## 1 Introduction  
Construction sites constitute highly dynamic environments in which workers execute diverse orders simultaneously. Workers need to perform tasks, interact with heavy construction equipment and keep an eye on their surroundings, which is difficult for complex tasks. This requires construction workers to have a high level of concentration to avoid mistakes. If the construction site is noisy and congested, it can be difficult for the construction workers to concentrate on their work and the environment at the same time. In addition, the continuous change of a construction site often leads to hazardous situations. Heavy construction machines move across the site to execute their jobs. Construction vehicles cross the worker's paths and cranes lift loads over their heads. In addition, pedestrian workers inevitably share the same workspaces with construction machines or interact with them in order to accomplish their orders [1]. As a result, worker's activities often happen in close proximity to heavy machinery. Hazardous situations such as close calls can occur as a consequence of this [2]. Furthermore, in certain cases, people can misjudge the danger. Due to the mentioned facts, it is to be expected that workflows on construction sites are not always ideal. In addition, the incidents lead to hazardous situations for pedestrians on construction sites. Thereby, the pedestrian worker can be injured or have a fatal accident. For these reasons, construction workers undergo regular training to raise their awareness with respect to hazardous situations [3] as well as to develop their knowledge and skills [4] to improve their workflows. Despite this effort, working in the surroundings of heavy construction machines remains to be a hazardous job. Identifying a reasonable workflow during its execution in a steadily changing environment also keeps to be a challenging concern. Accordingly, productivity and safety problems continue to occur on construction sites. Monitoring pedestrian workers on the sites from a top-view perspective could improve this situation. This way, the worker's trajectories could be analyzed and adaptations to their workflows could be made during their work [5]. In addition, a monitoring system would help the machine operators in their work, as they usually do not have a complete overview of the environment [1]. In this case, the positions and movement directions of workers who are nearby could be provided to the machine operators. This would allow them to recognize hazardous situations at an early stage and take appropriate action to prevent an accident. The mentioned scenarios represent possible applications of a monitoring system on construction sites, for which a suitable method has to be investigated. Therefore, in this paper, we only focus on the detection and tracking of construction workers, since this is the basis for a surveillance system. Different approaches have already been made in tracking pedestrian workers on construction sites. Depending on the surrounding, various technologies are used for monitoring workers in construction related scenarios [6]. The literature often refers to global navigation satellite system (GNSS) tags for outdoor localization on construction sites [7; 8]. This is mainly applied to track construction machines and equipment, but some approaches make use of GNSS to locate pedestrians on site [9; 10]. Near buildings, walls or large construction elements, GNSS-based localization is affected by multipath effects caused by reflections of the signal on these objects [11; 12]. Since construction workers often work near these objects, tracking such workers with GNSS becomes unreliable. Less sensitive approaches rely on radio-frequency technologies. These also include the attachment of tags to the worker's gear. Corresponding readers can either be stationary on the construction site or attached to construction machinery.