A proportional hazard model for the estimation of ionosphere storm occurrence risk

Severe Ionosphere magnetic storms are feared events for integrity and continuity of navigation systems such as EGNOS, the European SBAS (Satellite-Based Augmentation System) complementing GPS and an accurate modelling of this event probability is necessary. Our aim for the work presented in this paper is to give an estimation of the frequency of such extreme magnetic storms per time unit (year) throughout a solar cycle. Thus, we develop an innovative approach based on a proportional hazard model, inspired by the Cox model, with time dependent covariates. The number of storms during a cycle is supposed to be a non-homogeneous Poisson process. The intensity of this process could be expressed as the product of a baseline risk and a risk factor. Contrary to what is done in the Cox model, the baseline risk is one parameter of interest (and not a nuisance one), it is the intensity to estimate. As in Extreme Value Theory, all the high level events will be used to make estimation and the results will be extrapolated to the extreme level ones. After a precise description of the model, we present the estimation results and a model extension. A prediction for the current solar cycle (24th) is also proposed

Non-linearized amplifier and advanced mitigation techniques: DVB-S2X spectral efficiency improvement

The latest standardization DVB-S2X increases the achievable spectral efficiency of the satellite communications by around 15% in AWGN channel. In order to benefit from those improvements, the strong non-linear distortions introduced by the payload have to be overcome, mostly taking high back-off on the amplifier operation point. Nowadays, on- board amplifiers are linearized before being deployed, allowing low-complexity transmitters and receivers at the detriment of the payload's cost and reduced energy efficiency. In this paper, various techniques are investigated for the purpose of spectral efficiency improvement while releasing the amplifier linearization constraint. Iterative pre-distortion at the transmitter, turbo- equalization at the receiver and appropriate waveforms for transmission through non-linearized payload appear as strong candidates considering the results of this study

Comparative Ionosphere Electron Content Estimation Method in SBAS Performances

The activities on ionosphere delay estimation and associated covariance have known a renewed interest since 2011 when the increase of solar activity has caused strong performance disturbance of both operational Safety of life Satellite Based Augmentation Systems, WAAS and EGNOS. Different techniques are used depending the service provider. EGNOS has implemented Triangular Interpolation (TRIN) model (A.J. Mannucci et al. of ION GPS-93) whilst WAAS used Krieging algorithm methods. These methods react differently as function of the dynamics of the ionosphere, resulting in different level of performances. Moreover limitations are already well identified. The linear ionosphere spatial evolution over a facet is a strong assumption regarding TRIN model and, the Krieging method need of semi-variogram estimation that is independent from spatial correlation anisotropy. The purpose of the paper is to review and prototype different ways of computing ionosphere estimation delay and associated covariance. A review of state of art allowed to select methods. We consider on the on hand a compressed sample method aiming to decompose signal over a suitable orthogonal bases in very few component, and on the other hand spline techniques. Both methods have been analysed and roughly assessed. Comparisons of the performances are performed with respect to TRIN and Krieging methods based on the analysis of the temporal and spatial distribution of ionosphere pierce points (IPP) - and associated L1 ionosphere delays. In a first time we present each method and their applications in the interpolation ionosphere context. In a second time we found out some particular signature for each method in function of ionosphere dynamic layer by analysing accuracy, integrity and availability of the system. In a last time we provide a table of results that summarise the performances reached for each method. In the paper we present results and recommendation from this experimentation in order to identify the method providing the best behavior in case of nominal and strong ionosphere condition

Piecewise Volterra Series Approximation for Improved Non-Linear Channel Modelization and Detection

International audienceIn satellite communications, the non-linear distortions introduced by the amplifier in the payload have to be overcome. When advanced mitigation techniques are considered at the receiver side, the current channel model is often based on Volterra series derived from an approximation of the non linear transfer function of the on-board amplifier. This nonlinear model is conditioning the performance at the receiver side. In this paper, a new non-linear model is proposed, leading to improved receiver performances. The polynomial approximation is improved considering both the usual model truncation to the 3rd order and the signal fluctuation at the input of the amplifier. First, the impact of the polynomial order of the AM/AM and AM/PM curve approximation is studied. Then, a non-linear model is derived based on a piecewise polynomial approximation of the amplifier response. Based on this refined nonlinear model, significant detection performance improvements are shown for both Nyquist and Faster-than-Nyquist rates