell in 1864 predicted the existence of electromagnetic radiation and formulated the basic theory (Maxwell's equations) – Maxwell's theory was verified experimentally by Hertz in 1887

REVISION 

Wireless Communications – On December 12, 1901, Guglielmo Marconi successfully received a radio signal at Signal Hill in Newfoundland, North America, which was transmitted from Cornwall, England-a distance of about 1700 miles – Marconi is credited with the development of wireless telegraphy

REVISION  Wireless

Communications – amplitude modulation (AM) broadcast was started in 1920 – in 1933, Edwin Armstrong built and demonstrated the first frequency modulation (FM) communication system

REVISION 

Wireless Communications – first television system was built in the United States by Vladimir Zworykin and demonstrated in 1929 – commercial television broadcasting began in London in 1936 by the British Broadcasting Corporation (BBC) – colour TV in late 1960' – digital TV, high-definition TV

REVISION  Wireless

Communications – satellite named Telstar 1 was launched in 1962 and used to relay TV signals between Europe and the United States – commercial satellite communication services began in 1965 with the launching of the Early Bird satellite

REVISION 

Wireless Communications – first global mobile satellite communication system (Iridium) in operation in 1999 – mobile cellular systems developed since 1980' • analog (TACS, AMP) • digital (GSM, CDMA, D-AMP) • third generation (wideband CDMA)

ANALOG SIGNAL  designed

to send messages or information from a source that generates the messages to one or more destinations

ANALOG SIGNAL information source – voice (speech source) – picture (image source) – plain text in some particular language, such as English, Japanese, German, French, etc – output is described in probabilistic terms, that is the output of a source is not deterministic 

ANALOG SIGNAL 

input transducer – convert the output of a source into an electrical signal that is suitable for transmission – a microphone serves as the transducer that converts an acoustic speech signal into an electrical signal – a video camera converts an image into an electrical signal

ANALOG SIGNAL 

transmitter – converts the electrical signal into a form that is suitable for transmission through the physical channel or transmission medium – in radio and TV broadcast, the Office Of the Telecommunication Authority (OFTA) specifies the frequency range for each transmitting station

ANALOG SIGNAL  transmitter

– the transmitter must translate the information signal to be transmitted into the appropriate frequency range that matches the frequency allocation assigned to the transmitter – signals transmitted by multiple radio stations do not interfere with one another

ANALOG SIGNAL  transmitter

– the transmitter must translate the information signal to be transmitted into the appropriate frequency range that matches the frequency allocation assigned to the transmitter – signals transmitted by multiple radio stations do not interfere with one another

ANALOG SIGNAL  channel

– physical medium used to send the signal from the transmitter to the receiver

ANALOG SIGNAL  channel

– wireline channel • twisted-pair • coaxial cable  optical fiber

ANALOG SIGNAL  channel

– wireless channel • normally atmosphere (free space) • electromagnetic energy is coupled to the propagation medium by an antenna which serves as the radiator

ANALOG SIGNAL 

channel – underwater acoustic channels • electromagnetic waves do not propagate over long distances under water except at extremely low frequencies • acoustic signals propagate over distances of tens and even hundreds of km

ANALOG SIGNAL  channel

– storage channels • magnetic tape • digital audio tape • magnetic disk • VCD • DVD

ANALOG SIGNAL  receiver

– recover the message signal contained in the received signal  if the message signal is transmitted by carrier modulation, the receiver performs carrier demodulation to extract the message front the sinusoidal carrier

ANALOG SIGNAL  output

transducer – convert the electrical signals that are received into a form that is suitable for the use; e.g., acoustic signals, images, etc.

analog signals – continuous-time signal waveforms • analog sources – information sources that produce analog signals • analog communication systems – analog signals transmitted directly via carrier modulation over the communication channel and demodulated accordingly at the receiver • e.g. AM, FM 

DIGITAL SIGNAL  digital

signals are transmitted via digital modulation and demodulated as a digital signal at the receiver

CONT  information

source – analog signal • e.g. audio or video signal – digital (discrete) signal • e.g. output of a keyboard

CONT  source

encoder – converts the output of either an analog or a digital source into a sequence of binary digits • represent the source output (message) by as few binary digits as possible • data compression

CONT  channel

encoder – introduces in a controlled manner some redundancy in the binary information sequence from the source encoder – increases the reliability of the received data and improves the fidelity of the received signal

CONT  digital

modulator – serves as the interface to the communications channel – maps the binary information sequence into signal waveforms e.g. '0' → waveform s0(t); '1' → waveform s1(t)

CONT  channel

– introduces noise and distortion to the transmitted waveform

CONT  digital

demodulator – processes the channel-corrupted transmitted waveform and reduces each waveform to a single number that represents an estimate of the transmitted data symbol (binary or M-ary)

CONT  channel

decoder – attempts to reconstruct the original information sequence from knowledge of the code used by the channel encoder and the redundancy contained in the received data

CONT source decoder – accepts the output sequence from the channel decoder and attempts to reconstruct the original signal from the source – difference between the original signal and the reconstructed signal is a measure of the distortion introduced by the digital communications system 