Velocity is one of several attributes NI-VRTS uses to configure the simulated object. VRTS uses this attribute to calculate and simulate a Doppler effect.

When a signal reflects off a moving object, the returning signal is subject to the Doppler effect and therefore experiences a frequency shift. During object simulation, VRTS mimics the Doppler effect of a moving object by shifting the frequency of the signal.

Frequency shift can be understood mathematically as



where
  • fr is the shifted frequency
  • ft is the original frequency
  • c is the speed of light
  • v is the object velocity

VRTS accomplishes this frequency shift using a Variable Delay Generator (VDG). The VDG combines the radar signal under test with a signal from a frequency generator to produce a shifted signal. The frequency shifts higher if the simulated object has a positive velocity and lower if the simulated object has a negative velocity.

In LabVIEW, set the Velocity property to the desired velocity of your simulated object.

Note The Velocity property is used only to apply the Doppler effect to the signal and does not automatically change the distance of the simulated object in order to simulate motion. However, users can simulate motion by creating a loop within LabVIEW.