An efficient algorithm for range, range rate ambiguity resolution in MPRF pulse Doppler radars

In this paper we propose an ambiguity resolution algorithm to estimate the range and range rate of targets detected by a pulse Doppler radar using Medium Pulse Repetition Frequency (MPRF) waveform. Here we consider the case of multiple target scenario with both range and range rate ambiguous. Numerous algorithms are proposed to solve the problem of ambiguity resolution using Chinese reminder theorem, Maximum Likelihood approach incorporating a clustering algorithm. Few studies are also carried out to study the robustness of these approaches in the presence of measurement errors. But these algorithms assume at least one axis measurement is unambiguous before clustering happens. Generally the ambiguity resolution employs multiple Pulse Repetition Frequency(PRF) waveforms. In this paper we propose to solve the ambiguity resolution problem in range-range rate joint domain using novel clustering approach. The algorithm takes in to account the range migration of targets across the coherent processing interval (CPI, a batch of transmission pulses with identical waveform parameters). The correlation gates for clustering is computed using the expected measurement accuracy of range and range rate, which are functions of signal to noise ratio (SNR). The paper proposes the efficient approach based on two passes to unambiguously determine range and range rate in two dimensional space. In the first pass the coarse correlation gates are used in range direction to group unfolded range measurements from different PRF's disregarding the range rate information. In the second pass, the range and range rate unfolding is carried out on the groups formed in first pass. The second pass employs finer range and range rate correlation gates. Range migration compensation is carried out in second pass. The range rate correlation gate accounts for range rate walk through across CPIs. Simulation studies are carried out to evaluate the resolution capability of closely spaced targets, ambiguity resolution in multiple target scenarios. The ghosts generated in dense target scenario is also quantified using simulations. Constraints required to be posed for waveform synthesis is discussed in brief.