Amplitude modulation or am is the process of varying the instantaneous amplitude of carrier signal accordingly with instantaneous amplitude of message signal. Nov 28, 2012 in this tutorial i give a brief introduction to the three basic digital modulation techniques. Pdf an analysis on digital modulation techniques for. 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.
Fleury navigation and communications navcom department of electronic systems aalborg university, dk. Amplitude modulation am frequency modulation fm phase modulation pm amplitute modulation. An analysis on digital modulation techniques for software defined radio applications. There are four major modulation techniques used by communication systems nowadays to transport baseband digital data onto a carrier. The most important digital modulation techniques are based on keying such as. Ieee communications magazine 1 index modulation techniques for 5g wireless networks ertugrul basar, senior member, ieee abstract the increasing demand for higher data rates, better quality of service, fully mobile and connected wireless. Common digital modulation techniques and pulse modulation methods.
This is a rectangular representation of the polar diagram. Digital modulation methods can be considered as digital toanalog conversion and the corresponding demodulation or detection as analogto digital conversion. Quadrature phase shift keying qpsk another extension of psk is the digital modulation technique which is a higher order of psk that uses a four level phase state to transmit 2bitssymbol simultaneously, by selecting one of the four possible equally spaced carrier phase shift of 0. Digital modulation in digital communications, the modulation process corresponds to switching or keying the amplitude, frequency, or phase of a sinusoidal carrier wave according to incoming digital data three basic digital modulation techniques amplitudeshift keying ask special case of am. Using amplitude modulation to shift the baseband signal fm radio 88mhz108 mhz. The digital modulator device provides interface between the transmitter and the channel. Depending on which parameter of the carrier signal is varied in accordance with the digital message signal, we obtain three main variants of digital modulation called amplitude shift keying ask, frequency shift keying fsk and phase shift keying psk. Modulation, analog modulation, digital modulation, am,fm,pm. Comparative analysis of digital modulation techniques in lte. We are all familiar with the common analog modulation techniques of amplitude modulation am and frequency modulation fm. Ask fsk psk modulation digital modulation techniques amplitude, frequency and phase shift keying duration.
Also, the thesis examines the qualitative and quantitative criteria used in selection of one modulation technique over the. Each radio station is assigned 200 khz, to transmit a stereo audio. Therefore, the degree of effective amplitude modulation in a system will affect some distortion parameters. Metrics for digital modulation power efficiency ability of a modulation technique to preserve the fidelity of the digital message at low power levels designer can increase noise immunity by increasing signal power power efficiency is a measure of how much signal power should be increased to achieve a particular ber for a given. It may come as a surprise for us to realise that the first modulation of. Similar to the analog, in this system, the type of the digital modulation is decided by the variation of the carrier wave parameters like amplitude, phase and frequency. Emphasis is placed on explaining the tradeoffs that are made to optimize efficiencies in system design. Jun 26, 2018 this video covers the various digital modulation techniques. There are broadly 3 aspects to a signal that can be modulated. The changes in the carrier signal are chosen from a finite number of m alternative symbols the modulation alphabet. Digital modulation 1 lecture notes ingmar land and bernard h.
Nptel provides elearning through online web and video courses various streams. Represent each possible signal as a vector in a euclidean space spanned by an orthonormalbasis. 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. Pulseamplitude modulation pam pulsewidth modulation pwm pulseposition modulation ppm. The basic digital modulation includes askfsk technologies which simplified the. These techniques are also called as digital modulation techniques digital modulation provides more information capacity, high data security, quicker system availability with great quality communication. Hence, modulation can be objectively defined as the process of converting information so that it can be successfully sent through a medium. Modulation schemes coherent and incoherent systems. The word optical is used because are talking about optical communication otherwise this material is essentially digital modulation. Indian institute of technology kanpur national programme. Analog modulation uses mainly am amplitude and fm frequency modulations.
Digital modulation provides more information capacity, high data security, quicker system availability with great quality communication. A read is counted each time someone views a publication summary such as the title, abstract, and list of authors, clicks on a figure, or views or downloads the fulltext. Agilent digital modulation in communications systems an. In this lesson, these modulation techniques are introduced. In the present chapter, well discuss about different modulation scheme in. The digital codes or signals are modulated by different kinds of variable analog carieer to enhance the power transmission efficiency and avoid the interference by other communication bands in air. The paper presents the characteristics of the modulation techniques and determines the. Dey, department of electrical engineering,iit bombay. Lecture 15 digital modulation techniques part 4 youtube. The modulation operation may make the signal less vulnerable to noise and interference, e.
The carrier wave is switched on and off to create pulses such that the signal is modulated. To transmit 0,we change the amplitude keeping the frequency constant 10. Digital modulation is very similar to analog modulation. Digital modulation function is widely used in wireless communication. Jun 10, 2010 for ease of analog or digital information transmission and reception, modulation is the foremost important technique. Modern mobile communication systems use digital modulation techniques. Brief notes on the importance of the course and how it fits into the curriculum 8. Digital toanalog signals is the next conversion we will discuss in this chapter. Industry trends over the past few years a major transition has occurred from simple analogue amplitude modulation am and frequencyphase modulation fmpm to new digital modulation techniques. When linked to the process of modulation the term coherence relates to the ability of the modulator to control the phase of the signal, not just the frequency. Hence, digital modulation techniques have a greater demand, for their capacity to convey larger amounts of data than analog ones. The use of amplitudemodulated analog carriers to transport digital information is a relatively lowquality, lowcost type of digital modulation and, therefore, is seldom used except for very lowspeed telemetry circuits. The modulation scheme needs to be cost efficient circuitry should be simple to implement and inexpensive e.
Electrical engineering digital communication nptel. The digital modulation can be classified mainly either on the basis of their bandwidth characteristics of compaction. These are not modulation schemes in the conventional sense since they are not. This thesis deals with the current digital modulation techniques used in industry. The three main types of digital modulation are frequency shift keying fsk, phase shift keying psk and amplitude shift keying ask. We said that in analog communications you modulate the amplitude the phase or the frequency directly as a function of the modulating signal m of t the message. Dm stands for digital modulation and is a generic name for modulation techniques that uses discrete signals to modulate a carrier wave. Modulation avoids any interference between the two signals and also ensures that signal errors are avoided during transmission. Most communications systems fall into one of three categories. The terms coherent and incoherent are frequently used when discussing the generation and reception of digital modulation. Fsk frequency shift keying qpsk quadrature phase shift keying qam quadrature amplitude modulation. Each symbol represents n bits, and has m signal states, where m 2n.
Digital modulation techniques for more information. Amplitudeshift keying ask frequencyshift keying fsk phaseshift. Nyquist criterion, raised cosine family of pulses, intersymbol interference digital modulation techniques i. All about modulation basic concepts, signal space, constellations and phase shift keying modulations psk, qpsk, oqpsk, mpsk. The scheme easily supports the use of a multipleaccess technique generic carrier model c. Chapter 6modulation techniques shandong university. Thus, if mt is the message signal and ctacosw c t then am signal ft is written as. Digital modulation techniques in the techniques of digital modulation, an analog signal is modulated with a binary code. Ieee communications magazine 1 index modulation techniques. Digital modulation in communications systems an introduction.