Riza Akturan

Bio: Riza Akturan is an academic researcher from University of Texas at Austin. The author has contributed to research in topics: Digital image processing & Communications satellite. The author has an hindex of 4, co-authored 7 publications receiving 54 citations.

Photogrammetric mobile satellite service prediction

Abstract: Photographs of the sky, taken through a fish-eye lens with a 180° field-of-view in several environments, were analysed for the skyline, a quantity useful to designers of mobile satellite communications systems. Above 10° elevation, on average 98% of the sky is visible in rural, 95% in suburban, 77% in urban Austin, and 68% in urban San Antonio.

Satellite-PCS channel simulation in mobile user environments using photogrammetry and Markov chains

Abstract: In this paper, we present a system that models the land-mobile satellite communication channel with a Markov chain approach supported by images of the mobile Earth station's (MES) environment. Our method employs a video camera with a fish-eye lens capturing image sequences of the user environment from the position of the moving MES, image and signal processing algorithms to recognize propagation path states and extract their duration and transition probabilities, and modeling of the communication channel characteristics using the theory of Markov stochastic processes combined with statistical fade distributions appropriate for given path states. The results demonstrate that the procedure provides a full statistical characterization of the narrow-band land-mobile satellite propagation channel in several environments.

Propagation modeling in land mobile satellite systems using photogrammetry

Abstract: We present a system that substitutes video image processing for propagation measurements and permits flexible fade simulation of land mobile satellite communication (LMSC) systems. Our method is based on deriving environmental characteristics from fisheye lens videos, using image processing algorithms. We employ the processed images to track the propagation state (clear, shadowed by vegetation or blocked) along the satellite-Earth communication path. Analyzing sequences of images results in a propagation state time series which is input to a channel simulator. In this paper, we present the optical measurement system, the image processing algorithms and channel simulation procedures. Finally, we compare simulation results with actual satellite fade measurements.

Optically derived elevation angle dependence of fading for satellite PCS

Abstract: Images of urban Japan taken vertically through a 180 deg fisheye lens were analyzed to derive, as a function of elevation the fraction of sky that is clear, shadowed by trees, or blocked by buildings. At 32 deg elevation, results match those derived from satellite measurements fit to a 3-state fade model. Using the same model, for the first time the elevation angle dependence of mobile satellite fading is predicted.

Photogrammetric satellite PCS channel modeling using Markov chain approach

Abstract: We present a system that uses a Markov chain approach to model the communication channels using videos of the environments in land mobile satellite (LMS) personal communication systems (PCS). Our method is based on capturing fish-eye lens images of the environments and, using very effective image and signal processing algorithms, modeling the communication channel characteristics using the theory of Markov stochastic processes. The resulting Markov chain models provide a full characterization of the narrowband LMS PCS propagation channel statistics in the selected environments. We present our imaging system and propagation channel modeling procedure in detail and discuss the results.

Land mobile GNSS availability and multipath evaluation tool

Abstract: Applications of global navigation satellite system (GNSS) in land transportation systems are already extensively deployed and will certainly continue to grow especially in the framework of intelligent transport systems. However, one of the best-known drawbacks of such a system is the lack of satellite visibility in dense urban areas as well as in some specific embedded railway environments. This restricts considerably GNSS use for extended safety related applications. In this paper, a new tool is proposed to predict the availability of a satellite constellation from the point of view of the land transportation user. Knowing the trajectory of a land vehicle, the tool predicts the number of satellites that will be received and produces a safety criterion able to qualify the GNSS localization result. A first version of the tool, already in operation, merges an image processing approach providing the knowledge of the land environment, and the output of a satellite tracking program predicting satellite positions in the sky. This allows us to determine, using a simple optical approach, the number of satellites received in line-of-sight or blocked, with regard to the nearby environment of the receiving antenna. Results obtained in railway as well as in road environments show that satellite signals received by multipath are often used by GNSS receivers in the localization process. Thus, propagation characteristics of the satellite signals in an urban canyon configuration were characterized to determine when a signal received by reflected ray is used by the receiver or not. A criterion related to the satellite elevation is defined to improve the overall performance of the predictive tool. Comparisons with real measurements are commented on. Both simulations and measurements are very similar.

Channel characterisation for spread spectrum satellite communications

Abstract: The paper examines the characteristics of satellite propagation channels for spread spectrum communications. Based on measurement campaigns at L-band, the signal bandwidth is determined when the channel becomes frequency-selective. A wideband channel model for land mobile satellite (LMS) services is presented which characterises the time-varying transmission channel between a satellite and a mobile user terminal. The parameters of the model are the results of fitting procedures applied to the measured data. The parameters are given for various environments and elevation angles. For satellite diversity, the correlation of two independent channels is determined. This channel property is applicable to wideband and narrowband channel models.

Path diversity for LEO satellite-PCS in the urban environment

Abstract: A new method for analyzing the propagation aspects of mobile satellite systems is introduced. It consists of: (1) taking fisheye lens images at potential user locations; (2) extracting path state information (clear, shadowed, or blocked) as a function of look angles from the images; and (3) combining each path state for single or multiple satellites in a specific constellation with frequency-appropriate statistical fade models to predict overall performance measures such as fade dependence with elevation angle or path-diversity gain. The advantage of the method is that it minimizes the need for expensive propagation campaigns. The importance of including specular reflections and diffraction under urban blockage conditions is established. From images obtained in urban Japan, a fade-lapse rate with elevation of 0.2 dB/degree is deduced for fades exceeded about 10% of the time. Path-diversity gain for combining and hand-off diversity is found for up to four-fold diversity at a high-, mid-, and low-latitude location for the Globalstar constellation. With two-fold diversity and neglecting implementation losses, the fade margin required for 80% and 95% coverage at mid-latitude urban locations is reduced from 16 to 6 dB and from 25 to 16 dB, respectively.

Shadowing correlation assessment and modeling for satellite diversity in urban environments

Abstract: Non-geostationary orbit satellite networks have dynamic, yet deterministic topologies. This paper deals with the consequences of relying on the use of multiple visible satellites to improve availability with time/locations through satellite diversity techniques. The assumption of independent blockage events in two different satellite-to-mobile links is generally not accurate and information on shadowing correlation should be taken into account in the assessment of availability.In this paper a shadowing correlation study for urban environments is presented and a model for the real environments, as well as for a generic urban environment is inferred. The model proposed here is simple and can be run on a computer. It also relates urban and constellation geometries thus allowing the identification of those cases for which satellite diversity gain should be expected. As a result of this analysis and modelling, we present empirical analytical expressions describing positive correlation coefficient as a function of satellite angular separation (azimuth and elevation). We also show that an angle exists above which correlation can be negative and satellite diversity can sensibly improve link availability. Copyright © 2002 John Wiley & Sons, Ltd.

Propagation model for building blockage in satellite mobile communication systems

Abstract: A propagation model for building blockage in satellite mobile communication systems is developed. This model characterizes the signal transmitted from a low-Earth orbiting (LEO) satellite when there is an obstruction in the path of the signal. The obstruction is assumed to be a man-made structure. The analysis is performed using the uniform theory of diffraction (UTD). Using this method, both single and double diffractions from the structure edges were included. Direct and reflected rays from the ground and building were also included, whenever the satellite signal was not completely obstructed. The satellite is assumed to be moving along a circular orbit while the receiver is stationary. The normalized signal level (in decibels) and the signal attenuation rate (in decibels per second) are computed. Such information is considered very useful in developing the mobile system's hand-off algorithm.