This paper proposes and evaluates a modular architecture of an autonomous unmanned aerial vehicle (UAV) system for search and rescue missions. Multiple multicopters are coordinated using a distributed control system. The system is implemented in the Robot Operating System (ROS) and is capable of providing a real-time video stream from a UAV to one or more base stations using a wireless communications infrastructure. The system supports a heterogeneous set of UAVs and camera sensors. If necessary, an operator can interfere and reduce the autonomy. The system has been tested in an outdoor mission serving as a proof of concept. Some insights from these tests are described in the paper.

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Work on coordinated multi-robot exploration often assumes that all areas to be explored are freely accessible. This common assumption does not always hold, especially not in search and rescue missions after a disaster. Doors may be closed or paths blocked detaining robots from continuing their exploration beyond these points and possibly requiring multiple robots to clear them. This paper addresses the issue how to coordinate a multi-robot system to clear blocked paths. We define local collaborations that require robots to collaboratively perform a physical action at a common position. A collaborating robot needs to interrupt its current exploration and move to a different location to collaboratively clear a blocked path. We raise the question when to collaborate and whom to collaborate with. We propose four strategies as to when to collaborate. Two obvious strategies are to collaborate immediately or to postpone any collaborations until only blocked paths are left. The other two strategies make use of heuristics based on building patterns. While no single strategy behaves optimal in all scenarios, we show that the heuristics decrease T. Andre ( ) · C. Bettstetter Networked and Embedded Systems, AlpenAdria-Universität Klagenfurt, Lakeside Park B02a, Klagenfurt, Austria e-mail: torsten.andre@aau.at C. Bettstetter Lakeside Labs GmbH, Lakeside Park B04b, Klagenfurt, Austria the time required to explore unknown environments considering blocked paths.

Abstract-Multihop and multipoint transmissions are two of the main features towards an increased spectral efficiency for the LTE-Advanced mobile radio system. Fixed wireless relays with in-band backhauling are considered as a multihop technique in LTE-Advanced. Relays improve cell capacity and cell edge user performance depending on the deployment. In this paper, at first, results for the peak spectral efficiency of LTE-Advanced are presented and secondly, an analytical model to calculate the cell spectral efficiency of relay enhanced cell deployments in the context of the IMT-Advanced evaluation is presented. The developed model is applied to the LTE-Advanced system comparing different relay deployments with different frequency reuse schemes.