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Framläggningar

  • 2026-09-28 kl 14:15 i Transformen

    Decentralized Target Tracking Using Direction-of-arrival Sensors - Analysis of Different State Representations

    Författare: William Olsson
    Handledare: Louise Lennartsson
    Examinator: Gustaf Hendeby
    Nivå: Avancerad (30hp)

    Direction-of-arrival tracking is critical in many applications, for example, tracking with sensor arrays consisting of radio antennas, microphones, or hydrophones. Tracking a target's position generally requires multiple sensors, and decentralized networks are of particular interest due to their robustness and scalability. However, decentralized trackers rely on single-sensor direction-of-arrival estimates, which pose significant challenges due to nonlinearities and limited observability. To handle this, previous research has proposed alternative state representations to Gaussians in Cartesian coordinates, such as Gaussians in modified polar coordinates or particle filters. This thesis evaluates several such alternatives in a decentralized setting, in particular: trackers based on an extended Kalman filter using Cartesian, polar, and modified polar coordinates, and trackers based on particle filters.

    Constructing a decentralized tracker using polar or modified polar coordinates requires modifications to classic fusion methods to handle the non-Euclidean geometry of a polar representation, namely, that bearings are periodic and ranges are positive. Three algorithms to handle this are proposed: Cartesian coordinate-fusion (CC-fusion), difference-fusion, and translation-fusion. CC-fusion relies on transforming the state and performing fusion in Cartesian coordinates, while difference and translation-fusion rely on wrapping the bearings. All methods successfully handle nonlinearities, and it is shown that difference and translation-fusion are equivalent.

    To evaluate trackers, simulations were run using three different sensor networks and trajectories randomly sampled from a constant velocity motion model. The trackers were evaluated in scenarios with and without a known prior, and in scenarios with communication failures. The scenarios were designed to evaluate different aspects of tracker behaviour, rather than to replicate real-world conditions.

    In these simulations, the evaluated representations offered small, if any, advantages over the standard Cartesian coordinate tracker,
    though the similarity may be caused by the evaluated scenarios not being sufficiently challenging. Nonetheless, modified polar coordinates could still be an appropriate option, as they performed better in one of the scenarios with decreased communication while performing nearly identically to Cartesian coordinates in other scenarios. Polar coordinates, however, showed no indication of improved performance, consistent with previous literature where polar coordinates are rarely proposed. Of the proposed fusion methods, CC-fusion appears to be preferable for modified polar-coordinate trackers.

    Particle filter-based trackers could match the Cartesian coordinate tracker's performance under suitable parameter choices, but that performance was highly dependent on those choices, and several configurations were prone to divergence. This suggests that any implementation should be preceded by an evaluation of parameters for the specific application. Given this sensitivity and the limited performance benefits over other trackers, together with the added bandwidth and computational requirements, particle filter-based tracking is unlikely to be justified for applications resembling those evaluated here.