Sensors 2020, 20, 2196 14 of 21
the main peak. These secondary peaks induce a second operation region of the MLE between the CRB and the threshold. Indeed, in this intermediate operation region, the MLE jumps between secondary peaks because of the noise, which introduces estimation errors. Note that this is the effect known as false locks in high-order BOC signals such as the BOC(15,2.5) used in the Galileo E1 PRS. Then, the use of meta-signals can improve the delay estimation with respect to the Galileo E5a, E5b, E6, and the complete E5 signals if the receiver is able to cope with such false locks or the SNR at the output of the matched filter is high enough. In addition, to reach such centimeter-level accuracy the receiver needs to exploit a huge bandwidth; thus, depending on the application and design constraints, a wise choice may be to use the E5 AltBOC(15,10). To summarize, the E5 signal can reduce the delay standard deviation by a factor of 28, 12, and 8 with respect to the GPS L1 C/A, Galileo E6B, and Galileo E5b-I/GPS L5 signals, respectively. An additional factor of 2.5 and 3.5 can be obtained by means of meta-signals. These results confirm that AltBOC-type signals can provide decimetric accuracy, thus being a promising solution (and the only one) for code-based precisepositioning.
Regarding the first question, at a representative SNR out = 25 dB operation point at the output
of the MLE, it was found that the time-delay standard deviation using BPSK and BOC-type signals ranges between 2.24 m for GPS L1 C/A and 64 cm for the GPS L5 or the individual E5 components, i.e., E5a or E5b. Using the complete E5 signal, we can reduce the delay standard deviation by a factor 28, 12, and 8 with respect to the GPS L1 C/A, Galileo E6B, and Galileo E5b-I/GPS L5 signals, respectively, that is, a standard deviation of 8 cm. This performance can be further improved by an additional factor of 2 and 3 using the E5b-E6 and E5a-E6 meta-signals, for which we obtained 3.5 and 2.5 cm, respectively. The latter comes at the expense of possible false locks due to high secondary correlation peaks and a huge bandwidth. With respect to the second question, only the AltBOC-type signals can provide decimetric precision, thus only the E5 and GNSS meta-signals can be considered as an option for code-based precisepositioning. For instance, using the complete E5 signal, the 3σ time-delay error is below 25 cm. Obviously, to reach such precisions, we still need to be able to correct for external errors such as ionospheric/tropospheric delays, as well as orbital or satellite clock errors as in PPP solutions, but this could also be exploited to avoid carrier phase ambiguity fixing in code-based RTK solutions. The latter may be a promising line to be explored, because such ambiguity fixing is essentially the bottleneck of RTK techniques, and is still an open issue when using a large number of satellites in multi-constellation/multi-frequency architectures. In addition, exploiting long coherent integration times, we may be able to reach code-based sub-cm accuracy. Finally, we also derived a new sample-based joint delay/phase estimation CRB, which was used to characterize the possible performance improvement of phase-based techniques in the AltBOC-type signals context. It was found that the phase CRB do not depend on the signal, and therefore the gain provided by the phase exploitation must not be worth the ambiguity resolution complexity in AltBOC-type architectures. The results presented in this contribution open the door to new precisepositioning receiver design.
Low-cost PrecisePositioning for Road Users: Overview and Challenges
It can be seen that code measurement availability is very good in the 3 environments. This result could be expected as the uBlox LEA-4T is a high-sensitivity receiver. Additionally, it can be denoted that Doppler measurements have a significantly higher availability than carrier phase measurements, their availability being as high as pseudoranges availability. Moreover, availability of carrier phase measurements is significantly worse on forest roads than on Bordeaux’s beltway, while pseudorange measurements availability in both environments is similar. It can come from the fact that trees and foliage close to the road attenuates the signal coming from satellites. As phase lock loop has a higher tracking loss threshold than delay lock loop, the satellite signal might be sufficiently strong to track code measurement but too weak to keep carrier phase lock. However, the availability of at least 5 carrier phase measurements remains over 95% in all environments. Therefore precisepositioning techniques are theoretically available in these environments, provided measurements accuracy is sufficient.
To obtain a high-accuracy Chang’e 3 lander positioning firstly is the key element in mission operations and scientific investigations. High-precision coordinates for the Chang’e 3 lander can be used as control points for transforming the coordinates from the local lunar coordinate system to the global coordinate system of moon. Furthermore, a high- precision lander positioning algorithm will have the potential to contribute the high-accuracy model of the rotation and orientation of moon in the future with the long-term radio measurements for landers. The accuracy of positioning of the Chang’e 3 lander determined by the Narrow Angle Camera of the NASA Lunar Reconnaissance Orbiter (LRO) spacecraft was approximately 20 meters ( Liu et al. , 2015 ). The estimated positioning diﬀerences for the lander based on multiple observables, including one-hour eﬀective time three-way range, VLBI delay measurements, and two-hour VLBI delay rate measurements (13:12-15:12 observing time on 14 December, 2013, UTC), were 50 meters with respect to the results using LRO photographs ( Huang et al. , 2014 ; Li et al. , 2014 ). Cao et al. ( 2016 ) adopted united X-band and VLBI measurements (one hour on December 14 and two hours on December 17, 2013, UTC), and obtained deviations of less than 100 meters in the three dimensions compared with LRO photograph results. The accuracy of the Chang’e 3 lander positioning based on only VLBI observations (December 20 to 23, 2013, UTC) was up to the hundred-meter level ( He et al. , 2017 ). The accuracy from lander/quasars VLBI joint observations (OCEL program, Haas et al. ( 2016 )) was down to ten meters ( Klopotek et al. , 2019 ), but observations from multiple antennas in diﬀerent countries were needed, with all the subsequent organizational complexities.
