From the Characterization of Ranging Error to the Enhancement of Nodes Localization for Group of Wireless Body Area Networks

International audienceTime-based localization in Wireless Body Area Networks (WBANs), has attracted growing research interest for the last past years. Nodes positions can be estimated based on peer-to-peer radio transactions between devices. Indeed, the accuracy of the localization process could be highly affected by different factors , such as the WBAN channels where the signal is propagating through, as well as the nodes mobility that bias the peer-to-peer range estimation, and thus, the final achieved localization accuracy. The goal of this paper consists in characterizing the impact of mobility and WBAN channel on the ranging and localization estimation, based on real mobility traces acquired through a motion capture system. More specifically, the ranging error is evaluated over all the WBANs links (i.e. on-body, off-body and body-to-body links), while an impulse Radio Ultra-Wideband (IR-UWB) physical layer, as well as a TDMA-based Medium Access Control (MAC) are playing on. The simulation results show that the range measurement error can be modeled as a Gaussian distribution. To deal with the gaus-sianity observation of ranging error and to provide high positioning accuracy, an adjustable extended Kalman Filter (EKF) is proposed

Annulation d'interférence dans les systèmes optiques à accès multiple par répartition de codes (O-CDMA)

- Dans cet article, nous présentons l'étude d'un récepteur à annulation parallèle d'interférence précédé d'un limiteur optique, pour un système DS-CDMA optique. Le but de ce récepteur est de réduire l'Interférence d'Accès Multiple (IAM) due aux codes optiques unipolaires. Nous montrons que l'utilisation du récepteur présenté permet d'améliorer le système, au niveau de la longueur des codes utilisés, ou au niveau de la gestion des séquences allouées aux utilisateurs actifs

Antarctic Ice Sheet elevation impacts on water isotope records during the Last Interglacial

Plain Language Summary The Last Interglacial period (LIG, 116,000 to 130,000 years ago) was globally ∼ 0.8 °C warmer than today at its peak, with substantially more warming at the poles. It is a valuable analogue for future global temperature rise, especially for understanding rates and sources of polar ice melt and subsequent global sea level rise. Records of water stable isotopes from Antarctic ice cores have been crucial for understanding past polar temperature during the LIG. However we currently lack a framework for estimating how changes in the ice sheet elevation, alongside sea‐ice feedbacks, affect these water stable isotopes. To address this, we examine the effect of the Antarctic Ice Sheet (AIS) elevation on water stable isotopes, using an ensemble of climate simulations where we vary the AIS elevation. We observe that (i) water stable isotope values lower with increasing AIS elevation following linear relationships, (ii) the effect of sea‐ice induced by AIS elevation is small so the effect of AIS elevation can be isolated. Finally, this study provides appropriate elevation‐water stable isotope gradients for the reconstruction of the AIS topography using ice cores. Abstract Changes of the topography of the Antarctic ice sheet (AIS) can complicate the interpretation of ice core water stable isotope measurements in terms of temperature. Here, we use a set of idealised AIS elevation change scenarios to investigate this for the warm Last Interglacial (LIG). We show that LIG δ 18 O against elevation relationships are not uniform across Antarctica, and that the LIG response to elevation is lower than the preindustrial response. The effect of LIG elevation‐induced sea ice changes on δ 18 O is small, allowing us to isolate the effect of elevation change alone. Our results help to define the effect of AIS changes on the LIG δ 18 O signals, and should be invaluable to those seeking to use AIS ice core measurements for these purposes. Especially, our simulations strengthen the conclusion that ice core measurements from the Talos Dome core exclude the loss of the Wilkes Basin at around 128 ky

Assessing the robustness of Antarctic temperature reconstructions over the past 2 millennia using pseudoproxy and data assimilation experiments

The Antarctic temperature changes over the past millennia remain more uncertain than in many other continental regions. This has several origins: (1) the number of high-resolution ice cores is small, in particular on the East Antarctic plateau and in some coastal areas in East Antarctica; (2) the short and spatially sparse instrumental records limit the calibration period for reconstructions and the assessment of the methodologies; (3) the link between isotope records from ice cores and local climate is usually complex and dependent on the spatial scales and timescales investigated. Here, we use climate model results, pseudoproxy experiments and data assimilation experiments to assess the potential for reconstructing the Antarctic temperature over the last 2 millennia based on a new database of stable oxygen isotopes in ice cores compiled in the framework of Antarctica2k (Stenni et al.,). The well-known covariance between δ 18 O and temperature is reproduced in the two isotope-enabled models used (ECHAM5/MPI-OM and ECHAM5-wiso), but is generally weak over the different Antarctic regions, limiting the skill of the reconstructions. Furthermore, the strength of the link displays large variations over the past millennium, further affecting the potential skill of temperature reconstructions based on statistical methods which rely on the assumption that the last decades are a good estimate for longer temperature reconstructions. Using a data assimilation technique allows, in theory, for changes in the δ 18 O-temperature link through time and space to be taken into account. Pseudoproxy experiments confirm the benefits of using data assimilation methods instead of statistical methods that provide reconstructions with unrealistic variances in some Antarctic subregions. They also confirm that the relatively weak link between both variables leads to a limited potential for reconstructing temperature based on δ 18 O. However, the reconstruction skill is higher and more uniform among reconstruction methods when the reconstruction target is the Antarctic as a whole rather than smaller Antarctic subregions. This consistency between the methods at the large scale is also observed when reconstructing temperature based on the real δ 18 O regional composites of Stenni et al. (2017). In this case, temperature reconstructions based on data assimilation confirm the long-term cooling over Antarctica during the last millennium, and the later onset of anthropogenic warming compared with the simulations without data assimilation, which is especially visible in West Antarctica. Data assimilation also allows for models and direct observations to be reconciled by reproducing the east-west contrast in the recent temperature trends. This recent warming pattern is likely mostly driven by internal variability given the large spread of individual Paleoclimate Modelling Intercomparison Project (PMIP)/Coupled Model Intercomparison Project (CMIP) model realizations in simulating it. As in the pseudoproxy framework, the reconstruction methods perform differently at the subregional scale, especially in terms of the variance of the time series produced. While the potential benefits of using a data assimilation method instead of a statistical method have been highlighted in a pseudoproxy framework, the instrumental series are too short to confirm this in a realistic setup

