Analog modulation delas with the voice, video and regular waves of base band signals. Two attractive modulation schemes are pulse position modulation ppm and multipulse ppm mppm. Linear modulation we are typically interested in locating a messagesignal to some new frequency location, where it can be ef. Here we will discuss in details, pulse modulation and pulse modulation techniques like pulse amplitude modulation pam, pulse width modulation pwm, pulse position modulation. Therefore, the degree of effective amplitude modulation in a system will affect some distortion parameters. Digital modulation 1 lecture notes ingmar land and bernard h.
In both the techniques, the baseband information is converted to radio frequency signals, but in analog modulation these rf communication signals are continuous range of values, whereas in digital modulation these are prearranged discrete states. The function qz denotes a gaussian pdf with zero mean and vari ance 1. Modulation and demodulation medium, it would be dif. Course overview timeseries representation of signals typically think of a signal as a \time series, or a sequence of values in time t ft useful for saying what is happening at a particular time not so useful for capturing the overall characteristics of the signal. Digital phasemodulated pm signals phase shift keying or psk. Milstein, fellow, ieee abstracta robust coded scheme for progressive multimedia transmission is proposed for additive white gaussian noise. The modulators used are memoryless as neither the instantaneous phase. Another issue of commonly used active load modulation techniques is a rather shallow backoff efficiency enhancement of about 6db. Chapter 6modulation techniques shandong university. A tutorial introduction to optical modulation techniques. All about modulation basic concepts, signal space, constellations and phase shift keying modulations psk, qpsk, oqpsk, mpsk.
Spectrum of a pm or fm signal with sinusoidal modulation 47. Modulation is the process of superimposing a low frequency signal on a high frequency carrier signal. Forward error correction in memoryless optical modulation. In this case, modulation symbols rather than bits, characters, or data packets are asynchronously transferred. Recall that our goal is to transmit data over a commu nication link, which we achieve by mapping the. The waveforms, definition and basic concepts of each digital. 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. Phaseshift keying psk binary psk bpsk, using m2 symbols. Using this technique, all the signalsignal distortions can be compensated for by processing the signal at the transmitter, at the receiver, or at both. Ii digital communication techniques 50 3 pulse amplitude modulation pam 51. All about modulation part i basic concepts, signal space, constellations and phase shift keying modulations psk, qpsk, oqpsk, mpsk. Ee4512 analog and digital communications chapter 6 the dsbsc am coherent receiver has a bandpass filter centered at f c and with a bandwidth of twice the bandwidth.
Modulati on techniques are commonly classified into continuous wave cw modulation and pulse pu modulation. Hence, digital modulation techniques have a greater demand, for their capacity to convey larger amounts of data than analog ones. Demodulation is the opposite process of modulation. Since frequency modulation is a nonlinear process, an exact description of the spectrum of an frequencymodulated signal for an arbitrary message signal is more complicated than linear process. The transmitted signal can be memoryless or with memory. Signal modulation has an important impact on the system performance in optical communication. Information theory is a mathematical approach to the study of coding of information along with the quantification, storage, and communication of information.
The likelihood ratio of receiving value y in a slot is denoted by lyp. Pulse duration modulation pdm or pulse width modulation pwm. Pulseposition modulation ppm is a form of constrained ono. Demodulation and detection schemes for a memoryless. Since modern modulation signals have papr of about 10db, achieving deeper backoff enhancement can further improve the overall efficiency. Memoryless modulation versus modulation with memory.
Demodulation and detection schemes for a memoryless optical. Spectral regrowth analysis at the output of a memoryless power amplifier with multicarrier signals. Modulation schemes coherent and incoherent systems. The code produced by a discrete memoryless source, has to be efficiently represented, which is an important problem in communications. As of this writing, the popular mobile telephony networks 4glte and wireless networking systems ieee 802. The modulation scheme can be viewed as a mappin g from the current state and the current input of the modulator to the set of output signals resulting in a new state of the modulator. A binary memoryless source is a dms with a binary symbol al phabet. Cutoff rate performance of memoryless modulation schemes operating on slowfading rician channels t kyuhyoun park and james w. 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. Multipulse pulseposition modulation on discrete memoryless. For example, in telegraphy, we use morse code, in which the alphabets are denoted by marks and spaces.
