Abstract: Parameter estimation in a C/A code GPS receiver by the well known maximum likelihood method was analyzed by theoretical means and computer simulation.It is somewhat a software signal processor between the receiver front end and the following navigation processor in a GPS receiver.If the GPS satellite orbit data was simulated,the GPS raw observations obtained may be used to form a navigation solution such as position,velocity,clock offset etc.The advantages of computer software method over the hardware method in analysis of the GPS signal and system are obvious.