Amplitude and phase modulation can be used together. Amplitude modulation am changes only the magnitude of the signal. Basic concepts of modulation three kinds of modulations modulation is the process of facilitating the transfer of information over a medium. The term digital baseband modulation or digital baseband transmission is synonymous to line codes. Radio waves can carry audio, video, and digital information over great distances by using changes in a carrier waves amplitude, frequency, or phase to represent the information being transmitted. Both modulated carriers are summed to result in a signal with amplitude and phase modulation. In commercial tv transmission in india, picture and speech signals are. The audio waveform modifies the amplitude of the carrier wave and determines. Demodulation channel decoding is the corresponding process at the receiver of converting the received waveform into a. It conveys two analog message signals, or two digital bit streams. We discuss discrete changes in the characteristics of the carrier digital modulation in 14. Multiplexingmedium access control 2 digital modulation 3 why modulate.
We are all familiar with the common analog modulation techniques of amplitude modulation am and frequency modulation fm. Digital modulation in communications systems an introduction. Pulse amplitude modulation pulse code modulation sampling. Polar view of digital iq modulation contd transmission signal is sine wave at frequency f 0 with information encoded in discrete values of amplitude and phase. Pulse amplitude modulation has some applications, but it is not used by itself. Frequency modulation fm looks similar to phase modulation, though frequency is the controlled parameter, rather than relative phase. Amplitude modulation a continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. The idea is simple, though the notion that it can be used to modulate signals for transmission was hardly obvious before its discovery. In digital transmission, the modulation technique that requires minimum bandwidth is. The components of each carrier are called inphase and quadrature. These signals carry the information through modulation.
A digital signal, representing the binary digits 0 and 1 by a series of on and off amplitudes, is impressed onto an analog carrier wave of constant amplitude and frequency. It may come as a surprise for us to realise that the first modulation of electrical. To recover mtfrom st, we require the use of coherent detection. In this type of modulation, amplitude a c and angular frequency. In amplitude shift keying ask, the modulated wave represents the series of bits by shifting abruptly between high and low. The heterodyne principle is the basic idea governing several different modulation schemes. I analog and digital transmission of data simon haykin encyclopedia of life support systems eolss note that unlike amplitude modulation, the envelope of a dsbsc modulated wave is different from the message signal. Note that the frequency modulation and phase modulation of a carrier wave is collectively called the angle modulation. Each symbol represents n bits, and has m signal states, where m 2n. A digital terrestrial transmission dvbt for a single television channel can utilise upto.
Chapter 11 digital data transmission by baseband pulse. It is often called as am and is commonly used in transmitting a piece of information through a radio carrier wave. Pulse amplitude modulation pulse code modulation sampling rate. Pulse amplitude modulation is one of the kinds of modulation techniques used in signal transmission. Pulse amplitude modulation is the simplest form of modulation. When expressed as a percentage it is the same as the depth of modulation. Farshad lahouti january 20, 2003 winter 2003 uw, ece 318 lecture notes 2 information source signal modulator propagation channel signal demodulator information destination analog communication system analog signals may be transmitted directly via carrier modulat ion over. Ee4512 analog and digital communications chapter 6 the analytical signal for double sideband, large carrier amplitude modulation dsblc am is. Amplitude modulation definition, types, solved examples. Objective questions and answers on digital communication. To extend the range your voice can reach, we need to. Chapter 11 digital data transmission by baseband pulse amplitude modulation pam contents slide 1 pulse amplitude modulation pam slide 2 block diagram of pam system slide 3 pam block diagram description slide 4 block diagram description cont.
Thus, dsbsc with an analog message is called amplitude modulation, while the same dsbsc transmission with a digital message is called onoff keying. Modulation is the process of encoding information from a message source in a manner suitable for transmission. The amplitude modulation am modulation index can be defined as a measure of the amplitude variation upon a carrier. In particular, we discuss amplitude and frequency modulation. Message information can be transmitted in either the ampli tude, frequency, or phase of the carrier, or a combination thereof, in either analog or digital format. Amplitude shift keying ask in the context of digital communications is a modulation process, which imparts to a sinusoid two or more discrete amplitude levels. The amplitude modulation am modulation index can be defined as the ratio of the peak. Modulation is the process whereby message information is embedded into the ra dio frequency carrier. Overmodulation overmodulation is a condition that occurs when an excessive intelligence signal overdrives an am modulator making %m 100% because e i e c modulated carrier amplitude reach value greater than double of unmodulated value it produces a distortion known as sideband splatter, which results on transmission at frequencies outside. In general it involves translating a baseband signal source. Amplitude modulation is used in computer modems, vhf aircraft radio, and in portable twoway radio frequency modulation 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. Amplitude modulation is mostly used in the form of electronic communication. Multiple choice questions and answers on modulation and demodulation.
The rate of change of the ask waveform baud is the same as. Digital amplitude modulation involves varying the amplitude of a carrier wave in discrete sections according to binary data. We consider binary modulation schemes and multilevel modulation schemes here. Phase modulation pm changes only the phase of the signal. In addition to reading the questions and answers on my site, i would suggest you to check the following, on amazon, as well. Amplitude modulation is a process by which the wave signal is transmitted by modulating the amplitude of the signal. Sound transmission in air has limited range for the amount of power your lungs can generate. These are related to the number of levels adopted by the digital message. Learn about baseband digital data transmission over bandlimited channels by pam. The most straightforward approach to digital amplitude modulation is onoff keying. Quadrature amplitude modulation qam is the name of a family of digital modulation methods and a related family of analog modulation methods widely used in modern telecommunications to transmit information. For a binary message sequence there are two levels, one of which is. In amplitude modulation, the amplitude or strength of the carrier oscillations is varied. To understand the theoretical foundations of analog communications as well as of doublesideband amplitude modulation and demodulation dsbam to design the simulink model of the dsbam to analyze each signal in time and frequency domains using time scope and spectrum analyzer.