Bandwidth of narrowband fm is the same as that of am. In this modulation, the signal is sampled at regular intervals and each sample is made proportional to the amplitude of the modulating signal. Request pdf digital phase modulation and demodulation digital phase modulation is a class of power and bandwidthefficient modulations widely used in telecommunications. These methods contrast with amplitude modulation, in which the amplitude of the carrier wave varies, while the frequency and phase remain constant. Am has only two sidebands usb and lsb and the bandwidth was found to be 2 fm. Carrier and upper side band are in phase and lower side band is out of phase with carrier the given signal is narrow band fm signal option d 7. Amplitude modulation, am, is one of the most straightforward.
Amamplitude modulation fmfrequency modulation pmphase modulation in phase modulation, modulation index is directly proportional to modulating voltage only while in frequency modulation, modulation index is also inversely proportional to modulat. Phase modulation pm phase shift keying psk digital modulation amplitude shift keying ask. Angle modulation changes the phase of a signal as well as its amplitude, where amplitude modulation leaves the phase unchanged. In phase modulation pm the instantaneous angular frequency. When noise occurs naturally in radio systems, frequency modulation with sufficient bandwidth provides an advantage in cancelling the noise. The bandwidth is the difference between lowest and highest frequencies of the signal. This bandwidth is in principle determined by the carrier lifetime 204. A modulation signal is cos40000, where the baseband. Bpsk, qpsk, msk frequency shift keying, fsk quadrature amplitude modulation, qam. Frequency modulation is a type of angle modulation.
Phase modulation weichih wang southern taiwan university of technology. Application engineer lian zhao, principal engineer hari shankar, and validation test engineer ariel nachum, inphi corporation abstract this paper discuss the theory behind differential phase shift keying dpsk and differential quadrature phase shift keying dqpsk modulation formats and explains in. Amplitude modulation am changes only the magnitude of the signal. For amplitude modulated wave, the bandwidth is given by. Among the types of modulation techniques, the main classification is continuouswave modulation and pulse modulation. The general form of a sinusoidal signal can be written as ft.
Phase modulation is another type of angle modulation very similar to frequency modulation. Modification in phase according to low frequency will give phase modulation. Phase modulation pm is a form of modulation that represents information as variations in the instantaneous phase of a carrier wave. A typical audio frequency of 3000 hz has a wavelength of 100 km and would need an effective antenna length of 25 km. Modulation allows for the designated frequency bands with the carrier frequency at the center of the band to be utilized for communication and allows for signal multiplexing. Pulse modulation timedivision multiplex tdm continued necessary bandwidth for tdm signal transmission as only the amplitude information is important here, the absolute minimum bandwidth required such that the information in each sampled channel remains independent of that in the. Frequency modulation and phase modulation are closely related. Angle modulation, ii lecture topics fm bandwidth and carsons rule. The components of each carrier are called inphase and quadrature. Early developers thought that bandwidth could be reduced to 0. In this scheme during every bit duration, denoted by t, one of two phases of the carrier is transmitted. There are many ways to embed a message in a carrier. This approach is called angle modulation, and includes frequency modulation fm and phase modulation pm. Pdf on the combining of the amplitude and phase modulation in.
The amplitude of the carrier is maintained constant. The transmission bandwidth bt is approximately proportional to d. However, it usually becomes smaller than this maximum value due to the electrical parasitics associated with the packaging. In particular, we discuss amplitude and frequency modulation. Pulse amplitude modulation is the basic form of pulse modulation. Frequency modulation and phase modulation are the two complementary principal methods of angle modulation. Frequency modulation fm frequency shift keying fsk phase modulation pm phase shift keying psk digital modulation amplitude shift keying ask. Angle modulation is nonlinear and complex to analyze.
A technique to reduce phasefrequency modulation bandwidth. Similarly, the narrowband approximation for phase modulation is. If both the amplitude and the phase are varied proportional to the information signal, quadrature amplitude modulation qam results. This parameter is defined as the ratio of the half power bandwidth. Bandwidth bw is the difference between the highest and lowest frequencies of. The major advantage of this approach is that it allows the tradeoff between bandwidth and noise performance. For a single large sinusoidal signal, pm is similar to fm, and its bandwidth is approximately. Ask, fsk, psk, and qam are all forms of digital modulation. Effect of selfphase modulation on the pulse bandwidth. The modulation bandwidth of the rsoa is typically in the range of ghz. Slide 3 discretetime fm modulator slide 4 single tone fm modulation slide 5 single tone fm cont. It encodes a message signal as variations in the instantaneous phase of a carrier wave.
