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2.1 Amplitude modulation

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This chapter presents the use of the DSK6713 to demonstrate the features of Amplitude Modulation (AM) transmission and reception. The model runs in real-time and enables the use to select the AM detector as well as the transmission and reception parameters (modulation index and carrier frequency).

Introduction

This chapter presents the use of the DSK6713 to demonstrate the features of Amplitude Modulation (AM) transmission and reception. The model runs in real-time and enables the use to select:

  1. The AM algorithm
  2. The transmission and reception parameters (modulation index and carrier frequency).

The process comprises:

  1. Creating a simulation model (not R-T) for the AM transmitter/receiver.
  2. Migration to Real-time of the Simulation Model
  3. Building a Graphic Users Interface (GUI) to operate the real-time implementation.

Related files

Simulation

The environment

Figure 1 shows the data flow for the AM modulation simulation. The AM modulation model receives an input signal from an external signal generator, modulates it and displays the modulation on the scope.

Simulation Environment

The procedure

Building the transmitter

The basic modulation mathematical description is given by:

y ( t ) = [ 1 + m ( t ) ] cos ( 2πf c t ) size 12{y \( t \) = \[ 1+m \( t \) \] "cos" \( 2πf rSub { size 8{c} } t \) } {}
Where:
cos ( 2πf c t ) size 12{"cos" \( 2πf rSub { size 8{c} } t \) } {} - The carrier signal
m ( t ) size 12{m \( t \) } {} - The modulation index
AM Transmission Principle
  • Start by creating a new model in Simulink ®
  • Open the Simulink library browser and add the DSP sine-wave to your model. This blocks will represent the information signal m(t).
The Sine Wave Generator Block
  • Configure the Sine Wave Generator Block (Double click on the DSP sine object). Set the sine frequency to 1000 Hz, sample time to 1/96000, samples per frame to 64 and close the box, and change its label to “information”.
Information Signal Configuration Parameters
  • Use the same block to create the carrier signal. You may copy the block already created or select it form the Simulink library. Set the carrier frequency to 15,000 Hz. The remaining parameters are identical to the ones of the information signal. Change its label to “carrier”
  • Add new DSP-constant to your model:
Adding a DSP constant
  • Double-click on the constant object and set its constant value to 1.5:
Set a constant value
  • Add a new adder object from:
Addes
  • Add a new multiplexer from the same directory as the adder (choose “product”).
  • Add a new scope object:
Scope
  • Set the number of frames parameter to 5. This parameter determines the horizontal scaling of the presented signal.
Vector Scope Configuration
  • Place the objects in the following way:
The Transmitter Model
  • Run the model, pause the simulation and activate the scope window. The modulated signal should be displayed as follows:
AM Modulation Signal
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Source:  OpenStax, From matlab and simulink to real-time with ti dsp's. OpenStax CNX. Jun 08, 2009 Download for free at http://cnx.org/content/col10713/1.1
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