Channels combining techniques for a novel two steps acquisition of new composite GNSS signals in presence of bit sign transitions

In this paper, the problem of acquiring new composite 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 the Galileo E1 Open Service (OS) signals, in each period of the primary spreading sequence the presence of a potential sign reversal can reduce the correlation gain. Moreover, the sign transition present on the block of samples being processed produces a Cross Ambiguity Function (CAF) peak splitting along the Doppler 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 method has been proposed in order to cope with the CAF peak impairments. Due to the availability of data and pilot components separately broadcast in the new composite GNSS signals, in order to overcome the power loss problem and also to mitigate the CAF peak splitting impairments, novel non-coherent and differentially coherent channels combining techniques based on two steps acquisition scheme have been proposed for jointly combining data and pilot components to recover all the transmitted power from both channels. The proposed two steps channels combining acquisition techniques have been deeply characterized from a statistical point of view. Monte Carlo simulation campaigns have been performed on the simulated Galileo E1 OS signals to evaluate the performances of the proposed acquisition techniques in order to support the theoretical analysis.