Optimal Relay Location and Oppοrtunistic User-Scheduling for Stratospheric Communications

This paper investigates the outage performance of a Decode-and-Forward (DF) Multi-User (MU) stratospheric relay communication system operating over GeneralizedGamma (GG) fading channels. This system consists of multiple users-sources, multiple users-destinations and a High-Altitude Platform (HAP) acting as a relay station in the stratosphere. Geometry-based optimal relay location with fixed power allocation is proposed, in order to minimize the outage probability. Exact and approximated expressions for the Endto-End (E2E) outage probability are derived and opportunistic scheduling is applied, where the Source-Destination (SD) pair with the highest instantaneous E2E Signal-to-Noise Ratio (SNR) is scheduled for communication. The results highlight the gains offered by the opportunistic SD scheduling and the optimization of the relay location on the overall performance. Keywords-Generalized Gamma (GG) fading; High-Altitude Platforms (HAPs); Multi-User (MU); oppurtunistic scheduling; outage probability; relay location.

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