The basic types of modulation are angular mo dulation including the special cases of phase and frequency modulation and amplitude modulation. Digital communication tutorial in pdf tutorialspoint. 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. Weexpresstheresultinganglewe express the resulting anglemodulatedwaveasmodulated wave as 4. Problem 3 the output signal from an am modulator is. 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. In pulse modulation, a periodic sequence of rectangular pulses, is used as a carrier wave. Chapter 6modulation techniques shandong university. Jan 18, 2017 i think the spelling need to be checked,as ppt hasnt a meaning, anyhow, modulation means to include a certain message from any type into another transmitted carrier signal, including it has three types,am,fm, and pm pm is phase modulation wh. Selfphase modulation is an important effect in optical systems that use short, intense pulses of light, such as lasers and optical fiber communications systems6. The phase modulated signal st is thus described in the time domain by. For example, the message signal mt is made up of two different components m t and m. A sinusoid has three different parameters than can be varied. Frequency modulation fm looks similar to phase modulation, though frequency is the controlled parameter, rather than relative phase.
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. In case of dispute, the reference shall be the printing on etsi printers of the pdf version kept on a specific network drive. 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. Quadrature phase shift keying modulation pdf quaternary phase shift keying qpsk. Just as in radio, optical systems started out with amplitude modulation, which is known as onoffkeying or ook. Frequency modulation the frequency of the carrier signal is proportional to the modulating signal phase modulation the phase of the carrier signal is proportional to the modulating signal 2 cos 0. In words, the angle is used to carry information in a.
Pm and digital modulation s p where 2 is the pkpk phase change in one symbol duration, t for digital signals the modulation index. Basic concepts, signal space, constellations and phase shift keying. Pdf the modulation ratio in comprehensive twodimensional gas. Conclusion the effect of self phase modulation on optical fiber is reported in this paper. The change in phase, changes the frequency of the modulated wave. But we are getting ahead of ourselves, as we have not yet even defined what am is. The frequency of the wave also changes the phase of the wave.
This was because optical detectors are only sensitive to amplitude optical power and not to phase, and manipulating the phase of optical signals at high frequencies is difficult. If the phase of the high frequency carrier wave is varied in accordance with the instantaneous value of the modulating signal, then such a technique is called as phase modulation. These effects are seen from the eye diagrams drawn for the different values ofdispersion. Demodulation channel decoding is the corresponding process at the receiver of converting the received waveform into a. In nonlinear digital phase modulation with memory, the modulated signal is constrained to maintain a constant envelope and continuous phase, avoiding abrupt changes in phase. Hapter modulation and demodulation mit opencourseware. Amplitude and phase modulation can be used together. Where n index of refraction of medium wave travels. In theory an fm signal contains an infinite number of side frequencies so that. Phaseshift keying psk all of these techniques vary a parameter of a sinusoid to represent the information which we wish to send. Modulation shifts center frequency of basebandsignal up to the radio carrier basic schemes amplitude modulation am amplitude shift keying ask frequency modulation fm frequency shift keying fsk phase modulation pm phase shift keying psk digital modulation. Depending on the nature of the relationship between.
Digital modulation in communications systems an introduction. Phase modulation works by modulating the phase of the signal, i. The transmission bandwidth required by dsb sc is b t2b. Modulation modulation is the process whereby some characteristic of one wave is v aried in accordance with some characteristic of another wave. The amplitude of the fm signal is constant at all times and is independent of the modulation signal.
The application of the heterodyne principle to modulation is shown schematically in figure 143. In other words the speed of rotation around the circle is modulated about the mean value. We therefore assume mta mcos2 f mtfor pm and mta msim2 f mtfor fm. Phase modulation is one of the two principal forms of angle modulation, together with frequency modulation the phase of a carrier signal is modulated to follow the changing signal.
Amplitude modulation a1 49 you will see in this experiment, and in others to follow, that there is no problem in generating an am signal with a depth of modulation exceeding 100%, and without any rf distortion whatsoever. Modulation in this chapter, we are going to learn basic principles of modulation. You can publish your book online for free in a few minutes. Dpsk can be significantly simpler to implement than ordinary psk since there is.
