Land Mobile Satellite Channel Research Articles

A Trace-Time Framework for Prediction of Elevation Angle Over Land Mobile LEO Satellites Networks

Elevation angle is one of the most significant parameters of land mobile satellite channels, subject to rapid variations in the case of Low Earth Orbit (LEO) satellite systems. In this paper a novel trace-based framework is proposed and analyzed which is capable of predicting elevation angle as a function of time during satellite visibility window. Trace-time based modeling makes the framework practical for real-time evaluation of elevation angle and its alteration incurred by communication links in LEO satellite systems. The proposed method is particularly suitable for development of communication channel models and services in mobile LEO satellite networks where path variability is of great importance.

Approximate Outage Analysis of Land Mobile Satellite Systems in Lognormally Shadowed Rician Channels

Among the proposed models for land mobile satellite (LMS) channels, the shadowed Rice model proposed originally by Loo, has found wide applications in different frequency bands. In Loo's model, it is assumed that the received signal is affected by nonselective Rice fading with lognormal shadowing on the direct component only, while the diffuse scattered component has constant average power level. The resulting composite probability density function (PDF) includes an infinite-range integral and is not available in closed-form, thereby making the performance evaluation of LMS communication links in these channels cumbersome. To bypass this problem, in this paper an approximation method is developed which makes it possible to describe the envelope PDF as a sum of weighted Rice's PDFs. Therefore, in contrast with Loo's PDF, the proposed method leads to an easy-to-use, closed-form approximate expression for the PDF and also for the most statistical characteristics, such as cumulative distribution function and moments of the signal envelop in shadowed Rice channels. Based on the derived expressions, the performance analysis of a single receiver operating over lognormally shadowed Rice channel is investigated in terms of the outage probability. Numerically evaluated results show the good accuracy of the proposed approximation method.

On the Combination of Tropospheric and Local Environment Propagation Effects for Mobile Satellite Systems Above 10 GHz

Land mobile satellite (LMS) channels at the L (1/2 GHz) and S (2/4 GHz) frequency bands are mainly affected by propagation effects due to the local environment of a mobile terminal, such as multipath, shadowing, and blockage. Future systems for mobile satellite services (MSS) will operate at higher frequency bands, such as Ku (12/14 GHz) and Ka (20/30 GHz), where the tropospheric propagation effects also play an important role. Experimental campaigns conducted so far for Ku/Ka-band LMS channels have not considered any possible correlation between the tropospheric and local environment propagation effects. However, recent experimental work has indicated that these fading effects are not independent. As a first analytical approach to this open problem, a novel statistical analysis is presented in this paper. Emphasis is put on Ku/Ka-band LMS channels whose fading events can be modeled by the Ricean distribution with a relatively high <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> -factor. A novel analytical relationship between the Ricean <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> -factor and the rain attenuation effects is derived, and based on them, an analytical statistical prediction model for the distribution of the Ricean <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> -factor is derived. Particular attention is paid to the rainfall spatial inhomogeneity, as well as to the different effects of the climatic area of interest (temperate versus tropical) on the Ricean <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> -factor statistics. Thus, the presented analysis considers both spatially correlated bivariate lognormal and gamma statistics for the accurate characterization of rain attenuation. The proposed models are flexible and incorporate the impact of several critical operational, climatic, and geometrical parameters of an LMS channel on its multipath behavior under rainfall conditions. Useful numerical results are provided, specific future planned work is outlined, and the need for further experimental verification data is also pointed out.

Channel modeling and influenced factor analysis of the broadband dual-orthogonal polarized MIMO land mobile satellite channel

Channel modeling and influenced factor analysis of the broadband dual-orthogonal polarized MIMO land mobile satellite channel

Land Mobile Satellite Channel Simulator Along Roadside Trees

In this letter, we study the signal fading for the land mobile satellite (LMS) channel caused by roadside trees. A channel simulator is developed, which takes into account the signal fading caused by position-dependent tree-scattered fields and by swaying tree components. The model is validated in terms of the cumulative distribution functions (cdfs) of the received signal and the Ricean K-factor and level crossing rate using measurements at 2 GHz. The agreement found between the measured and simulated statistics is satisfactory.

