Orange S.A.

About: Orange S.A. is a company organization based out in Paris, France. It is known for research contribution in the topics: Terminal (electronics) & Signal. The organization has 6735 authors who have published 9190 publications receiving 156440 citations. The organization is also known as: Orange SA & France Télécom.

Process for the acceptance of a virtual prepaid card use request permitting the reuse of its serial number

Abstract: The present invention relates to a process for accepting a request for use of a virtual prepaid card involving the following stages: a user of a virtual prepaid card is connected to a server containing a data base, particularly version numbers, which are incremented when the corresponding cards are empty or obsolete, said user is authenticated with the server by communicating thereto an authentication sequence and a version number, said server supplies these numbers to a security processor having the capacity to recalculate the authentication sequence and check the validity thereof, in the case of the validity thereof, the processor transmits to the server a consumption authorization, after receiving said authorization the server gives agreement to the use request, within the limits of the credit remaining on the card and the validity date of the latter.

Security Analysis of SHA-256 and Sisters

Abstract: This paper studies the security of SHA-256, SHA-384 and SHA-512 against collision attacks and provides some insight into the security properties of the basic building blocks of the structure. It is concluded that neither Chabaud and Joux’s attack, nor Dobbertin-style attacks apply. Differential and linear attacks also don’t apply on the underlying structure. However we show that slightly simplified versions of the hash functions are surprisingly weak : whenever symmetric constants and initialization values are used throughout the computations, and modular additions are replaced by exclusive or operations, symmetric messages hash to symmetric digests. Therefore the complexity of collision search on these modified hash functions potentially becomes as low as one wishes.

Analysis of RF exposure in the head tissues of children and adults

Abstract: This paper analyzes the radio frequencies (RF) exposure in the head tissues of children using a cellular handset or RF sources (a dipole and a generic handset) at 900, 1800, 2100 and 2400 MHz. Based on magnetic resonance imaging, child head models have been developed. The maximum specific absorption rate (SAR) over 10 g in the head has been analyzed in seven child and six adult heterogeneous head models. The influence of the variability in the same age class is carried out using models based on a morphing technique. The SAR over 1 g in specific tissues has also been assessed in the different types of child and adult head models. Comparisons are performed but nevertheless need to be confirmed since they have been derived from data sets of limited size. The simulations that have been performed show that the differences between the maximum SAR over 10 g estimated in the head models of the adults and the ones of the children are small compared to the standard deviations. But they indicate that the maximum SAR in 1 g of peripheral brain tissues of the child models aged between 5 and 8 years is about two times higher than in adult models. This difference is not observed for the child models of children above 8 years old: the maximum SAR in 1 g of peripheral brain tissues is about the same as the one in adult models. Such differences can be explained by the lower thicknesses of pinna, skin and skull of the younger child models.

Distributed Adaptive Power Allocation for Wireless Relay Networks

Abstract: In this paper, we consider a 2-hop wireless diversity relay network. We explore transmit power allocation among the source and relays to maximize the received signal to noise ratio (SNR) at the destination. We consider two relay protocols, "amplify and forward" (AAF) and "decode and forward" (DAF) and design the respective power allocations for both uneeded and coded systems. For a 2-hop relay system with one relay node, we derive a closed-form power allocation solution and, based on it, we propose a relay activation condition. If and only if the fading channel coefficients satisfy this condition, the relay transmits the signals to the destination; otherwise, the relay will stay in the idle state. For a system with more than one relay node, general closed-form power allocation solutions based on an exact SNR expression are difficult to derive; we hence, calculate a SNR upper bound and derive a sub-optimum power allocation solution based on this bound. The simulation results show that for a 2-hop diversity relay channel with one relay node the proposed adaptive power allocation (APA) scheme yields about 1- 2 dB SNR gains compared to the equal power allocation. This SNR gain increases monotonically as the number of relays increases

Pilot-aided channel estimation for OFDM/OQAM

Abstract: OFDM/offsetQAM is an interesting alternative to classical OFDM modulation, as it does not require the use of guard interval. This characteristic makes its spectral efficiency optimal. On the other hand, this modulation is less robust to Rayleigh fading channel. Indeed, when classical channel estimation used for OFDM modulation is applied straightforwardly to OFDM/OQAM modulation, an intrinsic inter-symbol-interference is observed. This deeply degrades its performances. In this paper, we theoretically explain this phenomenon and propose a reliable method to significantly reduce it. Results of different methods of pilot-aided channel estimation over delay-Doppler channels are shown in this paper.