Scalable telecommunications over ultra-low-bandwidth radio backbones

HF and VHF radios retain considerable operational benefits for disaster communications. In particular, they can be the only available communications channel into a disaster zone, and are capable of communications over tens to thousands of kilometers. However, their bandwidth is extremely limited, as low as 1 bit/second, which has previously limited their utility as a backbone for public telecommunications. The Serval Mesh already includes the Low-Bandwidth Asynchronous Rhizome Delivery (LBARD) function, which scales down to 10s of bytes per second, and allows for near real-time two-way encrypted and authenticated text messaging using Android mobile telephones. In this paper, we present several improvements to LBARD, including a locality heuristic algorithm that allows for effective prioritization of HF transmission queues. The improvements enable LBARD to scale down to the ultra-low bandwidths (as low as 1bit/second) of even older HF radio equipment. Simulation and live HF-radio test results of a proof of concept are presented confirming the possibility of delivering hundreds to tens of thousands of text messages to be delivered per day using commercially-off-the-shelf HF radio equipment. In doing so, we create a new use-case for existing HF radios, and create the tantalizing possibility of providing basic day-to-day mobile telecommunications in regions too isolated to be viably serviced by other means.