A GNSS software receiver approach for the processing of intermittent data

In a GNSS software receiver, blocks of digitized intermediate-frequency (IF) data are prepared at the front end and sent to the baseband processing unit for processing. A problem that is observed in practice, especially when the GNSS software unit is co-located with mobile phone unit or when the interface between the front end and main processor is subject to interrupts, is that the digitized IF data are subject the intermittency. An improper buffering scheme at the front end may also lead to such phenomena. This type of data intermittency leads to burst-type errors (rather than bit-type errors) on the data to be processed. The burst-type errors pose a challenge for the tracking of the GNSS signals. Indeed, if not properly handled, a typical tracking algorithm is not able to accommodate such a large data gap. In the paper, a decision-aided tracking algorithm is developed for the successful tracking of codes and phases. The effects of data intermittency on code and phase tracking are analyzed. To accounting for the effect without going through the reacquisition process, a detector based on signal power and continuity is then implemented to serve as a detector for decision making. It is shown, through the processing of field gathered data, that the proposed algorithm can indeed be able to continuously track codes and phases in the presence of data intermittency.