Alexander Ihlow

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.

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.

Estimation of fading parameter correlation for modeling the land mobile satellite channel

This paper addresses the correlation of fading signal parameters for dual-satellite land mobile satellite (LMS) channels. We use Loos model to describe the slow and fast variations that occur due to varying shadowing conditions and multipath fading, respectively. Loos parameters (mean power of direct signal component, standard deviaton of direct signal component, and average multipath power) are estimated segment-by-segment from fading signals of two simultaneously measured geostationary satellites using a curve-fitting approach. The parameter correlation between the signals of the two satellites is investigated. A significant correlation is found in the mean power of the direct signal components in some environments, when both satellites are shadowed or blocked by obstacles.

Modeling of the Land Mobile Satellite Channel considering the Terminal’s Driving Direction

A precise characterization of the Land Mobile Satellite (LMS) channel, that is, the channel between a satellite and a mobile terminal, is of crucial importance while designing a satellite-based communication system. State-of-the-art statistical LMS channel models offer the advantage of requiring only a few input parameters, which include the environment type and the elevation angle of the satellite. However, the azimuth angle relative to the driving direction of the mobile terminal is usually ignored, as its proper modeling requires either an extensive measurement campaign or a significant effort from the user, as a precise geometrical description of the scenario is required. In this contribution we show that the impact of the driving direction on the channel statistics is not negligible and requires to be modeled explicitly. Moreover, we propose a statistical LMS channel model whose parameters are obtained via an image-based state estimation method. The image-based method is verified by a comparison with measured radio frequency signal levels. The proposed method allows obtaining a complete statistical description of the channel for arbitrary elevation and azimuth angles.

High time-resolution spectrum occupancy model for testing of cognitive radio devices

The ubiquitous problem of radio spectrum scarcity caused by ever-increasing traffic, e.g. in mobile communications, demands measures. One approach would be secondary use of spectrum by radio devices with cognitive abilities employing dynamic spectrum access. In order to avoid interference with the primary use of the spectrum, such cognitive devices must be thoroughly tested. In this paper, we present a high time-resolution model of spectrum occupancy, stemming from the activity of primary users, for testing purposes. The proposed model is based on a few statistical parameters and includes a novel parameter adaptation procedure that improves the accuracy of current models significantly. The intended use of the model is over-the-air testing of cognitive devices, for instance for prototyping purposes, e.g. evaluation of the achievable performance, or for conformance testing. The model parameters are extracted from measurement data in the GSM 900 downlink band obtained at the Ilmenau University of Technology campus. However, the modeling approach is not restricted to GSM 900 but lends itself to other bands and radio technologies, too.

Speeding up 3D SAFT for ultrasonic NDT by sparse deconvolution

In this paper we propose to pre-process ultrasonic measurements (A-scans) in Non-Destructive Testing (NDT) by sparse deconvolution before post-processing the data with the Synthetic Aperture Focusing Technique (SAFT). Compared to state-of-the-art SAFT post-processing of raw A-scan measurements, pre-processing by sparse deconvolution can improve NDT in the following ways: First, the temporal resolution of signal reflections is increased. Second, because the A-scans appear as a sparse signal of spikes, it is possible to formulate the time-domain SAFT algorithm in a new fashion that is both faster compared to conventional SAFT and the deconvolved input data can be focussed better leading to a higher resolution. Since sparse deconvolution could be implemented directly into the ultrasonic probe hardware/software measurement setup, this approach can significantly speed up measurements in time-critical environments. We test the proposed scheme on CIVA simulation data as well as measurements and show B- and C-images of raw SAFT vs. Orthogonal Matching Pursuit (OMP) + SAFT and Basis Pursuit Denoising (BPDN) + SAFT.

Measurement-Based Performance Analysis of Cooperative Diversity for Satellite Terminals in a Moving Convoy

In this paper we discuss the impact of cooperative satellite diversity on the availability of the land mobile satellite (LMS) channel. By the use of multiple terminals the overall probability to encounter conditions where all terminals are in a bad channel state is reduced. This reduction depends on the number of terminals and the terminal distance. The results presented in this paper are completely based on the analysis of measurements. These were conducted for two geostationary satellites and four different environments using a single mobile satellite terminal. Thus, in order to virtually increase the number of terminals we rely on a convoy scenario using shifted versions of the data. Analyzing up to four cooperative terminals and different terminal distances a significant bad state reduction is already achieved for rather small distances.

Photogrammetric satellite service prediction - Correlation of RF measurements and image data

This paper addresses the image-based characterization of the land mobile satellite channel. In a measurement campaign, the signal power levels of the Satellite Digital Audio Radio Services (SDARS) in the U.S. were recorded. In parallel, a fisheye camera on the roof of the measurement van continuously acquired images of the upper hemisphere. Using time, location and heading information from GPS, the satellite positions are determined in the hemispheric images. Analyzing the regions around the satellites by image processing methods, the degree of visibility of the satellites is extracted which acts as an indicator for the current shadowing conditions. Using this optical method, shadowing parameters for the land mobile satellite channel of arbitrary satellite constellations can be derived. This method can be helpful for cost-efficient, large-scale network planning.

State Modelling of the Land Mobile Propagation Channel with Multiple Satellites

We evaluate a new approach for multisatellite state modelling: the Master-Slave approach. By this concept slave satellites are modelled according to an existing master, whereas the correlation between multiple slaves is omitted. Master-Slave is therefore a generic name for a state modelling concept, for which different realisations are possible. As a possible realisation we present the Conditional Assembling Method. For modelling of only two satellites (one master and one slave), the Conditional Assembling Method enables an accurate resimulation of the correlation coefficient between the satellites and the probabilities of single and combined states. Based on this condition, the performance of Master-Slave for three, four, and five satellites is evaluated in terms of state probability modelling. Therefore, the correlation coefficients and the all bad-state probabilities with Master-Slave are compared with the measurements for different elevation angles and azimuth angle separations of the multisatellite system. Master-Slave has a high modelling error in case of small azimuth separation between the slave satellites (except that one slave has a small azimuth separation to the master). Furthermore, a master satellite with a high elevation provides a lower probability error compared to a master with low elevation.

QoS prediction for mobile satellite broadcasting with angle diversity based on measurements

To meet the high quality of service requirements for mobile satellite applications, diversity combining techniques are used to mitigate fading effects in the satellite propagation channel. In this paper the performance of multi-satellite diversity (or angle diversity) in combination with time diversity is presented. The achievable diversity gain depends on the environmental conditions, the satellite elevation and the angular separation of the satellites. To assess the performance of multi-satellite systems, high-power broadcasting signals in the S-band from HEO and GEO satellites of the Sirius XM Radio system were recorded simultaneously along the east coast of the USA. Based on the measured signal power levels, the ESR(5) fulfillment criteria are predicted for various configurations incorporating different margins, time interleaver lengths, and satellite constellations. The results are presented for six different environments: urban, suburban, commercial, forest, intermediate tree shadowed, and highway.