{HEAD ~ The time synchronization schemes} based on a Global Positioning System and a wide area communication network can be combined to synchronize {TAIL ~ the stationary clocks} of phasor measurement units of a wide area monitoring system to a central server clock at a Network Control Center of the system 
combined to synchronize
{ HEAD ~ The time synchronization schemes } based on a Global Positioning System and a wide area communication network can be combined to synchronize { TAIL ~ the stationary clocks } of phasor measurement units of a wide area monitoring system to a central server clock at a Network Control Center of the system
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH