Bandpass modulation and demodulation techniques communication systems, dept. Ee4512 analog and digital communications chapter 5 chapter 5 digital bandpass modulation and demodulation techniques binary amplitude shift keying pages 212219. For the love of physics walter lewin may 16, 2011 duration. The optimum receiving filter for accomplishing this is called a matched filter or correlator, described in sections 3. In this lab, students investigate two methods to recover an amplitude modulation am signal in order to develop an understanding of the demodulation process in the time and frequency domain. Represent each possible signal as a vector in a euclidean space spanned by an orthonormalbasis. Double sideband dsb is one of the easiest modulation techniques to understand, so it is a good starting point for the study of modulation.
There are three aspects of a signal that can be modulated. Pdf format this file type includes highresolution graphics and schematics when applicable. The demodulation demonstration is set up by configuring the board for 100% modulation and connecting one channel of the scope to the audio waveform at tp1 and the other channel the output. The changes in the carrier signal are chosen from a finite number of m alternative symbols the modulation alphabet. Baseband modulationdemodulation techniques wikiversity. This is then fed to the demodulation circuitry later. In order to demodulate single sideband, ssb, it is necessary to reintroduce the carrier. The carrier tone simplifies demodulation but carries no information. First, students will generate an am signal using data from a file, and then they will use the envelope detector method to recover the original message by connecting the am signal to a rectifier and the. Bandpass modulation or passband modulation refers to modulation of signal over a carrier frequency. A combined equipment for modulation and demodulation is called a modem. Modulation and demodulation of rf signals by baseband. Modulation is the act of changing a signal to transmit useful data. Single sideband ssb is a common analog modulation scheme for voice communications.
In amplitude modulation or am, the carrier signal has its amplitude. The process by which digital symbols are transformed into waveforms that are compatible with the characteristics of the channel. Dsbsc demodulation using matlab linkedin slideshare. What are the different between baseband transmission and. Dec 27, 2016 neel ave a good answer as far as am transmission, but there are several other modulation modes, like fm, frequency modulation, where the amplitude remains constant, but the frequency varies up and down from a central value. The instructor would begin the demodulation demonstration by providing some background material on the concept of demodulation. Amplitude modulation matlab ammod mathworks united kingdom. Wave fundamentals and modulation demonstration board. Matlab code of single sided band modulation and demodulation. The modulated signal has zero initial phase and zero carrier amplitude, so the result is suppressedcarrier modulation. Rf modulation and demodulation of audio and video signals. The message signal is, for example, a function of the sound to be reproduced by a. If we consider the voice signal then voice signal band is approximately 4khz.
For demodulation, the modulation oscillators frequency and phase must be exactly the same as the demodulation oscillators otherwise, distortion and or attenuation will occur. Fsk modulationdemodulation ni community national instruments. Hi, i am new to labview and have been learning using tutorials that i find in here. Digital modulation methods can be considered as digitaltoanalog conversion and the corresponding demodulation or detection as analogtodigital conversion. May 10, 2014 demodulation is done by multiplying the dsbsc signal with the carrier signal. This modulation is called double side band dsb modulation. Dsbsc can be demodulated if modulation index is less than unity. A type of dsb, called binary phaseshift keying, is used for digital telemetry. Baseband modulation and demodulation techniques are fundamental to communication systems. For the purpose of our discussion ook modulation onoff key is the special case of ask amplitude shift key modulation where no carrier is present during the transmission of a zero.
The amplitude is the power or intensity of the signal, the frequency is how often the signal repeated itself, and the phase describes where in the cycle the waveform is with respect to time. The carrier signal and x have a sampling frequency fs. Information can be sent from a transmitter to a receiver by means of modulation and demodulation, respectively, whether those signals are light waves moving through optical cables, radio waves through metallic cables, or radio. Modulation types of modulation definition applications. Ee4512 analog and digital communications chapter 5 chapter 5 digital bandpass modulation and demodulation techniques. The waveforms normally take the form of shaped pulses.
