Doppler frequency is calculated by the formula $f_{d} = 2*v_{r}/\lambda$, where $v_{r}$ is the radial velocity and $\lambda$ is the radar wavelength.
Normally FFT is used to detect the doppler frequency(A bank of FFT filters is used for Doppler frequency estimation).
Assume that sampling frequency is fixed as $4*f_{max}$, where $f_{max}$ is the maximum $f_{d}$ corresponding to the maximum radial velocity.
Now I have to determine the number of FFT points to be employed in the FFT calculation. How can I determine this.
In other words, which target parameter determines the Doppler frequency resolution.