Apr 17, 2017 here we will discuss in details, pulse modulation and pulse modulation techniques like pulse amplitude modulation pam, pulse width modulation pwm, pulse position modulation ppm and pulse. Represent each possible signal as a vector in a euclidean space spanned by an orthonormalbasis. Multipulse pulseposition modulation on discrete memoryless channels. Optical modulation a tutorial introduction to optical modulation techniques by gary breed editorial director t his article introduces the subject of optical modulation, the process of applying information to a light wave. For this to happen, there are code words, which represent these source codes. The gaussian qfunction and the euclidean distances among the constellation points may be used for quantifying the lower or upper bound of the system.
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. Optimal memoryless relays with noncoherent modulation. Analog sinusoidal modulation analog sinusoidal modulation techniques. Consequently, the first digital communication systems were based on singlecarrier techniques, and this remained the case until the 1990s, when multicarrier modulations became popular. In pulse width modulation or pulse duration modulation, the width of the pulse carrier is varied in accordance with the sample values of message signal or modulating signal or modulating voltage. From analysis of modulation techniques, the system could use more appropriate modulation technique to suit the channel quality, thus we can deliver the optimum and efficient system parameters. Coded hierarchical modulation for wireless progressive image transmission suayb s. Coded hierarchical modulation for wireless progressive image. Source coding theorem the code produced by a discrete memoryless source, has to be efficiently represented, which is an important problem in communications.
Cutoff rate performance of memoryless modulation schemes. Different types of modulation techniques in communication systems. However if st is sinusoidal, then the instantaneous frequency deviation of the anglemodulated signal is sinusoidal. In the process of modulation, usually the transmitted signals are bandpass signals suitable for transmission in the bandwidth providedsuitable for transmission in the bandwidth provided by the communication channel. When evaluating the performance of a system, typically, the ber performance is the salient metric 14, 9. Digital modulation in communications systems an introduction. One approach to reduce this interference, known as frequencydivision multiplexing, allocates different carrier frequencies to different users or for dif. This chapter describes the essential principles behind.
Hapter modulation and demodulation mit opencourseware. The double sideband baseband spectrum is shifted linearly in the rf range. This is a rectangular representation of the polar diagram. More specifically, this paper provides explicit development and numerical evaluation of the cutoff rate of memoryless modulation schemes for the slowfading rician channel not. Where as digital modulations are with bit streams or symbols from computing vevices as base band signals. Accordingly, these two modulation methods are equivalent. 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.
This is in contrast to oqpsk, which is memory less. Modulation techniques pwm and pulse code modulation. Quadrature amplitude modulation with amplitude modulation. Fleury navigation and communications navcom department of electronic systems aalborg university, dk. Free space optical using different modulation techniques a. Analog modulation techniques am modulation, fm modulation, single side band modulation, ssb, bandwith of fm signals, phase modulation, angle modulation, pdf file. Pulse modulation techniques pam, pwm, ppm, pcm pulse. Those light waves may be sent through a transparent medium as a laser beam, or contained within a fiber optic cable. Conditional probabilities and the memoryless property daniel myers joint probabilities for two events, e and f, the joint probability, written pef, is the the probability that both events occur. All the types of modulation described so far have been linear. Digital modulation 1 department of electronic systems. Modulation, analog modulation, digital modulation, am,fm,pm. Active load modulation for high efficiency rf transmitters.
Ask fsk psk modulation digital modulation techniques. Compared to the known results that optimal memoryless relays for the case of coherent binaryphaseshiftkeying bpsk are combinations of softinformation and a hardlimiter, the noncoherent. Both matlab code and simulink have been used for simulation. Digital modulation provides more information capacity, high data security, quicker system availability with great quality communication. In the transmitter, n uncoded real or complex baseband modulation symbols x xk e. The terms coherent and incoherent are frequently used when discussing the generation and reception of digital modulation.651 787 937 1363 273 988 270 1489 68 598 63 1512 165 1281 297 716 1058 1006 1167 185 614 729 341 964 1484 74 1541 1106 985 191 1104 160 1015 826 1113 142 66 1366