Channel Modeling for Multiple Satellite Broadcasting Systems

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In this contribution we present the results of a study on land mobile satellite channel models for satellite systems with multiple satellites. The slow fading of our channel model for several satellites is based on a Markov channel state model for joint processes while the Probability Density Function (PDF) of the signal amplitude within each state is fitted to the Loo distribution. The correlation between two satellite channels and the channel spatial autocorrelation have also been studied. We show that a channel state model that uses a Markov state model of order one or of a fixed higher order is not appropriate if the state duration is of very high importance, which can be the case in the process of system planning. Therefore, we propose a dynamic higher order Markov state model for joint processes that depends on the current state duration. This approach models precisely any PDF of the channel state duration for both single and multiple satellite broadcasting systems while having a significantly lower computational complexity than a fixed higher order Markov model. It models the channel states of the whole system correctly, as well as the channel states of each satellite observed independently. It is able to capture the state correlation between multiple satellites. We also study possible approximations of the proposed models in order to reduce their computational complexity while having a good PDF match. Our channel state models are validated by measurements. </para>

An Extended Loo Model with Inhomogeneous Scattering and its Statistical Properties

In this paper, an analytical model for a land mobile satellite channel is introduced that takes into consideration the Generalized Rice model for characterizing the small scale (fast) fading. The proposed model is enriched by the property of non-homogeneous scattering allowing higher flexibility and a more comprehensive description of the channel. In addition, a lognormal process affects the line of sight component, in order to characterize the large scale (slow) fading due to the shadowing effect caused by physical obstacles such as trees and small buildings. The main statistical properties of the model are investigated. Exact solutions for the power spectral density, the probability density function of the envelope and phase, and the cumulative distribution function of the envelope are derived. Approximate solutions for the level crossing rate and the average duration of fades are obtained. The validation of the model is confirmed by simulation and demonstrated by providing the best fit to certain measurement data corresponding to conditions of light and heavy shadowing. As a conclusion, the extended Loo model is applicable in realistic land mobile satellite channels subjected to various conditions and can be preferable because of its outperformance.

Efficient repair mechanism of real-time broadcast services in hybrid DVB-SH and cellular systems

In order to ensure good video quality and location-independent access to multimedia content, digital video broadcasting-satellite service to handhelds (DVB-SH) takes advantage of several innovative techniques. The major one is the forward error correction (FEC) scheme implemented at the link layer called multiprotocol encapsulation-inter-burst FEC (MPE-IFEC). MPE-IFEC supports reception in situations of long duration erasure spanning several consecutive time slice bursts (lasting several seconds) due to characteristics of the land mobile satellite channel which are easily hampered by obstacles such as trees, buildings, or overpasses. However, when deep signal fades last for larger durations, the MPE-IFEC correction capacity is insufficient and MPE-IFEC fails, causing a service interruption. In this paper, we propose a repair mechanism and a suitable architecture for real-time streaming service error handling with reduced degrading effects such as picture freeze, video frame degradation, and video lag. Based on an analytical model of the performance of the MPE-IFEC, an iterative algorithm is proposed where the probability of recovery of lost bursts is computed and updated. The proposed algorithm controls the retransmission request on the cellular network. Simulation results show that by recovering only some specific lost bursts via the cellular path, the quality of experience here expressed in terms of burst error rate is improved.

Measurement and Modeling of the Land Mobile Satellite Channel at Ku-Band

This paper presents the results of a measurement campaign conducted in the winter of 2002 around the city of Munich in southern Germany. The primary goal was to evaluate the link performance of the land mobile satellite channel at Ku-band and to characterize the temporal behavior of the channel to help in the evaluation of different fade mitigation techniques for future mobile satellite systems that aim at employing this frequency band. To achieve this objective, first- and second-order channel statistics will be presented, the outage probability of the channel analyzed, and a Markov-chain-based narrowband channel model proposed.

A novel approach to model the land mobile satellite channel through reversible jump markov chain monte carlo technique

A key issue in the design of a mobile satellite communication system is an adequate knowledge of the statistical behavior of the propagation channel. To achieve this goal, the development of very accurate models plays a very important role. In contrast to traditional multi-state Markov chain based models, the novel approach proposed in this paper makes no prior assumptions on the number of states or on the statistical distributions characterizing each state. The sequence of channel states is blindly estimated using a Reversible Jump Monte Carlo Markov Chain algorithm.

