Roberto Prieto-Cerdeira

The PARIS Ocean Altimeter In-Orbit Demonstrator

Mesoscale ocean altimetry remains a challenge in satellite remote sensing. Conventional nadir-looking radar altimeters can make observations only along the satellite ground track, and many of them are needed to sample the sea surface at the required spatial and temporal resolutions. The Passive Reflectometry and Interferometry System (PARIS) using Global Navigation Satellite Systems (GNSS) reflected signals was proposed as a means to perform ocean altimetry along several tracks simultaneously spread over a wide swath. The bandwidth limitation of the GNSS signals and the large ionospheric delay at L-band are however issues which deserve careful attention in the design and performance of a PARIS ocean altimeter. This paper describes such an instrument specially conceived to fully exploit the GNSS signals for best altimetric performance and to provide multifrequency observations to correct for the ionospheric delay. Furthermore, an in-orbit demonstration mission that would prove the expected altimetric accuracy suited for mesoscale ocean science is proposed.

Versatile two-state land mobile satellite channel model with first application to DVB-SH analysis†

Standardization activities on Digital Video Broadcasting–Satellite services to Handheld Devices (DVB-SH) have driven the need for a consolidated Land Mobile Satellite (LMS) narrowband channel model. In the DVB-SH system, the satellite broadcasts a signal carrying multimedia services aimed directly to a variety of mobile (handheld or vehicular) and fixed terminals. A three-state LMS channel model that describes the narrowband propagation channel in three possible shadowing states—line-of-sight conditions, moderate shadowing and deep shadowing—had been selected as a baseline for physical layer simulation of the DVB-SH waveform. This type of model, capable of generating complex time series, was originally selected, because it is the simplest model that allows the simulation of first- and second-order effects of the LMS channel in a realistic manner. The main limitations of such model are, first of all, that a classification in three states does not necessarily correspond with reality and, secondly, that the statistical parameters for each state were fixed for a given scenario and elevation angle. Those limitations may impact the selection of Physical Layer parameters of the DVB-SH standard. A new channel model is proposed based on the original three-state model including two major modifications: a reduction in the number of states and the introduction of a versatile selection of statistical parameters describing each state. Furthermore, the state machine is governed either by Markov or by semi-Markov chains. The new-state classification does not necessarily correspond to intuitive physical definitions of the states as before (line-of-sight, shadowing) but instead to channel variations that share similar statistical characteristics. The two-states are termed for convenience, Good and Bad states, representing a range of LOS-to-moderate shadowing and moderate-to-deep shadowing, respectively. For the model parameters selection, datasets at L- and S-band have been analysed using an iterative algorithm that includes automatic data classification and parameter extraction. The proposed model is considered more suitable for the analysis of DVB-SH test cases. This study starts with an overview of the main DVB-SH system parameters and assumptions. The original three-state model is briefly introduced; the new model is presented in detail, including simulator implementation. Finally, both models and experimental data sets are compared on a statistical basis. The performance of both models are discussed to show how effective the model is for the representation of shadowed conditions and therefore, its suitability for the analysis and optimal configuration of the physical and link layer parameters (namely physical layer interleaver size, link layer protection time, overall redundancy, etc.). Copyright

Review of generative models for the narrowband land mobile satellite propagation channel

The land mobile satellite (LMS) propagation channel is frequently described using statistical models. These models usually make different assumptions regarding the behavior of the direct signal, the diffuse multipath component and the shadowing effects. This paper analyzes the theoretical formulation and implementation of time-series synthesizers based on three typical statistical models: Loo, Corazza–Vatalaro and Suzuki, describing their similarities and differences. The discussion is not limited to the amplitude of the complex envelope but also to the phase variations and Doppler spectra. Finally, guidelines are also provided for comparing model parameters supplied by different authors. Copyright

A wideband, directional model for the satellite‐to‐indoor propagation channel at S‐band

This paper presents a hybrid empirical-statistical model for the satellite-to-indoor propagation channel at S-band derived from measurements using a helicopter to simulate the satellite. The measurements have been carried out by means of a wideband, circularly polarized channel sounder in a SIMO (Single Input Multiple Output) configuration, allowing the derivation of entry loss, wideband and spatial model parameters. It is hoped that this paper will provide relevant information on the satellite-to-indoor channel given the large amount of experimental data available, covering a significant member of different buildings of various types, and the amount of measurement configurations: elevations and azimuths. Copyright

State modelling of the land mobile propagation channel for dual-satellite systems

