Providing an accurate global time reference to indoor computer based equipment

Accurate, global time references are often required in computer systems, for example when logging event occurrences. Use of the global positioning system (GPS) is one means of achieving this, but adequate reception inside a building is often difficult. An obvious solution to this problem is to separate the GPS receiver and the computer by using a local radio link. Unfortunately, this solution introduces other problems due to the bandwidth required for the local communication system. This paper addresses solutions to this problem whereby low power radio telemetry units can be used to provide all computers within receiving range with a globally synchronised knowledge of time to an accuracy of 1 μs.