How to model and simulate Quadrature Modulation in Matlab Simulink | applied electronics engineering


How to model and simulate Quadrature Modulation in Matlab Simulink

By Applied Electronics - Wednesday, January 4, 2017 No Comments
RF design is an exciting work and this blog post shows how easy it is to model an RF system using Matlab. A simple system level model is created for Quadrature Modulation. Quadrature modulation is a bandwidth conservation modulation technique that is widely used in television system and in radio application. QAM and QPSK are examples where quadrature modulation is used.

First create a new simulink model. Save the model in some directory and give it a name.

The construct the block diagram as shown in the following picture.

Starting from the left of the block diagram, is the message signal source. The message signal source is a pure sinusoid with frequency in the range of that of human voice range-1500Hz and the amplitude is 1V.

The next block is the inport block that accepts signal from simulink and converts the signal type to the SimRF.
The RF configuration block is required and the setting are set to default.

Next is the carrier signal generator which is the continuous wave source block from the source panel in the SimRF block section. The carrier frequency was set to 2.4GHz which is the frequency used in WLAN and others. The setting for this block is shown below-

The phase shifter is part of the modulation circuit which produces 90 degree out of phase signal. Nothing is required to set it.

The input message signal and the carrier signal gets mixed in the inphase arm and quadrature arm by the two mixers. The same setting are set in the two mixers.

The output from the two mixers gets combined by the signal combiner and again no modification is required for this block.

The resistor at the end of the system represents load at 50ohm. This could be for example a model for antenna.

The rest blocks on the rights are the Outport and scope for manipulating and viewing the signals from the outputs of the SimRF blocks. The same configuration is used for the 3 outport and the setting for one of them is shown below.

Now the simulation is run for a time of 1e-2 and the resulting graph is shown below.

In the above waveform diagram the top waveform corresponds to the upper inphase arm, the middle corresponds to the lower quadrature arm and the buttom one corresponds to the modulated QAM signal.

Also see DSB Amplitude modulation with Matlab


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