Antarctic climate variability on regional and continental scales over the last 2000 years

Climate trends in the Antarctic region remain poorly characterized, owing to the brevity and scarcity of direct climate observations and the large magnitude of interannual to decadal-scale climate variability. Here, within the framework of the PAGES Antarctica2k working group, we build an enlarged database of ice core water stable isotope records from Antarctica, consisting of 112 records. We produce both unweighted and weighted isotopic (delta O-18) composites and temperature reconstructions since 0 CE, binned at 5- and 10-year resolution, for seven climatically distinct regions covering the Antarctic continent. Following earlier work of the Antarctica2k working group, we also produce composites and reconstructions for the broader regions of East Antarctica, West Antarctica and the whole continent. We use three methods for our temperature reconstructions: (i) a temperature scaling based on the delta O-18-temperature relationship output from an ECHAM5-wiso model simulation nudged to ERA-Interim atmospheric reanalyses from 1979 to 2013, and adjusted for the West Antarctic Ice Sheet region to borehole temperature data, (ii) a temperature scaling of the isotopic normalized anomalies to the variance of the regional reanalysis temperature and (iii) a composite-plus-scaling approach used in a previous continent-scale reconstruction of Antarctic temperature since 1 CE but applied to the new Antarctic ice core database. Our new reconstructions confirm a significant cooling trend from 0 to 1900 CE across all Antarctic regions where records extend back into the 1st millennium, with the exception of the Wilkes Land coast and Weddell Sea coast regions. Within this long-term cooling trend from 0 to 1900 CE, we find that the warmest period occurs between 300 and 1000 CE, and the coldest interval occurs from 1200 to 1900 CE. Since 1900 CE, significant warming trends are identified for the West Antarctic Ice Sheet, the Dronning Maud Land coast and the Antarctic Peninsula regions, and these trends are robust across the distribution of records that contribute to the unweighted isotopic composites and also significant in the weighted temperature reconstructions. Only for the Antarctic Peninsula is this most recent century-scale trend unusual in the context of natural variability over the last 2000 years. However, projected warming of the Antarctic continent during the 21st century may soon see significant and unusual warming develop across other parts of the Antarctic continent. The extended Antarctica2k ice core isotope database developed by this working group opens up many avenues for developing a deeper understanding of the response of Antarctic climate to natural and anthropogenic climate forcings. The first long-term quantification of regional climate in Antarctica presented herein is a basis for data-model comparison and assessments of past, present and future driving factors of Antarctic climate

Neonatal Handling Affects Durably Bonding and Social Development

The neonatal period in humans and in most mammals is characterized by intense mother-young interactions favoring pair bonding and the adaptation of neonates to their new environment. However, in many post-delivery procedures, human babies commonly experience combined maternal separation and intense handling for about one hour post-birth. Currently, the effects of such disturbances on later attachment and on the development of newborns are still debated: clearly, further investigations are required. As animals present good models for controlled experimentation, we chose domestic horses to investigate this issue. Horses, like humans, are characterized by single births, long lactating periods and selective mother-infant bonds. Routine postnatal procedures for foals, as for human babies, also involve intense handling and maternal separation. In the present study, we monitored the behavior of foals from early stages of development to “adolescence”, in a normal ecological context (social groups with adults and peers). Experimental foals, separated from their mothers and handled for only 1 hour post-birth, were compared to control foals, left undisturbed after birth. Our results revealed short- and long-term effects of this unique neonatal experience on attachment and subsequent social competences. Thus, experimental foals presented patterns of insecure attachment to their mothers (strong dependence on their mothers, little play) and impaired social competences (social withdrawal, aggressiveness) at all ages. We discuss these results in terms of mother-young interactions, timing of interactions and relationships between bonding and subsequent social competences. Our results indicate that this ungulate species could become an interesting animal model. To our knowledge, this is the first clear demonstration that intervention just after birth affects bonding and subsequent social competences (at least until “adolescence”). It opens new research directions for studies on both humans and other animals