44 4. DesignFigure 4.1 Highlevel overview over the localization framework showing the majorcomponents, their relationships and the communication channels. The employedcommunication protocol is always HTTP.4. The Evaluator is a component that is needed for determining the differenterrors that arise during the localization process. These errors are aggregatedover the collected corpus of paths and therefore used for evaluating the overallsystem performance under different conditions.5. The last component can informally be labelled General Infrastructure, asit contains subcomponents suited for data-persistency or configurability, theHTTP-Server, rendering engines and other required application infrastructure.The primary communication channels between these various components and theconsumers are shown in Figure 4.1. Of available consumers there are:1. The GPU-nodes for running a computational expensive radio propagation sim-ulation with the PHOTON raytracer.2. The devices, representing a class of Wi-Fi capable hardware like smartphones,tablets, laptops other forms of mobile computing devices.3. A Fat Client for debugging and evaluating the overall system performance andthe generated radio propagation models.4. Different browsers, either on a desktop PC complementing the Fat Client fordebugging and evaluation, or on a device for the interaction with the localiza-tion application.4.2 Radio PropagationThe performance of the indoor localization system is strongly coupled with the ac-curacy of the estimation of the signal strength for each AP at a given location.Therefore, the first task is to obtain such a signal strength map by the means ofa radio propagation model. Instead of using an empirical propagation model thatrequires extensive manual calibration via collecting measurements, the decision was,