Understand concepts of digital modulation and learn new digital modulation techniques in. Types of amplitude modulation am double sideband with carrier we will call it am. The choice of digital modulation scheme will significantly affect the characteristics, performance and resulting physical realisation of a communication system. Simulation is used to compare the performance and tradeoffs of three popular systems, msk, gmsk and bpsk, including analysis of key parameters such as occupied. The simplest digital modulation technique is amplitudeshift keying ask, where a binary information signal directly modulates the amplitude of an analog carrier. Digital modulation 1 lecture notes ingmar land and bernard h. Frequency modulation fm is the most popular analog modulation technique used in mobile communications systems. Digital communication, need of digital modulation, advantages of digital communication, disadvantages of digital communication, basic encoding techniques or digital modulation techniques, amplitude shift keying, coherent ask detector, non coherent ask detector, frequency shift key or binary ask, fsk transmitter or.
Digital modulation 1 department of electronic systems. Hence, digital modulation techniques have a greater demand, for their capacity to convey larger amounts of data than analog ones. Amplitude shift keying is a process of shifting the amplitude of carrier signal between two levels depending on whether 1 or 0 is to be transmitted. Using amplitude modulation to shift the baseband signal fm radio 88mhz108 mhz. Pdf analog and digital communication pdf notes adc. The digital modulator device acts an interface between the transmitter and the channel. The main advantages of the digital modulation over analog modulation include available bandwidth, high noise immunity and permissible power. Demodulation channel decoding is the corresponding process at the receiver of converting the received waveform into a. Digital modulation techniques in digital communication, modulating signal is binary data or an mary encoded version. 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.
The transmission bandwidth required by dsb sc is b t2b. Digital modulation methods can be considered as digitaltoanalog conversion and the corresponding demodulation or detection as analogtodigital conversion. Physical transmission is the lowest layer function except, perhaps, how i lay cable we are usually concerned with we. Each radio station is assigned 200 khz, to transmit a stereo audio. What determines how successful a receiver will be in interpreting an incoming signal.
The output of a pcm will resemble a binary sequence. In fact, all radio channels in the am band use this type of modulation. Data digital computer output or pcm channel telephone channel, microwave link, etc. The higher frequency signal indicates a mark and the lower indicates a space.
Principles of digital modulation wireless tict4d lab. Uses the 5bit baudot encoding invented in 1870 this is the origin of the word baud. Murat torlak introduction in a digital communication system, the source to be transmitted is discrete both in time and amplitude digital information carrying signals must be first converted to. Analog and digital modulation, by dr e k rotich kipnoo what is modulation. For a better quality and efficient communication, digital modulation technique is employed. Information and entropy, conditional entropy and redundancy, shannon fano coding, mutual information, information loss due to noise, source codings huffman code, variable length coding, source coding to increase average lnfomtation per bit. Modulation is the process by which we map information on to a carrier. In digital modulation, a message signal is converted from analog to digital message, and then modulated by using a carrier wave. Most communications systems fall into one of three categories. This lecture introduces the principle of digital modulation, which serves as the bridge between the cyber world and the physical world. This is the same as the am modulation above but without the carrier. Hapter modulation and demodulation mit opencourseware. The definition of nonlinear is that superposition does not. There are many modulation techniques, which are classified according to the type of modulation employed.
Each symbol represents n bits, and has m signal states, where m 2n. Notes for digital communication techniques dct by srikrishna bardhan lecture notes, notes, pdf free download, engineering notes, university. Rtty radioteletype is a very old fsk mode that printed digital messages out onto paper. Has a shift to figures character that changes what the codes mean so numbers and punctuation can be sent, and of course a shift. Agilent digital modulation in communications systems an.
Modulation is the process of encoding information from a message source in a manner suitable for transmission. Where as digital modulations are with bit streams or symbols from computing vevices as base band signals. One category uses a constant amplitude carrier and carries the information in phase or frequency variations, known as phase shift keying or frequency shift keying fsk. 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. In digital communication, modulating signal is binary data or an mary encoded version. 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.
