Analog Communication (PDF) - Lectures

‫كلية الد فاع الجوي‬ ‫جامعة االسكندرية‬  ‫بسم هللا الرحمن الرحيم‬ ‫” وقل إعملوا فسيرى هللا عملكم ورسوله والمؤمنون“‬ ‫العظيم‬ ‫هللا‬ ‫سورة التوبة(األية ‪(105‬‬ ‫صدق‬ ‫‪Dr.waleed‬‬ ‫‪Agamy el masry‬‬ ‫‪Analog Comm...

‫كلية الد فاع الجوي‬ ‫جامعة االسكندرية‬  ‫بسم هللا الرحمن الرحيم‬ ‫” وقل إعملوا فسيرى هللا عملكم ورسوله والمؤمنون“‬ ‫العظيم‬ ‫هللا‬ ‫سورة التوبة(األية ‪(105‬‬ ‫صدق‬ ‫‪Dr.waleed‬‬ ‫‪Agamy el masry‬‬ ‫‪Analog Communication‬‬ ‫االتصاالت التشابهية‬ ‫الهد ف من دراسه هذا المنهج‬ ‫تعيلم الطالب االتي ‪-:‬‬ ‫‪ -1‬مقدمه عامه عن أنظمة االتصاالت المستخدمه قديما ثم دراسة نظام‬ ‫االتصاالت الشابهية مع توضيح الغرض من كل جزء فيه‬ ‫‪ -2‬دراسة أنواع االشارات وأسلوب ايجاد التوزيع الترددي لها‬ ‫‪ -3‬دراسة تفصيليه لكل أنواع التعديل المستخدم في انظمة‬ ‫‪ -4‬دراسة قناة االتصال مع توضيح تأثيرها‬  Analog Communication 1- Introduction 2- Introduction to signals 3- Analysis and transmission of signals Analog modulation techniques (a) Continuous Wave Modulation 4- Amplitude modulation 5- Angle modulation ( Frequency M., Phase M. ) (b) Pulse Modulation 6- Pulse Modulation ( PAM , PDM , PPM ) 7- Noise. Dr.Waleed agamy CHAPTER 1 Dr.sherif samir Ahmed Zi163927 carrierpigeon GLO TORCH 1- Introduction In the past, message have been carried by runners, Carrier pigeons , drum beats and torches. These schemes were adequate for the distance and data rates of the age. In most parts of the world these modes of communication have been superseded by electrical communication systems , which can transmit signals over much longer distance and the speed of light with high data rate.  A Basic communication system Electrical Input information signal Modulated signal Input message Input Source Transmitter Transducer Base band Band path signal signal Human voice Television picture Teletype message data Transmitted antenna Electro magnetic wave Distortion Attenuation Channel Interference Human Received antenna Television Computer Electrical Received signal signal output Destination Receiver Transducer Output information Output message Dr.sherif samir Ahmed The components of the communication system :- The source : Originate a message such as Human voice , Teletype message , television picture or data. Input transducer : Covert the nonelectric information to electric signal referred to as the baseband signal or message signal. Transmitter : Modifies the baseband signal for efficient transmission. (( Encryption – Encoder – Modulation – Amplification )) The communication channel : it is a medium such as wire , coaxial cable , a wave guide , optical fiber or radio link through which the transmitter output is sent. (( Interference , Attenuation , distortion ))  Receiver : Reprocesses the signal received from the channel by undoing the signal modification made at the transmitter. (( Demodulation - Filtrations – Decoder – Decryption – Amplification )) Output transducer : Convert the electrical signal to the original form. The destination : It is the unit to which the message is communicated.  The communication channel A channel acts partly as a Filter to attenuate the signal and distort its waveform. The signal attenuation increases with the length of the channel. The waveform of the signal is distorted because different frequency component in the signal are suffered by attenuation and phase shift. Types of distortion :- - Linear distortion - Non linear distortion The distortion can be partly corrected at the receiver by use an equalizer with gain and phase characteristic complementary to those of the channel.  The signal is not only distorted by the channel but also it is also contaminated along the path by undesirable signals lumped under the broad term noise. Noise → it is random and unpredictable signals. Types of noise :- 1- External noise Interference from signals transmitted near by channels. Human-made noise generated by faulty contact switches for electrical equipment , automobile ignition radiation , fluorescent lights 2- Internal noise noise result from thermal motion of electrons in conductors , Random emission or recombination of charge carriers in electron devices. The Signal – to – Noise Ratio (SNR) :- Is defined as the ratio of the signal power to the noise power Channel Bandwidth B , The Rate of communication R and SNR The Bandwidth of a channel :- is the range of frequencies that it can transmit with reasonable fidelity. To understand the relation between B and R Consider the possibility of increasing the speed of Information transmission by time compression of the signals. If the signal is compressed in time by a factor of 2 , It can transmitted in half the time , and the speed of transmission is doubled. The frequencies of its components are doubled. To transmit this signals without distortion, The channel bandwidth must also doubled. Thus, the rate of information transmission R directly proportional to the channel bandwidth B  The relation between SNR and quality of transmission The signal power S is related to the quality of transmission ↑ Increasing the signal power S. ↑ Increasing the signal – to – Noise Ratio ( SNR ). ↓ Reduces the effect of the channel noise. ↑ The information is received more accurately. ↑ Increased the quality of transmission. ↑ A large SNR also allows transmission over a longer distance.  