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Obstacles, such as buildings and trees, interfere with radio wave signal propagation by contributing fading and shadowing effects. To produce results that accurately reflect real-world topologies, models must address the radio-interfering conditions that obstacles present. Failing to account for the effects of obstacles can therefore inaccurately overstate network performance. An obstacle shadowing model was implemented for the ns-3 network simulation toolset and tested using an ns-3 script for wireless vehicular ad hoc network (VANET) scenarios and obstacle data from Open Street Map (OSM). Results show that deterministic obstacle shadowing compares differently than stochastic Nakagami-m fading. The obstacle shadowing model algorithm can be executed in time complexity similar to other simpler models. Including realistic obstacle shadowing in simulation modeling improves performance assessment.

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High safety and performance requirements drive the mission criticality of space exploration systems. There is often only one chance for mission success, and failure can be fatal. Although proximate causes of failure are often technical, root causes are usually mismanagement of the social context, leading to human error. Thus, while needing to maintain safety standards and faced with budgetary cuts and industry globalization, the space industry is driven to consider alternate methodologies by which to achieve success and limit failure. While Agile practices produce much interest within all aspects of mission-critical systems engineering, there is not much supporting data with respect to specific applicability of practices within the space industry. The need to review space-based systems engineering methodologies and to contemplate the applicability of disparate software engineering techniques, such as Agile, motivates the following research objective: The goal of this research is to identify which Agile practices, if any, are desirable and suitable for space-based systems engineering. Although some Agile practices may be discarded outright, others seem quite useful and should be given consideration. Scrum and eXtreme Programming (XP) show particular potential as does practicing hybrid approaches that combine Agile practices with existing formal methodologies and engineering standards.