Dual frequency GPS receiver, operating under encryption conditions

摘要

The use of dual frequencies improves the accuracy of position determination. The high frequency reception provides two digital outputs containing the same code. These are received via two respective carriers. Two sets of replicas of a code near to the code are generated, as well as local images of the two carriers. Punctual and differential correlations are effected, followed by quadratic transformations which are effected between the two digital outputs and the code replicas of the two sets. Time data is also obtained enabling determination of the position of the receiver. Between each correlation and its quadratic transformation there is a low pass filtering, matched to the spectrum of the difference between the real code and the code.