Provided herein are systems and methods that enable a navigation receiver
to determine receiver position using a low ppm (Parts Per Million) Real
Time Clock (RTC) under weak satellite signal reception conditions without
the need for timing information from navigation satellites or aiding
systems. Under weak signal conditions, the receiver is unable to
demodulate navigation data bits but may be able to synchronize with the
one ms PN sequences and 20 ms data bit edges of a received signal. In
this case, the receiver is unable to determine the signal travel time
from the navigation data bits resulting in one ms and/or 20 ms integer
ambiguities in the travel time. Systems and methods are provided for
resolving these one ms and/or 20 ms integer ambiguities and correct or
reconstruct the pseudorange measurements accordingly. The reconstructed
pseudorange measurements are used to accurately determine the receiver
position.