Achieving high reliability in Aerial-Terrestrial networks: Opportunistic space-time coding

To rapidly deploy a communication network in the aftermath of disaster or emergency event, an Aerial-Terrestrial architecture integrating aerial base stations mounted on the balloons has been investigated in EU FP7 ABSOLUTE project. Since the signal coverage provided by aerial base stations is patchy and unstable, the opportunistic relaying is applied to increase the link reliability and the system robustness. However, the performance of relay selection drastically degrades due to the outdated Channel State Information (CSI) from the feedback delay over the Aerial-to-Terrestrial radio channels. In this paper, therefore, we present a novel method named opportunistic space-time coding (OSTC) to combat the outdated CSI. The link reliability in terms of outage probability is evaluated using both Rayleigh channels and the realistic models of Aerial-to-Terrestrial and Device-to-Device channels. The numerical results reveal that OSTC obviously outperforms the opportunistic relaying in the presence of outdated CSI. Moreover, the improvement of reliability comes without any sacrifice in the spectral efficiency.