The quality of service of mobile satellite reception can be improved by using multi-satellite diversity (angle diversity). The recently finalised MiLADY project targeted therefore on the evaluation and modelling of the multi-satellite propagation channel for land mobile users with focus on broadcasting applications. The narrowband model combines the parameters from two measurement campaigns: In the U.S. the power levels of the Satellite Digital Audio Radio Services were recorded with a high sample rate to analyse fast and slow fading effects in great detail. In a complementary campaign signals of Global Navigation Satellite Systems (GNSS) were analysed to obtain information about the slow fading correlation for almost any satellite constellation. The new channel model can be used to generate time series for various satellite constellations in different environments. This article focuses on realistic state sequence modelling for angle diversity, confining on two satellites. For this purpose, different state modelling methods providing a joint generation of the states ‘good good’, ‘good bad’, ‘bad good’ and ‘bad bad’ are compared. Measurements and re-simulated data are analysed for various elevation combinations and azimuth separations in terms of the state probabilities, state duration statistics, and correlation coefficients. The finally proposed state model is based on semi-Markov chains assuming a log-normal state duration distribution.

Distribution and mitigation of higher‐order ionospheric effects on precise GNSS processing

Higher-order ionospheric effects (I2+) are one of the main limiting factors in very precise Global Navigation Satellite Systems (GNSS) processing, for applications where millimeter accuracy is demanded. This paper summarizes a comprehensive study of the I2+ effects in range and in GNSS precise products such as receiver position and clock, tropospheric delay, geocenter offset, and GNSS satellite position and clock. All the relevant higher-order contributions are considered: second and third orders, geometric bending, and slant total electron content (dSTEC) bending (i.e., the difference between the STEC for straight and bent paths). Using a realistic simulation with representative solar maximum conditions on GPS signals, both the effects and mitigation errors are analyzed. The usage of the combination of multifrequency L band observations has to be rejected due to its increased noise level. The results of the study show that the main two effects in range are the second-order ionospheric and dSTEC terms, with peak values up to 2 cm. Their combined impacts on the precise GNSS satellite products affects the satellite Z coordinates (up to +1 cm) and satellite clocks (more than ±20 ps). Other precise products are affected at the millimeter level. After correction the impact on all the precise GNSS products is reduced below 5 mm. We finally show that the I2+ impact on a Precise Point Positioning (PPP) user is lower than the current uncertainties of the PPP solutions, after applying consistently the precise products (satellite orbits and clocks) obtained under I2+ correction

Mobile satellite broadcasting with angle diversity - performance evaluation based on measurements

This paper focuses on the achievable angle diversity gain in mobile satellite broadcasting in various environments. Multiple satellite signals within the S-band were recorded simultaneously along the east coast of the U.S. over a traveling distance of 3700 km. The first-order statistical data analysis shows that the required C/N margin for a certain service availability can be significantly decreased by combining two satellite signals. Depending on their elevation angles, the diversity combining gain is analyzed in terms of cumulative distribution functions (CDFs) for various environments. The results for angle diversity are compared to time diversity using an interleaver of variable length. Combining angle diversity and time interleaving results in a further improvement of the service availability.

MIMOSA–a dual approach to detailed land mobile satellite channel modeling

SUMMARY As multiple-input-multiple-output (MIMO) transmission technologies are common in terrestrial mobile communications and getting attention for mobile broadcasting satellite systems, the need for a comprehensive MIMO channel model for the dual-polarized land mobile satellite (LMS) channel arises. In the course of the Characterisation of the MIMO Channel for Mobile Satellite Systems (MIMOSA) project, two complementary modeling approaches have been developed that form a dual model. They provide a scalable modeling solution, which permits a user selectable level of simulation complexity and detail. The models have been evaluated by comparing their results with data gathered from the extensive field trials carried out within the MIMOSA project. This paper describes the dual wideband-modeling and narrowband-modeling approaches, provides examples of the usage and provides some evaluation results. Copyright

MIMOSA --Analysis of the MIMO channel for LMS systems

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 PARIS in-orbit demonstrator

Mesoscale ocean altimetry remains being a challenging area for satellite observations. Conventional nadir looking radar altimeters can make observations only along the satellite ground track and many of them are needed to sample the sea surface at the required spatial and temporal resolutions. The Passive Reflectometry and Interferometry System (PARIS) using GNSS reflected signals was proposed as a means to perform ocean altimetry along several tracks simultaneously spread over a wide swath. The present paper describes such an instrument specially conceived to fully exploit the GNSS signals for best altimetric performance, and to provide multi-frequency observations to correct for the ionospheric delay. Instrument calibration strategy is also discussed. Furthermore an in-orbit demonstration mission is proposed that would prove the expected altimetric accuracy suited for mesoscale ocean science.