Frequency Shift Keying FSK is the digital modulation technique in which the frequency of the carrier signal varies according to the digital signal changes. FSK is a scheme of frequency modulation. The output of a FSK modulated wave is high in frequency for a binary High input and is low in frequency for a binary Low input.
The binary 1s and 0s are called Mark and Space frequencies. The following image is the diagrammatic representation of FSK modulated waveform along with its input. The FSK modulator block diagram comprises of two oscillators with a clock and the input binary sequence. Following is its block diagram. The two oscillators, producing a higher and a lower frequency signals, are connected to a switch along with an internal clock. To avoid the abrupt phase discontinuities of the output waveform during the transmission of the message, a clock is applied to both the oscillators, internally.
The binary input sequence is applied to the transmitter so as to choose the frequencies according to the binary input. There are different methods for demodulating a FSK wave. The main methods of FSK detection are asynchronous detector and synchronous detector. The synchronous detector is a coherent one, while asynchronous detector is a non-coherent one. The block diagram of Asynchronous FSK detector consists of two band pass filters, two envelope detectors, and a decision circuit.
Following is the diagrammatic representation. The signal in each envelope detector is modulated asynchronously. The decision circuit chooses which output is more likely and selects it from any one of the envelope detectors. It also re-shapes the waveform to a rectangular one. The block diagram of Synchronous FSK detector consists of two mixers with local oscillator circuits, two band pass filters and a decision circuit.
The FSK signal input is given to the two mixers with local oscillator circuits. These two are connected to two band pass filters. These combinations act as demodulators and the decision circuit chooses which output is more likely and selects it from any one of the detectors. The two signals have a minimum frequency separation. For both of the demodulators, the bandwidth of each of them depends on their bit rate.
This synchronous demodulator is a bit complex than asynchronous type demodulators.
Frequency Shift Keying Advertisements. Previous Page. Next Page. Previous Page Print Page. Dashboard Logout.This technical brief covers the basic characteristics of a digital modulation scheme known as quadrature phase shift keying.
In the world of wired electronics, analog signals exhibit continuous variations whereas digital signals assume ideally one of two discrete states. This distinction can be extended to systems that transmit data via electromagnetic radiation instead of electric current traveling through wires.
When used for analog signals, frequency modulation and amplitude modulation lead to continuous variations in the frequency or amplitude of a carrier wave.
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When modulation techniques are used for digital communication, the variations applied to the carrier are restricted according to the discrete information being transmitted. These schemes cause the carrier to assume one of two possible states depending on whether the system must transmit a binary 1 or a binary 0; each discrete carrier state is referred to as a symbol.
This two-bits-per-symbol performance is possible because the carrier variations are not limited to two states. In ASK, for example, the carrier amplitude is either amplitude option A representing a 1 or amplitude option B representing a 0. In QPSK, the carrier varies in terms of phase, not frequency, and there are four possible phase shifts. We can intuitively determine what these four possible phase shifts should be: First we recall that modulation is only the beginning of the communication process; the receiver needs to be able to extract the original information from the modulated signal.
Next, it makes sense to seek maximum separation between the four phase options, so that the receiver has less difficulty distinguishing one state from another. Note: The phase-shift-to-digital-data correspondence shown above is a logical though arbitrary choice; as long as the transmitter and receiver agree to interpret phase shifts in the same way, different correspondence schemes can be used. The following table should clarify this:. Compared to modulation schemes that transmit one bit per symbol, QPSK is advantageous in terms of bandwidth efficiency.
For example, imagine an analog baseband signal in a BPSK binary phase shift keying system. BPSK uses two possible phase shifts instead of four, and thus it can transmit only one bit per symbol. The baseband signal has a certain frequency, and during each symbol period, one bit can be transmitted. A QPSK system can use a baseband signal of the same frequency, yet it transmits two bits during each symbol period.
Thus, its bandwidth efficiency is ideally higher by a factor of two. The article is good at explaining what QPSK is but I feel it leans too much on the four state design aspect. Perhaps this could be addressed briefly in the article. Don't have an AAC account? Create one now.Publicada em 8 de abr de Enviar pesquisa. O slideshow foi denunciado. Inicie em. Mostre SlideShares relacionados no final. Full Name Comment goes here. Are you sure you want to Yes No.
K Ganpati Shrinivas Sharma. Kuldeep Verma. Kaoutar Abarkach. Ahmed El Sebai. Exibir mais. Sem downloads. Nenhuma nota no slide. Modulation 1. Digital Modulation Lectures 1 2. Change which part of the Carrier? Phase Shift Keying PSK Major drawback — rapid amplitude change between symbols due to phase discontinuity, which requires infinite bandwidth.
Linear change Amplitude or phase 2. Non linear modulation techniques change frequency. The previous symbol serves as an estimate of the channel. A no-change condition causes the modulated signal to remain at the same 0 or 1 state of the previous symbol. DPSK Pulse Carrier Carrier: A train of identical pulses regularly spaced in time 16 Pulse-Amplitude Modulation PAM Modulation in which the amplitude of pulses is varied in accordance with the modulating signal.
