Communications link time transfer to improve navigation system accuracy

A differential navigation system using time transfer to improve accuracy of a calculated position determination of a mobile roving navigation receiver;

• the system comprising:
• a mobile roving navigation receiver configured to:
• receive and process navigation signals to determine position and,
• provide a first navigation time mark;
• a first communications device configured to:
• provide a first communications time mark, and
• make a comparison of the first communications time mark to the first navigation time mark to compute a first time offset;
• where the comparison has level of resolution is as fine as on an order of 10 nanoseconds;
• a two-way communications link over which the first communications device communicates messages;
• a second navigation receiver configured to:
• receive and processing navigation signals to determine position, which position is compared with a known position of the second navigation receiver and used to determine differential correction signals to be transmitted to said mobile roving navigation receiver and
• provide a second navigation time mark;
• and
• a second communications device, which is time offset with respect to said first communications device by a second time offset, said second communications device being configured to:
• receive messages from the two-way communications link,
• provide a second communications time mark, and
• compare the second navigation time mark to the second communications time mark to obtain a third time offset, and for transmitting the third time offset over the two-way communications link to the first communications device;
• wherein the first communications device is further configured to:
• receive the third time offset from the two-way communications link,
• compute the second time offset, and
• compute a mobile roving navigation receiver to second navigation receiver time offset to provide clock aiding to the mobile roving navigation receiver.