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On the Application of the Baum-Welch Algorithm for Modeling the Land Mobile Satellite Channel

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  • Digitale Netze
Disciplines
  • Communication
  • Computer Science
  • Design
  • Mathematics

Abstract

untitled On the Application of the Baum-Welch Algorithm for Modeling the Land Mobile Satellite Channel Bala´zs Matuz, Francisco La´zaro Blasco and Gianluigi Liva Abstract—Accurate channel models are of high importance for the design of upcoming mobile satellite systems. Nowadays most of the models for the land mobile satellite channel (LMSC) are based on Markov chains and rely on measurement data, rather than on pure theoretical considerations. A key problem lies in the determination of the model parameters out of the observed data. In this work we face the issue of state identification of the underlying Markov model whose model parameters are a priori unknown. This can be seen as a hidden Markov model (HMM) problem. For finding the maximum likelihood (ML) estimates of such model parameters the Baum-Welch (BW) algorithm is adapted to the context of channel modeling. Numerical results on test data sequences reveal the capabilities of the proposed algorithm. Results on real measurement data are finally presented. I. INTRODUCTION Satellite services to mobile users are experiencing a renewed interest thanks to the licenses granted for S-band usage for broadcast and interactive services [1]–[3]. The underlying communication channel, referred to as land mobile satellite channel (LMSC), is characterized by strong variations of the received signal power. Obstacles in the propagation path between the satellite and the mobile terminal, such as buildings or trees may cause shadowing or even a complete blockage of the signal. With increasing frequency and decreasing elevation angle such events become more and more likely and strongly impact service availability. A further source of fading is due to multipath propagation: objects in the vicinity of the receiver are source of reflections that cause constructive or destructive interference. In the past several authors proposed Markov chain models to describe the behavior of the LMSC [4]– [8]. The modeling approach can be divided into two stages. First

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