European Space Agency
European Space Agency
The objectives of the project are to study the characteristics of fading from satellite systems using angle diversity (spatial diversity) for different reception scenarios and to develop a suitable channel model.
The project covers a measurement campaign, statistical analysis and the development of a model capable of air-interface designs and performance analysis.
Two measurement campaigns are planned:
The activity is supported by ICO Global Communications (ICO). ICO provides access to their MEO satellite, which is fully operational and only partly used for other applications. This allows the transmission of sequences from the satellite suitable for wideband channel measurements.
The goal is the development of an enhanced multistate channel model covering the effects of multi-satellite systems with angle diversity.
Today, terrestrial repeaters are installed in areas where the satellite cannot provide a sufficient QoS. With angle diversity it may be feasible to cover many of these areas without terrestrial repeaters. A key issue is therefore the selection of environments and usage scenarios where a satellite system with angle diversity can provide a sufficient QoS and is not already covered by a single satellite system.
Two main benefits from angle diversity are expected:
The project shall provide:
The main goal of the project is the development of a model useful for verification of systems with:
The efficiency of angle diversity is strongly dependent on the correlation of fades in the respective diversity propagation paths. Consequently, the main goal is to extend an existing LMS model to include angle diversity. The LMS model typically includes a statistical approach based on a Markov-model to generate time series. The channel model can be split into a slow or “large-scale fading model” (LSFM) and a fast or “small scale fading model” (SSFM). The slow fading model can, for example, be implemented by a Markov-model. For each state transition the key parameters of the fading channel (mean signal level, Rice factor, etc.) are selected using a statistical model using for each state a different distribution.
The fast fading effects are typically implemented by well-known models and assumptions like the Wide Sense Stationary – Uncorrelated Scattering (WSSUS). The goal of the project is to develop a LSFM1 (representing signal 1) and LSFM2 (representing signal 2). Special focus will be on the correlation between LSFM2 and LSFM1.
The gain resulting from the angle diversity depends highly on the satellite constellation parameters (elevation, azimuth angles) and the environment (narrow or wide streets, etc). Accordingly, it is planned to make the measurements for different elevations, azimuth and separation angles. Especially for GEO stationary satellites the trade-off between high separation angle and better elevation becomes relevant. If the separation angle is increased orbital positions have to be selected resulting in a lower elevation. Therefore, special attention shall be put on the parameter range relevant for Europe. A first set of data is already available from measurements in the U.S. Many of the scenarios in the U.S. may not be typical for Europe. Therefore, a measurement campaign in Europe is considered as essential to ensure that the model covers scenarios typical for Europe.
The project started with a literature, experiment and data review, after the requirements for the experiment and the measurement equipment and a preliminary design were reviewed at the Preliminary Design Review in April 2008.
The Critical Design Review included complete measurement campaign planning and measurement equipment design, and also a preliminary integration and testing of the equipment. The measurements were scheduled between August and December 2008 with the first results reviewed by end of October. After that, data analysis and model development will happen with a preliminary model by March 2009. The activity concludes with a Final Review in October 2009.
The project has been extended by a CCN for three purposes:
The MiLADY project was finished in October 2009. The final presentation has been held in September 2010 together with the two other projects funded by ESA: J-ORTIGIA and Channel Measurement Equipment (CME). The MiLADY CCN has been finalized in 2011; the final presentation has been held during the ESA propagation workshop in December 2011.
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The first measurement campaign in the US was carried out successfully in September 2008. Measurement data were recorded for a total of 3700 km of drive tests along the US East coast. The campaign started in Jacksonville, Florida and ends up in Portland, Maine (see below). Signals from 4 visible satellites in S-band at 2.3 GHz were recorded in parallel.
During the project, the objective of the second measurement campaign was refocused and the originally planned MEO experiments were replaced by GPS measurements in Europe. The GPS satellite system has the advantage, that it provides a multi-satellite constellation for simultaneous measurements of L-band signals at 1575 MHz (8 signals in average), thus allowing analysing many different angle diversity constellations. A disadvantage is the fact, that the channel impulse response cannot be measured, preventing the analysis of the wideband characteristics of the propagation channel. Different routes were selected in the centre and the vicinity of Erlangen, covering multiple environments such as urban and suburban.
Each of the roads was driven multiple times to obtain a significant amount of satellite orbit positions for angle diversity analysis.
The new MiLADY LMS narrowband channel model for SISO and MISO (angle diversity) satellite constellations as depicted in the figure below has been developed within the CCN. The MiLADY model extends the latest 2-state SISO model as described in [Prieto10] by modifying the generator architecture and by extending the model databases. After the consolidation of the MiLADY SISO model, it has been further extended to support MISO satellite constellations.
The key characteristics of the MiLADY SISO and MISO narrowband channel model are:
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Further detailed information about the measurement campaigns and the analysis results can be found in several publications about the MiLADY project:
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