Cooperative OTH communications for airborne networks: Opportunities and challenges

We propose a distributed cooperative communication scheme for airborne networks allowing increased range and throughput for over-the-horizon (OTH) communication via the high-frequency (HF) band. By exploiting multiple airborne radios in a collaborative fashion, we can obtain diversity gains similar to Multiple Input Single Output (MISO) allowing increased link reliability and increased throughput for a given range and power. The scheme is based on randomized space-time coding in the framework of distributed cooperative networks where each airborne node may broadcast its own message as well as relay messages to either a terrestrial or airborne destination in a decentralized fashion. This decentralized approach to cooperative communication allows for simplified network formation and organization but does present its own challenges. The main challenge is the receiver design which is complicated due to the time and frequency dispersion caused by both node asynchrony as well as the notoriously difficult HF propagation environment. This paper discusses our transmission protocol and our approach to the receiver design, which merges compressed sensing ideas with a basis expansion of the channel capturing the cooperative HF channel response.