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Abstract: This paper describes the necessary means to combine multiple Ettus Research USRP X310 software-defined radios to a multichannel coherent receiver for direction-of-arrival (DoA) and passive radar applications. The requirements to combine several software-defined radios to a multichannel coherent receiver are examined in general. In particular the requirement of phase coherence necessitates a closer look on the receiver synchronization, since the straightforward approach of synchronizing the systems with a common reference clock will in most cases lead to phase ambiguities between the channels. The mechanism inducing these phase ambiguities between several systems that are phase-locked to a common reference is discussed in detail. Results regarding the achieved phase stability and a preliminary measurement demonstrating the DoA capabilities of the system are shown.
Abstract: We present a study of border surveillance systems for automatic threat estimation. The surveillance systems should allow border control operators to be triggered in time so that adequate responses are possible. Examples of threats are smuggling, possibly by using small vessels, cars or drones, and threats caused by unwanted persons (e.g. terrorists) crossing the border. These threats are revealed by indicators which are often not exact and evidence for these indicators incorporates significant amounts of uncertainty. This study is linked to the European Horizon 2020 project ALFA, which focuses on the detection and threat evaluation of low flying objects near the strait of Gibraltar. Several methods are discussed to fuse the indicators while taking the uncertainty into account, including Fuzzy Reasoning, Bayesian Reasoning, and Dempster-Shafer Theory. In particular the Dempster-Shafer Theory is elaborated since this approach incorporates evaluation of unknown information next to uncertainty. The method is based on belief functions representing the indicators. These functions show a gradual increase or decrease of the suspiciousness depending on input parameters such as object speed, size etc. The fusion methods give two output values for each track: a suspect probability and an uncertainty value. The complete dynamic risk assessment of detected flying objects is evaluated by the automatic system and targets with probabilities exceeding a certain threshold and appropriate uncertainty values are presented to the border control operators.