An improved direct acquisition scheme for rapid P code acquisition

To resolve the problem of ambiguity caused by the folding used widely in direct acquisition (DA) of the precision code (P code) in the global positioning system (GPS), a two-step DA scheme is proposed based on the zero-padding and local P code modification. The coarse acquisition is achieved in the first step based on the folding, which allows us to maintain the advantage of the folding, and the zero padding with a local code modification performs the fine acquisition in the second step, removing the problem of ambiguity. In numerical results, the proposed DA scheme is found to provide a shorter mean acquisition time over the conventional DA schemes in most of the jamming-to-signal ratio (JSR) range of practical interest.