Air Interfaces for Satellite Based Digital TV Broadcasting in the Railway Environment

This paper deals with the analysis of possible air interfaces to be employed in order to provide digital TV services to high speed trains via satellite. This turns out to be an extremely challenging issue, since in addition to traditional impairments characterizing the land mobile satellite channel, one has to face the presence of frequent tunnels, whose duration can easily reach several kilometers, and the presence of a variety of peculiar obstacles, such as electrical trellises and posts with and without brackets, which may result in frequent and deep fades. A large variety of possible solutions, based on standardized air interfaces with proper modifications, are analyzed by means of extensive software simulations, showing that effective solutions can be devised. Some consideration concerning the deployment of terrestrial gap-fillers to bridge the satellite connectivity inside long railway tunnels, large train station and within dense urban areas are also briefly addressed.

An enhanced Markov chain based model for the narrowband LMS channel in built-up areas

In this paper, a technique to derive the transition probabilities for a Markov chain model for the land mobile satellite (LMS) channel in built-up areas is presented. This technique contributes to improving empirically derived parameters in that it can account for elevation and street orientation effects as well as building density. Physical-statistical or ‘virtual city’ techniques are used to relate observed edification statistics to signal attenuation statistics. This methodology can also be applied to generating correlated time-series for simultaneous links to a constellation of satellites from the same mobile terminal. The proposed approach also allows the generation of enhanced time-series which take into account diffuse multipath and diffraction effects. Copyright © 2005 John Wiley & Sons, Ltd.

Improving Link Layer Performance on Satellite Channels With Shadowing Via Delayed Two-Copy Selective Repeat ARQ

This paper focuses on improving performance of land mobile satellite channels (LMSCs) at high band (Ka-band or EHF band), where shadowing is the primary impediment to reliable data transmission. Compared with multipath fading, shadowing exists on a longer time scale; hence, interleaving to combat shadowing introduces unacceptably large decoding delay. We use Lutz's model to investigate bit-error rate/packet-error rate (BER/PER) performance of interleaving with various forward error correction (FEC) coding as a function of different channel parameters to demonstrate its limited effectiveness for combatting burst errors whose mean duration significantly exceed a link layer (LL) packet. We propose a delayed two-copy selective repeat ARQ (DTC-SR-ARQ) scheme, whereby two copies of a packet are sent-the second with a delay relative to the first-in every transmission or retransmission. Closed-form expressions for mean transmission time, success probability, and residual loss probability are provided and simulations used to validate the analysis. Furthermore, the issue of optimum delay is addressed as well, and a simple yet effective strategy is suggested to support transmission control protocol (TCP) traffic over this data link layer. DTC-SR-ARQ is shown to achieve much shorter additional delay than interleaving and compared with normal SR-ARQ, reduces mean transmission time at expense of a small increase in residual packet loss probability. Furthermore, ns2 simulation results show that for TCP traffic, DTC-SR-ARQ acquires higher end-to-end throughput than normal SR-ARQ.

A new simple model for land mobile satellite channels: first- and second-order statistics

We propose a new shadowed Rice (1948) model for land mobile satellite channels. In this model, the amplitude of the line-of-sight is characterized by the Nakagami distribution. The major advantage of the model is that it leads to closed-form and mathematically-tractable expressions for the fundamental channel statistics such as the envelope probability density function, moment generating function of the instantaneous power, and the level crossing rate. The model is very convenient for analytical and numerical performance prediction of complicated narrowband and wideband land mobile satellite systems, with different types of uncoded/coded modulations, with or without diversity. Comparison of the first- and the second-order statistics of the proposed model with different sets of published channel data demonstrates the flexibility of the new model in characterizing a variety of channel conditions and propagation mechanisms over satellite links. Interestingly, the proposed model provides a similar fit to the experimental data as the well-accepted Loo's (1985) model but with significantly less computational burden.