Compare the digital communication schemes like differential pcm systems dpcm, delta modulation, and adaptive delta modulation. Chapter 6modulation techniques shandong university. The carrier wave is switched on and off to create pulses such that the signal is modulated. Coded modulation pcm is a form of modulation where there is no carrier, so that makes it a pure digital system. Digital modulation can then be defined as the process. Digital communication notes pdf dc lecture notes 4. This application note introduces the concepts of digital modulation used in many communications systems today. Analog modulation delas with the voice, video and regular waves of base band signals.
Of them all, the digital modulation technique used is pulse code modulation pcm. Modulation is the process of superimposing a low frequency signal on a high frequency carrier signal. Both amplitude and phase of ft carry information of ft. Digital modulation eit, electrical and information technology. Understand concepts of digital modulation and learn new digital modulation techniques in communication systems to make informed decisions to optimize your systems. Digital modulation is the process by which a sequence of pulses message of duration t is transformed into a sequence of sinusoidal waveforms, st of duration t. Emphasis is placed on explaining the tradeoffs that are made to optimize efficiencies in system design. Introduction, ask modulator, coherent and noncoherent ask detector, fsk modulator, spectrum of. The binary signal when ask modulated, gives a zero value for low input while it gives the carrier output for high input the following figure represents ask modulated waveform along with its. Analog and digital modulation notes analog and digital. Amplitude shift keying ask is a type of amplitude modulation which represents the binary data in the form of variations in the amplitude of a signal. There are two types of modulation analog and digital. The function qz denotes a gaussian pdf with zero mean and vari ance 1. Using iq modulation amplitude and phase control to.
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. Bpsk, qpsk, msk frequency shift keying, fsk quadrature amplitude modulation, qam. Modulation in this section, we will study about what modulation is. The changes in the carrier signal are chosen from a finite number of m alternative symbols the modulation alphabet. Categories of modulation analog and digital types of modulation analog and digital 3. Similar to the analog, in this system, the type of the digital modulation is decided by the variation of. Or the process of modulation can be defined as varying the rf carrier wave in accordance with the intelligence or information in a low frequency signal. Frequency shift keying is a process of shifting the frequency of the carrier. Digital modulation in communications systems an introduction. Digital modulation in communications systems keysight. Digital modulation digital modulation function is widely used in wireless communication. The basic digital modulation includes askfsk technologies. In digital modulation techniques, an analog carrier signal is modulated by a binary code. There are two major categories of digital modulation.
Digital data, digital signal equipment less complex and expensive than digital toanalog modulation equipment analog data, digital signal permits use of modern digital transmission and switching equipme nt digital data, analog signal some transmission media will only propagate analog signals e. For binary modulation schemes, a binary information bit is mapped directly to a signal and s contains only 2. Digital modulation provides more information capacity, high data security, quicker system availability with great quality communication. Digital modulation involves choosing a particular analog signal waveform s i t from a finite set s of possible signal waveforms based on the information bits applied to the modulator. The application of the heterodyne principle to modulation is shown schematically in figure 143. Digital channels synchronization modulation digital communications i slide 41 physical transmission how do i get bits down a piece of wire.
Or modulation is defined as the precess by which some characteristics, usually amplitude, frequency or phase, of a carrier is varied in. Modulation, analog modulation, digital modulation, am,fm. The channel noise is neglected in this lecture, and how to demodulate the signal under noise using optimal detection principles is the theme of the next lecture. The digital modulation schemes can be categorized basically either on the basis of. This is the most widely used type of am modulation.
Digital modulation and demodulation fsk,psk,bpsk,qpsk techniques. Digital modulation techniques ppt linkedin slideshare. Frequency versus amplitude modulation l amplitude modulation am l changes the amplitude of the carrier signal according to the amplitude of the message signal. Demodulation is the opposite process of modulation.
Fleury navigation and communications navcom department of electronic systems aalborg university, dk. This modulates, carrier usually sinusoidal, with fixed frequency. A signal is pulse code modulated to convert its analog information into a binary sequence, i. It involves translating a baseband message signal to a bandpass signal at frequencies that are very high compared to the baseband frequency.