GPS over Fibre Solution from Chronos

ViaLite from PPM

A Scandinavian telecoms operator required a highly reliable link between the synchronisation equipment in its switch room and the GPS antenna which had to be installed some 500m from the equipment in an electrically isolated area, without compromising the GPS signal.

Chronos’ solution was to supply a TimeProvider node clock from Microsemi together with a fibre driver from PPM, contained in an IP66 enclosure.

Using an electrical-optical-electrical conversion the interface between the GPS TimeProvider Interface Unit (TPIU) and the TimeProvider was taken over optical fibre with no degradation of timing performance. This high reliability connection can transmit timing signals over fibres up to 10km in length.

The solution consisted of a “Head-End” wall mounted module to be co-located with the TPIU near the antenna and an equipment room unit mounted in the TimeProvider rack.

TimeProvider from Microsemi

A three fibre bundle was used to link the two fibre transceivers which manages communications between the TPIU and TimeProvider and the composite timing signal from the antenna. The use of optical fibres overcomes restrictions due to electrical isolation and electromagnetic interference and provides advantages over conventional electrical alternatives.

The TimeProvider communicates with the TPIU using a proprietary protocol to compensate for cable attenuation and time delay. This utilises three fibres to manage the transmit and receive data.

TimeProvider

An electrical to optical converter module is mounted at the “Head-End” close to the antenna TPIU and supplies power to the TPIU. It provides the conversion into the optical domain in order to pass the composite timing signal, which includes the 1pps for GPS timing antenna, back to the TimeProvider and through a separate dedicated fibre.

The optical signal can then be taken into the electrically isolated environment where an optical to electrical converter unit is mounted close to the TimeProvider in the equipment rack. This provides the necessary alarm management and extracts the timing information for electrical connection to the TimeProvider itself.

Custom engineered cables between the fibre interface units and the Time Provider ensure correct and accurate operation with necessary power and alarm management.

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