FireChat connects all nearby phones into a network and uses this network to pass messages. Today, we are launching private off-the-grid messaging. FireChat uses unlicensed spectrum to create a heterogenous ad hoc network for messaging. Connections using unlicensed spectrum are fairly short-range: about 40 yards in most situations, but up to 70 if the conditions are right. While the throughput of these connections differs depending on technology — Wi-Fi Direct is considerably faster than Bluetooth Low Energy — the range is pretty similar.
Sourced through Scoop.it from: medium.com
By Stanislav Shalunov. If even a small fraction of people are connected to the Internet, they can help bridge any gaps that might arise below percolation threshold. In effect, when Internet connectivity is taken into account, you only need enough density to connect to someone, not to everyone, to pass messages.