Used e. Pulse-Duration Modulation PDM Modulation in which the duration of pulses is varied in accordance with the modulating signal. Deprecated synonyms: pulse-length modulation, pulse-width modulation.
Coherent Detection An estimate of the channel phase and attenuation is recovered. It is then possible to reproduce the transmitted signal and demodulate. Requires a replica carrier wave of the same frequency and phase at the receiver.
Also known as synchronous detection I. Highly linear amplifiers required. This scheme produces the lowest envelope variations. QPSK GMSK is probably most widely associated wit the 2G GSM mobile communications system where it proved to be an effective form of modulation. It was one of the reasons that GSM cellphones had a long battery life in view of the high efficiency that could be obtained from the RF power amplifiers.
One of the problems with standard forms of PSK is that sidebands extend out from the carrier. Here there are no phase discontinuities because the frequency changes occur at the carrier zero crossing points.
This arises as a result of the unique factor of MSK that the frequency difference between the logical one and logical zero states is always equal to half the data rate. This can be expressed in terms of the modulation index, and it is always equal to 0. A plot of the spectrum of an MSK signal shows sidebands extending well beyond a bandwidth equal to the data rate.
This can be reduced by passing the modulating signal through a low pass filter prior to applying it to the carrier. The requirements for the filter are that it should have a sharp cut-off, narrow bandwidth and its impulse response should show no overshoot. The ideal filter is known as a Gaussian filter which has a Gaussian shaped response to an impulse and no ringing. Because of the effect of the linear phase change, the power spectral density has low side lobes that help to control adjacent-channel interference.
However the main lobe becomes wider than the quadrature shift keying. The most obvious way is to filter the modulating signal using a Gaussian filter and then apply this to a frequency modulator where the modulation index is set to 0.
This method is very simple and straightforward but it has the drawback that the modulation index must exactly equal 0. In practice this analogue method is not suitable because component tolerances drift and cannot be set exactly. A second method is more widely used. Here what is known as a quadrature modulator is used. The term quadrature means that the phase of a signal is in quadrature or 90 degrees to another one. The quadrature modulator uses one signal that is said to be in-phase and another that is in quadrature to this.
In view of the in-phase and quadrature elements this type of modulator is often said to be an I-Q modulator.
Using this type of modulator the modulation index can be maintained at exactly 0.Documentation Help Center Documentation. The output is a baseband representation of the modulated signal. You can specify additional name-value pair arguments in any order as Name1Value1The object's PhaseOffset property is set to phaseand the other specified properties are set to the specified values.
Unless otherwise indicated, properties are nontunablewhich means you cannot change their values after calling the object. Objects lock when you call them, and the release function unlocks them. If a property is tunableyou can change its value at any time. Phase of zeroth point of constellation in radians, specified as a finite real scalar.
Output datatype, specified as either doublesingle or Custom. Fixed-point data type of output, specified as a numerictype Fixed-Point Designer object with a signedness of Auto. This property applies when you set the OutputDataType property to 'Custom'. BPSK Modulated baseband signal, returned as a column vector or matrix of the same size as the input signal.
To use an object function, specify the System object as the first input argument. For example, to release system resources of a System object named objuse this syntax:.
This example creates binary data, modulates it, and then displays the data using a scatter plot. Phase modulation is a linear baseband modulation technique in which the message modulates the phase of a constant amplitude signal. The probability of a bit error in an AWGN channel is.
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To modulate a binary phase shift signal: Create the comm. BPSKModulator object and set its properties. Call the object with arguments, as if it were a function.
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Actions Shares. No notes for slide. Phase shift keying Presentation 1. Nishita Gogoi 2. PSK is a modulation technique used by modems in which different phase angles in the carrier signal are used to represent the binary states of 0 and 1. Instead of operating with respect to a constant reference wave, the broadcast can operate with respect to itself.
Changes in phase of a single broadcast waveform can be considered the significant items. In this system, the demodulator determines the changes in the phase of the received signal rather than the phase relative to a reference wave itself. The mathematical analysis shows that QPSK can be used either to double the data rate compared with a BPSK system while maintaining the same bandwidth of the signal, or to maintain the data-rate of BPSK but halving the bandwidth needed.
Conceptual transmitter structure for QPSK. The binary data stream is split into the in-phase and quadrature-phase components 8. Receiver structure for QPSK.Publicada em 28 de nov de Enviar pesquisa. O slideshow foi denunciado. Gostou do documento? S views Advantages of qpsk by Vinaysrichand Ban Inicie em. Mostre SlideShares relacionados no final. Full Name Comment goes here. Are you sure you want to Yes No. Aldi Angsar. Bhargav Borisagar. Rina Prihaty. Exibir mais.
Sem downloads. Nenhuma nota no slide. Qpsk 1. Latar Belakang Inovasi pada teknologi telekomunikasi berkembang secara cepat dan selaras dengan perkembangan karakteristik masyarakat modern yang memiliki mobilitas tinggi, mencari layanan yang fleksibel, serba mudah dan memuaskan dan mengejar efisiensi di segala aspek.
Frequency Shift Keying
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