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. The terms coherent and incoherent are frequently used when discussing the generation and reception of digital modulation. 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 techniques in the techniques of digital modulation, an analog signal is modulated with a binary code. Indian institute of technology kanpur national programme. Represent each possible signal as a vector in a euclidean space spanned by an orthonormalbasis. Digital modulation methods can be considered as digital toanalog conversion and the corresponding demodulation or detection as analogto digital conversion. 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. Digital modulation provides more information capacity, high data security, quicker system availability with great quality communication.
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. The left and right channels each limited to 15khz are multiplexed into a single baseband signal using amplitude modulation using frequency modulation to shift the baseband. Therefore, the degree of effective amplitude modulation in a system will affect some distortion parameters. Digital modulation techniques for more information.
Lecture 15 digital modulation techniques part 4 youtube. The changes in the carrier signal are chosen from a finite number of m alternative symbols the modulation alphabet. Pdf an analysis on digital modulation techniques for. Electrical engineering digital communication nptel. 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. The digital modulation can be classified mainly either on the basis of their bandwidth characteristics of compaction. Each radio station is assigned 200 khz, to transmit a stereo audio. Modern mobile communication systems use digital modulation techniques. Digital toanalog signals is the next conversion we will discuss in this chapter. Nptel provides elearning through online web and video courses various streams. It may come as a surprise for us to realise that the first modulation of. Digital modulation in communications systems an introduction. Hence, modulation can be objectively defined as the process of converting information so that it can be successfully sent through a medium.
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. 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. 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. Modulation avoids any interference between the two signals and also ensures that signal errors are avoided during transmission.
The scheme easily supports the use of a multipleaccess technique generic carrier model c. The modulation operation may make the signal less vulnerable to noise and interference, e. An analysis on digital modulation techniques for software defined radio applications. The carrier wave is switched on and off to create pulses such that the signal is modulated. Analog modulation uses mainly am amplitude and fm frequency modulations. Digital modulation function is widely used in wireless communication. Nov 28, 2012 in this tutorial i give a brief introduction to the three basic digital modulation techniques.
The digital modulator device provides interface between the transmitter and the channel. We are all familiar with the common analog modulation techniques of amplitude modulation am and frequency modulation fm. These are not modulation schemes in the conventional sense since they are not. Also, the thesis examines the qualitative and quantitative criteria used in selection of one modulation technique over the. Ask fsk psk modulation digital modulation techniques amplitude, frequency and phase shift keying duration. 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. Amplitudeshift keying ask frequencyshift keying fsk phaseshift. 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. Fleury navigation and communications navcom department of electronic systems aalborg university, dk. Amplitude modulation or am is the process of varying the instantaneous amplitude of carrier signal accordingly with instantaneous amplitude of message signal.
The word optical is used because are talking about optical communication otherwise this material is essentially digital modulation. Each symbol represents n bits, and has m signal states, where m 2n. Agilent digital modulation in communications systems an. This is a rectangular representation of the polar diagram. Digital modulation 1 lecture notes ingmar land and bernard h. 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. Coherent binary modulation formats,coherent qam, mary modulation techniques. There are broadly 3 aspects to a signal that can be modulated. Modulation, analog modulation, digital modulation, am,fm,pm. Jun 26, 2018 this video covers the various digital modulation techniques. The most important digital modulation techniques are based on keying such as. In this lesson, these modulation techniques are introduced. Emphasis is placed on explaining the tradeoffs that are made to optimize efficiencies in system design.
Comparative analysis of digital modulation techniques in lte. Ieee communications magazine 1 index modulation techniques. Nyquist criterion, raised cosine family of pulses, intersymbol interference digital modulation techniques i. Modulation schemes coherent and incoherent systems. Hence, digital modulation techniques have a greater demand, for their capacity to convey larger amounts of data than analog ones. There are four major modulation techniques used by communication systems nowadays to transport baseband digital data onto a carrier. Amplitude modulation am frequency modulation fm phase modulation pm amplitute modulation. The three main types of digital modulation are frequency shift keying fsk, phase shift keying psk and amplitude shift keying ask. Dm stands for digital modulation and is a generic name for modulation techniques that uses discrete signals to modulate a carrier wave. Dey, department of electrical engineering,iit bombay. Using amplitude modulation to shift the baseband signal fm radio 88mhz108 mhz. 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. Brief notes on the importance of the course and how it fits into the curriculum 8.
Most communications systems fall into one of three categories. Fsk frequency shift keying qpsk quadrature phase shift keying qam quadrature amplitude modulation. Chapter 6modulation techniques shandong university. Common digital modulation techniques and pulse modulation methods. The modulation scheme needs to be cost efficient circuitry should be simple to implement and inexpensive e.
Jun 10, 2010 for ease of analog or digital information transmission and reception, modulation is the foremost important technique. To transmit 0,we change the amplitude keeping the frequency constant 10. Digital modulation is very similar to analog modulation. 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.364 563 1435 1040 410 1393 1458 1280 791 1427 17 230 1004 323 705 1277 378 13 1378 660 541 180 424 1525 504 1164 1200 451 1255 1463 1069 454 787 774 498 354 1200 373 618 497