Doppler Signature Separation of Mixed O/X-Mode Over-The-Horizon Radar Signals

In this paper, we consider the Doppler signatures of local multipath target signals in an over-the-horizon radar and the objective is to separate signals corresponding to the ordinary (O) and extraordinary (X) propagation modes. As signals of these two modes are reflected at different ionosphere heights, the rendered Doppler signatures are more complicated and cannot be directly analyzed for parameter estimation using conventional local multipath models which are developed for a single propagation mode. We consider a mixed O/X-mode signal model and analyze the resulting Doppler signatures comprising of more signal components. It is shown that sparsity-based methods estimate the Doppler components with improved resolution and accuracy. Moreover, the proposed group sparsity-based strategy enables separation of the resolved Doppler components corresponding to the two propagation modes. We present the simulation results for a challenging scenario where the multipath Doppler signatures corresponding to the two modes are interlaced.