GNU RADIO : Modulations de base : quelques diagrammesstssnsb.free.fr/telecharger/blusson/stsse2/radiologiciel/gnuradio... · GNU RADIO : MODULATIONS DE BASE : QUELQUES DIAGRAMMES

GNU RADIO : MODULATIONS DE BASE :QUELQUES DIAGRAMMES...

Objectifs : Etre capable d'utiliser GNU RADIO pour les modulationscourantes

1. Introduction.......................................................................................................32. QAM..................................................................................................................4

2.1. Introduction................................................................................................42.2. Les différentes étapes et réglages...............................................................52.3. Diagramme complet...................................................................................8

3. PSK....................................................................................................................93.1. Les différentes étapes et réglages...............................................................93.2. Le diagramme complet.............................................................................13

4. Delta modulation.............................................................................................144.1. Les différentes étapes et réglages............................................................144.2. Le diagramme complet.............................................................................17

5. GMSK.............................................................................................................185.1. Introduction..............................................................................................185.2. Les différentes étapes et réglages............................................................195.3. Le diagramme complet.............................................................................21

6. GFSK...............................................................................................................226.1. Les différentes étapes et réglages............................................................226.2. Le diagramme complet.............................................................................24

7. OFDM.............................................................................................................257.1. Introduction..............................................................................................257.2. Les différentes étapes et réglages............................................................267.3. Diagramme complet et courbe obtenue....................................................28

8. Un récepteur FM.............................................................................................298.1. Les différentes étapes et réglages............................................................298.2. Le diagramme complet.............................................................................31

9. Traitement du signal........................................................................................329.1. La décimation...........................................................................................329.2. L'interpolation..........................................................................................359.3. La quantification......................................................................................39

10. Filtre réjecteur...............................................................................................4310.1. Introduction............................................................................................4310.2. Les différentes étapes et réglages..........................................................4310.3. Le diagramme complet...........................................................................4510.4. Les courbes résultantes..........................................................................45

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GNU RADIO : Modulations de base : quelques diagrammes...

11. DELAY.........................................................................................................4611.1. Le diagramme complet...........................................................................46

1. INTRODUCTIONGNU Radio est un logiciel libre permettant de faire de la radio logiciel.

Le ''companion'' permet de créer des diagrammes afin de réaliser vos montagesen assemblant des blocs visuels. Ces blocs sont en fait des scripts Python ou desobjets développés en C++ (rapidité).

Voici quelques exemples pour des modulations numériques de base. Cesdiagrammes sont tirés du site http://fr.scribd.com et publiés par Rakesh S K .

Au fur et à mesure des exemples les blocs sont expliqués. Important les instruments doivent être pris soit dans QT GUI ou dans WXGUI en fonction du paramètrage du bloc ''option''.

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https://www.scribd.com/user/206784970/Rakesh-S-K


2. QAM

2.1. IntroductionWhat do you mean by QAM modulation? Quadrature amplitude modulation (QAM) is both an analog and a digitalmodulation scheme. It conveys two analog message signals, or two digital bitstreams, by changing (modulating) the amplitudes of two carrier waves, usingthe amplitude-shift keying (ASK) digital modulation scheme or amplitudemodulation (AM) analog modulation scheme. The two carrier waves, usuallysinusoids, are out of phase with each other by 90° and are thus called quadrature carriers or quadrature components hence thename of the scheme. The modulated waves are summed, and the final waveformis a combination of both phase-shift keying (PSK) and amplitude-shift keying(ASK), or (in the analog case) of phase modulation (PM) and amplitudemodulation. In the digital QAM case, a finite number of at least two phases andat least two amplitudes are used. PSK modulators are often designed using theQAM principle, but are not considered as QAM since the amplitude of themodulated carrier signal is constant. QAM is used extensively as a modulationscheme for digital telecommunication systems. Arbitrarily high spectralefficiencies can be achieved with QAM by setting a suitable constellation size,limited only by the noise level and linearity of the communications channel. In aQAM signal, there are two carriers, each having the same frequency butdiffering in phase by 90 degrees (one quarter of a cycle, from which the termquadrature arises). One signal is called the I signal, and the other is called the Qsignal. Mathematically, one of the signals can be represented by a sine wave,and the other by a cosine wave. The two modulated carriers are combined at thesource for transmission. At the destination, the carriers are separated, the data isextracted from each, and then the data is combined into the original modulatinginformation

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2.2. Les différentes étapes et réglages