Introduction angle modulation modulation where the angle of a sinewave carrier is varied as a function of the intelligence amplitude. Amplitude modulation am is an analog and linear modulation process as opposed to frequency modulation fm and phase modulation pm. Nbfm has power 1 2a 2, which does not depend directly on mt. Phase modulation is one of the two principal forms of angle modulation, together with frequency modulation. Recall, the bandwidth of a complex signal like fm is the difference between its highest and lowest frequency components, and is expressed in hertz hz. Interference when two or more optical waves are present simultaneously in the same region of space, the total wave function is the. Such an overmodulated wave causes interference, which cannot be eliminated. Both modulated carriers are summed to result in a signal with amplitude and phase modulation. Digital phase modulation and demodulation request pdf. There are two common forms of angle modulation, namely, phase modulation and frequency 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.
Modulation bandwidth an overview sciencedirect topics. Phase modulation pm changes only the phase of the signal. By comparison, a typical fm carrier is 100 mhz, with a wavelength of 3 meters, and would have an 80 cm long antenna that is 31. Understand the bandwidth requirement channel bandwidth signal bandwidth understand the principle of amplitude modulation know how to modulate a signal to a certain frequency know how to demodulate a signal back to the baseband can write the equation and draw block diagram for both modulation and demodulation. Pm and digital modulation s p where 2 is the pkpk phase change in one symbol duration, t for digital signals the modulation index. Angle modulation further breaks down into phase and frequency modulation. What is the difference between phase modulation and.
Bandwidthefficient digital modulation with application to deepspace communications jpl publication 0017 june 2001 the research described in this publication was carried out at the jet propulsion laboratory, california institute of technology, under a contract. A hybrid of amplitude and phase mapping is called quadrature amplitude modulation qam. The continuous wave modulation techniques are further divided into amplitude modulation and angle modulation. Frequency modulation fm looks similar to phase modulation, though frequency is the controlled parameter, rather than relative phase. The bandwidth of a communication link, or in general any system, was loosely defined as the width of the frequency interval such that input sinusoidal frequencies within this interval will appear at the output without significant amplitude or phase change. The input to a coherent detector is dsbsc signal plus noise. Phase modulation pm is a modulation pattern for conditioning communication signals for. Fm signals have the same peak frequency deviation, then when mt is a sinusoidal signal set such that the pm and note.
Angle modulation automatic frequency control modulation for a list of other modulation techniques. Depending on the nature of the relationship between. However, this improvement in performance is achieved transmission bandwidth. A technique to reduce phasefrequency modulation bandwidth in a polar rf transmitter article in circuits and systems i. In chapter1, we investigated the way of modulating a sinusoidal carrier wave using am technique. Amplitude and phase modulation can be used together. Anglemodulation,ii lecturetopics fmbandwidthandcarson.
Pm changes the phase angle of the complex envelope in direct proportion to the message signal. A technique to reduce phasefrequency modulation bandwidth in. Amplitude modulation simply requires the carrier amplitude a cto vary linearly with respect to m. There is another way of modulating a, sinusoidal carrier wave, namely, angle modulation in which the angle of the carrier wave is varied according to the baseband signal. This type of modulation is commonly used for broadcasting music and speech, magnetic tape recording systems, two way radio systems and video transmission systems.
For digital phase modulation, we only modulate the phase of the carrier. As the value of the modulation index increases, the carrier experiences a 180 o phase reversal, which causes additional sidebands and hence, the wave gets distorted. In analog modulation we were interested in the snr, but recall from chapter 10. Nbfm signal has bandwidth 2b, same as bandwidth of am. A continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. Before we study in detail about pam lets know the concepts of. Pdf a method of contemporary use of digital and analog modulation on the same bandwidth is described. Slide 6 narrow band fm slide 7 bandwidth of an fm signal slide 8 demod. Phase modulation pm amount of phase change on angle of carrier is proportional to intelligence amplitude. Example commercial fm signals use a peak frequency deviation of. A large value of implies a large bandwidth since there will be many. Bandwidthefficient digital modulation with application to. Definition of an fm signal for a baseband signal, xt. Phase modulation pm is a modulation pattern for conditioning communication signals for transmission.
1229 680 727 502 929 551 691 1112 1005 299 153 1310 168 482 1256 763 549 1432 1150 189 1318 747 926 978 1434 1440 97 224 108 1437