A noncoherent detector has only one input, namely, the modulated signal port. And accordingly they are classified into diffrent categories as 1. Eee2009eee2009 communicationscommunications contents introduction to communication systems analogue modulation am, dsbsc, vsb, ssb, fm, pm, narrow band fm, pll demodulators, and fll loops sampling systems time and frequency division multiplexing systems, nyquist principle, pam, ppm, and pwm. This portion will outline the need for bandpass modulation and also will discuss about certain basic modulation schemes. To improve the quality of reception to increase the range of communication need of demodulation the wireless signal consists of radio frequency high frequency carrier wave modulated by audio frequency low frequency. Communications toolbox includes tools using either matlab or simulink for analog passband modulation. Ask, fsk, and psk can be readily extended to multiple level mary signaling and demodulated coherently or non coherently. The ber performance improvement for qpsk modulation when using loglikelihood ratio llr instead of harddecision demodulation in a convolutionally coded communication link. Amplitude modulation is defined as the process in which the amplitude of the carrier wave ct is varied about a mean value, linearly with the baseband signal. I am trying to create a vi that will input an audio signal from mydaq and do fsk modulation then demodulate and output using my laptop speakers. The channel refers to the physical medium carrying the information signal voice, video, data etc. The detector calculates the coordinates of the incoming signal by correlating it with locally generated sin and cos waveforms. On the receiver side a demodulator is used to detect the signal and reverse the modulation process.
With llr demodulation, one can use the viterbi decoder either in the unquantized decoding mode or the softdecision decoding mode. Ee4512 analog and digital communications chapter 5 the development of the optimum receiver for bandpass signals. Restoring or recovering the message signal from the received modulated waveform that is generally corrupted by noise types of am detectors. Bandpass modulation bandpass modulation the amplitude, frequency, or phase of a radio frequency rf carrier, or a combination of them, is varied in accordance with the information to be transmitted. The goal of the receiving filter is to recover a baseband pulse with the best possible signaltonoise ratio snr, free of any isi. Rf modulation and demodulation of audio and video signals any information that is broadcast over the airwaves is broadcast via what are known as radio waves.
In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. Chapter 5 digital bandpass modulation and demodulation. Jun 17, 2014 introduction to modulation and demodulation 1. The symbol mapper takes bits and converts them into symbols a. The modulation scheme needs to be cost efficient circuitry should be simple to implement and inexpensive e. Amplitude modulation am is similar to dsb but has the advantage of permitting a simpler demodulator, the envelope detector. Bandpass modulationdemodulation techniques wikiversity. Ook, ask and fsk modulation in the presence of an interfering signal this paper discusses three popular modulation schemes in the presence of an interfering signal. Bandpass modulation and demodulation engineering360.
In these techniques the signal to be transmitted is sent by modulating either one or more of the three properties of carrier wave. Single sideband modulation, ssb demodulation electronics notes. Chapter 5 digital bandpass modulation and demodulation techniques. Ee4512 analog and digital communications chapter 3 chapter 3 digital baseband modulation techniques goals in communication system design pages 7576. Bandpass ask is similar to baseband pulse amplitude modulation pam in chapter 2, baseband modulation and demodulation, but fsk, psk, and qam are new nonlinear modulation techniques. Need of modulation and demodulation demodulationdetection chap. We can define amplitude modulation by saying that a modulating signal, should produce an am wave of the form well use s instead of v or e to indicate that were talking about a modulated quantity and that it can be either a field or a voltage. In this article, we are going to briefly talk about what modulation is and the need for it. In addition to a variable bandpass filter, one auto notch and one manual notch filter can be utilized to eliminate interfering signals. Demonstrate the modulation and demodulation process of ssb.
The process of modulation in a communication system increases its cost and complexity. As described in previous pages, single sideband is a form of amplitude modulation where the carrier and one sideband have been suppressed or reduced in level. However, modulation is extensively used in most communication systems. The demodulation performs one fft operation per received ofdm symbol to recover the received subcarrier values. Two signals are involved in the modulation process. By the end of this experiment, the student should be able to. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. Baseband modulators line coders sequence of bits are modulated into waveforms before transmission. From here on, we can do a variety of things such as suppress the carrier, use one band or the other etc all of these are variations of the double side band dsb amplitude modulation. Radio frequency rf is the rate of oscillation or frequency at which a particular type of information is transmitted over the airwaves. Process by which a property or a parameter of a signal is varied in proportion to a second signal. In digital modulation, an analog carrier signal is modulated by a discrete signal.
Modulation and demodulation introduction a communication system that sends information between two locations consists of a transmitter, channel, and receiver as illustrated in figure 1. Eventually i would like to send the modulated signal to another computer, but for now i am only learning how to do this. Digital bandpass modulation and demodulation techniques coherent demodulation of bandpass signals pages 225236. These values are then used to construct each column of the output resource array. Matlab code of single sided band modulation and demodulation 1 need bpsk modulation and demodulation code in matlab 2 depsk modulation and demodulation matlab code 0. Communication systems has used a very clever technique called modulation to increase the reach of the signals. That means voice signal contains frequencies ranging from 04khz.
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