An Efficient Time-frequency Algorithm for the Weak Signal Acquisition of Modernized GNSS Signals

The new GPS/Galileo/Compass signals use much longer code lengths and higher code frequencies than the GPS L1 C/A signal. As a result, they can provide improved ranging and anti-jamming performances. Unfortunately, their acquisition complexity is significantly higher, especially in the high sensitivity or weak signal acquisition context. Acquisition of very weak signals requires long integration times, but the integration time is often limited because of the code phase shifting induced in the receiver by an unmatched code frequency. Therefore, for the purpose of minimizing the acquisition time, a new algorithm that we named “slope parallel frequency and code searching (SPFCS)”, has been developed and is presented in this paper. This algorithm combines the parallel frequency searching and parallel code phase searching together in a novel way, and satisfies the requirements for providing standalone high sensitivity (i.e., without any network or additional sensors’ assistance). In order to assess its performance, we consider in this paper the acquisition of the GPS L5 pilot signal. Our simulation results indicate that the proposed algorithm can successfully acquire, without assistance, L5 signals as low as 15 dB-Hz with 35 kHz Doppler shifts, and a computational burden over 2 to 4 times smaller at 15 dB-Hz and 18 dB-Hz, respectively, as compared to the traditional parallel code phase search (PCS) or double block zero padding (DBZP) methods.

Cross-band aided acquisition on HEO orbit

Cyril Botteron, Vincenzo Capuano, Pierre-André Farine, Jérôme Leclère, Jia Tian, Yanguang Wang, Wei Wang

Global positioning system (GPS) has been demonstrated to be a valid and efficient system for various space applications in low Earth orbit (LEO) and medium Earth orbit (MEO), such as for location determination and time synchronization. However, in highly elliptical and high Earth orbits (HEO), the number of existing space applications is much smaller because of the very weak power of the received signals and the bad geometric dilution of precision (GDOP). To counteract these problems, one method is to add an L5 processing module to the existing L1 C/A receiver module. Indeed, tracking the L5 signal brings several benefits: 1) a higher ranging precision; 2) a pilot channel allowing long integration times, which is helpful for both acquisition and tracking. But this also implies several drawbacks, especially in resource restricted conditions: 1) the length of the fast Fourier transforms (FFTs) and the amount of memory needed for the L5 acquisition module is huge; 2) the acquisition time is very long because of the secondary code and large frequency search space due to the long integration time. In this paper, a cross-band aided acquisition method for the L1&L5 signals is presented, which satisfy the requirements for extremely high sensitive environment without any further assistance. Compared to a traditional architecture that would acquire the L1 and L5 signals sequentially, this method acquires the L1 signal in the first place because its structure is simpler and there is no need to search the secondary code, then uses this information to reduce the code and frequency search space of the L5 signals. This brings huge benefits to the receiver: 1) the resources needed for the L5 acquisition are tremendously reduced; 2) the acquisition time for the L5 signal is considerably reduced. The implementation on an Altera Stratix III FPGA shows that about 7 % of the logic, 18 % of the multipliers and 47 % of the memory can be saved with the proposed method, while the acquisition time is reduced by 99 %.

International Astronautical Federation2014

Comparison Framework of FPGA-based GNSS Signals Acquisition Architectures

Cyril Botteron, Pierre-André Farine, Jérôme Leclère

The acquisition of Global Navigation Satellite Systems signals using Code Division Multiple Access can be performed through classical correlation or using a Fourier transform. These methods are well known but what is missing is a comparison of their performance for a given hardware area or target. This paper presents this comparison for Field Programmable Gate Arrays, describing the different parameters involved in the acquisition, detailing some optimized implementations where hardware elements are duplicated, and estimating and discussing the performances. The influence of the Doppler effect on the code, is also discussed as it plays an important role, particularly for new signals using a high chipping rate.

Institute of Electrical and Electronics Engineers2013

Improving the Performance of the FFT-based Parallel Code-phase Search Acquisition of GNSS Signals by Decomposition of the Circular Correlation

Cyril Botteron, Pierre-André Farine, Jérôme Leclère

This paper proposes alternative architectures to perform a circular correlation using the Fast Fourier Transform (FFT) by decomposing the initial circular correlation into several smaller circular correlations. The approach used is similar to the Fast Finite Impulse Response (FIR) Algorithms (FFAs). These architectures improve the performance in terms of reduced processing time or resource usage, and consequently lower the energy consumption. The results can be applied to any system that performs circular convolution or correlation. In this paper, the application is the acquisition of Global Navigation Satellite System (GNSS) signals with the FFT-based Parallel Code-phase Search (PCS), and more precisely on the GPS L1 C/A signal, when the target considered is a Field Programmable Gate Array (FPGA). In this context, it is for example shown that it is possible with one of the proposed architectures to reduce the logic usage by 11 %, the memory usage by 41 %, and the Digital Signal Processing (DSP) block usage by 32 %, while keeping the same processing time. With another architecture, it is shown that the processing time can be halved by increasing the logic usage by only 35 %, while reducing the memory usage and keeping the same DSP usage. Note that the proposed approach is not based on an approximation of the traditional method, but a modified implementation providing the same result. Thus, there is no loss of sensitivity.

2012

Cross-band aided acquisition on HEO orbit

Cyril Botteron, Vincenzo Capuano, Pierre-André Farine, Jérôme Leclère, Jia Tian, Yanguang Wang, Wei Wang

International Astronautical Federation2014