Method and apparatus for eliminating ionospheric delay error in global positioning system signals

DETAILED DESCRIPTION The present invention utilizes a semi-codeless technique to obtain ionospheric delay measurements by utilization of some knowledge of the E (or Y) code.
An algorithm that makes use of some knowledge of the Y code characteristics is known as a semi-codeless technique.
All of the knowledge of the E code utilized in the present invention is available in the open literature.
Industry measurements of live GPS signals have reported in the open literature that the E code has a bandwidth of approximately 500 kHz.
The present invention utilizes a method to acquire and track P code for L1 and L2 to effectively cross correlate the two frequencies in a 500 kHz bandwidth.
The reduced bandwidth cross correlation technique of the present invention provides an improvement in the correlation SNR on the order of 13 dB.
Accordingly, it is a goal of this invention to provide a method and apparatus for improving the accuracy of the commercial GPS signal.
It is a further goal of the present invention to be able to measure the ionospheric delay of the GPS signal without knowledge of the E (or Y) code sequence.
Another goal of the present invention is to reduce the noise in the L1/L2 delay measurement by increasing the signal to noise ratio.
These and other goals may be achieved by accounting for the error caused by ionospheric delay of the GPS signal.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention and together with the general description, serve to explain the principles of the invention.