The GPS time signal is used to synchronize transmissions of packets from the base stations to the mobile phones.  This keeps th
e phone and base station synchronized to minimize collisions with packets from other phones using the same base or cell.  Prope
r time synchronization between bases is important to avoid dropouts when handing off a phone from one base station to another.

There would likely be a loud protest if the GPS signal was degraded so much that it caused the cell system to quit working.  Co
nversely, it is unlikely that the cell phone folks would build a system on something that was by definition selectively availab
le.  Perhaps even the degraded signal is good enough for them.  If so I would think it is also good enough for seismographic da
ta logging.

__________________________________________________________

Public Seismic Network Mailing List (PSN-L)