Apparently, the UK government wants to convert the OneWeb satellites into its own UK SatNav system, following Brexit which limits the UK's access to Galileo's Public Regulated Service [reports from the BBC and theRegister].
While, some reports are less and some are skeptical on the technical viability, I haven't seen any reports detailing how one might convert a communications satellite into a SatNav satellite. After all, the satellites involved in the GPS or Galileo systems carry atomic clocks and other special equipment.
So, how would one cobble together a SatNav system from comms satellites already in orbit?
What features implemented in comms satellites can be exploited for determining the location of a ground receiver?