  We study the target parameter estimation for sub-Nyquist pulse-Doppler radar.
Several past works have addressed this problem but either have low estimation
accuracy for off-grid targets, take large computation load, or lack versatility
for analog-to-information conversion (AIC) systems. To overcome these
difficulties, we present a general and efficient estimation scheme. The scheme
first formulates a general model in the sense that it is applicable to all AICs
regardless of whether the targets are on or off the grids. The estimation of
Doppler shifts and delays is performed sequentially, in which the Doppler
estimation is formulated into a spatial spectrum estimation problem and the
delay estimation is decomposed into a series of compressive parameter
estimation problems with each corresponding to an estimated Doppler shift. By
the sequential and decomposed processing, the computational complexity is
substantially reduced, and by the parametric estimation techniques, the high
accurate estimation is obtained. Theoretical analyses and numerical experiments
show the effectiveness and the correctness of the proposed scheme.