Cpm is an example of nonlinear digital phase modulation with memory. Quadratic phase shift keying qpsk modulation technique. Phase shift keying psk all of these techniques vary a parameter of a sinusoid to represent the information which we wish to send. Both amplitude and phase of ft carry information of ft. This changes the phase of the signal from what it would have been if no modulation was applied. The amount of frequency shift, produced by a phase modulator increases with the modulating frequency. Basic concept of modulation the information source typically a low frequency signal referred to as the baseband signal carrier a higher frequency sinusoid example. The resulting signal is called the modulated signal in general, it is a bandpass signal. Npdf can be availed only once by a candidate in hisher career.
Modulation can be defined as the process of impressing information from a modulating signal onto another signal called the carrier. Phase modulation weichih wang southern taiwan university of technology. Angle modulation is the process in which the frequency or the phase of the carrier varies according to the message signal. Digital phase modulation and demodulation request pdf. Though they are related, their relationship is not linear. Interference when two or more optical waves are present simultaneously in the same region of space, the total wave function is the sum of the individual wave functions. Principles of communication modulation tutorialspoint. Graph for quality factor versus dispersionwith self phase modulation spm and without self phase modulation spm. The audio information in a tv channel is a frequency modulated carrier placed 4. Amplitude modulation of a sine or cosine carrier results in a variation of the. The software provides frequency, time, and modulationdomain analysis results in a.
Their signal waveform expressions, signal constellations, and power. Phase modulation pm is a modulation pattern for conditioning communication signals for transmission. Lowfrequency baseband sign it is thus translated to a high frequency carrier such that the information is coded in the variations in one of the parameters of the carrier. The continuous analog signal st is a baseband signal with the information content voice or music to be transmitted. Phase modulation pm changes only the phase of the signal. In this method of modulation the amplitude of the carrier wave is maintained constant. Agilent digital modulation in communications systems an.
Modulation is a process of mapping such that it takes your voice as an example of a signal converts it into. This is further divided into analog and digital modulation. In phase modulation pm the instantaneous angular frequency. The phase of the carrier is advanced or retarded up to 90o over the course of a bit period depending on the data pattern, although the rate of change of phase is limited with a gaussian response. Phaseshift keying psk is a digital modulation scheme that conveys data by.
This is further divided into frequency and phase modulation. Mentor must hold a regular academicresearch position in a recognized institution in india. Phase modulation is an indirect method of producing fm. This variation in refractive index will produce a phase shift in the pulse, leading to a change of the pulses frequency spectrum. Pdf on jan 1, 2016, philip john marriott and others published the modulation ratio in. The net result of this is that depending on the bandwidth time product bt. I think the spelling need to be checked,as ppt hasnt a meaning, anyhow, modulation means to include a certain message from any type into another transmitted carrier signal, including it has three types,am,fm, and pm pm is phase modulation wh. Frequency modulation and phase modulation are closely related.
Both pm and fm waves violate the principle of superposition. Spectra have a typical trapezoidal shape in linear frequency and amplitude in decibels. Modulation l, in which the carrier frequency is near baseband. The phase change is converted into an intensity change using interferometric schemes machzehnder, michelson, fabryperot or sagnac forms. At the receiver side, these variations are detected through the demodulation process to recover.
The other type of modulation in continuouswave modulation is the angle modulation. There are two common forms of angle modulation, namely, phase modulation and frequency modulation. We begin our discussion of digital modulation by starting with the three basic types of. Phase modulation pm phase shift keying psk digital modulation amplitude shift keying ask. Again gmsk can be viewed as either frequency or phase modulation. Fm signals have the same peak frequency deviation, then when mt is a sinusoidal signal set such that the pm and note. Network analysis measurements offer more information about a circuit or system, but the. The commonly used class of digital phase modulation schemes, that is, mary phase shift keying mpsk, are described in detail. 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. Therefore we only consider the case where the message signal mtis a sinusoidal signal.
Linear modulation one scheme is to simply square the received dsb signal x2 r. Qpsk and uses this discussion as a vehicle for development of generic. All about modulation part i basic concepts, signal space, constellations and phase shift keying modulations psk, qpsk, oqpsk, mpsk. Inphase, quadrature phase components of the modulated signal. Although the general aspects on the workings of the lc phase modulator have been described in many articles and textbooks, the. 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. Interferometer criteria for waveguide or fiber optic based.
685 1197 1145 121 1047 600 1204 1199 526 1169 929 634 1515 230 1049 951 1286 1370 323 488 1252 339 289 1223 1576 1023 1343 520 1041 1495 25 683 1249