A differential post detection technique for two steps GNSS signal acquisition algorithm

In this paper, the problem of acquiring weak Global Navigation Satellite System (GNSS) signals of the next generation systems (such as Galileo and GPS modernization) is addressed and analyzed, focusing the majority of the attention to the problem of managing the higher sign reversal transition rate due to the navigation message in the data channel and to the secondary code in the pilot channel. It must be considered that in case of Galileo E1 Open Service (OS) signals, in each period of the primary spreading code the presence of a potential bit sign reversal can reduce the correlation gain. Moreover, the sign transition occurred on the block of samples being processed produces a Cross Ambiguity Function (CAF) peak splitting along the Doppler shift axis of the search space matrix constructed during the acquisition stage and it may lead to a wrong Doppler estimate. Here, a new two steps acquisition strategy has been proposed in order to mitigate the CAF peak impairments. To circumvent the limitations of the conventional acquisition approaches, differentially coherent detection scheme has been considered to achieve better acquisition sensitivity for a fixed signal-to-noise ratio (SNR). When two steps acquisition strategy is employed in the differentially coherent detection scheme, the bit sign transition problem can be solved and much improved acquisition sensitivity can be obtained specifically in a severe weak signal environment. The validity and effectiveness of the proposed two steps differentially coherent acquisition technique will be deeply assessed with simulation campaigns in terms of detection and false alarm rates, which will be presented by means of Receiver Operating Characteristic (ROC) curves in comparison with the state-of-the-art acquisition approaches.