No Cellular Coverage
If your site does not have sufficient cellular signal to enable internet access for the rover and base, then it is still possible for the rover to connect directly to the base using a local WiFi network.
It is also possible to use a pair of radio modems but we have found that not only does this add significantly to the cost, it is also relatively unreliable. This is particularly true in tournament conditions where there are likely to be other sources of radio interference such as video transmitters used for boat to shore video. At one site in the UK where early testing was done, the radars at a nearby airport, turned quoted 40km radio modems into 300metre ones!
We have experimented with a WiFi setup based on long range units manufactured by Ubiquiti Networks. A detailed description is here