Force Microscope under different environmental temperatures. Specifically, the proposed nonlin- ear models can be implemented with the motion control systems of the piezoceramic actuators of the Atomic Force Microscope to enhance the accuracy of the piezoceramic actuators. For the design of positioning manipulator-based piezoceramic actuators, the proposed nonlinear models can enhance the precision tracking control of these manipulators [4, 5, 6, 11, 12, 13, 14, 16, 19, 24] . For example, the positioning accuracy of the ultramicroscopic imaging can be enhanced by con- sidering the uncertainties due to the temperature effects in piezoceramic actuators  . This could minimize the overall positioning errors of the ultramicroscopic imaging. The proposed models can develop the applications of the piezoceramic actuator in hydraulic- and pneumatic-piezoceramic valves. Specifically, the proposed models can provide uncertainties of fluid flow in hydraulic- and pneumatic-piezoceramic valves due to the temperature effects [7, 8] . For fuzzy-based hystere- sis models that consider the frequency of the input voltage as a factor in hysteresis modeling
N to the correct integer value in real-time. The ambiguity resolution requires the use of sophisticated techniques like the so-called LAMBDA method (Joosten & Tiberius, 2000). When ambiguities are solved, the user can start to measure precise positions. Equation (2.8) remains a valid mathematical model for double differences as long as residual atmospheric errors remain negligible with respect to GPS carrier wavelength (about 20 cm). This assumption is verified in usual conditions (Leick, 2004). In practice, disturbed meteorological and/or Space Weather conditions can be the origin of small-scale (a few kilometres) atmospheric variability which can itself strongly degrade or even prevent ambiguity resolution due to the fact that, in that case, the mathematical model given by equation (2.8) does not adequately represent the observed double differences.
There is no simple relationship between a given ionospheric There is no simple relationship between a given ionospheric
activity (TEC) and the positioning error.
activity (TEC) and the positioning error.
– A given ionospheric activity (TEC) will not always result in the same A given ionospheric activity (TEC) will not always result in the same
Confronting the mass market customers until 2017, a market of single-frequency (single- or multi- constellation) equipment is persistent although precisepositioning technologies have been developed for high-end multiple-frequency receivers . Besides, the quality of raw measurements collected with low-cost systems, typically a low-cost receiver and a patch antenna, is not sufficient to achieve a reliable integer ambiguity resolution, without mentioning the quality degradations in the dynamic conditions . Many precisepositioning techniques have been devised to improve the positioning accuracy, such as the Real-Time Kinematic (RTK) and the Precise Point Positioning (PPP) techniques , , . PPP takes advantages of precise corrections of ephemeris and clock errors affecting raw measurements provided by IGS or other organizations. Nevertheless, a long convergence period is required as single- frequency ambiguities are estimated float while residual errors are lumped into integer ambiguities, such that these are not integer anymore. RTK eliminates most measurements errors, which are spatially correlated, by differencing measurements with a reference station. Typically, a centimeter-level accuracy is achievable with RTK with only a few seconds of convergence time, in a short-baseline configuration under an open-sky condition .
4.2 Pose Error Model Suitability
This analysis has employed a simple, general purpose error model based on Gaussian statistics. The sta- tistical behavior of real positioning systems is more complex and highly variable between system type and conguration. Pose error is also very dicult to char- acterize and quantify in practice. Furthermore, each type of pose error eect has been studied in isolation. Multiple types of pose error in combination will inter- act in a non-linear manner. Nevertheless, while its limitations are acknowledged, the pose error model employed here should form a suitable basis for un- derstanding pose error eects and in selecting coun- termeasures to deal with them.
