Precise absolute time transfer from a satellite system

A receiver unit adapted for use in attenuated or jammed environments, comprising:

• an antenna adapted to receive a signal from a satellite acquisition channel or a messaging channel;
• a processor;
• a receiver clock;
• and
• a memory for storing a plurality of machine readable instructions which when executed by the processor cause the receiver unit to:
• receive data from the acquisition channel or the messaging channel, wherein the data has a frame structure,
• use the data to determine an identity of the satellite and a position of the satellite,
• correct for signal time of flight using the identity of the satellite and the position of the satellite,
• use the data as a time reference to align the receiver clock to the frame structure,
• with the receiver clock aligned to the frame structure, receive a precision time signal from the satellite, wherein the precision time signal comprises a periodic repeating code,
• determine a timing phase of the code, and
• use the timing phase to determine a precise absolute time.