There is a strong demand for the multi-constellations compatible Global Navigation Satellite System (GNSS) acquisition scheme, since it is able to acquire signals from different constellations to increase availability of satellites. However, the presence of multiple modulation modes and diverse Pseudo-Random-Noise (PRN) code lengths makes the design challenging. Moreover, existing schemes consume a lot of hardware resources. Hence, we present an innovative Field Programmable Gate Array (FPGA)-based lowcomplexity and multi-constellation compatible GNSS acquisition scheme to provide a solution for the above-mentioned challenges. This scheme is based on the proposed Improved Serial-Parallel Matched Filter structure that not only requires less hardware resources than conventional structures but also performs all operations in a pipeline to simplify the implementation in FPGA. Additionally, the maximum likelihood criterion is used to obtain decision statistics, which ensures the compatibility between BPSK and sBOC (1,1) signals. Furthermore, a three-step method to acquire signals with a long PRN code is proposed. This also guarantees the compatibility among signals with different PRN code lengths. Finally, a new aided acquisition method to accelerate the acquisition process of signals with a long PRN code is proposed. Experimental results show this scheme is capable of acquiring multi-constellations civil GNSS signals, and therefore it has high practical value. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
The BDS-3 recently started broadcasting a new civil B1C signal to provide open services for global users, which brings benefits to GNSS-based applications. The BDS-3 B1C signal modulates a long secondary code on the primary code in the pilot component, and it is useful to acquire the secondary code so as to extend coherent integration time when acquiring weak BDS-3 B1C signals. However, the long secondary code of the BDS-3 B1C signal puts FFT-based and multi-hypothesis-based secondary code acquisition methods in trouble from the high computational burden. Therefore, the authors propose a novel secondary code acquisition algorithm called the partial correlation method (PCM) for the BDS-3 B1C signal. The PCM acquires the secondary code in three steps to reduce the complexity and acquisition time, and it supports up to 110 ms coherent integration and can be applied for the case of C=N 0 ≥ 25 dB -Hz, which satisfies most cases. Further, a matched-filter-based architecture of the PCM is presented. Additionally, the characteristic length vector to determine the secondary code chip position quickly is proposed, which is better than the existing characteristic length method. Finally, experimental results based on real BDS-3 B1C signals data show that the proposed PCM is effective.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Fine Doppler frequency estimation has an important role in accelerating the convergence of the tracking loop in a global navigation satellite system (GNSS) receiver to achieve short time to first fix. BDS-3 started broadcasting a civil B1C signal to provide open services for global users, which is beneficial for GNSS-based applications. Therefore, a fine Doppler frequency acquisition algorithm based on an adaptive filter is proposed, whose purpose is to acquire the BDS-3 B1C signal Doppler frequency accurately after the completion of coarse acquisition. The proposed algorithm is based on a first-order complex-coefficients adaptive filter. The adaptive filter depends on the proposed adaptation algorithm to track the input BDS-3 B1C signal. An accurate Doppler frequency estimate is extracted. Simulation results show the proposed algorithm has high acquisition sensitivity, high acquisition accuracy, short acquisition time, and few hardware resources consumption, and also works well under many different coarse acquisition strategies. Overall, the proposed algorithm is better than the generic second-order frequency locked loop. Consequently, the proposed algorithm has high practical value.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
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