Abstract In this article, unmanned aerial vehicle (UAV) as a half-duplex decode-and-forward (DF) relay constructs a reliable link between the indoor user and the outdoor base station (BS) in an emergency scenario. During the outdoor–indoor signal propagation, the signal passing through the wall accelerates signal fading makes the signal fading model for outdoor communication not applicable to outdoor–indoor communication and increases the outage probability of the link. We propose an outdoor–indoor signal fading model and derive a closed expression of the outage probability. In order to minimize the outage probability and ensure that each link has the same outage probability, we made a decision-making scheme and designed a location optimization-power allocation-bandwidth allocation fairness (LPB-fairness) algorithm. The decision-making scheme iteratively optimizes two sub-problems: location optimization and power-bandwidth allocation. The simulation results show that reasonable location optimization, power allocation and bandwidth allocation can ensure the minimum outage probability, and the gaps of outage probability between relay links are within 1%.