We begin our discussion of digital modulation by starting with the three basic types of digital modulation techniques. Lecture notes on analogue communication techniques. Note that the commercial radio systems adopted the names of the modulation schemes that they emply, but there are other systems that also use amplitude and. Amplitude modulation is a process by which the wave signal is transmitted by modulating the amplitude of the signal. Modulation and demodulation does not catch any channel noise. If the amplitude of the high frequency carrier wave is varied in accordance with the instantaneous amplitude of the modulating signal, then such a technique is called as amplitude modulation. Accordingly it is worth looking at some of the disadvantages of amplitude modulation. Types of modulation 6 flynnkatz 7810 analog modulation amplitude modulation, am frequency modulation, fm double and single sideband, dsb and ssb digital modulation phase shift keying. Digital modulation in communications systems an introduction. Amplitude modulation, spectrum of am signal, the balanced modulator, the square law demodulator, dsbsc, ssbsc and vsb, their methods of generation and demodulation, carrier. So now lets discuss different types of pulse modulation techniques in detailpulse modulation can be categorized broadly into two types. We can choose the signal constellation such that the amplitude is the same for all signal alternatives, by placing the signal vectors on a circle in the signal space.
Pdf simulation of analog modulation and demodulation. Digital data on analog signals there are two important factors that govern the e ectiveness of a digital modulation technique. Analog communication pulse modulation tutorialspoint. This can be achieved by passing the signal through a stage that runs into limiting.
So a longer vector has a larger amplitude and hence higher energy. Introduction to communication system, need for modulation, frequency division multiplexing, amplitude modulation, definition, time domain and frequency domain description. This form of modulation varies the frequency in line with the modulating signal. Both modulated carriers are summed to result in a signal with amplitude and phase modulation. Frequency modulation, fm frequency modulation has the advantage that it is possible to limit amplitude noise on the signal because it is only the frequency variations that carry the required information. Amplitude modulation am is a modulation technique where the. The basic theory and equations behind amplitude modulation are relatively straightforward and can be handled using straightforward trigonometric calculations and manipulation. To study different amplitude modulation scheme to study generation and detection of am signals to study application of am double sideband suppressed carrier dsbsc modulation double sideband large carrier dsblc modulation. Pdf communication systems a lecture notes by mahesh lohith. Why modulation is used suitable for signal transmission distanceetc multiple. Ask, fsk, psk, and qam are all forms of digital modulation. Emphasis is placed on explaining the tradeoffs that are made to optimize efficiencies in system design.
Amplitude shift keying in ask, the amplitude of the signal is changed in response to information and all else is kept fixed bit 1 is transmitted by a signal of one particular amplitude. A continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. Amplitudeshift keying ask frequencyshift keying fsk phaseshift keying psk all of these techniques vary a parameter of a sinusoid to. Modulation is a process by which some characteristics of the carrier signal like its amplitude, frequency or phase are varied in proportion to message signal. The amplitude modulation and frequency modulation are graphically shown in. In this type of modulation, the frequency of the carrier signal varies in accordance with the message signal, and other parameters like amplitude and phase remain constant. Fm radio speech signal time time amplitude carrier amplitude frequency modulation fm highest frequency lowest frequency signal goes negative noise has a greater effect on amplitude than frequency sufficient to detect zero crossings to reconstruct the signal easy to eliminate amplitude distortion constant envelope, i. Digital modulation techniques ppt linkedin slideshare.
What is amplitude modulation, am electronics notes. These two signals, usually sinusoidal functions such as sine and cosine, are 90 degrees out of phase with each other and are therefore called quadrature carriers. Digital modulation and demodulation fsk,psk,bpsk,qpsk techniques. The continuous wave modulation techniques are further divided into amplitude modulation and angle modulation. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. The message signal is, for example, a function of the sound to be reproduced by a. Pm or phase modulation is the process of varying the instantaneous phase of carrier signal accordingly with instantaneous amplitude of message signal. In this chapter, let us discuss the following analog pulse modulation techniques.
