Weak global navigation satellite system signal acquisition with bit transition

Abstract

This study analyses the bit transition and integration over multiple code periods in weak global navigation satellite system signal acquisition. Bit transition must be considered in weak signal environments as it causes a correlation peak splitting reducing the correlation gain. In this study, a modified time parallel acquisition (MTPA) scheme is designed to solve the bit transition problem, and different accumulation schemes over multiple code periods are proposed to detect weak signals. Especially, a fast Fourier transform-based symbol combination for bit transition algorithm, which is suitable for the MTPA scheme, is presented in order to accelerate the coherent accumulation. Simulation results, along with the receiver operative characteristic curves, are presented to verify the performance of the MTPA and accumulation algorithms.

FFT Splitting for Improved FPGA-Based Acquisition of GNSS Signals

“…Finally, we compare the resources for an FPGA-based receiver. Remember that the 5-FFT solution has a complexity similar to the algorithms proposed in [1,5] (since they all compute five FFTs of same length); thus, the following results regarding the complexity and the FPGA implementations for the 5-FFT solution are valid for these algorithms too.…”

“…For example, some authors proposed performing averaging in the Doppler search space [8]; having two steps to first find the code delay and then the Doppler frequency [6]; or generating two local codes, with and without a transition, requiring the computation of five FFTs instead of the usual three [1,5]. However, since these methods change the essential correlation operation (the result is not only a usual correlation between the incoming and local signals), there is a negative impact on the signal-to-noise ratio (SNR) and thus on the probability of detection compared to the 3-FFT solution.…”

“…Next, this solution will be called the 5-FFT solution (as for the 3-FFT solution, the FFT of the local code could be precomputed, but we do not consider this case here). Note that this solution has a complexity similar to the algorithms proposed in [1,5], since they all compute five FFTs of same length. The difference is that our algorithm computes exactly the correlation and thus the detection performance is not affected but the algorithm can be applied only for a certain range of sampling frequencies, whereas the algorithms in [1,5] affect the detection performance but they can be applied for any sampling frequency; therefore, the best solution depends on the context.…”

“…The question of computing a circular correlation between a local code replica and an incoming code having a bit sign transition is a recurrent problem in global navigation satellite system (GNSS) [1][2][3][4][5][6][7][8][9]. This problem, already present with the GPS L1 C/A signal, is even more important with the modern GPS and Galileo signals, because of the higher data rate and the presence of the secondary code that imply a potential bit sign transition in each consecutive period of the primary code.…”

GNSS Signals Acquisition and Tracking in Unfavorable Environment

“…This is shown to be sensitive to bit transition and computationally efficient while conserving the same Signal to Noise Ratio (SNR) at the DBZP output as that at the output of the traditional correlator. The DBZP method was then followed by the Modified Time Parallel Acquisition scheme based on the Fast Fourier Transform (FFT) algorithm and proposed in [38] to solve the transition problem. Here, both coherent and non-coherent accumulation methods have been tested after bearing some changes [39].…”