An EM algorithm for multipath state estimation in OTHR target tracking

Multi-path tracks of a single target exist in skywave over-the-horizon radar (OTHR) surveillance, due to the availability of multiple signal propagation paths through the ionosphere. Different from the traditional multipath data association and estimation methods for OTHR target tracking, a novel scheme for joint multipath data association and state estimation (JMAE) is developed based on the expectation-maximization (EM) framework. The proposed scheme has the iterative optimization of identification (including data association and ionospheric mode identification) and estimation (including path-conditional state estimation and multipath track fusion). Due to the mechanism of iterative optimization, the closed loop between identification and estimation is established, which is desirable to deal with the coupling issue of identification risk and estimation errors. The simulation shows that JMAE is superior to the well-known multipath probabilistic data association (MPDA).