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The Cu(II)-catalyzed electrophilic cyclization reaction between o-hydroxyarylenaminones and 3-diazoindolin-2-imines furnished 3-indolyl-4H-chromen-4-ones in moderate to good yields with a broad sub...

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.

Reaching the Moon poses very strict requirements in terms of performance, flexibility and cost for all the spacecraft subsystems. These requirements become more stringent if the mission is designed to be accomplished using a small satellite. The navigation subsystem is without any doubts essential and nowadays, several systems offer different solutions to the navigation problem. Global Navigation Satellite Systems (GNSSs) such as GPS, GLONASS, or the future Galileo and BeiDou systems, introduce an easier way to provide an autonomous on-board orbit determination system; they only require the realization and installation of an on-board GNSS receiver, with low-cost, low-power consumption and limited mass and volume. While GNSS receivers have been already exploited with success for Low Earth Orbit (LEO), their use for very High Earth Orbit (HEO) up to the Moon altitude is still at the research stage. In this context, the purpose of this research is to determine the potential achievable accuracy of a code-based GNSS receiver solution, during the whole trajectory to reach the Moon. GPS, Galileo, and GPS-Galileo combined (dual constellation) solutions are estimated, by considering constellations availability, pseudorange error factors and geometry factors. Unlike previous investigations, our study is making use of a very accurate multi- GNSS constellation simulator "Spirent GSS8000", which supports simultaneously the GPS and Galileo systems and the L1, L5, E1, and E5 frequency bands. The contribution of this study, based on the achieved results, clearly demonstrates that GNSS signals can be tracked at the Moon's surface, but not with the current GNSS receiver's technology for terrestrial use. A possible navigation solution we consider and discuss uses a double constellation GPS-Galileo receiver aided by external on board systems in order to improve the accuracy of the navigation solution and achieve the required sensitivity.

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 %.