Space Communications

Microwaves propagation modelling in clear air troposphere (i.e. without rain) is investigated. Large scale variations of refractivity are computed from mesoscale meteorological modelling. Small scale variations are deduced from large scale considering that the inertial regime of Kolmogorov spectrum is established. The propagation effects are estimated applying launching ray to take into account large scale refractivity effects and resolution of Parabolic Wave Equation with Multiple Phase Screen technique for small scale. The proposed approach has been evaluated versus earth satellite measurements of log-amplitude scintillation measured at Louvain-la-Neuve.

To insure a favourable link budget in order to reach the required availabilities and to counteract severe propagation impairments, Fade Mitigation Techniques (FMT, such as adaptive coding [8, 9]) have to be implemented in the fixed satellites telecommunications systems. To develop, test and adjust the real-time algorithms of these adaptative FMTs, a good knowledge of the dynamics of the propagation channel is required and realistic attenuation time series are needed to feed system simulators. Unfortunately, the low number of available propagation experiments at Ka-band and above unavoidably leads to the use of channel models allowing synthetic total attenuation time series to be generated. The aim of this paper is first of all to present the justification of the parameterization used in Recommendation ITU-R P.1853–1 which has not been published in the open literature. Secondly, some limitations are highlighted before moving on an overview of a more simplified new channel model to synthesize total attenuation time series.

The main objective of the ESA ARTES 5.1 Contract 20887/07/NL/LvH “Verification of Propagation Impairment Mitigation Techniques” with Politecnico di Milano as Prime, ONERA and Space Engineering as subcontractors, was to validate the channel models and related input data appropriate for the design, analysis and/or control phase of Propagation Impairments Mitigation Techniques (PIMTs), both for the Broadcasting Satellite Service (BSS) and the Interactive Multimedia Broadband Service (IMMBS). For the BSS scenario, which is the focus of this paper, the On Board Antenna Pattern Reconfiguration (OBAPR) PIMT is investigated, using as channel models the rain field generators able to provide the spatial distribution of rain across the service area on the basis of large-scale meteorological forecasts. Their performance were tested using either radar data or a large dataset of beacon measurements collected in Europe during the OLYMPUS experiment.

Propagation effects such as rain or clouds attenuation cause deeper fades in the Ka-band than at lower frequencies. In this collaborative paper, the main results of four long-term Ka-band propagation campaigns are presented. The experiments are carried out in Ottawa, Canada; Aveiro, Portugal; Madrid, Spain; and Toulouse, France. Attenuation statistics are derived from satellite beacon data collected over 6 years at Aveiro, 5 years at Ottawa and Madrid and 2 years at Toulouse. Multi-year measurements allow the production of more stable statistics reflecting the long-term behavior of propagation phenomena and to investigate its year-to-year variability. The beacon signal data was monitored and collected on a continuous basis over the whole measurement period. After a brief introduction of the experiments, rain rate and excess attenuation results are discussed, first for a common measurement period and later for the whole database available. Seasonal attenuation statistics for Ottawa and Aveiro are compared. Finally, fade duration and fade slope statistics derived at three locations are presented and discussed.

Reconfigurable on-board antenna systems are a potential solution to mitigate the effect of atmospheric fades in broadband SatCom. The on-board power is dynamically shared among the users according to the time and space-varying meteorological conditions in the service area by tuning the antenna radiation pattern. An efficient algorithm of dynamic on-board power allocation is presented here. Preliminary results show the superiority of the adaptive technique over a state-of-the-art fixed antenna system in terms of on-board power reduction to achieve a given service availability target.

This paper reports on satellite beacon measurements at 12.7 GHz from late October 2010 until the end of June 2012 at two geographically separated Arqiva Teleport sites in Southern England in order to obtain propagation data to be used in operational decision making and improvement of the scientific understanding of such effects. These sites operate at very low elevation angles (4.1 and 5.3 degrees) and therefore experience significant propagation effects. Measurements are on-going to achieve meaningful long term statistics, however there is value in comparing the results obtained at both sites over the common period of measurement data to date (approximately 20 months). The measurements are performed at 1/2 second intervals and statistical analysis applied. A primary objective of this work is to assess the influence of tropospheric scintillation and consequently the paper will focus on this with the addition of some lesser material on rain fade effects. The measurements and analysis have been performed as a collaborative effort between Arqiva and staff who work at the University of Surrey. It is emphasised that the primary objective of this work is to assess the influence of tropospheric scintillation and rain attenuation from an operational perspective and to a lesser extent from an academic viewpoint.

Multipaths are one of the major sources of errors for satellite navigation systems. The goal of this article is to present some advances on propagation channel modelling for GNSS mobile users and to show how GNSS receiving algorithms are sensitive to the modelling of the channel. Two channel characteristics are analysed in the paper: the resolution of the environment (level of detail), and the resolution of the channel, meaning the number of significant echoes in the tapped-delay line. Particular focus is made on mitigation techniques using antenna arrays to reject multipath. The influence of the channel model will be then interpreted considering three different types of GNSS receiver algorithms, namely conventional DLL/PLL, beam forming and SAGE/STAP algorithm.

