COURSE MATERIAL ANALOG COMMUNICATIONS SYSTEM (15A04402) LECTURE NOTES B.TECH (II - YEAR & II - SEM) Prepared by: Dr. S. MUNI RATHNAM, Professor & HOD Department of Electronics and Communication Engineering VEMU INSTITUTE OF TECHNOLOGY (Approved By AICTE, New Delhi and Affiliated to JNTUA, Ananthapuramu) Accredited By NAAC & ISO: 9001-2015 Certified Institution Near Pakala, P. Kothakota, Chittoor- Tirupathi Highway Chittoor, Andhra Pradesh - 517 112 Web Site: www.vemu.org COURSE MATERIAL JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY ANANTAPUR II B.Tech II-Sem (E.C.E) T Tu C 3 1 3 (15A04402) ANALOG COMMUNICATION SYSTEMS Course Outcome: C223.1_1: Explain the different Modulation & Demodulation Techniques of Amplitude Modulation System. C223.1_2: Explain the different Modulation & Demodulation Techniques of Angle Modulation System. C223.1_3: Describe the noise effect of noise on performance of Amplitude & Angle Modulation System. C223.1_4: Demonstrate different Discrete Modulation & Demodulation Techniques. C223.1_5: Apply the concept of information theory to analyze the Channel Capacity. UNIT- I: Introduction: Elements of communication systems, Information, Messages and Signals, Modulation, Modulation Methods, Modulation Benefits and Applications. Amplitude Modulation & Demodulation: Baseband and carrier communication, Amplitude Modulation (AM), Rectifier detector, Envelope detector, Double sideband suppressed carrier (DSB-SC) modulation & its demodulation, Switching modulators, Ring modulator, Balanced modulator, Frequency mixer, sideband and carrier power of AM, Generation of AM signals, Quadrature amplitude modulation (QAM), Single sideband (SSB) transmission, Time domain representation of SSB signals & their demodulation schemes (with carrier, and suppressed carrier), Generation of SSB signals, Vestigial sideband (VSB) modulator & demodulator, Illustrative Problems. UNIT- II: Angle Modulation &Demodulation: Concept of instantaneous frequency, Generalized concept of angle modulation, Bandwidth of angle modulated waves – Narrow band frequency modulation (NBFM); and Wide band FM (WBFM), Phase modulation, Verification of Frequency modulation bandwidth relationship, Features of angle modulation, Generation of FM waves – Indirect method, Direct generation; Demodulation of FM, Band Pass Limiter, Practical frequency demodulators, Small error analysis, Pre- emphasis, & De-emphasis filters, FM receiver, FM Capture Effect,. Carrier Acquisition- phased locked loop (PLL), Costas loop, Frequency division multiplexing (FDM), and Super-heterodyne AM receiver, Illustrative Problems. UNIT- III: Noise in Communication Systems: Types of noise, Time domain representation of narrowband noise, Filtered white noise, Quadrature representation of narrowband noise, Envelope of narrowband noise plus sine wave, Signal to noise ratio & probability of error, Noise equivalent bandwidth, Effective noise temperature, and Noise figure, Baseband systems with channel noise, Performance analysis (i.e. finding SNR expression) of AM, DSB-SC, SSB-SC, FM, PM in the presence of noise, Illustrative Problems. UNIT- IV: Analog pulse modulation schemes: Pulse amplitude modulation – Natural sampling, flat top sampling and Pulse amplitude modulation (PAM) & demodulation, Pulse-Time Modulation – Pulse Duration and Pulse Position modulations, and demodulation schemes, PPM spectral analysis, Illustrative Problems. Radio Receiver measurements: Sensitivity, Selectivity, and Fidelity. COURSE MATERIAL UNIT- V: Information & Channel Capacity: Introduction, Information content of message, Entropy, Entropy of symbols in long independent and dependent sequences, Entropy and information rate of Markoff sources, Shannon’s encoding algorithm, Discrete communication channels, Rate of information over a discrete channel, Capacity of discrete memoryless channels, Discrete channels with memory, Shannon – Hartley theorem and its implications, Illustrative problems. Text books: 1. B. P. Lathi, “Modern Digital and Analog Communication Systems,” Oxford Univ. press, 3rd Edition, 2006. 2. Sham Shanmugam, “Digital and Analog Communication Systems”, Wiley-India edition, 2006. 3. A. Bruce Carlson, & Paul B. Crilly, “Communication Systems – An Introduction to Signals & Noise in Electrical Communication”, McGraw-Hill International Edition, 5th Edition, 2010. References: 1. Simon Haykin, “Communication Systems”, Wiley-India edition, 3rd edition, 2010. 2. Herbert Taub& Donald L Schilling, “Principles of Communication Systems”, Tata McGraw-Hill, 3rd Edition, 2009. 3. R.E. Ziemer& W.H. Tranter, “Principles of Communication-Systems Modulation & Noise”, Jaico Publishing House, 2001. 