Signal Processing

The Raw data produced by a Doppler radar is a time series of I and Q values for each particular range bin (~50 values, one I and one Q from each pulse). Signal processing is the complex computational procedure that converts these time series to estimates of R, v and w for each range bin. Signal processing is done in either the "frequency domain" or in the "time domain"
  • Frequency domain = Fourier Transform techniques
  • Time domain = Pulse Pair processing

Signal Processing also involves filtering out of

  • Ground clutter
  • System noise
Pulse Pair processing is computationally less intensive than Fourier Transform techniques
 
Recall from physics, the Doppler frequency shift ...
 
 
There is a technical problem, with measuring small frequency shift (say 400 hz) on a 6 Ghz signal, within a 2 microsecond pulse: current technology cannot do it. Instead, we measure the change in phase from pulse to pulse.
 
 
Figure 7.
 
Doppler detects the phase change between the transmitted and received signal for each range bin. One pulse is not enough - several must be averaged to get reliable signal. A histogram of velocity measurements is assembled for each bin. The creation of a spectrum of velocities is done through the Fast Fourier Transform (FFT). The mean velocity and spectral width can be calculated.