Automotive Adaptive Cruise Control Using FMCW Technology using Triangular sweep

I am studying example of Automatic Cruise control of vehicle in matlab, The portion of Example where 'Triangular Sweep' is explained, i have some doubts about it. I think its not triangular sweep, because when i get properties of wave i get following,

Properties:
      SampleRate: 150000000 
       SweepTime: 0.002     
  SweepBandwidth: 150000000 
  SweepDirection: 'Triangle'
   SweepInterval: 'Positive'
    OutputFormat: 'Sweeps'  
       NumSweeps: 1

Since NnmSweeps is 1, so it's still chirp up sweep not triangle sweep, for triangle sweep , the NumSweeps should be 2, but when i make this Numsweeps 2, i get the error, can you explain why you call it Triangle Sweep with 1 NumSweeps, and if it is not Triangle Sweep then how can you find ? fbu_rng and fbd_rng

Reference: %% Automotive Adaptive Cruise Control Using FMCW Technology

Answer 1

[Honglei Chen]

Hi Ali,

I assume you are simply running the script for that demo. You are right that during the one triangle period consists of two sweeps. Therefore, in the later stage, the upsweep and downsweep are separately processed. The upsweep is contained in

xr(1:2:end)

and the down sweep is in

xr(2:2:end)

The value of NumSweeps simply control how many sweeps to output each time. You can certainly do all processing if you choose to set NumSweeps to 2. However, in that case, you will need to adjust other components in the program so they expect both up and down chirp in column.

HTH

[AR]

thank you for the answer, but i could not understand how xr(1:2:end) is the up sweep and xr(2:2:end) is the down sweep????

[Honglei Chen]

Because in the first sweep, it goes up and then in the second sweep, it goes down, and it repeats this cycle periodically.