In the continuouswave modulation, a high frequency sine wave is used as a carrier wave. Next topic pulse code modulation pulsecode modulation pcm is used to digitally represent sampled analog signals. The modulating signal contains the intended message or information sometimes consisting of audio data, as in am radio. Modulating wave, the carrier wave and the modulated waves are graphically shown in the. The components of each carrier are called inphase and quadrature. If we were to implement every possible combination of demodulation algorithm, carrierrecovery technique, and clock regeneration as a distinct model, the combinatorial explosion of different models would become unmanageable. It is the standard form of digital audio in computers, cds, digital telephony and other digital audio applications. The demonstration centers around a number of signals displayed in both the time domain and the frequency domain using a signal generator, an oscilloscope to view the signal. Other methods of demodulating an am signal use synchronous techniques and provide much lower levels of distortion and improved reception where. Hence, digital modulation techniques have a greater demand, for their capacity to convey larger amounts of data than analog ones.
The two common forms of analog modulation are amplitude modulation. It can be achieved in a number of ways, but the simplest uses a single diode rectifier circuit. Jul 30, 2019 amplitude modulation is used in computer modems, vhf aircraft radio, and in portable twoway radio. The power efficiency is the ability of a modulation technique to preserve the.
Amplitude modulation refers to the process in which amplitude of the carrier wave is varied with the message signal. The simulation of modulation schemes such as amplitude modulation and frequency modulation are designed using vi models are used as reference for designing fire rescue system 14. In continuous wave modulation amplitude modulation, frequency modulation, phase modulation the carrier wave used is continuous in nature, while in case of pulse modulation, the carrier wave is in the form of pulses. This is further divided into amplitude and angle modulation. In this chapter, we will be discussing the most prominent digital modulation techniques. Fsk frequencyshift keyi slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. There are many types of digital modulation techniques and we can even use a combination of these techniques as well. In modulation, one characteristic of a signal generally a sinusoidal wave known as the carrier is changed based on the information signal that we wish to transmit modulating signal. Modulation is defined as a process by virtue of which, some characteristic of a high frequency sinusoidal wave is varied in accordance with the instantaneous amplitude of the baseband signal. Vestigial sideband amplitude modulation vsbam is a modulation that improves the spectral e. Modulationtypesamplitude,frequency,phase modulation. This principle is at the heart of amplitude modulation. That could be the amplitude, phase, or frequency, which result in amplitude modulation am, phase modulation pm, or frequency modulation fm. Amplitude modulation was developed in the beginning of the 20th century.
Mary quadrature amplitude modulation mqam is a modulation scheme that conveys data by modulating the data transmission onto the amplitude via two carrier signals. Signal encoding techniques the notes in this document are based largely on chapter 5 of the textbook sta05. The idea is simple, though the notion that it can be used to modulate signals for transmission was hardly obvious before its discovery. The information is considered as the modulating signal and it is superimposed on the carrier wave by applying both of them to the. If both the amplitude and the phase are varied proportional to the information signal, quadrature amplitude modulation qam results. Where, fc carrier frequency a maximum value of unmodulated signal. What is modulation modulation in the modulation process, some characteristic of a high frequency carrier signal bandpass, is changed according to the instantaneous amplitude of the information baseband signal. The fact that rapidly modulating the amplitude of one wave results in a waveform identical to playing two notes of different frequencies is quite remarkable and for more information. Amplitude modulation is mostly used in the form of electronic communication.
Amplitude modulation definition, types, solved examples. Amplitude modulation is a very basic form of modulation, and although its simplicity is one of its major advantages, other more sophisticated systems provide a number of advantages. Pdf analog communication system pdf notes ac notes sw. Quadrature amplitude modulation an overview sciencedirect. Quadrature amplitude modulation with amplitude modulation.
There are many methods of generating am, and this experiment explores only one. Amplitude modulation am is the process in which the amplitude of the carrier signal is varied in accordance with the information signal. Among the types of modulation techniques, the main classification is continuouswave modulation and pulse modulation. Modulation is necessary in all of the above scenarios. Amplitude modulation, am, is one of the most straightforward ways of modulating a radio signal or carrier. Pulse amplitude modulation pam theory of and its applications. If the unmodulated carrier signal is represented by. Two signals are involved in the modulation process. The paper then explains the analog to digital conversion techniques including the basics about sampling theorem, pulsecode modulation, quantization of signals followed by digital modulation techniques like amplitude shift keying. In a hybrid modulation with the following constellation pattern, the outlying signal sig2, has higher energy i. It is often called as am and is commonly used in transmitting a piece of information through a radio carrier wave.