LMS Markov model and its use for power control error impact analysis on system capacity

We present a wideband land mobile satellite channel model based on a three-state Markov chain model valid for any kind of satellite constellation and for L, S, and Ka bands. Data from measurement campaigns was used to extract the parameters for the statistical distributions involved in the model. We also present a methodology describing how to use the proposed channel model to interface with system-level analysis. We use the time series generated by the model to parameterize power control (PC) imperfection as a function of the environment and user speed by acting upon the time series through a seven-level PC algorithm. We then apply the obtained parameterization to the analysis of a direct sequence-code division multiple-access scenario with users requiring different quality-of-service (QoS). It is shown that request of different QoS produces an unbalance in the users power distribution and less users can be served with the most demanding QoS. PC error worsens this effect and considerably reduces capacity efficiency which is highly dependent on the environment and mobile speed. Bit-error rate statistics are also investigated through the log-normal characterization obtained by using the channel model obtaining results on the effect of required E/sub b//(N/sub o/+I/sub o/) of a particular user.

Ka-band land mobile satellite channel model incorporating weather effects

A Ka-band land mobile satellite (LMS) channel model which is able to take into account weather impairments is proposed. The statistics of the received signal and the BER performance of the system under the proposed channel model are obtained and compared with the results generated using Loo's weather-affected LMS channel model. The proposed Ka-band (20/30 GHz) LMS channel model is shown to be more reasonable as it gives realistic results.

Propagation considerations and fading countermeasures for mobile multimedia services

AbstractThis paper presents a summary of land mobile satellite (LMS) channel characteristics derived from several measurement campaigns. Narrowband and wideband measurements allow a broad interpretation of the LMS channels. Channel models and its parameters have been derived from the measured data as well. Furthermore, the impact of the LMS channel on the communication service is investigated and possible countermeasures are discussed. Link margins, power control schemes and satellite diversity can compensate the fading on the transmission links. The benefit of adaptive receivers and the dependence on the signal bandwidth are investigated, too. Copyright © 2001 John Wiley &amp; Sons, Ltd.

Physical–statistical methods for determining state transition probabilities in mobile‐satellite channel models

AbstractSignal propagation in land mobile satellite (LMS) communication systems has for the last decade become an essential consideration, especially when high‐rate data services are involved. As far as urban or suburban built‐up areas are concerned, the extent of the influence is mainly restricted to the roadside obstacles, since the satellite is positioned at relatively high elevation angles in most practical situations. Probably, the most common model currently used for representing the LMS channel is the Lutz model, which uses two states to represent line‐of‐sight and non‐line‐of‐sight conditions. Transitions between these states are described by transition probabilities which are a function of the environment and the satellite elevation angles. Similarly, an extension to the model allows a four‐state description to be used for the states associated with a pair of satellites used in a dual‐diversity configuration. Calculation of the transition probabilities then requires knowledge of the correlation between the two channels, which in turn depends on the spatial characteristics of the local environment around the mobile.In both cases, the transition probabilities have been derived basically from measurements in the past. In the new approaches described in this paper, physical–statistical principles are applied to construct analytical formulas for the probabilities of shadowing and the correlation between states. These expressions apply particularly to systems operated in built‐up environments, and have been checked against numerical experiments and against direct measurements. In both cases excellent agreement is obtained. Copyright © 2001 John Wiley &amp; Sons, Ltd.

Statistical modeling of the LMS channel

In this paper, a statistical model for the land mobile satellite (LMS) channel is presented. The model is capable of describing both narrow- and wide-band conditions. The other relevant characteristic is that it can be used to study links with geostationary as well as nongeostationary satellites. The model is of the generative type, i.e., it is capable of producing time series of a large number of signal features: amplitudes, phases, instantaneous power-delay profiles, Doppler spectra, etc. Model parameters extracted from a comprehensive experimental data bank are also provided for a number of environments and elevation angles at L-, S-, and Ka-bands.

A simple figure of merit for evaluating interleaver depth for the land-mobile satellite channel

The selection of interleaver depth for the land-mobile satellite channel is investigated by analyzing the performance of convolutionally encoded BPSK and DPSK over a frequency-nonselective correlated Ricean fading channel. By extending previous analyses of partially interleaved convolutional codes over such channels, a new figure of merit-which is a function of the channel correlation function-is identified. Simulation results for the first-order Butterworth, Jakes (1974), and Divsalar (1991) fading spectra are presented which demonstrate the applicability of the figure of merit as an aid in interleaver design. The figure of merit also tracks the nonmonotonic, or quasi-oscillatory, behavior of the decoded bit error rate with increasing interleaver depths in those situations where this occurs.