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2.3. Diagramme complet


3. PSK


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3.2. Le diagramme complet


4. DELTA MODULATION


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5. GMSK

5.1. Introduction What is GMSK modulation?Gaussian Minimum Shift Keying, or to give it its full title Gaussian filteredMinimum Shift Keying, GMSK, is a form of modulation used in a variety ofdigital radio communications systems. It has advantages of being able to carrydigital modulation while still using the spectrum efficiently. One of theproblems with other forms of phase shift keying is that the sidebands extendoutwards from the main carrier and these can cause interference to other radio communications systems using nearby channels. In view of the efficientuse of the spectrum in this way, GMSK modulation has been used in a numberof radio communications applications. Possibly the most widely used is theGSM cellular technology which is used worldwide and has well over 3 billionsubscribers.Generating GMSK modulation There are two main ways in which GMSK modulation can be generated. Themost obvious way is to filter the modulating signal using a Gaussian filter andthen apply this to a frequency modulator where the modulation index is set to0.5. This method is very simple and straightforward but it has the drawback thatthe modulation index must exactly equal 0.5. In practice this analogue methodis not suitable because component tolerances drift and cannot be set exactly.

A second method is more widely used. Here what is known as a quadraturemodulator is used. The term quadrature means that the phase of a signal is inquadrature or 90 degrees to another one. The quadrature modulator uses onesignal that is said to be in-phase and another that is in quadrature to this. Inview of the in-phase and quadrature elements this type of modulator is oftensaid to be an I-Q modulator. Using this type of modulator the modulation index

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can be maintained at exactly 0.5 without the need for any settings oradjustments. This makes it much


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6. GFSK


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7. OFDM

7.1. Introduction What is OFDM?Cyclic prefix insertion is commonly used in orthogonal frequency divisionmultiplexing (OFDM) systems as a way to mitigate the effects of intersymbol-interference (ISI). It copies the end section of an inverse fast Fourier transform(IFFT) packet to the beginning of an OFDM symbol. Usually the length of thecyclic prefix is longer than the length of the dispersive channel to completelyremove ISI. OFDM modulation therefore mostly revolves around cyclic prefix: OFDM modulation includes IFFT operation andcyclic prefix insertion; OFDM demodulation includes cyclic prefix removaland FFT operation. Modern communications systems feature highly dynamicscalability, which often requires changing system parameters on-the-fly basedon channel conditions and user quality of service (QoS) requirements. Thisdesign example demonstrates cyclic prefix insertion and removal for areconfigurable OFDM system using the Altera FFT MegaCore function. Itsupports run-time reconfiguration of FFT size and cyclic prefix size. You canapply such designs to many different systems, such as OFDM-based wirelesscommunications systems, including WLAN, WiMAX, and 3GPP2 long termevolution (LTE) systems, as well as digital video broadcast (DVB) systems.Orthogonal frequency-division multiplexing (OFDM) is a method of encodingdigital data on multiple carrier frequencies. OFDM has developed into a popularscheme for wideband digital communication, whether wireless or over copperwires, used in applications such as digital television and audio broadcasting,DSL Internet access, wireless networks, power line networks, and 4G mobilecommunications. OFDM is a frequency-division multiplexing (FDM) schemeused as a digital multi-carrier modulation method. A large number of closelyspaced orthogonal sub-carrier signals are used to carry data on several paralleldata streams or channels. Each sub-carrier is modulated with a conventionalmodulation scheme (such as quadrature amplitude modulation or phase-shiftkeying) at a low symbol rate, maintaining total data rates similar toconventional single-carrier modulation schemes in the same bandwidth

The primary advantage of OFDM over single-carrier schemes is its ability tocope with severe channel conditions (for example, attenuation of highfrequencies in a long copper wire, narrowband interference and frequency-selective fading due to multipath) without complex equalization filters. Channelequalization is simplified because OFDM may be viewed as using many slowly

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modulated narrowband signals rather than one rapidly modulated widebandsignal. The low symbol rate makes the use of a guard interval between s ymbols affordable, making it possible to eliminate intersymbol interference(ISI) and utilize echoes and time-spreading (on analogue TV these are visible asghosting and blurring, respectively) to achieve a diversity gain, i.e. a signal-to-noise ratio improvement. This mechanism also facilitates the design of singlefrequency networks (SFNs), where several adjacent transmitters send the samesignal simultaneously at the same frequency, as the signals from multiple distanttransmitters may be combined constructively, rather than interfering as wouldtypically occur in a traditional single-carrier system.


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7.3. Diagramme complet et courbe obtenue

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8. UN RÉCEPTEUR FM


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9. TRAITEMENT DU SIGNAL

9.1. La décimation

IntroductionLa décimation consiste à diminuer le nombre d'échantillon par seconde dans unsignal.

Les différentes étapes et réglages

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Le diagramme complet

Les courbes résultantes

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9.2. L'interpolation

IntroductionL'interpolation permet d'augmenter le nomre d'échantillon par seconde dans unsignal.