The channel Bandwidth B and the signal power S are exchangeable If a given rate of information transmission requires a channel bandwidth B1 and signal – to - noise ratio SNR1 Then , it is possible to transmit the same information over a channel bandwidth B2 and signal – to – noise ratio SNR2 B1 SNR2 = (SNR1 ) B2 Dr.sherif samir Ahmed Modulation Techniques Analog modulation techniques Digital modulation techniques Continuous Wave Modulation Pulse Modulation Amplitude modulation Pulse Amplitude Pulse Time Frequency modulation Modulation (PAM) Modulation (PTM) Phase modulation Pulse Duration Modulation (PDM) Pulse Position [ Pulse Width Modulation (PPM) Modulation ]( PWM )  Modulation The baseband signal produced by various information sources are not always suitable for direct transmission over a given channel. These signal are usually further modified to facilitate transmission, this conversion process is known as “ Modulation “. In this process: (( Modulation )) The baseband signal is used to modify some parameter of high frequency signal “ Carrier signal “. Example: A carrier signal C(t) is sinusoid of high frequency and one of its parameters such as Amplitude , Frequency or Phase is varied in proportional to the baseband signal g(t).  Constant amplitude , High freq. ,constant phase Carrier signal c(t) c(t ) c(t ) = A sin (2f c t +  ) t Baseband signal g(t) g (t ) t AM → the carrier amplitude g AM (t ) varies in proportional to g(t). t g FM (t ) FM → the carrier frequency varies in proportional to g(t). t What is Modulation ? Modulation is a process that causes shift in the range of frequencies In a signal. c(t ) t g (t ) t g AM (t ) t g FM (t ) t  Why we make Modulation ? 1 – Modulation for frequency multiplexing 1 Ch.1 1 Ch.2 Ch.3 f f 2 f1 f2 f3 De- 2 f Multiplexer f multiplexer 3 f 3 f By modulating several baseband signals and shifting their spectrum to no overlapping bands, We can use all the available bandwidth through Frequency Division Multiplexing ( FDM ). Multiplexing → make modulation De-multiplexing → make Demodulation Ch.1 Ch.2 Ch.3 Ch.4 Ch.5 Ch.6 Ch.7 Ch.8 Ch.9 Ch.10 FDM f1 f2 f3 f4 f5 f6 fN frequency  2 – Modulation for design practical antenna The length ( L ) of antenna is direct proportional to the wavelength (  ) of transmitted signal.   c L= or where = 2 10 f Example : Find the optimum and worst length for the antenna if the frequency of the transmitted signal is 100 Hz. c 3 *108 Optimum length L= = = 1500 Kmeter 2 f 2 *100 Not practical c 3 *108 Worst length L= = = 150 Kmeter 10 f 10 *100  Example : if the above signal is modulated by a carrier signal with carrier frequency 1 GHZ.. Find the optimum and worst length for The antenna? c 3 *108 Optimum length L= = 9 = 15 cm 2 f 2 * (10 ) 8 c 3 *10 Worst length L= = 10 = 3 cm 10 f 10 Note : The length of the antenna is inversely proportional To the frequency of transmitted signal. 3 – Modulation for narrow banding The receiving antenna band is depend on the ratio between the minimum and maximum components in the signal. Example : Assume audio signal in range : 50 Hz → 10 KHz.  Ratio = (10*103 ) / 50 = 200 For this ratio , the antenna can’t receive all the frequency components in this range. By using modulation with carrier frequency fc = 106  Ratio = ( 10*103+106 ) / ( 50 +106 ) = 1.01 The ratio is decreased (( narrow banding )) so we can Receive all components easily. 4 – Modulation for frequency assignment in mobile system. By assignment a carrier to each user to use it for modulation. 5 - Effecting exchange of SNR and B.W. B1 SNR2 = (SNR1 ) B2 SNR1 → Signal – to – Noise Ratio of baseband signal. SNR2 → Signal – to – Noise Ratio of modulated signal. B1 → Bandwidth of baseband signal. B2 → Bandwidth of modulated signal. For modulated signal → B2 > B1 We require small SNR. → we require small transmitted power.  Radio Frequency Spectrum 1 – Extremely Low Frequency ( ELF ) 30 Hz → 300 Hz. 2 – Voice Frequency ( VF ) 300 Hz → 3 KHz. 3 – Very Low Frequency ( VLF ) 3 KHz → 30 KHz. 4 – Low Frequency ( LF ) 30 KHz → 300 KHz. 5 – Medium Frequency ( MF ) 300 KHz → 3 MHz. 6 – High Frequency ( HF ) 3 MHz → 30 MHz. 7 – Very High Frequency ( VHF ) 30 MHz → 300 MHz. 8 – Ultra High Frequency ( UHF ) 300 MHz → 3 GHz. 9 – Super High Frequency ( SHF ) 3 GHz → 30 GHz. 10 – Extra High Frequency ( EHF ) 30 GHz → 300 GHz.  Radio Frequency Spectrum ELF VF VLF LF MF 30 Hz 300 Hz 3 KHz 30 KHz 300 KHz 3 MHz 550 1650 Audio Frequency Band KHz KHz AM HF VHF UHF SHF 3 MHz 30 MHz 300 MHz 3 GHz 30 GHz EHF 300 GHz 88 108 MHz MHz FM Radio Frequency Band Micro Wave Band 300 GHz IR Band Dr.sherif samir Ahmed