Real null frames seem to have been first considered by Zeeman  as a device for a technical proof. Derrick  discovered a class of them as particular symmetric frames, later studied by Coll and Morales , who also proved that real null frames constitute a causal class among the 199 possible ones . Coll  seems to have been the first to construct physical coordinate systems by means of light beams. The real null frames associated to light beams are, in some sense, dual to emission frames: they are the natural vectors which are null in this case, while the covectors are space- like. Symmetric real null frames have also been proposed by Finkelstein and Gibbs  as a checkerboard lattice for a quantum space-time. It is also Coll [9, 10, 11] which seems the first to have been proposed the physical construction of relativistic coordinate systems by means of broadcast light signals, whose natural coframe is an emission frame. Bahder  has obtained explicit calculations for the vicinity of the Earth at first order in the Schwarzschild space-time, and Rovelli  has developped a particular case where emitters define a symmetric frame in Minkowski space-time, as representative of a complete set of gauge invariant observables. Blagojevi`c et al.  analysed and developped the symmetric frame considered in Finkelstein and Rovelli papers. Recently Lachi`eze-Rey  has considered applications of emission coordinates to cosmology and positioning. Some more specific papers on positioning systems have been published [16, 23, 17, 18, 19, 20, 22, 21], an international school has been devoted to the subject , and some works are in progress [25, 28, 27, 26].
Nuclear positioning: a matter of life
Cell organization, and in particular how organelles are distributed in the cell, is often used by physio- pathologists to visually identify cell types in an organism. Behind this simple fact, it suggests that the positioning of sub-cellular structures is not occurring randomly but by active manners. Three hundred years ago, Leeuwenhoek reported the existence of a structure which will be then called the nucleus. It is the biggest organelle in eukaryotic cells, and has been described to be actively displaced in a large range of organisms and tissues. One of the first nuclear movements in an organism life occurs just after fecondation, when the two pronuclei moves towards each other in the egg (Van Beneden, 1883). After this first discovery, other nuclear movements has been described, such as in plants in 1903 (SENN, 1908) or occurring during neuroepithelium development in 1935 (Sauer, 1935). The latter was called interkinetic nuclear movement (INM). Whether nuclear movement has a function for cell fate and also how this is achieved needed to be further investigated. Several groups have tackled this question in different organisms and cell systems; it reveals similarities in the modus operandi between them but also particularities that could be associated with specific requirements for cell function. INM, for example, has been observed in other tissues and organisms, and defects in this movement lead to severe developmental defects, such as Lissencephaly. In Drosophila, inhibiting nuclear movement in the oocyte affects the polarity and therefore the future segmentation of the embryo.
Total 549 25 948
Analysing these statistics on our dataset provides an answer to the following five validation questions:
1) Simplicity: Is our metamodel simple to model cloud systems? The response to this question is yes as our metamodel contains only twelve concepts – eight from the OCCI Core Model and four new ones – allowing to model seven cloud computing domains, when other concurrent cloud standards like CIMI  or TOSCA  define a huge set of concepts, and only addressed IaaS and cloud applications, respectively. 2) Consistency: Is our precise semantics of OCCI consis- tent for modeling any OCCI systems? The response to this question is yes as there are no contradictions between our twenty five OCL invariants, else EMF-VF will not evaluate our whole dataset as correct (last column in Table I is equals to the number of instances multiplied by the number of invariants).
Our EM pulse injection setup is depicted in Figure 2. The voltage pulse generator delivers a square voltage pulse with a transition time of 2 ns, a maximum amplitude of 200 V in absolute value, and a minimum width of 6 ns. The voltage pulse is converted into a current variation in the coil at the tip of the handcrafted injection probe shown in Figure 3. The probe is made of three turns of copper wire around a ferrite core about 500 µm in diameter. It is attached to a micrometer positioning table, which coordinates in the target referential are denoted by x and y over the the surface of the device, and z in the orthogonal direction. The z-coordinate is fixed, so that the distance between the die and the probe tip is about the thickness of the LQFP package. A trigger signal generated by the device under test synchronizes the voltage pulse with the operation of the microcontroller. A constant delay can be set between the rising edge of the trigger and the generation of an electromagnetic pulse. A personal computer sets the injection parameters and orchestrates the operation of the positioning table, the pulse generator, and the device under test.
1 Polychrony on Polarsys: an Eclipse project of the Polarsys Industry
Working Group, http://www.polarsys.org/projects/polarsys.pop
of the actual dependency which may cause the compiler to approximate dependencies, like in the example above. Contribution. We propose a more precise deadlock detection approach for deadlock-free checking of synchronous programs deﬁning multi-clocked embedded real-time systems in the Signal language. Our approach permits the compiler to detect deadlocks more precisely when dealing with numerical expres- sions. In our solution, the data dependencies among signals are represented by Synchronous Data-ﬂow Dependency Graphs (SDDGs). A SDDG is a labeled directed graph in which each node is a signal or clock variable and each edge represents a dependency between two nodes. Each edge is labelled by a condition at which the dependency is effective. We borrow the Boolean-interval abstraction from  to encode the clock labels. That means every signal is associated with a pair of the form (clock, value), where clock is a Boolean function and value is a Boolean or numerical function, abstracted as an interval. We use a SMT solver to reason on the labels when deciding a dependency cycle in a SDDG to stand for a deadlock. We show how our approach addresses the limitation of the current deadlock detection used in the Signal compiler through a concrete example.