Optimal path-control for dual-frequency overlay GNSS receivers

This paper presents a general overlay based front-end architecture that enables the joint reception of two signals broadcast in separate frequency bands, sharing just one common baseband stage. The consequences of this overlay in terms of signal quality are analyzed and it is shown that the noise floor superposition results in non-negligible signal degradations. However, it is also demonstrated that these degradations can be minimized by judiciously setting the relative gain between the two signal paths. As an illustration, the analytical optimal path- control expression to combine overlayed signals in an ionospheric- free pseudorange is derived for both Cramer-Rao Lower Bound and practical code tracking parameters

Implementation and optimization of a Galileo E1 two-step tracking algorithm using data/pilot combining and extended integration time

This paper brings additional light on the previously proposed two-step tracking algorithm for E1 CBOC tracking. More specifically, assesment of the different DLL and PLL tracking loop architectures are analyzed, taking into consideration coherent and non-coherent data and pilot channel combining schemes and increasing integration time beyond data bit period, which is 4 ms for E1 CBOC signal. Our assessment is based on implementing the different tracking loop architectures in a software receiver fed with RF samples generated with a full constellation Galileo E1 simulator. The results are obtained for integration times equal and above the data bit period (i.e, from 4 to 20 ms) and for high to low C/No (i.e, from 41 down to 26 dB-Hz). Also, the influence of the secondary code removal on the tracking loops is shown using a specially conceived algorithm to acquire it. Robustness of the tracking loops is tested under low C/N 0, in order to investigate the channel combining strategies. Four different combining cases are tested. Finally, performance analyses are presented and the results are discussed

Low-cost, 4-system, precise GNSS positioning: A GPS, Galileo, BDS and QZSS ionosphere-weighted RTK analysis

With the combination of emerging GNSSs, single-frequency (SF) precise RTK positioning becomes possible. In this contribution we evaluate such low-cost ublox receiver and antenna performance when combining real data of four CDMA systems, namely L1 GPS, E1 Galileo, L1 QZSS, and B1 BDS. Comparisons are made to more expensive dual-frequency (DF) GPS receivers and antennas. The formal and empirical ambiguity success rates and positioning precisions will first be evaluated while making use of L1+E1, so as to investigate whether instantaneous SF RTK is possible without the need of B1 BDS or L1 QZSS. This is followed by an analysis of the SF 4-system model performance when the residual ionosphere can be ignored and modeled as a function of the baseline length, respectively. The analyses are conducted for a location in Dunedin, New Zealand, and compared to Perth, Australia with the better visibility of BDS and QZSS. The results indicate that successful instantaneous and precise RTK positioning is feasible while using L1 GPS and E1 Galileo data, and that the SF 4-system model is competitive to DF GPS even when residual ionospheric delays are present. We finally demonstrate that when the impact from the ionosphere increases and more than one epoch is needed for successful ambiguity resolution, the SF 4-system model performance can still remain competitive with the DF GPS receivers. This is particularly true in Perth with more satellites and when higher than customary elevation cut-off angles need to be used to avoid low-elevation multipath

Antidepressive effects of targeting ELK-1 signal transduction

International audienceDepression, a devastating psychiatric disorder, is a leadingcause of disability worldwide. Current antidepressants addressspecific symptoms of the disease, but there is vast roomfor improvement1. In this respect, new compounds that actbeyond classical antidepressants to target signal transductionpathways governing synaptic plasticity and cellular resilienceare highly warranted2–4. The extracellular signal–regulatedkinase (ERK) pathway is implicated in mood regulation5–7, butits pleiotropic functions and lack of target specificity prohibitoptimal drug development. Here, we identified the transcriptionfactor ELK-1, an ERK downstream partner8, as a specificsignaling module in the pathophysiology and treatment ofdepression that can be targeted independently of ERK. ELK1mRNA was upregulated in postmortem hippocampal tissuesfrom depressed suicides; in blood samples from depressedindividuals, failure to reduce ELK1 expression was associatedwith resistance to treatment. In mice, hippocampal ELK-1 overexpressionper se produced depressive behaviors; conversely,the selective inhibition of ELK-1 activation prevented depression-like molecular, plasticity and behavioral states inducedby stress. Our work stresses the importance of target selectivityfor a successful approach for signal-transduction-basedantidepressants, singles out ELK-1 as a depression-relevanttransducer downstream of ERK and brings proof-of-conceptevidence for the druggability of ELK-1