Hazra, Sayantan2015-09-222023-10-202015-09-222023-10-202014ROLL NO. 09610205https://gyan.iitg.ac.in/handle/123456789/458Supervisor: Ratnajit BhattacharjeeThis research deals with various aspects of channel modeling in land mobile satellite (LMS) communications. In this work, we investigate on the eऍect of propagation phenomena speciऒc to diऍerent propagation scenarios on signal received by an LMS receiver. We sort out the propagation scenarios usually encountered by an LMS receiver and analyze the chain of mechanisms that contribute to the fading eऍects in that particular scenario. From this analysis, we conclude what type of mathematical formulation and what statistical distributions are appropriate to take into account the eऍect of the actual propagation phenomena which occur for pertaining to certain scenario. The complex envelope processes proposed this way are used for narrowband and wideband LMS channel modeling. We include the eऍect of directivity of LMS antenna systems in the three-dimensional (3D) scattering models available in literature. This signiऒcantly modiऒes the expression of autocovariance function and second order moments useful for calculation of some important second order statistics. We propose two narrowband models based on complex envelope processes with additive and multiplicative interaction of shadow fading and small-scale fading with 3D scattering mechanism. By comparing with measurement results of second order statistics available in literature, we show that the additive model can be used to depict a wide variety of fading situations for ओat urban and suburban areas while the model based on multiplicative process is applicable to areas shadowed by irregular terrain and trees. For calculation of statistics in multipath frequency-selective wideband channel we propose a new mathematical framework which is also used for state-based models. We also compute channel capacity for all kind of channel models dealt throughout the thesis.enELECTRONICS AND ELECTRICAL ENGINEERINGThesis