Improvement of time difference of arrival measurements resolution by using fractional delay filters in a direct sequence-code division multiple access radionavigation system

This study presents a method of improving time measurements resolution in a direct sequence-code division multiple access receiver by using a fine code tracking loop based on fractional delay filtering of a despreading sequence. It briefly describes the structure of a generic digital code tracking loop and the proposed modification which allows to measure time difference of arrival values with the subsample resolution, together with suggestions to reduce computational complexity by storing the set of samples of fractionally-delayed signals in memory. The proposed solution was tested in a laboratory and in real environment in a radionavigation system built in Gdansk University of Technology.