Modulation techniques lmodulation can be done by varying the l amplitude l phase, or l frequency of a high frequency carrier in accordance with the amplitude of the message signal. Note that, in fm, the sidebands are on both sides of the carrier. Rappaports text is also a good reference for wireless signal propagation rap95. Oct 28, 2016 the most fundamental digital modulation techniques are based on keying. Chapter 7 multiple division techniques outline frequency division multiple access fdma time division multiple access tdma code division multiple access cdma comparison of fdma, tdma, and cdma walsh codes nearfar problem types of interferences analog and digital signals basic modulation techniques amplitude modulation am. Frequency modulation frequency modulation is a change in the carrier frequency fc with all other factors remaining constant. Bpsk, qpsk, msk frequency shift keying, fsk quadrature amplitude modulation, qam.
Chapter 6modulation techniques shandong university. In pulse amplitude modulation pam technique, the amplitude of the pulse carrier varies, which is proportional. The aim of this topic is to explore the reasons for using modulation. Amplitude modulation can be accomplished by multiplying the carrier sine wave by a gain or attenuation factor that varies in accordance with the intelligence signal 2. The method of varying amplitude of a highfrequency carrier wave in accordance with the information to be transmitted, keeping the frequency and phase of the carrier wave unchanged is called amplitude modulation.
Understanding modern digital modulation techniques. In pulse amplitude modulation pam technique, the amplitude of the pulse carrier varies, which is proportional to the instantaneous amplitude of the message signal. A tutorial on the most common digital modulation techniques used in both wireless and wired communications and how they compare to one another in spectral efficiency with relevant examples. Amplitude modulation can be carried out by linearly combining the carrier and intelligence signals then applying the result to a nonlinear component or circuit. A typical audio frequency of 3000 hz has a wavelength of 100 km and. Modulation, analog modulation, digital modulation, am,fm,pm. The pulse may take any real voltage value that is proportional to the value of the original waveform. In fm, the amplitude of the modulating carrier is kept constant while its frequency is varied by the modulating message signal. The original waveform amplitude is quantized with a resulting loss of information. No information is lost, but the energy is redistributed in the frequency domain. A typical f c for lowrate telephone line modems is 1800 hz approximate center of 300 3400 band, and for 1200 baud signaling 1200 pulses per. Pulse modulated signals, such as pam, pwm, ppm, pcm and dm are actually baseband.
It was the earliest modulation technique used to transmit voice by radio. Amplitude modulation is used in computer modems, vhf aircraft radio, and in portable twoway radio. Another way to think is to realize that we are really plotting the amplitude. Berrou c, glavieux a, thitimajshima p 2010 near shannon limit errorcorrecting pdf. Amplitude modulation early radio ee 442 spring semester.
Amplitude modulation is an increase or decrease of the carrier voltage ec, will all other factors remaining constant. Amplitude modulation, spectrum of am signal, the balanced modulator, the square law. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. Chapter 7 multiple division techniques outline frequency division multiple access fdma time division multiple access tdma code division multiple access cdma comparison of fdma, tdma, and cdma walsh codes nearfar problem types of interferences analog and digital signals basic modulation techniques amplitude modulation am frequency modulation fm. This application note introduces the concepts of digital modulation used in many communications systems today. Most communications systems fall into one of three categories. Lecture notes on analogue communication techniques 1. After continuous wave modulation, the next division is pulse modulation. It is a modulation system in which the signal is sampled at regular intervals and each sample is made proportional to the amplitude of the signal at the instant of sampling.
Winter 2003 uw, ece 318 lecture notes 7 amplitude modulation am ch. Note that this is the addition of two parts, a dc term and an ac term. Principles of communication modulation tutorialspoint. Ee3 lab 1 amplitude modulation and demodulation broadcast analog television tv signals have a bandwidth of approximately 6mhz and this is achieved with a quadrature modulation. There are no amplitude scales shown, but you should be able to deduce the depth of modulation 1 by inspection. Digital modulation relies on digital signal processing, such as digitaltoanalog converters dacs at a receiver and analogtodigital converters adcs at a transmitter to transform analog information e. Complete notes download link ac notes analog communication pdf free download unit i introduction.
Phase modulation phase modulation is a change in the carrier phase angle. Pulse amplitude modulation is a technique in which the amplitude of each pulse is controlled by the instantaneous amplitude of the modulation signal. Classification and types of analog modulation double sideband suppressed carrierdsb sc introduction. Typically the carrier amplitude a and the message signal mt are. Essentially an amplitude modulated wave consists of a radio frequency carrier a sine wave at one frequency, typically in the radio frequency portion of the spectrum. Tcom 370 notes 995 modulation and demodulation modems for.
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