Combining secondary code correlations for fast GNSS signal acquisition

Abstract

The secondary codes of the modern GNSS signals bring some notable advantages, however they constitute a challenge for the acquisition process. Indeed, it becomes much more difficult to extend the coherent integration time with these codes. Several methods have been proposed for increasing the coherent integration time when there is a secondary code. Basically, the methods fall into two categories : 1) Methods with long coherent integration times, which require synchronization with the secondary code and imply a significant computational burden, and 2) Methods with short coherent integration times, which test all possible combinations for the secondary code. Since this leads to an exponential increase in the number of combinations, the coherent integration time remains limited, while non-coherent integrations are not usable. Therefore, there is currently no effective solution with intermediate coherent integration time, which would enable moderate to high sensitivity, while maintaining a reasonable level of complexity. In this paper, a method is proposed to address this problem. The method combines secondary code correlations to reduce the number of possible secondary code delays and reduce the complexity. In exchange, there is a loss in the signal-to-noise ratio as compared to the full secondary code correlation. It is shown that the proposed method offers similar or better performance than the short integration times method, in addition to offering the possibility of using non-coherent integrations, and offers lower complexity than the traditional long integration times method with greater sensitivity.