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08. Analysis of the Recorded Signal in Simulink

Purpose of the section

To learn how to use Simulink to read a recorded IQ signal and visually analyze its time-domain and spectral characteristics.

In this block, Simulink is needed not only as a modeling environment, but also as a tool for building the engineering chain:

recorded real signal → block-based analysis model → confirmation of signal behavior

This is important because in later blocks the course will rely on Simulink as a bridge between:

  • theory;
  • model;
  • fixed-point;
  • hardware implementation.

2. What the student should do

In this work, the student should:

  • load the IQ file into a Simulink model;
  • represent it as a complex signal;
  • display the time waveform;
  • display the spectrum;
  • compare the result with MATLAB and HDSDR;
  • prepare the model for reuse in later work.

3. General logic of the model

The simplest analysis model should include:

  1. A file data source.
  2. Formation of I and Q channels.
  3. Combination into a complex signal.
  4. Time-domain analysis.
  5. Spectral analysis.
  6. Display of the results.

An approximate block structure:

  • Binary File Reader (raw interleaved files) or From Multimedia File (WAV recordings), both from DSP System Toolbox
  • Data Type Conversion
  • Demux / Selector
  • Real-Imag to Complex
  • Time Scope
  • Spectrum Analyzer

If the file format is not supported directly, one can:

  • first load it into the MATLAB workspace;
  • then use a block that feeds the signal into Simulink.

5. What must be configured

Before running the analysis, define:

  • sampling frequency;
  • data type;
  • length of the analyzed fragment;
  • I/Q format;
  • spectral display scale.

6. Minimum task for the first block

The student should build a model that allows:

  • taking an IQ recording;
  • forming a complex stream;
  • showing the time waveform;
  • showing the spectral peak of the test tone.

This is already enough for Simulink to become part of the practical route of the course.

7. What should be observed

In the time domain

  • regular signal structure;
  • stable amplitude;
  • no gross distortions.

In the spectrum

  • a pronounced peak;
  • stable frequency position;
  • noise floor;
  • possible side components.

8. Comparison with other tools

After analysis in Simulink, it is useful to compare the result with:

  • observation in HDSDR;
  • the MATLAB spectrum;
  • analysis in Python.

The student should make sure that the same signal:

  • is recognizable in different environments;
  • gives consistent results;
  • confirms the correctness of the experiment.

9. Practical value of this stage

This stage is especially important because later Simulink will be used not only for analysis, but also for:

  • signal synthesis;
  • fixed-point preparation;
  • structural description of the chain;
  • transition to hardware implementation.

So even in the first block Simulink should become a “working tool” for the student, not just a theoretical environment.

10. What to include in the report

It is recommended to include:

  • an image of the Simulink model;
  • the time-domain analysis window;
  • the spectral analysis window;
  • a short description of model parameters;
  • a comparison with MATLAB or HDSDR.

11. Conclusions

After completing this section, the student should:

  • be able to use Simulink to analyze a recorded IQ signal;
  • understand how a real recording is inserted into a block model;
  • see the link between offline analysis and future hardware implementation.