What do you mean by interpolation? In the mathematical field of numerical analysis, interpolation is a method of constructing new data points within the range of a discrete set ofknown data points. In engineering and science, one often has a number of datapoints, obtained by sampling or experimentation, which represent the values ofa function for a limited number of values of the independent variable. It is oftenrequired tointerpolate (i.e. estimate) the value of that function for an intermediate value of theindependent variable. This may be achieved by curve fitting or regressionanalysis. A different problem which is closely related to interpolation is theapproximation of a complicated function by a simple function. Suppose theformula for some given function is known, but too complex to evaluateefficiently. A few known data points from the original function can be used tocreate an interpolation based on a simpler function. Of course, when a simplefunction is used to estimate data points from the original, interpolation errorsare usually present; however, depending on the problem domain and theinterpolation method used, the gain in simplicity may be of greater value thanthe resultant loss in accuracy. There is also another very different kind ofinterpolation in mathematics, namely the "interpolation of operators". Theclassical results about interpolation of operators are the Riesz – Thorin theorem and the Marcinkiewicz theorem. There are also many othersubsequent results. In the domain of digital signal processing, the terminterpolation refers to the process of converting a sampled digital signal (suchas a sampled audio signal) to a higher sampling rate (Upsampling) using variousdigital filtering techniques (e.g., convolution with a frequency-limited impulse signal). In this application there is a specificrequirement that the harmonic content of the original signal be preservedwithout creating aliased harmonic content of the original signal above theoriginal Nyquist limit of the signal (i.e., above fs/2 of the original signal sample

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rate). An early and fairly elementary discussion on this subject can be found inRabiner and Crochiere's book Multirate Digital Signal Processing


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Les courbes résultantes

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9.3. La quantification

Introduction What do you mean by Decimation? In digital signal processing, decimation is the process of reducing the samplingrate of a signal. Complementary to interpolation, which increases sampling rate,it is a specific case of sample rate conversion in a multi-rate digital signalprocessing system. Decimation utilizes filtering to mitigate aliasing distortion,which can occur when simply down sampling a signal.[3] A system component that performs decimation is called a decimator.Decimation reduces the data rate or the size of the data. The decimation factor isusually an integer or a rational fraction greater than one. This factor multipliesthe sampling time or, equivalently, divides the sampling rate. For example, if16-bit compact disc audio (sampled at 44,100 Hz) is decimated to 22,050 Hz,the audio is said to be decimated by a factor of 2. The bit rate is also reduced inhalf, from 1,411,200 bit/s to 705,600 bit/s, assuming that each sample retains itsbit depth of 16 bits. Decimation by an integer factor, M, can be explained as a2-step process, with an equivalent implementation that is more efficient: 1.Reduce high-frequency signal components with a digital low-pass filter. 2.Down sample the filtered signal by M; that is, keep only every sample. Down sampling alone causes high-frequency signal components to bemisinterpreted by subsequent users of the data, which is a form of distortioncalled aliasing. The first step, if necessary, is to suppress aliasing to anacceptable level. In this application, the filter is called an anti-aliasing filter,and its design is discussed below. Also see under sampling for informationabout down sampling band-pass functions and signals.

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La courbe résultantes

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10. FILTRE RÉJECTEUR

10.1. Introduction

In signal processing, a band-stop filter or band-rejection filter is a filter thatpasses most frequencies unaltered, but attenuates those in a specific range tovery low levels. It is the opposite of a band-pass filter. A notch filter is a band-stop filter with a narrow stopband (high Q factor). Narrow notch filters(optical) are used in Raman spectroscopy, live sound reproduction (publicaddress systems, or PA systems) and in instrument amplifiers (especiallyamplifiers or preamplifiers for acoustic instruments such as acoustic guitar,mandolin, bass instrument amplifier, etc.) to reduce or prevent audio feedback,while having little noticeable effect on the rest of the frequency spectrum(electronic or software filters). Other names include 'band limit filter', 'T-notchfilter', 'band-elimination filter', and 'band-reject filter'. Typically, the width ofthe stopband is 1 to 2 decades (that is, the highest frequency attenuated is 10 to100 times the lowest frequency attenuated). However, in the audio band, a notchfilter has high and low frequencies that may be only semitones apart. Abandpass filter allows signals within a selected range of frequencies to be heardor decoded, while preventing signals at unwanted frequencies from gettingthrough. A bandpass filter also optimizes the signal-to-noise ratio andsensitivity of a receiver


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10.4. Les courbes résultantes

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11. DELAY


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Documents

GNU RADIO : Modulations de base : quelques diagrammesstssnsb.free.fr/telecharger/blusson/stsse2/radiologiciel/gnuradio... · GNU RADIO : MODULATIONS DE BASE : QUELQUES DIAGRAMMES