61 research outputs found
Impact of Imperfect Parameter Estimation on the Performance of Multi-User ARGOS Receivers
No full textIn this paper, we analyze the performance of Successive Interference Cancelation (SIC) receivers in the context of the ARGOS satellite system. Multi-user SIC receivers are studied in presence of imperfect estimates of signal parameters. We derive performance graphs that show the parameter ranges over which a successful demodulation of all users is possible. First, the graphs are derived in the context of perfect parameter estimation. Then, imperfect parameter estimation is considered. Erroneous estimations affect both the amplitude and the time delay of the received signal. Carrier frequencies are assumed to be accurately measured by the receiver. ARGOS SIC receivers are shown to be both robust to imperfect amplitude estimation and sensitive to imperfect time delay estimation
Non Data Aided Parameter Estimation for Multi-User ARGOS Receivers
No full textIn this paper, parameter estimators are analyzed in
the context of Successive Interference Cancelation (SIC) receivers for the ARGOS system. A Non Data Aided (NDA) feed forward estimator is proposed for the amplitude and the carrier phase parameters. Time delays are assumed to be known. A Window Accumulator (WA) is used to reduce the influence of the additive noise. In the presence of frequency offset, the window length L cannot be chosen arbitrarily large but an optimal length Lopt can be determined. However, because the estimator induces a different optimal length for each parameter, a trade-off must be made. We show that a window length of around 35 samples induces mean square errors (MSEs) lower than 0.012 for both parameters. The MSE of the proposed estimator is also compared to the Modified Cram´er Rao Bound (MCRB)
Compact dual-polarized VHF microstrip antenna for satellite applications
No full textThis paper presents the design of a compact dual-polarized VHF microstrip antenna for modern small satellites. It consists of a slot-loaded annular-ring microstrip antenna printed on a light substrate to reduce its mass. A simple matching circuit is proposed to match the high input impedance of this antenna while enabling the generation of a dual linear-polarization. The size of the proposed design is finally equal to 450 mm at 161 MHz, i.e. y0/4
Pathological complete response rate and disease-free survival after neoadjuvant chemotherapy in patients with HER2-low and HER2-0 breast cancers
No full textInternational audienceBackground: Half of HER2-negative breast cancers (BC) show HER2-low expres-sion. The strong efficacy of recent anti-HER2 antibody-drug conjugates (ADC) in HER2-low tumours has risen the interest of HER2-low as a proper BC subtype. Chemosensitivity and prognosis of this subtype are not clear when compared to HER2-0 tumours. We investigated the pathological complete response (pCR) and disease-free survival (DFS) rates in BC patients receiving neoadjuvant chemotherapy for HER2-low or HER2-0 tumours.Methods: Data were collected from the Institut Paoli-Calmettes database. HER2-low tumours were defined by HER2 IHC score of 1+ or 2+ with negative FISH, and HER2-0 by IHC score of 0. Clinicopathological characteristics, pCR (defined as [ypT0/ypTis] and [pN0sn or ypN0]) and DFS rates were compared between the two cohorts.Results: From Jan/2005 to Jun/2021, 1111 patients receiving neoadjuvant chemotherapy were evaluable. The incidence of HER2-low was 41%, including 63% of hormone receptor (HR) -positive and 37% of HR-negative tumours (p < 0.001). In the whole population, the pCR rate was lower in HER2-low (23%) versus HER2-0 (30%) tumours (p = 0.013), but this association was lost in multivariate analysis. In HR-positive patients, HER 2-low negatively impacted pCR rates when compared to HER2-0 (10% vs. 16%, p = 0.046), but not in HR-negatives (46% vs. 42%), and this result was maintained in multivariate analysis. No correlation existed between DFS and HER2-status. Conclusion: HER2-low is associated with HR positivity. HER2 status did not impact pCR in HR-negative patients, whereas HER2-low was associated with lower pCR rate in HR-positive patients. 2022 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)
Multi-user detection for the ARGOS satellite system
No full textInternational audienceIn this paper, we evaluate several multiuser detection (MUD) architectures for the reception of asynchronous beacon signals in the ARGOS satellite system. The case of synchronous signals is studied first. Though impractical, this case provides useful guidance on the second part of the study, that is, the design of MUD receivers for asynchronous users. This paper focuses more particularly on successive interference cancellation (SIC) receivers because they have been shown to achieve a good performance complexity trade-off. Several Eb=N0 degradation curves are obtained as a function of channel parameters. With these curves, a performance analysis is presented in order to determine in which conditions it is possible to successfully decode none, one, or more beacon signals. We show that SIC receivers can improve the percentage of served beacons from 50% to more than 67% for a population of 37,600 beacons
Multiuser Detection For Asynchronous ARGOS Signals
No full textIn this paper, we investigate the application of multiuser detection techniques to a Low Polar Orbit (LPO) mobile satellite used in the ARGOS system. These techniques are used to mitigate the multiple access interference in the uplink transmission of the system. Unlike CDMA, due to the Doppler Effect, each signal has a different received carrier frequency and a different propagation delay. Multiuser detection techniques are proposed for asynchronous
transmission in ARGOS system: the maximum likelihood detector, the conventional detector, and the sequential
interference cancellation detector, as solutions to tackle the interference effects. Bit Error Rate performance graphs are shown for these techniques
Performance of TOA and FOA-based localization for Cospas-Sarsat search and rescue signals
No full textBornes de Cramér-Rao modifiées pour le temps d'arrivée et la période symbole. Application aux signaux de recherche et de sauvetage
No full textNational audienceCet article étudie la performance des estimateurs de temps d’arrivée de signaux de détresse qui sont définis par des formes d’onde ayant des transitions douces. Ces signaux sont utilisés dans le système de recherche et sauvetage par satellite Cospas-Sarsat. Nous proposons un modèle de signal basé sur des transitions sigmoïdales. Des expressions analytiques des bornes de Cramér-Rao modifiées associées aux paramètres de ce modèle sont déterminées. Les expressions obtenues sont faciles à interpréter, car elles dépendent analytiquement des paramètres du système. Des simulations effectuées avec des signaux réalistes concordent avec les résultats théoriques
Modified Cramér-Rao lower bound for TOA and symbol width estimation. An application to search and rescue signals
No full textInternational audienceThis paper focuses on the performance of time of arrival estimators for distress beacon signals which are defined by pulses with smooth transitions. These signals are used in the satellite-based search and rescue Cospas-Sarsat system. We propose a signal model based on sigmoidal functions. Closed-form expressions for the modified Cramér-Rao bounds associated with the parameters of this model are derived. The obtained expressions are easy to interpret since they analytically depend on the system parameters. Simulations conducted on realistic search and rescue signals show good agreement with the theoretical results
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