In this paper we present an enhanced version of previous narrowband land mobile satellite, LMS, channel models. Some of the shortcomings of the previous models have been identified and corrections proposed. The model is well suited for generating synthetic time-series.

This paper addresses the statistical modelling of MIMO-LMS fading channels. In the absence of accurate experimental results, a statistical model for the characterization of MIMO-LMS channels is proposed based on consolidation of available experimental results for SISO-LMS, SIMO-LMS and MISO-LMS as well as on their extrapolation to the MIMO-LMS and satellite diversity cases of interest.

MIMO systems are already state-of-the-art in terrestrial systems. With the availability of satellites with higher EIRP the high spectrum efficiency offered by MIMO systems becomes applicable to satellite-based systems, too. The MIMOSA project covers the evaluation of the satellite MIMO channel characteristics by field measurements. In particular, the estimated capacity increase for mobile reception is evaluated. The measurements have been completed, but the analysis is still ongoing. This paper describes the measurement setup and includes selected results from the statistical analysis.

The objective of this study, named AWARDS (Advanced microWAve Radiometers in Deep space Stations), is the preliminary design of a transmission Media Calibration System (MCS) to be located at an ESA Deep Space Antenna (DSA) site. The crucial aspect is the capability to accurately retrieve the tropospheric path delay along the line-of-sight of the deep space probe in order to allow precise tropospheric calibration of deep space observables (range and range-rate) with particular reference to the BepiColombo spacecraft and its primary DSA at Cebreros (ES). The study focuses on two main aspects which lead to the preliminary design of the Mercury Orbiter Radioscience Experiment (MORE) MCS: the characterization of current microwave radiometers (MWRs) available at ESA/ESTEC and the atmospheric fluctuation effects on the MCS error budget, in terms of the Allan standard deviation (ASD). In the course of the study, further critical aspects have been identified (effects of Sun contamination, effects of ground noise emission), and mitigation strategies have been proposed. The final outcome is a preliminary design of the MWR (and the entire MCS) to be deployed at the ESA/ESTRACK (ESA Tracking station network) sites and being compliant with MORE requirements.

Two events with contrasting drop fall velocity versus drop shape characteristics are discussed. The events were captured by two collocated 2D video disdrometers, as well as a C-band polarimetric radar, 15 km away. Contoured images of the drops as well as their fall velocities from the disdrometer measurements, together with the analysis of simultaneously recorded radar observations, point towards the possibility of mixed mode drop oscillations (including the horizontal mode) occurring for the second event. The first event – which occurred 7 days prior - did not show any unusual characteristics, and represents the majority of the recorded events. Results are presented and discussed.

This paper describes a wave propagator that can be used to simulate radio occultation measurements. The wave propagator is used to simulate a number of radio occultations based on European Centre for Medium-range Weather Forecasts (ECMWF) atmospheric profiles. The output from the wave propagator is used as input to a Full Spectrum Inversion (FSI) retrieval module, which calculates geophysical parameters. These parameters are compared to the ECMWF atmospheric profiles. We also compare the output from the wave propagator with that of a 3D ray tracer. Such comparisons can be used to reveal system errors and get a better understanding of the physics of the problem and the retrieval errors in the inversion of radio occultation measurements.

The provision of multimedia services via a non-geostationary satellite system requires advanced traffic engineering procedures. It includes adaptive routing, adaptive forwarding and appropriate signalling. In this study, we evaluate the impact of different signalling procedures on the performance of a network. The signalling procedures were used in conjunction with traffic class dependent routing, smoothed link-cost functions and adaptive forwarding alleviates the oscillations in the traffic distribution. The performance of the proposed signalling procedures is evaluated in two different traffic load scenarios. The simulation results are presented in terms of the average packet delay in the network and the average normalized data throughput. The simulation results indicate that the proposed triggered signalling significantly decreases the signalling load, while the network's performance is not deteriorated in terms of packet delay and data throughput.

The present paper studies, interference issues arising from, the spectral and spatial coexistence between terrestrial stations participating in fixed wireless networks or in a point-to-point link and satellite terminals belonging to a satellite communication network, operating at frequencies above 10 GHz. Rain attenuation is considered to be the dominant fading mechanism at this frequency range. The acceptable intersystem interference probability (AIIP) of the carrier-to-interference ratio (CIR) of a terrestrial station interfered by a satellite is defined and analytically calculated. Adaptive power control schemes are assumed to operate for both networks. The correlated propagation fading phenomena over multiple terrestrial and slant paths are accurately incorporated. The proposed model is physical and can be applied on a global scale since incorporates properly the local climatic conditions concerning the point rainfall rate and the spatial rainfall inhomogeneity. Useful numerical results of the present model are finally provided and the impact of various crucial operational and geometrical parameters of satellite and fixed wireless networks’ coexistence is also examined.