The invention concerns a machine-readable medium having instructions stored therein, which when executed by a processor of an apparatus remote from a mobile global positioning system (GPS) receiver cause the processor to perform a method for determining the position of the mobile GPS receiver, the mobile GPS receiver being located within a cell served by a cell site and being coupled to a cell-based cellular communication device transmitting and receiving cellular communications signals to and from the cell site, the method comprising:
monitoring transmissions of cellular communications signals corresponding to the cellular communication signals received by said cell-based cellular communication device from said cell site;
determining a time-of-day of at least a portion of said transmissions;
receiving from said mobile GSP receiver, a relative time of pseudoranges measurement with respect to a time indicator within the cellular communication signals received by said cell-based cellular communication device from said cell site;
determining the time of pseudoranges measurement at the mobile GPS receiver from said time-of-day and said relative time; and
wherein the position of said mobile GPS receiver is determined using said determined time of pseudoranges measurement.