Cognitive OFDM system detection using pilot tones second and third-order cyclostationarity

The emerging trend to provide users with ubiquitous seamless wireless access leads to the development of multi-mode terminals able to smartly switch between heterogeneous wireless networks. This switching process known as vertical handoff requires the terminal to first detect the surrounding networks it is compatible with. In the context where these networks are cognitive, this can be challenging since the carrier frequency of their access point may change over the time. One solution to overcome this challenge is to embed network specific signatures in the PHY layer. We here focus on cognitive OFDM systems and advocate to embed signatures onto pilot tones since (i) it makes possible to discriminate systems with the same modulation parameters (ii) it creates easy to intercept signatures implying short detection latency (iii) it avoids adding any side information dedicated to detection that would reduce systems capacity. We propose two complementary signature/detection schemes based on second and third-order statistics, respectively. The first scheme relies on redundancy between pilot symbols and the second is based on the use of maximum-length sequences. Detailed numerical examples demonstrate the efficiency of the two detection criteria in realistic environments.     

Non data-aided SNR estimation of OFDM signals

This letter deals with the problem of non data aided (NDA) signal to noise ratio (SNR) estimation of OFDM signals transmitted through unknown multipath fading channel. Most of existing OFDM SNR estimators are based on the knowledge of pilot sequences which is not applicable in some contexts such as cognitive radio for instance. We show that it is possible to take advantage of the periodic redundancy induced by the cyclic prefix to get an accurate NDA SNR estimator. Numerical simulations highlight the benefit of the proposed method compared with the state of the art.     

Compressible turbulent boundary layers on a strongly heated wall

This paper concerns the theoretical and experimental modelling of the flat wall, highly heated, compressible turbulent boundary layer. Its final objective is to develop a numerical Navier-Stokes solver and to conclude on its capability to correctly represent complex aerothermic viscous flows near the wall. The paper presents a constructed numerical method with particular attention given to the turbulence modelling at low Reynolds number and comparisons with supersonic and transonic experimental data. For the transonic experiment, very high wall temperature (T _w=1100K) is realized. The method of this difficult experimental set up is discussed. The comparison between experimental and computational data conducts to the first conclusion and gives some indications for the future work.