Could existing cellular network base stations be this ground based backup navigation system?
https://people.engineering.osu.edu/sites/default/files/2022-...
This is a deliberate design decision, because even a low-altitude aircraft would have hundreds of cell towers in sight and would overwhelm the network when handsets tried to register on all of them.
But also: Pilots like being able to have guarantees about system accuracy. We get notices anytime even a single GPS satellite is out of service (even though there are 31 of them), and have software tools in the aircraft to predict if there will be any signal degradation along our route (RAIM). I can't imagine having anything near that level of guarenteed safety with an ad-hoc system like described.