Direct Height Estimation for Low-Elevation Target Using Bistatic MIMO Radar Under Complex Multipath Interference

In a high-coherence multipath propagation environment, the localization of low-elevation targets such as unmanned aerial vehicles (UAVs) and flying birds is a challenging problem, particularly in terms of target height estimation. The prevailing algorithms for estimating the height of low-elevation targets with bistatic multiple-input multiple-output (MIMO) radar typically follow a two-step process. First, the target elevation angles observed by the transmitter and receiver are estimated separately. Second, based on each estimated angle, the corresponding target heights are calculated and then fused to obtain the final height estimate. However, these algorithms rely on data-level fusion and do not fully utilize the information contained in the received signal, resulting in suboptimal performance. To address this problem, we propose a direct height estimation method for low-elevation targets using bistatic MIMO radar, accounting for complex multipath interference. Unlike conventional two-step algorithms, the proposed method directly estimates the target height from the received signals, rather than deriving it by fusing height estimates observed by the transmitter and receiver. This method fully exploits the information contained in the received signals, thereby significantly improving the estimation accuracy. Finally, the Cramér-Rao bound (CRB) is derived as a theoretical benchmark to evaluate the performance of the proposed method. This method effectively mitigates the impact of complex multipath interference without requiring prior knowledge of the terrain or reflection paths. Simulation results validate the effectiveness and superiority of the proposed method.