4. George Kennedy and Bernard Davis, “Electronics & Communication System”, TMH, 2004. Course Code: 15A04402 Analog Communication System (ACS) UNIT-I AMPLITUDE MODULATION 1. Elements of Communication System: Communication is a process of conveying or transmitting information from one point to another point. Basically it contains three blocks as shown in figure. Transmitter Channel Receiver Functions of Transmitter: ▪ It converts one form of energy into another form. ▪ Amplification (Voltage and Power) ▪ Frequency translation – Modulation ▪ Radiation or Transmission. Functions of Channel: ▪ Interconnects Transmitter and Receiver ▪ While transmitting information from transmitter to receiver, Noise will be added by the channel Functions of the Receiver: ▪ Reception ▪ Selection ▪ Amplification (Voltage and Power) ▪ Frequency translation – De-Modulation ▪ It converts one form of energy into another form. Signal: It is physical quantity which varies with respect to time or space or any independent or dependent variable Message:It is sequence of symbols. Example: Happy New Year 2019. Information:The content of message is called information and it is inversely proportional to probability occurrence of symbols. 1 1 Information I α . I = 푙표푔 ( ) and units of information is “Bits”. 푃 2 푃 Modulation: It is process of varying the characteristics (Amplitude of Frequency or Phase of carrier signal in accordance with the instantaneous values of the modulating signal. or It is a frequency translation technique which isused in transmitter to convert base band signal into band pass signal. 2. Benefits of Modulation or Need for Modulation: • To reduce the Length or height of antenna i.e length l=λ= C/f • For Multiplexing • For Narrow banding • To reduce noise effect • To avoid Equipment limitation 3. Types of Modulation: A) Amplitude Modulation B) Frequency Modulation C) Phase Modulation 4. Power and Current Relation in AM: 푚 2 Power relation: 푃 = 푃 (1 + 푎 ) 푡 푐 2 푚 2 Current relation 퐼 = 퐼 √(1 + 푎 ) 푡 푐 2 Vemu Institute of Technology, Dept. of E.C.E, P.Kothakota, Chittoor, A.P - 517 112. Page 1 Course Code: 15A04402 Analog Communication System (ACS) 5. Expression of AM: Modulating Signal m(t) = Am Cos ωmt and Carrier c(t) = Ac Cos ωct Aam(t) = Ac Cos(ωct) + Acma/2 { Cos(ωc-ωm)t + Cos(ωc+ωm)t} AM Contains: Unmodulated carrier, Lower side band and upper side band. 퐴푚 퐴푚푎푥−퐴푚푖푛 Modulation index is 푚푎 = = 퐴푐 퐴푚푎푥+퐴푚푖푛 퐴푚 = Peak amplitude of modulating signal ,퐴푚푖푛 = Minimum amplitude of Amplitude modulated signal 퐴푐 = Peak amplitude of carrier signal, 퐴푚푎푥 = Peak or maximum amplitude of Amplitude modulated signal 6. Efficiency of AM: In AM wave, the ratio of useful message power (PSB = PLSB +PUSB) to total power ( Pt = PC + PLSB + PUSB) is called “efficiency or transmission efficiency”. 푃푆퐵 Efficiency ɳ = 푃푡 푃푆퐵 The percentage of efficiency % ɳ = x100 푃푡 Percentage of efficiency in terms of modulation index 2 푚푎 The percentage of efficiency % ɳ = 2x100Maximum efficiency occurs at ma = 1 and it is 33.33%. 2+푚푎 33.33% of total power is existed in sidebands (LSB & USB) and 66.67% of total power existed in unmodulated carrier which does not contain message or information. If carrier is removed from AM to improve the power efficiency then it contains Double Side Bands with Suppressed Carrier and it is called DSB-SC. If carrier and either of sideband is removed from AM then it contain only Single Side Band with Suppressed carrier and It’s called SSB-SC. If AM signal contains one full side band and part of other side band with suppressed carrier then it is called Vestigial Side Band Suppressed Carrier VSB-SC. 7.Comparison between AM, DSB-SC, SSB-SC and VSB-SC AM DSB-SC SSB-SC VSB-SC Parameter 2f 2f f Between f & 2f Band Width (Hz) m m m m m 33.33% 100% 100% 100% Power efficiency Percentage of 00.00% 66.67% 83.33% Between 66.67% & 83.33% power saving Frequency fc, fc-fm&fc+fm fc-fm&fc+fm fc-fm or fc+fm Between DSB-SC & SSB-SC Components Transmission of Transmission of Transmission of Transmission of Video Signal Application Audio Signal color Signal Voice Signal Envelope Synchronous Synchronous Synchronous Demodulator Circuit Complexity Less More More More Less More More More SNR 8. Switching Modulator: Switching Modulator which is used to generate AM signal which is shown in figure. Vemu Institute of Technology, Dept. of E.C.E, P.Kothakota, Chittoor, A.P - 517 112. Page 2 Course Code: 15A04402 Analog Communication System (ACS) Switching Modulator which is used to generate both AM signal. Circuit Operation: 1. Summer block produces an output, which is the addition of modulating and carrier signals. V1 (t) = m(t) + c(t) = m(t) + 퐴푐 Cos (2π푓푐t) 2. Switching diode is summer block produces an output, which is the addition of modulating and carrier signals. V1 (t) = m(t) + c(t) = m(t) + 퐴푐 Cos (2π푓푐t) 3. V1 (t) is applied as an input of diode. Assume, the magnitude